Articles de revues : « Transformation de phase austénite-Ferrite »

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Kanter, Daniel, Yves Bolender, Christophe Rapin et Marie-Pierryle Filleul. « L’effet mémoire de forme est-il une réalité clinique pour le 35° Copper Ni-Ti® ? Étude par calorimétrie différentielle à balayage ». L'Orthodontie Française 84, n^o 3 (septembre 2013) : 259–69. http://dx.doi.org/10.1051/orthodfr/2013057.

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Introduction : Les alliages à base de nickel-titane-cuivre sont censés exprimer un effet mémoire de forme : refroidis en phase basse température puis soumis à une déformation apparemment plastique, ils devraient retrouver leur forme initiale par simple réchauffage en phase haute température. Les alliages à base de nickel-titane peuvent présenter différentes phases cristallographiques : martensite, austénite et une phase intermédiaire inconstante, la phase R. L’effet mémoire de forme est généralement associé à la transformation de martensite en austénite mais il peut aussi accompagner la transformation de phase R en austénite. Les températures buccales n’étant pas compatibles avec un alliage totalement martensitique, la présente étude vise, pour le 35° Copper Ni-Ti®, à rechercher la présence de phase R aux températures buccales et donc la possibilité d’exploiter l’effet mémoire de forme de la phase R en clinique. Matériels et méthodes : Trente fils 35° Copper Ni-Ti® provenant de deux lots distincts ont été consécutivement examinés par calorimétrie différentielle à balayage en cycles partiels, limités aux températures rencontrées dans la cavité buccale (de 0 °C à 50 °C). La présence d’une phase cristallographique intermédiaire a été recherchée sur les thermogrammes. Les températures de transformation ont été déterminées et les deux lots ont été comparés par le test U de Mann et Whitney. Résultats : Au chauffage, tous les fils sont passés directement de martensite en austénite. Af (moyenne = 33,5 °C, écart-type = 0,8 °C) était généralement inférieure à la température indiquée par le fabricant et une différence statistiquement significative (p ≤ 0,01) a été observée entre les deux lots. Conclusions : La présence de phase R n’a pas été détectée et les températures de transformation n’étaient pas constantes. Cette étude met en question la réalité clinique d’un effet mémoire de forme pour les fils 35° Copper Ni-Ti®.

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Padilha, Angelo Fernando, D. J. M. Aguiar et R. L. Plaut. « Duplex Stainless Steels : A Dozen of Significant Phase Transformations ». Defect and Diffusion Forum 322 (mars 2012) : 163–74. http://dx.doi.org/10.4028/www.scientific.net/ddf.322.163.

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During processing or use, duplex stainless steels are subject to a great number of significant phase transformations, such as solidification, partial ferrite transformation to austenite, ferrite eutectoid decomposition to sigma phase plus austenite, chi phase precipitation, chromium carbide precipitation, chromium nitride precipitation, ferrite spinodal decomposition, phase dissolution during solution annealing, forming of two types (epsilon and alpha prime) of strain induced martensite, martensite reversion to austenite, ferrite and austenite recrystallization. This paper summarizes the phase transformations that occur (individually or combined) in duplex stainless steels and presents some new results.

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Li, Li Zhang, He Wei, Lin Lin Liao, Yin Li Chen, Hai Feng Yan, Guang Hua Liu et Zhi Wei Sun. « Continuous Cooling Phase Transformation Rule of 20CrMnTi Low-Carbon Alloy Steel ». Materials Science Forum 944 (janvier 2019) : 303–12. http://dx.doi.org/10.4028/www.scientific.net/msf.944.303.

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Gear steel is a ferritic steel. In the rolling process, the ideal structure is ferrite + pearlite, and bainite or martensite is not expected. However, due to the high alloy content, the hardenability is good, and the bainite or martensite structure is very likely to be generated upon cooling after rolling. In this paper, phase transformation rules during continuous cooling of 20CrMnTi with and without deformation were studied to guide the avoidance of the appearance of bainite or martensite in steel. A combined method of dilatometry and metallography was adopted in the experiments, and the dilatometer DIL805A and thermo-simulation Gleeble3500 were used. Both dynamic and static continuous cooling transformation (CCT) diagrams were drawn by using the software Origin. The causes of those changes in starting temperature, finishing temperature, starting time and transformation duration in ferrite-pearlite phase transformation were analyzed, and the change in Vickers hardness of samples with different cooling rate was discussed. The results indicate that with different cooling rate, there are three phase transformation zones: ferrite-pearlite, bainite and martensite. Deformation of austenite accelerates the occurrence of transformation obviously and moves CCT curve to left and up direction. When the cooling rate is lower than 1 °C/s, the phases in samples are mainly ferrite and pearlite, which is the ideal microstructure of experimental steel. As the cooling rate increases, starting temperature of ferrite transformation in steel decreases, starting time reduces, transformation duration gradually decreases, and the Vickers hardness of samples increases. Under the cooling rate of 0.5 °C/s, ferrite transformation in deformed sample starts at 751.67 °C, ferrite-pearlite phase transformation lasts 167.9 s, and Vickers hardness of sample is 183.4 HV.

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Cheng, Wei Chun, Kun Hsien Lee, Shu Mao Lin et Shao Yu Chien. « The Observation of Austenite to Ferrite Martensitic Transformation in an Fe-Mn-Al Austenitic Steel after Cooling from High Temperature ». Materials Science Forum 879 (novembre 2016) : 335–38. http://dx.doi.org/10.4028/www.scientific.net/msf.879.335.

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Fe-Mn-Al steels with low density have the potential to substitute for TRIP (transformation induced plasticity) steels. For the development of Fe-Mn-Al TRIP steels, phase transformations play an important role. Our methods of studying the phase transformations of the Fe-16.7 Mn-3.4 Al (wt%) austenitic steel include heating and cooling. We have studied the martensitic transformation of the ternary Fe-Mn-Al steel. Single austenite phase is the equilibrium phase at 1373 K, and dual phases of ferrite and austenite are stable at low temperatures. It is noteworthy that lath martensite forms in the prior austenite grains after cooling from 1373 K via quenching, air-cooling, and/or furnace-cooling. The crystal structure of the martensite belongs to body-centered cubic. The formation mechanism of the ferritic martensite is different from the traditional martensite in steels. Ferrite is the stable phase at low temperature.

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Spiridonova, K. V., I. Yu Litovchenko, N. A. Polekhina, V. V. Linnik, T. A. Borisenko, V. M. Chernov et M. V. Leont’eva-Smirnova. « Structural-phase transformations of 12% chromium ferritic-martensitic steel EP-823 ». Izvestiya. Ferrous Metallurgy 66, n^o 6 (29 décembre 2023) : 725–32. http://dx.doi.org/10.17073/0368-0797-2023-6-725-732.

