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SM40C 강의 열처리가 피로균열전파속도에 미치는 영향
금창훈,권숙인 ( C . H . Keum,S . I . Kwun ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.2
The effect of the microstructural change on the near threshold fatigue crack growth rate in SM40C steel has been studied using the ΔK decreasing method. Below the total strain amplitude of 0.56%, cyclic softening occured, whereas above this value cyclic hardening occurred in the pearlitic lamellar structure. However, in the spherodized structure the cyclic hardening solely occurred. The crack growth rate in the near-threshold region was decreased with increasing prior austenite grain size and this was due to surface roughness. The crack growth rate of the spherodized structure was lower than that of the pearlite lamellar structure and the ΔK_(th) of the former was higher than that of the latter. It was understood that the crack propagates preferentially through the ferrite phase. The intergranular facets in the near-threshold region appeared in the spherodized structure.