Analysis of Large-Dimension Rare Earth Inclusion in Steels by Metallographic Microscope and TEM

The mechanism of formation of the large-dimension rare-earth(RE) inclusions in steels is discussed by TEM(Transmission Electron Microscope) taking steel 5CrNiMo with addition of RE as example. The two or several large-dimension RE inclusions come out independent nucleation which grow up into a 0.3~0.5 micron in length, then attract and integrate into the large-dimension with 1~5 micron in length. Though the dimension difference between the RE inclusions is varied, the shape is spherical or approximate spherical or elliptical, but no sharply corneous, because RE can promote the inclusion shape variation through metamorphism.