JP6344495B1 - Vacuum carburizing and nitriding treatment method for steel - Google Patents
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Abstract
【課題】減圧浸炭処理と浸窒処理を連続して行う場合であって、かつ、少なくとも浸窒処理を行う熱処理炉として量産炉を用いる場合の最適条件を備えた減圧浸炭浸窒処理方法を提供すること。
【解決手段】０．１８〜２．００質量％のＣｒを含有する鋼材に対して、減圧浸炭処理と浸窒処理とを連続して行い、少なくとも浸窒処理を行う熱処理炉として量産炉を用いる。浸窒処理は、９００℃〜９７０℃の処理温度Ｔ（℃）の範囲内であって、雰囲気圧力Ｐ（Ｐａ）が、ＰＨ１とＰＨ２のうち低い値からなる上限ＰＨ（Ｐａ）と、ＰＬ１とＰＬ２のうちの低い値からなる下限ＰＬ（Ｐａ）の範囲内の条件で行う。ＰＨ１＝１０００００、ＰＨ２＝−４０５００×［Ｃｒ］＋２０５×Ｔ−３００００、ＰＬ１＝７２０００、ＰＬ２＝（−６５．１×Ｔ＋５１０００）×［Ｃｒ］＋Ｔ×４６４−３５６１５０
【選択図】図１Disclosed is a reduced pressure carburizing and nitriding treatment method having optimum conditions when a reduced pressure carburizing treatment and a nitriding treatment are performed continuously and at least when a mass production furnace is used as a heat treatment furnace for performing the nitriding treatment. To do.
A mass production furnace is used as a heat treatment furnace for performing a low-pressure carburizing treatment and a nitriding treatment continuously on a steel material containing 0.18 to 2.00% by mass of Cr, and at least performing the nitriding treatment. . Nitrogenation treatment is within the range of a treatment temperature T (° C.) of 900 ° C. to 970 ° C., and the atmospheric pressure P (Pa) is an upper limit PH (Pa) having a lower value of PH1 and PH2, and PL1 It is performed under the condition within the lower limit PL (Pa) consisting of a lower value of PL2. PH1 = 100000, PH2 = −40500 × [Cr] + 205 × T-30000, PL1 = 72000, PL2 = (− 65.1 × T + 51000) × [Cr] + T × 464-356150
[Selection] Figure 1
Description
本発明は、鋼材の減圧浸炭浸窒処理方法に関する。 The present invention relates to a reduced pressure carburizing and nitriding method for steel materials.
鋼部品の表面を浸炭処理により改質した浸炭鋼部品が広く用いられている。近年の鋼部品を用いた製品の軽量化及び小型化の要求から、鋼部品に付与される面圧が増大すると共に、回転部品として用いられる場合の回転数が増加する傾向にあり、従来以上に鋼部品に求められる耐久性が高くなってきている。 Carburized steel parts in which the surfaces of steel parts are modified by carburizing treatment are widely used. Due to the recent demand for weight reduction and downsizing of products using steel parts, the surface pressure applied to steel parts tends to increase, and the number of rotations when used as rotating parts tends to increase. The durability required for steel parts is increasing.
このような耐久性の高い浸炭鋼部品には、Ｎｉ、Ｍｏ、Ｃｒ等が添加された合金鋼を母材として使用し、熱軟化抵抗性を高めることが有効である。しかし、これらの合金鋼を浸炭用の母材として用いることは、添加する合金元素が高価なことによるコスト増の問題と、母材強度の必要以上の向上によって加工性が悪化するという問題が生じる場合がある。 For such a highly carburized steel part, it is effective to use alloy steel to which Ni, Mo, Cr, or the like is added as a base material to increase thermal softening resistance. However, the use of these alloy steels as a base material for carburizing raises the problem of cost increase due to the expensive alloying elements to be added and the problem that workability deteriorates due to an unnecessary increase in the strength of the base material. There is a case.
一方、母材となる鋼への合金元素の添加を少なく抑えつつ鋼部品表面強度を高める方法として、侵入型元素であるＣ、Ｎを鋼部品の表面に強制的に固溶させ、転位の歪を形成させる浸炭浸窒処理がある。従来の浸炭浸窒処理は、９００℃以上の処理温度でガス浸炭処理を施した後に、鋼材の温度を８５０℃程度まで降温した条件でガス浸窒処理を行うというものである。この方法では、処理時間が比較的長く、従来の浸窒を行わない浸炭処理に比べてコストが大きく増加することを避けることができない。浸炭浸窒処理の時間短縮を目的とした技術としては、たとえば浸炭時に減圧化された雰囲気内に浸炭ガスをパルス状に導入する減圧浸炭を採用して浸炭処理の時間短縮を図ったり、特許文献１に記載のものが提案されている。 On the other hand, as a method for increasing the surface strength of steel parts while suppressing the addition of alloying elements to the base steel, the interstitial elements C and N are forcibly dissolved on the surface of the steel parts, and the distortion of dislocations There is carburizing and nitriding treatment to form. In the conventional carburizing and nitriding treatment, after the gas carburizing treatment is performed at a treatment temperature of 900 ° C. or higher, the gas nitriding treatment is performed under the condition that the temperature of the steel material is lowered to about 850 ° C. In this method, the treatment time is relatively long, and it is unavoidable that the cost is greatly increased as compared with the conventional carburizing treatment without nitriding. As a technique for shortening the time of carburizing and nitriding treatment, for example, reducing the time of carburizing treatment by adopting reduced pressure carburizing that introduces carburizing gas in a pulsed manner into the atmosphere reduced at the time of carburizing, patent document 1 has been proposed.
浸炭時に減圧する浸炭処理方法の採用は、浸炭処理の時間の短縮に寄与するが、当然のごとく、浸炭処理後に別工程として行う浸窒処理の時間短縮には寄与しない。また、特許文献１は、Ｃ含有率を中炭素鋼の範囲にすると共にＣｒ含有率を低くした鋼を用いることにより、浸炭窒化処理時間の短縮を図るというものであるが、浸炭窒化処理の処理温度条件の最適化については殆ど検討されていない。一方、浸炭処理後の浸窒処理の温度を浸炭処理温度に近づければ、浸炭処理終了から浸窒処理開始までの間の時間を短縮するとともに浸窒処理をより高温で行うことで浸窒処理自体の処理時間も短縮することが可能と考えられる。しかしながら、単純に、浸窒処理温度を浸炭処理温度に近い温度、具体的には９００℃以上の温度とした場合には、浸窒処理時に雰囲気ガスとして用いるアンモニアガスの分解が進みやすくなり、鋼中に狙いとする濃度の窒素を侵入させることができないという問題がある。 Adoption of a carburizing method that reduces the pressure during carburizing contributes to shortening the time of carburizing treatment, but as a matter of course, does not contribute to shortening the time of carburizing treatment performed as a separate process after carburizing treatment. Patent Document 1 is intended to shorten the carbonitriding time by using steel having a C content in the range of medium carbon steel and a low Cr content. There has been little study on optimization of temperature conditions. On the other hand, if the temperature of the nitrocarburizing treatment after the carburizing treatment is brought close to the carburizing treatment temperature, the time from the end of the carburizing treatment to the start of the nitriding treatment is shortened, and the nitriding treatment is performed at a higher temperature to perform the nitriding treatment. It is considered possible to shorten the processing time of itself. However, simply, when the nitriding temperature is set to a temperature close to the carburizing temperature, specifically 900 ° C. or more, the decomposition of ammonia gas used as the atmospheric gas during the nitriding treatment is likely to proceed. There is a problem that the target concentration of nitrogen cannot enter.
