Effect of shot peening on the fatigue resistance of laser surface melted 20CrMnTi steel gear

The effect of combined laser surface melting and shot peening (LSMSP for short) on fatigue resistance of 20CrMnTi steel gear is investigated in this paper. After laser surface melting (LSM) treatment to gear tooth flanks, gear was treated by shot peening (SP) with different peening intensities. The residual stresses, full width at half maximum (FWHM), microhardness, retained austenite volume fraction and surface roughness of the LSMSP gear were measured. The Forschungsstelle für Zahnräder und Getriebebau (FZG) back-to-back spur gear test rig was used for fatigue experiments. Experimental results showed that compressive residual stress in the LSMSP gear tooth firstly increased to a maximum value and then decreased to stress state of the substrate. With improving strength of shot peened specimen, maximum values and depths of compressive residual stresses increased in the LSMSP gear. Owing to grain refinement, FWHM of the LSMSP gear tooth was broadened obviously along the direction of depth. Through LSMSP treatment, the retained austenite volume fraction of the LSMSP gear was lower than 5% in the LSMSP surface layer. The microhardness of the LSMSP gear tooth has been raised above 20%. The fatigue and wear resistance of the LSMSP gear was much better than that of the LSM and SP gears.