Analysis on causes of ultrasonic flaw detection in wind power gear steel
Ultrasonic testing is one of the methods used for detecting defects in large-scale wind power gear steel,and the presence of defects indicates non-compliance with performance standards.To address the frequent occur-rence of ultrasonic flaw detection in wind power gear steel,the causes of these defects was investigated.Through defect observation and refining process sampling analysis,the types of defects and their formation stages were iden-tified.Then,the formation causes of defect inclusions was determined combined with thermodynamic calculations and process improvement measures was proposed.The results show that these ultrasonic flaw detections are large-sized inclusions formed by the aggregation of solid magnesium aluminum spinel and liquid CaO-MgO-Al2 O3-SiO2 in-clusions,with a small amount of CaS attached to the periphery.The size of these defect inclusions ranges from 30 μm to 100 μm.Analysis finds that low[Al]content in the VD process steel is the root cause of the formation of high SiO2 content CaO-MgO-Al2O3-SiO2 inclusions.Due to low[Al]content,[Si]in the steel liquid reduces the Al2O3 in the inclusions,forming high SiO2 content CaO-MgO-Al2O3-SiO2 inclusions.As[Al]content in the steel liquid rised again,the SiO2 in the inclusions are partially reduced,but some high SiO2 content CaO-MgO-Al2 O3-SiO2 inclusions are still remained.Increasing[Al]mass fraction in the steel liquid during the VD process to above 0.010％is a reasonable measure to reduce the occurrence of CaO-MgO-Al2 O3-SiO2 inclusions with high SiO2 con-tent,thereby effectively reducing the incidence of ultrasonic testing defects in wind power gear steel.
wind power gear steelultrasonic flawinclusionrefining processCaO-MgO-Al2O3-SiO218CrNiMo
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