40Cr steel is laser quenched by the NEL-2500A rapidly axial flow CO2 laser. Then the martensite induced by laser quenched is shocked by Nd：YAG laser again. Through comparing and analyzing the appearance and size of m...40Cr steel is laser quenched by the NEL-2500A rapidly axial flow CO2 laser. Then the martensite induced by laser quenched is shocked by Nd：YAG laser again. Through comparing and analyzing the appearance and size of martensite, the dislocation density in microstmcture between the treated zones by laser quenched and by laser quenched plus laser shock, the following results are shown： The second martensite obtained by laser compound treatment is more fmer compared with those obtained by laser quenched; In the hardened zones obtained by compound treatment, a lot of slender second twin crystal martensites are induced; A lot of more high density dislocation tangles and cellular dislocations are generated. From the transmission electron microscope （TEM） micrograph after compound treatment, there are not only long lath and short nubbly martensites arranged in cross direction, but also massive nubbly and small short nubbly martensites arranged in longitudinal direction. Some martensites look like the broken blocks of quenched martensites. These new martensites are inserted transversely in the quenched martensites with large tangle. And they make quenched martensites break into pieces. Compared with the quenched martensites, the size of fresh martensites are smaller, about 0.3-0.5 μm.展开更多
A comparative investigation was conducted to evaluate the microstructure,mechanical properties,and corrosion resistance of hot-stamped steels fabricated via the compact strip production(CSP)and conventional cold-rolli...A comparative investigation was conducted to evaluate the microstructure,mechanical properties,and corrosion resistance of hot-stamped steels fabricated via the compact strip production(CSP)and conventional cold-rolling methods.CSP steel exhibited an initial microstructure comprising ferrite,pearlite,and minor bainite,which retained a characteristic hot-rolled banded structure with refined ferrite grains(5.7μm).In contrast,conventionally processed steel displayed coarser equiaxed ferrite(9.8μm).In terms of mechanical properties,CSP parts demonstrated superior tensile strength(>1433 MPa)and elongation(>6.48%)compared to conventional counterparts(average elongation of 5.27%).However,CSP samples showed a 23 HV lower hardness,attributed to a deeper decarburization layer.Enhanced strength in CSP steel was linked to finer prior austenite grains and dislocation density inherited from the initial microstructure,despite potential undissolved cementite at lower austenitizing temperatures.Corrosion testing revealed improved resistance in CSP-processed steel,likely due to finer grains acting as barriers to corrosion propagation.The trade-offs in CSP are highlighted:while achieving higher strength-ductility synergy and corrosion resistance,decarburization effects necessitate optimization to mitigate hardness reduction.The potential of CSP for high-performance automotive applications requiring balanced mechanical and anti-corrosion properties is underscored.展开更多
A heat treatment process, quenching-tempering-partitioning （Q-T-P）, has been applied to a low carbon martensitic stainless steel 06Crl3Ni4Mo. By using this process, ultrafine reversed austenite can be obtained at ro...A heat treatment process, quenching-tempering-partitioning （Q-T-P）, has been applied to a low carbon martensitic stainless steel 06Crl3Ni4Mo. By using this process, ultrafine reversed austenite can be obtained at room temperature. The microstructures of the reversed austenite and the martensite matrix were characterized by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS） in detail. The results show that the ultrafine reversed austenite is enriched in Ni resulting in the austenite stability at room temperature. Two new types of nano-scale carbide precipitates are found in the martensite matrix. Detailed analysis suggests that the two nano-scale precipitates can be identified as ω phase and λ phase carbides, respectively. The orientation relationship between the ω phase and matrix is [011]α [/[2110]ω and （211）α//（0110）ω, while that between the X phase precipitate and matrix is [011]α][[0001]λ and （200）α/（1210）λ. For the present steel, the ultrafine reversed austenite and carbide precipitates obtained by Q-T-P treatment provide a good combination of high strength and toughness.展开更多
Laser transformation hardening （LTH） was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd：YAG laser to obtain optimum hardness. The influences of process parameters （laser pulse en...Laser transformation hardening （LTH） was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd：YAG laser to obtain optimum hardness. The influences of process parameters （laser pulse energy, duration time, and travel speed） on the depth and hardness of laser treated area were investigated. Image analysis of SEM microstructure of AISI 420 showed that plate-like carbide have almost fully and （30-40）% of globular carbide particles dissolved into the matrix after laser transformation hardening by pulsed laser and the microstructure was refined to obtain controlled tempered martensite microstructure with 450 VHN hardness.展开更多
