RU2553107C2 - Strengthening method of items from low-carbon steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to steel items carbonization, and can be used for surface hardening of machine an machinery parts out of low-carbon steel. Items are carbonized in solid carburizing compound, then they are cooled, subjected to double hardening and low-temperature tempering. The carbonization is performed at 900°C. The following compound is used as solid carburizing compound, containing in wt %: cast-iron shaving with average grains size 0.5 mm - 10, barium carbonate BaCO₃ - 10, and carbonic substance with fibrous structure - 80 comprising in wt % iron - 10, hydrogen - 0.8, and carbon - 89.2, that is produced by catalytic thermal pyrolysis of the associated petroleum gas of Bayadynskoe Field under contact with iron oxide catalysts at temperature 660°C, with feed space velocity 1000 hours^-1 for 3 hours with further screening of the fraction 100-250 micron by fractionation of the created mass in molecular sieves. After carbonization the items are cooled to 100°C, then subjected to double hardening including first hardening at 820°C, and second hardening at 770°C, then low tempering is performed at 150°C.

EFFECT: required diffusion saturation by carbon is ensured, uniform depth of the layer over the item is ensured, reduced power consumption, and reduced needed in cooling by water solution of the cooling liquid and emulsifier addition.

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Description

The invention relates to the field of cementation of steel products and can be used for surface hardening of machine parts and mechanisms by heat treatment in a solid carburetor environment.

The classical method of steel cementation is known by diffusion saturation with powder media placed in pressurized containers using furnace heating [L. Voroshnin Theory and technology of chemical-thermal treatment: a training manual. Minsk: New Knowledge, 2010, p. 88]. The disadvantage of this method is the high duration of the technological stages of the process, affecting the energy intensity, as well as the need to maintain the contents of the container under isothermal heating for uniform diffusion saturation of the steel.

A known method of heat treatment of steel parts to increase their strength characteristics, which consists in saturating the surface layer with carbon at a heating temperature of 930-950 ° C, followed by quenching in oil and low-temperature tempering [Pat. 2087550 Russian Federation, IPC C21D 1/42, C23C 8/22. Method for heat treatment of alloy steel parts / applicant and patent holder Avtovaz Joint Stock Company -№95114513 / 02; declared 08/04/1995; publ. 08/20/1997].

When implementing this method, additional high-temperature tempering of heat-treated steel parts, quenching by high-frequency currents, cooling in a 5-10% aqueous solution of coolant with the addition of emulsifiers and subsequent low-temperature tempering are required.

The prototype for the execution of the technological stages of the process is a method of hardening low carbon steels [Pat. 2094485 Russian Federation, IPC C21D 1/78, C23C 8/20. Method for hardening low-carbon steels / applicant and patent holder Joint-stock company “Ramenskoye instrument-making design bureau” - 95120485/02; declared 12/05/1995; publ. 10.27.1997], in which the parts are placed in a box with a solid carburetor and heated to a temperature of 930 ° C. Cementation is carried out to a depth of 1 mm. The parts are cooled in a box in air to 680-550 ° C, incubated for 0.3-0.5 hours, heated to 800-820 ° C and quenched.

The disadvantages of the prototype include the need for a second hardening at 820 ° C, in which, due to double heating, decarburization of the surface layer that has already been cemented is likely, which can lead to a loss of wear resistance and a decrease in the life of the part. When implementing the prototype, a 10% solution of NaCl in water is used to provide low-temperature hardening, which is carried out in coal of unknown origin and, accordingly, uncertain physicochemical properties. Also not shown are the characteristics and composition of the solid carburetor used to achieve the objectives of the invention.

The technical result of the invention is to provide the required diffusion saturation with carbon, achieving uniformity of the layer depth over the product area, reducing energy costs, and also the absence of the need for cooling with an aqueous solution of a cooling liquid and an emulsifier additive,

The technical result is achieved in that in the method of hardening products from low carbon steel, including cementing in a solid carburetor, cooling, double hardening and low temperature tempering, characterized in that the cementation is carried out at 900 ° C, and a composition containing in wt. . %: pig-iron shavings with an average granule size of 0.5 mm - 10, barium carbonate BaCO ₃ - 10 and carbon fiber substance - 80, consisting in wt. % of: iron - 10, hydrogen - 0.8 and carbon - 89.2, which was obtained by thermocatalytic pyrolysis of associated petroleum gas of the Bayadinsky field in contact with an iron oxide catalyst at a temperature of 660 ° C, a feed volumetric rate of 1000 hours ^-1 for 3 hours followed by screening of the 100-250 micron fraction by fractionation of the resulting mass on molecular sieves, while after cementation the products are cooled to 100 ° C, then double hardening is carried out, including the first hardening at a temperature of 820 ° C, and W another quenching - at a temperature of 770 ° C, after which a low tempering is carried out at a temperature of 150 ° C.

