Microstructure evolution and micro-mechanical behavior of secondary carbides at grain boundary in a Fe-Cr-W-Mo-V-C alloy

The microstructure evolution and micro-mechanical behavior of secondary carbides at grain boundary in a Fe-Cr-W-Mo-V-C alloy for cold work roll were systematically investigated in this study. The typical microstructures at the characteristic temperature of 1240 °C, 1200 °C and 1150 °C were observed by Optical Microscope and Field Emission Scanning Electron Microscope. The hardness values of secondary carbides were predicted and measured by first-principles calculation, Vickers hardness tester and nanoindentation technique. The fracture toughness (KC) values were calculated by a method known as Indentation Microfracture. Single-pass scratch tests were carried out to investigate the micro-scale wear behavior of secondary carbides. The macroscopic pin-on-disk test was also performed. The results show that the secondary carbide at grain boundary contains secondary MC, M2C and M7C3. The formation of secondary MC and M7C3 belongs to the precipitation and growth process, while secondary M2C is the result from the growth of eutectic M2C. In the studied alloy, M7C3 is a dominant carbide in quantity, and has higher hardness than secondary M2C and the matrix, and processes the better toughness than secondary MC, whose hardness almost reaches 30 GPa, and can also effectively resist the crack initiation and propagation, which therefore makes a significant contribution to the wear resistance of the alloy.