The Effects of the Microstructural Change of Dual Phase Steel on Fatigue Fracture Propagation

J. Ocean Eng. Technol. 1991;5(2):58-66.

Oh Sae-Wook,Kim Ung-Jip

복합조직강의 미시조직변화가 피로파괴전파에 미치는 영향

오세욱,김웅집

동아대학교,동아대학교

Keywords: Plastc constraint Effect, Fatigue Limit, Initial Fatigue Crack, Fatigue Crack Propagation, Crack Propagation Rate, Stress Intensity Factor

핵심용어: 소성구속효과, 파로한도, 초기파로구열, 파로구열전파, 구열전파속도, 응력확대 계수

Abstract

Not only difference of fatigue crack growth and propagation behavior resulted from the grain size, the hardness ratio and volume fraction in M.E.F. dual phase steel composed of martensite in hard phase and ferrite in soft phase, but also the effects of the plastic constraint were investigated by fracture mechanics and microstructural method. The main results obtained are as follows: 1) The fatigue endurance of M.E.F. steel increases with decreasing the grain size, increasing the ratio of hardness and volume fraction. 2) The initiation of slip and crack occures faster as the stress level goes higher. These phenomena result from the plastic constraint effect of the second phase. 3) The crack propagation rate in the constant stress level is faster as the grain size gets larger, the ratio of hardness lower and volume fraction smaller.