Many techniques are used to increase the hardness or strength of a metal or alloy. First, measuring the elements is important to select the right metal. Additionally, you need to know that some metals are hardened, including low-carbon steel, cast iron, high-carbon steel, and high-strength low-alloy steel.
It is very important to learn about the outer surface of the metal as this surface is subject to the most abrasion and direct impact. For some metals, surface hardness is adjusted to ensure that the toughness of a metal or alloy substrate is sufficient through a process called hardening.
What is case hardening?
Case hardening is also called “surface hardening”. It is a heat treatment process that makes the surface layer of a metal part hard, while the interior of the part remains comparatively soft.
For low-carbon iron or steel, hardening usually involves introducing additional carbon or nitrogen to the surfaces.
Hardened parts are ideal for parts that are in constant contact with hard or abrasive parts, as hardened parts are more resistant to wear and are generally stronger than parts that have gone through the “full hardening” process, such as the inner core. of the hardened part is soft and therefore can withstand more tension without tearing. Layer hardening involves using lower temperatures to deform even various metals, such as a thin layer of steel, during production.
Types of Hardening Methods
Heating and quenching
There are three common case hardening processes. The first “heating and quenching” is also called flame or induction hardening. As the name suggests, this metal case hardening process involves flame or heat, where a high carbon steel part is heated to an extreme temperature by an oxygen gas flame or by induction heating. The heated piece of carbon steel is then quickly cooled by a coolant (usually water). Only steel or iron with sufficient carbon content can achieve good results with this flame hardening. The carbon content should be 0.3-0.6% C by weight. For steel or iron materials with lower carbon content, there are other processes such as nitriding and carburizing.
Nitriding
Nitriding is another form of hardening technique in which steel parts are heated in an ammonia and ammonia environment to a range of 484-621°C. The depth of the hardened surface depends on how long the steel parts remained in the ammonia environment. This method requires the use of elements such as chromium, molybdenum and aluminum to form nitrides that harden steel parts.
Carburization
For steel parts containing carbon in the range of 0.1 to 0.3% by weight, the surface hardening technique of carburizing is a good option. In this process, steel parts are placed in a carbon-enriched atmosphere and heated to 9,000°C for a set period of time. The steel is then tempered so that the carbon is trapped in the steel parts. Carburized steel can be re-hardened by flame or induction because carburized steel parts have sufficient carbon content to be re-hardened.
Advantages of hardening
First, the steel part becomes significantly more wear-resistant because hardening significantly improves the hardness of hardened metals, while the core of the steel part remains comparatively soft and flexible. By obtaining a softer core, the piece is able to absorb and relieve stress. Typically, you save money in the long run because you can use the item longer and don't have to buy it as often.
Secondly, hardening makes steel parts easier to machine. It is well known that steel parts are difficult to machine. For parts that require extreme hardness, the ideal method is to machine a mild steel material and then harden the part to the desired hardness.
Third, a hardened part is easier to weld than a non-hardened part.
This process is beneficial for objects that require a tough outer layer to resist wear and tear, but must remain soft on the inside to absorb shock. Below are some benefits of hardening.
How to remove the oxide layer from hardened parts
After the hardening process, the steel part has a black, uneven layer of oxidation, which many people find irritating but acceptable. However, we know a customer who really cares about the aesthetics of a tempered steel piece.
As you can see from the parts in the photos above, one is a part we made from stainless steel. The piece has not undergone any treatment such as hardening and has a shiny, steel-like appearance, with some CNC tool marks visible on the surface. The piece below is also a stainless steel piece. The only difference is that the bottom part has been hardened (to 55 HRC). The black layer of oxidation on the surface of the part is unevenly distributed: it looks like black spots have been spread on the surface. The stainless steel was stained by the steel.
Polishing processes
The most obvious solution would be to polish the oxidation layer. However, polishing is quite expensive for steel even if only a prototype is made. As many people know, metal parts are very difficult to polish. Additionally, some areas, such as small dents and grooves, cannot be reached during polishing.
Hardening of parts in vacuum
Hardening the steel part in a vacuum environment can be an ideal way to prevent black oxidation. Because for oxidation to occur, oxygen must be present. If there is no oxygen present, oxidation does not occur.
The steel part in the example above has been vacuum hardened. After the hardening process, no surface treatments or post-treatments were carried out. The piece has a natural surface. The only disadvantage of this hardening process may be its high cost. If you just want to make a prototype, it will probably be very difficult to find a supplier who can do this.
Glass bead blasting
If you still want a more uniform finish than in the photo, we recommend fine sandblasting (the beads are made of glass). Bead blasting is very common and very inexpensive. You can find sandblasted parts everywhere: keyboards, the back of your cell phone, stands…
First hardening, then machining
Perhaps the best method for removing black oxidation is to first harden the material using the traditional quenching process and then grind off the oxidation while machining the part with CNC machines, rather than first machining the part with the CNC machine and then hardening it using a conventional machine. process. (CNC machining is a subtraction process, that is, a process in which the desired part is produced by grinding the unwanted material from a block material.)
There are no additional costs for the process and no oxidation layers form, even in areas of very small grooves or dents.
The limitation of this process would be the hardness of the hardened part. This method will not work if the steel material has been hardened to a value of HRC60, which is very hard and the CNC router would likely not be able to cut the hardened steel without breaking. Unhardened steel materials are difficult to machine, let alone harden.
Subsequent curing application
These forms of post-hardening increase strength and wear resistance by diffusing carbon into the surface of steel components using various approaches. Furthermore, several manufacturing companies apply hardening processes even to low carbon steel parts after machining.
University Degree
Case hardening is a common heat treatment process. Nitriding, carburizing, and heating and quenching are three typical types of hardening. To remove the oxidation layer from hardened steel, the steel can be polished, sandblasted, vacuum hardened, and first hardened and then post-hardened. During hardening technology, the steel is given a controlled but critical temperature. However, elevated temperatures are generally possible depending on the material and the cooling process.