Example. 10 g of iron oxide FeO is loaded into a 1-liter quartz reactor, heated to 660 ° C, then thermocatalytic pyrolysis is carried out by supplying the associated gas of the Bayandy field, the composition of which is given in Table 1, to the FeO layer, with a volume velocity of 1000 h ^-1 . After 3 hours, the process is stopped. The resulting carbon substance has a fibrous structure, while ensuring a uniform distribution of FeO throughout the structure of the carbon substance, the physicochemical properties of which are shown in Table 2. Next, the resulting carbon substance is cooled to 20 ° C and subjected to fractionation on molecular sieves, while taking fraction 100 -250 microns. A carburizer for cementation is prepared by adding cast iron shavings with an average grain size of 0.5 mm (10% of the total mass), barium carbonate BaCO ₃ (10% of the total mass) to the carbon substance (80% of the total mass) and uniform mixing.

Parts made of steel grade Art. 20, is placed in a metal container, on the bottom of which a layer of a carburetor 20 mm thick is covered. After laying, the parts are covered with a 20 mm thick carburetor layer on top. The carburetor is tightly tamped. A sheet of asbestos is laid on top, covered with quartz sand. The container is closed with a lid and is sealed by coating with refractory clay. Next, the container with the parts laid is installed in a CHO-4.8.4 / 10I1 electric chamber furnace of resistance CHO-4.8.4 / 10I1 heated to a cementation temperature of 900 ° C and kept therein depending on the required thickness of the cementation layer.

After the stages of cementation, cooling to 100 ° C and unloading are completed, the parts are subjected to double hardening and low-temperature tempering. The first hardening, necessary to fix the structure of the core of the part, which overheats during the cementation process, is carried out at a temperature of 820 ° C. A second hardening at 770 ° C gives high hardness to the surface layer. Low tempering tempering at 150 ° C.

Quality control is carried out by the effective thickness of the cementation layer, which is determined by its hardness and structure. Hardness is measured by rapid analysis using an ultrasonic hardness tester MIC10. The border of the cementation zone is a structure consisting of perlite and ferrite in equal proportions and corresponds to a carbon concentration of 0.4% of the total mass. Qualification carburizing layer thickness is adopted in hardness of heat-treated samples in presence of a solid carburizing, carburizing layer beyond the end zone is received zone with a hardness of 40-45 HRC _e. The test results are presented in table 3.

The achieved value of the depth of the cementation layer and the hardness index on the Brinell scale (HB) shows that the proposed method provides a uniform depth of cementation over the area of the sample, allows to increase the efficiency of the process through the use of scarce resources in the industry and, accordingly, non-deficient resources of associated petroleum and natural gas, and also to exclude the expensive stage of cooling with aqueous solutions of a cooling liquid with the addition of emulsifiers and other widely discussed in the modern literature ternativnye methods such as purge gases container, vibration application of high frequency currents and so forth. The present invention can be widely used in various fields gas industry, mechanical engineering and metallurgy.

Claims (1)

A method of hardening products from low carbon steel, including cementing in a solid carburetor, cooling, double hardening and low temperature tempering, characterized in that the cementation is carried out at 900 ° C, and a composition containing in wt. %: pig-iron shavings with an average granule size of 0.5 mm - 10, barium carbonate BaCO ₃ - 10 and carbon fiber substance - 80, consisting of, in wt. %, iron - 10, hydrogen - 0.8 and carbon - 89.2, which was obtained by thermocatalytic pyrolysis of associated petroleum gas of the Bayadinskoye field in contact with an iron oxide catalyst at a temperature of 660 ° C, a volumetric feed rate of 1000 hours ^-1 for 3 hours, followed by sieving the fraction of 100-250 microns by fractionation of the resulting mass on molecular sieves, while after cementation the products are cooled to 100 ° C, then double hardening is carried out, including the first hardening at a temperature of 820 ° C, and the second Oh quenching - at a temperature of 770 ° C, after which a low tempering is carried out at a temperature of 150 ° C.