Microstructure and mechanical properties of AISI 316L steel with an inverse gradient nanostructure fabricated by electro-magnetic induction heating

In this paper, we proposed an inverse gradient nanograined structure (IGNS) to improve the mechanical behavior of an austenitic stainless steel. Using high strain cold rolling and subsequent ultra-high-frequency electromagnetic induction heating, we successfully fabricated an IGNS layer on AISI 316L stainless steel, within which the grain size exponentially decreases from the micrometer scale in the surface to the nanometer scale in the inner center. Microstructure evolution was systematically characterized by transmission electron microscopy. The uniaxial tensile test result shows a superior strength-ductility synergy in the IGNS sample. It obtained a yield strength of 842 MPa and a uniform elongation of 16%. A linear relationship between yield strength and uniform elongation was exhibited in IGNS samples with different volume fractions. Effects of the IGNS layer on strength and ductility were examined. Additionally, the effect of recrystallized grain distribution on mechanical properties was discussed.