On the Main Factors Contributing to Improvment of Fatigue Strength of Induction Hardened Steel with Notches

Abstract

In the previous study, a report was given of the studies made of the fatigue strength of induction hardened steel with respect to residual stress, micro strain, and particle size. It has been found since that the micro strain and the particle size are more influencial than the residual stress on the fatigue limit of the induction hardened smooth specimen.In the present paper, a report is made of experimental investigation of the relation of hardened depth, stress concentration, residual stress, and the integral width of X-ray diffraction line, to the fatigue strength of induction hardened steel with notches.It has been found that all the specimens tested show a linear relation between the endurance limit and the integral width of X-ray diffraction line, regardless either of the stress concentration or of the hardened depth.The following similar relation of the notched specimen to that of the smooth specimen between the endurance limit and the integral width is obtained;β×σwn=σwo+C2Bnwhere σwn=The endurance limit of notched specimenβ=The strength reduction factorσwo=The endurance limit at zero integral widthC2=ConstantBn=The integral width of the notched specimenThe relation between the integral width and the endurance limit is discussed from the physical point of view by analysing the diffraction profile by Hall's method. In consequence it is clarified that the micro strain and particle size have larger influence than the residual stress, on the endurance limit of hardened steel.