Differences Between Carbon Steel and Black Steel
08 August 2022
What is Carbon Steel?
Carbon steel is a form of steel that contains a high level of carbon. The presence of carbon in steel increases the hardness but reduces the ductility of the end product, whether that be a steel beam or a steel column, steel with a low level of ductility is more prone to fracturing under heavy loads, which may make it unsuitable for some applications, as it’s much safer for steel to slowly deform rather than immediately fracture.
Generally, carbon steel is often split into three different categories:
Low Carbon Steel
Low carbon steel, more commonly referred to as mild steel, contains a low level of carbon, typically between 0.05% and 0.30% by weight. Mild steel is useful for many different applications, and often contains other components such as aluminium to enhance the steel's properties.
Medium Carbon Steel
Medium carbon steel contains around 0.31% to 0.60% carbon by weight, resulting in a much harder steel that becomes difficult to cut and weld. A higher level of manganese is usually added to medium carbon steel during the process in order to increase its strength and corrosive resistance.
High Carbon Steel
High carbon steel has a much higher level of carbon content of between 0.61% and 1.50% by weight. It is sometimes referred to as ‘Carbon tool steel’ because its high level of strength and hardness make it much more difficult to cut and weld. Due to the increased hardness, high carbon steel tends to snap rather than bend when put under a high level of tensile strength.
What is Black Steel?
Black steel refers to steel that has not undergone a galvanisation process for corrosive protection. The steel instead undergoes a chemical process called blackening, resulting in the formation of a hardened iron oxide or magnetite surface. This surface creates an increased protection against corrosion and abrasion but does little to add to the structural strength of the steel, making it less popular than carbon steel in the majority of applications.
Resistance to Corrosion
Carbon steel tends to be very susceptible to corrosive agents, including chlorine, bleach, strong acids and even air at high humidities. This is because these corrosive agents, or humid air, react with the carbon atoms within the carbon steel.
Black steel, on the other hand, is resistant to corrosion and abrasion due to its high levels of surface magnetite. This is why black steel is frequently used for applications such as pipes, where it may have to come into contact with corrosive agents.
Composition
Carbon steel has a higher carbon content than regular steel, whilst black steel gets its name from the black-coloured iron oxide which is used to coat its surface. Black steel is formed through the layering of malleable iron, whereas carbon steel is formed in a seamless process.
The seamless process used in the fabrication of carbon steel, along with the fact that it’s an alloy, resulting in a much harder steel, suitable for applications that require an increased level of tensile strength. Black steel, on the other hand, has a very strong resistance to corrosion and abrasion, which make it perfect for pipes, especially those carrying corrosive agents.
Eco-friendliness
As things go, steel is naturally a fairly eco-friendly material. This is why black steel is the more eco-friendly and sustainable option, since the blackening process simply adds a layer of hardened iron oxide, whereas carbon steel must undergo a carburising process, which releases more CO2 into the atmosphere than the blackening process that black steel must undergo.
If the environment is to be considered, black steel is the winning choice. However, if you require a stronger type of steel for immense structural loads or similar load-bearing activity, carbon steel will almost always be the superior choice.
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