JP5837282B2 - Surface modification method - Google Patents
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- JP5837282B2 JP5837282B2 JP2010057430A JP2010057430A JP5837282B2 JP 5837282 B2 JP5837282 B2 JP 5837282B2 JP 2010057430 A JP2010057430 A JP 2010057430A JP 2010057430 A JP2010057430 A JP 2010057430A JP 5837282 B2 JP5837282 B2 JP 5837282B2
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- 238000002715 modification method Methods 0.000 title claims description 7
- 239000007789 gas Substances 0.000 claims description 132
- 238000000034 method Methods 0.000 claims description 92
- 238000005255 carburizing Methods 0.000 claims description 88
- 238000002407 reforming Methods 0.000 claims description 44
- 238000011282 treatment Methods 0.000 claims description 32
- 238000010438 heat treatment Methods 0.000 claims description 26
- 238000005256 carbonitriding Methods 0.000 claims description 23
- 229910000831 Steel Inorganic materials 0.000 claims description 20
- 239000010959 steel Substances 0.000 claims description 20
- 230000004048 modification Effects 0.000 claims description 12
- 238000012986 modification Methods 0.000 claims description 12
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- 239000011261 inert gas Substances 0.000 claims description 5
- 239000004215 Carbon black (E152) Substances 0.000 claims description 4
- 229930195733 hydrocarbon Natural products 0.000 claims description 4
- 150000002430 hydrocarbons Chemical class 0.000 claims description 4
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims 2
- 229910021529 ammonia Inorganic materials 0.000 claims 1
- 239000001257 hydrogen Substances 0.000 claims 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims 1
- 238000004381 surface treatment Methods 0.000 claims 1
- 239000000047 product Substances 0.000 description 34
- 230000003647 oxidation Effects 0.000 description 26
- 238000007254 oxidation reaction Methods 0.000 description 26
- 238000010791 quenching Methods 0.000 description 25
- 230000000171 quenching effect Effects 0.000 description 25
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 16
- 229910052799 carbon Inorganic materials 0.000 description 16
- 230000000052 comparative effect Effects 0.000 description 16
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 12
- 239000012159 carrier gas Substances 0.000 description 9
- 230000001590 oxidative effect Effects 0.000 description 8
- 230000001154 acute effect Effects 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 6
- IUVCFHHAEHNCFT-INIZCTEOSA-N 2-[(1s)-1-[4-amino-3-(3-fluoro-4-propan-2-yloxyphenyl)pyrazolo[3,4-d]pyrimidin-1-yl]ethyl]-6-fluoro-3-(3-fluorophenyl)chromen-4-one Chemical compound C1=C(F)C(OC(C)C)=CC=C1C(C1=C(N)N=CN=C11)=NN1[C@@H](C)C1=C(C=2C=C(F)C=CC=2)C(=O)C2=CC(F)=CC=C2O1 IUVCFHHAEHNCFT-INIZCTEOSA-N 0.000 description 5
- 229910002091 carbon monoxide Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 229910001567 cementite Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000006837 decompression Effects 0.000 description 1
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000005121 nitriding Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
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Description
本発明は、ガス浸炭処理又はガス浸炭窒化処理によって表面及び表面近傍に酸化物が生成した鋼製の被処理品の表面を改質する方法に関する。 The present invention relates to a method for modifying the surface of a steel article to be processed in which oxides are generated on the surface and in the vicinity of the surface by gas carburizing or gas carbonitriding.
現在、鋼製部品等の金属製部品に施す表面硬化処理として、浸炭法及び浸炭窒化法が最も多く適用されている。浸炭法及び浸炭窒化法としては、ガス法、真空法、及び真空法とガス法の両方を組み合わせた方法があるが、これらの中でもガス浸炭法及びガス浸炭窒化法は、処理品質の安定性や経済性が優れていることから、現在のところ最も多く適用されている。 Currently, the carburizing method and the carbonitriding method are most frequently applied as surface hardening treatments for metal parts such as steel parts. As the carburizing method and the carbonitriding method, there are a gas method, a vacuum method, and a method in which both the vacuum method and the gas method are combined. Among these methods, the gas carburizing method and the gas carbonitriding method include stability of processing quality, It is most widely used at present because of its economic efficiency.
ガス浸炭法及びガス浸炭窒化法においては、処理の自動化の観点から、キャリヤーガス（搬送ガス）とエンリッチガスによる浸炭が主に採用されている。キャリヤーガスを浸炭炉内に導入する方法としては、ＲＸガス（ＣＯ，Ｈ2 ，Ｎ2 を主成分とする吸熱型変成ガス）を外部から供給する方法や、液体のメタノール（ＣＨ3 ＯＨ）を直接浸炭炉内に供給してキャリヤーガス（ＣＯ，Ｈ2 を主成分とするガス）を生成させる方法等がある。一方、エンリッチガスとしては、プロパンガス（Ｃ3 Ｈ8 ）等の炭化水素ガスを使用する場合が多い。 In the gas carburizing method and the gas carbonitriding method, carburizing with a carrier gas (carrier gas) and an enriched gas is mainly employed from the viewpoint of automation of processing. As a method for introducing the carrier gas into the carburizing furnace, RX gas (an endothermic modified gas mainly composed of CO, H 2 , and N 2 ) is supplied from the outside, or liquid methanol (CH 3 OH) is used. There is a method of generating a carrier gas (a gas mainly composed of CO and H 2 ) by directly supplying it into the carburizing furnace. On the other hand, hydrocarbon gas such as propane gas (C 3 H 8 ) is often used as the enriched gas.
