The synthesis of stainless steel comprises four main steps. 2
The first step of synthesizing stainless steel is to melt all of the raw materials (iron, chromium, silicon, nickel, carbon, nitrogen and manganese) together in a furnace for about 8 to 12 hours at very high temperatures. When everything is melted together, the steel is cast into either rectangular, round, square or tube shapes.
The second step is forming. The semi-finished steel is heated again and passed through huge rolls to make sheets, strips and plates. After the steel is formed, it often goes through annealing. Annealing is a treatment consisting of heating the metal and letting it cool very slowly to reduce internal stresses and increase toughness. Some types of stainless steel are heat treated to increase strength (this is called age hardening), but this requires very precise control and any small mistake can drastically affect the properties of the metal. This process can be used in one of two ways: with higher temperatures, the material will have lower strength but will be tougher whereas, with lower temperatures, the material will have higher strength but low fracture toughness. This problem can be solved a post-ageing quenching, a rapid cooling of the material that can increase the toughness without lowering the strength.
Something to remember is that the heat treatment depends on the type of stainless steel (listed in the introduction).
The third big step in the synthesis of stainless steel is descaling. Descaling is necessary because of the excess material formed on the material when annealed. This build-up can be removed using a variety of techniques, the two most common being pickling (which uses an acid bath) and electrocleaning (which uses an electric current and phosphoric acid). As the type of heat treatment is different depending on the type of steel, so is the descaling.
The fourth and final step is processing. It starts with the material being cut or trimmed to obtain the desired shape and size. There are many ways to do this, including special knives, saws, flames and lasers, or even plasma cutting 11. This is followed by adding a surface finish to the steel to adjust the appearance to the use of the material later on. Certain finishes have special properties, like the easiness of cleaning or better corrosion resistance. These finishes are produced by rolling and buffing. Different temperatures will have different appearances: for example, hot rolling will give a dull finish whereas cold rolling will give a bright finish. A mirror finish (with is common) can be obtained by buffing the steel with grinding wheels.
After all those steps are completed, the stainless steel is ready to be shipped and distributed to the consumer. They might wish to join multiple elements of stainless steel, which is most commonly done with welding. Fusion welding and resistance welding will achieve different results because they use different sources of heat.
