Comparison of ductile crack growth resistance of austenitic, niobium-stabilized austenitic, and austeno-ferritic stainless steels

Fracture toughness and ductile crack growth properties are compared room and elevated temperatures by using the J integral concept for three grades: an austenitic stainless steel water-quenched from different temperatures, a niobium-stabilized austenitic stainless steel containing niobium carbides and niobium carbonitrides in an austenitic matrix, and an austeno-ferritic stainless steel that contains about 50% ferritic phase in an austenitic matrix and shows higher tensile properties compared with the two other grades. The J-R curves of the two austenitic grades are mainly dependent upon the inclusion content and the direction of the crack growth plane. Some results show the influence of residual stress level on J-R curves. The J/sub lc/ and dJ/da values for the austeno-ferritic grade cannot be explained only by the roles of the inclusion content and the crack growth plane direction; a specific behavior of the ferritic phase in this duplex steel may decrease J/sub lc/ compared with the two austenitic grades