Dissertations / Theses on the topic 'Martensitic stainless steel Metallography'
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Morgan, Terence S. "Microstructural effects of neutron irradiation on ferritic/martensitic stainless steels." Thesis, Loughborough University, 1992. https://dspace.lboro.ac.uk/2134/13768.
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A commercial grade 12%CrMo VNb ferritic/martensitic stainless steel in the form of parent plate and high-nickel off-normal weld material has been fast neutron irradiated to equivalent damage levels of 33 and 50 dpa at 400 and 465°C respectively. The microstructural and microchemical changes induced in the irradiated material, together with as-tempered and thermal control material, have been determined to high resolution by conventional transmission electron microscopy and the use of a field emission gun scanning transmission electron microscope (FEGSTEM). Equilibrium (co )segregation of chromium, molybdenum and phosphorus was detected at boundary planes in thermally aged material, with greater enrichment at the higher ageing temperature. The relative magnitudes of apparent phosphorus segregation at the two temperatures were in accordance with McLean's model governing the kinetic approach to equilibrium. The electron probe I segregant interaction was modelled in an attempt to deconvolute true segregant concentrations from derived concentration profiles: these 'deconvoluted' concentrations approximated those predicted by McLean's model. The net effects of irradiation on parent plate interfacial microchemistry were found to be to: (i) inhibit the (co )segregation of chromium, molybdenum and phosphorus, (ii) cause chromium depletion from adjacent to boundary planes, (iii) cause enrichment of silicon at prior austenite and lath boundaries during irradiation at 400°C and (iv) cause enrichment of nickel at lath boundary planes only, at both temperatures. The radiationinduced precipitates ~C and G phase, both nickel- and silicon-rich, were observed. The fully martensitic off-normal weld metal transformed to a duplex austenite!ferrite structure during irradiation at 465°C; in contrast the thermal control was at least metastable. The transformation was thought to be a martensitic reversion, facilitated by radiation-generated dislocation loops acting as nucleation sites. The austenite was heavily voided (-15 vol.%); the ferrite was relatively void-free. Depletion of the oversized solutes chromium, manganese and molybdenum and enrichment of nickel, silicon, aluminium and traces of titanium were detected at void interfaces in the austenite: little segregation could be discerned at voids in the ferrite. Overall, the results within this work and in comparison to previous studies highlight the sensitivity to initial composition, microstructure and heat treatment that the 12%Cr ferritic/martensitic steels display in their response to irradiation.
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Naraghi, Reza. "Martensitic Transformation in Austenitic Stainless Steels." Thesis, KTH, Metallografi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37214.
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Martensitic transformation is very important in austenitic stainless steels where the transformation induced plasticity phenomenon provides a combination of good mechanical properties, such as formability and strength. However, the difficulty of predicting the material behaviour is one of the major drawbacks of these steels. In order to model this behaviour it is of great importance to be able to characterize the morphology, crystallography and the amount of different types of martensite. The morphology and crystallography of thermal and deformation induced lath martensite in stainless steels were re-examined by means of optical microscopy and electron backscatter diffraction (EBSD) technique. The experiments were performed on AISI301, 304 and 204Cu austenitic stainless steels. Plastic deformation was carried out by means of uniaxial tensile tests at the strain rate of to produce strain induced α’-martensite at a temperature ranging from 0 to 60ºC. An in-situ measurement of the martensite content was performed during the tensile testing using a Ferritescope to provide the necessary experimental values for modelling. Optical microscopy revealed the morphology of the strain induced α’-martensite as sets of thin parallel needles that go through the parent austenite grain and stop at the grain or annealing twin boundaries. Large amount of α’-martensite could be seen at the intersection of shear bands. However, considerable amount of α’-martensite was also observed when only one set of bands is activated. EBSD was successfully used to analyze the morphology and crystallography of martensite. The α’-martensite maintained the Kurdjumov-Sachs (K-S) orientation relationship with the austenite phase. Although all six possible variants did not appear within a single packet, one or two variants were often favoured out of six related to the specific {111} plane. The misorientations between the neighbouring variants were mainly <111> 60º or <110> 49.5º.
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Danks, J. "Cyclic creep of T316 stainless steel." Thesis, Coventry University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328644.
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Buckley, J. R. "Hydrogen embrittlement of austenitic stainless steel." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315550.
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Butler, J. J. F. "Hydrogen embrittlement of austenitic stainless steel." Thesis, University of Newcastle Upon Tyne, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374127.
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O'Donnell, I. J. "Ductile fracture in type 316 stainless steel." Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356270.
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Mattin, Sarah Patricia. "Nucleation of corrosion pits on stainless steel." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321495.
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Pirouznia, Pouyan. "High cycle fatigue properties of stainless martensitic chromium steel springs." Thesis, KTH, Materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103201.
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For many materials and components like in high speed trains and airplanes fatigue failures occur in the range of over 107 load cycles which is called the high cycle fatigue range. A modern version of the springs was invented which are applied in a certain application. Ultrasonic fatigue testing (20 kHz machine) was conducted for evaluating the steel of the springs. This research explores the fundamental understanding of high cycle fatigue testing of strip steel and assesses a stainless martensitic chromium steel at the high cycle fatigue range. Finite element modeling was conducted to gain knowledge about the effect of various parameters. Significant attention was devoted to the fatigue failure initiations by SEM/EDS. The work demonstrated that the method of investigation for high cycle fatigue test is reliable. Fatigue failure at this range was initiated by internal defects which all included non-metallic inclusion. A critical distance was defined Within the strip fatigue specimen where all the fatigue failure initiated. The 3D stress field in the specimen was determined by FEM modeling and the local applied stress at the whole of the flat part of specimen and critical distance was estimated. FEM was also employed to give additional information about the effect of parameters. It was established that damping had the largest influence. The local applied stress of the fatigue test was calculated by means of FEM and SEM analysis. It was used to adjust the S-N curve which resulted in 15% lower values than the nominal applied stress.
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Hedström, Peter. "Deformation induced martensitic transformation of metastable stainless steel AISI 301 /." Luleå : Luleå University of Technology, 2005. http://epubl.luth.se/1402-1757/2005/79.
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Hedström, Peter. "Deformation induced martensitic transformation of metastable stainless steel AISI 301." Licentiate thesis, Luleå, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25748.
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Metastable stainless steels are promising engineering materials demonstrating good corrosion resistance and mechanical properties. Their mechanical properties are however significantly affected by the deformation induced martensitic transformation. Hence, in order to use these steels to their full potential it is vital to have profound knowledge on this martensitic phase transformation. The aim of this thesis was therefore to investigate the evolution of phase fractions, texture, microstrains and microstructure to improve the current understanding of the deformation induced martensitic transformation in AISI 301. To investigate the deformation behavior of AISI 301, in-situ high-energy x- ray diffraction during tensile loading has been performed on samples suffering different cold rolling reduction. Ex-situ transmission electron microscopy, electron back-scattered diffraction and optical microscopy were also used to characterize the microstructure at different deformation levels. The results show that parts of the austenite transforms to both ά- martensite and ε-martensite during deformation of AISI 301. The transformation behavior of ά-martensite is however completely different from the transformation behavior of ε-martensite. ε-martensite forms in a parabolic behavior, while the ά-martensite transformation can be divided in three characteristic stages. The third transformation stage of ά-martensite has previously not been reported and it is characterized by a series of rapid transformations, each of which is followed by a period of yielding without any transformation. Moreover, the lattice strain evolution in the austenite at high plastic strains was found to be oscillatory, which is correlated with the stepwise transformation of ά-martensite as well as changes in x-ray peak broadening. This behavior was also coupled with the evolution of microstructure, where a distinct banded structure consisting of slip bands and Ü-martensite was observed at low plastic strains. This banded structure was however broken at high plastic strains when the ά-martensite grew larger and formed a block- shaped morphology. These findings lead to the conclusion that the three stages of ά- martensite transformation is due to different stages of nucleation and growth. The ά-martensite will first form as small nucleus, mainly at dislocation pile-ups along slip bands. The nucleuses will grow moderately in size and the structure will become saturated with nucleuses. Hence, the only way more ά-martensite can form is by growth of the existing nucleuses. This growth is very localized and seen as bursts in the transformation curve. The oscillatory behavior observed for the lattice strains during martensite formation possibly originate when semicoherent boundaries between austenite and ά-martensite become incoherent as the ά-martensite grow large.Godkänd; 2005; 20061213 (haneit)
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Barlow, Lilian D. "The effect of austenitising and tempering parameters on the microstructure and hardness of martensitic stainless steel AISI 420." Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-11262009-182934/.
