Journal articles: 'Austenite-Ferrite phase transformation'

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Padilha, Angelo Fernando, D. J. M. Aguiar, and R. L. Plaut. "Duplex Stainless Steels: A Dozen of Significant Phase Transformations." Defect and Diffusion Forum 322 (March 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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Villalobos Vera, Doris Ivette, and Ivan Mendoza Bravo. "Effect of annealing temperature on the microstructure of hyperduplex stainless steels." Ingeniería Investigación y Tecnología 20, no. 2 (March 1, 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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Bräutigam–Matus, Krishna, Gerardo Altamirano, Armando Salinas, Alfredo Flores, and Frank Goodwin. "Experimental Determination of Continuous Cooling Transformation (CCT) Diagrams for Dual-Phase Steels from the Intercritical Temperature Range." Metals 8, no. 9 (August 28, 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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Wang, Qihui, Kun Chen, Kejia Liu, Lianbo Wang, Yu Chu, and Bichen Xie. "Study on Characterization of Phase Transition in Continuous Cooling of Carbon Steel Using In Situ Thermovoltage Measurement." Coatings 14, no. 8 (August 3, 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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Cheng, Wei Chun, Kun Hsien Lee, Shu Mao Lin, and 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 (November 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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Yu, Dunji, Yan Chen, Lu Huang, and 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, no. 9 (September 11, 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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Sun, Fei, Yoshihisa Mino, Toshio Ogawa, Ta-Te Chen, Yukinobu Natsume, and Yoshitaka Adachi. "Evaluation of Austenite–Ferrite Phase Transformation in Carbon Steel Using Bayesian Optimized Cellular Automaton Simulation." Materials 16, no. 21 (October 28, 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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Hu, Feng, and Kai Ming Wu. "Isothermal Transformation of Low Temperature Super Bainite." Advanced Materials Research 146-147 (October 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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Zrník, Jozef, O. Muránsky, Petr Lukáš, Petr Šittner, and Z. Nový. "In Situ Neutron Diffraction Analysis of Phase Transformation Kinetics in TRIP Steel." Materials Science Forum 502 (December 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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Lee, Sang Hwan, Jong Min Choi, Yeol Rae Cho, and Kyung Jong Lee. "The Effects of Si and Deformation on the Phase Transformation in Dual Phase Steels." Solid State Phenomena 124-126 (June 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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Lischewski, I., and Günter Gottstein. "Orientation Relationship during Partial α-γ-Phase Transformation in Microalloyed Steels." Materials Science Forum 495-497 (September 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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Liu, Jiang, Guanghua Wen, Yunfeng Li, Ping Tang, and Linqing Luo. "Effect of γ→α Phase Transformation on Refining Austenite Grains of Microalloyed Steel in Continuous Casting by Simulation." High Temperature Materials and Processes 35, no. 7 (August 1, 2016): 653–59. http://dx.doi.org/10.1515/htmp-2015-0027.

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AbstractThe formation of coarse prior austenite grain is a key factor to promote transverse crack, and the transverse crack susceptibility can be reduced by refining the austenite grain size. In the present study, the high-temperature confocal laser scanning microscope (CLSM) was used to simulate and study the effect of two γ→α phase transformation conditions on the refinement of the prior austenite grains. Under the condition of the uniform distribution of the second phase precipitation, the effect of the distribution of the proeutectoid ferrite at different cooling rates and refinement of prior austenite grain were investigated. The results indicate that, at a cooling rate of 5.0°C s–1, the austenite grain size undergoing TH1 thermal cycle was 31% smaller than the austenite grain undergoing TH0 thermal cycle. Under TH0 cooling system, the proeutectoid ferrite was uniformly distributed in the austenite matrix; under TH1 cooling, the proeutectoid ferrite precipitated and mainly concentrated along the austenite grain boundaries to form developed-film-like ferrite, which is favorable to break the prior austenite grain boundaries. After the first phase transformation, the film-like ferrite improved the nucleation conditions of new austenite grains, thus more new austenite grains splitted the prior austenite grains, ultimately refining the prior austenite grains.

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Yanagida, Akira, J. Jin Shan Liu, and Jun Yanagimoto. "Ferrite Transformation Kinetics of Severely Hot-Deformed Austenite." Materials Science Forum 706-709 (January 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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Skowronek, Adam, Mateusz Morawiec, Aleksandra Kozłowska, and Wojciech Pakieła. "Effect of Hot Deformation on Phase Transformation Kinetics in Isothermally Annealed 3Mn-1.6Al Steel." Materials 13, no. 24 (December 20, 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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Mecozzi, Maria Giuseppina, C. Bos, and Jilt Sietsma. "3D Cellular Automata Modelling of Solid–state Transformations Relevant in Low–alloy Steel Production." Solid State Phenomena 172-174 (June 2011): 1140–45. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.1140.

