JP2008031539A - Microwave carburizing furnace and carburizing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave carburizing furnace with which the microwave is used and the carburization is performed under non-electrode and atmospheric pressure, and the carburizing treatment method for iron and steel material by using this carburizing furnace. <P>SOLUTION: In a microwave irradiation chamber for introducing the microwave, an atmospheric gas supplying mechanism for supplying the atmospheric gas containing at least Ar and O<SB>2</SB>and a rapid-cooling mechanism for cooling a material to be treated after carburizing with cooling medium, are provided so that the treating material composed of the iron and steel material and carbon source needed to the carburization, are prepared in the microwave irradiation chamber. The carbon source is supplied with the solid or the gas. The microwave is irradiated under a state that the material to be treated, the carbon source and the atmospheric gas containing Ar and O<SB>2</SB>exist, and Ar plasma is generated with the reaction of the carbon source and the oxygen and , the generation of CO accompanied with the reaction and excitation, carbon ion is generated to carburize the material to be treated. Thereafter, the material to be treated is rapidly cooled with a cooling medium to apply the quenching. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a carburizing furnace using a microwave as a heating source, and also relates to a method of carburizing a steel material using the carburizing furnace.

  At present, microwaves are used for heating, drying and sterilizing foods, and for solidifying polymer materials and firing ceramics. A microwave generally refers to an electromagnetic wave having a frequency of 300 MHz to 300 GHz. In heating of so-called dielectrics such as water, polar molecules such as water, polymers and ceramics, the electric field of the microwave plays a major role. On the other hand, very recently it has been reported that microwaves can heat metal powders or metal masses.

  Research on irradiating metal materials with microwaves has been underway since the 1990s. Research on surface modification using microwaves is particularly active. There are Patent Documents 1 to 4 as techniques for surface modification using microwaves. These are inventions related to an apparatus for generating plasma mainly by microwaves. The method of generating plasma by microwaves is mainly a method of providing electrodes, and the configuration of the apparatus itself is an extremely important technical factor. Although there is Patent Document 5 regarding generation of electrodeless plasma, the apparatus itself has a complicated configuration. In addition, microwave surface modification is mainly applied to nitriding and film formation, and does not cover carburizing / quenching processes that require special temperature patterns.

  Conventional carburizing processes are mainly solid carburizing, gas carburizing, plasma carburizing and the like. Among these, the plasma carburizing method has a faster processing time than other processes. However, the atmosphere needs to be a reduced pressure atmosphere in which plasma is easily generated, and the process and equipment tend to be complicated. Further, in the conventional plasma carburizing method, since the heating itself is the same as the conventional heater heating, there is no temporal advantage difference with respect to the temperature rising process that occupies a large proportion of the process time as compared with other methods.

JP 2005-235464 A JP-A-9-235686 JP 2004-14631 A JP 2003-62452 A JP 2005-196980 A

  As described above, the conventional surface modification treatment by microwave does not cover the carburization treatment.

  An object of the present invention is to provide a microwave carburizing furnace that can perform carburization under an electrodeless and atmospheric pressure using a microwave, and a carburizing method of a steel material using the carburizing furnace.

The present invention relates to a microwave carburizing furnace that uses a microwave as a heat source and generates a plasma at an atmospheric pressure and generates a plasma at an atmospheric pressure, and performs a carburizing process, the microwave irradiation chamber into which the microwave is introduced, and the microwave irradiation An atmosphere gas supply mechanism for supplying an atmosphere gas containing at least Ar and O ₂ to the chamber; and a quenching mechanism for cooling the workpiece after carburization with a cooling medium, and the microwave irradiation chamber is made of a steel material. The microwave carburizing furnace is characterized in that a carbon source necessary for the workpiece and carburizing is provided.

Further, the present invention is a method for carburizing a workpiece made of a steel material using a microwave as a heating source, in the presence of an atmosphere gas containing the workpiece, a carbon source, and Ar and O _2. Irradiate microwaves to generate Ar plasma by the reaction of the carbon source and oxygen and the accompanying generation and excitation of CO, to generate carbon ions to carburize the workpiece, and then to cool the workpiece with a cooling medium. A microwave carburizing method characterized by quenching and quenching.

  According to the present invention, it is possible to provide a carburizing furnace that uses a microwave as a heating source and performs carburizing at no pressure and at atmospheric pressure, and a method for carburizing a steel material using the carburizing furnace.

  The carburizing furnace of the present invention is extremely simple and does not use electrodes for generating plasma in the furnace. The generation of plasma is mainly caused by chemical reaction and gas excitation under microwave irradiation.

