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Quenching and partitioning (Q&P) heat treatments have recently gained attention as promising methods for the third generation of advanced high‐strength steels, particularly in industrial applications like automotive. This study investigates the microstructural evolution during Q&P in two medium‐carbon high‐silicon and aluminum‐alloyed steels, exploring potential additional phase transformations controlling the final structure. The choice to focus on Si and Al‐ medium‐carbon steel is linked to the lower cost of these elements compared to commonly alloying elements like Ti, Cr, Mo, and V, while still achieving high mechanical properties through Q&P. The Q&P process is analyzed by varying the volume fraction of primary martensite (M1) at 0.25, 0.50, and 0.75, with partitioning temperatures ranging from 350 to 550 °C for 30 min. At 350 °C, a significant volume fraction of stabilized austenite (up to 0.3) is observed. However, concurrent reactions such as nanostructured bainite and martensite formation lead to deviations from the theoretical constrained carbon equilibrium (CCE). At higher temperatures (450–550 °C), tempering reactions, including cementite precipitation and pearlite formation, reduced the austenite final fraction. The study highlights that heat treatment design, particularly partitioning temperature, must be tailored to the specific steel composition due to the varying effects of Si and Al. [ABSTRACT FROM AUTHOR]

The strength of ultra-low carbon maraging stainless steels can be significantly enhanced by precipitating nanoscale intermetallic secondary phases. Retained or reversed austenite in the steel can improve its toughness, which is key to achieving an ideal combination of strength and toughness. Ti and Al are often used as cost-effective strengthening elements in maraging stainless steels but the synergistic toughening and strengthening mechanisms of Ti and Al have not been studied. To investigate the synergistic toughening and strengthening mechanisms of Ti and Al in Co-free maraging stainless steels, this paper focuses on the microstructure and mechanical properties of three alloys: Fe-12Cr-11Ni-1.7Al-0.5Ti (Steel A), Fe-12Cr-11Ni-0.5Ti (Steel B), and Fe-12Cr-11Ni-1.7Al (Steel C). The impact of Ti and Al on the microstructure and mechanical properties was investigated using X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and thermodynamic simulations. The relationship between microstructure, strength, and toughness is also discussed. The results indicated that Steel A, containing both Al and Ti, exhibited the highest strength level after solution treatment at 900 °C, with an ultimate tensile strength reaching 1571 MPa after aging at 540 °C. This is attributed to the simultaneous precipitation of spherical β-NiAl and rod-shaped η-Ni3Ti phases. Steel B, with only Ti, formed a significant amount of Ni-rich reversed austenite during aging, reducing its ultimate tensile strength to 1096 MPa. Steel C, with only Al, showed a high strength–toughness combination, which was achieved by forming dispersive nano-sized intermetallic precipitates of β-NiAl in the martensitic matrix with a slight amount of austenite. It is highlighted that Al has superior toughening and strengthening effects compared to Ti in the alloy system. [ABSTRACT FROM AUTHOR]

For more than 20 years, high‐temperature laser scanning confocal microscopy (HT‐LSCM) has become worldwide a proven technique for observing various metallurgical phenomena in situ. HT‐LSCM turns out to be a reliable and effective method for the observation of quantification austenite grain growth kinetics in steel, being highly relevant in casting and steel processing. In the present article, the measurement technique is briefly introduced followed by some basics on austenite grain growth. Finally, selected examples of recent research activities are discussed, including investigations into pure iron and the systems Fe–P, Fe–C, Fe–Al–N, and Fe–C–Nb–N. The influence of P on the grain growth kinetics is remarkable. At 1350 °C, the final grain size decreases from 255 μm in pure iron to 145 μm by adding 0.044 wt% P. In contrast, C enhances the grain growth in specific alloying ranges (0–0.30 wt%C), particularly at elevated temperatures. For a Al content of 0.025 wt% and only 50 wt ppm N, AlN loses the pinning effect above 1150 °C. In case of Nb(C,N), an elevated Nb content (0.085 wt%) provides stabilization of Nb(C,N) at 1150 °C, but at 1250 °C, no pinning of Nb(C,N) is visible anymore. [ABSTRACT FROM AUTHOR]

Objective: The present study aimed to evaluate the phase transformation behavior and elemental analysis of thermomechanical-treated nickel–titanium (NiTi) rotary instruments, TruNatomy (Dentsply Sirona), HyFlex CM (coltene, Whaledent), and Neoendo Flex (Orikam healthcare India), using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and energy dispersive X-ray spectrometry. Materials and Methods: A total of 18 NiTi rotary instruments, TruNatomy, Hyflex CM, Neoendo Flex, taper. 04, size 25 (except TruNatomy, size 26) were selected and were divided into three groups (n = 6). Three NiTi files from each group were investigated for the DSC test (n = 3). The two segments of each sample were cut carefully by slow-speed water-cooling carborundum disc at 3 mm from the tip and then 4 mm from the previous section. The mass of the samples was measured on the electronic balance and samples that weighed 10–15 mg were loaded into a 40 µL aluminum crucible. The samples are then subjected first to a heating cycle from 0°C to 100°C and subsequently a cooling cycle from 100°C to 0°C in the differential scanning calorimeter (Mettler-Toledo, NIT Srinagar) at a rate of 10°C min−1. XRD (Make. Rigaku Japan, smart lab 3kW, NIT Srinagar.) was performed to verify the DSC results. The remaining two samples from each group (n = 2) were subjected to XRD analysis. The sample preparation for XRD analyses was done precisely with slow speed water cooled carborundum disc and samples were sectioned into three segments. Each segment was 5 mm long and grounded to obtain a uniform smooth plane. The data obtained from DSC and XRD were subjected to origin 8.5 software and graphs were obtained that depict the transformation temperature and phase composition, respectively. Alloy distribution and trace elements of the NiTi rotary instruments were done using energy dispersive spectrometry microanalysis. Results: The DSC results showed that the TruNatomy, Hyflex CM, and Neo Endo instruments had an Austenite finish (Af) temperature exceeding 37°C. The XRD graphs show the different intensity peaks that correspond to the various phases of NiTi rotary instruments. The TruNatomy is predominantly Austenite, Hyflex CM exists mainly in R-phase with a variable amount of austenite and martensite, while Neoendo flex endo mostly contains austenite phase. The elemental analysis revealed that all three file systems show Nickel and Titanium within their bulk structure in an equiatomic ratio. Conclusion: This study concluded that TruNatomy is predominantly martensite with a variable amount of austenite phase. There are differences in thermal transition temperature between the files. [ABSTRACT FROM AUTHOR]