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A three-dimensional cellular automata (CA) model is developed for the kinetic and microstructural modelling of the relevant metallurgical mechanisms occurring in the annealing stage of low–alloy steels: recrystallisation, pearlite–to–austenite transformation and ferrite–to–austenite transformation on heating and austenite–to–ferrite transformation on cooling. In this model the austenite–to–ferrite transformation is described by a mixed–mode approach, which implies that the transformation kinetics is controlled by both the interface mobility and the diffusivity of the partitioning elements. This approach also allows incorporation of the ferrite nucleation occurring on structural defects. The developed CA algorithm, in which the transformation rules for the grain boundary and interface cells are controlled by the growth kinetics of the forming phase, allows three-dimensional systems to be treated within relatively short simulation times. The simulated microstructure reproduces quite well the microstructure observed in experimental samples. A good agreement is obtained between the experimental and simulated ferrite recrystallisation and ferrite and austenite transformation kinetics. The present approach also models the development of the carbon concentration profile in the austenite, which is, for instance, essential for subsequent martensite formation.

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Jonas, John J., Clodualdo Aranas Jr., Samuel F. Rodrigues, and In Ho Jung. "Dynamic Transformation during Plate and Strip Rolling." Materials Science Forum 879 (November 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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Hwu, Y. J., and J. G. Lenard. "Phase Transformation Temperatures of an Ultra-Low Carbon Steel." Journal of Engineering Materials and Technology 120, no. 1 (January 1, 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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Meiser, Jerome, and Herbert Urbassek. "Ferrite-to-Austenite and Austenite-to-Martensite Phase Transformations in the Vicinity of a Cementite Particle: A Molecular Dynamics Approach." Metals 8, no. 10 (October 17, 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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Li, Zhao Dong, Zhi Gang Yang, Tao Pan, Zhi Xin Xia, and Chi Zhang. "Analytical Modeling of Austenite Growth and Phase Evolution during Reverse Transformation from Pearlite in High Carbon Steels." Solid State Phenomena 172-174 (June 2011): 1201–6. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.1201.

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Based on an analytical one-dimensional model, austenite growth into pearlite lamella and the corresponding phase evolution during isothermal reverse transformation to austenite at 1000-1183 K in Fe-C fully pearlitic steels containing 0.6-1.0 mass% C (in the austenite single phase field of Fe-C phase diagram) were simulated. It was found that the rate of austenite growth into ferrite increases faster with increasing reversion temperature than into cementite. Three types of phase evolution dependent on reversion temperature and carbon content were classified: 1) cementite rather than ferrite disappears first; 2) ferrite and cementite simultaneously disappear; 3) ferrite rather than cementite disappears first. The type of phase evolution in a hypoeutectoid steel heated above its Ae3temperature possibly changes in the order of 1), 2) and 3) as the reversion temperature increases. For eutectoid and hypereutectoid steels, the phase evolution during isothermal reversion always obeys the type 3).

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Gautam, J. Prakash, A. Miroux, Jaap Moerman, and Leo Kestens. "Tnr Dependent Hot Rolling Microstructure and Texture Development in C-Mn Dual Phase and HSLA Steels." Defect and Diffusion Forum 391 (February 2019): 120–27. http://dx.doi.org/10.4028/www.scientific.net/ddf.391.120.

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No recrystallization of austenite, Tnr, has an important influence on the transformed phase fractions and the final crystallographic texture after hot deformation. This paper investigates the evolution of microstructure and texture components during hot-rolling in two austenitic region based on Tnr along with three different cooling trajectory and coiling in dual-phase steels and high strength low alloys steel. The recrystallization of the austenite, the austenite deformation followed by the austenite-to-ferrite transformation influence the final microstructure and texture in dual phase steels, have been examined by means of optical microscopy, X-ray diffraction (XRD) measurements. Recrystallized and deformed austenite have clearly different texture components and, due to the specific lattice correspondence relations between the parent austenite phase and its transformation products, the resulting ferrite textures are different as well.

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Li, Zhuang, Di Wu, Wei Lv, and Ming Fu Shao. "Phase Transformation Behavior during Continuous Cooling of Fe-C-Mn-Si Multiphase Steels." Applied Mechanics and Materials 377 (August 2013): 123–27. http://dx.doi.org/10.4028/www.scientific.net/amm.377.123.

