高C-高Cr系冷間工具鋼の焼入特性に及ぼすC-Crの影響

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The performance of cold work die steels such as D2 type depends upon the addition of C and Cr. The effects of them on the properties of specimens as quenched are summarized below for 8 alloys containing 0.6 to 1.5% C, 5 to 12% Cr, 1% Mo and 0.3% V.(1) Carbon increases the hardness and the retained austenite for alloys as quenched, while chromium decreases both values. The effect of two alloying elements are expressed by the following equations throngh the parameter, K=[%Cr]-6.8×[%C].H=65.8-0.42K±0.4 (HRC)Vγ=15.2-1.05K±1.5 (%)Where H is the maximum Rockwell C hardness for each alloy quenched from various austenitizing temperatures and Vγ is the vol.% of retained austenite in the sample with the maximum hardness.(2) The ratio of Cr to C contents controls the response of alloys to austenitizing temperatures. The alloys with the above ratio of 8 to 10 and K of about 2 gain higher and rather constant hardness in the wide range of austenitizing temperatures.(3) Carbon as well as chromium retard the grain growth of austenite. The grain size number of austenite shows the maximum when the parameter, L=[%Cr]+15.5×[%C], reaches 25 to 28.(4) The amount of coarse undisolved carbides rises rapidly after the above parameter L is over 25.
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