Effect of Nanometer Calcium and Magnesium Oxides Addition on the Cast Microstructure Grain Size of Pipeline Steel

Abstract

Nanometer calcium and magnesium oxides were added into molten steel by the carrier method in the experiment. The experiment takes the X80 pipeline steel as the research object and analyses the effect of nanometer calcium and magnesium oxides addition on the cast microstructure grain size. The grain size of the cast microstructure in each sample was measured by the cutting line method. The results show that the nanometer oxides addition has a great influence on the cast microstructure grain size. When adding 0.01 wt% nanoCaO or MgO oxides, the grain size decreases from 0.664 mm to 0.632 mm and 0.457 mm, respectively. When adding 0.02 wt% nanoCaO or MgO oxides, the grain size becomes finer, and the cast microstructure is remarkably refined. In contrast with the grain size of no nanometer oxides addition, the grain size decreases from 0.644 mm to 0.438 mm and 0.389 mm and is refined by 1.47 and 1.66 times, respectively. When adding 0.05 wt% nanoMgO oxides, the grain size does not decrease, but increases to 0.778 mm. The reason is that as the amount of adding oxides increases, the dispersity of the nanometer oxides becomes worse, and the agglomeration of the grains occurs. Therefore, the nanometer oxides can not achieve the role of grain refinement.