Case hardening is a process which involves adding a hard, protective shell to the outside of an otherwise soft steel. This process allows for intricately shaped metals to possess a strength and toughness that they otherwise wouldn't be able to possess.
One of the most sophisticated and common forms of case hardening is carburizing. This is a method which involves introducing steel items to carbon atoms.
Looking to learn a little more about the carburization of steel? Read on! This guide has everything you need to know.
What is Carburization
Carburization is a process which involves taking a low carbon steel and transforming it into a high carbon steel. This is done by exposing it to an atmosphere which is dense in carbon. Generally, items are carburized in furnaces, vats, and other enclosed entities.
By heating a steel item in a carbon-dense atmosphere, said item will allow carbon atoms to attach to its surface on a molecular level. After these carbon atoms have attached to its surface, it will gain both hardness and strength.
One of the most popular forms of case hardening, carburization can provide steel items with varying levels of hardness. Generally, the higher the heat, and the longer the duration of the carburization process, the harder the carburized item will be.
Carburizing Steel - The Processes
There is not just one carburization process available. In fact, generally, there are four different types of carburization used. Each different process offers its own advantages and disadvantages.
The four processes are as follows:
Vacuum Carburization
First, we'll discuss the process of vacuum carburization. In this process, steel alloys are put in an oxygen-free, low-pressure environment. Then, a gas such as hydrocarbon is pumped into the environment, allowing carbon molecules to attach to said alloys.
Because the process is void of oxygen, it makes the oxidation of steel alloys a near impossibility. This allows for high heats to be injected into the contained atmosphere, greatly expediting the carburization process.
This process is performed within a sealed furnace. Unless the furnace can entirely seal off oxygen, it can not carry out the desired process.
Liquid Carburization
Liquid carburization is a form of carburization which takes place in a sort of liquid vat. This vat is filled with a mixture of substances, typically including cyanide and salt.
While metal alloy items are being submerged in this concoction, they come into contact with a collection of carbon molecules. Generally, these carbon molecules will diffuse into the alloyed items in a rapid manner, allowing for a hard case to form in just a short time.
Steels which have been liquid carburized typically possess high levels of carbon and low levels of nitrogen.
Pack Carburization
Pack carburization is a process which involves placing steel items into a furnace in close proximity to high-carbon items. These high-carbon items include everything from carbon powder, to cast iron particles, and more.
After you've inserted these items, they will be heated with the use of carbon monoxide. This gas is a reducer of carbon, causing carbon to pull from the surface of the carbon-dense items which were placed in the furnace. After these carbon molecules are no longer attached, they will diffuse into the surfaces of the steel items which are to be carburized.
This is the easiest of the carburization methods to pull off. In fact, you might even be able to pull it off in a garage or home workshop.
The problem with it is that it's unreliable and inconsistent. While it will allow for carbon diffusion, this diffusion typically won't occur uniformly across an entire steel item.
Gas Carburization
The last carburization method we'll discuss is gas carburization. Gas carburization shares similarities with pack carburization, necessitating the pumping of carbon monoxide. The difference is that it doesn't necessitate the presence of carbon-dense items.
In this process, carbon monoxide is continuously pumped into an enclosed environment. This environment is heated at extremely high temperatures. High temperatures allow carbon molecules to diffuse into the steel items which are being hard cased.
One of the most popular carburization processes in the world, it consistently produces a uniformly-carburized steel. This makes it very useful for mass carburization purposes.
Benefits of Carburized Steel
There are a variety of benefits which come with carburized steel. Below, we'll review these benefits at length.
Very Hard Exterior
It's simple: steel which has been carburized will have a very hard exterior. This allows it to take on a great deal of physical trauma without wearing down prematurely.
While there are steels out there with harder surfaces than carburized steel, they're not as malleable or affordable. In essence, they don't provide the coveted combination of soft interior and hard exterior that carburized steel offers.
Soft Interior
Another major benefit of carburized steel is that it possesses a soft interior. Because it possesses a soft interior, it's easy to manipulate into different shapes. This makes it especially useful for when you're trying to manufacture intricate metal items with hard surfaces (ie. internal machine components).
Some uncarburized steel alloys provide natural surface hardness. However, they don't provide the internal softness needed to be intricately shaped and formed. In essence, they don't provide the coveted combination of soft interior and hard exterior which is provided by carburized steel.
Relatively Inexpensive
If you're buying a steel alloy simply for its surface hardness, carburized steel is easily the most affordable option. The carburization process is much cheaper than the production of certain steel alloys.
Trying to manufacture hard steel products on a mass scale? Carburization is the most cost-effective option.
Benefit from the Magic of Carburizing
Do you have a need for carburized items? Looking to benefit from the magic of carburizing? If so, we here at Miheu are the people to see.
We are highly experienced in the carburization of a number of different items. These items include automotive components (axles, shafts, gears, etc.), machine parts (counter knives, clamps, flanges, etc.), stamped entities, and much more.
Contact us today to discuss your carburization needs!