JPH01212748A - Rapid carburizing treatment for steel - Google Patents

Abstract

PURPOSE:To subject a steel to rapid carburizing treatment to a sufficient surface carbon content by repeating, plural times, a treatment in which case-hardening steel parts are carburized to a proper limit by means of heating and the flow of carburizing gas and further carbon is diffused in an inert gas or in vacuum. CONSTITUTION:Carburizing is carried out by placing parts made of case- hardening steel into a furnace to apply heating to the above parts and also allowing a carburizing gas, such as C3H8, to flow. At this time, carbon is allowed to enter into solid solution to the austenite solid solution limit of the steel at the carburizing temp., and carburizing is limited to a degree precipitating no coarse carbide. Subsequently, the carburizing gas in the furnace is exhausted and, by introducing an inert gas or maintaining the inside of the furnace in vacuum, the above carbon existing in the form of solid solution is diffused. Further, the above carburizing treatment and diffusion treatment are repeated twice or more, followed by the required heat treatment such as quench-and-temper treatment. By this method, carburizing is carried out in a shorter time than conventional one as a whole and sufficient surface carbon content is secured in the course of the above procedure to produce carburizing effects.

Description

【発明の詳細な説明】 ［産業上の利用分野］ 本発明は、ｗＡ製の部品の浸炭処理方法の改良に関する
。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a carburizing method for parts made of wA.

［従来の技術］ たとえば自動車や建設機械などを構成する機械構造用部
品の中には、疲れ強さと表面の耐摩耗性をか・ねそなえ
ていることを要求されるものがある。[Prior Art] For example, some mechanical structural parts constituting automobiles, construction machinery, etc. are required to have fatigue strength and surface wear resistance.

この要求にこたえるには、多くの場合、肌焼鋼を材料と
して部品を製作し、表面を浸炭処理して硬化したものが
使用されている。To meet this demand, in many cases parts are manufactured from case-hardened steel and the surface is hardened by carburizing.

現在、機械構造用部品の浸炭処理法の主流は、ガス浸炭
法である。　コスト低減の要請から、最近では、短時間
で浸炭処理が行なえるよう、真空浸炭法、イオン浸炭法
などカーボンポテンシャルの高い浸炭法が実施されるよ
うになってきている。Currently, the mainstream carburizing method for mechanical structural parts is gas carburizing. Due to the demand for cost reduction, carburizing methods with high carbon potential such as vacuum carburizing method and ion carburizing method have recently been implemented so that carburizing treatment can be carried out in a short time.

ところが、カーボンポテンシャルの高い浸炭法で浸炭す
ると、鋼部品の表層部においてＣ濃度がオーステナイト
固溶限を超えて網目状の粗大な炭化物が生成し、物性が
劣るばかりか、疲れ強さも低下するおそれがある。　一
方で、浸炭効果を１ｑるための最低限の炭素量を確保し
ようとすれば、現実には表層部に粗大炭化物の生成する
ことが避けられないのが実情である。　そこで、この粗
大炭化物をオーステナイト組織に再固溶させる工程が必
要となる。However, when carburizing is performed using a carburizing method with a high carbon potential, the C concentration in the surface layer of steel parts exceeds the austenite solid solubility limit, producing coarse mesh-like carbides, which not only deteriorate physical properties but also pose a risk of reducing fatigue strength. There is. On the other hand, if one attempts to secure the minimum amount of carbon to increase the carburizing effect by 1q, the reality is that the formation of coarse carbides in the surface layer is unavoidable. Therefore, a step is required to dissolve the coarse carbide into the austenite structure again.

再固溶化に要する時間は、一般に浸炭に要する時間の３
倍以上であるから、全体の処理時間は、浸炭時間の少な
くとも４倍となる。　従って、たとえカーボンポテンシ
ャルの高い浸炭法を用いて、浸炭効果を得るために必要
な炭素量を供給する時間を短縮したとしても、粗大炭化
物の消失に要する時間が短縮できなければ、全処理時間
を短縮するという目的にかなわない。The time required for re-solid solutionization is generally 3 times the time required for carburization.
The total processing time is at least four times the carburizing time. Therefore, even if a carburizing method with a high carbon potential is used to shorten the time required to supply the amount of carbon necessary to obtain the carburizing effect, if the time required for the disappearance of coarse carbides cannot be shortened, the total processing time will be reduced. It does not serve the purpose of shortening it.