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Gardner, L. "A new approach to structural stainless steel design." Thesis, Imperial College London, 2002. http://hdl.handle.net/10044/1/8862.
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Benítez, Vélez Soraya. "Oxidation kinetics and mechanisms in HT-9 ferritic/martensitic stainless steel." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012151.
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Hirsch, Michael Robert. "Fretting behavior of AISI 301 stainless steel sheet in full hard condition." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24759.
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Haddad, Naseem Issa Abdallah. "The development of microstructure in duplex stainless steel welds." Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/221890.
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Sillo, C. E. "Microstructural and chemical studies of stainless steel/refractory interactions." Thesis, University of Sheffield, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291003.
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Ren, Gang. "Corrosion and passivity of 13Cr supermartensitic stainless steel." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609807.
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Zangiabadi, Amirali. "Low-temperature interstitial hardening of 15-5 precipitation hardening martensitic stainless steel." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1480769348244855.
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Laws, Mark S. "Segregation at grain boundaries in sensitised A.I.S.I. 316 stainless steel." Thesis, University of Surrey, 1990. http://epubs.surrey.ac.uk/799994/.
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Shenton, Paul Aidan. "Grain growth during the thermomechanical processing of austenitic stainless steel." Thesis, University of Sheffield, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364249.
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Tibblin, Fritjof. "Characterization of a newly developed martensitic stainless steel powder for Laser and PTA cladding." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-163788.
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A newly developed martensitic stainless steel powder, called “powder A”, designed for surface coating with laser cladding and PTA cladding was characterized. The purpose with powder A is to achieve both good corrosion resistance and wear resistance in a stainless steel grade. The investigation of powder A was divided into cladding characterization, microstructural investigation and a property comparison to existing grades 316 HSi and 431 L. Powder A was successfully deposited with laser cladding, exhibiting a wide process window, and PTA cladding. In both cases no preheating was required and no cracks were formed. The microstructure examination indicates that powder A has a martensitic structure possibly containing small amounts of ferrite in the grain boundaries. Thermodynamic calculations in computer software Thermo-Calc 4.1 supported this theory. The microstructure of powder A proved to be very stable over a wide range of cladding parameters. Powder A was significantly harder than 316 HSi and 431 L and had better corrosion resistance than 431 L in a chloride environment. Powder A had similar corrosion properties as 316 HSi in the experiments made .The wear performance of the powder A coatings was similar to 431 L. This was surprising since the hardness of the powder A coatings is significantly higher compared to 431 L.
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DeMania, Deborah Ann. "The influence of martensitic transformation on the formability of 304L stainless steel sheet." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11488.
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Alnajjar, Michella. "Corrosion properties of 17-4 PH martensitic stainless steel obtained by additive manufacturing." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEM035.
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Ce travail de thèse porte sur la corrosion de l'acier inoxydable à durcissement structural 17-4 PH élaboré par fabrication additive par fusion sélective laser (SLM).Nous avons montré que la microstructure de l'acier 17-4 PH fabriqué par SLM est ferritique, contrairement à l'acier corroyé qui a une microstructure martensitique typique. Ceci résulte des vitesses de refroidissement et de chauffage très élevées (105-106 K/s) qui empêchent la formation de l'austénite et conduisent à une rétention complète de ferrite δ issue de la solidification.Nous avons mené une étude comparative de corrosion électrochimique à l'aide de courbes de polarisation anodiques dans des solutions chlorurées acides. Le matériau SLM présente une meilleure résistance à la corrosion généralisée que le matériau corroyé. Ce résultat est lié à l'absence d'inclusions MnS dans le matériau SLM. Au contraire, dans le matériau corroyé, la dissolution des inclusions MnS conduit à une redéposition d'espèces riches en soufre sur toute la surface, ce qui déstabilise le film passif.Nous avons également mené une étude de la fragilisation par l'hydrogène. Cette étude a montré une sensibilité plus forte du matériau SLM, qui peut s'expliquer par la différence de microstructure, en particulier la taille grains. Le matériau SLM, ferritique, présente une fissuration sous-critique transgranulaire, dont l'initiation est pilotée par le niveau de contrainte et la quantité d'hydrogène introduite dans le matériau. Au contraire, dans l'acier corroyé, martensitique, la fissuration sous-critique suit les anciens joints austénitiques. On montre par ailleurs que son initiation nécessite un minium de déformation plastiqueThis PhD thesis focuses on the corrosion properties of 17-4 PH precipitation hardenable stainless steel obtained by additive manufacturing, specifically by Selective Laser Melting (SLM).It was shown that the microstructure of 17-4 PH steel fabricated by SLM was ferritic, in contrast to the typical martensitic microstructure of wrought 17-4 PH steel. This was correlated to the high cooling and heating rates (105-106 K/s) experienced during SLM that suppressed the δ ferrite to austenite transformation and retained the δ ferrite until the end of fabrication.A comparative electrochemical study was conducted on both steels. It was found that the SLM-ed steel had superior general corrosion resistance than the wrought steel. This was attributed to the absence of MnS inclusions in the SLM-ed steel. In contrast, in the wrought material, the dissolution of the MnS inclusions resulted in the redeposition of sulphur-rich species all over the surface, which contributed to the destabilization of the passive film.A hydrogen embrittlement study was also conducted. It was found that the SLM-ed ferritic steel was more susceptible to hydrogen embrittlement than the wrought martensitic steel. The difference in microstructure, specifically the grain size, played a major role in this difference in behavior. In the SLM-ed ferritic steel subcritical cracking was transgranular and its initation was governed by the stress level and the amount of hydrogen introduced into the material. On the other hand, in the wrought martensitic steel, subcritical cracking was along the prior austenitic grain boundaries and it was shown that its initiation required at least a small amount of plastic deformation
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McCann, Scott. "A study of environmental exposure on structural adhesively bonded austenitic stainless steel." Thesis, Sheffield Hallam University, 2003. http://shura.shu.ac.uk/20033/.
