WHAT IT IS
Iron with a little carbon
Britannica defines steel as an alloy of iron and carbon with up to 2 percent carbon. With more carbon than that, the material counts as cast iron.
Compare the recipesWHAT STEEL IS MADE OF
Iron, plus
a pinch.
Steel is mostly iron, with a little carbon.
Look inside the metal
UP TO 2%carbon makes it steel
- Iron plus carbon
- Chromium for stainless
- Melt it, make it again
- One metal, many recipes
That small amount of carbon is what separates steel from cast iron. Add enough chromium and you get stainless steel, first melted in Sheffield in 1913. And when steel is finished with, it can be melted and made again.
Updated
THE SHORT ANSWER
A small change
in the recipe.
Steel is a family of recipes built on iron.
A few percent of one ingredient changes everything.
STAINLESS
Sheffield, 1913
On 13 August 1913 Harry Brearley melted a steel with 12.8% chromium and 0.24% carbon. He was looking for a steel that resisted wear in rifle barrels, not rust.
Read the story
RECYCLING
Made again and again
worldsteel says recycled steel keeps the properties of the original steel, and calls steel the most recycled material in the world.
See the numbersA QUICK LOOK INSIDE
What is in
the metal?
Pick a metal to see what goes into it beyond plain iron. The bar shows how far the recipe moves from simple iron and carbon.
Figures from Britannica and the International Stainless Steel Forum. Exact recipes vary from grade to grade.
TWO NUMBERS WORTH KNOWING
A thin film,
a long life.
One figure on what makes steel stainless,
one on how much steel has been made again.
10.5%
Minimum chromium in stainless steel
Every stainless steel has at least 10.5% chromium by mass. The chromium forms an oxide film about 130 Ångströms thick that renews itself if it is scratched.
STAINLESS · ISSF
25bn tonnes
Steel recycled since 1900
worldsteel says the industry has recycled over 25 billion tonnes of steel since 1900, and around 680 million tonnes in 2021 alone.
RECYCLING · WORLDSTEEL
worldsteel also reports that making a tonne of steel now takes 40% of the energy it did in 1960, and that around 90% of the water used in steelmaking is cleaned and reused or returned.
FOUR THINGS TO NOTICE
Steel is
everywhere already.
You do not need a laboratory to see these ideas at work. A cutlery drawer and a look around the street will do.
Look for 18/8 on cutlery
It names a stainless recipe; the 8 is the 8% nickel in grade 304.
Scratch, then wait
When the surface film on stainless steel is damaged, the chromium underneath forms fresh oxide and the film renews itself.
Keep steel in the loop
Recycled steel keeps the properties of the original, so steel sent for recycling can become new steel.
Think in decades
Packaging and vehicles come back for recycling after a short or medium life; bridges and buildings hold their steel for decades or centuries.
THE SHEFFIELD STORY
Looking for one thing,
finding another.
In 1912 the Firth Brown research laboratories in Sheffield were asked to look into why rifle barrels wore away. Harry Brearley tested chromium steels from 6% to 15% chromium, etching samples with acid and studying them under a microscope.
He called the result rustless steel, and the first stainless cutlery was made from it at Portland Works in Sheffield. Those early knife blanks and blades are still kept at Cutlers' Hall.
Questions
Questions people ask
What is the difference between steel and iron?
Steel is an alloy of iron and carbon with up to 2 percent carbon, according to Britannica. With a higher carbon content, the material is defined as cast iron.
What makes stainless steel stainless?
Chromium. All stainless steels contain at least 10.5% chromium, which forms a thin, tough oxide film on the surface. If the film is damaged, more chromium is exposed and a new film forms.
Who invented stainless steel?
Harry Brearley's 1913 melt in Sheffield is often called the first stainless steel, though Portland Works notes that other claims exist based on earlier research into chromium steels.
What does 18/8 mean on cutlery?
It refers to grade 304 stainless steel. The International Stainless Steel Forum notes that this grade contains 8% nickel, added to improve corrosion resistance.
Does recycled steel lose quality?
worldsteel says recycled steel keeps the inherent properties of the original steel, and that its quality can even improve on recycling.