TEMPER BRITTLENESS OF COMPLEX ALLOY STRUCTURAL-STEELS

Alloying of steel with a large quantity of carbide-forming elements leads to an increase in the resistance of martensite to tempering and precipitation of special carbides at higher tempering temperatures. The embrittlement of steels of the 20Kh3MVF and 25KhMF type during tempering at 500-650 degree , which is due to precipitation of special carbides in the boundaries of prioraustenite grains, occurs by a mechanism of the irreversible temper brittleness type. Steels of the 20Kh3MVF type should not be tempered at temperatuares below 680 degree , which ensure a yield strength not over 60 kgf/mm**2. A higher strength produced by lowering the tempering temperature is undesirable, since it may lead to embrittlement.