Microstructure and wear behaviour of laser hardened SAE 4130 steels

Low alloy SAE 4130 steel had been laser hardened for the microstructure, hardness and wear characterisation. An almost fully martensitic layer, with case depth of approximately 0.5 mm, was obtained by defocusing a fibre laser by 50 mm. The best results were produced by 600 W laser powers, a beam defocusing of 50 mm and a speed of 8 or 10 mm/s, where a maximum hardness of 390 HV was obtained compared to 220 HV of the base material. The laser treated surfaces presented a combination of oxides and wear behaviour distinctly superior to the bare surface. The coefficients of friction (COF) of the lasered surfaces were approximately half of the bare condition. The average COF maximum value and standard deviation was superior for the bare compared to the lasered conditions. Finally, the wear rate is three times larger in the unlasered sample compared to the laser treated ones.