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In the present paper, controlled cooling of Fe-C-Mn-Si multiphase steel was conducted by a laboratory hot rolling mill. The results show that polygonal ferrite, granular bainite and the stable retained austenite can be obtained through hot deformation and subsequent two steps cooling pattern. The amount of ferrite increased with the duration of intermediate air cooling during controlled cooling. The formation of the bainitic ferrite resulted in the carbon concentration enrichment in austenite further during the simulated coiling. This increases the stability of the remaining austenite. Satisfactory mechanical properties can be obtained through hot rolling process and two steps cooling pattern in this work due to the TRIP effect of the stable retained austenite.

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Karmakar, Anish, R. D. K. Misra, Suman Neogy, and Debalay Chakrabarti. "Development of Ultra-Fine Grained Dual-Phase Steels: Mechanism of Grain Refinement during Inter-Critical Deformation." Materials Science Forum 783-786 (May 2014): 674–78. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.674.

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Heavy deformation of metastable austenite (below Ae3) or both austenite and ferrite in the two-phase region (between Ar3 and Ar1) has been found to develop ultra-fine ferrite grain structures with average grain sizes less than 3 μm. The sequence of different dynamic softening mechanisms involved in the grain refinement during heavy intercritical deformation, such as, dynamic recovery, dynamic recrystallization, and dynamic strain induced austenite→ferrite transformation, has been analyzed by considering strain partitioning between austenite and ferrite. Grain refinement is expected to be dictated by dynamic strain induced transformation (DSIT) at higher deformation temperatures (>1100°C) and pronounced dynamic recovery of ferrite at lower deformation temperatures (<1100°C). Evolution of crystallographic texture was dependent on the grain refinement mechanism and gamma fiber components (ND//<111>) and alpha fiber components (RD//<110>) dominated the texture at higher and lower deformation temperatures, respectively.

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Lee, Sang Min, Young Jae Kwon, Duk Lak Lee, Sang Hyun Cho, Sun Keun Hwang, and Yeon Chul Yoo. "Formation of Ultra Fine Ferrite and Determination of Critical Strain in the Strain Induced Dynamic Transformation for 0.22C-Mn Steel." Materials Science Forum 510-511 (March 2006): 514–17. http://dx.doi.org/10.4028/www.scientific.net/msf.510-511.514.

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The low carbon steel of 0.22wt% carbon was tested to estimate the dynamic phase transformation behavior from austenite to ferrite. The samples were deformed at just above Ar3 temperature by hot torsion at condition of strain rate (0.5/sec) and strain (5.0). The flow curve obtained at just above Ar3 significantly differed from others due to dynamic transformation. Based on the analysis of flow stress curve and observation of micro-structure evolution, the initiation and finish points of strain induced dynamic transformation (SIDT) could be determined. An inflection point observed at early deformation range (0.2–0.3) from the work-hardening rate and stress plot meant that new ferrite grains were nucleated in austenite matrix and these nuclei could be also confirmed by optical microscope. Subsequently in strain range of 0.7-1.0, the flow stress had the maximum value and new fine ferrite grains were dynamically generated inside untransformed austenite grains as well as prior austenite grains. The dynamic phase transformation induced by deformation made eventually fine ferrite grains under 3 ㎛ and decreased stress level with a fixed gradient.

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Liu, Dong Sheng, Matthias Militzer, and Warren J. Poole. "Microstructure Model for a Dual-Phase Steel." Materials Science Forum 539-543 (March 2007): 4391–96. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4391.

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The microstructural evolution has been studied for hot rolling of a dual-phase steel with a lean C-Mn-Si chemistry. This study includes the investigation of austenite grain growth during reheating, constitutive behaviour and static recrystallization kinetics of austenite, and austenite decomposition during simulated run-out table cooling conditions. To develop and validate the microstructure models for these phenomena, experimental studies have been carried out in the laboratory using a Gleeble 3500 thermomechanical simulator. The hyperbolic sine relationship between flow stress and Zener-Hollomon parameter is employed to describe the constitutive behaviour. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory is used to predict the static recrystallization kinetics. Ferrite transformation start is described with an approach that considers early growth of corner nucleated ferrite. The fraction of ferrite transformed from austenite during continuous cooling is described using the JMAK approach in combination with the additivity rule. The ferrite grain size is quantified as a function of the transformation start temperature. The overall microstructure model has been validated based on a number of laboratory simulations of the entire hot strip rolling and controlled cooling process with an emphasis on industrially relevant run-out table cooling strategies.

