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Asselin, Cosson Théotime. "Étude des effets de fermeture des fissures de fatigue sous chargement à rapport de charge négatif". Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2024. http://www.theses.fr/2024ESMA0030.
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La fatigue est avec la corrosion sous contrainte le principal moteur des dégradations observées sur les composants du parc nucléaire français. Les chargements induisant de la fatigue oligocyclique dans les composants primaires sont d’origine thermique et peuvent être à rapport de charge négatif. La justification des composants vis-à-vis de la propagation de fissure en fatigue est actuellement effectuée de manière pénalisante, sans prise en compte du sillage plastique. Des travaux de R&D sont donc requis pour améliorer les modèles de propagation en fatigue pour des chargements variables. C’est dans ce contexte que s’inscrivent les travaux présentés dans ce mémoire, avec une attention particulière portée aux effets de fermeture de fissure qui sont précisément à même de rendre compte des effets d’histoire. A cet effet, une campagne d’essais de référence à rapport de charge positif est d’abord mise en œuvre sur éprouvettes normalisées. Des essais de fissuration pilotés en déformation totale ont ensuite été conduits sur éprouvettes uniaxiales contenant un défaut initial. Un dispositif expérimental original utilisant les techniques de H-DIC (DIC enrichie en mécanique de la rupture) et le suivi de la différence de potentiel électrique permet de suivre la propagation de la fissure tout en évaluant les taux d’ouverture de fissure. Il est montré que pour les deux matériaux de l’étude les taux d’ouverture varient en fonction du niveau de sollicitation appliquée et du rapport de charge, et dans une moindre mesure de la profondeur de fissure. Une méthode couplant les résultats expérimentaux avec un modèle éléments finis développé sous Cast3M permet de définir des forces motrices fondées respectivement sur le facteur d’intensité de déformation et l’intégrale J. L’évaluation des forces motrices montrent l’importance de la prise en compte des effets de fermeture afin d’obtenir une loi de propagation réaliste pour les deux matériaux de l’étude. Une loi de propagation fondée sur l’intégrale Jeff est obtenue pour les deux matériaux et permet de s’affranchir de la dépendance au rapport de charge, niveau de déformation dans l’analyse de la propagation de fissureFatigue, along with stress corrosion is the main cause of degradation observed in the components of French nuclear power plants. The justification of components regarding fatigue crack propagation is currently considered in a penalising way without taking into account the loading history. The study of fatigue closure effects makes it possible to determine driving forces representative of crack propagation. Loads inducing low cycle fatigue in primary components are of thermal origin. A campaign of reference tests on standardised specimens was first carried out before controlled total deformation tests on uniaxial specimens. An experimental set-up using Heaviside-DIC and electrical potential difference monitoring techniques was used to monitor crack propagation while evaluating crack opening rates at the surface and averaged over the specimen. It is shown that for the two materials studied, crack opening rates vary as a function of the level of stress applied, the load ratio and, to a lesser extent the crack depth. The combination of experimental results and the development of finite-element models makes it possible to define and evaluate driving forces based on deformation intensity factors and the J integral. A new crack propagation driving force calculation method adapted to cases of confined plasticity at the crack tip and to cases of generalised plasticity has been defined, making it possible to obtain a unified propagation law for each material that does not depend on the load ratio or the stress level
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Cussac, Paul. "Influence d’imperfections surfaciques sur la tenue en fatigue de composants nucléaires". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0001.
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Dans le contexte de l’industrie nucléaire, la présence éventuelle d’imperfections surfaciques pouvant être générées par des chutes ou frottements d’outils lors de la fabrication et la maintenance des composants se doit d’être justifiée vis-à-vis du phénomène de fatigue. L’objectif premier de cette étude est d’évaluer dans quelle mesure la présence d’imperfections de surface de l’ordre de quelques dixièmes de millimètre de profondeur peut impacter la durée de vie en fatigue oligocyclique. En parallèle, cette étude cherche à décrire, de manière qualitative et quantitative, l’amorçage et la propagation des fissures à partir de ces imperfections. Afin de répondre à ces objectifs, une campagne d’essais de fatigue uni-axiale, menée en contrôle de déformation totale imposée, a été mise en œuvre avec des éprouvettes cylindriques (Φ 9 mm). Les imperfections de surface ont été introduites artificiellement sur les éprouvettes à l’aide de deux dispositifs permettant l’usinage d’entailles de faibles dimensions. Afin de suivre les phases d’amorçage, de micro et de macro propagation des fissures à partir des imperfections de surface, la méthode du suivi de potentiel électrique a été principalement employée. Des actions expérimentales et numériques complémentaires ont été réalisées afin de calibrer le suivi de potentiel. Les résultats de la campagne d’essais réalisée mettent en évidence une influence significative de la présence d’imperfections sur la tenue en fatigue des éprouvettes étudiées. La mise en œuvre du suivi de potentiel électrique a permis de déterminer les cinétiques d’amorçage et de propagation à partir des entailles artificiellement introduites. L’identification d’un paramètre représentatif de la force motrice de propagation dans le contexte de plasticité généralisée associé aux essais réalisés a par ailleurs permis d’exploiter les données relatives aux cinétiques de propagation dans une optique prédictiveGiven the stringent requirements of high levels of safety in nuclear components, stakeholders of the French nuclear industry must anticipate the presence of residual surface imperfections in these components. Such imperfections could be introduced during manufacturing or maintenance operations. The incidence of surface irregularities on the fatigue strength of metallic components has tobe considered. Meanwhile, nuclear components can be loaded under low-cycle fatigue and large-scale plasticity conditions. The first objective of this work isthento assess to what extent the fatigue life of typical nuclear materials may be affected by the presence of such surface irregularities. In parallel, thisstudy aims at describing, qualitativelyand quantitatively, the crack initiation and propagation from these imperfections. In order to meet these objectives, a uni-axial fatigue test campaign, conducted under fully-reversed total axial strain control, in the air at room temperature, has been carried out on the cylindrical specimens (Φ 9 mm). Surface imperfections were artificially introduced onto the specimens. The electric potential trackingmethod has been mainly usedto monitor the crack initiation, micro and macro propagation phases from surface imperfections. Additional experimental and numerical actions have been carried out to calibrate the potential monitoring. The results of thetest campaigndemonstrate a significant influence of the presence of imperfections on the9 mm specimensfatigue strength. The useof electrical methodhas allowedto determine crackinitiation and growth ratesfrom surface imperfections. The identification of a representative parameter of the propagation driving force,in the context of generalized plasticity associated with the tests carried out,has also allowed to analysedata relating to propagation kinetics in a predictive perspective
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Romo, Arango Sebastian A. "Low-Cycle Fatigue of Low-Alloy Steel Welded Joints". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1573054310351145.
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Yin, Maggie Huaying Materials Science & Engineering Faculty of Science UNSW. "Metal dusting of iron and low alloy steel". Awarded by:University of New South Wales. School of Materials Science and Engineering, 2006. http://handle.unsw.edu.au/1959.4/25188.
