One of the major challenges for Europe’s future steel production will be minimizing the inherent process emissions in the production of crude steel based on iron ores. In this case, mainly the reduction of CO2 emissions is a focus. One promising process to overcome these problems is the hydrogen plasma smelting reduction (HPSR) process. This process has been studied for several years already at the Chair of Ferrous Metallurgy at Montanuniversitaet Leoben. The work presented focused on the stability of plasma arcs in the DC transferred arc system of the HPSR process. The stable operating plasma arc is of utmost importance for the future development of the process. The major objective is the definition of the most favorable conditions for this kind of arc. Therefore, tests were conducted to define fields of a stable operating plasma arc for multiple gas compositions and process variables. For several gas compositions of argon, nitrogen, argon/nitrogen, argon/hydrogen and nitrogen/hydrogen, fields of stability were measured and defined. Besides, the major influencing parameters and trends for the fields of stability were evaluated and are shown in this work.

With the European Green Deal (EGD), the European Union will become 2050 the first carbon-neutral continent. Additionally, greenhouse gas (GHG) emissions should be reduced by 55% by 2030 compared to 1990. [1][2][3] With a proportion of around 7%, the iron and steel industry significantly contributes to anthropogenic CO 2 emissions worldwide. [4] Europe (EU28) produced 2 019 649 million tonnes of crude steel via the integrated route, blast furnace (BF)-basic oxygen furnace (BOF), which accounts for 59.1% of the total production in Europe. Worldwide, about 70% of the 1.87 billion tonnes (2020 [5] ) of crude steel are produced via the BF-BOF route per year. During this established process, specific estimated emissions of 1,8 t CO 2 /t steel are generated with an energy demand of 12.31 GJ tHM À1 and 1.22 tCO 2 tHM À1 for the blast furnace alone. [3,6,7] To reduce or avoid these greenhouse gas emissions in steel production, the European Steel Association's members created two main technology pathways: smart carbon usage (SCU) and carbon direct avoidance (CDA). SCU consists of process integration (PI) to modify existing processes and technologies based on fossil fuel and carbon capture and utilization (CCU) to use the emissions to produce essential chemicals.However, CDA is focusing on developing production processes that are not producing direct CO 2 emissions because carbon carriers are left out of the process. This can be achieved with green electricity or hydrogen as a reduction agent or both. [6,8] Hydrogen Plasma Smelting ReductionThe so-called hydrogen plasma smelting reduction (HPSR) process is one of these crucial technologies for green steelmaking in the future and is being studied by several working groups. [9][10][11] The Montanuniversitaet Leoben, Austria, has been working on this research topic for more than ten years. [12][13][14][15][16][17] With this process, iron ore fines are melted and reduced to metallic iron, leaving only steam as a by-product. A thermal transferred direct current arc is ignited between a hollow graphite electrode (HGE) and the melting pool. Gases such as hydrogen, argon, nitrogen, and iron ore fines (<150 μm) are injected through the electrode. Due to the high thermal energy of the arc, gas molecules or atoms transform in several intermediate stages until the ionized state is reached. In this final stage, the highest reduction potential occurs. Decisive for the degree of ionization, hydrogen utilization and reduction kinetics are the stability of the arc and the position of the focal spot. It has already been investigated that argon acts as a stabilizer in gas