RU2561552C2 - Carboniser for carbonisation of low carbon steel items - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to the carbonisation of steel items, and can be used for surface strengthening of the machine parts and machinery by means of the heat treatment in solid carboniser. The carboniser for the carbonisation of the low carbon steel items contains in form of the by-product of the incomplete combustion of the natural gas in the gas-operated heat generating equipment of the gas distribution and compressor stations of the main gas lines, cast iron shavings with average size of pellets 0.5 mm, and barium carbonate, upon the following components ratio in wt %: fine-grained soot - 80, cast iron shavings - 10, and barium carbonate - 10.

EFFECT: assurance of required diffusion saturation of steel items with the carbon, uniform depth of layer over the item area, and reduced energy consumption.

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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.

Known compositions of mixtures and pastes for cementation based on charcoal, coke, soot with the addition of activators - urea (urea), carbonates and acetates of sodium, potassium and barium [1]. The compositions are quite versatile, but not technologically advanced due to the impossibility of providing stable saturation of low-carbon steels with carbon.

Known composition in the form of a paste containing soot and up to 55% urea, used in temperature ranges 550-600 ° C [2]. The composition is not effective enough for high-temperature cementation and is applicable to a limited number of steels.

The known composition of a solid carburetor, consisting of charcoal (10-15%), semicoke (75-80%) and an activator - barium acetate (5-10%), for cementation of steel products [3]. The disadvantage is the need to use solid carburetor in the formulation as the main component - semi-coke, which, being an effective energy fuel, easily ignites under the influence of temperature, while releasing unstable volatile hydrocarbon compounds into the reaction zone. This may adversely affect the fire and explosion safety of the process.

The prototype is the composition of the following formulation [4]:

1) carbon-containing substance - sludge from wastewater treatment plants from paper production (90-92%);

2) one of the carbonates of metals of I or II group of the Periodic system of chemical elements (8-10%).

The disadvantage of the prototype is that the formation of a saturating carbon-containing substance occurs from precipitation of industrial effluents directly during the cementation process. Moreover, the composition of the sediments contains a large number of substances of various chemical nature (rosin glue, kaolin, starch, urea and melamine-formaldehyde resins, etc.), which, providing increased moisture resistance and capillarity of the carburizer, do not affect the formation of a carbon-containing substance and are essentially ballast during carbon saturation of steel products. This entails an increase in the energy intensity of the process, affects the depth, quality, duration and effectiveness of cementation.

The technical result of the invention is: providing the required diffusion saturation with carbon, achieving uniformity of the depth of the layer over the area of the product and reducing energy costs.

The technical result is achieved by the fact that in the known composition of the carburizer for cementing steel products containing one of the carbonates of metals of group I or II of the Periodic system of chemical elements, instead of the carbon-containing substance obtained from sludge from industrial wastewater treatment plants from paper production, highly dispersed soot is used as a by-product incomplete combustion of natural gas during the operation of gas-using heat-generating equipment at gas distribution and compressor stations gas mains. The composition of natural gas is shown in table 1.

Despite its relatively low efficiency in terms of efficiency and the presence of a number of other technological drawbacks, direct gas heaters and with intermediate heat carrier heating (such as PGA-200 and PTPG-30) are widely used in the gas industry to prevent hydrate formation before throttling at gas distribution stations and fuel preparation, launch units

and pulse gas compressor stations. Based on the operating experience of this equipment, the formation of fine soot is due to the design features of the sub-alkaline gas burners, which do not provide the necessary regulation of the air supply to the combustion zone and mixing of the gas-air mixture in the burner, which leads to chemical underburning. At the same time, due to incomplete heat dissipation, additional costs of fuel gas, fees for excess emissions of carbon monoxide into the atmosphere, environmental burden due to the need to bury highly dispersed soot as a by-product of a carcinogen or to search for alternative ways of its disposal increase.

