Study On Deformation Behavior Of Bloom At Solidification End During The Convex Roll Reduction Process

During the continuous casting process of the bloom,the convex roll reduction will make a significance in improving the quality of the bloom.Based on the continuous casting bloom of 360 mmx450 mm made in a domestic steel plant,the 45#steel bloom has been studied with the practical production condition.A three dimensional thermal mechanical coupled model has been established to analyze the deformation of convex roll and bloom with different transition region structures,the optimal sizes of the convex roll with gradual changing curvature as well as the variations of bloom temperature,solidified shell growth and solidification shrinkage.The stress and strain variations of bloom have also been discussed during the convex roll reduction.The main conclusions are as follows:(1)Compared to convex roll with leg,circular arc and hypotenuse transition region structures,the transition region structure with gradual changing curvature has the minimal influence on deformation of convex roll and bloom.(2)The optimal sizes of the convex roll with gradual changing curvature applied for the bloom of 360 mmx450 mm are as follows:the length of flat roll area is 200 mm,the height of flat roll area is 30 mm and the length of gradual changing curvature area is 80 mm.(3)The surface center temperature of bloom drops rapidly in the mold and drops slowly in the secondary cooling zone and air cooling zone.The center temperature of bloom drops slowly before the solidification end while it drops rapidly after the solidification end.The growth rate of solidified shell appears to be a trend of "fast-slow-fast",The casting speed makes a great influence on solidification process.While the casting speed increases,the temperature of the bloom rises and the solidification end moves backward.(4)The solidification shrinkages of different bloom surface locations are different.At the end of the strand,the shrinkage decreases in the direction of surface center to corner.The shrinkages of surface center and comer are 6.90 mm and 6.40 mm respectively while the casting speed is 0.55 m/min.The casting speed makes a great influence on solidification shrinkage.While the casting speed increases 0.05 m/min,the total shrinkage of bloom surface center decreases about 0.50 mm.(5)During the reduction process of convex roll with gradual changing curvature,the strains of bloom characteristic points keep rising with a ladder-like tendency.The strain of the contact endpoint between bloom and convex roll changes rapidly,the strain value reaches 0.280 after the convex roll reduction.The stress of bloom surface fluctuates violently during the reduction process,the stress of corner has the most violent fluctuation and the value of stress is 147.52 MPa.(6)Center porosity defect has been improved obviously after the convex roll with gradual changing curvature is put into operation.