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Stainless steel
4-20 usd/kg
Stainless steels have very good corrosion resistance compared to carbon steels, coupled with impressive mechanical properties. This combination is the result of the addition of a relatively high proportion of alloys, in particular chromium (Cr). They tend to be more expensive, and so reserved for applications that demand their superior properties.
Based on their crystalline structure, they are grouped in five families: ferritic, austenitic, martensitic, precipitation-hardening (PH) and duplex. Ferritic stainless steel is not seen much outside industrial applications, automotive and white goods, for which it is well suited. The lower alloy content makes it less expensive than the more common austenitic types.
Austenitic stainless steel, which includes the very popular 300 series, is a good all-rounder with high resistance to corrosion. It is non-magnetic (which makes it easy to distinguish from other steels), with excellent formability, machining properties and weldability.
Martensitic stainless steel has high hardness and strength, good for industrial applications, household appliances and some knife blades, with moderate resistance to corrosion. Its high hardness makes it relatively more difficult to form, cut and weld.
Duplex types are a modification on austenitic grades, designed to provide higher strength with comparable or improved corrosion resistance. PH stainless steels are a family of corrosion resistant alloys, which can be heat treated to tensile strength several times greater than austenitic types. They are used in very demanding applications in aerospace, off-shore and nuclear energy, for example.
Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products
Type 304 (UNS S30400, DIN 1.4301) is the most common austenitic stainless steel, accounting for around half of all stainless steel produced. It contains 17.5-19.5% chromium (Cr), 8-10.5% nickel (Ni), 2% manganese (Mn), 1% silicon (Si), 0.07% carbon (C) and small amounts of other alloys. It is also known as 18/8 (or 18/10), which is derived from the nominal composition of 18% Cr and 8% Ni (or 10% Ni).
Due to it’s ingredients, corrosion and heat resistance, and good mechanical properties, type 304 is a versatile metal available in most forms and formats. It is sufficiently ductile to be drawn into deep profiles, such as saucepans, sinks and dustbins. It is resistant to most chemicals and is durable in typical food processing environments; qualities utilised in commercial and domestic kitchens, kitchen utensils, vacuum flasks and cups (thermos), industrial food production, cookware, tableware and packaging.
It cannot be hardened by thermal treatment, but strength and hardness can be increased through cold working, with subsequent reduction in ductility and formability. It has excellent welding characteristics, with and without filler metals, using standard fusion methods. Post-weld annealing is not required when welding thin sections however heavy welded sections may require some post-weld annealing for optimal corrosion resistance.
Applications include springs, screws, nut and bolts, building facades, furniture, lighting and industrial equipment; it can be found in all fields of industrial, commercial and domestic manufacturing.
Modified grades:
– Type 304L is the low carbon version of type 304. It is used in heavy gauge components for improved weldability.
– Type 304H, a high carbon content equivalent, is preferred for high temperature applications above 500 degC and up to 800 degC.
