JP6543208B2 - Gas carburizing method and gas carburizing apparatus - Google Patents

Description

  The present invention relates to a gas carburizing method and a gas carburizing apparatus which is a surface hardening method in which carbon is infiltrated into a surface layer of steel by a gas to form a solid solution, and in particular relates to performing carburizing under normal pressure.

  Conventionally, there are two methods of carburizing with gas, a method of carburizing under normal pressure (approximately atmospheric pressure) and a method of carburizing under reduced pressure (vacuum). Generally, the former is gas carburized, the latter is It is called vacuum carburization. Among these, gas carburizing supplies an enrichment gas (carburizing gas with a high carbon concentration) together with a carrier gas (a carrier gas with a low carbon concentration) in a furnace under normal pressure in which a work is arranged, Carburizing is promoted by promoting the penetration of hydrogen by enriched gas.

As a carrier gas in gas carburization, an endothermic conversion gas (RX gas) and a thermal decomposition gas of alcohols are generally used. Further, as the enrichment gas, methane (CH ₄ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ) or the like is used. In the atmosphere control in the furnace in gas carburizing, the amount of supply of the enrichment gas is adjusted so that the carbon concentration (carbon potential) in the atmosphere matches the preset target value. Further, as an invention by the inventor of the present invention, there is also a method of controlling the atmosphere in the furnace with higher accuracy by supplying a gas mainly composed of carbon dioxide or air to the furnace in addition to the enriched gas (for example, , Patent Document 1).

  Gas carburizing has the advantage of low installation cost as compared with vacuum carburizing because there is no need to depressurize the inside of the furnace. In addition, because it is possible to control the atmosphere in the furnace and has a long track record, it is possible to perform carburization with stable quality and high reproducibility, and because quality assurance is easy, it is widely used in various fields. It is done.

  In vacuum carburization, a reduced pressure (vacuum) state is used instead of a carrier gas in gas carburization, and carburizing is performed by supplying a carburizing gas corresponding to an enriched gas in a furnace under reduced pressure in which a work is disposed. In vacuum carburization, it is difficult to control the atmosphere in the furnace because of the low pressure, and the target carbon concentration is maintained by managing process conditions such as carburizing temperature, carburizing time, furnace pressure, carburizing gas supply amount and diffusion time. It is like that.

Conventionally, methane, propane, butane, etc. were used as carburizing gases in vacuum carburizing, but these gases generate uneven carburization when the amount supplied is small, and thermal decomposition when the amount supplied is large. There is a problem that control is difficult because a large amount of soot is generated in the furnace (so-called sooting occurs). For this reason, in recent years, highly reactive acetylene (C ₂ H ₂ ) has come to be used in place of these gases (see, for example, Patent Document 2).

  Vacuum carburizing has the advantage of having a short processing time as compared to gas carburizing due to high temperature processing. In addition, vacuum carburization has gradually become widespread because the use of acetylene as the carburizing gas substantially eliminated the problems of carburization unevenness and wrinkles.

Japanese Examined Patent Publication 1-38846 Patent No. 2963869 gazette

  However, vacuum carburization requires not only a vacuum furnace, but also has a high facility cost compared to gas carburizing, and as shown in Patent Document 2, it is necessary to maintain the inside of the furnace at an extremely low pressure. As a result, there has been the problem that the operating costs have risen. Further, as described above, in vacuum carburization, it is difficult to directly control the atmosphere in the furnace, so it is difficult to adopt vacuum carburization in a field where management of the furnace atmosphere is required as a product specification. There has been a demand for a gas carburizing method capable of performing carburization quickly and with high precision.

  An object of the present invention is to provide a gas carburizing method and a gas carburizing apparatus capable of performing carburization with high accuracy and high speed under normal pressure.

  (1) The present invention is a gas carburizing method of heating a work accommodated in a heat treatment furnace under normal pressure and supplying a carrier gas and a carburizing gas into the heat treatment furnace, wherein nitrogen or nitrogen is used as the carrier gas It is a gas carburizing method characterized in that a mixed gas of chain unsaturated hydrocarbon is used, and a chain unsaturated hydrocarbon or a mixed gas of chain unsaturated hydrocarbon and nitrogen is used as the carburizing gas.

  (2) The present invention is also characterized in that the carburizing gas is intermittently supplied into the heat treatment furnace while maintaining the inside of the heat treatment furnace at a predetermined carburizing temperature. It is a gas carburizing method.

  (3) The gas according to the above (1) or (2), characterized in that the present invention uses a mixed gas of a chain unsaturated hydrocarbon and nitrogen identical to the carburizing gas as the carrier gas. It is a carburizing method.

