Effect of Postweld Heat Treatment on Laser‐Welded Duplex Stainless Steel: Crystallographic Patterns and Fatigue Behavior

This study investigates the influence of laser welding and postweld heat treatment (PWHT) on the fatigue behavior of a UNS S32304 duplex stainless steel (DSS), with emphasis on the relationship between crystallographic misorientation and fatigue performance. Laser processing led to a fully ferritic microstructure in the fusion zone, accompanied by chromium nitride precipitation and a significant reduction in austenite content. The applied PWHT at 1150 °C for 10 min promoted the reformation of austenite, refined the microstructure, and dissolved the nitrides, reestablishing a near‐balanced phase proportion. However, fatigue tests revealed that despite the improved phase balance, the PWHT condition exhibited lower fatigue resistance compared to both the as‐welded and the base metal conditions. Detailed microstructural and crystallographic analyzes indicated that fatigue behavior is governed not only by phase fraction but also by grain morphology, misorientation distributions, and ferrite‐austenite orientation relationships (OR). The predominance of high‐angle grain boundaries and specific OR, especially after PWHT, facilitated crack nucleation, offsetting the benefits of phase rebalancing. These findings challenge the assumption that restoring phase balance through PWHT is sufficient to recover the mechanical performance of laser‐welded DSS, particularly under cyclic loading conditions.