JP2012177154A - High-carbon steel pipe excellent in cold workability, machinability and hardenability, and method for producing the same - Google Patents
High-carbon steel pipe excellent in cold workability, machinability and hardenability, and method for producing the same Download PDFInfo
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- 229910000677 High-carbon steel Inorganic materials 0.000 title claims abstract description 41
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 20
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 63
- 239000010959 steel Substances 0.000 claims abstract description 63
- 229910001567 cementite Inorganic materials 0.000 claims abstract description 47
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 claims abstract description 47
- 239000002245 particle Substances 0.000 claims abstract description 38
- 238000005096 rolling process Methods 0.000 claims abstract description 26
- 239000000203 mixture Substances 0.000 claims abstract description 19
- 230000009467 reduction Effects 0.000 claims abstract description 18
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 11
- 230000001186 cumulative effect Effects 0.000 claims abstract description 8
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 230000009466 transformation Effects 0.000 claims description 17
- 238000000034 method Methods 0.000 claims description 12
- 229910052804 chromium Inorganic materials 0.000 claims description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 229910052758 niobium Inorganic materials 0.000 claims description 7
- 229910052721 tungsten Inorganic materials 0.000 claims description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
- 239000011159 matrix material Substances 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 abstract description 15
- 239000000463 material Substances 0.000 abstract description 13
- 238000000137 annealing Methods 0.000 abstract description 8
- 229910052748 manganese Inorganic materials 0.000 abstract description 4
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 3
- 229910052698 phosphorus Inorganic materials 0.000 abstract description 3
- 238000002791 soaking Methods 0.000 abstract description 2
- 230000000694 effects Effects 0.000 description 22
- 238000005520 cutting process Methods 0.000 description 20
- 239000000047 product Substances 0.000 description 11
- 238000010791 quenching Methods 0.000 description 8
- 230000000171 quenching effect Effects 0.000 description 8
- 239000006185 dispersion Substances 0.000 description 7
- 238000003466 welding Methods 0.000 description 7
- 230000006698 induction Effects 0.000 description 6
- 230000006872 improvement Effects 0.000 description 5
- 150000001247 metal acetylides Chemical class 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 238000004581 coalescence Methods 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 238000005482 strain hardening Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 239000011800 void material Substances 0.000 description 3
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 239000013585 weight reducing agent Substances 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 238000010622 cold drawing Methods 0.000 description 1
- 238000010273 cold forging Methods 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
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- 238000011156 evaluation Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
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Abstract
Description
本発明は、自動車のラックピニオン型ステアリング装置等に組み込まれるステアリングラックバー、あるいはステアリングシャフト、ドライブシャフト等の自動車部品用として好適な、高炭素鋼管およびその製造方法に係り、とくに、冷間加工性、被削性および焼入れ性の向上に関する。 TECHNICAL FIELD The present invention relates to a high carbon steel pipe suitable for use in automobile parts such as a steering rack bar or a steering shaft and a drive shaft incorporated in a rack and pinion type steering device of an automobile, and a manufacturing method thereof. It relates to improvement of machinability and hardenability.
近年の、地球環境の保全という観点から自動車の燃費改善が強く要望され、自動車車体の軽量化が進められている。このような自動車車体の軽量化要求から、自動車のハンドルの動きを車輪に伝達するステアリング装置に組み込まれる、例えば、ステアリングラックバー、ステアリングシャフトなどのステアリング関連部品、あるいは、エンジンの動力を車輪に伝達する、例えばドライブシャフトなどの駆動軸関連部品、においても、棒鋼を用いた中実タイプに代えて、鋼管を用いた中空タイプが採用されるようになっている。 In recent years, there has been a strong demand for improving the fuel efficiency of automobiles from the viewpoint of protecting the global environment, and the weight reduction of automobile bodies has been promoted. In response to such demands for reducing the weight of automobile bodies, steering-related parts such as steering rack bars and steering shafts, or engine power transmitted to wheels, are incorporated into steering devices that transmit the movement of automobile handles to wheels. For example, in a drive shaft related part such as a drive shaft, a hollow type using a steel pipe is adopted instead of a solid type using a steel bar.
ステアリングラックバー、ステアリングシャフト、あるいはドライブシャフト等の素材として使用される鋼管には、冷間引抜加工、冷間プレスあるいは冷間鍛造などの、冷間加工が施され、さらに切削加工が施されて、最終部品形状とされ、さらにその後、部品としての所定の強度を付与するために、焼入れ処理が施される場合が多い。
例えば、中空ステアリングラックバーでは、非特許文献１に記載されるように、高炭素鋼管を素材として、冷間で管上面部に平坦部を加工し、ついで該平坦部に切削加工で歯型を形成し最終形状としたのち、高周波焼入れを施して、所定の強度を付与され製品とされる。このように、中空ステアリングラックバーの素材である鋼管には、冷間加工、切削加工、焼入れ処理が施されるため、冷間加工性、被削性および焼入れ性に優れる鋼管であることが要求される。
Steel pipes used as materials for steering rack bars, steering shafts, drive shafts, etc. are subjected to cold working such as cold drawing, cold pressing or cold forging, and further subjected to cutting. In many cases, a final part shape is formed, and then a quenching process is performed to give a predetermined strength as a part.
For example, in a hollow steering rack bar, as described in Non-Patent Document 1, a high carbon steel pipe is used as a raw material, a flat part is machined on the upper surface of the pipe in a cold state, and then a tooth mold is formed by cutting on the flat part. After the final shape is formed, induction hardening is performed to give a predetermined strength to obtain a product. As described above, since the steel pipe that is the material of the hollow steering rack bar is subjected to cold working, cutting, and quenching, it is required to be a steel pipe that is excellent in cold workability, machinability, and hardenability. Is done.
