| The membrane water-wall is widely used as the inner wall of large boilers to improve the sealing performance of the boiler and the utilization rate of the fuel.It also reduces the thickness and weight of the furnace wall.However,the membrane water-wall is easily corroded under high temperature and pressure,which results in short service life.Therefore,some foreign engineers attempted to obtain a cladding of Nickel-based alloy on the surface of membrane water-wall to solve the high temperature corrosion problem.The effects of three different heat input and three-point constraints on transient temperature field and residual stress-strain field when surface welding on membrane water-wall were simulated by ANSYS.In addition,related experiments were conducted to verify the accuracy of simulation.Ultimately,the welding method which could effectively control the structural deformation of the membrane water-wall when surface welding was explored.The results of temperature field showed that the temperature of the position reached the melting point rapidly when the heat source arrived during the heating process.After the heat source leaved,the temperature quickly dropped to 600 ° C,but the cooling rate is significantly less than the heating rate.The temperature field exhibited a quasi-steady state after heating by heat source for 10 seconds.With the heat input increasing,the maximum temperature of the molten pool increased,and the difference of temperature reached 100 ° C or more,but the cooling rate was slower.On the other hand,the thickness of the welding bead increased,the width of heat affected zone became larger,the number of columnar crystals grain decreased,and the number of equiaxed crystals grain increased.Besides,the content of ferrite increased,while the content of pearlite decreased and the Widmannstatten structure appeared.The stress-strain field results showed that the picture of residual stress distribution obtained by three different heat inputs had similar profiles.However,as the heat input increased,the area of residual stress concentration in the membrane water-wall increases,while the maximum stress value was decreased slightly.The residual structure deformation also increased from 5.4mm to 6.2mm as the heat input increased.When initial constrains were applied before surface welding,the residual tensile stresses were mainly concentrated near the restraining position,while the stress at other locations is relatively small.The residual distortion after the surface welding was significantly reduced with a maximum deformation of 0.8mm occurring in the direction of the width.These simulation results indicate that applying initial constrains will effectively control the structural deformation of membrane water-wall which caused by surface welding.By comparison,the residual deformation results from the simulation coincided with the experimental data,with a slight difference of 14.8%.This indicates that the computational simulation has high reliability and accuracy.By controlling the amount of heat input via CMT and applying initial constrains,the post-welding distortion of the membrane water-wall could be effectively controlled to obtain well-formed welded joints with low rate of dilution. |
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