Yongshun Yang

Isothermal Compressive Superplastic Deformation and its Constitute Equation of Structural Steel and Tool Steel

The microstructure of structural steel (40Cr) and tool steel (T10A) samples and its surface are respectively fined through salt-bath cyclic quenching (SCQ) and high frequency hardening (HFH), then the superplasticity is studied under isothermal compressive superplastic deformation condition. The experimental results indicate that the true stress-strain curves of 40Cr and T10A steel are separately shown to take place obvious superplastic flow characteristic at the temperature of 730-770 °C 710-770°C and at the initial strain rate of 1.7-50×10 -4 s -1 2.5-8.3×10 -4 s -1 , its strain rate sensitivity are respectively 0.30-0.38 and 0.32-0.50, the steady superplastic flow stress are respectively 60-70 MPa and 35-45 MPa, the superplastic flow activation energy are respectively 198-217 KJ/mol and 182-195 KJ/mol, and they are close to α-Fe grain boundary self-diffusion activation energy. The compressive superplastic constitute equations of both steels are correspondingly set up. Due to the finer microstructure of HFH, it appears higher strain rate sensitivity value, smaller the steady superplastic flow stress and the superplastic flow activation energy, so it has better capability of superplastic deformation.