ガス浸炭法、ガス浸炭窒化法いずれにおいても、浸炭炉内での浸炭反応は、下記の（１），（２），（３）式で表すことができる。（１），（２），（３）式において（Ｃ）は、鋼中に浸透した炭素を表す。
２ＣＯ＝（Ｃ）＋ＣＯ2 ・・・（１）
ＣＯ＝（Ｃ）＋１／２Ｏ2 ・・・（２）
ＣＯ＋Ｈ2 ＝（Ｃ）＋Ｈ2 Ｏ ・・・（３）
In both the gas carburizing method and the gas carbonitriding method, the carburizing reaction in the carburizing furnace can be expressed by the following equations (1), (2), and (3). In formulas (1), (2), and (3), (C) represents carbon that has penetrated into the steel.
2CO = (C) + CO 2 (1)
CO = (C) + 1 / 2O 2 (2)
CO + H 2 = (C) + H 2 O (3)
また、ガス浸炭窒化法の場合は、浸炭ガスに主にＮＨ3 ガスを加えて浸炭炉内に添加することにより、（４）式のように鋼中に窒素を浸透拡散させる。（４）式において（Ｎ）は、鋼中に浸透した窒素を表す。
ＮＨ3 ＝（Ｎ）＋３／２Ｈ2 ・・・（４）
キャリヤーガスを使用する目的は、浸炭に必要なＣＯやＨ2 を供給することである。また、エンリッチガスを使用する目的は、浸炭炉内に存在するＣＯ2 ，Ｏ2 ，Ｈ2 Ｏという酸化性ガスと反応させて、その添加の有無により酸化性ガスの量を増減させることである。すなわち、ガス浸炭法やガス浸炭窒化法においては、鋼中に浸透した炭素（Ｃ）の表面炭素濃度は、（１），（２），（３）式中の還元性ガスＣＯ，Ｈ2 と酸化性ガスＣＯ2 ，Ｏ2 ，Ｈ2 Ｏとの濃度比によって決定する。
In the case of the gas carbonitriding method, NH 3 gas is mainly added to the carburizing gas and added to the carburizing furnace, so that nitrogen is infiltrated and diffused into the steel as expressed by equation (4). In the formula (4), (N) represents nitrogen that has penetrated into the steel.
NH 3 = (N) + 3 / 2H 2 (4)
The purpose of using the carrier gas is to supply CO and H 2 necessary for carburizing. The purpose of using the enriched gas is to react with an oxidizing gas such as CO 2 , O 2 , and H 2 O existing in the carburizing furnace, and to increase or decrease the amount of the oxidizing gas depending on whether or not it is added. . That is, in the gas carburizing method and the gas carbonitriding method, the surface carbon concentration of carbon (C) that has penetrated into the steel is the reducing gases CO and H 2 in the formulas (1), (2), and (3). It is determined by the concentration ratio with the oxidizing gases CO 2 , O 2 , and H 2 O.
そのため、このようなガスの平衡反応によるガス浸炭法やガス浸炭窒化法では、浸炭する温度域において鉄は酸化することはないが、鋼中の合金成分であるＣｒ，Ｍｎ，Ｓｉ等は浸炭ガス中の微量の酸化性ガス（ＣＯ2 ，Ｏ2 ，Ｈ2 Ｏ）によって酸化される。その結果、鋼製部品の表面及び表面近傍に、粒界酸化とそれに伴う不完全焼入れ層とが形成されることとなる。そして、このことにより、その部分の硬さが低下し、耐摩耗性や耐疲労強度が低下する。 Therefore, in such a gas carburizing method or gas carbonitriding method using an equilibrium reaction of gas, iron is not oxidized in the carburizing temperature range, but the alloy components such as Cr, Mn, and Si are not carburized gas. Oxidized by a small amount of oxidizing gas (CO 2 , O 2 , H 2 O). As a result, grain boundary oxidation and an accompanying incomplete quenching layer are formed on the surface of the steel part and in the vicinity of the surface. And the hardness of the part falls by this, and wear resistance and fatigue strength fall.
一方、真空浸炭法及び真空浸炭窒化法は、下記の（５）式のように、主にアセチレンガス（Ｃ2 Ｈ2 ）等の炭化水素ガスの一方的な分解反応（非平衡反応）による浸炭法である。
Ｃ2 Ｈ2 ＝２（Ｃ）＋Ｈ2 ・・・（５）
真空浸炭法及び真空浸炭窒化法においては、ガス法とは異なり、浸炭炉内に酸化性ガスがほとんど存在しないので、粒界酸化とそれに伴う不完全焼入れ層とが表面及び表面近傍に生じることはほとんどない。
On the other hand, the vacuum carburizing method and the vacuum carbonitriding method are mainly carburized by unilateral decomposition reaction (non-equilibrium reaction) of hydrocarbon gas such as acetylene gas (C 2 H 2 ) as shown in the following formula (5). Is the law.
C 2 H 2 = 2 (C) + H 2 (5)
In the vacuum carburizing method and the vacuum carbonitriding method, unlike the gas method, there is almost no oxidizing gas in the carburizing furnace, so that grain boundary oxidation and the accompanying incomplete quenching layer occur on and near the surface. rare.
しかしながら、この真空浸炭法及び真空浸炭窒化法は、ガス法のようなガスの平衡反応によるものではなく、炭化水素ガスの一方的な分解反応、いわゆる非平衡反応であるため、雰囲気制御することが困難である。また、平衡反応ではないため、当然に被処理品の平坦部と鋭角部とでは炭素濃度が異なる。すなわち、鋭角部の炭素濃度の方が平坦部の炭素濃度よりも高くなり、場合によっては、鉄炭化物であるセメンタイトが析出することもある。鋭角部にセメンタイトが析出すると、その被処理品の寿命が極端に低下することが知られている。
このようなことから、真空浸炭法とガス浸炭法を組み合わせた浸炭方法により、被処理品の平坦部と鋭角部の炭素濃度の均一化を図る技術が提案されている（特許文献１，２を参照）。
However, the vacuum carburizing method and the vacuum carbonitriding method are not based on a gas equilibrium reaction as in the gas method, but are unilateral decomposition reactions of hydrocarbon gas, so-called non-equilibrium reactions, so that the atmosphere can be controlled. Have difficulty. Moreover, since it is not an equilibrium reaction, naturally the carbon concentration differs between the flat portion and the acute angle portion of the article to be processed. That is, the carbon concentration in the acute angle portion is higher than the carbon concentration in the flat portion, and in some cases, cementite that is iron carbide may be precipitated. It is known that when cementite precipitates at an acute angle portion, the life of the article to be treated is extremely reduced.
