Influence of Pre-Torsion Strengthening on the Fatigue Properties Of 45 Crnimova Ultra-High Strength Steel

Abstract

Aiming at the demand for fatigue life improvement of 45CrNiMoVA ultra-high strength steel shaft parts, a pre-torsion strengthening process using a combination of two different angles before and after was proposed based on the mechanisms of strain hardening, fine grain strengthening and dislocation strengthening. Through surface integrity measurement, torsional fatigue test and fatigue fracture characterization of the specimens, the main surface integrity factors affecting the fatigue life of the pre-torsion strengthening were analyzed. The results indicated that the grain size was refined and the plastic deformation was increased by the two-angle pre-torsion strengthening compared with the single-angle pre-torsion strengthening. The obtained surface residual compressive stress sx was the main factor affecting the fatigue life of pre-torsion strengthening, and the change in pre-torsion angle results in a significant secondary strengthening layer in the subsurface layer of the material. The increase of the second pre-torsion angle will reduce the fatigue life, while the increase of the first pre-torsion angle will increase the fatigue life. In summary, the study of the pre-torsion strengthening process with different combinations of angles has a guiding significance for improving the fatigue life of ultra-high strength steel.

Keywords: Ultra-high strength steel, Pre-torsion, Fatigue properties, surface integrity, fracture orientation