High Temperature Mechanical Properties of Harmonic Structure Designed SUS304L Austenitic Stainless Steel

Abstract

Through many years, conventional material developments have emphasized on microstructural refinement and homogeneity. However, "nanoand Homogeneous "microstructures do not, usually, satisfy the need to be both strong and ductile, due to the plastic instability in the early stage of the deformation. As opposed to such a “nanoand homo-“microstructure design, we have proposed “Harmonic Structure” design. The harmonic structure has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on micro-but homogeneous on macro-scales. In the present work, the harmonic structure design has been applied to SUS304L austenitic stainless steel via a ball milling process and a large size (50 mm in diameter) SPS sintering process. At a macro-scale, the harmonic structure SUS304Lcompacts exhibited significantly better combination of strength and ductility, under quasi-static tensile loadings, as compared to their homogeneous microstructure counterparts. High temperature tensile tests revealed that they also indicated high strength at elevated temperatures.