JP3862790B2

JP3862790B2 - High pressure fuel injection pipe material and method for manufacturing the same

Info

Publication number: JP3862790B2
Application number: JP28010196A
Authority: JP
Inventors: 正佳臼井
Original assignee: Usui Co Ltd
Current assignee: Usui Co Ltd
Priority date: 1996-10-01
Filing date: 1996-10-01
Publication date: 2006-12-27
Anticipated expiration: 2016-10-01
Also published as: JPH10103188A

Description

【０００１】
【発明の属する技術分野】
本発明は内燃機関の燃料供給路として使用する燃料噴射管の管材およびその製造方法に係り、より詳しくは一般にディーゼル内燃機関に使用する管径約４ｍｍ乃至１５ｍｍ、肉厚約１ｍｍ乃至６ｍｍ程度の比較的細径厚肉で内圧疲労強度および振動疲労強度の高い高圧燃料噴射管材およびその製造方法に関する。
【０００２】
【従来の技術】
近年、ディーゼルエンジンの排ガス規制によるＮＯｘの低減や黒煙対策としての燃料の高圧化の傾向に伴い、高圧燃料噴射管には繰返し高圧力疲労に対する耐久性（内圧疲労強度）および耐キャビテーションエロージョン性に加え、エンジンや車体からの振動に対する耐久性（振動疲労強度）が一層要求されている。かかる要求のために従来のディーゼル内燃機関用の高圧燃料噴射管には、外径に対し２５乃至４０％の肉厚を有する厚肉の細径鋼管が用いられている。
【０００３】
従来のこれら高圧燃料噴射管材には、▲１▼高圧配管用素管を数回の焼鈍と引抜加工を繰返して所望の規定寸法に伸管し、この最終仕上げ伸管材に対し焼鈍処理を施さない管材と、▲２▼高圧配管用素管を数回の焼鈍と引抜加工を繰返して所望の規定寸法に伸管した後、焼鈍処理を施した管材の２種類あって、いずれも最終引抜加工は３０〜４０％の減面率で伸管している。すなわち、▲１▼は引抜により加工硬化したまま使用する管材であり、バウシンガ効果により外表面側の硬度が高くなることにより引張強度が高くなり、高振動疲労強度を有する反面、内圧に対する疲労強度は低い。この内圧に対する疲労強度が低い理由は、管内表面側も引抜加工により一方向に圧延されたと同様な偏平な結晶組織となっていることおよび、引抜加工による残留応力が残っていることがその原因と考えられている。一方、▲２▼の引抜加工後焼鈍して使用する管材の場合は、焼鈍により組織が再結晶組織となり、また加工による残留応力が消失することにより、内圧疲労強度は高いが、加工硬化組織がほとんど除去されることにより管外表面側の硬度が低下するため、振動疲労強度は加工硬化状態より低くなる。なお、バウシンガ効果とは、加工硬化した材料の変形抵抗、すなわち予変形と同一方向の降伏応力に比較して、その材料を逆方向に変形するときの降伏応力が大きく低下する現象のことであり、疲労硬化、疲労軟化に直接結びつく現象である。
【０００４】
【発明が解決しようとする課題】
本発明は従来の前記▲１▼の引抜により加工硬化したまま使用する管材（未焼鈍材）と、▲２▼の引抜加工後焼鈍して使用する管材（焼鈍材）の欠点を解消するためになされたもので、最終引抜加工工程における減面率を変えることによって、最終引抜加工後に焼鈍処理することなく振動疲労強度および内圧疲労強度の優れた高圧燃料噴射管材を得ることを目的とするものである。
【０００５】
【課題を解決するための手段】
本発明に係る高圧燃料噴射管材は、最終仕上伸管を減面率１．２〜６．４％にて空引きした単一管」体からなる細径厚肉金属管であって、外表面部組織が圧延組織となしかつ外表面部が加工硬化されて高い振動疲労強度を有することを特徴とするものである。また、この高圧燃料噴射管材の製造方法としては、単一管体からなる細径厚肉金属鋼管を焼鈍と引抜加工を施して管内外径を所定の最終寸法に仕上げ、該最終仕上伸管の焼鈍処理を施さない高圧燃料噴射管材の製造方法において、最終仕上工程にて当該伸管材を減面率１．２〜６．４％にて空引きして外表面部組織を圧延組織とするとともに加工硬化させて外表面部の振動疲労強度を高めることを特徴とするものである。
【０００６】
