Study On The Fabrication Process And Tempering Treatment Of Alloy Steel By Wire And Laser Additive Manufacturing

Wire and laser additive manufacturing is a forming technology which uses high-energy laser beam as energy source and metal wire as raw material to deposited metal materials on the substrate layer by layer.Currently,most additive manufacturing of metals are powder-based processes,few studies have been focused on the wire-based,let alone its post treatment.In this study,JS80 alloy steel wires were used as the raw material to fabricate the alloy steel by wire laser additive manufacturing.Single bead single layer,multi bead single layer,single bead multi layer,and multi bead multi layer experiments were conducted.Moreover,single bead single layer and multi bead single layer specimens were tempered under different conditions.Firstly,the shape character,microstructure,properties of single bead single layer specimen were investigated.Results showed that the cross section of the specimen consisted of deposited zone,heat-affected zone,and matrix.Owing to the difference of cooling rate,microstructure and hardness of deposited zone and heat-affected zone were different.The relation between process parameters and deposition quality was investigated by control variable method to find optimum parameters.Aspect ratio,contact angle,and dilution rate changed with laser power,wire feed speed,but had little relation with the travel speed.Orthogonal experimental results showed that laser power and wire feed speed had great impact on macrostructure of cross section of deposited layer,and the optimum parameters were obtained.Laser power and wire feed speed played a vital role on the microstructure and hardness of deposited layer.Aiming to improve the microstructure and mechanical properties,tempering was performed on the single bead single layer specimen.With the increase of tempering temperature,the structure changed continuously and the hardness decreased gradually.After tempering at 400?,coarse martensite in the deposited zone and fine acicular martensite in the heat affected zone transformed into tempered martensite,and carbides were dispersing distributed.When the steel was tempered at 500?,tempered troostite was formed,and a great deal of carbides precipitated.When the temperature was 600? and 650?,the microstructure transformed into tempered sorbite,granular cementite precipitated.After tempering,carbides and cementite in the heat affected zone were more than the deposited zone.The decline in the hardness was rapid in the heat affected zone and relatively slow in the deposited zone.On the basis of single bead single layer,multi bead single layer deposition was carried out.There were different microstructures in the deposited layers,therefore,multi bead single layer specimens were tempered.The results showed that tempering treatment improved microstructure and properties of deposited layer effectively.The 600? tempering was the optimum heat treatment,of which microstructure in all zones were tempered sorbite and has similar hardness.Single bead multi layer and Multi bead multi layer deposition experiments were implemented on the basis of single bead single layer.Single bead multi layer deposited specimens compacted without obvious defects.The microstructure of the intermediate region was granular bainite,and the microstructure of top and bottom of the sample were columnar and equiaxed dendrites,respectively.The hardness of top region was slightly higher,while the hardness of other region was about 265 HV.The density and elastic modulus were 99.89% and 211 Gpa,respectively.The alloy steel had good mechanical properties.The results indicated that presence of molten pool boundary resulted in a slight decrease of ultimate strength,yield strength and ductility in the build direction.Tensile fracture showed ductile fracture morphology.Incomplete fusion defects existed in the multi bead multi layer specimen.Due to laser cyclic heat treatment,the microstructure and hardness of deposited layer were inhomogeneous.The failure of the multi bead multi layer specimen exhibited ductile fracture with dimples,and the strength was higher than that of single bead multi layer specimen,while the plasticity is much lower due to the existence of unfused defects and the inhomogeneity of the structure,and cracks appear on its fracture surface.