Influence of notch on fatigue properties of nitrided CrNiW steel in very high cycle regime
SUN Zhen-duo1, HOU Dong-bo1, LI Wei2, ZHANG Ming-yang1
1. School of Quality and Technical Supervision, Hebei University, Baoding 071000, Hebei, China; 2. School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China
Abstract：In order to study the influence of notch sensitivity on fatigue properties of nitrided CrNiW steel,a smooth specimen and two notched specimens with concentration factor Kt=1.20 and Kt=1.55 were designed,respectively. The very high cycle fatigue tests were carried out by using nitrided CrNiW steel. The microstructure of the fatigue specimen was observed by SEM. The relationship of notch fatigue factor Kf,notch sensitivity index q and number of cycles to failure Nf were analyzed. The results show that,the case-nitriding has little effect on the improvement of fatigue strength of steel. For the smooth specimen and the notch specimen with Kt=1.20,the failure modes can be classified as surface induced failure and the interior induced failure where the defects are limited in the non-nitriding area. For the notch specimen with Kt=1.55,interior failure induced by the inhomogeneous matrix area within the nitrided layer is observed,which is a new failure characteristic. The duplex S-N property of smooth specimen is not obvious. However,there is a duplex S-N property with surface induced failure and interior induced failure as Kt=1.20,and there is a duplex S-N property only with surface induced failure which occurs in the short life regime and the VHCF regime as Kt=1.55. With the increase of Kt,the phenomenon of multiple interior crack sites is replaced by the single interior crack site,and the interior defect position gradually moves towards the surface of specimen,and the shape of fisheye first approximately exhibits the oblate with major axis at x direction,followed by the circular shape,and then the elliptical shape with major axis at y direction. The Kt has a large effect on fatigue life with surface failure,but has a little effect on fatigue life with interior failure.
孙振铎, 侯东勃, 李伟, 张明洋. 缺口对渗氮CrNiW钢超高周疲劳特性的影响[J]. 钢铁, 2021, 56(3): 120-129.
SUN Zhen-duo, HOU Dong-bo, LI Wei, ZHANG Ming-yang. Influence of notch on fatigue properties of nitrided CrNiW steel in very high cycle regime[J]. Iron and Steel, 2021, 56(3): 120-129.
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2021, Vol. 56 
