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Showing papers on "Bainite published in 2022"


Journal ArticleDOI
Lihe Qian1, Lihe Qian1, Zhi Li1, T.S. Wang1, Dongdong Li1, Fucheng Zhang1, Jiangying Meng1 
TL;DR: In this paper, the role of pre-formed martensite (PM) in below-Ms bainite formation, microstructure, crystallography, strain partitioning and mechanical properties of a low-carbon bainitic steel were investigated using electron-backscattered diffraction, transmission electron microscopy, micro digital image correlation technique and mechanical tests.

27 citations


Journal ArticleDOI
Lihe Qian1
TL;DR: In this paper , the role of pre-formed martensite (PM) in below-Ms bainite formation, microstructure, crystallography, strain partitioning and mechanical properties of a low-carbon bainitic steel were investigated using electron-backscattered diffraction, transmission electron microscopy, micro digital image correlation technique and mechanical tests.

24 citations


Journal ArticleDOI
TL;DR: In this article , the effect of electrolyte presence on the corrosion evolution and stress corrosion cracking (SCC) behavior of E690 steel in the simulated marine environment is investigated, and the steel exhibits the highest and lowest corrosion rate in splash and immersion environment, respectively, attributed to the differences in oxygen availability, rust layer property, and scour stress.

22 citations


Journal ArticleDOI
TL;DR: In this paper, ultrafast heating at the rates of 10−300°C/s was employed as a new strategy to anneal a cold-rolled 7wt% Mn steel, followed by the immediate cooling.

21 citations


Journal ArticleDOI
TL;DR: In this article , the deformation-induced crystal orientation evolution, localized strain concentration, slip transfer, and geometrically necessary dislocation (GND) density were tracked on polygonal ferrite (PF) and bainite dual-phase steel.
Abstract: In-situ tensile test accompanied by electron backscatter diffraction (EBSD) analyses were performed on polygonal ferrite (PF) and bainite dual-phase steel, selected regions of interest were analyzed following plastic deformation of the steel. Deformation-induced crystal orientation evolution, localized strain concentration, slip transfer, and geometrically necessary dislocation (GND) density were tracked. Results revealed that heterogeneity deformation facilitated formation subregions with crystal orientation deviation in grain and fragmented the grain by the new low angle grain boundaries (LAGBs) or medium angle grain boundaries (MAGBs). The PF grains with ND//<111> preferred crystal orientation exhibited high orientation stability, and almost all load axes of the selected PF grains moved to the [101] pole, resulting in enhancing {111} <110> orientation component at high strain levels. With the lattice rotation during deformation, the high angle grain boundaries (HAGBs) can change to MAGBs, which was beneficial to maintain coordination deformation among grains. Localized strain concentration can be decreased by the slip transfer across the PF grain boundaries or bainite/PF phase boundaries, which reduced the risk of micro-void formation. Additionally, the variation of α 12 GND tensor average value (Ave. α 12 ) revealed that the ferrite was continuous plastic deformation, while the bainite occurred stage hardening. The required strain for the coordination deformation was controlled by strain hardening behavior. • The deformation behavior of ferrite and bainite dual phase was studied by in situ EBSD. • Orientation evolution revealed the grains heterogeneous deformation and texture evolution behavior. • The factors of affecting slip transfer were proposed. • α 12 GND tensor average value was used to describe the coordinated deformation.

20 citations


Journal ArticleDOI
TL;DR: In this article, electron backscatter diffraction (EBSD) analyses were performed on polygonal ferrite (PF) and bainite dual-phase steel, selected regions of interest were analyzed following plastic deformation of the steel.
Abstract: In-situ tensile test accompanied by electron backscatter diffraction (EBSD) analyses were performed on polygonal ferrite (PF) and bainite dual-phase steel, selected regions of interest were analyzed following plastic deformation of the steel. Deformation-induced crystal orientation evolution, localized strain concentration, slip transfer, and geometrically necessary dislocation (GND) density were tracked. Results revealed that heterogeneity deformation facilitated formation subregions with crystal orientation deviation in grain and fragmented the grain by the new low angle grain boundaries (LAGBs) or medium angle grain boundaries (MAGBs). The PF grains with ND// preferred crystal orientation exhibited high orientation stability, and almost all load axes of the selected PF grains moved to the [101] pole, resulting in enhancing {111} orientation component at high strain levels. With the lattice rotation during deformation, the high angle grain boundaries (HAGBs) can change to MAGBs, which was beneficial to maintain coordination deformation among grains. Localized strain concentration can be decreased by the slip transfer across the PF grain boundaries or bainite/PF phase boundaries, which reduced the risk of micro-void formation. Additionally, the variation of α12 GND tensor average value (Ave. α12) revealed that the ferrite was continuous plastic deformation, while the bainite occurred stage hardening. The required strain for the coordination deformation was controlled by strain hardening behavior.

