Many cases are reported where a certain amount of the residual austenite, often a very considerable amount, still remains in the structure of a hardened steel. in most cases this residual austenite is considered as an undesirable phenomenon, for the following reasons:

• As the austenite is much less hard than martensite, the hardness of a 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 many 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 a 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 an 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 the cryogenic hardening:

• In Automotive industry: cryogenic hardening is mostly used in case of the applications related to automotive industry.
• Applications in the mechanical industry: It includes different motors, pumps, washers as well as small bolts.It is mostly used in cutting tools industry for manufacturing cutters, blades, knives, etc.
• Cryogenic hardening is also find its use in the Aerospace and defense sector. It is used in landing systems and controlling systems.