In casting production, especially when using scrap steel recarburization, recarburizers act like "energy supplements" in molten iron. Their selection directly impacts the intrinsic quality (such as metallographic structure and mechanical properties) and surface finish of the final casting, and also profoundly influences production costs and efficiency. Currently, recarburizers on the market are primarily categorized into four main categories: graphitized recarburizers, petroleum coke recarburizers, natural graphite recarburizers, and coal-based recarburizers. These products differ significantly in composition, processing, and application scenarios.
Source and performance differences:
- Graphitized recarburizers are high-end products produced through high-temperature treatment above 2500°C. They have a fixed carbon content of 98%-99.5% and a sulfur content below 0.05%, demonstrating excellent recarburization efficiency (absorption rate of 90%-95%).
- Petroleum coke recarburizers, made from oil refining byproducts and calcined at 1200-1500°C, have a fixed carbon content of 90%-98%. The sulfur content is typically 0.3%-0.7%. While natural graphite recarburizers offer environmental advantages, their dense crystal structure results in an absorption rate of only 60%-75%, and their sulfur content fluctuates widely (0.1%-1.5%).
- Coal-based recarburizers have low fixed carbon content (80%-90%) and high sulfur content (0.5%-2%).
Application Differences:
High-end ductile iron and critical gray iron castings (cylinder blocks, cylinder heads, hydraulic components, etc.):
Artificial graphite recarburizers are the preferred choice. Extremely low sulfur, nitrogen, and ash content are key to ensuring spheroidization, reducing nitrogen pores, and achieving pure molten iron. Ultra-high and stable absorption rates ensure precise control of carbon content.
General gray iron castings and ductile iron castings with lower requirements:
Calcined petroleum coke recarburizers are the mainstream, economical, and practical choice. They have high fixed carbon content, good absorption rate, and relatively controllable sulfur content. They are lower in cost than artificial graphite and can meet the performance requirements of most conventional castings. For cost-sensitive, ordinary gray iron castings with relaxed sulfur/nitrogen requirements, calcined anthracite recarburizer may be the preferred choice. Its core advantage is its lowest price. However, it also has disadvantages: high sulfur, nitrogen, and ash content pose significant risks, and its absorption rate is unstable and low.
Cost Considerations:
Artificial graphite: While it has the highest unit price, its exceptionally high absorption rate and stability often require a lower addition amount to achieve the target carbon content. More importantly, its improved quality (reduced scrap, improved performance), reduced pig iron usage, and reduced costs for defect treatment caused by sulfur, nitrogen, and ash content offer significant advantages from an overall cost perspective, particularly in high-end casting production.
- Calcined petroleum coke: It strikes a good balance between unit price, absorption rate, and performance, offering a high overall cost-effectiveness, making it a widely used workhorse.
- Calcined anthracite: It has the lowest unit price, but its low absorption rate means more weight must be added to achieve the same carbon content. High sulfur, nitrogen, and ash content can significantly increase the risk of casting defects (porosity, slag inclusions, and brittleness), leading to higher scrap rates, increased processing costs, and unstable performance. While seemingly inexpensive, this may not always be worth the cost, especially when quality requirements are stringent or scrap quality fluctuates significantly.
When selecting a recarburizer, casting manufacturers should look beyond the simple price tag and comprehensively consider their product positioning, quality requirements, raw material (especially scrap) conditions, melting processes and equipment, and overall costs (including quality losses). A recarburizer precisely matched to process requirements can become a powerful engine for achieving superior casting quality and improving economic efficiency.
