On the Changes of Residual Stress Due to Slip Bands Accumulation

概要

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An experimental study is made on the changes of residual stress in the rapid heat treated low carbon steel specimens under fatigue loading with special interest in the relationship between the slip bands formation observed by an optical microscope (×200 and ×400) and the fading out of residual stresses. Especially, authors take note of the magnitudes of residual stress before and after the fatal crack propagation into the martensite. Detailed microstructural observation through an optical microscope shows that at stress amplitudes below the yield stress (0.2% proof stress), when cracks are staying in the ferrite, the release of residual stresses is caused by the cumulative plastic deformation by slip bands in the retained ferrite. Then, they relieve more as the crack begins its propagation into the martensite. On the other hand, at the stress amplitudes above the yield stress a large amount of release of residual stresses could be caused by cumulative plastic deformations both in the retained ferrite and in the martensite.
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