Method of carburizing parts made of “18ХГТ” steel using paste based on carbon-comprising components

Abstract

FIELD: steels.SUBSTANCE: invention relates to a method for carburizing parts made of “18ХГТ" steel using a paste based on carbon-comprising components. The surface of said part is prepared, a cementation paste mixed with dextrin glue is applied in a layer of 1.5-2 mm, and dried at 80 °C for 15-30 min, carburization, hardening at 825-840 °C and low tempering at 150-200 °C for 2 hours. The specified paste comprises the following components, wt.%: barium carbonate 20-21, gas soot “ДГ-100” 53, bentonite 9 and ground quartz powder 17-18. Cementation is carried out at a temperature of 920-960 °C for 4-6 hours in a sealed container with a filler consisting of the following components: charcoal 50%, chamotte 40% and barium carbonate 10%. The microhardness of the surface layer is 58-62 HRC and the depth of the hardened layer is 1.0-1.1 mm.EFFECT: improved performance.5 cl

Description

[0001] The invention relates to the field of metallurgy and can be used for chemical-thermal treatment of structural steels, in particular 18KhGT steel, used in mechanical engineering for the manufacture of parts requiring high wear resistance of the surface.

[0002] Carburizing is applied to parts made of low-carbon steels 18ХГТ, 20Х, 20Х2Н4МА and other grades, widely used in the production of critical machine parts.

[0003] A known method for case-hardening 18KhGT steels (RU patent 2456712, published July 20, 2012, bulletin no. 20) involves applying a paste containing graphite, barium carbonate, and EVT enamel to the surface of the part. After application, the paste is dried at 100-200°C, then case-hardened at 900°C for 4-6 hours. The parts are then quenched at 825-840°C in oil and tempered at 180-200°C.

[0004] The disadvantages of this method are the need to use additional gas or solid media, low carburization rate, difficulties with local surface treatment, low technological flexibility and high labor intensity, as well as environmental restrictions due to the possible release of harmful substances.

[0005] A method is known for carburizing steel products in a solid carburizer (patent RU 2286172 published 10 / 27 / 2006, bulletin No. 19), where the parts are placed in boxes with a solid saturating composition and processed at a temperature of 920-950 °C.

[0006] The disadvantages of this method are the uneven saturation of carbon, especially on complex surfaces, the long duration of the process (8-12 hours), the need to use large volumes of carburizer and the labor intensity of preparing parts for processing.

[0007] A method of gas carburizing is also known (SU 863713 A1, published 15.09.81, bulletin No. 34), which consists in the fact that after loading the products into the carburizing furnace, a carbon-containing gas or liquid is fed into it.

[0008] The disadvantages of this method are the complexity of the equipment, the need for precise control of the gas environment, high energy consumption and limitations on the size of the parts being processed.

[0009] Also known is a method of vacuum carburizing steel parts with threaded elements (RU 2693064, published 04.11.1970, Bulletin No. 7), which ensures uniform saturation with carbon even in hard-to-reach places.

[0010] The disadvantages of this method are the need to create a vacuum, the complexity of the technology and limited applicability for mass production.

[0011] The technical objective of the invention is to develop a method for carburizing parts made of 18KhGT steel, which ensures an increase in the speed and uniformity of saturation of the surface with carbon, simplification of the processing technology and the production of a carburized layer with high surface hardness.

[0012] The technical result of the invention is to ensure the microhardness of the surface layer of 58-62 HRC and the depth of the hardened layer of 1.0-1.1 mm.

[0013] The said technical result is achieved by the fact that in the method of carburizing parts made of 18KhGT steel using a paste based on carbon-containing components, including preparing the surface of the part, applying a 1.5-2 mm layer of carburizing paste mixed with dextrin glue, drying at 80 °C for 15-30 minutes, carburizing, hardening and low tempering at 150-200 °C for 2 hours, a carburizing paste is used containing the following components, wt.%: barium carbonate - 20-21, gas soot DG-100 - 53, bentonite 9 and ground powdered quartz - 17-18, while carburizing is carried out at a temperature of 920-960 °C for 4-6 hours in a sealed container with a filler consisting of 50% charcoal, 40% chamotte and 10% barium carbonate, and hardening is carried out at 825-840 °C.

[0014] Preparation of the surface of the part before applying the paste is carried out by cleaning and degreasing.

[0015] In one embodiment of the method, cementation is carried out at a temperature of 950 °C for 5 hours.

[0016] The parts are packed in a sealed container with the mentioned filler, which provides a protective atmosphere from oxidation during heat treatment.

[0017] When implementing the method, a cemented layer with a depth of 0.8-1.2 mm and a microhardness of 58-62 HRC is formed.

[0018] The method of carburizing 18KhGT steels using a paste based on carbon-containing and binding components is carried out as follows.

[0019] The first step is to prepare the part's surface. The 18KhGT steel part is thoroughly cleaned of contaminants and degreased to ensure good adhesion of the paste to the surface. Foreign equivalents of 18KhGT steel include German 20MnCr5 (DIN 1.7147) and French 20MC5 (NF A 35-551).

