JP2008081813A

JP2008081813A - Gas carburizing method

Info

Publication number: JP2008081813A
Application number: JP2006265000A
Authority: JP
Inventors: Toru Inagaki; 徹稲垣
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 2006-09-28
Filing date: 2006-09-28
Publication date: 2008-04-10

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas carburizing method where the difference in the degree of carburizing in accordance with the position of the object to be treated in a carburizing furnace can be reduced. <P>SOLUTION: In the gas carburizing method where a carburizing gas is fed into a gas carburizing furnace 12 under a prescribed temperature, thus the object to be treated arranged in the gas carburizing furnace 12 is subjected to carburizing treatment, before the carburizing stage where the carburizing gas is fed into the gas carburizing furnace 12, a soaking stage where the carbon potential of the atmosphere in the gas carburizing furnace 12 reaches the carbon concentration of the object to be treated or below is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、鉄鋼材料等の被処理品に浸炭性ガスを供給して浸炭処理を行うガス浸炭方法に関する。 The present invention relates to a gas carburizing method for performing a carburizing process by supplying a carburizing gas to an article to be processed such as a steel material.

従来、ガス浸炭方法として、ガス変成炉を用いた方法が現在に至るまで広く用いられている。これは、炭化水素系ガスおよび空気を原料として、ガス変成炉で変成ガスを作り、浸炭工程でのカーボンポテンシャルより低いベースガスとして浸炭炉に供給し、さらに高い所要のカーボンポテンシャルに調整するために、炭化水素系ガスをエンリッチガスとして浸炭炉に供給し、８００℃以上の温度下で被処理品の浸炭処理を行う方法である（例えば、特許文献１参照）。
特開２００５−２００６９５号公報 Conventionally, as a gas carburizing method, a method using a gas shift furnace has been widely used until now. This is because in order to adjust the gas to a higher required carbon potential, hydrocarbon gas and air are used as raw materials, and the gas is converted in a gas conversion furnace and supplied to the carburizing furnace as a base gas lower than the carbon potential in the carburizing process. In this method, a hydrocarbon-based gas is supplied as an enriched gas to a carburizing furnace, and a carburizing process is performed on an object to be processed at a temperature of 800 ° C. or higher (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-200695

しかし、多数の被処理品が浸炭炉内に配置される場合、被処理品の配置される位置によって昇温の速さ、浸炭ガスの流れ易さに差が生じる。昇温が速く浸炭ガスが流れ易い位置にある被処理品は浸炭され易く、昇温が遅く浸炭ガスが流れ難い位置にある被処理品は浸炭され難い。つまり、昇温が速く浸炭ガスが流れ易い位置にある被処理品と昇温が遅く浸炭ガスが流れ難い位置にある被処理品とで、浸炭量に差が生じる。このため、浸炭処理が行われた後の段階では、浸炭炉内での被処理品の位置によって、浸炭の度合いに差（バラツキ）が生じる可能性がある。 However, when a large number of products to be processed are arranged in the carburizing furnace, there are differences in the speed of temperature rise and the ease of flow of the carburizing gas depending on the position of the products to be processed. An article to be treated at a position where the temperature rise is fast and the carburizing gas easily flows is easily carburized, and an article to be treated at a position where the temperature rise is slow and the carburizing gas hardly flows is hardly carburized. That is, there is a difference in the amount of carburization between the article to be processed at a position where the temperature rise is fast and the carburizing gas easily flows and the article to be treated at a position where the temperature rise is slow and the carburizing gas hardly flows. For this reason, at the stage after the carburizing process is performed, there is a possibility that a difference (variation) occurs in the degree of carburizing depending on the position of the article to be processed in the carburizing furnace.

よって、本発明は上記の問題点に鑑みてなされたものであり、浸炭炉内での被処理品の位置による浸炭の度合いの差を小さくできるガス浸炭方法を提供することを課題とする。 Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a gas carburizing method capable of reducing the difference in the degree of carburization depending on the position of the article to be processed in the carburizing furnace.

上記課題を解決するために、本発明にて講じた技術的手段は、請求項１に記載の様に、所定の温度下にある浸炭炉内に浸炭ガスを供給することで、該浸炭炉内に配置された被処理品の浸炭処理を行うガス浸炭方法であって、前記浸炭ガスが前記浸炭炉内に供給される浸炭工程の前に、該浸炭炉内の雰囲気のカーボンポテンシャルが前記被処理品の炭素濃度以下とする均熱工程を有する構成としたことである。 In order to solve the above-mentioned problem, the technical means taken in the present invention is, as described in claim 1, by supplying a carburizing gas into a carburizing furnace under a predetermined temperature. A carburizing method for carburizing the article to be treated, wherein the carbon potential of the atmosphere in the carburizing furnace is the carburizing process before the carburizing gas is supplied into the carburizing furnace. In other words, it has a soaking process in which the carbon concentration is less than or equal to the carbon concentration of the product.

