Study On Formation Mechanism And Control Of Oxide Scale For Environmental Friendly C72DA Wire Rod

In recent years,green environmental protection has become the development theme in the steel industry.Because of serious pollution to ecological environment,the pickling descaling method was replaced by mechanical descaling method.If there is residual scale on the surface of the wire rod after mechanical descaling,the surface quality of the product will be seriously damaged and the competitiveness of the enterprise will be reduced.Steel and iron industry improved the mechanical descaling effect by increasing the thickness of the scale,but increased the amount of steel loss at the same time,and there is still the phenomenon of incomplete descaling.On the premise of ensuring the mechanical properties of steel,how to control the oxide scale reasonably is the key to improve the mechanical descaling performance.Therefore,aiming at the above problems,this paper study high temperature oxidation behaviors of the target steel and hot deformation behavior of oxide scale under different hot rolling conditions and the effects of rolling temperatures,laying temperatures and cooling rates on the oxide scale structure evolution.Based on the experimental research results,hot rolling production process was optimized and the industrial trial production was conduct.The main conclusions of this paper are as follows:(1)Oxidation kinetics experiments were conducted to study the oxidation behaviors of the target steel at high temperatures,it was obtained that the oxidation weight curves follow the linear law at 1050～1150℃,while the oxidation weight curves follow the parabolic rule in the range of 1200～1250℃.With the increasing oxidation temperature,the grains size on the surface of the scale increases and the inside of the oxide scale gradually densification.(2)The dynamic growth process of the scale on the surface of the target steel was studied by in-situ observation experiment.The results showed that the grains on the surface of the scale change from honeycomb to flocculent,and finally change to multilateral shape,accompanied by blistering and microcrack healing.The blistering and healing mechanisms were analyzed.The enrichment of carbon at the interface between oxide scale and matrix results in the blistering of oxide scale.The air diffuses into the inner part of the scale,and the oxidation-reduction reaction takes place,which plays a role in healing of the microcracks.(3)The thermal deformation behaviors of the scale under different rolling conditions were systematically studied,and it was found that the scale was mainly flaked with the increase of reduction,and the scale was stratified under 900℃.The degree of FeO fragmentation and Fe3O4 spalling increases with the increase of rolling reduction.It is confirmed that the deformation behaviors of oxide scale mainly occur in the FeO layer,and the plasticity of FeO increases with the increasing temperature.(4)The effects of different rolling temperatures,laying temperatures and cooling rates on the structure of oxide scale was studied by thermo-mechanical simulator.The results showed that the original Fe3O4 content decreases and FeO content increased with the increase of rolling and laying temperatures.With the increase of cooling rate,the diffusion ability of ions is reduced.The size of the proeutectoid Fe3O4 changes from bulk into island,and the content of the proeutectoid Fe3O4 decreases gradually.(5)Based on the experimental research results and the site conditions,the controlling scheme of C72DA was put forward.Industrial trial production results show that the thickness of oxide scale and the loss of steel are significantly reduced under the premise of ensuring the mechanical properties.FeO is the main component in the structure of oxide scale.There is no oxide residue on the surface of wire rod after mechanical descaling,which meets the mechanical descaling requirements of downstream users.