Some of you out there may already be aware that steel is a mixture of iron with carbon and small amounts of other metals. Pure iron can be melted and shaped, but also tends to be somewhat soft, but by adding carbon, this will help to vitally strengthen the metal. Black carbon steel is made during the manufacturing procedure when high temperatures form a thin layer of oxidized iron on the outer surface. The majority of carbon steels contain from one to two percent carbon.
Carbon binds chemically with the iron in steel alloys, which creates a much stronger material than pure iron. After increasing the carbon content, the material becomes firmer, but at the very same time it also becomes more brittle, or likely to break under any kind of stress or load. Any steel which contains over 2% carbon is deemed cast iron, which can be utilised for piping and non-building materials, but is considered too brittle for structural steel.
Protection from Rust and Corrosion
Iron will react with oxygen in the air or moisture, which then creates iron oxide (or rust), that will then cause parts to fail, so it is normally coated to prevent any surface rust. One benefit of black carbon steel is the natural anti-corrosion property of a black iron oxide coating, due to the oxide blocking oxygen from the iron underneath. This thin oxide layer is created at high temperatures, developing a strong layer with no need for further coating. There is also another method of cold chemical metal blackening of steel, (and other ferrous metals), which is possible with the process working at room temperature without the need for a hot solution.
To apply where corrosion protection is essential, carbon steel must be either painted or galvanized. Galvanizing is done by way of an acid wash and then dipping the steel into a molten zinc bath. The zinc easily makes a protective outside layer upon the steel. Galvanizing also aids in improving the working lifetime of steel parts.
Where it is used
Black carbon steel is often applied to gas or water utility piping, because of its low cost and possible to be welded using common welding methods. A number of long-distance oil pipelines use black carbon steel piping, due to the pipe being easy to connect in the field and its rust resistance. This steel can be utilised in climates or conditions that can accelerate corrosion, but then some extra treatment such as anodes might be necessary.
Some cookware is called black steel, but that dark colouring is actually a product of a special oil treatment called seasoning, not from manufacturing. Carbon steel is often coated with oil to prohibit it from rusting, and steel cookware can be oiled and heated up to absorb oil molecules. The steel will then slightly darken and have some rust-preventive properties, but, this seasoning is only temporary and must be applied again over time.
Whenever you see black carbon steel, you can tell your friends how it was made!