Have you ever wondered about the processes involved in stainless steel manufacturing? Here they are.
1. Melting and Casting
The raw materials are melted in an electric furnace at a very high temperature. This process takes 8 to 12 hours and, when finished, the product is cast into semi-finished forms. These are basically billets (round or square shapes that are 1.5 inches or 3.8 centimetres thick) or blooms (rectangular shapes). These semi-finished forms also include rods, slabs and tube rounds.
2. Forming
The next step is the forming operation, which begins with hot rolling. During this process, the steel is heated and passed through huge rolls. Slabs are formed intostrip, sheet and plate. Blooms and billets are formed into bar and wire. Bars come in different grades and shapes. Wire, plate and strip are usually measured in centimetres and inches. The measurement for the wire is usually up to 0.5inch (1.27 cm) indiametre or size. The plate is usually over 10 inches wide (25.4 cm) and 0.1875 inch (0.47 cm) thick. The sheet is less than 0.1875 inch (0.47 cm) thick and 24 inches (61 cm) wide. The strip is less than 0.185 inch (0.47 cm) thick and less than 24 inches (61 cm wide).
3. Heat Treatment
After the stainless steel is formed, most of these products go through annealing, a heat treatment process where steel is first heated then cooled under the right conditions to soften the metal and relieve internal stress. The process can lead to different results. For instance, the higher temperature ageing process produces a tougher material with a lower strength while a lower ageing temperature produces high strength steel with low fracture toughness.
Note that the heating rate to reach the required ageing temperature doesn’t usually affect the properties of steel, but the cooling rate does. The required heating temperature for the ageing process is 900-1000° Fahrenheit (482 to 537° Celsius). On the other hand, a particular cooling process requires water quenching the material in an ice-water bath for at least two hours. The temperature required for this process is usually 35° Fahrenheit (1.6° Celsius).
Heat treatment and water quenching are technical processes, so they should be properly done to get perfect results. The type of heat treatment you use depends on the type of steel you’re dealing with. Ferritic, martensitic and austenitic steels require varied heating processes. Austenitic steels are usually heated to temperatures of 1900° Fahrenheit and above (1037° Celsius). Note that water quenching is used for thick sections while air blasting (or air cooling) is for thin sections. A great idea is to clean part surfaces before heat treatment, as this helps you get rid of contaminants and achieve the proper heat treatment results.
4. Descaling
Annealing leads to a scale or a build-up to form on the steel. If this happens, the build-up can be removed through a number of processes, including pickling and electro-cleaning. In electro-cleaning, an electric current is used to get rid of the scale. Meanwhile, in the picking process, a nitric-hydrofluoric acid bath is used to descale the steel.
5. Cutting
Cutting the steel is a vital process and is necessary for two reasons: it can help you get the desired blank shape or size and trim the parts to the required size. Mechanical cutting of stainless steel is done by a number of methods. These include straight and circle shearing. Straight shearing is accomplished by guillotine knives while circle shearing is done by circular knives. Horizontal and vertical cutting can also be accomplished with the use of high-speed blades. Blanking and nibbling are also used to cut irregular shapes. Cutting can also be accomplished by flame cutting and plasma jet cutting.
6. Finishing
Surface finishing is a crucial part of the stainless steel fabrication process. Some surfaces require smooth finishing while others require rough finishing.
Finishing can also be categorised according to the specific result at the end of the process and the finishing method used. Examples are the dull, bright and mirror finish. Some processes used in finishing are buffing and tumbling.
7. Manufacturing at the Fabricator or End User
After the packing and shipping of finished goods to the end user or fabricator, a number of other steps are required. A little more shaping is done by methods such as press forming, roll forming, extrusion, press drawing, forging and extrusion. Further heat treating and cleaning processes are also required.
The process of joining different parts of stainless steel together is done by welding. In this context, the most common forms of welding are fusion and resistance welding. After the welding of the different parts of the stainless steel, the welded areas are usually cleaned and polished.
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