Analysis of Dynamic Mechanical Behavior of Hot Formed Steel

The tensile tests of hot formed steels with strength grades of 1500, 1800 and 2000 MPa at strain rates of 0.001~500 S⁻¹ were carried out by using electronic universal testing machine and Zwick high speed tensile testing machine respectively. The strength indexes of three experimental steels, the plastic elongation strength R_p0.2 and the tensile strength R_m are quantitatively analyzed in combination with dynamic factors. The results show that the strain rate sensitivity of the three experimental steels decreases with the increase of material strength grade. The strain rate sensitivity of R_P0.2 of the three experimental steels is higher than that of R_m. Both R_P0.2 and R_m of the 1500 MPa test steel show obvious strain rate sensitivity, and the strain rate sensitivity is the highest in the strain rate range from 100 to 500 s⁻¹. R_m of the 1800 MPa test steel and R_P0.2 and R_m of the 2000 MPa test steel have no obvious strain rate sensitivity, indicating that with the increase of material strength grade, the softening effect caused by the adiabatic temperature rise gradually counteracts the strain rate strengthening effect. The plasticity index of the test steel after fracture shows obvious strain rate sensitivity at strain rates from 1 to 500 s⁻¹, mainly due to the obvious effect of adiabatic temperature rise. The phenomenon of adiabatic temperature rise cannot be ignored at high strain rates.