The way thermocyclic treatment tool steel

 

(57) Abstract:

The invention relates to the field of metallurgy, namely, heat treatment of steels in the manufacture of tools and machine parts in mechanical engineering. Perform repeated heating of the samples above ANDClat 130-170oWith speeds 6-35 deg/s, the cooling in the loop below ANDClcarried out in the molten salt to a temperature of 680-750oWith aged at this temperature 3-9 min, cooling in oil after heating in the last cycle with subsequent tempering is carried out at a temperature of 200-400oC. These techniques on samples reduce time consuming process thermocyclic treatment, the increase in hardness and strength properties while maintaining high impact strength, and thus increase the operational strength of the tool under dynamic loads. table 1.

The invention relates to metallurgy, in particular to a method of heat treatment of tool steels for dies of cold deformation, and can be used in the manufacture of tools and machine parts in machinery.

The known method thermocyclic treatment of steel, including multiple heating above ACl30-50ooC to remove the internal stresses [1].

The disadvantages of this method is that increasing the ductility of steel is not accompanied by the necessary high level of its strength properties, as well as the complexity and duration of the method, since its implementation requires heating and cooling up to 10 times, which inevitably leads to oxidation of the surface of the product and scale formation due to the entire process of heat treatment in the air.

The closest in technical essence (prototype) is a method thermocyclic treatment of tool steels, including multiple heating above AClon 40-80oC with a speed of 250-350oC/min, cooling in the loop below AClto a temperature of 560-620oC in the molten salt with exposure at this temperature until the end _ transformations, cooling in water or oil after heating in the last cycle, after which carry out your vacation at 180-220oC [2].

The disadvantage of this method for dies of cold deformation of steels HM, HF and others like them, is that the process of complete metamorphosis _ pri whole process thermocyclic treatment, because it requires 3-4 cycle, and, in addition, this method does not provide the necessary high level of durability due to low temperature heating (ACl+(40-80oC)) in a loop and, consequently, high wear resistance of the tools produced by this method.

The essence of the invention is achieved in that in the known method tematicheskoe processing tool steel, which carry out repeated heating above AClcooling in the loop below ACland cooling in oil after heating in the last cycle with the subsequent vacation, multiple heating is carried out above AClat 130-170oC with a speed of 6 to 35 deg/s, and the cooling cycle is carried out in the molten salt to a temperature of 680-750oC with a holding time at this temperature, 3-9 minutes, and vacation is conducted at a temperature of 200-400oC.

The technical result is to reduce the time consuming process thermocyclic treatment and increased hardness while maintaining the toughness of steel, which improves wear resistance of the tool.

Implementation of the proposed method with these modes allows you to save your toughness with increasing ti mixture and austenite, conducive to a favorable structural state in the final structure of steel.

For the manufacture of die tooling of cold deformation is widely used steel HM, HF. The presence in the structure of these steels a large number of carbides provides on the one hand, the high wear resistance of the tool, and on the other, leads to low toughness. Most legirovannoi steel creates resistant to dissolution of carbides. Increase the quenching temperature above ACl+ 170oC for greater dissolution of carbides and obtain the required hardness of martensite leads to an increase in grain size in the steel, resulting in a decrease in ductility and toughness. Lowering the degree of alloying of austenite always leads to a decrease in its resistance to a more rapid and complete disintegration. Accelerated heating up to the temperature of 130-170oC above AClwith the speed 6-35 deg/s and cooling the molten salt to 680-750oC with thermal Cycling can reduce the austenite degree of dissolution of the alloying elements. After 2-4 times for such heating and cooling is formed sverkhelastichnosti structure. All this ultimately leads to the weal. In addition, the proposed method reduced the processing time by reducing the exposure time at the lower temperature in the cycle (with a few hours to 3-9 minutes).

The increase in hardness and strength while maintaining a high level of impact strength can improve operational stability dies of cold deformation.

The way thermocyclic treatment tool steel is carried out as follows. Take samples of steel HM, HF and subjected to heating to 960-1000oC (above AClat 130-170oC) speed 6-35 deg/s in molten chloride salts. They are then cooled to a temperature of 680-750oC (below AClby dragging them to another melt of a mixture of chloride salts aged 3-9 minutes at the same temperature 680-750oC. they are Then again heated to 960-1000oC by moving in the first molten salt, cooled to 680-750oC transfer to the second melt was kept at this temperature, etc. After the third heating to 960-1000oC the samples are cooled in oil or nitrate (hold hardening with subsequent tempering at 200 to 400oC.

Examples of the method thermocyclic treatment tool steel.

Example con> with the speed 6-35 deg/s in molten chloride salts. They are then cooled to a temperature of 730oC by transferring to another melt of a mixture of chloride salts aged 3-9 minutes at the same temperature 730oC. they are Then again heated to 980oC by moving in the first molten salt, cooled to 730oC transfer to the second melt was kept at this temperature, etc. After the third heating to 980oC is cooled in the oil are hardening with subsequent tempering at 200oC.

To obtain comparative data in parallel conduct heat treatment on standard technologies: hardening from 1030oC plus vacation at 200oC [3].

An example of the prototype method.

Take samples of steels HM, HF and subjected to four heating to a temperature of 880oC with a speed of 250-350oC/min in molten chloride salts and cooling to a temperature of 590oC by moving the second molten chloride salts. After the fourth heating to 880oC the samples are cooled in oil (spend quenching) and spend the holiday at 200oC. research Results are summarized in the table (see the table at the end of the description).

As the table shows, the use of the proposed 2 times in comparison with traditional hardening while maintaining high hardness [3], as well as to increase the hardness and strength properties of steel while maintaining the toughness and reduce the processing time compared with thermocyclic treatment regime known of the prototype method. Improving complex of mechanical properties can improve operational tool life, especially those dynamic loads.

Sources of information

1. USSR author's certificate N 1379322, class C 21 D 1/78. The way thermocyclic treatment of carbon steel.

2. RF patent N 2078440, class C 21 D 1/78. The way thermocyclic treatment tool steel (prototype).

3. Baskin Y. A., Ushakov B. K., Szekely, A., Technology of heat treatment of steel. - M.: Metallurgiya, 1986. - S. 364-372.

4. Popov, A. A., Popov, L. E. Isothermal and thermokinetic diagrams of the collapse of the supercooled austenite. Directory of the workstation. - M.: Metallurgy, 1965. - S. 416-418.

The way thermocyclic treatment of tool steels, including multiple heating above AC1cooling in the loop below AC1cooling in oil after heating in the last cycle with the subsequent vacation, characterized in that multiple heating is carried out above AC113 C with a holding time at this temperature, 3 - 9 min, and the vacation is conducted at a temperature of 200 - 400oC.

 

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