Abstract
The time-temperature range of the formation of metastable and stable carbides and their rate of growth during the ageing of three grades of low carbon steel containing Si in the range from 0.3 to 1.52 mass% have been studied using TEM. In comparison to steels with higher amount of Si (3 mass% and more), stable carbide particles started precipitating quite early during ageing and at lower temperatures in the investigated steels. Thus, inhibition of the transition of metastable to stable carbide was negligible. The growth-rate of carbide particles for the 0.3%Si steel was appreciable; however, the same for the steels with 1.1 and 1.5%Si was slower. These findings together with the observations on sites of nucleation of the carbides have been rationalised on the basis of the role of silicon in modifying the activity coefficient of carbon in ferrite and the stability of the carbides.
