Investigation On Low Temperature Annealing Process And Mechanism Of Cold Drawn High Carbon Pearlitic Wire

With the development and maturation of PV technology,there are higher and higher requirement for silicon chip cutting technology.As cutting carrier,the high-drawing carbon pearlite steel wire also has very high performance requirements.For the high-drawing pearlitic high-carbon steel wire,the low temperature annealing treatment may effectively improve the yield strength and tensile strength.The thesis systematically studied the influence law of low temperature annealing process on the mechanical properties(tensile strength,yield strength,elongation,hardness,etc.)of steel wire.Secondly,through the microstructure characterization,the thesis explained the reinforcement mechanism of colddrawing steel wire and the internal cause of the change of the mechanical properties in the process of low temperature annealing process.Besides,the thesis provides beneficial guidance for the reasonable design of low temperature annealing process.First of all,this thesis designed the annealing process for different temperatures(100℃,120℃,140℃,160℃,180℃,200℃,220 ℃ and 240℃ respectively),and systematically tested and analyzed the tensile strength,yield strength and elongation of high-carbon pearlitic steel wire.According to the study results,within the range of 100℃~140℃ of annealing,as the temperature rose,the tensile strength increased,and reached the maximum 3847 MPa at 140℃;and then,tensile strength fell sharply with the increase of annealing temperature;within the range of 100℃~180℃ of annealing,as the temperature rose,the yield strength increased obviously,and reached the maximum 3784 MPa at 180℃;And then,yield strength fell sharply with the increase of annealing temperature.As the annealing temperature rose,elongation fell sharply from 2.45% before annealing to 2.17% at 160℃,while the decline of elongation fell after 160℃,and reached the minimum 2.13% at 240℃.Obviously,suitable low-temperature annealing technology may improve the mechanical properties of cold-drawing steel wire.Microhardness test was conducted on the different radius of the drawing of the steel wire which involved no annealing and involved annealing at different temperature.The test data showed that:(1)the steel wire drawing state hardness increased to 857 HV at the core from 801 HV at the surface,showing that processing hardening degree of surface layer to core gradually increased in the process of severe cold-drawing;(2)steel wire presented different change rule at different radius of hardness after low temperature annealing.In the 180℃ low temperature annealing process,hardness decreased by 7HV at 68?m on longitudinal and cross section,while hardness increased by 18 HV at 91?m on longitudinal cross section.Due to larger core deformation,and higher dislocation density,carbon atoms were more likely to precipitate near dislocation form the higher density of hardening of the particles in the annealing process.As a result,the core hardness increased,and the surface area hardness reduced.In this thesis,system characterization was carried on the pearlitic high-carbon steel wire of different drawing and annealing state by means of optical microscope(OM)and scanning electron microscope(SEM)has.Besides,the strength of the internal mechanism was analyzed and discussed.Based on the study results,with the increase of variable in colddrawing process,the initial random order of lamellar pearlite layer structure evolved into a long fibrous tissue along the direction of drawing in the drawing process;material strength improved significantly;and the uniformity of long fibrous tissue changed in the low temperature annealing process.When annealing intensity reached the peak at 180℃,its structure uniformity was the best,and the intensity began to decline at 240℃ of annealing,and structure recrystallization occurred coarsening due to reply.As seen from the observation of the cross section tissue,there was precipitation phenomenon in the second phase particle;along with the annealing temperature,the second phase particles started to precipitate;when the intensity peak occurred at 180℃,there was the largest number of second phase particles;and at 240℃ of annealing,the second phase particle grew up obviously,and coarsened,and the strength began to fall sharply.In this thesis,the change rule of mechanical properties under different annealing temperature are obtained through study on the high-carbon pearlitic steel wire low temperature annealing process,and the optimized low-temperature annealing technology is also developed,i.e.heat preservation for 30 min at 160℃.The process has been applied to actual production and achieved remarkable effect,and it may greatly improve the efficiency of the wafer cutting.