このような問題を解決すべく、本発明の出願人は、既に減圧浸窒処理時において被処理材中の含有元素の中で特にＮの鋼中への侵入に大きな影響を及ぼすＣｒの含有率の値と最適な減圧浸窒処理条件との関係を明確にする技術の提案を行っており、減圧浸炭処理と減圧浸窒処理との総合的な処理時間を従来よりも大幅に短縮することに成功した（特許文献２）。 In order to solve such a problem, the applicant of the present invention has already determined that the Cr content ratio which has a great influence on the penetration of N into the steel among the elements contained in the material to be treated at the time of reduced pressure nitriding treatment. Has been proposed to clarify the relationship between this value and the optimum reduced pressure nitriding treatment conditions, and the overall processing time for reduced pressure carburization and reduced pressure nitriding treatment will be significantly reduced compared to the conventional method. Successful (Patent Document 2).
この減圧浸窒処理条件の最適化は、数多くの実験に基づいて完成されたが、前記特許文献２に明確な記載はないものの、その実験は、実験室におけるφ１５０ｍｍ、長さ８００ｍｍ程度の管状炉といった１回の処理能力が数ｋｇ程度の小型熱処理炉を使用してなされたものである。そのため、窒化（浸窒処理）に用いるアンモニアガスを炉内に導入し、そのアンモニアガスが被処理材としての鋼材の表面に到達するまでの距離及び時間、その後炉から排出されるまでの距離及び時間は、実際に量産時に使用される大型の量産炉とは異なる状況となる。そこで、量産のための最適条件を見出すため、さらなる検討を行ったところ、特許文献２の条件は、試験片数本レベルを熱処理ができれば目的を達成できる前記管状炉等の実験室にある小型炉を使用する場合には最適な条件として利用できるが、量産時に用いられる大型処理炉で製造する場合には、小型炉とは最適条件に差異が生じ、そのままの条件での量産適用ができないことが判明した。 Although the optimization of the reduced pressure nitriding treatment conditions has been completed based on a number of experiments, although there is no clear description in Patent Document 2, the experiment was conducted in a tubular furnace having a diameter of about 150 mm and a length of about 800 mm in the laboratory. Such a one-time processing capability is made using a small heat treatment furnace of about several kg. Therefore, ammonia gas used for nitriding (nitriding treatment) is introduced into the furnace, the distance and time until the ammonia gas reaches the surface of the steel material as the material to be treated, the distance until it is discharged from the furnace, and The time is different from that of a large-scale mass production furnace that is actually used for mass production. Therefore, further investigations were made to find the optimum conditions for mass production. The condition of Patent Document 2 is a small furnace in a laboratory such as a tubular furnace that can achieve its objective if heat treatment can be performed for several test pieces. Can be used as optimum conditions, but when manufactured in a large processing furnace used for mass production, there is a difference in the optimum conditions from a small furnace, and mass production cannot be applied under the same conditions. found.
本発明は、かかる背景に鑑みてなされたものであり、減圧浸炭処理と浸窒処理を連続して行う場合であって、かつ、少なくとも浸窒処理を行う熱処理炉として大型の量産炉を用いる場合の最適条件を備えた減圧浸炭浸窒処理方法を提供しようとするものである。 The present invention has been made in view of such a background, and is a case where a reduced-pressure carburizing process and a nitriding process are continuously performed, and at least a large-scale mass production furnace is used as a heat treatment furnace for performing a nitriding process. The present invention is intended to provide a reduced pressure carburizing and nitriding treatment method having the optimum conditions.
本発明の一態様は、０．１８〜２．００質量％のＣｒを含有する鋼材に対して、減圧浸炭処理と浸窒処理とを連続して行い、かつ、少なくとも浸窒処理を行う熱処理炉として量産炉を用いる減圧浸炭浸窒処理方法であって、
上記浸窒処理は、９００℃〜９７０℃の処理温度Ｔ（℃）の範囲内であって、雰囲気圧力Ｐ（Ｐａ）が、下記のＰＨ１とＰＨ２のうち低い値からなる上限ＰＨ（Ｐａ）と、下記のＰＬ１とＰＬ２のうちの低い値からなる下限ＰＬ（Ｐａ）の範囲内の条件で行うことを特徴とする鋼材の減圧浸炭浸窒処理方法にある。
ＰＨ１＝１０００００（Ｐａ）
ＰＨ２＝−４０５００×［Ｃｒ］＋２０５×Ｔ−３００００（Ｐａ）
ＰＬ１＝７２０００（Ｐａ）
ＰＬ２＝（−６５．１×Ｔ＋５１０００）×［Ｃｒ］＋Ｔ×４６４−３５６１５０（Ｐａ）
（ただし、［Ｃｒ］は鋼材におけるＣｒ含有率（質量％））
One embodiment of the present invention is a heat treatment furnace in which a low-pressure carburizing treatment and a nitrocarburizing treatment are continuously performed on a steel material containing 0.18 to 2.00% by mass of Cr, and at least the nitriding treatment is performed. A reduced pressure carburizing and nitriding method using a mass production furnace as
The above nitriding treatment is within the range of the treatment temperature T (° C.) of 900 ° C. to 970 ° C., and the atmospheric pressure P (Pa) is an upper limit PH (Pa) having a lower value of the following PH1 and PH2. Further, the present invention is a reduced pressure carburizing and nitriding method for steel, which is performed under conditions within a range of a lower limit PL (Pa) consisting of a low value of the following PL1 and PL2.
PH1 = 100000 (Pa)
PH2 = −40500 × [Cr] + 205 × T-30000 (Pa)
PL1 = 72000 (Pa)
PL2 = (− 65.1 × T + 51000) × [Cr] + T × 464-356150 (Pa)
(However, [Cr] is the Cr content in steel (mass%))
上記減圧浸炭浸窒処理方法は、浸窒処理時において被処理材中の含有元素の中で特にＮの鋼中への侵入に大きな影響を及ぼすＣｒの含有率の値と最適な浸窒処理条件との関係を明確にすることにより、減圧浸炭処理と浸窒処理との総合的な処理時間を従来よりも大幅に短縮するものである。特に、浸窒処理を行う熱処理炉として大型の量産炉を用いる場合の条件を明確にして、量産時の処理時間の短縮を可能とするものである。ここで言う大型の量産炉とは、明確に数値で範囲を限定するのは難しいが、あえて記載するのであれば、概ね１回の処理で少なくとも１００ｋｇ以上の鋼材を処理可能な炉のことを言う。 The above-mentioned reduced pressure carburizing and nitriding treatment method is characterized by the Cr content value and the optimum nitriding treatment conditions that have a great influence on the penetration of N into steel among the elements contained in the material to be treated during the nitriding treatment. This makes it possible to significantly reduce the total processing time of the reduced pressure carburizing process and the nitrocarburizing process as compared with the prior art. In particular, the conditions for using a large-scale mass production furnace as a heat treatment furnace for performing nitriding treatment are clarified, and the processing time during mass production can be shortened. The large-scale mass production furnace here means that it is difficult to clearly limit the range by numerical values, but if it is intentionally described, it means a furnace capable of treating at least 100 kg of steel material in one treatment. .