  Since the conventional microwave irradiation equipment is not intended for carburizing, it does not have a quenching mechanism necessary for performing carburizing and quenching. The present invention includes a quenching mechanism for the purpose of quenching in a microwave carburizing furnace. By using the carburizing furnace and the carburizing method of the present invention, it is possible to dramatically increase the processing time compared to the conventional method. Moreover, carburization can be performed while suppressing the temperature rise of the substrate due to the selective heating property unique to microwaves. In the present invention, an ultrafine crystal structure material whose structure changes rapidly with respect to temperature can be carburized without causing almost any change in crystal structure.

  The present invention is applied to carburizing treatment of steel materials. In general, carburized products of steel materials are intended to provide wear resistance. Plant components such as electric power and chemistry, power equipment components, and machinery related to transportation such as railways, ships, land transportation, aviation, and space. Used for components, home appliance parts, construction machine parts, molds, machine tool parts, machine fastening parts, medical parts, etc. The present invention can be applied to the entire technical field to which conventional carburized products are applied.

  Microwave heating can be heated locally compared to the conventional plasma carburizing method, and energy can be concentrated on the object, so that the temperature can be raised extremely rapidly. In addition, plasma generated by microwave irradiation is extremely useful for surface cleaning and generation of carbon ions during carburizing treatment. Conventional plasma carburizing generates plasma using electrodes in a reduced pressure atmosphere. In the present invention, plasma can be generated under atmospheric pressure by irradiating microwaves and using no electrode, but instead controlling the atmosphere. As described above, there is Patent Document 1 or the like as a surface treatment apparatus that generates plasma under atmospheric pressure by using a microwave. Compared with these conventional devices, the carburizing furnace of the present invention uses a microwave as a heating source, does not use an electrode, is equipped with a quenching facility for quenching immediately after carburizing, which is a dedicated carburizing facility. There is a feature.

  The metal can be heated by microwaves. The magnetic field of microwaves is considered to play a large role in the effect, and the effect is remarkable in the magnetic material even with the metal material. Steel materials are magnetic materials and are easily heated by microwaves. On the other hand, carburized carbon atoms are strongly excited by an electric field. That is, iron and carbon are shaken by waves with different phases, that is, an electric field and a magnetic field. By this action, the diffusion rate of carbon in iron under microwave irradiation becomes faster than conventional heater heating, and the carburizing time can be shortened compared to the conventional case.

  Furthermore, in the case of microwave heating, since the furnace wall other than the sample is not heated, the sample can be rapidly cooled. Further, in the microwave carburizing furnace, the time for heating, carburizing, and cooling can be reduced as compared with the conventional method.

  Microwaves can sufficiently heat and carburize steel at a frequency of 2.45 GHz by a magnetron that is widely used. However, when the microwave irradiation mode is set to the single mode, it is preferable to set the frequency to about 1 GHz because of the size of the sample to be carburized, because the electromagnetic field region becomes wider. When the irradiation mode is a single mode, energy can be concentrated in a small area, which is advantageous for high-speed heating. If the object is small and small, the process can be further speeded up by processing with a single-mode furnace, and extremely high productivity can be realized depending on the size and production volume of the object. Have great advantages.

  On the other hand, when the frequency is about 30 GHz, there is an effect of suppressing high-temperature oxidation of the metal material. In the carburizing process, oxidation of the crystal grain boundaries of the sample is also a major issue, and extremely high-quality carburizing can be performed by suppressing high-temperature oxidation. For the above reasons, the microwave frequency is preferably in the range of 1 GHz to 30 GHz.

  Samples that have been carburized must be quenched after carburizing. Quenching is a hardening treatment using martensitic transformation of iron, and quenching can be performed by cooling steel heated to a γ transformation temperature at a cooling rate of a certain level or higher. Judgment as to whether or not baking has been performed is made based on whether or not the hardness after processing is more than twice the hardness before processing. In normal plasma carburizing or gas carburizing, cooling is often performed by introducing an inert gas such as pressurized He into the furnace. In the microwave carburizing furnace of the present invention, only the vicinity of the sample is heated, and the furnace wall and the like are not heated and are processed at atmospheric pressure. Therefore, the furnace is opened immediately after heating to handle the sample. It is possible. Quenching by oil cooling can be performed by providing a cooling chamber adjacent to the furnace. Further, when the cooling medium is water, it is also possible to cool by introducing water directly into the furnace. Even if the inside of the furnace gets wet, it is possible to immediately evaporate the water by irradiating it with microwaves, and it is possible to immediately restore the state in which there is no hindrance to the next processing.