Given the critical role that metastable retained austenite (RA) plays in advanced high-strength steel (AHSS), there is significant interest in obtaining a comprehensive understanding of its stability, to achieve excellent mechanical properties. Despite considerable attention and numerous studies, the significance of individual contributions of various microstructural factors (size, crystallographic orientation, surrounding phases, etc.) on the stability of RA remain unclear, partly due to the difficulty of isolating the direct effects of these factors. In this study, we examined the influence of microstructural factors while minimizing the effect of chemical composition on the mechanical stability of RA. We accomplished this by comparing the austenite (γ) stability in two distinct microstructures: a two-phase RA/martensite microstructure and a one-phase γ microstructure, both with nearly identical γ compositions. We employed in situ high-energy X-ray diffraction during uniaxial tensile testing conducted at both room temperature and 100 °C, facilitating the continuous monitoring of microstructural changes during the deformation process. By establishing a direct correlation between the macroscopic tensile load, phase load partitioning, and the γ/RA transformation, we aimed to understand the significance of the microstructural factors on the mechanical stability of the RA. The results indicate that very fine RA size and the surrounding hard martensitic matrix (aside from contributing to load partitioning) contribute less significantly to RA stability during deformation than expected. The findings of this study emphasize the critical and distinct influence of microstructure on γ/RA stability. [ABSTRACT FROM AUTHOR]

Upon solidification, graphitic cast irons undergo a volume change whose amplitude depends on two opposite terms, the contraction associated with austenite formation and the expansion due to graphite crystallization. During cooling after solidification, further precipitation of graphite occurs that continuously changes the physical properties of the material and possibly affects the eutectoid transformation that transforms the matrix from austenitic to ferritic or ferritic-pearlitic. This work intended to study the density of graphitic cast irons at high temperature, i.e., in the temperature range where the matrix is austenitic. High-temperature laboratory X-rays have been carried out on several alloys containing various carbon and silicon contents to characterize the austenite mean lattice parameter. By complementing these results with literature data, a statistical analysis was carried out that expresses the austenite mean lattice parameter as a function of temperature and composition, evidencing the high uncertainty related to the austenite carbon content. Finally, one of the investigated alloys was submitted to a simultaneous dilatometry and X-ray analysis in a synchrotron from room temperature to 1050 °C. The data are used to discuss the austenite lattice parameter prediction and the possibility of density prediction. [ABSTRACT FROM AUTHOR]

Various techniques, such as optical microscopy, high‐temperature confocal laser scanning microscopy, scanning electron microscopy, electron backscatter diffraction, and thermodynamic calculations, are employed to analyze the optimization mechanism of Ce on the inclusions and microstructures in F38MnVS as‐cast samples. The results show that the addition of Ce inhibits MnS precipitation at the grain boundaries and significantly reduces the diameters and aspect ratios of the inclusions. After Ce treatment, a new type of composite inclusion appears in the steel. The modification of the inclusions by Ce promotes the optimization of the as‐cast microstructure during solidification, which mainly exhibits austenite grain refinement and polygonal ferrite formation in the grains. Based on the misfit degree theory, the refinement of the austenite grains is because of the nucleation of austenite grains facilitated by Ce2O2S and CeAlO3. The increased nucleation of the intragranular polygonal ferrite is mainly attributed to Ce2O2S, Ce2S3, CeAlO3, and VC, which can promote the nucleation of α‐Fe. Simultaneously, the addition of Ce reduces the phase transition temperature, increases the driving force of the phase transition, and increases the nucleation rate. This study's results can provide a reference for the application of Ce treatment in the preparation of nonquenched tempered steel for automobiles. [ABSTRACT FROM AUTHOR]

Cold metal transfer (CMT)–wire arc additive manufacturing (WAAM) exhibits great potential in the production of large structural metallic components. Many studies have focused on the microstructure and mechanical properties of the parts produced using CMT–WAAM. However, the corrosion resistance of such parts has barely been investigated. In this study, parts of stainless steel (SS) 308L were fabricated using CMT–WAAM. Further, the microstructure and corrosion resistance in different areas of the parts were analyzed. The microstructure of such parts comprised austenite and ferrite. The residual ferrite was distributed in austenite in the form of strips and skeletons. The electrochemical corrosion testing revealed that the corrosion performance of the middle sample was the best while that of the bottom sample was the worst. [ABSTRACT FROM AUTHOR]

The carbide precipitation of H13 steel and its effect on hardness and friction and wear resistance are investigated by microstructure observation, phase analysis, and mechanical property test. Results show that the tempering hardness is mainly related to the content of secondary carbides. After solution treatment in the temperature range of 1040–1070 °C, quenching and tempering, with the increase of the solution temperature, the content of secondary carbides and hardness of H13 steel in the tempering microstructure increase first and then decrease, and both reach the maximum value when the solution temperature is 1060 °C. The change of hardness is consistent with that of the content of secondary carbides. When the solution temperature is 1040 °C, the wear mass loss of the tempered H13 steel is the least, which is 4.63 mg, indicating that its wear resistance is the best, and this is caused by the presence of more undissolved carbides in the tempering microstructure. With the increase of the solution temperature, the wear mass loss increases gradually, and the wear resistance decreases, which is mainly related to the content decrease of undissolved and secondary carbides and the content increase of residual austenite. [ABSTRACT FROM AUTHOR]

Duplex stainless steels are composed of ferrite and austenite in equal volume fractions of these phases, which provides an excellent combination of mechanical properties and corrosion resistance, especially when compared with conventional stainless steel grades. When these steels are welded, there are significant changes in the austenite-to-ferrite ratio therefore in their final properties. Nowadays, the ferritoscope is the unique non-destructive technique used to quantify these two phases content in situ. This tester instrument is limited to the evaluation of large areas, is not suitable for the heat affected zone and is also very sensitive to the surface finish, being considered an intermediate precision technique. So, it is necessary to develop more reliable field techniques. In this research, thermoelectric power measurements and induced current techniques are proposed to evaluate the phase quantification in S32205 welds. According to the results, both techniques are reliable and highly sensitive to phase changes in the weld bead, heat affected zone and base metal. For the thermoelectric power technique, a probe with nickel tip should be used to obtain the highest sensitivity and for the induced current technique, a probe type-pencil with a central frequency of 6 MHz should be used. [ABSTRACT FROM AUTHOR]

