alloyant
A material added to a metal (possibly itself an alloy) to alter its properties.
alloyant: the ingredient that changes how metal behaves
An alloyant is any material mixed into molten base metal to shift its mechanical, chemical, or thermal properties. Copper added to iron makes steel harder. Manganese reduces brittleness. Silicon improves fluidity during casting. The alloyant dissolves into the base metal, forming a solid solution or precipitate phases that change grain structure, strength, corrosion resistance, or workability.
Alloyants fall into two broad categories: intentional additions and residual elements. Intentional alloyants are weighed and charged into the melt at specific percentages, sometimes in the form of master alloys, pre-made intermediates with high concentrations of the desired element. Residual alloyants arrive in recycled scrap or ore and must be tolerated or removed depending on specifications. A steel mill accepting cuprous scrap, for instance, accepts copper as an unintended alloyant; too much copper embrittles the steel.
Choosing and measuring alloyants
Selection depends on the property being engineered. Nickel and chromium increase corrosion resistance in stainless grades. Molybdenum and vanadium raise hardness and heat resistance at elevated temperatures. Boron, added in fractions of a percent, hardens through grain refinement. Titanium and aluminum scavenge oxygen and nitrogen from the melt. Cost, availability, and melt temperature all constrain choice. A foundry may use a different cobalt alloyant than a steel mill because foundry temperatures and holding times differ.
Alloyant content is measured as a percentage by weight in the final product. A specification might call for 17 to 19 percent chromium and 8 to 10 percent nickel in 304 stainless steel. Actual charge calculations must account for oxidation losses, which vary by element and process, chromium loss during steel melting can exceed 20 percent. This is why metallurgists add more alloyant than the final spec requires and rely on analysis to confirm results.
The term alloyant is older and less common than alloying element, which is now the standard in technical writing and textbooks. You will see both used interchangeably in foundries and mills, though alloyant carries an older, more European usage. Neither term includes the base metal itself, though a base metal in one alloy can become an alloyant when added to another, nickel, for example, is the base metal of Ni-Cu alloys but an alloyant when added to steel.