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The features of phase transformations of 12 % chromium ferritic-martensitic steel EP-823 under heating and cooling conditions in the temperature range from 30 to 1100 ℃ were studied by the methods of high-temperature X-ray diffraction analysis (XRD) in situ and differential scanning calorimetry (DSC). According to XRD in situ data, upon heating, the temperatures of the beginning and end of the (α → γ) transformation of ferrite (martensite – austenite) are Ac1 ≈ 880 °C, Ac3 ≈ 1000 °C, respectively. Upon cooling, a diffusion (γ → α) transformation occurs with critical points – Аr1 ≈ 860°С (beginning temperature) and Аr3 ≈ 840 °С (end temperature). According to DSC data, during heating, the critical points of the (α → γ) transformation are Ac1 ≈ 840 °C and Ac3 ≈ 900 °C. During cooling, a martensitic (γ → α) transformation is realized with critical points of the beginning of Ms = 344 ℃ and the end of Mf = 212 ℃ of this transformation. The XRD in situ analysis revealed no precipitation of carbide phases under heating and cooling conditions of steel EP-823. Position of the critical points of phase transformations depends on the research method (XRD in situ or DSC), which is determined by the difference in effective (taking into account the time for shooting in the XRD method) heating-cooling rate. The effect of elemental composition on the position of critical points of phase transformations and the formation of structural-phase states of ferritic-martensitic steels is discussed. It is shown that the increased content of ferrite-stabilizing elements (Cr, Mo, Nb) in composition of EP-823 steel, compared with other steels of the same class, expands the region of existence of the ferrite phase, which can contribute to an increase in the temperature of Ac1 .

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Xia, Pei Pei, Liu Qing Yang, Xiao Jiang Guo et Ye Zheng Li. « Continuous Cooling Phase Transformation Rules of High Nb X80 Pipeline Steel ». Materials Science Forum 850 (mars 2016) : 916–21. http://dx.doi.org/10.4028/www.scientific.net/msf.850.916.

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The microstructural evolution of the high Nb X80 pipeline steel in Continuous Cooling Transformation (CCT) by Gleeble-3500HS thermal mechanical simulation testing system was studied, the corresponding CCT curves were drawn and the influence of some parameters such as deformation and cooling rate on microstructure of high Nb X80 pipeline steel was analyzed. The results show that as cooling rate increased, the phase transformation temperature of high Nb X80 steel decreased, with the microstructure transformation from ferrite-pearlite to acicular ferrite and bainite-ferrite. When cooling rate was between 20°C/s and 30°C/s, the microstructure was comparatively ideal acicular ferrite, thermal deformation accelerates phase transformation notably and made the dynamic CCT curves move upward and the initial temperature of phase transformation increase obviously. Meanwhile the thermal deformation refined acicular ferrite and extended the range of cooling rate accessible to acicular ferrite.

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Wang, Qihui, Kun Chen, Kejia Liu, Lianbo Wang, Yu Chu et Bichen Xie. « Study on Characterization of Phase Transition in Continuous Cooling of Carbon Steel Using In Situ Thermovoltage Measurement ». Coatings 14, n^o 8 (3 août 2024) : 980. http://dx.doi.org/10.3390/coatings14080980.

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In this paper, a self-designed and enhanced thermovoltage measuring device was built to capture thermovoltage curves of 45 steel during continuous cooling. The phase zones of the thermovoltage curve were interpreted based on the Engel–Brewer electron theory and Fe-Fe3C phase diagram. The results show that the curve was stratified into three homogeneous phase zones and two-phase transition zones as follows: Zone Ι: single-phase austenite (A) zone; Zone III: austenite and ferrite (A+F) homogeneous phase zone; Zone V: ferrite and pearlite (P+F) homogeneous phase zone; Zone II: austenite to ferrite (A-F) phase transition zone; and Zone IV: austenite to pearlite (A-P) phase transition zone. Notably, the deflection point marked the transition temperature, which indicates that the thermovoltage curve can quantitatively characterize phase formation and transformation, as well as the phase transformation process. Furthermore, the sample was quenched at the measured ferrite phase transition temperature. Microstructure observations, electron probe microanalyzer (EPMA) and microhardness measurements corroborated our findings. Specifically, our experiments reveal ferrite precipitation first from the cold end at the phase transition temperature, leading to increased carbon content in adjacent austenite. The results of this study achieved the in situ characterization of bulk transformations during the materials heat treatment process, which expands the author’s research work conducted previously.

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Villalobos Vera, Doris Ivette, et Ivan Mendoza Bravo. « Effect of annealing temperature on the microstructure of hyperduplex stainless steels ». Ingeniería Investigación y Tecnología 20, n^o 2 (1 mars 2019) : 1–6. http://dx.doi.org/10.22201/fi.25940732e.2019.20n2.024.

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Samples of hyperduplex stainless steels were produced experimentally and exposed to different conventional annealing heat treatments in order to obtain the microstructural balance of 50% ferrite and 50% austenite. To differentiate the ferrite and austenite from any secondary phase, selective etching was used and quantitative metallography was performed to measure the percentage of phases. Results showed that conventional annealing heat treatments promote the transformation from ferrite to sigma phase and secondary austenite, suggesting a higher occurrence of sigma phase in the experimental hyperduplex alloys compared to other duplex alloys due to the superior content of chromium and molybdenum. On the other hand, a balanced microstructure free of secondary phases was accomplished increasing the temperature of the annealing heat treatment, which allowed the transformation of ferrite into austenite during cooling.

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Bilovol, V., et R. Martínez-García. « Phase transformation of strontium hexagonal ferrite ». Journal of Physics and Chemistry of Solids 86 (novembre 2015) : 131–37. http://dx.doi.org/10.1016/j.jpcs.2015.07.006.

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Hug-Amalric, Aurélie, Xavier Kleber, Jacques Merlin, Hélène Petitgand et Philip Meilland. « Characterization of Metallurgical Transformations in Multi-Phase High Strength Steels by Barkhausen Noise Measurement ». Materials Science Forum 539-543 (mars 2007) : 4283–88. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4283.

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The potentialities of using the magnetic Barkhausen noise measurement in characterization of metallurgical transformations have been highlighted in multi-phase High Strength (HS) steels. This kind of steels are composed of different metallurgical constituents, such as ferrite, bainite, martensite or residual austenite. Recently, we found that it was possible to assess the proportion of phases in ferrite-martensite steels and in industrial Dual-Phase steels too. In this work, we show that the Barkhausen noise measurements can be also suitable to follow bainitic transformation in a TRIP steel.

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Lee, Sang Hwan, Jong Min Choi, Yeol Rae Cho et Kyung Jong Lee. « The Effects of Si and Deformation on the Phase Transformation in Dual Phase Steels ». Solid State Phenomena 124-126 (juin 2007) : 1617–20. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.1617.

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The effect of Si on phase transformation was well known in dual phase steels. Si promoted the ferrite transformation and the enriched C in untransformed austenite prohibited the transformation at intermediate temperature range resulting in the formation of lower bainite and martensite at low temperature range. In addition, during continuous cooling with fast cooling rate, it was very hard to differentiate one phase from the others. In order to clarify the effects of Si on the austenite-to-ferrite transformation quantitatively, the start temperatures of bainite(BS) and martensite(MS) as well as ferrite(Ae3) and pearlite(Ae1) were calculated by thermodynamic analysis. LVDT measured by dilatometer and 1st differentiation peaks of LVDT were examined with microstructures, which gives a possibility of the phase separation. In CCT diagrams, it was also found that large austenite grain size(AGS) widened the gap between the transformation start(Ts) and end(Tf) when Si was added.

