Cryogenic
treatment refers to process the blank at -190℃-230℃, which
has a broad application prospect, such as non-ferrous metal, ferrous metal,
metal alloy, carbide, plastic, silicate and so on. The basic principle is that
in the process of metal hardened to cooling by heat treatment, which produces
alloy and carbon dissolved and combined with the formation of austenite(Austenitic
is a lamellar microstructure, usually ɣ-Fe solid solution in a
small amount of non-magnetic solid solution of carbon) and diffusion; in the
cooling process, since the low temperature produce suppress the formation of
martensite(The crystal structure of martensite is body-centered tetragonal
(BCT). High carbon steel is usually accelerated cooling to obtain such
organizations and high strength and hardness of steel is one of the main
features of martensite.), the final transition point (Mf) is definitely low.
Austenite
is very unstable and easily decomposes at low temperature, so the original
defects (pores and internal stress concentration part) and becomes plastic flow
structure refinement. Therefore, as long as put the metal at ultra-low
temperature, the austenite is converted into martensite, which eliminates the
internal stress. In addition, due to the contraction of the tissue volume at
ultra-low temperature, Fe lattice constant decreases and
the driving force to strengthen the precipitation of carbon atoms, so a lot of
martensitic matrix deposited ultrafine carbides. The strength of these
ultra-fine crystalline materials will improve and increase the wear resistance
and rigidity. And Ultra-low temperature can also be transferred metal atom
transport capacity, which makes the atoms can not be separated and become
closer.
There are some experiments shows that high-pressure
vessel after cryogenic treatment can meet the requirements of the strength of solid
propellant rocket; some down-hole equipment for sour oil field after cryogenic
treatment can improve the corrosion resistance and the welding cracks; some
parts of the alloy cryogenic treatment, volume stability, dimensional stability
and strength has been greatly improved.
At
present, cryogenic treatment mainly applied in tool steel, non-ferrous metal
applications under development step, here we discuss that the tungsten copper
contacts cryogenic treatment process conditions affect its properties. Tungsten
copper contact is a psudoalloy, which is composed of two kinds of immiscible
and has a great difference in physical and chemical properties metals. There is
no phase change in the reaction and it is brittle so that it is difficult to
adapt conventional heat treatment hardening process to improve its relative
performance. Cryogenic treatment is undoubtedly an ideal choice.
Viewed
from the micro-structure, after cryogenic treatment, W matrix disperse a large
number of Cu phase and the organization has significantly refined, which is due
to precipitation of Cu solute in W after cryogenic treatment. In addition, it
also can be found that with the increase in the copper content, the segregation
phenomenon is also becoming increasing apparently. Copper particles dispersed
precipitated tissue thinning, and atomic displacement volume shrinkage,
tungsten copper contact density and overall strength has also improved.
While its hardness and strength has greatly improved
after cryogenic treatment, and electrical conductivity with increasing tungsten
content decreases. This is due to cryogenic treatment makes a lot of
precipitated Cu and W form a solid solution, and is proportional to the
electrical conductivity of tungsten copper contacts with the copper content. Overall,
tungsten copper contacts after cryogenic treatment, may be little alternative
to tungsten copper copper-tungsten less, not only improves performance, but
also reduce costs.
If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.
