Effects Of The Low Temperature Rolling On Microstructures And Mechanical Property Of A Boron Microalloyed Medium-carbon Steel

Until now, the low temperature rolling process has find increasing application prospects in the wire manufacturing. Wires achieved by the low temperature process can be directly used in fastening pieces manufacturing by cold-heading processing without annealing. As a result, the periodic time of fastening piece manufacturing can be reduced leading to the lower cost of fastening pieces. In this paper, based on the thermal simulation tests, the low temperature rolling process has been investigated. The flow stress behavior of a boron microalloying medium carbon steel were researched by the higher thermal simulation tests. After that, as simulated the low temperature rolling process by the finite element analysis, the temperature distribution of the wire in the cross section was investigated. The results reveal:(1) The low temperature rolling process which deformed at the range from 760℃to 820℃and initial cooled at the range from 750℃to 840℃can increase the percentage of ferrite and the number of spheroidized pearlite. The process which deformed at 790℃and initial cooled at 780℃is optimal. By this way, the passing rate of cold-heading of theΦ6.5mm wires is 99.2%. This number ofΦ12mm wires is 87%.(2) In the hot compression deformation, the relation of the flow stress,the strain rate and the deformation temperature was investigated. The flow stress decreased as deformation temperature increased and became higher as strain rate rises. It indicates that the boron microallying medium carbon steel is a positive strain rate sensitive material. The deformation energy(Q) is 306.79(KJ/mol) and the flow stressε=3.50759×1012[sinh(0.00858σ)]4.88778 exp(-306.7904/RT) constitutive equation was(3) As simulated the by the finite element analysis, the strain field and temperature field in the low temperature rolling process were researched. The temperature gradient ofΦ12mm wires in the phase change zone can result in the non-homogeneous microstructure and the low passing rate of cold-heading. The temperature distribution in the cross section ofΦ12mm wires can improve by prolongating the restoring time after water-cooling. Used in that, the passing rate of cold-heading of theΦ12mm wires was improved to 99.2% without annealing.