Regular Article

Effect of SiO₂ containing slag for electroslag remelting on inclusion modification of 42CrMo steel

¹ The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, PR China
² Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, PR China
³ Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, PR China
⁴ School of Metallurgy, Northeastern University, Shenyang 110004, PR China

^* e-mail: liguangqiang@wust.edu.cn

Received: 21 May 2019
Accepted: 23 October 2019

Abstract

Five heats were carried out to study the effects of SiO₂ containing slag for electroslag remelting (ESR) on inclusion characteristics of 42CrMo steel. Fluoride vaporization at elevated temperature from slags was also explored by thermogravimetric analysis. The results show that fluoride vaporization is dominated by slag viscosity and component activities in the melt. Slag composition has an important effect on the composition of the oxide inclusion. For 70 wt% CaF₂–30 wt% Al₂O₃ slag, the compositions of oxide inclusions in remelted steel show no obvious differences compared with the virgin steel. Whereas, SiO₂ content in oxide inclusions of steel processed by slag bearing SiO₂ show an increasing trend with increase of SiO₂ content in 50 wt% CaF₂–CaO–SiO₂ slag, and the MgO · Al₂O₃ inclusions are modified to (Al,Ca,Mg,Si)O inclusions with low melting temperature. Al₂O₃ contents in oxide inclusions are also closely related to the Al₂O₃ concentration in the molten slag, which increase with the addition of Al₂O₃ in slag bearing SiO₂. In testing various slags, the incorporation of slag T2 with 50 wt% CaF₂–30 wt% CaO–20 wt% SiO₂ shows the highest cleanliness in remelted steel. This implies that slag T2 can be a promising slag for ESR process of alloy steel requiring Al content refinement due to less fluoride vaporization from slag and better inclusions modification.