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Geissler, J., C. Mesplont, S. Vandeputte, and 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, no. 11 (November 1, 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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Liu, Man, Guang Xu, Guanghui Chen, and Zhoutou Wang. "Study on the transformation and microstructure evolution during hot-charging rolling process of a weathering steel." Metallurgical Research & Technology 117, no. 3 (2020): 304. http://dx.doi.org/10.1051/metal/2020027.

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The effect of hot-charging temperature (HCT) on the transformation and microstructure evolution of a weathering steel was investigated by metallography and dilatometry. The results show that the microstructure consisted of ferrite and pearlite in all specimens when the HCT was between 500 ∼ 850 °C. The difference was that pearlite amount increased obviously at 750 °C, which is detrimental to the plasticity of steels. The reason for more pearlite is that ferrite and austenite coexisted at 750 °C, which belongs to the dual-phase region temperature. The reversed transformation of ferrite to austenite happened and the pre-existing austenite became coarse during the secondary austenization. The carbon content in fine reversed austenite was relatively low, while the coarse austenite contained higher carbon content, which decomposed into blocky pearlite in the final cooling process. Therefore, to obtain the desirable ferrite phase, the HCT of about 750 °C should be avoided. The results provide theoretical reference for optimizing hot-charging rolling process parameters.

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Vodárek, Vlastimil, Carl Peter Reip, and Anastasia Volodarskaja. "Microstructure Evolution in Belt-Casted Strip of Grain Oriented Electrical Steel." Key Engineering Materials 810 (July 2019): 82–88. http://dx.doi.org/10.4028/www.scientific.net/kem.810.82.

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This paper deals with the formation and decomposition of Widmanstätten austenite during solidification of the thin belt-casted strip made of a grain oriented electrical steel (GOES). Solidification of liquid steel starts with the formation of d-ferrite. Cooling in the delta + gama phase field results in the formation of a small fraction of Widmanstätten austenite by displacive transformation accompanied by carbon partition. Widmanstätten austenite laths have an orientation relationship with the ferrite grain into which they grow. Furthermore, they form a flat low energy interface along the ferrite grain boundary. In order to minimize the interfacial energy, ferrite grain boundaries in the vicinity of flat austenite/ferrite interface facets are forced to migrate which results in straightening of these grain boundaries. If parallel Widmanstätten austenite laths form in two adjacent ferrite grains, zig–zag ferrite grain boundaries arise. Precipitation of sulphides along ferrite/austenite interfaces make it possible to study the early stages of austenite decomposition under the delta + gama phase field. It starts with the formation of epitaxial ferrite accompanied by further partitioning of carbon into remaining austenite. The growth of epitaxial ferrite into the flat ferrite/austenite interface facets along ferrite grain boundaries results in a wavy shape of these ferrite grain boundaries. Finally austenite transforms either to pearlite or to plate martensite.

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Mueller, Josh, David Matlock, John Speer, and Emmanuel De Moor. "Accelerated Ferrite-to-Austenite Transformation During Intercritical Annealing of Medium-Manganese Steels Due to Cold-Rolling." Metals 9, no. 9 (August 23, 2019): 926. http://dx.doi.org/10.3390/met9090926.

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Prior cold deformation is known to influence the ferrite-to-austenite (α → γ) transformation in medium-manganese (Mn) steels that occurs during intercritical annealing. In the present study, a 7Mn steel with ultra-low residual carbon content and varying amounts of prior cold deformation was intercritically annealed using various heating rates in a dilatometer. The study was conducted using an ultra-low carbon steel so that assessments of austenite formation during intercritical annealing would reflect the effects of cold deformation on the α → γ transformation and Mn partitioning and not effect cementite formation and dissolution or paraequilibrium partitioning induced austenite growth from carbon. Increasing prior cold deformation was found to decrease the Ac1 temperature, increase austenite volume fraction during intercritical annealing, and increase the amount of austenite nucleation sites. Phase field simulations were also conducted in an attempt to simulate the apparent accelerated α → γ transformation with increasing prior cold deformation. Mechanisms for accelerated α → γ transformation explored with phase field simulations included an increase in the amount of austenite nucleation sites and an increased Mn diffusivity in ferrite. Simulations with different amounts of austenite nucleation sites and Mn diffusivity in ferrite predicted significant changes in the austenite volume fraction during intercritical annealing.

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29

Kawata, Hiroyuki, Kunio Hayashi, Natsuko Sugiura, Naoki Yoshinaga, and Manabu Takahashi. "Effect of Martensite in Initial Structure on Bainite Transformation." Materials Science Forum 638-642 (January 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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30

Yu, Peng, Lin Zhang, Lin Xiu Du, and Jun Hu. "Mesoscopic Simulation of the Ferrite Nucleation on Austenitic Grain Boundary for Nanograined Steel." Materials Science Forum 817 (April 2015): 731–35. http://dx.doi.org/10.4028/www.scientific.net/msf.817.731.

