ＳＵＳ３１０Ｓステンレス鋼の機械的性質に及ぼすアルミニウム拡散被覆の影響

Abstract

A new method has been developed to diffuse aluminum onto austenite stainless steel sheet. In the present study, samples diffused Al onto SUS 310S stainless steel were made by changing the thickness of Al foil attached on the surface of SUS 310S and varying heat treatment conditions. The structural changes in the diffusion layer and the mechanical properties of the samples were then investigated. The diffusion layer consisted of two layers: Layer I was α2 (FeAl) and layer II was a mixed structure of NiAl and α. Kirkendall voids were observed between the two layers. The hardness of layer I increased with increasing Al concentration, which was consistent with that of Fe-Al intermetallic compounds reported by others. That of layer II and the substrate was hardly changed by the aluminized coating. Tensile properties were strongly affected by surface cracks occurring on the diffusion layer during loading. The number of serrations appeared after yielding on the stress-strain curve correlated to that of cracks. The yield strength of layer I was evaluated by rule of mixtures, in which the yield strength had a peak in the vicinity of an Al concentration of 20wt% because of the strengthening mechanism brought about by mixing ordered and disordered phases. The tensile strength and elongation of samples decreased with increasing the thickness of the diffused layer and decreasing Al concentration due to the effect of three-axis stress under the crack tip.