High-alloy martensite in the surfacing layer of hot-rolling supporting rollers during the tempering process

Abstract

Flux-cored wire for surfacing hot-rolling supporting roller was developed and the specimens of surfacing layers were tempered at different temperatures. In order to characterize the high-alloy martensite in the surfacing layer during the tempering process, the microstructure and phase structure of the surfacing layer were analyzed, respectively. The nanoindentation hardness and phase transformation temperature of the high-alloy martensite were measured. The crystal structure of each phase was analyzed. The results show that the microstructure of the as-welded surfacing layer consists of martensite and retained austenite. Meanwhile, the high-alloy martensite with white reticular morphology is distributed on the crystal boundary. With increase of the tempering temperature, the high-alloy martensite disappears gradually, and the black reticular microstructure finally appears when the tempering temperature is 650°C. The high-alloy martensite, whose average nanoindentation is 14.33GPa, shows bulk morphology in field emission scanning electron microscope and starts to dissolve in the matrix at 420°C. The contents of the alloy elements in the high-alloy martensite are higher than those in the normal one. However, the former decrease rapidly after tempering at 650°C. The high-alloy martensite shows the body-centered tetragonal crystal structure, and the c-axis of the high-alloy martensite is longer than that of the normal one.