| The exploitation of offshore hydrocarbon resource is an important means to alleviate energy shortage,the production and transportation equipments for this situation requires high strength and corrosion resistance.Bimetal composites are the most economical way to meet the needs.Cladding is one of the highly efficient and reliable methods for preparing this material.However,there are few systematic studies on the influencing factors of microstructure and performance of cladding layer.In this paper,the hot-wire TIG was used to clad Inconel 625 on the surface of AISI 8630 steel.The effects of cladding process parameters,post-weld heat treatment(PWHT)process,small pore size and surface roughness of base material on mechanical properties and corrosion resistance of the cladding layer were studied.Provide theoretical and experimental support for the application of bimetallic composites material in offshore hydrocarbon resource production and transportation equipments.The main research results of this paper are as follows:The cladding process parameters affect the structure and properties of the cladding layer by influencing the bath temperature gradient G and the cooling rate R.When the preheating temperature rises from 140? to 300?,the G and R of the bath were reduced,the weld depth,weld width,dilution rate,flat crystal width and grain size of the heat affected zone(HAZ)were increased slightly,the hardness was reduced from 232HV10 to 197HV10 and corrosion resistance was declined.The cladding current affect the microstructure and properties of the cladding layer and the base metal by influencing the dilution rate.When the cladding current increased from 230 A to 290 A,the dilution rate raised from 0.314 to 0.371,corrosion resistance was declined,the size of cladding microstructure and ferrite content were increased,the martensite content and the hardness were decreased.When the current comes to 290 A,the widmanstatten structure of HAZ in base material become coarser and affected material performance.The welding voltage has a great influence on the welding width.When the welding voltage raised from 12.5V to 15.5V,the welding width increased 2.46 mm.The rising in cladding voltage alleviates the "depletion" phenomenon of the grain boundary,reduced the corrosion rate from 0.143 to 0.114.When the welding speed has been increased from 250mm/min to350mm/min,the dilution rate decreased from 0.326 to 0.271,the corrosion resistance was improved and the grain size of the structure was decreased.Appropriate increased in cladding speed could control the volume of widmanstatten.When the welding speed was 270mm/min,the hardness reached to the maximum value 219HV10.PWHT facilitated the uniform distribution of the structure and composition of the cladding layer and the base metal.The presence of Cr and Mo elements made the base metal had more resistant to tempering.With the increased of PWHT temperature,the HAZ structure of the base metal was continuously increasing and the hardness of the cladding layer was decreased,the hardness of HAZ decreased first and then increased continuously,The corrosion resistance of the cladding layer was increased.When the PWHT temperature was 850?,the ferrite size was too large and affected the usability.When the PWHT temperature came to 650?,the impact and tensile properties of the heat affected zone were the best,the impact strength of-60? was 42.7J and the tensile yield strength was 714 MPa.Considering,the recommended PWHT temperature was 650?.The surface roughness of the substrate affected the cladding heat-input by the "trap" effect and then influenced the cladding structure and performance.With the decrease of surface roughness value,the trap effect was weakened and the dilution rate was reduced correspondingly.However,when the roughness value was less than 0.8?m,the decreasing trend was not obvious.When the surface roughness of the substrate decreased from 12.5?m to 0.4?m,the content of Fe in the cladding layer was decreased by about 10%,the corrosion resistance was increased by32% and the cladding layer was more uniform.Orthogonal experimental design was used to optimize the process of surfacing of small holes with diameter of 35 mm.The optimum process parameters were arc voltage 12.5V,cladding current 180 A,cladding speed 20cm/min,wire feed speed 160cm/min.The content of Fe,Ni,Cr,Mo and Nb in the cladding layer was 20%,54%,15%,6% and 4% respectively and the distribution was uniform.The hardness of small holes layer was about 13HV10 and lower than that of non-small holes.The corrosion resistance of the workpiece has been improved by about 7times,which improved the service life of offshore hydrocarbon resource production and transportation equipments. |
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