WO2019087619A1 - Carburization method - Google Patents

Carburization method Download PDF

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Publication number
WO2019087619A1
WO2019087619A1 PCT/JP2018/035314 JP2018035314W WO2019087619A1 WO 2019087619 A1 WO2019087619 A1 WO 2019087619A1 JP 2018035314 W JP2018035314 W JP 2018035314W WO 2019087619 A1 WO2019087619 A1 WO 2019087619A1
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Prior art keywords
temperature
carburizing
diffusion
treated
carbon
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PCT/JP2018/035314
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French (fr)
Japanese (ja)
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拓也 北
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株式会社デンソー
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Priority to CN201880069859.4A priority Critical patent/CN111315914A/en
Priority to EP18873525.2A priority patent/EP3705598A4/en
Publication of WO2019087619A1 publication Critical patent/WO2019087619A1/en

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment

Definitions

  • the present disclosure relates to a carburizing method.
  • an atmospheric gas carburizing method for an object to be treated made of carbon steel
  • a vacuum carburizing method for example, an atmospheric gas carburizing method, a vacuum carburizing method, an atmospheric pressure direct carburizing method and the like are known.
  • the atmosphere gas carburizing method the carburizing process is performed under atmospheric pressure, using the mixed gas generated in the shift furnace and the source gas.
  • the vacuum carburizing method carburizing is performed using only the source gas under reduced pressure.
  • the atmospheric pressure direct carburizing method the carburizing process is performed under atmospheric pressure using the raw material gas and the dilution gas.
  • a diffusion process is usually performed to diffuse the carbon injected on the surface of the object to be treated to the inside of the object after the carburizing step.
  • Patent Document 1 discloses a carburizing method for performing a diffusion process in which carburized carbon is diffused into the object to be treated in a state of maintaining a treatment temperature after performing carburizing treatment for a predetermined time. ing.
  • the above-described carburizing method generally requires a certain processing time or more because it is limited by temperature. Therefore, from the viewpoint of productivity improvement etc., it is desirable to shorten the processing time.
  • carbon is dissolved and diffused on the surface of the object to be treated, so that the treatment time can be shortened by raising the carburizing temperature and the diffusion temperature.
  • the treatment temperature is equal to or higher than the eutectic temperature of carbon steel, the object to be treated may be melted. Therefore, in actual production, both the carburizing treatment temperature and the diffusion treatment temperature are usually made equal to or less than the eutectic temperature of carbon steel.
  • the diffusion process is performed in the state where the carburizing process temperature is maintained as it is, it is also difficult to shorten the diffusion process time.
  • An object of this indication is to provide the carburizing method which can aim at shortening of processing time, controlling melting of the processing object made from carbon steel.
  • One aspect of the present disclosure includes a carburizing step of carburizing a carbon steel object to be treated, and a diffusion treatment of diffusing carbon injected on the surface of the object to be treated in the carburizing step to the inside of the object to be treated And a diffusion step of In the above diffusion step, As the surface carbon concentration of the object to be treated is reduced by the internal diffusion of the carbon, In the temperature diagram above the carburizing temperature and in the equilibrium phase diagram of the carbon steel, the temperature of the diffusion processing is raised continuously or stepwise within the temperature range below the solidus temperature for ⁇ Fe at the lowered surface carbon concentration. , It is in the carburizing method.
  • the melting point of the surface layer of the object to be treated is increased as the surface carbon concentration of the object to be treated is decreased by the internal diffusion of carbon.
  • this phenomenon is used to raise the diffusion processing temperature within the above-mentioned specific temperature range as the surface carbon concentration of the object to be treated is lowered by the internal diffusion of carbon. Therefore, according to the above-mentioned carburizing method, shortening of processing time by shortening of diffusion processing time can be attained, controlling fusion of a processing object made of carbon steel.
  • FIG. 1 is an explanatory view schematically showing a heat treatment pattern in the carburizing method of Embodiment 1.
  • FIG. 2 is an explanatory view schematically showing an equilibrium phase diagram of carbon steel constituting an object to be treated used in the carburizing method of Embodiment 1.
  • FIG. 3 is a graph showing the relationship between the carbon concentration and the distance from the surface of the object to be treated after carburizing treatment at the time of preparation of Sample 1;
  • FIG. 4 is a diagram showing a heat treatment pattern at the time of preparation of sample 1, FIG.
  • FIG. 5 shows (a) an appearance photograph of the sample 1 and (b) a cross-sectional photograph of the sample 1
  • FIG. 6 is a diagram showing a heat treatment pattern at the time of preparation of sample 1C
  • FIG. 7 shows (a) an appearance photograph of sample 1C and (b) a cross-sectional photograph of sample 1C.
  • the carburizing method of Embodiment 1 will be described with reference to FIGS. 1 and 2.
  • the carburizing method of the present embodiment has a carburizing step and a diffusion step, as shown in FIG.
  • the carburizing step is a step of carburizing a carbon steel object to be treated.
  • the diffusion process is a process of performing a diffusion process to diffuse the carbon injected on the surface of the object to be treated in the carburizing process into the inside of the object to be treated.
  • the carburizing step and the diffusion step can be specifically a carburizing step and a diffusion step in a vacuum carburizing method or a direct atmospheric pressure carburizing method.
  • the vacuum carburizing method carburizing is performed using only the source gas under reduced pressure.