  (4) The present invention is also the gas carburizing method according to any one of the above (1) to (3), characterized in that acetylene or a mixed gas of acetylene and nitrogen is used as the carburizing gas.

  (5) The present invention is also the gas carburizing method according to any one of the above (1) to (4), characterized in that acetylene having a purity of 99% by volume or more is used as the carburizing gas.

  (6) The present invention is also the gas carburizing method according to any one of the above (1) to (5), characterized in that nitrogen used as the carrier gas is separated from air by pressure swing adsorption. .

  (7) The present invention also relates to a heat treatment furnace for accommodating a work under normal pressure, a heating device for heating the inside of the heat treatment furnace, a carrier gas supply system for supplying a carrier gas into the heat treatment furnace, and the inside of the heat treatment furnace. A carburizing gas supply system for supplying a carburizing gas to the carrier gas supply system, wherein the carrier gas supply system supplies nitrogen or a mixed gas of nitrogen and a chain unsaturated hydrocarbon as the carrier gas, and the carburizing gas supply system It is a gas carburizing apparatus characterized in that a chain unsaturated hydrocarbon or a mixed gas of a chain unsaturated hydrocarbon and nitrogen is supplied as the carburizing gas.

  (8) The present invention also includes a control device for controlling the carburizing gas supply system to intermittently supply the carburizing gas into the heat treatment furnace. It is a gas carburizing device.

  ADVANTAGE OF THE INVENTION According to the gas carburizing method and gas carburizing apparatus which concern on this invention The outstanding effect that it is possible to perform carburization of high speed and high precision under normal pressure can be show | played.

It is the schematic which showed the structure of the gas carburizing apparatus which concerns on embodiment of this invention. It is a figure showing an example of the time chart of the gas carburizing method. It is the graph which showed the result of the hardness test in the example of the present invention. (A) It is a microscope picture of the cross section in the surface vicinity of a test piece. (B) It is a microscope picture of the cross section in the inside of a test piece. (A) It is a microscope picture of the cross section in the surface vicinity of a test piece. (B) It is a microscope picture of the cross section in the inside of a test piece. (A) It is a microscope picture of the cross section in the surface vicinity of a test piece. (B) It is a microscope picture of the cross section in the inside of a test piece.

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

  FIG. 1 is a schematic view showing the configuration of a gas carburizing apparatus 1 according to the present embodiment. As shown in the figure, the gas carburizing apparatus 1 controls the temperature and atmosphere in the heat treatment furnace 10, the gas supply apparatus 20 for supplying various gases into the heat treatment furnace 10, and the heat treatment furnace 10 that accommodates the workpiece 100. And a control unit 30.

  The heat treatment furnace 10 accommodates and heats the workpiece 100, which is a material to be treated, in the furnace 10a, and performs carburization with the atmosphere gas in the furnace 10a. The heat treatment furnace 10 is configured such that the furnace interior 10a is kept warm by a suitable heat insulating material. In addition, the heat treatment furnace 10 is configured such that the atmosphere gas in the furnace 10a is appropriately discharged to the outside along with the gas supply from the gas supply device 20, and the furnace 10a has a normal pressure (approximately pressure) during processing. It is supposed to be maintained at atmospheric pressure). Further, the furnace interior 10a is configured to be able to accommodate a plurality of workpieces 100 in a state of being placed on an appropriate jig 11 or the like.

The heat treatment furnace 10 includes a heating device (for example, a radiant tube heater) 12 for heating the furnace interior 10a, a thermometer (for example, a thermocouple) 13 for measuring the temperature of the furnace interior 10a, and oxygen (O ₂ ) in the furnace 10a. An oxygen concentration meter 14 for measuring the concentration, a hydrogen concentration meter 15 for measuring the hydrogen (H ₂ ) concentration of the furnace 10 a, and a stirring device (for example, fan) 16 for stirring the atmosphere gas in the furnace 10 a There is.

  The oximeter 14 detects the oxygen concentration in the furnace 10 a based on the electromotive force generated by the oxygen concentration difference between both ends of the zirconia element. For this reason, an air unit 17 for supplying reference air (air) is connected to one end of the zirconia element to the oximeter 14. Also, the hydrogen concentration meter 15 uses a heat conduction type that detects the hydrogen concentration based on the difference in the thermal conductivity of the measurement gas and the standard gas in order to enable continuous measurement.

