In this article we will discuss about:- 1. Meaning of Deep Cryogenic Process 2. Advantages of Cryo Treated Tools 3. Cryogenics Technology for Quality Improvement and Cost Reduction 4. Metallurgy and Mechanics.
Meaning of Deep Cryogenic Process:
Deep Cryogenic process is a process of cold (dry thermal) treatment at – 185°C. It is controlled very precisely. It is used in fields of super conductors, cryomicrobiology and space applications.
Cryo temperatures (- 185°C) are required to effect a complete molecular change in most alloy steels, making all the retained austenite turn to martensite, a denser refined mix, smaller and more uniform than austenite. Deep Cryo processing physically transforms the micro structure into new, more refined uniform micro structure which is stronger. This process will also thermally stress relieve partly.
It is observed that the number of countable small carbides increase throughout a heat treatable steel from 33,000 per sq. millimeter to over 80,000 per sq. millimeter as a result of cryo processing. The increase in carbides adds greatly to the wear resistance of parts.
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The carbides make a refined flat “Super Hard” surface on the metal. A refined surface structure is not only more wear resistant but also results in reduced friction and heat thus allowing more rapid movement and more horsepower.
In Cryo process, a computer acts as a process controller to operate descent, soak and ascent modes. The materials are cooled slowly to – 185°C. The dry process prevents metals being subjected to Liquid Nitrogen and eliminates risk of thermal shock.
Advantages of Cryo Treated Tools:
i. Cryo process is different from all types of surface treatment coatings, in that in cryo, a permanent, irreversible change is imparted, completely, through and through the metal structure. Coatings are applied from the outside-in, adding internal energy. Cryo treatment from the inside-out, internal energy is removed.
ii. Coatings are only few microns thick on the surface, whereas the entire mass is treated in Cryo Treatment.
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Cryo treated tools can be reground 6 to 60 times.
Cryogenics Technology for Quality Improvement and Cost Reduction:
Cryogenics finds place in production treatment to produce super high-strength steels, better machine ability, greater corrosion resistance, greater impact resistance and lower stress corrosion. This process is also used to relieve residual stresses and improve dimensional stability.
Several establishments are using this proprietary cryogenic process to effect dramatic changes in the characteristics of metals and non-metals. The technology revolves around a sophisticated processor and a time temperature software. The software contains several ramp and soak phases, each phase catering to certain specific characteristic changes in the material, resulting in drastically improved performance and longer useful life for both metal and non-metal products.
The process is now used for the treatment of a variety of components, made of steel, copper, super alloys, titanium, powder metal parts, cast or forged. The entire spectrum of the engineering industry including tools and dies significantly benefit from this technology.
Metallurgy and Mechanics:
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This one time treatment, tinkers with materials at the molecular level resulting in homogeneity of the crystal structure, highly refined grain structure (new ultra-fine carbide particles are formed which are uniformly dispersed throughout the material matrix), while dissolving all gaps and dislocations, improving structural compactness and impact strength.
Cryogenic processing also reduces deformation (resulting in less removal of material during tool redressing), prevents concentrated heat-built-up, increases hot hardness and toughness.
Several materials like 316 SS, 410 SS, 4142 CR-MO STEEL, S-2, M-1 tool steel show improved corrosion resistance between 30 per cent and 80 per cent in highly corrosive environment of H2S at two atmospheres. Further all retained austenite is converted to a fine martensite matrix. This martensite formation and the fine carbide formation work together to reduce abrasive wear by several magnitudes. The uniformity in the material matrix makes it a process of great significance altering the conventional thinking on improving materials.
The additional fine carbide particles help support the fine martensite matrix, thus making it very difficult to dig out lumps of the material, resulting in greatly reduced wear rate. Unlike in other material processes, micro hardness profile across any cross-reaction of a cryo-treated component is a near straight line.
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This process is also used to relieve residual stresses and improve dimensional stability. This helps close tolerance machining (with high quality finish).
This process advantages affect every sphere of our engineering industry extending from copper electrodes to compact disks. Infact, treated copper electrodes serve 400 percent longer, milling tools, drill bits, piston rings exhibit 100 to 1,200 per cent increase in service life. Dies often outlast non-treated ones by two to eight times.
Cryo-treated automobile engine components exhibit 50 to 200 per cent increase in service life. Ball and roller bearings show 200 to 700 per cent improvement in load and wear characteristics. Treated musical strings and compact disks exhibit deeper resonance.
Broaches average 300 to 550 per cent increase in life. Cryognic treatment of cobalt end mills showed 26 times the wear life as against untreated ones. Cryogenically treated carbide tools’ performance increased by 400 per cent.