JP2005179714A - Carburizing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carburizing method capable of shortening the carburizing time and controlling the carbon potential. <P>SOLUTION: The carburizing method to store a steel work W in a carburizing chamber 11 and carburize it comprises a first carburizing step of supplying enrich gas into the carburizing chamber 11 to carburize the steel work W under a pressure reducing state, and a second carburizing step of supplying carrier gas and enrich gas into the carburizing chamber 11 to carburize the steel work W under the pressure higher than the pressure in the first carburizing step. The first carburizing step is performed in, for example, 5-30 minutes. In the second carburizing step, the pressure in the carburizing chamber is, for example, the atmospheric pressure. The carburizing time can be shortened compared with that by a known gas carburizing method using carrier gas, and carbon potential can also be controlled. Excellent carburization can be performed without deposition of cementite. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a carburizing method for steel material.

  As a carburizing method for steel materials, a modified gas (endthermic gas) obtained by using a mixed gas of hydrocarbon gas and air as a raw material and using an endothermic modified gas generator is used as a carrier gas. A method of carburizing by supplying a hydrocarbon-based gas as an enriched gas for obtaining a predetermined carbon potential together with a carrier gas into a carburizing chamber (a gas carburizing method using a carrier gas) has been widely used. In this gas carburizing method, the carbon potential is indirectly calculated by measuring the concentration or partial pressure of the gas components that make up the carburizing room atmosphere, and the amount of enriched gas supplied is adjusted based on the result. Carburization can be controlled.

  Usually, in such a gas carburizing method using a carrier gas, the carbon penetration per unit time is increased to shorten the processing time by setting the atmospheric carbon potential higher than the target surface carbon concentration. ing. In the subsequent diffusion process, carbon is diffused, and the surface carbon concentration and carburization depth are adjusted. However, too much enriched gas (hydrocarbon gas) is supplied to the carburizing chamber to increase the carbon potential during carburizing, so there is a risk of sooting (generation of soot). There is. At present, the gas carburizing method using carrier gas is a relatively well-established technology among many carburizing methods, but it is still not sufficient from the viewpoint of energy and the global environment. Further improvements are desired. One approach is to reduce processing time. And shortening the processing time also leads to a reduction in the amount of gas used and energy.

  On the other hand, recently, a carburizing method called a vacuum carburizing method (or a reduced pressure carburizing method) is becoming widespread. Normally, in the vacuum carburizing method, hydrocarbon gas such as methane gas or propane gas is added directly into the carburizing chamber under reduced pressure without using carrier gas. It is considered that the activated carbon generated by the hydrocarbon gas added in this way decomposes on the surface of a high-temperature steel product enters the steel product material. Such a vacuum carburizing method has a higher carbon inflow rate into the steel product than the gas carburizing method using the carrier gas described above, and can obtain a desired carburizing depth in a short time.

  Conventionally, as this vacuum carburizing treatment method, a saturated hydrocarbon gas is directly supplied into a furnace and treated at a pressure of 10 to 70 kPa, as well as acetylene as disclosed in JP-A-8-325701. A method of processing at a pressure of 1 kPa or less using a gas, as disclosed in JP 2000-1765 A, using a mixed gas of ethylene gas or ethylene gas and acetylene gas at a pressure of 1 to 10 kPa. Methods for processing are known.

JP-A-8-325701 JP 2000-1765 A

  However, the vacuum carburizing method still has the problem that it is difficult to control the carbon potential in the carburizing room atmosphere. Unlike the gas carburizing method using the carrier gas described above, the vacuum carburizing method generally adjusts the carburization depth and surface carbon concentration by controlling the time of carburization and diffusion. , It depends largely on experience (know-how).

  Accordingly, an object of the present invention is to provide a carburizing treatment method that can shorten the treatment time and can also control the carbon potential.

