Characterization on carbide of a novel steel for cold work roll during solidification process

A novel steel for cold work roll was developed in this work. Its phase structures were determined by X-ray diffraction, and phase transformation temperatures during the cooling process were measured by Differential Scanning Calorimeter. The Fe-C isopleths of the steel were calculated by Thermo-Calc to preliminarily determine the characteristic temperatures of the different phases. Then the specimens were quenched at these characteristic temperatures. The typical microstructures were observed by Optical Microscopy and Field Emission Scanning Electron Microscopy with Energy Disperse Spectroscopy. The results show that α-Fe, MC, M2C and M7C3 precipitate when the specimen is cooled slowly to room temperature. According to the DSC curve and the Fe-C isopleths, the characteristic temperatures of the phase transformation and carbide precipitation are chosen as 1380 °C, 1240 °C, 1200 °C and 1150 °C respectively. Primary austenite precipitates at 1380 °C, then eutectic reaction occurs in residual liquid after quenching and the eutectic microstructures distribute along the crystal grain boundary. The eutectic MC is leaf-like and eutectic M2C is fibrous-like. Both of them precipitate in ternary eutectic reaction simultaneously at 1240 °C, grow together in the form of dendrite along the crystal grain boundary. Secondary MC precipitates from the austenitic matrix at 1200 °C and nucleates at the position where eutectic MC located accompanied by the dissolving of eutectic carbides. The mixed secondary M2C and M7C3 precipitate at 1150 °C. The secondary M2C is strip-like and honeycomb-like, while the M7C3 is chrysanthemum-like and maze-like.