Microstructure evolution of hot work tool steel 5CrNiMoV throughout heating, deformation and quenching

Abstract

The microstructure evolutions of hot work tool steel 5CrNiMoV throughout the heating, deformation and quenching procedures are investigated. Microstructures of the heated, compressed, and cooled specimens are observed by high-temperature confocal laser scanning microscope (HT-CLSM), optical microscope, and electron backscatter diffraction (EBSD). The measurement shows that the austenite transformation starts at 730 °C and ends at 765 °C. After the temperature exceeds 850 °C during the heating, the in-situ observed grains are first refined by static recrystallization (SRX) and then grow with the holding time, accompanied by the grain boundary gradually become straight. The microstructures of hot compressed specimens indicate that the dynamic recrystallization (DRX) fraction increases with growing temperature and strain, in which discontinuous dynamic recrystallization (DDRX) is the main mechanism of DRX. The grain boundaries formed by DDRX are serrated and have a larger curvature, which are different from those formed by SRX and subsequent grain growth. The lath martensite generated from the water quenching following the compression tends to align parallel to each other in the prior austenite grain (PAG). It comprises the packets containing the elongated blocks with the same habit planes.