Research On Repair Of Low Press Urelast Stage Blade Of Steam Turbine By Gas Tungsten Arc Weld

The damage of low pressure last stage blades is a common phenomenon of steam turbine machines in many powder stations,which does not result in the decrease of efficiency of generating set and hence reducing the economic benefits,but also influence the secure operation when serious fractures occur.However,it is regretful that,there is still not an effective method that can repair the damaged blades under located condition,which requires the repairing layer to have a good combination with the base metal and excellent erosion resistance,and makes sure the characters of the steam turbine are not destroyed.In order to overcome the above problems,a simple gas tungsten arc weld(GTAW)method to effectively repair the damaged blades is explored in this paper tries.Two kinds of typical blade materials 05Crl7Ni4Cu4Nb and 20Cr13 are used as parent materials,and many joints are obtained by welding under different processing parameters.Then,the welding joints are studied by using visual inspection,metallographic observation,fatigue evaluation and micro-hardness tests.Based on the experimental results,the effect of welding parameters on the microstructure and mechanical properties are analyzed,and hence an optimized welding repairing crafts,such as welding current,gas-flow rate,pre-heating and post-heating temperatures and so on,are obtained finally.The main conclusions of this paper can be presented as follows.1.When martensitic stainless steel with the same composition with base metal was used as welding materials,post-heat treatments were always necessary while Ni based austenitic alloy was used as welding materials,post-heat treatments could be ignored.The best post-heat treatments for 05Cr17Ni4Cu4Nb blades were 1040? solution followed by 600? aging,and that for 20Crl3 blades was 710? tempering.2.Defects could be reduced and grain size in heat-affected zone could be controlled by adjusting welding parameters,and thus the fatigue life of welding joints could be improved.High cycle fatigue life of heat-treated 05Cr17Ni4Cu4Nb and 20Cr13 welding joint could reach as high as 87%and 91%of base materials.3.The improvement of impact toughness of 05Cr17Ni4Cu4Nb welding joint could be attributed to fine equiaxed grains in welding seam,and that of 20Cr13 steel is the result of transformation from tempered martensite to tempered sorbate.4.By using Ni based welding materials and submerged GTAW method,the damage and local line defects in the low pressure last stage blades could be repaired under located condition.The repaired blades can satisfy the operation requirements,and the steam turbine had worked for two years without any accidents.