  • the direct atmospheric pressure carburizing method the carburizing process is performed using the source gas and the dilution gas under atmospheric pressure.
  • the atmosphere gas carburizing method it is difficult to improve the carburizing treatment temperature and the diffusion treatment temperature in order to maintain the atmosphere.
  • the vacuum carburizing method and the atmospheric pressure direct carburizing method can easily improve the carburizing treatment temperature and the diffusion treatment temperature as compared with the atmospheric gas carburizing method. Therefore, according to the above configuration, the processing time can be easily shortened.
  • Vacuum carburizing method a raw material gas used in the atmospheric pressure directly carburizing method, for example, CH 4, etc. C 2 H 2, C 3 H 8, hydrocarbon gas such as C 4 H 10 and the like.
  • a dilution gas used in the atmospheric pressure direct carburizing method N 2 and the like can be mentioned.
  • the dilution gas has the roles of making the source gas equal to or less than the explosive pressure, suppressing the generation of soot, and ensuring the flow rate of supplying the source gas to the object to be treated.
  • the lower limit of the carburizing temperature in the carburizing process can be, for example, preferably the A3 line temperature or higher from the viewpoint of the austenite formation temperature and the like.
  • the upper limit of the carburizing temperature in the carburizing step may be selected from a temperature lower than the eutectic temperature of the carbon steel constituting the object to be treated so that decomposition of the raw material gas does not occur.
  • the upper limit of the carburizing temperature in the carburizing step may be preferably 1100 ° C. or less, more preferably 1050 ° C. or less.
  • the temperature of the object to be treated can be raised by heater heating or the like.
  • the diffusion treatment temperature is raised continuously or stepwise as the surface carbon concentration of the object to be treated is decreased by the internal diffusion of carbon.
  • the diffusion treatment temperature is set to a temperature exceeding the carburization treatment temperature. This is to improve the diffusion processing speed and improve the overall processing speed by setting the temperature above the carburizing temperature.
  • the diffusion treatment temperature is an equilibrium phase diagram (Fe-C phase diagram) of carbon steel constituting the object to be treated as exemplified in FIG. The temperature is lower than the temperature of the phase line JQ. That is, as shown in FIG.
  • the diffusion treatment temperature at the surface carbon concentration during diffusion is a temperature below the temperature Td of the point D intersecting the solid line JQ for .gamma.Fe when the surface carbon concentration Cd during diffusion. Be done. This is because melting of the object to be treated made of carbon steel occurs when rapid temperature rise exceeding the solidus line JQ temperature for ⁇ Fe is carried out at the surface carbon concentration lowered by diffusion.
  • the processing time can be shortened by shortening the diffusion processing time while suppressing the melting of the carbon steel object to be treated. it can.
  • the equilibrium phase diagram of carbon steel which comprises a process target object is determined by the material of carbon steel.
  • J is a peritectic reaction point
  • Tp is a peritectic temperature
  • Q is a carbon solid solution maximum point of ⁇ Fe
  • E is a eutectic point
  • Te is a eutectic temperature
  • S is a co-crystal point.
  • Ts is the eutectic temperature.
  • the maximum value of the diffusion treatment temperature can be equal to or higher than the eutectic temperature of the carbon steel constituting the object to be treated.
  • the maximum value of the diffusion treatment temperature is selected so as not to exceed the solidus temperature for ⁇ Fe as described above.
  • the diffusion process is performed at a temperature higher than the eutectic temperature of the carbon steel.
  • the diffusion processing temperature can be controlled by controlling the temperature rising rate. According to this configuration, it is easy to raise the diffusion processing temperature continuously or stepwise. Therefore, according to this configuration, the above-described effects can be made reliable.
  • the diffusion treatment temperature can be raised by high frequency heating. According to this configuration, compared to heater heating, the temperature can be raised to a predetermined diffusion processing temperature more quickly, and it is easy to control the temperature rising rate. Therefore, according to this configuration, it is easy to shorten the processing time by shortening the diffusion processing time.
  • a hardened layer can be formed on the surface layer of the object to be treated by passing through the quenching step of quenching the object to be treated after the above-mentioned diffusion step.
  • Known conditions can be applied to the quenching conditions and the like.
  • the prepared object to be treated was carburized under the following carburizing conditions.
  • -Carburizing condition- Atmospheric pressure Atmospheric pressure
  • Gas type N 2 gas (99% by volume) + C 2 H 2 gas (1% by volume)
  • Heat treatment conditions After heating to 1050 ° C, hold for 250 seconds
  • the object to be treated after the carburizing treatment was subjected to diffusion treatment under the following diffusion treatment conditions.
  • -Diffusion processing conditions Atmospheric pressure: Atmospheric pressure
  • Gas type N 2 gas
  • Heat treatment conditions Temperature rising from 1050 ° C. to 1275 ° C. at a heating rate of 11 ° C./sec, holding for 26 seconds
  • the object to be treated after the diffusion treatment was quenched by water cooling.
  • Sample 1 was produced by the above.
  • the carburizing method of this example is a direct atmospheric carburizing method.
  • the surface carbon concentration in the processing target after carburizing processing at the time of preparation of the sample 1 was 1.55 mass%.
  • FIG. 3 shows the relationship between the distance from the surface of the object to be treated after carburizing treatment to the depth direction and the carbon concentration at the time of preparation of the sample 1.
  • FIG. 4 shows a heat treatment pattern at the time of preparation of the sample 1.
