Mechanism of trace cerium in ultra-clean IF steel

The existence forms of cerium in ultra- IF steel,in which the contents of oxygen and sulphur were both less than 0.000 6%,were studied by chemical analysis,thermodynamic calculation,micro- examination and hardness measurement. And the effects of cerium on Al2O3 inclusions,microstructure and hardness were discussed. The results show that,when the cerium content was between 0.006 1% and 0.009 3%,the solid solubility of cerium range from 0.004 1%to 0.006 7%. About seventy percent of cerium is in the form of solid solution,the rest of cerium is in the form of inclusions,and there is no Ce- Fe intermetallic compound in the steel. By adding cerium,Al2O3 inclusions are modified into smaller globular Ce Al O3 inclusions. Cerium played a role in modifying inclusions in the steel. Cerium has the effect of refining the microstructures of the steel. The greater the amount of solid solution of cerium was,the finer the crystalline grains were. When the content of cerium are 0.006 1% and 0.009 3%,Rockwell hardness increases by 7.6% and 12.7% respectively compared with IF steel without cerium.