［発明が解決しようとする課題］ 本発明の目的は、肌焼鋼の部品を浸炭する技術において
、全体として従来より短い時間で実施でき、その間に十
分な表面炭素量を確保して浸炭効果を得ることのできる
、鋼の浸炭処理方法を提供することにある。[Problems to be Solved by the Invention] The purpose of the present invention is to provide a technology for carburizing case-hardened steel parts that can be carried out in a shorter time than conventional methods, while ensuring a sufficient amount of surface carbon to achieve the carburizing effect. An object of the present invention is to provide a method for carburizing steel.

［課題を解決するための手段］ 本発明の鋼の迅速浸炭処理方法は、肌焼鋼で製作した部
品を炉に入れて加熱し、（Ａ＞浸炭ガスを流通させてそ
の浸炭温度における鋼のオーステナイト固溶限まで炭素
を固溶させる浸炭と、（Ｂ）炉内の浸炭ガスを排気して
、不活性ガスを流入するかまたは真空に保持して炭素を
拡散させる処理とを２回以上繰り返し、その後に熱処理
することを特徴とする。[Means for Solving the Problems] The rapid carburizing method for steel of the present invention involves heating parts made of case-hardened steel in a furnace, passing carburizing gas (A), and carburizing the steel at the carburizing temperature. Carburizing to dissolve carbon up to the austenite solid solubility limit, and (B) exhausting the carburizing gas in the furnace and injecting inert gas or keeping it in vacuum to diffuse carbon are repeated two or more times. , followed by heat treatment.

オーステナイト固溶限まで炭素を固溶させるとは、炭素
が鋼のＡ。−近く固溶したが未だ析出しない状態だけで
なく、微量の炭化物が析出しても、微細であって、続く
拡散の工程により容易に再固溶する程度に止っている状
態をも包含する。Carbon is dissolved in steel up to the austenite solid solution limit. - It includes not only a state in which carbide has almost dissolved into solid solution but has not yet precipitated, but also a state in which even if a small amount of carbide precipitates, it is so fine that it is easily re-dissolved in the subsequent diffusion process.

本発明で処理の対象とする肌焼鋼は、クロム鋼、ニッケ
ルクロム鋼、クロムモリブデン鋼またはニッケルクロム
モリブデン鋼などの各種合金鋼を包含する。Case hardening steels to be treated in the present invention include various alloy steels such as chromium steel, nickel-chromium steel, chromium-molybdenum steel, and nickel-chromium-molybdenum steel.

熱処理は、従来の浸炭による表面硬化処理において行な
っていた、焼入れ焼もどし処理を実施すればよい。The heat treatment may be performed by quenching and tempering, which has been performed in the conventional surface hardening treatment by carburizing.

浸炭は、真空浸炭またはイオン浸炭、好ましくは後者に
よって行なう。　イオン浸炭法による場合、浸炭に先立
って、後記する実施例に示すように、ＡｒおよびＨ２雰
囲気下におけるグロー放電をしばらく行ない、部品の表
面を清浄化することが好ましい。Carburizing is carried out by vacuum carburizing or ionic carburizing, preferably the latter. In the case of using the ion carburizing method, it is preferable to perform glow discharge in an Ar and H2 atmosphere for a while to clean the surface of the component, as shown in the examples described later, prior to carburizing.

［作　用］ 本発明の浸炭処理は、部品の表層部への炭素の浸炭を従
来のように一度に行なうのではなく、粗大炭化物を析出
させない限度で浸炭を行なってはそのつと炭素の拡散を
行ない、これを２回以上繰り返すことによって、粗大炭
化物の再固溶に要する長い処理時間を省略し、全体とし
て浸炭処理の所要時間を短縮したものでおる。[Function] In the carburizing treatment of the present invention, carbon is not carburized into the surface layer of the part all at once as in the conventional method, but carburization is performed to the extent that coarse carbides are not precipitated, and the diffusion of carbon is thereby prevented. By repeating this process twice or more, the long treatment time required for solid solution of coarse carbides can be omitted, and the time required for carburizing treatment can be shortened as a whole.

