Stainless steel
In many situations galvanised mild steel does not give adequate protection. This is where the special oxide film formed on Chromium alloyed stainless steels becomes useful.
Many types of stainless steels have been developed to resist different corrosion environments and working conditions ensuring that works are safe, things last longer and our food is hygienic. Stainless steel is even used in the process of cleaning up exhaust gases from cars and power stations.
Stainless steel is also recyclable: when scrapped, it can be re-melted to make something new.
Stainless steels are Chromium-containing steel alloys. The minimum Chromium content of the standardised stainless steels is 10,5 %. Chromium makes the steel 'stainless' -- this means improved corrosion resistance. The better corrosion resistance is due to a Chromium oxide film that is formed on the steel surface. This extremely thin layer, under the right conditions, is also self-repairing.
Beside Chromium, typical alloying elements are Molybdenum, Nickel and Nitrogen. Nickel is mostly alloyed to improve the formability and ductility of stainless steel. Alloying these elements brings out different crystal structures giving different properties in machining, forming, welding etc.
The major types of stainless steel are:
- Austenitic stainless steels, which can be hardened by cold working, meet a wide range of design criteria. They are essentially non-magnetic although they may become slightly magnetic due to cold working.
- Martensitic stainless steels are straight-chromium types that can be hardened by heat treatment. They are magnetic.
- Ferritic stainless steels, like Martensitic stainless steels, are straight-chromium types and they are magnetic. Ferric stainless steel, however, cannot be hardened by heat treating and only moderately hardened by cold working.
One of the most widely used general-purpose stainless steels. It possesses an excellent combination of strength, corrosion resistance and fabricates well. To reduce carbide precipitation when welding, use 1.4307 for its lower-carbon content.
EN 1.4401 (Austenitic)
Superior corrosion resistance compared to other 300 series alloys when used in harsh corrosive environments (e.g. sea water, chemicals, etc.). To reduce carbide precipitation when welding, use 1.4404 for its lower-carbon content.
EN 1.4541 (Austenitic)
Titanium stabilised stainless steel to prevent intergranular formation of chromium carbide. It exhibits strength characteristics superior to those of 1.4301 stainless, thus making it best suited for parts which cannot be subsequently annealed.
EN 1.4512 (Ferritic)
The lowest chromium content of the stainless steels, combines good elevated temperature corrosion resistance with medium strength, good formability and overall cost.
EN 1.4016 (Ferritic)
A general-purpose non-heat-treatable chromium type used for highly polished trim applications in mild atmospheres. Its strengths are in ductility, formability, good corrosion and oxidation resistance, thermal conductivity and finish quality.