Based on gradient control of carbon partitioning between martensite and austenite during heat treatment of steels,a stepping-quenching-partitioning(S-Q-P) process is developed for high strength steels.The S-Q-P proces...Based on gradient control of carbon partitioning between martensite and austenite during heat treatment of steels,a stepping-quenching-partitioning(S-Q-P) process is developed for high strength steels.The S-Q-P process involves several quenching processes at progressively lower temperatures between martensite-start(Ms) and martensite-finish(Mf) temperatures,each followed by a partitioning treatment at either the initial quenching temperature or above that temperature.A novel microstructure is designed based on the S-Q-P process.Sizes and distributions of retained austenite and high-carbon martensite surrounded by martensite laths can be manipulated by the partitioning duration and temperature,and quenching temperature of the S-Q-P process.Alloying element Si is employed in the S-Q-P steel to suppress formation of carbides and create suitable amount of retained austenite.A steel of 0.39C-1.22Mn-1.12Si-0.23Cr(wt.%) treated by the S-Q-P process is endowed with some special microstructural characteristics:some strips of retained austenite located at edges of martensite blocks with high density of dislocations and between martensite laths,some small blocks of twinned martensites distributed among bundles of the low-carbon martensite lath.The mechanical properties of the medium carbon steel after the S-Q-P process can reach ultimate tensile strength(Rm) of 1240 MPa,total elongation(EI) of 25%,and product of strength and ductility(PSD) of 31.2 GPa% that are much more improved than those after the conventional quenching-tempering(Q-T) and currently prevailing quenching-partitioning(Q-P) treatments.The PSD of the tested steel after the S-Q-P process increases by 67% and 32% as compared with those after the Q-T and Q-P processes,respectively.展开更多
A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite ...A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite to austenite,volume fraction and distribution of the retained austenite resulting from the following quenching of the steels could be effectively controlled,and then the synthesized mechanical properties of the steels would be improved.In this paper,20SiMn2MoVA steel was treated with conventional quenching-tempering(Q-T),currently prevailing quenching-partitioning(Q-P) and S-Q-P processes,respectively.The results indicated that the volume fraction of the retained austenite of the steel treated by Q-P and S-Q-P processes increased significantly that resulted in the increase of ductility and decrease of strength.The product of strength and ductility of the steel treated by S-Q-P process reached 23.7GPa%,that was increased by about 13% and 7% compared with that after Q-T and Q-P processes,respectively.Compared with the great improvement of the synthesized mechanical property obtained by S-Q-P process with another steel 35SiMn,there would be some factors that deteriorated the effect of S-Q-P process on 20SiMn2MoVA steel.It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite.As a result,less austenite would remain after final quenching and mechanical properties of the steel would be influenced.The results would be beneficial for understanding the principle of S-Q-P process and improving the design of the S-Q-P steel compositions.展开更多
In this study,the three-windows method,the jump-ratio method and the R-map method in energy-filtered transmission electron microscopy(EFTEM) have been applied to mapping carbon distribution in 35SiMn steel after a que...In this study,the three-windows method,the jump-ratio method and the R-map method in energy-filtered transmission electron microscopy(EFTEM) have been applied to mapping carbon distribution in 35SiMn steel after a quenching-partitioning treatment.The carbon contamination is successfully suppressed by using EFTEM and plasma-cleaning TEM samples.Compared to the three-windows method and the jump-ratio method,the R-map method provides carbon distribution with less noises,and is insensitive to changes in sample thickness.We have demonstrated that the R-map method is a better way for carbon mapping in middle-carbon steel without the influence of carbon contamination.展开更多
基金supported by the National Basic Research Program of China (973 program) (Grant No. 2010CB630805)
文摘Based on gradient control of carbon partitioning between martensite and austenite during heat treatment of steels,a stepping-quenching-partitioning(S-Q-P) process is developed for high strength steels.The S-Q-P process involves several quenching processes at progressively lower temperatures between martensite-start(Ms) and martensite-finish(Mf) temperatures,each followed by a partitioning treatment at either the initial quenching temperature or above that temperature.A novel microstructure is designed based on the S-Q-P process.Sizes and distributions of retained austenite and high-carbon martensite surrounded by martensite laths can be manipulated by the partitioning duration and temperature,and quenching temperature of the S-Q-P process.Alloying element Si is employed in the S-Q-P steel to suppress formation of carbides and create suitable amount of retained austenite.A steel of 0.39C-1.22Mn-1.12Si-0.23Cr(wt.%) treated by the S-Q-P process is endowed with some special microstructural characteristics:some strips of retained austenite located at edges of martensite blocks with high density of dislocations and between martensite laths,some small blocks of twinned martensites distributed among bundles of the low-carbon martensite lath.The mechanical properties of the medium carbon steel after the S-Q-P process can reach ultimate tensile strength(Rm) of 1240 MPa,total elongation(EI) of 25%,and product of strength and ductility(PSD) of 31.2 GPa% that are much more improved than those after the conventional quenching-tempering(Q-T) and currently prevailing quenching-partitioning(Q-P) treatments.The PSD of the tested steel after the S-Q-P process increases by 67% and 32% as compared with those after the Q-T and Q-P processes,respectively.
基金supported by the National Basic Research Program of China("973" Program) (Grant No. 2010CB630805)
文摘A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite to austenite,volume fraction and distribution of the retained austenite resulting from the following quenching of the steels could be effectively controlled,and then the synthesized mechanical properties of the steels would be improved.In this paper,20SiMn2MoVA steel was treated with conventional quenching-tempering(Q-T),currently prevailing quenching-partitioning(Q-P) and S-Q-P processes,respectively.The results indicated that the volume fraction of the retained austenite of the steel treated by Q-P and S-Q-P processes increased significantly that resulted in the increase of ductility and decrease of strength.The product of strength and ductility of the steel treated by S-Q-P process reached 23.7GPa%,that was increased by about 13% and 7% compared with that after Q-T and Q-P processes,respectively.Compared with the great improvement of the synthesized mechanical property obtained by S-Q-P process with another steel 35SiMn,there would be some factors that deteriorated the effect of S-Q-P process on 20SiMn2MoVA steel.It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite.As a result,less austenite would remain after final quenching and mechanical properties of the steel would be influenced.The results would be beneficial for understanding the principle of S-Q-P process and improving the design of the S-Q-P steel compositions.
基金supported by the National Basic Research Program of China(Grant Nos.2010CB630800 and 2009CB623701)National Natural Science Foundation of China(Grant No.51001064)+1 种基金the Innovation Method Program(Grant No.2010IM031300)Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No. 20100002120047)
文摘In this study,the three-windows method,the jump-ratio method and the R-map method in energy-filtered transmission electron microscopy(EFTEM) have been applied to mapping carbon distribution in 35SiMn steel after a quenching-partitioning treatment.The carbon contamination is successfully suppressed by using EFTEM and plasma-cleaning TEM samples.Compared to the three-windows method and the jump-ratio method,the R-map method provides carbon distribution with less noises,and is insensitive to changes in sample thickness.We have demonstrated that the R-map method is a better way for carbon mapping in middle-carbon steel without the influence of carbon contamination.
