Crystallographic analysis of fatigue fracture initiation in 8Ni-0.1C martensitic steel. (February 2021) - Okada, Kazuho
Highlights: Crystallographic features of fatigue fracture in martensitic steel were investigated. Fatigue cracks were initiated at block boundaries due to strain incompatibility. Stage I cracks mainly propagated along block boundaries. Almost all of the transgranular cracks were parallel to {0 1 1}M planes. Abstract: The present paper investigated characteristics of fatigue fracture behavior, particularly initiation stage of fatigue fracture (Stage I), in an as-quenched martensitic steel from microstructural and crystallographic points of view. The detailed crystallographic orientation analysis using EBSD revealed that block boundaries in lath martensite structure were the most preferential initiation sites for fatigue cracks. We found that incompatibility of plastic strains between adjacent blocks was the origin for the formation of initial fatigue cracks at block boundaries. Moreover, plastic deformation along {0 1 1} slip planes also played an important role on the transgranular crack propagation.