THE GROWTH OF MICROSTRUCTURALLY SMALL FATIGUE CRACKS IN A FERRITIC‐PEARLITIC STEEL

Abstract
Abstract— The growth behaviour of microstructurally small fatigue cracks was investigated with smooth specimens of a ferritic‐pearlitic steel, S45C. under rotating bending. The effects of microstructure, particularly the role of pearlite structure, on crack growth were evaluated based on detailed microscopic observations. In the region smaller than a certain crack length. small cracks tended to grow preferentially in the ferrite structure, and the crack growth rates decreased markedly at ferrite‐pearlite boundaries when small cracks grew into the pearlite from the ferrite. The above region of crack length, i.e. the length of microstructurally small cracks, depended on stress level, increasing with decreasing stress level. The growth mechanism is also discussed in terms of the results obtained from fractogrdphy.

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