| With the gradual development of the shipbuilding industry,countries in the world have extensive research on the field of ship plate steel with high strength and good ductility required for development.A large number of studies have shown that the main role of rare earth elements in the steelmaking industry is to affect the composition,geometry,size and volume fraction of inclusions,as well as to refine grains and purify molten steel.As a result,the mechanical properties of steel,such as toughness,and corrosion resistance may be improved.In this experiment,EH40 steel plates with different rare earth Ce content were produced through composition design,simulated smelting and simulated rolling.Using optical microscope(OM),scanning electron microscope(SEM),Thermo-Cala software,transmission electron microscope(TEM)electron backscatter diffraction(EBSD)and electrochemical testing system and other analytical instruments,through thermal deformation treatment,the processing temperature is 900℃,1000℃ and 1100℃,to study the mechanical properties and microstructure morphology of EH40 ship plate steel with different rare earth co.the result shows:The stress-strain curve of EH40 ship plate steel was obtained by double-pass thermal compression test.According to the stress-strain curve,the addition of rare earth could increase the recrystallization volume fraction and promote the occurrence of recrystallization.Adding a small amount of rare earth element Ce can increase the yield strength Re by 56.6MP and tensile strength Rm by 39.9MP.The stress-strain curve of EH40 ship plate steel was obtained by double-pass thermal compression test.According to the calculation of stress strain curve,,the addition of rare earth increases the recrystallization volume fraction by 20.4%,which promotes the recrystallization.The addition of rare earth can change the shape and size of the inclusion formed in steel.Adding high level of rare earth elements into the matrix steel can promote the formation of rare earth matrix inclusions,improve the inclusion morphology at the bottom of the dimple,make the sheet inclusions become mixed inclusions with regular spherical rare earth aluminate,and increase the comprehensive mechanical properties of EH40 ship plate steel.The result of image analysis shows that the area fraction and size of inclusions have no obvious trend of change,and the larger inclusion and higher area fraction will lead to poor mechanical properties.Recrystallization and precipitation of the second phase occurred in the matrix of high rare earth steel,which resulted in a great decrease in the hardness of the steel matrix.MnS formation is inhibited in rare earth steel,which is a favorable position for Nb-rich phase precipitation.Therefore,adding not more than 400 ppm of rare earth elements into steel can inhibit the formation of coarse Nb based NbC precipitation. |
