Study of Non-Newtonian Behavior of CaO-SiO 2 -Based Mold Slag and Its Effect on Lubrication in Continuous Casting of Ste
- PDF / 1,199,486 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 103 Downloads / 149 Views
DUCTION
A non-Newtonian fluid is a fluid that does not follow Newton’s law of viscosity. Its viscosity depends on the imposed shear rate at constant temperature.[1] For most metallurgical slags, such as the refining slag in ladle and the flux in tundish, the fluidity in production is relatively good at high temperature. Thus, these slags are often considered Newtonian fluids.[2] However, in continuous casting of steel, liquid slag at the meniscus infiltrates the channel between the solidifying shell and copper plate and lubricates the strand surface. As temperature decreases in the withdrawal direction, crystallite precipitation forms a second solid phase and increases the slag viscosity, resulting in some non-Newtonian behavior[3] under varying stress levels in the mold-strand channel.
XIAOBO YAN, MEIJUAN GAN, HUAZHI YUAN, QIANGQIANG WANG, SHENGPING HE, and QIAN WANG are with the College of Materials Science and Engineering, and Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and Advanced Materials, Chongqing University, Chongqing 400044, China. Contact e-mail: [email protected]; [email protected] Manuscript submitted September 21, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Moreover, the suspension of high-melting point particles, such as undissolved alumina clusters,[4] TiC, and TiN,[5,6] can also yield non-Newtonian slag behavior. Lubrication plays an importance role in the smooth demolding and uniform growth of solidifying shell during continuous casting, which can be realized by appropriately reducing the slag viscosity. However, if slag entrapment is an issue, especially during high-speed continuous casting, the slag viscosity is demanded to increase to reduce the number of entrapped particles, which inevitably comes at the expense of a lower powder consumption.[7] Hence, a balance is required and the mold slag should have shear thinning,[8] a characteristic non-Newtonian behavior. The viscosity at the surface of the steel top should be high enough to alleviate slag entrainment, and the viscosity in the lower mold should be low enough to maximize lubrication,[9,10] as the lubricant area suffers higher shear rate from compressive and tensile stresses during mold oscillation. Several special slags have been designed to perform the above for particular steel grades or casting conditions.[1,10,11] Table I summarizes studies[1,3,5,8,10–14] on non-Newtonian behavior of continuous casting slag and its use in production. Generally, the shear thinning of molten slag is explained by temporary viscosity loss.[8] Molecular bonds within liquid slag are randomly oriented before any shear stress is applied. However, those bonds
Table I. Authors
Studies of the Non-Newtonian Behavior of Continuous Casting Slag Methods
Bru¨ckner et al.
dynamic relaxation test
Sorimachi et al.
friction simulator
Matsushita et al.
stress relaxation test
Watanabe et al.
rotational viscometer, laboratory continuous caster, actual casting test
Shin et al.
rotational viscometer
Shin et al.
rotational viscometer
Zhen et al.
rot
Data Loading...
