In electric arc furnace (EAF) steelmaking, a violent boiling accident refers to an abnormal and hazardous process event caused by a sudden and intense acceleration of the decarburization reaction. When this occurs, molten steel, slag, and furnace gas may violently erupt from the furnace, leading to equipment damage, serious safety risks to operators, and unplanned production stoppages.
Understanding the mechanism, causes, and prevention of violent boiling is therefore essential for safe and stable EAF operation.
Characteristics of Violent Boiling During Decarburization
Under normal conditions, decarburization in an electric arc furnace proceeds in a controlled manner, with CO gas generation absorbed and buffered by the slag layer. A violent boiling accident occurs when the decarburization rate increases sharply within a very short time, typically reaching approximately 0.10–0.15% carbon per unit time.
When gas generation exceeds the buffering capacity of the slag, the molten bath becomes unstable. This instability results in severe bath agitation, slag foaming failure, and the violent ejection of molten materials and high-temperature fumes from the furnace.
Common Causes of Violent Boiling in EAF Steelmaking
Violent boiling accidents are closely related to process imbalance during the decarburization stage. The most common causes include the following.
Water Ingress Into the Molten Bath
Leakage from water-cooled panels, furnace roofs, or oxygen lances may allow cooling water to enter the molten steel. At steelmaking temperatures, water rapidly vaporizes or decomposes, producing a sudden volume expansion that can instantly trigger violent boiling. This is considered one of the most dangerous accident scenarios in EAF operation.
Collapse of Cold Zones Into the Bath
Even in modern electric arc furnaces, temperature and composition are not completely uniform. When solid or semi-molten scrap from colder zones collapses into a high-temperature decarburization zone, the local reaction balance is disrupted, causing a sharp increase in decarburization intensity.
Poor Coordination Between Oxygen Blowing and Power Input
If oxygen blowing and electrical heating are not properly matched, the molten bath may become fully melted while decarburization does not start in a timely manner. As a result, iron oxide (FeO) accumulates in the slag. Once decarburization finally initiates, the reaction may occur abruptly, leading to violent boiling.
Prolonged Slag Blowing for Dephosphorization
During certain operating stages, especially when the carbon content is in the range of 0.2%–0.8%, extended slag blowing aimed at enhancing dephosphorization may cause excessive FeO enrichment in the slag. This creates highly unstable conditions once decarburization is triggered.
Violent Boiling Mechanisms in Modern Electric Arc Furnaces
In modern EAFs, violent boiling accidents are often associated with non-uniform bath conditions and sudden reaction zone shifts.
Oxygen is mainly consumed in localized high-temperature areas, while cold zones may still contain unmelted scrap or soft-melted materials. When high-carbon material from these zones suddenly enters a low-carbon decarburization region, the reaction rate increases sharply, resulting in violent bath boiling.
In addition, within a certain oxygen supply range, the decarburization rate is controlled by carbon diffusion toward the reaction interface. The corresponding carbon range, commonly referred to as the critical carbon range, is typically about 0.2%–0.8%. Within this range, process disturbances are more easily amplified, especially when slag FeO concentration is high.
Why Low Slag Basicity Is a Frequent Cause of Violent Boiling
Slag basicity has a direct influence on its ability to transfer oxygen to the molten steel. Low-basicity slag exhibits poor mass transfer capability, which promotes FeO accumulation in the slag phase.
When decarburization eventually begins, the excessive FeO rapidly participates in the reaction, releasing large amounts of CO gas in a short time and destabilizing the bath. Production experience has consistently shown that violent boiling accidents occur more frequently under low-basicity slag conditions.
Identifying and Responding to Water-Leak-Induced Violent Boiling
Violent boiling caused by water leakage usually presents clear warning signs:
- During the melting stage, abnormal yellow flames may appear inside the furnace or in the exhaust duct.
- White steam mixed with flame may violently eject from the furnace door.
- In the oxidation stage, the molten steel exhibits extremely violent boiling accompanied by a sharp increase in exhaust gas volume.
Once water leakage is suspected, oxygen blowing and power input must be stopped immediately, and emergency shutdown systems for power and cooling water should be activated. The furnace should remain stationary, and personnel must evacuate the area promptly to prevent escalation of the accident.
Control of Violent Boiling Under Different Oxygen Lance Technologies
Consumable Oxygen Lance Operation
When using consumable oxygen lances, preventing violent boiling relies on limiting FeO enrichment and ensuring smooth decarburization initiation. Key measures include appropriate lance angles, controlled slag formation, adequate bath stirring through power input, and coordinated carbon injection to stabilize slag chemistry.
Supersonic Coherent Jet Oxygen Lances
Supersonic coherent jet technology is theoretically capable of reducing violent boiling risk. However, industrial practice shows that violent boiling can still occur—and may be more severe—if operating conditions are not well controlled.
Major contributing factors include insufficient slag basicity, poor coordination between oxygen supply and bath heating, malfunctioning carbon injection systems, and high concentrations of alloying elements that suppress decarburization reactions.
Effective prevention focuses on maintaining appropriate slag basicity (around 2.0), optimizing scrap mix and charging practice, ensuring stable carbon injection, avoiding strong oxygen blowing at low bath temperatures, and enhancing bath stirring through electrical input.
Why Steelmaking Is Not Recommended at Low Oxygen Pressure
When oxygen pressure is too low, the oxygen jet cannot effectively penetrate the slag–metal interface, significantly reducing bath stirring intensity. This condition favors FeO accumulation in the slag and increases the risk of violent boiling.
Insufficient oxygen supply also disrupts the transition from the melting stage to the oxidation stage, complicates dephosphorization and decarburization, and makes temperature control more difficult. As a result, both operational safety risks and production costs increase, making low-pressure oxygen blowing unsuitable for EAF steelmaking.
