| The 1500 mm hot rolling production line is the key technology innovation project,has been put into operation at the end of June 2005 and the monthly production in early August of that year.The annual production capacity of the product line is 2 million tons.The main types of steel are carbon structural steel,high-quality carbon structural steel,low alloy high strength structural steel and pipeline steel.The 1500 mm cold rolling production line of the project was put into operation in 2006.Currently has 1 turbulent shallow pickling line,2 1500mm UCM reversible cold rolling mill,1 degreasing cleaning line,24 full hydrogen bell type annealing furnace,1 four roll skin pass mill line,1 tension leveler line and 1 heavy winding line,etc..In order to broaden the scope of product sales,increase market competitiveness,strip production line joint technology center,and actively carry out the steelmaking process for stamping steel research and development,has completed the Japanese standard,German standard and American Standard common stamping steel production.On this basis,after the user visits and market research,began in 2012 to develop DDQ of deep drawing steel,but in the actual production yield strength and high tensile strength,low elongation and hardening exponent n and plastic strain ratio R fluctuations and other issues,in the process of using is the feedback for the user a problem of stamping easy to crack,bad shape,surface quality is not up,can not form a stable mass production,process optimization and improvement of the system is in urgent need of a thorough.In order to solve the problems existing in production,the production process of deep drawing steel of DDQ grade were analyzed,in-depth research,improvement in the mechanical properties of DDQ grade deep drawing steel plate to improve the quality and improve the surface quality,explore its influence factors,the process of cold rolling system optimization and improvement,and provides a theoretical basis for the adjustment of the process parameters in production,and ultimately the performance of the product is improved,to meet the needs of users,and achieved good economic and social benefits.The main results were as follows:(1)The annealing temperature and holding time have obvious effects on the microstructure and mechanical properties of DDQ cold rolled sheets.When the insulation temperature is increased from 710 to 750,the stamping performance will be improved.Appropriately prolonging the annealing holding time can improve the N and R values of DDQ deep drawing steel.When the holding time is over 14h,the holding time is further extended,and the deep drawing property is not changed obviously.(2)The hot rolling temperature is 695～700,the cold rolling reduction rate remains 69%,and the recrystallization annealing temperature is 738～750 degrees centigrade.The elongation index is stable and meets the requirements of the users under the technological conditions.(3)After annealing,the strip has a yielding platform,and if the outside tensile stress exceeds the yield strength at the entrance S roll,a transverse fold is produced.Reduce the transverse creases are the main measures to improve the quality of plate rolling,the micro wave of bilateral control,improve the annealing craft system,reasonable matching of elongation set,increase flat S roll crown.(4)The main reason of the strip surface emulsion spot is due to the presence of concentrated emulsion cold strip partial surface oxidation formed in the storage stage after rolling,part of the oil into or attached form spot in the early formation of iron oxide has loose above.The main measures to solve the black emulsion cleaning performance of emulsion,enhance export mill sweeping effect,improve the shape quality of strip,the model on the suction stripper,the frequency for milk,improve the precision of operation.(5)The macular on the surface of the steel plate is the corrosion of iron oxide(Fe3O4)mixed with alpha hydroxy iron oxide(FeOOH).The occurrence of macular is closely related to the cleanliness of the raw materials.To solve the macular problem fundamentally,the cleanliness of the raw materials should be controlled from the source.(6)With the increase of cold rolling reduction rate,the average yield strength and tensile strength of deep drawing steel show an upward trend,and when the reduction rate is above 80%,the strength change range decreases.(7)The annealed texture of DDQ deep drawing steel is mainly composed of strong<111>//RD fiber texture and weak<110>//RD texture.The formation of disordered hot rolled textures during hot rolling has a lower strength level;the cold rolling process forms a distorted banded structure and is prepared for the annealing recrystallization process.In the cold rolling process,the {111} surface tends to rotate in parallel with the plate surface,forming grain boundaries and internal shear bands,thus providing nucleation sites for recrystallization during annealing. |
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