Materials, heat treatment, technology, design manufacture

摘要

A new cast hot-working die steel(CHD steel) has been developed, through optimization of alloy composition design, alloying, inoculation and modification. The steel shows better hardenability and lower thermal sensibility, and its microstructure tempered at 450°C, consist of lath martensite, bainite, a little amount of retained austenite and carbides, so it has good properties of strength and toughness. The martensite with high-densely dislocation, is of high thermal stability, not liable to recovery and recrystallize, and even remains lath shape when tempering at 650°C. It is also found that a great number of stable carbides Mo{sub}2C and V{sub}4C{sub}3 precipitated during tempering and servicing reveals precipitated hardening. the new cast hot-working die steel gives higher thermal-fatigue resistance with longer initiation life, slower propagation rate, less severe craze, higher resistance to oxidation and softening. Compared with that of conventional 5CrMnMo forged steel, the use life of the die made of the new cast steel was increased by a factor of 40%- 100%. This die has the following advantages: higher resistance to thermal fatigue, fewer machining allowance, no needing forging, higher economic benefit and wider application prospects.