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Metal dusting is a kind of catastrophic corrosion phenomenon that can be observed in several of petrochemical processes. It occurs on iron-, nickel- and cobalt-base metals in carbonaceous atmospheres at high temperature when gaseous carbon activity is higher than one. The process is particularly rapid for ferritic alloys The aim of this project was to compare the dusting kinetics of pure iron and a 2.25Cr-1Mo alloy steel under CO-H2-H2O atmosphere at 650??C. Polished (3??m) samples of iron and the steel were exposed to flowing CO-H2-H2O gas atmospheres at 650??C, when the gases were supersaturated with respect to graphite. The partial pressure of CO was varied between 0.25 and 0.9 atm, and the carbon activity was varied from 2.35 to 16, in order to obtain a series of experimental conditions. In most experiments, pO2 was less than 7.37E-24 atm, and no iron oxide could form. However, Cr2O3 would always have been stable. When exposed to these gases, both iron and steel developed a surface scale of Fe3C which was buried beneath a deposit of carbon, containing iron-rich nanoparticles (the dust). Examination by Scanning Electron Microscopy allowed the observation of fine and coarse carbon nanotubes, and also spiral filaments. However, the morphology of the graphitic carbon was not sensitive to pCO and aC. Moreover, the carbon deposit was gas permeable, allowing continuing gas access to the underlying metal. At a fixed=4.5, the carburizing rate clearly increased with CO content from 0.25 to 0.68 atm. However, increasing the CO content to higher value led to decreased rates, indicating that carburizing rate reaches a maximum value at pCO=0.68 atm. When pCO was fixed at 0.25 atm and 0.68 atm, and carbon activity was varied. The induction period was extended by the formation of protective oxide layers at low values of carbon activity (aC= 2.35 and 2.55) where pO2 exceed the iron oxide formation value. For other reaction conditions, the carbon uptake rate for iron and steel did not increase with aC. The present work showed that the carbon deposition rates were not proportional to pCO or pCOpH2. Instead, the rate was affected by the partial pressure of all three reaction gases, and the carbon uptake rate for both materials could be expressed at r=k1pCOpH2+k2pCO2+k3pH22 and the rate constant k3 has a negative value, corresponding to coke gasification. From XRD analyses, it was found that cementite was the only iron-containing phase in the dusting product. The cementite particles acted as catalysts for carbon deposition from the gas. The same deposition process at the surface of the cementite layer led to its disintegration, thereby producing the particles. This disintegration process was faster on the steel than on pure iron. Consequently, the rates of both metal wastage and coke accumulation were faster for the steel. It is concluded that chromium and molybdenum do not stabilize the carbide but accelerate its disintegration process. It is suggested that Cr2O3 fine particles in the cementite layers provide more nucleation sites in the cementite layer on steel, explaining its more rapid dusting kinetics. However, appropriate methods of proving this assumption, such as TEM and FIB, are required.
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Myers, M. R. "Damage accumulation in a low alloy ferritic steel". Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370975.
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A study has been made of creep damge accumulation in two casts of l%.Cr-1/2%i.Mo low alloy steel. Creep tests and creep crack growth tests have been carried out at 823K to determine the nature of the damage accumulation and to attempt to relate microscopic damage mechanisms to the macroscopic fracture parameters. Four types of specimen were tested and failure of all occurred by the continuous nucleation. growth and coalescence of grain boundary cavities. A mechanism for the growth of cavities is suggested. based on grain boundary diffusion coupled with geometric constraint. The influence of continuous cavity nucleation has also been considered and it is suggested that this phenomenon initially increases the rate of diffusive cavity growth. However continuous nucleation decreases the growth rate once the latter becomes constrained. The effect of stress-state is also considered and increasing triaxiality is shown to have little effect on the unconstrained diffusive growth but it decreases the constrained growth rate by increasing the overall constraint in the specimen. Predicted growth rates give good agreement to those observed experimentally for both notched and un-notched creep specimens. Reasonable agreement is also observed to the predicted rupture lives although the predictions suggest notch strengthening whilst experimentally notch weakening is observed. This is thought to be due to non-uniform damage formation on loading. Based on the above concepts of cavity growth, constitutive equations are presented to predict the time dependence of creep strain. These are found to give good agreement to the experimentally determined strain rates, lending further support for the development of continuum damage mechanics as a means of assessing creep crack growth behaviour.
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Boåsen, Magnus. "Modeling framework for ageing of low alloy steel". Licentiate thesis, KTH, Hållfasthetslära (Inst.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-246036.
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Ageing of low alloy steel in nuclear applications commonly takes the form as a hardening and an embrittlement of the material. This is due to the evolution of the microstructure during irradiation and at purely thermal conditions, as a combination or separate. Irradiation introduces evenly distributed solute clusters, while thermal ageing has been shown to yield a more inhomogeneous distribution. These clusters affect the dislocation motion within the material and results in a hardening and in more severe cases of ageing, also a decreased work hardening slope due to plastic strain localization into bands/channels. Embrittlement corresponds to decreased fracture toughness due to microstructural changes resulting from ageing. The thesis presents a possible framework for modeling of ageing effects in low alloy steels.In Paper I, a strain gradient plasticity framework is applied in order to capture length scale effects. The constitutive length scale is assumed to be related to the dislocation mean free path and the changes this undergoes during plastic deformation. Several evolution laws for the length scale were developed and implemented in a FEM-code considering 2D plane strain. This was used to solve a test problem of pure bending in order to investigate the effects of the length scale evolution. As all length scale evolution laws considered in this study results in a decreasing length scale; this leads to a loss of non-locality which causes an overall softening at cases where the strain gradient is dominating the solution. The results are in tentative agreement with phenomena of strain localization that is occurring in highly irradiated materials.In Paper II, the scalar stress measure for cleavage fracture is developed and generalized, here called the effective normal stress measure. This is used in a non-local weakest link model which is applied to two datasets from the literature in order to study the effects of the effective normal stress measure, as well as new experiments considering four-point bending of specimens containing a semi-elliptical surface crack. The model is shown to reproduce the failure probability of all considered datasets, i.e. well capable of transferring toughness information between different geometries.Åldring av låglegerade stål i kärntekniska användningsområden framträder typiskt som ett hårdnande och en försprödning av materialet. Detta på grund av utvecklingen av mikrostrukturen under bestrålning och under rent termiska förhållanden. Bestrålning introducerar jämt fördelade kluster av legeringsämnen. Termisk åldring har däremot visats ge upphov till en mer ojämn fördelning. Klustren hämmar dislokationsrörelsen i materialet och ger därigenom upphov till en ökning av materialets sträckgräns, vid en mer påtaglig åldring det även leda till ett sänkt arbetshårdnande på grund av lokalisering av plastisk töjning i s.k. kanaler/band. Försprödning är en sänkning av materialets brottseghet som en följd av de mikrostrukturella förändringar som sker vid åldring. Arbetet som presenteras i den här avhandlingen har gjorts i syfte till att ta fram ett möjligt ramverk för modellering av låglegerade stål.I Artikel I, används en töjningsgradientbaserad plasticitetsteori för att kunna fånga längdskalebeteenden. Längdskalan i teorin antas vara relaterad till dislokationernas medelfria väg och den förändring den genomgår vid plastisk deformation. Flera utvecklingslagar för längdskalan har analyserats och implementerats i en finita element kod för 2D plan deformation. Denna implementering har använts för att lösa ett testproblem bestående av ren böjning med syfte att undersöka effekterna av utvecklingen hos längdskalan. Alla de utvecklingslagar som presenteras i artikeln ger en minskande längdskala, vilket leder till vad som valt att kallas förlust av icke-lokalitet. Fenomenet leder till ett övergripande mjuknande vid fall där den plastiska töjningsgradienten har stor inverkan på lösningen. Resultaten är i preliminär överenstämmelse med de typer av lokalisering av plastisk töjning som observerats i starkt bestrålade material.I Artikel II utvecklas ett generaliserat spänningsmått i syfte att beskriva klyvbrott, här benämnt effektivt normalspänningsmått. Detta har använts i samband med en icke-lokal svagaste länk modell, som har applicerats på två experimentella studier från den öppna litteraturen i syfte att studera effekterna av det effektiva normalspänningsmåttet. Utöver detta presenteras även nya experiment på ytspruckna provstavar under fyrpunktsböj. I artikeln visas att modellen återskapar sannolikheten för brott för alla undersökta experimentuppställningar, d.v.s. modellen visas vara väl duglig för att överföra brottseghet mellan geometrier.
QC 20190312
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Chatterjee, Amit. "Hydrogen degradation of plain carbon and low alloy steels /". The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487264603219536.
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Donohoe, C. J. "Corrosion fatigue of a high strength low alloy steel". Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322985.
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Walker, Nigel Stuart. "Type IV creep cavitation in low alloy ferritic steel weldments". Thesis, University of Bristol, 1997. http://hdl.handle.net/1983/efa6973c-9a3d-4a95-8297-61f12cbde92d.
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Cooper, David. "The boundary lubricated friction and wear of low alloy steel". Thesis, Aston University, 1989. http://publications.aston.ac.uk/8067/.