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Structural adhesive bonding is becoming a popular alternative to the more traditional joining methods, such as spot and laser welding, for joining metallic substrates intended for structural applications. Structural adhesive bonding offers many advantages, for example enhancing fatigue resistance, the ability to join dissimilar materials and providing cost effective joining solutions. The work presented in this thesis studies the effectiveness of bonding austenitic stainless steel using a two-part structural epoxy adhesive. A comprehensive review of literature has been carried out covering the mechanisms of adhesion, the importance of surface pre-treatments and surface analytical techniques used to evaluate the chemical and physical attributes of substrates prior to bonding and the failure analysis of fracture surfaces. In addition techniques used to study the environmental durability and fatigue performance of adhesive joints has being appraised. The first experimental phase evaluated the effect of commercially available stainless steel finishes on adhesive joint durability using the standard overlap specimen. Environmental exposure included natural outdoor weathering and a high humidity environment coupled with the application of an applied load. It was noted that to further appraise more durable pre-treatments used prior to bonding different testing configurations was required. Perforated single overlap joints and wedge test specimens were used to assess eleven different pre-treatments, ranging from relatively simply to more complex electro-chemical techniques. All pre-treatments included in the research were physically and chemically characterised using scanning electron microscopy (SEM), surface profilometry and X-Ray Photoelectron Spectroscopy (XPS). The complementary data from the perforated lap shear and wedge crack extension testing ranked the pre-treatment used in a similar fashion. The two most durable treatment were the Accomet C proprietary coating and the sulphuric acid sodium dichromate anodisation process. A pattern emerged revealing the more durable pre-treatments produced higher Cr:Fe ratios on the surface. Post failure analysis of fractured specimens was carried out using SEM and XPS. It was shown that after the environmental exposure of specimens to a high humidity hydro-thermal stress regime the most durable pre-treatments initially failed cohesively within the adhesive and then interfacially between the adhesive and associated oxide layer. The second stage of the experimental work evaluated the fatigue performance of single overlap joints. The fatigue performance of joints was increased using cost-effective surface conditioning techniques. It was also shown the fatigue response of the adhesive joints is dependant upon test frequency, the effect of which being more prominent at low frequencies. The effect of mean load has also been evaluated, and revealed a reduction in load amplitude seriously diminishes the fatigue lifetime of specimens. The effects of aqueous ageing in distilled water at ambient temperatures was assessed. It was shown that continuous immersion for up to 72 weeks caused total delamination of the adhesive from the substrate. It was postulated that moisture ingression into the interfacial region fills air voids and caused the adhesive to displace from the adherend. An elastic model based on beam theory has being developed to determine the elastic rotation of the overlap region of single lap joints under the application of a tensile load. The model was validated by experimental results, and evaluated the effects of adherend thickness and overlap length. The model has the potential to aid engineers when designing structures using adhesive bonding, especially concerning thin gauge applications where plastic deformation can occur under comparatively small loads.
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van, Niekerk Cornelis Janse. "In-situ alloying of AISI 410L martensitic stainless steel with nitrogen during laser cladding." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61341.
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The feasibility of in-situ alloying of AISI 410L martensitic stainless steel with nitrogen during Nd-YAG laser cladding was investigated with the aim of achieving a nitrogen content of at least 0.08 wt% and fully martensitic microstructures in the final clad deposit. Two in-situ nitrogen alloying techniques were studied.
In the first set of experiments, the absorption of nitrogen from nitrogen-rich gas atmospheres was studied. Laser cladding with commercially available AISI 410L powder was performed using nitrogen-rich shielding and carrier gas. A marginal increase in deposit nitrogen content was observed, with the clad deposit displaying low hardness and mostly ferritic microstructures. Poor nitrogen absorption from nitrogen-containing atmospheres during Nd-YAG laser cladding is generally attributed to the short thermal cycle and to suppression of plasma formation above the weld pool.
In the remaining experiments, Si3N4 powder was investigated as an alternative source for nitrogen during cladding. The addition of Si3N4 to the AISI 410L powder feed resulted in clad microstructures consisted of columnar -ferrite grains with martensite on the grain boundaries, higher hardness and an increase in deposit nitrogen content (to a maximum of 0.064 wt% nitrogen). Higher nitrogen contents in the clad deposit, however, significantly increased the volume percentage porosity in the clad layer. This prompted an investigation into the feasibility of raising the nitrogen solubility of the alloy through additions of manganese and nickel to the powder feed.
Thermodynamic modelling revealed that the addition of manganese to AISI 410L powder increases the nitrogen solubility limit due to its negative interaction parameter with nitrogen. The addition of up to 3.5 wt% manganese to AISI 410L powder containing Si3N4 significantly increased the nitrogen solubility in the deposit. A martensitic microstructure with 0.12 wt% nitrogen and a peak hardness of 410 HV was achieved without any adverse increase in porosity in the clad layer. The clad nitrogen content easily exceeded the minimum requirement of 0.08 wt%.
High nickel concentrations in AISI 410L stainless steel expand the austenite phase field at the expense of -ferrite and alter the solidification mode from ferritic to austenitic-ferritic. The addition of up to 5.5 wt% nickel, or combinations of nickel and manganese, to the nitrogen-alloyed AISI 410L powder feed raised the deposit nitrogen content, but not to the same extent as those deposits alloyed with manganese only. Since more austenite is present on cooling in nickel-alloyed AISI 410L deposits, less nitrogen is rejected to the liquid phase on solidification, resulting in higher nitrogen contents and less porosity in the room temperature microstructures.
The amount of dilution during single-track laser cladding is mainly influenced by the specific energy per unit mass delivered by the laser beam. The clad height is strongly influenced by the powder deposition rate, whereas the bead width is influenced by the wettability of the deposits during laser cladding. During multi-track cladding, the observed percentage porosity is a function of the aspect ratio of the individual beads making up the clad layer, the deposition rate and the clad height. High deposition rates result in thicker layers, increasing the distance that N2 gas bubbles have to travel to escape to the atmosphere, while a high aspect ratio favours interbead porosity. The results suggest that in-situ nitrogen alloying during laser cladding should preferably be performed at low deposition rates to ensure higher clad nitrogen contents and hardness, lower clad heights, less dilution and less porosity.Dissertation (MEng)--University of Pretoria, 2016.
Materials Science and Metallurgical Engineering
MEng
Unrestricted
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Benchouieb, Rachid. "Effect of multi-pass hot rolling on recrystallisation behaviour of ferritic stainless steel." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389668.
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Ionescu-Gabor, Sorin. "Study and empirical modelling of recrystallisation annealing of martensitic chromium steel strip by means of EBSD." Licentiate thesis, KTH, Materials Science and Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10539.
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Recrystallisation annealing, a repeated heat treatment between different stages of cold rolling of martensitic chromium steel strip, is successful when neither high rolling forces nor wear of the working rolls occur during the subsequent cold rolling. Mechanical properties as tensile strength, yield, elongation or hardness have been, by tradition, the criteria that described the quality of the annealing process. In recent years, the development of the measurement equipment in the rolling mills and of the instruments for material investigations has accentuated more and more the role played by the microstructural properties in the evaluation of the heat treatment. Two microstructural characteristics of the degree of annealing are, firstly and most important, the recrystallisation degree, and, secondly, the secondary carbide density.
The sample manufacturing and heat treatment, modelling and microstructure investigations by light optical- (LOM) and scanning electron microscopy (SEM) described in this article were carried out at Sandvik Materials Technology’s R&D Department and Bell Furnace Line in Sandviken, Sweden, while microstructure investigations and evaluation by scanning electron microscopy with field emission gun (FEG-SEM) and electron back scatter diffraction (EBSD) were done at the Corrosion and Metals Research Institute (KIMAB) in Stockholm, Sweden.
The first part of this work shows that, in contrast to the traditional methods LOM and SEM, that use chemical etching for the preparation of the samples, EBSD can successfully characterise recrystallised structures in annealed martensitic chromium steels. Unlike conventional microscopy with LOM and SEM, EBSD is able to reveal the grain geometry, as well as to separate and identify the different phases in this kind of steels (ferrite, M23-, M6-carbides). Important parameters such as grain size, particle size and recrystallised fraction can be measured with high accuracy. This information can be used to understand, evaluate, control and even predict the recrystallisation annealing of martensitic chromium steel.
