| The rapid development of advanced equipment manufacturing industry such as energy-saving environmental protection,ocean engineering,petrochemical engineering will inevitably put forward higher requirements for the quality of key materials.Super austenitic stainless steel has excellent strength and corrosion resistance,is one of the key materials urgently needed by advanced equipment manufacturing industry when it is used in areas with serious material corrosion.The development and application of super austenitic stainless steel are mainly concentrated in foreign countries.At present,China has only realized the localization of he first generation of super austenitic stainless steel 904L and the second generation of super austenitic stainless steel 254SMO,but in the production process of which there are still many bottleneck problems.The third generation of super austenitic stainless steel 654SMO is in the research and development stage.There are many problems in the production process of super austenitic stainless steel 654SMO:(1)The volume shrinkage of 654SMO slab is very serious during continuous casting process,which leads to easy cracking on the surface of slab;(2)The content of alloy elements is high for 654SMO,which leads to the serious central element segregation and secondary phase precipitation;(3)Grain coarsening and high temperature oxidation are serious during homogenization process of slab,and cracking is easy during hot continuous rolling.Based on above problems,the application of feeding strip technology has been proposed in this paper,which is,decreasing central superheat rapidly and increasing nucleation particles through the feeding strip technology,so that the equiaxed crystal rate is improved and the equiaxed crystal is refined.This paper has used the commercial software Fluent,coupled Launder-Sharma low Reynolds turbulence model,the enthalpy-porosity technology,VOF multiphase model,built a 3D solidification model during vertical slab continuous casting process with or without strip feeding.The flow field,temperature field and solidified shell distribution have been simulated,the effects of strip feeding speed and temperature during unilateral strip feeding process have been analyzed in detail,and the growth process of solid strip in superheated melt and the flow direction and spatial distribution of molten strip have been studied at the same time.Simulation results show,the flow field still maintains "double roll" pattern after strip feeding into the mold.Strip grows quickly when starts to be fed;strip grows slowly when strip is fed around SEN port;at the time that strip is fed beyond SEN port,its growth speed increases suddenly,as strip is fed into melt,the speed of strip growth gradually decreases.Under the condition that strip can be fed through the SEN port,molten strip mainly flows toward center and replaces superheated liquid steel,central temperature thus decreases significantly.Under the condition that strip can’t be fed through the SEN port,molten strip flows toward side of slab and solidification trend of solidified shell in the mold becomes more obvious.In the unilateral strip feeding situation,as strip feeding speed increases or feeding temperature decreases,the depth of strip feeding will be larger,and the superheat of more central melt will decrease.Strip feeding can promote solidification trend of solidified shell in the mold,the improvement effect of bilateral strip feeding is better.Bilateral strip feeding can improve symmetry of flow and temperature field compared to unilateral strip feeding,and the improvement effect of bilateral strip feeding on temperature field is better compared to unilateral strip feeding.Based on the established mathematical model,the influence of feeding vibrating strip unilaterally on the flow field,temperature field and solidified shell distribution of liquid steel has been studied.Simulation results show,the flow field still maintains"double roll" pattern after feeding vibrating strip unilaterally.A part of liquid steel around strip is carried by strip and flows toward two sides of strip.Only a little part of liquid steel has enough momentum to bypass strip again to form a complete backflow after bypassing the steel strip,most flows down along the casting direction after bypassing the steel strip or hitting the narrow face of the mold.Feeding non-vibrating strip unilaterally can reduce the central superheat by 2～6 K,and feeding vibrating strip can reduce the central superheat by about 5 K on this basis.The effect of feeding vibrating strip unilaterally on the growth of solidified shell is much more obvious than that of feeding non-vibrating strip,and the no solidified shell formation due to the wash of superheated liquid steel almost completely disappears. |
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