The microstructural heterogeneity in thick-Sect.15CrNi3MoV steel forgings caused by cooling rate gradients during quenching critically impacts their mechanical reliability.Combining finite element simulation and multi...The microstructural heterogeneity in thick-Sect.15CrNi3MoV steel forgings caused by cooling rate gradients during quenching critically impacts their mechanical reliability.Combining finite element simulation and multi-scale physical simulations,the microstructure evolution was decoded,and an optimised heat treatment process was designed for a 10-t large-tube forging.Key findings reveal that the cooling rate dictates phase transformation:the surface forms martensite,while the centre develops martensite and granular bainite with metastable martensite-austenite(M-A)constituents.During tempering,prolonged holding at 650℃ drives the decomposition of M-A constituents into fine carbides,with 12-h tempering achieving optimal strength–toughness balance.Crucially,carbide uniformity eliminates property gradients across 140 mm in thickness,suppressing embrittlement risks.Moreover,in the 180-mm-thick plate,the large-sized M-A constituents formed due to incomplete quenching,resulting in the carbide aggregations after tempering,which deteriorates the impact toughness.By integrating numerical simulation with validations from laboratory-scale and pilot-scale physical simulations,the relationship between microstructure and properties can be precisely predicted.Implementing the optimised process(890℃/8 h water quenching+650℃/12 h tempering)on the 10-t large-tube forging demonstrates homogeneous properties.Thus,a generic methodology was provided for tailoring heat treatment protocols in ultra-thick alloy steel components.展开更多
The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by c...The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2024YFB3714200)the National Natural Science Foundation of China(Grant Nos.52173305,52101061,52233017,52203384 and U244120568)+2 种基金the Key Program of the Chinese Academy of Sciences(Grant No.RCJJ-145-24-40)Ling Chuang Research Project of China National Nuclear CorporationCNNC Science Fund for Talented Young Scholars.
文摘The microstructural heterogeneity in thick-Sect.15CrNi3MoV steel forgings caused by cooling rate gradients during quenching critically impacts their mechanical reliability.Combining finite element simulation and multi-scale physical simulations,the microstructure evolution was decoded,and an optimised heat treatment process was designed for a 10-t large-tube forging.Key findings reveal that the cooling rate dictates phase transformation:the surface forms martensite,while the centre develops martensite and granular bainite with metastable martensite-austenite(M-A)constituents.During tempering,prolonged holding at 650℃ drives the decomposition of M-A constituents into fine carbides,with 12-h tempering achieving optimal strength–toughness balance.Crucially,carbide uniformity eliminates property gradients across 140 mm in thickness,suppressing embrittlement risks.Moreover,in the 180-mm-thick plate,the large-sized M-A constituents formed due to incomplete quenching,resulting in the carbide aggregations after tempering,which deteriorates the impact toughness.By integrating numerical simulation with validations from laboratory-scale and pilot-scale physical simulations,the relationship between microstructure and properties can be precisely predicted.Implementing the optimised process(890℃/8 h water quenching+650℃/12 h tempering)on the 10-t large-tube forging demonstrates homogeneous properties.Thus,a generic methodology was provided for tailoring heat treatment protocols in ultra-thick alloy steel components.
基金supported by the Science and Technology Planning Joint Program of Liaoning Province(Applied Basic Research Project,No.2023JH2/101700054).
文摘The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.