The second part of this work presents how the results from microstructure description by EBSD can be directly used in relatively simple empirical models for determination of recrystallisation degree as function of the annealing parameters and the deformation history. EBSD was applied to evaluate the degree of recrystallisation in a series of annealing tests, with the purpose to model recrystallisation temperature in two types of martensitic chromium steel strip, a traditional one and one alloyed with molybdenum, cold rolled with different amounts of reduction and annealed with different temperatures, soaking times and heating rates. The empirical quadratic models were built with Umetrics’ software for experimental design, MODDEÒ 8.0 and they defined the recrystallisation degree (limits for LAGB and HAGB were set to 1.5° and 7.5° for the first grade and 2.5° and 10° for second one) and the secondary carbides density as functions of annealing temperature, soaking time and cold reduction (the factor heating rate was removed as nonsignificant). To be observed that these empirical models were fit much better for the recrystallisation degree than for the secondary carbides density.
The modelling work described above, together with the implementation of online physical temperature models in the bell annealers may lead to an increased productivity in the production plant by shortening the annealing cycle and minimising scrap and thus to an economical gain of ca 1,5 MSEK per year at Sandvik Materials Technology.
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Prasannavenkatesan, Rajesh. "Microstructure-sensitive fatigue modeling of heat treated and shot peened martensitic gear steels." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31713.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: David L. McDowell; Committee Member: G. B. Olson; Committee Member: K. A. Gall; Committee Member: Min Zhou; Committee Member: R. W. Neu. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Angella, Giuliano. "Strain path, flow stress and microstructure evolution of an austenitic stainless steel at high temperature." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251254.
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Lee, Chihoon. "Phase Transformations Accompanying Low-Temperature Carburization of Martensitic Stainless Steels under Paraequilibrium Conditions." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1325878014.
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Jayaraman, Vikram. "Production, characterization and testing of Tempered Martensite Assisted Steels (TMAS) obtained via subcritical annealing of cold rolled TRIP steels." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99769.
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The requirement for lighter, safer and fuel efficient cars has created a major stir in the steel research society to develop advanced automotive steels. Since there is a trade off between strength and ductility, most of the conventional high strength steels do not address the strength-formability combination. With the realization of the TRIP phenomenon first in austenitic stainless steels, a new generation of advanced steels called TRIP steels were realised with an inexpensive and easier to process C-Mn-Si chemistry. TRIP or TRransformation Induced Plasticity is a phenomenon where the timely strain induced transformation of Retained Austenite (RA) to Martensite locally strengthens the steel at the point of plastic instability, causing failure by necking to be postponed and shifted elsewhere along the steel. This phenomenon repeated over and over again allows increased levels of strength and ductility, prior to fracture.In current TRIP grades, the retained austenite particles present have to posses certain characteristics such as, optimum carbon concentration, optimum grain size and morphology etc. in order to account toward mechanical properties. Such limiting characteristics in turn minimize the processing window and make TRIP processing expensive and difficult to control. In this work, it is suggested that Tempered Martensite Assisted Steels (TMAS) obtained from TRIP steels via subcritical annealing of cold rolled TRIP steels may potentially replace TRIP steels. Relationship between the retained austenite volume fractions and mechanical properties was developed for TRIP steels. The effect of variation of retained austenite on tempered martensite volume fraction in TMAS, which in turn affect the mechanical properties was also investigated in depth. Results indicate that tempered martensite particles in TMAS do not have any limiting factors as in the case of RA in TRIP steels, in order to contribute toward enhancement of mechanical properties. Results also indicate that TMAS offers better strength levels compared to TRIP steels for same the level of formability.
Retained austenite volume fractions in TRIP steels were measured through XRD. Cold rolling of the samples was done in a laboratory scale rolling machine. The microstructures were analysed using conventional and color etching techniques. A new color etching technique for viewing all the four major phases in TRIP steel was developed in this work. The mechanical properties of both TRIP and TMAS were assessed by shear punch testing. And finally, the relationship between tempered martensite volume fraction and TMAS properties was developed and was compared to TRIP properties.
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Powell, D. J. "A study of the precipitation, creep and creep-fatigue characteristics of a 20/25/Nb-stabilised stainless steel." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370959.
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Rimko, Marcel. "Struktura a vlastnosti martenzitických korozivzdorných ocelí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417077.
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The final thesis deals with martensitic stainless steel and their mechanical properties. The theoretical part consists of information about corrosion, chemical composition, heat treatment and mechanical properties of various types of steel. The practical part deals with the influence of the cooling rate during heat treatment and nickel content on the mechanical properties and microstructure of the GX4CrNi13-4 steel.
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Martin, Diaz Ulises. "STRESS CORROSION CRACKING OF AUSTENITIC STAINLESS STEEL REBAR IN SIMULATED CONCRETE PORE SOLUTION INFLUENCED BY STRAIN-INDUCED MARTENSITIC TRANSFORMATION." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1626520184452948.
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Chen, Meichuan. "Synchrotron Radiation X-ray Diffraction Study on Microstructural and Crystallographic Characteristics of Deformation-Induced Martensitic Transformation in SUS304 Austenitic Stainless Steel." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215535.
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Liu, Jikai. "Influence of metallurgical phase transformation on crack propagation of 15-5PH stainless steel and 16MND5 low carbon steel." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00833206.
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Ou study focuses on the effects of phase transformations on crack propagation. We want to understand the changes of fracture toughness during welding. In this work, fracture toughness is expressed by J-integral. There are many experimental methods to obtain the critical toughness JIC but they are impractical for our investigation during phase transformation. That is the reason why we have proposed a method coupling mechanical tests, digital image correlation and finite element simulation. The fracture tests are implemented on pre-cracked single edge notched plate sample which is easy for machining and heat conduct during phase transformation. The tests are conducted at different temperatures until rupture. Digital image correlation gives us the displacement information on every sample. Each test is then simulated by finite element where the fracture toughness is evaluated by the method G-Theta at the crack propagation starting moment found by potential drop method and digital image correlation technical. Two materials have been studied, 15Cr-5Ni martensitic precipitation hardening stainless steel and 16MND5 ferritic low carbon steel. For these two materials, different test temperatures were chosen before, during and after phase transformation for testing and failure characterization of the mechanical behavior. Investigation result shows that metallurgical phase transformation has an influence on fracture toughness and further crack propagation. For 15-5PH, the result of J1C shows that the as received 15-5PH has higher fracture toughness than the one at 200°C. The toughness is also higher than the original material after one cycle heat treatment probably due to some residual austenite. Meanwhile, pure austenite 15-5PH at 200°C has higher fracture toughness than pure martensitic 15-5PH at 200°C. For 16MND5, the result also proves that the phase transformation affects fracture toughness. The as received material has bigger J1C than the situation where it was heated to 600°C. On the other hand, the material at 600°C just before isothermal bainite transformation after the austenitization during cooling process also has higher fracture toughness than the one at 600°C before austenitization. These two conclusions are consistent well with the result of 15-5PH. But the final situation of 16MND5 after one cycle heat treatment has a slightly smaller J1C than the receiving situation. It means that one cycle heat treatment hasn't an significant influence on 16MND5fracture toughness. Conclusions show that one should pay attention to the heating period before austenitization of the substrate material when people do the welding as the higher temperature will bring the lower fracture toughness during this process. While during cooling period, the fracture toughness doesn't change a lot during, before or after the cooling induced phase transformation. Even for 15-5PH, it has a better fracture toughness after the martensite transformation than before.
