Study on residual stress evolution of laser cladding low chromium carbon alloy on low-pressure rotor

Abstract

The in-service behavior of low-pressure rotor components can potentially be impacted by the residual stress distribution of cladding layers. To predict the evolution of residual stress in a multi-pass multi-layer cladding, a thermal-metallurgical-mechanical model that incorporates the effect of solid-state phase transformation (SSPT) is proposed. In the multi-pass case, high longitudinal tensile stress peaks were generated in the former pass, reaching 588 MPa. With multi-pass deposition, the maximum transverse and longitudinal stresses in the substrate increased to 282 and 523 MPa, respectively, which were adjacent to the heat-affected zone (HAZ). In the multi-layer case, multiple thermal cycles had a significant effect on increasing the longitudinal stress of the substrate plate. The maximum of longitudinal stress reached 634 MPa. In the case of the multi-pass multi-layer, the fluctuation of residual stress was generated inside and on the top surface of the cladding layers. The transverse tensile stress changed from 110 to 10 MPa, and the longitudinal tensile stress decreased from 385 to 173 MPa. The interval of high tensile stress was related to the hatch space of the laser beam. In the simulation of the cladding process on a low-pressure rotor, the residual-stress distributions were not uniform along the cladding sequence. Owing to the heat accumulation and scanning strategy, a compressive stress zone adjacent to the endpoint of the cladding sequence, emerged in the cladding layers and substrate. From the simulation results, to estimate the high residual stress and ease the non-uniform residual stress, the laser scanning strategy should be changed in the actual manufacturing process.