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Pin on disc wear machines were used to study the boundary lubricated friction and wear of AISI 52100 steel sliding partners. Boundary conditions were obtained by using speed and load combinations which resulted in friction coefficients in excess of 0.1. Lubrication was achieved using zero, 15 and 1000 ppm concentrations of an organic dimeric acid additive in a hydrocarbon base stock. Experiments were performed for sliding speeds of 0.2, 0.35 and 0.5 m/s for a range of loads up to 220 N. Wear rate, frictional force and pin temperature were continually monitored throughout tests and where possible complementary methods of measurement were used to improve accuracy. A number of analytical techniques were used to examine wear surfaces, debris and lubricants, namely: Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), Powder X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), optical microscopy, Back scattered Electron Detection (BSED) and several metallographic techniques. Friction forces and wear rates were found to vary linearly with load for any given combination of speed and additive concentration. The additive itself was found to act as a surface oxidation inhibitor and as a lubricity enhancer, particularly in the case of the higher (1000 ppm) concentration. Wear was found to be due to a mild oxidational mechanism at low additive concentrations and a more severe metallic mechanism at higher concentrations with evidence of metallic delamination in the latter case. Scuffing loads were found to increase with increasing additive concentration and decrease with increasing speed as would be predicted by classical models of additive behaviour as an organo-metallic soap film. Heat flow considerations tended to suggest that surface temperature was not the overriding controlling factor in oxidational wear and a model is proposed which suggests oxygen concentration in the lubricant is the controlling factor in oxide growth and wear.
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Chen, Jhewn-Kuang. "Effects of alloying elements upon austenite decomposition in high strength low alloy steels". Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-10102009-020227/.
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Schroth, James Gregory. "Combined mode I - mode III fracture toughness of a high-strength low-alloy steel /". The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260859496482.
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Stratford, G. C. "Type IV cracking in 1¼Cr - ½Mo low alloy steel welds". Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639124.
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Service experience has shown the main form of medium to long term damage and failure in low alloy steel weldments to be "TYPE IV" creep cracking in the intercritically transformed region of the heat affected zone (HAZ). This research programme aimed to define the fabricational, loading and microstructural factors which lead to this form of damage. Research welds, which were an accurate model of the geometry and microstructure of steam pipe weldments, were fabricated in tubular testpieces using standard welding techniques. The welds were subjected to a post-weld heat treatment (PWHT) of 700oC or 750oC for two hours. Whilst the heat treatment reduced the hardness of the welds, significant changes in microstructure were only seen in the 750oC PWHT weld. Uniaxial creep tests were performed on base metal and cross-weld specimens. Post-weld heat treatment increased the creep deformation and reduced the failure life of base metal specimens. For cross-weld specimens in the as-welded condition, the susceptibility for low ductility TYPE IV failure in the HAZ was invariably found to be linked to the sub-surface development of creep cavities and cracks. All specimens tested in the as-welded condition failed in a low ductility TYPE IV mode. For all cross-weld specimens, the susceptibility to low ductility failure was linked to factors which affect the base metal ductility, such as PWHT and test temperature. Thus, specimens with a PWHT of 750oC or those with a PWHT of 700oC tested at a temperature greater than 580oC were found to fail in a high ductility manner in the base metal region. Tubular specimens were tested at elevated temperature under internal pressure and applied end-load conditions. Results showed that deformation and fracture were dependant on temperature and axial stress and that sub-surface TYPE IV damage had developed in the HAZ of 700oC PWHT welds.
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MAMANI, JULIO DAMIAN SUNI. "QUANTIFICATION OF AUSTENITE-MARTENSITE IN LOW ALLOY STEEL BY IMAGE ANALYSIS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=22902@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O objetivo deste trabalho foi desenvolver uma metodologia para quantificação, por microscopia, do microconstituinte Austenita-Martensita (AM) em um aço de alta resistência e baixa liga (ABRL) da classe API5LX80. Foram obtidas imagens de Microscopia Ótica (MO) em campo claro e Eletrônica de Varredura (MEV), nos modos de elétrons secundários (SE) e retroespalhados (BSE). As imagens foram quantificadas por Processamento e Análise Digital de Imagens (PADI) e os resultados dos dois tipos de microscopia foram comparados. O principal desafio foi discriminar AM em meio a uma microestrutura multifásica complexa, com frações variadas de ferrita, bainita e do próprio AM. Para revelar a presença de AM foram testadas diferentes sequências de ataques químicos e eletrolíticos. Os resultados demostraram que o ataque químico misto, acrescentando um passo Lepera modificado gerou uma melhora acentuada do contraste em imagens de MO e de MEV no modo BSE. Imagens de MEV no modo SE apresentaram problemas de borda devido à posição do detector de elétrons, o que impediu a correta discriminação das regiões de AM. No modo BSE, a tensão de aceleração foi reduzida para 5 kV, para reduzir a penetração do feixe de elétrons e aumentar o contraste devido à fina camada de AM. Estas imagens foram filtradas para reduzir ruído e segmentadas por limiar simples para quantificar o AM. Nas imagens coloridas de MO, o AM foi segmentado por limiares nos espaços de cor RGB e HSB e em seguida foi quantificado. Utilizando Microscopia Co-Localizada (MCL) foram obtidas imagens de campos idênticos no MEV e no MO, permitindo comparar as técnicas. Mostrou-se que, no mesmo aumento, a microscopia ótica tende a subestimar a fração de AM quando comparada à microscopia eletrônica de varredura, no modo BSE.
This dissertation proposed the development of a quantification method, by microscopy, of the microconstituent Martensite-Austenite (MA) in a High Strength Low Alloy (HSLA) steel of the API5LX80 class. Images were obtained by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), in secondary electron (SE) and backscattered electron (BSE) modes. Digital Image Processing and Analysis (IA) was employed to process and quantify the acquired images and compare the results of the two types of microscopy. The main challenge was to discriminate the MA amidst a complex multiphase microstructure with varying fractions of ferrite, bainite and MA itself. To reveal the MA different chemical and electrolytic etching sequences were tested. The results showed that a mixed combination with an extra step of modified LePera etchant issued the best contrast for both OM and BSE mode SEM. SEM images in SE mode showed edge problems due to the location of the electron detector, what prevented the correct discrimination of MA regions. The accelerating voltage in the BSE mode was reduced to 5 kV which in turn decreased beam penetration and increase contrast due to the thin MA layer. These images were filtered to reduce noise and segmented by a simple threshold to quantify MA. In the color OM images MA was segmented by thresholds in the RGB or HSB color spaces and subsequently quantified. Employing Co-Site Microscopy images of identical fields acquired by OM and SEM, a direct comparison of the techniques was allowed. It was show that, for the same magnification, optical microscopy tends to underestimate the MA fraction when compared to electron microscopy in BSE mode.
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Dawud, Sattar J. "Oxidational wear of low alloy steel in gases other than air". Thesis, Aston University, 1992. http://publications.aston.ac.uk/8096/.
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A pin on disc wear machine has been used to study the oxidational wear of low alloy steel in a series of experiments which were carried out under dry wear sliding conditions at range of loads from 11.28 to 49.05 N and three sliding speeds of 2 m/s, 3.5 m/s and 5 m/s, in atmosphere of air, Ar, CO2, 100% O2, 20% O2-80% Ar and 2% O2-98% Ar. Also, the experiments were conducted to study frictional force, surface and contact temperatures and surface parameters of the wearing pins. The wear debris was examined using x-ray diffraction technique for the identification of compounds produced by the wear process. Scanning electron microscopy was employed to study the topographical features of worn pins and to measure the thickness of the oxide films. Microhardness tests were carried out to investigate the influence of the sub-surface microhardness in tribological conditions. Under all loads, speeds and atmospheres parabolic oxidation growth was observed on worn surface, although such growth is dependent on the concentration of oxygen in the atmospheres employed. These atmospheres are shown to influence wear rate and coefficient of friction with change in applied load. The nature of the atmosphere also has influence on surface and contact temperatures as determined from heat flow analysis. Unlubricated wear debris was found to be a mixture of Fe_2O_3, Fe_3O_4 and FeO oxide. A model has been proposed for tribo-oxide growth demonstrating the importance of diffusion rate and oxygen partial pressure, in the oxidation processes and thus in determination of wear rates.
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Hu, Wei. "Data-driven metallurgical design for high strength low alloy (HSLA) steel". [Ames, Iowa : Iowa State University], 2008.
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De, Souza Bott Ivani. "The role of microstructure in the temper embrittlement of low alloy steels". Thesis, Sheffield Hallam University, 1987. http://shura.shu.ac.uk/19544/.