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Bräutigam–Matus, Krishna, Gerardo Altamirano, Armando Salinas, Alfredo Flores et Frank Goodwin. « Experimental Determination of Continuous Cooling Transformation (CCT) Diagrams for Dual-Phase Steels from the Intercritical Temperature Range ». Metals 8, n^o 9 (28 août 2018) : 674. http://dx.doi.org/10.3390/met8090674.

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The phase transformation kinetics under continuous cooling conditions for intercritical austenite in a cold rolled low carbon steel were investigated over a wide range of cooling rates (0.1–200 ∘ C/s). The start and finish temperatures of the intercritical austenite transformation were determined by quenching dilatometry and a continuous cooling transformation (CCT) diagram was constructed. The resulting experimental CCT diagram was compared with that calculated via JMatPro software, and verified using electron microscopy and hardness tests. In general, the results reveal that the experimental CCT diagram can be helpful in the design of thermal cycles for the production of different grades of dual-phase–advanced high-strengh steels (DP-AHSS) in continuous processing lines. The results suggest that C enrichment of intercritical austenite as a result of heating in the two phases (ferrite–austenite) region and C partitioning during the formation of pro-eutectoid ferrite on cooling significantly alters the character of subsequent austenite phase transformations.

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Sun, Fei, Yoshihisa Mino, Toshio Ogawa, Ta-Te Chen, Yukinobu Natsume et Yoshitaka Adachi. « Evaluation of Austenite–Ferrite Phase Transformation in Carbon Steel Using Bayesian Optimized Cellular Automaton Simulation ». Materials 16, n^o 21 (28 octobre 2023) : 6922. http://dx.doi.org/10.3390/ma16216922.

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Austenite–ferrite phase transformation is a crucial metallurgical tool to tailor the properties of steels required for particular applications. Extensive simulation and modeling studies have been conducted to evaluate the phase transformation behaviors; however, some fundamental physical parameters still need to be optimized for better understanding. In this study, the austenite–ferrite phase transformation was evaluated in carbon steels with three carbon concentrations during isothermal annealing at various temperatures using a developed cellular automaton simulation model combined with Bayesian optimization. The simulation results show that the incubation period for nucleation is an essential factor that needs to be considered during austenite–ferrite phase transformation simulation. The incubation period constant is mainly affected by carbon concentration and the optimized values have been obtained as 10−24, 10−19, and 10−21 corresponding to carbon concentrations of 0.2 wt%, 0.35 wt%, and 0.5 wt%, respectively. The average ferrite grain size after phase transformation completion could decrease with the decreasing initial austenite grain size. Some other parameters were also analyzed in detail. The developed cellular automaton simulation model combined with Bayesian optimization in this study could conduct an in-depth exploration of critical and optimal parameters and provide deeper insights into understanding the fundamental physical characteristics during austenite–ferrite phase transformation.

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Yu, Dunji, Yan Chen, Lu Huang et Ke An. « Tracing Phase Transformation and Lattice Evolution in a TRIP Sheet Steel under High-Temperature Annealing by Real-Time In Situ Neutron Diffraction ». Crystals 8, n^o 9 (11 septembre 2018) : 360. http://dx.doi.org/10.3390/cryst8090360.

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Real-time in situ neutron diffraction was used to characterize the crystal structure evolution in a transformation-induced plasticity (TRIP) sheet steel during annealing up to 1000 °C and then cooling to 60 °C. Based on the results of full-pattern Rietveld refinement, critical temperature regions were determined in which the transformations of retained austenite to ferrite and ferrite to high-temperature austenite during heating and the transformation of austenite to ferrite during cooling occurred, respectively. The phase-specific lattice variation with temperature was further analyzed to comprehensively understand the role of carbon diffusion in accordance with phase transformation, which also shed light on the determination of internal stress in retained austenite. These results prove the technique of real-time in situ neutron diffraction as a powerful tool for heat treatment design of novel metallic materials.

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Arh, Boštjan, Franc Tehovnik et Franci Vode. « Transformation of the δ-Ferrite in SS2343 Austenitic Stainless Steel upon Annealing at 1050 °C, 1150 °C and 1250 °C ». Metals 11, n^o 6 (9 juin 2021) : 935. http://dx.doi.org/10.3390/met11060935.

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The solidification behaviors of laboratory cast austenitic SS2343 stainless steel in terms of the volume fraction of δ-ferrite in the as-cast state and its transformation after subsequent annealing were investigated. Monitoring of morphological transformations of δ-ferrite in the microstructure show the progress of δ-ferrite dissolution. Annealing tests were conducted at 1050 °C, 1150 °C and 1250 °C with soaking times of 5 and 40 min. The thermodynamic prediction and metallographic identification of δ-ferrite are presented. The ferrite fractions were measured using a magnetic method and determined to be in the range between 10.7% and 14.6%. The volume share of δ-ferrite decreased with an increase in temperature and the time of annealing. About 50–55% the δ-ferrite was effectively transformed. The δ-ferrite phase, originally present in a dendritic morphology, tends to break up and spheroidize. The morphology varies from vermicular, lacy and acicular shapes to globular for higher temperatures and for longer exposure times. In the δ-ferrite after annealing, concentrations of Cr and Mo decrease, and conversely the concentration of Ni increase, all by small, but significant, amounts. The observed changes in the solute concentration can be explained in terms of the transformation of ferrite into austenite and sigma phases.

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Li, Xianchao. « Secondary-phase Transformation of Duplex Stainless Steels during Industrial Manufacturing ». Journal of Physics : Conference Series 2541, n^o 1 (1 juillet 2023) : 012030. http://dx.doi.org/10.1088/1742-6596/2541/1/012030.

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Abstract A new type of lean S32205 duplex stainless steel was studied on its secondary phase formation during industrial manufacturing. Different from the common S32205 duplex stainless steels, such lean S32205 duplex stainless steels contain more carbon and nitrogen elements, which promotes the formation of Cr2N and Cr23C6 secondary precipitations. The secondary-phase transformation is preferred at boundaries, either in the ferrite phase or at interphase interfaces after rolling, and even a few secondary precipitates can be found at the as-cast ferrite grain interiors as well. The influence of the secondary phase transformations on pitting resistance and hot ductility was investigated.

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Skowronek, Adam, Mateusz Morawiec, Aleksandra Kozłowska et Wojciech Pakieła. « Effect of Hot Deformation on Phase Transformation Kinetics in Isothermally Annealed 3Mn-1.6Al Steel ». Materials 13, n^o 24 (20 décembre 2020) : 5817. http://dx.doi.org/10.3390/ma13245817.

