CREEP AND CREEP RATE CURVES OF A 10CR-30MN AUSTENITIC STEEL DURING CARBIDE PRECIPITATION

The effect of carbide precipitation on creep and creep rate curves was investigated for 10Cr-30Mn austenitic steel containing 0.003 to 0.55 wt pet carbon. After solution annealing, the specimens were subjected to creep testing at 873 K for up to 30 Ms (8300 hours). In the low-carbon steels containing below 0.1 wt pet carbon, where carbide precipitation scarcely occurred, the decrease in creep rate with time in the transient creep region was described by log e = A - (1/3) log t, where A is a constant depending on stress and carbon concentration. On the other hand, in the high-carbon steels containing above 0.2 wt pet carbon, where extensive precipitation of M(23)C(6) occurred, the creep rate decreased significantly at long times above 3 to 5 ks (1 hour), deviating from the preceding equation for the low-carbon steels. The Johnson-Mehl equation with the time exponent n = 2/3 provided a reasonable approximation for the significant decrease in creep rate at long times. This resulted from a stress-induced precipitation of M(23)C(6) on dislocation lines produced by creep deformation. The rate constant of the Johnson-Mehl equation depended on carbon concentration but not on stress levels examined.