1989 Volume 75 Issue 3 Pages 517-522
Plain bending fatigue strength has been investigated about the surface layer strengthened hot rolled steel sheets produced by intercritical rolling of cast composite ingot which in the surface layers, about 0.01%Nb-0.1%V are added on the 0.14%C-0.5%Mn base composition. Following results are obtained.
(1) The ratio of fatigue limit to tensile strength becomes as high as about 0.67 in the polished specimens of 20% surface fraction. This value is very high compared with that of conventional uniform hot rolled steel sheets.
(2) Fatigue limit of the 8% prestrained specimen is 4 kgf/mm2 lower than that of the non-strained at the 20% surface fraction. This decrease is caused by very low work-hardening property and residual tension stress in the surface layers.
(3) It is thought that fatigue limit of surface layer strengthened hot rolled steel sheets is determined by that of surface or inner layer at large or small surface fraction each. At this transient region of surface fraction (1020%), the ratio of fatigue limit to tensile strength becomes maximum.