好ましくは、請求項２に記載の様に、前記均熱工程は、前記被処理品の炭素濃度が０．１５〜０．４５％の鋼材の場合、前記カーボンポテンシャルが前記被処理品の炭素濃度よりも０．０５〜０．１５％低い状態で行われると良い。 Preferably, as described in claim 2, in the soaking step, when the carbon concentration of the article to be treated is a steel material of 0.15 to 0.45%, the carbon potential is the carbon concentration of the article to be treated. It is good to be carried out in a state lower by 0.05 to 0.15%.

請求項１に記載の発明によれば、浸炭炉内のうち、昇温が速く浸炭ガスが流れ易い位置にある被処理品が、浸炭工程の前に脱炭される。つまり、浸炭工程が行われる前の段階で、浸炭され易い位置にある被処理品の炭素濃度が、浸炭され難い位置にある被処理品の炭素濃度に比べて下がる。したがって、浸炭ガスが浸炭炉内に供給される浸炭工程において、浸炭工程初期では、浸炭炉内での被処理品の位置によって被処理品の炭素濃度に差を生じさせ、浸炭工程が行われた後の段階では、浸炭炉内での被処理品の位置による浸炭の度合いの差（バラツキ）を小さくできる。 According to the first aspect of the present invention, in the carburizing furnace, the article to be processed located at a position where the temperature rises quickly and the carburizing gas easily flows is decarburized before the carburizing step. That is, in the stage before the carburizing step is performed, the carbon concentration of the article to be processed at a position that is easily carburized is lower than the carbon concentration of the article to be processed at a position that is not easily carburized. Therefore, in the carburizing process in which the carburizing gas is supplied into the carburizing furnace, the carburizing process is performed at the initial stage of the carburizing process, causing a difference in the carbon concentration of the processed product depending on the position of the processed product in the carburizing furnace. In a later stage, the difference (variation) in the degree of carburization depending on the position of the workpiece in the carburizing furnace can be reduced.

請求項２に記載の発明によれば、炭素濃度が０．１５〜０．４５％の鋼材を浸炭処理する場合に、浸炭炉内での鋼材の位置による浸炭の度合いの差（バラツキ）を小さくできる。 According to the second aspect of the present invention, when carburizing a steel material having a carbon concentration of 0.15 to 0.45%, the difference (variation) in the degree of carburization depending on the position of the steel material in the carburizing furnace is reduced. it can.

以下、本発明を実施するための最良の形態を、図面を基に説明する。 The best mode for carrying out the present invention will be described below with reference to the drawings.

図１は、本発明に係るガス浸炭方法に使用されるガス浸炭システム１の概略図である。図１に示すように、ガス浸炭システム１は、原料ガスを変成・分解することにより得られた変成ガスを供給するガス変成炉１０と、エンリッチガスを供給するエンリッチガス供給装置１４と、前記変成ガス及び前記エンリッチガスとを導入し、被処理品の浸炭処理を行うガス浸炭炉１２と、添加ガスをガス浸炭炉１２に供給する添加ガス供給装置１６と、からなる。 FIG. 1 is a schematic view of a gas carburizing system 1 used in a gas carburizing method according to the present invention. As shown in FIG. 1, the gas carburizing system 1 includes a gas shift furnace 10 that supplies a shift gas obtained by shift and decomposition of a raw material gas, an enrich gas supply device 14 that supplies an enrich gas, and the shift gas. It comprises a gas carburizing furnace 12 for introducing a gas and the enriched gas and carburizing the object to be processed, and an additive gas supply device 16 for supplying the additive gas to the gas carburizing furnace 12.

