Effect Of Rare Earth Ce On The Purifying Degree And Microstructure And Mechanical Properties Of Q345H Beam Steel

With low-alloy steel widely used in high-rise buildings, shipbuilding, Bridges, oil and gas pipeline and Marine facilities, it is required with high strength, toughness, low temperature performance, welding, and excellent resistance to hydrogen-induced cracking performance.In order to improve strength and toughness of high strength low-alloy steel, expand its application fields, high strength low alloy steels as the research object. LF+VD refining processes were simulated. The0.2%C-0.5%Si-1.5Mn%-xCe steels were prepared in vacuum induction furnace by refining after adding Ce to Q345H beam steel. With the results of chemical composition, inclusion morphology, organization structure and mechanical performance, the effects and mechanism of Ce on deoxidization and desulfurization(cleanliness), inclusion degeneration and the influence of organization and strength and toughness were studied, therefore the basic experimented data can be provided for the application of RE in the high strength low-alloy steel. It is very important significance to construct resource-saving and environment-friendly society.The main conclusions as follows:1. O and S content present reduction trend of exponential type with the increase of the content of Ce in the molten steel. When Ce content is0.012%, O and S are reduced to0.0009%and0.0010%respectively;The result showed that rare earth elements have strong ability of deoxidizing and desulfurizing;But when Ce content continue to be increased, O and S content almost the almost remain the same amount in the steel.2. Adding Ce element,15μm Al2O3-SiO2inclusions with angular and MnS of long strips and large volume have changed into RE compound inclusion that is1-2μm or even<300nm. It is show that rare earth Ce have strong ability of deoxidizing and desulfurizing;But when Ce content continue to be increased, O and S content almost the almost remain the same amount in the steel.The result showed that rare earth Ce has effect of reducing the inclusion size and modifying inclusion.3. when the content of Ce is0.001%～0.045%(mass fraction), The size of the grain varied significantly and the grains became small and uniform. The relative amounts of pearlite were influenced by the content of Rare Earth Ce. The distance of pearlite lamellar decreased with the increasing of Ce content. The results showed that the organizational structure of the steel was changed significantly by adding Ce.4. By adding Ce in the steel, the strength and toughness of the steel were significantly improved, the yield ratio decreased, the seismic performance of the H class steel was optimized.The yield strength of the steel reached to477MPa, the tensile strength of the steel reached to695MPa and the elongation of the steel reached to29.84%when the content of Ce was0.012%. The yield strength, the tensile strength and elongation of the steel were about28.57%,40.69%and24.92%higher than that of the steel without Ce, respectively. The impact performance of the steel was2.43times as much as that of the steel without Ce. The results showed that the mechanical properties of the steel were improved by adding Ce significantly.