Evaluation and improvement of pearlite microstructure and mechanical properties in 45Cr4NiMoV and 50Cr5NiMoV steels
Kai-quan Liu1,2,3, Xue-jiao Zhang2,3, Xiao-yang Song2, Lin Zhao4, Lin Zhu2,3
1 State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, Hebei, China; 2 Tianjin Heavy Industries Research & Development Co., Ltd., CFHI, Tianjin 300457, China; 3 China First Heavy Industry, Qiqihar 161042, Heilongjiang, China; 4 Central Iron and Steel Research Institute Co., Ltd., Beijing 100081, China
Evaluation and improvement of pearlite microstructure and mechanical properties in 45Cr4NiMoV and 50Cr5NiMoV steels
Kai-quan Liu1,2,3, Xue-jiao Zhang2,3, Xiao-yang Song2, Lin Zhao4, Lin Zhu2,3
1 State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, Hebei, China; 2 Tianjin Heavy Industries Research & Development Co., Ltd., CFHI, Tianjin 300457, China; 3 China First Heavy Industry, Qiqihar 161042, Heilongjiang, China; 4 Central Iron and Steel Research Institute Co., Ltd., Beijing 100081, China
摘要 The microstructure and mechanical properties of pearlite in 45Cr4NiMoV and 50Cr5NiMoV steels were studied and compared. The microstructural characteristics of pearlite of two steels were carefully examined by optical microscopy, scanning electron microscopy and transmission electron microscopy (TEM), and the type, size and relative amount of extracted carbide particles were analyzed by X-ray diffraction and TEM coupled with selected area electron diffraction. The hardness, tensile property, impact and fracture toughness of pearlite of two steels were also evaluated. Besides, the carbide dissolution kinetics of 45Cr4NiMoV and 50Cr5NiMoV steels were clarified. The results indicated that the carbides in 50Cr5NiMoV steel exhibited higher dissolution temperature than those in 45Cr4NiMoV steel, which induced different morphologies of pearlite after eutectoid transformation. Compared to the pearlite with lamellar M23C6 carbides in 45Cr4NiMoV steel, the pearlite with the mixture of spheroidized M7C3 and lamellar M23C6 carbides in 50Cr5NiMoV steel possessed higher impact and plane-strain fracture toughness but lower hardness and strength, because different pearlite morphologies led to different mechanical properties. In order to further improve the comprehensive properties of the steels, the fraction of M7C3 for the material with acceptable properties was examined and dissolution kinetic of M7C3 was calculated. Therefore, the austenitizing temperature and holding time could be appropriately selected to keep enough undissolved M7C3 in the steels.
Abstract：The microstructure and mechanical properties of pearlite in 45Cr4NiMoV and 50Cr5NiMoV steels were studied and compared. The microstructural characteristics of pearlite of two steels were carefully examined by optical microscopy, scanning electron microscopy and transmission electron microscopy (TEM), and the type, size and relative amount of extracted carbide particles were analyzed by X-ray diffraction and TEM coupled with selected area electron diffraction. The hardness, tensile property, impact and fracture toughness of pearlite of two steels were also evaluated. Besides, the carbide dissolution kinetics of 45Cr4NiMoV and 50Cr5NiMoV steels were clarified. The results indicated that the carbides in 50Cr5NiMoV steel exhibited higher dissolution temperature than those in 45Cr4NiMoV steel, which induced different morphologies of pearlite after eutectoid transformation. Compared to the pearlite with lamellar M23C6 carbides in 45Cr4NiMoV steel, the pearlite with the mixture of spheroidized M7C3 and lamellar M23C6 carbides in 50Cr5NiMoV steel possessed higher impact and plane-strain fracture toughness but lower hardness and strength, because different pearlite morphologies led to different mechanical properties. In order to further improve the comprehensive properties of the steels, the fraction of M7C3 for the material with acceptable properties was examined and dissolution kinetic of M7C3 was calculated. Therefore, the austenitizing temperature and holding time could be appropriately selected to keep enough undissolved M7C3 in the steels.
Kai-quan Liu,Xue-jiao Zhang,Xiao-yang Song, et al. Evaluation and improvement of pearlite microstructure and mechanical properties in 45Cr4NiMoV and 50Cr5NiMoV steels[J]. Journal of Iron and Steel Research International, 2022, 29(12): 1995-2005.
2022, Vol. 29 
