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. Key words: RH degasser, chemical reheating, IF steel, steel cleanliness IntroductionIn general, it can be said that to date, there have only been a few research papers published regarding the impact of chemical reheating on the cleanliness of heats processed at an RH (RH-OB) degasser. This technological operation represents one way of feeding the oxygen into the liquid steel. As well, depending on a number of other process parameters, it can strongly affect the degree of its cleanliness, casting conditions and consequently, the quality results of the final processed material. Fig. 1 characterizes the typical temperature increase related to the amount of oxygen blown at the RH degassing station with steel grades deoxidized only by aluminum, or by a combination of aluminum and silicon. It is evident that the processed steel grades deoxidized only by aluminum have particularly at high volume of oxygen blown, higher efficiency of the chemical reheating process [1 -4]. In this regard, the greatest attention should be paid to the conditions of formation and to the ways of minimizing the occurrence of mainly small alumina inclusions (under 10µm). Besides this, the area of concern is often focused also on other complex types of inclusions, in particular based on Titanium, whereas in view of its alloying, these steel grades exhibit the negative impact thereof on the conditions of removing inclusions from the molten steel and related issues during their casting [5 -7]. Fig. 2 indicates that the heat treatment of the processed heats in terms of the chemical reheating leads to a significant deterioration of steel cleanliness through the increase of concentration of Al2O3 inclusions in heat, mainly during the oxygen blowing for the reheating [8]. Although this finding is a common feature of most of the available research work on this topic, opinions and findings concerning the overall final level of steel cleanliness
<p>This paper deals with the examination of the impact of steel cast speed on the occurrence of the non-metallic inclusions due to the investigation of the individual samples taken at different steel cast speeds. The aim of this paper was to identify and describe the relation between the non-metallic inclusions occurring in the metal and the cast speed variations at the continuous casting machine. The non-metallic inclusions within this investigation were identified by the method (AES) based on the atomic emission spectroscopy that evaluates the occurrence of the determined elements in the metal. This method applies the principle of the light emitting acquired by the high-voltage spark supply. The investigation of the impact of both the technological production parameters, and the casting on the cleanliness of the given absorption quality of steel leads to their optimization, as well as, to total minimization of occurrence of the non-metallic inclusions in the steel volume were studied.</p>
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 Al x O y 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 Al x O y basis.Keywords: steel cleanliness, secondary metallurgy, continuous casting, inclusions in steel 1 Introduction It is necessary to ensure and maintain a high purity of produced steel especially for those types designed for a specific application. Regulation of the non-metallic inclusion content, amount and distribution has an essential impact on the steel purity [1]. Development of packaging materials significantly relates to thin electrolytically tinned sheets, which are nearly irreplaceable in some branches of the packaging sector. They are mainly used in the food industry [2-5] thanks to their slim thickness, wide range of mechanical properties, high corrosion resistance and of course their harmlessness to health. The ability to regulate, respectively to control the concentration, morphology and composition of the non-metallic inclusions [6,7] represents one of the most important factors to the improvement of steel purity, respectively the quality improvement of steel products. It is important to study the increased concentration distribution of the nonmetallic inclusions due to its impact on steel product quality in the form of the resulting defects [8,9]. The priority is to decrease the number of defects inside the steel ingot that results from the non-metallic inclusions present in steel [10]. The non-metallic inclusions present in metal are of different origins, e.g. from deoxidation, refractory materials, slag entrainment, casting powders and entrainment of the clogged parts of the submerged entry nozzle into the metal volume [11][12][13][14][15][16]. According to professional literature, during the continuous casting of steel on the casting equipment, casting with stable speeds is preferred. Generally, changes of speed in the casting process in production are inevitable [17]. A negative impact on the non-metallic inclusions to
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