Influence Of δ Ferrite Transformation On Solidification Of316Stainless Steel In Continuous Casting

The usability performance of the iron and steel materials decides that most of thempossess peritectic reaction. Special characteristic of this kind of steel is the shrinkage ofvolume in peritectic reaction which will inevitably bring the air gap between the shell andmould wall. This is the important factor of unstable thermal conductivity, and will generatesome defects. So it is very important to investigate the influence of the primary δ ferritecontent which controlls the peritectic reaction. The commercial software-ANSYS wasused, and the thickness data of the breakout slab shell from Royal Institute of Technology,Sweden, was employed to calculate the heat transfer coefficient to investigate the influenceof δ ferrite content, the casting speed and the superheat on the thickness growth of shell inmould in316austenite stainless steel. Two dimension model was established, outlettemperature, surface temperature change and thickness change of the solidified shell weresimulated as five different δ ferrite content,0%,25%,50%,75%and100%, and threetypes of casting speed,0.4m/min,0.5m/min and0.6m/min, and three different superheat,30℃,40℃and50℃. Then the law of shell thickness evolution was discussed. Thethickness of the breakouting of slab shell in the mould which was offered by a CSPcontinuous casting plant, was also meatured and compared with the result of simulation todemonstrate the correctness of the simulation.The results show that δ ferrite transformation is root of the causes for the irregularsolidification of steel in mould in continuous casting process, which resulted in thedifference of the surface temperature is about200℃within100mm at vertical direction,maybe this will lead to crack on surface. The difference of surface temperature is increasedas the amount of transformation of δ ferrite increaced, and all of the shell thickness in themould will become thinner. The ratio of thickness difference vary in a range,8.6-30%, andlead to thickness of thin solidified shell have great changes. This phenomenon will increasethe possibility of crack and breakout apperance in the shell. Although the difference ofsurface temperature will become smaller and improve the uniformity of the solidified shellas increased casting rate, it has not large influence. The superheat has not influence onnon-uniformity of the shell thickness. The experimental data display that thickness of shellat edge was thicker than thickness of shell at center, and has larger thickness change.Thickness fluctuation not only occurs at vertical direction but also appears at horizontal direction. The thickness of shell change periodically like wave-shape, this is coincidedvery well with simulation.Simulation result presented that δ ferrite content, casting speed and superheat hasdifferent influence on the thickness of shell in the mould. This will offer the clues andevidence for researching the growth of shell thickness in the mould and improving heattransfer.