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 , , , 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.
Highlights
Ultra-high-strength (UHS) steel is mainly used for load-bearing components of large ships, bridges, power station equipment, mining machinery, and other large welded components, and the forming of profiles, sheet metal or parts often undergoes a hot deformation or hot working process
UHS steel is used as the research object in this work, the response of its flow stress to strain rate and deformation temperature is obtained by isothermal compression tests, and the constitutive equation considering strain-dependent constants is derived, the reliabil3 of 16 ity discussion is carried out, the applicability of the plastic instability criteria is evaluated, an accurate processing maps is drawn, and the optimum coupling of process parameters such as strain rate, deformation temperature, and strain is obtained
The flow stress decreases with the increase of the deformation temperature, and increases with the increase of the strain rate, while a similar phenomenon was reported by Xu et al [24] and Chen et al [25]
Summary
Ultra-high-strength (UHS) steel is mainly used for load-bearing components of large ships, bridges, power station equipment, mining machinery, and other large welded components, and the forming of profiles, sheet metal or parts often undergoes a hot deformation or hot working process. Ε, σ and T are the strain rate sensitivity, strain rate, flow stress, and deformation temperature, respectively All these criteria based on the Lyapounov function are necessary conditions for the identification of stable flow regimes, and it is necessary to use these criteria to avoid instabilities and to impose considerable restrictions on the useful ranges of processing parameters. UHS steel is used as the research object in this work, the response of its flow stress to strain rate and deformation temperature is obtained by isothermal compression tests, and the constitutive equation considering strain-dependent constants is derived, the reliabil of 16 ity discussion is carried out, the applicability of the plastic instability criteria is evaluated, an accurate processing maps is drawn, and the optimum coupling of process parameters such as strain rate, deformation temperature, and strain is obtained. Thermal simulation machine was used for isothermal compression tests and the specimen size was Φ 8 and mm Methods
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