The Effect Of Refining Slag On The Cleanliness Of Heavy Rail Steel And Bearing Steel

Heavy rail steel and bearing steel play significant roles in the development of society.The products of these steels with high quality are needed urgently in the modern industry.Excellent abrasion performance,fatigue strength and less brittle fractre are required so that the steel products’ cleanliness have to be better.Refining slag have remarkable effects on steel’s cleanliness and inclusions.However,there was less progress about the development of refining slag for heavy rail steel and bearing steel in domestic.There is a lack of relevant researches about the effect of refining slag with different preparation methods on steel’s cleanliness.This research prepared several kinds of refining slag with different treatments and chemical compositions.The physical and chemical properties and crystal structures of these slags were researched by the apparatus of melting point and speed,X-ray diffractometer and so on.Then slag-metal reaction experiments were carried on with the refining slags prepared.The Oxygen and Nitrogen Analyzer and Carbon and Sulfur Analyzer were used to detect the mass fraction of the oxygen and sulfur in the steel samples of all the experiments so that the deoxidation and desulfuration properties of the refining slags could be studied.The size and number of the inclusions in the end samples of all the experiments were studied by optical microscope,the morphology and composition of these inclusions were detected by scanning electron microscope.The resultsbased on these research showed that:(1)There were significant effect on the refining slag’s physical and chemical properties and crystal structures by different cooling methods.The slag by water cooling were full of glass phase or microcrystal phase inside,while the slag cooled slowly crystallized absolutely.The melting point of the slags by water cooling were the lowest and their melting speed were highest,while the melting point of the slags blending by machine were the highest and their melting speed were lowest.Among the slags with same treatment,the refining slag whose basicity is 2.5 of the heavy rail steel and the slag whose number of w(CaO)/w(Al2O3)is 0.94 of the bearing steel had higher melting point and lower melting speed.(2)Different treatment methods didn’t have remarkable effect on the deoxidationvelocity of refining slag.Among the slags with same treatment,the refining slag whose basicity is 2.5 of the heavy rail steel and the slag whose number of w(CaO)/w(Al2O3)is 1.65 of the bearing steel had higher speed of deoxidation.(3)Different treatment methods didn’t change the desulfuration effect of balance in the end,but it could change the desulfuration rate in the beginning of refining process and the time reaching desulfuration balance.The desulfuration velocity in the beginning of the slag cooling by water,the slag cooled slowly and the slag blending by machine decreased systematically.Among the slags with same treatment,the refining slag whose basicity is 2.5 of the heavy rail steel and the slag whose number of w(CaO)/w(Al2O3)is 1.65 of the bearing steel had higher desulfuration rate and velocity in the beginning of refining process.(4)The inclusions of the experiment use slag cooling by water were less and smaller than the counterparts of slag cooled slowly and slag blending by machine.Among the slags with same treatment,the refining slag whose basicity is 2.5 of the heavy rail steel and the slag whose number of w(CaO)/w(Al2O3)is 1.65 of the bearing steel were easier to decrease the size and amount of inclusions.(5)In the heavy rail steel used the refining slag whose basicity is 2.5 inclusions of Al2O3·MgO·SiO2·MnS,Al2O3·MgO·SiO2·MnO,SiO2 and MnS decreased remarkably,while the inclusions of Al2O3·MgO·SiO2,spinel and Ba-bearing increased.In the bearing steel used the refining slag whose number of w(CaO)/w(Al2O3)is 1.65,inclusions of spinel decreased,while the inclusions of Al2O3·MgO·SiO2·CaO increased.There was hardly any SiO2 and MnS.(6)The main multiphase inclusion in the heavy rail steel was MnO-Al2O3-SiO2.The inclusions in the steel used the slag whose basicity is 1.5 was more inclined to focus on the low melting point area in the phase diagram.This result demonstrated that the refining slag of lower basicity had better effect on the control of inclusions’ plastification.