Effect of Temperature on Diffusion Bonding for Austenite/dual Phase Stainless Steel: Experimental and First‐Principles Calculations

Joining austenitic (304) and duplex (S32304) stainless steels via diffusion bonding leverages their complementary properties but faces challenges in controlling interfacial element diffusion and stability. This study systematically investigates the temperature dependance (800–1200 °C) of microstructure evolution and mechanical properties in 304/S32304 diffusion‐bonded joints, integrating experimental characterization with first‐principles calculations. Key findings reveal that an optimal bonding temperature of 1100 °C yielded a maximum tensile strength of 720 MPa, approaching 95% of 304 base material strength. Microstructural analysis showed a significant transformation of 13% austenite to ferrite in S32304 and a remarkable increase in recrystallized grains from 3% to 94%. Crucially, first‐principles calculations demonstrate that Mn diffusion played a dominant role in destabilizing interfacial Cr 2 O 3 oxides, facilitating their transformation to Mn x O y , which aligns with experimental energy‐dispersive spectroscopy observations. This Mn‐induced oxide transformation, alongside enhanced elemental interdiffusion and void closure at elevated temperatures, governed the interfacial stability and joint performance. The integrated experimental‐theoretical approach provided unprecedented atomic‐scale insights into the diffusion mechanisms and interfacial oxide evolution, establishing a fundamental basis for optimizing diffusion bonding parameters of dissimilar stainless steels in demanding applications.