Ferrous and Non-Ferrous Metals: Definitions, Differences and Examples
Send an enquiryA ferrous metal is a metal or alloy in which iron is the principal element. The word comes from ferrum, the Latin for iron. The ferrous metals are iron itself and its alloys: carbon steel, alloy steel, stainless steel, cast iron and wrought iron. A non-ferrous metal is a metal or alloy in which iron is not the principal element: aluminium, copper, zinc, lead, tin, nickel, titanium, magnesium, the precious metals, and alloys based on them such as brass, bronze and the nickel alloys. The practical differences between the two groups follow from iron. Ferrous metals are dense, strong and comparatively cheap, most of them are magnetic, and all except stainless steel rust when they are left unprotected. Non-ferrous metals are chosen for properties that iron lacks, such as low density, high electrical conductivity or resistance to corrosion. They cost more per kilogram and are mostly not magnetic, with nickel and cobalt as the exceptions.
Ferrous metals
Steel is the main ferrous metal. EN 10020 defines steel as a material in which the mass of iron is greater than that of any other single element and whose carbon content is generally below 2 percent. The steels divide into three families by composition. Carbon steel is iron with carbon and small amounts of manganese and silicon, graded by its carbon content. Alloy steel adds chromium, molybdenum, nickel or vanadium to improve hardenability and strength, as in EN19 and EN24. Stainless steel carries at least 10.5 percent chromium, which forms a thin passive oxide film on the surface and protects the iron beneath it.
Cast iron contains more than about 2 percent carbon. The carbon is present as graphite or as iron carbide, which lowers the melting point and makes the metal easy to cast into complex shapes, but leaves most cast irons brittle compared with steel. Wrought iron has very little carbon and contains fibres of slag; mild steel has replaced it in almost every use. Every one of these materials is iron with small or moderate additions, which is why they share density and, with the exception of austenitic stainless steel, magnetism.
Non-ferrous metals
Aluminium, at a density of 2.70 grams per cubic centimetre, is about a third as heavy as steel. It forms a protective oxide film in air and conducts electricity well, which makes it the metal of aircraft structures, window frames, overhead power lines and drink cans. Copper is the standard metal for electrical wiring, motor windings and heat exchangers. Its main alloys are brass, copper with zinc, and bronze, copper with tin. Zinc is used to galvanise steel. Lead serves in batteries and radiation shielding, and magnesium where the lowest density is needed. Gold, silver and platinum form the precious metals.
Nickel and titanium are the non-ferrous metals closest to stainless steel in service. Nickel alloys such as Inconel 600, Inconel 625 and Monel 400 are chosen for hot chlorides, hydrofluoric acid and temperatures above the useful range of stainless steel. Some of them contain iron: Inconel 600 has 6 to 10 percent and Monel 400 up to 2.5 percent. They are still non-ferrous, because nickel is the principal element; the classification follows the base metal, not the presence of iron. Titanium, at 4.51 grams per cubic centimetre, combines high strength with low density and resists chlorides through its own passive oxide film. The grade reference describes both families on the nickel alloy and titanium pages.
| Metal | Group | Density, g/cm3 | Melting point, degrees Celsius | Magnetic |
|---|---|---|---|---|
| Iron | Ferrous | 7.87 | 1,538 | Yes |
| Nickel | Non-ferrous | 8.90 | 1,455 | Yes |
| Titanium | Non-ferrous | 4.51 | 1,668 | No |
| Copper | Non-ferrous | 8.96 | 1,085 | No |
| Aluminium | Non-ferrous | 2.70 | 660 | No |
| Magnesium | Non-ferrous | 1.74 | 650 | No |
| Zinc | Non-ferrous | 7.14 | 420 | No |
| Lead | Non-ferrous | 11.34 | 327 | No |
Differences between ferrous and non-ferrous metals
The table compares the two groups as a whole. Single metals cross the line on one property or another, and the main exceptions are named in the cells.
| Property | Ferrous metals | Non-ferrous metals |
|---|---|---|
| Principal element | Iron | Aluminium, copper, nickel, titanium, zinc, lead, magnesium and others |
| Magnetism | Magnetic, except austenitic stainless steel in the annealed condition | Not magnetic, except nickel, cobalt and some nickel alloys |
| Corrosion | Carbon steel, alloy steel and cast iron rust unless coated; stainless steel resists corrosion | Do not rust; most form a protective oxide or patina |
| Density, g/cm3 | 7.7 to 8.0 for steels | 1.74 (magnesium) to 11.34 (lead) among the common base metals |
| Strength | High, and raised further by heat treatment | Low in pure aluminium, copper and lead; high in titanium alloys and nickel alloys |
| Cost per kilogram | Lower | Generally higher |
| Recycling | Recovered from mixed waste by magnets and remelted | Recovered by eddy current and by analysis; recycled aluminium needs about 5 percent of the energy of primary metal |
| Typical uses | Structures, machinery, shafts, fasteners, tools, pressure equipment | Electrical conductors, aircraft and transport, packaging, coatings, chemical plant |
Rust is hydrated iron oxide, so strictly only a ferrous metal rusts. Non-ferrous metals corrode in their own ways: aluminium and copper form stable surface layers, and zinc corrodes in preference to steel, which is why it is used as a protective coating on steel. Density separates the groups less cleanly than the names suggest. Every steel sits in a narrow band close to 7.85, while the non-ferrous metals range from magnesium, at under a quarter of that figure, to lead and gold, well above it, with zinc, copper and nickel close to steel. The steel and aluminium guide compares the two most common structural metals in more detail.
