Research On Process Of Wear Resistant Coating On Water-cooled Wall By TIG Cladding

Water-cooled wall made of 20 g steel is the main part for receiving heat in a power station boiler.If it is worn down during operation,anti-friction coating is required to repair it.In this paper,the coating was fabricated on 20 g steel substrate by TIG cladding with nickel-based self-fluxing powder as cladding material.The microstructure and properties of nickel-based coating were analyzed.Through in-situ synthesis reinforced phases were added in the coating and the typical microstructure was analyzed.The effect of process parameters and the composition of powder on the microstructure and properties of coatings were studied.Combining experimental results and thermodynamic calculation,the mechanism of synthesizing enhanced phase was investigated.The coating was fabricated with nicked-based self-fluxing alloy powder Ni₄₅ as cladding material.The effect of cladding current,cladding speed,arc length and shielding gas flow on the cladding coating was studied.When cladding current was 120 A,cladding speed was 2.5mm/s,arc length was 8mm,shielding gas flow was 8L/min,the cladding coating with good macroscopic morphology could be obtained.The cladding coating is mainly composed of Fe-Ni solid solution,and its hardness was up to 3₄₅ HV,which was about 2 times of that of the base m etal.(Ni₄₅+Ti+BN)was used as cladding material to increase the wear resistance of cladding coating through in-situ synthesizing reinforced phases.The cladding coating was mainly composed of Fe-Ni solid solution and Ti N and Ti B2 reinforced phases.The reaction mechanism of in-situ synthesizing reinforced phases in the cladding coating was analyzed by thermodynamic calculation and element area scanning.The effect of cladding process parameters and powder composition on the microstructure and properties of cladding layer was studied.With the increase of heat input,the hardness of cladding layer increased gradually.Increasing the ratio of BN,the cladding hardness increased first and then decreased.When the ratio of?Ti + BN?increased,the number of the reinforced phase improved,as the same as the hardness.However,when the ratio of?Ti+BN?reaches a certain value,the hardness would not be improved obviously.The highest hardness could be obtained when BN/Ti was 2/3,mass fraction of?Ti + BN?was 25%,cladding current was 120 A,and cladding speed was 3mm/s,which is 425.15 HV.(Ni₄₅-Ti-B₄C)was used as cladding material because BN was easily to sublimate instead of melting.The typical microstructure of cladding coating was analyzed,which was composed of three parts: Fe-Ni solid solution,enhanced phase Ti C,Ti B2 and ferrite.The effect of cladding current,cladding speed,and powder composition on the microstructure and properties of cladding coating was studied.When the heat input was not enough,t he powder was not completely melted or reacted,but high heat input lead to excessive melting base metal.When the ratio of B₄ C ratio increased,the size of reinforced phases increased in the coating.With the mass fraction of?Ti+B₄C?increasing,the number of reinforced phases and hardness of the coating increased simultaneously,but too much?Ti+B₄C?result in macroscopic defects.When B₄C/Ti was 1/3,mass fraction of?Ti + B₄C?was 25%,cladding current was 120 A,and cladding speed was 3mm/s,the hardness of coating was 468.2HV.