Effect Of Rare Earth Ce And Heat Treatment Process On The Structure And Properties Of U75V Heavy Rail Steel

In recent years,the density of railway transportation has increased,the speed of trains has increased,and the volume of carrying capacity has increased.The quality requirements of heavy rail steel have become higher and higher.In this thesis,U75V heavy rail steel is used as the basic steel grade,and the rare earth element Ce is added to the steel to explore the effect of rare earth Ce on the structure,inclusions and properties of heavy rail steel.Three furnaces of test steel were smelted using a vacuum induction furnace under laboratory conditions.Through Zeiss metallographic microscope,impact testing machine,MTS universal testing machine,salt spray corrosion test chamber,X-ray diffractometer and other instruments,the properties of rare earth Ce on U75V heavy rail steel structure,hardness,impact energy,tensile strength and other properties are analyzed.The Sigma300field emission scanning electron microscope was used to count the composition,shape,size,and quantity of the inclusions in the test steel,and the typical inclusions were analyzed.The results showed that:Rare earth Ce can refine the structure of the test steel and make the grain distribution more uniform;when the content of rare earth Ce is 22ppm,the number of inclusions in the test steel is reduced by 52.4%,and the total area is the smallest;after adding rare earth Ce,Mn S,Al₂O₃inclusions are reduced,the Ce content of 22ppm Mn S inclusions in the test steel decreased by 56.5%,the average area decreased by 3.54μm²,the number of single Al₂O₃inclusions was greatly reduced,when the rare earth Ce content is 46ppm,the test steel The size of rare earth composite inclusions increased.After heat treatment of rare earth steel,it is found that when the holding time is 60min,as the heating temperature increases,the average grain size increases from 8.87μm to22.36μm,and the grains are more uniform,the number of inclusions decreases,and the area increases first The tendency to decrease afterwards.When the heating temperature is1100℃,with the extension of the holding time,the average grain size increases from11.33μm to 35.85μm,and the number of inclusions also decreases,but the area of the inclusions first decreases and then increases.The impact toughness,tensile strength and elongation of the test steel increase with the increase of rare earth content.When the rare earth content is 46ppm,the impact absorption energy increases from 3.45J to 4.5J,which is an increase of 30.4%;The strength increased slightly from 1052.6MPa to 1095.8MPa;the elongation increased from9.81%to 10.7%;the hardness decreased with the increase of rare earth content,from383.2HV to 342.8HV;the center of the tensile fracture appeared Fiber zone,and a small amount of dimples appeared,which changed from brittle fracture to mixed fracture.The addition of rare earth Ce improves the strength and toughness of steel.In the salt spray corrosion test of the test steel,the corrosion products are allα-FeOOH,Fe₃O₄,γ-FeOOH and a small amount ofβ-FeOOH.As the content of rare earth increases,the content ofγ-FeOOH decreases and the content ofα-FeOOH increases.The corrosion resistance becomes better.