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Cryogenic treatment is an extension of the heating /
quenching/ tempering cycle i.e. Conventional metallurgical practice.
It involves lowering of the temperature of the material of the material with
the help of liquid nitrogen to -320 Degree Farenheight in a patented deep
cryogenic treatment system controlled by a highly sophisticated
microprocessor. This highly controlled thermal; cycle eliminates any
possibility of thermal shocks. The tool life is substantially enhanced by 3
known mechanisms.
a) Cryogenic is the only known process where in a short period of 50-70 Hrs.
There is a conversion of significant amount of retained Austanite to
martensite which is the desirable molecular structure for dimensional
stability to the material.
b) By cooling the material to about -320 degree farenheight and bringing it
back to room temperature the material goes through a tempering process
leading to formation of fine nitrogen carbides (ETA carbides) which enhances
the wear resistance of the material.
c) Cryogenic treatment causes relief of residual stresses i.e., the removal
of stress concentrators which prevent fractures and raises the fracture
resistance and hence wear resistance of the material.
Cryogenic treatment can be applied to all known tools material to increase
wear resistance. DEE TEE recommends that cryo be carried out post heat
treatment before final finishing. Any increase of hardness is for the
optimum benefit in the working of the tool material and will not make the
tool brittle. It works equally well on coated tools.
1) Retained Austenite :
Austenite is a softer grain structure a part of it is always present after
heat treatment. So after the steels are quenched from austenitising
temperature( Hardening Temperature) a position of austenite always remains
untransformed nd is referred as retained austenite. Higher the carbon
content in steel higher is the content of austenite retained after
quenching. By applying cryogenic treatment, retained austenite is
transformed into the harder, more durable grain structure-martensite. The
range of retained austenite in a material after heat treatment maybe as high
as 50% or as low as 3% of the retained austenite is converted martensite. As
greater amount of R.A is transformed, and wear resistant martensite is
increased, the material.
2) Fine Carbide Precipitation :
Fine eta (n) carbide precipitates are formed during the cryogenic treatment.
These are in addition to the larger carbide particles present before
cryogenic treatment. These fine precipitates or fillers along with the
larger particles, form A denser, more coherent and much tougher matrix in
material.
Benefits of cryogenic treatment process :
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Cryogenically treated material shows a marked increase in wear resistance.
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While regrinding, less stock is removed from Cryo treated tools resulting in
longer tool life.
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The most significant change is increased toughness.
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The process is also used extensively to relieve residual stresses
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The Cryo treated material becomes less brittle.
It has been observed at DEE TEE that the hardness of Cryo treated tools
increase by 1-1.5 HRC after cryogenic treatment. DEE TEE recommends
tempering after Cryo
Almost any kind of tool steel or dynamic part, for whatever application,
will exhibit some kind of life increase. As less tools are needed there is
substantial saving in consumption. Additional saving includes less downtime
and less maintenance and changeover time, which brings production cost
lower. Different material show following improvement in tool life, in term
of wear resistence.
Change of entire structure : unlike surface treatments such as plating and
carburizing, Cryo affects the entire structure of the part. A tool is not
affected by subsequent grinding or sharpening. Only one treatment is
necessary for the life of the tool. With the inner structure being stronger,
wear is again reduced as the surface has more support behind it.
Denser Microstructure : Since the molecules pack together tighter, the
surface is more even, the result is a larger contact area at the surface,
reducing friction, heat and wear. The two samples above show this difference
in material density. The treated sample on the right has a much finer and
denser microstructure.
OTHER ARTICLES
NON
DESTRUCTIVE TESTING OF COLD ROLLING MILL ROLLS
SUB ZERO
TREATMENT (Reduction in Retained Austenite)
TUBE CUT OFF KNIVES
TIGHTER
MANUFACTURING TOLERANCE FOR ROTARY
CUTTER,
SLITTING KNIFE AND SPACER.
HINTS & TIPS ON THE APPLICATION OF
SLITTER TOOLING
GUIDELINES
FOR RAW MATERIAL SELECTION FOR SLITTING LINE TOOLING
SHEAR BLADES AND MACHINE KNIVES
PRECAUTION & ORDERING
TIPS FOR FRICTION SAWS
FINS AN IMPORTANT
COMPONENT OF TUBE MAKING
IMPORTANT FACTORS
IN COLD ROLLING MILL ROLLS
DEE TEE FORGES YET AHEAD IN SEARCH OF
EXCELLENCE
SLITTER TOOLING OVER ARM
SEPARATORS |
