Evolution of carbides in cold-work tool steels

Abstract This study aimed to present the complete history of carbide evolution in a cold-work tool steel along its full processing route for fabrication and application. A sequence of processes from cast to final hardening heat treatment was conducted on an 8% Cr-steel to reproduce a typical commercial processing route in a small scale. The carbides found at each process step were then identified by electron diffraction with energy dispersive spectroscopy in a scanning or transmission electron microscope. After solidification, MC, M 7 C 3 and M 2 C carbides were identified and the last one dissolved during hot compression at 1180 °C. In a subsequent annealing at 870 °C followed by slow cooling, M 6 C and M 23 C 6 were added, while they were dissolved in the following austenitization at 1030 °C. After the final tempering at 520 °C, fine M 23 C 6 precipitated again, thus the final microstructure was the tempered martensite with MC, M 7 C 3 and M 23 C 6 carbide. The transient M 2 C and M 6 C originated from the segregation of Mo and finally disappeared due to attenuated segregation and the consequent thermodynamic instability.