For this reason, a technique for making the carbon concentration of the flat portion and the acute angle portion of the article to be processed uniform by a carburizing method combining a vacuum carburizing method and a gas carburizing method has been proposed (see Patent Documents 1 and 2). reference).
しかしながら、特許文献１，２に提案の浸炭方法は、ガス浸炭期においては炉内に酸化性ガスが生成されるため、当然に粒界酸化とそれに伴う不完全焼入れ層が表面及び表面近傍に生じることになる。
そこで、本発明は上記のような従来技術が有する問題点を解決し、ガス浸炭処理又はガス浸炭窒化処理によって表面及び表面近傍に粒界酸化とそれに伴う不完全焼入れ層とが生じている鋼製の被処理品に対して好適な表面改質方法であり、粒界酸化とそれに伴う不完全焼入れ層とを低減して前記被処理品の表面品質を向上させる表面改質方法を提供することを課題とする。
However, in the carburizing methods proposed in Patent Documents 1 and 2, since an oxidizing gas is generated in the furnace during the gas carburizing period, the grain boundary oxidation and the accompanying incomplete quenching layer naturally occur on the surface and in the vicinity of the surface. It will be.
Therefore, the present invention solves the problems of the prior art as described above, and is made of steel in which grain carburization or gas carbonitriding causes grain boundary oxidation and an accompanying incomplete quenching layer on and near the surface. The present invention provides a surface modification method that is suitable for an article to be processed and that improves the surface quality of the article to be processed by reducing grain boundary oxidation and the accompanying incomplete quenching layer. Let it be an issue.
前記課題を解決するため、本発明は次のような構成からなる。すなわち、本発明の表面改質方法は、ガス浸炭処理又はガス浸炭窒化処理が施されて表面及び表面近傍に酸化物が生成した鋼製の被処理品に改質処理を施して、前記被処理品の表面改質を行うに際して、圧力０．０１Ｐａ以上３０００Ｐａ以下の改質処理室内に入れた前記被処理品を、下記の３つの条件Ａ，Ｂ，Ｃのうちのいずれかの導入ガス条件下、温度７００℃以上１２００℃以下で１０分以上１８０分以下熱処理することを特徴とする。
（条件Ａ）前記改質処理室に導入ガスを全く導入しない。
（条件Ｂ）前記改質処理室に１種以上の還元性ガスを導入ガスとして導入する。
（条件Ｃ）前記改質処理室に不活性ガス及び１種以上の還元性ガスの混合ガスを導入ガスとして導入する。
In order to solve the above problems, the present invention has the following configuration. That is, in the surface modification method of the present invention, a gas carburizing process or a gas carbonitriding process is performed to perform a modification process on a steel processed product in which an oxide is generated on the surface and in the vicinity of the surface. When performing surface modification of a product, the product to be treated placed in a reforming chamber having a pressure of 0.01 Pa or more and 3000 Pa or less is introduced under any of the following three conditions A, B, and C. The heat treatment is performed at a temperature of 700 ° C. to 1200 ° C. for 10 minutes to 180 minutes.
(Condition A) No introduction gas is introduced into the reforming chamber.
(Condition B) One or more reducing gases are introduced into the reforming chamber as an introduction gas.
(Condition C) A mixed gas of an inert gas and one or more reducing gases is introduced as an introduction gas into the reforming chamber.
ガス浸炭処理又はガス浸炭窒化処理が施されることによって、鋼製の被処理品の表面及び表面近傍には粒界酸化とそれに伴う不完全焼入れ層とが生じるが、本発明の表面改質方法に係る改質処理を該被処理品に施せば、表面及び表面近傍に生成している酸化物が還元されるため、粒界酸化とそれに伴う不完全焼入れ層とを低減することができる。 By performing the gas carburizing process or the gas carbonitriding process, grain boundary oxidation and an incompletely hardened layer are caused on the surface and in the vicinity of the surface of the steel processed article. Since the oxide produced on the surface and in the vicinity of the surface is reduced when the article to be treated is subjected to the modification treatment according to, grain boundary oxidation and the incomplete quenching layer accompanying it can be reduced.
本発明の表面改質方法の実施の形態について、以下に詳細に説明する。
鋼製の被処理品にガス浸炭処理又はガス浸炭窒化処理を施すと、前記被処理品の表面が酸化されて、表面及び表面近傍に粒界酸化とそれに伴う不完全焼入れ層とが生じる。粒界酸化とそれに伴う不完全焼入れ層が生じると、その部分の硬さが低下し、前記被処理品の耐摩耗性や耐疲労強度が低下するので、耐摩耗性や耐疲労強度を向上させるため、粒界酸化とそれに伴う不完全焼入れ層とを低減して前記被処理品の表面品質を向上させる改質処理を施した。この改質処理について以下に説明する。
Embodiments of the surface modification method of the present invention will be described in detail below.
When a gas carburizing treatment or a gas carbonitriding treatment is performed on a steel workpiece, the surface of the workpiece is oxidized, and grain boundary oxidation and an accompanying incomplete quenching layer are generated on the surface and in the vicinity of the surface. When grain boundary oxidation and the accompanying incomplete quenching layer occur, the hardness of the part decreases, and the wear resistance and fatigue strength of the article to be treated decrease, so that the wear resistance and fatigue resistance are improved. For this reason, the grain boundary oxidation and the incomplete quenching layer associated therewith were reduced to improve the surface quality of the article to be treated. This reforming process will be described below.