In order to achieve this goal, according to the present invention, a steel product is stored in a carburizing chamber and carburized, and a hydrocarbon gas is supplied into the carburizing chamber and the steel product is carburized under reduced pressure. There is provided a carburizing method characterized by having a first carburizing process and a second carburizing process for supplying a carrier gas and an enriched gas into a carburizing chamber and carburizing a steel product under a pressure higher than that of the first carburizing process. . According to this carburizing method, a high carbon concentration layer is formed on the surface of the steel product in a shorter time in the first carburizing process, and in the latter carburizing process, the high carbon concentration layer on the surface of the steel product is controlled while controlling the carburizing potential. Spread. Thereby, desired carburizing characteristics can be obtained in a shorter time than a carburizing method using a conventional carrier gas. Examples of the hydrocarbon gas supplied to the carburizing chamber in the early carburizing process and / or the enriched gas supplied to the carburizing chamber in the later carburizing process include C ₃ H ₈ gas, C ₃ H ₆ gas, and C ₄ H ₁₀ gas. , C ₂ H ₂ gas, C ₂ H ₄ gas, C ₂ H ₆ gas, or CH ₄ gas. In the initial carburizing step, C ₂ H ₂ gas may be supplied into the carburizing chamber, and the steel product may be carburized at a pressure in the carburizing chamber of 0.1 kPa to 1 kPa. Moreover, the initial carburizing step is, for example, 5 to 30 minutes. In the late carburizing process, the steel product may be carburized with the carburizing chamber pressure set to atmospheric pressure. Further, in the late carburizing step, an oxidizing gas composed of one or more of air, O ₂ gas, and CO ₂ gas may be supplied into the carburizing chamber. Further, a diffusion process may be performed after the late carburizing process.

  According to the present invention, it is possible to provide a carburizing method that can shorten the processing time as compared with a conventional gas carburizing method using a carrier gas and can also control the carbon potential. According to the present invention, good carburization can be performed without precipitation of cementite. In addition, a stable furnace atmosphere can be obtained by controlling the carbon potential, and as a secondary effect, it can be expected to reduce the variation in carburization between production lots.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic layout diagram of the carburizing and treating apparatus 1. FIG. 2 is an explanatory diagram of the carburizing chamber 11.

  As shown in FIG. 1, in the carburizing and treating apparatus 1, a carburizing chamber 11 and an oil quenching chamber 12 are provided on the left and right of the transfer chamber 10, and a gas cooling chamber 13 is provided on the back of the transfer chamber 10. is there. The carburizing chamber 11 is a heat treatment facility for carburizing the surface of the steel product W. An insertion door 15 that can be opened and closed is provided on the front surface of the transfer chamber 10. Partition doors 16, 17, 18 that can be opened and closed between the transfer chamber 10 and the carburizing chamber 11, between the transfer chamber 10 and the oil quenching chamber 12, and between the transfer chamber 10 and the gas cooling chamber 13, respectively. Is provided. In the oil quenching chamber 12, an openable / closable take-out door 20 is provided on a side surface facing the partition door 17.

  As shown in FIG. 2, a heater 27 surrounded by a heat insulating material 26 made of ceramic fiber having a low heat dissipation amount and a low heat storage amount is disposed inside a furnace shell 25 which is a casing of the carburizing chamber 11. . A steel product W to be carburized is inserted into the heater 27. Thus, a fan 28 for agitating the internal atmosphere of the carburizing chamber 11 is provided above the steel product W inserted inside the heater 27.

Inside the furnace shell 25, the hydrocarbon-based gas sent from the hydrocarbon-based gas supply unit 30 is supplied via the pipe line 32 while the supply amount is controlled by the mass flow controller 31. Similarly, a hydrocarbon-based gas as an enriched gas sent from the enriched gas supply unit 33 is supplied into the furnace shell 25 through a conduit 35 while the supply amount is controlled by the mass flow controller 34. The Examples of hydrocarbon gases (including those used as enriched gases) include C ₃ H ₈ gas, C ₃ H ₆ gas, C ₄ H ₁₀ gas, C ₂ H ₂ gas, and C ₂ H ₄ gas. , C ₂ H ₆ gas, or CH ₄ gas is used. Similarly, the oxidizing gas sent from the oxidizing gas supply unit 36 is supplied into the furnace shell 25 through the conduit 38 while the supply amount is controlled by the mass flow controller 37. As the oxidizing gas, for example, one or more of air, O ₂ , and CO ₂ are used. Similarly, the carrier gas sent from the carrier gas supply unit 39 is supplied into the furnace shell 25 through the conduit 41 while the supply amount is controlled by the flow rate adjusting valve 40. As the carrier gas, for example, a modified gas (endthermic gas) obtained by using a mixed gas of hydrocarbon gas and air as a raw material and using an endothermic modified gas generator is used. In addition, although not shown, N ₂ gas sent from an appropriate N ₂ supply unit is supplied to the transfer chamber 10, the carburizing chamber 11, the oil quenching chamber 12, and the gas cooling chamber 13 while the supply amount is controlled. It has become so.