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A detailed investigation has been carried out to study the effects of heat treatment on the susceptibility to temper embrittlement (Ductile-Brittle transition temperature and low energy fracture characteristics) of eleven experimental steels. These experimental alloys represented a range of compositions related to engineering steels and corresponded to a nominal composition of 0.34 mass%C with alloying additions of Cr, Ni and Mo in varying combinations. These alloys were doped with P and Sb to study the effect of these additions on the susceptibility to temper embrittlement. These steels were investigated in the pearlitic, bainitic and tempered martensitic conditions to establish the role of microstructure. Heat-treated alloys were characterised by fracture studies including Izod impact testing and subsequent electron microscopy. Simultaneous Auger electron spectroscopy and energy dispersive X-ray analysis coupled with with Secondary Ion Mass Spectrometry were used to study the fracture surfaces and bulk compositions of the embrittled structures. It has been established that intergranular embrittlement in a quenched and tempered martensite microstructure was associated with the presence of P, whereas the initial intergranular embrittlement in a bainitic microstructure was associated with the segregation of Sb. It is suggested that the lower C activity produced in tempered martensite structures allows P migration to the grain boundaries causing intergranular embrittlement which was attributed to the development of M[7]C[3].Alloys in isothermally transformed bainitic condition showed that the predominant carbide precipitate was M3C which increased the C activity at the prior austenite grain boundaries with a resultant decrease in P concentration and consequently an absence of intergranular failure in the early stages of embrittlement. The increased C activity continued to prevent appreciable P segregation but was not sufficient to inhibit the co-segregation of Ni and Sb after extended ageing times when the bainitic alloys began to fail by intergranular fracture. After prolonged ageing increased Ni and Sb concentrations at the grain boundaries were associated with the formation of a fine grain boundary precipitate which was low in Cr. The tendency to fail by the low energy intergranular mode of failure was always greater in the tempered martensites, even when the bainites were significantly harder.
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Wilson, Peter. "Remanent creep life prediction in low-alloy ferritic steel power plant components". Thesis, University of Cambridge, 1991. https://www.repository.cam.ac.uk/handle/1810/221887.
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Anyanwu, Ezechukwu John. "Low Alloy Steel Susceptibility to Stress Corrosion Cracking in Hydraulic Fracturing Environment". University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1398948610.
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Wrigley, Nigel Stuart. "The fracture characteristics of a boron containing high strength low alloy steel". Thesis, University of Salford, 1994. http://usir.salford.ac.uk/43037/.
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This study is concerned with the fracture characteristics of RQT 701; a possible contender for the replacement of HY 100, the existing 690MNm-2 (100,000psi) strength level Naval quality steel. RQT 701 is a low nickel, boron containing quenched and tempered steel which is less expensive than HY 100 due to a lower nickel content. The hardenability is maintained by the boron addition. The preliminary testing of RQT 701 showed a variation in the impact transition temperature through the thickness of the plate. This study examines the possible causes of this variation in impact properties and makes a full assessment of the mechanical properties of RQT 701. A full metallographic investigation has been carried out using quantitative metallography, scanning electron microscopy and transmission electron microscopy. The effect of heat treatment on the steel's hardenability and mechanical properties has been studied so that suggestions to produce optimum properties of RQT 701 could be made. A full fractographic study has also been undertaken. The relationship between fracture characteristics, microstructure and hardenability has been discussed. A parallel investigation of HY 100 plate has been carried out. A comparison between the microstructures and fracture properties has been made and the relative merits of the two steels discussed.
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Mohamed, Abdul Aziz Bin. "Creep life prediction of low alloy steel using neural network analysis of NDT". Thesis, Cranfield University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266946.
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Perrin, Ian James. "Computer-based type IV creep CDM design of low alloy ferritic steel weldments". Thesis, University of Manchester, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.617095.
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Coimbatore, Dhandayuth Venkatesh. "Cerium chloride inhibition for high strength low alloy steel exposed to sulphide polluted seawater". University of Western Australia. School of Mechanical Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0134.
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[Truncated abstract] Corrosion of steel structures caused by sulphide is a common engineering problem encountered by many industries, such as the petroleum, chemical processing, mining and mineral processing industries. The control of sulphide corrosion is still a controversial topic among corrosion engineers. There is an absence of guideline for a reliable acceptable limit of sulphide level in service and each processing industry has its own empirical values. Selection of inhibitors in the sulphide environment depends on laboratory testing before its actual application in pipelines and reaction vessels. Many investigators have postulated the corrosion mechanisms due to sulphide based on operating envelopes such as pH, chloride, manganese, hydrogen sulphide, sulphate reducing bacteria levels and inhibitor concentration. It is recommended in the literature that the batch dosing of inhibitor and biocide needs to be evaluated in regards to sulphide reducing bacteria (SRB) level, which may produce sulphide concentrations up to 2000 ppm. Although sulphide scale formation may protect the base metal by providing a physical barrier, the detrimental effects of sulphide are often inevitable, such as stress corrosion cracking, hydrogen embrittlement, etc. Currently, there are many chemicals that are used as inhibitors to prevent corrosion by scavenging the sulphide from the environment. Cerium, a rare-earth element, is not used as inhibitor in the sulphide environment. Also, there are no previous research findings on the effects of compounds of rare-earth metals, such as cerium chloride (CeCl3), in sulphide environment. This research examines the corrosion behaviour of 0.4Mo-0.8Cr steel, a High Strength Low Alloy (HSLA) steel, in sulphide-polluted artificial seawater with the addition of CeCl3 and glutaraldehyde. ... It is postulated that the moderate inhibiting effect of CeCl3 is due to the scavenging effect thereby forming Ce2S3 complex. Further reaction of sulphide with steel resulted in ferrous sulphide, leading to an increased corrosion rate. It is also concluded that the CeCl3 interferes with both anodic and cathodic reactions in deaerated conditions. Addition of glutaraldehyde in the sulphide-polluted seawater was found to decrease the corrosion rate. According to the electrochemical measurements conducted, the concurrent addition of glutaraldehyde and CeCl3 appeared to have an added effect on reducing the corrosion of the steel, as evidenced by the increase of the open circuit potential during the short-term testing. From the weight loss measurements after 60 days, sulphide pollution in deaerated seawater was found to increase corrosion rate. This is attributed to the increase of sulphide activity whereby continual dissolution of steel was encountered. From the weight loss tests, it was found that the addition of CeCl3 and glutaraldehyde reduced the corrosion rate of the steel in the solutions containing 0-10 ppm sulphide. There is no noticeable corrosion rate decrease for the solution containing 100 ppm sulphide. The added effect of CeCl3 and glutaraldehyde to the SRB medium has resulted in lower corrosion rates. Further detailed experimentation is required to elucidate the corrosion reduction mechanism in glutaraldehyde-containing environments.
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Storer, S. M. "Simulation of heat affected zone microstructures in ½Cr - ½ Mo - ¼V low alloy steel weldments". Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639121.
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The microstructures developed in the heat affected zone of low alloy steel weldments are critically dependent upon the alloy composition and the thermal cycles introduced by the welding process. Review of available literature indicates that although a significant amount of research has been performed examining microstructural development, the bulk of this work has either been aimed at steels for low temperature application or has been used to overcome reheat cracking in ½ Cr- ½ Mo- ¼ V steels. In general it appears that the measures taken to prevent reheat cracking which occurs early in the life of a weld, i.e., limiting the carbon and vanadium content and adopting procedures which result in significant refinement of weldment structures, may well have been responsible for promoting the long term, in-serve creep damage. Thus in the present programme, research has concentrated on establishing the factors affecting the formation of austenite on reheating, the growth of these austenite grains as well as considering microstructural transformations on cooling with the view to optimising both short term and long term performance.
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Needham, William Donald. "Stress corrosion cracking and hydrogen embrittlement of thick section high strength low alloy steel". Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/10945/22123.