引抜加工による伸管材の場合、振動疲労強度に一義的に大きな影響を与えるのは管の外表面側であり、内圧疲労強度に大きな影響を与えるのは管の内表面側であることから、振動疲労強度および内圧疲労強度の優れた高圧噴射管材を得るには、管の外表面側を圧延組織（加工組織）とし、内表面側を焼鈍状態のままとすることが有効であるとの知見に基づいて、最終仕上伸管を管の内表面側に加工の影響が出ないように外表面のみを軽く引抜加工することにより、管の内圧疲労強度を保有した状態で振動疲労強度を向上させることができることを見い出したのである。
【０００７】
すなわち、本発明では最終仕上伸管を減面率１．２〜６．４％にて空引きすることにより、振動疲労強度については管外周側がバウシンガ効果を有した状態で、管内周側が焼鈍状態と同じ内圧疲労強度を保有することができる管材を見い出したのである。ここで、空引きとは管を外側からダイスで絞って外径を小さくすることを意味し、この最終仕上伸管の空引きの減面率を１．２〜６．４％に限定したのは、１．２％未満では管外側の加工による硬さが不足し、所望の振動疲労強度が得られず、他方、６．４％を超えると管外側は十分に硬化し、振動疲労強度は向上するが、管の内側まで加工の影響が生じて硬化し、管内表面側の硬度が高くなり内圧疲労強度が低下するためである。したがって、最終仕上伸管を減面率１．２〜６．４％にて空引きした場合には、管の外側においては加工の影響により圧延組織（加工組織）となり、また加工硬化するが、内側は加工の影響が出ないことにより最終引抜加工前の焼鈍状態のままとなり、引抜加工後焼鈍処理せずして振動疲労強度および内圧疲労強度の優れた高圧噴射管材が得られる。
【０００８】
また、本発明に係る高圧燃料噴射管材の製造方法は、単一管体からなる細径厚肉金属鋼管を焼鈍と引抜加工を施して管内外径を所定の最終寸法に仕上げる際に、最終仕上工程における当該伸管を減面率１．２〜６．４％にて空引きし、引抜加工後は焼鈍処理を施さない方法であるが、引抜加工前の焼鈍処理は素管の組織を再結晶組織とし、また引抜加工による残留応力を消失させるためであり、その熱処理温度条件としては７５０〜９００℃程度が一般的である。
【０００９】
なお、本発明の対象鋼としては、炭素鋼（ＳＴＳ３５）、ステンレス鋼、マンガン鋼等がある。
【００１０】
【発明の実施の形態】
本発明の高圧燃料噴射管材の製造方法は、単一管体からなる細径厚肉金属鋼管を焼鈍と引抜加工を複数回繰返し、最終の伸管工程において減面率１．２〜６．４％にて空引きして所定製品管サイズに仕上げて、振動疲労強度および内圧疲労強度の優れた高圧噴射管材を得る方法である。
【００１１】
例えば、直径３４ｍｍ×肉厚４．５ｍｍの母管から製品管サイズの直径６．４ｍ×肉厚４．６ｍｍに引抜加工する場合は、まず母管を焼鈍炉で８００℃の温度で焼鈍し、第１伸管工程にて直径２７ｍｍ×肉厚３．７ｍｍに伸管する。続いて、この管材を再び焼鈍炉で８００℃の温度で焼鈍した後、第２伸管工程にて直径２２ｍｍ×肉厚３．２ｍｍに伸管する。以後同様に各伸管工程毎に８００℃焼鈍を繰返し、最終伸管工程で減面率１．２〜６．４％にて空引きして製品管サイズ直径６．４ｍｍ×肉厚２．３ｍｍに伸管する。これにより、管外側はバウシンガ効果により高い振動疲労強度を有し、管内側は組織の再結晶化と残留応力の消失により硬度が低下することにより内圧疲労強度を保有した高圧燃料噴射管材が得られる。このようにして得られた製品管サイズの管材は切断工程で製品長さに切断した後、メッキ工程、曲げ工程等を経て製品となる。
【００１２】
【実施例】
噴射管素材として材質ＳＴＳ３５、外径３４ｍｍ、肉厚４．５ｍｍの母管（シームレスパイプ）を使用し、焼鈍および伸管を繰返して最終伸管工程において減面率１．２〜６．４％にて空引きして得た製品サイズが外径６．４ｍｍ、肉厚２．３ｍｍの高圧燃料噴射管材の振動疲労強度を表１に、従来の未焼鈍材と比較して示す。表１中、従来品Ａは引抜により加工硬化したまま使用する管材（未焼鈍材）、同Ｂは最終引抜加工後焼鈍して使用する管材（焼鈍材）のことである。また、本実施例における本発明の減面率別の管外面からの距離と硬度の関係を、従来品Ａと比較して図１に示す。
なお、振動疲労強度試験は、所望長さの管材の一端を固定し、他端を振動付与ロールにてクランプして管材に上下振動（片振幅δ＝３．５ｍｍ）を付与し、破断までの振動の繰返し数を測定する方法により行った。
【００１３】