The gas supply device 20 includes a carrier gas as a base gas of the atmosphere in the furnace 10a, a carburizing gas for supplying carbon (C) to be intruded into the work 100, and an ammonia (NH ₃ ) gas for carbonitriding. Is supplied to the furnace 10a. Therefore, the gas supply apparatus 20 includes a carrier gas supply system 21 for supplying a carrier gas, a carburizing gas supply system 22 for supplying a carburizing gas, an ammonia gas supply system 23 for supplying an ammonia gas, and supply systems 21 to 23. And a connecting pipe 24 for connecting the inside of the furnace 10a.

Further, the gas supply device 20 supplies nitrogen (N ₂ ) to the carrier gas supply system 21, and supplies acetylene (C ₂ H ₂ ) to the carrier gas supply system 21 and the carburizing gas supply system 22. An acetylene supply source 26 and an ammonia supply source 27 for supplying ammonia to the ammonia gas supply system 23 are provided. Although details will be described later, in the present embodiment, direct carburization similar to vacuum carburization can be performed under normal pressure, so the term "carburizing gas" is used instead of the enriched gas.

  The carrier gas supply system 21 includes a gas mixer 21a for mixing nitrogen from the nitrogen supply source 25 and acetylene from the acetylene supply source 26, a supply piping 21b for connecting the gas mixer 21a and the connection piping 24, and a supply piping 21b. A solenoid valve 21c provided in the middle and a flow meter 21d for measuring the flow rate of the carrier gas are provided.

  The carrier gas is the base gas of the atmosphere in the furnace 10a as described above, and is supplied to prevent the mixing of oxygen in the atmosphere and to prevent the furnace 10a from becoming an oxidizing atmosphere. In the present embodiment, a gas obtained by mixing a small amount of acetylene with nitrogen, which is an inert gas, is used as a carrier gas, instead of the conventional endothermic shift gas (RX gas) and the thermal decomposition gas of alcohols.

The gas mixer 21a is controlled by the control device 30 to add and mix a predetermined amount of acetylene from the acetylene source 26 with nitrogen from the nitrogen source 25 to generate a carrier gas. It is a chain unsaturated hydrocarbon having a triple bond, and oxygen and water (H ₂ O) are mixed in the nitrogen from the nitrogen source 25 by mixing appropriately reactive acetylene (HC≡CH) Also, it is possible to cancel the influence of these on carburization.

Specifically, oxygen in the furnace 10a is a factor that inhibits carburization because it is preferentially adsorbed on the surface of the workpiece 100, but acetylene is reacted with oxygen as shown in the following formula (a). By producing carbon monoxide (CO) and hydrogen, the oxygen concentration in the furnace 10a can be reduced.
C ₂ H ₂ + O ₂ → 2CO + H ₂ (a)

Also, water (steam) can be decomposed in the furnace 10a to form oxygen together with hydrogen, but the water concentration in the furnace 10a is reduced by reacting acetylene with water as in the following equation (b) be able to.
C ₂ H ₂ + 2H ₂ O → 2CO + 3H ₂ (b)

  The controller 30 controls the mixing amount of acetylene to the carrier gas in the gas mixer 1 a based on the measurement result of the oximeter 14. That is, when the oxygen concentration in the furnace 10a is high, the mixing amount of acetylene is increased, and when the oxygen concentration in the furnace 10a is low, the mixing amount of acetylene is reduced. In addition, acetylene which did not react with oxygen or water will contribute to carburization as a carburizing gas.

  The mixing amount of acetylene in the carrier gas depends on the amount of oxygen and water mixed in the nitrogen from the nitrogen source 25 but is in the range of 0.1 to 3.0% by volume with respect to the whole carrier gas. Is preferred. In the case where the amount of oxygen and water mixed is small, it is possible to use nitrogen alone as the carrier gas without mixing acetylene.

  The carburizing gas supply system 22 includes a supply pipe 22b connecting the acetylene supply source 26 and the connection pipe 24, a solenoid valve 22c provided in the middle of the supply pipe 22b, and a flowmeter 22d for measuring the flow rate of the carburizing gas. There is. The carburizing gas supplies the carbon necessary for carburizing as described above. In the present embodiment, acetylene, which is a chain unsaturated hydrocarbon, is used as a carburizing gas, similarly to the gas mixed with the carrier gas.

When a chain unsaturated hydrocarbon such as acetylene is used as a carburizing gas, a chain saturated hydrocarbon such as propane (C ₃ H ₈ ) is used because of its high reactivity (high adsorption on the surface of the work 100) Processing time can be reduced more than in the case. Furthermore, in the present embodiment, by forming the carrier gas from a mixed gas of nitrogen and acetylene, since the carbon supply source is substantially acetylene only, it is possible to control the carburizing amount with high accuracy.