そして、上記処理前半の減圧浸炭処理では浸炭段階での処理時間短縮に寄与する減圧浸炭処理を採用し、これまでと同様に処理温度を上記特定の高温範囲内とし、かつ、後半の処理である上記浸窒処理は、基本的な条件として、処理温度Ｔ（℃）としては比較的高温の９００℃〜９７０℃とし、雰囲気圧力Ｐ（Ｐａ）としては、上述した上限ＰＨ（Ｐａ）と下限ＰＬ（Ｐａ）の範囲内の条件とする。 And, the reduced pressure carburization treatment in the first half of the treatment employs a reduced pressure carburization treatment that contributes to shortening of the treatment time in the carburization stage, and the treatment temperature is within the specific high temperature range as before, and is the latter half treatment. In the nitriding treatment, as basic conditions, the treatment temperature T (° C.) is a relatively high temperature of 900 ° C. to 970 ° C., and the atmospheric pressure P (Pa) is the above-described upper limit PH (Pa) and lower limit PL. The condition is within the range of (Pa).
上限ＰＨ及び下限ＰＬを上記のごとく定めることによって、９００〜９７０℃という高温条件においても、Ｃｒ含有率と処理温度Ｔとを加味して最適な浸窒条件（窒素ポテンシャル）が得られる雰囲気圧力Ｐの範囲の上限及び下限を定めることができる。この範囲に定めることによって、浸窒処理を大型の量産炉を用いて行う場合において、効率よく処理を進めることが可能となり、浸窒処理自体の短縮化を図ることができる。 By determining the upper limit PH and the lower limit PL as described above, the atmospheric pressure P can be obtained under the high nitriding conditions (nitrogen potential) in consideration of the Cr content and the processing temperature T even under high temperature conditions of 900 to 970 ° C. The upper and lower limits of the range can be defined. By setting it within this range, when the nitriding process is performed using a large-scale mass production furnace, the process can be efficiently advanced, and the nitriding process itself can be shortened.
さらに、これらの条件を全て具備するように処理温度Ｔ及び雰囲気圧力Ｐを決定することにより、浸窒処理の処理温度と、９００℃以上の処理が不可欠である減圧浸炭処理の処理温度との差を極力小さくすることができ、浸炭処理温度から浸窒処理温度への降温時間の短縮と浸窒処理温度の高温化による浸窒時間の短縮の効果によって、減圧浸炭処理と浸窒処理とを連続して行う場合の総合的な処理時間を従来よりも大幅に短縮することができる。 Furthermore, by determining the treatment temperature T and the atmospheric pressure P so as to satisfy all of these conditions, the difference between the treatment temperature of the nitriding treatment and the treatment temperature of the reduced pressure carburizing treatment in which treatment of 900 ° C. or more is essential. The reduced-pressure carburizing treatment and the nitriding treatment are continuously performed by the effect of shortening the cooling time from the carburizing temperature to the nitriding temperature and shortening the nitriding time by increasing the nitriding temperature. Thus, the total processing time can be significantly reduced compared to the conventional method.
上記減圧浸炭浸窒処理方法は、上述したごとく、０．１８〜２．００質量％のＣｒ（クロム）を含有する鋼材に対して行うものである。ここで、Ｃｒ含有率の下限を０．１８％とするのは、鋼の強度（内部硬さ）を確保するためである。Ｃｒ含有率の上限を２．００質量％とするのは、Ｃｒ含有率が高すぎると侵入させたＮが固溶せずにＣｒと結合して粗大なＣｒＮが生成されやすくなり、粗大なＣｒＮによる疲労強度低下が懸念されると共に本来狙っているＮ固溶による表面硬度向上効果が得られにくくなるためである。 As described above, the reduced pressure carburizing and nitriding method is performed on a steel material containing 0.18 to 2.00% by mass of Cr (chromium). Here, the reason why the lower limit of the Cr content is set to 0.18% is to ensure the strength (internal hardness) of the steel. The upper limit of the Cr content is set to 2.00% by mass. If the Cr content is too high, the intruded N does not form a solid solution but is bonded to Cr and easily forms coarse CrN. This is because there is a concern about a decrease in fatigue strength due to N, and it is difficult to obtain the effect of improving surface hardness due to the originally aimed N solid solution.
上記減圧浸炭処理は、一般的な公知の条件で行うことができる。例えば、減圧浸炭処理は、９００〜１０５０℃の処理温度（鋼材の温度）にて行うことができる。減圧浸炭処理を９００℃以上とすることにより、浸炭処理を確実に行うことができる。一方、減圧浸炭処理の上限温度は、結晶粒が粗大化防止の観点から決めることができ、例えば、１０５０℃とすることができる。なお、処理時間短縮のためには、浸炭処理をより高い温度で行うことが好ましいが、高温で処理するほど、前記の通り浸炭処理後における鋼材の結晶粒が粗大化しやすくなるため、その点を考慮した処理時間の設定が必要である。 The said reduced pressure carburizing process can be performed on general well-known conditions. For example, the reduced-pressure carburizing process can be performed at a processing temperature (temperature of the steel material) of 900 to 1050 ° C. By setting the reduced pressure carburizing process to 900 ° C. or higher, the carburizing process can be reliably performed. On the other hand, the upper limit temperature of the reduced pressure carburizing treatment can be determined from the viewpoint of preventing the crystal grains from being coarsened, and can be set to 1050 ° C., for example. In order to shorten the processing time, it is preferable to perform the carburizing process at a higher temperature.However, as the processing is performed at a higher temperature, the crystal grains of the steel material after the carburizing process are likely to become coarser as described above. It is necessary to set the processing time in consideration.
なお、上記減圧浸炭処理は、具体的には、ガスによる減圧浸炭処理であり、上記処理温度に維持した処理炉内に浸炭用ガスをパルス状に導入しながら行う。すなわち、減圧浸炭処理時の雰囲気圧力は、大気圧よりも低い圧力に減圧した状態で行う。具体的には、パルス状に導入した浸炭雰囲気の最大時圧力は、５０〜３０００Ｐａの範囲とすることが好ましい。浸炭用ガスとしては、たとえば、炭化水素ガス、特に、アセチレン、プロパン等を用いることができる。 The reduced-pressure carburizing process is specifically a reduced-pressure carburizing process using gas, and is performed while introducing a carburizing gas in a pulsed manner into a processing furnace maintained at the processing temperature. That is, the atmospheric pressure during the reduced pressure carburizing process is performed in a state where the pressure is reduced to a pressure lower than the atmospheric pressure. Specifically, it is preferable that the maximum pressure of the carburizing atmosphere introduced in a pulse shape is in a range of 50 to 3000 Pa. As the carburizing gas, for example, a hydrocarbon gas, particularly acetylene, propane or the like can be used.