所定の部品強度を焼入れ処理により確保するためには、素材鋼管のＣ含有量を高くする必要がある。しかし、Ｃ含有量を高くすると冷間加工性が低下する。このため、従来から、高炭素鋼では球状化焼鈍を行い、強度を低下させることが行われていた。しかし、球状化焼鈍では、約700℃で数時間という長時間の熱処理となり、生産性が低下し、製造コストが高騰するという問題がある。 In order to ensure a predetermined part strength by quenching, it is necessary to increase the C content of the material steel pipe. However, when the C content is increased, the cold workability is lowered. For this reason, conventionally, high carbon steel has been subjected to spheroidizing annealing to reduce the strength. However, the spheroidizing annealing has a problem that the heat treatment takes a long time of about 700 ° C. for several hours, the productivity is lowered, and the manufacturing cost is increased.
このような問題に対し、例えば特許文献１には、２％以下のＣを含有する鋼をＡc１点以上に加熱したのち、熱間圧延における仕上圧延前に、（Ａr１−50℃）以下（Ａr１−200℃）以上の温度域まで冷却し、その後引き続いて仕上圧延により10％以上の塑性変形を加え、それによって発生する変形熱により、再びＡc３点以下Ａc１−100℃以上の温度域に到着せしめ、その後、Ａe１点以下500℃以上の温度域に７分以上保持して球状化組織を得る棒鋼の製造方法が記載されている。特許文献１に記載された技術では、仕上圧延前に一旦炭化物を生成させ、仕上圧延によって炭化物を変形破壊すると同時に変形熱による昇温により炭化物の分断を図り、その後の冷却、恒温保持で炭化物の球状化を図るとしている。特許文献１に記載された技術によれば、圧延ままで球状化組織が得られるため、その後の球状化焼鈍時間を大幅に短縮でき、用途によっては球状化焼鈍を完全に省略することも可能であるとしている。 In order to solve such a problem, for example, in Patent Document 1, a steel containing 2% or less of C is heated to Ac 1 point or more and then (Ar 1 -50 ° C.) or less before finish rolling in hot rolling. (Ar 1 -200 ℃) cooled to a temperature above range, followed by finish rolling by a plastic deformation of 10% or more then added, whereby the deformation heat generated, less Ac 1 -100 ° C. or more again Ac 3 point There is described a method for producing a bar steel which arrives at a temperature range and then holds it in a temperature range of Ae 1 point or less and 500 ° C. or more for 7 minutes or more to obtain a spheroidized structure. In the technique described in Patent Document 1, carbide is once generated before finish rolling, and the carbide is deformed and fractured by finish rolling, and at the same time, the carbide is divided by temperature rise by deformation heat, and then the carbide is cooled and maintained at a constant temperature. It is going to be spheroidized. According to the technique described in Patent Document 1, since a spheroidized structure can be obtained as it is rolled, the subsequent spheroidizing annealing time can be significantly shortened, and depending on the application, spheroidizing annealing can be omitted completely. There is.
また、特許文献２には、質量％で、Ｃ：0.25〜0.50％、Si：0.35％以下、Mn：0.60〜1.59％、Ｓ：0.0025％以下、Ｐ：0.010％以下を含む鋼管に、（Ａc１変態点温度−20℃）〜（Ａc１変態点温度）に加熱し、その温度で所定時間保持したのち空冷するか、あるいは（Ａc１変態点温度）〜（Ａc１変態点温度＋30℃）に加熱し、その温度で所定時間保持したのち、0.01〜1.0℃/s で（Ａr１変態点−20℃）〜（Ａr１変態点）の温度まで冷却し、その後空冷するか、あるいはその温度で所定時間保持したのち空冷する、冷間加工性と焼入れ性に優れた電縫鋼管の製造方法が記載されている。特許文献２に記載された技術によれば、良好な冷間加工性と、焼入れによる十分な強度上昇が得られる良好な焼入れ性を有する電縫鋼管が得られるとしている。 Patent Document 2 discloses a steel pipe containing, by mass%, C: 0.25 to 0.50%, Si: 0.35% or less, Mn: 0.60 to 1.59%, S: 0.0025% or less, and P: 0.010% or less (Ac Heat to 1 transformation point temperature -20 ° C to (Ac 1 transformation point temperature) and hold at that temperature for a predetermined time and then air cool or (Ac 1 transformation point temperature) to (Ac 1 transformation point temperature + 30 ° C) And then, at a temperature of 0.01 to 1.0 ° C./s, cooled to a temperature of (Ar 1 transformation point −20 ° C.) to (Ar 1 transformation point) and then air cooled or the temperature And a method for producing an electric-welded steel pipe excellent in cold workability and hardenability that is air-cooled after being held for a predetermined time. According to the technique described in Patent Document 2, it is said that an electric-welded steel pipe having good cold workability and good hardenability capable of obtaining a sufficient strength increase by quenching can be obtained.
しかしながら、特許文献１に記載された技術では、炭化物の球状化にともなって生じる、高周波焼入れ性の低下や、切削抵抗の増加による切削工具の寿命低下、仕上げ面の劣化などの問題は依然として残されたままとなっている。また、特許文献２に記載された技術では、冷間加工性、焼入れ性は向上するが、切削抵抗の増加による切削工具の寿命低下、仕上げ面の劣化など、被削性低下という問題が、依然として残されたままとなっている。 However, the technique described in Patent Document 1 still has problems such as a decrease in induction hardenability, a decrease in the life of a cutting tool due to an increase in cutting resistance, and a deterioration in the finished surface caused by the spheroidization of carbides. It has been left. Further, in the technique described in Patent Document 2, cold workability and hardenability are improved, but there are still problems of lower machinability such as a reduction in the life of the cutting tool due to an increase in cutting resistance and a deterioration in the finished surface. It is left behind.
本発明は、かかる従来技術の問題を有利に解決し、優れた冷間加工性、被削性および焼入れ性を兼備した、高炭素電縫鋼管およびその製造方法を提供することを目的とする。 It is an object of the present invention to provide a high carbon electric resistance welded steel pipe and a method for producing the same, which advantageously solves the problems of the prior art and has excellent cold workability, machinability and hardenability.