  In addition, although the high reactivity of acetylene may cause excess carburization, in the present embodiment, generation of excess carburization is prevented by intermittently (pulsively) supplying carburizing gas to the furnace interior 10a. It is like that. Specifically, the controller 30 intermittently supplies the carburizing gas to the furnace 10a by opening the solenoid valve 22c for a predetermined opening time (for example, 120 seconds) at a predetermined interval (for example, 300 seconds). . By intermittently supplying the carburizing gas in this manner, excessive supply of carbon can be suppressed, and diffusion of carbon in the work 100 can be promoted, so that occurrence of local carburization unevenness can be prevented. Is possible. Also, the occurrence of sooting can be prevented.

  The purity of acetylene as a carburizing gas is not particularly limited, but in order to enhance the accuracy and responsiveness of atmosphere control in the furnace 10a, impurities other than nitrogen (especially oxygen, water and hydrocarbons) It is preferable that the amount be small. Specifically, the content of impurities other than nitrogen in the carburizing gas is preferably 1% by volume or less, more preferably 0.5% by volume or less, and more preferably 0.01% by volume or more Most preferred.

  The ammonia gas supply system 23 includes a supply pipe 23 b connecting the ammonia supply source 27 and the connection pipe 24, a solenoid valve 23 c provided in the middle of the supply pipe 23 b, and a flow meter 23 d measuring the flow rate of ammonia gas. There is. Ammonia gas is supplied to the furnace 10a together with the carburizing gas when performing carbonitriding. By adding a small amount of ammonia together with the carburizing gas to the carrier gas, high quality carbonitriding can be performed without generating sooting. That is, the gas carburizing apparatus 1 of the present embodiment can also perform carbonitriding.

  The connection piping 24 is piping which connects each supply piping 21b-23b and the furnace interior 10a. The connection piping 24 may connect each supply piping 21b-23b to the furnace interior 10a collectively, and may connect to the furnace interior 10a separately.

  The nitrogen supply source 25 is composed of a nitrogen gas generator of PSA type, and nitrogen is separated from the air by pressure swing adsorption (PSA) and supplied to the carrier gas supply system 21. The nitrogen supply source 25 may be configured of a container containing nitrogen gas or liquid nitrogen, but in order to stably supply nitrogen at a relatively low cost, nitrogen gas of the PSA system is used. It is preferred to construct the nitrogen source 25 from the generator.

  The nitrogen gas generator of the PSA type has more mixing of oxygen and water compared to liquid nitrogen, but in the present embodiment, the influence of these impurities is eliminated by mixing acetylene in advance as described above. It is like that.

  The acetylene source 26 is composed of a container containing acetylene. As described above, it is preferable that acetylene as the carburizing gas has a smaller amount of impurities other than nitrogen. Therefore, it is preferable that the acetylene source 26 supply high purity acetylene, and it is more preferable not to use a solvent such as acetone or dimethylformamide (DMF). Specifically, it is preferable that the acetylene supply source 26 supply acetylene having a purity of 99% or more, and it is more preferable if acetylene having a purity of 99.5% or more is supplied, and the purity is 99.9 It is most preferable to supply at least% of acetylene.

  In the present embodiment, although acetylene is supplied from one acetylene supply source 26 to both the carrier gas supply system 21 and the carburizing gas supply system 22, the carrier gas supply system 21 and the carburizing gas supply system 22 are both supplied. An acetylene source 26 may be provided separately for each. The acetylene to be mixed with the carrier gas is preferably of high purity, but it is not necessary to be as pure as carburizing gas due to the small amount used, and may be, for example, acetylene for welding.

The ammonia supply source 27 is composed of a container containing ammonia. Although not shown, the gas supply device 20 further includes a hydrogen sulfide supply source for supplying hydrogen sulfide (H ₂ S) gas to the furnace 10 a and a hydrogen sulfide gas supply system, and the sulfurized carburization and the sulfurized carburization are performed. It may be configured to be capable of performing nitriding.

  The control device 30 is composed of an appropriate microcomputer or PC. The control device 30 controls the heating device 12 based on the signal output of the thermometer 13 so that the temperature in the furnace 10 a becomes a preset temperature. The control device 30 also controls each of the solenoid valves 21c to 23c of the gas supply device 20 to supply necessary gas to the furnace interior 10a at a predetermined timing.

  Furthermore, the control device 30 controls the gas mixer 21a as described above based on the signal output of the oximeter 14 to adjust the amount of acetylene to be mixed with the carrier gas. Further, the control device 30 controls the solenoid valve 22 c based on the signal output of the hydrogen concentration meter 15 to adjust the amount of carburized gas supplied to the furnace 10 a. The measured temperature, oxygen concentration and hydrogen concentration in the furnace 10a are output to an external device and recorded as necessary.