浸炭および拡散の繰り返し数は、肌焼鋼の鋼種、処理温
度および必要な浸炭法さなどから浸炭に要する時間を決
定し、それに応じて適当な回数を選べばよい。　１回の
浸炭時間を必要以上に短くして拡散回数を増やすことは
、もちろん不利益である。　必要な浸炭層深さや浸炭量
の限界からみて、３０回が限度であろう。The number of repetitions of carburizing and diffusion can be determined by determining the time required for carburizing based on the type of case hardening steel, treatment temperature, required carburizing method, etc., and selecting an appropriate number of times accordingly. Of course, it is disadvantageous to increase the number of times of diffusion by making one carburizing time shorter than necessary. Considering the required depth of the carburized layer and the limit of the amount of carburization, the maximum number of times would be 30 times.

［実施例］ 第１表に示すＮＱ１〜３の組成の合金を溶製した。[Example] Alloys having compositions NQ1 to NQ3 shown in Table 1 were melted.

各材料の試験片をイオン浸炭炉に入れて炉内を１Ｏ−２
Ｔｏｒｒまで減圧し、８８０℃に加熱俊、ＡｒおよびＨ
２を供給して炉内圧を２　Ｔ　ｏｒｒに調整した。　試
験片を陰極とし、陽極との間に３００Ｖの直流電圧を印
加して、グロー放電を起させた。　前処理として２０分
間、Ａｒおよびト１のイオンによる表面清浄化を行なっ
てからＡｒおよびＨ２を排気した。　続いて浸炭ガスと
してＣ３Ｈ８を使用して浸炭を行ない、ガスを排気して
温度だけ保持する拡散を組み合わせて、下記のＡないし
Ｃいずれかの処理を施した。A test piece of each material was placed in an ion carburizing furnace, and the inside of the furnace was heated to 1O-2.
The pressure was reduced to Torr, heated to 880°C, Ar and H
2 was supplied to adjust the furnace pressure to 2 Torr. The test piece was used as a cathode, and a DC voltage of 300 V was applied between it and the anode to cause glow discharge. As a pretreatment, the surface was cleaned with Ar and To1 ions for 20 minutes, and then Ar and H2 were exhausted. Subsequently, carburizing was performed using C3H8 as a carburizing gas, and one of the following treatments A to C was performed in combination with exhausting the gas and diffusion to maintain the temperature.

処理Ａ　（比較例） 浸炭を２時間行なった後、拡散を４時間行なう（計６時
間） 処理Ｂ　（本発明） 浸炭を４０分間行なった後、拡散を８０分間行ない、こ
れを３回繰り返す（計６時間）処理Ｃ（比較例） 浸炭を２時間行なった後、再固溶化処理を７時間行なう
（計９時間〉 上記の浸炭−拡散の俊、８３０℃に３０分間保持してか
ら油冷する焼入れ、および１６０℃に２時間保持してか
ら放冷する焼もどしを行なった。Treatment A (comparative example) Carburizing was performed for 2 hours and then diffusion was performed for 4 hours (total 6 hours) Treatment B (present invention) Carburizing was performed for 40 minutes and then diffusion was performed for 80 minutes, and this was repeated three times ( 6 hours in total) Treatment C (comparative example) After carburizing for 2 hours, re-solution treatment for 7 hours (9 hours in total) Using the above carburizing-diffusion method, holding at 830°C for 30 minutes and then oil cooling. and tempering, which was held at 160° C. for 2 hours and then allowed to cool.

処理後の各試験片の表面硬さ、有効硬化層深さおよび回
転曲げ疲れ強さを測定するとともに、粗大炭化物の有無
を調べた。　結果を、第２表に示す。The surface hardness, effective hardened layer depth, and rotary bending fatigue strength of each test piece after treatment were measured, and the presence or absence of coarse carbides was examined. The results are shown in Table 2.

