Key Processing Points for Using Graphite Petroleum Coke Carburizing Agents in Different Furnace Types

Graphite petroleum coke carburizing agents are high-purity carbonaceous additives prepared from petroleum coke through high-temperature graphitization treatment (above 2800℃). They are widely used in the steel smelting and casting industries. Compared to ordinary carburizing agents, graphite petroleum coke carburizing agents have significant advantages such as high fixed carbon content (98%–99.5%), extremely low sulfur content (<0.05%), low nitrogen content, low ash content, and high absorption rate, making them a key auxiliary material for the production of high-end steel products and castings.

In practical applications, different furnace types have different process requirements for the use of graphite petroleum coke carburizing agents due to differences in smelting principles, melting environments, and process paths. Correctly mastering the key processing points for various furnace types is crucial to ensuring carburizing effects, reducing production costs, and improving product quality.

Electric arc furnace steelmaking is currently one of the important application scenarios for graphite petroleum coke carburizing agents, mainly suitable for the production of special steels, alloy steels, and high-end cast steel parts.

1. Timing and Sequence of Addition

Electric arc furnace carburization typically employs in-lamb carburization during the tapping process. Before tapping, the weighed carburizing agent is prepared according to the process card requirements. During tapping, after approximately 20 tons of molten steel have flowed out, in-lamb alloying and slag formation begin. Deoxidizer, carburizing agent, alloying materials, and slag-forming materials are added sequentially, completing all additions before the tapping volume reaches 80 tons. The carburizing agent yield is calculated at 100%, and the amount added is adjusted according to the ladle carbon content requirements for different steel grades.

2. Temperature Control Requirements

The tapping temperature of an electric arc furnace is typically between 1610℃ and 1700℃. For steel grades with a large amount of alloying added, the tapping temperature can be appropriately increased by approximately 20℃. Before adding carbon, it is important to thoroughly remove any floating slag from the furnace to prevent it from affecting carbon dissolution and absorption.

3. Furnace Type and Process Matching

Electric arc furnaces should flexibly select the type of carbon raiser based on steelmaking requirements: during the charging and melting stages, calcined petroleum coke can be used to reduce raw material costs; however, when entering the refining stage or when higher steel quality is required, graphitized petroleum coke should be used to meet the requirements of low sulfur, low nitrogen, and high absorption rates.

Medium-frequency induction furnaces are mainly used in casting production and are the mainstream equipment for producing cast iron, ductile iron, and cast steel parts. Graphite petroleum coke carbon raisers are widely used in medium-frequency furnaces.

1. Addition Method

During melting in a medium-frequency induction furnace, the carbon raiser should be added to the lower middle part of the furnace along with the furnace charge according to the specified ratio or carbon equivalent requirements, achieving a recovery rate of over 95%. 1. **High-Proportion Scrap Steel Carburizing Process:** If a high-proportion scrap steel carburizing process is used, it is recommended to add the carburizing agent to the furnace in batches, placing it between the scrap steel layers to improve absorption uniformity.

2. Particle Size Selection:

The larger the furnace diameter and capacity, the larger the particle size of the carburizing agent should be; conversely, the smaller the diameter and capacity, the smaller the particle size should be. Specifically: 0.5–2.5 mm particle size is suitable for electric furnaces under 1 ton; 2.5–5 mm particle size is suitable for electric furnaces of 1–3 tons; and 5.0–20 mm particle size is suitable for electric furnaces of 3–10 tons. Furthermore, among the same type of carburizing agent, finer particle sizes result in faster absorption and better absorption effects.

3. Temperature Control and Stirring:

The optimal dissolution and absorption window for carburizing is 1450–1500℃. Stirring the molten iron is beneficial for carbon dissolution and diffusion; it is advisable to ensure complete dissolution of the carburizing agent. However, excessive stirring time will exacerbate carbon loss and affect the furnace lining life.

4. Influence of Chemical Composition

Silicon and sulfur in molten iron hinder carbon absorption, reducing the carbon additive absorption rate; while manganese aids carbon absorption. In actual production, the charging sequence is usually "add manganese first, then carbon, and finally silicon."