Strength, stiffness and weight
Steel is the stiffest of the common structural metals. Its elastic modulus is about 200 GPa, against about 69 GPa for aluminium, and titanium alloys sit a little above half the figure for steel. A steel shaft or beam therefore deflects less under a given load than an aluminium or titanium part of the same section. The modulus changes little with alloying or heat treatment, so this comparison holds for almost every grade in each group. Strength behaves differently: it depends on the alloy and its condition more than on the base metal. Annealed pure aluminium, copper and lead are soft, while quenched and tempered alloy steels and aged titanium and nickel alloys carry high loads. Where weight matters, the deciding figure is strength divided by density. On that measure titanium alloys and the high-strength aluminium alloys compete with steel, which is why both are used in aircraft structures. Steel keeps the advantage wherever stiffness, cost or wear resistance decides the choice.
Is stainless steel ferrous?
Stainless steel is a ferrous metal. Iron is its principal element: grade 304 is iron with about 18 percent chromium and 8 percent nickel, and iron makes up the balance. It is sometimes taken for a non-ferrous metal, because it shares their resistance to corrosion and because a magnet does not pick up the austenitic grades. Neither point changes the classification. Stainless steel is a steel under EN 10020, and its magnetism depends on its crystal structure, as the article on which metals are magnetic explains. The differences between stainless steel and ordinary steel are set out in carbon steel versus stainless steel.
How scrap metal is sorted
The magnet is the first sorting tool for scrap metal. Shredded scrap passes large magnets that lift out the carbon steel and cast iron. The rest goes to an eddy current separator, in which a spinning magnetic rotor induces currents in pieces of aluminium and copper and throws them clear of the belt while non-metallic material falls away. Iron must be removed before this stage, because ferrous pieces heat up in the rotor's field and can damage the machine.
Neither step tells one non-ferrous metal from another, and neither separates austenitic stainless steel, which a magnet does not hold, from the non-ferrous stream. For that, scrap yards and steel plants use chemical analysis. A handheld X-ray fluorescence analyser reads chromium, nickel, molybdenum and the other alloying elements from the surface of a piece. An optical emission spectrometer sparks a prepared sample and also measures carbon, which X-ray fluorescence cannot measure reliably; that difference matters when separating low-carbon grades such as 304L and 316L from their standard versions. Aluminium shows what the sorting is worth: remelting it takes about 5 percent of the energy needed to make primary metal, and about 75 percent of all the aluminium ever produced is still in use.
A ferrous producer
Laxcon Steels is a ferrous producer. It melts stainless and alloy steel in its own melting shop. Incoming scrap passes a radiation detection gate before it reaches the furnace, and optical emission spectrometers confirm the chemistry of each heat against the grade before it is cast. The steel is rolled into hot rolled round bar from 16 to 125 mm and finished as bright bar from 5 to 115 mm. The composition window of each grade is listed in the grade reference.
Frequently asked questions
Is stainless steel a ferrous metal?
Yes. Iron is the principal element of every stainless steel, which makes it a ferrous metal and a steel. It is sometimes taken for a non-ferrous metal because it resists corrosion and because the austenitic grades are not magnetic, but neither property changes its classification.
Is aluminium ferrous or non-ferrous?
Aluminium is non-ferrous. It contains no iron beyond small impurity levels, it does not rust, and a magnet does not hold to it. At 2.70 grams per cubic centimetre it is about a third as dense as steel.
Are all ferrous metals magnetic?
No. Carbon steel, alloy steel, cast iron and the ferritic, martensitic and duplex stainless steels are magnetic, but austenitic stainless steels such as 304 and 316 are not magnetic when annealed. In the other direction, nickel and cobalt are non-ferrous and magnetic, so a magnet test separates most ferrous from most non-ferrous metals but is not a definition.
Why do non-ferrous metals not rust?
Rust is hydrated iron oxide, and a non-ferrous metal has no iron to form it. Non-ferrous metals still corrode: aluminium forms a thin oxide film that normally protects it, copper turns green with a patina, and zinc corrodes in preference to the steel it coats, which protects the steel.
Sources
- EN 10020, Definition and classification of grades of steel.
- EN 10088-1, Stainless steels, list of stainless steels.
- CRC Handbook of Chemistry and Physics: densities and melting points of the elements; magnetic susceptibility of the elements.
- Special Metals Corporation technical bulletins: Inconel alloy 600, Inconel alloy 625 and Monel alloy 400.
- TWI, technical knowledge: ferrous and non-ferrous metals.
- International Aluminium Institute and The Aluminum Association: aluminium recycling data.