  The inside of the furnace shell 25 (the carburizing chamber 11) is depressurized to a desired pressure by a vacuum pump 46 through a pipe 45. The pressure in the internal atmosphere of the carburizing chamber 11 is detected by the pressure gauge 50 and input to the controller 51. Further, the temperature of the internal atmosphere of the carburizing chamber 11 is detected by the thermocouple 52 and input to the controller 51.

The internal atmosphere of the carburizing chamber 11 is sampled by the sampling device 54 through the pipe line 53. The internal atmosphere of the carburizing chamber 11 sampled by the sampling device 54 is analyzed by the two atmosphere analyzers 55 and 56, respectively. One atmosphere analyzer 55 is a CO gas partial pressure meter or CO gas concentration meter, and the CO gas partial pressure or CO gas concentration detected by the atmosphere analyzer 55 is input to the controller 51. The other atmospheric analyzer 56 is a CO ₂ gas partial pressure meter or a CO ₂ gas concentration meter. Similarly, the CO ₂ gas partial pressure or CO ₂ gas concentration detected by this atmospheric analyzer 56 is also input to the controller 51. Is done. Further, the internal atmosphere of the carburizing chamber 11 is sampled by the atmosphere analyzer 61 through the pipe line 60. The atmosphere analyzer 61 is an O ₂ gas partial pressure meter or an O ₂ gas concentration meter. Similarly, the O ₂ gas partial pressure or O ₂ gas concentration detected by the atmosphere analyzer 61 is also input to the controller 51. .

  Thus, the controller 51 calculates the carbon potential of the internal atmosphere of the carburizing chamber 11 based on the input temperature, pressure (each partial pressure), and each concentration. Based on the calculated value, the mass flow controllers 31, 34, 37, and 40 are controlled via the controller 62, and the heater 27 and the vacuum pump 46 are controlled to control the carbon potential of the internal atmosphere of the carburizing chamber 11. Set to desired value.

  In the carburizing and treating apparatus 1 configured as described above, the insertion door 15, the partition doors 16, 17, and 18 and the extraction door 20 are all closed at first. Then, as the previous state, the temperature of the internal atmosphere of the carburizing chamber 11 is heated and held at a predetermined temperature (preferably 850 ° C. to 1050 ° C.) by the heater 27, and the pressure of the internal atmosphere of the carburizing chamber 11 is reduced to vacuum. The pressure is reduced to 0.1 kPa or less by the pump 46. Also, the pressure of the internal atmosphere of the quenching chamber 12 is reduced to 0.1 kPa or less by a vacuum pump (not shown). Moreover, the temperature of the quenching oil arrange | positioned in the quenching chamber 12 is heated to the temperature used as predetermined | prescribed temperature at the time of quenching of the steel material goods W mentioned later. On the other hand, the pressure inside the transfer chamber 10 is set to atmospheric pressure.

  First, the insertion door 15 on the front surface of the transfer chamber 10 is opened, and the steel product W is inserted into the transfer chamber 10. Then, the insertion door 15 is closed, and the inside of the transfer chamber 10 is decompressed to 0.1 kPa or less by a vacuum pump (not shown). Thereafter, the partition door 16 between the transfer chamber 10 and the carburizing chamber 11 is opened, the steel product W is carried into the carburizing furnace 11, and the partition door 16 is closed. The movement of the steel product W between the transfer chamber 10 and the carburizing chamber 11 and the movement of the steel product W between the transfer chamber 10 and the quenching chamber 12 described later are not shown, but are motor-driven chains. It is carried out by a conveying device such as a conveying device or roller hearth.

After the partition door 16 is closed and the carburizing chamber 11 is sealed, the steel product W is heated in the carburizing chamber 11 by a heater 27 under a reduced pressure for a predetermined time (for example, 15 minutes). Thereafter, N ₂ gas is supplied into the carburizing chamber 11 and the internal atmosphere is restored to a predetermined pressure (for example, 100 kPa). In this way, the temperature raising / soaking process of the treatment material W is performed in an N ₂ atmosphere. Then, after the treatment material W is sufficiently heated and soaked to the carburizing temperature, the pressure of the internal atmosphere of the carburizing chamber 11 is reduced again to 0.1 kPa or less by the vacuum pump 46.