ガス変成炉１０は、炭化水素系ガスと空気との混合ガスを原料ガスとして、その原料ガスを高温で変成・分解する。次いで、これにより得られた変成ガス（浸炭ガス）をガス浸炭炉１２に供給する。当該変成ガスは浸炭処理後の目的のカーボンポテンシャル（Ｃｐ）より低く、本実施形態においては、浸炭処理でのベースガスとするため又はガス浸炭炉１２内に炉外からの空気の侵入を防止するために、ある程度の炉内圧を維持するためにガス浸炭炉１２に供給される。 The gas shift furnace 10 uses a mixed gas of hydrocarbon-based gas and air as a source gas, and converts and decomposes the source gas at a high temperature. Next, the modified gas (carburizing gas) obtained in this way is supplied to the gas carburizing furnace 12. The metamorphic gas is lower than the target carbon potential (Cp) after the carburizing process, and in this embodiment, the base gas in the carburizing process is used, or intrusion of air from outside the furnace into the gas carburizing furnace 12 is prevented. Therefore, the gas is supplied to the gas carburizing furnace 12 in order to maintain a certain furnace pressure.

エンリッチガス供給装置１４は、カーボンポテンシャルが高い炭化水素系ガス等のガスをエンリッチガス（浸炭ガス）としてガス浸炭炉１２に供給する。また、エンリッチガス供給装置１４は、ガス浸炭炉１２内のカーボンポテンシャル（Ｃｐ）が所定の範囲内になるように、酸素センサー（図示せず）等で計測しながら、自動可変調整弁又はＯＮ−ＯＦＦ弁等で調整するための自動演算機能を備えている。 The enrich gas supply device 14 supplies a gas such as a hydrocarbon-based gas having a high carbon potential to the gas carburizing furnace 12 as an enrich gas (carburizing gas). Further, the enrich gas supply device 14 measures the automatic variable adjustment valve or the ON− while measuring with an oxygen sensor (not shown) or the like so that the carbon potential (Cp) in the gas carburizing furnace 12 is within a predetermined range. An automatic calculation function for adjusting with an OFF valve or the like is provided.

ガス浸炭炉１２（浸炭炉）は、変成ガスとエンリッチガスとを導入し、所定温度・所定時間で被処理品の浸炭処理を行う。ガス浸炭炉１２内には、多数の被処理品が配置される。なお、本実施形態における被処理品は、炭素濃度が０．１５〜０．４５％の鋼材である。 The gas carburizing furnace 12 (carburizing furnace) introduces a metamorphic gas and an enriched gas, and performs a carburizing process on an object to be processed at a predetermined temperature and a predetermined time. A large number of articles to be processed are arranged in the gas carburizing furnace 12. In addition, the to-be-processed goods in this embodiment are steel materials with a carbon concentration of 0.15-0.45%.

添加ガス供給装置１６は、変成ガスとエンリッチガスがガス浸炭炉１２に供給される浸炭工程の前に、添加ガスをガス浸炭炉１２に供給する。 The additive gas supply device 16 supplies the additive gas to the gas carburizing furnace 12 before the carburizing step in which the modified gas and the enriched gas are supplied to the gas carburizing furnace 12.

図２に、ガス浸炭炉１２における浸炭処理のヒートパターンの一例を示す。図３は、ガス浸炭炉１２の模式図である。図２において、実線で示されるのは、ガス浸炭炉１２のうち昇温が速く浸炭ガスが流れ易い位置（Ａ位置、図３参照）でのパターンで、点線で示されるのは、ガス浸炭炉１２のうち昇温が遅く浸炭ガスが流れ難い位置（Ｂ位置、図３参照）でのパターンである。 In FIG. 2, an example of the heat pattern of the carburizing process in the gas carburizing furnace 12 is shown. FIG. 3 is a schematic diagram of the gas carburizing furnace 12. In FIG. 2, a solid line indicates a pattern at a position (A position, see FIG. 3) in the gas carburizing furnace 12 where the temperature rise is fast and the carburizing gas easily flows, and a dotted line indicates the gas carburizing furnace. 12 shows a pattern at a position where the temperature rise is slow and the carburizing gas hardly flows (position B, see FIG. 3).

図２に示すように、ガス浸炭炉１２におけるＡ位置の温度は、運転開始から徐々に上昇し、浸炭温度（所定の温度）に達した時点から一定時間保持される。一方、ガス浸炭炉１２におけるＢ位置は、Ａ位置に比べて昇温が遅い。このため、Ａ位置が浸炭温度に到達した時点では、Ｂ位置は昇温の途中で、Ｂ位置の温度は浸炭温度に到達していない。Ａ位置が浸炭温度に到達してからＢ位置が目的の浸炭温度に到達するまでの間、Ａ位置の温度は一定時間保持される（均熱工程）。 As shown in FIG. 2, the temperature at the position A in the gas carburizing furnace 12 gradually increases from the start of operation, and is maintained for a certain period of time after reaching the carburizing temperature (predetermined temperature). On the other hand, the temperature rise at the B position in the gas carburizing furnace 12 is slower than that at the A position. For this reason, when the position A reaches the carburizing temperature, the position B is in the middle of temperature increase, and the temperature at the position B has not reached the carburizing temperature. The temperature at the A position is maintained for a certain period of time from when the A position reaches the carburizing temperature until the B position reaches the target carburizing temperature (soaking step).

