Research And Control Of Non-metallic Inclusions In Countries Sulphurized And Aluminized Steel

Mechanical,automotive,aviation and other industries require special steel performance during the vigorous development,the steel is not only to ensure its own mechanical properties?such as strength,toughness,etc.?,but also to ensure the machinability.Adding some aluminum that can refine the grain toughness of the steel,and sulfur which improve cutting performance,can produce excellent process performance of Al and S-containing steel.Al and S-containing steel has good toughness and machinability,but it can easily generate a large number of MnS and Al₂O₃ inclusions,which affects the steel purity.Therefore,the study of the types of non-metallic inclusions in the steel,size,quantity and distribution is necessary.In this paper,a typical Al and S-containing steel FAS2225 was studied.The number,distribution and aspect ratio of the inclusions in the vertical and horizontal directions of the circular billet were quantitatively analyzed by using the metallographic microscope and the data processing software Image-Pro Plus 6.0.Experiments show that the number of inclusions was more in the center of the billet and the horizontal radius of 1/2 than edge parts.And the overall distribution in steel was relatively dispersed.The number of spheroidal inclusions with a small aspect ratio of 1.5 was about 61.1%,which indicated that the quantity and shape control of non-metallic inclusions in steel were ideal.The observation of non-metallic inclusions by scanning electron microscopy and energy dispersive spectroscopy is mainly MnS inclusions,with a certain amount of Al₂O₃ inclusions and multiple composite inclusions.Electrolysis experiments showed that large-size inclusions were mainly about 10-20?m,and the morphology was mainly spherical-like,which was similar to the conclusion of metallographic microscopy and SEM+EDS.Inclusions in Al and S-containing steel were observed in situ by high-temperature laser confocal microscopy with 1?/s and 5?/s,10?/s heating rate.The results showed that the slow heating rate was more conducive to the spheroidization and quantitative control of MnS.The insulation treatment of samples at the solution temperature of MnS showed that Mn S inclusions was more conducive to morphology and quantity control with 180 min insulation treatment.According to the parameters of molten steel composition,temperature and other parameters in the process of smelting,the thermodynamic calculation of formation conditions of nonmetal inclusions in steel was carried out.The results showed that the actual industrial production of Al and S-containing steel would inevitably produce Al₂O₃inclusions.When molten steel in the solidification process temperature reached1373 K,it began to produce Mn S inclusions,and steelmaking process can produce Al-O-Mg based inclusions and Al-O-Ca based inclusions with a very low content of Mg and Ca.