The martensitic/ferritic steels have been used as boiler and turbine materials in power plants, and also been selected as potential materials for structural materials in nuclear reactors. In this paper, the kinetic an...The martensitic/ferritic steels have been used as boiler and turbine materials in power plants, and also been selected as potential materials for structural materials in nuclear reactors. In this paper, the kinetic analysis of the martensite formation and microstructural control of high-Cr martensitic/ferritic steels are reviewed. A modular approach, incorporating Fisher partitioning nucleation and anisotropic growth for impingement, was proposed to describe the martensite formation kinetics under different cooling rates.The kinetic analysis suggested a thermal-activated growth feature occurring during the martensitic transformation of martensitic steels. The microstructure can be tuned by composition optimization and various combinations of heat treatment parameters(temperature, time, severe and minor deformation).For the application in power plant, the potential of boundary-design, refinement of original austenite grain size and the final martensitic lath, pinning effect of stable carbides, in improving the performances of martensitic/ferritic steels at elevated temperatures should be investigated more thoroughly.Furthermore, efforts should be made to explore the effects of retained austenite on the improvement of high-temperature creep strength. For the application of nuclear plants, attempts should also be made to produce Fe powders with uniformly distributed oxide particles by chemical reactions.展开更多
Recent accomplishment by the SWIP for the reduced activation ferritic/martensitic steel CLF-1 development has been reviewed. It＇s found that CLF- 1 steel has better room temperature tensile properties than Eurofer97 ...Recent accomplishment by the SWIP for the reduced activation ferritic/martensitic steel CLF-1 development has been reviewed. It＇s found that CLF- 1 steel has better room temperature tensile properties than Eurofer97 steel and has a fully martensitic microstructure.展开更多
Different fragments of a hot-rolled and homogenized Cu–Zn–Al shape memory alloy（SMA） were subjected to thermal cycling by means of a differential scanning calorimetric（DSC） device. During thermal cycling, heatin...Different fragments of a hot-rolled and homogenized Cu–Zn–Al shape memory alloy（SMA） were subjected to thermal cycling by means of a differential scanning calorimetric（DSC） device. During thermal cycling, heating was performed at the same constant rate of increasing temperature while cooling was carried out at different rates of decreasing temperature. For each cooling rate, the temperature decreased in the same thermal interval. During each cooling stage, an exothermic peak（maximum） was observed on the DSC thermogram. This peak was associated with forward martensitic transformation. The DSC thermograms were analyzed with PROTEUS software： the critical martensitic transformation start（Ms） and finish（Mf） temperatures were determined by means of integral and tangent methods, and the dissipated heat was evaluated by the area between the corresponding maximum plot and a sigmoid baseline. The effects of the increase in cooling rate, assessed from a calorimetric viewpoint, consisted in the augmentation of the exothermic peak and the delay of direct martensitic transformation. The latter had the tendency to move to lower critical transformation temperatures. The martensite plates changed in morphology by becoming more oriented and by an augmenting in surface relief, which corresponded with the increase in cooling rate as observed by scanning electron microscopy（SEM） and atomic force microscopy（AFM）.展开更多
基金This project is supported by National Natural Science Foundation of China (No. 50451004)Talent Foundation of Jiangsu University, China.
文摘40Cr steel is laser quenched by the NEL-2500A rapidly axial flow CO2 laser. Then the martensite induced by laser quenched is shocked by Nd：YAG laser again. Through comparing and analyzing the appearance and size of martensite, the dislocation density in microstmcture between the treated zones by laser quenched and by laser quenched plus laser shock, the following results are shown： The second martensite obtained by laser compound treatment is more fmer compared with those obtained by laser quenched; In the hardened zones obtained by compound treatment, a lot of slender second twin crystal martensites are induced; A lot of more high density dislocation tangles and cellular dislocations are generated. From the transmission electron microscope （TEM） micrograph after compound treatment, there are not only long lath and short nubbly martensites arranged in cross direction, but also massive nubbly and small short nubbly martensites arranged in longitudinal direction. Some martensites look like the broken blocks of quenched martensites. These new martensites are inserted transversely in the quenched martensites with large tangle. And they make quenched martensites break into pieces. Compared with the quenched martensites, the size of fresh martensites are smaller, about 0.3-0.5 μm.
基金National Key Research and Development Program of China(Grant No.2021YFB3702405)the National Natural Science Foundation of China(Grant No.52471036)the Basic and Applied Basic Research Foundation of Guangdong Province(Grant No.2023A1515012363).
文摘A comparative investigation was conducted to evaluate the microstructure,mechanical properties,and corrosion resistance of hot-stamped steels fabricated via the compact strip production(CSP)and conventional cold-rolling methods.CSP steel exhibited an initial microstructure comprising ferrite,pearlite,and minor bainite,which retained a characteristic hot-rolled banded structure with refined ferrite grains(5.7μm).In contrast,conventionally processed steel displayed coarser equiaxed ferrite(9.8μm).In terms of mechanical properties,CSP parts demonstrated superior tensile strength(>1433 MPa)and elongation(>6.48%)compared to conventional counterparts(average elongation of 5.27%).However,CSP samples showed a 23 HV lower hardness,attributed to a deeper decarburization layer.Enhanced strength in CSP steel was linked to finer prior austenite grains and dislocation density inherited from the initial microstructure,despite potential undissolved cementite at lower austenitizing temperatures.Corrosion testing revealed improved resistance in CSP-processed steel,likely due to finer grains acting as barriers to corrosion propagation.The trade-offs in CSP are highlighted:while achieving higher strength-ductility synergy and corrosion resistance,decarburization effects necessitate optimization to mitigate hardness reduction.The potential of CSP for high-performance automotive applications requiring balanced mechanical and anti-corrosion properties is underscored.