次に、上記浸窒処理は、上述したごとく、基本的な処理温度（鋼材の温度）Ｔ（℃）として、９００〜９７０（℃）の範囲を選択し、従来の８５０℃程度に比べて高い範囲に限定する。これにより、処理時間の低減を図る。一方、浸窒処理温度が高すぎると、窒素源としてのアンモニアを処理炉内に導入した際の窒素と水素への分解が過度に進みすぎて浸窒効果が低下するおそれがあるため、上限値は９７０℃とする。 Next, as described above, the nitriding treatment is selected from the range of 900 to 970 (° C.) as the basic treatment temperature (steel temperature) T (° C.), which is higher than the conventional 850 ° C. Limited to range. Thereby, reduction of processing time is aimed at. On the other hand, if the nitriding treatment temperature is too high, decomposition of nitrogen and hydrogen when ammonia as a nitrogen source is introduced into the treatment furnace excessively progresses and the nitriding effect may be reduced. Is 970 ° C.
また、浸窒処理の雰囲気圧力Ｐの上限ＰＨ（Ｐａ）は、ＰＨ１とＰＨ２のうち低い値とする。
ＰＨ１＝１０００００（Ｐａ）、
ＰＨ２＝−４０５００×［Ｃｒ］＋２０５×Ｔ−３００００（Ｐａ）、
すなわち、ＰＨ２の算出値が１０００００未満の場合には、その値が上限ＰＨとなり、ＰＨ２の算出値が１０００００以上の場合には、ＰＨ＝１０００００となる。
Further, the upper limit PH (Pa) of the atmospheric pressure P for the nitriding treatment is set to a lower value of PH1 and PH2.
PH1 = 100000 (Pa)
PH2 = -40500 × [Cr] + 205 × T-30000 (Pa)
That is, when the calculated value of PH2 is less than 100,000, the value is the upper limit PH, and when the calculated value of PH2 is 100,000 or more, PH = 100000.
ＰＨ１は、大気圧に相当し、設備の都合上大気より加圧可能にすることは難しいため、量産における浸窒処理として実現可能な上限圧力を定めたものであり、ＰＨ２は、過剰浸窒による残留オーステナイトの増加や窒化物の析出による強度への悪影響の可能性を確実に低減することができる範囲の上限圧力として、Ｃｒ含有率と処理温度Ｔとの関係からその限界値を導いたものである。 PH1 corresponds to atmospheric pressure, and it is difficult to pressurize from the atmosphere due to facilities, so the upper limit pressure that can be realized as nitriding treatment in mass production is determined. PH2 is due to excessive nitriding As the upper limit pressure within the range that can reliably reduce the possibility of adverse effects on strength due to increase in retained austenite and precipitation of nitride, the limit value is derived from the relationship between Cr content and processing temperature T. is there.
また、浸窒処理の雰囲気圧力Ｐの下限ＰＬ（Ｐａ）は、ＰＬ１とＰＬ２のうちの低い値とする。
ＰＬ１＝７２０００（Ｐａ）、
ＰＬ２＝（−６５．１×Ｔ＋５１０００）×［Ｃｒ］＋Ｔ×４６４−３５６１５０（Ｐａ）、
すなわち、ＰＬ２の算出値が７２０００未満の場合には、その値が下限ＰＬとなり、ＰＬ２の算出値が７２０００以上の場合には、ＰＬ＝７２０００となる。
Further, the lower limit PL (Pa) of the atmospheric pressure P for the nitriding treatment is set to a lower value of PL1 and PL2.
PL1 = 72000 (Pa)
PL2 = (− 65.1 × T + 51000) × [Cr] + T × 464-356150 (Pa),
That is, when the calculated value of PL2 is less than 72000, the value is the lower limit PL, and when the calculated value of PL2 is 72000 or more, PL = 72000.
窒素源となるアンモニアガスは、高温になればなるほど分解しやすくなり、かつ、雰囲気圧力を低くすればするほど分解しやすくなる。多くの実験の結果、量産炉を用いる場合には、本願におけるＣｒ含有範囲において、処理温度が９００〜９７０℃の範囲においては、雰囲気圧力を７２０００Ｐａ以上に保つことによって、炉内に生じるアンモニアガスの分解を考慮しても、浸窒に必要なＮを供給可能であることがわかった。その上で、処理温度が比較的低い領域においては、Ｃｒ含有率に応じてさらに低い圧力を設定可能であることがわかり、その下限値がＰＬ２によって示せることが判明したのである。 Ammonia gas, which is a nitrogen source, becomes easier to decompose as the temperature rises, and becomes easier to decompose as the atmospheric pressure is lowered. As a result of many experiments, when a mass production furnace is used, in the Cr content range in the present application, in the range of 900 to 970 ° C., by maintaining the atmospheric pressure at 72000 Pa or more, the ammonia gas generated in the furnace It has been found that N necessary for nitriding can be supplied even when decomposition is taken into consideration. In addition, it was found that in the region where the processing temperature is relatively low, a lower pressure can be set according to the Cr content, and the lower limit value can be indicated by PL2.
上記の処理温度Ｔと雰囲気圧力Ｐとの関係を図１に示す。同図は、横軸に浸窒処理時の処理温度Ｔ（℃）を、縦軸に雰囲気圧力Ｐ（Ｐａ）をとったものである同図中上述したＰＨ１、ＰＨ２、ＰＬ１、ＰＬ２及びＴ１＝９００℃、Ｔ２＝９７０℃の位置を示した。量産炉を用いる場合の浸窒処理条件をこれらの基準に囲まれた範囲（条件設定範囲Ｓ）内で選定することにより、適度な浸窒処理を効率よく実施することが可能となる。 The relationship between the processing temperature T and the atmospheric pressure P is shown in FIG. In the figure, the horizontal axis represents the treatment temperature T (° C.) during the nitriding treatment, and the vertical axis represents the atmospheric pressure P (Pa). PH1, PH2, PL1, PL2, and T1 = The position at 900 ° C. and T2 = 970 ° C. was indicated. By selecting the nitriding treatment conditions in the case of using a mass production furnace within a range (condition setting range S) surrounded by these standards, it is possible to efficiently carry out an appropriate nitriding treatment.
