Rational technology for the deoxidation and out-of-furnace treatment of low-silicon steel

Abstract

1110 1 Nonmetallic inclusions cause many defects in ready rolled products. In particular, surface defects identified as slivers, i.e., lines along the rolling direc tion, belong to them. Such defects are mainly typical of rolled sheets made of low carbon carbon killed (LCAK) steel. Figure 1 shows a characteristic surface defect (scab) of a 1.5 mm thick roll sheet made of low silicon low carbon steel.The authors of [1] believe that the damage of rolled products by linear surface defects correlates with the total oxygen content, which is usually determined on liquid samples taken from a tundish.We estimated the effect of the oxygen activity on the aluminum loss and the contamination of liquid steel by nonmetallic inclusions before the end of blow ing and before tapping. To this end, we performed a series of experimental heats of low carbon low silicon steel; the end product had [C] = 0.03-0.06% and [Si] < 0.03%.The steel was melted in a 350 t converter, and the oxygen activity in the melt was determined using fall ing sensors and Celox probes (before tapping). The measurement results (Fig. 2) show that the oxygen activity is higher than 800 ppm at a mass fraction of carbon of 0.04% or lower, which results in significant specific consumption of aluminum (2.7-2.8 kg/t). We found that the maximum mass fraction of aluminum fixed in oxides (estimated as [Al] tot -[Al] diss ) increases with the degree of metal oxidation before tapping. When low silicon steel is melted, the process of deox idation substantially affects the supply of silicon to the metal in tapping from a converter, since the possibility of reduction of silicon from a converter slag should be taken into account (Fig. 3). 1 Reported at the XI International Congress of Steelmakers, Nizhni Tagil, October 2010.Preliminary deoxidation of a liquid steel in tapping from a steel melting unit is a rational method for decreasing its contamination by oxide nonmetallic inclusions.We added carbon containing materials (calcium carbide, coke breeze) at the beginning of heat tapping and found that a decrease in the degree of metal oxida tion before the introduction of aluminum decreases both its specific consumption and the maximum steel contamination by oxide nonmetallic inclusions.More promising technological abilities are opened up by preliminary deoxidation by silicon and manganese containing ferroalloys followed by aluminum deoxidation and finishing in a ladle-fur nace unit.Manganese silicates form upon complex deoxida tion of steel by silicon and manganese. As follows from the MnO-SiO 2 slag phase diagram [2], the liq uid nonmetallic inclusions at 1550-1600°C contain 25-50 wt % SiO 2 .We compared the reactions of steel deoxidation by silicon and manganese and foundWe processed the isoactivity diagram of the MnO-SiO 2 system and found the following depen] 2 a SiO 2 ( ) , = = a Mn [ ] a Si [ ] Mn [ ] Si [ ] ≈ K MnO K SiO 2 a MnO ( ) a SiO 2 ( ). = Abstract-A rational technology is proposed for the deoxidation of low silicon steel. It includes preliminary deoxidation b...

The effects of deoxidation practice on the quality of thin foil low-carbon steel

“…The effects of deoxidation sequence on inclusion size and morphology, in particular, have been the subject of discussion for long time and significant discussion still prevail. Some authors propose that the deoxidants should be introduced starting with the lower deoxidation power silicon, followed by aluminum, while others recommend the complete addition of aluminum directly to the fully oxidized bath, as tapped [4][5][6][7]. The objective of this work is to compare quality and cost indicators for the two practices and to understand the processes occurring in each deoxidation practices using thermodynamics.…”

The analysis of the steel deoxidation process in a vacuum installation

“…Steel deoxidation process is done through the following methods: precipitation (by using ferroalloys), diffusion (by using reducing or synthetic slag) -in the furnace [5] or in the secondary treatment aggregate [6], [7], and using a vacuum [8]. By using vacuum steel deoxidation, can be obtained grade steels with high purity.…”