Advantages

The purpose of DCT on steel alloys is to transform retained austenite and raise the hardness of the as-quenched structure. Austenite (essentially a soft form of iron) is a solid solution of carbon and iron that is formed during the quenching phase of heat treatment. Austenite is weak and undesirable because it contains less crystalline interfaces to help hold the metal together. When carbon steels are cryogenically treated, the austenite structure is transformed slowly into a highly organized grain structure called martensite, which is a body centered tetragonal crystal structure. Martensite is a finer and harder material that brings very desirable high wear resistance to carbon steels. There could be up to 40% residual austenite in heat-treated ferrous metals. That percentage can be lowered to as little as 1% in some cases with deep cryogenic treatment. Martensite is also formed during the quenching phase of heat treatment. There is always a certain amount of martensite present, but prior to cryogenic treatment, the ratio of strong martensite to weak austenite is always less than favorable. This untransformed austenite is brittle and lacks dimensional stability, which permits the metal to deform (break/crack/fracture) more easily under load. To eliminate austenite, the quenching temperature must be lowered. At extremely low temperatures, austenite is unstable and readily transitions into martensite. The result is a significantly improved part or tool with no cracking, warping, or other cryogenically imposed defects. Improvement in durability can be more than 100%. Another advantage of deep cryogenic treatment is the increased efficiency in dissipating heat. This means gears, engines, transmissions, and disc brakes all run cooler, and cutting tools last longer.

Improved dimensional stability is also achieved. This is especially important for progressive dies where cumulative tolerances are critical. Subzero treatments have as their ultimate goal an increase in wear resistance, improved bending fatigue life, and minimization of residual stress. Residual stress within a part can reduce that part’s overall performance. This is a direct result of the nonuniform nature of such stress. Stress boundary areas are susceptible to micro cracking which leads to fatigue and eventual failure. Residual stress is created during manufacturing operations. These can be amplified by sequential operations required to produce a finished part.

Benefits of Deep Cryogenic Treatment (DCT):

• Increase resistance to abrasive wear
• Achieved throughout the entire part by just one permanent treatment
• Converts the grain structure of the entire part - not just the exterior surfaces
• Refinishing or regrinds do not affect the permanent improvements
• Transforms most retained austenite to hard martensite
• Forms micro-fine carbide fillers to enhance carbide structures
• Increases durability and extends life
• Decreases residual stress in all alloys
• Decreases brittleness
• Increases tensile strength, toughness, and dimensional stability
• Works on new or used tools/parts/components
• Treated parts can reduce downtime, require less maintenance, reduce defects, and increase productivity
• Deep cryogenic processing is compatible with other surface treatments (TiN, Chrome, Teflon, etc.) Note that these coatings are only on the surface of the part. Coatings wear out and their bond to the base material can be weakened over time
• Alloy steel cutting tools stay sharper longer, exhibit fewer micro-cracks, and have less chipping – without the need for performance coatings
• Deep cryogenic processing results in the orderly arrangement of crystals, increases internal bonding energy, and achieves a structural balance throughout the mass of the material

The grain structure changes in cryo treated materials were very significant.
Results of microanalysis were:

• 50%-75% decrease in grain size in treated specimens
• Much more uniform distribution of carbon
• Alleviation of grain boundaries