Constitutive relationships of 21-4 N heat-resistant steel for the hot forging process

Abstract

The Gleeble-1500D thermal simulator was used for the isothermal compression test of 21-4N heat-resistant steel under the T range of 1273–1453 K and ε˙ of 0.01–10s−1. Using the obtained stress - strain data, various parameters of the Fields–Backofen (F-B), the modified F–B (m–F–B) equations and the modified Zerilli–Armstrong (m–Z–A) equations were calculated respectively. The constitutive equations of 21-4N heat-resistant steel based on the F–B, the m–F–B and the m–Z–A were established. Second, the predictive ability of the three constitutive equations were evaluated using the correlation coefficient (R), average absolute relative error (AARE) and the relative error (r). Third, the established model was imported into Deform-3D to simulate the valve forging process of 21-4N heat-resistant steel, and the distribution rules of the effective stress, effective strain, temperature and damage condition of the forging were analyzed. Finally, a hot forging experiment was performed on a 160t hot die forging press. Results show that the flow stress of 21-4N heat resistant steel is affected by temperature, strain rate and strain. The m–F–B and m–Z–A models can describe the rheological behavior of 21-4N heat-resistant steel, while the original F–B model has a high predictive ability, but only under low temperature, low strain rate and small deformation. The simulation process can be completed successfully, indicating that the established models can be used for the simulation study of the thermal deformation of 21-4N heat-resistant steel and all models are correct. The results can provide some important basic data for the simulation of 21-4N heat resistant steel in the plastic deformation process.

Keywords

• Fields–Backofen model
• Zerilli–Armstrong model
• 21-4N
• Hot deformation behavior
• Constitutive model
• Finite element simulation