本発明者らは、上記した目的を達成するために、高炭素電縫鋼管の冷間加工性、被削性、焼入れ性に及ぼす各種要因の影響について、鋭意研究を行った。その結果、組織因子のうち、フェライト基地中に分散析出するセメンタイトの粒径、セメンタイト粒子の分散間隔が、高炭素鋼管の冷間加工性、被削性、焼入れ性、とくに被削性に影響する重要なファクターであることに想到した。 In order to achieve the above-mentioned object, the present inventors have intensively studied the influence of various factors on the cold workability, machinability, and hardenability of a high carbon electric resistance welded steel pipe. As a result, among the structure factors, the particle size of cementite dispersed and precipitated in the ferrite matrix and the dispersion interval of the cementite particles affect the cold workability, machinability, hardenability, especially machinability of high carbon steel pipes. I came up with an important factor.
というのは、フェライトとセメンタイトの混合組織では、フェライトとセメンタイトで塑性変形能に差があるため、とくに切削加工時には、塑性変形により、フェライトとセメンタイトとの界面にボイドが発生し、セメンタイトの剥離が生じたり、複数のボイドが合体して、クラックとなりやすい。このようなセメンタイトの剥離やボイドの合体等が生じると、切削仕上げ面が劣化し、被削性が低下することになる。そこで、更なる研究を行った結果、切削加工に際し、セメンタイトの剥離やボイドの合体等が生じない、セメンタイトの粒径と分散間隔が存在することを見出した。セメンタイトの粒径と分散間隔を、適正な範囲に調整することにより、切削加工に際し、セメンタイトの剥離やボイドの合体等が生じないで、良好な切削仕上げ面が得られ、被削性が顕著に向上するという知見を得た。 This is because, in the mixed structure of ferrite and cementite, there is a difference in plastic deformability between ferrite and cementite. It is likely to occur or a plurality of voids coalesce to form a crack. When such cementite peeling or void coalescence occurs, the cut finish surface deteriorates and the machinability deteriorates. As a result of further research, it was found that there is a cementite particle size and dispersion interval that do not cause cementite peeling or void coalescence during cutting. By adjusting the particle size and dispersion interval of cementite to an appropriate range, there will be no cementite peeling or void coalescence during cutting, resulting in a good cutting finish and remarkable machinability. The knowledge that it improves is obtained.
そして、被削性が良好となる、セメンタイトの粒径と分散間隔の範囲が、平均粒径で0.1μｍ以上0.5μm未満、各粒子の分散間隔が隣接する粒子間の表面から表面の間隔で0.5〜10μmであることを見出した。このようなセメンタイトが分散した組織の高炭素鋼管であれば、優れた冷間加工性、優れた被削性、優れた焼入れ性を兼備する鋼管となることを知見した。 And, the range of the cementite particle size and the dispersion interval is good in machinability, the average particle size is 0.1 μm or more and less than 0.5 μm, and the dispersion interval of each particle is 0.5 to the surface-to-surface interval between adjacent particles. It was found to be ˜10 μm. It has been found that a high-carbon steel pipe having a structure in which cementite is dispersed is a steel pipe having excellent cold workability, excellent machinability, and excellent hardenability.
さらに、本発明者らは、更なる研究の結果、セメンタイトの分散が上記したような適正な範囲となる組織を有する高炭素電縫鋼管とするためには、高炭素鋼管を、Ａc３変態点以上に加熱したのち、900℃以下の温度域での累積圧下率：30〜70％で、圧延終了温度：900℃〜（Ａc１変態点）とする縮径圧延を施すことが肝要であることを見出した。
本発明は、かかる知見に基づき、さらに検討を加えて完成されたものである。すなわち、本発明の要旨はつぎのとおりである。
Furthermore, as a result of further research, the present inventors have determined that the high carbon steel pipe has an Ac 3 transformation point in order to obtain a high carbon electric-welded steel pipe having a structure in which the dispersion of cementite is within the appropriate range as described above. After heating as above, it is important to perform reduction rolling at a rolling reduction temperature of 900 ° C. to (Ac 1 transformation point) at a cumulative reduction ratio of 30 to 70% in a temperature range of 900 ° C. or less. I found.
The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
（１）質量％で、Ｃ：0.25〜0.60％、Si：0.01〜2.0％、Mn：0.2〜3.0％、Al：0.001〜0.1％、Ｐ：0.001〜0.05％、Ｓ：0.02％以下、Ｎ：0.0010〜0.0100％、Ｂ：0.0003〜0.0050％、Ca：0.0001〜0.0050％を含み、残部Feおよび不可避的不純物からなる組成と、基地相がフェライト相で、該基地相中にセメンタイト粒子が分散した組織を有し、前記セメンタイト粒子の平均粒径ｄが0.1μm以上0.5μm未満で、かつ隣接するセメンタイト粒子の表面−表面間の平均距離Ｌが0.5〜10μmであることを特徴とする冷間加工性、被削性および焼入れ性に優れた高炭素鋼管。 (1) By mass%, C: 0.25 to 0.60%, Si: 0.01 to 2.0%, Mn: 0.2 to 3.0%, Al: 0.001 to 0.1%, P: 0.001 to 0.05%, S: 0.02% or less, N: A composition comprising 0.0010 to 0.0100%, B: 0.0003 to 0.0050%, Ca: 0.0001 to 0.0050%, the balance consisting of Fe and inevitable impurities, and a structure in which the matrix phase is a ferrite phase and cementite particles are dispersed in the matrix phase Cold workability, wherein the cementite particles have an average particle diameter d of 0.1 μm or more and less than 0.5 μm, and an average distance L between the surfaces of adjacent cementite particles is 0.5 to 10 μm. High carbon steel pipe with excellent machinability and hardenability.
（２）（１）において、前記組成に加えてさらに、質量％で、Cu：2.0％以下、Cr：2.0％以下、Mo：2.0％以下、Ｗ：2.0％以下、Ｖ：1.0％以下、Nb：0.1％以下のうちから選ばれた１種または２種以上を含有することを特徴とする高炭素鋼管。
（３）（１）または（２）において、前記組成に加えてさらに、質量％で、Ti：0.1％以下を含有することを特徴とする高炭素鋼管。
(2) In (1), in addition to the above composition, in terms of mass%, Cu: 2.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, W: 2.0% or less, V: 1.0% or less, Nb : High carbon steel pipe characterized by containing one or more selected from 0.1% or less.
