In laymen terms, freezing metal parts to make them stronger. Cryogenic tempering isn't a completely new idea. The freezing of metal in an effort to increase its durability and strength has been practiced for some thirty years within various industries. The tool and die industry regularly uses this approach to temper and extend the life of steel tooling bits. The advent of "deep cryogenics" opens new possibilities, in the case of brake rotors and brake drums.
By cryo-treating a metal part, the molecular structure is made more uniform, more durable and much stronger. Cryogenic tempering changes the areas of weaker, potentially brittle deposits called "austenite" into harder, more uniform particles called "martensite". These particles are responsible for the exceptional wear characteristics imparted by the process, due to a denser molecular structure and a reduction in porosity. In brake rotors, the process allows the rotor to absorb and sustain more heat which is the most common cause of brake failure.
The cryogenic system consists of a special enclosure unit, equipped with state of the art thermal sensors, a computer system utilizing highly specialized software and dewars of liquid nitrogen. The process itself takes approximately 72 hours to complete, any faster and metals may run the possibility of thermal shocking. Metal parts are slowly reduced beyond 300 degrees below zero, where they remain for hours, at which point the enclosure is raised back to room temperature at the same rate it was reduced.
The end results are brakes with unsurpassed rotor and pad life, decreased stopping distances, brake fading and the elimination of uneven transfer layers or sometimes known as “pad-imprinting” or, "warped rotors".
- The A.R.T. system is capable of treating a wide variety of materials ferrous & non-ferrous metals, metallic alloys, carbides, and plastics.
- Soft austenites carbon is changed to hard, more stable, abrasion resistant and higher heat-resistant martensites a supersaturated solid solution of carbon in iron. Martensite is the hardest and strongest of the microconstituents and is formed from austenite during quenching of hardenable steels.
- Cryogenic treatment improves the preferential precipitation of additional very hard, fine eta-carbides throughout the martensitic matrix of the metal.
- The materials’ porosity is reduced, due to a denser molecular structure supported by the additional fine carbides and tight BCT (body-centered tetragonal) lattice structure.
- The objective is to reverse the residual stress across the metal’s cross section via freezing, then heating the metal up, and creating a neutral stress throughout the metal.
- Thermal and mechanical stresses are relieved, reducing the possibility of micro-cracking, fractures and edge chipping, the principal causes of tool failure. Because residual stresses affect the ability of the cutting edge to absorb energy, tools that are stress-relieved by the controlled deep cryogenic process are not only highly abrasion resistant but are also more resistant to residual stresses.
- In the case of steel and steel alloys, the molecular structure of the material is realigned by the reduction of the atoms built-in kinetic energy.
BENEFITS OF CRYOGENIC TREATMENT
- Increased abrasive wear life
- Increased strength and toughness
- Increased corrosive wear life
- Improved impact strength
- Increased fatigue limit
- One time permanent treatment, it lasts the entire life of the tool (refinishings or re-grinds do not affect the permanent improvements)
- Does not cause dimensional changes
- May be applied to new or used components
- Very cost effective, actually saves time and money by decreasing downtime, reducing replacement and maintenance costs and reduces the number of broken parts
- Relieves stresses
- Enhances structural stability
- Enables you to use less expensive stock parts to reap benefits and performance equal to or greater than parts costing over twice as much
- Is compatible with tool or component surface treatments ( TiN, chrome, Teflon, etc.)
- Creates a denser molecular structure resulting in a larger contact surface area which reduces friction, heat and wear
The end results are brakes with unsurpassed rotor and pad life, decreased stopping distance, and the elimination of brake fade and rotor warpage.
A.R.T. believes that cryo-treating and gas port slotting makes their product the best in the market with performance, durability and a good value.
If you would like futher reading on the curent theory of martensite tempering you may find the following papers interesting reading.