Stainless steel can be fabricated using any of the traditional forming and shaping methods but it requires a more delicate approach.
Stainless steel is a very common material to use in fabrication projects, thanks to its versatility and durability, among others. Stainless steel possesses high good corrosion resistance which makes it the primary option for industries such as pharmaceuticals, food, petrochemicals and machinery.
The versatility of stainless steel requires different fabricating techniques.
2. Material Selection
There are 4 groups of stainless steel grades; austenitic, ferritic, martensitic and duplex. The prevailing grade in the market is austenitic which is made from steel, nitrogen, nickel and manganese. Ferritic grades contains carbon steel and chromium. Duplex is combination of austenite and ferrite in different ratios.
The fabrication method depends on the grade and its alloys. Each grade has their own features to differentiate fabrication procedures.
3. Welding Stainless Steel
All metals have different welding characteristics. For MIG or TIG welding, an inert gas or gas mixture is necessary. Argon – CO2 gas mixture prevents the chromium and nickel from oxidizing. Stainless steel can also be stick welded but MIG and TIG will provide better weld quality.
Figure 1 Stainless Steel Welding
The filler metal of stainless steel can significantly affect the quality of the weld. The filler metal must be equal to or smaller than the base metal to match the parent material’s durability. Moreover, the filler metal and the base metal must be chemically compatible in order to not undermine the chemical characteristics of the welded parts.
Stainless steel is a sensitive material which requires delicate weld preparation practices such as thorough surface preparation prior to commencement of welding. Shoddy surface cleaning may compromise the material features such as corrosion resistance. Surface cleaning material such as a brush may be used but it is essential that these tools were not being used for other types of metal.
A proper welding gap is also necessary for stainless steel in order to not require an excess of welding. Since stainless steel is very sensitive to heat, excess welding may cause the material to heat up.
4. Stainless Steel Surface Finishes
Common finish types for stainless steel are mill finish, No. 4 finish and mirror polish. An appropriate abrasive should be used for the desired surface finish. The used abrasive should not be used for other kind of metal to prevent contamination and compromise corrosion resistance. It’s ideal to use abrasives which are designed specifically for stainless steel. They will cut faster, last longer, and reduce heat better.
Figure 2 Stainless Steel Surface Finish
Stainless steel is softer metal than carbon steel and it is easier to damage the work piece. Stainless steel also changes its colour with high heat, therefore, exposure to excessive grinding or finishing can turn the metal a purple or brown colour. This would require an additional process to remove discoloration, which will increase the fabrication cost. When using abrasive products, it is essential to avoid over pressure to not over heat the metal.
Stainless steel has definite advantages over other metals and, it’s one of the most expensive metal. This high cost puts additional pressure on fabricators to be more careful in fabrication processes. Stainless steel should be fabricated in a specialized clean workshop to prevent contamination. Also it required specialist steel contractors with stainless steel experience.