The objective of this study was to analyze the thermodynamic feasibility of forming nanobainite in Al-alloyed medium-Mn steels through intercritical annealing (IA) and subsequent heat treatments. The research aimed to determine the influence of IA temperature and Mn content on the stability of austenite, the Ms temperature, and the resulting bainite plate thickness (BPT). Our findings indicate that the IA temperature range of 780–860 °C effectively decreased the Ms temperature, facilitating the formation of nanobainite. The results demonstrated that a higher Mn content increases an austenite fraction during IA, thus enhancing the potential for nanobainite formation. For the 3MnNb steel, the IA temperature of 860°C was sufficient to achieve bainitic plates thinner than 100 nm, whereas the 4MnNb steel required lower IA temperatures due to its higher Mn content. The transformation kinetics was found to be faster in 3MnNb steel, with a complete transformation time of 300 min, compared to approximately 600 min for the 4MnNb steel. Dilatometric analysis confirmed that the real austenite fractions were approximately 20% higher than the ones predicted by thermodynamic simulations, indicating potential limitations of the commercial software in accurate predicting the experimental conditions. The obtained results validate the proposed heat treatment strategy for achieving nanobainitic structures in medium-Mn steels. [ABSTRACT FROM AUTHOR]

The present study explores the application of single‐step quenching and partitioning (QP) treatments to low‐silicon commercial AISI 4140 steel. Fractions between 4.6% and 7.8% of retained austenite (RA) are stabilized at room temperature. Specimens quenched at 240 °C and partitioned for 10 min exhibit the highest tensile strength, surpassing 2000 MPa, with an elongation at break of up to 10%. This condition marks the effectiveness of austenite in improving tensile properties. Partitioning times exceeding 5 min lead to a second deformation stage, linked to an intense strain‐induced transformation of austenite into martensite. Comparative quenching and tempering (QT) treatments are conducted to highlight the role of RA in enhancing ductility. The QP samples show improved ductility and strain hardening. Furthermore, an energetic approach is employed to highlight the stability of RA by analyzing the difference in the tensile curves observed between QP and QT conditions. A critical value for stability is reached between 5 and 10 min of partitioning. The work proves the viability of successfully applying QP on AISI 4140 achieving high mechanical properties and improved ductility. [ABSTRACT FROM AUTHOR]

This article focuses on the influences of austenitizing temperature and holding time on the grain sizes of 1800 MPa ultrahigh strength steel (UHS‐1800). When the austenitizing temperature increases from 900 to 990 °C and the holding time is 5 min, the austenite grain size increases from 12.60 to 20.88 μm. When the austenitizing temperature is 930 °C and the holding time increases from 3 to 9 min, the grain size increases from 13.52 to 17.22 μm. When the austenitizing temperature increases from 900 to 990 °C and the holding time is 5 min, the radiuses of the second‐phase particles increase from 15.23 to 25.36 nm. When the austenitizing temperature is 930 °C and the holding time increases from 3 to 9 min, the radius of the second‐phase particle increases from 15.72 to 20.50 nm. On this basis, a prediction model for austenite grain growth suitable for UHS‐1800 hot stamping process is proposed. The growth model of the austenite grain can accurately predict the grain growth behavior during the hot stamping process, with a maximum error of 5.35% compared to experiments. [ABSTRACT FROM AUTHOR]

Simultaneously enhancing the strength, plasticity, and toughness of metal materials has been a prominent research objective. In this study, the precipitation of nano-scale vanadium carbide particles at a lower tempering temperature is controlled to achieve three key benefits: reducing lattice distortion in bainitic ferrite, strengthening through precipitation, and enhancing the toughness of bainitic ferrite, while also maintaining the content and stability of retained austenite. The adopted procedure increases the comprehensive mechanical properties of steel by 17%. In particular, the room-temperature impact toughness is increased by 41%. This comprehensive microstructure optimization endows bainitic steel with an excellent combination of mechanical properties. [ABSTRACT FROM AUTHOR]

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The super duplex stainless steel (SDSS) powder SAF2507 was deposited using directed energy deposition. In the as-built state, the microstructure consists of a nearly balanced ferrite–austenite ratio, with an austenite content of 47 vol.%, in contrast to the SDSS processed by the powder bed method, which produces a very low austenite content. This work investigated the differences in the microstructure, mechanical and corrosion properties of the "high-austenite" as-built state and the solution-annealed (SA) state (at 1100 °C for 60 min, followed by quenching in water). In the SA state, an increase in austenite content to 55 vol.% was observed. In addition, the partitioning of alloying elements into austenite and ferrite also occurred, the austenite grains coarsened and a ferrite grain size reduction was found. Microstructural changes were evident in the development of the mechanical properties. The increase in austenite content was accompanied by an increase in the elongation, and conversely, both the yield strength and ultimate tensile strength decreased. No secondary phases, such as carbides or sigma phase, were observed in either state. Both the as-built and solution-annealed samples exhibited a passivation zone in model seawater at 70 °C, but at the same time, the corrosion current density (icorr) of the as-built state was five times higher. [ABSTRACT FROM AUTHOR]

Bainitic microstructures in high‐strength steels are obtained either by continuous cooling or isothermal holding. Both scenarios necessitate faster cooling to keep the parent austenite phase untransformed till the bainite‐start temperature. The present study reports the development of bainitic microstructure in a low‐carbon steel with minimal alloying additions, under continuous cooling at very slow rates, similar to furnace cooling. For understanding the related transformation pathways, samples from the forged‐steel ingot are austenitized and cooled at different rates, viz. water quenching, air cooling, and furnace cooling. Microstructural characterization reveals development of acicular microstructures in all samples including the forged one, with gross absence of carbides. X‐ray diffraction confirms the ferritic nature of acicular plates and also indicated retained austenite present in some samples, the content of which could be correlated to the extent of bainitic transformation. Thermodynamic calculations together with microstructural observations (e.g., ferrite plate size) and hardness data established the development of fully martensitic microstructure on water quenching, while that of a mixed microstructure comprising predominantly of bainite in the forged, air cooled, and furnace‐cooled condition. The aforementioned findings could have wider implications in developing fully bainitic microstructures in large components, where uniform rapid cooling is not practically feasible. [ABSTRACT FROM AUTHOR]

