Effect of CaO/Al₂O₃ ratio on desulphurization and non-metallic inclusions in low-density steel

Abstract

To determine the effect of the CaO/Al 2 O 3 ratio on desulphurization and inclusion evolution in lowdensity steel, a series of laboratory-scale experiments are performed. The results show that violent reaction occurs at the interface between refining slag and molten steel. As the slag-steel reaction progresses, (CaO) and (MgO) are reduced to [Ca] and [Mg] by dissolved [Al]. The deoxidation product Al 2 O 3 dissolves into the slag and accumulates at the slag-steel interface. The evolution process of the sulphide inclusions is CaS → MgS → MnS. The sulphide outer layer wraps AlN and spinel inclusions, floats up and is absorbed by the top slag. During refining process, the accumulated Al 2 O 3 at the slag-steel interface easily forms MgO•Al 2 O 3 . Finally, a dense spinel layer can be formed at the slag-steel interface, which inhibits the desulphurization reaction. Reducing the C/A ratio can reduce the formation of MgO•Al 2 O 3 and has a positive effect on the desulphurization in low-density steel. The influence of the C/A ratio on desulphurization kinetics should be considered in the design of slag composition.

Motion behaviour of solid inclusions at the steel–slag interface in high-Al steel

“…By combining Equation (1) and Equation ( 2), the stokes velocity and critical velocity of film formation for inclusions with diameters ranging from 5 to 300 μm can be determined, as depicted in Figure 4. To account for the low-density property of high-Al steel, which has a calculated density of 5240 kg/m 3 for Fe-15Mn-10Al-0.7C steel [5] according to Equation ( 26) [30], additional curves can be incorporated. The critical diameters for film formation in pure iron and high-Al steel are observed to be around 150 and 250 μm, respectively.…”

“…Of all the inclusions, the solid inclusions such as Al 2 O 3 , AlN and MgO·Al 2 O 3 spinel are considered as detrimental phases for steelmaking and casting process [1,2]. Although the interfacial tension between solid inclusion and steel is higher than that of liquid inclusion and steel, which makes solid inclusion float out faster than liquid inclusion [3], the solid inclusions with small diameter ( d I < 5 μm) cannot be efficiently eliminated [4,5]. With the development of special steel such as TWIP steel in recent years, more attention has been paid to how to minimize the solid inclusions in high-Al steel.…”

High-temperature electrochemistry of calcium

“…The phase diagram of the CaCl2-CaF2-CaO system has a eutectic point with parameters of 625°C and liquid phase composition (mol %): 79CaCl2-17CaF2-4CaO and a peritectic point at 660°C and composition (mol%): 67CaCl2-23CaF2 -10CaO. At 700°C, there is a fairly large area of the liquid state (mol%): CaCl2-(10-30)CaF2- (10)(11)(12)(13)(14)(15)CaO. This system in the studied part is lower melting than CaCl2-CaO, therefore it is of even greater interest for studying the processes of electrochemical production of calcium and developing new technologies.…”

“…At the analysis of the mechanism of the О 2ion discharge at the oxygen-evolving anode authors (12) divides the total reaction:…”

“…The main areas of stable consumption of calcium and its alloys are calciumthermal production of metals (Ni, Cu, Fe, Cr, Th, U, REM, etc.) [9][10][11] and steel deoxidation [12][13][14]. Along with this, the possibility of using calcium in calcium-ion, calcium-air and calcium-sulphur batteries, which can replace more expensive lithium-ion batteries [15][16][17][18][19][20], as well as in hydrogen storage [21], is being actively studied.…”