  • the temperature rise rate is controlled, and as the surface carbon concentration of the object to be treated is decreased by the internal diffusion of carbon, the carburization treatment temperature is exceeded and the equilibrium state diagram of carbon steel, The diffusion treatment temperature is raised continuously within a temperature range below the solidus temperature for ⁇ Fe at reduced surface carbon concentrations.
  • a sample 1C was produced in the same manner as the sample 1 except that the temperature rising rate of the heat treatment condition under the diffusion treatment condition was 16 ° C./sec, and the holding time in the diffusion step was 29 seconds.
  • the reason for making the holding time in the diffusion step longer than in the case of the preparation of the sample 1 is that the diffusion time is required because the temperature is raised at high speed.
  • the heat processing pattern at the time of preparation of sample 1C is shown in FIG.
  • the diffusion treatment temperature is reduced by the internal diffusion of carbon in the equilibrium phase diagram of carbon steel by intentionally performing rapid temperature increase excessively in the diffusion treatment step.
  • the temperature was higher than the solidus temperature for when ⁇ Fe.
  • the present disclosure is not limited to the above embodiments and experimental examples, and various modifications can be made without departing from the scope of the invention. That is, although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments, structures, and the like. The present disclosure includes various modifications and variations within the equivalent range. In addition, various combinations and forms, and further, other combinations and forms including only one element, or more or less than these elements are also within the scope and the scope of the present disclosure.
  • the diffusion processing temperature is continuously raised within the above-described specific temperature range by controlling the temperature rising rate, but in addition to the above, the temperature rising rate is controlled to It is also possible to raise the diffusion treatment temperature stepwise within the specified temperature range.

Abstract

The carburization method has: a carburization step where a carbon steel treatment object is carburized; and a diffusion step for carrying out a diffusion treatment where carbon injected into the surface of the treatment object in the carburization step is diffused into the interior of the treatment object. This carburization method raises, as the surface carbon concentration of the treatment object decreases due to the internal diffusion of carbon, the diffusion treatment temperature continuously or in stages during the diffusion step within a temperature range higher than the carburization treatment temperature but lower than the solidus of γFe at the decreased surface carbon concentration in the equilibrium diagram of carbon steel.

Description

浸炭方法Carburizing method 関連出願の相互参照Cross-reference to related applications
　本出願は、２０１７年１０月３０日に出願された日本出願番号２０１７－２０９６１０号に基づくもので、ここにその記載内容を援用する。 This application is based on Japanese Patent Application No. 2017-209610 filed on October 30, 2017, the contents of which are incorporated herein by reference.
　本開示は、浸炭方法に関する。 The present disclosure relates to a carburizing method.
　従来、炭素鋼製の処理対象物に対する浸炭方法としては、例えば、雰囲気ガス浸炭方法、真空浸炭方法、大気圧直接浸炭方法などが知られている。雰囲気ガス浸炭方法では、大気圧下、変成炉にて生成された混合ガスと原料ガスとを用いて浸炭処理が行われる。真空浸炭方法では、減圧下、原料ガスのみを用いて浸炭処理が行われる。大気圧直接浸炭方法では、大気圧下、原料ガスと希釈ガスとを用いて浸炭処理が行われる。これら浸炭方法では、通常、浸炭工程後、処理対象物の表面に注入された炭素を処理対象物の内部へ拡散させるため、拡散処理が行われる。 Heretofore, as a carburizing method for an object to be treated made of carbon steel, for example, an atmospheric gas carburizing method, a vacuum carburizing method, an atmospheric pressure direct carburizing method and the like are known. In the atmosphere gas carburizing method, the carburizing process is performed under atmospheric pressure, using the mixed gas generated in the shift furnace and the source gas. In the vacuum carburizing method, carburizing is performed using only the source gas under reduced pressure. In the atmospheric pressure direct carburizing method, the carburizing process is performed under atmospheric pressure using the raw material gas and the dilution gas. In these carburizing methods, a diffusion process is usually performed to diffuse the carbon injected on the surface of the object to be treated to the inside of the object after the carburizing step.
　例えば、特許文献１には、所定時間の間、浸炭処理を行った後、処理温度を維持した状態で、浸炭された炭素を処理対象物の内部へ拡散させる拡散処理を行う浸炭方法が開示されている。 For example, Patent Document 1 discloses a carburizing method for performing a diffusion process in which carburized carbon is diffused into the object to be treated in a state of maintaining a treatment temperature after performing carburizing treatment for a predetermined time. ing.
特開２０１２－２５９９８号公報JP 2012-25998 A
　上述した浸炭方法は、一般に、温度により制約を受けるため、一定以上の処理時間を必要とする。そのため、生産性向上等の観点から、処理時間の短縮化を図ることが望まれている。上述した浸炭方法では、処理対象物の表面に炭素を固溶、拡散させることから、浸炭処理温度、拡散処理温度を上げることによって処理時間の短縮化を図ることができる。しかしながら、処理温度が炭素鋼の共晶温度以上になると、処理対象物が融解するおそれがある。そのため、実生産上では、浸炭処理温度、拡散処理温度ともに、炭素鋼の共晶温度以下とされるのが通常である。また、拡散処理は、浸炭処理温度をそのまま維持した状態で行われるため、拡散処理時間の短縮化も難しい。 The above-described carburizing method generally requires a certain processing time or more because it is limited by temperature. Therefore, from the viewpoint of productivity improvement etc., it is desirable to shorten the processing time. In the above-described carburizing method, carbon is dissolved and diffused on the surface of the object to be treated, so that the treatment time can be shortened by raising the carburizing temperature and the diffusion temperature. However, when the treatment temperature is equal to or higher than the eutectic temperature of carbon steel, the object to be treated may be melted. Therefore, in actual production, both the carburizing treatment temperature and the diffusion treatment temperature are usually made equal to or less than the eutectic temperature of carbon steel. Moreover, since the diffusion process is performed in the state where the carburizing process temperature is maintained as it is, it is also difficult to shorten the diffusion process time.