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An experimental study was conducted to evaluate the corrosion performance of weldments of a high strength low alloy(HSLA) steel in a simulated seawater environment. This steel, designated HSLA80, was developed by the United States Navy for use in ship structural applications. Stress corrosion CRACKING(SCC) and hydrogen embrittlement(HEM) were investigated by conducting 42 Wedge-Opening load(WOL) tests as a function of stress intensity and corrosion potential and 33 Slow Strain Rate(SSR) tests as a function of strain rate and corrosion potential. The corrosion potentials were chosen to simulate the environmental conditions of free corrosion, cathodic protection and hydrogen generation. The results from this investigation indicated that HSLA 80 base metal and weldments were susceptible to hydrogen assisted cracking(HAC) in a seawater environment under conditions of continuous plastic deformation and triaxial stress in the presence of hydrogen. The heat-affected zone of the weldment was found to be the most susceptible portion of the weld joint. A lower bound was established for the critical stress intensity for stress corrosion cracking for HSLA 80 base metal and weldments.(Theses)
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Lewis, Colin Andrew. "Prediction of thermal stress and strain generated during the quenching of low-alloy steel". Thesis, Sheffield Hallam University, 1990. http://shura.shu.ac.uk/19954/.
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The free edge of a quenched plate is subject to zero stress in a direction perpendicular to this edge. Therefore the thermal stresses set up in such a component must be modified in the vicinity of the edge in order to allow the required stress configuration to be produced. This is referred to as the 'edge effect' and its magnitude is conventionally estimated by the well-known Saint Venant Principle. However a detailed understanding of the variation in stress in such a specimen is not well understood and it has been the objective of the present programme to make a detailed elastic/plastic analysis of the stress generation process using a finite element method. To this end a disc specimen has been considered, so that both experimental and theoretical estimates of the stress fields are not influenced by the presence of sharp corners, which lead to a very complex stress system. The stress generation process has been followed by a finite element axisymmetric model. The use of such a plane strain representation has been checked by comparison with a full 3 dimensional elastic analysis, at a very early stage in the process when plastic flow was not present. The results obtained by the two methods of calculation were in good agreement and justify the use of the plane strain model. The finite element programme calculated the thermal history of the specimen by the Crank-Nicholson method, and the weighted mean technique was selected as the best method of smoothing the results. The effects of different element stress functions, and element size, as well as time and load steps have been studied and the optimum combination selected. Considerable difficulty had been experienced with the stability of the results, which was found to be due to limitations in the BERSAFE finite element package. The elimination of this problem led to a situation where successive stages in the stress generation process were calculated and examined with confidence, although great care was required to balance the time step with the thermal loading step. The results from this model in the central region of the plate were ingood agreement with those results reported by earlier workers. The complex variation of stress distribution predicted by the model asthe free edge is approached has been examined and justified against theclassical governing equations. This includes non-linear decay of in-plane stresses and the development of axial and shear stresses near the edge of the plate. A further product of this work has been an evaluation of the development of plastic zones during the quench process. Although the effect of the edge on the inplane stresses differs with axial position in the plate, the derivation of an overall edge correction factor (which is a mean ratio of average stress to the stress on the axis) provides a value which is consistent with the Saint Venant Principle. Therefore, it is concluded that the use of edge correction factors based on the linear decay of in-plane stresses from a position that is one plate's thickness from the edge is satisfactory for determining "real" body stresses from a finite difference model.
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Rose, Scott Anthony. "The Effect of Cooling Rate of Friction Stir Welded High Strength Low Alloy Steel". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4181.
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The friction stir welding of steel has produced a hard zone in several different alloys. Despite its detrimental effects on weld toughness, the reasons behind neither its formation nor a method of reducing its size or effects have been explored. Recent advances in process control allow for direct heat input control, which combined with the use of backing plates of different thermal conductivity allows for an expansion of the process window. These control methods also affect the HAZ cooling rate by providing greater range (a 60% increase compared to a fixed backing plate) and control (five welds within 16 °C/s). This increased range produced microstructures consisting of various forms of ferrite at lower cooling rates and bainite at higher cooling rates. The hard zone was determined to be the result of the formation of the bainite at higher cooling rates and was avoided by keeping the cooling rate below 20 °C/s in HSLA-65.
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Evins, Joseph Lee. "Dependence of Strength on Corrosion-Fatigue Resistance of AISI 4130 Steel". Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5265.
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Automobile components are often exposed to aggressive environments as a result of aqueous salts from the road coming into contact with unprotected steel. This situation greatly reduces both the life and the appearance of the affected parts. Ultra-high strength steel parts are suspected to exhibit poor corrosion-fatigue properties and be more susceptible to corrosion in general.
In this study, the effect of strength level on the decrease in fatigue life of AISI 4130 steel when exposed to an aqueous salt solution is quantified. The observed mechanical properties including corrosion-fatigue behavior are examined with consideration to different microstructural characteristics resulting from heat treatments to the steel. The hardness and tensile properties of the test material were characterized before fatigue testing. Fatigue tests were completed in both air and salt solution to determine the effect on fatigue life of the latter environment. Following fatigue testing, the fracture surface was examined using a scanning electron microscope (SEM) to determine the failure mode.
Six strength levels of AISI 4130 steel were investigated ranging from 837 to 1846 MPa (121 268 ksi). The frequency of loading used for corrosion-fatigue tests was 1 Hz and the stress ratio for each test was constant at R = 0.1. The corrosion-fatigue tests consisted of the specimen being submerged in an aqueous solution of sodium chloride, calcium chloride, and sodium bicarbonate and fatigued until failure. The solution was maintained at room temperature with constant aeration to ensure constant oxygen levels. The parameters of interest were the applied loads and the cycles to failure.
There were four primary findings of the study. First, decreases in fatigue life of the material caused by the corrosive environment ranged from 100% in the lowest strength level to 190% in the higher strength levels. This result showed that higher strength in this steel corresponds to increasing detriment to fatigue life when the material is exposed to an aqueous salt environment. Second, evidence was found that the salt solution lowered the fatigue limit for each strength level studied in this material. All specimens that were tested in the corrosive environment failed in less than 150,000 cycles, while some specimens fatigued in the air environment experienced run-outs at over 106 cycles. Third, the decrease in fatigue life was attributed to the presence of martensite in the structure of the steel. It was noted that the higher the martensite content, the larger the decrease in fatigue life when exposed to the corrosive environment. Finally, the fracture surfaces of fatigued specimens revealed that a similar cracking mode was present for each strength level in both environments. Enhanced crack initiation was, therefore, assumed to be the cause of the decrease in fatigue life between the air and aqueous salt environments.
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Razzak, Mohammad. "Precipitation and abnormal grain growth in low alloy steels". Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-01015867.
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The objective of this thesis is to further understand the austenite Abnormal Grain Growth (AGG) phenomenon in relation with precipitation state in a low alloy steel. The abnormal grain growth is addressed from both experimental and numerical modeling point of view. Prior austenite grain size distribution, precipitation volume fraction and size distribution evolution of the different heat treated states are experimentally determined for two different industrial alloys (steel-A and steel-B) in different heat treated states and experimental results are compared with model predictions. A two-step modeling technique is adopted in this study: precipitation modeling and abnormal/normal grain growth modeling. The abnormal/normal grain growth modeling is done using a simplified analytical model where the grain growth is assumed to be driven by the decrease in interfacial energy. Both the conventional Zener pinning and corner pinning by precipitate is considered as boundary movement retarding forces. The precipitation model is based on the Classical Nucleation and Growth Theories. The assumption of homogeneous precipitate nucleation and growth gave a good prediction of volume fraction, mean radius and size distribution in comparison with the experimental results. Two coupled modeling approaches of abnormal grain growth and precipitation model: ①Soft coupling and ②Dynamic coupling; shed light on the different physical parameters controlling the grain growth condition in a particular material's state. A reasonable prediction of AGG and NGG is obtained from both approaches. The dynamic coupled modeling enabled us to paint a comprehensive time-temperature mechanism map of grain growth conditions. It is found that AGG in the austenitic state depends strongly on the initial grain size distribution and precipitation state. The modeling and the experimental results showed that the precipitation state evolution (increasing or decreasing volume fraction) also impact normal/abnormal grain growth. Plausible explanations in relation with the mean austenite grain size and the precipitation state are derived for the AGG phenomenon from the present work.
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Åkerlund, Elin, Rebecka Havo, Åberg Jakob Jonsson, Patrik Österberg i Mikael Fredriksson. "High Performance Steel for Percussive Drilling". Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-323387.
