High cycle fatigue response of grain refined EUROFER97

The present paper has investigated the high cycle fatigue behavior of EUROFER97 steel submitted to a novel process consisting of cold rolling with reduction ratio of 80 % followed by a heat treatment at 650 degrees C for 1 h. This process had already proved to be highly effective under static loads leading to a significant improvement in yield stress. The fatigue tests have been performed with 0.2 load ratio at room temperature. Results indicate that the fatigue strength of the steel submitted to the novel treatment is comparable to that of the standard EUROFER97. Moreover, the fatigued samples underwent a microstructural evolution consisting of grain size increase and texture change due to the stress-driven instability of grain boundaries, especially LAGBs. The collapse of some boundaries involves partial annihilation and re-arrangement of dislocations, and grain coalescence. As a consequence of such microstructural change the material softens with hardness variations up to 8 %.