表１より、本発明品▲１▼〜▲４▼は従来品Ａ、Ｂと比較していずれも振動疲労強度および内圧疲労強度の両特性が高いことがわかる。また、図１より明らかなごとく、従来の通常伸管・未焼鈍材Ａの場合は、管外表面側および内表面側共にＨｍｖ２２０程度と高硬度となっていることから、振動疲労強度は高いが、内圧疲労強度は低い。これに対し、本発明品▲１▼〜▲４▼はすべて管外表面硬度は従来品Ａよりは低いものの高レベルにあることから高振動疲労強度が得られ、また管内表面硬度はＨｍｖ１２０〜１４０の範囲にあることから、従来品Ｂの焼鈍材の硬度（全体がＨｍｖ１２０〜１３５）とほぼ同程度となっていることから、管内表面は加工の影響を受けることなく内圧疲労強度が保有されることがわかる。また、減面率が１．２％未満では管外表面付近の硬度がＨｍｖ１４０以下に下がることが予想されることから振動疲労強度の向上効果は期待できず、他方、減面率が６．４％では管外面から２．０ｍｍすなわち管内表面から０．３ｍｍの所までもＨｍｖ１４０程度となっていることから、６．４％を超える減面率で空引きすれば管内表面に対する加工の影響が大きくなることが十分に予想されるため、空引きの最大減面率は６．４％が限度であることがわかる。
【００１４】
【表１】

【００１５】
【発明の効果】
以上説明したごとく、本発明の高圧燃料噴射管材は、内圧疲労強度のみならず高い振動疲労強度に富み、繰返し高圧力疲労に対する耐久性（内圧疲労強度）に優れるとともに、エンジンや車体からの振動に対する耐久性にも優れるという効果を有する。また、本発明方法によれば、既存の伸管設備と一般的な焼鈍設備で引抜工程を増加させることなく高内圧疲労強度と高振動疲労強度を有する高圧燃料噴射管材を得ることができるので、製造コストが高くつくことがなく、高品質の高圧燃料噴射管材を低コストで提供することができるという優れた効果を奏する。
【図面の簡単な説明】
【図１】本発明の実施例における最終引抜工程での減面率別の管外面からの距離と硬度の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pipe material of a fuel injection pipe used as a fuel supply path of an internal combustion engine and a method for manufacturing the same, and more particularly, a comparison of a pipe diameter of about 4 mm to 15 mm and a wall thickness of about 1 mm to 6 mm generally used for a diesel internal combustion engine. TECHNICAL FIELD The present invention relates to a high-pressure fuel injection pipe material having a small and thick diameter and high internal pressure fatigue strength and vibration fatigue strength, and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, with the trend of reducing NOx due to exhaust gas regulations of diesel engines and increasing the pressure of fuel as a measure against black smoke, high-pressure fuel injection pipes have improved durability against high-pressure fatigue (internal pressure fatigue strength) and resistance to cavitation erosion. In addition, durability (vibration fatigue strength) against vibrations from the engine and the vehicle body is further required. In order to meet such demands, a high-pressure fuel injection pipe for a conventional diesel internal combustion engine uses a thick thin steel pipe having a thickness of 25 to 40% with respect to the outer diameter.