また、同図には、予備下限圧力ＰＬ３として、７００００Ｐａの位置を破線で示してある。特許文献１に示した実験室の小型実験炉で行う場合には、このＰＬ３が最高圧力となるが、このＰＬ３以下の範囲においては、浸窒処理炉の大きさに関係なく、条件が成立する範囲を含むこととなる。そのため、減圧浸炭処理炉として量産炉を選択した場合、特許文献１に開示された範囲を除く範囲は、ＰＬ３＝７００００Ｐａを超える範囲となる。 Further, in the figure, the position of 70000 Pa is indicated by a broken line as the reserve lower limit pressure PL3. In the case of performing in the small laboratory furnace in the laboratory shown in Patent Document 1, this PL3 becomes the maximum pressure, but in the range below this PL3, the condition is satisfied regardless of the size of the nitriding furnace. It will include the range. Therefore, when a mass production furnace is selected as the reduced pressure carburizing treatment furnace, the range excluding the range disclosed in Patent Document 1 is a range exceeding PL3 = 70000 Pa.
なお、特許文献２での評価時に用いた実験用の小型炉である管状炉（φ１５０ｍｍ×長さ８００ｍｍ）との間で、最適条件に差異が生じた理由は以下の通りと推定される。すなわち、処理炉内に浸窒のため導入されたアンモニアガスは、処理炉内でも分解されながら、導入口から排出口に流れるが、処理鋼材が試験片数本レベルの小型炉の場合は、炉内容積が小さく、導入口と排出口の距離も短いため、雰囲気ガスの攪拌等を行う等の対策によって、導入口側と排出口側及び被処理材の挿入位置間で窒素ポテンシャルに差異がない状態で雰囲気ガスの制御をすることが可能である。 The reason why the optimum conditions differed from the tubular furnace (φ150 mm × length 800 mm), which is a small experimental furnace used at the time of evaluation in Patent Document 2, is estimated as follows. In other words, the ammonia gas introduced for nitriding into the processing furnace flows from the inlet to the outlet while being decomposed in the processing furnace, but in the case of a small furnace with several treated steel parts, Since the internal volume is small and the distance between the inlet and outlet is short, there is no difference in nitrogen potential between the inlet side, the outlet side, and the insertion position of the material to be treated by measures such as stirring the atmospheric gas. It is possible to control the atmospheric gas in the state.
ところが、処理炉が少なくとも１００ｋｇ以上の鋼材を１度に処理できる量産に使用可能な大型炉になると、処理炉内の雰囲気ガスの均一化を目的とする攪拌を積極的に行っても、導入口側と排出口側及び被処理材の挿入位置の間で窒素ポテンシャルに差異が生じ、導入口側から浸窒処理を行うのに十分な量のアンモニアガスを供給しても、処理鋼材の位置に達する前に窒素ポテンシャルが低下し、小型炉と同じ雰囲気圧に制御しても小型炉で得られた表面窒素濃度まで浸窒させることができなくなるためと考えられる。従って、量産に用いられる大型炉での処理の場合には、このような窒素ポテンシャルの低下による影響分を考慮して、特許文献２で指定された雰囲気圧に比べ、高めの圧とする必要がある。以上の検討の結果、本発明の浸窒処理では、大気圧と同じ雰囲気圧も含む圧とする必要があるため、先願で使用した減圧という言葉は用いていない。 However, when the processing furnace becomes a large-sized furnace that can be used for mass production capable of processing at least 100 kg of steel material at a time, even if the stirring for the purpose of uniformizing the atmospheric gas in the processing furnace is actively performed, Even if a sufficient amount of ammonia gas is supplied from the inlet side to perform the nitriding treatment, there will be a difference in the position of the treated steel material. This is thought to be because the nitrogen potential drops before it reaches, and even if the atmospheric pressure is controlled to be the same as that of the small furnace, it is impossible to perform nitriding to the surface nitrogen concentration obtained in the small furnace. Therefore, in the case of processing in a large furnace used for mass production, it is necessary to set the pressure higher than the atmospheric pressure specified in Patent Document 2 in consideration of the influence of such a decrease in nitrogen potential. is there. As a result of the above examination, in the nitriding treatment of the present invention, it is necessary to set the pressure to include the same atmospheric pressure as the atmospheric pressure, so the term “depressurization” used in the previous application is not used.
また、上記減圧浸炭処理と浸窒処理とは連続して実施されるが、上記減圧浸炭処理の処理温度と上記浸窒処理の処理温度を実質的に同一温度とすることが好ましい。これにより、鋼材の温度変更時間を余分にとる必要がなく、浸炭処理後すぐに浸窒処理を行うことができるため、その分全体の処理時間をより短縮することができる。ここで、実質的に同一温度とは、全く同じ温度である場合だけでなく、たとえば±１０℃以内の差違であって、温度変更時間を別途とる必要がない場合をも含むものである。 Moreover, although the said reduced pressure carburizing process and a nitriding process are implemented continuously, it is preferable that the process temperature of the said reduced pressure carburizing process and the process temperature of the said nitriding process shall be substantially the same temperature. Thereby, it is not necessary to take extra time for changing the temperature of the steel material, and the nitriding treatment can be performed immediately after the carburizing treatment, so that the entire treatment time can be shortened accordingly. Here, “substantially the same temperature” includes not only the case where the temperatures are exactly the same, but also the case where there is a difference within ± 10 ° C., for example, and it is not necessary to separately take a temperature change time.
また、上記減圧浸炭浸窒処理方法を適用する鋼材としては、Ｃｒ含有率が上記特定の範囲内であれば、他の添加成分の含有率に大きな制限はなく、従来から浸炭処理や浸炭浸窒処理を施されてきたいわゆる肌焼鋼であれば問題なく使用できる。主要な添加成分と含有率の例を以下に示す。成分範囲は、過去に提案された開発鋼を含み、焼戻し軟化抵抗向上のための成分や、結晶粒粗大化防止のための成分を含むが、いずれにしても公知の成分であり、個々の成分の効果は、公開済公報に記載されているので、各成分毎の限定理由の説明は省略する。 In addition, as a steel material to which the reduced pressure carburizing and nitriding treatment method is applied, as long as the Cr content is within the above specific range, the content of other additive components is not greatly limited, and conventionally, carburizing and carburizing and nitrocarburizing are performed. So-called case-hardened steel that has been treated can be used without problems. Examples of main additive components and contents are shown below. The component range includes developed steels proposed in the past and includes components for improving temper softening resistance and components for preventing crystal grain coarsening. Since the effect is described in the published gazette, the explanation of the reason for limitation for each component is omitted.
Ｃ（炭素）は、必須添加成分である。Ｃ含有率は、０．１０〜０．３０質量％程度が好ましい。 C (carbon) is an essential additive component. The C content is preferably about 0.10 to 0.30% by mass.
以下に、Ｃ以外の主要成分の好ましい含有率の例を示す。
Ｓｉ（ケイ素）：０．１０〜１．５０質量％、
Ｍｎ（マンガン）：０．５０〜２．００質量％、
Ｐ（リン）：０．０３５質量％以下、
Ｓ（硫黄）：０．０３５質量％以下、
Ｍｏ（モリブデン）：０〜０．８０質量％（任意添加元素）、
Ａｌ（アルミニウム）：０．０２０〜０．０６０質量％、
Ｎ（窒素）：０．００８０〜０．０２５０質量％、
Ｎｂ（ニオブ）：０〜０．１２質量％（任意添加元素）
Below, the example of the preferable content rate of main components other than C is shown.