まず、浸炭処理又は浸炭窒化処理が施されて表面及び表面近傍に酸化物が生成した鋼製の被処理品を、改質処理室内に入れ、真空ポンプ等の減圧装置を用いて改質処理室内を減圧する。そして、改質処理室内に導入する導入ガスの条件を下記の３つの条件Ａ，Ｂ，Ｃのうちのいずれかとして、所定の時間熱処理する。
（条件Ａ）改質処理室に導入ガスを全く導入しない。
（条件Ｂ）改質処理室に１種以上の還元性ガスを導入ガスとして導入する。
（条件Ｃ）改質処理室に不活性ガス及び１種以上の還元性ガスの混合ガスを導入ガスとして導入する。
First, a steel product to be treated, which has been subjected to carburizing or carbonitriding and having oxides formed on the surface and in the vicinity of the surface, is placed in the reforming chamber, and then used in a reforming chamber using a decompression device such as a vacuum pump. The pressure is reduced. Then, heat treatment is performed for a predetermined time with the condition of the introduced gas introduced into the reforming chamber as one of the following three conditions A, B, and C.
(Condition A) No introduction gas is introduced into the reforming chamber.
(Condition B) One or more reducing gases are introduced into the reforming chamber as an introduction gas.
(Condition C) A mixed gas of an inert gas and one or more reducing gases is introduced as an introduction gas into the reforming chamber.
例えば、被処理品に施された浸炭処理がガス浸炭法である場合は、その浸炭期又は拡散期が終了した時点で、上記のような改質処理を施せばよい。そうすれば、被処理品の各部分における炭素濃度の均一性が保たれつつ、浸炭処理により表面及び表面近傍に生成した酸化物が還元されるため、酸化物の量が低減する。その結果、表面及び表面近傍に生じた粒界酸化とそれに伴う不完全焼入れ層も低減する。 For example, when the carburizing process performed on the product to be processed is a gas carburizing method, the above-described reforming process may be performed at the time when the carburizing period or the diffusion period ends. If it does so, since the oxide produced | generated on the surface and the surface vicinity by a carburizing process is reduced, the amount of oxides reduces, maintaining the uniformity of the carbon concentration in each part of to-be-processed goods. As a result, the grain boundary oxidation occurring on the surface and in the vicinity of the surface and the accompanying incomplete quenching layer are also reduced.
また、被処理品に施された浸炭処理が、真空浸炭法とガス浸炭法を組み合わせた浸炭方法である場合は、そのガス浸炭期が終了した時点で、上記のような改質処理を施せばよい。そうすれば、被処理品の各部分における炭素濃度の均一性が保たれつつ、ガス浸炭期に表面及び表面近傍に生成した酸化物が還元されるため、酸化物の量が低減する。その結果、表面及び表面近傍に生じた粒界酸化とそれに伴う不完全焼入れ層も低減する。
改質処理終了後の被処理品は、粒界酸化が増加しないように、真空中、Ｎ2 中、Ｎ2 と還元性ガスとの混合ガス中等で焼入れ保持温度まで降温し、均熱を０分以上１２０分以下とり、その後に油焼入れ等を行って焼入れすればよい。
In addition, when the carburizing process applied to the product to be processed is a carburizing method that combines the vacuum carburizing method and the gas carburizing method, the above-described reforming process may be performed at the end of the gas carburizing period. Good. If it does so, since the oxide produced | generated on the surface and the surface vicinity in the gas carburizing period is reduced, the amount of oxides reduces, maintaining the uniformity of the carbon concentration in each part of to-be-processed goods. As a result, the grain boundary oxidation occurring on the surface and in the vicinity of the surface and the accompanying incomplete quenching layer are also reduced.
The processed product after the reforming treatment is cooled to the quenching holding temperature in a vacuum, in N 2 , in a mixed gas of N 2 and a reducing gas, etc., so that grain boundary oxidation does not increase, and soaking is 0 More than 120 minutes and less, and then quenching by oil quenching.
改質処理の温度は、７００℃以上１２００℃以下とすることが好ましい。７００℃未満であると、還元力が弱いため、粒界酸化とそれに伴う不完全焼入れ層を十分に低減することが困難となるおそれがある。また、還元力を補うために処理時間を長くすると、ランニングコストが上昇してしまう。一方、１２００℃超過であると、還元力は強くなり、処理時間も短くできるが、被処理品の材料である鋼材の結晶粒が粗大化するという問題が生じるおそれがある。このような不都合がより生じにくくするためには、改質処理の温度は、８００℃以上９８０℃以下とすることがより好ましい。なお、結晶粒が粗大化しにくいような特殊元素を含有する鋼材であれば、改質処理の温度を１２００℃超過とすることも可能である。 The temperature of the reforming treatment is preferably 700 ° C. or higher and 1200 ° C. or lower. If the temperature is lower than 700 ° C., the reducing power is weak, so that it may be difficult to sufficiently reduce the grain boundary oxidation and the incompletely hardened layer accompanying it. In addition, if the processing time is lengthened to supplement the reducing power, the running cost increases. On the other hand, when it exceeds 1200 ° C., the reducing power becomes strong and the processing time can be shortened, but there is a possibility that the crystal grains of the steel material, which is the material to be processed, become coarse. In order to make such inconvenience less likely to occur, the temperature of the reforming treatment is more preferably set to 800 ° C. or higher and 980 ° C. or lower. In addition, if it is a steel material containing the special element which a crystal grain does not coarsen easily, it is also possible to make the temperature of a modification process exceed 1200 degreeC.