(3) The high carbon steel pipe according to (1) or (2), further containing Ti: 0.1% or less by mass% in addition to the above composition.
（４）高炭素鋼管を素材鋼管とし、該素材鋼管に、加熱・均熱したのち縮径圧延を施し製品鋼管とする高炭素鋼管の製造方法であって、前記素材鋼管を、質量％で、Ｃ：0.25〜0.60％、Si：0.01〜2.0％、Mn：0.2〜3.0％、Al：0.001〜0.1％、Ｐ：0.001〜0.05％、Ｓ：0.02％以下、Ｎ：0.0010〜0.0100％、Ｂ：0.0003〜0.0050％、Ca：0.0001〜0.0050％を含み、残部Feおよび不可避的不純物からなる組成を有する高炭素鋼管とし、前記縮径圧延を、Ac３変態点以上に加熱・均熱したのち、圧延終了温度：900℃〜（Ac１変態点）、900℃以下の温度域での累積縮径率：30〜70％である縮径圧延とすることを特徴とする冷間加工性、被削性および焼入れ性に優れた高炭素鋼管の製造方法。 (4) A high carbon steel pipe is used as a raw steel pipe, and the raw steel pipe is heated and soaked, and then subjected to reduced diameter rolling to obtain a product steel pipe. C: 0.25 to 0.60%, Si: 0.01 to 2.0%, Mn: 0.2 to 3.0%, Al: 0.001 to 0.1%, P: 0.001 to 0.05%, S: 0.02% or less, N: 0.0010 to 0.0100%, B: A high carbon steel pipe containing 0.0003 to 0.0050%, Ca: 0.0001 to 0.0050% and having the balance Fe and unavoidable impurities, and the reduced diameter rolling is heated and soaked to the Ac 3 transformation point or higher and then rolled. End temperature: 900 ° C. to (Ac 1 transformation point), cumulative reduction in temperature range below 900 ° C .: cold workability and machinability characterized by reduced diameter rolling of 30 to 70% And a method for producing a high carbon steel pipe excellent in hardenability.
（５）（４）において、前記高炭素鋼管が、前記した組成の高炭素鋼帯を、連続的にロール成形し、略円筒状のオープン管とし、該オープン管の端部同士を電縫溶接してなる造管工程を経た、高炭素電縫鋼管であることを特徴とする高炭素鋼管の製造方法。
（６）（４）または（５）において、前記組成に加えてさらに、質量％で、Cu：2.0％以下、Cr：2.0％以下、Mo：2.0％以下、Ｗ：2.0％以下、Ｖ：1.0％以下、Nb：0.1％以下のうちから選ばれた１種または２種以上を含有することを特徴とする高炭素鋼管の製造方法。
(5) In (4), the high carbon steel pipe continuously roll-forms the high carbon steel strip having the composition described above to form a substantially cylindrical open pipe, and the ends of the open pipe are electro-welded. A high carbon steel pipe manufacturing method characterized by being a high carbon electric-welded steel pipe that has undergone a pipe making process.
(6) In (4) or (5), in addition to the above composition, in terms of mass%, Cu: 2.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, W: 2.0% or less, V: 1.0 % Or less, Nb: 1 type or 2 types or more selected from 0.1% or less are contained, The manufacturing method of the high carbon steel pipe characterized by the above-mentioned.
（７）（４）ないし（６）のいずれかにおいて、前記組成に加えてさらに、質量％で、Ti：0.1％以下を含有することを特徴とする高炭素鋼管の製造方法。 (7) The method for producing a high carbon steel pipe according to any one of (4) to (6), further comprising Ti: 0.1% or less by mass% in addition to the above composition.
本発明によれば、球状化焼鈍を施すことなく、球状化焼鈍を施したものと同等以上の優れた冷間加工性を有し、かつ被削性、高周波焼入れ性にも優れた、ステアリングラックバーあるいはステアリングシャフト、ドライブシャフト等の自動車部品用として好適な、高炭素鋼管を容易に、しかも安価に製造でき、産業上格段の効果を奏する。さらに、本発明によれば、自動車車体の軽量化に寄与し、地球環境の保全に貢献できるという効果もある。 According to the present invention, the steering rack has excellent cold workability equivalent to or better than that obtained by spheroidizing annealing without spheroidizing annealing, and also has excellent machinability and induction hardening properties. High carbon steel pipes suitable for automobile parts such as bars, steering shafts and drive shafts can be manufactured easily and inexpensively, and have a remarkable industrial effect. Furthermore, according to the present invention, there is an effect that it contributes to the weight reduction of the automobile body and can contribute to the preservation of the global environment.
まず、本発明高炭素鋼管の組成限定の理由について説明する。以下、とくに断わらない限り、質量％は単に％で記す。
Ｃ：0.25〜0.60％
Ｃは、焼入れ硬さを増加させる作用を有し、所望の部品強度を確保するために重要な元素である。このような効果を得るためには、0.25％以上の含有を必要とする。一方、0.60％を超える含有は、冷間加工性を顕著に低下させるとともに、溶接性を低下させ、電縫溶接を行なう場合には、電縫溶接部の品質低下を招く。このようなことから、Ｃは0.25〜0.60％の範囲に限定した。なお、好ましくは0.30〜0.50％である。
First, the reason for limiting the composition of the high carbon steel pipe of the present invention will be described. Hereinafter, unless otherwise specified, mass% is simply expressed as%.
C: 0.25 to 0.60%
C has an effect of increasing the quenching hardness and is an important element for ensuring a desired component strength. In order to obtain such an effect, the content of 0.25% or more is required. On the other hand, if the content exceeds 0.60%, the cold workability is remarkably lowered and the weldability is lowered. When performing electric resistance welding, the quality of the electric resistance welding portion is deteriorated. Therefore, C is limited to the range of 0.25 to 0.60%. In addition, Preferably it is 0.30 to 0.50%.
