Views: 0 Author: Site Editor Publish Time: 2026-05-04 Origin: Site
If you’ve been around a melt shop for any length of time, you already know that clean steel isn’t just about removing sulfur or phosphorus. The real headache often starts downstream—clogged casting nozzles, stringers in the final product, or rejected coils. That’s where calcium silicon (CaSi) comes in.
Calcium silicon is not a new product. But using it the right way? That’s where many steelmakers still leave money on the table. Let’s walk through how to use CaSi effectively, without the lab coat theory.
Before we talk about how to add it, let’s quickly cover why. In liquid steel, alumina (Al₂O₃) inclusions are hard, sharp, and cluster together. When you pour that steel, these clusters build up on the tundish nozzle, killing your casting sequence.
Calcium modifies those alumina inclusions into liquid calcium aluminates (like 12CaO·7Al₂O₃). Liquid inclusions don’t stick. They stay small, stay separate, and float out or pass through the nozzle without trouble.
In short: CaSi turns a clogging problem into a clean casting process.
Most modern shops use CaSi cored wire. Lump CaSi (added to the ladle top) is unpredictable because calcium has a low boiling point—about 1484°C, while your steel is around 1600°C. Add lumps, and most of the calcium vaporizes before it does any good.
Cored wire allows you to inject calcium deep into the ladle, below the slag layer. The steel pressure keeps the calcium in solution long enough to react with inclusions.
For most BOF and EAF shops: use 55/30 CaSi wire (55% calcium, 30% silicon, balance iron). Some prefer 60/25. The exact grade matters less than how you feed it.
This is where experience separates good steel from great steel.
Do not add CaSi right after tapping. Why? Your slag is too oxidizing at that point. Calcium will react with oxygen in the slag before it ever touches your inclusions.
The sweet spot is after deoxidation (Al or Si-Mn) and after slag reduction, but before final temperature adjustment.
Typical sequence in a ladle furnace (LF) station:
Tap steel with Al for rough deoxidation.
Transfer to LF, start argon stirring.
Add slag conditioners (lime, fluorspar, or synthetic slag).
Allow slag to become white or gray (reduced).
Now add CaSi wire – usually in the last 10–15 minutes of LF treatment.
Soft stir for 5–8 minutes after CaSi injection.
Do not add CaSi too late—within 5 minutes of casting start. You need time for modified inclusions to float up or distribute evenly.
There’s no universal number, but a good starting point for aluminum‑killed steel is:
0.8 to 1.2 kg CaSi per ton of steel (for 55/30 wire)
If you use pure calcium wire, that number drops. But for CaSi wire, 1 kg/ton is a common baseline.
Then adjust based on:
Total aluminum added – more Al means more alumina, which means more CaSi.
Slag basicity – high basicity slags (CaO/SiO₂ > 2.5) reduce calcium efficiency.
Nozzle clogging history – if your last heat clogged at 80 tons, bump up 0.2 kg/ton.
One practical rule: inject until you see a slight, stable increase in calcium activity, but not so much that you reoxidize the steel. Too much calcium creates CaS inclusions or calcium aluminates that are actually higher melting. There’s a window.
Cored wire is useless if you feed it incorrectly. Here’s what works in real mills:
Feed speed: 2.5 to 4.5 m/s. Too slow, and the wire melts in the slag. Too fast, and it hits the bottom before melting properly.
Argon stirring: moderate. You want enough flow to mix, but not so strong that the wire shoots straight to the wall. A soft “rolling” surface motion is ideal.
Injection depth: at least 2 meters below the slag surface. For a 150-ton ladle, that’s usually 60–70% of the way down.
If you see bright flashes or heavy fuming at the ladle surface, your feed speed is too low. The calcium is vaporizing on top.
Even experienced melters make these errors:
1. Adding CaSi without deoxidizing first
Calcium is a strong deoxidizer, but that’s not its job here. If you add it to non‑killed steel, it will form CaO instead of modifying alumina. You’ll waste product and still have clogging.
2. Over‑stirring after injection
Hard argon stirring after CaSi reoxidizes the steel. Keep it soft. Just enough to see the surface move.
3. Using the same practice for all steel grades
Low‑carbon Al‑killed steel needs CaSi. Silicon‑killed or semi‑killed steel usually does not—calcium will form silicates that are worse than the original inclusions.
4. Ignoring the ladle refractory
Basic ladle linings (magnesia‑carbon) react with calcium. You’ll lose 15–25% of your calcium efficiency compared to a neutral lining.
Don’t expect 100% calcium recovery. In real production:
Cored wire, good practice: 15–25% calcium recovery into the steel
Lump addition: 3–8% (not recommended except for very specific cases)
Best case (perfect slag, deep injection, neutral refractory): up to 30%
This is normal. The goal isn’t high calcium in the final steel—it’s inclusion modification. Even 15 ppm of soluble calcium is often enough.
You don’t need an expensive lab test for every heat. Use these shop-floor indicators:
Tundish nozzle life – If you go from 2 hours to 6+ hours between changes, you’ve got it right.
Castable sequence length – A good CaSi practice adds 3–5 more heats per tundish.
Slag appearance after CaSi – A slightly foamy, dark grey slag is fine. A bright white crusty slag means over‑treatment.
Calcium‑to‑aluminum ratio – In the final steel, a Ca/Al weight ratio of 0.08 to 0.12 is the target zone for most Al‑killed grades.
Calcium silicon reacts with moisture. Wet CaSi can release acetylene, phosphine, or even hydrogen. Store bags or coils in a dry area. If you see condensation on a wire reel, don’t feed it until it’s dried.
Also, never add CaSi to a ladle with a wet bottom. You’ve probably heard the stories – steam explosion + molten metal = bad day.
Using CaSi in steelmaking isn’t complicated, but it is precise. Get the timing right (after deoxidation, before final temp), use cored wire at the right speed, and soft stir afterward. Start at 1 kg/ton and adjust based on nozzle clogging.
Clean steel sells. Clogged nozzles cost time, money, and customer trust. CaSi, used correctly, is one of the cheapest insurance policies in your melt shop.