Microalloying of Nb has been commonly utilized to enhance the structure and mechanical properties of advanced high‐strength steel (AHSS), but its application in medium‐Mn low‐density steel has been relatively understudied. This study aims to investigate the evolution of nano‐scale precipitates and mechanical properties of Fe‐12Mn‐9Al‐3Cr‐1.4C‐0.02/0.04Nb low‐density steels. The findings reveal that the austenite grain size of 0.04Nb steels is approximately half that of 0.02Nb steels due to the precipitation of NbC particles. Moreover, the addition of Nb is found to elevate the formation energy of κ‐carbide, thereby impeding its growth and coarsening. Consequently, the intragranular κ‐carbides in 0.04Nb steels are consistently smaller than those in 0.02Nb steels, with no coarsened intergranular κ‐carbides detected in either steel variant after aging treatment at 723–823 K. Despite a slight reduction on precipitation strengthening of κ‐carbides with higher Nb content, the yield strength of 0.04Nb steels exceeds that of 0.02Nb steels by ≈71 MPa, mainly due to additional fine grain strengthening and dislocation strengthening. The strengthening mechanisms in the Nb‐containing low‐density steels are analyzed quantitatively. The role of Nb in regulating the microstructure and mechanical properties of medium‐Mn low‐density steels is comprehensively discussed, offering valuable insights for the alloy design of low‐density steel. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure and mechanical properties of a new type of low Ni duplex stainless steel after resistance spot welding were studied. The welding current has a great influence on the welding performance of resistance spot welding, so it is necessary to clarify the influence law and mechanism of welding current on the welding performance of low Ni duplex stainless steel. The microstructure of the samples under different welding currents was analyzed in detail by EBSD, and the mechanical properties of the treated samples were measured. The results show that the volume fraction of austenite in nugget zone is affected by changing welding current. This is because the higher cooling rate of resistance spot welding inhibits the phase transformation of ferrite to austenite and reduces the volume fraction of austenite, resulting in the imbalance of ferrite and austenite phases. When the welding current is the largest, the cooling rate is the lowest, which corresponds to the highest austenite volume fraction. [ABSTRACT FROM AUTHOR]

Structure and mechanical properties for experimental heat-resistant steels with 12% Cr with a ferritic or ferritic- martensitic structure, as well as austenitic steel 08Kh18N10T after quenching from different temperatures (950 – 1250°C), are studied. The behavior of steels of different groups, classified according to structural features (grain size and phase content), under these conditions is analyzed. The effect of heating temperature for hardening on yield strength of steels at 20 and 720°C during static compression tests is demonstrated. [ABSTRACT FROM AUTHOR]

The paper studies the alloying effect of the quenched Ni-low (Ni49.5Ti35.5Hf15)100–XNbX and Ni-rich (Ni50.3Ti34.7Hf15)100–XNbX alloys (X = 0, 15 at.% Nb) on the B2-B19' martensitic transformation, viscoelastic properties and microstructure. Alloying of Ni-low and -rich alloys with Nb, provides the β-Nb phase precipitation within the (Ti, Hf)2Ni phase. After alloying, the transformation temperature and austenite elastic modulus decrease in Ni-low alloys and increase in Ni-rich alloys, thus making them similar. [ABSTRACT FROM AUTHOR]

The duplex stainless steels show improved localized corrosion resistance and strength comparing to the austenitic stainless steels. All of the duplex stainless steels solidify as pure ferrite and the double microstructure is evolving during the solid-state, diffusion driven phase transformation. In this research nitrogen and oxygen containing argon-based shielding gases were used. It was found that the nitrogen and oxygen addition significantly increased the weld metal austenite content, up to +27%. The oxygen addition also improved the weld dissolved oxygen content with up to +0.09%, and the weld penetration depth with up to +3.3 mm. [ABSTRACT FROM AUTHOR]

Overcoming the trade-off relationship between strength and ductility has always been a challenge. In this article, a neatly arranged ultrafine bainite that is composed of multi-scale retained austenite was obtained by introducing weak chemical heterogeneity in low-alloy steel. The optimized microstructure makes transformation-induced plasticity (TRIP) behavior and coordinating deformation behavior between each phase to be smoother. This results in better comprehensive properties, with 28.5% and 9% increases in uniform elongation and toughness, respectively, and a similar strength. This study provides a new way to improve the properties of low-alloy steels. A strategy of weak chemical heterogeneity has been proposed in low-alloy steel, which effectively optimizes the microstructure and enhances the plasticity and toughness of steel. [ABSTRACT FROM AUTHOR]

Over the past decades, intensive efforts have been dedicated to overcoming the strength-ductility trade-off dilemma of advanced high-strength steels by creating multi-phase microstructures with chemical heterogeneity. This paper presents a brief summary of the advancements in medium Mn steel (MMnS), which has garnered prominence in automobile applications due to its high strength coupled with good toughness achieved via the modulation of retained austenite (γret) stability. We examine the optimization of integral mechanical attributes such as strength, ductility and toughness. MMnS can reach an ultimate tensile strength (UTS) beyond 2200 MPa; however, there is a steep decline in toughness below 100 J when the UTS is > 1200 MPa. The relevant mechanisms including novel alloying design strategies, innovative processing routines such as flash processing, chemical boundary engineering and meticulous modulation of γ stability through chemical heterogeneity are analyzed. Furthermore, the potential avenues for research and innovation in MMnS are outlined by incorporating laser additive manufacturing technologies. [ABSTRACT FROM AUTHOR]

By analyzing element segregation and dendritic growth kinetics in combination with microstructure observation and thermodynamic calculation, the influence mechanism of vanadium addition on the dendritic structure and precipitated phase in 30Cr15Mo1N ingots was elucidated. With vanadium addition, the carbonitride types in 30Cr15Mo1N ingots include lamellar M23(C,N)6, globular M2(C,N), and blocky M(C,N). The as-cast structure of the 30Cr15Mo1N ingot is divided into two parts: the dendritic structure, which is mainly composed of martensite and residual austenite, and the interdendritic region, which is primarily composed of precipitated phases like proeutectoid ferrite and carbonitrides. On the one hand, increasing the vanadium content can reduce the amount of martensite and residual austenite in the ingot by suppressing the growth of dendrites and reducing the size of dendrites. On the other hand, the amount of proeutectoid ferrite in the 30Cr15Mo1N ingots increased with an increase in vanadium content and distance from the center due to element segregation in the residual molten steel of the interdendritic region. Under the combined effect of element segregation in the interdendritic region and restricted dendritic growth, the size of carbonitrides showed an increasing trend with increasing the vanadium content. [ABSTRACT FROM AUTHOR]

