Effect of Rare Earth Ce on the Evolution of Inclusions in 20MnTiB Cold Heading Steel

Industrialized tests were carried out to produce 20MnTiB cold heading steel with different rare earth （Ce） contents， the effect of Ce on the evolution of inclusions during the production of 20MnTiB cold heading steel based on Ca treatment was investigated through experimental observations and thermodynamic calculations. The results show that after Ce treatment， the large-size spheroidal Al2O3-MgO-CaO-CaS inclusions were metamorphosed and decomposed into about 1 μm spheroidal CeAlO3-MgO-CaO -CaS inclusions， and irregular inclusions of this type around 2 μm were metamorphosed and sphericalized. After hot rolling， the inclusions in the 0Ce specimen wire rod elongated along the rolling direction， the inclusions were larger in size and more irregular in shape， in addition， long strips of MnS inclusions were found. However， in the 27Ce specimen， the S element content was reduced by 40% after Ce treatment， which inhibited the formation of MnS inclusions during the solidification process， and the small-sized， spherical-like characteristics of the inclusions in the wire rods did not change after rolling. The thermodynamic calculations are in agreement with the experimental results. After Ce treatment， the metamorphic decomposition of large-sized and irregular inclusions， the metamorphic spheroidization of small-sized and irregular inclusions， and the disappearance of MnS inclusions avoided the stress concentration caused by the irregular morphology of inclusions in the process of cold heading， which is conducive to the enhancement of the cold heading performance of the test steel and the reduction of the possibility of cold heading cracking. The results can provide technical and theoretical support for the further development of new rare earth microalloyed cold heading steels.