Welding Repair Of Blade Cracks And Wear Defects In Hydraulic Turbine

Whether it is to reduce the frequency of cracking of the blades, or to improve the repair effect of the repair welding of the blade cracks, the crack of the turbine blade has been plagued by the hydropower station. At present,most of the power plants use manual arc welding to repair the surface defects of turbine blades, but the effect is not satisfactory. Therefore this paper attempts to study the use of Gas Tungsten Arc Welding (GTAW).In this paper, two kinds of common hydraulic turbine blade manufacturing materials: ZG20SiMn low alloy steel and ZGOCr13Ni5Mo low carbon martensite stainless steel as base material, and its surface mechanical processing out of holes:as a blade crack. The use of GTAW were welded joints. Through the joint appearance inspection, metallographic analysis, micro morphology analysis and micro hardness analysis, determine the optimal welding parameters such as welding current, gas flow and protection, preheating temperature and post welding tempering temperature, etc.(1) Using GTAW to repair the material of ZG20SiMn steel, the heat affected zone of the welded joint is easy to appear the hard martensite structure and increase the cracking tendency.The microstructure of martensite in the heat affected zone can be reduced, and the microstructure of the joint can be improved by using the appropriate pre-welding temperature, welding current and heat treatment;(2) Using GTAW to repair the material of 0Cr13Ni5Mo stainless steel, welded found weld by metallurgical defects caused stress concentration increases the cracking tendency and the weld near the precipitation of brittle and hard sigma phase, destruction of the mechanical properties of the joints. The study, through the use of preheating before welding, front and back through the gas protection, prevent welding hot near the fusion line, reducing cooling degree, thereby reducing the sigma phase precipitation; through the tempering temperature range between 550℃ to 650℃ in the heat treatment process, can best reduce residual stress. At the same time, in the process of post weld heat treatment weld will precipitate M23C6 carbides, increase the cracking tendency, leading to joint pass rate.