次に、改質処理の圧力は、０．０１Ｐａ以上３０００Ｐａ以下とすることが好ましい。０．０１Ｐａ未満であると、還元力は強いため粒界酸化とそれに伴う不完全焼入れ層の低減には好適であるが、そのような圧力にするには排気能力の大きい真空ポンプを使用するか、又は、高真空に引ける数種類の真空ポンプを使用する必要があるため、コストが高くなるという問題がある。一方、３０００Ｐａ超過であると、還元力が弱いため、粒界酸化とそれに伴う不完全焼入れ層十分を十分に低減することが困難となるおそれがある。また、還元力を補うために処理時間を長くすると、ランニングコストが上昇してしまう。このような不都合がより生じにくくするためには、改質処理の圧力は、１．３Ｐａ以上３３３Ｐａ以下とすることがより好ましく、１Ｐａ以上１３３Ｐａ以下とすることがさらに好ましい。 Next, the pressure of the reforming treatment is preferably set to 0.01 Pa or more and 3000 Pa or less. If it is less than 0.01 Pa, the reducing power is strong, so it is suitable for reducing grain boundary oxidation and the accompanying incomplete quenching layer. To achieve such pressure, should a vacuum pump with a large exhaust capacity be used? Alternatively, it is necessary to use several types of vacuum pumps that can draw a high vacuum, which increases the cost. On the other hand, if it exceeds 3000 Pa, the reducing power is weak, and therefore it may be difficult to sufficiently reduce the grain boundary oxidation and the accompanying incomplete quenching layer. In addition, if the processing time is lengthened to supplement the reducing power, the running cost increases. In order to make such inconvenience less likely to occur, the pressure of the reforming treatment is more preferably 1.3 Pa or more and 333 Pa or less, and further preferably 1 Pa or more and 133 Pa or less.
また、改質処理の時間は、１０分以上１８０分以下とすることが好ましい。１０分未満であると、還元するための時間が不十分で、粒界酸化とそれに伴う不完全焼入れ層十分を十分に低減することが困難となるおそれがある。一方、１８０分超過であると、ランニングコストが高くなる場合がある。このような不都合がより生じにくくするためには、改質処理の時間は、２０分以上９０分以下とすることがより好ましい。 Further, the modification treatment time is preferably 10 minutes or more and 180 minutes or less. If it is less than 10 minutes, the time for reduction is insufficient, and it may be difficult to sufficiently reduce the grain boundary oxidation and the accompanying incomplete quenching layer. On the other hand, if it exceeds 180 minutes, the running cost may increase. In order to make such inconvenience less likely to occur, it is more preferable that the time for the modification treatment be 20 minutes or more and 90 minutes or less.
さらに、改質処理において導入ガスとして使用される還元性ガスの種類は、特に限定されるものではないが、例えば、ＣＨ4 ，Ｃ3 Ｈ8 ，Ｃ2 Ｈ2 ，Ｃ2 Ｈ4 等の炭化水素ガスや、Ｈ2 ，ＣＯ，ＮＨ3 やその他の変成ガスがあげられる。これらの還元性ガスは１種類を単独で使用してもよいが、２種以上を混合して使用してもよい。また、還元性ガスと混合されて混合ガスを構成する不活性ガスの種類は、被処理品に対して不活性な性質であるならば特に限定されるものではないが、例えば、Ｎ2 ，Ａｒ，Ｈｅ等やその他の変成ガスがあげられる。これらの不活性ガスは１種類を単独で使用してもよいが、２種以上を混合して使用してもよい。 Further, the type of reducing gas used as the introduction gas in the reforming treatment is not particularly limited, but for example, carbonization such as CH 4 , C 3 H 8 , C 2 H 2 , C 2 H 4, etc. Examples thereof include hydrogen gas, H 2 , CO, NH 3, and other modified gases. These reducing gases may be used alone or in combination of two or more. The type of the inert gas mixed with the reducing gas to form the mixed gas is not particularly limited as long as it is inactive with respect to the article to be processed. For example, N 2 , Ar , He and other metamorphic gases. These inert gases may be used alone or in combination of two or more.
このような改質処理を行う改質処理装置は、特に限定されるものではなく、温度，圧力，及び導入ガス条件を上記のように制御可能な改質処理室を備えていればよい。例えば、浸炭装置が改質処理室を備えている場合は、浸炭室でガス浸炭を行った後に、被処理品を浸炭室から改質処理室に移して、改質処理室内で改質処理を行うことができる。また、浸炭室を減圧する手段を備えていれば、通常の浸炭装置を改質処理装置として使用することができる。すなわち、浸炭装置の浸炭室で被処理品のガス浸炭を行った後に、浸炭室を減圧して、そのまま浸炭室内で上記改質処理を行うことができる。 The reforming apparatus for performing such a reforming process is not particularly limited as long as it includes a reforming process chamber in which the temperature, pressure, and introduced gas conditions can be controlled as described above. For example, when the carburizing apparatus has a reforming treatment chamber, after performing gas carburizing in the carburizing chamber, the product to be treated is transferred from the carburizing chamber to the reforming treatment chamber, and the reforming treatment is performed in the reforming treatment chamber. It can be carried out. If a means for reducing the pressure of the carburizing chamber is provided, a normal carburizing apparatus can be used as the reforming apparatus. That is, after performing the gas carburization of the article to be processed in the carburizing chamber of the carburizing apparatus, the carburizing chamber can be decompressed and the reforming process can be performed in the carburizing chamber as it is.
このように、改質処理を行う改質処理装置は、浸炭処理と改質処理とを同一の室内で行うタイプの装置でもよいし、浸炭処理と改質処理とを同装置内の別の室内で行うタイプの装置でもよい。さらに、浸炭装置とは別体の改質処理装置を用意して、被処理品の改質処理を行ってもよい。すなわち、浸炭装置でガス浸炭を行った後に、浸炭装置にてガス冷却又は油焼入れして室温まで冷却した被処理品を、別体の改質処理装置で改質処理してもよい。そして、さらに焼入れや焼戻しを施してもよい。
なお、本実施形態は本発明の一例を示したものであって、本発明は本実施形態に限定されるものではない。例えば、本発明の表面改質方法に係る改質処理は、浸炭処理又は浸炭窒化処理が施された被処理品に対して好適であるが、窒化処理，酸窒化処理，酸炭窒化処理等の他の処理が施された被処理品に対しても適用することができる。
Thus, the reforming apparatus that performs the reforming process may be a type of apparatus that performs the carburizing process and the reforming process in the same room, or the carburizing process and the reforming process may be performed in different chambers in the apparatus. It may be a device of the type performed in Further, a reforming apparatus that is separate from the carburizing apparatus may be prepared to perform the reforming process on the product to be processed. That is, after performing gas carburizing with a carburizing apparatus, the article to be processed that has been cooled to room temperature by gas cooling or oil quenching with the carburizing apparatus may be reformed with a separate reforming apparatus. Further, quenching and tempering may be performed.
