Austenite formation behavior of duplex stainless steel welds

Abstract

The generation behavior of the γ-phase was investigated during the weld of the duplex stainless steels by using the molten Sn quenching technique. The γ formed in primary δ-phase grain boundary after 96-142℃ undercooling from equilibrium temperature and precipitated in the grain after 166-262℃ undercooling. The concentration of N in γ-phase was clearly observed, but the distribution of Ni and Mo between δ/γ was very small. It is thought that the growth of the γ advances by diffusion of N. Crystallographic relations of Kurdjumov-Sachs(K-S) existed between δ and Widmanstätten-γ, and γ plate grew up in <111> δ directions. The growth rate of γ plate at 1100℃ estimated in this work was 0.463mm/s and it was much lower than predicted value under the assumption of para-equilibrium of N and Zener-Hillert equation. Furthermore, the value calculated by the Trivedi equation considering the Gibbs-Thomson effect was also 2.1 to 7 times faster than the measured value. The decrease of N diffusivity was thought to affect the growth rate of γ-phase, because Cr contained 25mass% in duplex stainless steel has negative interaction with N.