Effect Of Controlled Cooling Under Electrical Contact Heating On Microstructure And Properties Of Carbon Steel Wire

In this paper,the 70 steel wire is taken as the research object,and the traditional lead bath heat treatment process is replaced by a new type of air-cooling process under the condition of electric contact heating.Study single factors:the magnitude of wind pressure,the magnitude of current and the rate of movement of the steel wire on the microstructure and mechanical properties of the steel wire.The CCT curve of 70steel is obtained by designing different cooling rates by thermomechanical simulator,which provides a theoretical basis for the air cooling process.Then,the changes of microstructure and texture of the steel wire after air-cooling were studied.The main conclusions are as follows:?1?The dynamic CCT curve of 70 steel for steel wire was measured by expansion method combined with metallographic-hardness method.The critical point of 70 steel was A_c1=722°C and A_C3=770°C,which provided a theoretical basis for the heat treatment process of the steel.Under different cooling rate conditions,the high temperature zone is mainly pearlite transformation,and the rapid cooling condition is mainly martensite transformation.?2?Under the condition of electric contact heating,under the condition that the heating current and the moving speed of the steel wire are constant,as the wind pressure increases,the degree of supercooling increases,the microstructure of the pearlite refines,and the pearlite colony of the steel wire decreases,and the interlayer spacing of the pearlite is reduced.The tensile strength,elongation,and reduction in area are increased.When the wind pressure is 0.26 Mpa,the optimal mechanical properties of the steel wire are obtained.Under the condition that the wind pressure is constant and the steel wire moving speed is constant,the magnitude of the current is controlled within a certain range.When the current is 88 A,the optimal mechanical properties of the steel wire are obtained.Under the condition that the wind pressure is constant and the current is constant,the magnitude of the steel wire moving speed is controlled within a certain range.When the steel wire moving speed is 0.785 m·s^-1,the optimal mechanical properties of the steel wire are obtained.?3?The strength of the steel wire is mainly affected by the grain size,the interlayer spacing of the pearlite,dislocations,and nano-cementite.The smaller the pearlite layer spacing,the greater the intensity,and the nano-cementite second phase particles also play a strengthening role,which increases the strength under the common action.Plasticity is mainly affected by the size of the pearlite colony.The smaller the pearlite colony size,the higher the area shrinkage,that is,the better the plasticity.?4?During the deformation of the steel wire,the cementite changes.As the strain increases,the pearlite structure gradually changes into the direction of drawing,forming a lamellar structure parallel to the drawing direction.The wire has a<110>silk texture in the parallel drawing direction during the deformation process of the drawing.As the strain increases,the<110>silk texture strength increases,and the composition of other textures weakens.