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Kusunoki, Takuya. "Quantification of the Tempering Response in Type 410 Steel Welds." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1607011624665895.
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Lin, Sen. "Deformation-Induced Martensitic Transformation and Mechanical Properties of Duplex and Austenitic Stainless Steels : A Synchrotron X-Ray Diffraction Study." Thesis, KTH, Metallografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233334.
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Metastable austenitic and duplex stainless steels are widely used materials in industrial anddomestic applications, owing to their attractive characteristics such as good corrosion resistanceand favorable mechanical properties. Both types of steel experience enhanced mechanicalproperties during plastic deformation due to the formation of the martensite phase from theparent austenite phase, this is called deformation-induced martensitic transformation (DIMT).It is therefore of technical interest to study the transformation mechanism and its impact onmechanical properties for a better understanding and ultimately for developing new materialswith improved performance in certain applications. In the present thesis, two austenitic stainless steels (201Cu, HyTens® 301) and two duplexstainless steels (FDX25®, FDX27®) were investigated. Samples were tensile tested during insitusynchrotron radiation experiments performed at the Cornell High Energy SynchrotronSource (CHESS), Ithaca, USA. Tests were performed at both room temperature and at elevatedtemperatures. The collected diffraction data were then processed by software such as Fit2D andMATLAB. Quantitative phase fraction analysis based on the direct comparison method wasperformed successfully. Microstructural analysis of samples before deformation and after thefull tensile testing was also performed using electron microscopy. The deformation induced martensitic transformation took place in HyTens 301, FDX25 andFDX27, but in 201Cu the austenite was stable during the tensile tests conducted here. The a’-martensite formed in a significantly higher fraction than the ε-martensite in all alloys. At roomtemperature, the critical stress levels for martensitic transformation were 490 MPa, 700 MPaand 700MPa for HyTens 301, FDX25 and FDX27, respectively.
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Patra, Anirban. "Modeling the mechanical behavior and deformed microstructure of irradiated BCC materials using continuum crystal plasticity." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50366.
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The mechanical behavior of structural materials used in nuclear applications is significantly degraded as a result of irradiation, typically characterized by an increase in yield stress, localization of inelastic deformation along narrow dislocation channels, and considerably reduced strains to failure. Further, creep rates are accelerated under irradiation. These changes in mechanical properties can be traced back to the irradiated microstructure which shows the formation of a large number of material defects, e.g., point defect clusters, dislocation loops, and complex dislocation networks. Interaction of dislocations with the irradiation-induced defects governs the mechanical behavior of irradiated metals. However, the mechanical properties are seldom systematically correlated to the underlying irradiated microstructure. Further, the current state of modeling of deformation behavior is mostly phenomenological and typically does not incorporate the effects of microstructure or defect densities.
The present research develops a continuum constitutive crystal plasticity framework to model the mechanical behavior and deformed microstructure of bcc ferritic/martensitic steels exposed to irradiation. Physically-based constitutive models for various plasticity-induced dislocation migration processes such as climb and cross-slip are developed. We have also developed models for the interaction of dislocations with the irradiation-induced defects. A rate theory based approach is used to model the evolution of point defects generated due to irradiation, and coupled to the mechanical behavior. A void nucleation and growth based damage framework is also developed to model failure initiation in these irradiated materials. The framework is used to simulate the following major features of inelastic deformation in bcc ferritic/martensitic steels: irradiation hardening, flow localization due to dislocation channel formation, failure initiation at the interfaces of these dislocation channels and grain boundaries, irradiation creep deformation, and temperature-dependent non-Schmid yield behavior. Model results are compared to available experimental data.
This framework represents the state-of-the-art in constitutive modeling of the deformation behavior of irradiated materials.
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Rosa, Guilherme Cortelini da. "Estudo da usinabilidade no torneamento a seco do aço inoxidável martensítico AISI 420 C endurecido com ferramenta de metal-duro." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/165625.
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O estudo de usinabilidade de um material é muito importante para a determinação das características de fabricação por usinagem. Este estudo se aplica ao aço inoxidável martensítico AISI 420 C endurecido, usado na fabricação de peças de alta precisão, instrumentos cirúrgicos, eixos, turbinas e cutelaria. Deste modo, realizaram-se investigações utilizando corpos de prova endurecidos (têmpera e revenimento) com durezas de (48 1) e (53 2) HRC no torneamento a seco utilizando ferramentas de metal-duro classe ISO S com grãos extrafinos e revestimento PVD. Para estes corpos de prova variaram-se a velocidade de corte e o avanço e avaliaram-se as forças de usinagem e as tensões residuais geradas na peça. Para o material com 53 HRC, também foram analisadas a vida da ferramenta e a rugosidade. Na análise dos resultados obtidos para o material com 48 HRC, as tensões residuais tornaram-se menos compressivas (circunferencial) e mais trativas (axial) com o aumento do avanço. Além disso, os menores valores de tensão residual foram gerados utilizando menor avanço com maior velocidade de corte. Nos ensaios para o material a 53 HRC, o tempo de vida da ferramenta ficou entre 100 e 350 min para as condições ensaiadas. Os desgastes de flanco e entalhe foram evidenciados em todas as situações. O flanco da ferramenta também apresentou adesão de material da peça em todas as condições. Ao analisar os insertos em seu fim de vida, constatou-se que os mecanismos de desgastes predominantes foram a abrasão e o atrittion. Nas condições mais severas, a superfície da ferramenta exibiu trincas mecânicas e a camada subsuperficial da peça apresentou modificações microestruturais. Os perfis e os parâmetros de rugosidade registrados foram afetados pelo desgaste ao longo da vida da ferramenta. Com relação às tensões residuais circunferenciais geradas com a ferramenta nova, estas foram, em sua maioria, tensões de compressão. Com a progressão do desgaste de flanco, houve um aumento dos valores das tensões (de compressivas para menos compressivas ou até mesmo trativas). Já para as tensões axiais, os valores mostraram a tendência de se manterem compressivos. Observou-se para os perfis de tensões analisados que as tensões residuais foram compressivas e dependeram da profundidade da camada subsuperficial. Portanto, dentro das condições estudadas, conclui-se que peças de AISI 420 C endurecido podem ser fabricadas por torneamento de acabamento com ferramentas de metal-duro, permitindo obter vida longa para a ferramenta de corte, baixos valores de rugosidade, bem como valores de tensão residual compressiva, que são dados de usinabilidade importantes para esse material.The study of the material’s machinability is very important for the determination of important machining properties. This logic applies to hardened martensitic stainless steel AISI 420 C used in the manufacture of high precision parts, surgical instruments, shafts, turbines and cutlery. In this way, investigations were carried out using hardened workpieces (quenching and tempering) with hardness of (48 1) and (53 2 HRC) in dry turning using ISO-S grade carbide tools with extra-fine grains and PVD coating. For these workpieces, the cutting speed and the feed rate were varied and the machining forces and the residual stresses generated in the part were evaluated. For the material with 53 HRC, the tool-life and the surface roughness were also analyzed. In the analysis of the results obtained for the material with 48 HRC, residual stresses become less compressive (circumferential direction) and more tensile (axial direction) with increasing feed-rate. Moreover, smaller values of residual stress were generated using lower feed-rate at higher cutting speed. In the tests for the material at 53 HRC, the tool-life was between 100 and 350 min for the conditions tested. Flank and notch wear were evidenced in all situations. The flank face of the tool also showed adhesion of the workpiece material under all cutting conditions. When analyzing the inserts at their end of life, it was verified that the main mechanisms of tool wear were abrasion and attrition. In addition, under the most severe cutting conditions, the flank face of the tool exhibited mechanical cracks and the subsurface layer of the workpieces presented microstructural modifications. The registered profiles and roughness parameters were affected by wear during the tool-life. With respect to the circumferential residual stresses generated with the fresh tool, these were mostly compressive stresses. With the progression of tool flank wear, there was an increase in the values of the residual stress (from compressive to less compressive or even tractive). For the axial residual stresses, the values showed a tendency to remain compressive. It was observed for the residual stress profiles analyzed that the residual stresses were compressive and depended on the depth of subsurface layer. Therefore, within the cutting conditions considered, it can be concluded that hardened martensitic stainless steel AISI 420 C parts can be manufactured by finishing turning with carbide tools, allowing long tool-life, low surface roughness values, as well as compressive residual stress values, which are important machinability information for this material.