Si：0.01〜2.0％
Siは、脱酸剤として作用するとともに、固溶して強度増加に寄与する元素である。このような効果を得るためには、0.01％以上の含有を必要とする。一方、2.0％を超える含有は、冷間加工性が低下するのに加えて、電縫溶接を行う場合には、電縫溶接時に酸化物を形成し、アップセット後も残留するため、電縫溶接部の品質低下を招く。このため、Siは0.01〜2.0％の範囲に限定した。なお、好ましくは0.1〜0.5％である。
Si: 0.01-2.0%
Si is an element that acts as a deoxidizer and contributes to an increase in strength by solid solution. In order to acquire such an effect, 0.01% or more of content is required. On the other hand, if the content exceeds 2.0%, cold workability is deteriorated. In addition, when performing electro-resistance welding, an oxide is formed during electro-resistance welding and remains after upsetting. The quality of the weld will be reduced. For this reason, Si was limited to the range of 0.01 to 2.0%. In addition, Preferably it is 0.1 to 0.5%.
Mn：0.2〜3.0％
Mnは、焼入れ性を向上させるとともに、固溶して強度増加に寄与する元素である。このような効果を得るためには、0.2％以上の含有を必要とする。一方、3.0％を超える含有は、冷間加工性が低下するとともに、電縫溶接を行う場合には、電縫溶接部にMn酸化物が残存しやすくなり、電縫溶接部の品質低下を招く。このようなことから、Mnは0.2〜3.0％の範囲に限定した。なお、好ましくは0.5〜2.0％である。
Mn: 0.2-3.0%
Mn is an element that improves the hardenability and contributes to an increase in strength by solid solution. In order to obtain such an effect, the content of 0.2% or more is required. On the other hand, when the content exceeds 3.0%, cold workability is deteriorated, and when performing ERW welding, Mn oxide tends to remain in the ERW weld, resulting in deterioration of the ERW weld quality. . For these reasons, Mn is limited to the range of 0.2 to 3.0%. In addition, Preferably it is 0.5 to 2.0%.
Al：0.001〜0.1％
Alは、脱酸剤として有効に作用する元素である。このような効果を得るためには0.001％以上の含有を必要とする。一方、0.1％を超えて含有すると、アルミナ系介在物が増加し、表面性状を低下させる。このため、Alは0.001〜0.1％の範囲に限定した。なお、好ましくは0.01〜0.05％である。
Al: 0.001 to 0.1%
Al is an element that effectively acts as a deoxidizer. In order to obtain such an effect, a content of 0.001% or more is required. On the other hand, if the content exceeds 0.1%, alumina inclusions increase and the surface properties are lowered. For this reason, Al was limited to the range of 0.001 to 0.1%. In addition, Preferably it is 0.01 to 0.05%.
Ｐ：0.001〜0.05％
Ｐは、強度増加に寄与する元素であり、このような効果は0.001％以上の含有で顕著となる。一方、Ｐは偏析しやすい元素であり、0.05％を超えて含有すると、粒界偏析や中心偏析が顕著になり、延性が低下するとともに、溶接性の顕著な低下を招く。このため、Ｐは0.001〜0.05％の範囲に限定した。なお、好ましくは0.001〜0.02％である。
P: 0.001 to 0.05%
P is an element contributing to an increase in strength, and such an effect becomes remarkable when the content is 0.001% or more. On the other hand, P is an element that easily segregates, and if it exceeds 0.05%, grain boundary segregation and center segregation become prominent, ductility is lowered, and weldability is significantly lowered. For this reason, P was limited to the range of 0.001 to 0.05%. In addition, Preferably it is 0.001 to 0.02%.
Ｓ：0.02％以下
Ｓは、鋼中では硫化物系介在物として存在し、成形加工時に介在物が割れの起点になる恐れが高いため、できるだけ低減することが望ましいが、0.02％以下であれば許容できる。このようなことから、Ｓは0.02％以下に限定した。なお、好ましくは0.01％以下である。また、過度のＳの低減は、精錬コストの高騰を招くため、0.0001％以上とすることが好ましい。
S: 0.02% or less S is present as sulfide inclusions in steel, and the inclusions are likely to become the starting point of cracking during forming. Therefore, it is desirable to reduce as much as possible, but if 0.02% or less acceptable. For these reasons, S is limited to 0.02% or less. In addition, Preferably it is 0.01% or less. Moreover, excessive reduction of S causes a rise in refining costs, so 0.0001% or more is preferable.
Ｎ：0.0010〜0.0100％
Ｎは、固溶して強度の増加に寄与する元素である。このような効果を得るためには、0.0010％以上の含有を必要とする。一方、0.0100％を超える含有は、加工性の低下を招く。このため、Ｎは0.0010〜0.0100％の範囲に限定した。なお、好ましくは0.0050％以下である。
N: 0.0010 to 0.0100%
N is an element that contributes to an increase in strength by solid solution. In order to acquire such an effect, 0.0010% or more needs to be contained. On the other hand, if the content exceeds 0.0100%, the workability is reduced. For this reason, N was limited to the range of 0.0010 to 0.0100%. In addition, Preferably it is 0.0050% or less.
Ｂ：0.0003〜0.0050％
Ｂは、粒界に偏析して少量の含有で鋼の焼入れ性を顕著に向上させる元素である。このような効果を得るためには、0.0003％以上の含有を必要とする。一方、0.0050％を超えて含有しても、効果が飽和し含有量に見合う効果を期待できないため、経済的に不利となるうえ、粒界に多量に偏析して粒界破壊を促進する。このため、Ｂは0.0003〜0.0050％の範囲に限定した。なお、好ましくは0.0005〜0.0030％である。
B: 0.0003-0.0050%
B is an element that segregates at the grain boundaries and significantly improves the hardenability of the steel with a small amount. In order to acquire such an effect, 0.0003% or more needs to be contained. On the other hand, if the content exceeds 0.0050%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous and segregates in large amounts at the grain boundaries to promote grain boundary fracture. For this reason, B was limited to the range of 0.0003 to 0.0050%. In addition, Preferably it is 0.0005 to 0.0030%.
