| Most of the sudden accidents in power plants are due to the service of boiler pipelines at high temperatures,accelerating the oxidation and corrosion of pipelines,resulting in thinning and bursting of pipelines,which seriously affects the safe operation of power plants.At present,316 stainless steel is used in the key parts of boiler pipeline in thermal power generation.However,316 stainless steel is austenite single phase structure at high temperature or room temperature,which cannot be applied to the demand environment of both hot corrosion resistance and high strength.Moreover,316 stainless steel is prone to hot corrosion defects in a specific environment(600??800?).These problems limit its application in boiler pipes.Therefore,how to enhance its strength and improve its hot corrosion performance in specific environments has become a research hotspot in recent years.Based on this,FeCrAlSi coating was prepared on the surface of 316 stainless steel by laser cladding.The microstructure and properties of FeCrAlSi coating under different process parameters and the continuous hot corrosion behavior of the coating in 75wt.%Na2SO4+25wt.%K2SO4 mixed salt at 800°C were studied.The main research contents and conclusions are as follows:(1)The influence of laser cladding process parameters(laser power,scanning speed)on the geometric characteristics of FeCrAlSi coating was studied.The results show that the dilution rate of FeCrAlSi coating is affected by the scanning speed and laser power.When the scanning speed is 11 mm/s and the laser power is 1600 W,the dilution rate is the highest(54.7%).When the scanning speed is 7 mm/s and the laser power is 1600 W,the dilution rate is the lowest(40.4%).(2)The effects of laser cladding process parameters(laser power,scanning speed)on the phase composition and microstructure of FeCrAlSi coating were studied.The results show that the FeCrAlSi coating is mainly composed of Fe-Cr solid solution and Al Fe intermetallic compound.With the increase of scanning speed and laser power,the diffraction peak intensity increases first and then decreases in varying degrees.The grain structure also shows grain refinement and the increase of white flake aluminum phase.When the scanning speed is 7mm/s and the laser power is 1600 W,the area of white flake aluminum phase is the largest.(3)The effects of laser cladding process parameters(laser power,scanning speed)on the microhardness and friction and wear properties of FeCrAlSi coating were studied.The results show that when the scanning speed is 7 mm/s and the laser power is 1600 W,the FeCrAlSi coating has good metallurgical bonding with the substrate and no defects such as pore cracks.The corresponding average microhardness value is 340.4 HV0.2,the average friction coefficient is 0.735,and the wear volume is 0.288 mm3.The microhardness and friction and wear properties of the coating are better than those of the coating prepared under other parameters,and are greatly improved compared with the substrate.(4)After continuous hot corrosion for 2 h,the protective Al2O3 film was formed due to the highest affinity of Al to O,which effectively prevented the formation of internal oxides and sulfides.After 10 h of continuous hot corrosion,the newly formed porous Al2O3 film has a decrease in protection due to the formation of an alkaline melting environment at the molten salt/coating interface,and the corrosive medium and O can be diffused through micropores,thus accelerating the hot corrosion.After continuous hot corrosion for 40 h,due to the upward diffusion of Cr through porous Al2O3 film,continuous spherical flocculent Cr2O3 film was gradually formed.After 70 h of continuous hot corrosion,the penetration of Al2O3 towards the substrate is more obvious due to the intensified internal oxidation of Al.After continuous hot corrosion for 100 h,Si O2 appeared in the inner corrosion layer,which inhibited the infiltration of Al2O3 towards the substrate.At the same time,the outer corrosion layer formed(Cr,Fe)2O3+Al2O3 protective film,which effectively slowed down the oxidation and vulcanization reaction. |
PDF Full Text Request