The Research Of Optimization On Secondary Cooling System Of 45steel Billet Continuous Casting At Nansteel

According to the internal defect of billet, crack of workpiece, crack of rolled products and crack of hot jump-test,the result of EDS and simulation comfirmed that the main reasons are inclusion content of billet too high and fallacious distribution of inclusion.The unreasonable secondary cooling system is also the reason of crack in the billet of 45# steel produced by Nanjing Iron & Steel Co.Ltd.Because of the fast rhythm of production for 45# steel,the method to reduce inclusion content by slow down production rhythm is infeasible.This paper controlled the size and distribution of sulfide by the optimization of secondary cooling system,for enhance critical stress and reduce thermal stress of billet.At first, the cold state characteristic of the nine kinds of nozzles for billet caster at Nansteel was systemically tested in this paper.The results were attained by experiment to offer the comparative accurate boundary condition for computer simulation.The optimization of nozzle type is slso based on these test results.According to the specific conditions of casters,the heat transfer mathematics model of secondary cooling system on billet continuous casting at Nansteel was established based on the existing software framework.The software was modified and improved.It will be used for evaluation and optimization of current secondary cooling system.The secondary cooling system in Nansteel was optimized from three aspects that nozzle types, nozzle arrangement and water supplying principle in secondary cooling.These optimization schemes were control the size,distribution of sulfide and the thermal stress of billet based on results of simulation.These were validated by field test.According to the results of metallographic observation and statistical of inclusion for the billet from field test of caster 2#,the control to size and distribution of sulfide by optimization of secondary cooling system have been confirmed.But the crack is still exist when inclusion content is too high. Therefore,the control of incluson content is indispensable to further improve the quality of 45# steel billet.