Original Article

Effect of ladle lining system refractories on the cleanliness of heavy-rail steel U75V

Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing (USTB), Beijing 100083, China

^* e-mail: 18235111315@163.com

Received: 29 June 2023
Accepted: 15 October 2023

Abstract

To understand the effect of refractories in the ladle lining system on the evolution of inclusions in the secondary refining process, refractory samples were taken from different locations in the ladle system (Slag lining bricks, Sidewall bricks, Refractory mortar, and Bottom bricks). Laboratory experiments were carried out using heavy-rail steel slab samples (Si-Mn-killed steel) and different refractory bricks. The four kinds of refractory bricks can be roughly divided into 3 categories: (1) MgO-Al₂O₃-C system (MAC, high MgO>55%); (2) Al₂O₃-MgO-C system (AMC, low MgO<13%); (3) Al₂O₃-SiO₂ system (AS). The results show that after the reaction between molten steel and refractory materials, both AMC (slag lining bricks and sidewall bricks) and MAC (bottom bricks) will dissolve their component Al₂O₃, increasing [%Al] content in molten steel, forming MgO-Al₂O₃ type inclusions, and the dissolution of its component MgO depends on the content of MgO. When MgO>55%, MgO will dissolve. When MgO<13%, due to the low activity of MgO, MgO will not dissolve. MgO inclusions were found in the steel when the MgO content in the refractory was higher than 55%. MgO inclusions may originate from the refractory itself. The reduction of TiO₂ in the AS (refractory mortar) by [%Al] and [%Si] in the steel increases the [%Ti] content of the steel, forming Ti-containing inclusions.