@spot_material
hello@spotmaterial.com
Carbon steel
0.5-1.1 usd/kg
Steel is an immensely important material. Made up of iron (Fe) and 0.06-2% carbon (C), plain carbon steel is the basis upon which all steels are built, including stainless steel and alloy steel. From relatively ductile and formable low carbon steels – referred to as mild steel, they make up the majority of all steel produced – through ultra strong high carbon steel, this group offers something for every type of application. Indeed, it surrounds us in our daily lives in applications including tinplate packaging and food cans, toys, buildings and bridges, automotive bodywork and components, and industrial components. The difficulty with carbon steels is that they have very high corrosion rate, in the order of 20-50 micrometres per year, when exposed to weathering. Therefore, if used outdoors or exposed to an oxidising environment, they must be protected, such as with galvanising, metal plating, powder coating or painting.
While steel has some incredible attributes, and is irreplaceable in many applications, its downfall is its relatively high density. Compared to engineering plastics, and nonferrous alloys, such as aluminium, it is quite heavy for the same thickness; and it can be expensive to form and fabricate. Plastics are injection moulded into complex and lightweight parts in a single step, which is hard to beat in many engineering applications. And aluminium can be extruded into complex shapes with very low investment costs. Even so, steel remains the most significant engineering and construction material, second only to concrete in terms of global production volumes, and has the highest recycling rates of all – its magnetic properties make it relatively easy to recover from mixed waste. Today, new steel products contain on average around 30% recycled steel.
There are two main processes used to produce steel: basic oxygen steelmaking (BOF), which accounts for the majority, and electric arc furnace (EAF) steelmaking. While the BOF process is used to make primary steel from iron ore and coal and produces the highest quantity of emissions, EAF uses recycled material and be powered with renewable energy. The Steel Manufacturer’s Association claims that EAF operations produce twice the steel with 75% less greenhouse gas emissions compared to BOF production.
According to World Steel Association, carbon steel production has an average of 1.91 kgCO2e/kg, with basic oxygen steelmaking (BOF) at 2.33 and accounting for around 70% of global production, and electric arc furnace (EAF) at 0.66. On average, 20 MJ of energy is required for every kg of crude steel.
High carbon steels contain 0.6-1% carbon (C) and 0.3-0.9% manganese (Mn). They are the hardest and strongest of the carbon steels, but less ductile, more brittle and difficult, if not impossible, to weld. They are used for demanding applications that require high strength and wear resistance – and where formability and welding are not essential – such as in machine building, automotive and construction. High-carbon steel has good ‘memory’, causing it to spring back to its original shape after stretching. This property is useful in clips (retaining and spring), fasteners (appliances and electronics), springs and high-strength wire, for example.
Some notable types and grades:
– 1065 (UNS G10650, DIN 1.1230), with 0.65% C, has high tensile strength and surface hardness. It is used to manufacture parts that require strength and wear resistance, such as machine blades, washers, chains, brackets, brake disks and gears.
– 1095 (UNS G10950 DIN 1.1274), with 0.95% C, also known as spring steel, has high surface hardness coupled with high strength and wear resistance. It is used in springs for very demanding applications, such as in automotive suspension. It is also popular in the manufacture of machined or forged cutlery, knives, blades, axes and katana (the long, single-edged sword used by Japanese samurai). Its hardness makes for a very good cutting edge and it is easy to sharpen. However, it is prone to rust if not oiled and cared for. Adding a small amount of chromium helps to maintain a bright and tarnish-free finish, such as 5160 and 5210 chromium alloy steels. The famous laminated Damascus steel is a mix of high carbon and nickel-alloy steel (such as 15N20 / 75Ni8 / 1.5634), for example, folded together in many layers. While the alloy steel provides flexibility and toughness, the high carbon layers create the razor-sharp edge.
