EFFECT OF LASER HARDENING ON BENDING FATIGUE OF SEVERAL STEELS

The effect of laser hardening was studied on the bending fatigue prope rties of 3 steels, equivalent to AISI 4140, AISI 4130 and AISI 1035, r espectively. It was found that laser hardening procured a marked incre ase of the fatigue limit, 30% for smooth specimens and 60% for notched specimens, both hardened to a depth of about 0.5 mm; and over 100% fo r notched specimens hardened to a depth of 0.8 mm. Based on the concep t of local fatigue strength, quantitative analyses were carried out us ing the depth profiles of hardness and residual stresses. In conjuncti on with a yielding criterion, both the fatigue limits and the fatigue origin sites could be predicted. The results showed that for all group s but one, the increased fatigue limit could be mainly attributed to t he increased hardness by the laser hardening. In addition, the analyse s indicated that surface yielding due to too high a compressive stress could have resulted in failure in the notched specimens.