ナノ組織工具鋼の組織と機械的性質 - 日立金属

Microstructures and Mechanical Properties of Nano-Structured Tool Steels Kota Kataoka Hideshi Nakatsu Hot work tool steels generally have a tempered martensitic structure and are highstrength materials. It is necessary to use grain refinement strengthening to give both ofhigher strength at high temperature and toughness than that of conventional steels. In thisstudy, hot work tool steels with ultra-fine grained structure were developed using amechanical alloying treatment. The powder mixture of an atomized JIS SKD61 steelpowder and an Y 2 O 3 powder were mechanically alloyed using a planetary ball mill. Themechanically alloyed powder was packed in a stainless steel tube in a vacuum and thenconsolidated by hot rolling for full densification. The consolidated material wasaustenitized at 1,293 K, which is the general austenitizing temperature of SKD61 steel,and then oil-quenched. Through this process, nano-structured tool steels with equiaxedgrains of 500 nm or less in diameter was obtained. The strength properties of this steelwere comparable to those of a JIS SKH51 high speed steel produced by melting and a hotworkingprocess. Furthermore, it was found that the nano-structured tool steel has thesame hardness and twice the toughness as conventional SKH51 steel. Key Word R&D StageDevelopment 8

Fig. 10 Kota KataokaHideshi Nakatsu 13