Hybrid nanostructure stainless steel with super-high strength and toughness

摘要

The objective of the present study is to obtain the super-high strength and toughness stainless steel through hybrid nanostructure design. The hybrid nanostructured stainless steel was fabricated by two cold rolling and annealing processes. The second cold-rolled and annealing was carried out on bimodal microstructure which was obtained by the first cold-rolled and annealing on the original microstructure. The bimodal structure consisting of nanometer grains and a small amount of micrometer grains which were distributed in band. After the second cold-rolled and annealing, both the original coarse grain zone (micrometer grains) and fine grain zone (nanometer grains) formed their own finer bimodal microstructure and the bands of the grain distribution became narrower. In our investigations, the hybrid nanostructure obtained by two cold rolling and annealing processes had finer grains and narrower bands of the grain distribution. Meanwhile the results of tensile experiment showed that the yield strength (1221 MPa) and tensile strength (1376 MPa) of the hybrid nanostructure were greatly improved in the situation that the decrease of the toughness (ε_t=45,3%) was not significant compared with the bimodal microstructure. It is obvious that the yield strength of the hybrid nanostructure increased by 2.7 times and the total elongation still remained at the level of 45.3% compared with the original microstructure. Mainly because we embed the soft micrometer grains into the hard nanometer grains to form the lamellar interphase structure. The back-stress hardening, dislocation hardening, TWP effect and TRIP effect produced by the hybrid nanostructure during tensile process contributed to high strength and toughness. And this contribution was more pronounced when the width of lamellar become narrower.