1. Blast Furnace Injection Application

Petroleum coke can be used as injection fuel in blast furnaces, replacing some pulverized coal. This improves the permeability and thermal efficiency of the blast furnace and promotes the reduction reaction of iron ore. The blast furnace's ability to withstand high blast temperatures is greatly affected by the quality of raw materials and fuels. Combining petroleum coke injection with technologies such as high oxygen enrichment can leverage the energy-saving effect of replacing coke with coal at high blast temperatures.

2. Carbon Addition in the Ironmaking Stage

Adding graphite petroleum coke during the ironmaking process can effectively increase the carbon content in the molten iron, providing a compositional basis for subsequent converter steelmaking. The basic requirements for recarburizing agents used in blast furnaces are high fixed carbon content, low impurity content, and moderate particle size to ensure good reaction efficiency and furnace stability.

Converter steelmaking mainly produces medium and high carbon steels, and recarburizing is usually completed during the tapping process.

1. Technical Requirements

When smelting medium and high carbon steels in converters, graphite petroleum coke with low impurity content is used as a recarburizing agent. Specific requirements for recarburizing agents used in top-blown converter steelmaking are: fixed carbon ≥ 96%, volatile matter ≤ 1.0%, sulfur ≤ 0.5%, moisture ≤ 0.5%, and particle size between 1 and 5 mm. Particles that are too fine are easily burned off, while those that are too coarse float on the surface of the molten steel and are not easily absorbed.

2. Addition Method and Timing

Converter recarburizing is mainly done during the tapping process. Low-sulfur calcined petroleum coke or graphitized petroleum coke is preferred, requiring rapid dissolution, non-floating, and no smoke. Adding a carburizing agent during the semi-steel tapping process not only provides excellent carburization but also has almost no impact on the overall steelmaking production rhythm.

3. Oxygen Content Management

During the vanadium extraction process in the converter, a large amount of oxygen is blown into the molten iron, resulting in a high oxygen content in the semi-steel, which makes the molten steel prone to turbulence after tapping. Therefore, the deoxidation status of the molten steel should be monitored before carburization in the converter, and a deoxidizer should be used if necessary to ensure the absorption rate of the carburizing agent.

1. Steel Grade Determines Carburizer Grade

For common carbon steel, rebar, and other conventional steel grades, calcined petroleum coke carburizer (96%–98.5% fixed carbon, 0.3%–0.7% sulfur) can be used; for high-quality carbon steel, low-alloy steel, and high-strength steel, low-sulfur calcined petroleum coke (98%–99% fixed carbon, ≤0.3% sulfur) is recommended; for high-carbon steel, bearing steel, spring steel, alloy structural steel, and other high-end steel grades, graphitized petroleum coke carburizer (98.5%–99.5% fixed carbon, ≤0.05% sulfur) should be used.

2. Particle Size Matches Furnace Capacity

The furnace diameter and capacity are the core criteria for selecting carburizer particle size. Small-capacity electric furnaces use fine particles to accelerate dissolution and absorption, while large-capacity electric furnaces use coarse particles to reduce oxidation loss.

3. Process Adaptability

Electric arc furnace steelmaking allows for flexible switching of recarburizer types at different stages; medium frequency furnace casting requires selecting the appropriate degree of graphitization based on the casting material grade; converter recarburization emphasizes dissolution rate and appropriate particle size; blast furnace injection focuses on fuel substitution effect and furnace stability.

As the steel industry moves towards green and high-end development, the demand for high-quality graphite petroleum coke recarburizers continues to grow. Different furnace types have different emphasis on the process requirements of recarburizers. In practical applications, production enterprises should scientifically select the type of recarburizer and process parameters based on furnace characteristics, steel grade requirements, and cost budget, optimizing the charging sequence and temperature control to achieve cost reduction and efficiency improvement while ensuring product quality. In the future, specialized recarburizer products with higher purity, lower impurities, and better suitability for intelligent smelting will become the mainstream direction in the industry.