Toughness and fractography of austenitic type 304 stainless steel with sensitization treatments at 973 K

Abstract

It is shown that the fracture toughness in type 304 austenitic stainless steel can be obtained from convenient measurements of the dimple size at the bottom of the cup portion in the fracture surface of round tension samples, employing SEM techniques and quantitative fractography. K_IC measurements were performed for sensitized samples after heating for 1, 12, 24, and 48 h at 973 K. Fracture toughness is shown to decrease monotonically with increasing time of heat treatment. Two models based on axial stress conditions, Krafft's model and a model proposed by Schwalbe and Backfisch, were tested and compared with Barsom and Pellegrino's model, which reflects closely the necessary plane strain conditions for K_IC measurements. The crack growth increment was considered equal to the dimple size, which was measured by means of the mean intercept length of three dimensional bodies or mean chord in space, L₃.