20 citations


Journal ArticleDOI
TL;DR: In this paper , ultrafast heating at the rates of 10-300 °C/s was employed as a new strategy to anneal a cold-rolled 7wt% Mn steel, followed by the immediate cooling.

20 citations


Journal ArticleDOI
TL;DR: In this paper , the microstructure evolution and corresponding mechanical properties of the nanostructured bainite tempered at a temperature ranged from 180 °C to 400 °C were studied via X-ray diffraction, transmission electron microscope and high-resolution thermal dilatometer.
Abstract: The previous research on tempered nanostructured bainite has been mainly focused on the carbide precipitation at high temperatures with few details on nanostructured bainite tempered at lower temperatures. In this research, the microstructure evolution and the corresponding mechanical properties of the nanostructured bainite tempered at a temperature ranged from 180 °C to 400 °C were studied via X-ray diffraction, transmission electron microscope and high-resolution thermal dilatometer. Results show that retained austenite occurred bainitic transformation when the tempering temperature ranged from 210 °C to 320 °C. The amount of newly formed bainite increased at first and then decreased slightly with increasing tempering temperature. When the tempering temperature reached 380 °C and higher, the cementite precipitated from retained austenite and reduced the stability of over-stable retained austenite. As a result, it can be concluded that stress-induced martensitic transformation would occur easily in retained austenite during deformation process, leading to the optimum increase of retained austenite contribution to toughness. coefficient of carbon increased sharply, the dispersed cementite particles precipitated between the nanostructured bainitic plates, inhibiting coarsening of bainitic plates when the tempering temperature reached 380 °C. Finally, nanostructured bainitic plates only coarsened slightly. Therefore this high-carbon high-silicon nanostructured bainitic plate possess a high dimensional stability.

16 citations


Journal ArticleDOI
TL;DR: In this article, the microstructure evolution and corresponding mechanical properties of the nanostructured bainite tempered at a temperature ranged from 180°C to 400°C were studied via X-ray diffraction, transmission electron microscope and high-resolution thermal dilatometer.
Abstract: The previous research on tempered nanostructured bainite has been mainly focused on the carbide precipitation at high temperatures with few details on nanostructured bainite tempered at lower temperatures. In this research, the microstructure evolution and the corresponding mechanical properties of the nanostructured bainite tempered at a temperature ranged from 180 °C to 400 °C were studied via X-ray diffraction, transmission electron microscope and high-resolution thermal dilatometer. Results show that retained austenite occurred bainitic transformation when the tempering temperature ranged from 210 °C to 320 °C. The amount of newly formed bainite increased at first and then decreased slightly with increasing tempering temperature. When the tempering temperature reached 380 °C and higher, the cementite precipitated from retained austenite and reduced the stability of over-stable retained austenite. As a result, it can be concluded that stress-induced martensitic transformation would occur easily in retained austenite during deformation process, leading to the optimum increase of retained austenite contribution to toughness.