Ca：0.0001〜0.0050％
Caは、非金属介在物（硫化物系介在物）の形状を球状とする、介在物の形態制御に有効に寄与する元素である。非金属介在物の形状を球状とすることは、非金属介在物まわりの応力集中度を低下でき、成形加工時の割れの起点、疲労破壊時の割れの起点の減少に繋がる。このような効果を得るためには、0.0001％以上の含有を必要とする。一方、0.0050％を超える含有は、非金属介在物量の増加を招き、鋼の清浄度の低下に繋がる。このため、Caは0.0001〜0.0050％の範囲に限定した。なお、好ましくは0.0001〜0.0030％である。
Ca: 0.0001 to 0.0050%
Ca is an element that makes the shape of non-metallic inclusions (sulfide-based inclusions) spherical and contributes effectively to the inclusion morphology control. Making the shape of the non-metallic inclusions spherical can reduce the stress concentration around the non-metallic inclusions, leading to a decrease in the starting point of cracks during the forming process and a starting point of cracks during fatigue failure. In order to acquire such an effect, 0.0001% or more of content is required. On the other hand, the content exceeding 0.0050% leads to an increase in the amount of non-metallic inclusions, leading to a decrease in the cleanliness of the steel. For this reason, Ca was limited to the range of 0.0001 to 0.0050%. In addition, Preferably it is 0.0001 to 0.0030%.
上記した成分が基本の成分であるが、本発明では、これら基本の組成に加えてさらに、選択成分として、Cu：2.0％以下、Cr：2.0％以下、Mo：2.0％以下、Ｗ：2.0％以下、Ｖ：1.0％以下、Nb：0.1％以下のうちから選ばれた１種または２種以上、および／または、Ti：0.1％以下を、選択して含有できる。
Cu：2.0％以下、Cr：2.0％以下、Mo：2.0％以下、Ｗ：2.0％以下、Ｖ：1.0％以下、Nb：0.1％以下のうちから選ばれた１種または２種以上
Cu、Cr、Mo、Ｗ、Ｖ、Nbはいずれも、鋼の強度増加に寄与する元素であり、必要に応じて選択して１種または２種以上含有できる。
The above components are basic components. In the present invention, in addition to these basic compositions, Cu: 2.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, W: 2.0% Hereinafter, one or two or more selected from V: 1.0% or less, Nb: 0.1% or less, and / or Ti: 0.1% or less can be selected and contained.
One or more selected from Cu: 2.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, W: 2.0% or less, V: 1.0% or less, Nb: 0.1% or less
Cu, Cr, Mo, W, V, and Nb are all elements that contribute to an increase in the strength of steel, and can be selected as necessary and contained in one or more.
Cuは、焼入れ性の向上を介して、強度増加に寄与し、耐疲労特性の向上に有効な元素であり、このような効果を得るためには、0.01％以上含有することが好ましい。一方、2.0％を超える含有は、冷間加工性が著しく低下する。このため、含有する場合には、Cuは2.0％以下に限定することが好ましい。なお、より好ましくは0.1〜1.0％である。
Crは、焼入れ性の向上を介して、強度増加に寄与する元素である。このような効果を得るためには、0.01％以上含有することが好ましい。一方、Crは酸化物を形成しやすく、2.0％を超える含有は、電縫溶接を行なう場合に、電縫溶接部にCr酸化物が残存しやすく、電縫溶接部の品質が低下しやすい。このため、含有する場合には、Crは2.0％以下に限定することが好ましい。なお、より好ましくは0.1〜1.0％である。
Cu is an element that contributes to an increase in strength through improvement in hardenability and is effective in improving fatigue resistance. To obtain such an effect, Cu is preferably contained in an amount of 0.01% or more. On the other hand, if the content exceeds 2.0%, the cold workability is remarkably lowered. For this reason, when it contains, it is preferable to limit Cu to 2.0% or less. More preferably, it is 0.1 to 1.0%.
Cr is an element that contributes to an increase in strength through improvement of hardenability. In order to acquire such an effect, it is preferable to contain 0.01% or more. On the other hand, Cr tends to form an oxide, and if it exceeds 2.0%, Cr oxide tends to remain in the ERW weld when ERW welding is performed, and the quality of the ERW weld tends to deteriorate. For this reason, when contained, Cr is preferably limited to 2.0% or less. More preferably, it is 0.1 to 1.0%.
Moは、焼入れ性の向上、さらには炭化物による析出強化を介して、強度増加に寄与し、耐疲労特性の向上に有効な元素である。このような効果を得るためには、0.01％以上含有することが好ましい。一方、2.0％を超える含有は、冷間加工性が著しく低下するうえ、多量の含有は材料コストの高騰に繋がる。このため、含有する場合には、Moは2.0％以下に限定することが好ましい。なお、より好ましくは0.1〜0.5％である。 Mo is an element that contributes to an increase in strength through improvement of hardenability and further precipitation strengthening by carbides, and is effective in improving fatigue resistance. In order to acquire such an effect, it is preferable to contain 0.01% or more. On the other hand, if the content exceeds 2.0%, the cold workability is remarkably lowered, and if the content is too large, the material cost increases. For this reason, when it contains, it is preferable to limit Mo to 2.0% or less. In addition, More preferably, it is 0.1 to 0.5%.
Ｗは、炭化物による析出強化を介して強度増加に寄与する元素である。このような効果を得るためには、0.01％以上含有することが好ましい。一方、2.0％を超える含有は、必要以上に多量の炭化物が析出し、冷間加工性の低下を招くうえ、多量の含有は材料コストの高騰に繋がる。このため、含有する場合には、Ｗは2.0％以下に限定することが好ましい。なお、より好ましくは0.1〜0.5％である。 W is an element that contributes to an increase in strength through precipitation strengthening by carbides. In order to acquire such an effect, it is preferable to contain 0.01% or more. On the other hand, if the content exceeds 2.0%, a larger amount of carbide precipitates than necessary, which leads to a decrease in cold workability, and a large content leads to an increase in material cost. For this reason, when contained, W is preferably limited to 2.0% or less. In addition, More preferably, it is 0.1 to 0.5%.
