Effect of La-Ce Rare Earth on Inclusions and Impact Properties of Q345D Steel

Abstract

The effects of La-Ce rare earth treatment on inclusions， continuous casting castability and steel properties of Q345D structural steel were analyzed by field test. The results showed that the alloy yield of RE in Q345D structural steel was 21. 5%. Compared with the heats without RE addition， the desulfurization rate increased by 37. 5%， and the unit inclusion density decreased from 80. 16/mm2  to 60. 78/mm2 . The inclusions in molten steel before La-Ce rare earth treat ment were mainly MgO-Al2O3-CaO composite inclusions. The modification effect of La-Ce rare earth treatment on small size （ D≤5 μm ） inclusions was more obvious. Small size inclusions were modified into （La-Ce-S） and （La-Ce-Al-S-O） rare earth inclusions. La-Ce rare earth treatment can significantly reduce the aspect ratio of MnS inclusions in steel， so that the morphology of MnS inclusions after rolling was closer to ellipse without long linear， which was the main reason for the increase of transverse impact energy of Q345D structural steel by 20%.

Keywords

• la-ce rare earth treatment； q345d structural steel； transverse impact energy； inclusion modification； refine； cleanliness