Si (silicon): 0.10 to 1.50 mass%,
Mn (manganese): 0.50 to 2.00% by mass,
P (phosphorus): 0.035% by mass or less,
S (sulfur): 0.035 mass% or less,
Mo (molybdenum): 0 to 0.80 mass% (optionally added element),
Al (aluminum): 0.020 to 0.060 mass%,
N (nitrogen): 0.0080 to 0.0250 mass%,
Nb (niobium): 0 to 0.12% by mass (optionally added element)
なお、鋼材には、上記添加元素以外には、Ｆｅ（鉄）及び不可避的不純物が含まれる。 The steel material contains Fe (iron) and inevitable impurities in addition to the additive elements.
本願における減圧浸炭浸窒処理方法の実施例につき、比較例と共に説明する。
まず、表１に示すごとく、Ｃｒ含有率が異なる６グループ（Ｇ１〜Ｇ６）の１８種類の鋼材を試料として準備した。Ｇ１グループの試料１〜３は、Ｃｒ含有率が約０．２０％の試料である。Ｇ２グループの試料４〜６は、Ｃｒ含有率が約０．５０％の試料である。Ｇ３グループの試料７〜９は、Ｃｒ含有率が約０．８０％の試料である。Ｇ４グループの試料１０〜１２は、Ｃｒ含有率が約１．１０〜１．２０％の試料である。Ｇ５グループの試料１３〜１５は、Ｃｒ含有率が約１．６０％の試料である。Ｇ６グループの試料１６〜１８は、Ｃｒ含有率が約２．００％の試料である。
Examples of the reduced pressure carburizing and nitriding method in the present application will be described together with comparative examples.
First, as shown in Table 1, 18 types of steel materials of 6 groups (G1 to G6) having different Cr contents were prepared as samples. Samples 1 to 3 in the G1 group are samples having a Cr content of about 0.20%. Samples 4 to 6 in the G2 group are samples having a Cr content of about 0.50%. Samples 7 to 9 of the G3 group are samples having a Cr content of about 0.80%. Samples 10 to 12 of the G4 group are samples having a Cr content of about 1.10 to 1.20%. Samples 13 to 15 of the G5 group are samples having a Cr content of about 1.60%. Samples 16 to 18 of the G6 group are samples having a Cr content of about 2.00%.
上記各試料は、いずれも、表１に示された化学成分組成に調整して得られた鋼塊に対して、鍛伸、焼き鈍し処理を施し、機械加工によりφ２６ｍｍ×４０ｍｍの円柱状の試験片に加工したものである。これらの試料に対して、次のような減圧浸炭浸窒処理を実施した。 In each of the above samples, the steel ingot obtained by adjusting the chemical composition shown in Table 1 is subjected to forging and annealing treatment, and a cylindrical test piece having a diameter of 26 mm × 40 mm by machining. Is processed. These samples were subjected to the following reduced-pressure carburizing and nitriding treatment.
＜減圧浸炭浸窒処理＞
上記各試料を量産用の大型バッチ炉（炉内の内寸法：１２００ｍｍ×１３００ｍｍ×８００ｍｍ、処理能力：２００ｋｇ）に装入し、各試料の温度を減圧浸炭処理温度まで昇温する。本例では、表２に示すごとく、減圧浸炭処理温度として、９００℃、９３０℃、９５０℃及び９７０℃の４種類の温度を用いた。そして、浸炭ガスとしてアセチレンを処理炉内にパルス状に導入し、導入時の最大雰囲気圧力を１５０Ｐａに設定して、９００秒保持し、減圧浸炭処理を行う。
<Low pressure carburizing and nitriding treatment>
Each sample is charged into a large-scale batch furnace for mass production (inner dimensions in the furnace: 1200 mm × 1300 mm × 800 mm, processing capacity: 200 kg), and the temperature of each sample is raised to the reduced pressure carburizing temperature. In this example, as shown in Table 2, four temperatures of 900 ° C., 930 ° C., 950 ° C., and 970 ° C. were used as the reduced pressure carburizing temperature. Then, acetylene as a carburizing gas is introduced into the processing furnace in a pulsed manner, the maximum atmospheric pressure at the time of introduction is set to 150 Pa, and held for 900 seconds to perform a reduced pressure carburizing process.
次に、この減圧浸炭処理に連続して浸窒処理を行う。浸窒処理の処理温度Ｔ（℃）は、直前の減圧浸炭処理温度と同じ温度（表２〜表５中の「処理温度」）に設定する。そして、アンモニアを処理炉内に導入しながら、所定の雰囲気圧力Ｐの値に設定して、９００秒保持し、その後油焼き入れを行う。本例では、浸窒処理の雰囲気圧力Ｐとして、５００００Ｐａ、６００００Ｐａ、７００００Ｐａ、７２０００Ｐａ、８００００Ｐａ、９００００Ｐａ及び１０００００Ｐａの７種類の圧力を用いた。 Next, a nitriding treatment is performed continuously to the reduced pressure carburizing treatment. The treatment temperature T (° C.) of the nitriding treatment is set to the same temperature as the immediately preceding reduced pressure carburizing treatment temperature (“treatment temperature” in Tables 2 to 5). Then, while introducing ammonia into the processing furnace, it is set to a predetermined atmospheric pressure P value, held for 900 seconds, and then oil quenching is performed. In this example, seven types of pressures of 50000 Pa, 60000 Pa, 70000 Pa, 72000 Pa, 80000 Pa, 90000 Pa, and 100000 Pa were used as the atmospheric pressure P for the nitriding treatment.
＜浸窒性評価＞
浸窒処理が効果的になされたか否かについては、上記の減圧浸炭浸窒処理後の各試料表面の窒素濃度を測定することにより評価した。なお、測定した窒素濃度の結果から、処理後の窒素濃度の傾向は、表２〜５の結果に示すように、ほぼＣｒ含有率で決定されることがわかった。測定は、同じ条件について３本ずつ試験片を準備し、３本の試験片それぞれの表面窒素濃度を測定し、その平均値を用いて評価した。窒素濃度の測定は、ＥＰＭＡを用いて行った。表面窒素濃度が０．３０質量％以上の場合を、窒素濃度の点からは浸窒処理が適切に行われていると判断した。
<Nitrogen evaluation>
Whether or not the nitriding treatment was effectively performed was evaluated by measuring the nitrogen concentration on the surface of each sample after the reduced pressure carburizing and nitriding treatment. In addition, it turned out that the tendency of the nitrogen concentration after a process is substantially determined by Cr content rate, as shown in the result of Tables 2-5 from the result of the measured nitrogen concentration. For the measurement, three test pieces were prepared under the same conditions, the surface nitrogen concentration of each of the three test pieces was measured, and the average value was used for evaluation. The nitrogen concentration was measured using EPMA. When the surface nitrogen concentration was 0.30% by mass or more, it was determined that the nitriding treatment was appropriately performed from the point of nitrogen concentration.
