Influence of high temperature softening and solid solution on intergranular corrosion susceptibility of Super304H stainless steel

Abstract

Thermos-mechanical processes were investigated to suppress the high intergranular corrosion sensitivity of Super304H austenitic stainless steel. The microstructure and grain boundary character distribution were characterised, respectively, by scanning electron microscope and electron backscatter diffraction analysis. The degree of sensitisation (DOS) was evaluated by the double-loop electrochemical polarisation reactivation test. The results show that the bulk primary Nb(C,N) particles were dissolved more into the matrix after high temperature softening at 1300°C for more than 30 min and the special boundaries (∑ ≤ 29) maintained at the same level as the as-received state after solid solution at 1150°C. The DOS was decreased after high-temperature softening and solid solution treatments, which was attributed mainly to the dissolution of primary bulk Nb(C,N) phase during high-temperature softening and the dispersive precipitation of the secondary fine Nb(C,N) phase during solid solution, which had effectively consumed carbon.