Next, the mass flow controller 31 is opened, and for example, C ₃ H ₈ gas, C ₃ H ₆ gas, C ₄ H ₁₀ gas, C ₂ H ₂ gas, C ₂ H ₄ gas, C ₂ H ₆ gas, CH ₄ gas A carburizing gas composed of one or more hydrocarbon-based gases is supplied into the carburizing chamber 11, and the internal atmosphere in the carburizing chamber 11 is restored to a predetermined pressure (for example, 0.1 to 10 kPa). . In addition, when the internal atmosphere in the carburizing chamber 11 is reduced to less than 0.1 kPa, the carburizing ability is lost. On the other hand, if the internal atmosphere in the carburizing chamber 11 is larger than 10 kPa, a problem of sooting occurs. In the case of using _C 2 _{H 2} gas as a hydrocarbon gas, that causes pressure recovery inside atmosphere in the carburizing chamber 11 in the range of 0.1~0.7kPa preferred. Thus, while maintaining the internal atmosphere in the carburizing chamber 11 at a predetermined pressure, a carburizing gas composed of a hydrocarbon-based gas is supplied into the carburizing chamber 11 at a predetermined flow rate (for example, C ₂ H ₂ gas is 2 liters / min). While supplying, a pre-carburizing process (vacuum carburizing process) for carburizing a steel product under reduced pressure is performed for a predetermined time.

  Here, the time required for the initial carburizing process is a time for sufficiently increasing the surface carbon concentration of the steel product W to be processed (preferably 5 minutes or more), and a time during which cementite precipitation and coarsening does not occur. (Preferably within 30 minutes).

After completing the previous carburizing step, the flow control valve 40 is opened, and a carrier gas made of, for example, a modified gas (endthermic gas) is supplied into the carburizing chamber 11, and the internal atmosphere in the carburizing chamber 11 is changed to the aforementioned previous carburizing. The pressure is restored to a pressure higher than that in the process (for example, atmospheric pressure). Then, after the return pressure of the carburizing chamber 11 is completed, the carrier gas is supplied to the carburizing chamber 11 at, for example, 50 liters / min while maintaining the pressure, and the mass flow controller 34 is opened, for example, C ₃ H ₈ gas, Hydrocarbon gas as an enriched gas such as one or more of C ₃ H ₆ gas, C ₄ H ₁₀ gas, C ₂ H ₂ gas, C ₂ H ₄ gas, C ₂ H ₆ gas, CH ₄ gas, etc. By supplying a carburizing gas consisting of the above into the carburizing chamber 11, a late carburizing process (gas carburizing process) is performed.

On the other hand, in this late carburizing step, the mass flow controller 37 is opened and, for example, an oxidizing gas composed of one or more of air, O ₂ gas, and CO ₂ gas is supplied into the carburizing chamber 11.

In this late carburizing process, the mass flow controllers 31, 34, 37 and the heater 27 are controlled, and the carbon potential of the internal atmosphere of the carburizing chamber 11 is controlled at a desired value while maintaining a predetermined carburizing pressure (for example, atmospheric pressure). Is possible. That is, in the late carburizing process, the pressure in the atmosphere inside the carburizing chamber 11 is detected by the pressure gauge 50 and input to the controller 51. Further, the temperature of the internal atmosphere of the carburizing chamber 11 is detected by the thermocouple 52 and input to the controller 51. Further, the internal atmosphere of the carburizing chamber 11 is sampled by the sampling device 54 through the pipe line 53. The internal atmosphere of the carburizing chamber 11 sampled by the sampling device 54 is analyzed by the two atmosphere analyzers 55 and 56, respectively, and the CO gas partial pressure or CO gas concentration detected by the atmosphere analyzer 55 and the atmosphere analysis are analyzed. The CO ₂ gas partial pressure or CO ₂ gas concentration detected by the device 56 is input to the controller 51. Further, the internal atmosphere of the carburizing chamber 11 is sampled by the atmosphere analyzer 61 through the pipe line 60. Then, the O ₂ gas partial pressure or the O ₂ gas concentration detected by the atmosphere analyzer 61 is input to the controller 51. Thus, the controller 51 calculates the carbon potential of the internal atmosphere of the carburizing chamber 11 based on the input temperature, pressure (each partial pressure), and each gas concentration. Based on the calculated value, the mass flow controllers 31, 34, and 37 are controlled via the controller 62 to adjust the supply amount of each gas into the carburizing chamber 11. If necessary, the heater 27 and the vacuum pump 46 are also controlled. Thus, the carbon potential of the internal atmosphere of the carburizing chamber 11 is set to a desired value.