16 citations


Journal ArticleDOI
TL;DR: In this paper, the microstructure evolution, impact toughness and fracture mechanism of X100 steel welds with different Ti content using laser-MAG hybrid welding were investigated. And the results illustrated that with increasing Ti content, the outer layer inclusion composition evolved from mostly Al2O3 to Ti2O 3 and finally to TiC.
Abstract: Laser-MAG hybrid welding has a wide range of application prospects for pipeline steel welding, because it combines the advantages of arc welding and laser welding. However, the brittle microstructure of bainite or martensite in hybrid welding results in low impact toughness, and thus it cannot be used in pipeline laying. Hence, in this study, we induced acicular ferrite (AF) into laser-MAG hybrid welds, because of its good impact toughness. We prepared X100 steel welds with different Ti content using laser-MAG hybrid welding. Then, the microstructure evolution, impact toughness and fracture mechanism of the welds with different Ti content were investigated. The results illustrated that with increasing Ti content, the outer layer inclusion composition evolved from mostly Al2O3 to Ti2O3 and finally to TiC. Thus, Ti2O3 induced AF nucleation by forming an Mn-depleted zone, which caused the volume fraction of AF to initially increase and then decrease. The impact toughness also changed accordingly (16.3 → 21.9→8.7J) and the cracks nucleated and propagated in granular bainite during impact fracture. When they encountered AF, the cracks deflected and even stopped propagating. Therefore, by controlling the Ti content in the laser-MAG hybrid weld, the impact energy at −40 °C was higher than in the base metal. In addition, the higher quantity of AF with a high effective grain boundary density (0.57/μm) and low kernel average misorientation value could effectively hinder crack propagation and consequently improve impact toughness.

15 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of surface modified nanoparticles (NPs) on the inclusion refinement and microstructure evolution, deoxidized experiment ingots with different amounts of modified NPs were manufactured under different cooling conditions.

Journal ArticleDOI
TL;DR: In this article , the authors explored mechanisms for improving the mechanical properties and retained-austenite (RA) stability of a Q&P steel by adjusting the phase ratio.
Abstract: In this study we explored mechanisms for improving the mechanical properties and retained-austenite (RA) stability of a Q&P steel by adjusting the phase ratio. With increasing annealing temperature, the yield strength of the steel increased and the ductility firstly increased and then decreased. These observations are closely related to the specific phase constituent and retained austenite stability produced by the Q&P process. The hard phase (tempered martensite, bainite, martensite-austenite island/secondary martensite) fraction increased with increasing annealing temperature, and the RA size and morphology changed from large, blocky to small, blocky and lath-like. At 800 °C, the phase ratio of RA, bainite, ferrite, and initial martensite is 2:1:2.2:2, which produced the superior combinations of yield strength (σy), tensile strength (σTS), and ductility (δ) (e.g. σy = 960 MPa, σTS = 1450 MPa, δ = 28%; or σy = 1320 MPa, σTS = 1540 MPa, δ = 14%). The superior mechanical properties are attributed to the coordinated deformation between hard phase and soft phase and TRIP effect.

Journal ArticleDOI
TL;DR: In this article , the microstructure evolution, impact toughness and fracture mechanism of X100 steel welds with different Ti content using laser-MAG hybrid welding were investigated. And the results illustrated that with increasing Ti content, the outer layer inclusion composition evolved from mostly Al2O3 to Ti2O 3 and finally to TiC.
Abstract: Laser-MAG hybrid welding has a wide range of application prospects for pipeline steel welding, because it combines the advantages of arc welding and laser welding. However, the brittle microstructure of bainite or martensite in hybrid welding results in low impact toughness, and thus it cannot be used in pipeline laying. Hence, in this study, we induced acicular ferrite (AF) into laser-MAG hybrid welds, because of its good impact toughness. We prepared X100 steel welds with different Ti content using laser-MAG hybrid welding. Then, the microstructure evolution, impact toughness and fracture mechanism of the welds with different Ti content were investigated. The results illustrated that with increasing Ti content, the outer layer inclusion composition evolved from mostly Al2O3 to Ti2O3 and finally to TiC. Thus, Ti2O3 induced AF nucleation by forming an Mn-depleted zone, which caused the volume fraction of AF to initially increase and then decrease. The impact toughness also changed accordingly (16.3 → 21.9→8.7J) and the cracks nucleated and propagated in granular bainite during impact fracture. When they encountered AF, the cracks deflected and even stopped propagating. Therefore, by controlling the Ti content in the laser-MAG hybrid weld, the impact energy at −40 °C was higher than in the base metal. In addition, the higher quantity of AF with a high effective grain boundary density (0.57/μm) and low kernel average misorientation value could effectively hinder crack propagation and consequently improve impact toughness.

