The Growth Behaviour of Microstructurally Small Fatigue Cracks in a Ferritic-Pearlitic Steel

Abstract

The growth behaviour of microstructurally small fatigue cracks has been investigated with smooth specimens of a ferritic-pearlitic steel, S45C, under rotating bending. The effects of microstructure, particularly the roles of pearlite structure, on crack growth were evaluated based on detailed microscopic observations. In regions smaller than a certain crack length, cracks tended to grow preferentially in ferrite structure, and crack growth rates decreased markedly at ferrite-pearlite boundaries when cracks grew into pearlite structure from ferrite structure. The above region of crack length, i. e. the length of a microstructurally small crack, depended on stress level and increased with decreasing stress level. The growth mechanism is also discussed in terms of the results of fractography. © 1988, The Japan Society of Mechanical Engineers. All rights reserved.