Fracture toughness and ductile crack growth properties of 316L stainless steel at room temperature and at 550°C are determined using the J-integral concept. Two plates of 316L stainless steel containing, due to their different melting processes, different amounts and sizes of inclusions are characterized in terms of JIc and slopes of the J-R curves. The variations of these properties with the inclusion content and size, the proportion of second phases (carbides, δ ferrite, σ phase), and the position of the crack propagation plane with respect to the rolling direction are studied. Tension and impact tests carried out in the same conditions are used to compare the different toughness criteria.
The results obtained show thatl1c and JIc and dJ/da levels are very sensitive to inclusion content and shape and to the presence of transgranular carbides and a phase. Small amounts of li ferrite and intergranular carbides seem to have little influence. JIc and dJ/da criteria are more sensitive to the presence of inclusions or second phase than the Charpy V-notch criterion. The choice of the blunting line equation used to determine JIc values is discussed in terms of crack-opening displacement measurements during crack-tip blunting.
An approach is made to determine the influence of specimen size on the results obtained in JIc tests for an austenitic stainless steel.