  The microwave carburizing furnace of the present invention generates a plasma by a chemical reaction of an atmospheric gas caused by microwave irradiation and gas excitation. Therefore, there is no need to install an electrode in the furnace.

  The carburizing method of the present invention can be realized by using a carbon source and a steel material to be processed in the furnace and using a mixed gas of Ar and oxygen in the atmosphere. By irradiating microwaves in this state, plasma is easily generated even under atmospheric pressure. Oxygen reacts with carbon to produce CO. CO is a polar molecule and is excited when irradiated with microwaves. The generation of Ar plasma is induced by the reaction of the carbon source and oxygen, the accompanying generation of CO, and the excitation of the gas. When Ar becomes plasma, it has the effect of sputtering the surface of the steel sample to expose the metal active surface and also generating carbon ions. Carburization occurs when carbon ions come into contact with the metal active surface.

CO also plays a role in reducing the sample surface and supplying carbon to the sample surface. When the amount of CO generated by the reaction between the carbon source and oxygen is very small, the introduction of CO gas and / or hydrocarbon gas from the outside to the atmospheric gas improves the carburizing efficiency and further increases the carburizing speed. You can speed up. Further, by adding H ₂ to the atmosphere, the reduction of the surface oxide film proceeds very rapidly, and the process time can be shortened. Accordingly, the atmosphere of the carburizing method is desirably a mixed gas of Ar and O ₂ or an atmosphere in which at least one of CO, a hydrocarbon-based gas, and H ₂ is mixed. However, when H ₂ and hydrocarbon gas are used, O ₂ gas needs to be kept at a low concentration below the explosion limit and becomes difficult to handle. Therefore, it can be treated only with Ar, O ₂ and CO as much as possible. preferable.

  The carbon source is supplied as a solid or a gas. In the case of a solid carbon source, for example, it is desirable that the carbon powder is brought into close contact or contact with the steel sample by coating or spraying. When using a gas as a carbon source, it is desirable to include at least one of CO and hydrocarbon gas in the atmospheric gas.

  When the carbon source is brought into close contact with or in contact with the surface of the steel sample, the supply of C can be rapidly advanced. This is because CO gas generated by the reaction between the carbon source and oxygen is efficiently supplied to the sample surface, and atomic diffusion proceeds by direct contact between the carbon source and the sample surface. In particular, under microwave irradiation, the carbon source is more easily heated than the sample, so that the carbon source side is preferentially heated while the sample temperature is kept low, and the temperature on the steel sample side can be kept low. At this time, if the treatment is performed while cooling the steel sample side, the temperature rise inside the steel sample can be suppressed to a very low level, for example, an ultrafine crystal steel material that is likely to undergo thermal structural change or deterioration. It is useful for carburizing treatment. Here, the ultrafine crystal steel material is a steel material having a crystal grain size of 1 μm or less. In the ultrafine crystal steel material having a crystal grain size of 1 μm or less, it is possible to increase the strength to 1000 MPa or more without impairing the toughness by strengthening the grain refinement. However, when the ultrafine crystal steel material is heated to a region where it undergoes γ transformation, crystal growth occurs abruptly and returns to ordinary steel. In the present invention, since the carburizing treatment can be performed in a short time while keeping the temperature of the base material low, the coarsening of crystal grains of the ultrafine crystal steel material is suppressed and the mechanical properties of the base material are impaired. Surface treatment is possible.

A multimode furnace is shown in FIG. 1 as an embodiment of the microwave carburizing furnace according to the present invention. The carburizing furnace of FIG. 1 includes a microwave irradiation furnace 100 with a built-in microwave irradiation function, and an atmosphere gas supply pipe 101 for supplying an atmosphere gas containing Ar and O ₂ to the furnace, and a cooling gas supply pipe 102. is set up. Inside the microwave irradiation furnace 100, a micro diffusion fan 103, a susceptor 104, a susceptor manipulating rod 105, and a refrigerant spray nozzle 106 are installed. A temperature measurement window 107 is provided in a part of the wall of the microwave irradiation furnace. In addition, a cooling chamber 108 is provided adjacent to the microwave irradiation furnace, and the microwave irradiation furnace and the cooling chamber are connected by a gate 109. The operation of the gate is linked to the microwave output system, and the microwave output is turned off before the gate is opened. Therefore, any liquid can be placed in the cooling chamber 108. In addition, the microwave output is turned off even when the refrigerant is sprayed. As a quenching mechanism for quenching after carburizing, it is sufficient to provide only one of the cooling gas supply means and the cooling chamber, but in this embodiment, both can be arbitrarily selected.