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The kinetics of ferritic transformation and the corresponding microstructural evolution in 0.17C-3.1Mn-1.6Al-0.04Nb-0.22Mo-0.22Si medium-Mn steel during isothermal annealing was investigated in dilatometric studies. The material was subjected to thermal and thermo-mechanical treatments aimed at obtaining, by the austenite → ferrite transformation, a sufficient fraction of ferrite to stabilize the retained austenite by C and eventual Mn partitioning. The samples were isothermally held for 5 h in a temperature range from 600 to 750 °C to simulate simplified temperature conditions of an industrial coiling process following hot rolling. Some of the samples were plastically deformed at a temperature of 900 °C before isothermal holding in order to study the effect of hot deformation on the kinetics of phase transformations. After the dilatometric investigations the material was subjected to light and scanning electron microscopy to reveal relationships between the holding temperature, deformation and microstructure evolution. Hardness tests were performed to assess the mechanical behavior. A significant effect of manganese in slowing down diffusional transformations during the cooling of steel was found. The influence of austenite deformation on the kinetics of austenite to ferrite transformation was noted. The plastically deformed samples showed an accelerated start of ferritic transformation and the extension of its range. During dilatometric tests, low-range dynamic ferritic transformation was recorded, which was also confirmed by the microscopic tests.

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Hu, Feng, et Kai Ming Wu. « Isothermal Transformation of Low Temperature Super Bainite ». Advanced Materials Research 146-147 (octobre 2010) : 1843–48. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.1843.

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Fine-scale bainitic microstructure with excellent mechanical properties has been achieved by transforming austenite to bainite at low temperature ranging from 200oC to 300oC. Microstructural observations and hardness measurements show that transformed microstructures consist of bainitic ferrite and carbon-enriched retained austenite. The thickness of bainitic ferrite plates is less than 50 nm. The hardness reaches approximately 640 HV1. Strong austenite and/or large driving force at the low transformation temperature leads to ultra fine bainitic ferrite plates. X-ray diffraction analysis indicates that low-temperature bainite transformation is an incomplete reaction. The carbon content in carbon-enriched retained austenite is below the para-equilibrium (Ae3′) phase boundary predicted. The carbon content in bainitic ferrite is less than that T0′ phase boundary predicted.

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Yanagida, Akira, J. Jin Shan Liu et Jun Yanagimoto. « Ferrite Transformation Kinetics of Severely Hot-Deformed Austenite ». Materials Science Forum 706-709 (janvier 2012) : 1562–67. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1562.

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The ferrite transformation kinetics of severely hot-deformed austenite has been studiedby considering ferrite nucleation from dislocation cell blocks inside austenite grains. The size ofdislocation cell blocks and ferrite grain size just after phase transformation are acknowledged to beinversely proportional to the square root of dislocation density. It is found that the ferrite nucleationrate in this area can reach the saturated state at a high temperature just under Ae3, and the ferritetransformation finishes within a very short time. The kinetics of ferrite volume fraction and theferrite grain growth after phase transformation for plain carbon (0.1%C, 0.2%Si, 1.0%Mn) steelhave been studied using a THERMECMASTER hot-compression testing machine. These modelscan be applied to the hot and warm forming processes of plain carbon steel to predict the ferritetransformation from severely deformed austenite.

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Wang, Yu Hui, Ya Nan Zheng, Tian Sheng Wang, Bo Liao et Li Gang Liu. « Phase Transformation Behaviors of Nb-V-Ti Microalloyed Pipeline Steel X70 ». Advanced Materials Research 750-752 (août 2013) : 380–84. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.380.

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The CCT (continuous cooling transformation) diagrams of the Nb-V-Ti without Mo containing microalloyed pipeline steel X70 were investigated. The microstructures observed in continuous cooled specimens are composed of P (pearlite), PF (polygonal ferrite), QF (quasi-polygonal ferrite), and GF (granular bainite ferrite). At low cooling rates between 0.1°C/s and 1°C/s, the microstructure of the steel consisted of banded ferrite and pearlite but higher cooling rates suppressed its formation.

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Kawata, Hiroyuki, Kunio Hayashi, Natsuko Sugiura, Naoki Yoshinaga et Manabu Takahashi. « Effect of Martensite in Initial Structure on Bainite Transformation ». Materials Science Forum 638-642 (janvier 2010) : 3307–12. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.3307.

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Lath-shaped upper bainite structures play a very important role in many high-strength steels (HSSs) and ultra high-strength steels (UHSSs). Although bainite transformation is strongly affected by the initial structure, the effect of the second phase in a multi-phase structure is yet to be clearly understood. It is significant for the advancement of UHSS to study this effect. The aim of this study is to clarify the effect of martensite, which forms before bainite, in Fe-0.2C-8Ni alloy. The bainite transformation from an austenite and martensite dual-phase structure is faster than that from single-phase austenite and the nucleation of bainitic ferrite laths are accelerated around martensite. This effect of martensite on bainite kinetics is equivalent to that of polygonal ferrite when their volume fractions are almost the same. This suggests that the boundary between martensite and austenite is a prior nucleation site of bainitic ferrite. Martensite also affects the crystallographic features of bainite. The orientations of bainitic ferrite laths tend to belong to the same block with martensite adjacent. This tendency intensifies with an increase of the transformation temperature of bainite, resulting in the formation of huge blocks consisting of bainitic ferrite and martensite laths at high temperatures (693K and 723K). In contrast, at a low temperature (643K), bainitic ferrite laths belong to same packet as martensite and have several orientations. This change of crystallographic features with transformation temperature can explain with the driving force of the nucleation of bainitic ferrite.

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Dere, Emine Gözde, Hemant Sharma, S. Eric Offerman et Jilt Sietsma. « The Effect of NbC Precipitates and Nb in Solid-Solution on the Phase Transformation Kinetics in High-Purity Fe-C-Mn-Nb Alloys ». Solid State Phenomena 172-174 (juin 2011) : 499–504. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.499.

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The precipitation of NbC in austenite is an important mechanism for improving the strength of steel because NbC-precipitates are known to decrease the ferrite grain size during the subsequent phase transformations upon cooling. The effect of the interaction between niobium (Nb) in solid solution and NbC-precipitates on the austenite-to-ferrite phase-transformation kinetics is not entirely clear. We study a high-purity Fe-C-Mn-Nb alloy cooled at different rates. Different annealing times at 850°C were applied to create different number densities and sizes of the NbC-precipitates in order to study the effect of NbC precipitation on the transformation kinetics. The alloy that is used in this study has an atomic ratio of Nb:C=1.3:1. The fraction of ferrite is measured as a function of temperature during cooling by means of dilatometry. The ferrite grain size is measured by means of optical microscopy. The results are interpreted with thermodynamic and kinetic models.

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Ivanisenko, Julia, Witold Łojkowski et Hans Jorg Fecht. « Stress- and Strain Induced Phase Transformations in Pearlitic Steels ». Materials Science Forum 539-543 (mars 2007) : 4681–86. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4681.