[0003]
In these conventional high-pressure fuel injection pipe materials, (1) the high-pressure piping base pipe is repeatedly annealed and drawn several times to the desired specified dimensions, and the final finished drawn pipe material is not annealed. There are two types of pipe materials: (2) tube material for high-pressure piping, pipes that have been annealed several times after being repeatedly annealed and drawn several times, and then subjected to annealing treatment. The tube is drawn with a reduction in area of 30 to 40%. That is, (1) is a tube material that is used while being work hardened by drawing, and the tensile strength is increased by increasing the hardness on the outer surface side due to the Bauschinger effect, while it has high vibration fatigue strength, but the fatigue strength against internal pressure is Low. The reason why the fatigue strength with respect to the internal pressure is low is that the inner surface of the tube has a flat crystal structure similar to that rolled in one direction by drawing, and the residual stress due to drawing remains. It is considered. On the other hand, in the case of the pipe material that is used after annealing after drawing process (2), the structure becomes a recrystallized structure due to annealing, and the residual stress due to processing disappears. Since the hardness on the outer surface side of the tube is lowered by being almost removed, the vibration fatigue strength becomes lower than that in the work hardening state. The Bauschinger effect is a phenomenon in which the yield stress when deforming the material in the opposite direction is greatly reduced compared to the deformation resistance of the work-hardened material, that is, the yield stress in the same direction as the pre-deformation. It is a phenomenon directly related to fatigue hardening and fatigue softening.
[0004]
[Problems to be solved by the invention]
The present invention eliminates the disadvantages of the conventional pipe material (unannealed material) that is used while being worked and hardened by drawing (1) and the pipe material (annealed material) that is used after annealing (2). The purpose of this is to obtain a high-pressure fuel injection pipe material with excellent vibration fatigue strength and internal pressure fatigue strength without annealing after the final drawing process by changing the area reduction rate in the final drawing process. is there.
[0005]
[Means for Solving the Problems]
The high-pressure fuel injection tube material according to the present invention is a thin metal tube having a small diameter and a thick metal pipe composed of a single pipe body obtained by emptying the final finished drawn pipe at a surface area reduction ratio of 1.2 to 6.4%. part tissue in which no a rolled structure and the outer surface is characterized by having a high vibration fatigue strength are work hardened. In addition, as a method of manufacturing this high-pressure fuel injection pipe material, a thin and thick metal steel pipe made of a single pipe body is annealed and drawn to finish the pipe inner and outer diameters to a predetermined final dimension, and the final finished drawn pipe In the manufacturing method of the high-pressure fuel injection tube material that is not subjected to the annealing treatment, the outer surface portion structure is made a rolled structure by emptying the drawn tube material at a surface reduction ratio of 1.2 to 6.4% in the final finishing step. It is characterized by increasing the vibration fatigue strength of the outer surface by work hardening .
[0006]
In the case of drawn pipes by drawing, the vibration fatigue strength is primarily influenced by the outer surface side of the pipe, and the internal pressure fatigue strength is greatly influenced by the inner surface side of the pipe. In order to obtain a high-pressure jet tube material with excellent fatigue strength and internal pressure fatigue strength, it is effective to keep the outer surface side of the tube as a rolled structure (processed structure) and leave the inner surface side in an annealed state. Based on this, the fatigue fatigue strength can be improved while maintaining the internal pressure fatigue strength of the tube by lightly drawing only the outer surface so that the final finished drawn tube is not affected by the processing on the inner surface side of the tube. I found out that I could do it.