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Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched. The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.
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Åkerlund, Elin, Åberg Jakob Jonsson, Patrik Österberg, Rebecka Havo i Mikael Fredriksson. "High Performance Steel for Percussive Drilling". Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-323808.
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Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m^1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched. The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.
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Chikwanda, Hilda Kundai. "Microstructural characterisation and remanent creep life evaluation of a 12CrMoVNb steel". Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363846.
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Almansour, Mansour A. "Sulfide stress cracking resistance of API-X100 high strength low alloy steel in H2S environments". Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/267.
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Sulfide Stress Cracking (SSC) resistance of the newly developed API-X100 High Strength Low Alloy (HSLA) steel was investigated in the NACE TM0177 "A" solution. The NACE TM0177 "A" solution is a hydrogen sulfide (H2S) saturated solution containing 5.0 wt.% sodium chloride (NaC1) and 0.5 wt.% acetic acid (CH3COOH). The aim of this thesis was to study the effect of microstructure, non-metallic inclusions and alloying elements of the X100 on H2S corrosion and SSC susceptibility. The study was conducted by means of electrochemical polarization techniques and constant load (proof ring) testing. Microstructural analysis and electrochemical polarization results for X100were compared with those for X80, an older generation HSLA steel. Uniaxial constant load SSC testing was conducted using X100 samples and the results were compared with those reported for older generation HSLA steels.
Addition of H2S to the NACE TM0177 "A" solution increased the corrosion rate of X100from 51.6 to 96.7 mpy. The effect of H2S on the corrosion rate was similar for X80. The corrosion rate for X80 increased from 45.2 to 80.2 mpy when H2S was added to the test solution. Addition of H2S enhanced the anodic kinetics by forming a catalyst (FeHSads) on the metal surface and as a result, shifted the anodic polarization curve to more current densities. Moreover, the cathodic half cell potential increased due to the decrease in pH, from 2.9 to 2.7, which shifted the cathodic polarization curve to more current densities. The increase in both the anodic and cathodic currents, after H2S addition, caused the rise in the corrosion current density.
In H2S saturated NACE TM-0177 "A" solution, the X100 steel corrosion rate was higher than the X80 steel by 20%. Longer phase boundaries and larger nonmetallic inclusions in the X100 microstructure generated more areas with dissimilar corrosion potentials and therefore, a stronger driving force for corrosion. Higher density of second phase regions and larger nonmetallic inclusions acted as an increased cathode area on the X100 surface which increased the cathodic current density and consequently, increased the corrosion current density.
Proof ring tests on the X100 gave a threshold stress value, C5th, of 46% YS, 343.1 MPa(49.7 ksi). The main failure was caused by SSC cracking. SSC nucleated at corrosion pits on the metal surface and microcracks in the metal body and propagated perpendicular to the applied stress. Hydrogen Induced Cracking (HIC) was observed in the X100. HIC cracks nucleated at banded martensite-ferrite interfaces and propagated along the rolling direction parallel to the applied tensile stress through the softer ferrite phase.
When compared to older HSLA grades, the X100 tested in this study had a high SSC susceptibility and therefore, is not be recommended for H2S service applications. The high X100 SSC susceptibility was caused by the material high corrosion rates in H2Smedia which formed corrosion pits that acted as crack initiation sites on the metal surface and provided more hydrogen that migrated into the steel. In addition, the X100
inhomogeneous microstructure provided a high density of hydrogen traps in front of the main crack tip which promoted SSC microcrack formation inside the metal. Microcracks in the metal body connected with the main crack tip that originated from corrosion pits which assisted SSC propagation.
34
O'Brien, Evan Daniel. "Welding with Low Alloy Steel Filler Metal of X65 Pipes Internally Clad with Alloy 625: Application in Pre-Salt Oil Extraction". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469018389.
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Tang, Zhenghua. "Optimising the transformation and yield to ultimate strength ration of Nb-Ti micro-alloyed low carbon line pipe steels through alloy and microstructural control". Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-07212007-110711.
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Millar, Peter G. "Corrosion fatigue crack propagation behaviour of a high strength low alloy steel in a synthetic sea water environment". Thesis, Cranfield University, 1986. http://dspace.lib.cranfield.ac.uk/handle/1826/4443.
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The corrosion fatigue crack propagation behaviour of a high strength low alloy steel, N-A-XTRA 70, in a synthetic sea water solution was tested using S. E. N. specimens subjected to a loading frequency of 0.1 Hz and a load ratio of 0.6. In order to simulate the conditions encountered by a thumbnail type crack several specimens from each of the microstructural types tested, namely parent plate, heat affected zone and heat treated material, had their crack sides covered by transparent plastic covers. Severe overprotection and slight underprotection conditions were produced using cathodic protection potentials of -1400, -1300, -1200 and -700 mV (S. C. E. ). The Paris relationship da/dN = CLKm was found to be a useful tool in describing the crack propagation rate data. Results obtained, presented in the form of plots of log da/dN against log AK, show that for parent plate, H. A. Z. and heat treated material, covering the crack sides of specimens produces enhanced corrosion fatigue crack propagation rates, at cathodic protection potentials of -1400 and -1300 mV (S. C. E. ), when compared to non covered specimens. This trend was also true for H. A. Z. specimens at a potential of -700 mV (S. C. E. ). For parent plate specimens, however, covering the crack sides at a potential of -700 mV (S. C. E. ) produced reduced crack propagation rates over non covered specimens. It is believed restriced oxygen access may account for these results. Plots of the Paris exponent m and constant C for the three microstructures tested produced three lines of the form m= alnC +b where a and b were found to be dependent upon material parameters. Comparison of results with BS 4360: 50D revealed that N-A-XTRA 70 exhibited superior fatigue performance when tested in air but behaved worse under conditions of free corrosion.
37
Haji, Hasan Abdalla. "An analysis of microstructure and crystallographic texture in friction stir welded high strength low alloy steel". Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589542.
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Abdullah, J. B. "The assessment of high temperature damage in 2.25 Cr - IMo low alloy steel using ultrasonic techniques". Thesis, Swansea University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.635833.
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In petrochemical plants and power generating utilities, creep behaviour will affect the service life of components operating at elevated temperatures and stresses. Non-destructive techniques which detect creep damage are therefore important for assessing the remaining service life of the affected components. Whilst various non-destructive techniques have been reported, further studies are necessary to refine and assess the potential of these techniques for quantitative measures to be used for residual life-time prediction. In this thesis, the use of ultrasonic techniques to quantify creep cavitation in 2.25Cr-1Mo low alloy steel was explored. In contrast to conventional methods which only examine surface effects, these approaches should be capable of monitoring both surface and volumetric changes. A computer-based ultrasonic system was developed and testing procedures to characterise the metallurgical variables and creep damage in both ferritic and bainitic 2.25Cr-1Mo steel materials have been established. To evaluate the effects of high temperature exposure to assess microstructural changes and the development of creep damage, a systematic approach with a three-stages experimental work has been undertaken. Firstly, the effects of grain size and phase transformation product on ultrasonic behaviour were evaluated. Samples have been prepared with ferritic and bainitic microstructures. Austenitisation procedures were selected so that samples were produced with average grainsizes in the range 21 to 96 μm. Secondly, ultrasonic techniques were used to characterise microstructural changes due to thermal ageing effects. Materials in ferritic and bainitic microstructures were aged at 700°C for times from 2 to 2000 hours. Thirdly, the assessment of creep damage using ultrasonic techniques was undertaken. This was performed on specimens which had been subjected to creep at various stresses, in a temperature range of 575 to 625°C. In all cases, ultrasonic measurements were supported by optical microscopy, tensile testing and surface hardness measurements to document metallurgical condition.
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Herbst, Matthias G. J. "Effect of chloride on environmentally assisted cracking of low alloy steels in oxygenated high temperature water". Thesis, Liverpool John Moores University, 2014. http://researchonline.ljmu.ac.uk/4569/.
