Chapter 1.5 - Converter Steelmaking

Abstract

The basic idea of converter processes is to convert carbon-rich liquid, blast furnace hot metal to low-carbon steel. The converter processes emerged in the mid-19th century with the invention of the Bessemer process based on bottom-blowing of air to decarburize hot metal. Oxygen refining was developed about one century later, first by oxygen-blowing through a lance and later by oxygen bottom-blowing through nozzles. Thereafter, modern oxygen steelmaking has evolved with numerous variants and modifications. Nowadays, the BOF process and other oxygen converter variants account for roughly 70% of the global production of carbon steel. A comparable breakthrough in stainless steelmaking was the commissioning of the first argon-oxygen decarburization (AOD) converters in the late 1960s. The great innovation was to use inert gases (initially argon but later also nitrogen) to achieve more selective oxidation of carbon and produce low-carbon stainless steel economically. Another principle to promote decarburization is to apply vacuum technology. Industrial vacuum-oxygen decarburization (VOD) converters emerged since the 1960s and serve both as an alternative to AOD-type dilution processes or as a supplement in a combined process route. This chapter reviews the main chemistry and phenomena in converter processes, as well as mainstreams of the developments and a future snapshot. The greatest future challenge for converter technology is the urgent need to reduce the global CO2 emissions of steelmaking. This may eventually lead to completely new meltshop layouts, not only in carbon steelmaking but also in stainless steelmaking if techno-economically viable CO2-free ferrochrome production technologies become available.