Journal ArticleDOI
TL;DR: In this article , the authors made the chemical heterogeneity in steel consisting of mostly martensite with retained austenite by applying intercritical annealing prior to full austenitization.

Journal ArticleDOI
TL;DR: In this article, the authors made the chemical heterogeneity in steel consisting of mostly martensite with retained austenite by applying intercritical annealing prior to full austenitization.

Journal ArticleDOI
TL;DR: In this paper , the effect of nano-bainite microstructure and residual stress on friction properties of M50 bearing steel was analyzed after austempered at 200 °C for 2 h, 16 h and 32 h.

Journal ArticleDOI
TL;DR: In this article , different heat treatments were performed in order to study two different bainite morphologies, granular and lath-like, obtained at different cooling rates in a low carbon microalloyed steel.

Journal ArticleDOI
TL;DR: In this article, the effect of nano-bainite microstructure and residual stress on friction properties of M50 bearing steel was analyzed after austempered at 200°C for 2h, 16h and 32h.

Journal ArticleDOI
TL;DR: In this article , the microstructure and mechanical properties of the FSWed joints were investigated using electron backscattering diffraction (EBSD) and tensile testing and hardness testing.
Abstract: In the current work, mild steel used in shipbuilding applications was friction-stir-welded (FSWed) with the aim of investigating the microstructure and mechanical properties of the FSWed joints. Mild steel of 5 mm thickness was friction-stir-welded at a constant tool rotation rate of 500 rpm and two different welding speeds of 20 mm/min and 50 mm/min and 3° tool tilt angle. The microstructure of the joints was investigated using optical and scanning electron microscopes. Additionally, the grain structure and crystallographic texture of the nugget (NG) zone of the FSWed joints was investigated using electron backscattering diffraction (EBSD). Furthermore, the mechanical properties were investigated using both tensile testing and hardness testing. The microstructure of the low-welding-speed joint was found to consist of fine-grain ferrite and bainite (acicular ferrite) with an average grain size of 3 µm, which indicates that the temperature experienced above A1, where a ferrite and austenite mixture is formed, and upon cooling, the austenite transformed into bainite. The joint produced using high welding speed resulted in a microstructure consisting mainly of polygonal ferrite and pearlite. This could be due to the temperature far below A1 experienced during FSW. In terms of joint efficiency expressed in terms of relative ultimate tensile, the stress of the joint to the base material was found to be around 92% for the low-speed joint and 83% for the high-welding-speed joint. A reduction in welding was attributed to the microstructure, as well as the microtunnel defect formed near the advancing side of the joint. The tensile strain was preserved at 18% for low welding speed and increased to 24% for the high welding speed. This can be attributed to the NG zone microstructural constituents. In terms of crystallographic texture, it is dominated by a simple shear texture, with increased intensity achieved by increasing the welding speed. In both joints, the hardness was found to be significantly increased in the NG zone of the joints, with a greater increase in the case of the low-welding-speed joint. This hardness increase is mainly attributed to the fine-grained structure formed after FSW.

