In order to develop the high-temperature forging process of high-quality 20MnCr5(SH) gear steel, according to the physical characteristics of high-temperature hot deformation of 20MnCr5(SH), the single pass hot pressing test was carried out in the temperature range of 930–123 °C and the strain rate range of 0.002–2s−1 by using a Gleeble-1500D thermal simulator. The stress-strain curve of 20MnCr5(SH) was analyzed and confirmed by microstructure analysis. The dynamic recrystallization occurred, and the constitutive equation of 20MnCr5(SH) high temperature flow stress was established. Considering that the traditional Arrhenius constitutive equation does not consider the effect of strain on the constitutive equation, a strain modified Arrhenius constitutive equation is proposed. The results show that the correlation is 0.9895 and the average relative error is 8.048%, which verifies the stress prediction ability of the strain modified constitutive equation. According to the dynamic material theory and instability criterion, the processing maps of 20MnCr5(SH) are obtained. It is therefore considered that 20MnCr5(SH) is most suitable for thermoplastic processing at strain rate of 0.05–1s−1 and temperature of 1030–1100 °C.
Aiming at the aging problem of insulating silicone rubber for new energy vehicles, this paper studies the equations of the aging of silicone rubber and its dielectric properties based on first-principles calculations. First, through the analysis of the microscopic mechanism of silicone rubber aging, the equations of the aging of silicone rubber and the rupture of the molecular main chain is obtained. Then the equations of silicone rubber molecular length and dielectric constant are solved by density functional theory. Ultimate, a molecular chain scission model of silicone rubber was built, and the micro-dielectric relationship was extended to the macroscopic level. The equation of the norm molecular length of silicone rubber and the dielectric constant is obtained. It provides an important theoretical basis for the aging detection of insulating silicone rubber for new energy vehicles based on electromagnetic waves.
In order to optimize the thermal forging process of 37CrS4 special steel, single-pass thermal pressing tests are conducted, and a strain compensation Arrhenius constitutive equation is proposed based on the stress-strain curves of 37CrS4 at the temperature of 900-1100 • C and the strain rate of 0.1-10 s −1 . The stress values calculated from the equation are in good agreement with the counterparts in the thermal simulation compression test. The high correlation between the calculated and experimental data verifies the correctness of the strain compensation based on Arrhenius constitutive equation. According to the dynamic material model and instability criterion, the processing maps of 37CrS4 are established. It is concluded that 37CrS4 is more suitable for thermal working at a strain rate of 0.1-0.37 s −1 and temperature of 1000-1100 • C.
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