均熱工程の間、ガス浸炭炉１２には、添加ガス供給装置１６によって添加ガスが供給される。添加ガスは、ガス浸炭炉１２内の雰囲気のカーボンポテンシャルを下げるためのものである。添加ガスとして、例えば、酸素ガス、二酸化炭素ガスを用いることができる。添加ガスは、ガス浸炭炉１２内の雰囲気のカーボンポテンシャルが被処理品の炭素濃度以下となるように供給される。本実施形態では、被処理品の炭素濃度が０．１５〜０．４５％の場合、ガス浸炭炉１２内の雰囲気のカーボンポテンシャルが被処理品の炭素濃度よりも０．０５〜０．１５％低いカーボンポテンシャルとなるように、添加ガスが供給される。具体的には、ガス浸炭炉１２内の雰囲気のカーボンポテンシャルが０．０５〜０．１５％となるように、添加ガスが供給される。ガス浸炭炉１２内の雰囲気のカーボンポテンシャルが０．０５％より小さいと、すなわち、被処理品表面の炭素濃度を０．０５％以下にしてしまうと、浸炭開始時の被処理品の組織がオーステナイト単相にならない。例えば、８７０℃浸炭の場合、均熱中の脱炭により被処理品表面の炭素濃度が０．０３％となると、浸炭開始時の組織は、フェライト（α）＋オーステナイト（γ）となる。炭素の拡散係数は、フェライト、オーステナイトで異なるため、炉内の被処理品全体及び／又は被処理品個体内において、浸炭深さのバラツキ助長要因となる。 During the soaking process, an additive gas is supplied to the gas carburizing furnace 12 by an additive gas supply device 16. The additive gas is for lowering the carbon potential of the atmosphere in the gas carburizing furnace 12. For example, oxygen gas or carbon dioxide gas can be used as the additive gas. The additive gas is supplied so that the carbon potential of the atmosphere in the gas carburizing furnace 12 is equal to or lower than the carbon concentration of the product to be processed. In the present embodiment, when the carbon concentration of the product to be processed is 0.15 to 0.45%, the carbon potential of the atmosphere in the gas carburizing furnace 12 is 0.05 to 0.15% higher than the carbon concentration of the product to be processed. The additive gas is supplied so as to have a low carbon potential. Specifically, the additive gas is supplied so that the carbon potential of the atmosphere in the gas carburizing furnace 12 is 0.05 to 0.15%. If the carbon potential of the atmosphere in the gas carburizing furnace 12 is less than 0.05%, that is, if the carbon concentration on the surface of the object to be processed is 0.05% or less, the structure of the object to be processed at the start of carburizing is austenite. Not single phase. For example, in the case of 870 ° C. carburization, when the carbon concentration on the surface of the article to be processed is 0.03% due to decarburization during soaking, the structure at the start of carburization is ferrite (α) + austenite (γ). Since the diffusion coefficient of carbon differs between ferrite and austenite, it becomes a factor for promoting the variation in the carburization depth in the entire article to be treated in the furnace and / or in the individual article to be treated.

上記の均熱工程の後、変成ガス及びエンリッチガスがガス浸炭炉１２内に供給される浸炭工程（図２参照）が行われ、ガス浸炭炉１２内に配置された被処理品の浸炭処理が行われる。 After the above-mentioned soaking step, a carburizing step (see FIG. 2) in which the metamorphic gas and the enriched gas are supplied into the gas carburizing furnace 12 is performed, and the carburizing treatment of the workpieces disposed in the gas carburizing furnace 12 is performed. Done.

図４は、炭素濃度が０．２２％の鋼材を用いた時の浸炭処理の実験結果を示す図で、均熱工程での諸条件等を示す。同図に示す様に、本発明の方法、すなわち、浸炭工程が行われる前にガス浸炭炉内の雰囲気のカーボンポテンシャルが被処理品の炭素濃度以下となる工程を設けた場合は、そうでない場合（比較例１、２）と比べて、「被処理品の表面より０．７５ｍｍ位置の炭素濃度」、「有効浸炭深さの差」の項目からわかるように、浸炭の度合いの差（バラツキ）が小さくなっている。 FIG. 4 is a diagram showing experimental results of carburizing treatment when a steel material having a carbon concentration of 0.22% is used, and shows various conditions in the soaking process. As shown in the figure, when the method of the present invention, that is, when the carbon potential of the atmosphere in the gas carburizing furnace is less than or equal to the carbon concentration of the article to be processed before the carburizing process is performed, Compared with (Comparative Examples 1 and 2), the difference in the degree of carburization (variation), as can be seen from the items “carbon concentration at 0.75 mm from the surface of the object to be treated” and “difference in effective carburization depth” Is getting smaller.