The damage to the shear-punched surface layers such as strain-hardening, strain-induced martensite transformation, and micro-void initiation behaviors was evaluated in the third-generation low-carbon advanced ultrahigh-strength TRIP-aided bainitic ferrite (TBF), bainitic ferrite–martensite (TBM), and martensite (TM) steels. In addition, the surface layer damage was related to (1) the mean normal stress generated during shear-punching and (2) microstructural properties such as the matrix structure, retained austenite characteristics, and second-phase properties. The shear-punched surface layer damage was produced under the mean normal stress between zero and negative in all the steels. The TBM and TM steels achieved relatively small surface layer damage. The small surface layer damage resulted in excellent cold stretch-flangeability, with a high crack-propagation/void-connection resistance on hole expansion. [ABSTRACT FROM AUTHOR]

This study examines the effects of stick-out, welding current, welding speed, and voltage on the mechanical characteristics and microstructure of MIG welding on SUS 304 stainless steel and S20C steel. The Taguchi method was used to maximize the experiment's outcomes. Fine columnar dendrites formed at fusion sites, and δ-ferrite phases with dark lines and shapes accumulated between the fusion line and the austenite phases. A welding current of 110 A, voltage of 15 V, welding speed of 500 mm/min, and stick-out of 12 mm were the optimal settings for the ultimate tensile strength (UTS). The UTS value confirmation was 469.4 MPa, which agrees with the estimated value determined using the Taguchi technique. The tensile test revealed that welding current had a far greater impact on mechanical qualities than welding voltage, speed, and stick-out distance. The ideal welding parameters for flexural strength were as follows: stick-out of 12 mm, arc voltage of 15 V, welding speed of 450 mm/min, and welding current of 110 amp. The Taguchi method is useful, as evidenced by the validation of the flexure strength of 1937.45 MPa, which is much greater than the other samples. The impact of the thermal annealing process on the mechanical characteristics of the dissimilar weld joints could be the subject of future research. The investigation results may offer more insightful information about the dissimilar welding field. [ABSTRACT FROM AUTHOR]

In this paper, the nucleation and growth of austenite are controlled through a two-step annealing process to achieve multi-scale distribution and content increase of retained austenite in low manganese series medium-Mn steel. Combining SEM, EBSD, AES, and other experimental equipment, the evolution rules of the microstructure, properties, and element distribution behavior of the test steel during the annealing process are studied. Compared with one-step annealing, the two-step annealing significantly broadens the size distribution range of retained austenite. In the first step, after annealing at a higher intercritical temperature (760 °C), the ferrite and the M/A island are obtained, completing the initial partition of Mn and the refinement of microstructures. During the second step of annealing (720 °C), the primary Mn-rich martensite region provides higher nucleation driving force and finer dispersed nucleation sites, promoting the nucleation and growth of reverse transformation austenite. At the same time, the metastable-retained austenite formed after the first step of annealing continues to grow through interface movement. Furthermore, a high proportion (23.4%) of retained austenite with multi-scale distribution is formed in the final microstructure, and the product of strength and elongation increased from 21.8 GPa·% by the one-step annealing process to 30.1 GPa·%. [ABSTRACT FROM AUTHOR]

In this study, austenite formation in 201 austenitic stainless steel was observed in two steps during solidification. Initially, austenite (γ1) precipitated and grew on δ-ferrite during the peritectic reaction (δ + liquid → γ1) and formed directly from the residual liquid (γ2). With the addition of Co, from 0.09 to 0.51 wt.%, the dendrite morphology of ferrite changed from columnar dendritic to equiaxed dendritic. Primary ferrite phase morphology changes resulted in an austenite microstructure composed of a uniform dispersion of fine grains. Both ε-martensite (hcp) and α′-martensite (bct) were present in the microstructure due to the deformation of austenite particles by the impact force. The impact toughness increased by 33% as the cobalt content increased to 0.51 wt.%. [ABSTRACT FROM AUTHOR]

The microstructural evolution of austenite during hot deformation determines the mechanical properties of steel products. Consequently, industrial applications necessitate a thorough comprehension and modeling of this process. Under varied hot deformation conditions, the flow stress, microstructure evolution, and constitutive modeling of a Cu-bearing steel were examined. At various temperatures and strain rates, compression experiments are conducted, and the resulting microstructures were studied by electron backscatter diffraction (EBSD). Our results indicate that fine prior austenite grains with an average diameter of 22.1 m and a high-angle grain boundary density of 0.25 m1 were produced at a deformation temperature of 950 °C and a strain rate of 1 s−1. The dominating rotating cube components ({001}) in the sample deformed at 1150 °C were gradually replaced by the γ-fiber texture component as the deformation temperature decreased. To accurately predict the flow behavior of this steel, we proposed an improved Arrhenius constitutive model that accounts for strain rate and adiabatic temperature rise. With a correlation coefficient (Rc) of 0.9936, a root mean square error (RMSE) of 4.92%, and a relative error (δ) of 6.05 MPa, our results demonstrate that this model predicts the flow stress of the experimental steel with good precision. This research contributes to the development of high-performance steel products by shedding light on the microstructural evolution and flow behavior of Cu-containing steels under hot deformation conditions.

This study investigates the tempering behavior of bainite and martensite in a medium carbon, high silicon steel, with a focus on the microstructural evolution and the attainment of equilibrium, over a temperature range of 200–650 °C. The dissimilarities between the characteristics of the two initial microstructures, both comprising a C-saturated tetragonal ferrite matrix and retained austenite, are reflected in the differences observed in their evolution towards equilibrium as the tempering temperature increases. Therefore, while retained austenite plays a pivotal role in the bainitic microstructure, in the martensitic microstructure it is the ferritic matrix, which is highly dislocated and enriched in carbon, that plays a determinant role. The findings demonstrate that while both bainite and martensite can converge towards the same equilibrium state upon high-temperature tempering (600–650 °C), the pathway to this convergence is markedly different, with bainite exhibiting a slower transformation rate. This path to equilibrium has been characterised by means of high-resolution dilatometry, scanning electron microscopy and detailed X-ray diffraction analysis. This has provided a dynamic and detailed picture of the most relevant microstructural changes and tempering mechanisms in high silicon steels. It has also provided a foundation for tailoring heat treatment processes to optimise the mechanical properties of advanced bainitic and martensitic steels.

