Effect of Prior Deformation on the 76-K Fracture Toughness of AISI 304L and AWS 308L Stainless Steels

In this study, the effect of service-induced deformation on the toughness of AISI 304L and its weld metal, A WS 308L was determined. Low temperature compressive loading in the laboratory produced larger deformations. Crack initiation toughness, K_IC(J), and tearing resistance, dJ/da, at 76 K were evaluated as a function of martensite content, a measure of the deformation in these steels. The results showed that the toughness properties of the 304L decrease gradually as the martensite content increases from the 5 to 8 percent level found in the service condition to the 45 percent level obtained by compressive loading. The decrease was less than that expected on the basis of the increased flow stress. The toughness properties of the 308L weld metal decreased more sharply with increased martensite content than those of the 304L. The sharp decrease is associated with a degradation of the properties of the delta ferrite rather than that of the austenite.