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Production practices of IF (interstitial free) steel grades intended for the most qualitatively demanding automotive applications calls for their continuous optimization. Precise control of steelmaking operation conditions leads to a minimization of clogging issues during their casting, but is also related to surface quality imperfections of finished material. With the aim to study the impact of RH degasser practices on cleanliness of the IF steel grades, the influence of heat chemical reheating was verified. While detailed analyses confirmed overall worse results and a higher presence of specific nonmetallic particles on steel samples collected from such treated heats, the limited reheating practice did not seem detrimental.

This paper details the study of interstitial aluminium impact on non-metallic inclusion occurrence on the basis of individual samples examination taken during steel production and processing. The aim was to identify and describe the relation between the content of interstitial aluminium in metal volume and the concentration of non-metallic inclusions on AlxOy basis occurring in steel. The identification of the non-metallic inclusions occurring in liquid steel was within this study implemented by the (AES) method based on the atom emission spectrometry evaluating the presence of the respective elements in the metal volume. This method works on a principle of emitted light from the existing source with a high voltage spark. The results of this study indicate a correlation between the interstitial aluminium content and concentrations of non-metallic inclusions on the AlxOy basis.

The work addresses the production of medium-Mn steels with an increased Al content. The special attention is focused on the identification of non-metallic inclusions and their modification using rare earth elements. The conditions of the thermomechanical treatment using the metallurgical Gleeble simulator and the semi-industrial hot rolling line were designed for steels containing 3 and 5% Mn. Hot-working conditions and controlled cooling strategies with the isothermal holding of steel at 400°C were selected. The effect of Mn content on the hot-working behaviour and microstructure of steel was addressed. The force-energetic parameters of hot rolling were determined. The identification of structural constituents was performed using light microscopy and scanning electron microscopy methods. The addition of rare earth elements led to the total modification of non-metallic inclusions, i.e., they replaced Mn and Al forming complex oxysulphides. The Mn content in a range between 3 and 5% does not affect the inclusion type and the hot-working behaviour. In contrast, it was found that Mn has a significant effect on a microstructure.

The process of vacuum degassing occurs during the secondary refining of special steels. Its main function is to remove undesirable gases. However, during this process, flotation phenomenon and inclusions absorption are reported. The aim of the present work was to study the slag viscosity and vacuum degassing (tank type) capacity in steel cleanliness from an industry perspective. To achieve this objective, slag and steel samples were taken before and after the vacuum stage. The results in steel cleanliness were related to a kinetic stirring parameter (βs) of the vacuum station and to the effect of slag viscosity. The removal of inclusions during the vacuum stage reached 64, 75 and 78% in the diameter ranges of 2.5-5, 5-15 and ≥ 15 µm, respectively. After the degassing process, the composition of non-metallic inclusions seemed to approach the slags' chemical compositions. The stirring process in the vacuum degassing station promotes a significant decrease in the inclusion densities for the 2.5-15 µm diameter range and also in the sulfur content in liquid steel. Regarding the effective viscosities of slags, it was concluded that lower values (0.20 Pa.s) increased slag capacity in inclusion removal, whereas higher values (> 0.40 Pa.s) were detrimental to steel cleanliness.

© 2015 ISIJ. The alloy/liquid Fe interaction behaviour at early stages of deoxidation/alloying have considerable influence on the mechanical properties of steel products. The interfacial reaction between FeMnSi and liquid Fe, as well as the inclusion formation, were experimentally studied at the addition early stages based on quenched FeMnSi-Fe diffusion couples. The microstructure and composition of the quenched diffusion couple were evaluated and the inclusions in the reaction zone were characterised. Five regions were distinguished in the quenched reaction zone, i.e. (1) a solidified Fe shell, (2) a α1 phase consisting of a solid α1 phase and a Fe-Mn-Si liquid melt at the experimental temperature, (3) eutectic α1+Fe5Si3 and (4) eutectic Mn5Si3+MnSi phases, which are liquid at the experimental temperature and (5) the origina FeMnSi alloy which did not melt during the interaction. Plenty of oxysulphide inclusions are observed in the reaction zone: Fe(O,S) inclusions formed in the bulk iron and an inclusion poor zone is observed in the nner part of the Fe shell. Large amounts of tiny (Mn,Si)O inclusions formed in the α1 phase near the Fe/α1 interface and large (Mn,Si)(O,S) inclusions precipitated in the liquid phase after solidification. ispartof: ISIJ International vol:55 issue:8 pages:1661-1668 status: published

The aim of this study is to determine the optimal chemical composition of the tundish flux, which can efficiently absorb macro and micro inclusions from 16MnCrS5 case hardening steel. Computation of phase diagram is used as an approach to understand properties and behavior of tundish slags in casting conditions. Thermodynamic computation of steel − slag reactions is performed to find out the capability of different tundish slags to absorb inclusions. Industrial trials are, then, carried out with the slags to verify their functionality, when casting several heats in sequence. Results show that by tailoring tundish slag composition the steel cleanliness can be improved. Basic Ca–Mg–aluminate type slags have potential for wide use, as they can be easily adjusted chemically stable against the steel and have ability to absorb inclusions. The slag optimization is, however, a complex issue depending for example on the steel grade.