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We use the cellular automaton (CA) modeling to investigate the ferrite nucleation on the austenite grains. On the basis of the thermodynamics and kinetics of phase transformation from austenite to ferrite, the CA modeling demonstrates that the size of nucleated ferrite grains is increased with increasing of cooling rates, and nucleation process is finished instantly at a given cooling rate. The initial austenite grain size plays an important role in the obtained ferrite nucleation number, and the potential nucleation cells are increased.

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31

Dere, Emine Gözde, Hemant Sharma, S. Eric Offerman, and 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 (June 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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32

Nguyen Duong Nam, Hoang Thanh Thuy, Dinh Van Hien, and Sai Manh Thang. "Study on phase transformation of CMnSi steel when heat treatment." GSC Advanced Engineering and Technology 1, no. 1 (May 30, 2021): 001–5. http://dx.doi.org/10.30574/gscaet.2021.1.1.0021.

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After manufacturing, if the CMnSi steel was heat treatment, it would create the multi-phase microstructure consists of highly ductility ferrite matrix, martensite, bainite and amounts of austenite. Thereby, the strength and ductility of the steel were improved. In the process of improving the quality of steel, there will be two processes: the plastic deformation process and the heat treatment process. In this paper, we present the study on the microstructure and mechanical properties of CMnSi steel which was heated. The heat treatment process of CMnSi steel is a special heat treatment process including the process of heating the steel to austenite temperature at 900 °C then keeping the heat to ensure uniformity of steel. This steel was cooled quickly from austenite temperature to phase transformation temperature which had bainite transformation equal to about 400 °C (this temperature is determined by CCT diagram). The results of microstructure analysis show that by the heat treatment process, the microstructure of steel is included three main phases: ferrite, bainite, and residual austenite. The results of mechanical tests show that after the heat treatment, the strength limit of steel is 1141 MPa, the elastic limit is 943 MPa and the elongation is 36%.

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33

Rijkenberg, R. Arjan, Maxim P. Aarnts, Floor A. Twisk, Marga J. Zuijderwijk, M. Knieps, and H. Pfaff. "Linking Crystallographic, Chemical and Nano-Mechanical Properties of Phase Constituents in DP and TRIP Steels." Materials Science Forum 638-642 (January 2010): 3465–72. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.3465.

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This paper discusses practical EBSD strategies for identification and partitioning of phase constituents in DP and TRIP microstructures including martensite, retained-austenite, bainite, intercritical and epitaxial ferrite. EBSD data is complemented with nano-indentation analysis, providing evidence of indentation-induced phase transformation of retained-austenite in TRIP steel and micro-crack initiation at the interface between ferrite and mechanically transformed martensite.

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34

Fu, J. W., Y. S. Yang, J. J. Guo, J. C. Ma, and W. H. Tong. "Formation of two-phase coupled microstructure in AISI 304 stainless steel during directional solidification." Journal of Materials Research 24, no. 7 (July 2009): 2385–90. http://dx.doi.org/10.1557/jmr.2009.0282.

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Formation and evolution details of a two-phase coupled microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification. Results show that the coupled growth microstructure, which is composed of thin lath-like ferrite (δ) and austenite (γ), crystallizes first in the form of colony from the melt. As solidification develops, the retained liquid transforms into austenite gradually. On cooling, solid-state transformation from ferrite to austenite results in the disappearance of part thinner ferrites and the final two-phase coupled microstructure is formed after the solid-state transformation. The formation mechanism of the two-phase coupled microstructure is analyzed based on the nucleation and constitutional undercooling criterion (NCU) before steady-state growth of each phase is reached.

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35

Zhao, Yan, Lifeng Fan, and Bin Lu. "Effect of Reverse-phase Transformation Annealing Process on Microstructure and Mechanical Properties of Medium Manganese Steel." Materials 11, no. 9 (September 6, 2018): 1633. http://dx.doi.org/10.3390/ma11091633.

