Effect of Rare Earth Ce on Modifying Inclusions in Al-killed X80 Pipeline Steel

Effect of RE on modifying inclusions in Al-killed X80 pipeline steel was studied by Ce treatment. The results show that Ce treatment modified and refined inclusions. The typical inclusions were MnS + Al2O3–MnS → MnS + Ce–Al–O–MnS + Ce–O–MnS → MnS + Ce–S–MnS + Ce–S + Ce–O–S–MnS + Ce–O–S → Ce–S + Ce–O–S in the sample with Ce content of 0, 0.0045, 0.018 and 0.025 wt%, respectively. With the increase in Ce content from 0 to 0.025 wt%, the mean size of inclusions decreased firstly from 2.41 to 1.80 μm and then increased to 1.87 μm, and the proportion of inclusions smaller than 2 μm gradually increased, while the proportion of inclusions larger than 3 μm decreased firstly and then increased due to the aggregation of Ce–O–S inclusions. The number density, largest size and mean size of single MnS decreased after Ce treatment.