Enhanced carbon diffusion efficiency and work hardening effect of AISI 9310 steel via pre-laser shock peening

Abstract

By using pre-laser shock peening (pre-LSP), low temperature carburizing (LC) is successfully applied in AISI 9310 steel to obtain a carburized layer that is approximately 34 μm thickness, which is thicker than the carburized layer achieved by LC alone of about 10 μm. Pre-LSP enhances diffusion mechanism including two factors: structural and kinetic. Structurally, LSP induces density dislocation such as dislocation walls (DWs) that evolve into grain boundaries (GBs), thereby providing paths for accelerating carbon atom diffusion. This transformation results in an increase in Kernel average misorientation (KAM), high angle GBs (HAGBs), and deformed grains. Kinetically, LSP lowers activation energy, making it easier for carbon to diffuse in BCC ferrite. Furthermore, the LSP-LCed sample exhibits a work hardening depth of 400 μm, which is significantly higher than the 60 μm work hardening depth of LCed sample. The main composition of carburized layer is hard Fe3C phase, which exists mostly along α-Fe GBs. The compound work hardening effect observed in the LSP-LCed sample is attributed to plastic deformation induced by pre-LSP and the formation of hard Fe3C phase via LC. This study presents a new method for strengthening contact component with interfacial damage requirements, such as wear and contact fatigue resistance.