Disperse ferrite is generally embedded in lightweight steel, yet exhibits decent performance, thereby prompting a question: can heterogeneous design optimize it? Here, two representative structures, featured with discontinuous fibrous and dispersed ferrite separately embedded in the austenite matrix, were constructed as examples to address the issue. A heterostructure with fibrous ferrite shows a remarkable product (49 GPa·%) of ultimate strength and total elongation, standing out among other lightweight steels. Superior strength-ductility synergy is primarily attributed to hetero-deformation-induced strengthening and hardening. Abundant hetero-interactions imparted by phase boundaries, dense slip bands in austenite and dislocation networks inside ferrite serve as underlying physical mechanisms. [ABSTRACT FROM AUTHOR]

Purpose. The study is aimed at evaluating the effect of the isothermal transformation temperature on the structure and properties of low-carbon steel. Methodology. The material for the study was a 3 mm diameter wire made of mild steel with the following chemical composition: 0.21% C, 0.47% Mn, 1.2% Si, 0.1% Cr, 0.03% S, 0.012% P. The 0.3 m long wire samples were subjected to austenitizing at 920 °C for 8...9 min, after which they were held isothermally for 11 min at temperatures of 650...200 °C, followed by cooling in air. The strength, plastic properties, and strain hardening coefficient were determined from the analysis of tensile curves. Findings. It was found that a decrease in the temperature of isothermal transformation, starting from 450...400 °C, increases the amount of Widmannstätten ferrite due to the disappearance of polyhedral ferrite grains. At the same time, the number of areas with locally located dispersed cementite particles similar to pearlite colonies increases, and bainite crystals appear. Against the background of a sharp decrease in the strain hardening coefficient in the range of 450...400 °C, the ability of the bainite phase to undergo plastic deformation should be considered one of the reasons for the delay in density reduction. Originality. The effect of steel hardening with a decrease in the pearlite transformation temperature is based on the grinding of ferrite grains, an increase in the amount of Widmannstätten ferrite, and the dispersion of pearlite colonies. The strengthening effect of steel with a bainite structure is based on an increase in the degree of supersaturation of the solid solution with carbon atoms and dispersion hardening by particles of the carbide phase. Practical value. The optimal structural state of steel intended for the manufacture of such critical elements as a support beam, railroad car bogie, etc. is a mixture of phase components with different dispersion and morphology, and their quantitative ratio is determined by the operating conditions of a particular product.

This paper investigates the metallurgical factors contributing to the non-conformance in mechanical properties observed in Maraging 250 steel (M250) holding pins after the aging process. Results revealed a significant difference in the mechanical properties between the aged as-received pins and the aged as-annealed rods. Microstructural analysis highlighted the influence of processing conditions, including straightening and centerless grinding, on the material's behavior during aging. Moreover, the presence of retained austenite was found to exceed specified limits in the as-received rods that exhibited mechanical property non-conformance. In this study, a comprehensive metallurgical analysis was conducted to understand the factors contributing to the non-conformance in mechanical properties of aged M250 holding pins and essential steps required for improving the reliability and performance of these components. By gaining insights into the microstructural changes and associated material behavior, appropriate process optimizations and quality control measures can be implemented to ensure the attainment of desired mechanical properties. [ABSTRACT FROM AUTHOR]

Maraging steels achieve the highest strength limit when aged around 480 °C. Some research has been carried out on this treatment at temperatures different from 480 °C to improve the toughness and magnetic properties of this metal. This research uses Mössbauer spectroscopy, X‐ray diffraction (XRD), hardness measurements, and transmission electron microscopy (TEM) to investigate the phase transformation process of solution‐treated Maraging‐300 steel specimens aged at 520, 560, and 600 °C. The results indicate that the precipitation of intermetallic compounds, which are responsible for the improvement of mechanical properties, occurs similarly to precipitation at the temperature of 480 °C within the first hour of ageing. The coexistence of precipitates and the austenitic phase is detected, and a crystalline/magnetic transition zone is suggested in the material for longer times and higher ageing temperatures. [ABSTRACT FROM AUTHOR]

Conventional welding processes destroy the unique microstructural characteristics in nanobainitic steels. A novel method, i.e. tailored friction stir welding (FSW) and postheat treatment, was employed to overcome this problem. The postprocessing austempering was carried out on friction stir welded high-carbon steel to obtain nanobainite, and obtained microstructural characteristics were compared to that achieved by simple isothermal bainite transformation. Bainitic sheaves and austenite microblocks could be achieved in both production procedures. However, bainitic ferrites and austenite films within the bainitic sheaves were thinner, and austenite microblocks were finer when implementing the post-processing heat treatment after FSW. FSW enhanced the hardness of the primary steel from 385 HV to above 800 HV, which was maintained at about 520 HV even after post-heat treatment, higher than that of after implementing the isothermal bainite transformation (490 HV). This achievement can be related to FSW that reduced the mean diameter of austenite blocks, the thickness of bainitic ferrite, and the thickness of austenite films from 3820, 138, and 122 nm to 2200, 92, and 78 nm, respectively. Moreover, the microstructure and hardness of various microstructural zones of friction stir welded sample before and after heat-treatment were analyzed and discussed in detail. The outcome of this study can be applied in academic and industrial areas to propose a cost-effective method to weld nanobainitic steels. [ABSTRACT FROM AUTHOR]

The current study investigated the effect of static recrystallisation (SRX) of parent austenite microstructure on the lath martensite intervariant boundary network. In general, the misorientation angle distribution of lath martensite exhibited a bimodal distribution in the range of 10–22 deg and 47–60 deg for all thermomechanical conditions, closely matching the misorientations expected from the ideal Kurdjumov-Sachs orientation relationship. Nevertheless, the population of 60 deg misorientation angle initially reduced with the extent of softening up to 50 pct beyond which it progressively increased to a maximum in the fully recrystallised condition. This was closely consistent with the trend noticed for the 60 deg/[110] intervariant boundaries having twist character. This was explained through the distinct variant selection mechanism occurring due to the change in the parent austenite grain characteristics (i.e., size and deformed state) upon static recrystallisation. The recrystallisation initially led to the formation of fine dislocation-free parent austenite grains up to 50 pct softening, promoting a 4-variant (V1V2V3V4) clustering arrangement to decrease the strain related to the martensite transformation. In turn, this promoted the formation of symmetric tilt 60 deg/ 11 1 ¯ intervariant boundaries, which ultimately reduced the 60 deg/ 110 boundaries. Further softening, accompanied with the growth and/or coalescence of parent austenite grains, altered the variant clustering to a 3-variant arrangement (V1V3V5) and the increase in 60 deg/ 110 twist intervariant boundaries. Indeed, the martensite boundary network was largely controlled by the SRX parent austenite characteristics (i.e., size), which can be controlled to enhance the materials performance for a given application. [ABSTRACT FROM AUTHOR]

