Effect Of Rare Earth Ce On The Microstructure And Mechanical Properities Of65Mn Steel

The demand of domestic spring steel largely increased with the rapiddevelopment of aerospace, automotive, railway, engineering machinery andelectronics industry. Although the technology level and production of domesticspring steel has been matched with domestic consumption, the import of highquality spring steel is still great, which largely hinder the sustainable andhealthy development of domestic spring steel industry, product structure ofenterprises and domestic economy. Due to its special working conditions suchas stretch, extrusion, bend, impact, the steel is necessary to have not only astable chemical composition and high steel cleanness, but also fine matrixorganization and excellent mechanical properties. According to the currentinternational and domestic process of spring steel and metallurgy theoryfrontier research results, wide application of65Mn steel is as the researchobject, the research around the project of raising molten steel cleanliness,controlling inclusions characteristic and organization, improving theperformance of spring steel, then taking a basis and systematic theory research.In order to control the microstructure, inclusions characteristic andmechanical of65Mn steel. By metallurgical thermodynamics calculation andscale research, on the basis of the influence of trace rare earth Ce on springsteel microstructure, inclusions characteristic and mechanical properties were studied. Quantitative research the change of microstructure, metamorphicinclusions and mechanical properties of0.65%C-0.35%Si-1.20%Mn steel withCe content were analyzed and discussed. The basic experiment data wasprovides for the application of rare earth elements in high carbon spring steel.It has a great significance for developing fine crystallization method of steelmaterials, adjusting the varieties of steel and low cost manufacturing hightoughness steel produce technology.The conclusions can be drawn as followings through experimentalresearch, analysis and calculation.(1) When the Ce content was0.0046%, the content of oxygen and sulfurwere reduced to0.0017%and0.0012%. The content of oxygen and sulfur werereduced by81.5%and76.9%, respectively.(2) When Ce content was within0~0.0046%, large size, long strips MnSinclusions were metamorphosed into1~2μm ellipsoid or spherical MnS andrare earth sulfide inclusions, irregular large size of oxide inclusions weremetamorphosed into1~2μm ellipsoid or spherical with Ce2O2S and Ce2O3composite inclusions.(3)With Ce content increasing, the total density of inclusions increased,the number of inclusions which diameter were more than2μm is greatlyreduced. The number of inclusions which diameter were1~2μm significantlyincreased, which could be used as heterogeneous nucleation of ferrite.(4) With the trace element Ce adding into steel, the matrix grainorganization largely refined, the spacing of pearlite lamellar is smaller. WithCe content was within0~0.0046%, the pearlites grain size decreased from21.65μm to13.74μm, matrix grain size increased1.34times, pearlite spacingdecreased from264nm to116.77nm.(5) The mechanical properties of steel were improved significantly withthe Ce content increasing. When the Ce content reched0.0046%, the specimens’ yield strength, tensile strength, elongation and impact toughnessreach to714.38Mpa,864.70Mpa,22.75%and37J, which respectivelyincreased by4.00%、11.47%、68.52%and45.10%compared with0%specimen.