RU2017860C1 - Method for gas cementation of large-sized articles - Google Patents

Abstract

FIELD: processing large-sized articles. SUBSTANCE: articles are heated, heating time being 0.33-0.44 of diffusion sustaining time at carbon potential of atmosphere 0.1-0.2. Sustaining time is 0.32-0.85 of diffusion sustaining time at carbon potential 0.7-0.8. Then articles are cooled, cooling time being 0.009-0.11 of diffusion sustaining time at carbon potential of atmosphere 1.2-1.3. The process is carried out in atmosphere of nitrogen, natural gas and air during their uninterrupted circulation. Quantity of nitrogen which is fed for all the stages of the process during 1 h is 0.95-1.0 of furnace's volume. Natural gas is fed by main and regulating canals at volumes 0.6-0.7 and 0.3-0.4 respectively. EFFECT: increases working period of articles. 1 tbl

Description

 The invention relates to inorganic chemistry, in particular to methods of chemical-thermal treatment used in mechanical engineering and other industries.

 A known method of gas cementation of steel products in the directional circulation, including the stage of heating, saturation, diffusion and chilling, in which the cementation atmosphere in the furnace is created by feeding endothermic gas into the working space from an endothermic installation and a controlled addition of hydrocarbon gas (natural gas, city gas, propane, butane, etc.).

 Closest to the proposed method is the gas cementation method adopted for the prototype of large-sized steel products, including heating in an atmosphere of nitrogen, natural gas and air, diffusion holding and curing with a given value of the carbon potential at each stage of the process under continuous circulation.

 The disadvantage of this method is the insufficient value of the coefficient of mass transfer β, the shallow depth of the cementation site and, as a result, the low uniformity of processing, which leads to a decrease in the service life of the products.

 The aim of the invention is to increase the uniformity of processing and increase due to this service life of products.

 This goal is achieved by the fact that in the method of gas cementation of large-sized steel products, including heating in an atmosphere of nitrogen, natural gas and air, diffusion holding undercoating with a given value of the carbon potential at each stage of the process under continuous circulation, nitrogen is fed into the furnace for 1 h at at all stages of processing in the amount of 0.95-1.0 of the furnace volume, natural gas is supplied to the working volume through the main and control channels at all process stations with the supply of 0.6-0.7 natural gas volumes ohm and 0.3-0.4 - through the control channel, heating is carried out for 0.33-0.44 of the time of diffusion exposure at a carbon potential of the atmosphere of 0.1-0.2 with a supply of 1 hour hydrocarbon mixture in an amount of 0 , 9-1.0 of the furnace volume with a ratio of air and natural gas of 0.01-0.15, diffusion exposure is carried out first for 0.32-0.85 of the total time at a carbon potential of 1.2-1.3 with a feed for 1 h of the mixture in an amount of 1.7-1.75 of the volume of the furnace with a ratio of air and natural gas 0.75-0.8, and then for 0.15-0.68 with a carbon potential of 0.7-0, 8 with the supply for 1 h of the mixture in quantity 1.7-1.75 volume of the furnace with a ratio of air and natural gas 0.9-0.95, and undermining is carried out for 0.09-0.11 from the time of diffusion exposure at a carbon potential of the atmosphere of 1.2-1.3 with a supply for 1 h of a hydrocarbon mixture in an amount of 1.65-1.7 of the volume of the furnace with a ratio of air and natural gas of 0.65-0.7.

 The proposed method of gas cementation is implemented as follows.

 In a cementing furnace, for example a shaft furnace, in which the atmosphere is circulated by a fan at a speed of 0.6 m / s; 1.2 m / s-1.5 m / s serves (directly into the working space) nitrogen, natural gas and air.

 Natural gas is fed into the working volume of the furnace through the main channel to the control channels at all stages of the process with the supply of 0.6-0.7 volume of natural gas through the main channel and 0.3-0.4 through the control channel. The cementation process of large-sized steel products is carried out according to the following stages: heating, saturation, diffusion and curing. At all stages of the treatment, nitrogen is fed into the furnace for 1 h in the amount of 0.95-1.0 of the furnace volume.

 The experiments were conducted on a Northrop mine electric furnace at the Kuibyshevburmash Production Association. The details of the drill bit-paws and cones made of steel 14KHNZMA and 15NZMA were subjected to processing.

 Products were loaded into shaft furnaces in baskets with a trellised bottom. To protect products from direct radiation from heaters, a heat shield (muffle) was installed between them.

The furnaces are equipped with fans located in the hearth of the furnace, creating an intense circulation of the furnace atmosphere. The controlled atmosphere was also supplied at the bottom of the furnace. The tightness of the working space of the furnace is achieved using sand shutters. The volume of the working space of the furnace is ≈ 3.4 m ³ . The required depth of cementation is 1.8-1.9 mm, the duration of the cementation process is 9 hours.

Process temperature:
Heating 800-940 ^о С
Saturation of 940 ^{° C}
Diffusion 940 ^{° C}
Basting 900 ^о С
The experimental results are summarized in the table.

 From the data of the table it follows that the quality of the cemented layer fully meets the requirements of the OCT for the distribution of carbon concentration, hardness and microstructure. The duration of the cementation process was reduced by 15-20% compared with traditional technology.

 Using the method allows to increase the uniformity of processing and thereby increase the service life of the processed products. In this regard, the reliability and durability of the drilling tool is increased by 3%, and the productivity of the equipment is increased by 5%.

Claims (1)

 METHOD OF GAS CEMENTATION OF LARGE-SIZED PRODUCTS, including heating in an atmosphere of nitrogen, natural gas and air, diffusion holding and stirring with a given value of the carbon potential at each stage of the process under continuous circulation, characterized in that, in order to increase the uniformity of processing and increase due to this the service life of the products, nitrogen is supplied to the furnace in one hour at all stages of processing in the amount of 0.95 - 1.0 volume of the furnace, natural gas is supplied to the working volume through the main and control channels n and at all stages of the process with the supply of 0.6 - 0.7 volume of natural gas through the main and 0.3 - 0.4 through the control channel, heating is carried out for 0.33 - 0.44 of the time of diffusion exposure at a carbon potential of the atmosphere 0 , 1 - 0.2 with the supply in one hour of a hydrocarbon mixture in an amount of 0.9 - 1.0 volume of the furnace with a ratio of air and natural gas of 0.01 - 0.15, diffusion exposure is carried out first for 0.32 - 0, 85 of the total time with a carbon potential of 1.2 - 1.3 with a supply in one hour of a mixture in the amount of 1.7 - 1.75 of the furnace volume with a ratio of air and natural gas of 0.75 - 0.8, and then for 0.15 - 0.68 with a carbon potential of 0.7 - 0.8 with a supply in one hour of a mixture in the amount of 1.7 - 1.75 of the furnace volume with a ratio of air and natural gas 0 , 9 - 0.95, and stirring is carried out for 0.09 - 0.11 from the time of diffusion exposure at a carbon potential of the atmosphere of 1.2 - 1.3, with the supply of 1 h of hydrocarbon mixture in an amount of 1.65 - 1, 7 from the volume of the furnace with a ratio of air and natural gas of 0.65 - 0.7.

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