ここで有効硬化層深さとは、試験片の断面においてその
端から硬度を測定し深さに対応してグラフをかき、グラ
フにおいて硬度５５０Ｈｖとなる点の、試験片の表面か
らの距離をいう。Here, the effective hardened layer depth refers to the distance from the surface of the test piece to the point where the hardness is 550 Hv on the graph by measuring the hardness from the end of the cross section of the test piece and drawing a graph corresponding to the depth.

回転曲げ疲れ強さは、平行部が直径８履の平滑試験片を
使用し、下記の条件で測定した。The rotational bending fatigue strength was measured under the following conditions using a smooth test piece with a parallel portion having a diameter of 8 shoes.

回転ｒｉ　　　１，０００万回 回転速度　　　３，５００ｒｌ）ｍ 温　度　　　　　　室　　　温 第２表の結果かられかるように、処理Ａを施したものは
、粒界に粗大炭化物が存在し、回転曲げ疲れ強さが低下
している。　これに対して本発明に従う処理Ｂを行なっ
たものは、同じ処理時間でありながら、粗大炭化物は認
められず、回転曲げ疲れ強さは処理Ａを施したものの約
３倍である。Rotation ri 10 million times Rotation speed 3,500 rl) m Temperature Room temperature As can be seen from the results in Table 2, the grains subjected to treatment A have coarse carbides in the grain boundaries and have low rotational bending fatigue strength. The quality is decreasing. On the other hand, in the specimens subjected to treatment B according to the present invention, no coarse carbides were observed, and the rotational bending fatigue strength was approximately three times that of treatment A.

一方、処理Ｃによるものも粗大炭化物はみられず、回転
曲げ疲れ強さは処理Ａの場合の約１．５倍であるが、処
理Ｃは処理Ｂの１．５倍の処理時間を必要としている。On the other hand, no coarse carbides were observed in the case of treatment C, and the rotational bending fatigue strength was about 1.5 times that of treatment A, but treatment C required 1.5 times the treatment time of treatment B. There is.

第　　　１　　　表 残部Ｆｅ 第　　　２　　　表 ［発明の効果］ 本発明の迅速浸炭処理方法は、カーボンポテンシャルの
高いイオン浸炭法などのもつ利点、すなわち迅速に目的
の炭素量を浸炭できるという点を確保した上で、カーボ
ンポテンシャルが高いがゆえの問題点、すなわち粗大炭
化物の生成がひきおこす疲れ強さの低下を避けることに
成功した方法である。Table 1 Remaining Fe Table 2 [Effects of the Invention] The rapid carburizing method of the present invention has the advantages of the ion carburizing method, which has a high carbon potential, that is, the ability to quickly carburize the desired amount of carbon. This method succeeded in avoiding the problem caused by the high carbon potential, that is, the decrease in fatigue strength caused by the formation of coarse carbides.

つまり、旧来の浸炭法により得られていたものと同等の
特性をもつ製品を、従来技術より迅速に製造することが
できる技術である。　処理時間の短縮がコスト低減に寄
与することは、いうまでもない。In other words, it is a technology that can produce products with properties equivalent to those obtained by conventional carburizing methods more quickly than conventional technologies. Needless to say, shortening processing time contributes to cost reduction.

特許出願人　　　大同特殊鋼株式会社 代理人　　弁理士　　須　賀　総　夫Patent applicant: Daido Steel Co., Ltd. Agent: Patent attorney, Souo Suga

Claims (1)

【特許請求の範囲】 肌焼鋼で製作した部品を炉に入れて加熱し、 （Ａ）浸炭ガスを流通させてその浸炭温度における鋼の
オーステナイト固溶限まで炭素を固溶させる浸炭と、 （Ｂ）炉内の浸炭ガスを排気して、不活性ガスを流入す
るかまたは真空に保持して炭素を拡散させる処理とを２
回以上繰り返し、その後に熱処理を行なうことを特徴と
する鋼の迅速浸炭処理方法。[Claims] Parts made of case-hardened steel are placed in a furnace and heated; (A) carburizing by passing carburizing gas to dissolve carbon up to the austenite solid solubility limit of the steel at the carburizing temperature; B) Exhaust the carburizing gas in the furnace and introduce an inert gas or keep it in a vacuum to diffuse carbon.
A method for rapid carburizing treatment of steel, characterized by repeating the process several times or more, followed by heat treatment.