Continuous casting billet: The raw material for long product Steel rolling

When it comes to producing long steel products like rebar, fil machine, rails, et sections structurelles, one raw material stands out for its efficiency, consistency, et la rentabilité: le billette de coulée continue. Aujourd'hui, sur 97% of long product laminage d'acier operations in China use continuous casting billets instead of traditional steel ingots. This shift isn’t just about modernization—it’s about better quality, lower energy use, and higher yield.

Dans cet article, we’ll walk through everything you need to know about continuous casting billets—from how they’re made, what types of steel they can carry, their advantages in laminage d'acier, and real production data that matter on the shop floor.

What Is a Continuous Casting Billet?

A continuous casting billet is a semi-finished steel product formed by pouring molten steel into a water-cooled mold, where it solidifies into a long rectangular or square cross-section. Unlike old-fashioned ingot casting, which requires multiple reheating steps, continuous casting produces a uniform, ready-to-roll billet in a single, uninterrupted process.

These billets typically range from 120mm × 120mm à 180mm × 180mm in size and are cut into fixed lengths—usually between 6 à 12 mètres—depending on the rolling mill’s requirements.

Why Continuous Casting Replaced Ingot Casting

Back in the 1980s, most steel plants used ingot casting. But that method had major drawbacks: high energy loss, low yield, and inconsistent internal quality. Aujourd'hui, continuous casting dominates because it solves these problems.

As shown above, continuous casting improves nearly every aspect of steel production. Pour laminage d'acier mills, this means fewer rejects, lower fuel bills, and faster throughput.

How Continuous Casting Works – Step by Step

The process starts after steelmaking and ends with a ready-to-roll billet. Here’s how it flows:

1. Ladle Transfer: Molten steel from the BOF or EAF is poured into a ladle and transported to the continuous caster.
2. Métallurgie en poche (LF): The steel undergoes refining—temperature adjustment, désulfuration, alloying—to meet precise chemistry specs.
3. Argon Stirring & Répartiteur: The ladle pours steel into a tundish, which acts as a buffer. Argon gas stirs the melt to ensure uniform composition.
4. Mold Casting: Steel flows into a copper mold cooled by water. The outer shell solidifies in seconds while the core remains liquid.
5. Secondary Cooling Zone: The strand moves through spray-cooled chambers where it fully solidifies.
6. Strand Cutting: Once solid, the strand is cut into billets using an automatic flame or mechanical shear.
7. Hot Charging or Storage: Billets go directly to the reheating furnace (hot charge) or are stacked for later use.

This entire process runs at speeds between 1.8 à 3.0 mètres par minute, depending on section size and steel grade. Par exemple, a 150mm × 150mm billet casting speed is typically around 2.2 m/mon.

Steel Grades Suitable for Continuous Casting and Rolling

Not all steels can be continuously cast, but the vast majority used in long product laminage d'acier can. Below is a breakdown of common steel families and their casting feasibility.

As of 2023, sur 180 nuances d'acier are successfully produced via continuous casting globally. En Chine, the adoption rate reached 97.9% of total crude steel output in 2010, and it has only increased since.

Advantages of Using Continuous Casting Billet in Steel Rolling

For rolling mill operators, the benefits go beyond just material supply. Here’s what really matters on the production floor:

• Higher Dimensional Accuracy: Billets from continuous casting have tight tolerances—±0.5mm on side length—which ensures stable entry into the rolling stands.
• Better Internal Quality: Controlled cooling reduces centerline segregation and porosity, leading to fewer cracks during rolling.
• Direct Hot Charging: Billets can go straight from caster to furnace at 800–1000°C, saving up to 50 Kwh / tonne in fuel.
• Less Scale Formation: Shorter reheating time means less iron oxide scale, improving surface finish of final products.
• Higher Rolling Yield: Mills report 1–2% higher yield when using continuous casting billets vs. ingots.

Real-World Production Parameters from Chinese Mills

To give you a practical sense of how this works, here are actual operating parameters from several large-scale long product mills in China.

These numbers are not theoretical—they reflect real operating conditions. Par exemple, a wire rod mill using 130mm billets can achieve casting speeds up to 3.0 m/mon thanks to electromagnetic stirring and dynamic soft reduction technologies.

Challenges and Limitations

While continuous casting is dominant, it’s not perfect. Some steels still require ingot casting due to metallurgical or economic reasons.

Steels That Can’t Be Continuously Cast (Yet)

• High-alloy tool steels: Grades like 5CrNiMoV and H13 have narrow freezing ranges and are prone to cracking.
• High-speed steels: W18Cr4V and M42 require very slow solidification to avoid carbide segregation.
• Superalloys: Materials like GH4169 (Inconel 718) need directional solidification, often done in vacuum.

Economically Not Viable for Small Batches

Even if a steel grade can be cast continuously, it may not make sense for small orders. Setting up a caster for a 50-ton batch isn’t cost-effective. In such cases, ingot casting remains practical.

The Future: Toward Near-Net Shape and Direct Rolling

The next frontier in laminage d'acier is eliminating the reheating furnace altogether. Some advanced mills are already using direct hot charging or even direct rolling of continuous casting billets.

In direct rolling, billets exit the caster at 1000–1100°C and go straight into the roughing mill—no storage, no reheating. This can save up to 80 Kwh / tonne and reduce CO₂ emissions by 60 kg per ton of steel.

Mills in Baosteel, Shagang, and HBIS have implemented such systems for carbon steels and low-alloy grades. The key is tight coordination between caster and mill—timing must be within minutes.

Final Thoughts for Rolling Mill Engineers

If you’re running a long product laminage d'acier doubler, your choice of raw material directly impacts quality, cost, and uptime. Continuous casting billets offer proven advantages: better yield, lower energy use, and higher consistency.

While not every steel grade can be cast this way, sur 97% of common long product steels—from rebar to spring steel—can. And with ongoing advances in mold design, electromagnetic stirring, and process control, the gap is closing fast.

Whether you’re optimizing your current process or planning a new line, understanding the full potential of continuous casting billets is essential. It’s not just about keeping up with technology—it’s about staying competitive in a global market where every kWh and every percentage point of yield counts.