Surface Wrinkle Defect Analysis And Pass Optimization Of SCM435 Cold Heading Steel Wire

SCM435 cold heading steel has high static strength,impact toughness,creep strength and durability,and was widely used in products with special performance requirements,such as automotive engine fasteners,connectors,and ultra high strength grade hex head bolts,studs,hexagon socket screws,etc.Surface wrinkle defects caused in the hot rolling process will cause a series of problems such as pull fracture,cold cracking and so on.In this paper,the wrinkle defect on the surface of SCM435 highspeed wire was studied,and the solution to the wrinkle defect was explored.The main research contents and results are as follows:(1)Through field inspection,it was found that the cause of the wrinkle defect on the surface of SCM435 wire rod is unreasonable design of 6 rough rolling passes.Combining with the finite element method,the simulation and diagnosis of 6 rough rolling passes of original passes were carried out,the shortcomings of original passes design were analyzed,and optimization scheme of passes is put forward.(2)Influence of plastic strain energy density distribution and normal velocity gradient of contact surface on the tendency of wrinkle defects was studied,it provides technical indication for pass optimization.It was concluded that the greater the plastic strain energy density and the greater the absolute value of the velocity gradient,the more likely material produce surface wrinkle defects.(3)The true stress-true strain curve of SCM435 were obtained by Gleeble thermal simulation experiment,and the DMM thermal processing chart was drawn.The suitable process window and instability interval of SCM435 were obtained.(4)The plasticity strain energy density and normal velocity gradient were used as the indicators to investigate the possibility of wrinkle defects in pass rolling,to verify the rationality of the optimized pass,and the practice of the optimized pass.The production practice shows that the surface wrinkle depth of the finished SCM435 is less than 1% when it is more than 30 micron and less than 10% when it is more than 20 micron,which proves that the optimized pass design meets the expected standard...