3% Cr-1% Mo系熱間工具鋼の2次硬化特性と焼もどしにおける軟化特性について

概要

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The quenched and tempered hardness fluctuates with microstructures as quenched. The effect of quenched microstructures such as martensite, bainite and retained austenite on the tempering characteristics was studied, especially on secondary hardening and softening during tempering in 3% Cr-1% Mo hot work tool steel.As a result, it was confirmed that the tempering characteristics, such as hardness, microstructures and sequence of changes in the carbide structures were significantly affected by retained austenite. The hardness after tempering above 500°C increased with retained austenite. The increment of secondary hardening, H in Rockwell C scale, is directly proportional to the percentage of volume fraction of retained austenite in as-quenched condition, Vγ, following the equation: H=0.33Vγ. The resistance of softening on tempering above 600°C also increased with increased retained austenite.It was assumed that the rate determining process of secondary hardning is the diffusion process of carbon in austenite and that of softening during tempering is the diffusion process of chromium in ferrite from their activation energies.
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