Modes and tools for turning hardened steel

Properties of hardened metals

Hardening of metals is a procedure for processing a material at high temperatures to a certain limit and further cooling. During the hardening process, a phase transformation occurs from austenite to martensite. After hardening, the mechanical properties of steels change: strength and hardness increase, while brittleness also increases and ductility decreases. To reduce brittleness and improve ductility, I subject the steel to temper annealing.

Hardened steel can be processed using different methods:

turning;
milling;
drilling;
grinding.

But, for any type of processing, cutting modes should be chosen correctly, since due to thermal effects, the fragility of the metal increases. In addition, it quickly accumulates heat at the cutting site, which leads to material sticking to the turning tool and its rapid wear.

Steel turning

Temperature of critical points of steel 45

As previously noted, to improve the performance properties of the metal, heat treatment is carried out. It involves exerting a certain influence on the structure, after which the crystal lattice is rearranged and the qualities change. When carrying out heat treatment, critical points are often taken into account. Processing of steel St 45 is carried out taking into account the following factors:

Temperature conditions. It is important to choose the right temperature, since too low will cause incomplete heating of the structure and complete restructuring of the structure will not occur. Too high an indicator causes overheating of the metal, as well as the appearance of scale. A variety of settings can be used to ensure that the required temperature is applied. An example would be blast furnaces or electrical installations. Melting temperatures that are too high determine that it is quite difficult to harden the steel in question at home.
Rate of temperature increase. The heating rate can also determine which qualities will be transferred to the processed product. Modern equipment allows you to control the heating rate with high precision. For example, HDTVs have an electronic control unit; electrical energy is converted into magnetic energy, which causes heating of the structure.
The length of time between exposure to different temperatures. When heat treating all metals, the presence of three critical points is taken into account and taken into account. The length of exposure may depend not only on the chemical composition of the material, but also on the size and shape of the workpiece.
Features of the cooling process. The quality of the resulting product largely depends on the conditions under which the cooling process took place. For example, it is possible to use oil or water, as well as various powders as a cooling medium.

Quite often, HDTV is used to change the qualities of a metal. It is characterized by high efficiency in application, as well as ease of use. Today there are models that, if desired, can be installed in a home workshop.

Critical points are considered to be temperatures at which restructuring of the structure occurs. There are three main temperature points that are displayed on the plotted diagram.

Attention is also paid to choosing a more suitable cooling medium. For example, it is possible to carry out cooling in water. However, such an environment leads to uneven cooling, which leads to scale and other problems. For higher quality, oil is used. Large workpieces can be cooled in the open air, since it takes a long time to reduce the temperature.

Cutting conditions when turning hardened steel

To obtain a high-quality part, roughing and finishing of hardened steel on lathes must be carried out taking into account the following recommendations:

Start work at low speed and with the smallest depth of cut. This will allow you to obtain a small angle and achieve correct edge processing, which will have a positive effect on the service life of the tool.
To achieve high quality surface finish of the part and reliability of the insert, increase the feed gradually. This approach will also improve chip removal and crushing.
When finishing machining, select a cutting depth greater than the insert nose radius. This will eliminate the risk of deviation and allow you to achieve high precision when working with the internal surfaces of workpieces.
Do not operate at very low cutting speeds as this will distort the tooling and workpiece.

A significant role when turning hardened steel is played by the use of coolant, which not only increases the reliability of the metal processing process, but also increases the productivity of the equipment and the quality of the finished product. It is important to use coolant correctly:

for rough and semi-finish turning, it is recommended to opt for the lower coolant supply; in the case of finishing machining, preference should be given to equipment with a high-precision lower coolant supply;
The level of coolant supply pressure must be adjusted in each specific case, depending on the cutting depth, material supply, nozzle diameter, and grade of steel being processed.

The book is devoted to cutting processing of hardened alloy structural steels. It presents the results of research and data from advanced manufacturing experience in the field of turning, face milling, drilling, reaming, countersinking and threading of hardened steels. It contains practical recommendations for choosing the design and geometry of the tool, as well as cutting conditions. The book is intended for engineering and technical workers of machine-building plants. It can also be useful to researchers and students of mechanical engineering universities and technical schools.

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Selecting a cutting tool for turning hardened steel

Turning hardened steel is one of the most difficult tasks in metalworking, which is best solved using the following types of cutting equipment:

Carbide inserts are a versatile and economical option that is resistant to abrasive wear. This tool is best suited for working with steel with a hardness of no more than 55 HRC. At higher specifications, the tool life will be significantly reduced.
Ceramic plates – equipment made of mixed ceramics or reinforced with special crystals. It can last a long time even when working with very hard steel, but the surface processed by such a plate will not be of very high quality. Therefore, they are recommended for rough and semi-finish turning.
Cubic Boron Nitride (CBN) inserts are a high-strength cutter that can handle hardened steel up to 65 HRC and allows for perfect metal finishing results with up to 70% time savings in the production process.