稀土La对2.0 GPa超高强度钢中夹杂物和性能的影响OA

The effects of adding different mass fractions of rare earth La on the inclusions,microstructure,and mechanical properties of 2.0 GPa ultra-high strength steel,which was smelted by a vacuum induction furnace,have been investigated by means of a metallographic microscope,scanning electron microscope,EBSD analysis,XRD diffraction,and tensile and impact tests.The results reveal that as the mass fraction of La increases from 0(no addition)to 0.003 2％and then further to 0.022％in the steel,inclusions evolve from MgO·Al2O3 to LaAlO3-La2O2S complex,and later to rare earth composite oxysulfides LaS-La2O2S.The volume fraction of retained austenite after aging is from 1.85％to 3.05％and then to 5.17％,with the improvement rates of 64.9％and 69.5％,respectively.The Charpy impact energy increases from 11.9 J to 14.1 J and then to 15.3 J,with the improvement rates of 18.5％and 8.5％,respectively.Rare earth La plays a key role in modifying and spheroidizing inclusions in the steel,and increases the volume fraction of retained austenite,leading to a significant increase in impact energy.However,when La is excessively added to a mass fraction of 0.022％,the yield strength of the steel decreases from 1.596 GPa to 1.476 GPa,with a decrease of 0.120 GPa.It is concluded that the optimal addition of rare earth La is 0.003 2％,in this case,contributing to a noticeable increase in the toughness of 2.0 GPa ultra-high strength steel.