[0007]
That is, in the present invention, the final finished drawn pipe is emptied at a surface area reduction ratio of 1.2 to 6.4%, so that the vibration fatigue strength is in a state where the outer peripheral side of the pipe has a Bauschinger effect and the inner peripheral side of the pipe is annealed. As a result, they have found a pipe material that can possess the same internal pressure fatigue strength. Here, empty drawing means that the outer diameter is reduced by squeezing the tube with a die from the outside, and the area reduction rate of empty drawing of this final finished drawn tube is limited to 1.2 to 6.4%. Is less than 1.2%, the hardness due to processing on the outside of the tube is insufficient, and the desired vibration fatigue strength cannot be obtained. On the other hand, if it exceeds 6.4%, the outside of the tube is sufficiently cured, and the vibration fatigue strength is Although it improves, it hardens | cures by producing the influence of a process to the inner side of a pipe | tube, the hardness of the pipe inner surface side becomes high, and internal pressure fatigue strength falls. Therefore, when the final finished drawn pipe is emptied at a surface area reduction ratio of 1.2 to 6.4%, the outside of the pipe becomes a rolled structure (working structure) due to the influence of processing, and work hardening occurs. Since the inside is not affected by the processing, it remains in the annealed state before the final drawing process, and a high-pressure injection pipe material excellent in vibration fatigue strength and internal pressure fatigue strength can be obtained without annealing after the drawing process.
[0008]
In addition, the method for producing a high-pressure fuel injection pipe according to the present invention provides a final finish when a thin and thick metal steel pipe comprising a single pipe body is annealed and drawn to finish the pipe inner and outer diameters to a predetermined final dimension. In this process, the drawn pipe is emptied at a surface area reduction ratio of 1.2 to 6.4% and is not subjected to an annealing process after the drawing process. This is to make the crystal structure and to eliminate the residual stress due to the drawing process, and the heat treatment temperature condition is generally about 750 to 900 ° C.
[0009]
The target steel of the present invention includes carbon steel (STS35), stainless steel, manganese steel and the like.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing a high-pressure fuel injection pipe material of the present invention, a thin steel metal pipe having a small diameter is repeatedly annealed and drawn several times, and the area reduction rate is 1.2 to 6.4 in the final drawing process. This is a method for obtaining a high-pressure jet pipe material excellent in vibration fatigue strength and internal pressure fatigue strength by emptying in% and finishing to a predetermined product pipe size.
[0011]
For example, when drawing from a diameter of 34 mm × wall thickness of 4.5 mm to a product tube size diameter of 6.4 m × wall thickness of 4.6 mm, the mother tube is first annealed at a temperature of 800 ° C. in an annealing furnace, In the first drawing process, the tube is drawn to a diameter of 27 mm and a wall thickness of 3.7 mm. Subsequently, the pipe material is annealed again at a temperature of 800 ° C. in an annealing furnace, and then drawn to a diameter of 22 mm × a thickness of 3.2 mm in a second drawing process. Thereafter, annealing at 800 ° C. is repeated for each drawing process in the same manner, and in the final drawing process, the tube is evacuated at a surface area reduction ratio of 1.2 to 6.4% to obtain a product pipe size diameter of 6.4 mm × wall thickness of 2.3 mm. To tube. As a result, the outer tube has high vibration fatigue strength due to the Bauschinger effect, and the inner tube has a low pressure due to recrystallization of the structure and disappearance of residual stress, thereby obtaining a high-pressure fuel injection tube material having internal pressure fatigue strength. . The tube material of the product tube size obtained in this way is cut into a product length in a cutting process, and then becomes a product through a plating process, a bending process, and the like.
