Research Of Refining And Continuous Casting Technology For High-speed Heavy Rail Steel Bloom

Severe standard has been established for heavy rail steel due to the high quality and high safety of high-speed railway. Therefore, the key technologies for improving the cleanliness and homogeneity of high-speed heavy rail steel, such as the oxidizing technology of non-aluminium, vacuum degassing, protective casting, the tundish metallurgical technology, strict casting speed and molten steel temperature control, dynamic secondary cooling and dynamic soft reduction control, are generally included in production.The present research is aiming to solve the refining and con-casting technology problems of high-speed heavy rail steel with the combination of simulation and experiment method. Based on the results of steel cleanliness control investigation, numerical simulation of the flow in tundish, high temperature mechanical properties test of con-casting blooms and the solidification and dynamic soft reduction models, the most important technical control points has been revealed, the details of which are as follows:1) The package technology has been developed for high cleaniness heavy rail steels. In order control the gas content and inclusions level, secondary refining process has been optimized by the non-aluminium deoxidizing technology, vacuum degassing, protective casting and the tundish metallurgical technology. The following gas and inclusions limitaion could be satisfied:[H]<2.5ppm, [N]<50ppm. T.O.<20ppm, [P]<0.020%, [S]<0.008%; For inclusions, type A< level 2, type B< level 1.5, type C< level 1, type D< level 1. The strand quality meets the standard of 200 km/h railway.2) The high temperature mechanical property of high-speed heavy railway steel under as cast conditions has been revealed. The third embrittlement temperature regions can be found in the range from 980℃ to 800℃, within which it is sensitive to crack due to the low hot ductility. In order to prevent the onset of cracks, the temperature during straightening and soft reducting should be higher than 960℃. The secondary cooling control system must be impoved during high cast speed to avoid cracking by increasing the strand surface temperature.3) The integrated dynamic soft reduction control model for bloom caster was developed, including dynamic thermal tracking model, dynamic soft reduction model and dynamic secondary cooling model. The relative tolerance of calculation and measurment is lower than 4% after model optimazition based on nail-shooting experiment.4) The control parameters for dynamic soft reduction have been propused for high-speed heave railway steels. The reasonal casting speed and temperature are suggested by comparison of the metallurgical effect of heavy steels of U71Mn, U76CrRe and 900A. A total of 355 experiments indicated that the integrated dynamic soft reduction control model was quite stable and effective. The central crack friction of strands in 0 and 1 grades increased from 96.5% to 98.52% with the dynamic soft reduction, and the middle crack friction also increased from 97.67% to 99.26%. Simultaneously, the carbon segregation rate lower than 1.08 increased to 83.1%.