When people think of cryogenics, their minds go toward the various medical procedures that use extreme cold, such as those used for cancer treatments or wart removals. However, these aren't the only situations where the extreme cold can produce amazing results.
One of the lesser known uses of cryogenic treatments relates to metal hardening. It can improve the strength of certain metals while enhancing the overall grain structure. But why would someone want to use such a complex process on metal parts? The simple answer is for increased performance.
Increased Durability
While most people are generally aware of different kinds of steel, they don't always know the benefits of each and how more favorable results can be obtained. Cryogenic hardening can help transform the austenite found in traditional heat-treated steel into martensite, a more hardened variant. That means you will have a metal with fewer imperfections and with a greater overall strength.
Improved Resistance to Wear
Cryogenically hardened steel is also more resistant to the damage caused by traditional wear and tear. The process increases the creation of eta-carbides which help bind the martensite matrix more effectively. Since the matrix is better formed, it resists traditional wear as well as corrosion.
Less Residual Stress
When metals go from a liquid state to a solid state, weak areas often develop within the structure. These weak points increase the likelihood of failure due to the imperfect structure. Cryogenic treatments help create a more uniform grain structure, lowering the number of weak points in the structure and decreasing the chance of failure when the metal is put under physical stress.
Uses for Cryogenically Hardened Parts
Metals that are cryogenically hardened can be used for more strenuous tasks with less associated risk than their untreated counterparts. This makes them ideal for systems under a significant amount of strain as well as notable heat variations.
One example is the use of cryogenically treated metals in performance engines. Treated metals often have increased efficiency while in use, and generally experience less friction than parts that were created more traditionally. Stress points are corrected, limiting the risk of cracking and failure, and allowing the entire system to work more reliably even under extreme circumstances.
How the Process is Done
Cryogenic treatments involve repeatedly cooling and heating the metals to specific points. Businesses that offer the service often set their own temperature range, so you can see a variance in the standards from one company to the next.
The temperature shifts are extreme regardless of the service chosen. For example, one company may slowly cool the metal to -350 degrees F before raising it back up to over 300 degrees F. The cycle is repeated multiple times, and each part of the cycle can around 12 hours depending on the target temperatures.
When engine components are treated, each piece must be managed separately. Then, after all of the cryogenic treatments have been completed, the engine is assembled. That means an ideal business offering the service will be able to complete the treatments effectively while also disassembling and reassembling the parts are needed.
The process changes the structure of all of the metal in the parts, and not just those areas closer to the surface. That means you get to experience the benefits of increased durability and improved wear throughout the whole of the piece. If grinding is required to achieve an ideal fit, you do not run the risk of grinding away the treated area, as all of the metal is in the same state.
Treatable Metals
Various forms of steel can be cryogenically treated. This includes high carbon, high chromium, and tool steels. The process can also be used on aluminum, copper alloys, cast iron, and magnesium.