Control theory and practice of argon bubble-induced internal defects in pipeline steel
With the rapid development of oil and gas industry,the requirements for the strength,toughness and weldability of pipeline steel are constantly increasing.Optimizing the argon sealing process during continuous casting is crucial for reducing or avoiding internal defects caused by argon bubbles,which is of great significance for improv-ing the quality of pipeline steel products.L485M pipeline steel was taken as the research object,the effect of the sealed argon flow rate of the submerged entry nozzle on the internal defects of the pipeline steel L485M was studied by controlling the sealed argon flow rate and the casting speed.Then optimized the argon flow rate and casting speed to solve the internal defects of the slab caused by the argon bubble.The results show that,the argon bubble is gener-ated when the flow rate is too high,which is easily captured by the solidification front of the slab and leads to the internal defects of the slab,formed elliptical flattened defects after rolling,distributed near the surface of the steel plate;An increase in argon sealing gas flow rate or casting speed will both lead to a higher occurrence rate of steel plate defects.Reasonable argon flow rate and casting speed of continuous casting machine are important parameters to ensure that bubbles can float up in time and not enter the slab.The reasonable casting speed of L485M pipeline steel slab with a specification of 260 mm×2 070 mm is 0.75m/min,and the argon flow rate of split nozzle should not be greater than 2.5 L/min.The integral nozzle can effectively avoid the internal defects caused by argon bubble.The research results are of great significance for improving the theoretical process of argon sealing in the continuous casting of pipeline steel and enhancing the quality of pipeline steel products.They also provide reference value for the optimization of the submerged entry nozzle sealing process for other steel grades,the effect of continuous casting speed on internal defects caused by argon bubbles in slab,and the behavior of argon bubbles in the protective continu-ous casting process.
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