Technique Research Of Laser Cladding Remanufacturing On Steam Turbine Rotor Shaft

Turbines are running at high temperatures and high pressures for a long time and the rotor shaft is easy to wear,which restricts the service life of the turbine rotor.Recently,with the development of laser technology,laser cladding technology has been reported to repair the damaged turbine rotor shafts,but the related researches are not enough.Therefore,turbine rotor shaft is taken as the research object,and the basic processes of laser cladding remanufacturing technology on turbine rotor are studied in this thesis.(1)Three different alloy powders named S1?S1L and S1 M are made for laser cladding,and the operation conditions of 28 CrMoNiV steam turbine rotors.Three types of cladding layers are prepared on the 28 CrMoNiV substrate by an optimized laser cladding parameter.The best cladding process of S1 powder is: laser power of 2100W-2700 W,scanning speed of 3mm/s,powder feed rate of 12g/min;The best cladding process of S1 L powder is: laser power of 2100W-2400 W,scanning speed 3mm/s,powder feed rate of 12 g/min;The best cladding process of S1 M powder is: laser power of 2700W-3000 W,scanning speed is 3mm/s,powder feed rate of 20 g/min.The best lap ratio of the three powders is 40%.(2)The microstructures of laser remanufacturing of cladding layers and heat affected zones are studied.The results show that the coatings contain the ferrite grains and eutectic phase.An typical laser cladding microstructure is observed.The mainly microstructure of the heat affected zone is martensite,and ?-ferrite is observed in the martensite,as a bad microstructure,it is relate to cracks initiate and propagate.The condition of ?-ferrite's production is analyzed by COMSOL and “multilayer cladding” is used to eliminate the ?-ferrite in martensite.(3)The mechanical properties of the coatings and the heat affected zones are studied.The results show that the average tensile strength of composite specimen(cladding material + substrate material)is 1246 MPa,which is 63% higher than that of the substrate;the average impact energy is 32.0J,which is 2 times higher than that of the substrate.The average tensile strength of single-cladding HAZ is 834 MPa,which is 9% higher than that of the substrate;the average tensile strength of three-layer cladding HAZ is 927 MPa,which is higher than the single-layer HAZ and the plasticity is increased,numerically closer to the property of substrate.(4)A wearing turbine rotor is remanufactured by laser cladding with the S1 M alloy powder for the S1 M coating,and the 28 CrMoNiV rotor reveals a similar hardness.The mechanical properties are tested.There is defect free in the coating with an average hardness of coating surface is 687 HL.The highest of total indicated runout of remanufactured zone is 6.25?m,corresponding to the specification.