12%Crマルテンサイトステンレス鋼の直接焼入

概要

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Direct quenching of 12%Cr martensitic stainless steels was attempted by air cooling after the hot rolling, because of a good hardenability and wide diameter range for air quenching of these materials. It is, however, probable for the impact toughness to be impaired by carbide precipitation on the grain boundaries during the cooling. The critical condition to prevent the precipitation can be described by the following equation, as a relation of carbon content of steel and the cooling rate or the bar diameter:C≤0.12+0.081 logVor C≤0.27-0.091 logD, where C=carbon content (%), V=mean cooling rate from 900 to 600°C (°C/sec)and D=diameter of bar (mm).Fine grained microstructure due to the direct quenching improves the ductile/brittle transition temperature and environmental fatigue strength of SUS403. As for the impact toughness of the steels with higher carbon content, SUS420J1 and SUS420J2, the direct quenching causes no improvement.
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