Journal ArticleDOI
TL;DR: In this article , the effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the straight wall parts are investigated, and the results show that the surface waviness of the SWP first decreases and then increases with the increase of inter layer temperature.
Abstract: The 300M steel straight wall parts (SWPs) are fabricated by wire arc additive manufacturing based on cold metal transfer technology. The effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the SWPs are investigated. The results show that the surface waviness of the SWP first decreases and then increases with the increase of interlayer temperature, and the lowest surface waviness is controlled in 0.47 mm at the interlayer temperature of 200 °C. In the top region, the microstructure mainly consists of untempered martensite and slightly changes with the increase of interlayer temperature. In the middle and bottom regions, the microstructure is mainly composed of tempered martensite as the interlayer temperature is 100 or 200 °C. However, when the interlayer temperature is increased above 400 °C, the needle-like bainite and feather-like bainite are gradually formed due to the slow cooling rate and long dwell time in the bainite transformation zone. The microhardness and ultimate tensile strength in the top region are significantly higher than those in the middle and bottom regions, which are attributed to the enhanced solid solution strengthening effect of untempered martensite. The tensile fracture morphology is transformed from the quasi-cleavage fracture mode to the ductile mode with the increase of interlayer temperature or the decrease of distance from the substrate.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the martensite decomposition behavior in medium-Mn steel by combining thermo-mechanical controlled processing (TMCP) and continuous cooling processes.
Abstract: The austenite decomposition behavior in medium-Mn steel was investigated here by combining thermo-mechanical controlled processing (TMCP) and continuous cooling processes. Microstructures were characterized by means of optical microscopy, electron probe micro analyzer, scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy. Furthermore, the effect of rolling reduction and cooling path on microstructural evolution and mechanical properties were studied. The results indicated that the austenite region was expanded by manganese, and the ferrite, pearlite, and bainite were not nucleated before martensite transformation even when the cooling rate was decreased to 0.07 °C/min. The approach to tailor yield ratio without compromising tensile strength depends on the control of martensite lath morphology and internal dislocation density. The resistance of lattice to shear transformation increases with the increasing strain hardening of prior austenite, which leads to decrease martensite-start (Ms) temperature. The martensite formed at lower transformation temperatures exhibited relatively high dislocation density and refined laths, resulting in high work-hardening capacity during the early stage of plastic deformation. The crack propagation can be effectively deviated or even terminated by high angle grain boundaries (HAGBs) and the nonparallel structures of martensite packets. These studies on the kinetics and thermodynamics of martensitic transformation confirmed the viability of processing continuously cooled medium-Mn steel in the hot rolling production line.

Journal ArticleDOI
01 Jan 2022
TL;DR: In this article , the authors investigated the martensite decomposition behavior in medium-Mn steel by combining thermo-mechanical controlled processing (TMCP) and continuous cooling processes.
Abstract: The austenite decomposition behavior in medium-Mn steel was investigated here by combining thermo-mechanical controlled processing (TMCP) and continuous cooling processes. Microstructures were characterized by means of optical microscopy, electron probe micro analyzer, scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy. Furthermore, the effect of rolling reduction and cooling path on microstructural evolution and mechanical properties were studied. The results indicated that the austenite region was expanded by manganese, and the ferrite, pearlite, and bainite were not nucleated before martensite transformation even when the cooling rate was decreased to 0.07 °C/min. The approach to tailor yield ratio without compromising tensile strength depends on the control of martensite lath morphology and internal dislocation density. The resistance of lattice to shear transformation increases with the increasing strain hardening of prior austenite, which leads to decrease martensite-start (Ms) temperature. The martensite formed at lower transformation temperatures exhibited relatively high dislocation density and refined laths, resulting in high work-hardening capacity during the early stage of plastic deformation. The crack propagation can be effectively deviated or even terminated by high angle grain boundaries (HAGBs) and the nonparallel structures of martensite packets. These studies on the kinetics and thermodynamics of martensitic transformation confirmed the viability of processing continuously cooled medium-Mn steel in the hot rolling production line.

Journal ArticleDOI
TL;DR: In this article , a U-Net model was trained to perform the segmentation of bainite, ferrite and martensite on EBSD maps using the kernel average misorientation and the pattern quality index as input.

Journal ArticleDOI
TL;DR: In this paper, the effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the SWPs are investigated, and the results show that the surface waviness of the straight wall parts first decreases and then increases with the increase of inter layer temperature.
Abstract: The 300 M steel straight wall parts (SWPs) are fabricated by wire arc additive manufacturing based on cold metal transfer technology. The effects of interlayer temperature on microstructure evolution and mechanical performance in the different regions of the SWPs are investigated. The results show that the surface waviness of the SWP first decreases and then increases with the increase of interlayer temperature, and the lowest surface waviness is controlled in 0.47 mm at the interlayer temperature of 200 °C. In the top region, the microstructure mainly consists of untempered martensite and slightly changes with the increase of interlayer temperature. In the middle and bottom regions, the microstructure is mainly composed of tempered martensite as the interlayer temperature is 100 or 200 °C. However, when the interlayer temperature is increased above 400 °C, the needle-like bainite and feather-like bainite are gradually formed due to the slow cooling rate and long dwell time in the bainite transformation zone. The microhardness and ultimate tensile strength in the top region are significantly higher than those in the middle and bottom regions, which are attributed to the enhanced solid solution strengthening effect of untempered martensite. The tensile fracture morphology is transformed from the quasi-cleavage fracture mode to the ductile mode with the increase of interlayer temperature or the decrease of distance from the substrate.

