Brittleness of Cr?Mo?V steel resulting from tempering

Abstract

1. 12KhMF and 15Kh1M1F steels are susceptible to embrittlement after tempering at 500–700°C. The decrease of the impact strength is accompanied by an increase of strength and of the coercive force—the result of secondary hardness. 2. Quenched and normalized Cr−Mo−V steels become brittle as the result of tempering. Annealing prevents embrittlement during tempering of 12Kh1MF steel. 3. The degree of embrittlement induced by tempering depends on the structure of the steel before tempering. Intermediate structures favor embrittlement during tempering, while a ferritic-pearlitic structure prevents embrittlement. 4. The main reason for embrittlement during tempering of boiler-plate steels of the pearlitic type is carbide formation during the decomposition of metastable intermediate structures. 5. The structure of the products of intermediate transformation depends on the austenization temperature and the cooling rate after austenization. The highest degree of embrittlement occurs in the presence of structures of the Widmanstatten type. 6. The formation of the Widmanstatten structure prevents the decrease of the austenization temperature and the increase of the cooling rate after austenization to 500/min and above and also decreases the cooling rate below 20/min. These facts decrease the susceptibility of the steel to embrittlement during tempering.