This study examined the effect of manganese (Mn) contents (3.12 to 8.97 pct) and three-pass deformation distributions on dynamic recrystallization (DRX) and dislocation evolution during hot compression of low-nickel duplex stainless steel (DSS). With a total deformation of 70 pct and a strain rate of 0.1 s−1, the study revealed that elevated Mn content enhances the ferrite phase's DRX, whereas austenite phase's dynamic recovery (DRV) varied with the deformation pass distribution. Changing the pass sequence (30 pct-10 pct-30 pct to 10 pct-30 pct-30 pct, and subsequently to 25 pct-35 pct-10 pct) in the 8.97 pct Mn sample, a reduction in the percentage of deformed grains in the austenite phase was observed. Furthermore, performing two consecutive passes with significant deformations was not favorable for ferrite DRX. Instead, it facilitated the development of subgrains within the austenite phase. The 25 pct-35 pct-10 pct deformation pattern in the 8.97 pct Mn sample led to twin boundaries formation, refining the coarse grains but impeding DRX, resulting in numerous austenite subgrains controlled by DRV. Conversely, a 30 pct-10 pct-30 pct deformation in the 8.97 pct Mn sample encouraged ferrite grains mainly displayed {001} and {111} recrystallization textures, thereby promoting DRX nucleation. The ferrite DRX process was primarily governed by continuous dynamic recrystallization (CDRX) mechanism, leading to the development of sizable, equiaxed grains with fewer dislocations. Kurdjumov-Sachs (K-S) relationship between the two phases enables dislocation slip from austenite to ferrite during compression deformation. With the increased addition of Mn, the ferrite underwent a gradual transition from a deformation texture to a recrystallization texture, whereas the austenite continued to be predominantly characterized by a deformation texture. The dynamic softening effect exhibited a more pronounced behavior in the 30 pct-10 pct-30 pct deformation condition for the sample with 8.97 pct Mn in comparison to the other deformation conditions. [ABSTRACT FROM AUTHOR]

Thermodynamic models were employed to determine the solubility product of aluminum nitride in steels containing the solid solution elements of Mn, Ni, Cr, and Mo. Specific solubility product expressions were developed and compared with previous results. Overall, good agreement was found, which showed the reliability of the calculation results. The effect of the solid solution elements of Mn, Ni, Cr, or Mo on the solubility products of aluminum nitride in steels was minimal. The final deduced solubility products in austenite and ferrite are given as follows. log γ K AlN = 4.21 - 10863 T + 0.004 + 82.6 T wt pct Mn γ + - 0.004 + 52.5 T wt pct Ni γ + - 0.006 + 139.1 T wt pct Cr γ + - 0.007 + 38.1 T wt pct Mo γ log α K AlN = 5.46 - 12937 T + - 0.007 + 40.6 T wt pct Mn α + 0.002 + 9.4 T wt pct Ni α + - 0.130 + 248.7 T wt pct Cr α + 0.072 - 175.0 T wt pct Mo α [ABSTRACT FROM AUTHOR]

In this study, a combined experimental and finite element modeling methodology (FEM) for a nanoindentation study is presented to quantitatively investigate the influence of hydrogen on the mechanical properties of ferrite and austenite in 2205 duplex stainless steel. The experimental results showed that, during hydrogen charging, the nano-hardness of ferrite and austenite gradually increased with time, showing a hydrogen-induced hardening phenomenon. After 3 h of hydrogen charging, the nano-hardness of both ferrite and austenite reached a saturation state, and the values of the nano-hardness of ferrite and austenite increased by 17.5% and 46.1%, respectively. FEM is employed by using a dual-phase microstructure-based model to reproduce nanoindentation load–displacement curves. To minimize the indentation size effect, an analytical correction model considering geometrically necessary dislocations (GNDs) was proposed. By considering GNDs, the errors between numerical predictions and experimental data reduced from about 50% to less than 5%. [ABSTRACT FROM AUTHOR]

The premartensite state of Ni–Mn–Ga magnetic shape memory alloy, sometimes called the martensite precursor state, was studied by careful and detailed measurement of the evolution of magnetization curves of magnetically closed samples to evidence local symmetry breaking. During the heating cycle after the martensite transformation, the magnetization loop slowly transforms from a typical sigmoidal shape, corresponding to the magnetization along the easy axis, to a constricted loop indicative of magnetization along a harder magnetic axis. These changes are explained by a switching of the macroscopic magnetic easy axis from [100] to [110]. Above the premartensite transformation temperature, the magnetic easy axis slowly changes back to [100]. After cooling the sample, starting at the Curie temperature, the process reverses. [ABSTRACT FROM AUTHOR]

The effect of niobium modification on refinement of primary austenite, shrinkage characteristic, and solidification behavior of medium-carbon cast steel melted in a medium-frequency induction furnace is studied. It is established that the modification with 0.1 wt.% niobium increases the fluidity of the steel liquid, enhances the feeding capacity of the cast steel, turns the dispersed shrinkage porosity into concentrated shrinkage cavity, changes the coarse dendrites to fine ones, even in equiaxed grain structures, and dwindles the primary austenite grain size greatly. Using electron microscopy and energy-dispersive analysis, it is discovered that niobium combines with carbon to form solid phase particles of NbC. These particles are chemically stable at high melting temperatures and facilitate the primary austenite nucleation effectively by non-spontaneous nucleating. A model of matching between the crystal lattices γ-Fe and NbC is suggested. The mechanism of NbC heterogeneous nucleation consists in that the primary austenite grows on {111}γ-Fe along to the closest-packed plane {111}NbC in crystal orientation ⟨ 011 ⟩ γ - Fe ‖ ⟨ 112 ⟩ NbC , and the mismatch δ ⟨ 111 ⟩ NbC ⟨ 111 ⟩ γ - Fe of the crystal planes is only 9.79%. [ABSTRACT FROM AUTHOR]

The effect of local high-speed intense dynamic action by a metal object (indenter) on the change in the structure of weld metal of high strength alloy steel welded with austenitic flux-cored wire with nitrogen is studied. It is established that after welding the weld metal structure consists of austenite and delta-ferrite (3 vol. %) with microhardness HV0.1 200–250. After intense dynamic action weld metal is strengthened by a γ → ε → α' mechanism due to work hardening and formation of deformation within the structure of α'-martensite in an amount of 10 vol.% and a small amount of ε‑martensite while maintaining the original amount of δ‑ferrite, and with an increase in microhardness by more than 1.7 times from the initial level. [ABSTRACT FROM AUTHOR]