In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, the modification treatment according to the surface modification method of the present invention is suitable for a workpiece subjected to carburizing treatment or carbonitriding treatment, such as nitriding treatment, oxynitriding treatment, oxycarbonitriding treatment, etc. The present invention can also be applied to products to be processed that have been subjected to other processing.
また、被処理品にガス浸炭処理又はガス浸炭窒化処理を施した際に生じる粒界酸化とそれに伴う不完全焼入れ層は、できるだけ少ない方が好ましいので、ガス浸炭処理，ガス浸炭窒化処理における各操作を下記のようにすることが好ましい。すなわち、昇温や降温を真空中、Ｎ2 中、Ｎ2 と還元性ガスとの混合ガス中等で行う、浸炭期にカーボンポテンシャルを高くすることによって酸化性ガスの量が少ない雰囲気で浸炭する、拡散期にキャリヤーガスのＣＯ濃度を下げることによって酸化性ガスの量が少ない雰囲気で拡散を行う、などである。これらは、いずれか１つを行ってもよいし、２つ以上を組み合わせて行ってもよい。このような操作によりガス浸炭処理又はガス浸炭窒化処理を施した被処理品に改質処理を行えば、粒界酸化とそれに伴う不完全焼入れ層をより一層低減することが可能である。 In addition, since the grain boundary oxidation and the incomplete quenching layer that accompanies the gas carburizing process or gas carbonitriding process on the product to be processed are preferably as small as possible, each operation in the gas carburizing process and gas carbonitriding process is preferable. Is preferably as follows. That is, the temperature is raised or lowered in vacuum, in N 2 , in a mixed gas of N 2 and a reducing gas, or the like, and carburized in an atmosphere with a small amount of oxidizing gas by increasing the carbon potential during the carburizing period. For example, diffusion is performed in an atmosphere with a small amount of oxidizing gas by reducing the CO concentration of the carrier gas during the diffusion period. Any one of these may be performed, or two or more thereof may be combined. By performing the reforming process on the article subjected to the gas carburizing process or the gas carbonitriding process by such an operation, it is possible to further reduce the grain boundary oxidation and the incomplete quenching layer associated therewith.
以下に実施例を示して、本発明をより詳細に説明する。
〔実施例Ａ〕
図１に示すような構造の２室バッチ型ガス浸炭炉（処理質量：２００ｋｇ／ｇｒｏｓｓ）を使用して、鋼製の被処理品のガス浸炭処理及び改質処理を行った。
まず、図１のガス浸炭炉の構造を説明する。このガス浸炭炉は、図示しない被処理品を収納してガス浸炭処理を施す加熱室２と、加熱室２でガス浸炭処理を施された被処理品をガス冷する前室１と、被処理品を油冷する油槽３と、を備えている。そして、前室１及び加熱室２は、図示しない真空ポンプにより減圧できるようになっている。
Hereinafter, the present invention will be described in more detail with reference to examples.
[Example A]
Using a two-chamber batch type gas carburizing furnace having a structure as shown in FIG. 1 (processing mass: 200 kg / gross), the gas carburizing process and the reforming process were performed on the steel products.
First, the structure of the gas carburizing furnace of FIG. 1 will be described. The gas carburizing furnace includes a heating chamber 2 that accommodates a workpiece to be processed (not shown) and performs a gas carburizing process, a front chamber 1 that gas-cools the workpiece that has been subjected to the gas carburizing process in the heating chamber 2, and a processing target. And an
前室１と加熱室２との間には開閉可能な中間扉が設けられていて、この中間扉が開状態となったときには両室１，２が連通するようになっている。また、前室１には開閉可能な前扉が設けられていて、この前扉が開状態となったときには前室１が外気と連通するようになっている。さらに、前室１の下方には、油槽３が連続して設けられていて、被処理品を油槽３内の油に浸漬することにより油冷できるようになっている。
An openable / closable intermediate door is provided between the front chamber 1 and the heating chamber 2, and the two chambers 1 and 2 communicate with each other when the intermediate door is opened. The front chamber 1 is provided with a front door that can be opened and closed. When the front door is opened, the front chamber 1 communicates with the outside air. Further, an
このようなガス浸炭炉を使用して、鋼（ＳＣＭ４１５）製の被処理品にガス浸炭処理を施した。まず、比較例１の被処理品は、メタノールを直接加熱室２内に供給してキャリヤーガスを生成させＣ3 Ｈ8 をエンリッチガスとする滴注式ガス浸炭法（浸炭期のカーボンポテンシャル（ＣＰ）は０．８％）にて、図２に示すような処理条件で浸炭処理を行った。すなわち、加熱室２内に被処理品を入れ、大気圧下９５０℃で１２０分間ガス浸炭を行った。その後、同じ加熱室２内で、被処理品を８５０℃に降温して３０分間保持した後に、１３０℃の油を備える油槽３に投入して油焼入れを行った。
Using such a gas carburizing furnace, a gas carburizing process was performed on an article to be processed made of steel (SCM415). First, the article to be treated of Comparative Example 1 is a drop-type gas carburizing method (carbon potential (CP of carburizing period (CP)) in which methanol is directly supplied into the heating chamber 2 to generate a carrier gas and C 3 H 8 is an enriched gas. ) Was 0.8%), and carburizing was performed under the processing conditions shown in FIG. That is, the article to be treated was placed in the heating chamber 2 and gas carburized at 950 ° C. for 120 minutes under atmospheric pressure. Thereafter, in the same heating chamber 2, the article to be treated was cooled to 850 ° C. and held for 30 minutes, and then put into an
次に、実施例Ａ１，Ａ２の被処理品は、メタノールを直接加熱室２内に供給してキャリヤーガスを生成させＣ3 Ｈ8 をエンリッチガスとする滴注式ガス浸炭法（浸炭期のカーボンポテンシャル（ＣＰ）は１．２％）にて、図３に示すような処理条件でガス浸炭処理を行った。すなわち、加熱室２内に被処理品を入れ、大気圧下９５０℃で７０分間ガス浸炭を行った。そして、ガス浸炭が終了したら、加熱室２内を減圧し、９５０℃で５０分間改質処理を行った。 Next, in the products to be processed in Examples A1 and A2, methanol was directly supplied into the heating chamber 2 to generate a carrier gas, and C 3 H 8 was used as an enriched gas. Gas carburizing treatment was performed under the treatment conditions shown in FIG. 3 at a potential (CP) of 1.2%. That is, the article to be treated was placed in the heating chamber 2 and gas carburized at 950 ° C. under atmospheric pressure for 70 minutes. When the gas carburization was completed, the inside of the heating chamber 2 was depressurized, and a reforming process was performed at 950 ° C. for 50 minutes.
