Correspondence of fracture surface features with mechanical properties in 304LN stainless steel

Ductile fracture behaviour of 304LN stainless steel at various strain rates has been studied through the examination of void morphologies (i.e. void size, void density and void size distribution) on the tensile fracture surface. An image-processing technique has been employed to quantify the metrices of voids on the fracture surface formed through the coalescence of microvoids. It is noted that at lower strain rates, when the void number density was higher and the average circular diameter of void was lower, the strength was higher and ductility was lower. At high strain rates, a reverse correlation between void features and mechanical properties was obtained. Deformation-induced martensite (DIM) was noted to be responsible for the high void number density at low strain rates. At high strain rates, DIM formation was suppressed due to adiabatic heating and hence a low void number density resulted.