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Sierra, Robinson. "Investigation of the mechanical behaviour of TRIP steels using FEM." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99793.
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The need to develop light-weight and high strength materials for car frames which improve fuel efficiency and provide increased passenger safety during dynamic events such as automobile crashes has been the focus of the steel and automobile industries for the past 30 years. In recent years, the development of high strength steels such as multi-phase TRIP (Transformation-Induced Plasticity)-aided steels have shown great promise due to their excellent combination of high strength and ductility. The savings in automobile weight is provided by the inherent strength of TRIP steels which allows for the use of thinner sections. The TRIP effect is characterized by the phenomenon known as strain-induced martensitic transformation (SIMT) which enhances the work hardenability of such steels as the austenite phase transforms to the much harder martensite phase during plastic straining. This results in a resistance to local necking which subsequently enhances the strength, ductility, and formability of such steels. However, various factors exist which affect the mechanical behaviour of TRIP steels. This study will aim, through the use of finite element models, to investigate the role and influence of each of these factors on the TRIP effect in type 304 austenitic and multi-phase TRIP steels. These factors include the rate at which the martensitic transformation proceeds, the state of stress to which the material is subjected to, the interaction between the surrounding matrix and embedded retained austenite islands in multi-phase TRIP steels, and the volume fraction and morphology of the retained austenite islands. Investigation of these factors will provide further insight on each of their contributions to the TRIP effect in order to exploit the potential benefits offered by these steels.
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El, Hilali Fatima. "Etude de la sensibilité à la dépassivation des aciers inoxydables martensitiques à durcissement par précipitation : conséquence sur la corrosion sous frottement et la corrosion sous contraintes." Châtenay-Malabry, Ecole centrale de Paris, 1987. http://www.theses.fr/1987ECAP0055.
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Etude de la sensibilité à la dépassivation de l'acier inoxydable martensitique 17-4 ph à durcissement par précipitation. Examen de la corrosion par piqures sans contrainte appliquée, de la corrosion sous frottement sous contraintes de cisaillement et de compression et de la corrosion sous contrainte de tension (méthode de traction lente)
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Ambrož, Ondřej. "Vliv podmínek tuhnutí na strukturu a vlastnosti austenitických chromniklových ocelí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-319276.
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The thesis deals with the influence of solidification conditions on structure and mechanical properties of austenitic stainless steels. The first part involves the distribution of stainless steels and a basic understanding of the issue of achieving the desired structure and mechanical properties. The second part is focused on austenitic steels and their basic characteristics. This section also describes the experiment and the results achieved. Finally, these results were evaluated and further research steps were recommended.
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Novotný, Jan. "Svařování martenzitické korozivzdorné oceli pomocí hybridní technologie Laser - TIG." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417122.
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Theoretical part of this thesis includes overview of laser welding technology and possible combinations with arc welding methods for meeting desired properties of the weld. It also explains mechanical testing and metallographic examination on welds. The experimental part deals with optimisation of process parameters during welding of martensitic stainless steel, used in energetic industry using hybrid laser - TIG technology in regard of mechanical properties of the weld, its structure and proposal of technological parameters.
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Bueno, Juliana Cristina. "Desenvolvimento da técnica de identificação de fases por metalografia óptica com nanoindentação em liga inoxidável com efeito de memória de forma." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263102.
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Orientador: Paulo Roberto MeiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-18T15:15:33Z (GMT). No. of bitstreams: 1 Bueno_JulianaCristina_M.pdf: 6612143 bytes, checksum: ff1f20ccef9c00e4455c0b43362c43ce (MD5) Previous issue date: 2005
Resumo: Neste trabalho foi estudada uma liga inoxidável Fe-Mn-Si-Cr-Ni-Co com efeito de memória de forma (EMF) e os objetivos principais foram otimizar a técnica de coloração por ataque químico (color etching) para identificação e análise das fases presentes na microestrutura, o que permitiu a determinação da dureza da martensita-? e da austenita-? através da técnica de nanoindentação. O desenvolvimento deste processo também permitiu a quantificação das fases e e g por microscopia óptica. A técnica de coloração por ataque químico consiste na utilização de reagentes específicos que resultam em uma microestrutura composta por várias colorações, o que permite identificar fases por microscopia óptica. Os resultados de dureza obtidos por nanoindentação foram de 7,0 GPa para a martensita-? e de 3,0 GPa para a austenita-?. Já para a fração volumétrica da martensita-?, os resultados obtidos por microscopia óptica variaram de 33 a 40 % para amostras no estado deformado. Para amostras de tamanho de grão 123 ?m e 3º ciclo de treinamento, os resultados foram coerentes com os obtidos por difração de raios X de trabalhos anteriores para a mesma liga
Abstract: In this work a Fe-Mn-Si-Cr-Ni-Co stainless alloy with shape memory effect (SME) was studied and the main objectives were to optimize the technique of coloration by chemical attack (color etching) for identification and analysis of the phases in the microstructure, allowing the determination of the ?-martensite and the -austenite hardness by nanoindentation technique. The development of this process also allowed the quantification of the ?- and ?- phases by optical microscopy. The technique of coloration by chemical attack consists in the use of specific reagents to identify phases by color using optic microscopy. The hardness obtained was 7.0 GPa for ?-martensite and 3.0 GPa for ?-austenite. The volume fraction of the ?-martensite, measured with optical microscopy varied from 33 to 40 % for samples in the deformed state. For samples with grain size of 123 ?m and after the 3º training cycle, the results were coherent with the obtained by X ray diffraction of previous works for the same alloy
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Saied, Mahmoud. "Experimental and numerical modeling of the dissolution of delta ferrite in the Fe-Cr-Ni system : application to the austenitic stainless steels." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI016/document.
