Alloy steel

1-20 usd/kg
Circularity potential
High
Strength
Very high
Production energy
Medium
Stiffness
Very high
Embodied CO2
Medium
Density
Extreme

The properties of steel are transformed with the addition of alloys – such as chromium (Cr), manganese (Mn) and silicon (Si) – and tempering (controlled heating and cooling cycles in manufacture). While adding no more than 0.05% alloy to a plain carbon steel can almost double its strength, the cost is raised only very slightly. Other alloys, such as copper (Cu) and Cr, are added to improve corrosion resistance and yield materials that can tolerate extremely corrosive environments, or be left outdoors unpainted for more than a century.

Steel is relatively low cost and grades have been developed to suit almost every imaginable application. Its properties are highly tailorable and as a result, it is used in packaging (coated mild steel or naked stainless), automotive (steels with tensile strength of more than 550 MPa are known as advanced high-strength steel, AHSS), furniture, construction, buildings, bridges, heavy duty equipment, manufacturing equipment, laboratory environments and shipbuilding. Its tolerance to low and high temperatures in service depends on the grade, with some tool steels able to withstand extreme loads and shocks, and maintain incredible hardness (equivalent to granite and concrete) at over 500 degC.

Heat treatment (tempering) is a critical step in the production of many high performance steels. It is as important as the ingredients for the mechanical properties of the final part. Typically carried out once forming and welding have been completed, a steel item may be worth many more times the initial cost of the base metal by this point. Therefore, processes have been developed to reduce the risk of distortion, cracking and other defects. It has evolved into a sophisticate and critical step in the production of many types of steel.


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


Plastic mould tool steels (P) are low-medium carbon steel with small amounts of alloy elements, such as manganese (Mn), silicone (Si), chromium (Cr) and nickel (Ni), for example. They are used to make mould tools for injection moulding and compression moulding plastic, as well as low-temperature casting alloys. Their chemistry has been optimised to suit the manufacturing processes used for these parts, as well as tempering and finishing steps. They are manufactured to precise specifications, to ensure uniform properties, and no pinholes, pores or other defects. Grades as follows:
– P2 (T51602)
– P3 (T51603) has good corrosion resistance coupled with high hardness and strength.
– P4 (T51604, DIN 1.2341) has improved high temperature resistance.
– P5 (T51605)
– P6 (T51606)
– P20 (T51620, DIN 1.2311) has very good machining, etching and polishing properties. Once tempered, it has good dimensional stability and uniform hardness. It is a popular choice for plastic and rubber mould tools.
– P21 (T51621) is a precipitation hardening steel that contains additional aluminium (Al), vanadium (V) and cobalt (Co). This results in a steel with excellent polishing properties. Therefore, it is used in plastic injection moulds that require a highly polished surface.


Design properties
Cost usd/kg
3-8
Embodied energy MJ/kg
20-29
Carbon footprint kgCO2e/kg
2-3
Density kg/m3
7800
Tensile modulus GPa
200
Tensile strength MPa
860-1850
Shear modulus GPa
80
Hardness Mohs
5-5.5
Brinell hardness HB
271-381
Poissons ratio
0.29
Thermal expansion (µm/m)/ºC
12.7
Melt temperature ºC
1460
Thermal conductivity W/mK
29
Temperature min-max °C
-40 to 500
Thermal
conductive
Electrical
conductor
Electrical resistivity µΩ⋅m
0.2