Distribution of Arsenic Inclusions in Rare Earth Steel Ingots
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. Types and Distribution of Inclusions
3.2. Chemical Composition Changes with La Addition
3.3. Formation Process and Distribution Mechanism of Inclusions
- (i)
- During the steelmaking process, La2O3 and La2O2S formed and floated up to the top surface of molten steel in the temperature range from 1600 °C to the liquidus, illustrated in Figure 9a. The formation of these inclusions took away most of the oxygen, including the part offered by alumina crucibles, as well as a part of the sulfur.
- (ii)
- As the consumption of soluble oxygen, lanthanum started to react mainly with sulfur and arsenic, and then LaS and La-S-As inclusions formed. As the temperature decreases, the first solidified part of the molten steel will be the surface, because the surface has the worst thermal insulation conditions. On the one hand, these inclusions floated up to the surface of molten steel and are easy to be captured. On the other hand, the unsolidified molten steel still flows, driven by the temperature gradient, as shown in Figure 9b. The overall solidification structures of the profile of the ingots can well explain this. As shown in Figure 9c, a hole exists at the center of the ingots, and some porous zones with strong columnar crystals exist below that can be seen even directly with the naked eyes. It is inferred that these porous zones are the last solidified part and have the highest temperature all the time. A temperature gradient, therefore, exists all the time also. In summary, the flow of molten steel, together with the buoyancy caused by the different densities between inclusions and molten steel, drives the inclusions to move. This leads to the enrichment of LaS and La-S-As inclusions at the surfaces of the ingots, especially near the top surface. It makes the inner part of the ingots almost free of LaS and La-S-As that dramatically decreases the concentrations of arsenic and sulfur.
- (iii)
- As the temperature went down, a few (La-S-As)-(La-As) and La-As inclusions formed during and after solidification, shown in Figure 9c. It is believed that the formation temperature of CeAs is at the end of solidification [3,29]. Therefore, the fact that La-As starts to form at the end of solidification is reasonable according to the similar chemical properties of La to Ce. However, these arsenic inclusions do not move away from the inner part of the ingots and do not affect the final arsenic concentration.
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Elements | C | Si | Mn | P | S | Al | O | As |
---|---|---|---|---|---|---|---|---|
Concentrations | 0.79 | 0.21 | 0.61 | 0.011 | 0.015 | 0.001 | 0.0024 | 0.010 |
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Wang, H.; Jiang, S.; Yu, P.; Bai, B.; Sun, L.; Wang, Y. Distribution of Arsenic Inclusions in Rare Earth Steel Ingots. Metals 2020, 10, 146. https://doi.org/10.3390/met10010146
Wang H, Jiang S, Yu P, Bai B, Sun L, Wang Y. Distribution of Arsenic Inclusions in Rare Earth Steel Ingots. Metals. 2020; 10(1):146. https://doi.org/10.3390/met10010146
Chicago/Turabian StyleWang, Hongpo, Silu Jiang, Peng Yu, Bin Bai, Lifeng Sun, and Yu Wang. 2020. "Distribution of Arsenic Inclusions in Rare Earth Steel Ingots" Metals 10, no. 1: 146. https://doi.org/10.3390/met10010146