INFLUENCES OF MATERIAL AND PROCESS PARAMETERS ON DELAYED FRACTURE IN TRIP-AIDED AUSTENITIC STAINLESS STEELS

摘要

The effects of material and process parameters on delayed fracture susceptibility of three AISI 301 steels have been studied by Slow Strain Rate Tests (SSRT) and Deep Drawing Tests (DDT). The parameters of austenite stability, presence of prior martensite nuclei and hydrogen content have been evaluated through analyzing the tensile strength, ductility, time to fracture and fracture surface of hydrogen pre-charged SSRT and DDT specimens. Steels having prior martensite nuclei or more unstable austenite were found more sensitive to delayed fracture. Besides, the time to fracture declined with increasing diffusive hydrogen content in a power-law manner. In addition, delayed fracture in DDT specimens could be prohibited by raising the forming temperature and punch velocity, owning to the suppressed phase transformation and partial residual stress relief. Fractographic studies revealed the transition of fracture mode from ductile to quasi-cleavage/inter-granular fracture depending on hydrogen content and stress triaxility.