Inclusions Control and Refining Slag Optimization for Fork Flat Steel

摘要

In order to investigate the causes of the large number of cracks and porosities formed in 33MnCrTiB fork flat steel produced by a special steel plant, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, and large sample electrolysis of the obtained steel samples were carried out in different steps of the steelmaking processes. The main micro-inclusions in the fork flat steel samples were Al 2 O 3 , CaO-MgO-Al 2 O 3 -SiO 2 , and TiN, and the macro-inclusions were mainly Al 2 O 3 , CaO-Al 2 O 3 , CaO-Al 2 O 3 -SiO 2 -TiO 2 , and CaO-MgO-Al 2 O 3 -SiO 2 -TiO 2 -(K 2 O) systems which originated from the ladle slag and mold flux in the production process. In order to reduce the number of micro-inclusions effectively, the control range of components in the refining slag was confirmed by the thermodynamic calculation, where the mass ratio of CaO/Al 2 O 3 should be in the range of 1.85–1.92, and the mass fraction of SiO 2 and MgO should be controlled to 7.5–20% and 6–8%, respectively. In addition, the numbers of macro-inclusions in the flat steel should be effectively reduced by optimizing the flow field of mold and preventing the secondary oxidation, and the flat steel quality problems caused by the inclusions can be improved by the optimization process above.