Cored wire, sometimes called flux cored wire or injection wire, is a composite product consisting of a steel outer sheath filled with a powdered or granular material. It is fed into molten steel through a wire feeder during ladle treatment, and it has become the standard way of introducing reactive elements that would otherwise be lost before they could do useful work.
Construction and General Characteristics
The wire is formed by folding a steel strip into a tube and filling it with powder as the tube closes, after which it is compacted and wound onto a coil. Diameters are typically in the range of about nine to sixteen millimetres, and the sheath thickness and the fill ratio are controlled so that the wire remains flexible enough to feed smoothly but strong enough not to split or buckle. The powder fill ratio is usually between about forty and sixty percent of the cross section, and it determines how much active material each metre of wire delivers. Consistent fill ratio and consistent powder chemistry are the two characteristics that users rely on most.
Why Deep Injection Matters
The main advantage of cored wire over simply adding lumps to the ladle is that the wire carries the powder beneath the metal surface and releases it deep in the bath. Reactive elements such as calcium have a low boiling point and a high affinity for oxygen and sulphur, so at the surface they would burn or vaporise and be lost. By injecting them deep, the reaction occurs in the body of the steel where it can modify inclusions and remove sulphur, and the recovery of the added element improves substantially. The steel sheath also slows the release, giving the element time to react before it escapes.
Composition and Types of Filling Powder
Many different powders are supplied in cored wire form. Calcium silicon wire is widely used for inclusion modification and deoxidation. Ferro calcium wire provides a strong calcium treatment in a controlled way. Pure calcium wire is used where a large amount of calcium modification is required. Other common fillings include ferrotitanium, ferroniobium, magnesium bearing compounds, carbon and sulphur bearing materials and rare earth additions. The choice depends on the intended metallurgical effect, and each type has its own recommended feed rate and treatment depth.
Functions in Ladle Treatment
In practice cored wire performs several functions. It deoxidises the steel and controls the level of dissolved oxygen. It modifies the shape and composition of inclusions so that they remain globular and are less likely to cause cracking or to clog casting nozzles. It removes sulphur when used with the appropriate materials. It adjusts the content of alloying and trace elements precisely. And because the addition is made at a controlled feed rate, it allows the steelmaker to target a narrow specification rather than working within a broad range, which improves consistency from heat to heat.
Feeding Practice and Selection
Successful use depends on matching the wire diameter, the powder fill and the feed rate to the ladle and the treatment station. Feed rate is usually expressed in metres per minute, and the total length is calculated from the required addition and the powder content per metre. Treatment depth, slag condition, temperature and the gas stirring practice all influence recovery, so a well defined procedure is essential. Buyers should confirm sheath thickness, fill ratio, powder chemistry, moisture and coil weight, and should ask for a sample to trial before committing to a regular supply.
Frequently Asked Questions
Q: What is cored wire made of?
It is a steel sheath filled with a compacted powder or granular material, supplied as a coil that is fed into molten steel during ladle treatment.
Q: Why inject powder instead of adding lumps?
Deep injection places reactive elements in the body of the steel where they can react before being lost to the slag or the atmosphere, improving recovery.
Q: What is calcium silicon cored wire used for?
It is used mainly for deoxidation and for modifying inclusions into a harmless globular shape, improving castability and steel cleanliness.
Q: What diameters are available?
Cored wire is commonly supplied between about nine and sixteen millimetres in diameter, with sheath thickness and fill ratio set for the application.
Q: How is the amount of wire calculated?
The required addition is divided by the active material content per metre of wire, and the resulting length is fed at the recommended rate.
