Coupled Thermo-mechanical Model For Soft Reduction For Continuous Casting Bloom

Heavy rail steel bloom is the base material of 300 km/h high-speed rail.Center segregation and center porosity often occurs in heavy rail steel bloom continuous casting production.The soft reduction technology is an effective way to control the quality defects such as center segregation of bloom,it has become the focus of production companies.According to the production process of U71 Mn bloom in a factory,the thermal-mechanical model of solidification and heat transfer of bloom and the thermal-mechanical model of soft reduction are established.Using MSC.Marc finite element software modeling and solving,shooting nail test to verify the solidification and heat transfer model.The effects of casting speed,cooling water and superheat degree on casting solidification and free thermal shrinkage of casting bloom.The deformation behavior and stress-strain distribution of bloom during soft reduction of continuous casting technological process parameters such as reduction amount and pressing position were studied.Research indicates:(1)With high casting speed,weak cooling water and high pouring temperature,the surface temperature of the heavy rail steel bloom is high,the temperature fluctuation is small,the temperature distribution of the section is even,and the two-phase interval and solidification end become longer.Solid phase rate 0.2 to 0.8,corresponding to the 1~4# racks.(2)In the solidification process of heavy rail steel bloom,the corner shrinkage is the largest,the narrow side is the second,and the wide side is the smallest.In the direction of casting,the solidification shrinkage rate of the casting blank gradually increases,the shrinkage amount of the air cooling section is the largest,the shrinkage of the bloom at the racks position is 4.56~8.11 mm.(3)The decrease of area of two-phase zone increases with the increase of reduction and the decrease of solid phase ratio.The area reduction rate of the two-phase zone increases with the increase of the reduction amount,and is less affected by the central solid phase rate of the slab.The flow of molten steel in the two-phase zone in the center of the slab can be promoted by adopting a larger reduction amount and solid phase ratio.(4)When the amount of reduction does not exceed 3 mm,any solid rate of soft reduction,crack sensitive area will not have the risk of pressure crack;When the amount of pressure is 4 mm,the solid phase rate cannot exceed 0.6;If you need to press down 5 mm,solid phase rate should not exceed 0.4.(5)Considering the influence of reduction process parameters on the area of twophase zone and strain in crack sensitive zone and the racks position,the reasonable reduction process parameters of heavy rail steel bloom under soft reduction are solid ratio of 0.6 ~ 0.8 and reduction amount of no more than 3 mm.