Ni and Mn enrichment effects on reformed austenite: thermodynamical and low cycle fatigue stability of 13%Cr–4%Ni and 13%Cr–6%Ni stainless steels

By comparing the behavior of 13%Cr–4Ni and 13%Cr–6Ni alloys, this paper investigated the effect of Ni and Mn enrichment on the amount, mechanical stability, and microstructure of reformed austenite. 4%Ni and 6%Ni–1.5%Mn weld multilayer deposits were made and heat treated to stabilize various amounts of austenite content at room temperature. The maximum austenite content has been obtained at the same temperature (630 °C for 1 h) for both alloys, but 3.6 times more austenite content was formed in the 6%Ni steel. For both alloys similar austenite contents were obtained by post-weld heat treating at different temperatures and were compared experimentally. Results showed that with the addition of Ni and Mn, thinner and lower Ni content austenite was formed. Moreover, austenite generated at lower temperature was mechanically more stable under low cycle fatigue loading. Its rate of transformation has been reduced by a factor of 2.3, resulting in the stabilization of twice more austenite after 20 cycles at 2% strain considering the results of the present study, it is concluded that Ni and Mn contents do significantly affect the mechanical stability of reformed austenite; furthermore austenite lamellae morphology and thickness also seem to play a significant role in stabilizing this phase.