　本開示は、炭素鋼製の処理対象物の融解を抑制しつつ、処理時間の短縮化を図ることが可能な浸炭方法を提供することを目的とする。 An object of this indication is to provide the carburizing method which can aim at shortening of processing time, controlling melting of the processing object made from carbon steel.
　本開示の一態様は、炭素鋼製の処理対象物を浸炭処理する浸炭工程と、上記浸炭工程にて上記処理対象物の表面に注入された炭素を上記処理対象物の内部へ拡散させる拡散処理を行う拡散工程と、を有する浸炭方法であって、
　上記拡散工程において、
　上記炭素の内部拡散によって上記処理対象物の表面炭素濃度が低下するのに従って、
　浸炭処理温度超、かつ、上記炭素鋼の平衡状態図で、上記低下した表面炭素濃度のときのγＦｅに対する固相線温度未満の温度範囲内で、連続的または段階的に拡散処理温度を上昇させる、
　浸炭方法にある。 One aspect of the present disclosure includes a carburizing step of carburizing a carbon steel object to be treated, and a diffusion treatment of diffusing carbon injected on the surface of the object to be treated in the carburizing step to the inside of the object to be treated And a diffusion step of
In the above diffusion step,
As the surface carbon concentration of the object to be treated is reduced by the internal diffusion of the carbon,
In the temperature diagram above the carburizing temperature and in the equilibrium phase diagram of the carbon steel, the temperature of the diffusion processing is raised continuously or stepwise within the temperature range below the solidus temperature for γFe at the lowered surface carbon concentration. ,
It is in the carburizing method.
　拡散工程では、炭素の内部拡散によって処理対象物の表面炭素濃度が低下するのに従い、処理対象物の表層部の融点が上がる。上記浸炭方法では、この現象を利用し、炭素の内部拡散によって処理対象物の表面炭素濃度が低下するのに従って、上記特定の温度範囲内で拡散処理温度を上昇させる。そのため、上記浸炭方法によれば、炭素鋼製の処理対象物の融解を抑制しつつ、拡散処理時間の短縮による処理時間の短縮化を図ることができる。 In the diffusion step, the melting point of the surface layer of the object to be treated is increased as the surface carbon concentration of the object to be treated is decreased by the internal diffusion of carbon. In the above-mentioned carburizing method, this phenomenon is used to raise the diffusion processing temperature within the above-mentioned specific temperature range as the surface carbon concentration of the object to be treated is lowered by the internal diffusion of carbon. Therefore, according to the above-mentioned carburizing method, shortening of processing time by shortening of diffusion processing time can be attained, controlling fusion of a processing object made of carbon steel.
　本開示についての上記目的およびその他の目的、特徴や利点は、添付の図面を参照しながら下記の詳細な記述により、より明確になる。その図面は、
図１は、実施形態１の浸炭方法における熱処理パターンを模式的に示した説明図であり、 図２は、実施形態１の浸炭方法で用いられる処理対象物を構成する炭素鋼の平衡状態図を模式的に示した説明図であり、 図３は、試料１の作製時における浸炭処理後の処理対象物表面から深さ方向への距離と、炭素濃度との関係を示したグラフであり、 図４は、試料１の作製時における熱処理パターンを示した図であり、 図５は、（ａ）試料１の外観写真、（ｂ）試料１の断面写真であり、 図６は、試料１Ｃの作製時における熱処理パターンを示した図であり、 図７は、（ａ）試料１Ｃの外観写真、（ｂ）試料１Ｃの断面写真である。 The above object and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the attached drawings. The drawing is
FIG. 1 is an explanatory view schematically showing a heat treatment pattern in the carburizing method of Embodiment 1. FIG. 2 is an explanatory view schematically showing an equilibrium phase diagram of carbon steel constituting an object to be treated used in the carburizing method of Embodiment 1. FIG. 3 is a graph showing the relationship between the carbon concentration and the distance from the surface of the object to be treated after carburizing treatment at the time of preparation of Sample 1; FIG. 4 is a diagram showing a heat treatment pattern at the time of preparation of sample 1, FIG. 5 shows (a) an appearance photograph of the sample 1 and (b) a cross-sectional photograph of the sample 1, FIG. 6 is a diagram showing a heat treatment pattern at the time of preparation of sample 1C, FIG. 7 shows (a) an appearance photograph of sample 1C and (b) a cross-sectional photograph of sample 1C.
