We see stainless steel everywhere. In hospitals, restaurants, our kitchen and in many products around the home. But what exactly is stainless steel? How is it made? What else should we know about it?
What makes this steel stainless is chromium. Average composition of stainless steel includes around 10.5% chromium which adds strength and corrosion-resistance.
What is stainless steel made of?
Stainless steel is an alloy made from iron, carbon, chromium and sometimes nickel and other metals. The chromium and nickel are what give stainless steel its unique properties and provide the corrosion-resistance it is best known for.
Stainless steel is actually a collective term for around 200 different alloys with similar properties. Key differences are the quantities of carbon and the mix of those extra metals added into the mix.
Types of stainless steel includes:
- Austenitic stainless steel – This steel uses austenite, a solid mix of iron and carbon to deliver a very tough, very resistant stainless steel.
- Ferritic stainless steel – This steel has just chromium and not nickel, up to 18% chromium to provide a stress-resistant and magnetic material.
- Duplex stainless steel – A mix of austenitic and ferritic steel that provides a combination of both characteristics.
- Martensitic stainless steel – A steel that has a higher carbon content and lower chromium to deliver a tough but less corrosion-resistant steel.
- Precipitation hardening stainless steels – Steel that combines austenitic and martensitic steel with added aluminium, molybdenum, niobium, titanium and copper to deliver high strength steel.
How is stainless steel manufactured?
Stainless steel is made using a process similar to mild steel, just with those extra metals added during the process.
It begins with:
Where the iron and the desired mixture of carbon is added and melted.
Once melted we need to remove the carbon from the metal using either Vacuum Oxygen Decarburization (VOD) or Argon Oxygen Decarburization (AOD). Either oxygen or argon is added to the metal to force out the carbon.
Once the elements are mixed and the carbon removed, the metal is tuned. Tuning is a process of finely controlling the amounts of chromium, nickel, silicon, manganese and nitrogen added to the mix until the metal is at the desired composition.
Once tuned, the steel can be formed into billets, blooms, slabs, tubes or rods. Then it can be formed using hot or cold rolling to shape the metal.
Next comes heat treatment and annealing. The metal is heated and cooled until it reaches the desired steel grade. Annealing is an optional process to soften the steel and improve its ability to be formed.
Descaling removes any scale on the surface of the steel created by annealing. A mix of acid or electrocleaning is used to descale the steel.
The steel is then cut into the desired size and then finished depending on the end product. It can be rolled, formed, cut, polished, buffed and etched depending on what you’re turning the stainless steel into.
What’s the difference between 316 and 304 stainless steel?
The difference between 316 and 304 stainless steel is purely down to how much alloy each steel contains.
- 304 stainless steel contains 18% chromium and 8% nickel.
- 316 stainless steel contains 16% chromium, 10% nickel and 2% molybdenum.
304 stainless steel
304 stainless steel is standard stainless so is corrosion resistant and hard-wearing in most situations.
304 stainless steel is known to be very corrosion resistant and is often found in kitchen appliances, commercial machinery, food processing equipment, architectural products, nuts, bolts and hardware, brewing, food and pharmaceutical uses.
316 stainless steel
316 stainless steel is known for its superb corrosion resistance and for being higher strength and more temperature resistant than 304 stainless steel.
316 stainless steel is often found in large scale food, chemical, pharmaceutical manufacturing machinery, construction, tubing, medical machinery and equipment, marine use and medical implants.
What’s the difference between mild steel and stainless steel?
The primary difference between mild steel and stainless steel is those added alloys we put into stainless. Mild steel is manufactured using just iron and carbon while stainless has chromium, nickel, silicon, manganese and perhaps other alloys added.
Those elements prevent rust, corrosion and means stainless steel can be used in clean situations such as food manufacturing, kitchen appliances, medicine, pharmaceuticals and other applications.
Stainless steel is also more expensive to manufacture, which is why you’ll see a price difference between our mild steel products and our stainless steel products.