Influence of heat treatments on the sensitization of a supermartensitic stainless steel

Supermartensitic stainless steels with 12-13% Cr show higher corrosion resistance than conventional grades such as UNS S42000 and S41000. The reduction of carbon content to less than 0.03%, and the addition of Ni and Mo are the most important compositional changes which enhances mechanical properties and corrosion resistance. Ti addition is used to combine with C and N, and avoid Cr carbides precipitation and to improve mechanical properties. In general, SMSS steels are quenched and tempered or double tempered. The purpose of this work was to investigate how the microstructure and the corrosion decay by sensitization are influenced by quenching and tempering heat treatments in a novel supermartensitic 13% Cr stainless steel with Ti addition. DL-EPR (double loop potentiokinetic electrochemical reactivation) test was used to obtain the degree of sensitization (DOS). The results show that, despite the extra low carbon content, and the stabilization with Ti, the material can become sensitized with heat treatments. The sensitization is rather related to Ti(C, N) precipitation and reverse austenite than to Cr carbides.