Iron

1.3-30 usd/kg
Circularity potential
High
Strength
Very high
Production energy
High
Stiffness
High
Embodied CO2
Medium
Density
Extreme

Iron is a valuable modern engineering material that, in the past, played an import role in the development of architecture and industry. Wrought iron, which is now largely only used for decorative purposes, allowed for longer uninterrupted structures in architecture, as well as elegant detailing that was not practical with other materials of the time. In structural applications, wrought iron has been replaced by steel, which is tougher and stronger.

Cast iron, on the other hand, offers many advantages over steel and other metals when it comes to endurance and dampening, especially in complex castings and large structural components. These three metals are primarily distinguished by their carbon content. Wrought iron contains almost no carbon (<0.035%), cast iron between 2-4% and steel between 0.06-2%. Alloys are mixed with cast iron and steel to further enhance mechanical properties and corrosion resistance. And this opens up opportunities for heat treatment to refine strength and hardness.


Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products


Grey cast iron (also gray cast iron) has a microstructure of flake graphite in a ferrous matrix that produces a grey coloured material. It is synonymous with cast iron, and often the material if something is designated as simply ‘cast iron’. It has excellent casting properties as a result of the high carbon (C) content, good machining properties (it is relatively soft, but brittle) with high stiffness and very good vibration dampening. It is suitable for intricate castings and parts that require complex or lengthy machining operations. A benefit of the graphite microstructure is it reduces wear on the cast iron by aiding lubrication on the surface. Applications include things like engine cylinder blocks, pump housings, gears, hydraulics, valve bodies, electrical boxes and weights, as well as cookware (pots and pans) and decorative architectural castings (handrails, ornaments, bathtub feet, lamp bases).

Grey cast iron consists of iron (Fe), 2.5-4% C, 1-3% silicon (Si) and other elements such as manganese (Mn), phosphor (P) and sulphur (S). The exact proportion depends on the grade and the mechanical properties depend on the ingredients. The graphite flakes, which are advantageous in some ways, introduce weakness into the material, resulting in relatively low tensile and impact strength.

Grades are designated according to tensile strength, which increases with a reduction in C and Si:
≥100 MPa as HT100, DIN GG10
≥150 MPa as HT150, DIN GG15, JIS FC150, ASTM Class 20A
≥200 MPa as HT200, DIN GG20, JIS FC200, ASTM Class 30B
≥250 MPa as HT250, DIN GG25, JIS FC250, ASTM Class 35B
≥300 MPa as HT300, DIN GG30, JIS FC300, ASTM Class C45
≥350 MPa as HT350, DIN GG35, JIS FC3500, ASTM Class C50


Design properties
Cost usd/kg
1.3-1.5
Embodied energy MJ/kg
20-50
Carbon footprint kgCO2e/kg
1.5-3
Density kg/m3
6900-7350
Tensile modulus GPa
130-160
Tensile strength MPa
260-340
Shear modulus GPa
31-60
Compressive strength MPa
1100-1300
Hardness Mohs
5
Brinell hardness HB
230-280
Poissons ratio
0.26
Thermal expansion (µm/m)/ºC
12
Melt temperature ºC
1376
Thermal conductivity W/mK
40-72
Temperature min-max °C
-150 to 450
Thermal
conductive
Electrical
conductor
Electrical resistivity µΩ⋅m
0.6-0.8