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La ferrite résiduelle δ est présente dans les microstructures de coulée des aciers inoxydables austénitiques. Elle résulte de la transformation incomplète δ→γ ayant lieu l'étape de solidification. Sa présence peut nuire à la forgeabilité à chaud des aciers inoxydables et peut conduire à la formation de criques de rives et de pailles en J lors du laminage à chaud des brames. Ce travail de thèse a pour but de comprendre les mécanismes de la transformation δ→γ à haute température dans les aciers inoxydables austénitiques via une modélisation expérimentale et numérique. La transformation a été étudié dans un alliage ternaire Fe-Cr-Ni coulé par lingot et de composition proche de celle des alliages industriels. Trois morphologies de ferrite ont été mises en évidence à l'état brut de solidification: lattes au bord du lingot, vermiculaire et lattes au centre. Leur cinétique de dissolution est étudiée à des températures allant de 1140°C à 1340°C et caractérisée en termes de fraction de ferrite et profils de composition du Cr et du Ni. La dissolution de la ferrite vermiculaire comprend trois étapes : une croissance initiale transitoire suivie par deux régimes de dissolution à haute puis à faible taux de transformation. D'un autre côté, il a été possible d'étudier la dissolution de la ferrite dans des microstructures multicouches élaborées par l'empilement de plaques de ferrite et d'austénite du système Fe-Cr-Ni et soudées à l'état solide par Compression Isostatique à Chaud puis réduits en épaisseurs par laminages successifs. L'étude et la caractérisation de la cinétique de dissolution de la ferrite est plus facile dans ces microstructures étant donnée la planéité initiale des interfaces δ/γ. L'analyse des résultats expérimentaux a été menée via le développement d'un modèle numérique, à interface mobile, de la transformation de phases δ→γ pilotée par la diffusion. La diffusion peut être traitée dans les géométries plane, cylindrique et sphérique. En guise de validation, le modèle a été utilisé pour analyser la dissolution de la ferrite dans les microstructures multicouches. Par la suite il a été appliqué au cas de la ferrite vermiculaire en usant d'une approche novatrice où la morphologie des dendrites est approximée par une combinaison de cylindres et de sphères. Malgré la simplicité des hypothèse sous-jacentes, le modèle a permis d'expliquer les mécanismes de croissance initiale et de changement de régime de dissolution. D'autre part, via une étude paramétrique, l'effet des données d'entrée a été étudié et les plus pertinentes d'entre eux en termes de prédiction quantitative ont été mises en avant, en particulier la description thermodynamique du digramme Fe-Cr-Ni, le gradient initial et la distribution des rayons des particules de ferriteResidual δ-ferrite is widely encountered in the as-cast microstructure of austenitic stainless steels. It stems from the incomplete high temperature solid-state δ→γ transformation occurring upon the solidification stage. Its presence has a detrimental effect the hot workability of stainless steels, leading to the formation of edge cracks and sliver defects during slabs hot rolling. This PhD work aims at bringing more understanding of the kinetics of high temperature δ→γ transformation in austenitic stainless steels via experimental and numerical modeling. The transformation was studied in a ternary Fe-Cr-Ni ingot-cast alloy with composition close to the industrial alloys. Three ferrite morphologies were identified: lathy at the edge of the ingot, vermicular and lathy at the center. Their dissolution kinetics were established at temperatures ranging from 1140°C to 1340°C and characterized in terms of ferrite fraction and Cr and Ni diffusion. The vermicular ferrite undergoes a transient growth followed by a high then a low rate dissolution regimes. On the other hand, ferrite dissolution was also studied in the multilayered microstructures. such microstructures were elaborated by alternating ferrite and austenite sheets of the Fe-Cr-Ni system, diffusion-bonded by Hot isostatic Pressing and reduced in thickness by successive rollings. Dissolution is easier to handle in such microstructures thanks to the initial planar δ/γ interfaces. Analysis of the experimental results were carried out with a numerical moving-boundary model of diffusion-controlled δ→γ transformation. Diffusion can be treated in the planar, cylindrical and spherical geometries. As a preliminary validation, the model was used to analyze kinetics of ferrite dissolution in the multilayered microstructures. It was then applied to the cast alloy using an original descriptive approach combining spheres and cylinders as equivalent morphology of dendritic ferrite. Although based on simplifying assumptions, the model was able to reproduce experimental results with satisfactory agreement. Mechanisms underlying the initial growth of vermicular ferrite and the transition in dissolution regimes were outlined. The effect of a wide range of input parameters has been considered and relevant parameters for quantitative calculations were brought to light, such as thermodynamical descriptions of the Fe-Cr-Ni system, composition gradients and distribution of ferrite's radii
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Beraldo, Camila Haga. "Efeito da temperatura de envelhecimento sobre as propriedades mecânicas e resistência à corrosão por pite do aço inoxidável martensítico endurecido por precipitação UNS S46500." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-15102014-163925/.
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Os aços inoxidáveis endurecidos por precipitação vêm sendo largamente empregados na indústria aeronáutica, por combinar resistência mecânica, tenacidade à fratura e resistência à corrosão. E deste modo, são materiais que possibilitam a substituição dos aços carbonos utilizados atualmente, que necessitam de tratamento superficial adicional, como o cádmio, para melhorar a resistência à corrosão. A utilização desses revestimentos traz desvantagens como o custo, a fabricação, a susceptibilidade à fragilização por hidrogênio além dos aspectos ambientais. Neste contexto, o aço endurecido por precipitação UNS S46500, designado como Custom 465® foi avaliado considerando o efeito da temperatura de envelhecimento sobre as propriedades mecânicas e a resistência à corrosão por pite. Amostras tratadas nas condições solubilizada e envelhecida a 510ºC (H950) e 538ºC (H1000) foram submetidas ao ensaio de tração, caracterização microestrutural e ensaios de polarização potenciodinâmica (PP) para determinar a resistência à corrosão por pite. Os exames microestruturais foram realizados com auxílio de microscopia óptica (MO), microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e difração de raios X. Também foram realizadas análises utilizando o software Thermo-Calc. A resistência à corrosão por pite foi avaliada em solução 0,6M NaCl com adições crescentes de Na2SO4. Os resultados obtidos nos ensaios de PP nas duas condições de tratamento térmico foram comparados entre si e com resultados disponíveis na literatura (CALDERÓN-HERNANDEZ, 2012) para o aço inoxidável UNS S30403 (304L). Os exames e análises da microestrutura revelaram que o aço Custom 465® envelhecido apresenta uma matriz martensítica, precipitados de fase chi, austenita e precipitados Ni3Ti. O tratamento H950 apresentou maior resistência mecânica e menor alongamento do que o tratamento H1000. Tal comportamento foi devido à produção de maior porcentagem de fase chi e menor porcentagem de austenita nesse tratamento de envelhecimento. Os diferentes tratamentos térmicos, condição solubilizada, H950 e H1000 apresentaram praticamente a mesma resistência à corrosão por pite. Por outro lado, o aço Custom 465® apresentou ótima resposta à inibição da nucleação de pite com adições crescentes de sulfato em meio de 0,6M NaCl, sendo que a condição H1000 se sobressai sobre a H950 nessa questão. Além disso, através da adição de sulfato foi 7 possível obter maior resistência a corrosão por pite do aço Custom 465® comparativamente ao aço 304L. Tal comportamento foi discutido em termos da afinidade química entre níquel, cloreto e sulfato, levando a maior resistência à corrosão por pite quando o aço contém maior teor de níquel (que é o caso do aço Custom 465®). Este trabalho indicou que o critério na escolha do tratamento de envelhecimento do aço Custom 465® deve ser o das propriedades mecânicas almejadas, uma vez que a resistência à corrosão por pite mostrou-se praticamente independente do tratamento térmico.The precipitation hardened stainless steels have been widely used in the aircraft industry to combine mechanical strength, fracture toughness and corrosion resistance. And therefore, are materials that enable replacement of the carbon steels used today, which require additional surface treatment, such as cadmium plating, to improve the corrosion resistance. The use of such coatings brings disadvantages such as cost, manufacturing, susceptibility to hydrogen embrittlement beyond environmental aspects. In this context, the precipitation hardened steel UNS S46500, known as Custom 465® were evaluated for the effect of aging temperature on the mechanical properties and the resistance to pitting corrosion .Treated samples in solubilized and aged condition at 510°C (H950) and 538ºC (H1000) were subjected to tensile strength test, microstructural characterization and potentiodynamic polarization (PP) tests to determine the pitting corrosion resistance. The microstructural studies were performed with the aid of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. Analyzes were also performed using the Thermo -Calc software. The resistance to pitting corrosion was evaluated at 0.6M NaCl solution with increasing additions of Na2SO4. The results obtained from tests of PP in both heat treatment conditions were compared with each other and with results available in the literature (CALDERÓN HERNANDEZ, 2012) to stainless steel UNS S30403 (304L). The analysis of the microstructure revealed that the steel aged Custom 465 ® presents a martensitic matrix, chi precipitates, Ni3Ti precipitates and austenite phase. The H950 age treatment had higher mechanical strength and lower elongation than the treatment H1000. Such behavior was due to the production of higher percentage of chi and a lower percentage of austenite phase in aging treatment. The different heat treatments, solubilized condition, H950 and H1000 showed almost the same pitting corrosion resistance. On the other hand, the Custom 465® showed good response to pitting inhibition with increasing nucleating additions of sulfate in 0.6M NaCl, with enhanced result for H1000 condition. Furthermore, by adding sulfate was possible to obtain greater pitting corrosion resistance of Custom 465® compared to the 304L steel. This behavior has been discussed in terms of the chemical affinity between nickel, chloride and sulphate, leading to higher pitting corrosion resistance when the steel contains a higher nickel 9 content (which is the case of steel Custom 465®). This study indicates that the criterion in selecting the aging heat treatment of Custom 465® steel must be the desired mechanical properties, since the pitting corrosion resistance was found to be substantially independent of heat treatment.
