Study of Inclusions in High Sulfur, Al-Killed Ca-Treated Steel via Experiments and Thermodynamic Calculations

Abstract

In the production of special steels, inclusions have a significant influence on final product quality. Moreover, there is a growing need for constant improvement of mechanical and machinability properties, such as in the production of complex pieces for the automotive applications. The main objective of this study was to conduct a thermodynamic study aimed at preventing clogging problems during continuous casting (CC) and the formation of undesirable inclusions. Alumina (Al2O3), spinels, and calcium sulfide (CaS) are potential sources of defects during rolling and steel forging. The specific goals of this study were: (1) To determine the phases and compounds formed in the inclusions as a function of composition and casting temperature adopted for high sulfur Al‐killed Ca‐treated steel, and (2) To establish chemical composition conditions resulting in the formation of less harmful inclusions for steel castability. Based on the literature and previous studies by the authors, calculations were carried out using FactSage commercial software and related databases. The calculations were performed using the steel temperature and chemical composition in the CC tundish. The results of these calculations were used to estimate the composition of steel and non‐metallic inclusions (oxides and sulfides) at the given steel temperature. Based on these calculations, it was predicted a calcium content range where inclusions contained a high proportion of liquid phase (i.e., “liquid window”). The results of thermodynamic simulation were compared to industrial outcomes in terms of inclusion composition and casting index. The thermodynamic predictions were validated and confirmed by industrial results.

Castability and Inclusions in a Low Sulfur Ca‐Treated Peritectic Steel for Two Deoxidation Techniques

“…It is interesting to note that the calcium amount and the calcium method for adding it inside the liquid steel were not changed. From the literature, it is known that the higher the O total content, the higher the calcium amount, which is needed to produce liquid inclusions . This is in agreement with the calculated castability windows and with the total oxygen measurements (Table ).…”

Effective Viscosity of Slag and Kinetic Stirring Parameter Applied in Steel Cleanliness During Vacuum Degassing

“…This study was performed by taking a total of 16 (sixteen) samples divided evenly before and after vacuum degassing treatment, considering (8) steel samples and (8) slag samples. Steel samples were collected using Samp-O-Line (from Heraeus Electro-Nite) without deoxidizer and analyzed by ASPEX equipment 13,[18][19][20][21] model Explorer, equipped with SEM/EDS system. The analyzed area for all steel samples composes the range of 54.3-83.6 mm 2 .…”

“…The analyzed area for all steel samples composes the range of 54.3-83.6 mm 2 . Steel chemical composition analyses were carried out using an ARL 3560 Optical Emission Spectrometer to determine calcium (Ca) and aluminum (Al) contents and LECO CS-444LS to determine sulfur (S) 4,21 contents. Finally, slag samples were analyzed by X-ray fluorescence (XRF) using Philips equipment, model PW2600.…”

“…Thus, these sulfide species were not considered to facilitate the inclusionary analysis. Furthermore, MnS inclusions may be formed probably as a consequence of the solidification process of the samples 21 and do not represent the reality of the liquid steel, at the vacuum degasser. Regarding liquid steel, the presence of oxy-sulfide type inclusions increases after vacuum.…”

Morphology of Solidification Structure and MnS Inclusion in High Carbon Steel Continuously Cast Bloom

“…is utilized to provide various kinds of oxide nuclei for MnS nucleation in molten steel, resulting in fine dispersion of MnS inclusions. Also the calcium treatment 16,17) and Rare-Earth-Metals (REM) treatment 18) are popular ways to modify sulfides in the molten steel before casting and obtain a homogeneous distribution of precipitated sulfides in the solidified steel. Moreover, high cooling intensity 19,20) is benefit for the formation of globular Type I MnS in steel during the solidification process through metastable monotectic reaction due to small temperature difference between the eutectic point and the monotectic point.…”