Steady-state Control On Automobile Sheet Quality Of O5 Grade

For the cold rolled plate used in the manufacture of the automobile panel, the perfect properties such as deep-drawing, non-aging and surface quality are required, to meet the requirements of unanimous geometry and surface state after stamping forming, the property stability is also required. The properties and property stability are closely related to the chemical composition, cleaness and microstructure and texture of the automobile sheet. The Accurate and stable control of the parameters employed in the smelting process, the continuous casting process and the rolling process is extremely significant in enhancing the property and property stability, decreasing defects probability, increasing finished product ratio and improving economic performance.In the production of automobile sheet of 05 grade of one internal iron and steel plant, there exist some problems such as the unstable mechanical properties, the high probability of surface defects and the low rolling yield which induce by the fluctuation of steel composition, the high total oxygen content, the high content of large scale non-metallic inclusions and the unstable rolling parameters according to the estimate of the steel production process. To avoid these problems, the researches on the steady-control of the steel compositions, the steel cleaness, the flow behavior of liquid steel in the mould, and the optimization of rolling parameters were carried out.The evolution behaviors of the compositions, the cleaness and the non-metallic inclusions during IF steel smelting process were studied through the industrial experiments. The results showed that, the steel compositions of C, Ti and total oxygen are mainly affected by the content of dissolved oxygen in the liquid steel of the end-point of BOF, the begin-point of RH refining and the end-point of vacuum decarburization, and also affected by the chemical reaction between the Ti-Fe alloy and the steel and the deoxidation product of Al2O3. To achieve the goal of steady control of the steel compositions and the cleaness, the content of dissolved oxygen at the key points during steel making process and the alloying time must be controlled accurately and stably.The Influences of the structure parameters of the the submerged entry nozzle such as the outlet shape, dip angle and the operating parameters such as the immersion depth of SEN, flow rate of blowing argon, continuous casting speed and its fluctuation during ladle alternation on the level fluctuation, surface bareness and slag entrapment were investigated through the physical and mathematical simulation. The results showed that, the appropriate parameters are as follows:square outlet shape of SEN, dip angle as 15°, immersion depth as 180±20mm, continuous casting speed as 1.1±0.1m·min-1, no blowing argon or flow rate of blowing argon with 6～8L·min-1, and continuous casting speed adjustment slightly for several times.The influences of parameters of coiling temperature, cold rolling reduction, annealing temperature and annealing velocity on the mechanical properties of DC06 grade automobile sheet were optimized through industrial experiments. The results showed that, the appropriate parameters are as follows:the tapping temperature of slab as 1190±20℃, the start rolling temperature as 1150±20℃, the end rolling temperature as 900±15℃, the coiling temperature as 720±15℃, the cold rolling reduction as 80%, the annealing temperature as 850±10℃, the annealling velocity as 200 m-min"1.The steady-state control technics were integrated and were applied in industrial production. The results showed that, the content of C, N and Ti can be controlled stably. The content of total oxygen content decreased significantly, the content of large scale non-metallic inclusions in slab of steady casting state decreased from 7.065 mg·(10kg)-1 to 1.538 mg·(10kg)-1, and the content of large scale non-metallic inclusions in transition slab decreased to 3.348 mg·(10kg)-1, the probability of surface defects induced by large scale non-metallic inclusions decreased to 16.28%. The properties and property controlling stability of yield strength, tensile strength, elongation, plastic strain ratio and strain hardening index were enhanced markedly.