At One Place

Does it rust?

55 materials, of which only 8 actually rust — because rust means iron oxide, and nothing without iron in it can rust however badly it corrodes.

Why the distinction matters

Iron oxide is porous and flaky. It falls off, exposes clean metal, and the reaction carries on inward until the object is gone. Aluminium, chromium, zinc and titanium form oxides that are dense, tightly bonded and self-healing within milliseconds of being scratched, so the reaction stops almost as soon as it starts. That single difference is why an untreated aluminium window frame outlives a painted steel one, and why adding about 11 % chromium to steel turns it stainless.

What actually rusts

Material What happens
iron Iron oxide is flaky and porous rather than protective, so rust does not stop the reaction — it exposes fresh metal and the corrosion continues inward until nothing is left.
mild steel Rusts readily and completely. Unprotected mild steel outdoors loses measurable thickness every year.
high-carbon steel Rusts. Higher carbon content does not help; the carbon changes hardness, not corrosion behaviour.
tool steel Most tool steels rust readily, which is why they are oiled. The corrosion-resistant grades are a minority.
gray cast iron Rusts fast when bare. Seasoning a pan is a polymerised oil layer that physically excludes water — it is a barrier, not a chemical passivation like stainless.
ductile iron Rusts, and is normally coated or cement-lined for buried water main use.
wrought iron Rusts, but noticeably more slowly than modern mild steel — the slag stringers in it interrupt the corrosion path, which is why Victorian wrought ironwork survives outdoors better than a modern steel replacement.
reinforced concrete The defining failure mode of the material. Chlorides from de-icing salt or sea air reach the steel, it rusts, the rust expands six-fold and splits the concrete. Cover depth over the bar is the single most important number in the specification.

