Direct Vanadium Alloying of Liquid Steel with Self‐Reduction Vanadium Slag Briquette

Abstract

Vanadium is one of the important alloying elements, which could effectively increase the strength, wear resistance, and plasticity of steels [1][2][3] and has been widely applied to high strength steel, high-speed tools steel, and bearing steel, etc. [4,5] At present, the vanadium is extracted from the co-production of hot metal in the BF-BOF process or is directly produced from the vanadium ore concentrate. [6][7][8] Traditionally, vanadium is added into liquid steel during the steelmaking process mainly in form of ferrovanadium. However, the production of ferrovanadium usually needs undergo a series of steps including roastingleaching, [9][10][11][12] purifying and pyrometallurgical process, [13][14][15] which causes high energy consumption and serious environmental pollution. Taking the production of 1 ton ferrovanadium FeV50 as an example, about 40 ton wastewater, 3 ton waste slag and a great quantity of exhaust gases (SO 2 , HCl, NH 3 , smoke dust) are produced. [16] Especially, high toxic hexavalent chromium (Cr 6þ ) in the wastewater would pollute the ecological environment seriously, and also would be ultimately enriched in organisms through the food chain, causing great harm to the human body. [17][18][19][20] In addition, the other metals in vanadium slag, including Cr, Mn, and Fe, could not be simultaneously recovered during the vanadium slag roasting procedure, resulting in a serious loss of valuable elements. Therefore, from both the environmental and economic perspective, it is very necessary to explore the feasibility of direct vanadium alloying with vanadium slag instead of ferrovanadium. In the present study, a direct alloying technology of liquid steel with self-reduction vanadium slag briquette was proposed, as illustrated in Figure 1. This method eliminates the production step of ferrovanadium and provides an alternative of compact process and cheap raw materials for producing vanadium-bearing steel, which has the advantages of reducing energy and material costs and alleviating environmental problems. In the self-reduction briquette, graphite powder was used as the reductant for the oxide components in vanadium slag, and the valuable elements of Fe, Mn, V, and Cr in vanadium slag would be reduced through carbothermic reduction under high temperature and eventually dissolved into liquid steel. Considering the strict requirements for P and S content in some special steels, the direct alloying method cannot be applied to the production of low sulfur and phosphorus steels. In the literatures, numerous studies were carried out to achieve the