How stainless steel is made

Stainless steel does rust, but only in its outer few layers of atoms, and the chromium under it stops the rest.

stations: 7
things upstream: 33
raw sources: 15
steps from the ground: 6

The short version

Stainless steel is melted from scrap and chromium-rich alloys in an electric arc furnace, then moved to a vessel where argon and oxygen are blown through it to burn out carbon. It is cast into slabs, hot-rolled into coils, pickled in acid, and cold-rolled and annealed to the final thickness and finish.

Arc-melt scrap and alloys

Stainless scrap, ordinary steel scrap and alloys rich in chromium, nickel and molybdenum are melted together by electric arcs. The chromium is the point. Ferritic grades carry 10.5 to 27 percent of it, and austenitic grades add nickel.

Goes in
Steel scrap Chromium Nickel
Burn off carbon with argon

The molten metal is poured into a second vessel where argon and oxygen are blown through it. Carbon leaves as carbon monoxide gas, while the chromium stays in the metal, and the final chemistry is adjusted. Before this process arrived in the 1950s and 1960s, large tonnages were costly to make.

Goes in
Oxygen gas Argon
Cast slabs and blooms

Continuous casters freeze the steel into slabs for flat products, typically about 20 centimeters thick and 2 meters wide, or into blooms for bars and wire rod.
Reheat and hot-roll

Slabs go back into a furnace, then through hot-rolling mills that squeeze them to coils about 3 millimeters thick. Blooms are rolled into bars or coiled wire rod.
Pickle off the scale

Hot rolling leaves a layer of dark oxide on the strip. The coils run through acid baths that dissolve it, exposing clean metal.
Cold-roll and anneal

The clean coil is rolled again at room temperature in multi-roll Sendzimir mills, then annealed in a protective atmosphere so the surface does not re-oxidize. Rolling and annealing are repeated until it hits the thickness and finish the buyer wants.
Slit, polish and form

Finished coils are slit into narrower strips or formed into tube. Bars are straightened and machined, and wire rod goes to drawing machines.

End of the lineStainless steel Next it goes into syringe, washing machine, electric kettle and 16 more.

Worth repeating

Harry Brearley found a corrosion-resistant steel in 1913 while looking for a better gun-barrel alloy in Sheffield.
The austenitic family, which includes the common 304 and 316 grades, makes up about two-thirds of all stainless steel.
A scratch on stainless steel heals itself, because the chromium film re-forms whenever oxygen reaches the bare metal.