Many cases are reported where a certain amount of the residual austenite, often a very considerable amount, still remains in the structure of hardened steel. in most cases this residual austenite is considered an undesirable phenomenon, for the following reasons:
- As the austenite is much less hard than martensite, the hardness of hardened steel containing residual austenite is well below the maximum
- As has been just pointed out, the residual austenite brings about a gradual, spontaneous change in dimensions of articles treated
- As the austenite is non-magnetic, its presence in steel magnets decreases the magnetic induction and, consequently, the lifting power of magnets.
- The residual austenite remains in the steel structure because for steels the austenite completes its transformation into martensite at temperatures well below zero. this suggests a simple method of removing residual austenite from the structure of hardened steel, consisting of cooling it to a temperature well below zero, i.e., of subjecting it to the sub-zero treatment. this is the method proposed by Professor A.P. Gulyaev in 1937.
Advantages of the cryogenic treatment
- It makes the process of machining a smoother and easier process.
- Cryogenic treatment results in increasing the electrical properties of the material.
- It also helps to reduce the resistance of the metal.
Following are the applications of cryogenic hardening:
- In the Automotive industry: cryogenic hardening is mostly used in the case of applications related to the automotive industry.
- Applications in the mechanical industry: It includes different motors, pumps, washers as well as small bolts. It is mostly used in the cutting tools industry for manufacturing cutters, blades, knives, etc.
- Cryogenic hardening is also found its use in the Aerospace and defence sector. It is used in landing systems and control systems.