Effect of slag composition and current density on ingot cleanliness during low-frequency/DC electroslag process

For in-depth investigation of the effect of low-frequency and DC remelting on the cleanliness of electroslag ingot, laboratory experiments were performed with different current densities and slag compositions to analyze the variation of oxygen content and inclusions in electroslag ingots. When 70% CaF 2 + 30% Al 2 O 3 binary slag is used for remelting, the current density has different effects on the cleanliness of electroslag ingots with different power supply modes. At the power frequency of 2 Hz, the oxygen content and the number of inclusions in the electroslag ingot increase significantly with the increase in remelting current density. By contrast, when consumable electrode connected to cathode (DCSP) or consumable electrode connected to anode (DCRP) is employed, the current density has little influence on ingot cleanliness. At the same current density, DCSP remelting has a more adverse effect on ingot cleanliness compared with DCRP remelting. Compared with the use of 70% CaF 2 + 30% Al 2 O 3 binary slag, using 60% CaF 2 + 20% Al 2 O 3 + 20% CaO ternary slag significantly reduces the oxygen content and the number of inclusions in electroslag ingots, regardless of whether low-frequency or DC electroslag remelting occurs. The increase in oxygen and inclusions in electroslag ingot is caused by the electrolysis of Al 2 O 3 in the slag pool. The increased inclusions mainly involve Al 2 O 3 or Al-containing oxides with small size. As regards the power supply mode, low frequency, DCRP, and DCSP promote the electrolysis of Al 2 O 3 in the slag pool. From the perspective of remelting slag composition, the slag with lower Al 2 O 3 content can reduce the pollution of electrolysis on electroslag ingot.