The name “stainless steel” applies to a group of iron based alloys that contain a minimum of 10.5% chromium. Other elements are added such as; manganese, silicon, phosphorus, sulphur, nickel and molybdenum. The amount of each of the elements can help improve resistance to corrosion and heat and can also help improve mechanical properties and fabricating characteristics. There are in excess of 50 different grades of stainless steel.
The most common grades of stainless fall under the following categories;
Austenitic: These are referred to by Type 300 and 200 series. They can be hardened by cold working but not heat treatment. They are essentially non-magnetic and have excellent corrosions resistance and good formability. They include 316 and 304 Stainless
Ferritic: identified as 400 series can be moderately hardened by cold working but not hardened by heat treatment. This group does not have as good a resistance to corrosion as austenitic stainless but does have good working properties.
Martensitic: This group is also identified in the 400 series and able to be hardened by heat. They are magnetic and have very average resistance to corrosion compared with Austenitic.
Stainless steel can be fabricated with similar methods used in fabricating carbon steels and other metals however stainless steel can differ in yield strength and hardness. All stainless has higher rates of hardening than carbon steel.
“Stainless Steel Fabrication can involve many different processes”
Drilling – 300 series stainless steel can be difficult. When a drill bit contacts the surface of the stainless and begins to penetrate the stainless hardens and it becomes more difficult to continue drilling. Drill bits need to be made from high speed steel carbide and used with a drilling compound/lubricant.
Cutting and Grinding – it is important when cutting stainless steel to avoid contamination by ferrous metals such as iron or steel. This can reduce the corrosion resistance and in fact increase the chances of the stainless corroding in a short amount of time. Cut edges should be dressed and chemically passivation with nitric acid to help reform the stainless steel’ oxide layer. Types of cutting include; mechanical shearing, sawing, circle shearing, band sawing, power hacksawing, blanking, punching and nibbling. Other forms of cutting fabrication include thermal/oxy cutting, plasma cutting, laser cutting and water cutting.
Bending Stainless Steel – Because stainless steel is hard is has tendency to spring back. Because of this the force applied to the stainless when bending must be more than the yield strength of the metal, spring back must also be accommodated for b over bending the stainless steel. Other types of bending include roll forming, roll bending and press break bending / folding.
After stainless steel fabrication is complete the fabricated area needs to be descaled. This is the removal of oxide scale. Descaling the fabricated surface can occur through several different processes; Pickling solutions contain 10 to 15% nitric acid and can be applied and washed of to leave the surface clean and free from impurities
Blasting, including; Grit Blasting, Bead Blasting and Sand blasting all have great results in removing scale and can leave different types of finished effects on the stainless surface.
Southern Stainless offer a variety of stainless steel fabrication services, please contact us for a personalised quote