Unravelling Interfacial Bonding Mechanism Under Heat Treatment in Hot Compression Bonding of Heterogeneous Stainless Steel and Mild Steel

Abstract

HCB was used to join stainless steel and mild steel with different compressive strains (5% to 40%). The bonded samples were then annealed, and the effect of this heat treatment on the microstructure and mechanical property of the interface bonding was systematically investigated. The hot compression process induces significant stored deformation energy, serves as a driving force for the formation of recrystallized fine grain layer (RGL) in subsequent annealing. During annealing, the stainless steel near the interface first undergoes austenite recrystallization, subsequently, the diffusion of Ni from stainless steel to mild steel reduces the stability of austenite, causing part of the austenite to transform into fine-grained ferrite upon cooling. For the mild steel near the interface, ferrite undergoes a phase transition to austenite upon heating, and subsequently returns to ferrite during cooling, leading to significant grain refinement. The annealing process not only eliminates the residual stress but also improves the bonding effect via promoting atomic diffusion. The diffusion of Ni leads to the precipitation of Ni-rich intermetallics, while Cr, in addition to partially forming a solid solution, can also precipitate at the boundary of coarse-grained mild steel in the form of Cr-rich intermetallics.

Keywords: Heterogeneous Interfacial Bonding, Hot Compression Bonding, Annealing Heat Treatment, diffusion, Recrystallization