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Stone, David Joseph. "Optimal Composition Window of Type 410 Welding Consumables and Base Metals for Hydro-processing Applications." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu149270477418846.
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Godin, Hélène. "Effet de la microstructure sur la transition ductile-fragile d'aciers inoxydables martensitiques emboutissables à chaud." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM036.
Full textAbstract:
Les aciers emboutissables à chaud sont utilisés pour alléger les pièces de structure automobile. Ilsprésentent une excellente combinaison entre aptitude à la mise en forme, résistance mécanique et ductilité. De nouvelles nuances d’aciers inoxydables martensitiques ont été développées pour cette application. Parmi les propriétés requises, la résilience est un indicateur de la capacité à absorber l’énergie d’un crash. Cependant, le lien entre la microstructure et la résistance au clivage de ces aciers restait à établir. Ces travaux traitent de l’influence de la composition chimique (teneur en niobium), du traitement d’austénitisation et du refroidissement après l’emboutissage à chaud, sur la microstructure et la résilience de ces aciers. Pour ce faire, une analyse microstructurale détaillée est effectuée après différents traitements thermiques. Les microstructures obtenues sont complexes, avec des lattes de martensite plus ou moins auto-revenues, de la ferrite résiduelle, des films d’austénite retenue et des carbures. Les transitions ductile-fragile ont été caractérisées par des essais Charpy sur une large gamme de températures. La contrainte critique de clivage a été déterminée en adoptant l’approche locale de la rupture et vaut 2400 MPa quelle que soit la microstructure. Le niobium a pour principal effet d’affiner la microstructure, ce qui permet d’augmenter la résistance à la propagation des fissures de clivage et d’améliorer significativement la transition ductile-fragile. De plus, l’austénite retenue, dont la fraction dépend du traitement thermique, fait varier l’écrouissage au début de la déformation plastique donc la déformation nécessaire pour atteindre localement la contrainte critique de fissuration par clivage. Ainsi, l’austénite résiduelle permet de diminuer considérablement la température de transition ductile-fragileHot stamping steels are widely used for lightweight automotive structural parts, because of their excellent combination of formability, strength and ductility. New hot stamping martensitic stainless steel grades have been developed for this application. Among key properties required for automotive structural parts, impact toughness is a useful indicator of crash worthiness. However, the link between microstructure and the brittle fracture resistance of these steels had still to be established. The present work examined the effect of the chemical composition (niobium addition), austenitization heat treatment, and cooling conditions after hot stamping, on the microstructure and impact toughness of these steels. In order to do this, a detailed analysis of the microstructures obtained after various heat treatments was done. The microstructures are complex, with more or less auto-tempered martensitic laths, untransformed ferrite, retained austenite, and fine alloy carbides. The ductile-to-brittle transition behavior was characterized using Charpy tests over a large temperature range. The critical cleavage fracture stress was determined to be around 2400 MPa whatever the microstructure, by applying the local approach to fracture. The main effect of niobium was torefine the grain size, resulting in a strong improvement of the ductile-to-brittle transition behavior by increasing the resistance to cleavage crack propagation. Moreover, the heat treatment impacts the retained austenite fraction and thus modifies incipient plasticity and the strain necessary to reach locally the criticalstress required to trigger cleavage fracture. In this way, retained austenite plays a determining role to decrease the ductile-to-brittle transition temperature
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Rocancourt, Norman. "Etude de solutions innovantes de dépôts de superalliages et traitements de surface pour augmenter la résistance à l'usure et le comportement des moules métalliques de verrerie." Thesis, Rouen, INSA, 2016. http://www.theses.fr/2016ISAM0014.
Full textAbstract:
Au cours des procédés de mise en forme du verre creux, les outillages de verrerie sont soumis à des conditions extrêmes avec des températures pouvant dépasser largement 650 °C. De plus, ces derniers sont exposés à des phénomènes d'abrasion sévères et à des réactions physico-chimiques complexes avec le verre fondu. Ceci est particulièrement accentué par les cycles thermiques dus aux contacts répétés avec le verre. L'objectif de ce travail de thèse est de proposer des solutions innovantes de dépôts de superalliages et/ou traitements de surface destinés à augmenter la durée de vie des outillages. Trois axes d'innovation sont présentés dans ce mémoire. Le premier concerne l'étude du dépôt de poudre composite Co/NiB par soudure PTA (Plasma Transfered Arc) sur des moules en alliage cuivreux. Le second est dédié à l'étude de la faisabilité technique d'un dépôt PVD (Physical Vapor Deposition) multicouche à gradient fonctionnel, présentant des caractéristiques intéressantes pour des applications verrières en termes de dureté et de stabilité thermique, sur des poinçons en acier AISI 431. Enfin, le troisième axe de recherche fait l'objet d'une analyse plus approfondie et concerne l'étude de la nitruration par implantation d'ions azotes multichargés, également sur un acier AISI 431. On observe après implantation une augmentation significative de la dureté (+ 240 %). Une approche multi-expérimentale et multi-échelle est alors proposée afin d'étudier la microstructure du matériau implanté ainsi que son évolution après un recuit de 1h à 650 °C de manière à anticiper le comportement du matériau en production, et de corréler ceci aux propriétés de duretéGlass moulds have to withstand very high temperatures which can far exceed 650 °C during the glass forming process. They are exposed to very tough conditions such as abrasive wear and physico-chemical reactions, accentuated by thermal shocks due to high speed contact with hot glass melt. The aim of this work is to find innovative solutions for superalloy coating or surface treatments in order to increase the service life of glass tools. Three innovation projects are presented in this report. The first one is dedicated to PTA (Plasma Transferred Arc) welded coating of composite Co/NiB powder on copper alloy moulds. The second one is about technical feasibility of a multilayer PVD (Physical Vapor Deposition) coating with properties congruent to glass production in term of hardness and thermal stability, on AISI 431 plunger stainless steel. Last but not least, the third innovative project is about nitriding by ion implantation with multicharged nitrogen ions on AISI 431 stainless steel. We notice after ion implantation a significant hardness increase (+ 240 %). A multi-experimental and multi-scale approach was carried out in order to study the implanted material microstructure and its evolution after annealing at 650 °C during 1h to predict the material behavior during production and correlate it to hardness properties