Previous studies on the austenite grain growth were mostly based on a fixed temperature, and the relationship between the austenite grain and austenitizing parameters was fitted according to the results. However, there is a lack of quantitative research on the austenite grain growth during the heating process. In the present work, based on the diffusion principle of the controlled Ti microalloying element, the diffusion process of carbonitrides containing Ti during the heating process was analyzed. Combined with the precipitation model and the austenite growth model, the prediction model of austenite grain growth of Ti microalloyed steel during different heat treatment processes was established. The austenite grain size versus the temperature at four different heating rates of 0.5, 1, 10, 100 °C/s was calculated. The grain growth behavior of austenite during the heating process of Ti microalloyed steel was studied by optical microscope, scanning electron microscope and transmission electron microscope. The experimental data of the austenite grain size was in good agreement with the calculation by the proposed model, which provides a new idea for the prediction of austenite grain size in non-equilibrium state during the heating process. In addition, for Ti-containing microalloyed steels, the austenite grain size increased with the increasing heating temperature, while it changed little by further prolonging isothermal time after certain heating time, which was related to the equilibrium degree of the precipitation and the dissolution of Ti element. The austenite grain coarsening temperature of the tested Ti microalloyed steel was estimated within 1100~1200 °C. [ABSTRACT FROM AUTHOR]

The objective of the present investigation is to synthesise and characterise the Cu-Al-Ag shape memory alloys with minor Mn addition. Synthesis of Cu-Al-Ag-Mn SMA was done by induction furnace and gravity die casting, with constant Ag/Mn ratio (5% Ag and 2% Mn), the aluminium composition is varied from 8% to 14%. The as-cast sample will be further subjected to thermo-mechanical treatment to produce a sheet which exhibits shape memory effect. This study is to determine the influence of Al content on shape memory characteristics, microstructure, and phase transformation temperatures. The phase fraction of β'1 increased from 56% to 67% along with subsequent reduction of γ1' phase fraction from 23% to 17%, which is essential for improvement of shape memory properties with increase of aluminium constituent. X-ray diffraction revealed that the crystalline size decreased 79 to 32 nm and lattice strains increased from 0.24% to 0.69% with increase of Aluminium. With an increase in aluminium content, the martensite transformation temperature decreased from 386°C to 246°C, and the shape memory effect increased from 81 to 90% strain recovery. The ability to control shape memory characteristics by changing Al composition will improve the scope for this alloy in various shape memory applications. [ABSTRACT FROM AUTHOR]

To enhance the rolling production efficiency of high‐manganese low‐nickel duplex stainless steel (DSS) and optimize hot compression parameters, hot compression with a range of 0.01–10 s−1/850–1150 °C and deformations of 70% is used to investigate the hot deformation behavior of 18Cr–11Mn–0.06Ni–0.19 N DSS, which reveals the differences in the recrystallization mechanism of two phases and their thermoplastic properties. The results show that strain partitioning and softening occur first in the ferrite phase, with the austenite phase undergoing complex and incomplete softening. Most ferrite experiences continuous dynamic recrystallization and develops a <001>//ND texture when deformed at 0.1–10 s−1/950 °C, with higher temperatures facilitating the merging of high‐angle grain boundaries. A deformation‐induced phase transformation from δ to γ occurs in ferrite when deformed at 0.01 s−1/850–950 °C. However, austenite softening is dominated by discontinuous dynamic recrystallization, enhanced by twinning‐induced strain‐induced boundary migration when deformed at 0.1 s−1/950 °C; dynamic recovery controlled by dislocations is enhanced when deformed at 0.1 s−1/1150°C and 10 s−1/950 °C. A strain‐compensated constitutive model with an average absolute relative error value of 7.8% is established to better predict the flow stresses. Experimental DSS displays optimal hot workability in the parameter ranges of 0.1 s−1/950–1050 °C. [ABSTRACT FROM AUTHOR]

The effects of nitrogen (N) and niobium (Nb) contents on the precipitation behaviors of AlN, Nb(C,N), and AlN‐Nb(C,N) precipitates and austenite grain growth during the pseudo‐carburizing process are investigated for the carburized steel SCr420H. The results indicate that an increase of N content from 0.011% to 0.019% leads to the emergence of fine and uniform austenite grain structure in the sample while being held at 930 °C for 6 h, which is attributed to a notable rise in the number density of AlN and a decrease in the coarsening rate of AlN. In the steel containing 0.023% Nb, the composite precipitates AlN‐Nb(C,N) play a primary role in the pinning effect on austenite grains growth. The isolated Nb(C,N) and AlN precipitates have minor pinning effects due to their very low volume fractions. Nb(C,N) cap forming on AlN substrate obeys the Shoji–Nishiyama orientation relationship. The favorable lattice matching between AlN and Nb(C,N) and accelerated coarsening rate of Nb(C,N) cap decrease hindrances to the nucleation, growth, and coarsening of Nb(C,N) on AlN substrate. Meanwhile, these simultaneous effects also suppress the same processes for the isolated Nb(C,N) in the matrix. [ABSTRACT FROM AUTHOR]

To measure textures of hot rolled martensitic and bainitic steels, electron backscatter diffraction (EBSD) is applied to large areas, each covering about a thousand of prior grains. A scanning step is selected to keep reasonable time of the data acquisition still providing in any grain a significant number of analyzed points. Contributions to the transformation texture appearing from deformation and recrystallization components of the parent texture are estimated with the Bain relationship. To assess the parent austenite state, their proportion is then expressed by a scalar parameter. The results are verified by independent metallographic data. Avoiding the reconstruction of prior grains, this statistical approach will facilitate evaluation of complex austenite structures with comparable fractions of dissimilar material states. [ABSTRACT FROM AUTHOR]

A systematic experimental study has been conducted on the simulated intercritical coarse‐grained heat affected zone of 690 MPa grade heavy‐plate medium Mn steel by tailoring heat input of the first welding pass to obtain the influence of initial microstructure on the austenite reversion mechanism, recrystallization, and resultant impact toughness. Results reveal that prior austenite grain size significantly increases from 30 ± 11, 41 ± 14 to 54 ± 15 μm with the increasing heat input from 15, 30 to 50 kJ cm−1, which affect the nucleation site of reversed austenite, recrystallization mechanism, and final microstructure. Accordingly, impact toughness is better at the heat input of 30 kJ cm−1 (75.2 ± 0.8 J) in comparison with that of 15 kJ cm−1 (63.3 ± 13.3 J) and 50 kJ cm−1 (26.7 ± 6.5 J) at −40 °C, which is mainly ascribed to the formation of lamellar heterogeneous structures, multiplication of slip system and morphology of high‐angle grain boundaries. [ABSTRACT FROM AUTHOR]