Carburizing experiments were performed using the carburizing furnace having the configuration shown in FIG. The wavelength of the microwave to be irradiated was 2.45 GHz. A sample 150 to be carburized was an steel material SCM415 having a component composition similar to ISO: 18CrMo4, and carbon powder was applied to the surface of the SCM415. Carbon was used as a susceptor 104 so as to cover the sample. Part of the microwave excites carbon, and the radiant heat of the generated carbon assists the temperature rise of the sample. A mixed gas of 90% Ar and 10% O ₂ was flowed into the furnace. The carburizing conditions were a temperature of 900 ° C. and a holding time of 3 minutes.

  With this setting, a maximum of 6 kW of microwave was irradiated. The target temperature was reached in 10 minutes. During microwave irradiation, plasma was observed throughout the furnace. After reaching the target temperature, the sample 150 was held for a predetermined time, and then the sample 150 was immediately dropped into the cooling chamber 108. Although the sample is dropped in the cooling chamber here, the quenching process may be performed by blowing He gas from the refrigerant spray nozzle 106 without dropping. In addition, when spraying the coolant from the coolant spray nozzle, it is preferable to move the susceptor so that the coolant directly hits the sample.

  Table 1 shows the hardness distribution in the vicinity of the surface after the quenching treatment. Even in a treatment of only 3 minutes, an improvement in hardness was recognized from the surface to about 200 μm, and it was found that carburizing and quenching was performed. In this process, the time required from setting the sample to taking it out was about 15 minutes. In normal plasma carburizing or gas carburizing, it takes several hours to set and take out a sample, but in the present invention, carburizing treatment can be performed in a very short time.

FIG. 2 shows an example of a single mode carburizing furnace as another embodiment of the present invention. The carburizing furnace of FIG. 2 includes a container 200 that can be evacuated before supplying atmospheric gas, an atmospheric gas supply pipe 201 that supplies atmospheric gas containing Ar and O ₂ to the container, and a gas refrigerant supply pipe. 202, a liquid refrigerant supply pipe 203 is installed. A part of the container is provided with an alumina window 204 for introducing a microwave (MW). In addition, a cooling chamber 205 is provided adjacent to the container 200, and the container and the cooling chamber are connected by a gate 206. In the single mode, unlike the multimode furnace, the micro diffusion fan can be omitted. The reason why both the gas refrigerant supply pipe and the liquid refrigerant supply pipe are provided is to allow any one to be selected arbitrarily. In the case of the apparatus of this embodiment, the volume is smaller than that of the multi-mode furnace and a strong electromagnetic field region can be created, so that higher-speed heating is possible. FIG. 3 shows the relationship between the temperature and the microwave irradiation time when the SCM 415 is heated in a strong magnetic field without inserting a susceptor. The output of the microwave was 2 kW. It can be seen that a heating rate of 100 ° C./min or more can be realized without a susceptor. In a single mode furnace, if a susceptor or the like is used, the iron-based material can be heated to about 900 ° C. within 5 minutes even at a power of 3 kW.

  Carburizing and quenching of ultrafine crystal ferritic steel was performed using the single mode furnace of FIG. FIG. 4 shows the relationship between the crystal grain size and hardness of the ultrafine crystal ferritic steel. The relationship between the crystal grain size and the strength of this sample can be expressed by the Hall Petch relationship, and the hardness of the ultrafine crystal ferritic steel is expressed by strengthening the crystal grain refinement. The hardness of the ultrafine crystal ferritic steel used for the carburizing process is about 400 HV.

The setting condition of the sample is shown in FIG. The sample was contacted with a susceptor and carbon source. Further, the back side of the sample was brought into close contact with a vessel wall surface filled with liquid nitrogen through a Cu sample holder to prevent an increase in the sample temperature. The atmosphere was 90% Ar-10% O ₂ mixed gas, and the carburizing conditions were 900 ° C. and 20 minutes. After reaching the target temperature, it was held for a predetermined time, and then the microwave output was reduced. Quenching was performed by cooling with liquid nitrogen through a Cu sample holder.

  Table 2 shows the hardness distribution near the surface after quenching. From the surface to the depth of about 500 micrometers, the improvement of hardness was recognized and it turned out that carburizing and quenching has been performed. In addition, it was found that the hardness of the ultrafine crystal ferritic steel in the base material is hardly reduced as compared with that before the treatment, and the coarsening of crystal grains is suppressed in the base material.

