Flow curves and microstructure of K107 tool steel subjected to compression tests at elevated temperatures

Hot compression tests were performed on K107 cold-work tool steel at various temperatures in range of 800-1200 °C and strain rates of 0.001-1 s−1. The microstructural evolutions including dynamic precipitation (DP) of carbide particles and dynamic recrystallization (DRX) mechanism were investigated by optical and FESEM-EBSD observations. The peak strain of flow curves showed uncommon increase within the temperature range of 900-1100 °C and strain rates of 0.001-0.01 s−1. Optical microscopy observations and image analysis quantifications showed that the uncommon behavior is associated with the formation of fine carbides by DP. At 1100 °C, the rate of DP reaches a maximum and then decreases at higher temperatures. Microstructural observations implied that DP could retard DRX at 900-1100 °C and strain rates of 0.001-0.01 s−1. The discontinuous DRX (DDRX) only appeared at 800 °C as the formation of grain boundary nucleation. At temperature range of 900-1100 °C, intensive DP on the grain boundaries could avoid DDRX. The continuous DRX (CDRX) was found as the major mechanism of dynamic softening at 900-1100 °C. It was found that the subgrain growth and progressive rotation lead to the transformation of sub-boundaries into high angle grain boundaries and propel CDRX.