Abstract
The present paper investigates distributions of α' martensitic phase on fatigue fracture surfaces in SUS 304 stainless steel specimens having through- and part-through-thickness cracks. The volume fraction V_α' of the α' phase transformed on fracture surfaces in the two types of specimens was measured after specimens had been fractured. The measurements were made with ferrite scope. On fracture surfaces, the contour maps of V_α' reflect the distributions of the maximum values of the stress intensity factor K_<max>. The contour maps look similar to crack shapes imprinted on fracture surfaces in the two types of specimens. The contour maps on through-thickness cracks have nearly rectangular shapes, whereas those on part-through-thickness cracks have semi-elliptical shapes. The values of V_α' measured on crack surfaces can be correlated with K_<max> values calculated at the measurement positions. The resultant V_α' vs. K_<max> plots fall within narrow bands whose upper and lower bounds are expressed as quadric curves. These results suggest that quantitative post-fracture analysis can be maid by measurement of V_α' on fracture surfaces with ferrite scope.