以上説明した様に、本発明のガス浸炭方法によれば、ガス浸炭炉１２内のうち、昇温が速く浸炭ガスが流れ易い位置（Ａ位置）にある被処理品が、浸炭工程の前に脱炭される。つまり、浸炭工程が行われる前の段階で、浸炭され易い位置にある被処理品の炭素濃度が、浸炭され難い位置にある被処理品の炭素濃度に比べて下がる。したがって、浸炭ガス（変成ガス、エンリッチガス）がガス浸炭炉１２内に供給される浸炭工程において、浸炭工程初期で、ガス浸炭炉１２内での被処理品の位置によって被処理品の炭素濃度差を生じさせ、浸炭工程が行われた後の段階では、ガス浸炭炉１２内での被処理品の位置による浸炭の度合いの差（バラツキ）を小さくできる。 As described above, according to the gas carburizing method of the present invention, the article to be processed in the gas carburizing furnace 12 at a position where the temperature rises quickly and the carburizing gas easily flows (position A) is before the carburizing step. Decarburized. That is, in the stage before the carburizing step is performed, the carbon concentration of the article to be processed at a position that is easily carburized is lower than the carbon concentration of the article to be processed at a position that is not easily carburized. Therefore, in the carburizing process in which carburizing gas (metamorphic gas, enriched gas) is supplied into the gas carburizing furnace 12, the carbon concentration difference of the object to be processed depends on the position of the object to be processed in the gas carburizing furnace 12 at the beginning of the carburizing process. In the stage after the carburizing step is performed, the difference (variation) in the degree of carburization depending on the position of the workpiece in the gas carburizing furnace 12 can be reduced.

本発明に係るガス浸炭方法に使用されるガス浸炭システム１の概略図。1 is a schematic view of a gas carburizing system 1 used in a gas carburizing method according to the present invention. ガス浸炭炉１２における浸炭処理のヒートパターンの一例を示す図。The figure which shows an example of the heat pattern of the carburizing process in the gas carburizing furnace. ガス浸炭炉１２の模式図。The schematic diagram of the gas carburizing furnace 12. 浸炭処理の実験結果を示す図。The figure which shows the experimental result of a carburizing process.

符号の説明Explanation of symbols

１ガス浸炭システム
１０ガス変成炉
１２ガス浸炭炉（浸炭炉）
１４エンリッチガス供給装置
１６添加ガス供給装置 1 Gas Carburizing System 10 Gas Transformation Furnace 12 Gas Carburizing Furnace (Carburizing Furnace)
14 Enriched gas supply device 16 Additive gas supply device

Claims

所定の温度下にある浸炭炉内に浸炭ガスを供給することで、該浸炭炉内に配置された被処理品の浸炭処理を行うガス浸炭方法であって、
前記浸炭ガスが前記浸炭炉内に供給される浸炭工程の前に、該浸炭炉内の雰囲気のカーボンポテンシャルが前記被処理品の炭素濃度以下とする均熱工程を有することを特徴とするガス浸炭方法。 A gas carburizing method for performing a carburizing process of an article to be processed disposed in the carburizing furnace by supplying a carburizing gas into the carburizing furnace under a predetermined temperature,
Before the carburizing process in which the carburizing gas is supplied into the carburizing furnace, the gas carburizing process includes a soaking step in which the carbon potential of the atmosphere in the carburizing furnace is equal to or lower than the carbon concentration of the article to be processed. Method.

前記均熱工程は、前記被処理品の炭素濃度が０．１５〜０．４５％の鋼材の場合、前記カーボンポテンシャルが前記被処理品の炭素濃度よりも０．０５〜０．１５％低い状態で行われることを特徴とする請求項１に記載のガス浸炭方法。 In the soaking step, in the case of a steel material in which the carbon concentration of the article to be treated is 0.15 to 0.45%, the carbon potential is 0.05 to 0.15% lower than the carbon concentration of the article to be treated. The gas carburizing method according to claim 1, wherein the gas carburizing method is performed.