Today we are taking a deep dive into stainless steel and how it is made. This type of steel is widely used. Chances are you own at least a few appliances that are made of stainless. I know my refrigerator is.
Stainless steel comes in many different types. At Norfolk Iron we supply two main types of stainless-Austenitic and Ferritic.
Austenitic is the most common of the stainless steel types. This includes the 200 and 300 series. The alloy contains a minimum of 16% chromium and is also composed of a significant amount of nickel and manganese (here is a link to a some periodic tables in the off chance you don’t know what I am talking about).
Austenitic stainless has excellent corrosion resistance, good ductility, non-magnetic properties, strength and weldability.
The most common type of austenitic stainless is type 304 due to its corrosion resistance to a wide range of industry exposures. This makes it ideal for foodservice equipment or any application where sanitation is required.
Ferritic alloys have lower corrosion resistance than austenitic alloys due to lower chromium (10.5-27%) content. This includes some of the 400 series of stainless, including 409 and 430. Ferritic stainless has good corrosion resistance, high strength and great workability.
How Stainless Steel is Made
The process of making stainless steel begins with extracting chromite (an iron chromium oxide) from underground mines. It is then crushed to produce a chromite concentrate. This is what makes stainless steel strong and corrosion resistant.
You wouldn’t want a stainless steel refrigerator that doesn’t hold up and corrodes, right? The product’s ability to hold up is the basically the point of buying stainless-aside from the appealing surface finish, of course.
The next step is to melt the chromium pellets together in an electric furnace with the other raw materials (iron ore, manganese, nickel, etc.) used for the specific stainless type. After melting, the material is formed into slabs and transferred to a hot rolling mill.
Once the slab arrives at the hot rolling mill it is transferred to another furnace and the hot material is then sent through a roughing mill. At the roughing mill it is rolled forwards and backwards to reduce the thickness. As the thickness is decreased it causes the slab to become a long strip that will later be wound up into a coil.
The long strip, or band, is passed through additional rolling mills to reduce the thickness even more. At this point it is coiled then cooled by water and transferred to a cold rolling mill.
When the material arrives from the hot rolling mill it is covered in a black scale.
At the cold rolling plant the material is uncoiled and passed through an annealing and pickling line to remove the black scale. The band is then reduced to the thickness specified by the customer and recoiled.
The coiled material is sent through another annealing and pickling process and rinsed with water.
Well, the stainless steel material goes through one final finishing step of removing the tension and improving the overall surface finish. The finished stainless is cut to the specified dimensions and shipped to customers around the world via train or barge.
When we receive the material we process it further to ensure our customers are getting the product they need. For more information about our stainless steel product offering, contact your local sales person.