Microstructure Evolutions at Severely-deformed Austenite/Martensite Interfaces of a Layer-integrated Steel

The microstructure evolution at interfaces of a layer-integrated steel sheet artificially constructed by ductile austenitic stainless (SUS304) and high-strength martensitic (SCM415) steel layers, which were bonded through a cold-rolling and a subsequent annealing at 1000°C, has been investigated using scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDS). We find that a significant microstructural reconstruction around the SUS304/SCM415 interface has been accomplished during a short-time annealing followed by water-quenching; the resultant microstructures are found to consist of recrystallized austenite and lath martensite grains for the SUS304 and SCM415 layers, respectively. Interestingly, the original SUS304/SCM415 interface appears to migrate and extend into the SUS304 side, an occurrence of which can be reasonably explained by the martensitic transformation across the composition-gradient interface during quenching. These microstructural evolutions fairly account for a microscopic mechanism on how hetero-interface bonding can be achieved via simple cold-rolling/annealing procedures.