また、本発明の浸炭浸窒処理については、前記特許文献２に比べ浸窒処理時の雰囲気圧を高めており、その影響から、前記特許文献２の処理後の鋼材に比べると、鋼中に粗大なＣｒＮが生成されやすい条件となっており、その点も考慮した条件の最適化が重要である。そこで、処理後の断面を光学顕微鏡を用いて撮像した断面組織画像を用いて、０．０４ｍｍ2の視野中での、円相当径３μｍ以上の窒化物が確認されるか否かを調べた。円相当径３μｍ以上の窒化物が１つでもあれば浸窒処理が適切でないと判断することができる。なお、ＣｒＮが生成すると、Ｎが鋼中のＣｒを消費し、マトリックスのＣｒ含有率が低下して焼入性の低下により表面硬化層の硬さが低下する。その結果狙いの強度向上効果が得られなくなるおそれがあるため、本来は、全く生成されないことが理想である。しかしながら、円相当直径で３μｍ未満のＣｒＮについては、比較的影響が小さく、後述のローラピッチング試験等によりその存在による悪影響がほぼ無視できることを確認しているため、上記の通りの判断基準とした。 In addition, the carburizing and nitriding treatment of the present invention has an increased atmospheric pressure during the nitriding treatment as compared to Patent Document 2, and due to its influence, compared with the steel material after the treatment of Patent Document 2 in the steel. It is a condition that coarse CrN is likely to be generated, and it is important to optimize the conditions in consideration of this point. Therefore, it was examined whether or not nitrides having an equivalent circle diameter of 3 μm or more in a visual field of 0.04 mm 2 were confirmed using a cross-sectional tissue image obtained by imaging the processed cross section using an optical microscope. If at least one nitride having an equivalent circle diameter of 3 μm or more is present, it can be determined that the nitriding treatment is not appropriate. In addition, when CrN produces | generates, N will consume Cr in steel, the Cr content rate of a matrix will fall, and the hardness of a surface hardening layer will fall by the hardenability fall. As a result, the target strength improvement effect may not be obtained. However, CrN having an equivalent circle diameter of less than 3 μm has a relatively small influence, and it has been confirmed by the roller pitching test described later that the adverse effects due to its existence can be almost ignored.
表２〜表５においては、上述した窒素濃度が０．３０質量％未満の場合を不適切条件として「−」で表し、窒素濃度が０．３０質量％以上であって、上述した円相当径３μｍ以上の窒化物が確認されなかった場合を適切条件として「○」で表示し、浸窒が過剰に進み、表面に侵入させたＮの一部がＣｒと結合して窒化物を形成した結果、円相当径３μｍ以上の窒化物が１つでも存在した場合は、測定した窒素濃度の値に関係なく、不適切条件として「×」で表した。 In Tables 2 to 5, when the above-mentioned nitrogen concentration is less than 0.30% by mass, it is represented by “−” as an inappropriate condition, the nitrogen concentration is 0.30% by mass or more, and the above-mentioned equivalent circle diameter The case where no nitride of 3 μm or more was confirmed is indicated as “◯” as an appropriate condition, and the result of the excessive nitriding, part of N that penetrated into the surface combined with Cr to form nitride When at least one nitride having an equivalent circle diameter of 3 μm or more was present, it was indicated as “x” as an inappropriate condition regardless of the measured nitrogen concentration value.
また、表２〜表５には、各条件ごとに前述した浸窒処理の雰囲気圧力Ｐの上限ＰＨ（Ｐａ）及び下限ＰＬ（Ｐａ）の算出手法に基づいて算出し、その値をそれぞれ「上限圧」及び「下限圧」として記載した。 In Tables 2 to 5, calculation is performed based on the calculation method of the upper limit PH (Pa) and the lower limit PL (Pa) of the atmospheric pressure P of the nitriding treatment described above for each condition. Pressure ”and“ lower limit pressure ”.
表２〜表５に示されているように、浸窒処理については、被処理材中のＣｒの含有率の値と処理温度Ｔとの関係から、上述した手法に基づいて適切な雰囲気圧力Ｐを導くことにより、９００℃〜９７０℃という高温域の処理温度Ｔの範囲内においても良好な浸窒処理を実施できることがわかる。そして、このような高温域での浸窒処理を実施できることにより、上述し実施例で示したように減圧浸炭処理と浸窒処理の処理温度を一致させることも可能となる。そのため、実際の量産においても、浸窒処理の処理温度と減圧浸炭処理の処理温度との差を極力小さくすることができ、浸炭処理温度から浸窒処理温度への降温時間の短縮と浸窒処理温度の高温化による浸窒時間の短縮の効果によって、減圧浸炭処理と浸窒処理とを連続して行う場合の総合的な処理時間を従来よりも大幅に短縮することができる。 As shown in Tables 2 to 5, with respect to the nitriding treatment, an appropriate atmospheric pressure P based on the above-described method is obtained from the relationship between the content value of Cr in the material to be treated and the treatment temperature T. From this, it can be seen that a good nitriding treatment can be carried out even within the processing temperature T in the high temperature range of 900 ° C. to 970 ° C. And since the nitriding process in such a high temperature range can be performed, it becomes possible to make the processing temperature of the reduced pressure carburizing process and the nitriding process coincide as described above. Therefore, even in actual mass production, the difference between the treatment temperature of the nitrocarburizing treatment and the treatment temperature of the reduced pressure carburizing treatment can be reduced as much as possible, shortening the cooling time from the carburizing treatment temperature to the nitriding treatment temperature, and the nitriding treatment Due to the effect of shortening the nitriding time by increasing the temperature, the total processing time in the case of continuously performing the reduced-pressure carburizing treatment and the nitriding treatment can be significantly shortened compared to the conventional case.
次に、ＣｒＮの生成がピッチング強度に及ぼすことを確認した別の実施例を示す。
＜ローラピッチング試験＞
本発明により処理した部品を歯車部品とすることを想定して、減圧浸炭浸窒処理を９５０℃にて実施し、かつ、浸窒処理の雰囲気圧力Ｐを１０００００Ｐａとした試料Ｎｏ．６、１０、１４に対してローラピッチング試験を実施した。評価基準材として、ガス浸炭を９５０℃にて実施して、浸窒処理を行わなかった試料Ｎｏ．１０に対しても同じローラピッチング試験を実施した。
Next, another example in which the generation of CrN has been confirmed to affect the pitching strength will be described.
<Roller pitching test>
Assuming that the part treated according to the present invention is a gear part, the sample No. 1 was subjected to reduced pressure carburizing and nitriding at 950 ° C. and the atmospheric pressure P of the nitriding was set to 100,000 Pa. A roller pitching test was performed on 6, 10, and 14. As an evaluation reference material, gas carburizing was performed at 950 ° C., and no nitriding treatment was performed. The same roller pitching test was carried out for 10.