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In order to develop a third-generation automobile steel with powerful strength and elongation, we propose a method through high temperature quenching and two-phase region reverse-phase transformation annealing to develop such steel with 0.13% C and 5.4% Mn. To investigate the microstructure evolution and mechanical properties of manganese steel, SEM, XRD and TEM are employed in our experiments. Experimental results indicate that the microstructure after quenching is mainly lath martensite microstructure with average of lath width at 0.5 μm. The components of the steel after along with reverse-phase transformation annealing are ultra-fine grain ferrite, lath martensite and different forms of austenite microstructure. When the temperature at 625 °C, the components of the steel mainly includes lath martensite microstructure and ultra-fine grain ferrite and the fraction of austenite volume is only 5.09%. When the annealing temperature of reverse-phase transformation increase into 650 °C and 675 °C, the austenite appears in the boundary of the ferritic grain boundary and the boundary of lath martensite as the forms of bulk and lath. The phenomenon appears in the bulk of austenite, and the size of is 0.22 μm, 0.3 μm. The fraction of austenite volume is 22.34% at 675 °C and decreases into 9.32% at 700 °C. The components of austenite mainly includes ultra-fine grained ferrite and lath martensite. Furthermore, the density of decreases significantly, and the width of martensite increases into 0.32 μm. In such experimental settings, quenching at 930 °C with 20 min and at 675 °C with 30 min reverse-phase transformation annealing, the austenite volume fraction raises up to 22.34%.

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36

Jonas, John J., Vladimir V. Basabe, and Chiradeep Ghosh. "Transformation of Deformed Austenite at Temperatures above the Ae₃." Materials Science Forum 706-709 (January 2012): 2740–45. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.2740.

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Recent observations regarding the transformation of deformed austenite are reviewed. It is shown that superequilibrium ferrite and pearlite can be formed at temperatures well above the Ae3 and Ae1, respectively. The role of the stored energy associated with the introduction of the dislocations introduced by the deformation is discussed. It is shown that the forward dynamic transformation into ferrite and pearlite is several orders of magnitude faster than the reverse static transformation back into austenite. The retarding effect of alloying additions such as niobium is also outlined. The results are interpreted in terms of the effect of deformation on the modified phase diagrams pertaining to the transformation of deformed austenite.

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37

Jonas, John J., Vladimir V. Basabe, and Chiradeep Ghosh. "Transformation of Deformed Austenite at Temperatures above the Ae₃." Materials Science Forum 706-709 (January 2012): 49–54. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.49.

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Recent observations regarding the transformation of deformed austenite are reviewed. It is shown that superequilibrium ferrite and pearlite can be formed at temperatures well above the Ae3 and Ae1, respectively. The role of the stored energy associated with the introduction of the dislocations introduced by the deformation is discussed. It is shown that the forward dynamic transformation into ferrite and pearlite is several orders of magnitude faster than the reverse static transformation back into austenite. The retarding effect of alloying additions such as niobium is also outlined. The results are interpreted in terms of the effect of deformation on the modified phase diagrams pertaining to the transformation of deformed austenite.

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38

Jonas, John Joseph, Clodualdo Aranas Jr., and Samuel F. Rodrigues. "Dynamic Transformation of Austenite at Temperatures above the Ae₃." Materials Science Forum 941 (December 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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39

Hug-Amalric, Aurélie, Xavier Kleber, Jacques Merlin, Hélène Petitgand, and Philip Meilland. "Characterization of Metallurgical Transformations in Multi-Phase High Strength Steels by Barkhausen Noise Measurement." Materials Science Forum 539-543 (March 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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40

Costa, F., and R. Barbosa. "Influence of heating rate and intercritical annealing temperature on the austenite formation of a cold rolled dual‐phase steel." Materialwissenschaft und Werkstofftechnik 55, no. 6 (June 2024): 889–99. http://dx.doi.org/10.1002/mawe.202300221.

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AbstractThis study investigated austenite formation in a cold‐rolled dual‐phase steel through thermal experiments in a dilatometer and a Gleeble machine, applying various intercritical annealing temperatures and different heating rates in a 60 % cold‐rolled ferrite‐pearlite banded microstructure. The microstructural characterization revealed that the transformation of lamellar pearlite into ferrite and spheroidized cementite aggregates started before the onset of austenite formation. Different degrees of overlap between the recrystallization of ferrite‐pearlite structure and austenite formation processes were observed, depending on the applied heating rates, which affected the austenite formation mechanisms and the microstructure morphology.

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41

Soliman, Mohamed, Heinz Palkowski, and Adel Nofal. "Thermo-Mechanically Processed Multi-Phase Ductile Iron: Microstructure Development." Key Engineering Materials 457 (December 2010): 199–204. http://dx.doi.org/10.4028/www.scientific.net/kem.457.199.

