Cryogenic Process

The cryogenic treating process creates a denser, more uniform grain structure that allows heat to be dissipated more quickly and uniformly. This tighter molecular structure also increases strength, wear life, and fatigue life.

Cryogenic Treatment or Cryogenic Processing as it is often called modifies the microstructure of metals by subjecting them to ultra-cold temperatures (down to –300ºF).

Cryogenic Treatment as a whole, promotes three transformations in heat-treated steels, cast irons and other metals:

1) More Consistent Crystal/Grain Structure

All steels need to be heat treated after being forged or cast. Heat treating is used to obtain desired characteristics in the steel including the conversion of the “unwanted” austenite crystal/grain structure to the more desired crystal/grain structure called martensite. While it is near impossible to get 100% martensitic crystal structure, all steels have a certain allowable percentage of “retained austenite” or “RA” that was not converted to martensite. It is widely accepted in the heat-treating industry that all heat-treated steels will have some percentage of RA after heat treatment, recipes routinely specify an RA will “not exceed” a certain percentage. Having said this, Cryogenic treatment can help promote the additional transformation of retained austenite into martensite. The additional conversion done through cryogenic treatment helps to further eliminate voids or imperfections in the steel’s microstructure. This is widely accepted and well-documented fact that is evident in X-Ray and SEM (scanning electron microscope) analysis of steels before and after cryogenic treatment.

2) Increased Carbon Structure In Steel

Steel is an alloy made by combining iron and other elements, the most common of being Carbon. By varying the amount of carbon and other elements and how they form in the steel, you can control the qualities of the steel such as the hardness, ductility, and tensile strength. When carbon is used, it’s content in the steel are generally between 0.2% and 2.1% by weight, depending on the grade Steel. The greater the carbon content the harder and stronger the steel will be, i.e. tool steels. So, knowing this, why would you need to do anything with steel? Well, when steels are cryogenically treated, the carbon structure is modified through a mechanism that is technically described as “the precipitation of eta-carbides”. After cryogenic treatment more fine carbides particles are formed, almost filling in where the alloying carbon missed. While it is not fully understood why this occurs, it is undisputed that it does happen and can also be seen through SEM (scanning electron microscope) analysis of steels that are cryogenically treated versus the non-cryogenically treated steel. The population of these eta-carbides – both brilliant ones (white ones) and dark ones (black ones) – is dramatically increased after cryogenic treatment.

3) Stress Relief

All metals – not just steel, (aluminum, copper, cast alloys, etc.) show benefits from the residual stress relief that deep cryogenic treatment promotes. All metals have residual stresses; they are created from the moment the metal “freezes” from its molten form into its solid form. Molten metal freezes – or transforms from its liquid phase to its solid phase – like water or other liquids that we are familiar with. As heat is extracted through cooling, dendrites (or crystals) form from the coolest areas first. Typically, these are the surfaces and edges. This irregular freezing results in natural stress lines where the dendrites collide or along the boundaries of the remaining liquid (molten) metal and the solid metal. After the metal is cast in its raw stock form, (e. g. block, billet, plate, round, etc.), it is heat treated to normalize the material and modify its properties (e.g. hardness, tensile strength, etc.). Once the raw stock is further modified, additional stresses are added (through its machining, cutting, grinding, forging, etc.) by the manufacturing process. When combined, all of these stresses form weak areas that are prone to fail through propagation of the stress lines into cracks. These are often characterized as fatigue failures or more simply “metal fatigue”. Cryogenic Treatment attacks the root cause – the residual stresses – cryogenic treatment greatly reduces or eliminates fatigue failures or cracks in metal components.

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