Study On Inclusion And Microstructure Of 4Cr5MoSiV1 Steel Containing Rare Earth Elements

4Cr5MoSiV1 steel is a kind of hot work die steel with excellent properties,which is widely used in hot forging,hot extrusion and casting of dies.The development level of molds directly determines the manufacturing level of a country.Although the total output value of my country’s molds ranks among the world’s forefront,its production and manufacturing are still in the imitation stage,and the products still have problems such as poor toughness and insufficient life,resulting in high-end molds that need to be imported.The performance of the material is determined by the structure,and the structure is closely related to the chemical composition and heat treatment process,and the rare earth in the steel has the effect of microalloying,improving the matrix and strengthening the grain boundary.Therefore,it is necessary to carry out research on high-quality rare earth die steels with better composition,structure and comprehensive mechanical properties to provide a certain theoretical basis for the improvement of the performance of my country’s 4Cr5MoSiV1 steel.In this study,4Cr5MoSiV1 steels with different Ce contents(0,0.011%,0.032%,0.055%)were designed,and the existence mode and uniformity of rare earths in the experimental steel,inclusions,microstructure and mechanical properties were studied.Separate the rare earth compound part in the experimental steel through electrolysis experiments,and obtain the content of Ce solid solution and compound in the experimental steel;observe the morphology of the inclusions in the experimental steel with the help of SEM,and use LSCM to take pictures and observe the polished structure of the experimental steel.The Image Pro Plus software counts the size of the inclusions to obtain the effect of Ce content on the inclusions in the experimental steel;observe the microstructure of the experimental steel under various processes with the help of OM,SEM,etc.,and analyze the thermal processing technology and Ce content on its microstructure After the experimental steel undergoes the same heat treatment process(quenching at 1040°C + tempering twice at 580°C),the hardness test,tensile test,and impact test are carried out to test various mechanical properties of the steel,and the tensile fracture shape is tested with the help of SEM Observe the appearance and explore the effect of Ce content on the mechanical properties of 4Cr5MoSiV1 steel.The results show that after adding Ce to 4Cr5MoSiV1 steel,on the one hand,the S content can be reduced from 0.010% to 0.0017%,which can purify molten steel,refine the structure,and reduce dendrite segregation;when the Ce content is 0.032%,the experimental steel The as-cast structure with more uniform composition and finer grains can be obtained.On the other hand,metamorphic inclusions change the type of inclusions,reduce the size of inclusions,and make spherical Al oxide inclusions and massive Mn sulfide inclusions transition to fine spherical rare earth inclusions;when the Ce content is 0.032% At the time,the average size of inclusions in the experimental steel was the smallest(5.067μm),which was 45.0% smaller than that without Ce(9.218μm).The effects of microstructure refinement and metamorphic inclusions both improved first and then worsened with the increase of Ce content.After the test steel undergoes the same heat treatment process,when the Ce content is 0.032%,the test steel can obtain a better microstructure.At this time,its tempering hardness,tensile strength,impact toughness,elongation and reduction of area have all Higher values,48.7HRC,1378 MPa,24.6J·cm-2,5.9% and 8.6%,respectively,compared with no Ce(45.3HRC,1246 MPa,21.4J·cm-2,4.8% and 6.3%)Increases by 7.5%,10.6%,15.0%,22.9% and 36.5%.