Abstract
Precipitation behavior of sigma (σ) phase was investigated for duplex stainless steel and its weld metals by reheating. The material used was SUS329J1 base metal, and the samples were single-pass welded using SMAW 329J4L (DP3) electrode and SMAW 329J3L (DP8) electrode.
The fine secondary austenite (γ*) was formed at primary austenite (γ) /ferrite (α) phase boundaries and grew into ferrite, and then σ phase began to precipitate at γ*/α phase boundaries and grew into ferrite for SUS329J1 base metal. In case of weld metals, γ* was formed both at γ/α phase boundaries and in the interior of ferrite matrix, and thereafter precipitation of a phase at γ*(γ)/α phase boundaries occurred. Time-Temperature-Precipitation (T-T-P) diagrams of sigma (σ) phase were constructed in order to investigate beginning of precipitation of sigma (σ) phase for SUS329J1 base metal and 329J4L (DP3), 329J3L (DP8) weld metals. As a result, the nose position in TTP diagram of σ phase was located at 1123 K for 0.06 ks for 329J4L (DP3) weld metal, while its position was located at 1123 K for 0.3 ks in case of 329J3L (DP8) weld metal which was lower chromium content.
