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METALWORKING EQUIPMENT METALWORKING EQUIPMENT
AND TOOLS AND TOOLS
tempered. After three times tempering at 560 °C with mode without intermediate removal of the charge from the heating chamber. For example: step
exposure for within an hour, the amount of retained heating → holding → isothermal hardening → triple tempering.
austenite decreases to 2 - 3 % and the expected If necessary, after removing the charge from the furnace, the products can be immediately,
hardness level is 64 - 65 HRC. without surface preparation, placed in the installation for applying hardening coatings.
In heat treatment of high-speed steels, cold Let's highlight the advantages of vacuum heat treatment in comparison with salt baths:
treatment is widely used. The hardened steel is cooled ● absence of environmental pollution;
to temperatures below the end point of the martensitic ● improving the quality of heat treatment due to obtaining high stable properties; more uniform
transformation of this steel, usually from minus 80 heating of products over the section, which reduces thermal stresses and reduces the amount
to minus 100 °C. After cold treatment, to relieve of deformation; slow heating in the range of austenite transformation, which creates conditions
internal stresses, the steel is subjected to a single for increasing the alloying of austenite due to a more complete dissolution of carbides, prevents
tempering at a temperature of 560 °C for an hour. the formation of grain size differences and reduces the upper limit of quenching temperatures;
Cold treatment should be carried out immediately lack of decarburization and de-alloying; obtaining a clean and light surface of products;
after quenching, otherwise the residual austenite will ● reducing the cost of heat treatment by eliminating the costs associated with cleaning and
stabilize and the subsequent transformation process
will be either difficult or impossible.
The austenitic phase in the temperature
range 625 - 350 °C is extremely stable and does
not undergo changes for a long time. Holding during
cooling in this temperature range does not change Austenite
the position of the point of the onset of martensitic Martensite
Ferrite
transformation, and upon subsequent cooling, the Fig. 7 Austenitizing temperature
stability of austenite does not differ from usual. This The temperature of the onset of martensitic transformation
circumstance makes it possible to carry out stepwise The temperature of the end of the martensitic transformation
isothermal hardening. Liquid quenching
The use of isothermal quenching can significantly reduce the geometric changes in parts Step gas quenching
and the possibility of cracking, since during this quenching it is possible to eliminate the previously
occurring thermal stresses by the time of the transformation of austenite, due to uneven cooling
of the products over the section, and the sharp diffusion-free martensitic transformation is
replaced by a slower diffusion transformation into acicular troostite and partly to martensite.
Until relatively recently, these processes could be realized by hardening in salt baths. Fig. 9. Curve of isothermal transformation of austenite.
Today, vacuum technologies are successfully used in the processing of a wide range of materials, rinsing products, as well as preparing the surface for
including the heat treatment of large-sized and cross-sectional dies made of tool steel and applying hardening coatings; energy saving; process
designed to operate at high temperatures. automation; significant improvement in working
Modern control interfaces make it much easier to work with heat treatment equipment. conditions; minimization or complete absence of
Controlling the cooling process of products allows you to control the formation of the the influence of the human factor; greater flexibility
microstructure, increase their reliability and operational resistance. All information about the in operation (the possibility of using equipment for
course of the process and the state of the furnace is displayed on a computer monitor. The various technological processes of heat treatment,
operator has at his disposal information that allows him to quickly influence the course of if necessary, combining the tempering operation
processing, making the necessary adjustments to the technological process. with the application of hardening coatings or, for
By setting the program, you can carry out a full cycle of heat treatment in automatic
example, after quenching by cryogenic treatment
with subsequent tempering).
The importance of vacuum heat treatment
and the equipment required for it is constantly
increasing. High-quality heat treatment of modern
tools is of key importance in the manufacturing
Fig. 10. Operator panel of the vacuum furnace in
operating mode. industry. Today, vacuum gas-pressure furnaces are
not inferior to oil quenching in terms of cooling speed,
making the treatment process environmentally
friendly and cost effective. Vacuum gas-fired furnaces are a significant alternative to most
atmospheric heat treatment and oil quenching technologies.

D. V. Novikov,
thermal equipment specialist of the Finval Group of Companies.

Fig. 8. Microstructure of high-speed steel R6M5 after a full cycle of heat treatment in a vacuum furnace

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