Study On The Surface Quality Control Mechanism Of Hot-Rolled Pickling Plate By FTSR Production Line

With the economic development of our country,the automobile and home appliance industries also grow rapidly.In order to enhance their own product quality,the customers require more and more high quality raw materials besides the internal cost reduction.In addition to improving the mechanical properties and reducing the weight,it also requires high surface quality raw materials which are easy to weld,oiled and painted to enhance the appearance of the effect,so cost-effective pickling plates are gradually receiving the customer’s favor.However,it was found that the pickling surface prone to oxide scale pressed into the skin,the strip color,landscape painting,over pickling and other defects in the actual production,the product greatly reduced the pass rate,a large number of products sub-sentenced or scrapped and the surface properties declined,seriously affecting the coating effect and unable to meet the requirements of steel appliances,then the corporate profits declined.At present,the conventional process acid pickling board surface defects have made great improvements,and for the short process,especially the FTSR production line,due to its special process characteristics,the factors affecting the pickling board defects and restrictions are not yet clear,which need researched of the production line system.In this paper,the target steel high temperature oxidation behavior was studied by using high temperature thermal analysis(TGA),electron probe X-ray microanalysis(EPMA),scanning electron microscopy(SEM)and other systems,the effects of rolling process,rolling temperature on the production of defect that oxide scale pressed into the skin were explored,and effects of coiling temperature and cooling rate on the transformation of oxide scale structure were studied by simulating onsite coiling process.At the same time,the on-line pickling process was simulated,and the effects of pickling speed,pickling temperature,pickling concentration on pickling surface quality were analyzed,finally combined with field research,improvement program of short-run hot-rolled pickling board defects was proposed.The main contents are as follows:(1)Through the experiments of high temperature oxidation of 1000-1200℃ for the target steel,the rate constant kp of oxidation weight gain at different temperatures was obtained and the oxidation activation energy of the target steel was obtained by linear fitting.By simulating oxidation behavior in the field tunnel heating furnace,the effects of two plus heating system and three plus heating system on the scale weight and thickness were studied;(2)Through the examination of oxide scale indentation defect of pickling plate,it was found that there are two main sources of oxide scale in the substrate,one is pressed by the oxide scale itself and the other is pressed by the exterior oxide scale;The effect of condition that rolling temperature is in the range of 800-1000℃ and the deformation is 10-30%on the production of oxide scale indentation defect,and the formation mechanism of oxide scale indentation defect was studied,which can provide the best production technology for the actual production;(3)The influence of coiling temperature and cooling rate on the structure of oxide scale was studied by simulating the coiling process,the co-precipitation and eutectoid reaction of FeO in the oxide scale were studied under continuous cooling conditions,thereby understanding the law of structure transformation of oxide scale;(4)The unprocessed oxide scale pickling mechanism was explored through the pickling kinetics experiment,and the optimal pickling temperature,acid concentration and pickling speed were determined by simulating the pickling process in the field,which can effectively reduce "over pickling" phenomenon.(5)In order to solve oxide scale indentation defect of the pickling plate surface and the longitudinal chromatic aberration defects,and improve the surface quality of steel,combined with the actual working conditions and experimental results of the pickling plate produced by FTSR,the whole process parameters of the hot pickling plate were optimized and the on-site industrial trial production was optimized.