組成変調型積層Co-Ni 合金めっきの製鋼用連続鋳造鋳型への適用

Abstract

With the aim of extending the lifetime of molds used for continuous steel casting, we developed a composition-modulated Co-Ni alloy plating with alternately laminated layers of different compositions. Alloy films with laminated structures comprising few-micrometer-thick layers were formed using a single plating bath by periodically altering the agitation intensity in the bath during plating. The hardness of the as-plated composition-modulated Co-Ni alloy film was 350 HV, which was higher than that of a conventional non-laminated Co-Ni alloy plating film. Heat treatment slightly decreased the hardness. Nevertheless, the composition-modulated film exhibited higher tensile strength and higher hardness than the conventional alloy film after heat treatment at temperatures of 200-700 ℃. The breaking elongation of the composition-modulated film increased to 30% after heat treatment at 700 ℃. Finally, the composition-modulated Co-Ni alloy plating was applied to a mold surface, which was then used for continuous steel casting. It exhibited excellent resistance against crack formation by thermal shock resulting from contact with molten steel during continuous casting.