実施例Ａ１は、加熱室２内に導入ガスを全く導入せず、圧力１Ｐａで５０分間熱処理を行い、実施例Ａ２は、加熱室２内に導入ガスとしてメタンガスを導入しながら（流量は３Ｌ／分）、圧力１０Ｐａで５０分間熱処理を行った。熱処理が終了したら、同じ加熱室２内で、被処理品を８５０℃に降温して３０分間保持した後に、１３０℃の油を備える油槽３に投入して油焼入れを行った。
実施例Ａ１，Ａ２及び比較例１の被処理品の表面及び表面近傍を検査して、粒界酸化の深さ及び不完全焼入れ層の深さを測定した。結果を表１に示す。
In Example A1, no introduction gas was introduced into the heating chamber 2 and heat treatment was performed at a pressure of 1 Pa for 50 minutes. In Example A2, methane gas was introduced into the heating chamber 2 as an introduction gas (the flow rate was 3 L / Min), heat treatment was performed at a pressure of 10 Pa for 50 minutes. After the heat treatment was completed, the article to be treated was cooled to 850 ° C. and held for 30 minutes in the same heating chamber 2, and then put into an
The surface of the article to be processed of Examples A1 and A2 and Comparative Example 1 and the vicinity of the surface were inspected, and the depth of grain boundary oxidation and the depth of the incompletely quenched layer were measured. The results are shown in Table 1.
その結果、実施例Ａ１，Ａ２の被処理品は、比較例１の被処理品に比べて粒界酸化の深さ及び不完全焼入れ層の深さが小さかった。この結果から、粒界酸化の深さ及び不完全焼入れ層の深さが改質処理により低減されたことが分かる。各被処理品の平坦部と鋭角部の表面炭素濃度を測定したところ、いずれの被処理品も両部の表面炭素濃度は均一で、実施例Ａ１，Ａ２、比較例１の間で差異はなかった。 As a result, the processed products of Examples A1 and A2 had a smaller depth of grain boundary oxidation and an incompletely hardened layer than the processed products of Comparative Example 1. From this result, it can be seen that the grain boundary oxidation depth and the depth of the incompletely quenched layer were reduced by the modification treatment. When the surface carbon concentration of the flat portion and the acute angle portion of each processed product was measured, the surface carbon concentration of both processed products was uniform, and there was no difference between Examples A1 and A2 and Comparative Example 1. It was.
また、比較例１の被処理品を切断し、その切断面を走査型電子顕微鏡で観察した結果を、図４の（ａ）に示し、同じく実施例Ａ１の切断面を走査型電子顕微鏡で観察した結果を、図４の（ｂ）に示す。この図から、実施例Ａ１の被処理品は、比較例１の被処理品と比べて、粒界酸化の深さが浅いことが分かる。また、被処理品の仕上り肌についても、表１に示すように、実施例Ａ１，Ａ２の被処理品は、比較例１の被処理品と比べて光輝であった。 Moreover, the to-be-processed goods of the comparative example 1 were cut | disconnected, the result of having observed the cut surface with the scanning electron microscope is shown to (a) of FIG. 4, and the cut surface of Example A1 is similarly observed with the scanning electron microscope The result obtained is shown in FIG. From this figure, it can be seen that the processed product of Example A1 has a shallower grain boundary oxidation depth than the processed product of Comparative Example 1. In addition, as shown in Table 1, the finished products of the processed products of Examples A1 and A2 were brighter than the processed products of Comparative Example 1.
〔実施例Ｂ〕
実施例Ａで使用したものとは別のバッチ型ガス浸炭炉（処理質量：５０ｋｇ／ｇｒｏｓｓ）を使用して、鋼（ＳＣＭ４１５）製の被処理品のガス浸炭処理を行った。
まず、比較例２の被処理品は、この浸炭炉の浸炭室内にメタノールを直接供給してキャリヤーガスを生成させＣ3 Ｈ8 をエンリッチガスとする滴注式ガス浸炭法（浸炭期のカーボンポテンシャル（ＣＰ）は０．９％）にて、図５に示すような処理条件でガス浸炭処理を行った。すなわち、浸炭室内に被処理品を入れ、大気圧下９３０℃で１２０分間ガス浸炭を行った。そして、浸炭室内で被処理品を８５０℃に降温して３０分間保持した後に、１３０℃の油を備える油槽に投入して油焼入れを行った。
[Example B]
Using a batch type gas carburizing furnace (processing mass: 50 kg / gross) different from that used in Example A, the steel (SCM415) processed product was gas carburized.