[0012]
【Example】
Using a STS35 material, a 34mm outer diameter and 4.5mm wall pipe (seamless pipe) as the injection tube material, annealing and drawing are repeated, and the area reduction rate is 1.2 to 6.4% in the final drawing process. Table 1 shows the vibration fatigue strength of a high-pressure fuel injection pipe material having an outer diameter of 6.4 mm and a wall thickness of 2.3 mm, which is obtained by evacuation in comparison with a conventional unannealed material. In Table 1, the conventional product A is a pipe material (unannealed material) used while being work-hardened by drawing, and B is a pipe material (annealed material) used after annealing after the final drawing process. In addition, the relationship between the distance from the pipe outer surface and the hardness according to the area reduction ratio of the present invention in the present embodiment is shown in FIG.
In the vibration fatigue strength test, one end of a pipe material having a desired length is fixed, the other end is clamped by a vibration applying roll, and vertical vibration (single amplitude δ = 3.5 mm) is applied to the pipe material. This was done by measuring the number of vibration repetitions.
[0013]
From Table 1, it can be seen that the products (1) to (4) of the present invention have higher characteristics of both vibration fatigue strength and internal pressure fatigue strength than the conventional products A and B. Further, as apparent from FIG. 1, in the case of the conventional normal drawn / unannealed material A, both the outer surface side and the inner surface side have a high hardness of about Hmv 220, so the vibration fatigue strength is high. The internal pressure fatigue strength is low. On the other hand, all the products (1) to (4) of the present invention have high vibration fatigue strength because the outer surface hardness of the tube is lower than that of the conventional product A, but high vibration fatigue strength is obtained, and the inner surface hardness of the tube is Hmv120 to 140. Therefore, since the hardness of the annealed material of the conventional product B (the whole is Hmv120 to 135) is almost the same, the inner surface of the pipe is not affected by the processing and has internal pressure fatigue strength. I understand that. In addition, if the area reduction rate is less than 1.2%, the hardness near the outer surface of the pipe is expected to be lowered to Hmv140 or less, so that the effect of improving the vibration fatigue strength cannot be expected, while the area reduction rate is 6.4. %, It is about Hmv140 from the outer surface of the tube to 2.0 mm, that is, 0.3 mm from the inner surface of the tube. Therefore, if the area is reduced by over 6.4%, the processing effect on the inner surface of the tube is large. Therefore, it can be seen that the maximum area reduction rate for emptying is 6.4%.
[0014]
[Table 1]

[0015]
【The invention's effect】
As described above, the high-pressure fuel injection pipe material of the present invention is rich not only in internal pressure fatigue strength but also in high vibration fatigue strength, excellent in durability against repeated high pressure fatigue (internal pressure fatigue strength), and with respect to vibration from the engine and the vehicle body. It has the effect of excellent durability. Further, according to the method of the present invention, it is possible to obtain a high-pressure fuel injection pipe material having a high internal pressure fatigue strength and a high vibration fatigue strength without increasing the drawing process in existing drawing equipment and general annealing equipment, There is an excellent effect that a high-quality high-pressure fuel injection pipe material can be provided at low cost without being expensive.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the distance from the outer surface of a pipe and the hardness according to the area reduction rate in the final drawing step in an embodiment of the present invention.

Claims

A small diameter thick metal tube made of a single tube which is sinking the final finish Shinkan at a reduction of area of 1.2 to 6.4%, without outer surface organization and rolled structure and the outer surface high-pressure fuel injection pipe material but characterized by having a high vibration fatigue strength are work hardened.

In a manufacturing method of a high-pressure fuel injection pipe material in which a thin-walled metal steel pipe made of a single pipe body is annealed and drawn to finish the inner and outer diameters of the pipe to a predetermined final dimension, and the final finished drawn pipe is not annealed. at the final finishing step by sinking the outer surface tissue is work hardening together when the rolling tissue at a reduction of area of 1.2 to 6.4% the Shinkan material vibration fatigue strength of the outer surface portion A method for producing a high-pressure fuel injection pipe material characterized by comprising the steps of: