The Tempered Hardness at Higher Temperature and Secondary Hardening Behavior in 1C-1Si-8Cr-2Mo Cold Work Die Steel

The tempering characteristics of 1C-1Si-8Cr-2Mo cold work die steel were investigated by measurements of tempered hardness after quenching or sub-zero treating, volume fraction of retained austenite, and identification of precipitated carbides. Retained austenite transformes to martensite at the tempering parameter range of 16 to 17×103, which is higher than that of SKD 11. Secondary hardness is due to transformation of retained austenite to martensite and precipitation of M6C carbide. The effect of transformation of retained austenite on secondary hardness is greater than that of carbide precipitation. It is necessary for dimensional stability of high C-high Cr steel dies to transform the retained austenite to martensite completely according to chemical instability mechanism, or to make the retained austenite stable thermally by reheating.