Theoretical Analysis of Bubble Nucleation in Molten Steel Supersaturated with Nitrogen or Hydrogen
- PDF / 1,896,665 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 44 Downloads / 218 Views
UCTION
IN metal-refining processes, one of the effective methods of removing inclusions is via bubble flotation. Currently, the methods of producing gas bubbles in liquid steel include ladle argon stirring,[1] pressure elevating and reducing method (PERM),[2–4] argon bubbling curtain in a tundish,[5] injecting gas from a shroud,[6] fine heterophases induced by explosive reaction,[7] ultrasonic cavitation bubbles,[8] etc. The PERM proposed by NKK Company in the early 1990s is an additional technique for removing micro-nonmetallic inclusions in molten steel.[2] The principle is as follows. First, liquid steel is pretreated in an environment with nitrogen or hydrogen at a high partial pressure, thus dissolving any nitrogen or hydrogen present in the liquid
KANGWEI LI, JIANHUA LIU, and JIE ZHANG are with the Engineering Research Institute, University of Science and Technology Beijing, No.30 Xueyuan Road, Haidian District, Beijing 100083, China. Contact e-mail: [email protected] SHAOBO SHEN is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, No.30 Xueyuan Road, Haidian District, Beijing 100083, China. Manuscript submitted July 28, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
steel. Second, the liquid steel is treated in a vacuum environment, allowing the supersaturated gas to precipitate and form a large number of dispersive and fine gas bubbles on the surface of the inclusions. Finally, the bubbles float up along with the inclusions, adhering to more number of inclusions as they float to the top. Hence, the micro-inclusions in the molten steel can be significantly reduced. A trial on small-scale high-temperature refining was conducted in our laboratory using this technology. It was proven that the total oxygen and micro-nonmetallic inclusions in the steel were significantly reduced.[9] Based on the principle of removing inclusions via bubble flotation, the technology can be divided into three stages: (1) dissolution of N2 or H2 in liquid steel, (2) nucleation of nitrogen or hydrogen bubbles, and subsequent growth in the liquid steel, and (3) floatation of bubbles along with the inclusions, and their subsequent removal. Bubble nucleation in liquid steel is the prerequisite for bubble formation, which is an important step in this technology. So far, no studies have been reported on the evolution of dissolved gas bubbles in molten steel supersaturated with N2 or H2. In the conventional vacuum-degassing processes, the concentration of nitrogen or hydrogen in molten steel is generally low. Thus, the precipitation
pressure of the nitrogen or hydrogen is not sufficiently high to overcome the static pressure of the liquid steel or the additional pressure due to the surface tension of the molten steel/gas phase, thereby making it difficult for bubble nucleation in molten steel. Hence, the dissolved nitrogen or hydrogen in the molten steel treated via conventional vacuum-degassing processes is largely removed via diffusion of nitrogen or hydrogen to the surface of the l
Data Loading...
