1998 Volume 84 Issue 6 Pages 446-451
The effects of alloying elements and carbon potential on the amount of retained austenite in carburized steels were investigated. First, the Ms temperature of high carbon steels was measured by means of a dilatometer. In high carbon region, the contribution of carbon content to Ms temperature became smaller than that of medium carbon steels, while the contribution of Mn, Cr and Mo which are substitutional elements became larger.
Next, 1.0mm thick specimens were gas-carburized at 1203K for 108ks to reach equilibrium, quenched into oil and tempered at 443K for 7.2ks. The equilibrium carbon content, which increased with increasing Mn, Cr and Mo content but decreased with increasing Si and Ni content, could be calculated from carbon potential in atmosphere and interaction parameters of carbon on these alloying elements. The amount of retained austenite could be calculated from the Ms temperature of high carbon steel as a function of the equilibrium carbon content, and a parameter which should be determined by quenching and tempering condition.
These results indicate that it is important for calculation of retained austenite content of carburized steels to take into account the change in contribution of alloying element to Ms temperature in high carbon region and the change in equilibrium carbon content due to chemical composition of steel.
