Study On The Parameters Of Dynamic Soft Reduction During Wide And Thick Slab Continuous Casting

In the continuous casting process, center segregation and porosity of continuous casting products can be moved by dynamic soft reduction technology on the end of solidification. Therefore, the study on the parameters of dynamic soft reduction has an important practical significance in practical production process.Based on the1650mm×250mm slab caster of a steel plant in China, this paper builds solidification heat transfer model, reduction gradient model and reduction efficiency model. On the basis, checking the influence that pouring technology have on process of the solidification and heat transfer model and soft reduction, as well as the influence of different liquid core thickness and reduction amout have on reduction efficiency. The main conclusions in the paper are summarized:(1) The surface temperature of slab wide center sharply drops within the mold, and then decreases slowly in secondary cooling zone, however there will be a reheating temperature at initial stage of each zone, and then gradually decreases as the slab moves into the radiation cooling zone. The temperature of central slab trends to quickly decrease after the end of the solidification during slab continuous casting. At the initial stage of the solidification during billet continuous casting, the solidified shell grows faster. In the middle of the solidification, the thickness of the solidified shell slowly increases. At the end of the solidification, the thickness of solidified shell grows fast again along the casting direction.(2) The liquidus line, the solidus line, the surface temperature of slab wide center and the temperature of central slab of the Q235B increase slowly with the improvement of super heat. When the casting speed is1.2m·min-1, the super heat goes up from21℃to41℃, the position of liquidus line and the solidus line disappeared above the meniscus increases from12.23m to12.99m and18.91m to19.63m. The improvement of casting speed has little influence on the surface temperature of slab wide center in the mold and secondary cooling zone of continuous casting, but has great influence on it in the air cooling zone. The casting speed goes up from1.0m·min-1to1.2m-min-1, the increase of the temperature of slab wide surface gradually goes from9℃at the entrance of the air cooling zone to60.2℃at the end of the air cooling zone. Meanwhile the position of liquidus line and the solidus line disappeared above the meniscus increases from12.26m to14.98m and19.43m to23.08m.(3) Soft reduction rate and gradient of slab decreased along with the casting direction, the curved lines are moved backward along with the casting direction with the increase of casting speed. The curved lines of soft reduction gradient and rate of slab are moved backward with the increase of casting speed. The faster of the casting speed is, the smaller of the maximum and minimum value of soft reduction gradient will be. Average soft reduction gradient represents approximate linear decreasing relationship with casting speed. The average soft reduction gradient of Q235B lowers0.024mm/m when the casting speed increases0.1m/min. Casting speed changes caused little impact to soft reduction rate and average gradient.(4) Super heat changes caused little impact on soft reduction gradient and gradient rate. When the super heats are21℃,31℃and41℃, the changes of soft reduction gradient of Q235B on the reduction zone are0.256mm/m～0.200mm/m,0.255mm/m-0.199mm/m and0.253mm/m-0.196mm/m respectively. The changes of soft reduction rate are0.307mm/min-0.240mm/min,0.306mm/min℃0.239mm/min,0.303mm/min-0.235mm/min respectively,The values of soft average reduction gradient are0.233mm/m,0.231mm/m and0.230mm/m respectively.(5) When the liquid core thickness is the same and the reduction amount is less than2.3mm, reduction efficiency of slab increases with the increase of reduction amount. When the reduction amount is bigger than2.2mm, reduction efficiency of slab keeps a certain value with the increase of reduction amount. When the reduction amount is smaller, the width spread efficiency of slab decreases with the increase of reduction amount. When the reduction amount is bigger than4mm, the width spread efficiency of slab decreases slowly. When the liquid core thickness is less than20mm, the increase of reduction amount will cause little impact to elongation efficiency. But when the liquid core thickness is bigger than20mm as well as the reduction amount is smaller, the elongation efficiency of slab decreases with the increase of reduction amount. When the reduction amount is bigger than2mm, the elongation efficiency of slab keeps a certain value.(6) When the reduction amount is less than2mm, the increase of reduction amount will cause the increase of reduction efficiency. When the reduction amount is bigger than2mm, the reduction efficiency of slab remains the same, and the reduction efficiency of slab affected mainly by thickness, the equation as follows. η=-0.019+0.01086H...