Cause analysis and process optimization of flaw detection in N08811 corrosion resistant alloy tube billet
N08811 is a typical Fe-Ni-based corrosion resistant alloy,which has excellent high temperature oxidation and corrosion resistance,and is widely used in petroleum,chemical,photovoltaic,nuclear power and other fields.Yongxing Special Materials Technology Co.,Ltd.is one of the major producers of Incoloy 800 series rods and wires in China.The problem of unqualified ultrasonic inspection often occurs in the production process,leading to the deg-radation or even scrapping of the finished product.In order to reduce the detection alarm rate,the defect types of N08811 tube billet were analyzed by scanning electron microscope.Then the evolution behavior of molten steel,slag and inclusions in smelting process was sorted out.Further,the formation mechanism of defects was analyzed using thermodynamic software such as FactSage and slag-steel equilibrium model.It is found that there are compound large size cluster inclusions with high melting point Al2O3-MgO-TiOx oxide and TiN at the detection alarm posi-tions.There is a strong reaction between molten steel and slag during AOD-LF smelting process,and the continuous slag-steel reaction results in the formation of a large number of small size Al2O3-MgO-TiOx high melting point inclu-sions in molten steel,which accumulate and induce the formation of TiN cluster inclusions during solidification.In order to reduce the formation of inclusions with high melting point,the balanced slag system with the steel was cal-culated based on the slag-steel balance model,and the original process was optimized and improved,as well as good practical results were obtained.After the process improvement,the yield of Al and Ti elements in the whole smel-ting process increases from 44.3％and 74.6％to 56.2％and 86.8％,respectively,the inspection pass rate of the tube blank increases from 77.26％to 96.23％,and the purity of the tube billet is significantly improved.The re-search results provide technical reference for the clean smelting of high aluminum-titanium Fe-Ni-based alloy.
Incoloy 800Fe-Ni based corrosion resistant alloyinclusionTiNcoexistence theory
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