The Quality Analysis Of The Scm435 Cold Forging Steel And Technical Research On Rolling Process

The SCM435 cold forging steel is a principal raw material for producing high level fastening piece. It has a high requirement on the chemical composition, surface quality, cold forging property and so on. Now, for the hot rolling wires the surface hardness is mainly HB310-325,because there is no hardness requirement in our production process.This thesis is based on the production field of the SCM435 cold forging steel, through some methods, decreasing the hardness and researching a pertinent rolling technology. The results are as follows:(1)From the test results and the CCT curve of the SCM435 steel, during the velocity of 1-10℃/s, bainite can be obtained, when the velocity is less than 1℃/s, the micro-structure of ferrite and perlite can be obtained. Through the slow cooling after rolling, finishing the phase transformation under the insulation course. So it is a key job to decrease the hardness of the SCM435 steel.(2) There is no insulation course in the front of roller way cooling transport line until 21 meters.Because of the faster cooling rate, the SCM435 steel has a higher hardness.Through the reforming of production line, it now has a better result.(3) The results indicate that:It can own a lower surface hardness through decreasing the finishing temperature,spinning temperature, and slowing the vilocity of rolled products during the insulation course.Through the slow cooling after rolling, finishing the phase transformation under the insulation course.In order to decrease the surface hardness, not only the spinning temperature must control at 800-850℃,but also slow cooling after rolling, the surface hardness can be decreased from HB310 to HB270.