  Then, after the late carburizing process is completed, a diffusion process after carburizing is performed. In this case, by controlling the mass flow controllers 31, 34, and 37, the supply amount of the hydrocarbon-based gas and the oxidizing gas to the carburizing chamber 11 is adjusted, and the internal atmosphere of the carburizing chamber 11 is controlled to a desired carbon potential. By doing so, the surface carbon concentration of the steel product W can be adjusted. Alternatively, the supply of each gas to the carburizing chamber 11 may be stopped, the inside of the carburizing chamber 11 may be evacuated again by the vacuum pump 37, and the steel product W may be held under reduced pressure to adjust the surface carbon concentration.

  Then, after completing the diffusion process for a predetermined time, the temperature of the internal atmosphere of the carburizing chamber 11 is lowered to a predetermined temperature. Thereafter, the partition door 16 between the transfer chamber 10 and the carburizing chamber 11 is opened, and the partition door 17 between the transfer chamber 10 and the quenching chamber 12 is also opened, and the steel product W is transferred from the carburizing chamber 11 to the transfer chamber 10 under reduced pressure. Is transferred to the quenching chamber via 12 and oil quenching is performed.

  Then, after the quenching is completed, the takeout door 20 is opened, and the steel product W is taken out from the quenching chamber 12. Note that the adjustment of the surface carbon concentration and the temperature control to the quenching temperature can be performed simultaneously.

  Thus, it is possible to shorten the processing time as compared with the conventional gas carburizing method using a carrier gas and to perform the carburizing process capable of controlling the carbon potential. The steel product W thus carburized is subjected to good carburization without precipitation of cementite.

In the latter carburizing process, the carbon potential in the carburizing chamber 11 is controlled by the CO gas partial pressure or CO gas concentration, the CO ₂ gas partial pressure or the CO ₂ gas concentration detected by the atmosphere analyzers 55, 56 and 61. In addition to the O ₂ gas partial pressure or O ₂ gas concentration, the H ₂ gas partial pressure or H ₂ gas concentration of the internal atmosphere of the carburizing chamber 11, the H ₂ O partial pressure or dew point of the internal atmosphere of the carburizing chamber 11, it may be performed based on the CH ₄ gas partial pressure or CH ₄ gas concentration of the inner atmosphere of the carburizing chamber 11. The carbon potential at that time may be set within a range where no soot precipitation occurs with reference to the carbon solubility limit determined by the carburizing temperature.

(Example 1)
In order to see the carburization results in the carburizing chamber, steel specimens were installed as rods of material SCR420H, diameter φ18 mm, and length 40 mm at positions 1 to 5 shown in FIG. 3 in the carburizing chamber. That is, when a steel product having a rectangular parallelepiped shape whose gross load is the maximum loading capacity of the carburizing chamber is inserted into the carburizing chamber, each rod-shaped specimen is installed at a position corresponding to the corner and center of the steel product. . This steel product (each bar specimen) was heated to a carburizing temperature of 950 ° C. in a carburizing chamber maintained at a pressure of 0.1 kPa or less and a temperature of 950 ° C.

FIG. 4 is an explanatory diagram showing processing steps (temperature raising / soaking step, carburizing step (early carburizing step and late carburizing step), diffusion step) according to Example 1 according to elapsed time. After heating for 15 minutes while evacuating the carburizing chamber, N ₂ gas was supplied to restore the pressure in the carburizing chamber to 100 kPa, and the temperature of the steel product was raised and soaked at 950 ° C. 90 minutes after carrying the steel product into the carburizing chamber, the carburizing chamber was evacuated again, and the pressure in the carburizing chamber was reduced to 0.1 kPa or less. Thereafter, C ₂ H ₂ gas was supplied into the carburizing chamber, and the carburizing process (vacuum carburizing treatment) was performed on the steel product for 10 minutes. During the previous carburizing process, C ₂ H ₂ was supplied into the carburizing chamber at 2 liters / min, and the pressure in the carburizing chamber was maintained at 0.67 kPa by controlling the exhaust speed of the vacuum pump.

