Study On Evolution Mechanism Of CASM Inclusion In Non-aluminum Deoxidation Heavy Rail Steel

The high-speed railway plays an irreplaceable role in the development and construction of the national economy in China.Because of the rapid development of high-speed railway,more high-quality rail steel is needed.Heavy rail steel is required to have excellent fatigue resistance,thereby increasing the service life of heavy rail steel and improving its service life.Therefore,higher requirements for the control of brittle inclusions containing alumina in heavy rail steel are put forward.Refining slag has a significant impact on inclusions in steel.The use of high basicity and alumina refining slag has been widely adopted at home and abroad,but the target components of inclusions still have some differences.This subject is based on industry research,analysing the types and characteristics of inclusions in heavy rail steel by metallographic microscope,SEM-EDS spectrum.The slag-steel refining experiment was carried out by the MoSi2 furnace,so that explore the influence of the refining slag system with different and high alumina mass fraction on the inclusion.Industrial test verify the feasibility of high alumina refining slag,and the four element compound inclusions of CaO-Al₂O₃-SiO₂-MgO formation mechanism are briefly analyzed.Through the above study,the main conclusions are as follows:(1)The typical inclusions mainly include CaO·Al₂O₃·SiO₂,CaO·Al₂O₃·SiO₂·MnS,CaO·Al₂O₃·SiO₂·MgO,CaO·Al₂O₃·SiO₂·MgO·MnS in heavy rail steel.And the alumina inclusion accounted for more than 70% of the total number of all inclusions,and the mass fraction of Al elements accounted for 5%to 15%,and the mass fraction of Si elements accounted for more than 15%;(2)The results of the laboratory slag-steel refining reaction show that the mass fraction of total oxygen in the steel decreases and then increases with the increase of the mass fraction of Al₂O₃ in the slag.When the mass fraction of Al₂O₃ is about 30%in refining slag,the mass fraction of total oxygen in steel is the smallest.The average diameter of inclusions in heavy rail steel decreases first and then increases with the increase of Al₂O₃ content in refining slag.The average diameter of inclusions is minimum when the mass fraction of Al₂O₃ is 20%? 30%in the refining slag;(3)High alumina slag refining industrial test results show that 2?m was significantly better than those of the original process of inclusion size less than steel;starting from the inclusion of average diameter per unit area,number and area percentage point,containing 20%to 30%Al₂O₃ industrial synthetic slag has the feasibility of reducing the size of inclusions in heavy rail steel;From the composition of inclusions look,the component from the CaO-Al₂O₃-2SiO₂ zone refining early gradually to 2CaO-Al₂O₃-SiO₂ phase transformation zone;(4)The CASM inclusions in heavy rail steel are mainly two types of Ca-Al-Si-Mg-Mn and Ca-Al-Si-Mg.Their main characteristics are Ca/Si ratio less than 1 and Ca/Si ratio greater than 2.The Mg elements in the inclusions of the four element system of CaO Al₂O₃ SiO₂ MgO are distributed uniformly around inclusions and are distributed around the inclusions.