The schematic block diagram of the multi-mode carburizing furnace which shows one Example of this invention. The schematic block diagram of the single mode carburizing furnace which shows the other Example of this invention. The diagram which shows the relationship between the temperature when SCM415 is heated in a strong magnetic field without putting a susceptor using the apparatus of FIG. 2, and microwave irradiation time. The diagram which shows the relationship between the crystal grain size and hardness of ultra-fine crystal ferritic steel. Schematic which shows the setting condition of the sample in the apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Microwave irradiation furnace, 101 ... Atmospheric gas supply pipe, 102 ... Cooling gas supply pipe, 103 ... Micro diffusion fan, 104 ... Susceptor, 105 ... Manipulation rod, 106 ... Refrigerant spray nozzle, 107 ... Temperature measurement window , 108 ... cooling chamber, 109 ... gate, 150 ... sample, 200 ... container, 201 ... atmospheric gas supply pipe, 202 ... gas refrigerant supply pipe, 203 ... liquid refrigerant supply pipe, 204 ... window, 205 ... cooling chamber, 206 ... Gate.

Claims (19)

A microwave carburizing furnace using a microwave as a heating source and generating a plasma at an atmospheric pressure and without an electrode, and performing a carburizing process, a microwave irradiation chamber into which a microwave is introduced, and Ar and An atmosphere gas supply mechanism for supplying an atmosphere gas containing O ₂ and a quenching mechanism for cooling the object to be processed after carburizing with a cooling medium, and the object to be processed and carburized of steel material in the microwave irradiation chamber A microwave carburizing furnace, which is equipped with the necessary carbon source.   2. The microwave carburizing furnace according to claim 1, further comprising a cooling chamber adjacent to the microwave irradiation chamber as the quenching mechanism.   The microwave carburizing furnace according to claim 1, further comprising a cooling gas supply mechanism that supplies a gaseous cooling medium to the microwave irradiation chamber as the quenching mechanism. _{2. The} microwave carburizing furnace according to claim 1, wherein at least one of CO and hydrocarbon gas is supplied from the atmospheric gas supply mechanism in addition to Ar and O ₂ . _{2. The} microwave carburizing furnace according to claim 1, wherein H ₂ is supplied from the atmospheric gas supply mechanism in addition to Ar and O ₂ . The microwave carburizing furnace according to claim 4, wherein H ₂ is further supplied from the atmospheric gas supply mechanism.   2. The microwave carburizing furnace according to claim 1, wherein an object to be processed having a solid carbon source on a surface portion is disposed in the microwave irradiation chamber.   The microwave carburizing furnace according to claim 1, wherein the frequency of the microwave is 1 GHz or more and 30 GHz or less.   The microwave carburizing furnace according to claim 1, further comprising a microwave irradiation furnace having a built-in microwave irradiation mechanism as the microwave irradiation chamber.   The microwave carburizing furnace according to claim 9, wherein a microwave diffusion fan is provided in the furnace of the microwave irradiation furnace.   The microwave carburizing furnace according to claim 9, wherein a susceptor is provided inside the microwave irradiation furnace.   The microwave carburizing furnace according to claim 1, wherein a microwave introduction window is provided in a part of the microwave irradiation chamber. A method of carburizing a workpiece made of a steel material using a microwave as a heating source, and irradiating the microwave in the presence of a workpiece, a carbon source, and an atmosphere gas containing Ar and O ₂ , Ar plasma is generated by the reaction between the carbon source and oxygen and the accompanying generation and excitation of CO, and carbon ions are generated to carburize the object to be processed, and then the object to be processed is quenched with a cooling medium and quenched. A microwave carburizing method characterized by The microwave carburizing method according to claim 13, wherein the atmosphere gas includes at least one of Ar and O ₂ , CO, and a hydrocarbon-based gas. The microwave carburizing method according to claim 13, wherein the atmosphere gas includes Ar, O _2, and H ₂ . The microwave carburizing method according to claim 14, further comprising H ₂ as the atmospheric gas.   14. The microwave carburizing method according to claim 13, wherein the carbon source is a solid or a gas, the solid is a carbon powder, and the gas is a CO or hydrocarbon gas.   The microwave carburizing method according to claim 13, wherein the workpiece is made of a steel material having a crystal grain size of 1 μm or less and a tensile strength of 1000 MPa or more.   The microwave carburizing method according to claim 13, wherein the frequency of the microwave is 1 GHz or more and 30 GHz or less.

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