JPS622625B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a carbonitriding method using a fluidized bed furnace. More specifically, the present invention relates to a method of carbonitriding in a low temperature zone (500°C to 580°C) using a fluidized bed furnace. (Prior Art) In order to improve the wear resistance, corrosion resistance, etc. of shafts, gears, etc., carbonitriding treatment has conventionally been performed in a low temperature zone. For example, the salt bath method involves treatment in a salt bath containing soda cyanide as the main component, or the gas furnace method involves treatment in a furnace supplied with an atmospheric gas containing a mixture of endothermic carburizing gas and ammonia gas. It is being carried out. However, the salt bath method has been considered difficult to implement due to pollution concerns, and the gas furnace method has the disadvantage of easily causing quality variations. We are in the process of developing. (Problems to be solved by the invention) The present invention was invented against this background, and is intended to be used in low-temperature zones to prevent pollution, prevent quality variations, and save energy. It is an object of the present invention to provide a carbonitriding method. (Means for solving the problem) The carbonitriding method of the present invention that achieves this objective is as follows:
Supplying an atmospheric gas containing a mixture of nitrogen, ammonia, and carbon dioxide or oxygen so that the refractory granules in the hearth can form a fluidized bed;
Fuel gas and the air necessary to combust the fuel gas are supplied slightly below or above the upper surface of the fluidized bed, and the fuel gas is combusted only in the region near the upper surface of the fluidized bed to lower the furnace temperature to 500°C. It is characterized by processing while maintaining the temperature between ℃ and 580℃. (Example) The following will explain based on the drawings. In FIGS. 1 and 2, atmospheric gas is supplied to the furnace 1 from the pipe 2, fuel gas is supplied from the pipes 3a and 3b, and the furnace 1 is supplied with the gas from the pipe 4a. , 4b supply the air necessary to combust the fuel gas. The atmosphere gas is a mixture of nitrogen, ammonia, and carbon dioxide or oxygen, and these are mixed into a mixture of 60% (nitrogen): 35% (ammonia): 5 through an appropriate mixing device (not shown). %(carbon dioxide)
or 60% (nitrogen): 39% (ammonia): 1% (oxygen). Further, as the fuel gas, hydrocarbon gas such as methane, ethane, propane, butane, or natural gas is used. Atmosphere gas is used to form a processing atmosphere and heat-resistant particles such as alumina particles and zircon sand in the container 7 are used in an amount necessary to form a fluidized bed, and fuel gas and air are used to maintain a predetermined temperature of the fluidized bed. Supply the required amount. Atmospheric gas supplied from the pipe 2 to the pressure chamber 5 of the furnace 1 is uniformly dispersed into the container 7 via a distribution plate 6 made of porous ceramic material. As the dispersion plate, a known suitable one such as a metal perforated plate is used. Alumina particles deposited on the dispersion plate 6 are fluidized to form a fluidized bed. Note that the upper surface of this fluidized bed is located at A in the figure. On the other hand, the piping 3a,
The required amount of fuel gas supplied through nozzle 8
It is ejected from a and 8b into the fluidized bed. Furthermore, the air supplied through the pipes 4a and 4b is also supplied to the nozzles 9a and 9.
b is ejected into the fluidized bed. These nozzles 8a, 8b and 9a, 9b are arranged slightly below the upper surface A of the fluidized bed, and the nozzles 8a, 8b are arranged slightly below the nozzles 9a, 9b. Therefore, the fuel gas ejected into the fluidized bed from the nozzles 8a and 8b is flown upward by the atmospheric gas supplied from the pipe 2 and rising in the fluidized bed, and is flowed upward from the nozzles 9a and 9b into the fluidized bed. The mixture becomes combustible when mixed with the air ejected inside, and when ignited by an ignition device (not shown), it burns and heats the fluidized bed. The fluidized bed is heated gradually downward from the upper surface A side, and after a predetermined time elapses, it is uniformly heated to a predetermined temperature. For example 570
℃±5℃. Note that the exhaust gas from the furnace 1 is exhausted through a filter 11 of a lid 10 that is removably attached to the upper end of the furnace 1. Articles to be treated, such as shafts and gears, are immersed into the fluidized bed from above the furnace 1 by suitable means (not shown) and supported by a horizontal grid 12. In this case, the lid 10 is removed from the furnace 1 in advance and reattached once the article is immersed in the fluidized bed. The article immersed in the fluidized bed is carbonitrided by contact with uniformly heated and flowing atmospheric gas. For example, a white ε layer of 15 to 20 microns can be obtained by treatment at 570 DEG C. for 2 hours. Note that during the process, the supply amount of atmospheric gas, fuel gas supply, and air supply amount are controlled to predetermined values. The carbonitrided article is taken out of the furnace by removing the lid 10 from the furnace 1 and using an appropriate means (not shown). During the treatment, surplus fuel gas that was not ejected into the fluidized bed from the nozzles 8a and 8b is transferred to the pipes 3a and 3b.
