ELECTRON THEORY ANALYSIS ABOUT THE INFLUENCE OF CR AND MN ON THE CARBIDE SPHEROIDIZATION BY HEAT-TREATMENT

It is found that the distribution of covalent electron pair number and covalent bond energy was nonuniform in carbides Fe3C, (Fe, Cr)(3)C an d (Fe, Mn)(3)C, in which the energy difference between the strongest a nd the weakest bonds is very great. A criterion of covalent bond break ing during the heat treatment of M3C pattern carbide is presented as f ollows. If the heat energy E-w from heat treatment is higher than the diffusion activation energy Q of carbon atom in gamma-Fe, the less the covalent bond energy E alpha is, the earlier the covalent bond alpha will be broken. According to the criterion, why the breaking of (Fe, M n)(3)C network was easier than that of Fe3C network and why the breaki ng of (Fe, Cr)(3)C network was more difficult than that of Fe3C networ k are explained. It is indicated that Mn promoted the carbide to be sp heroidized and Cr hindered the carbide from spheroidization during the heat treatment of carbides spheroidization.