In this embodiment, since a mixed gas of nitrogen and acetylene is used as the carrier gas and acetylene is used as the carburizing gas, oxygen atoms are only supplied as impurities to the furnace interior 10a. Therefore, carbon monoxide is only slightly present in the atmosphere of the furnace 10a, and the supply of carbon to the work 100 (ie, carburization) is performed directly from acetylene based on the following equation (c): It will be
C ₂ H ₂ → 2 C + H ₂ (c)

  Since the carrier gas contains hydrogen atoms only as impurities, the hydrogen concentration detected by the hydrogen concentration meter 15 is substantially equal to the concentration of hydrogen generated from acetylene which is a carburizing gas. And this hydrogen concentration will be approximately proportional to the amount of supply of carbon. That is, in the present embodiment, it is possible to control the carburizing amount for the workpiece 100 with high accuracy based on the hydrogen concentration in the furnace 10a. In addition, it is possible to prevent the occurrence of sooting based on the hydrogen concentration in the furnace 10a.

As the carburizing gas, in addition to acetylene, other chained unsaturated hydrocarbons having a triple bond such as propyne (CH ₃ C≡CH) or 1-butyne (CH ₃ CH ₂ C≡CH) are used, for example. To use other chain unsaturated hydrocarbons having a double bond such as ethylene (H ₂ C CCH ₂ ) and butadiene (CH ₂ CHCH—CH = CH ₂ ), for example. You may In addition, a mixed gas of a plurality of chain unsaturated hydrocarbons, or a mixed gas of a chain unsaturated hydrocarbon and nitrogen may be used as a carburizing gas. However, considering the point that stability decreases as the molecular weight increases and wrinkles are more likely to occur, the point with the triple bond is more reactive, and availability, etc., it is possible to use acetylene alone or acetylene as the carburizing gas. It is preferred to use a mixed gas of nitrogen.

  Similarly, although chain unsaturated hydrocarbons other than acetylene may be mixed with the carrier gas, it is preferable to mix acetylene for the reasons described above. In addition, although a chain-type unsaturated hydrocarbon different from the carburizing gas may be mixed with the carrier gas, from the viewpoint of simplification of the apparatus such as unifying the supply source, the gas mixed with the carrier gas and the carburizing may be mixed. It is preferred that the gases be identical chain unsaturated hydrocarbons.

  Next, a specific procedure of the gas carburizing method of the present embodiment will be described.

  FIG. 2 is a diagram showing an example of a time chart of the gas carburizing method of the present embodiment. In carburizing, while checking the flow meters 21d to 23d in advance, the opening degree of the flow control valve etc. (not shown) is adjusted, and the supply flow rate of the carrier gas and the carburizing gas is set. The supply flow rate of each gas is not particularly limited, and may be appropriately set according to the volume in the heat treatment furnace 10, the surface area of the work 100, the required curing depth, and the like.

  If the supply flow rate of each gas is properly set, the carburizing process is started. First, the controller 30 opens the solenoid valve 21c of the carrier gas supply system 21 to supply the carrier gas of a constant flow rate to the furnace interior 10a. If the decrease in the oxygen concentration in the furnace 10a detected by the oximeter 14 stops and the atmosphere in the furnace 10a is replaced by the carrier gas, the control device 30 controls the gas mixer 21a based on the oxygen concentration in the furnace 10a. Control the amount of acetylene to be mixed with the carrier gas. Thereafter, the control device 30 continues the control of the gas mixer 21a based on the carrier gas supply and the oxygen concentration in the furnace 10a, whereby the oxygen concentration in the furnace 10a is kept substantially at the minimum.

When the oxygen concentration in the furnace 10a becomes substantially minimum, the work 100 is placed in the furnace 10a. The workpiece 100 is accommodated in advance in a front chamber (not shown) provided adjacent to the heat treatment furnace 10, and conveyed to the furnace interior 10a by a dedicated conveyance device. If the workpiece 100 is placed in the furnace 10a, the controller 30 controls the heating unit 12 is heated a predetermined carburizing temperatures _{T 1} to the furnace 10a (Atsushi Nobori time _t 1).

If the furnace 10a becomes carburization temperature T _1, the control unit 30 controls the heating unit 12 so as to hold the furnace 10a to the carburization temperature T1. Then, if the soaking time t ₂ set in advance has elapsed, it starts supplying the carburizing gas by controlling the solenoid valve 22c of the carburizing gas supply system 22 into the furnace 10a.