is sent to the discharge side, and then sent back to the supply side. In addition, the exhaust gas can be completely burned by the air jetted into the space above the upper surface A of the fluidized bed from the auxiliary nozzles 13a and 13b provided in the pipes 4a and 4b, and cold air is also supplied to the passage 14. This can prevent the atmospheric gas in the dispersion plate 6 and the pressure chamber 5 from being excessively heated. In addition, in the figure, 15 is a heat insulating material. In the present invention, combustion gas and air may be supplied by the method shown in FIG. 3 or FIG. 4. In FIG. 3, air from the pipe 16 and fuel gas from the pipe 17 are mixed together at the jet port 18 and jetted slightly below the upper surface A of the fluidized bed. Also the fourth
In the figure, air from pipe 19 and pipe 20
The fuel gases from the fluidized bed are mixed together at the ejection port 21 and ejected horizontally slightly above the upper surface A of the fluidized bed. Note that the spout 21 may be arranged diagonally downward. Further, the pipe 19 and the pipe 20 may be arranged separately. In this case, the pipe 19 is arranged above the pipe 20. The fuel gas supplied into the furnace burns only in the area near the upper surface A of the fluidized bed, making it possible to create an atmosphere suitable for treating the lower part of the fluidized bed. Note that the atmospheric gas can have various mixing ratios of nitrogen:ammonia:carbon dioxide or oxygen, but it is preferable to have the above-mentioned mixing ratio. The temperature in the fluidized bed is controlled by controlling the supply amount and ratio of combustion gas and air, and the treatment temperature zone is preferably a low temperature zone of 500°C to 580°C. Furthermore, the nozzles 8a and 8b for ejecting fuel gas are not only provided so as to be able to eject only in the horizontal direction, but also to be able to eject only diagonally upward, only diagonally downward, or in multiple directions such as horizontally and diagonally up and down. It may be provided. The angle is preferably 60° or less when provided so that it can be ejected diagonally upward, and 30° or less when provided so that it can be ejected diagonally downward. Example 1 120 cells at a depth of about 500 mm in a container 7 with a diameter of 500 mm
Alumina particles in an amount of 80% above the mesh sieve and below the mesh sieve were charged, and gas was blown into the solution at a rate of 350 N/min through the dispersion plate 6, which was a perforated metal plate, to form a fluidized bed. The depth of the alumina layer during fluidization is 600mm
It was about 700mm. The gas composition during sample processing was 60% nitrogen, 35% ammonia, and 5% hydrogen dioxide, propane was used as the fuel gas, and the temperature of the fluidized bed was controlled to be 570°C ± 5°C. The processed sample has a diameter of 10 mm and a length of 250 mm.
A small hole was made in the top of a round bar made of SACM645 material, and a stainless steel wire was passed through the sample into the center of the fluidized bed so that the top end of the sample was submerged into the fluidized bed approximately 100 mm from the surface. After about 2 hours of immersion, the sample was pulled up and cooled. The sample was cut at a length of 125 mm in the longitudinal direction, and the Knoop hardness (HK) of the cross section was measured.
The results are shown in Table 1, and it can be seen that good hardness was obtained and sufficient carbonitriding was performed. Example 2 Using the same equipment as Example 1, using the same atmospheric gas composition and amount as Example 1, diameter 10 mm, length 30 mm.
When a round bar cut piece of S15C material was treated at 570℃ for 2 hours, the surface hardness (HK) was 550 and the hardening depth was 0.43mm.
It was hot. Comparative Example 1 Using a conventional atmosphere furnace, ammonia 50%, PX
Surface hardness (HK) when treating S15C material with the same dimensions at 570℃ for 2 hours in a 50% mixed gas atmosphere
was 510, and the hardening depth was 0.32 mm. Example 3 A cylindrical sample of SACM645 material with a diameter of 10 mm and a length of 30 mm was treated for 1 hour at different temperatures using the same apparatus as in Example 1 and flowing an atmospheric gas having the same composition. Table 2 shows the surface hardness (HK) of the obtained samples.
High hardness (HK) at processing temperature 500℃~580℃
It can be seen that is obtained.

