Stainless steel is 100% recyclable. An average stainless steel object is composed of about 60% recycled material of which approximately 40% originates from end-of-life products and about 60% comes from manufacturing processes. And because of its resistance to corrosion and staining, low maintenance and familiar lustre, stainless steel became an ideal material for many applications. Stainless steel is used in mould, industrial machine(for example, in an turnkey ice cream plant), household hardware, etc.
There are different types of stainless steels: when nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually non-magnetic and less brittle at low temperatures. For greater hardness and strength, more carbon is added. With proper heat treatment, these steels are used for such products as razor blades, cutlery, and tools.
Stainless steel is usually divided into 5 types by their crystalline structure:
1. Austenitic, or 200 and 300 series, stainless steels have an austenitic crystalline structure, which is a face-centered cubic crystal structure. This structure gives these steels their characteristic combination of weldability and formability. Corrosion resistance can be enhanced by adding Chromium, Molybdenum and Nitrogen. These steels are the most common. Austenite steels make up over 70% of total stainless steel production. Standard austenitic steels are vulnerable to stress corrosion cracking. Higher nickel austenitic steels(Superaustenitic stainless steels) have increased resistance to stress corrosion cracking.
2. Ferritic stainless steels generally have better engineering properties than austenitic grades, but have reduced corrosion resistance, because of the lower chromium and nickel content. They are also usually less expensive. Ferritic stainless steels lack of toughness in welds, so, they are usually limited in use to relatively thin sections.
3. Martensitic stainless steels are similar to ferritic steels in being based on Chromium but have higher Carbon levels up as high as 1%. Martensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machinable, and can be hardened by heat treatment.
4. Precipitation-hardening martensitic stainless steels have corrosion resistance comparable to austenitic varieties, but can be precipitation hardened to even higher strengths than the other martensitic grades. These steels can be machined to quite intricate shapes.
5. Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 50/50 mix, although in commercial alloys the ratio may be 40/60. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. Duplex stainless steels are weldable but need care in selection of welding consumables and heat input. They have moderate formability.