RU2690630C2 - Carburizer composition for carburizing parts from low-carbon steel - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to cementation of steel articles and can be used for surface hardening of parts of machines and mechanisms by their heat treatment in medium of solid carburizer. Composition of carburizer for carburizing articles from low-carbon steel contains, wt. %: iron chips with average size of granules of 0.5 mm - 10, barium carbonate BaCO- 10 and carbon substance - 80. Carbon substance consists of, in wt. %: amorphous carbon - 96.2, crystalline carbon - 2.85, iron - 0.94 and hydrogen - 0.01 and obtained by thermo-catalytic pyrolysis of gas condensate, taken from condensate collector of gas distribution station, under conditions of contact with iron oxide catalyst FeOat temperature of 550 °C, bulk feed rate of volume of 30 ml/min, for 5 hours, with subsequent screening of 50–150 mcm fraction by fractionation of formed mass on molecular sieves.EFFECT: providing required diffusion saturation with carbon, achieving uniform depth of layer along the area of the product and reducing power consumption.1 cl, 2 ex

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 carburizer.

There is a 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 (Patent 2087550 of the Russian Federation, IPC C21D 1/42, С23С 8/22 The method of heat treatment of parts made of alloyed steel / applicant and patentee of AvtoVAZ JSC - No. 95114513/02; declared 04.08.1995; publ. 20.08.1997).

The implementation of this method requires an additional high-temperature tempering of the heat-treated steel part, high-frequency quenching, the use of 5-10% aqueous coolant solution with the addition of emulsifiers and subsequent low-temperature tempering.

Known composition in the form of a paste containing carbon black and up to 55% urea, used in the temperature ranges 550-600 ° C (Patent 2254396 of the Russian Federation, IPC С23С 8/76. Method of carbonitriding metals in pastes / applicant and patentee Kursk State Agricultural Academy named after Prof. I.Ivanov - 2003128356/02; declared September 19, 2003; published June 20, 2005). The composition is applicable to a limited number of steels and is not effective enough at high temperature cementation.

The prototype is a composition containing pig iron chips, barium carbonate and carbon matter obtained by thermal catalytic pyrolysis

gaseous raw materials under conditions of contact with an iron oxide catalyst and subsequent fractionation of the resulting carbon mass on molecular sieves (2553107 Patent for the invention of the Russian Federation, IPC С23С 8/66 (2006.01). Hardening method for low carbon steel products / applicant and patent holder Gazprom Transgaz Ufa LLC - # 2013147091/02 (073215), announced on 10/23/2013; published on 10.06.2015).

The disadvantage of the prototype is a relatively low yield of carbon matter, since the ratio of atomic amount of carbon to hydrogen in the gas molecule is lower than in the molecule of liquid hydrocarbons. Also, the disadvantage is the increased energy consumption for thermocatalytic pyrolysis of gas at elevated temperatures due to the relatively high thermal stability of gaseous hydrocarbon gas molecules.

The technical result of the invention is the provision of the required diffusion saturation with carbon, the achievement of the uniform depth of the layer on the product area and the reduction of energy consumption.

The technical result is achieved in that in a known composition of a carburizer for cementation of products from low carbon steel containing barium carbonate and cast iron chips, a carbon substance is used - a product of thermal catalytic decomposition of gas condensate formed during throttling and separated when the standard cleaning system is transported through the main gas pipelines gas distribution station and the head gas distribution point. Physico-chemical properties of gas condensate are presented in table 1.

The carbonaceous substance is obtained according to the invention, by thermal catalytic pyrolysis of gas condensate in contact with the iron oxide catalyst Fe ₂ O ₃ at a temperature of 550 ° C and atmospheric pressure, the flow rate of the raw material is 30 ml / min, for 5 hours, s

subsequent screening fraction of 50-150 μm by fractionation of the resulting mass on molecular sieves.

Example. The quartz reactor of 1 liter was charged with 10 g of Fe ₂ O ₃ of iron oxide, was heated at atmospheric pressure to 550 ° C, then carried thermocatalytic pyrolysis by dispensing 30 ml / min in a layer of Fe ₂ O ₃ gas condensate selected while purging with condensate GDS-3. The fractional composition of the gas condensate is shown in Table 1. After 5 hours, the pyrolysis process is stopped. The resulting carbon substance consists of, in mass. %: amorphous carbon - 96.2, crystalline carbon - 2.85, iron - 0.94, hydrogen - 0.01 and has a soot structure, as evidenced by the results of electron microscopic analysis. This ensures a uniform distribution of iron atoms throughout the structure of the carbon substance, the physicochemical properties of which are given in Table 2. Next, the carbon material obtained is cooled to 20 ° C and subjected to fractionation on molecular sieves, selecting a fraction of 50-150 μm.

The carburizer for carburizing is prepared by adding to the carbon matter (80 wt.%) Cast iron chips with an average grain size of 0.5 mm (10 wt.%), Barium carbonate BaCO ₃ (10 wt.%) And uniform mixing.

The dismantled gear shaft of a KAMAZ gearbox, made of steel of the St20 brand, is placed in a metal container, at the bottom of which a layer of carburizer 30 mm thick is filled. After installation, the parts are covered with a 30 mm thick carburizer on top. Carburizer tightly tamped. A sheet of asbestos is laid on top, covered with quartz sand. The container is closed with a lid and ensure its sealing by coating with refractory clay. Next, the container with the installed parts is installed in an electric chamber furnace heated to a cementation temperature of 900 ° C

resistance of CHO-4.8.4 / 10I1 and maintain in it up to 7 hours, depending on the required thickness of the cementation layer.

After completion of the cementation stages, cooling to 100 ° C and unloading, the parts are subjected to double quenching and tempering. The first quenching required to correct the structure of the core of the part, which is experiencing overheating during the cementation process, is performed 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 to relieve temperature stress - at a temperature of 150 ° C.

Quality control is carried out on the effective thickness of the layer of cementation, which is determined by its hardness and structure. Measurement of hardness is performed by the method of rapid analysis using an ultrasonic hardness tester MIC10. The boundary 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. The assessment 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 НRC _{Э is} taken as the end of the cementation layer zone. The test results are presented in table 3.

The achieved values of the cementation layer depth and the Brinell hardness (HB) index show that the proposed carburizer provides a uniform sample cementation depth and reduces energy consumption by using gas condensate for producing carbon matter instead of a scarce gas raw material.

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

Claims (1)

The composition of the carburizer for the cementation of products from low carbon steel, containing, in wt.%: Cast iron chips with an average grain size of 0.5 mm - 10, barium carbonate BaCO ₃ - 10 and carbon substance - 80, characterized in that the carbon substance consists of, in wt.%: amorphous carbon — 96.2, crystalline carbon — 2.85, iron — 0.94, and hydrogen — 0.01 and obtained by thermal catalytic pyrolysis of gas condensate taken from the condensate collector of the gas distribution station under conditions of contact with iron oxide Fe ₂ O ₃ at a temperature of 550 ° C , the flow rate of feed 30 ml / min, for 5 h, followed by screening fraction 50-150 microns by fractionating the resulting mass on molecular sieves.