Crack Defect And Its Control In CoCrW Cemented Carbide Cladding By Arc

The screw sleeve is one of the most important parts of the screw feeder.It needs to be exposed to high temperature,high pressure,high wear and strong corrosion environment.The commonly used material for manufacturing the screw sleeve is austenitic stainless steel with good comprehensive mechanical properties,but the service life of austenitic stainless steel in the above environment is relatively short,Therefore,it is necessary to cladding high-performance metal layer on the surface of austenitic stainless steel to improve the service life of parts,in which CoCrW alloy is commonly used as cladding material.Arc cladding technology is a kind of manufacturing technology with low equipment cost and short production cycle.However,due to the characteristics of large heat input and large thermal deformation,it is easy to find cracks,which seriously affects the yield in the production process and the stability and safety of the equipment,and is not conducive to improving the economic benefits and competitiveness of manufacturers,Therefore,it is urgent to study the crack defect and its control of CoCrW alloy arc cladding layer.In this paper,austenitic stainless steel was used as the base of the screw sleeve,and CoCrW alloy was used as the cladding material.Using ANSYS numerical simulation software,the temperature distribution and thermal cycle curve under different process conditions were studied,and the effect of different process on the cooling rate and dilution rate of cladding layer was determined;The evolution rules of morphology,microstructure and properties of the cladding layer under different cladding processes were studied by cladding process test;The causes and control of the cracks were studied by means of microstructure analysis and composition analysis.Combined with the above research results,the crack free screw sleeve was successfully prepared,which realized better economic value.The numerical simulation results of temperature field show that the cooling process of cladding layer can be divided into four stages: high temperature rapid cooling stage,medium high temperature slow cooling stage,medium high temperature rapid cooling stage and low temperature slow cooling stage.The residence time of the cladding layer at 1300-1400? can be increased from 0.2s at 120 A to 0.7s and 0.8s at 180 A and 210 A.The residence time of the cladding layer in the temperature range of 1300-1400? can be increased from 0.6s to 1.1s at 400?.The residence time of the cladding layer at 1300-1400? can be increased from 0.5s to 0.7s when the substrate thickness is 15 mm by20mm.The results show that when the current increases from 150 A to 210 A,the warpage,penetration,width and dilution ratio of the cladding layer increase from 4mm,0.7mm,7.5mm and 0.050 to 6mm,1.2mm,9.5mm and 0.057 respectively,and the hardness decreases from 33 HRC to 30.9HRC,which also leads to grain coarsening.When the cladding track changes from the same direction to cross cladding,the warpage deformation decreases by 0.5mm,the overall height of cladding layer increases by 0.5mm,and the hardness decreases by 1.5HRC.The Z-shaped cladding track will make the edge of the cladding layer stay longer at high temperature,resulting in the increase of the melting amount of the matrix material,and the average hardness of the edge of the cladding layer is 2.56 HRC lower than that of the center.In this paper,the causes and control of cracks were studied by means of microstructure observation and composition analysis.It was found that under the normal preheating condition of 200?,because of the long length of cladding layer,the matrix temperature of the screw sleeve had been significantly reduced in the second half of the cladding process,and the preheating effect had been lost,which led to the generation of large stress,resulting in solidification cracks in the cladding layer High temperature crack and hydrogen induced crack;The results show that flame treatment can avoid the generation of high temperature plasticizing crack and hydrogen induced crack,but it can lead to the generation of liquefying crack;High preheating temperature will lead to liquefaction cracks,while high cladding speed will lead to structural stress and cracks.Finally,by preheating at 300? and arc cladding in the insulation box,the crack free spiral sleeve can be successfully produced.