Everything

Material Verdict What actually happens
mild steel Yes — it contains iron, so it rusts Rusts readily and completely. Unprotected mild steel outdoors loses measurable thickness every year.
aluminum It corrodes, but it does not rust Aluminium oxidises within milliseconds of exposure, and the oxide layer is dense, adherent and self-healing — the opposite of rust. This is why an untreated aluminium window frame outlasts a painted steel one.
water Neither rusts nor meaningfully corrodes Water does not rust; it is the agent that makes iron rust, together with oxygen. Neither alone is enough.
copper It corrodes, but it does not rust Copper forms a green patina of copper carbonate, which is protective and self-limiting. The Statue of Liberty is copper and its skin is about 2.4 mm thick after 140 years.
gold Neither rusts nor meaningfully corrodes Gold does not oxidise in air at any temperature. Gold recovered from shipwrecks after centuries is unchanged.
titanium It corrodes, but it does not rust Forms an extremely stable oxide film. Titanium is essentially immune to seawater, which is why it is used for submarine and marine hardware.
concrete It corrodes, but it does not rust Concrete itself does not rust; the steel inside it does, and that is the main way reinforced concrete fails. Rust occupies about six times the volume of the steel it came from, so it cracks the concrete outward from within — the stains and spalling on an old car park are that process.
stainless steel 304 It corrodes, but it does not rust Does not rust in normal use, because chromium oxide blocks it. It will stain and pit if the oxide layer is damaged and cannot re-form — under a rubber mat, or where iron particles from a grinder have embedded in the surface.
iron Yes — it contains iron, so it rusts Iron oxide is flaky and porous rather than protective, so rust does not stop the reaction — it exposes fresh metal and the corrosion continues inward until nothing is left.
air Neither rusts nor meaningfully corrodes Air does not corrode; it is half the reason other things do. Iron needs both oxygen and water to rust, and neither alone will do it.
ice Neither rusts nor meaningfully corrodes Does not corrode. It causes enormous mechanical damage by expanding about 9 % on freezing.
lead It corrodes, but it does not rust Forms a dull grey oxide-carbonate layer that protects it well. Lead roofing on cathedrals has lasted centuries.
tungsten It corrodes, but it does not rust Very resistant at room temperature; oxidises readily when hot, which is why filament bulbs had to be evacuated or gas-filled.
brass It corrodes, but it does not rust Tarnishes and can dezincify — in the wrong water chemistry the zinc leaches out and leaves a porous copper skeleton that looks intact and has almost no strength. Plumbing brasses are specified as dezincification-resistant for that reason.
pine Neither rusts nor meaningfully corrodes Does not corrode. It rots, which is a biological process rather than a chemical one and needs moisture and oxygen.
silver It corrodes, but it does not rust Silver tarnishes to silver sulfide, reacting with traces of sulfur in air rather than with oxygen — which is why it blackens faster near eggs, onions and rubber bands.
gray cast iron Yes — it contains iron, so it rusts Rusts fast when bare. Seasoning a pan is a polymerised oil layer that physically excludes water — it is a barrier, not a chemical passivation like stainless.
diamond Neither rusts nor meaningfully corrodes Chemically inert at room temperature. It burns in oxygen above about 800 °C.
high-carbon steel Yes — it contains iron, so it rusts Rusts. Higher carbon content does not help; the carbon changes hardness, not corrosion behaviour.
stainless steel 316 It corrodes, but it does not rust The added molybdenum makes 316 substantially better than 304 against chlorides, which is why it is the marine and swimming-pool grade.
granite Neither rusts nor meaningfully corrodes Extremely durable. Feldspar weathers to clay over geological time.
aluminum 6061 It corrodes, but it does not rust Self-passivating like pure aluminium. Anodising thickens that oxide deliberately.
soda-lime glass Neither rusts nor meaningfully corrodes Chemically very stable. It does slowly etch in strongly alkaline conditions, and hydrofluoric acid dissolves it outright.
PTFE Neither rusts nor meaningfully corrodes One of the most chemically inert materials there is; it resists nearly every solvent and acid.
marble Neither rusts nor meaningfully corrodes Does not rust, but it is calcium carbonate and dissolves in acid — which is why acid rain has eaten the detail off marble statues and why lemon juice etches a marble worktop permanently.
unidirectional carbon fibre composite It corrodes, but it does not rust The fibre does not corrode, but it is conductive and sits high on the galvanic series — bolt carbon fibre directly to aluminium and the aluminium corrodes away. Aerospace joints use an isolating layer for exactly this.
rigid PVC Neither rusts nor meaningfully corrodes Does not corrode, which is why it replaced iron for drainage. It does become brittle with ultraviolet exposure.
fibreglass (GRP) Neither rusts nor meaningfully corrodes Does not corrode, which is why boat hulls, ladders and chemical tanks are made of it.
bronze It corrodes, but it does not rust Very corrosion resistant, particularly in seawater, which is why ship propellers and bearings are bronze.
natural rubber Neither rusts nor meaningfully corrodes Does not corrode, but perishes — ozone and ultraviolet crack it, which is what has happened to old perished rubber bands.
paper Neither rusts nor meaningfully corrodes Does not corrode. Acidic paper self-destructs over decades, which is the slow-motion crisis in every library of twentieth-century books.
mercury Neither rusts nor meaningfully corrodes Does not rust. It does dissolve most other metals into amalgams, which is a different and more destructive problem — mercury on aluminium destroys it, which is why it is banned from aircraft.
aluminum 7075 It corrodes, but it does not rust Noticeably less corrosion resistant than 6061 — the zinc and copper that give it its strength also make it prone to stress-corrosion cracking, which is why aerospace 7075 is usually clad or anodised.
tungsten carbide It corrodes, but it does not rust The carbide is inert; the cobalt binder can corrode, which is why carbide tools pit in coolant over time.
silicone rubber Neither rusts nor meaningfully corrodes Extremely stable across a wide temperature range and resistant to ozone and ultraviolet, which is why it outlasts natural rubber outdoors.
zinc It corrodes, but it does not rust Zinc corrodes sacrificially — galvanised steel works because the zinc corrodes first and protects the iron beneath even where the coating is scratched through.
magnesium It corrodes, but it does not rust Corrodes readily, especially in salt, and is even more sacrificial than zinc — magnesium anodes protect water heaters and boat hulls by dissolving instead of them.
tool steel Yes — it contains iron, so it rusts Most tool steels rust readily, which is why they are oiled. The corrosion-resistant grades are a minority.
graphite Neither rusts nor meaningfully corrodes Does not rust. Oxidises above about 400 °C in air.
reinforced concrete Yes — it contains iron, so it rusts The defining failure mode of the material. Chlorides from de-icing salt or sea air reach the steel, it rusts, the rust expands six-fold and splits the concrete. Cover depth over the bar is the single most important number in the specification.
red oak Neither rusts nor meaningfully corrodes Does not corrode, but oak corrodes other things: its tannins react with iron to produce black iron-tannate staining, which is why oak is fastened with stainless or brass rather than steel.
tin-lead solder (60/40) It corrodes, but it does not rust Corrodes slowly. Flux residue left on a joint is more corrosive than the solder itself.
platinum Neither rusts nor meaningfully corrodes One of the least reactive metals there is; resists acids that dissolve gold.
tin It corrodes, but it does not rust Resists corrosion well, which is the entire reason for tin-plating steel food cans. Damage the tin and the steel beneath rusts fast.
Ti-6Al-4V titanium alloy It corrodes, but it does not rust Excellent, effectively immune in seawater and in the body.
nickel It corrodes, but it does not rust Highly corrosion resistant, which is why it is plated onto other metals and alloyed into stainless steel.
lead-free solder (SAC305) It corrodes, but it does not rust Corrodes slowly. Tin-rich alloys can grow whiskers over years, which has caused documented failures in aerospace and medical electronics.
chromium It corrodes, but it does not rust Chromium is the reason stainless steel is stainless: above about 10.5 % chromium content, the alloy forms a self-healing chromium oxide film that blocks further attack.
silicon carbide Neither rusts nor meaningfully corrodes Extremely resistant.
leather It corrodes, but it does not rust Does not rust, but vegetable-tanned leather is acidic and corrodes steel it touches — which is why old leather sword scabbards rust the blade and why leather watch straps mark cheap buckles.
wrought iron Yes — it contains iron, so it rusts Rusts, but noticeably more slowly than modern mild steel — the slag stringers in it interrupt the corrosion path, which is why Victorian wrought ironwork survives outdoors better than a modern steel replacement.
ductile iron Yes — it contains iron, so it rusts Rusts, and is normally coated or cement-lined for buried water main use.
Inconel 718 It corrodes, but it does not rust Exceptional, including at high temperature — which is what it exists for.
pewter It corrodes, but it does not rust Tarnishes slowly to a soft grey. Old pewter containing lead darkens more.
Monel 400 It corrodes, but it does not rust Outstanding against seawater and hydrofluoric acid; it was developed for marine and chemical service.

Common questions

Does aluminium rust?
No. Rust is iron oxide and aluminium contains no iron. Aluminium does oxidise, immediately and thoroughly, but its oxide is dense and self-healing and protects the metal underneath rather than destroying it.
Does stainless steel rust?
Not in normal use, because chromium forms a protective oxide film. It will stain and pit where that film cannot re-form — under a rubber mat, in stagnant chlorinated water, or where iron particles from a grinder have embedded in the surface.
Why does rust crack concrete?
Because rust occupies roughly six times the volume of the steel it came from. Reinforcing bar corroding inside concrete expands and splits it outward, which is the classic failure mode of reinforced concrete and why cover depth over the bar matters so much.