Journal ArticleDOI
TL;DR: In this article , the authors proposed a heterogeneous Q&P process based on Mn-heterogeneous austenite inherited from Mn-partitioned pearlite, which achieved a large RA fraction being dominant by film morphology.

Journal ArticleDOI
TL;DR: A prototype medium-Mn TRIP steel with a cold-rolled tempered martensite (CR) and martensitic (M) starting microstructures was subjected to continuous galvanizing line (CGL) compatible heat treatments as discussed by the authors .
Abstract: A prototype medium-Mn TRIP steel (0.2 C–6 Mn–1.7 Si–0.4 Al–0.5 Cr (wt %)) with a cold-rolled tempered martensite (CR) and martensitic (M) starting microstructures was subjected to continuous galvanizing line (CGL) compatible heat treatments. It was found that the M starting microstructures achieved greater than 0.30 volume fraction of retained austenite and target 3G properties (UTS × TE ≥ 24,000 MPa%) using an intercritical annealing temperature (IAT) of 675 °C with an IA holding time of 60–360 s, whereas the CR microstructure required an IAT of 710 °C and annealing times of 360 s or greater to achieve comparable fractions of retained austenite and target 3G properties. This was attributed to the rapid austenite reversion kinetics for the M starting microstructures and rapid C partitioning from the C supersaturated martensite, providing chemical and mechanical stability to the retained austenite, thereby allowing for a gradual deformation-induced transformation of retained austenite to martensite—the TRIP effect—and the formation of nano-scale planar faults in the retained austenite (TWIP effect), such that a high work-hardening rate was maintained to elongation of greater than 0.20. Overall, it was concluded that the prototype steel with the M starting microstructure is a promising candidate for CGL processing for 3G AHSS properties.

Journal ArticleDOI
Lihe Qian1
TL;DR: In this paper , the morphological and orientation relationship between ferrite and austenite during intercritical annealing, as well as their effects on subsequent bainite transformation were investigated by scanning electron microscopy, electron-backscattered diffraction, and dilatometry analysis.

Journal ArticleDOI
TL;DR: In this paper , the effect of two different prior austenite grain size (PAGS) on the microstructure development and in turn the tensile properties and fracture toughness of nano-structured bainitic steels was examined.

Journal ArticleDOI
TL;DR: In this article , the authors applied ausforming to the bainite steel during its coarse-grained heat-affected zone (CGHAZ) simulating process when the temperature of the thermal cycle decreased to 600 °C.
Abstract: The brittle martensite-austenite (M-A) constituents in the coarse-grained heat-affected zone (CGHAZ) of the bainite steel are known to have negative effect on toughness. To modify the microstructure of the M–A constituents and then improve the CGHAZ toughness, this work applied ausforming to the bainite steel during its CGHAZ simulating process when the temperature of the thermal cycle decreased to 600 °C. Morphology of the M–A constituents in the CGHAZ with and without the ausforming was observed by optical microscopy (OM) and scanning electron microscopy (SEM). The microstructure of the M–A constituents was characterized by transmission electron microscopy (TEM), the toughness of the specimens was assessed through instrumented Charpy impact test, and the crack behavior beneath the fracture was revealed by SEM. Results show that the ausforming contributes to the austenite formation within the M–A constituents, which helps to improve the CGHAZ toughness from 10.50 J to 33.70 J. This work proposed a nontraditional method that enables the microstructure modification of the M–A constituents and the toughness improvement in the CGHAZ.

Journal ArticleDOI
TL;DR: In this article, two wear-resistant steel plates with different Ni content were studied to reveal the significant role of Ni on hardenability from the perspective of crystallography, and the 0.44Ni steel was of higher hardness compared with 0.02Ni steel.