18CrNiMo7–6 gear steel was selected as the material and laser shock peening was primarily used as a pretreatment prior to gas carburizing

the aim of which is to improve the efficiency and further enhance the properties after gas carburizing. Optical microscope

surface roughness tester and Vickers micro-hardness tester were used to investigate the surface characteristics after laser shock peening and gas carburizing. The results show that under the same gas carburizing process of 910℃+4h

gas carburizing efficiency can be effectively enhanced by the pretreatment of laser shock peening

the carburizing layer increases from 1.24mm to 1.49mm

and the carburizing efficiency increases by around 20%. At the same time

the surface hardness is increased from 680HV0.05 to 700HV0.05. Especially

laser shock pretreatment can make the cross sectional hardness gradient decreased gentlely

thus enhance the bonding force between carburized layer and matrix. The mechanism why laser shock peening has significant effect on gas carburizing is as below: the surface rough increases from 0.12μm to 0.57μm

a deformation layer with thickness of about 220μm was formed after laser shock peening

and with much finer grain size. All the above factors are beneficial for absorption and diffusion inward of carbon atoms.