Study On The Effect Of Cold Deformation On Microstructure And Mechanical Properties Of SCM435 Cold Heading Steel After Spheroidizing Annealing

In order to achieve high quality spheroidizing of SCM435 wire rod,the effect of cold drawing deformation on microstructure and mechanical properties of wire spheroidizing annealing was studied.By means of scanning electron microscopy(SEM),microhardness test,tensile mechanical properties test and image software analysis,the microstructure and mechanical properties of annealed hot rolled wire and drawn wire were compared and studied,and a new efficient spheroidizing annealing process was proposed.The effect of annealing process parameters(annealing temperature and holding time)on microstructure and properties of hot-rolled SCM435 rod was studied.The results show that increasing the annealing temperature and extending the holding time can improve the spheroidization of the steel wire,decrease the strength and hardness of the steel wire,and increase the plasticity of the steel wire after annealing.When annealed at 720℃,the distribution of carbide in the microstructure is not uniform,and the distribution of particle size is different greatly.After annealing at 740℃,the microstructure has a good spheroidized morphology.With the extension of holding time,the size of spherical carbide particles gradually increases.When annealed at the critical temperature(760℃),the extension of holding time can make the distribution of carbide more uniform,but after annealing,it is easy to precipitate flake pearlite,reduce the microstructure spheroidization rate,and improve the hardness and tensile strength,which is not conducive to the improvement of material plasticity.The effect of cold drawing deformation on microstructure and mechanical properties of steel wire after annealing was studied.The results show that the cold drawing deformation has different effects on the different spheroidizing annealing modes.1 、 Under the subcritical spheroidizing annealing mode,the structure spheroidizing rate of the drawn wire after annealing is higher,the spheroidizing quality is higher,and the plasticity is better after annealing.After annealing at 720℃ for 4 h,the spheroidization rate of the 20% steel wire is increased to 90%,the elongation after fracture of the hot rolled wire is only 20% after annealing at 720℃ for 2 h,and the elongation of the 30% drawn wire is increased to 31% after annealing at 720℃ for 2 h(compared with the hot rolled wire,the elongation is increased by 55%).2、Under the intercritical spheroidizing annealing mode,the microstructure properties of the drawn wire are not significantly changed after annealing,and the existence of lamellar pearlite after annealing leads to the low spheroidizing rate of the structure,which is always below 80%.The elongation of the drawn wire and wire rod after annealing is maintained at about 26%,and there is no significant change.In order to improve the spheroidizing efficiency and quality,a new spheroidizing annealing process was designed,and the effect of cold drawing deformation on the microstructure and properties of steel wire treated by the new process was studied.The results show that the spheroidization rate of the drawn wire can be achieved by the new process.The spheroidization rate of the drawn wire can be achieved by the heat preservation treatment for about 2.5 h.The spheroidization rate of the drawn wire can be achieved by the new process,and there is no flake pearlite in the structure.