In electric arc furnace (EAF) steelmaking, the consumption curve of graphite electrodes is not a smooth line—it is more like a dynamic “health check report” of the smelting process. Changes in the shape of the curve directly reflect whether the smelting intensity is overloaded and whether the oxygen injection strategy is precise or crude. Simply put, smelting intensity determines the sublimation rate at the electrode tip, while the oxygen injection method dominates the oxidation consumption on the electrode sidewall; together, they shape the trend and slope of the consumption curve.
Smelting Intensity: Tip Consumption Hidden Behind Current and Arc Length
The consumption curve’s feedback on smelting intensity is very direct. In the early melting stage, to quickly bore through the scrap, high-voltage, long-arc, or high-current operation is usually adopted, and the curve often shows a steep rise.
From a mechanistic perspective, consumption at the electrode tip is proportional to the square of the current. This means that when you significantly increase the current to pursue a shorter smelting cycle (i.e., higher smelting intensity), losses at the tip caused by high-temperature sublimation and thermal stress increase exponentially. If the current density is too high (for example, exceeding about 20 A/cm² in an AC furnace), the electrode tip may even develop longitudinal or transverse cracks due to excessive thermal load, causing the consumption curve to show an abrupt, abnormal upward jump—usually a signal that the smelting intensity has exceeded the electrode’s tolerance limit.
In addition, smelting intensity indirectly affects the curve through arc stability. If high-intensity power is forced during stages when the scrap is not fully melted and the arc frequently breaks or “flashes,” mechanical impact and thermal shock increase the risk of electrode fracture, which appears on the curve as non-continuous mass loss (chipped pieces or breakage).
Oxygen Injection: The Regulating Valve That Makes the Curve “Fatter” or “Thinner”
Oxygen is used in EAF steelmaking for fluxing and decarburization, but it is a strong oxidant for graphite electrodes. The consumption curve is highly sensitive to oxygen injection, mainly through sidewall oxidation.
When the oxygen supply intensity in the furnace increases (e.g., when coherent jets or door lances are turned on), the oxidizing atmosphere in the furnace gas intensifies sharply. Graphite begins to oxidize noticeably at around 600°C, and above 750°C the oxidation rate rises sharply. Reflected in the consumption curve, the overall slope becomes steeper, and consumption is no longer concentrated only at the tip—the “thinning” rate of the electrode sidewall accelerates. Empirical formulas indicate that the oxygen-blowing-related constant K_OX directly determines the magnitude of sidewall oxidation consumption.
However, an excellent oxygen injection strategy (e.g., combined with foamy slag operation) can instead make the curve more “economical.” When oxygen is mainly used for reactions inside the molten bath, and thick foamy slag is created through carbon injection to fully bury the arc, the area of the electrode exposed to the oxidizing atmosphere is greatly reduced. At this point, although the smelting pace is fast, sidewall oxidation of the electrode is physically isolated by the foamy slag, and the consumption curve shows a relatively flat trend under high smelting intensity. Conversely, if oxygen injection is excessive and effective foamy slag is not formed, causing violent boiling or spattering in the furnace, this not only scours the electrode but also destroys the protective slag layer, causing the consumption curve to show a clear steep inflection point during the peak oxygen-blowing period.
Comprehensive Interpretation: The Secret of “Matching” Behind the Curve
Combining the two, the core secret revealed by the consumption curve is the “matching degree” between “power supply intensity” and “oxygen supply intensity.”
If the curve shows abnormally high tip consumption (reflected in rapid electrode shortening) while the sidewall remains relatively intact, it indicates that the smelting intensity (current) may be too high while chemical energy (oxygen) assistance is insufficient, causing electrical energy to be excessively converted into thermal load at the electrode tip. If the curve shows extremely rapid electrode “slimming” (severe sidewall oxidation) accompanied by poor slag conditions, it indicates that the oxygen injection intensity has exceeded the protection capacity of the slagging regime, and the oxidizing atmosphere is out of control. An ideal consumption curve should, while supplying high-intensity power, use precise oxygen injection combined with foamy slag to efficiently inject chemical energy into the molten bath, while suppressing both physical sublimation and chemical oxidation of the electrode to low levels.
Post time: Oct-28-2026