Stainless steel

4-20 usd/kg
Circularity potential
High
Strength
Very high
Production energy
High
Stiffness
Very high
Embodied CO2
High
Density
Extreme

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 430 (UNS S43000, DIN 1.4016) is a ferritic stainless steel with good formability and compatibility with welding. It is not as resistant to corrosion as type 304 austenitic stainless, but has particularly good resistance to nitric acid (used in the production of fertiliser), and is typically less expensive because it doesn’t contain nickel (Ni). It can be found in industrial applications, laboratory equipment and manufacturing. It contains 16-18% chromium (Cr), up to 1% silicon (Si) and manganese (Mn) and 0.12% carbon (C).

Although formability is slightly lower than for 304, it is non-hardeanble, which can be advantageous for cold working. And it has very good machining properties. Due to its balance of mechanical performance, formability and cost, it is found in many everyday objects, such as fridge enclosures, sinks, washing machine cabinets and the liners, stove trim, chimneys and automotive bodywork trim. Type 304 is generally preferred for parts that require a higher degree of forming or welding. Using a magnet helps to tell these two common stainless steels apart: type 304 is non-magnetic.

Modified grades:
– Type 430F contains an additional 0.15% sulphur (S), which improves machining properties. It is also referred to as a free-machine alloy.


Design properties
Cost usd/kg
2-6
Embodied energy MJ/kg
51-75
Carbon footprint kgCO2e/kg
4.7-6.8
Density kg/m3
7750
Tensile modulus GPa
200
Tensile strength MPa
450-600
Hardness Mohs
4.5-5
Brinell hardness HB
183-262
Poissons ratio
0.28
Thermal expansion (µm/m)/ºC
10.4
Melt temperature ºC
1425-1510
Thermal conductivity W/mK
23.9
Temperature min-max °C
-40 to 500
Thermal
conductive
Electrical
conductor
Electrical resistivity µΩ⋅m
0.6