（実施形態１）
　実施形態１の浸炭方法について、図１、図２を用いて説明する。本実施形態の浸炭方法は、図１に示されるように、浸炭工程と、拡散工程とを有している。浸炭工程は、炭素鋼製の処理対象物を浸炭処理する工程である。拡散工程は、浸炭工程にて処理対象物の表面に注入された炭素を処理対象物の内部へ拡散させる拡散処理を行う工程である。 (Embodiment 1)
The carburizing method of Embodiment 1 will be described with reference to FIGS. 1 and 2. The carburizing method of the present embodiment has a carburizing step and a diffusion step, as shown in FIG. The carburizing step is a step of carburizing a carbon steel object to be treated. The diffusion process is a process of performing a diffusion process to diffuse the carbon injected on the surface of the object to be treated in the carburizing process into the inside of the object to be treated.
　浸炭工程および拡散工程は、具体的には、真空浸炭方法、または、大気圧直接浸炭方法における浸炭工程および拡散工程とすることができる。真空浸炭方法では、減圧下、原料ガスのみを用いて浸炭処理がなされる。また、大気圧直接浸炭方法では、大気圧下、原料ガスと希釈ガスとを用いて浸炭処理がなされる。雰囲気ガス浸炭方法は、雰囲気を維持するために浸炭処理温度、拡散処理温度を向上させることが難しい。これに対し、真空浸炭方法、大気圧直接浸炭方法は、雰囲気ガス浸炭方法に比べ、浸炭処理温度、拡散処理温度を向上させやすい。そのため、上記構成によれば、処理時間の短縮化を図りやすくなる。 The carburizing step and the diffusion step can be specifically a carburizing step and a diffusion step in a vacuum carburizing method or a direct atmospheric pressure carburizing method. In the vacuum carburizing method, carburizing is performed using only the source gas under reduced pressure. In the direct atmospheric pressure carburizing method, the carburizing process is performed using the source gas and the dilution gas under atmospheric pressure. In the atmosphere gas carburizing method, it is difficult to improve the carburizing treatment temperature and the diffusion treatment temperature in order to maintain the atmosphere. On the other hand, the vacuum carburizing method and the atmospheric pressure direct carburizing method can easily improve the carburizing treatment temperature and the diffusion treatment temperature as compared with the atmospheric gas carburizing method. Therefore, according to the above configuration, the processing time can be easily shortened.
　真空浸炭方法、大気圧直接浸炭方法で用いられる原料ガスとしては、例えば、ＣＨ４、Ｃ２Ｈ２、Ｃ３Ｈ８、Ｃ４Ｈ１０等の炭化水素ガスなどが挙げられる。大気圧直接浸炭方法で用いられる希釈ガスとしては、Ｎ２等が挙げられる。なお、上記希釈ガスは、原料ガスを爆発圧以下にする、スス発生を抑制する、原料ガスを処理対象物まで供給する流量を確保するなどの役割を有する。 Vacuum carburizing method, a raw material gas used in the atmospheric pressure directly carburizing method, for example, CH 4, etc. C 2 H 2, C 3 H 8, hydrocarbon gas such as C 4 H 10 and the like. As a dilution gas used in the atmospheric pressure direct carburizing method, N 2 and the like can be mentioned. The dilution gas has the roles of making the source gas equal to or less than the explosive pressure, suppressing the generation of soot, and ensuring the flow rate of supplying the source gas to the object to be treated.
　浸炭工程における浸炭温度の下限は、例えば、オーステナイト形成温度などの観点から、好ましくは、Ａ３線温度以上とすることができる。浸炭工程における浸炭温度の上限は、原料ガスの分解が生じないように、処理対象物を構成する炭素鋼の共晶温度未満の温度から選択すればよい。浸炭工程における浸炭温度の上限は、好ましくは、１１００℃以下、より好ましくは、１０５０℃以下とすることができる。なお、浸炭工程を実施する前の昇温工程では、例えば、ヒータ加熱などによって処理対象物を昇温することができる。 The lower limit of the carburizing temperature in the carburizing process can be, for example, preferably the A3 line temperature or higher from the viewpoint of the austenite formation temperature and the like. The upper limit of the carburizing temperature in the carburizing step may be selected from a temperature lower than the eutectic temperature of the carbon steel constituting the object to be treated so that decomposition of the raw material gas does not occur. The upper limit of the carburizing temperature in the carburizing step may be preferably 1100 ° C. or less, more preferably 1050 ° C. or less. In the temperature raising step before carrying out the carburizing step, for example, the temperature of the object to be treated can be raised by heater heating or the like.
