The austempering above and below martensite transition temperature(M_(s))was employed in a medium-carbon low-alloy 40CrNiMo steel,and the bainite and martensite multiphase microstructures with different volume fractio...The austempering above and below martensite transition temperature(M_(s))was employed in a medium-carbon low-alloy 40CrNiMo steel,and the bainite and martensite multiphase microstructures with different volume fractions were obtained.Here,the effect of pre-existing martensite on subsequent transformation of bainite microstructure and mechanical properties is focused and researched.The microstructure with a volume fraction of pre-existing martensite(V_(PM)),bainite(V_(B)),and martensite/austenite(V_(M/A))constituents of approximately 28%,46%,and 26%,respectively could be obtained by austenitizing below M_(s)(280℃)for 1 h,and an optimum combination of strength,ductility,and impact toughness(yield strength of 1420 MPa,ultimate tensile strength of 1795 MPa,total elongation of 7.9%,and V-notch impact value of 37 J)was achieved.The considerable enhancement of mechanical properties in the sample austenitized below M_(s)is mainly ascribed to the formation of the pre-existing martensite,resulting in an effective reduction in the size of the bainite plates and martensite/austenite constituents.展开更多
基金support of the Natural Science Foundation of Shanxi Province,China(Nos.201901D111105,201901D111114).
文摘The austempering above and below martensite transition temperature(M_(s))was employed in a medium-carbon low-alloy 40CrNiMo steel,and the bainite and martensite multiphase microstructures with different volume fractions were obtained.Here,the effect of pre-existing martensite on subsequent transformation of bainite microstructure and mechanical properties is focused and researched.The microstructure with a volume fraction of pre-existing martensite(V_(PM)),bainite(V_(B)),and martensite/austenite(V_(M/A))constituents of approximately 28%,46%,and 26%,respectively could be obtained by austenitizing below M_(s)(280℃)for 1 h,and an optimum combination of strength,ductility,and impact toughness(yield strength of 1420 MPa,ultimate tensile strength of 1795 MPa,total elongation of 7.9%,and V-notch impact value of 37 J)was achieved.The considerable enhancement of mechanical properties in the sample austenitized below M_(s)is mainly ascribed to the formation of the pre-existing martensite,resulting in an effective reduction in the size of the bainite plates and martensite/austenite constituents.
