PHASE-COMPOSITION OF 1.5CR-1.0MO-0.3V ROTOR STEEL AS A FACTOR OF COOLING RATE FROM AUSTENITIC REGION

Carbide reactions in 1.5Cr-1.0Mo-0.3V steel are investigated at variou s thermal treatments at 550-650 degrees C. The cooling rate control wa s carried out by cooling the environment. Metal tempering was conducte d in the range 650-720 degrees C for up to 100 h. It is shown that the rate of preliminary cooling from the austenitic region has the princi pal effect on the carbide reaction nature. At rapid cooling (martensit e structure) the major carbide reaction during tempering and ageing is M(3)C --> M(7)C(3) whereas for cooling rate decreasing the reaction M (3)C --> M(23)C(6) prevails. Tempering and ageing change the quantitat ive characteristics of the carbide state without having an effect on t he major mechanism of transformation. The carbide reaction character i s compared with metal properties under the same time-temperature condi tions and the correlation between the structural state and metal servi ce properties is examined.