Fundamental Design of Steelmaking Refractories

8 Operation and Refractories for Secondary Steelmaking

8.1 Introduction

The primary steel process, including BOF and EAF, produces a certain limit of steel composition; thus further modification demands composition tuning and minimization of impurities. Several processes are adopted to control the resultant composition, primarily divided into two processes, without vacuum and with vacuum.

The vacuum process expedites producing ultralow carbon steel and excellent composition tuning of steel. In a broad sense, Ladle Heating Furnace (LHF) and Argon Oxygen Decarburization (AOD) are most common without a vacuum secondary steelmaking process. A ladle heating furnace (LHF) reheats the liquid steel from BOF. It utilizes electric energy through graphite electrodes to enhance and maintain the temperature and ensure steel homogenization temperature and chemistry through inert gas purging. Steel is refined and final composition is achieved. Argon Oxygen Decarburization (AOD) process is adopted for the low carbon content and chromium enriched stainless steel grade and other high grade alloys. In this process, oxygen is blown from the top lance, and a mixture of oxygen with argon is blown from side tuyeres for selective oxidation of carbon over alloy elements. AOD is usually used in conjunction with Induction Furnace (IF)/Electric Arc Furnace (EAF) route.

Most common and adopted vacuum processes are vacuum degassing (VD), vacuum arc degassing (VAD), vacuum oxygen degassing (VOD), and recirculation ...