Research And Application On Numerical Simulation Of Billet Continuous Casting And Direct Rolling Process

Direct rolling of rod and wire is a process which connects billet continuous casting with rolling mill directly,makes full use of the heat of molten steel itself,cancels the traditional reheating process of billet,and realizes direct rolling without heating.Its most significant advantage is to improve the original reheating and rolling mode of casting billet,shorten the process flow and achieve the purpose of energy conservation and emission reduction.Through the combination of field industrial test and finite element numerical simulation,the feasibility of adopting continuous casting and direct rolling process in rod and wire production was verified,and finally the process conditions were optimized to realize the industrial production of continuous casting and direct rolling of rod and wire.The main works accomplished are as follows: 1)the continuous casting process was studied,including drawing speed control,pouring temperature control,secondary cooling dynamic control and corner shape of casting billet,which influenced the continuous casting process and grasped how to achieve the industrial production technology of constant temperature casting;2)by studying the influence of straightening and cutting position,the multi-flow merging process and the design of conveying roller ways,a complete joining technology of billet continuous casting and steel rolling process is formed;3)by studying the deformation process of square billet rolling(rough rolling)in direct rolling and comparing with that of traditional heated billet rolling,a complete temperature control rolling technology is formed;4)good results have been achieved through the on-site industrial production inspection,which lays a foundation for realizing the industrial production and popularization of rod and wire rod direct rolling.Surface of research results of high-speed continuous casting and constant temperature billet discharging process:When the thickness of billet shell at the exit of 150 mm× 150 mm square billet continuous casting crystallizer is not less than 10 mm,the theoretical maximum casting speed of the caster is 3.0m / min.When maintaining a constant flow rate of 120 l / m2 min of secondary cooling water,the surface temperature of the casting billet increases by about 50 ℃ for every 0.4 m / min increase in casting speed.The amount of secondary cooling water flow directly affects the solidification of the casting blank and the fluctuation of the surface temperature of the casting blank.when the drawing speed is controlled within the range of 2.2 m / min to 3.0 m / min,the secondary cooling water flow should not exceed 80 l / m2 min to 100 l / m2 min.When the secondary cooling water flow exceeds 100 l / m2 min,although the cooling of the slab increases in the secondary cooling area,the temperature difference in the surface layer of the slab is very large,which will lead to a high subsequent return temperature and affect the quality of the slab.The superheat degree of pouring should be controlled at about 25 ℃ and the temperature fluctuation range should not be too large.it should be controlled within 5 ℃;The use of a larger radius fillet at the corner of the casting blank has an obvious influence on the temperature distribution of the casting blank.when the fillet radius is 10 %-15 % of the cross section of the casting blank,the temperature increase at the corner of the casting blank is the most obvious.For a 150 mm× 150 mm billet caster,when flame cutting is used,the temperature rise at the position 60 mm away from the cutting surface after cutting for 200 s is very high,which is greater than 50 ℃.it cannot meet the basic requirement of direct rolling billet for the billet surface temperature fluctuation.it is suggested to use mechanical cutting.When mechanical cutting is used to cut as soon as possible within 1.0m after stretching and straightening,the heat loss in this area can be minimized.Surface of research results of continuous casting and steel rolling process: The surface temperature of the casting billet is usually above 1000 ℃ and the conveying time is controlled within 230 s as far as possible from the casting machine outlet to the rolling mill inlet.The heat supply area of the casting blank is mainly within 25 mm of the surface layer of the casting blank,especially in the corner area of the casting blank.for every 50 Hz increase in frequency,the temperature increases by about 13 ℃ / min,and for every 400 a increase in current,the temperature increases by about 50 ℃ / min.When the initial temperature of the casting blank is controlled between 750 and 800 deg c,the induction heating time is short and the temperature is uniform;To the extent that the taper and friction force of the continuous casting crystallizer can be allowed,the design of taking larger rounded corners at the corners of the casting blank can reduce the temperature gradient during the transition from the surface of the casting blank to the corners and ensure the uniformity of the temperature distribution on the surface of the casting blank after induction heating,especially in the transition region of the corners.The research results of direct rolling deformation process show that: During the five-pass rolling deformation of rod and wire rod,the position where the equivalent strain of the direct rolling billet is larger is closer to the center of the billet than that of the traditional rolling,and the moving amount is about 10 mm-15 mm.the equivalent strain that the direct rolling billet can transfer to the center of the billet is 6 %-13 % larger than that of the traditional billet.The product performance test results show that: The mechanical properties and metallographic structure of the product at different starting temperatures of the direct rolling billet were measured,and the improvement effect of the direct rolling process on the product performance was confirmed.The pre-rolling temperature of the direct rolling casting blank is obviously lower than that of the traditional reheating casting blank,the rolling force is increased by 30 MPa-50 MPa,and the performance of the product can be improved by adopting a lower rough rolling temperature,which indicates that the direct rolling process can meet the requirements of product quality.