Study on Inclusions in X80 Pipeline Steel During Secondary Refining Process

X80 pipeline steel was produced with BOF-LF-RH-CC routine.During tapping aluminum was used to kill the liquid steel and high basicity and low oxidizing slag was made.The characteristics of non-metallic inclusions in steel were studied during secondary refining process.The results showed that after the secondary refining process the total oxygen content of steel is between 10×10-6 and 12×10-6.The proportion of inclusions with a size less than 20μm reached 90%.During the secondary refining process the content of MgO in inclusions decreased while the content of CaO increased gradually.After refining of steel the inclusions mainly contain MgO,Al2O3 and CaO,the average content of which amounts to 2.6%,53.7% and 43.7% respectively.These inclusions were covered with CaS and were liquid in molten steel,which infers that the inclusions were effectively modified.Soft bubbling of liquid steel after Ca treatment was proved to be an efficient way to remove fine inclusions from steel,with which 81% of inclusions smaller than 10μm were removed.