METHOD FOR HEAT TREATMENT OF FORMED FORGED PIECES Russian patent published in 2008 - IPC C21D1/56 C21D9/30 

FIELD: metallurgy, namely heat treatment of forged and formed parts operating in condition of sign variable loads.

SUBSTANCE: in order to improve fatigue strength of part by 15 - 20%, forged piece after heating is cooled till 200°C in quenching medium at rate exceeding critical one and then without further cooling it is subjected to tempering. At time moment of heating for tempering, structure contains dislocation (acicular) martensite and austenite. From acicular martensite ε-carbide phase and ferrite are separated. Residual austenite is converted to dislocation martensite decomposed by ε-carbide phase and ferrite. At further heating ε-phase is transformed to cementite of the same fraction size. In zone of maximum stress action, steel structure contains highly dispersed carbide phase and ferrite.

EFFECT: improved ultimate fatigue strength of parts.

1 tbl, 3 dwg, 1 ex