Ferrophosphorus: Composition, Grades and Metallurgical Properties

What Ferrophosphorus Is

Ferrophosphorus is an alloy of iron and phosphorus, produced in the electric furnace and supplied in lump or granular form. It is the standard carrier for adding phosphorus to a melt, because the alloy dissolves readily and the phosphorus recovery is predictable.

Grades are specified on phosphorus content, typically in the range of about 21% to 26% phosphorus, with limits on carbon, silicon and other elements.

Why Phosphorus Is Added

Phosphorus is normally kept low in structural steels because it embrittles them. In some products, however, it is added on purpose: it improves machinability, raises electrical resistivity in certain steels, and increases fluidity and wear resistance in some cast irons.

Ferrophosphorus lets the melt shop hit a target phosphorus range precisely rather than relying on residual scrap chemistry.

Use in Steel

In free-machining and some special steels, phosphorus is used to improve chip breaking and surface finish. In electrical steels, controlled phosphorus additions can raise resistivity and reduce core loss. The addition is made as ferrophosphorus, usually late in the heat to protect recovery.

Use in Cast Iron

In cast iron, phosphorus improves fluidity and can raise wear resistance, which suits certain automotive and machinery castings. It also affects the microstructure, so the level is matched to the casting section and the property target.

Specification and Handling

Because phosphorus is a strong embrittling element, grade and addition weight must be controlled tightly. Confirm the assay, the sizing and the carbon level before purchase, and store the alloy dry and separate from other ferroalloys.

A certificate of analysis for each lot allows the melt shop to calculate the charge accurately and to verify the final phosphorus content in the cast analysis.

Frequently Asked Questions

Q: What is ferrophosphorus?
An iron-phosphorus alloy used to add phosphorus deliberately to steel and cast iron melts.

Q: What is the typical phosphorus content?
Commercial ferrophosphorus grades generally range from about 21% to 26% phosphorus.

Q: Why add phosphorus if it normally embrittles steel?
Because in some grades it improves machinability, electrical resistivity or cast iron fluidity and wear resistance.

Q: When is the addition made?
Usually late in the heat or during tapping and ladle treatment, to protect recovery and final control.

Q: What must be checked before purchase?
The phosphorus assay, the sizing range, the carbon content and the accompanying certificate of analysis.