Interface and microstructure of heterogeneous laminated steels upon shear loading

The effects of interface spacing, austenite stability and recrystallization degree on the dynamic shear behaviors of heterogeneous laminated steels have been studied, and the corresponding dynamic deformation mechanisms have been revealed. The 6 and 18-layered laminated structures consist of a 304 L stainless steel as surface layers, and a low C steel and a medium-Mn steel as alternating center layers. The dynamic shear properties can be slightly enhanced with reduced interface spacing and significantly improved through a two-step heat-treated process. Superior synergy of dynamic shear strength and dynamic shear toughness can be achieved in the heterogeneous laminated steels, as compared to stainless steels and low alloy steels, including the base materials of 304 L stainless steel and low C steel. The austenite stability can be improved through a two-step heat treatment, leading to a relatively higher Mn enrichment in austenite compared to a one-step heat treated process. This increased austenite stability can elevate the stress or strain threshold for martensitic transformation, thereby postponing the martensite transformation to a larger shear strain range, i.e. from approximately 1.35 for the one-step heat-treated sample to approximately 2.45 for the two-step heat-treated sample. The higher temperature heating is employed in the two-step heat-treated process, enabling full recrystallization and thereby restoring the hardening capacity of the surface layers. Consequently, the combination of these two factors leads to significantly improved dynamic shear strain and toughness. • The coupling effects of austenite stability and recrystallization degree on the impact behaviors. • Smaller interface spacing induces slightly higher shear strain and toughness under dynamic loading. • Improving austenite stability enhances dynamic shear strain and toughness. • The restoration of the deformation capacity of surface layers improves dynamic shear strain and toughness.