Effect of Silicon on Thermal Stability of 4Cr3Mo2V Hot-Work Die Steel

Abstract

Thermal stability is one of the most basic high-temperature performance indices of hot die steel. It directly determines whether the mold can maintain good surface hardness, dimensional stability and material failure resistance for a long time under high temperature and high pressure, and then affect the service life of the material. In this paper, the effect of Si on the thermal stability of 4Cr3Mo2V hot-work die steel was studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to characterize the microstructure evolution. Thermodynamic analyses were carried out in combination with Thermo-Calc software to explore the mechanism affecting thermal stability. The results show that the thermal stability of the 1.0% Si-containing steel (referred to as 1.0 Si steel) sample exceeded that of the 0.3% Si-containing steel (referred to as 0.3 Si steel) sample. After tempering at 650 °C for 64 h, the matrices of the two tested steel samples mainly comprised large-sized M6C carbides. Additionally, the carbides in the 0.3 Si steel sample showed obvious aggregation growth, and a small number of round-like M23C6 carbides appeared, which decreased the hardness in the later stage of tempering. The average particle size of M6C in the 1.0 Si steel sample is 100–200 nm, the average particle size of M6C in the 0.3 Si steel sample is 100–400 nm, and 1.0 Si steel disperses and precipitates finer MC-type and M2C-type secondary carbides, so it has better thermal stability.