Hot Deformation Constitutive Equation and Plastic Instability of 30Cr4MoNiV Ultra-High-Strength Steel

Abstract

In this work, the hot deformation behavior of 30Cr4MoNiV ultra-high-strength steel is investigated by isothermal compression tests using the Gleeble-3500 thermal simulation machine (Dynamic Systems Inc., New York, NY, USA) at a temperature range of 1173–1373 K under the strain rate of 0.01–10 s−1. A constitutive equation with strain-dependent constants and processing maps suitable for 30Cr4MoNiV ultra-high-strength steel are established. The results show that the combination of the hyperbolic sine function and the Zener-Hollomon parameter can accurately represent the influences of deformation temperature, strain rate, and strain on the flow stress of the 30Cr4MoNiV ultra-high-strength steel. The applicability of plastic instability criteria such as m, m˙, S, S˙ and the instability parameter ξ are analyzed, the stability and instability regions are clarified accurately, and the optimized processing regions are given in the stability regions. The optimized regions are verified by the uniform equiaxed grains, and the plastic instability is validated by dynamic strain aging and the microstructure of the voids.

Keywords

• ultra-high-strength steel
• hot deformation
• constitutive equation
• processing maps
• plastic instability