Heat-Affected Zone Sensitization and Stress Corrosion Cracking in 12% Chromium Type 1.4003 Ferritic Stainless Steel

This document presents an overview of the findings of several investigations into the susceptibility of 12% Cr Type 1.4003 ferritic stainless steel to heat-affected zone sensitization and intergranular stress corrosion cracking. A description of the sensitization behavior of these steels is complicated by the partial transformation of δ-ferrite to austenite on cooling. During slow cooling or annealing below the A1 temperature (representing the phase boundary between the austenite and austenite+ferrite phase fields), this austenite decomposes to form desensitized ferrite and M23C6-type carbide precipitates. The rapid cooling rates associated with welding, however, prevent the transformation of austenite to ferrite at lower temperatures, and any austenite formed on cooling transforms to martensite below the Ms (martensite start) temperature. Four distinct modes of heat-affected zone sensitization have been identified to date. Sensitization of the martensite phase may occur on welding material inadvertently annealed above the A1 temperature (Mode 1), or when multiple welds are positioned in such a way that the heat-affected zone of the second pass overlaps the heat-affected zone of the first pass (Mode 2). Rapid cooling after very low heat input welding may sensitize the ferrite phase (Mode 3), whereas very slow cooling after welding at excessively high heat input levels may lead to the sensitization of the austenite phase (Mode 4). Results examining the influence of Modes 1 and 2 heat-affected zone sensitization on the incidence of intergranular stress corrosion cracking are presented.