Research On The Optimization Of Production Process For S08Al Cold-rolled Steel Sheet And The Corrosion Behavior Of Q235Steel In Jianlong Group

S08A1cold-rolled steel sheet and Q235steel are the two products with good sales and users among the main products manufactured by the Jianlong Iron&Steel Group Co. Ltd.(hereinafter referred to as Jianlong group). It is the key factor for controlling the development of the company whether or not they can be produced to meat the user’s demand.The production procedures of S08A1cold-rolled deep drawing steel are very complex including smelting, hot rolling, acid washing, cold rolling, annealing and temper rolling etc.. Quality of processing system in each procedure affects the quality of final product. Through optimizing chemical composition, advancing hot-rolling and cold-rolling processes, the elementary production of S08A1cold-rolled deep drawing steel has been successfully done in Jianlong group. However, the market and downstream client put forward the higher requirement on the cold-rolled products with increasing competition in market, the incessant extension of product application and continuous increase in fabricating cost. The Q235steels manufactured by Jianlong group are generally used in the industrial region of Tangshan city of Hebei province. The corrosion resistance when they are used in thus region is the reference point by which users decide wether or not they use the products.In this paper, selecting the S08A1cold-rolled deep drawing steel and Q235steel produced by Tangshan Jianlong industry Co Ltd. as the object of study (hereinafter referred to as the experimental steel), through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD), thermomechanical simulation, mechanical test, wether exposure test, measurement of the corrosion weight loss, rust layer structure analysis and so on, the hot deformation behavior of S08A1cold-rolled deep drawing steel under different conditions, the effects of coiling temperature and annealing temperature on its microstructure, properties and texture as well as the corrosion behavior of Q235steel under the given surroundings were investigated. The obtained major conclusions are as follows:1. The hot deformation behavior of the experimental steel S08A1at700～1050℃and with strain rates of0.01～10s-1was studied through single-pass compression experiment. The experimental results showed that:(1) The activation energy for the experimental steel during hot deformation in austenite range is273kJ/mol, and the hot deformation equation can be depicted as:(2) The dynamic softening activation energy for the experimental steel in ferrite range is282kJ/mol, and the hot deformation equation can be depicted as:2. In the range of coiling temperatures designed in this study, the volume fraction of {111}<UVW> texture component is the highest and the ratio of{111}<UVW>/{001}<110> is the largest for annealed cold-rolled experimental steel sheets when coiling temperature was592℃through integrating the mechanical properties of the hot rolled plate and the plate annealed after cold-rolled. Therefore, the experimental steel can obtain the excellent deep drawability when coiled at592℃.3. Microstructure and mechanical properties are the best, the volume fraction of {111}<UVW> texture component is the highest and the ratio of{111}<UVW>/{001}<110> is the largest when the experimental steels S08A1rolled by cold rolling ratio of73.3%and90%are annealled at690℃. Therefore the experimental steel annealed at690℃can obtain the optimum deep drawing property.4. The large grains, semi-network and network cementites which harm the deep drawability appeared in the microstructures of experimental steels S08A1annealed at700℃. Therefore, the annealing temperature should be controlled to be lower than700℃.5. The coarse grains near the surfaces and the mixed grains with different levels appeared in the edge microstructures of the experimental steels S08A1hot-rolled at lower finishing rolling temperatures and higher coiling temperatures. Annealing treatments can not obviously improve the defects in the hot-rolling microstructures. Cementites were distributed as obvious chainlike structure in the experimental steels produced at lower finishing rolling temperatures and higher coiling temperatures. Changing the annealing temperatures and the heating-up rate in the second section can not obviously improve their morphologies and distributions.6. Plain carbon steel Q235is corroded more quickly in the industrial region of Tangsha city than in the atmospheric environment of Tangshan urban. And the corrosion process is divided into three stages; the accelerated corrosion mainly occurs at the second and third stages; the products formed from corrosion at this region mainly are the iron hydroxyoxide and the magnetic iron oxide. The sulphate ion is the main factor to affect the secondly quick oxidization of this steel.7. The corrosion products formed during the atmospheric exposure of Q235steel in heavy industrial region of Tangshan city mainly consist of FeOOH and Fe3O4. As the corrosion time increases, the phase of ferrous sulfate appears in the corrosion products, and mainly is enriched in the outer rust layer.