2019 年 60 巻 9 号 p. 2003-2007
To investigate the precipitation behavior of super duplex stainless steel in its weld by friction stir welding (FSW) at a low welding speed, we carried out microstructural observation and analysis. An intermetallic compound phase, σ, was observed in the heat affected zone (HAZ). The σ phase precipitated at the interfaces between δ-Fe (ferrite) and γ-Fe (austenite) grains 1–2 mm away from the stir zone (SZ)/HAZ boundary. On the other hand, the Cr2N was observed together with the belt-like γ-Fe grain aggregates in the vicinity of the advancing side (AS) of the SZ. The other intermetallic phase, χ, was also observed at a triple junction of γ-Fe grains. This demonstrates that the precipitation of the Cr2N and χ phases correlates with the transformation of δ-Fe to γ′-Fe (secondary austenite).