　ここで、本実施形態の浸炭方法では、拡散工程において、炭素の内部拡散によって処理対象物の表面炭素濃度が低下するのに従い、連続的または段階的に拡散処理温度を上昇させる。この際、拡散処理温度は、浸炭処理温度を超える温度とされる。これは、浸炭処理温度を超える温度とすることにより、拡散処理速度を向上させ、全体の処理速度を向上させるためである。また、拡散処理温度は、図２に例示されるような、処理対象物を構成する炭素鋼の平衡状態図（Ｆｅ－Ｃ系状態図）で、上記低下した表面炭素濃度のときのγＦｅに対する固相線ＪＱ温度未満の温度とされる。つまり、図２に示すように、拡散中の表面炭素濃度のときにおける拡散処理温度は、拡散中の表面炭素濃度ＣｄのときにγＦｅに対する固相線ＪＱと交わる点Ｄの温度Ｔｄ未満の温度とされる。これは、拡散によって低下した表面炭素濃度のときに、γＦｅに対する固相線ＪＱ温度を超えるような急激な昇温が実施されると、炭素鋼製の処理対象物の融解が生じるためである。このように浸炭工程および拡散工程を実施する本実施形態の浸炭方法によれば、炭素鋼製の処理対象物の融解を抑制しつつ、拡散処理時間の短縮による処理時間の短縮化を図ることができる。 Here, in the carburizing method of the present embodiment, in the diffusion step, the diffusion treatment temperature is raised continuously or stepwise as the surface carbon concentration of the object to be treated is decreased by the internal diffusion of carbon. At this time, the diffusion treatment temperature is set to a temperature exceeding the carburization treatment temperature. This is to improve the diffusion processing speed and improve the overall processing speed by setting the temperature above the carburizing temperature. In addition, the diffusion treatment temperature is an equilibrium phase diagram (Fe-C phase diagram) of carbon steel constituting the object to be treated as exemplified in FIG. The temperature is lower than the temperature of the phase line JQ. That is, as shown in FIG. 2, the diffusion treatment temperature at the surface carbon concentration during diffusion is a temperature below the temperature Td of the point D intersecting the solid line JQ for .gamma.Fe when the surface carbon concentration Cd during diffusion. Be done. This is because melting of the object to be treated made of carbon steel occurs when rapid temperature rise exceeding the solidus line JQ temperature for γFe is carried out at the surface carbon concentration lowered by diffusion. Thus, according to the carburizing method of the present embodiment for carrying out the carburizing step and the diffusion step, the processing time can be shortened by shortening the diffusion processing time while suppressing the melting of the carbon steel object to be treated. it can.
　なお、処理対象物を構成する炭素鋼の平衡状態図は、炭素鋼の材質によって決定される。また、図２において、Ｊは、包晶反応点、Ｔｐは、包晶温度、Ｑは、γＦｅの炭素固溶最大点、Ｅは、共晶点、Ｔｅは、共晶温度、Ｓは、共析点、Ｔｓは、共析温度である。 In addition, the equilibrium phase diagram of carbon steel which comprises a process target object is determined by the material of carbon steel. In FIG. 2, J is a peritectic reaction point, Tp is a peritectic temperature, Q is a carbon solid solution maximum point of γFe, E is a eutectic point, Te is a eutectic temperature, S is a co-crystal point. The analysis point, Ts, is the eutectic temperature.
　本実施形態の浸炭方法において、拡散処理温度の最大値は、具体的には、処理対象物を構成する炭素鋼の共晶温度以上とすることができる。但し、拡散処理温度の最大値は、上述したように、γＦｅに対する固相線温度を超えないように選択される。この構成によれば、炭素鋼の共晶温度以上の高い温度で拡散処理がなされる。また、この構成によれば、炭素鋼の包晶温度近くまで拡散処理温度の高温化を図ることが可能となる。そのため、この構成によれば、拡散処理時間の短縮による処理時間の短縮化を図りやすくなる。 In the carburizing method of the present embodiment, specifically, the maximum value of the diffusion treatment temperature can be equal to or higher than the eutectic temperature of the carbon steel constituting the object to be treated. However, the maximum value of the diffusion treatment temperature is selected so as not to exceed the solidus temperature for γFe as described above. According to this configuration, the diffusion process is performed at a temperature higher than the eutectic temperature of the carbon steel. Moreover, according to this configuration, it is possible to increase the temperature of the diffusion processing temperature to near the peritectic temperature of carbon steel. Therefore, according to this configuration, it is easy to shorten the processing time by shortening the diffusion processing time.
　本実施形態の浸炭方法において、拡散処理温度は、昇温速度を制御することによって制御することができる。この構成によれば、連続的または段階的に拡散処理温度を上昇させやすい。そのため、この構成によれば、上述した作用効果を確実なものとすることができる。 In the carburizing method of the present embodiment, the diffusion processing temperature can be controlled by controlling the temperature rising rate. According to this configuration, it is easy to raise the diffusion processing temperature continuously or stepwise. Therefore, according to this configuration, the above-described effects can be made reliable.
　本実施形態の浸炭方法において、拡散処理温度は、高周波加熱によって上昇させることができる。この構成によれば、ヒータ加熱に比べ、所定の拡散処理温度まで迅速に昇温することができ、また、昇温速度の制御もしやすい。そのため、この構成によれば、拡散処理時間の短縮による処理時間の短縮化を図りやすくなる。 In the carburizing method of the present embodiment, the diffusion treatment temperature can be raised by high frequency heating. According to this configuration, compared to heater heating, the temperature can be raised to a predetermined diffusion processing temperature more quickly, and it is easy to control the temperature rising rate. Therefore, according to this configuration, it is easy to shorten the processing time by shortening the diffusion processing time.
　本実施形態の浸炭方法の使用時には、上述した拡散工程の後、処理対象物を焼入れする焼入工程を経ることにより、処理対象物の表層に硬化層を形成することができる。なお、焼入条件等については、公知の条件を適用することが可能である。 At the time of use of the carburizing method of the present embodiment, a hardened layer can be formed on the surface layer of the object to be treated by passing through the quenching step of quenching the object to be treated after the above-mentioned diffusion step. Known conditions can be applied to the quenching conditions and the like.
