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METALWORKING EQUIPMENT METALWORKING EQUIPMENT
AND TOOLS AND TOOLS
the amount of deformation of the products,
providing optimal conditions for
structural transformations.
Due to the use of the most modern
insulating materials for heating elements, the
processing process is characterized by high
temperature uniformity and stability
Convective heating is used in the working
chamber, which also has a qualitative effect
on the uniformity and homogeneousness of
heating. Heated gas the flow passing through
the cage gives off heat to it and ensures fast
and at the same time uniform heating at

Fig. 3 low temperatures. In vacuum furnaces with
convection heating and a multipurpose gas
● simplification of control and management of the technological process; cooling system, additional thermoelements
● high traceability of process parameters. are used, located at critical points of the
There is one significant drawback - high capital investment in the purchase and putting charge to provide automatic cooling control
the vacuum equipment into operation. Fig. 5. Structure of the tool area with strong decarburization by equalizing the temperature across the
At present, heat treatment of high-speed steel tools is carried out mainly in single-chamber surface layer and a pronounced uneven grain size (light section before martensitic transformation.
horizontal vacuum furnaces with quenching in an inert gas flow, including under excess pressure. area).. Let's point out the advantages of
The most popular among small and medium-sized enterprises of the machine-building convection heating over heating without convection:
complex are the designs of single-chamber furnaces, in which it is possible to carry out a full ● 30 % increase in charge heating rate in the temperature range 20 - 800 °C, which allows to
cycle of heat treatment in automatic mode without intermediate removal of the charge from shorten the heat treatment cycle and save energy;
the working chamber. These are vacuum ovens with convection heating and high pressure gas ● reduction of about 50 % of the time of heat treatment of products made of high-speed and
cooling. stamping steels;
Heat treatment in vacuum completely ● reducing the temperature gradient between the surface of the product and the core;
protects the surface of the product from oxidation ● reduction of the formation of cracks, which is associated with the uniformity of heating of the
and decarburization and causes degassing of product over the section and a decrease in the level of thermal stresses;
the charge. Before starting preheating and ● the ability to load a cage with a minimum distance between parts;
austenitizing, it is advisable to evacuate the ● possibility of carrying out a full cycle of heat treatment of products without unloading the
charge with parts to 10-4 - 10-5 mbar, this
will remove oxide films and protect surface of charge from the furnace.
workpieces. When austenitizing, a high vacuum The correct formation of the cage plays an
is not recommended, as this can facilitate important role in the final result. Thin-walled, non-rigid
the evaporation of individual components. parts, which are highly susceptible to uneven heating
The vapor partial pressure of the individual and cooling, should be properly positioned in the oven
components is significant when heat treated in cavity. Avoid placing such parts in close proximity to
the normal temperature range. Vapor pressure heating elements and cooling nozzles. At the same
of components such as Mn, Cr, Co, at 1000 °C time, vertical arrangement of parts is preferable. The
is 10-2 - 10-4 mbar, which coincides with the best effect is achieved by hanging the details, but this
values of the pressure of vacuum devices used solution is not always acceptable
in practice. In such conditions, one has to reckon The conditions for austenitizing in a vacuum
Fig. 4 single-cell furnace with the possibility of evaporation of individual furnace are different from those for austenitizing in salt
components or at higher temperatures maintain a vacuum in the range of 10-1 - 10-0 m bar. baths. Slow and uniform heating in vacuum furnaces
During heat treatment in vacuum furnaces, the cleanliness of the parts must be very creates favorable conditions for a more complete
strictly observed. Before heat treatment, parts should be thoroughly cleaned of dirt. So, for dissolution of primary carbides and an increase in the
example, 1 mg of oil contaminants at room temperature and 10-5 mbar turns into 14 m3 of alloying of austenite, while the upper limit of quenching
oil vapor, which must be removed from the vacuum space. The presence of water and other temperatures can be lowered by 20 - 30 °C and the Fig. 6
impurities (adhered particles of aluminum, plastics, acid residues) is also very harmful - they grain size in the structure can be reduced by 15 – 20 %
can cause significant harm. high speed steel versus heating in a salt bath. The duration of austenitizing in vacuum furnaces,
In compression vacuum furnaces, it is possible to heat products in a vacuum, and quench as a rule, does not exceed 25 minutes, depending on on the cross-section and packing density of
in an inert gas atmosphere under excess pressure, which allows: the cage (the exposure is selected at the rate of 40 - 60 seconds per 1 mm of the cross-section).
● to expand the possibilities of using vacuum equipment for heat treatment of products made In the case when the tool is heated in the fixtures, the time is increased by 15 – 20 %. The
of less alloyed steels; microstructure of hardened high speed steel consists of martensite, retained austenite (up to
● by quenching in an inert gas under pressure, to provide a clean, non-oxidized surface of 30 %) and a large amount primary carbides. The amount of retained austenite and the position
products, which in turn makes it possible to apply protective and hardening coatings without of the start and end points of the martensitic transformation depend on the temperature before
preliminary surface preparation; quenching.
● by changing the pressure, automatically regulate the cooling rate of the charge, reducing Retained austenite sharply deteriorates the cutting properties, so the hardened tool is

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