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METALWORKING EQUIPMENT METALWORKING EQUIPMENT
AND TOOLS AND TOOLS
FEATURES OF HEAT wash off the parts.

In the temperature range 700 - 950 °C,
TREATMENT OF FAST salt is used containing NaCl and Na2CO3, which
also has the property of decarburization. In this
CUTTING STEELS case, the decarburization process can also be
reduced by adding sodium cyanide. This salt is
easily washed off.
The selection of the appropriate Tool steels are rightfully considered one At 500 - 700 °C, you can use a salt
material is only one of the conditions for of the most difficult alloys in connection with containing BaCl2, NaCl and CaCl2. Due to the
the manufacture of high quality tools. the nature of the transformations taking place presence of calcium chloride, this salt strongly
The design, quality of manufacture and in them, the structure and variety of properties, absorbs moisture and is corrosive.
last but not least the surface hardened as well as the conditions of heat treatment. Salts containing saltpeter are used in the
heat treatment have a decisive influence temperature range of 170 - 500 °C. The presence
on the service life of the tool and, therefore, on the production volume. Heat treatment can of NaNO3 in the composition of these salts near
change the structure and properties of the future tool in a wide range. the upper limit of the temperature range makes
FAST CUTTING STEELS them explosive. It is inexpedient to cool steels
High-speed steels (GOST 19265-73) contain 0.7 - 1.5% C, up to 18% W, which is the heated above 950 °C in a salt bath due to its Fig. 1
main alloying element, up to 4.5% Cr, up to 5% Mo, up to 10% Co. The brands designation strong oxidizing effect on steel: the surface
contains the letter R from the word "rapid" - speed, the numbers behind this letter show the condition of the products will deteriorate, and the steel begins to partially melt. These salts are
average content of tungsten (P18, P9, etc.). easily washed off the surface. They are used for cooling and mainly for tempering.
Compared to tool steels that are not characterized by high heat resistance, high-speed However, products from a bath containing more than 10% sodium cyanide salt should not
steels provide high cutting speeds, while the tool life of the cutting edge increases by 10 - 30 be placed directly in a saltpeter salt bath. It is strictly forbidden to mix organic substances and
times. especially cyanide compounds into such baths, since such mixtures are explosive.
High speed steel is used as a tool material for making almost all types of cutting tools. Most of the salts used to heat parts contain various toxic substances.
In addition, high-speed steel is used for a number of parts operating at elevated temperatures If a wear-resistant coating is applied to the surface of the product, then the technological
(rolling bearings, dies, etc.). This is due to the fact that high-speed steel, like no other tool process should provide for the operation of final surface preparation, which includes:
material, combines high physical, mechanical, technological and operational properties. ● preliminary degreasing using highly toxic trichlorethylene or carbon tetrachloride;
The quality of the tool largely depends on the correct choice of steel grade for the respective ● ultrasonic cleaning using soda and sodium phosphate;
cutting tool, taking into account the basic properties of the steel. For example, for tools with ● rinsing in drinking and distilled water;
a simple shape in continuous turning, the service life is limited by secondary hardness, heat ● rinsing in alcohol with acetone.
resistance and wear resistance. For tools with It follows from the above that the technological process of heat treatment in salt baths is
complex shapes, as well as for tools used for extremely complicated, laborious and characterized by high toxicity
interrupted turning, the strength and toughness In addition, the increased heating rate of products in a mixture of salts leads to the
of steel are of great importance. appearance of a high temperature gradient between the surface and the core, which, in turn,
An increase in this or that property is determines a high level of thermal stresses and, as a consequence, deformation of products. The
achieved by changing the chemical composition high heating rate also determines the uneven grain size of the structure during austenitization and
and technology of steel production, as well as subsequent quenching. When processing products
the modes of its heat treatment. in a mixture of salts, it is almost impossible to avoid
The purpose of the heat treatment of tool decarburization and loss of alloying elements in the
steels is to create a structure in steel of a certain surface layers.
composition that provides such physical and The dimensions of the salt bath furnaces are
mechanical properties that are necessary during strictly limited. Therefore, modern heat treatment,
the operation of this tool. in order to avoid the formation of scale and
Heat treatment has a direct impact on the decarburization of large tools, today can no longer
durability of the tool, since the properties of the material from which the tool is made, formed do without vacuum devices for heat treatment, or
during processing, become final. using various gaseous protective media.

HEAT TREATMENT IN SALT BATHS HEAT TREATMENT IN VACUUM FURNACES
The classic heat treatment of tool steels is carried out in salt baths. The advantages of To date, the improvement and automation of
salt baths are manifested not only in fast heating, fast heat transfer, efficient heat removal, vacuum equipment have essentially revolutionized
economy and temperature control, but also in satisfactory protection of the surface from the heat treatment.
harmful effects of dirt. Let's list the main advantages of heat treatment
In the temperature range 1000 - 1350 °C, a salt containing BaCl2 or a salt containing in vacuum compared to traditional processing
BaCl2 and borax is used. The first largely decarburizes steel, and besides, it is difficult to wash Fig. 2 methods:
off parts. The salts are almost neutral, but as the bath becomes more dirty, a decarburization ● high stability of properties of processed parts from batch to batch, from detail to detail;
process can occur. ● lack of decarburized and de-alloyed layer;
Decarburization can be reduced or completely avoided by introducing sodium cyanide ● reduction of deformations;
or neutral (inert) substances (ferro-silicon, silicon carbides, borax). This salt is much easier to ● absence of environmental pollution and improvement of working conditions;

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