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INTRODUCTION
 Cryogenic treatment is methodology of ultra-low temperature processing of materials to enhance their properties to the desired levels. The precise cryogenic treatment cycle consists of three phases of descent, soak & ascend.
 Cryogenic tempering is the extreme cold to re-define the molecular structure in metals. Material subjected to deep cryogenic temperature develop a more uniform, redefined microstructure with greater density.
• Austenite, the softer molecules in the microstructure is transformed to harder Martensite. Maintaining deep cryogenic temperatures over an extended period of time, allow for the formation of binders.
• In Cryogenic treatment, the material is subjected to deep freeze temperature [-196 c] the Austenite is unstable in this temp and whole structure become Martensite.
• The soft retained Austenite structure of the metal is almost completely converted to tougher Martensite.
• Many small carbide particles are developed that fit between the existing larger carbon particles. The molecular structure of the materials is streamlined-smoothened while dimensions are not changed.
BENEFITS OF CRYOGENIC TREATMENT
Cryogenic treatment at -196 degree centigrade as reported results in following benefits:
1- Increased abrasive wear life in cutting tools, moulds, dies, bearings etc. increases tensile strength toughness and stability coupled with release of internal stress.
2- High corrosive resistance in chemical, food and oil equipment applications.
3- High erosive resistance to wind, water and other abrasive grit carriers.
4- Relieves stresses in complex tools, components and welds.
5- Relieves stress cracking in weld zones in corrosive atmosphere.
6- Improves surface finish in application where long life is needed.
7- Stabilizes the components, improves the machinability of aluminum and copper.
8- Increases electrode life in copper resistance welding.
9- Ideal for new or used tool and components.
10- One time permanent treatment, which lasts for entire life of the tool (refinishing or grinding does not effect the permanent improvement).
11- No dimensional changes.
12- Very cost effective, saving time and money by decreasing downtime, reducing replacement and maintaince costs through lower inventory control.
13- Enhances structure stability, compatible with tool or component surface treatments.
14- Creates denser structure resulting in larger surface area, which reduces friction, heat and wear.
INDUSTRIAL APPLICATIONS
1- Cryogenic processing makes parts tougher and uniform. But less brittle. As a result cutting tools, gears, chains, chains, bushings, welding tips, pump parts, cutters etc. will last two to five times longer.
2- Welding tips will last longer and require less electricity.
3- Light bulbs have shown a 75% drop in resistance, 40% brighter light and longer life because of the positive effects on the filament.
4- Spark plugs have demonstrated a 12.5% increased performance with a resulting fleet mileage improvement of 0.2-0.7 km/ltr . While this might not seem like much, it must be borne in mind that the mileage got from most commercial vehicles is about 4 km/ltr.
EXPERIMENTAL DETAILS
TEST CASTINGS
Standard cylindrical castings of (300 mm diameter x 260 mm length) were produced in carbon dioxide sand moulds. Test samples were cut from the castings machined and used for evaluating the properties.
MELTING AND POURING
Melting of charge was carried out using 1.25 tones capacity induction furnace, charge consisting of grey cast iron, pig iron returns (low sulphor content), mild steel scrap in the from of punching, runner and riser portions of ductile iron were melted in the furnace.
standard sandwich method of treatment was employed to get ductile iron castings. The final composition of the melt was aimed at 4.2 to 4.6% carbon equivalent according to IS400/12 specifications. The castings were allowed to solidify and after cooling they were taken out from the mould and used for preparing test specimens for different studies.
CRYOGENIC TREATMENT
The test specimens for various tests were machined from the best bars. These specimens were then subjected to cryogenic treatment. Liquid nitrogen was taken in a thermo Cole container of 5 liters capacity. The test specimens were completely immersed in liquid nitrogen for 24 hours. Liquid nitrogen was filled periodically into the container to compensate for evaporation.
TESTINGS
The test specimens were subjected to standard mechanical test such as tensile test, hardness test and impact test. Further, wear studies were conducted on dry sliding wear testing machine at a speed of 950 rpm and two loads of 750 gms and 1000 gms.
WEAR CHARACTERSTICS:
Fig-5 & Fig-6 shows the variation of displacement with for ductile iron & cryogenic treated ductile iron for loads of 750 gms & 1000 gms and at a speed of 950 rpm. A study of the fig. indicates that the displacement increases with increase in time.
The displacement value at a time of 500 secs, at 750 gms load. The fig. indicates displacement values shown by cryogenic treated ductile iron is less compared to as-cast ductile iron specimens which indicates that there is an improvement in wear resistance of ductile iron upon cryogenic treatment. A similar trend is observed at a load of 1000 gms also as shown in fig-8.
CONCLUSION
From the present study, it can be concluded that cryogenic treatment of ductile iron results in the improvement of tensile strength, hardness, and wear resistance. However, there is slight decrease in percentage elongation and impact strength values. Thus cryogenic treatment can be considered for industrial component which require strengths and wear resistance.