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The aim of this thesis was to derive a better understanding with regard to the effects of chloride on the general corrosion behaviour of low-alloy steels (LAS) in oxygenated high-temperature water (HTW) and to investigate the underlying mechanisms for crack initiation and propaga-tion due to chloride assisted environmentally assisted cracking (EAC). Therefore, systematic investigations on the effect of chloride on the EAC behaviour of LAS were performed to un-derstand and elucidate the underlying mechanisms. The overall thesis is divided into three parts focussing on the effect of chloride on: i) general corrosion, ii) crack initiation, and iii) crack growth of low-alloy steels in oxygenated high-temperature water. Studies on the effect of chloride on the general corrosion behaviour were performed by immer-sion tests that were evaluated using electrochemical monitoring techniques and different post-test investigation methods like SEM, ToF-SIMS, and others. From the performed investiga-tions it is concluded that the presence of small amounts of chloride in oxygenated HTW causes an incorporation of chloride into the oxide layer, a thinning of the oxide layer thickness, and pronounced pitting. The crack initiation susceptibility of LAS was investigated using CERT tests. These tests showed an increased number of crack initiation locations and a decrease of the elongation at fracture with increasing chloride concentrations. Crack growth rate tests clearly demonstrated that not the increase in the chloride concentration per se, but the conjoint occurrence of an active or dormant crack and increased chloride con-centration causes an increase in the observed crack growth rates. For practical applications of LAS in oxygenated HTW this means that short term transients seem to be not harmful regarding component integrity, but long term increased chloride con-centrations should by prohibited since they cause increased general corrosion of LAS. Taking crack initiation and crack growth into consideration, the conjoint occurrence of increased chlo-ride concentrations and mechanical straining at stress levels above the yield strength should be avoided.
40
Kilgallon, P. J. "The effect of sulphate reducing bacteria on the hydrogen absorption of cathodically protected high strength low alloy steel". Thesis, Cranfield University, 1994. http://dspace.lib.cranfield.ac.uk/handle/1826/7253.
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The hydrogen embrittlement of two HSLA steels was studied in conditions typical of the marine environment. Double cantilever beam specimens, heat treated to produce the microstructure in the heat affected zone of a weld, were tested in seawater containing sulphate reducing bacteria (SRB) over a range of cathodic protection (CP) potentials and the threshold stress intensities ([Threshold Stress Intensity]) were recorded. The hydrogen concentration absorbed by the steel ([Surface Hydrogen Concentration]) was measured and shown to be higher at more negative CP potentials and significantly increased when SRB were present. An inverse relationship was established between log [Threshold Stress Intensity] and [Surface Hydrogen Concentration]. It was concluded that crack propagation occurs by a single mechanism whether or not SRB are present. Three point bend specimens of both steels were machined from welded plate. Corrosion fatigue tests were carried out in seawater with and without SRB. The presence of active SRB caused increased crack growth rates. Sediment samples were collected from the River Mersey and the base of a North Sea platform. In addition, SRB were added as an inoculum to artificial seawater. SRB numbers were enumerated and their activities assessed by measuring the concentrations of sulphide generated. Hydrogen permeation tests were performed on steel held at a range of CP potentials and exposed to each environment. Measurements were also carried out in seawater containing chemically prepared sulphides. Hydrogen absorption was shown to be enhanced when SRB were present and to be related to the total sulphide (TS) concentration in the environment. High hydrogen concentrations were produced by chemically prepared sulphides and the nature and thickness of the sulphide film appeared to be important in determining the extent of hydrogen absorption. Chemically produced sulphide gave sustained levels of absorbed hydrogen, but those generated biogenically decayed rapidly unless the TS concentration was maintained in the solution.
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Maropoulos, S. "The effect of heat treatment on structure-property relationships in a low alloy Ni-Cr-Mo-V steel". Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370954.
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Jubica, Jubica. "Characterization of Secondary Carbides in Low-Alloyed Martensitic Model Alloy Tool Steels". Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284449.
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The development of tool steels for making and shaping other materials requires a better understanding of the material's properties during manufacture. These high-quality steels include many alloying elements, which give increased hardness during tempering. For producing hardened microstructures, austenite generation is essential. The martensite formed by rapid quenching of austenite followed by tempering helps develop high strength steels. Studying carbide precipitation is a challenge as they are very small in size, present only in small volume fractions and high number densities. The carbide reactions are complicated due to so-called metastable carbides, which are only present as part of the precipitation process. This work focuses on model alloys with two main elements in addition to iron and carbon, molybdenum, and vanadium, to clarify and simplify the carbide characterization. This is done to determine the effect of molybdenum and vanadium carbides on the overall hardness. In this work, two model alloys, A and B, are tempered at 550°C and 600°C with the same vanadium content but different molybdenum contents. The hardness of the materials is evaluated and compared at these temperatures. A more detailed characterization work is done for material A with Scanning Transmission Electron Microscopy-Energy Dispersive Spectroscopy (STEM-EDS) to understand the microstructure and analyze the precipitates. Simulations are performed with Thermo-Calc Prisma (TC-Prisma) to support the experimental work, which includes the simulation of the secondary carbide precipitation, mainly molybdenum carbides in material A tempered for 24h at 600°C, and predicts the carbide precipitation behavior in this steel. The results from STEM-EDS and TC-Prisma for material A, show that the small secondary carbides in the martensite contribute to the increased strength of material A. Due to the overaging of the carbides at 600°C, the hardness at 550°C is higher than at 600°C for material A. The given thesis work is an attempt to interpret the development of secondary carbides of Mo and V in the martensitic matrix and their role in the overall hardness.Den ständiga utvecklingen av högpresterande stål för transport, konstruktion och energisektorn kräver bättre förståelse för materialets egenskaper vid tillverkning. Dessa martensitiska stål inkluderar många legeringselement vilket ger ökad hårdhet vid härdning och anlöpning. Att studera utskiljning av karbider är en utmaning eftersom de är närvarande endast i liten volymsfraktion. Karbidreaktionerna är komplexa till följd av så kallade metastabila karbider vilka endast är närvarande vid en del av utskiljningsförloppet. För att tydliggöra och förenkla karbidkarakteriseringen fokuserar detta arbete på modellegeringar med två huvudelement utöver järn och kol, molybden och vanadin. Detta görs för att fastställa effekten av molybden och vanadinkarbider på den totala hårdheten. I detta arbete studeras två modellegeringar, A och B, härdade och anlöpta vid 550 °C och 600 °C med samma vanadininnehåll men olika molybdeninnehåll. Materialens hårdhet utvärderas och jämförs vid dessa temperaturer. Ett mer detaljerat karaktäriseringsarbete görs för material A med hjälp av STEM-EDS för att förstå mikrostrukturen och analysera utskiljningarna. Simuleringar görs med TC-PRISMA för att stödja det experimentella arbetet, vilket inkluderar simulering av den sekundära karbidutskiljningen och predikterar karbidstrukturen i dessa stål. Resultaten visar att de små sekundärkarbiderna i martensiten bidrar till den ökade styrkan hos material A. Hårdheten vid 550 °C är högre än vid 600 °C för material A eftersom både utskiljningen av karbider är sker långsammare och även dislokationsåterhämtning.
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Gould, Elijah Katunich. "Development of Constitution Diagram for Dissimilar Metal Welds in Nickel Alloys and Carbon and Low-Alloy Steels". The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1285007217.
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Wei, Lingyun 1972. "Investigating correlations of microstructures, mechanical properties and FSW process variables in friction stir welded high strength low alloy 65 steel /". Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3195.pdf.
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Wei, Lingyun. "Investigate Correlations of Microstructures, Mechanical Properties and FSW Process Variables in Friction Stir Welded High Strength Low Alloy 65 Steel". BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/2032.
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The present study focuses on developing a relationship between process variables, mechanical properties and post weld microstructure in Friction Stir Welded HSLA 65 steel. Fully consolidated welds can be produced in HSLA 65 steel by PCBN Convex-Scrolled-Shoulder-Step-Spiral (CS4) tool over a wide range of parameters. Microstructures in the nugget center (NC) are dominated by lath bainite and a few polygonal/allotriomorphic grain boundary ferrites. FSW dependent variables are related to FSW independent variables by non-linear relationship. Heat input is identified to be the best parameter index to correlate with microstructures. With increasing heat input, the volume of bainite is reduced, the shape of bainite is more curved and grain/lath size become coarser. A linear relationship was established between heat input and semi-quantitative post-weld microstructures based on the optical microstructures. Further analysis has been applied on the NC to obtain more fundamental understanding of FSW. The new approach via Orientation Imaging Microscopy (OIM) was developed to acquire quantitative microstructural data including bainite lath/packet and prior austenite grain size (PAG). A linear relationship between heat input and quantitative microstructural features in the NC have been established. Mechanical properties exhibits linear relationship with heat input. These correlations can be utilized to determine FSW weld parameter to get desired mechanical properties welds.
