Research and engineering application of DED laser cladding repair for steam turbine XM-25 alloy LP blades

High-strength martensitic precipitation-hardening stainless steel XM-25, characterised by its high strength, high hardness, and good workability, has been utilised in engineering as the low-pressure last stage blade of steam turbines. However, it is beset by the issue of water erosion. This paper focuses on the restoration of large blade workpieces made of XM-25 material, employing directed energy deposition (DED) laser cladding with parent material powder. The parameters for laser cladding include laser power of 1300 W, movement speed of 500 mm/min, and powder feed rate of 15 g/min. The performance of the XM-25 alloy after laser cladding restoration is evaluated through non-destructive testing (PT, RT), tensile testing, hardness testing, metallographic analysis, fracture morphology analysis, residual stress measurement, and high-cycle fatigue testing. Results indicate that the material after laser cladding exhibits an ultimate tensile strength exceeding 1200 MPa, a yield strength above 1050 MPa, microhardness above 415 HBW, residual stress at approximately 30% of the base material, and a fatigue limit of 586.25 MPa - 95% higher than the base material. These findings confirm the effectiveness of the proposed DED laser cladding method for restoring XM-25 turbine blades, offering a viable engineering solution for mitigating and repairing water erosion in steam turbine components.