（実験例）
＜試料１の作製＞
　Ｃ：０．１５質量％、Ｓｉ：０．２質量％、Ｍｎ：０．７５質量％、Ｃｒ：１．０５質量％、Ｍｏ：０．２質量％を含有し、残部がＦｅおよび不可避不純物よりなる炭素鋼から構成される処理対象物を準備した。なお、上記炭素鋼における共晶温度は、１１４３℃である。また、上記炭素鋼における包晶温度は、１４８５℃である。 (Experimental example)
<Preparation of Sample 1>
C: 0.15% by mass, Si: 0.2% by mass, Mn: 0.75% by mass, Cr: 1.05% by mass, Mo: 0.2% by mass, the balance being from Fe and unavoidable impurities A processing target consisting of carbon steel was prepared. The eutectic temperature in the above carbon steel is 1143 ° C. The peritectic temperature of the carbon steel is 1485 ° C.
　準備した処理対象物を、以下の浸炭処理条件で浸炭処理した。
　－浸炭処理条件－
　　雰囲気圧力：大気圧
　　ガス種：Ｎ２ガス（９９体積％）＋Ｃ２Ｈ２ガス（１体積％）
　　熱処理条件：１０５０℃まで昇温後、２５０秒間保持 The prepared object to be treated was carburized under the following carburizing conditions.
-Carburizing condition-
Atmospheric pressure: Atmospheric pressure Gas type: N 2 gas (99% by volume) + C 2 H 2 gas (1% by volume)
Heat treatment conditions: After heating to 1050 ° C, hold for 250 seconds
　上記浸炭処理後の処理対象物を、以下の拡散処理条件で拡散処理した。
　－拡散処理条件－
　　雰囲気圧力：大気圧
　　ガス種：Ｎ２ガス
　　熱処理条件：昇温速度１１℃/秒にて１０５０℃から１２７５℃まで昇温後、２６秒
　　　　　　　　間保持 The object to be treated after the carburizing treatment was subjected to diffusion treatment under the following diffusion treatment conditions.
-Diffusion processing conditions-
Atmospheric pressure: Atmospheric pressure Gas type: N 2 gas Heat treatment conditions: Temperature rising from 1050 ° C. to 1275 ° C. at a heating rate of 11 ° C./sec, holding for 26 seconds
　上記拡散処理後の処理対象物を、水冷にて焼入処理した。 The object to be treated after the diffusion treatment was quenched by water cooling.
　以上により、試料１を作製した。なお、本例の浸炭方法は、大気圧直接浸炭方法である。また、試料１の作製時における浸炭処理後の処理対象物における表面炭素濃度は、１．５５質量％であった。図３に、試料１の作製時における浸炭処理後の処理対象物表面から深さ方向への距離と、炭素濃度との関係を示す。また、図４に、試料１の作製時における熱処理パターンを示す。なお、試料１の作製では、昇温速度を制御することにより、炭素の内部拡散によって処理対象物の表面炭素濃度が低下するのに従って、浸炭処理温度超、かつ、炭素鋼の平衡状態図で、低下した表面炭素濃度のときのγＦｅに対する固相線温度未満の温度範囲内で、連続的に拡散処理温度を上昇させている。 Sample 1 was produced by the above. The carburizing method of this example is a direct atmospheric carburizing method. Moreover, the surface carbon concentration in the processing target after carburizing processing at the time of preparation of the sample 1 was 1.55 mass%. FIG. 3 shows the relationship between the distance from the surface of the object to be treated after carburizing treatment to the depth direction and the carbon concentration at the time of preparation of the sample 1. Further, FIG. 4 shows a heat treatment pattern at the time of preparation of the sample 1. In the preparation of sample 1, the temperature rise rate is controlled, and as the surface carbon concentration of the object to be treated is decreased by the internal diffusion of carbon, the carburization treatment temperature is exceeded and the equilibrium state diagram of carbon steel, The diffusion treatment temperature is raised continuously within a temperature range below the solidus temperature for γFe at reduced surface carbon concentrations.
　金属顕微鏡にて、試料１の表面に垂直な断面を観察したところ（図５（ａ）の線Ｌの位置）、図５（ｂ）に示されるように、処理対象物の溶解は確認されなかった。なお、この結果から、試料１の浸炭方法によれば、炭素鋼製の処理対象物の融解を抑制しつつ、処理時間の短縮化を図ることができるといえる。 When a cross section perpendicular to the surface of sample 1 is observed with a metallurgical microscope (the position of line L in FIG. 5A), as shown in FIG. 5B, the dissolution of the object to be treated is not confirmed The From this result, according to the carburizing method of the sample 1, it can be said that the processing time can be shortened while suppressing the melting of the object to be treated made of carbon steel.
＜試料１Ｃの作製＞
　拡散処理条件における熱処理条件の昇温速度を１６℃/秒とした点、拡散工程における保持時間を２９秒とした点以外は、試料１の作製と同様にして、試料１Ｃを作製した。なお、本例において、拡散工程における保持時間を、試料１の作製の場合よりも長くした理由は、高速で昇温した分、拡散時間を要するためである。図６に、試料１Ｃの作製時における熱処理パターンを示す。なお、試料１Ｃの作製では、拡散処理工程にて意図的に過度な急速昇温を行うことにより、拡散処理温度を、炭素鋼の平衡状態図で、炭素の内部拡散によって低下した表面炭素濃度のときのγＦｅに対する固相線温度を上回る温度とした。 <Production of Sample 1C>
A sample 1C was produced in the same manner as the sample 1 except that the temperature rising rate of the heat treatment condition under the diffusion treatment condition was 16 ° C./sec, and the holding time in the diffusion step was 29 seconds. In this example, the reason for making the holding time in the diffusion step longer than in the case of the preparation of the sample 1 is that the diffusion time is required because the temperature is raised at high speed. The heat processing pattern at the time of preparation of sample 1C is shown in FIG. In the preparation of sample 1C, the diffusion treatment temperature is reduced by the internal diffusion of carbon in the equilibrium phase diagram of carbon steel by intentionally performing rapid temperature increase excessively in the diffusion treatment step. The temperature was higher than the solidus temperature for when γFe.