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An overview of the mechanically driven phase transformations taking place in nanocrystalline pearlitic steels in conditions of the severe plastic deformation (SPD), i.e. combination of high pressure and strong shear strains will be given. Conditions of the discussed experiments (room temperature and moderate strain rates) exclude any thermal origin of the observed transformations. One of them is strain induced cementite decomposition, which is a well-documented phenomenon taking place at cold plastic deformation of pearlitic steels. We explain this process taking into account friction forces at the interface between the hard cementite and ferrite. Under the high pressures and stresses higher than the ferrite matrix yield stress, the later one behaves like a viscoelastic fluid. The friction at the precipitate/matrix interface leads to two effects. One is to induce high strains on the precipitates. This leads to shift of thermodynamic equilibrium towards dissolution of the cementite. The second is wear of the cementite phase due to friction at the ferrite/cementite interface and mechanically induced drag of carbon atoms by the ferrite. This had been recently confirmed in 3D AP experiments, which demonstrated that the process of cementite decomposition starts with depleting of carbides with carbon and formation of non-stoichiometric cementite. The existing theories of atom drag by moving dislocations (ballistic models) can be regarded as one of the many possible mechanism of wear discussed by the wear theory. In that respect the process can be called athermal, as temperature indirectly influences wear processes but is not their main cause. We observed also another strain driven transformation in nanocrystalline pearlitic steel during room temperature high pressure torsion. This is a stress induced α→γ transformation, which has never been observed at conventional deformation of coarse grained iron and carbon steels. This was concluded to have occurred due to a reverse martensitic transformation.

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Lischewski, I., et Günter Gottstein. « Orientation Relationship during Partial α-γ-Phase Transformation in Microalloyed Steels ». Materials Science Forum 495-497 (septembre 2005) : 447–52. http://dx.doi.org/10.4028/www.scientific.net/msf.495-497.447.

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The ferrite to austenite phase transformation in microalloyed steel was studied, with a special focus on the orientation relationship between prior ferrite and subsequent austenite. Also the role of growth selection and preferred nucleation was investigated in this context. Their effects were examined at partial phase transformation.

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Hou, Fei Fei, Atsushi Ito, Yu Bai, Akinobu Shibata et Nobuhiro Tsuji. « Microstructure Evolution and Change in Mechanical Properties of Medium Mn Steels during Thermomechanical Processing ». Materials Science Forum 941 (décembre 2018) : 346–51. http://dx.doi.org/10.4028/www.scientific.net/msf.941.346.

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Medium manganese steels are nowadays energetically investigated as the third generation advanced high strength steels (AHSS) because of their excellent balance between material cost and mechanical properties. However, the phase transformation and microstructure evolution in medium manganese steels during various heat treatments and thermomechanical processing are still unclear. The present study firstly examined kinetics of static phase transformation behavior and microstructural change in a 3Mn-0.1C medium manganese steel. Hot compression tests were also carried out to investigate the influences of high-temperature thermomechanical processing on the microstructure evolution. It was found that ferrite transformation was quite slow in static conditions but greatly accelerated by hot compression in (austenite and ferrite) two phase region. Dual phase microstructures composed of martensite and ferrite with ferrite grain sizes of 1~2 μm were obtained, which exhibited superior mechanical properties.

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Meiser, Jerome, et Herbert Urbassek. « Ferrite-to-Austenite and Austenite-to-Martensite Phase Transformations in the Vicinity of a Cementite Particle : A Molecular Dynamics Approach ». Metals 8, n^o 10 (17 octobre 2018) : 837. http://dx.doi.org/10.3390/met8100837.

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We used classical molecular dynamics simulation to study the ferrite–austenite phase transformation of iron in the vicinity of a phase boundary to cementite. When heating a ferrite–cementite bicrystal, we found that the austenitic transformation starts to nucleate at the phase boundary. Due to the variants nucleated, an extended poly-crystalline microstructure is established in the transformed phase. When cooling a high-temperature austenite–cementite bicrystal, the martensitic transformation is induced; the new phase again nucleates at the phase boundary obeying the Kurdjumov–Sachs orientation relations, resulting in a twinned microstructure.

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Geissler, J., C. Mesplont, S. Vandeputte et B. C. De Cooman. « Dilatometric study of the effect of soluble boron on the continuous and isothermal austenite decomposition in 0.15C–1.6Mn steel ». International Journal of Materials Research 93, n^o 11 (1 novembre 2002) : 1108–18. http://dx.doi.org/10.1515/ijmr-2002-0191.

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Abstract The effect of soluble boron on the phase transformations during either cooling and/or isothermal holding has been studied by means of dilatometry. Significant differences in the transformation behaviour were found for all austenite phase transformation reactions. In particular, the morphologies of ferrite and bainite were strongly affected by B alloying. The kinetics was studied in detail for the austenite decomposition reactions. Soluble B was found to be very effective in suppressing the carbide formation. It was also found to interact with the Mn partitioning to the austenite. As a result, the presence of Mn-rich regions in the final microstructures decreased strongly the Ac1 temperature during reheating. Isothermal transformations in the 450–660 °C temperature range showed that the incubation times for ferrite and pearlite formations were increased. The soluble B was found to affect strongly the nucleation rate. The growth kinetics was slower due to a solute drag effect caused by the partitioning of Mn. The kinetics of bainite formation was not affected by the presence of soluble B. Upper bainite was found to be acicular ferrite in the CMnB steel as a result of the heterogeneous nucleation of ferrite on TiN precipitates.

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Ledoux, Xavier, Francois Buy, Aurélien Perron, Eric Suzon, José Farré, Bernard Marini, Thomas Guilbert et al. « Kinetics of Sigma Phase Precipitation in Niobium-Stabilized Austenitic Stainless Steel and Effect on the Mechanical Properties ». Materials Science Forum 783-786 (mai 2014) : 848–53. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.848.

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Stabilized austenitic stainless steels are widely used in nuclear and oil industries. The 316 Nb steel grade presented in this study holds a small amount of delta ferrite in the austenitic matrix which tends to transform into sigma phase during prolonged exposures in the temperature range of 600-1000°C. Sigma phase is promoted by ferritic elements such as chromium, molybdenum, niobium and silicon. Time-Temperature-Transformation (TTT) diagram of the δ-ferrite evolution is established thanks to DSC experiments and quantitative metallographic analysis. It is observed that the highest sigma phase formation rate occurs between 800 and 900°C, and that the transformation of ferrite begins after a few minutes of exposure in this temperature range. The microstructure of transformed δ-ferrite is mostly dominated by the eutectoid mixture σ + γ2. Tensile tests were performed for three different cooling conditions: a significant embrittlement attributed to the δ-ferrite transformation is measured by a ductility loss for the lowest cooling rate.

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Zheng, Yaxu, Wei Shen, Liguang Zhu, Zhihong Guo, Qi Wang, Jie Feng, Yongliang Li, Ruifang Cao et Jiayi Wu. « Effects of composition and strain rate on hot ductility of Cr–Mo-alloy steel in the two-phase region ». High Temperature Materials and Processes 40, n^o 1 (1 janvier 2021) : 228–40. http://dx.doi.org/10.1515/htmp-2021-0025.