The supply of the carburizing gas is intermittently performed during carburization time t ₃ when set in advance. Specifically, the control device 30, the opening of the electromagnetic valve 22c of a predetermined opening time t _o, at a preset supplied intervals I _o, repeated by the number of repetitions n set in advance. Here, the supply intervals Io and is that interval timing of opening the solenoid valve 22c, interval after the opening time t _o to close the electromagnetic valve 22c until opening the next (solenoid valve 22c is closed Is not about time). Controller 30 also hydrogen concentration in the furnace 10a during carburization time t ₃ monitors, if it is determined that the hydrogen concentration is too high to shorten the next opening time t _o, is determined that the hydrogen concentration is too low If the next open time t _o is extended.

By intermittently supplying the carburizing gas, it is possible to prevent excessive carbon supply to the work 100 while using reactive acetylene, thus preventing the occurrence of uneven carburization and sooting. At the same time, it is possible to control the carburizing amount with high accuracy. Incidentally, one of the supply amount of the carburizing gas becomes the amount obtained by multiplying the open time t _o to the supply flow rate of the carburizing gas, the value obtained by multiplying n to which the total supply of the carburizing gas.

If the supply of the carburizing gas was carried out n times, the controller 30 holds between the diffusion time t ₄ when preset, the furnace 10a only the carrier gas in the state supplied to the carburization temperature T _1. During this time, carbon which has penetrated into the work 100 is appropriately diffused, and a hardened layer having a desired thickness (depth) is formed.

If diffusion time t ₄ has passed, the control device 30, the temperature is decreased quenching holding temperature T ₂ to the furnace 10a that is set in advance by controlling the heating device 12 (temperature lowering time t _5). Then, during the quenching retention time t _6, which is set in advance, so as to maintain the temperature of the furnace 10a hardenability holding temperature T _2, which controls the heating device 12. After quenching retention time t _6, the workpiece 100 is conveyed before the chamber by conveying device, it is immersed for Aburasho input time t ₇ before the oil tank provided on the chamber (not shown). Thereby, hardening is performed. Incidentally, oil tank in is held in quenching temperature T ₃ which is set in advance.

  By the above procedure, gas carburization for one lot of works 100 is completed. When processing the work 100 of the next lot, the control device 30 continues the supply of the carrier gas and the heating by the heating device 12 and repeats the above procedure. When the gas carburizing apparatus 1 is stopped, the electromagnetic valve 21c of the carrier gas supply system 21 is closed to stop the supply of the carrier gas, and the heating by the heating device 12 is stopped.

  In the present embodiment, the mixed gas of nitrogen and acetylene is used as the carrier gas, and acetylene is used as the carburizing gas, thereby simplifying the gas component of the atmosphere in the furnace. Thereby, it is possible to carry out direct carburization from acetylene by the same procedure as vacuum carburization while keeping the inside of the furnace 10a at normal pressure. Furthermore, by intermittently supplying the carburizing gas, it is possible to effectively prevent the occurrence of carburization unevenness and sooting. Moreover, since it is not necessary to decompress the furnace interior 10a, it is possible to reduce the equipment cost and the operation cost compared to vacuum carburization.

In the present embodiment as described above, by setting the opening time t _o of the feed flow and the solenoid valve 22c of the carburizing gas, it is set once the supply amount of the carburizing gas into the furnace 10a, carburizing A suitable receiver tank for temporarily storing carburizing gas may be provided in the gas supply system 22, and a single supply amount of carburizing gas to the furnace 10a may be set by the volume and pressure of the receiver tank. In this case, the carburizing gas can be supplied at once in a short time to the furnace 10a, so that the processing time can be further shortened. Further, the carburizing gas supply system 22 and the connection pipe 24 may be configured to blow out the carburizing gas from the plurality of nozzles toward the work 100 in the furnace 10a.

Further, in the present embodiment, the control device 30 adjusts the amount of acetylene to be mixed with the carrier gas based on the oxygen concentration in the furnace 10a during the supply of the carrier gas, but the amount of impurities in nitrogen is In the case where the fluctuation does not largely change, the mixing amount of acetylene may be fixed, and such feedback control may be omitted. Similarly, in the present embodiment, when the carburizing gas is supplied, the control device 30 adjusts the opening time t _o of the solenoid valve 22 c based on the hydrogen concentration in the furnace 10 a, but the opening time t _o is fixed. Such feedback control may be omitted. That is, the carburizing gas of the supply amount set in advance based on the hydrogen concentration value etc. in the processing results up to that time is supplied to the furnace 10a, and the hydrogen concentration in the furnace 10a is monitored and recorded for later confirmation. May be alone. Furthermore, depending on the carburizing condition, the carburizing gas may not be intermittently supplied to the furnace 10a, but the carrier gas and the carburizing gas may be continuously supplied at a predetermined flow ratio.