First, the article to be treated of Comparative Example 2 is a drop-type gas carburizing method in which methanol is directly supplied into the carburizing chamber of this carburizing furnace to generate carrier gas and enriched with C 3 H 8 (the carbon potential in the carburizing period). (CP) was 0.9%), and a gas carburizing process was performed under the processing conditions shown in FIG. That is, the article to be treated was placed in a carburizing chamber and gas carburized at 930 ° C. for 120 minutes under atmospheric pressure. And after lowering | hanging the to-be-processed goods to 850 degreeC in a carburizing chamber and hold | maintaining for 30 minutes, it injected into the oil tank provided with 130 degreeC oil, and performed oil quenching.
次に、実施例Ｂ１の被処理品は、比較例２の場合と全く同様にして９３０℃でガス浸炭を行った後に、加熱室では降温せず、前室にてＮ2 中で９３０℃から室温まで急冷した。そして、実施例Ａで使用したバッチ型ガス浸炭炉を用いて改質処理を行った。すなわち、実施例Ａで使用したガス浸炭炉の加熱室２内に、ガス浸炭された実施例Ｂ１の被処理品を入れ、加熱室２内に導入ガスを全く導入せず、圧力１Ｐａ、温度９３０℃で５０分間熱処理を行った。熱処理が終了したら、被処理品を加熱室２内にてＮ2 中で８５０℃に降温して３０分間保持した後に、１３０℃の油を備える油槽３に投入して油焼入れを行った。
実施例Ｂ１び比較例２の被処理品の表面及び表面近傍を検査して、粒界酸化の深さ及び不完全焼入れ層の深さを測定した。結果を表２に示す。
Next, the article to be processed in Example B1 was subjected to gas carburization at 930 ° C. in the same manner as in Comparative Example 2, and then the temperature was not lowered in the heating chamber, but from 930 ° C. in N 2 in the front chamber. Quenched to room temperature. And the reforming process was performed using the batch type gas carburizing furnace used in Example A. That is, the gas-carburized product to be treated of Example B1 is placed in the heating chamber 2 of the gas carburizing furnace used in Example A, and no introduction gas is introduced into the heating chamber 2 at a pressure of 1 Pa and a temperature of 930. Heat treatment was performed at 50 ° C. for 50 minutes. When the heat treatment was completed, the article to be treated was cooled to 850 ° C. in N 2 in the heating chamber 2 and held for 30 minutes, and then put into an
The surface of the article to be processed of Example B1 and Comparative Example 2 and the vicinity of the surface were inspected, and the depth of grain boundary oxidation and the depth of the incompletely quenched layer were measured. The results are shown in Table 2.
その結果、実施例Ｂ１の被処理品は、比較例２の被処理品に比べて粒界酸化の深さ及び不完全焼入れ層の深さが小さかった。この結果から、粒界酸化の深さ及び不完全焼入れ層の深さが改質処理により低減されたことが分かる。各被処理品の平坦部と鋭角部の表面炭素濃度を測定したところ、いずれの被処理品も両部の表面炭素濃度は均一で、実施例Ｂ１、比較例２の間で差異はなかった。また、被処理品の仕上り肌についても、実施例Ｂ１の被処理品は、比較例２の被処理品と比べて光輝であった。 As a result, the treated product of Example B1 had a smaller depth of grain boundary oxidation and an incompletely quenched layer than the treated product of Comparative Example 2. From this result, it can be seen that the grain boundary oxidation depth and the depth of the incompletely quenched layer were reduced by the modification treatment. When the surface carbon concentration of the flat part and the acute angle part of each processed product was measured, the surface carbon concentration of both processed products was uniform, and there was no difference between Example B1 and Comparative Example 2. In addition, regarding the finished skin of the treated product, the treated product of Example B1 was brighter than the treated product of Comparative Example 2.
本発明の表面改質方法に係る改質処理が施された鋼製部品は、自動車，建設機械，各種産業機械等に使用される部品として好適である。 Steel parts subjected to the modification treatment according to the surface modification method of the present invention are suitable as parts used in automobiles, construction machines, various industrial machines and the like.
１ 前室
２ 加熱室
３ 油槽
1 Front chamber 2
Claims (1)
前記ガス浸炭処理又は前記ガス浸炭窒化処理における前記被処理品の昇温は、炭化水素ガス、水素、及びアンモニアの少なくとも１種とＮ 2 との混合ガス中で行うとともに、
前記改質処理として、圧力０．０１Ｐａ以上３０００Ｐａ以下の改質処理室内に入れた前記被処理品を、下記の３つの条件Ａ，Ｂ，Ｃのうちのいずれかの導入ガス条件下、温度７００℃以上１２００℃以下で１０分以上１８０分以下熱処理することを特徴とする表面改質方法。
（条件Ａ）前記改質処理室に導入ガスを全く導入しない。
（条件Ｂ）前記改質処理室に１種以上の還元性ガスを導入ガスとして導入する。
（条件Ｃ）前記改質処理室に不活性ガス及び１種以上の還元性ガスの混合ガスを導入ガスとして導入する。 When the surface treatment of the article to be treated is performed by performing a modification treatment on the steel article to be treated in which gas carburizing treatment or gas carbonitriding treatment is performed and an oxide is generated on the surface and in the vicinity of the surface,
In the gas carburizing process or the gas carbonitriding process, the temperature of the article to be processed is increased in a mixed gas of N 2 and at least one of hydrocarbon gas, hydrogen, and ammonia ,
As the reforming treatment, the article to be treated put in a reforming treatment chamber having a pressure of 0.01 Pa or more and 3000 Pa or less is subjected to a temperature of 700 under an introduced gas condition in any of the following three conditions A, B, and C. A surface modification method characterized by performing a heat treatment at a temperature of not lower than 1200 ° C and not higher than 1200 ° C for not shorter than 10 minutes and not longer than 180 minutes.
(Condition A) No introduction gas is introduced into the reforming chamber.
(Condition B) One or more reducing gases are introduced into the reforming chamber as an introduction gas.
(Condition C) A mixed gas of an inert gas and one or more reducing gases is introduced as an introduction gas into the reforming chamber.
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