Ｖは、炭化物による析出強化を介して強度増加に寄与するとともに、焼戻軟化抵抗を増加させる元素である。このような効果を得るためには、0.01％以上含有することが好ましい。一方、1.0％を超えて含有しても、効果が飽和し、経済的に不利となるうえ、多量の含有は冷間加工性を低下させる。このため、含有する場合には、Ｖは1.0％以下に限定することが好ましい。なお、より好ましくは0.1〜0.5％である。 V is an element that contributes to an increase in strength through precipitation strengthening by carbide and increases the temper softening resistance. In order to acquire such an effect, it is preferable to contain 0.01% or more. On the other hand, if the content exceeds 1.0%, the effect is saturated and disadvantageous economically, and a large content reduces cold workability. For this reason, when it contains, it is preferable to limit V to 1.0% or less. In addition, More preferably, it is 0.1 to 0.5%.
Nbは、焼入れ性の向上、さらには炭化物による析出強化を介して、強度増加に寄与する元素である。このような効果を得るためには、0.0010％以上含有することが望ましい。一方、0.1％を超えて含有しても、効果が飽和し、経済的に不利となるうえ、多量の含有は冷間加工性を低下させる。このため、含有する場合には、Nbは0.1％以下に限定することが好ましい。なお、より好ましくは0.0010〜0.05％である。 Nb is an element that contributes to an increase in strength through improvement in hardenability and further through precipitation strengthening by carbides. In order to acquire such an effect, it is desirable to contain 0.0010% or more. On the other hand, if the content exceeds 0.1%, the effect is saturated and disadvantageous economically, and a large content reduces the cold workability. For this reason, when it contains, it is preferable to limit Nb to 0.1% or less. In addition, More preferably, it is 0.0010 to 0.05%.
Ti：0.1％以下
Tiは、炭化物、窒化物を形成し、熱処理時の結晶粒の粗大化を抑制する作用を有する元素であり、必要に応じて含有できる。このような効果を得るためには、0.001％以上含有することが望ましいが、0.1％を超える含有は、冷間加工性が低下する。このため、含有する場合には、Tiは0.1％以下に限定することが好ましい。なお、より好ましくは0.0010〜0.05％である。
Ti: 0.1% or less
Ti is an element that forms carbides and nitrides and has an action of suppressing coarsening of crystal grains during heat treatment, and can be contained as necessary. In order to acquire such an effect, it is desirable to contain 0.001% or more, but when it exceeds 0.1%, cold workability will fall. For this reason, when it contains, it is preferable to limit Ti to 0.1% or less. In addition, More preferably, it is 0.0010 to 0.05%.
上記した成分以外の残部は、Feおよび不可避的不純物からなる。なお、不可避的不純物としては、Ｏ：0.01％以下が許容できる。
つぎに、本発明高炭素鋼管の組織限定の理由について説明する。
本発明高炭素鋼管は、基地相がフェライト相で、該基地相中に、所定範囲の平均粒径を有するセメンタイト粒子が所定範囲の間隔で分散した組織を有する。セメンタイトが球状化することにより、冷間加工性が向上する傾向を示す。
The balance other than the components described above consists of Fe and inevitable impurities. As an inevitable impurity, O: 0.01% or less is acceptable.
Next, the reason for the structure limitation of the high carbon steel pipe of the present invention will be described.
The high carbon steel pipe of the present invention has a structure in which a matrix phase is a ferrite phase, and cementite particles having an average particle diameter in a predetermined range are dispersed in the matrix phase at intervals of a predetermined range. It shows a tendency for cold workability to improve due to spheroidization of cementite.
さらに、上記したセメンタイト粒子が分散した組織は、セメンタイト粒子の平均粒径ｄが0.1μm以上0.5μm未満で、かつ隣接するセメンタイト粒子の表面−表面間の平均距離Ｌが0.5〜10μmである組織とする。
セメンタイト粒子の平均粒径ｄ：0.1μm以上0.5μm未満
セメンタイト粒子の平均粒径ｄが、0.1μm未満と微細になりすぎると、冷間加工性を十分に向上させることができなくなる。一方、平均粒径ｄが、0.5μm以上と大きくなると、焼入れ加熱（高周波加熱）時にセメンタイトの固溶が不十分となり、焼入れ性が低下するため、所望の焼入れ硬さ（製品硬さ）を確保できなくなる。また、セメンタイトの大きさが大きすぎると、切削加工時の抵抗（切削抵抗）が増加し、切削工具の寿命低下を招く。このようなことから、セメンタイト粒子の平均粒径ｄを0.1μm以上0.5μm未満の範囲に限定した。なお、好ましくは0.3μm以上0.5μm未満である。
Furthermore, the structure in which the cementite particles are dispersed is a structure in which the average particle diameter d of the cementite particles is 0.1 μm or more and less than 0.5 μm, and the average distance L between the surface and the surface of the adjacent cementite particles is 0.5 to 10 μm. To do.
Average particle diameter d of cementite particles: 0.1 μm or more and less than 0.5 μm If the average particle diameter d of cementite particles is too fine, less than 0.1 μm, the cold workability cannot be sufficiently improved. On the other hand, if the average particle diameter d is as large as 0.5 μm or more, cementite solid solution becomes insufficient during quenching heating (high-frequency heating), and the hardenability deteriorates, so the desired quenching hardness (product hardness) is ensured. become unable. On the other hand, if the cementite is too large, the resistance during cutting (cutting resistance) increases, leading to a reduction in the life of the cutting tool. For this reason, the average particle diameter d of the cementite particles is limited to a range of 0.1 μm or more and less than 0.5 μm. The thickness is preferably 0.3 μm or more and less than 0.5 μm.