In this manner, after the pre-carburization process for 10 minutes was performed, the supply of C ₂ H ₂ was stopped. Subsequently, the carburizing chamber was returned to atmospheric pressure by supplying a carrier gas (endthermic gas) at 50 liters / min, and a late carburizing process (gas carburizing) was started. During the late carburizing process, the carrier gas was kept flowing at 50 l / min into the carburizing chamber, and the carburizing chamber pressure was maintained at atmospheric pressure. In addition, the carbon potential of the carburizing chamber atmosphere was controlled to 1.2% by adjusting the amount of C ₃ H ₈ and CO ₂ supplied to the carburizing chamber.

  After the late carburizing process for 150 minutes, the diffusion process was started. In this diffusion step, the carbon potential was controlled to 0.9%. After performing a diffusion process for 50 minutes, the carburizing chamber was evacuated again, and the steel product was oil-quenched in the quenching chamber via the transfer chamber.

  FIG. 5 shows the average carbon concentration distribution of the steel products installed in the five carburizing chambers in Example 1 where the carburizing and quenching process was completed in this way. As a result, the effective carburization depth (0.36% C) was 0.94 mm, and the surface carbon concentration was approximately 0.8 wt% C. When the time required for the carburizing process was compared between this Example 1 and a conventional gas carburizing method using a carrier gas (endothermic gas) (carburizing process carbon potential 1.2% control), Example 1 Compared with the carburizing process time of 160 minutes, in the case of the conventional gas carburizing process, the time is 190 minutes, which is a reduction of 30 minutes. In other words, the carburizing process time was reduced by about 16%.

  Thus, according to Example 1, it was possible to obtain a carburized layer having a required depth in a short time as compared with a gas carburizing method using a conventional carrier gas (endothermic gas). Furthermore, as with the conventional gas carburizing treatment method, the control of the carbon potential was easy, and good carburizing treatment could be performed without generation of soot and cementite precipitation.

(Example 2)
As in Example 1, in order to see the carburization result in the carburizing chamber, a rod-shaped specimen having a material SCR420H, a diameter φ18 mm, and a length of 40 mm was placed at positions 1 to 5 shown in FIG. Each was installed. That is, when a steel product having a rectangular parallelepiped shape whose gross load is the maximum loading capacity of the carburizing chamber is inserted into the carburizing chamber, each rod-shaped specimen is installed at a position corresponding to the corner and center of the steel product. . This steel product (each bar specimen) was heated to a carburizing temperature of 950 ° C. in a carburizing chamber maintained at a pressure of 0.1 kPa or less and a temperature of 950 ° C.

FIG. 6 is an explanatory diagram showing processing steps (temperature raising / soaking step, carburizing step (early carburizing step and late carburizing step), diffusion step) according to Example 2 according to the elapsed time. After heating for 15 minutes while evacuating the carburizing chamber, N ₂ gas was supplied to restore the pressure in the carburizing chamber to 100 kPa, and the temperature of the steel product was raised and soaked at 950 ° C. 90 minutes after carrying the steel product into the carburizing chamber, the carburizing chamber was evacuated again, and the pressure in the carburizing chamber was reduced to 0.1 kPa or less. Thereafter, C ₂ H ₂ gas was supplied into the carburizing chamber, and the carburizing process (vacuum carburizing treatment) was performed on the steel product for 30 minutes. During the previous carburizing process, C ₂ H ₂ was supplied into the carburizing chamber at 2 liters / min, and the pressure in the carburizing chamber was maintained at 0.67 kPa by controlling the exhaust speed of the vacuum pump.

Thus, after the 30-minute pre-carburization step, the supply of C ₂ H ₂ was stopped. Subsequently, the carburizing chamber was returned to atmospheric pressure by supplying a carrier gas (endthermic gas) at 50 liters / min, and a late carburizing process (gas carburizing) was started. During the late carburizing process, the carrier gas was kept flowing at 50 l / min into the carburizing chamber, and the carburizing chamber pressure was maintained at atmospheric pressure. In addition, the carbon potential of the carburizing chamber atmosphere was controlled to 1.2% by adjusting the amount of C ₃ H ₈ and CO ₂ supplied to the carburizing chamber.