基金financial support from the National Natural Science Foundation of China (No.51201162)the Youth Innovation Foundation from Institute of Metal Research, Chinese Academy of Sciences
文摘A heat treatment process, quenching-tempering-partitioning （Q-T-P）, has been applied to a low carbon martensitic stainless steel 06Crl3Ni4Mo. By using this process, ultrafine reversed austenite can be obtained at room temperature. The microstructures of the reversed austenite and the martensite matrix were characterized by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS） in detail. The results show that the ultrafine reversed austenite is enriched in Ni resulting in the austenite stability at room temperature. Two new types of nano-scale carbide precipitates are found in the martensite matrix. Detailed analysis suggests that the two nano-scale precipitates can be identified as ω phase and λ phase carbides, respectively. The orientation relationship between the ω phase and matrix is [011]α [/[2110]ω and （211）α//（0110）ω, while that between the X phase precipitate and matrix is [011]α][[0001]λ and （200）α/（1210）λ. For the present steel, the ultrafine reversed austenite and carbide precipitates obtained by Q-T-P treatment provide a good combination of high strength and toughness.
基金supported by the Tarbiat Modares University and Iranian National Center for Laser Science and Technology
文摘Laser transformation hardening （LTH） was applied to the surface of the AISI 420 martensitic stainless steel by a pulsed Nd：YAG laser to obtain optimum hardness. The influences of process parameters （laser pulse energy, duration time, and travel speed） on the depth and hardness of laser treated area were investigated. Image analysis of SEM microstructure of AISI 420 showed that plate-like carbide have almost fully and （30-40）% of globular carbide particles dissolved into the matrix after laser transformation hardening by pulsed laser and the microstructure was refined to obtain controlled tempered martensite microstructure with 450 VHN hardness.
基金the China National Funds for Distinguished Young Scientists (Grant No. 51325401)the International Thermonuclear Experimental Reactor (ITER) Program Special Project (Grant Nos. 2014GB125006 and 2015GB119001)+1 种基金the National High Technology Research and Development Program ("863" Program) of China (Granted No. SS2015AA042005)the National Natural Science Foundation of China (Grant No. 51474156)
文摘The martensitic/ferritic steels have been used as boiler and turbine materials in power plants, and also been selected as potential materials for structural materials in nuclear reactors. In this paper, the kinetic analysis of the martensite formation and microstructural control of high-Cr martensitic/ferritic steels are reviewed. A modular approach, incorporating Fisher partitioning nucleation and anisotropic growth for impingement, was proposed to describe the martensite formation kinetics under different cooling rates.The kinetic analysis suggested a thermal-activated growth feature occurring during the martensitic transformation of martensitic steels. The microstructure can be tuned by composition optimization and various combinations of heat treatment parameters(temperature, time, severe and minor deformation).For the application in power plant, the potential of boundary-design, refinement of original austenite grain size and the final martensitic lath, pinning effect of stable carbides, in improving the performances of martensitic/ferritic steels at elevated temperatures should be investigated more thoroughly.Furthermore, efforts should be made to explore the effects of retained austenite on the improvement of high-temperature creep strength. For the application of nuclear plants, attempts should also be made to produce Fe powders with uniformly distributed oxide particles by chemical reactions.
文摘Recent accomplishment by the SWIP for the reduced activation ferritic/martensitic steel CLF-1 development has been reviewed. It＇s found that CLF- 1 steel has better room temperature tensile properties than Eurofer97 steel and has a fully martensitic microstructure.
基金supported by the project PN-II-ID-PCE-2012-4-0033,contract 13/2013
文摘Different fragments of a hot-rolled and homogenized Cu–Zn–Al shape memory alloy（SMA） were subjected to thermal cycling by means of a differential scanning calorimetric（DSC） device. During thermal cycling, heating was performed at the same constant rate of increasing temperature while cooling was carried out at different rates of decreasing temperature. For each cooling rate, the temperature decreased in the same thermal interval. During each cooling stage, an exothermic peak（maximum） was observed on the DSC thermogram. This peak was associated with forward martensitic transformation. The DSC thermograms were analyzed with PROTEUS software： the critical martensitic transformation start（Ms） and finish（Mf） temperatures were determined by means of integral and tangent methods, and the dissipated heat was evaluated by the area between the corresponding maximum plot and a sigmoid baseline. The effects of the increase in cooling rate, assessed from a calorimetric viewpoint, consisted in the augmentation of the exothermic peak and the delay of direct martensitic transformation. The latter had the tendency to move to lower critical transformation temperatures. The martensite plates changed in morphology by becoming more oriented and by an augmenting in surface relief, which corresponded with the increase in cooling rate as observed by scanning electron microscopy（SEM） and atomic force microscopy（AFM）.
