Analysis on hot deformation and following cooling technology of 25Cr2Ni4MoVA steel

Abstract

The true stress–true strain curves of 25Cr2Ni4MoVA steel were obtained by uniaxial compression experiments at 850–1200 °C in the strain rate range of 0.001–10.0 s⁻¹. And the dynamic continuous cooling transformation curves were obtained at the cooling rate range of 0.5–15.0 °C s⁻¹ from the austenitization temperature of 1000 °C to the room temperature by pre-strain of 0.2 as well. The power dissipation map and the dynamic continuous cooling transformation diagram were constructed based on the data provided by these curves. Compared with the optical micrographs of the compressed samples, the full dynamic recrystallization region is located between 1000 and 1200 °C and at the strain rate range from 0.01 to 10.0 s⁻¹ with the power dissipation efficiency not less than 0.33. In the full dynamic recrystallization region, the power dissipation efficiency increases and the dynamic recrystallization activation energy decreases with the temperature increasing. With the strain rate decreasing, the power dissipation efficiency increases firstly and then starts to decrease as the strain rate is less than 0.1 s⁻¹, and dynamic recrystallization activation energy changes on the contrary. According to the dynamic continuous cooling transformation diagram, slow cooling is a better way for the hot-deformed piece with large size or complex shape to avoid cracking as the temperature of the piece is lower than 400 °C, and different cooling ways can be used for the hot-deformed piece with small size and simple shapes to obtain certain microstructure and meet good compressive properties.