Effect Of Trace Rare Earth On Inclusions,Microstructure And Properties Of HRB500E High Strength Seismic Reinforcement

Reinforced bar is a very important steel for building.In recent years,500MPa and above grade reinforcement has been popularized,especially HRB500E high-strength seismic reinforcement has been widely used in civil engineering due to its high strength,good comprehensive performance and many other advantages.However,HRB500E high strength seismic reinforcement has some limitations in its application field because of its poor impact toughness and low corrosion resistance.In order to expand the application scope of HRB500E high-strength seismic reinforcement and make it applied in extremely cold areas and marine environment,it is particularly important to improve the low-temperature impact toughness and corrosion resistance of HRB500E high-strength seismic reinforcement.Trace RE can effectively improve the impact toughness and corrosion resistance of steel,but the effect of rare earth on the performance of HRB500E high-strength seismic reinforcement is still lack of systematic research.In this paper,HRB500E high strength anti-seismic steel bar containing rare earth（RE）was trial produced by industrial test.The effects of Trace RE on inclusions,microstructure,mechanical properties and corrosion properties of the steel were studied by means of metallographic microscope,scanning electron microscope,material testing machine,pendulum impact testing machine and electrochemical workstation.The results are as follows:（1）RE can be added in smelting process,and the content of rare earth reaches0.0066%.After RE treatment,the sulfur content in steel decreased significantly,from0.024%to 0.013%,decreased 45.8%,and the cleanliness of steel liquid increased.（2）The size,morphology and quantity of inclusions changed after adding RE.The ellipsoidal and irregular shape of Al₂O₃-MnO-CaO in steel transforms into spherical REAl O₃ and REAl O₃-MnS.With the decrease of S content,the formation of MnS inclusions is hindered,single MnS inclusions disappear,the number of inclusions decreases obviously,and the average size decreases to 1.51μm.The transformation of inclusions is consistent with the thermodynamic calculation results,and the modification process of inclusions in the smelting process is further explained by the inclusion transformation model.（3）RE can refine the microstructure and pearlite lamellar spacing of HRB500E test steels.The results show that the average grain size of the steel decreases by 7.44%and the pearlite lamella decreases by 25%.（4）After adding RE,the mechanical properties of HRB500E test steels are improved.The tensile properties of HRB500E test steels at room temperature increased slightly,and the low temperature impact toughness at-40℃and-60℃increased by41.72%and 42.86%respectively.（5）The corrosion of conventional HRB500E steel is caused by the dissolution of MnS inclusions and the dissolution of matrix around Al₂O₃-MnO-CaO inclusions;The corrosion of HRB500E steel with RE is due to the dissolution of REAl O₃ and REAl O₃-MnS.REAl O₃ and REAl O₃-MnS inclusions can delay the formation of corrosion pits;After adding trace RE,the corrosion potential of HRB500E steel moves forward,the corrosion current decreased,and the corrosion resistance improved obviously.