　金属顕微鏡にて、試料１Ｃの表面に垂直な断面を観察したところ（図７（ａ）の線Ｌの位置）、図７（ｂ）に示されるように、処理対象物の表層部に溶解部Ｍが確認された。この結果から、試料１Ｃの浸炭方法では、処理時間の短縮化を図ることができても、炭素鋼製の処理対象物の融解を抑制することが困難であるといえる。 When a cross section perpendicular to the surface of the sample 1C is observed with a metallurgical microscope (the position of the line L in FIG. 7A), as shown in FIG. 7B, the dissolved portion in the surface layer of the processing object M was confirmed. From these results, it can be said that, in the carburizing method of Sample 1C, it is difficult to suppress the melting of the carbon steel object to be treated even if the treatment time can be shortened.
　本開示は、上記各実施形態、各実験例に限定されるものではなく、その要旨を逸脱しない範囲において種々の変更が可能である。すなわち、本開示は、実施形態に準拠して記述されたが、本開示は、当該実施形態や構造等に限定されるものではないと理解される。本開示は、様々は変形例や均等範囲内の変形をも包含する。加えて、様々な組み合わせや形態、さらには、それらに一要素のみ、それ以上、あるいはそれ以下、を含む他の組み合わせや形態をも、本開示の範疇や思想範囲に入るものである。例えば、上記実験例では、昇温速度を制御することにより、上述した特定の温度範囲内で連続的に拡散処理温度を上昇させたが、他にも、昇温速度を制御することにより、上述した特定の温度範囲内で段階的に拡散処理温度を上昇させることも可能である。 The present disclosure is not limited to the above embodiments and experimental examples, and various modifications can be made without departing from the scope of the invention. That is, although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments, structures, and the like. The present disclosure includes various modifications and variations within the equivalent range. In addition, various combinations and forms, and further, other combinations and forms including only one element, or more or less than these elements are also within the scope and the scope of the present disclosure. For example, in the above-described experimental example, the diffusion processing temperature is continuously raised within the above-described specific temperature range by controlling the temperature rising rate, but in addition to the above, the temperature rising rate is controlled to It is also possible to raise the diffusion treatment temperature stepwise within the specified temperature range.

Claims (5)

  1. 　炭素鋼製の処理対象物を浸炭処理する浸炭工程と、上記浸炭工程にて上記処理対象物の表面に注入された炭素を上記処理対象物の内部へ拡散させる拡散処理を行う拡散工程と、を有する浸炭方法であって、
    　上記拡散工程において、
    　上記炭素の内部拡散によって上記処理対象物の表面炭素濃度が低下するのに従って、
    　浸炭処理温度超、かつ、上記炭素鋼の平衡状態図で、上記低下した表面炭素濃度のときのγＦｅに対する固相線温度未満の温度範囲内で、連続的または段階的に拡散処理温度を上昇させる、
    　浸炭方法。     A carburizing step of carburizing a carbon steel object to be treated, and a diffusion step of diffusing carbon injected on the surface of the object to be treated in the carburizing step into the inside of the object to be treated Carburizing method having
    In the above diffusion step,
    As the surface carbon concentration of the object to be treated is reduced by the internal diffusion of the carbon,
    In the temperature diagram above the carburizing temperature and in the equilibrium phase diagram of the carbon steel, the temperature of the diffusion processing is raised continuously or stepwise within the temperature range below the solidus temperature for γFe at the lowered surface carbon concentration. ,
    Carburizing method.
  2. 　上記拡散処理温度の最大値が、上記炭素鋼の共晶温度以上とされる、請求項１に記載の浸炭方法。 The carburizing method according to claim 1, wherein the maximum value of the diffusion processing temperature is equal to or higher than the eutectic temperature of the carbon steel.
  3. 　上記拡散処理温度が、昇温速度を制御することによって制御される、請求項１または２に記載の浸炭方法。 The carburizing method according to claim 1, wherein the diffusion treatment temperature is controlled by controlling a temperature rising rate.
  4. 　上記拡散処理温度を、高周波加熱によって上昇させる、請求項１～３のいずれか１項に記載の浸炭方法。 The carburizing method according to any one of claims 1 to 3, wherein the diffusion treatment temperature is raised by high frequency heating.
  5. 　上記浸炭工程および上記拡散工程は、真空浸炭方法、または、大気圧直接浸炭方法における浸炭工程および拡散工程である、請求項１～４のいずれか１項に記載の浸炭方法。 The carburizing method according to any one of claims 1 to 4, wherein the carburizing step and the diffusion step are a vacuum carburizing method or a carburizing step and a diffusion step in an atmospheric pressure direct carburizing method.
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JP2001098343A (en) * 1999-07-21 2001-04-10 Daido Steel Co Ltd High bearing pressure resistant member and producing method thereof
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JP2019081925A (en) 2019-05-30
EP3705598A1 (en) 2020-09-09
CN111315914A (en) 2020-06-19
JP6812948B2 (en) 2021-01-13
EP3705598A4 (en) 2020-09-09

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