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Using thermo-mechanical simulator equipped with dilatometry system, two ductile iron alloys with different Mn-content are processed by combining both, well defined deformation process and subsequent controlled cooling in a single processing chain to control the final microstructure. Accordingly, ductile irons with four different structrues are produced namely, martensite, ausferrite, martensite+ferrite and ausferrite+ferrite. Depending on the dilatometric measurments, the ferrite formation temperature-range has been defined for both alloys. Preferential transformation of austenite to ferrite at graphite nodules during cooling is observed. It is also observed that the formation of ferrite during cooling results in both decreased martensite start of the undecomposed austenite and accelerated kinetics of ausferrite formation.

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42

BOBYR, S. V., E. V. PARUSOV, T. M. GOLUBENKO, and D. V. LOSHKAREV. "DEVELOPMENT AND IMPLEMENTATION OF A NEW METHOD FOR MODELING PHASE-STRUCTURAL TRANSFORMATIONS DURING COOLING OF ALLOY STEELS." Physical Metallurgy and Heat Treatment of Metals 1, no. 1 (96) (June 4, 2022): 17–23. http://dx.doi.org/10.30838/j.pmhtm.2413.240422.17.838.

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Formulation of the problem. Modern research on the phase transformations modeling in low-alloy steels allow solving the problem of phase transformations quantitative determination for a given chemical composition of steel and different cooling rates. However, the possibilities of available universal software products for the complex alloy steels analysis are limited. The impossibility for users to integrate their own subroutines according to the phase transformation diagrams is their main disadvantage. Purpose of research. Modeling phase-structural transformations during cooling of complex-alloy steels taking into account the formation of all structural components, in particular residual austenite. To research, steels 25Cr2Mo1V and 38CrNi3MoV and existing analytical models were used, which were adapted to carry out the relevant calculations. Results. A new method for modeling phase-structural transformations during cooling of alloy steels is developed. Structural diagrams depending on the rate of continuous cooling are constructed for the investigated steels. For the first time, the amount of residual austenite is taken into account according to the developed method. Under developed method thermokinetic diagrams of investigated steels austenite transformation are constructed. According to the diagrams, the decay of austenite steel 38CrNi3MoV begins at lower temperatures compared to steel 25Cr2Mo1V. Steel 25Cr2Mo1V, with continuous cooling at a rate of 1.0 °C/s (conditions close to natural air cooling), consists of 18 % ferrite, 1 % pearlite, 80 % bainite and 1 % residual austenite. Steel 38CrNi3MoV cooled at a rate of 1,0 °C/s consists of 2 % ferrite, 47,5 % bainite, 50 % martensite and 0,5 % residual austenite. It is shown that the calculated data correlate well with practical results at the conditions of natural air cooling.

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Cabus, C., H. Regle, and B. Bacroix. "Phases transformation textures in steels." Journal de Physique IV 120 (December 2004): 137–44. http://dx.doi.org/10.1051/jp4:2004120015.

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Low-carbon steels used for deep-drawability applications have properties which depend greatly on their crystallographic texture. It is therefore important to control the texture evolution during the thermomechanical processing. Until recently, little attention has been paid on the understanding of the textures formation after hot-rolling, which are produced by phase transformation, although it is recognised that they have an effect on the development of the texture in the further process (cold rolling and annealing). Indeed, one of the main difficulties consists in the measurement of texture above ambient temperature, in the austenite range. In the present work, EBSD technique is employed on a low-C steel and a method is proposed to determine local austenite orientation thanks to martensitic one, even if there is no residual austenite in the steel. The orientation relationships between the austenite phase and each of its product phases, here martensite and polygonal ferrite, are analysed and compared. Common Kurdjumov Sachs variants are detected for both phases. Variations in the intensities of these variants are also detected and could be due to the different phase transformation mechanisms, diffusion or shear.

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44

Landesberger, Martin, Robert Koos, Michael Hofmann, Xiaohu Li, Torben Boll, Winfried Petry, and Wolfram Volk. "Phase Transition Kinetics in Austempered Ductile Iron (ADI) with Regard to Mo Content." Materials 13, no. 22 (November 21, 2020): 5266. http://dx.doi.org/10.3390/ma13225266.

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The phase transformation to ausferrite during austempered ductile iron (ADI) heat treatment can be significantly influenced by the alloying element Mo. Utilizing neutron diffraction, the phase transformation from austenite to ausferrite was monitored in-situ during the heat treatment. In addition to the phase volume fractions, the carbon enrichment of retained austenite was investigated. The results from neutron diffraction were compared to the macroscopic length change from dilatometer measurements. They show that the dilatometer data are only of limited use for the investigation of ausferrite formation. However, they allow deriving the time of maximum carbon accumulation in the retained austenite. In addition, the transformation of austenite during ausferritization was investigated using metallographic methods. Finally, the distribution of the alloying elements in the vicinity of the austenite/ferrite interface zone was shown by atom probe tomography (APT) measurements. C and Mn were enriched within the interface, while Si concentration was reduced. The Mo concentration in ferrite, interface and austentite stayed at the same level. The delay of austenite decay during Stage II reaction caused by Mo was studied in detail at 400 °C for the initial material as well as for 0.25 mass % and 0.50 mass % Mo additions.