[Table] Example 4 Using the same equipment as used in Example 1, a test was conducted to confirm the uniformity of the process. First, thermocouples were attached to a basket with a diameter of 500 mm and a depth of 400 mm at 9 locations, 3 locations each at the top, center, and bottom, and the basket was immersed in a fluidized bed to measure the temperature at each location under the same conditions as in Example 1. It was measured. The results are shown in Table 3. Note that the upper end surface of the basket was located approximately 150 mm inside the surface of the fluidized bed. Measurements were taken at three different locations for each part.

[Table] Next, attach five round cut pieces of S15C material with a diameter of 10 mm and a length of 30 mm to the top, center, and bottom of the basket as samples, so that their upper ends are approximately 150 mm inside the fluidized bed. The samples were soaked for 2 hours at 570°C. After cooling, the thickness of the compound layer on the surface of each sample was measured using a microscope. In addition, the measurement positions were changed in each part, and measurements were taken at five locations. The results are shown in Table 4. This is better compared to conventional treatment using an atmospheric furnace of the same scale, where the compound layer thickness varied by ±15μ.

[Table] (Effects of the Invention) Based on the above, according to the present invention, the following effects can be obtained. (b) Because uniform temperature distribution and atmosphere can be obtained,
It is possible to prevent uneven carbonitriding from occurring and also to prevent deformation of the object to be treated. (b) Since the surface of the object to be treated is constantly activated by the flowing action of the refractory granules, the diffusion of carbon and nitrogen components is promoted. (c) An atmosphere suitable for carbonitriding can be easily obtained, and variations in quality can be reduced. (d) Heat transfer rate and carbonitriding rate are fast, and carbonitriding can be carried out reasonably. (e) There are no pollution or hygiene problems, making it safer and energy-saving.

【table】 [Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the furnace, FIG. 2 is a partial perspective view of FIG. 1, and FIGS. 3 and 4 are schematic diagrams showing other examples of the method of supplying fuel gas and air. 1: Furnace, 2: Piping for supplying atmospheric gas, 3
a, 3b: Piping for supplying fuel gas, 4a, 4
b: Piping that supplies the air necessary to burn the fuel gas, A: The top surface of the fluidized bed.

Claims (1)

[Claims] 1. An atmospheric gas containing a mixture of nitrogen, ammonia, and carbon dioxide or oxygen is supplied so that the refractory granules in the hearth can form a fluidized bed, and at a position slightly below or above the upper surface of the fluidized bed. The fuel gas and the air necessary to combust the fuel gas are supplied to the fluidized bed, and the fuel gas is combusted only in the region near the upper surface of the fluidized bed, thereby maintaining the furnace temperature at 500°C to 580°C. A fluidized bed carbonitriding method characterized by: