Growth Behavior in Carbide of High Carbon Low Alloy Steel during Sp heroidizing Treatment

Abstract

Several studies were made in the past on the spheroidization of carbide, however, most of them were on the phenomenology of spheroidization and few of them on the mechanism.
In this paper, we have systematically investigated about the effects of chromium content, pre-treating con-dition, austenitizing temperature and cooling rate in relation to the slow-cooling-method which is used for surface-hardened roll materials. The results are summarized as follows.
1) As the chromium content increases, the volume of carbide in austenite increases, and the austenitizing temperature for complete spheroidization becomes to cover a wide range. The critical carbide number for complete spheroidization in cooling rate of 20°C/hr is found to be 5×10⁹/mm³.
2) The carbide number after spheroidization agrees completely with that in austenite. Therefore it is the retained carbide in austenite that grows during slow cooling.
3) There is a critical cooling rate. The following relationship between the critical cooling rate (R
0) and the mean particle spacing (S) is obtained. R₀= 102×10^-1/S-183.6