Inclusion Evolution during Modification of Alumina Inclusions by Calcium in Liquid Steel and Deformation during Hot Rolling Process

The production of clean steel involves the controlling, elimination, or modification of nonmetallic inclusions. In Al-killed steels, alumina is the main type of inclusion. Calcium treatment, by wire feeding, is commonly used to modify solid alumina inclusions to calcium aluminates, which exists in a fully or partially liquid phase. Liquid inclusions can improve steel castability, but make inclusions size larger during hot rolling process if these inclusions have not been completely removed before casting, which can significantly affect the mechanical properties of final products.1) Previous researchers had extensively studied on CaO–Al2O3, MgO– CaO–Al2O3 or MgO–CaO–Al2O3–CaS inclusions, such as their characteristics and formation mechanism. Ye et al.2) found alumina inclusions were changed by calcium treatment with the path of Al2O3→CA6→CA2→CA→CAX(liquid) until the Al2O3 activity became so low that precipitation of CaS was occurred. Guo et al.3) proposed there were two manners for Al2O3 inclusion modification during LF refining process: the first manner was Al2O3→low modified calcium aluminates→liquid calcium aluminates, and the second was Al2O3→MgO·Al2O3 spinel→CaO–MgO–Al2O3 multi-component inclusion. Jiang et al.4) proposed that steel/slag reaction time had great effect on inclusion types, compositions and shapes. With the increase of reaction time, solid MgO– Inclusion Evolution during Modification of Alumina Inclusions by Calcium in Liquid Steel and Deformation during Hot Rolling Process