In Situ Observation of Calcium Aluminate Inclusions Dissolution into Steelmaking Slag
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In Situ Observation of Calcium Aluminate Inclusions Dissolution into Steelmaking Slag KEYAN MIAO, ALYSSA HAAS, MUKESH SHARMA, WANGZHONG MU, and NESLIHAN DOGAN The dissolution rate of calcium aluminate inclusions in CaO-SiO2-Al2O3 slags has been studied using confocal scanning laser microscopy (CSLM) at elevated temperatures: 1773 K, 1823 K, and 1873 K (1500 °C, 1550 °C, and 1600 °C). The inclusion particles used in this experimental work were produced in our laboratory and their production technique is explained in detail. Even though the particles had irregular shapes, there was no rotation observed. Further, the total dissolution time decreased with increasing temperature and decreasing SiO2 content in the slag. The rate limiting steps are discussed in terms of shrinking core models and diffusion into a stagnant fluid model. It is shown that the rate limiting step for dissolution is mass transfer in the slag at 1823 K and 1873 K (1550 °C and 1600 °C). Further investigations are required to determine the dissolution mechanism at 1773 K (1500 °C). The calculated diffusion coefficients were inversely proportional to the slag viscosity and the obtained values for the systems studied ranged between 5.64 9 1012 and 5.8 9 1010 m2/s. https://doi.org/10.1007/s11663-018-1303-y Ó The Minerals, Metals & Materials Society and ASM International 2018
I.
INTRODUCTION
INCLUSION formation during liquid steel refining is an unavoidable consequence of current steel making processes. The nature and quantity of the inclusions formed in steel is critical, as it affects both productivity and in-service properties of steel. These inclusions can be controlled by two approaches; the modification of their composition and morphology, or the removal of inclusions to the waste slag phase. Oxide and sulfide inclusions can be modified with the addition of calcium using powder injection or wire feeding. A well-known example is the modification of solid alumina inclusions into liquid, or partially liquid, calcium aluminate inclusions. There has been a debate about the correct reaction between dissolved calcium [Ca] and Al2O3 inclusions. Traditionally, the reactions of Al2O3 inclusions in calcium treatment were proposed as Eqs. [1] and [2] to form various types of calcium aluminate inclusions[1–3]
KEYAN MIAO, ALYSSA HAAS, MUKESH SHARMA, and NESLIHAN DOGAN are with the Steel Research Centre, Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. Contact e-mail: [email protected] WANGZHONG MU is with the Department of Materials Science and Engineering, Royal Institute of Technology in Stockholm, Brinellva¨gen 8, Stockholm, 100 44, Sweden. Manuscript submitted August 10, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
2 x½Ca þ 1 x Al2 O3 ¼ xCaO ð1 xÞAl2 O3 3 2 þ x½Al; 3
xCaO þ yAl2 O3 ¼ xCaO yAl2 O3 :
½1
½2
The melting point of calcium aluminates increases with increasing alumina concentration, to form stable solid inclusions at steelmaking temperatures. Insufficient o
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