Abstract
The electric arc furnace (EAF) process for steelmaking of Cr and Ni high alloyed stainless steel grades differs significantly from the steelmaking process of carbon steel due to the special raw materials and generally lower oxygen consumption. The special slag chemistry in the EAF process affects slag foaming and refractory wear characteristics due to an increased content of CrOx. A special slag diagram is presented in order to improve monitoring and control of slag compositions for Cr alloyed heats, with special focus on saturation to MgO periclase and dicalcium silicate C2S in order to minimize MgO losses from the refractory lining and to improve slag refining capability by avoidance of stable C2S. With the same diagram different EAF process strategies can be efficiently monitored, either at elevated CaO and basicity with lower spinel concentration and more liquid process slags near C2S saturation or at lower CaO content and basicity with increased spinel concentration and stiffer slags at MgO saturation but certainly no C2S stability. Examples for three industrial EAFs are given.
Highlights
Some 52.2 million tons of high alloyed and stainless steel grades were produced in 2019, i.e., approximately 2.8% of total steel production with an increasing trend due to global market demands
The modern production process is based on melting of steel scrap and alloys in an electric arc furnace (EAF) and subsequent decarburization and refinement of the molten metal in an argon-oxygen decarburization (AOD) converter or more rarely by vacuum oxygen decarburization (VOD) treatment
The EAF slags of this study are over-saturated with spinel phase
Summary
Some 52.2 million tons of high alloyed and stainless steel grades were produced in 2019, i.e., approximately 2.8% of total steel production with an increasing trend due to global market demands. The modern production process is based on melting of steel scrap and alloys in an electric arc furnace (EAF) and subsequent decarburization and refinement of the molten metal in an argon-oxygen decarburization (AOD) converter or more rarely by vacuum oxygen decarburization (VOD) treatment. Raw steel is melted from scrap in the EAF and liquid or solid Cr-alloys are added at the converter. Production of high-alloyed Cr or Cr-Ni molten metal in the EAF introduces additional metallurgical constraints to EAF process conditions. As oxidation of C and Cr in the molten metal occurs at very similar oxygen activities, special care is needed to minimize Cr losses, especially during oxygen injection in the EAF. The mixing of the steel melt in the EAF is insufficient and concentration gradients of C, Si and Cr may occur in the melt volume.
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