  After the late carburizing process for 80 minutes, the diffusion process was started. In this diffusion step, the carbon potential was controlled to 0.9%. After performing a diffusion process for 50 minutes, the carburizing chamber was evacuated again, and the steel product was oil-quenched in the quenching chamber via the transfer chamber.

  FIG. 7 shows the average carbon concentration distribution of the steel products installed in the five carburizing chambers in Example 2 where the carburizing and quenching process was completed in this way. As a result, the effective carburization depth (0.36% C) was 0.89 mm, and the surface carbon concentration was approximately 0.8 wt% C. In this Example 2 and the conventional gas carburizing method (carburizing process carbon potential 1.2% control) using a carrier gas (endothermic gas), the carburizing process (the carburizing process and the late carburizing process) was required. When the time was compared, the carburizing process time of Example 2 was 110 minutes, which was 80 minutes shorter than 190 minutes in the case of the conventional gas carburizing treatment method. In other words, the carburizing process time was reduced by about 58%. Thus, as in Example 1, a carburized layer having a required depth could be obtained in a shorter time than a conventional gas carburizing method using a carrier gas (endothermic gas). Furthermore, as with the conventional gas carburizing treatment method, the control of the carbon potential was easy, and good carburizing treatment could be performed without generation of soot and cementite precipitation.

  The present invention can be applied to carburizing treatment of steel products such as various parts.

It is a schematic layout of a carburizing and treating apparatus. It is explanatory drawing of a carburizing chamber. It is explanatory drawing which shows arrangement | positioning of the steel material goods in the carburizing chamber in Example 1 and 2. FIG. 6 is an explanatory diagram of a processing process according to Example 1. FIG. 2 is an average carbon concentration distribution diagram of the steel product of Example 1. FIG. FIG. 10 is an explanatory diagram of processing steps according to Example 2; It is an average carbon concentration distribution map of the steel product of Example 2.

Explanation of symbols

W Steel Products 1 Carburizing and Treating Device 10 Transfer Chamber 11 Carburizing Chamber 12 Oil Quenching Chamber 13 Gas Cooling Chamber 25 Furnace Shell 26 Heat Insulating Material 27 Heating Heater 28 Fan 30 Hydrocarbon Gas Supply Unit 31, 34, 37 Mass Flow Controller 33 Enriched Gas Supply unit 36 Oxidizing gas supply unit 39 Carrier gas supply unit 46 Vacuum pump 50 Pressure gauge 51 Controller 52 Thermocouple 54 Sampling device 55, 56, 61 Atmosphere analyzer 62 Controller

Claims (7)

A method of storing steel products in a carburizing chamber and carburizing them,
Carburizing process for supplying hydrocarbon gas into the carburizing chamber and carburizing steel products under reduced pressure,
A carburizing treatment method comprising a later carburizing step of supplying a carrier gas and an enriched gas into a carburizing chamber and carburizing a steel product under a pressure higher than that of the previous carburizing step. The hydrocarbon-based gas supplied into the carburizing chamber in the early carburizing process and / or the enriched gas supplied into the carburizing chamber in the later carburizing process are C ₃ H ₈ gas, C ₃ H ₆ gas, C ₄ H ₁₀ gas. The carburizing method according to claim 1, wherein the method is one or more of C ₂ H ₂ gas, C ₂ H ₄ gas, C ₂ H ₆ gas, and CH ₄ gas. 3. The carburizing method according to claim 1, wherein in the initial carburizing step, C ₂ H ₂ gas is supplied into the carburizing chamber, and the steel product is carburized at a pressure of 0.1 kPa to 1 kPa in the carburizing chamber. The carburizing method according to claim 1, 2 or 3, wherein the first carburizing step is 5 to 30 minutes. The carburizing treatment method according to claim 1, 2, 3, or 4, wherein in the latter carburizing step, the steel product is carburized by setting the carburizing chamber pressure to atmospheric pressure. 6. In the late carburizing step, oxidizing gas comprising one or more of air, O ₂ gas, and CO ₂ gas is supplied into the carburizing chamber. The carburizing method described. The carburizing method according to claim 1, 2, 3, 4, 5 or 6, wherein a diffusion step is performed after the late carburizing step.

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