  As described above, the gas carburizing method according to the present embodiment is a gas carburizing method of heating the workpiece 100 accommodated in the heat treatment furnace 10 under normal pressure and supplying the carrier gas and the carburizing gas into the heat treatment furnace 10. The carrier gas is nitrogen or a mixed gas of nitrogen and a chain unsaturated hydrocarbon, and the carburizing gas is a chain unsaturated hydrocarbon or a mixed gas of a chain unsaturated hydrocarbon and nitrogen.

  Further, the gas carburizing apparatus 1 according to the present embodiment includes a heat treatment furnace 10 for housing the work 100 under normal pressure, a heating device 12 for heating the inside of the heat treatment furnace 10, and a carrier gas for supplying a carrier gas into the heat treatment furnace 10. The carrier system is provided with a supply system 21 and a carburizing gas supply system 22 for supplying a carburizing gas into the heat treatment furnace 10. The carrier gas supply system 21 supplies nitrogen or a mixed gas of nitrogen and chain unsaturated hydrocarbon as a carrier gas. The carburizing gas supply system 22 supplies a chain unsaturated hydrocarbon or a mixed gas of a chain unsaturated hydrocarbon and nitrogen as a carburizing gas.

  With such a configuration, it is possible to carry out direct carburization from acetylene as in vacuum carburization while maintaining the inside of the furnace 10a at normal pressure, so that quick and high-precision carburization under normal pressure is possible. It can be performed.

Further, a gas carburizing method according to the present embodiment, while holding the heat treatment furnace 10 to a predetermined carburizing temperature T _1, intermittently supplying carburizing gas into the heat treatment furnace 10. In addition, the gas carburizing apparatus 1 includes a control device 30 that controls the carburizing gas supply system 22 so as to intermittently supply the carburizing gas into the heat treatment furnace 10. In this way, it is possible to appropriately suppress the supply of carbon to the work 100 while enabling rapid carburization with acetylene, so that the occurrence of uneven carburization and sooting can be prevented, and carburization can be prevented. The amount can be controlled with high precision.

  Further, in the gas carburizing method according to the present embodiment, it is preferable to use, as a carrier gas, a mixed gas of a chain unsaturated hydrocarbon and nitrogen which is the same as the carburizing gas. By doing this, the gas supply device 20 can be simplified and equipment cost can be reduced.

  Moreover, in the gas carburizing method according to the present embodiment, it is preferable to use acetylene or a mixed gas of acetylene and nitrogen as a carburizing gas. By using acetylene, which has both high reactivity and stability, and is easily available as a carburizing gas, shortening of the treatment time and high-precision control of the carburizing amount can be easily realized at low cost.

  Moreover, in the gas carburizing method according to the present embodiment, it is preferable to use acetylene having a purity of 99% by volume or more as the carburizing gas. In this way, the effects of impurities contained in the carburizing gas can be eliminated, and high precision carburization can be performed quickly. In addition, high purity acetylene generally in circulation can be used as it is as a carburizing gas.

  In the gas carburizing method according to the present embodiment, nitrogen used as a carrier gas is separated from air by pressure swing adsorption. By doing this, nitrogen can be stably supplied at low cost.

  As mentioned above, although the embodiment of the present invention was described, the gas carburizing method and gas carburizing apparatus of the present invention are not limited to the above-mentioned embodiment, and various modifications can be made within the scope of the present invention. Of course it is possible to add

  In addition, the actions and effects described in the above embodiment are only listing of the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are not limited to these.

  Hereinafter, examples of the present invention will be described. The present invention is not limited to the present embodiment.

  In the present example, carburizing was performed along the time chart shown in FIG. 2 with respect to four types of test pieces TP1 to TP4 using the gas carburizing apparatus 1 of the above embodiment. And while carrying out the hardness test by a micro Vickers hardness tester about each test piece TP1-TP4 after carburizing, the structure | tissue observation by an optical microscope was performed.

  The test piece TP1 is a cylindrical SCM 415 material with an outer diameter of 30 mm and a height of 30 mm, the test piece TP2 is a cylindrical SCM 415 material with an outer diameter of 15 mm and a height of 30 mm, and the test piece TP3 with an outer diameter of 30 mm, an inner diameter of 10 mm and a height The test piece TP4 was a cylindrical SCM 415 material having an outer diameter of 24 mm, an inner diameter of 10 mm, and a height of 30 mm.

