Research And Application On Process And Control For Dual-phase Steel Based On Ultra Fast Cooling In CSP

With the rapid development of automobile industry, we pay more attention to safety and energy saving issues. In order to achieve lightweight and security, high strength steel and advanced high strength steel become the development trend in automobile industry. In this paper, we focus on the effects of different technological parameters on the microstructure and properties of hot rolled dual phase steel and develope the ultra fast cooling foundation level automatic control system, evaluating the control effect of ultra fast cooling control system and analyzing the microstructure and properties of the actual product. The main research contents and results are as follows:(1) The effects of process parameters on the microstructure and mechanical properties of hot rolled dual phase steel was researched:as the finishing rolling temperature decreased, the tensile strength increased and ferrite microstructure became finer and more uniform with martensite distributed as island; as the intermediate temperature decreased, the tensile strength decreased and the ferrite content increased with smaller grain size with the distribution of martensite became more dispersed; it would be known that the coiling temperature should be below220℃, according to theoretical calculation of martensitic transformation temperature points and simulation on ultra fast cooling process of hot rolled strip.(2) The cooling process after rolling of different thickness steel was simulated:when the thickness reached13.0mm, the temperature difference of center and surface was37℃, the rising temperature of center was24℃after laminar cooling; the temperature difference of center and surface was120℃, the rising temperature of center was40℃after ultra fast cooling. The rising temperature of center and temperature difference of center and surface was low and had no more affect on the stability of performance in the thickness direction.(3) The ultra fast cooling fundamental level automatic control system was developed and control system monitor screen of cooling after rolling was designed. The control method of control system was followed:strip position tracking was the accumulation of actual strip speed and program scanning cycle; the water pressure was controlled by the method of pressure closed loop of power pump and fuzzy PID control of overflow valve; the pipe flow was controlled by the method of fuzzy control of regulating valve.(4) The effect of ultra fast cooling control system was analyzed and the microstructure and mechanical properties of hot rolled dual phase steel products was explained. Actual measured data showed that the water pressure was controlled at target value±0.05MPa, the pipe flow at target value±1m3/h, the intermediate temperature at670±10℃, the coiling temperature at target value±30℃. The control method had received good control effect and microstructure and properties of dual phase steel products was relatively stable, primely meeting the requirements for hot rolled dual phase steel organization and performance.