Influence Of δ Ferrite Transformation On Solidification Of 316 Stainless Steel In Continuous Casting

The usability performance of the iron and steel materials decides that most of them possess peritectic reaction. Special characteristic of this kind of steel is the shrinkage of volume in peritectic reaction which will inevitably bring the air gap between the shell and mould wall. This is the important factor of unstable thermal conductivity, and will generate some defects. So it is very important to investigate the influence of the primaryδferrite content which controlls the peritectic reaction. The commercial software-ANSYS was used, 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 influence ofδferrite content, the casting speed and the superheat on the thickness growth of shell in mould in 316 austenite stainless steel. Two dimension model was established, outlet temperature, surface temperature change and thickness change of the solidified shell were simulated as five differentδferrite content, 0%, 25%, 50%, 75% and 100%, and three types of casting speed, 0.4 m/min, 0.5 m/min and 0.6m/min, and three different superheat, 30℃, 40℃and 50℃. Then the law of shell thickness evolution was discussed. The thickness of the breakouting of slab shell in the mould which was offered by a CSP continuous casting plant, was also meatured and compared with the result of simulation to demonstrate the correctness of the simulation.The results show thatδferrite transformation is root of the causes for the irregular solidification of steel in mould in continuous casting process, which resulted in the difference of the surface temperature is about 200℃within 100mm at vertical direction, maybe this will lead to crack on surface. The difference of surface temperature is increased as the amount of transformation ofδferrite increaced, and all of the shell thickness in the mould will become thinner. The ratio of thickness difference vary in a range, 8.6-30%, and lead to thickness of thin solidified shell have great changes. This phenomenon will increase the possibility of crack and breakout apperance in the shell. Although the difference of surface temperature will become smaller and improve the uniformity of the solidified shell as increased casting rate, it has not large influence. The superheat has not influence on uniformity of the shell thickness. The experimental data display that thickness of shell at 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 coincided very well with simulation.Simulation result presented thatδferrite content, casting speed and superheat has different influence on the thickness of shell in the mould. This will offer the clues and evidence for researching the growth of shell thickness in the mould and improving heat transfer.