ローラピッチング試験は、外径１３０ｍｍ、厚みが１８ｍｍの円盤からなる大ローラをＳＣＭ４２０浸炭材で準備し、外径２６ｍｍ、幅が２８ｍｍからなる小ローラを前記試料Ｎｏ．６、１０、１４の鋼材で機械加工により製造し、上記の浸炭処理又は減圧浸炭浸窒処理を行った後、大ローラと小ローラを、４０％の周速差をつけた状態で互いに当接させて一定の面圧をかけた状態で回転（小ローラの回転数が２０００ｒｐｍ）させることにより行った。そして、前記試料Ｎｏ．６、１０、１４を減圧浸炭浸窒処理してなる小ローラについて、１０7回転させてもピッチングが発生しない限界の面圧を測定し、基準となる浸窒処理を行わなかった試料Ｎｏ．１０と比較して、求めた限界面圧が優れる場合を良好（○）、基準よりも低い場合を不良（△）として示した。また、上述した粗大なＣｒＮの有無についても表６に示した。 In the roller pitching test, a large roller made of a disk having an outer diameter of 130 mm and a thickness of 18 mm was prepared using an SCM420 carburizing material, and a small roller having an outer diameter of 26 mm and a width of 28 mm was prepared as the sample No. 1 described above. After machining with steel materials of 6, 10, and 14 and performing the above carburizing treatment or reduced pressure carburizing and nitriding treatment, the large roller and small roller are brought into contact with each other with a difference in peripheral speed of 40%. The rotation was performed with a constant surface pressure applied (the rotation speed of the small roller was 2000 rpm). And said sample No. With respect to the small roller obtained by subjecting pressure reduction carburizing and nitriding treatment of Nos. 6, 10, and 14, the surface pressure at the limit at which pitching does not occur even after 10 7 rotations was measured. The case where the obtained critical surface pressure was excellent compared with 10 was shown as good (◯), and the case where it was lower than the standard was shown as bad (Δ). Table 6 also shows the presence or absence of coarse CrN described above.
表６から明らかなように、適切な減圧浸炭浸窒処理を行うことによって、強度低下の原因となる粗大なＣｒＮの生成を抑制しつつ、表面に窒素を所定量侵入させることができ、その結果、従来の浸炭処理で強化を図った場合に比べても、面疲労強度のさらなる向上を実現できることがわかる。 As is apparent from Table 6, by performing an appropriate reduced pressure carburizing and nitriding treatment, it is possible to allow a predetermined amount of nitrogen to enter the surface while suppressing the generation of coarse CrN that causes a decrease in strength, and as a result. It can be seen that the surface fatigue strength can be further improved as compared with the case where the strengthening is achieved by the conventional carburizing treatment.
＜ＣｒＮ生成による表面硬度への影響＞
なお、ＣｒＮの生成により面疲労強度低下の生じた原因を確認するため、試料Ｎｏ．１４について、浸窒処理を９５０℃で雰囲気圧が９００００Ｐａと１０００００Ｐａの条件で行った試験片の表面硬度を確認したところ、ＣｒＮの析出が認められなかった前者の試験片が８１３ＨＶであったのに対し、ＣｒＮの析出が認められた後者の試験片は７５７ＨＶと、ＣｒＮの析出により、大きな硬度低下が起きることを確認できた。従って、この硬度低下の影響により面疲労強度が低下したものと推定される。
<Influence on surface hardness by CrN generation>
In order to confirm the cause of the decrease in the surface fatigue strength due to the formation of CrN, sample No. No. 14, the surface hardness of a test piece obtained by performing nitriding treatment at 950 ° C. and atmospheric pressures of 90000 Pa and 100000 Pa was confirmed. On the other hand, the latter test piece in which the precipitation of CrN was recognized was 757 HV, and it was confirmed that the hardness was greatly reduced by the precipitation of CrN. Therefore, it is presumed that the surface fatigue strength is reduced due to the influence of the hardness reduction.
Ｓ 条件設定範囲 S Condition setting range
Claims (2)
上記浸窒処理は、９００℃〜９７０℃の処理温度Ｔ（℃）の範囲内であって、雰囲気圧力Ｐ（Ｐａ）が、下記のＰＨ１とＰＨ２のうち低い値からなる上限ＰＨ（Ｐａ）と、下記のＰＬ１とＰＬ２のうちの低い値からなる下限ＰＬ（Ｐａ）の範囲内の条件で行うことを特徴とする鋼材の減圧浸炭浸窒処理方法。
ＰＨ１＝１０００００（Ｐａ）
ＰＨ２＝−４０５００×［Ｃｒ］＋２０５×Ｔ−３００００（Ｐａ）
ＰＬ１＝７２０００（Ｐａ）
ＰＬ２＝（−６５．１×Ｔ＋５１０００）×［Ｃｒ］＋Ｔ×４６４−３５６１５０（Ｐａ）
（ただし、［Ｃｒ］は鋼材におけるＣｒ含有率（質量％）） Low-pressure carburization using a mass production furnace as a heat treatment furnace for continuously performing a low-pressure carburizing treatment and a nitrocarburizing treatment on a steel material containing 0.18 to 2.00 mass% Cr. Nitrogen treatment method,
The above nitriding treatment is within the range of the treatment temperature T (° C.) of 900 ° C. to 970 ° C., and the atmospheric pressure P (Pa) is an upper limit PH (Pa) having a lower value of the following PH1 and PH2. A reduced-pressure carburizing and nitriding method for steel material, which is performed under conditions within a range of a lower limit PL (Pa) consisting of a lower value of PL1 and PL2 below.
PH1 = 100000 (Pa)
PH2 = −40500 × [Cr] + 205 × T-30000 (Pa)
PL1 = 72000 (Pa)
PL2 = (− 65.1 × T + 51000) × [Cr] + T × 464-356150 (Pa)
(However, [Cr] is the Cr content in steel (mass%))
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| JPH11158601A (en) * | 1997-12-01 | 1999-06-15 | Nippon Seiko Kk | Production of rolling member |
| JP2016517916A (en) * | 2013-04-17 | 2016-06-20 | エーエルデー・バキューム・テクノロジーズ・ゲーエムベーハーＡＬＤ Ｖａｃｕｕｍ Ｔｅｃｈｎｏｌｏｇｉｅｓ ＧｍｂＨ | Process and apparatus for thermochemically strengthening a workpiece |
| JP2014234552A (en) * | 2013-06-05 | 2014-12-15 | 大同特殊鋼株式会社 | Carburized component and method of manufacturing the same |
| JP2015010250A (en) * | 2013-06-27 | 2015-01-19 | 愛知製鋼株式会社 | Vacuum carbonitriding method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115747620A (en) * | 2022-10-26 | 2023-03-07 | 河钢股份有限公司 | Vacuum smelting method for precisely controlling nitrogen in gas-phase nitriding for smelting nitrogen-containing steel |
| CN115747620B (en) * | 2022-10-26 | 2023-11-21 | 河钢股份有限公司 | Vacuum smelting method for smelting nitrogen-containing steel by gas phase nitriding with accurate nitrogen control |
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| JP2018154885A (en) | 2018-10-04 |
| WO2018173588A1 (en) | 2018-09-27 |
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