Effect of Initial Iron Content in a Zinc Bath on the Dissolution Rate of Iron During a Hot Dip Galvanizing Process
- PDF / 3,985,910 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 48 Downloads / 247 Views
RING the hot dip galvanizing process, dross particles, which are intermetallic compounds of the Zn-Fe-Al system, affect the surface quality of the steel sheet. Thus, the changes in Fe or Al concentration in molten zinc have a significant impact on the production of high-quality steels. When a steel sheet is immersed in a zinc bath, dissolved iron creates the Fe-Zn and Fe-Al intermetallic compound layer on the surface of the steel sheet.[1,2] Additionally, dissolved iron from the steel sheet promotes the precipitation of d (FeZn10Alx), f (FeZn13), and g (Fe2Al5Znx) phase dross particles in molten zinc. The bulk of research with respect to the dross in molten zinc are based on thermodynamics and phase equilibria for the Zn-Al-Fe system by employing experimental and/or computational methodologies. In the
SANG MYUNG LEE and JOO HYUN PARK are with the Department of Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: [email protected] SUK KYU LEE is with the Technical Research Center, POSCO, Gwangyang 545711, Korea. DOO-JIN PAIK is with the Surface Treatment Plant I, Surface Treatment Department, POSCO, Gwangyang 545-711, Korea. Manuscript submitted August 12, 2016. Article published online January 17, 2017 1788—VOLUME 48A, APRIL 2017
modeling work of Nakano et al.,[3] the Zn-Al-Fe phase diagram (Zn-rich corner) was evaluated at full equilibrium from 693 K to 773 K (420 C to 500 C). In the modeling work of McDermid et al.,[4] solubility measurements and thermodynamic modeling were performed to depict the zinc-rich corner of the Zn-Al-Fe phase diagram. Park et al.[5] recently determined that the addition of Al into the Zn-Fe melt provided local supersaturation and depletion of Al content, resulting in the nucleation and growth of both Fe2Al5Znx and FeZn13. However, Al was continuously homogenized as the reaction proceeded, and thus a very fine and stable FeZn10Alx phase formed after 30 minutes. Alternatively, dross is generated due to the dissolution of iron from the steel sheet. Therefore, the kinetic study on the dissolution of iron is highly important. In the kinetic modeling work by Giorgi et al.,[6] the mass transfer coefficient of iron kM was taken as 1.7 9 105 m/s when iron was saturated in molten zinc at 733 K (460 C). Michal et al.[7–9] predicted the value of kM using Fick’s second law with the appropriate boundary condition derived from the iron concentration in the liquid zinc from Liu and Tang’s model and Toussaint et al.’s model.[7–9] The mass transfer coefficients previously reported are listed in Table I. Michal et al.[7] also found that the kM increased only slightly as the strip line speed increased and followed an Arrhenius relationship with the reciprocal of the strip METALLURGICAL AND MATERIALS TRANSACTIONS A
entry temperature. They also reported that an increase in Al concentration from 0.118 to 0.124 mass pct in the Zn bath caused a slight decrease in kM because the inhibition layer formed rapidly in a high Al content condition in the zinc bath. This inhibition layer
Data Loading...
