SU1723153A1 - Method of heat treatment of steel products - Google Patents

Abstract

The invention relates to mechanical engineering, specifically to the heat treatment of steel products, mainly large-sized tools from eutectoid alloyed steels. The method includes preliminary austenitization to temperatures not exceeding the critical point Asm. melt cooling at 400-550 ° C followed by quenching and tempering. The method allows to expand the technological capabilities during heat treatment of the tool by expanding the temperature range of heating for quenching, which is due to the retention of structurally free carbides as a result of preliminary austenitization from the proposed temperatures. 1 tab.

Description

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The invention relates to the heat treatment of metals and can be used. Vano when processing the tool, mainly large. from eutectoid alloyed steels.

Known methods of heat treatment of high carbon steels, including hypereutectoid, including heating for quenching to temperatures above AC1, quenching in water or oil and average tempering.

This treatment provides physical and mechanical properties characterized by high strength, but low ductility and toughness.

The closest to the present invention is a method of heat treatment of products mainly of high carbon steels, including quenching and from start-up, and before quenching, the product is heated to full

austenitization and subsequent aging in the molten salt at 400-550 ° C, and quenching is performed from temperatures. AC1 + (5-25) ° С. It allows one to obtain ultrafine grain and an increased complex of physicomechanical properties in products. Steel treated by this method has high strength and plastic characteristics. ; . -;;; "-. .

The disadvantage of this method is that preheating to temperatures of complete austenitization allows for final quenching from temperatures lying in a rather narrow range of AC1 + (5-25) ° C, which limits the technological capabilities of the tool. Heating to the temperature above results in noticeable grain growth due to the complete dissolution of the carbides in austenite during the preheating of the steel, a decrease in the toughness, the relative narrowing

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and lengthening. Modern thermal ovens are characterized by considerable thermal inertia, as a result of which it is difficult to ensure the heating and holding temperature intervals recommended in the prototype method. Furnaces of the type CHO, SNZ, for example SNZ-6.5.13.4.0 / 12, are designed to work with temperature fluctuations of ± (20-25) ° C, which leads to deterioration of properties in the products.

The purpose of the invention is the expansion of technological capabilities by expanding the temperature range of heating for quenching.

This goal is achieved by the fact that according to the method of heat treatment of products, including preliminary austenitization, followed by exposure to molten salts at 400-550 ° C. final quenching and tempering, preliminary austenitization is carried out to temperatures not exceeding the temperature of the AFM point, while maintaining structurally free carbides.

The heat treatment method, in which the preliminary austenitization is carried out to temperatures not exceeding AFM, allows the fine grain in the steel to be retained when heated for quenching to a temperature of (Aci-t-5-ACM-5) 0C, i.e. in a wider range. The structurally free carbides, which are not dissolved in the process of preliminary austenitization, are centers of transformation and at the same time inhibit the movement of the transition boundary a. The result is a fine grain and an increased complex of the physicomechanical properties of steel products, achieved in a wide range of quenching temperatures, which is technologically easier to achieve.

The essence of the method of heat treatment of steel products, such as large tools, is as follows. The product of eutectoid alloyed steels (with a content of alloying elements of more than 1%) is heated to temperatures below the critical point AFM, kept at this temperature to obtain a homogeneous structure over the cross section, make exposure in the molten salt at 400-550 ° C until complete decomposition of austenite to obtain a dispersed mixture with an inter-plate spacing of 0.05-0.5 µm / including the carbide phase. After that, the product is heated to the austenitization temperature in the range of (Aci + 5-Asm-5) ° C, aging is carried out and quenched in water or oil, followed by tempering, the temperature and duration of which are chosen depending on the requirements. to the product.

Due to the fact that the preliminary austenitization is carried out to temperatures

not exceeding Asm, persistent struc- ture-free carbides interfere with grain growth during final heating for quenching. This allows you to extend the temperature range of heating to (AC1 + 5-Asm-5) ° C,

This expands the technological capabilities of the heat treatment of the instrument.

