QUALITY  

Subzero Treatment

Sub zero also called as cryonegic treatment is modified cooling application and performed for tools which need high wear resistance.
In conventional hardening processes; tools steels are held at austenizing temperature and quenched at suitable quenching media and than cooled down to minimum possible temperature which is room temperature. This allows its structure to change to martensitic microstructure. Martensitic transformation, provides hardness increasing starts at 150-300^o C and does not finish at room temperature in high alloyed tool steels.
After conventional quenching there is retained austenite in microstructure of steel part in high quantity .(for 1.2379 retained austenite %12-20).

The best effective solution of preventing retained austenite is sub zero treatment after classical hardening process.
In subzero treatment pieces are cooled down to -185^oC with vapour of liquid nitrogen and gained super saturated martensitic microstructure. Eta carbides are precipitated in matrix at tempering, after subzero treatment. Depend on removing of retained austenite and precipitation of eta carbide maximum wear resistance is obtained at high alloy tools steels.

Subzero treatment is usually performed at stainless steels for increasing mechanical properties withotut decreasing corrosion resistance and at measuring tools for high dimensional stability.
Apart from industrial applications, subzero treatmens is used for some musical instruments such as trumpet, trambone, electro and acoustic guitar strings. In this application resonance of metal is increased and more dynamic tones are gained with sub zero.

TAMÇELİK has vacuum furnace with patented Schmetz-Cool Plus technology which is integrated system of vacuum hardening furnace and subzero equipment. The best property of this system is that after vacuum hardening subzero treatment can start without deductions.
With Cool-Plus technology uninterrupted subzero treatment can be done and maximum martensitic transformation can be achieved before retained austenite become stable. Absolute metalic bright surface qualities are guaranteed because the parts do not have any contact with the surrounding atmosphere after the sub zero treatment (no surface corrosion).
One of the advantages of sub zero with Cool-Plus technology temperatures directly measured from inside of the pieces and saved in computer.
• High wear resistance
• Depend on steel type 1-3 HRC hardness increase
• High toughness
• Minimum retained austenite
• Minimum dimensional change during service conditions.