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Abstract The hot tensile tests were conducted in this study to investigate the effects of Nb, B, Mo, and V on hot ductility of 25CrMo alloy steel in a temperature range of 650–850°C with strain rates of 0.005 and 0.5 s−1. Besides, the influences of ferrite transformation and precipitates on hot ductility were also investigated by the use of SEM and TEM. Thermo-Calc and J Mat Pro were used for calculating equilibrium precipitates and CCT curves, respectively. The results indicated that the hot ductility is deteriorated with the addition of 0.04% Nb due to Nb(C,N) particles and ferrite transformation. The addition of B inhibits ferrite transformation and improves hot ductility. The hot ductility is improved with increasing strain rate from 0.005 to 0.5 s−1 due to the nucleation and growth behavior of ferrite. The fast strain rate promotes nucleation of ferrite; however, the ferrite has no sufficient time to grow up. The addition of Mo inhibits ferrite transformation and improves hot ductility. The addition of 0.12% V has no obvious effect on ferrite transformation. The hot ductility has deteriorated a little with the addition of 0.12% V due to the solution V that increases stress during hot deformation.

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Hwu, Y. J., et J. G. Lenard. « Phase Transformation Temperatures of an Ultra-Low Carbon Steel ». Journal of Engineering Materials and Technology 120, n^o 1 (1 janvier 1998) : 19–25. http://dx.doi.org/10.1115/1.2806832.

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An ultra-low carbon steel is studied and the temperatures at which the austenite to ferrite transformations begin and are complete are determined. The methods of measurements of the temperatures are discussed. The effects of the cooling rate, initial austenite grain size, prestrain, residual strains, static recrystallization, and the mode of deformation on phase transformation temperatures are determined and discussed.

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Schneider, J., W. Jungnickel, W. Müller, Harti Hermann et R. Kawalla. « Hot Rolling of FeSi Steels – Effects by Hot Rolling in the Two Phase Region ». Materials Science Forum 704-705 (décembre 2011) : 1161–66. http://dx.doi.org/10.4028/www.scientific.net/msf.704-705.1161.

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Finish rolling in the two-phase region may offer new possibilities for improving the properties of the FeSi steels with phase transformation. Therefore a deeper understanding of the effects by hot rolling in the two phase region or mixed rolling: multistep hot rolling in the two phase region and in the ferrite region on the evolution of the microstructure is desirable. In this paper we will present the results of our experimental studies on the effect of hot rolling in the intercritical state on the hardening and softening in the ferrite state. It will be demonstrated that depending on the process conditions at hot rolling the austenite ferrite transformation affects the stress strain behaviour in the ferrite state at multistep hot rolling remarkable.

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Hwang, Byoung Chul, Chang Gil Lee et Sung Hak Lee. « Microstructure and Mechanical Properties of Ultra-High Strength Steel Plates with High Deformability ». Materials Science Forum 638-642 (janvier 2010) : 3266–71. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.3266.

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High deformability has been considered as a critical factor of ultra-high strength steel plates subjected to compressive, tensile, and bending deformation induced by large ground movements. In this paper, various dual phase microstructures consisting of soft ferrite and strong low-temperature transformation phases without deformation in the (austenite + ferrite) two-phase temperature region after controlled rolling were introduced and then the mechanical properties were discussed with emphasis on deformability such as yield ratio and uniform elongation. Ultra-high strength steel plates fabricated by a modified thermo-mechanical control process showed lower yield ratio of under 0.75 and higher uniform elongation of 5% as a minimum, as compared to commercial API X100 and X120 grade pipeline steels, without much sacrifice of Charpy impact properties because of an appropriate formation of soft ferrite and strong low-temperature transformation phases.

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Enomoto, Masato, Guo Hong Zhang et Kai Ming Wu. « Influence of High Magnetic Field on Ferrite Transformation in Fe-C Base Alloys ». Solid State Phenomena 172-174 (juin 2011) : 362–71. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.362.

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The characteristics and the mechanism of ferrite transformation in alloy steels which contain a carbide-forming element have attracted considerable attention for past decades. Since it is reported that the nucleation and growth of ferrite in Fe-C base alloys is accelerated by high magnetic field, the influence of a magnetic field of 12 Tesla on ferrite transformation was studied in a Fe-C- Mo alloy. Whereas a significant amount of expedition was observed at lower temperatures, the principal features of ferrite transformation, namely, a marked retardation of transformation at intermediate temperatures and premature cessation of transformation before it reaches the final equilibrium amount below the bay temperature were essentially retained. In contrast, the influence of magnetic field was much less at higher temperatures. These results are discussed in terms of the influence of magnetic field on the phase equilibrium and coupled-solute drag effects on the migration a/g phase boundary.

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Paúl, A., A. Beirante, Nuno Franco, Eduardo Alves et José Antonio Odriozola. « Phase Transformation and Structural Studies of EUROFER RAFM Alloy ». Materials Science Forum 514-516 (mai 2006) : 500–504. http://dx.doi.org/10.4028/www.scientific.net/msf.514-516.500.

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High temperature phase transformations in EUROFER reduced activation ferritic martensitic (RAFM) steel were studied in-situ by means of X-ray diffraction. Results show that, during slow cooling, the austenite to ferrite transformation takes place around 755 oC. Full transformation of the austenitic phase into pure martensite is observed for cooling above 5 oC/min. This transformation was found in samples annealed at 950 oC for 3 h and quenched in liquid nitrogen. TEM analyses reveal a high concentration of carbides along the grain boundaries of the martensitic structure. The thermal expansion coefficient derived from the measurements was 12.7x10-6 K-1.

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You, Jingtian, Zhiying Li, Jie Wang, Changrong Li, Zeyun Zeng, Shiwang Li et Sheng Huang. « Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar ». Materials 15, n^o 24 (14 décembre 2022) : 8940. http://dx.doi.org/10.3390/ma15248940.

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The effects of niobium and composite strengthening on the phase transformation characteristics and precipitation behavior of continuous cooling transformation of high-strength rebar during thermal deformation and subsequent cooling were investigated. The results show that when the cooling rate was within 0.3–5 °C/s, ferrite transformation and pearlite transformation occurred in the experimental steels. The Nb content increased to 0.062 wt.%, and the starting temperature of the ferrite transformation decreased. Meanwhile, the ferrite phase transformation zone gradually expanded, and the pearlite phase transformation zone gradually narrowed with the increase in the cooling rate. When the cooling rate was 1 °C/s, bainite transformation began to occur, and the amount of transformation increased with the increase in the cooling rate. It was found that the main precipitates in the experimental steels were (Nb, Ti, V)C, with an average particle size of about 10–50 nm. When the Nb content was increased to 0.062 wt.% and the cooling rate was increased to 5 °C/s, the ferrite grain size was reduced from 19.5 to 7.5 μm, and the particle size of the precipitate (Nb, Ti, V)C could be effectively reduced. The strength of the steel was significantly improved, but the elongation of the steel was reduced. However, the comprehensive mechanical properties of 0.062 wt.% Nb experimental steel was significantly improved at a cooling rate of 5 °C/s.

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Zhou, Le Yu, Tian Hao Cui, Bo Jiang, Chao Lei Zhang, Jian Zhong He et Ya Zheng Liu. « Effect of Mo on Transformation, Microstructure and Property of Hot-Rolled DP600 Steel ». Materials Science Forum 817 (avril 2015) : 560–64. http://dx.doi.org/10.4028/www.scientific.net/msf.817.560.

