Enhanced strength and toughness in 40CrNiMo steels by austempering below martensite start temperature
Xiao-xiao Liu1, Zheng Zhang1, Jie Zhang2, Ran Yang2, Cheng-shuang Yu2, Jun-wei Qiao1, Li-na Han1
1 College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China 2 Zhejiang Laifual Drive Co., Ltd., Shaoxing 312462, Zhejiang, China
Enhanced strength and toughness in 40CrNiMo steels by austempering below martensite start temperature
Xiao-xiao Liu1, Zheng Zhang1, Jie Zhang2, Ran Yang2, Cheng-shuang Yu2, Jun-wei Qiao1, Li-na Han1
1 College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China 2 Zhejiang Laifual Drive Co., Ltd., Shaoxing 312462, Zhejiang, China
摘要 The austempering above and below martensite transition temperature (Ms) 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 (VPM), bainite (VB), and martensite/austenite (VM/A) constituents of approximately 28%, 46%, and 26%, respectively could be obtained by austenitizing below Ms (280 °C) 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 Ms 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.
Abstract:The austempering above and below martensite transition temperature (Ms) 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 (VPM), bainite (VB), and martensite/austenite (VM/A) constituents of approximately 28%, 46%, and 26%, respectively could be obtained by austenitizing below Ms (280 °C) 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 Ms 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.
Xiao-xiao Liu,Zheng Zhang,Jie Zhang, et al. Enhanced strength and toughness in 40CrNiMo steels by austempering below martensite start temperature[J]. Journal of Iron and Steel Research International, 2022, 29(5): 810-818.