Effect of Silicon on the Kinetics of Nb(C, N) Precipitation during the Hot Working of Nb-bearing Steels.

The effect of Si on the rate of Nb(C, N) precipitation was investigated by using fractional softening measurements. Compression specimens, with diameters of 7.6 mm and lengths of 11.4 mm, were prepared from four Nb microalloyed steels containing a range of Si concentrations from 0.01 mass% to 0.41 mass%. Double-hit compression tests, with a strain of 0.3 for each pass and a strain rate of 0.1/sec., were employed. A solution heat treatment was applied immediately prior to each test. It was found that the rate of Nb(C, N) precipitation in hot deformed austenite increases with Si concentration. This phenomenon is attributed to the increases in the activities of C and N that result from Si addition.