High-cycle fatigue properties of microalloyed medium-carbon forging steel 45MnVS with modified sulfide
WANG Zhan-hua1, HUI Wei-jun1, ZHANG Yong-jian1, ZHAO Xiao-li1, HAO Yan-ying2, DAI Guan-wen2
1. School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China; 2. Technical Center, Shijiazhuang Iron and Steel Co., Ltd., HBIS Group, Shijiazhuang 050031, Hebei, China
Abstract：The elongated sulfide inclusion is primarily responsible for the mechanical properties anisotropy of hot-rolled and forged sulfur-containing structural steels. In order to explore the fatigue anisotropy of microalloyed ferritic-pearlitic forging steel with modified sulfide,high-cycle fatigue properties of a commercial microalloyed forging steel 45MnVS with as-forged and quenched and tempered (QT) microstructures was studied by using axial-force-controlled fatigue testing with a stress ratio of -1. The results show that the sulfides are primarily short rod-like or slightly elongated with an average length to width ratio of 3.4±1.7 and relatively uniformly distributed in the steel. Although there are still ductility and toughness anisotropy in the tested steel,this anisotropy is significantly lowered than that of other microalloyed medium-carbon forging steels which did not subjected to sulfide modification. The fatigue properties of the as-forged and QT samples in the transversal direction are slightly lower than those in the longitudinal direction,and the fatigue limit ratio of the QT samples (0.52-0.54) is notably higher than those of the as-forged samples (0.46). The transversal sample exhibits a slightly higher fatigue crack growth rate than the longitudinal sample only when the stress intensity factor range is higher than about 35 MPa·m1/2. Further fatigue fracture surface investigation revealed that the fatigue fractures are primarily initiated at short rod-like sulfides for both the as-forged and QT samples,and this influence is more notably for the QT sample. It is thus concluded that the fatigue anisotropy of the tested steel with modified sulfide is rather small and the anisotropy degree of the as-forged sample is slightly lower than of the QT sample,although the latter exhibits more superior fatigue properties than the former.
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2021, Vol. 56 