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In according with the transformation rules of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo tested steels, rolling experiment was carried out in lab. to analyze the effect of Mo on transformation, microstructure and property of high strength hot rolled dual phase steels. The results showed that the addition of element Mo decreased start temperature of ferrite transformation and restrains pearlite transformation. There was a metastable austenite zone between ferrite and bainite transformation zone of No.2 steel with 0.35% of Mo. After controlled rolling and step cooling process, dual phase microstructures in which fine martensite islands dispersed in soft ferrite matrix were obtained by two kinds of tested steel. With the addition of Mo, yield strength and tensile strength increased by 80MPa and 60MPa respectively, meanwhile, elongation increased slightly.

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Aksenova, Krestina, Victor Gromov, Yurii Ivanov, Rongshan Qin et Ekaterina Vashchuk. « Structural Phase Transformation of Rail Steel in Compression ». Metals 12, n^o 11 (20 novembre 2022) : 1985. http://dx.doi.org/10.3390/met12111985.

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The analysis of structure and defective substructure of rail steel in uniaxial compression to a degree of 50% is carried out. It is revealed that cold hardening has a multi-stage character and is accompanied by fragmentations of pearlite grains which is in field as the degree of deformation increases and reaches ≈ 0.4 volume of the foil studied at ε = 50%. The fragments being formed in ferrite plates are separated by low-angle boundaries. The average size of the fragmented ferrite decreases from 240 nm at ε = 15% to 200 nm at ε = 50%. Concurrently with the ferrite fragmentation, fragments of cementite are also observed. It is found that the sizes of the cementite fragments are in a range of 15 to 20 nm and depend weakly on the degree of sample deformation. The cementite fragmentation is caused by deformation-induced carbon dissolution and dislocation-induced fracture. The carbon atoms diffuse from cementite crystal to dislocations, which move through an interplanar space to form particles of tertiary cementite at nanoscale (2–4 nm). It is found that the increase in the degree of deformation is accompanied by a decrease in the scalar and an excess dislocation density. A physical interpretation of the observations has been given.

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Jonas, John Joseph, Clodualdo Aranas Jr. et Samuel F. Rodrigues. « Dynamic Transformation of Austenite at Temperatures above the Ae₃ ». Materials Science Forum 941 (décembre 2018) : 633–38. http://dx.doi.org/10.4028/www.scientific.net/msf.941.633.

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Under loading above the Ae3 temperature, austenite transforms displacively into Widmanstätten ferrite. Here the driving force for transformation is the net softening during the phase change while the obstacle consists of the free energy difference between austenite and ferrite as well as the work of shear accommodation and dilatation during the transformation. Once the driving force is higher than the obstacle, phase transformation occurs. This phenomenon was explored here by means of the optical and electron microscopy of a C-Mn steel deformed above their transformation temperatures. Strain-temperature-transformation (STT) curves are presented that accurately quantify the amount of dynamically formed ferrite; the kinetics of retransformation are also specified in the form of appropriate TTRT diagrams. This technique can be used to improve the models for transformation on accelerated cooling in strip and plate rolling.

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Long, Xiaoyan, Fucheng Zhang, Zhinan Yang et Ming Zhang. « Study on Bainitic Transformation by Dilatometer and In Situ LSCM ». Materials 12, n^o 9 (10 mai 2019) : 1534. http://dx.doi.org/10.3390/ma12091534.

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This study investigates the bainitic transformation kinetics of carbide-free bainitic steel with Si + Al and carbide-bearing bainitic steel without Si + Al, as well as the phase transformation and microstructure through in situ high-temperature laser scanning confocal microscopy. Results show that bainitic ferrite plates preferentially nucleate at the grain boundary. New plates nucleate on previously formed ones, including two dimensions which appear on a plane where a three-dimensional space of bainitic ferrite forms. Nucleation on the formed bainitic ferrite is faster than that at the grain boundary in some grains. The bainitic ferrite growth at the austenite grain boundary is longer and has a faster transformation rate. The bainitic ferrite growth on the formed bainitic ferrite plate is shorter and has a slower transformation rate. The location and number of nucleation sites influence the thickness of the bainitic ferrite. The higher the number of plates preferentially nucleating at the original austenite grain boundary, the greater the thickness of the bainitic ferrite.

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Liu, Yong Chang, F. Sommer et Eric J. Mittemeijer. « Kinetics of the Austenite-Ferrite Transformation with and without Applied Stress ». Solid State Phenomena 172-174 (juin 2011) : 1207–13. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.1207.

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The formation of ferrite (α) from austenite (γ) and vice versa, upon thermo-mechanical processing of steels, are phase transformations of great technological importance. Often these transformations occur in the presence of externally or internally imposed stress. This paper provides an overview of recent research on the quantitative analysis of the transformation kinetics of the γ®a and a®g transformations subjected to uniaxial compressive stress below the yield stress of g and a, based on the application of the high-resolution differential dilatometry and the modular model of transformation kinetics. The application of uniaxially compressive stresses leads to antagonistic effects on the transformation kinetics: the stress applied upon the γ®a transformation prompts the transformation, while it obstructs the a®g transformation. These results can be quantitatively discussed in terms of chemical driving forces and transformation-induced deformation energies.

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Jonas, John J., Clodualdo Aranas Jr., Samuel F. Rodrigues et In Ho Jung. « Dynamic Transformation during Plate and Strip Rolling ». Materials Science Forum 879 (novembre 2016) : 29–35. http://dx.doi.org/10.4028/www.scientific.net/msf.879.29.

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Torsion simulations were carried out of both plate (long interpass times) and strip (short interpass times) rolling. Both isothermal and continuous cooling conditions were employed. The dynamic transformation of austenite to ferrite was observed under all conditions and at all temperatures within the austenite phase field. About 8 to 10 volume percent ferrite was formed in a given pass, leading to about 50 - 70 % ferrite at the end of selected simulations. During the interpass intervals, some retransformation to austenite took place, the amount of which increased with holding time and temperature and decreased with the addition of alloying elements. It is shown that the driving force for the transformation is the softening associated with the replacement of work-hardened austenite grains by the softer alpha phase. The implications with respect to rolling load (i.e. mean flow stress) are also discussed.

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Gamsja¨ger, E., F. D. Fischer et J. Svoboda. « Interaction of Phase Transformation and Diffusion in Steels ». Journal of Engineering Materials and Technology 125, n^o 1 (31 décembre 2002) : 22–26. http://dx.doi.org/10.1115/1.1525251.

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During continuous casting low alloy steels undergo a proeutectoid γ (austenite)/α (ferrite) transformation at temperatures of about 1000 K and above. The continuous rearrangement of the iron-lattice (fcc to bcc) is accompanied by diffusion of dissolved components (C, Mn). The diffusion coefficient of carbon exceeds that of a substitutionally dissolved element by a factor of 104 to 105 at these temperatures. Therefore, Mn-diffusion does not influence the γ/α phase transformation provided that the mole fraction of Mn and the transformation temperature are low enough. In this case the γ/α transformation in the Fe-C-Mn system finally reaches paraequilibrium rather than orthoequilibrium. The time-dependent driving force of the phase transformation has been evaluated as a function of temperature and composition. Furthermore, the growth kinetics of the ferrite phase was calculated by a numerical routine.

