Evaluation of the softening mechanisms of AISI 4340 structural steel using hot torsion test

Abstract

We performed double hot torsion deformation tests on structural steel SAE 4340. The test temperature and strain rate were kept constant at 1050 °C and 0.2 s-1, respectively; while the applied strain (0.2 and 0.4) and the time between passes (1 s, 5 s and 40 s) were varied. The samples were heated to a temperature of 1200 °C, and maintained at this temperature for 180 s (soaking) for complete homogenization. This was followed by cooling at a mean rate of 1 °C/s until the temperature of deformation was reached. Evaluation of the softening characteristics of the static and metadynamic material was made from plastic flow curves. There were similar softening characteristics for both values of tested strains, with the softened fraction increasing with time between passes, and with increasing strain. It was observed that there was refinement in the grains of the material subjected to a deformation of 0.4.

Keywords

• Hot torsion
• fraction of softening
• AISI 4340 structural steel