Effects of continuous cast section size on torsion deformation and fatigue of induction hardened 1050 steel shafts

This study investigates the influence of continuous cast section size on the mechanical performance of induction hardened parts produced from steel bars. SAE 1050 steel from commercially produced Jumbo Blooms, Blooms, Rotary Round, and Billet were hot rolled into round bars with diameters of 37-44 mm. These bars were then normalized, machined into test specimens, the gauge sections were polished, and the specimens were case-hardened by induction hardening. Torsional monotonic and fully reversed cyclic fatigue tests were conducted to study the effect of the initial continuous cast section size on deformation and fatigue behaviors. Reduction ratios in this study ranged from a low of 20.4:1 for the Billet, up to a high of 142:1 for the Jumbo Bloom. Test results indicate that the continuous cast section size has only small effects on the torsion monotonic and cyclic deformation properties and negligible effect on the torsion fatigue performance. Small differences observed in deformation and fatigue properties between the four processes are attributed mostly to the variation in case and core hardness levels caused by small differences in chemistry, particularly carbon content. Variations in sulfur content also influence ductility and fatigue behavior. At high strains, the cracks initiated in shear as longitudinal cracks for all four materials. At low strains, the cracks initiated at the surface in tension as spiral cracks due to normal tensile stresses. (C) 2010 Elsevier B.V. All rights reserved.