Corrosion and toughness of experimental and commercial super ferritic stainless steels

The effect of minor alloying in a super ferritic stainless steel 26% Cr-3% Mo matrix was investigated. The corrosion resistance of several experimenta l heats was examined in terms of their sensitization and intergranular corr osion (IGA) susceptibility following a low-temperature anneal 620 degrees C ). Constant potential etching, electrochemical (electropotentio-kinetic rea ctivation [EPR]), and immersion (modified Strauss test) studies showed that the principal corrosion initiation site of heat-treated steels was intergr anular[ar even at low [C + NJ < 130 ppm) and relatively high [Nb + Ti] conc entrations. Despite the significant contribution of Nb and Ti to the IGA re sistance, these elements had a deleterious effect on the notch toughness. C harpy V testing demonstrated increases in the upper shelf energy and ductil e-to-brittle transition temperature (DBTT), the latter shifting from = -50 degrees C in the absence of stabilizing elements to > 25 degrees C for the stabilizing ratio [(Nb + Ti)(C + N)] > 9. Corrosion resistance of the exper imental heats was compared with that of several commercial alloys with inte rmediate stabilization ratios. The interaction of toughness and corrosion r esistance in ferritic stainless steel was discussed with respect to the lac k of consistency between published evaluation methods and the ideal stabili zation ratio at low IC + N] values.