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Ameri, Ali, Hongxu Wang, Zongjun Li, Zakaria Quadir, William D. A. Rickard, Manny Gonzalez, Paul J. Hazell et Juan P. Escobedo-Diaz. « Ferrite phase transformation in dual-phase steel under shock loading ». Materials Science and Engineering : A 802 (janvier 2021) : 140690. http://dx.doi.org/10.1016/j.msea.2020.140690.

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Yang, Hong Mei. « Continuous Cooling Transformation Behavior of X70 Pipeline Steel ». Advanced Materials Research 690-693 (mai 2013) : 2205–9. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.2205.

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The continuous cooling transformation behaviors were researched on X70 pipeline steel through two pass deformation and non-deformed austenite using Gleeble-3500 thermal mechanical simulator, and static continuous cooling transformation curve and dynamic continuous cooling transformation curve were measured through thermal dilation method and metallographic method. The influence of cooling rate and deformation parameters on microstructure was analyzed. The results show that the hot deformation accelerates the acicular ferrite and polygonal ferrite phase transformation, increases the starting transformation temperature and the finishing transformation temperature significantly, and shifts the CCT curve moving upward to the left side corner. Acicular ferrite is obtained in practice using accelerated cooling rate after deformation Acicular ferrite can be obtained in wider range of cooling rates, and microstructure and island structure is finer through hot deformation.

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Chu, Hung-Yang, Ren-Kae Shiue et Sheng-Yuan Cheng. « The Effect of Homogenization Heat Treatment on 316L Stainless Steel Cast Billet ». Materials 17, n^o 1 (31 décembre 2023) : 232. http://dx.doi.org/10.3390/ma17010232.

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This investigation aims to analyze the effect of homogenization heat treatment at 1240 °C for 2 and 6 h on the hardness, distribution, morphology, and chemical composition of the δ-ferrite and sigma phases in 316L stainless steel cast billet. A field emission scanning electron microscope, combined with electron back-scattered diffraction, a field emission electron probe microanalyzer with a wavelength dispersive spectrometer, and a Vickers microhardness tester are applied to identify various phase evolutions in the cast billet. The morphology of the δ-ferrite and sigma phases in the austenite matrix of the 316L cast billet are strongly related to the subsequent hot and cold wire drawings. The homogenization heat treatment is expected to provide a driving force to form spheroid interdendritic δ-ferrite and to minimize the amount of the brittle sigma intermetallic compound in the austenite matrix. The homogenization heat treatment at 1240 °C effectively spheroidized all δ-ferrites into blunt ones in the cast billet. The transformation of δ-ferrite into sigma is dominated by temperature and cooling rate. The fast air cooling after homogenization between 1240 and 850 °C retards the precipitation of the sigma in the δ-ferrite. There are two δ-ferrite transformation mechanisms in this experiment. The direct transformation of the δ-ferrite into sigma is observed in the as-cast 316L stainless steel billet. In contrast, the eutectoid transformation of the δ-ferrite into the sigma and austenite dominates the 316L cast billet homogenized at 1240 °C, with a slow furnace cooling rate.

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Zrník, Jozef, O. Muránsky, Petr Lukáš, Petr Šittner et Z. Nový. « In Situ Neutron Diffraction Analysis of Phase Transformation Kinetics in TRIP Steel ». Materials Science Forum 502 (décembre 2005) : 339–44. http://dx.doi.org/10.4028/www.scientific.net/msf.502.339.

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The precise characterization of the multiphase microstructure of low alloyed TRIP steels is of great importance for the interpretation and optimisation of their mechanical properties. In-situ neutron diffraction experiment was employed for monitoring of conditioned austenite transformation to ferrite, and also for retained austenite stability evaluation during subsequent mechanical loading. The progress in austenite decomposition to ferrite is monitored at different transformation temperatures. The relevant information on the course of transformation is extracted from neutron diffraction spectra. The integrated intensities of austenite and ferrite neutron diffraction profiles over the time of transformation are then assumed as a measure of the volume fractions of both phases in dependence on transformation temperature. Useful information was also obtained on retained austenite stability in TRIP steel during mechanical testing. The in-situ neutron diffraction experiments were conducted at two different diffractometers to assess the reliability of neutron diffraction technique in monitoring the transformation of retained austenite during room temperature tensile test. In both experiments the neutron investigation was focused on the volume fraction quantification of retained austenite as well as on internal stresses rising in structure phases due to retained austenite transformation.

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Kargul, T. « Investigations of Temperatures of Phase Transformations of Low-Alloyed Reinforcing Steel within the Heat Treatment Temperature Range ». Archives of Metallurgy and Materials 62, n^o 2 (1 juin 2017) : 891–97. http://dx.doi.org/10.1515/amm-2017-0131.

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AbstractThe paper presents the results of DSC analysis of steel B500SP produced in the process of continuous casting, which is intended for the production reinforcement rods with high ductility. Studies were carried out in the temperature range below 1000°C in a protective atmosphere of helium during samples heating program. The main objective of the study was to determine the temperature range of austenite structure formation during heating. As a result of performed experiments:Ac1s,Ac1f– temperatures of the beginning and finish of the eutectoid transformation,Ac2– Curie temperature of the ferrite magnetic transformation and the temperature Ac3of transformation of proeutectoid ferrite into austenite were elaborated. Experimental determination of phase transformations temperatures of steel B500SP has great importance for production technology of reinforcement rods, because good mechanical properties of rods are formed by the special thermal treatment in Tempcore process.

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Xu, Zhanyuan, Jinglian Fan, Tao Liu, Yong Han et Hongbo Zhang. « Calcination induced phase transformation in MnZn ferrite powders ». Journal of Alloys and Compounds 814 (janvier 2020) : 152307. http://dx.doi.org/10.1016/j.jallcom.2019.152307.

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Beladi, Hossein, Ilana B. Timokhina, Subrata Mukherjee et Peter D. Hodgson. « Ultrafine ferrite formation through isothermal static phase transformation ». Acta Materialia 59, n^o 10 (juin 2011) : 4186–96. http://dx.doi.org/10.1016/j.actamat.2011.03.043.

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Fan, Guang Wei, Jie Liu, Pei De Han, Guan Jun Qiao et Jian Feng Yang. « Effect of Warm Processing Parameters on the Precipitation of γ'-Phase in 2205 Duplex Stainless Steels ». Materials Science Forum 620-622 (avril 2009) : 165–68. http://dx.doi.org/10.4028/www.scientific.net/msf.620-622.165.

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Effect of the warm processing parameters (the strain rate, forming temperature and deformation degree ) on the γ' metastable phase transformation in 2205 duplex stainless steel has been studied. The γ' metastable phase was located within the ferrite phase. Dynamic recovery took place only within the γ phase, and dynamic recrystallization underwent for the ferrite phase. The γ' metastable phase transformation was affected by the deformation degree and about 15% deformation led to appearance of the γ' metastable phase. γ' metastable phase formation by the precipitation of intragranular γ' was favored by increasing ageing time, and the size and content of γ' metastable phase were related to deformation temperature and strain rates.

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Articles de revues sur le sujet « Transformation de phase austénite-Ferrite »

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