ANALYSIS AND OPTIMIZATION OF CORNER CRACK OF HRB500VNb BILLET AT HIGH DRAWING SPEED
By comparing the low magnification structure of HRB500VNb billets produced by the Long Materials Division of HBIS Group Tangsteel with HRB500 billets,and combining with numerical simulation of the temperature field at the corners of HRB500VNb billets,the causes of corner cracks in the billets were analyzed.The results indicate that the probability of HRB500VNb experiencing corner cracks above 2.0 level is significantly higher than that of HRB500.By reducing the water volume of the mold from 160 t·h-1 to 130 t·h-1,the water flow rate from 12.46 m/s to 10.34 m/s,and the radius of the mold corner from 8 mm to 10 mm,the heat transfer in the corner of the casting billet is weakened.Optimize the physicochemical parameters of the mold powder,reduce the viscosity,melting point and alkalinity of the protective slag,increase the melting rate,and improve the heat transfer between the casting billet and the mold.The water in the first zone of the second cooling is reduced by 8％,the water in the third zone of the second cooling is increased by 6％,the overall specific water is reduced by 0.2 L/kg,and the cooling speed of the casting billet is slowed down.Using low sulfur,phosphorus hot metal and high-quality scrap steel,the steel composition of converter should ensure w(P)not more than 0.037％,w(S)not more than 0.028％to reduce the Angle crack caused by inclusions;After the process optimization,the maximum level of corner crack of HRB500VNb billet is 3,and the proportion of corner crack of 2.5 or above is reduced from 53.62％to 16.09％,and the quality of billet is obviously improved.
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