The carburizing temperature _{T 1} of the 930 ° C. in the time chart of FIG. 2, the quenching holding temperature _{T 2} is 870 ° C., an oil quenching temperature _{T 3} was set to 65 ° C.. The heating time t1 is 60 minutes, the soaking time t2 is 30 minutes, the carburizing time t3 is 90 minutes, the diffusion time t4 is 120 minutes, the cooling time t5 is 30 minutes, and the quenching holding time t6 is The oil quenching time t7 was set to 15 minutes at 30 minutes.

As a carrier gas, a mixed gas of nitrogen and acetylene having a purity of 99% by volume was used, and as the carburizing gas, acetylene having a purity of 99% by volume was used. The supply flow rate of the carrier gas was 1 m ³ / hour, and the supply flow rate of the carburizing gas was 2 liters / minute. The carburizing gas supply interval _Io was set to 300 seconds, and the number of repetitions n was set to 20 times. Further, the open time t _o of the solenoid valve 22 c was set to 120 seconds, and 4 liters of carburized gas was set to be supplied for each supply.

  The measurement load of hardness test is 0.1kgf, the distance from the surface is 0.05mm, 0.1mm, 0.2mm, 0.5mm, 0.7mm, 1.0mm, 1.2mm, 1.5mm and 2 The measurement was carried out at nine points of .0 mm. In the tissue observation, a cross section near the carburized surface and a cross section inside the non-carburized surface were observed and photographed.

  FIG. 3 is a graph showing the results of the hardness test. As shown in the figure, in any of the test pieces TP1 to TP4, it was confirmed that the hardness in the vicinity of the surface is approximately HV 800, and the effective curing depth of HV 500 or more is 1 mm or more. In addition, it was also confirmed that the degree of decrease in hardness in the depth direction was moderate, and carbon was properly diffused in the steel material, and a substantially ideal hardness distribution could be obtained.

  FIG. 4 (a) is a micrograph of a cross section in the vicinity of the surface of the test piece TP1, and FIG. 4 (b) is a micrograph of a cross section in the inside of the test piece TP1. 5 (a) is a photomicrograph of a cross section in the vicinity of the surface of the test piece TP2, and FIG. 5 (b) is a photomicrograph of a cross section in the inside of the test piece TP2. 6 (a) is a micrograph of a cross section in the vicinity of the surface of the test piece TP4, and FIG. 6 (b) is a micrograph of a cross section in the inside of the test piece TP4. As shown in these figures, it was confirmed that good tissue could be obtained either near or inside the surface.

  That is, according to the gas carburizing method and the gas carburizing apparatus 1 of the above embodiment, it has been confirmed that carburizing of good quality can be processed in a short time.

  The gas carburizing method and the gas carburizing apparatus according to the present invention can be utilized in the field of surface hardening of steel.

DESCRIPTION OF SYMBOLS 1 gas carburizing apparatus 10 heat treatment furnace 12 heating apparatus 21 carrier gas supply system 22 carburizing gas supply system 30 control apparatus 100 work T ₁ carburizing temperature

Claims (7)

A gas carburizing method for heating a work housed in a heat treatment furnace under normal pressure and supplying a carrier gas and a carburizing gas into the heat treatment furnace ,
As the carburizing gas, a chain unsaturated hydrocarbon or a mixed gas of a chain unsaturated hydrocarbon and nitrogen is used ,
A mixed gas of a chain unsaturated hydrocarbon and nitrogen, which is the same as the carburizing gas, is used as the carrier gas .
Gas carburizing method. The carburizing gas is intermittently supplied into the heat treatment furnace while keeping the inside of the heat treatment furnace at a predetermined carburizing temperature.
The gas carburizing method according to claim 1. Acetylene or a mixed gas of acetylene and nitrogen is used as the carburizing gas,
A gas carburizing method according to claim 1 or 2 . Acetylene having a purity of 99% by volume or more is used as the carburizing gas,
The gas carburizing method according to any one of claims 1 to 3 . The nitrogen used as the carrier gas is separated from air by pressure swing adsorption.
The gas carburizing method according to any one of claims 1 to 4 . A heat treatment furnace that holds the work under normal pressure;
A heating device for heating the inside of the heat treatment furnace;
A carrier gas supply system for supplying a carrier gas into the heat treatment furnace;
A carburizing gas supply system for supplying carburizing gas into the heat treatment furnace ;
The carburizing gas supply system supplies a chain unsaturated hydrocarbon or a mixed gas of a chain unsaturated hydrocarbon and nitrogen as the carburizing gas ,
The carrier gas supply system supplies, as the carrier gas, a mixed gas of a chain unsaturated hydrocarbon and nitrogen which is the same as the carburizing gas .
Gas carburizing equipment. A controller is provided to control the carburizing gas supply system so as to intermittently supply the carburizing gas into the heat treatment furnace.
The gas carburizing apparatus according to claim 6 .