Relatively harmless to the environment is the proposed method of using highly dispersed soot in the formulation of the carburetor for cementing products from low carbon steel. These products are operated in the same operating production, where the finely dispersed soot itself was obtained, and require increased hardness and wear resistance due to various conditions or requirements for ensuring the reliability of the operation of technological equipment.

Example 1. Fine soot is obtained during the scheduled shutdown of the PGA-200 gas heater installed in the auxiliary unit at the industrial site of the gas compressor station by opening the casing, subsequent mechanical choking of the chimney, and collection and cleaning of corrosion products. Fine soot consists in mass. % of: iron - 0.4; hydrogen - 1.2 and carbon - 98.4. Physico-chemical properties of fine soot are shown in table 2.

Example 2. Fine soot is obtained during the scheduled shutdown of the PTPG-30 gas heater installed at the gas distribution station by opening the casing, subsequent mechanical choking of the chimney, and collecting and cleaning corrosion products. Fine soot consists in mass. % of: iron - 0.5; hydrogen - 1.0 and carbon - 98.5. Physico-chemical properties of fine soot are shown in table 2.

A carburizer for cementation is prepared by adding cast iron shavings with an average granule size of 0.5 mm (10% wt.), Barium carbonate BaCO ₃ (10% wt.) To uniformly dispersed soot (80% wt.) And uniform mixing.

Bearing base plates of the ducts of gas pumping units (hereinafter referred to as details) made of steel of the grade St20 are placed in a metal container, to the bottom of which a layer of a carburetor 30 mm thick is covered. After laying, the parts are covered with a 30 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, the parts are subjected to double hardening and 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. The second hardening at a temperature of 770 ° C gives high hardness to the surface layer of the part. 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 the corresponding carbon concentration is 0.4% of the total mass. Estimation of the thickness of the cementation layer is taken by the hardness of the heat-treated samples in the presence of a solid carburizer, the zone with a hardness of 40-45 НРС _{Э is} taken as the end of the zone of the cementation layer. The test results are presented in table 3.

The achieved values of the depth of the cementation layer and the hardness index on the Brinell scale (HB) show that the proposed method provides a uniform depth of cementation over the area of the sample, can improve the efficiency and environmental friendliness of the process by using a by-product of production - highly dispersed soot.

The invention can find wide application in various fields of the gas industry, engineering and metallurgy.

Information sources:

1. Reference. Chemical-thermal treatment of metals and alloys, ed. L.S. Lyakhovich. - M.: Metallurgy, 1981. - 288 p.

2. Pat. No. 2254396, Russian Federation, IPC С23С 8/76. Method for nitrocarburizing metals in pastes / applicant and patentee Kursk State Agricultural Academy named after prof. I.I. Ivanova - 2003128356/02; declared 09/19/2003; publ. 06/20/2005.

3. Copyright certificate No. 111009, USSR, IPC С23С 8/66. Solid carburetor / L.A. Luksha - 581698; declared 08/06/1956; publ. 01/01/1957.

4 Pat. No. 1836486, Russian Federation, IPC С23С 8/66. Carburizer for cementing steel products / applicants and patent holders I.M. Spiridonova, S.B. Pilyaeva, V.F. Syutkin, Yu.A. Malyk - 5039776; declared 04/24/1992; publ. 08/23/1993.

Claims (1)

A carburetor for cementing low-carbon steel products containing a carbon-containing substance and one of the metal carbonates of group I or II of the Periodic system of chemical elements, characterized in that it additionally contains cast iron shavings with an average grain size of 0.5 mm, while the carbon-containing substance is a highly dispersed soot in the form of a by-product of incomplete combustion of natural gas in gas-using heat-generating equipment of gas distribution and compressor stations GOVERNMENTAL gas, and one of said carbonate is barium carbonate at the following component ratio, wt.%: highly dispersed carbon black - 80, iron shavings - 10 and barium carbonate - 10.