Effect of initial microstructure on surface relief and fatigue crack initiation in AISI 410 ferritic-martensitic steel

Abstract

This work is focused on the effect of the initial tempered-lath microstructure on the surface relief and nucleation of microstructurally short fatigue cracks developed during low-cycle fatigue tests of the ferritic-martensitic AISI 410 steel. Transmission and scanning electron microscopy as well as electron back-scattered diffraction were used to study the surface-damage evolution in smooth, cylindrical, notched specimens. Results from the electron back-scattered diffraction analysis broaden the understanding of the processes of nucleation of microstructurally short fatigue cracks in the initial tempered-lath microstructure of AISI 410 ferritic-martensitic steels. Results prove that during fatigue, microcracks nucleate mainly at high-angle boundaries represented by block subunit interfaces formed in this tempered microstructure. Besides, the progress of fatigue cycling causes the reorientation of the {112} <111> systems to a direction more favourable to slip, giving rise to the formation of extrusions within the blocks and consequently the formation of microcracks.