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


Water-hardening tool steel (W) are so-called, because they are water quenched. They are high-carbon steel – 0.6-1.4% carbon (C) – with the addition of small amounts of chromium (Cr) and vanadium (V). The high carbon content means they tend to be strong an hard, but brittle. They are competitively priced and so popular in the production of tools and dies, including drills, blanking dies, woodworking tools, metal cutting tools, cutlery and machine parts. They have excellent machining properties and can be formed with all conventional metalworking processes. However, they have relatively poor toughness and so are avoided in applications that require energy absorption or impact loading.

Notable examples include:
– W1 (A686, UNS T72301, DIN 1.1654) is used for hand metal cutting tools (blacksmithing) and cutlery, for example.
– W2 (135Cr3, UNS T72302, DIN 1.2008) is used for machinery, rasps, files, razor blades and knife blades.
– W3 (UNS T72305) is a hard-wearing steel used to make instruments, cutting tools, moulds and gears.


Design properties
Cost usd/kg
1-2
Embodied energy MJ/kg
20-29
Carbon footprint kgCO2e/kg
2-3
Density kg/m3
7830
Tensile modulus GPa
205
Tensile strength MPa
1680-1800
Hardness Mohs
5.5-6
Brinell hardness HB
335-498
Poissons ratio
0.29
Thermal expansion (µm/m)/ºC
10.4
Melt temperature ºC
1410-1450
Thermal conductivity W/mK
48
Temperature min-max °C
-250 to 500
Thermal
conductive
Electrical
conductor
Electrical resistivity µΩ⋅m
0.3