Impact of interpass temperature on the microstructure and mechanical properties of super duplex stainless steel in CW-GMA additive manufacturing

This study investigates the influence of interpass temperature (IPT) on microstructure evolution and mechanical properties of super duplex stainless steel (SDSS) manufactured by cold wire gas metal arc (CW-GMA) additive manufacturing. Thermal cycle analysis showed that cooling rates were not significantly affected by IPT under constant process parameters. However, higher IPTs resulted in higher thermal accumulation and extended exposure to elevated temperatures. Microstructural characterisation revealed the transformation of δ-ferrite grains into various austenitic phases and secondary chromium nitrides during cooling. Fine, needle-like secondary austenite formation was more pronounced at higher IPTs, driven by chromium nitride precipitation near layer transitions. Mechanical testing demonstrated consistent ultimate tensile strength around 810 MPa across IPTs, with ductility variations attributed to porosity. Hardness profiles were uniform, averaging approximately 300 Hv. These findings suggest that while IPT influences thermal accumulation and microstructural details, its effect on ferrite-to-austenite ratio and mechanical properties is minimal. Optimising IPT remains essential for increasing the productivity of SDSS in CW-GMA additive manufacturing.