Spot Weldability and Fatigue Property of Hot-Rolled High-Strength Sheet Steels for Wheel Usage

Spot weldabilities and fatigue properties of hot-rolled high strength sheet steels for wheel use, with tensile strength of 45 to 60 kgf/mm² were investigated. The specimens used were phosphorus-niobium bearing steel (P-Nb steel), phosphorus-manganese bearing steel (P-Mn steel) and conventional carbon-manganese bearing steel (C-Mn steel). The P-Nb steel and the P-Mn steel have been developed by the authors for wheel rim use and wheel disc use, respectively.

The P-Nb steel showed higher static strengths in welded joints compared with other steels, which is important for steels used for rims. Fatigue strengths of spot welded joints were compared using fracture mechanics. It is confirmed that application of fracture mechanics is a powerful method to assess fatigue strength of various types of spot welded joints.

High fatigue strength after strain-aging is required for steels used for wheel disc use. The P-Mn steel had better fatigue strength in the strain-aged condition than the conventional C-Mn steel both in out-of-plane bending mode and in 0-tension mode. The difference in the fatigue properties between the two steels was considered to be due to the difference in deformation behavior after strain aging treatment.