The role of alloying elements
The role of Cr: Chromium significantly increases the hardenability of steel and effectively improves the tempering stability of steel. As the carbon content in steel increases, carbides such as (Fe·Cr)3C and (Fe·Cr)23C are sequentially generated. These carbides have good stability, thereby reducing the overheating sensitivity of the steel and improving the steel's resistance to heat. Abrasive. Chromium has a passivating effect on the steel surface, making the steel resistant to oxidation. However, higher chromium content increases carbide heterogeneity and the amount of retained austenite. Generally, in low alloy steel, the mass fraction of chromium is 0.5% ~ 1.5%; in high toughness mold steel, the mass fraction of chromium is 4% ~ 5%; in high wear-resistant micro-deformation mold steel, the mass fraction of chromium It is 6%~12%.
The role of Mo: Molybdenum can improve hardenability and high-temperature creep strength, and its tempering stability and secondary hardening effect are also stronger than those of chromium; it can also inhibit the second type of temper brittleness caused by Cr, Mn, and Si. However, molybdenum increases the tendency of decarburization. The mass fraction of molybdenum in commonly used mold steel is 0.5%~5%.
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