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Buntain, Ryan John. "Effect of Microstructure on Hydrogen Assisted Cracking in Dissimilar Welds of Low Alloy Steel Pipes Joined with Nickel Based Filler Metals". The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577785066479763.
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Andersson, Jim. "Manufacturing of Welded Rings : Evaluation of Post-Weld Operations". Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-74578.
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Pipe and ring blanks can be produced in several different ways. Today's focus on environmental effects motivates companies to develop processes that are as efficient as possible in their production. Ringsvets AB is a company that produces pipe and ring blanks from a flat stock by rolling and welding the piece to make it stay in its desired form. The direct benefit of the method is the minimizing of material loss, and it has thereby both environmental and economical advantages. The downside of the method is that the processes involved changes the mechanical behavior of the ring, locally around the weld zone. The focus of this master thesis is the processes and how they affect the material, both microstructure and behavior. The processes involved are; rolling, welding, shaping, brushing, forging, heat treatment, and calibration. The purpose of this work was to elevate the knowledge and understanding of the processes at Ringsvets. The goals were to give a theoretical description of them along with practical test results and explanations of how and why they function in reality. A literature study has been conducted which provided a theoretical basis on how the material reacts on certain processes. Practical examination of samples from current production has been done to get evidence of how well the processes are used, and how well they function, in today's production. Lastly, the main focus of the thesis, an evaluation has been made; do theory and practice correlate, and should anything be changed to correlate better? The results showed that the first operations do not alter the material behavior to an unacceptable extent. Forging, on the other hand, gives the material a very high hardness in the weld zone, and that needs to be corrected. The following heat treatment should compensate for that in a perfect world, but does not in reality. The finished ring shows good properties in general but with places where the heat treatment has failed to correct the uneven behavior induced by earlier operations. The heat treatment requires some adjustments before it functions as intended. Some grainshas not been recrystallized which makes them very hard and non-ductile. Future tests using a higher temperature or a longer heat treatment time would reveal the best way to adjust the heat treatment to obtain the desired properties. Other changes in the processes could also be benecial. Interesting things to try and change would, for example, be the degree of deformation in the forging, which affects the recrystallization temperature. Notes should be taken that this examination is done on just one sample of just one size. Analyses of different samples of different sizes should be done to ensure of the accuracy of the examination.
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ムハマド, リファイ, i Muhammad Rifai. "Mechanical and corrosion properties of ultrafine-grained low C, N Fe-20%Cr steel produced by equal channel angular pressing". Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902984/?lang=0, 2015. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902984/?lang=0.
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Equal-channel angular pressing (ECAP) is one of the severe plastic deformation (SPD) to produce ultra-fine grain (UFG) material, and its principle and microstructural developments. The majority of papers on SPD materials have been devoted to the face centered cubic (FCC) structure materials such as Al, Cu and Ni. The UFG of high alloy ECAP processing has been difficult up to now, but we were successful in this study. Fe-20%Cr steel with extremely low C and N has different slip behavior from the FCC. The mechanical properties and corrosion resistance were investigated in term microstructural evolution during ECAP processing.博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
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Zhang, Yunbo. "Effect of microstructure on oxidative wear of a dual-phase low-alloy steel under different gaseous atmospheres, sliding speeds, and oxidation temperatures". Electronic Thesis or Diss., Compiègne, 2022. http://www.theses.fr/2022COMP2699.
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Le comportement tribologique des aciers à double phase a été étudié aux effets de différentes fractions volumiques de martensite (MVF), d'environnements gazeux et de vitesses de glissement, à l'aide d'un tribomètre à bille sur disque, dans des conditions de charge constante et de glissement par friction sèche. Par ailleurs, le comportement tribologique des couches d'oxyde formées à différentes températures et MVF a été étudié par nanoindentation et par des expériences de grattage. Les expériences de glissement à sec ont démontré qu'une MVF plus faible, des vitesses de glissement plus élevées et des environnements CO2 réduisent considérablement les taux d'usure en raison d'une meilleure oxydation ainsi que de la formation de couches d'oxyde protectrices sur les surfaces usées. Les essais de grattage des couches d'oxyde ont montré que le taux d'usure des couches d'oxyde de même composition diminuait à mesure que le MVF augmentait. La résistance à l'usure de la couche d'oxyde dominée par FeO est la plus mauvaise. Dans les mêmes conditions, la couche d'oxyde formée sur la martensite présente une résistance spécifique à l'usure plus élevée que celle formée sur la ferriteThe tribological behavior of dual-phase steels was investigated at the effects of different martensite volume fraction (MVF), gaseous environments, and sliding velocities, using a ball-on-disk tribometer, under constant load and dry friction sliding conditions. Furthermore, the tribological behavior of oxide layers formed at different temperatures and MVF was investigated by nanoindentation and scratching tests. Dry sliding experiments demonstrated that lower MVF, higher sliding velocities, and CO2 environments significantly reduce wear rates due to improved oxidation as well as the formation of protective oxide layers on the worn surfaces. Scratch tests of oxide layers revealed that the wear rate of same composition oxide layers decreased with increasing MVF. The wear resistance of the FeO-dominated oxide layer is the worst. Under the same conditions, the oxide scale formed on martensite has higher specific wear resistance than that formed on ferrite
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Thompson, Alan. "High Strain Rate Characterization of Advanced High Strength Steels". Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2831.
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The current research has considered the characterization of the high strain rate constitutive response of three steels: a drawing quality steel (DDQ), a high strength low alloy steel (HSLA350), and a dual phase steel (DP600). The stress-strain response of these steels were measured at seven strain rates between 0. 003 s-1 and 1500 s-1 (0. 003, 0. 1, 30, 100, 500, 1000, and 1500 s-1) and temperatures of 21, 150, and 300 °C. In addition, the steels were tested in both the undeformed sheet condition and the as-formed tube condition, so that tube forming effects could be identified. After the experiments were performed, the parameters of the Johnson-Cook and Zerilli-Armstrong constitutive models were fit to the results. In order to determine the response of the steels at strain rates of 30 and 100 s-1, an intermediate rate tensile experiment was developed as part of this research using an instrumented falling weight impact facility (IFWI). An Instron tensile apparatus was used to perform the experiments at lower strain rates and a tensile split-Hopkinson bar was used to perform the experiments at strain rates above 500 s-1
A positive strain rate sensitivity was observed for each of the steels. It was found that, as the nominal strength of the steel increased, the strain rate sensitivity decreased. For an increase in strain rate from 0. 003 to 100 s-1, the corresponding increase in strength at 10% strain was found to be approximately 170, 130, and 110 MPa for DDQ, HSLA350, and DP600, respectively.
The thermal sensitivity was obtained for each steel as well, however no correlation was seen between strength and thermal sensitivity. For a rise in temperature from 21 to 300 °C, the loss in strength at 10% strain was found to be 200, 225, and 195 MPa for DDQ, HSLA350, and DP600, respectively for the 6 o?clock tube specimens.
For all of the alloys, a difference in the stress ? strain behaviour was seen between the sheet and tube specimens due to the plastic work that was imparted during forming of the tube. For the DP600, the plastic work only affected the work-hardening response.
It was found that both the HSLA350 and DDQ sheet specimens exhibited an upper/lower yield stress that was amplified as the strain rate increased. Consequently the actual strength at 30 and 100 s-1 was obscured and the data at strain rates above 500 s-1 to be unusable for constitutive modeling. This effect was not observed in any of the tube specimens or the DP600 sheet specimens
For each of the steels, both the Johnson-Cook and Zerilli-Armstrong models fit the experimental data well; however, the Zerilli-Armstrong fit was slightly more accurate. Numerical models of the IFWI and the TSHB tests were created to assess whether the experimental results could be reproduced using the constitutive fits. Both numerical models confirmed that the constitutive fits were applied correctly.