What Cored Wire Actually Does in the Ladle
Cored wire is a delivery system, not simply an alloy. Powdered alloy or pure metal is encased in a thin steel strip and injected into the melt with a wire feeder, so the additive is released below the slag layer instead of floating on top and burning in the air. The benefit of the technique is recovery: reactive elements such as calcium and magnesium have low boiling points, and feeding them deep into the steel or iron by wire gives the particle a residence time that a lump addition cannot. The choice of core chemistry then follows the metallurgical task, whether that is deoxidation, desulphurisation, inclusion shape control, inoculation of grey iron or spheroidisation of ductile iron.
Core Chemistry and the Job It Performs
| Core type | Nominal composition | Typical duty |
|---|---|---|
| Calcium silicon cored wire | Ca 30 percent, Si 60 percent; also Ca 28 percent, Si 55 percent | deoxidation and inclusion modification in steel |
| Pure calcium cored wire | Ca 98 percent minimum | desulphurisation and inclusion shape control |
| Calcium iron cored wire | Ca 30 percent minimum, balance iron | calcium treatment where a dense core is preferred |
| Ferrosilicon magnesium cored wire | Si 40 to 46 percent, Mg 25 to 30 percent, rare earth 2 percent | spheroidisation of ductile iron |
| Ferrosilicon cored wire | Si 72 to 75 percent | inoculation and silicon adjustment |
| Magnesium cored wire | Mg metal core | desulphurisation and nodularising |
The core alloys themselves are covered by recognised specification standards: calcium silicon by GB/T 3419, ferrosilicon by GB/T 2272 and ISO 5445, and manganese metal by GB/T 2774. A purchase specification should reference the core alloy standard, then add the wire parameters that the standard does not cover.
Wire Parameters That Decide Recovery
Three physical parameters matter as much as core chemistry. Diameter sets how much core mass can be delivered per metre and how fast the wire can enter the melt without kinking. Fill ratio, the mass of core per metre of wire, is the figure to quote on the order; a nominal 9 mm pure calcium wire carrying 58 to 68 grams of calcium per metre behaves very differently from a lighter-filled wire of the same diameter. Strip thickness and seam construction determine whether the wire survives the feeder rolls and the slag entry; seamless or locked-seam construction is preferred where core moisture pickup or open-seam splitting is a concern. Moisture content of the core must be controlled, because hydrated calcium or magnesium compounds release gas and create porosity and pinholes in the cast product.
Reference Price Levels for Cored Wire
The tables below record reference quotations published in China for 10 October. Export levels are USD per tonne FOB Tianjin Port; domestic levels are yuan per tonne including tax and are not directly comparable with export prices.
| Export product | Index | Reference price, USD/tonne FOB Tianjin |
|---|---|---|
| Calcium silicon cored wire | Ca30Si60, dia. 13 mm | 1,300 to 1,330 |
| Calcium silicon cored wire | Ca28Si55, dia. 13 mm | 1,150 to 1,180 |
| Pure calcium cored wire | Ca 98 percent minimum, dia. 9 mm, 58 to 68 g Ca/m | 1,420 to 1,490 |
| Domestic product, yuan/tonne including tax | Area | Reference range |
|---|---|---|
| Calcium silicon wire Ca30Si58, dia. 13 mm | Jiangsu | 9,200 to 9,400 |
| Calcium silicon wire Ca28Si55, dia. 13 mm | Henan | 8,200 to 8,400 |
| Solid pure calcium wire Ca 98 percent minimum, dia. 9 mm | Zhejiang, Henan, Jiangsu | 10,200 to 10,600 |
| Seamless metal calcium wire Ca 97 to 98 percent, dia. 9 mm, strip 1.0 mm | Shandong | 10,000 to 10,300 |
| Seamless metal calcium wire Ca 97 to 98 percent, dia. 9 mm, strip 1.0 mm | Henan, Inner Mongolia | 9,700 to 10,000 |
| Spheroidised wire Si42-46 Mg25 RE2, dia. 13 mm | Inner Mongolia | 9,400 to 9,600 |
| Spheroidised wire Si40 Mg30 RE2, dia. 13 mm | Liaoning | 10,100 to 10,500 |
| Calcium iron wire FeCa30 minimum, dia. 13 mm | Jiangsu and Henan | 9,100 to 9,200 |
Feeding Practice and What Controls Yield
Recovery of a reactive element never reaches the fed quantity. Calcium boils at about 1,484 C, so part of the core leaves the melt as vapour bubbles and escapes through the slag, and only a fraction dissolves into the steel. Practice therefore focuses on limiting loss: feed rate matched to the wire diameter so that the strip melts at a controlled depth, consistent wire entry angle, adequate ladle depth above the injection point, and a slag that is fluid enough to let bubbles escape without carrying metal. For ductile iron treatment, magnesium recovery depends strongly on the reaction chamber or sandwich method used and on the treatment temperature; measuring nodularity and the graphite form on a cast sample is the routine control check, with graphite form evaluated using the reference charts of ISO 945-1 and ASTM A247.
Quality Control and Documentation
For each batch the useful record is core composition analysed on a representative sample, fill mass per metre, strip thickness and tensile strength, wire diameter and ovality, core moisture, and packing condition. Coils should be supplied on rigid spools with the wire dry and protected, because moisture absorbed in transit creates porosity in the first heats after delivery. A certificate that states only the alloy grade without the fill mass per metre is incomplete, since the same grade can be supplied at different fill levels and will then behave differently at the feeder.
Frequently Asked Questions
Q: Why use cored wire instead of dropping alloy lumps into the ladle?
A: Because the wire releases the alloy below the slag and deep in the melt. Reactive elements such as calcium and magnesium gain residence time and recovery, and the addition becomes repeatable heat after heat.
Q: What is the most important parameter on a cored wire order?
A: Fill mass of core per metre of wire, together with core analysis and diameter. Diameter alone does not describe how much active element the wire delivers.
Q: Is pure calcium wire suitable for desulphurisation of low-sulphur steel?
A: It is used for calcium treatment and inclusion shape control, and calcium has a strong affinity for sulphur. The practical limit is the low boiling point of calcium, so deep injection and controlled feed rate are essential.
Q: How is wire consumption calculated for a heat?
A: From the target addition of active element, the fill mass per metre and the expected recovery. Recovery should be taken from plant data for the same wire, ladle and practice rather than from a generic figure.
Q: Can one feeder run different wire types?
A: Usually yes, but the drive rolls, straightener and guide tube must be set for the actual diameter and strip stiffness, and the feed rate must be re-tuned. Crushed or kinked wire causes inconsistent addition and can block the injection lance.
Q: What causes porosity after a wire addition?
A: Most often moisture carried in with the core, or a slag that is too viscous to release gas. Drying the core, sealing the coil and controlling slag fluidity remove most of the problem.