Thermofluid Behavior During Post‐VD Soft Argon Stirring of X80 Pipeline Steel: Coupled Modeling and Industrial Validation

Abstract

Postvacuum degassing (VD) soft argon stirring controls temperature homogenization and interfacial stability during clean steel refining. A 3D transient coupled flow and heat‐transfer model was developed for a 210 t ladle during post‐VD soft stirring of X80 pipeline steel. Four quantitative indicators were defined: temperature mixing time, dead‐zone fraction, near‐interface flotation potential, and interfacial disturbance risk. Model predictions were compared with industrial inclusion statistics obtained by scanning electron microscopy‐energy dispersive spectroscopy and automated ASPEX analyses. Reasonable adjustment of argon flow rate within the specified process window effectively lowers the inclusion risk. Industrial measurements showed that increasing the soft‐stirring flow rate from 50 to 60 NL/min reduced the number density of large inclusions from 0.061 to 0.020 mm −2 in molten steel at the end of soft stirring and from 0.070 to 0.030 mm −2 in rolled plate. The combined numerical and industrial results indicate that an increase in flow rate from 50 to 60 NL/min reduces the mixing time by 51 s and lowers the density of large inclusions by over 50%, offering the best trade‐off between inclusion removal and process stability under the current conditions.