Effect of the Slag Composition on the Process Behavior, Energy Consumption, and Nonmetallic Inclusions during Electroslag Remelting

Abstract

Electroslag remelting (ESR) is a well-established secondary refining process for many steels and Ni-base alloys with highest requirements regarding material properties. The main purposes are a dense solidification of ingots with a low degree of segregation as well as the reduction of medium-sized and especially complete removal of large nonmetallic inclusions (NMI). The specific energy consumption of ESR is documented in the range from 880 to over 2000 kWh t À1 . [1][2][3][4][5][6][7] Rising requirements regarding sustainability, emission control, and environmental protection have triggered new awareness for this topic. [4,8,9] Besides plant geometry and design, the customarily CaF 2 -based slag plays the key role in the heat generation and energy consumption of ESR. Key properties are the melting point as well as the electrical and thermal conductivity. [2,10] Other factors such as fill ratio and the amount of slag, or the melt rate can also have a strong effect. [4,8,[11][12][13][14][15][16] According to Holzgruber, [16] rising fill ratios up to 0.4 lead to a reduction in specific energy consumption due to a better heat transfer into the electrode and less radiation losses at the free slag surface. A further increase in fill ratio surprisingly resulted in a reversed trend due to changing immersion depths. Results from Li et al., [14] both laboratory scale and industrial size, demonstrate the strong effects of fill ratio (0.24 and 0.6) and electrical conductivity on the specific energy consumption with values below 1000 kWh t À1 at higher fill ratios combined with low or no CaF 2 -containing slags. CaF 2 -free slags in Brückmann and Schwerdtfeger [17] confirmed their particular advantage in specific energy consumption with values below 1000 kWh t À1 .There are only few reports of systematic research on energy consumption in ESR on the industrial scale. A recent investigation with a wider variation of slags is documented in refs. [5][6][7], and confirms an almost linear increase with electrical conductivity. A similar but less pronounced increase is reported in Jäger and Kühnelt [18] for slag composition with a wide variety of CaF 2 contents and a significantly higher fill ratio. A recent summary on the different effects of the fill ratio and the electrical conductivity on the specific energy consumption can be found in Schneider et al., [4] indicating that the energy consumption data from laboratory scale