Impact toughness of a gradient hardened layer of Cr5Mo1V steel treated by laser shock peening

Abstract

Laser shock peening (LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts. Cr5Mo1V steel exhibits a gradient hardened layer after a LSP process. A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer. Assuming a linearly gradient distribution of impact toughness, the parameters controlling the impact toughness of the gradient hardened layer were given. The influences of laser power densities and the number of laser shots on the impact toughness were investigated. The impact toughness of the laser peened layer improves compared with an untreated specimen, and the impact toughness increases with the laser power densities and decreases with the number of laser shots. Through the fracture morphology analysis by a scanning electron microscope, we established that the Cr5Mo1V steel was fractured by the cleavage fracture mechanism combined with a few dimples. The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.

Characterization of a Laser Surface-Treated Martensitic Stainless Steel

“…Clearly the impact energy tended to increase between the heat input range of 15–30 J·mm −2 ( Figure 15 ). This observation was in accord with previously reported results although that the laser type was a Q-switched pulsed laser, in contrast with the present continuous laser [ 31 ]. The reason for this increase was due to the residual compressive stress induced by a laser surface treatment which was able to restrain the growth of the crack.…”

Crack Propagation Behavior of Impact Fracture in Case Hardening Steel Subjected to Combined Heat Treatment with Excess Vacuum Carburizing and Subsequent Induction Hardening

“…Studies on the effect of residual stress on toughness are limited compared to fatigue fracture studies. It has been reported that compressive residual stress can effectively contain crack propagation and improve fracture toughness, as measured by Shea,23) Chaundhury, 24) Dejun et al 25) and Xia et al 26) In this study, as γ R b decreased, σ b tended to decrease (Fig. 14), and the crack propagation seemed to be suppressed.…”