[0020] Next, prepare the cementation paste. The paste contains the following components (wt%):

[0021] • barium carbonate (BaCO3) – 20-21

[0022] • gas soot DG-100 – 53-54

[0023] • bentonite – 8-9

[0024] • ground powdered quartz (Marshalite) – 17-18

[0025] The resulting dry mixture is mixed with dextrin glue in a ratio of 3:1 to obtain a homogeneous paste.

[0026] Apply the resulting paste to the prepared surface of the part in a layer 1.5-2 mm thick. Application can be done with a brush, roller, or dipping, depending on the part's configuration.

[0027] After application, the paste is dried at 80°C for 15-30 minutes to remove moisture and fix the layer on the surface of the part.

[0028] Dried parts are packed in a sealed container with a filler consisting of the following components: 50% charcoal, 40% chamotte, and 10% barium carbonate. This filler prevents surface oxidation of the part and creates a favorable environment for the carburizing process without the formation of harmful compounds.

[0029] Carburizing is carried out at a temperature of 920-960°C for 4-6 hours. At these temperatures, the surface of the part is actively saturated with carbon from the paste and filler.

[0030] After carburizing, the parts are quenched at a temperature of 825-840 °C in an oil environment to fix the structure and increase the hardness of the surface layer.

[0031] The final stage is low tempering at a temperature of 150-200 °C for 2 hours to relieve internal stress and stabilize the structure.

[0032] The results of the studies showed the following characteristics of the obtained cemented layers:

[0033] • Cemented layer depth: 0.8-1.2 mm

[0034] • Surface layer microhardness: 58-62 HRC

[0035] • Cementite content in the surface layer: 8-12%

[0036] • Uniformity of carbon distribution across the layer thickness: ±5%

[0037] • Coating adhesion to the base: 30-35 MPa

[0038] • Wear resistance compared to non-cemented steel: increased by 3.5-4 times.

[0039] Advantages of the invention

[0040] High cementation speed: Due to active gas formation and the “spongy” structure of the coating, a cemented layer depth of 1.0 mm is achieved in 4.5 hours instead of 6 hours when using traditional methods, which speeds up the process by 25%.

[0041] Uniform carbon saturation: The paste ensures uniform distribution of carbon over the entire treated surface, including complex profiles and hard-to-reach places.

[0042] Environmental Safety: No toxic or volatile substances in the processing process minimizes environmental risks and simplifies environmental compliance.

[0043] Universality of application: The method is applicable both in mass and individual production, for parts of various configurations and sizes.

[0044] Cost-effectiveness: The use of readily available and abundant components reduces the cost of the process by 15-20% compared to traditional methods.

[0045] Increased coating strength: The addition of ground quartz powder (Marshalite) to the paste composition increases the strength of the formed layer by 20-25% due to improved structure and adhesion.

[0046] Process flexibility: The ability to tightly pack parts in a container increases process productivity and reduces energy costs.

[0047] The proposed method is cost-effective, as it reduces the carburization process time to 4-6 hours instead of 8-12 hours when using a solid carburizer, reducing energy consumption by 25-30%. The method eliminates the need for complex equipment to create a vacuum or precisely control the gas environment, reducing capital costs by 20-25%.

[0048] The technology does not require the use of harmful chemicals and does not generate hazardous waste, minimizing environmental control and waste disposal costs. The resulting carburized layers increase the service life of components by 40-45% compared to components treated with traditional carburizing methods.

[0049] Optimum processing mode (temperature 950°C for 5 hours) provides the best cost-effectiveness ratio with a surface layer microhardness of 58-62 HRC and a hardened layer depth of 1.0-1.1 mm.

Claims

1. A method for carburizing parts made of 18KhGT steel using a paste based on carbon-containing components, including preparing the surface of the said part, applying a 1.5-2 mm layer of carburizing paste mixed with dextrin glue, drying at 80 °C for 15-30 min, carburizing, hardening and low tempering at 150-200 °C for 2 hours, wherein the said paste contains the following components, by weight: barium carbonate - 20-21, gas soot DG-100 - 53, bentonite - 9 and ground powdered quartz - 17-18, characterized in that the carburizing is carried out at a temperature of 920-960 °C for 4-6 hours in a sealed container with a filler consisting of the following components: charcoal 50%, chamotte 40% and barium carbonate 10%, and hardening is carried out at 825-840 °C.

2. The method according to paragraph 1, characterized in that the preparation of the surface of said part before applying said paste is carried out by cleaning and degreasing.

3. The method according to paragraph 1, characterized in that the cementation is carried out at a temperature of 950 °C for 5 hours.

4. The method according to paragraph 1, characterized in that the parts are packed in a sealed container with the said filler, which provides an atmosphere protective against oxidation during heat treatment.

5. The method according to paragraph 1, characterized in that a cemented layer with a depth of 0.8-1.2 mm and a microhardness of 58-62 HRC is formed.