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45

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, no. 2 (June 1, 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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46

Long, Xiaoyan, Fucheng Zhang, Zhinan Yang, and Ming Zhang. "Study on Bainitic Transformation by Dilatometer and In Situ LSCM." Materials 12, no. 9 (May 10, 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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47

Hell, Jean Christophe, Moukrane Dehmas, Guillaume Geandier, Nathalie Gey, Sebastien Allain, Alain Hazotte, and Jean Philippe Chateau. "Influence of the Austempering Temperature on the Microstructure and Crystallography of a Carbide-Free Bainitic Steel." Solid State Phenomena 172-174 (June 2011): 797–802. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.797.

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We elaborated two carbide-free bainitic steels with different microstructures through specific heat treatments and alloy design. EBSD analysis was used to point out major differences in these microstructures. In-situ characterizations of the bainitic transformation were performed by high energy synchrotron diffraction to go further into the study of each phase characteristics. The elaborated microstructures exhibited various phase fractions of bainitic ferrite, retained austenite and blocks of martensite and retained austenite. Moreover, the volume fraction of retained austenite increased with higher austempering temperatures. On the other hand, the austempering temperatures showed a strong influence on the kinetics of the bainitic transformation. Isothermal transformation under Ms showed a two stage transformation which led first to the formation of self-tempered martensite and then to bainitic ferrite. Furthermore, the evolution of the austenitic cell parameter showed enrichment in carbon ruled by diffusional mechanisms.

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48

Zheng, Cheng Wu, Dierk Raabe, and Dian Zhong Li. "Numerical Simulation of Dynamic Strain-Induced Austenite-Ferrite Transformation and Post-Dynamic Kinetics in a Low Carbon Steel." Materials Science Forum 706-709 (January 2012): 1592–97. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1592.

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2-D cellular automaton model was developed to simulate the dynamic strain-induced transformation (DSIT) from austenite (γ) to ferrite (α) and the post-dynamic kinetic behavior in a low carbon steel with the purpose of developing a methodology of mesoscopic computer simulation for an improved understanding of the formation of ultra-fine ferrite (UFF) in DSIT and the conservation of this microstructure during the post-deformation period. The predicted microstructure obtained after DSIT was compared with a quenched dual-phase steel. Its microstructure, consisting of fine-grained ferrite and fine islands of retained austenite dispersed in the matrix, were found to be in good agreement with the predictions. The simulated results indicate that the refinement of ferrite grains produced via DSIT can be interpreted in terms ofunsaturatednucleation andlimitedgrowth mechanisms. It is also revealed that continuing transformation from retained austenite to ferrite and the reverse transformation both could take place simultaneously during the post-deformation isothermal holding. A competition between them exists at the early stage of the post-dynamic transformation.

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49

Godet, S., J. C. Glez, Y. He, J. J. Jonas, and P. J. Jacques. "Grain-scale characterization of transformation textures." Journal of Applied Crystallography 37, no. 3 (May 11, 2004): 417–25. http://dx.doi.org/10.1107/s0021889804007320.

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Orientation relationships during the austenite-to-ferrite (γ-to-α) phase transformation were investigated using electron back-scattered diffraction (EBSD) on a bainitic steel containing retained austenite. The steel was hot rolled within the austenite phase field, but below the `no-recrystallization' temperature, to two different strains. The observed orientation relationships between the bainite and retained austenite are expressed in Rodrigues–Frank space. The exact Kurdjumov–Sachs relation was never found. The local spread of orientation in the parent austenite (owing to deformation) is seen to be inherited by the bainite. This is attributed to the displacive mode of transformation to bainite. The influence of austenite prior deformation on the occurrence of variant selection was also studied. It is shown that a critical strain is necessary in order to observe a significant amount of variant selection.

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Chu, Hung-Yang, Ren-Kae Shiue, and Sheng-Yuan Cheng. "The Effect of Homogenization Heat Treatment on 316L Stainless Steel Cast Billet." Materials 17, no. 1 (December 31, 2023): 232. http://dx.doi.org/10.3390/ma17010232.

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Abstract:

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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Journal articles on the topic 'Austenite-Ferrite phase transformation'

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