PRI me R. Of the HVG eutectoid steel (content, wt.%: Carbon 1.03, manganese 0.97, silicon 0.3, chromium 1.1, tungsten 1.4

5 manufactured standard samples for tensile and toughness tests. Processing was performed according to the proposed method and the method prototype. The samples were heated in an argon atmosphere in an oven at

0 790 and 860 ° C for 12 minutes (impact samples) and 7 minutes (tensile samples). Then they were transferred to the sodium nitrate melt and kept until the austenite decomposition was complete. Temperature of salt

5 baths varied to 610 ° C. Further cooling was carried out in air. Heating for quenching was performed in a laboratory oven in an argon atmosphere at 760 and 800 ° C. The holding at these temperatures was 1 and 0.6 min for the impact and tensile samples, respectively. Then quenched in oil followed by tempering at 600 ° C for 30 and 20 minutes for impact samples.

5 and samples for stretching. The difference in time to leave is explained by the different effective cross sections of the samples. Mechanical properties of samples tested after various thermal regimes

0 processing given in the table.

Austenitization at 790 ° C (which is 20 ° C below Asm) and isothermal cooling in. melt at 400-550 ° С, ensuring the preservation of structurally free carbs, allows to obtain a high complex of physicomechanical properties after final quenching and tempering (modes 1, 2, 3, 6, 7, 8, 8-26-26). The heating temperature for quenching was 760 and 800 ° С, which

0 by 15 ° C above Ac1 and 10 ° C below Asm, respectively. Such processing corresponds to the proposed method. Modes 11-20. Performed with deviations from the proposed c. exceeding the temperature of preliminary austenization (АСм + 50 ° С), which corresponds to the one proposed in the prototype. Subsequent cooling from this temperature in the molten salt in the range of 400-550 ° C. and final hardening from 800 ° C (AC1 + 55 ° C, which is higher than the limits of the temperature range of the prototype) provides a reduced level of toughness and plastic characteristics. Isothermal cooling in the melt at a temperature above 550 ° С or below 400 ° С impairs the complex of physicomechanical properties, in particular, somewhat decreases the tensile strength and impact strength.

Thus, the proposed data in comparison with the prototype show the possibility of expanding the temperature range of heating for quenching within the above limits while maintaining sufficient

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high complex physical and mechanical properties.

Fo rmu l and z obn e-A method for heat treatment of steel products, mainly large-sized tools made of eutectoid alloyed steels, including austenitization, cooling with exposure to molten salts at 400-550 ° С and tempering, characterized in that, in order to expand the technological capabilities by expanding the temperature range of heating for quenching, austenitization is carried out at temperatures AC1-Asm.

Claims (1)

Claim A method of heat treatment of steel products, mainly large tools made of eutectoid alloy steels, including austenitization, cooling with exposure to molten salts at 400-550 ° C and tempering, characterized in that, in order to expand technological capabilities by expanding the temperature range of heating under quenching, austenitization is carried out at temperatures Ac1-Asm. Mode, ff Austenitization temperature, ^ Isothermal cooling temperature, С Hardening temperature, ° С Temporary resistance to a gap, With ₈ , "MPa Relative extension, J.ioot Relates. constriction, φ L Xi Impact Strength, J / cm® ’ 1 790 400 760 1872 2 34 < 51 2 460 1865 ι 2 34 52 3 550 1850 2 35 53 4 350 1836 2 thirty 46 5 610 1830 2 29th 47 6 400 800 1915 2 32 52 7 460 19th 3 32 52 8 550 1892 3 33 54. 9 350 1872 2 29th 45 10 610 1864 2 31 49 eleven 860 400 760. 1941 1 31 fifty 12 460 1935 2 32 fifty thirteen 550 1933 2 .32 52 14 350 1930 1 29th 45 fifteen 610 1933. 2 31 fifty 16 400 800 1967 1 23 40 17 460 1965 1 23 42 18 550 1957 g 25 34 19 350 1950 1 21 38 20 610 1939 1 23 41 21 745 460 760 1760 3 36 54 22 * 800 1833 2 34 51 23 810 460 760 1850 2 ' 35 47 24 800 1885 2 34 46 25 790 460 750 1885 2 35 53 26 790 460 800. 1910 3 32 52