The Effect Of Rare Earth Ce On Inclusions And Thermal Fatigue Properties Of 21CrMo10 Tube Die Steel

In this paper,21CrMo10 tube die steel was taken as the research object,adding different amounts of cerium,to explore the effect of cerium on the structure,inclusions,mechanical property and thermal fatigue property of the steel.Through the thermodynamic calculation,the formation and modification mechanism of cerium inclusions in steel were predicted and verified,and the following conclusions were drawn:?1?The inclusions in cerium-free steel were mainly Al₂O₃ and MnS,the size of inclusions was 5¹0?m and the shape of inclusions was irregularly.after the addition of cerium,the inclusions were modified into Ce₂O₂S and CeAlO₃.When the cerium content is 0.014%,the number of inclusions less than 5?m was largest.And when the cerium content was up to 0.044%,the deoxidization rate and desulfurization rate in steel was reached 54.5%and 35.8%respectively,.compared with the without cerium steel.So,cerium plays a significant role in deoxidation and desulfurization in steel.?2?According to the calculation of Gibbs free energy of rare earth inclusions show that,at 1873 K,the inclusions of Ce₂O₂S and CeAlO₃ were mainly in steel.The addition of cerium in 21CrMo10 steel can cause the conversion of CeAlO₃ to Ce₂O₂S,and Ce₂O₂S and CeAlO₃ were coexisted in the steel,the thermodynamic calculation results were consistent with the observation results of scanning electron microscope.?3?Through observation of the microstructure of as-cast steel,it was found that the addition of cerium can improve the microstructure of steel.The grain refinement was most obvious when the content of cerium was 0.014%.When the content of cerium was 0.044%in steel,compared to the steel without cerium,cerium was delayed the growth of austenite grains at 900?and 1000?,the effect of inhibiting the growth of austenite grains in steel was more obvious.?4?Cerium was improved the room temperature tensile and impact properties of21CrMo10 steel.When the content of cerium is 0.014%,the number of tensile strength,yield strength,and impact energy was reached 773 MPa,879 MPa,and 223 J.Compared with cerium-free steel,which were increased 7.8%,7.2%,and 16.15%,and the elongation and shrinkage also was increased by 2%and 4%.?5?After the samples were tempered at 635?,670?,730?,and 760?,compared with the without cerium steel,the hardness,yield strength,tensile strength,and impact energy of the steel with a cerium content of 0.014%were greatly improved.With the increase of tempering temperature,the number and size of carbides in the steel were increased rapidly.Cerium was retard the growth of tempered carbides in steel,which better control the size of carbides and more increased the dispersion of carbides in steel.?6?The results after 650?thermal fatigue cycle test show that,when the content of cerium is 0.014%,compared with the steel without cerium,the growth rate and hardness decay rate of the main cracks were reduced by 20%and 10.6%,cerium was better improved the thermal fatigue performance of steel.