Simulation Study On Heat Transfer And Solidification Structure Of 280mm×320mm Bearing Steel Continuous Casting Bloom

Bearing steel is an indispensable special steel in the fields of railway transportation,aerospace,mechanical manufacturing,wind power generation and the other fields.There is a serious central segregation defect in GCr15 bearing steel continuous casting billet produced by a steel company in China.Through on-site sampling analysis,the macrostructure and carbon segregation distribution of bearing steel continuous casting billet were studied;the heat transfer model and solidification structure model of GCr15 bearing steel continuous casting slab with 280 mm and 320 mm cross section were established and verified.By numerical simulation method,the change regulation of temperature field,shell thickness and solidification structure of GCr15 bearing steel continuous casting slab during solidification under different continuous casting process conditions were calculated and discussed.The following conclusions are drawn:(1)Hot pickling experiments were carried out on GCr15 bearing steel continuous casting billet samples,and the results showed that segregation is distributed in concentric circles on the cross section of the billet;it is distributed in a periodic v shape in the longitudinal section.(2)When the casting speed is 0.7m/min.the superheat is 20? and the secondary cooling water ratio is 0.2L/kg,the heat transfer model is used to analyze the temperature field of GCr15 bearing steel continuous casting billet and the growth condition of the billet shell.The results show that the temperature gradually decreases from the central position of the billet cross section to the corner of the billet,but the temperature gradient shows an increasing trend;in the early and late stage of solidification,the growth rate of solidified shell is faster.(3)The influence of casting speed and superheat on heat transfer of continuous casting billet was analyzed by using heat transfer model.the results show that: for every 0.1 m/min increase of casting speed,the positions where the liquidus and solidus in the center of bloom cross-section disappear are shifted backward by 1.07 m and 4.07 m respectively;for every 10? increase in superheat,the disappearance positions of liquidus and solidus have shifted backward by 0.71 m and 0.33 m.(4)The solidification structure of GCr15 bearing steel continuous casting billet was simulated at the casting speed of 0.7m/min,superheat of 20? and secondary cooling water ratio of 0.2L/kg.the results showed:the percentage of equiaxed crystal zone was about 29.1%,which was not much different from the percentage of equiaxed crystal zone measured after actual pickling of 28.7%.(5)The influence of casting speed and superheat on the equiaxed crystal ratio in the center of the slab was analyzed by using the solidification structure coupling model.The results showed that the casting speed increased from 0.6 m/min to 0.8 m/min,and the central equiaxed crystal ratio decreased from 30.4% to 28.1%.when the superheat degree increases from 10 ? to 30 ?,the central equiaxed crystal ratio decreases from 37.9% to 23%.