Effect of strain amplitude on thermo-mechanical fatigue behavior and microstructure evolution of SDHC steel

Abstract

The thermo-mechanical fatigue behavior of SDHC (4Cr5Mo2VCo) hot working die steel under different mechanical strain amplitudes (0.7%, 0.9%, 1.1%) was studied by MTS thermo-mechanical fatigue hydraulic servo testing machine. The microstructure evolution of the material during thermo-mechanical fatigue was discussed by means of scanning electron microscopy and transmission electron microscopy. The results show that the thermo-mechanical fatigue stress-strain hysteresis loop of SDHC steel is asymmetrically distributed about the origin. The larger the strain amplitude is, the larger the hysteresis loop area is, and the more serious the material is damaged. In the stress cycle response curve, when the material is subjected to high strain amplitude, the energy loss increases and the life cycle becomes shorter; as the strain amplitudes increase, the dislocation tangles weaken, and the segregated dislocations gradually disperse, resulting in a decrease in dislocation density. There are mainly M23C6, M7C3, M2C and MC(M=Cr, Mo, V, Fe)carbides in the microstructure. When the strain amplitude is small, the precipitation and growth of carbides are more obvious.

Keywords

• hot work die steel
• strain amplitude
• thermomechanical fatigue behavior
• microstructure