隣接するセメンタイト粒子の表面−表面間の平均距離Ｌ：0.5〜10μm
隣接するセメンタイト粒子の表面−表面間の平均距離Ｌは、切削加工後の仕上表面の性状に影響する。平均距離Ｌが0.5μm未満では、切削加工時にフェライトとセメンタイトとの界面で生じたボイド同士が連結し、クラックとなる可能性が高く、切削仕上げ面の表面性状が低下する。一方、10μmを超えると、セメンタイトの大きさが必然的に大きくなり、焼入れ性が低下するとともに、切削抵抗が増加し被削性が低下する。このようなことから、本発明では、隣接するセメンタイト粒子の表面−表面間の平均距離Ｌを0.5〜10μmの範囲に限定した。なお、好ましくは５μm以下である。
Average distance L between surfaces of adjacent cementite particles: 0.5 to 10 μm
The average distance L between the surfaces of adjacent cementite particles affects the properties of the finished surface after cutting. When the average distance L is less than 0.5 μm, voids generated at the interface between ferrite and cementite are connected to each other at the time of cutting, and there is a high possibility that a crack will occur, and the surface properties of the finished surface of the cutting will be reduced. On the other hand, if it exceeds 10 μm, the size of cementite will inevitably increase, hardenability will decrease, cutting resistance will increase, and machinability will decrease. For this reason, in the present invention, the average distance L between the surfaces of adjacent cementite particles is limited to a range of 0.5 to 10 μm. In addition, Preferably it is 5 micrometers or less.
セメンタイトの平均粒径ｄと、隣接する粒子の表面−表面間の平均距離Lとを、上記した範囲内に調整することにより、冷間加工性、焼入れ性および被削性を兼備した高炭素鋼管とすることができる。
つぎに、本発明高炭素鋼管の好ましい製造方法について説明する。
まず、素材鋼管として、上記した組成を有する高炭素鋼管を用いる。なお、素材鋼管は、上記した組成を有する鋼管であれば、継目無鋼管、電縫鋼管、鍛接鋼管でもよく、とくに素材鋼管の製造方法を限定する必要はない。
By adjusting the average particle diameter d of cementite and the average distance L between the surfaces of adjacent particles within the above range, a high carbon steel pipe having both cold workability, hardenability and machinability. It can be.
Below, the preferable manufacturing method of this invention high carbon steel pipe is demonstrated.
First, a high carbon steel pipe having the above-described composition is used as the raw steel pipe. The material steel pipe may be a seamless steel pipe, an ERW steel pipe, or a forged steel pipe as long as it has the above-described composition, and there is no need to particularly limit the manufacturing method of the material steel pipe.
例えば、電縫鋼管は、通常、鋼帯を、連続的にロール成形し、略円筒状のオープン管とし、該オープン管の端部同士を電縫溶接してなる造管工程を施されて製造される。使用する鋼帯は、上記した組成を有する熱延鋼帯とすることが製造コストの低減という観点から好ましいが、冷延鋼帯でもなんら問題はない。
素材鋼管である高炭素鋼管を、Ac３変態点以上、望ましくは1100℃以下の加熱温度に加熱し、均熱する。加熱温度がAc３変態点未満では、電縫溶接部への炭素の拡散が十分でなく、焼入れ時に局部的に硬度が低くなる可能性がある。一方、加熱温度が1100℃を超える高温となると、鋼管の表面性状が低下する。なお、加熱温度での保持時間（均熱時間）は0.1〜10min程度とすることが表面性状、および均質化の観点から好ましい。
For example, ERW steel pipes are usually manufactured by subjecting a steel strip to continuous roll forming to form a substantially cylindrical open pipe, and a pipe forming process in which the ends of the open pipe are welded together by electro-welding. Is done. The steel strip to be used is preferably a hot-rolled steel strip having the above-described composition from the viewpoint of reducing manufacturing costs, but even a cold-rolled steel strip has no problem.
A high carbon steel pipe, which is a raw steel pipe, is heated to a heating temperature not lower than the Ac 3 transformation point, preferably not higher than 1100 ° C., and soaked. When the heating temperature is less than the Ac 3 transformation point, carbon is not sufficiently diffused into the ERW weld, and there is a possibility that the hardness is locally lowered during quenching. On the other hand, when the heating temperature is higher than 1100 ° C., the surface properties of the steel pipe are lowered. The holding time at the heating temperature (soaking time) is preferably about 0.1 to 10 min from the viewpoint of surface properties and homogenization.
加熱後、素材鋼管には、縮径圧延が施される。
縮径圧延は、圧延終了温度：900℃〜（Ac１変態点）とし、900℃以下の温度域での累積縮径率：30〜70％とする圧延とする。なお、圧延開始から圧延終了までの累積縮径率は、素材鋼管の寸法、製品鋼管の寸法によるが、パーライトを分断し微細なセメンタイトを形成するという観点から30〜75％の範囲とすることが好ましい。
After heating, the material steel pipe is subjected to reduced diameter rolling.
The diameter reduction rolling is a rolling at a rolling end temperature: 900 ° C. to (Ac 1 transformation point) and a cumulative diameter reduction ratio in a temperature range of 900 ° C. or lower: 30 to 70%. The cumulative diameter reduction ratio from the start of rolling to the end of rolling depends on the dimensions of the raw steel pipe and the product steel pipe, but may be in the range of 30 to 75% from the viewpoint of dividing pearlite to form fine cementite. preferable.
鋼管表面温度で、圧延終了温度が、900℃を超えた高温では、圧延中に炭化物が存在しなくなり、セメンタイトの球状化が達成されない。また、製品鋼管の表面性状が低下する。一方、Ac１変態点未満では、得られるセメンタイトが過度に微細になり、分散間隔も狭くなるため、切削仕上げ面が低下する。このため、圧延終了温度は900℃〜（Ac１変態点）の範囲の温度に限定した。なお、好ましくは850〜750℃である。 When the rolling finish temperature is higher than 900 ° C. at the surface temperature of the steel pipe, carbide is not present during rolling, and spheroidization of cementite is not achieved. Moreover, the surface properties of the product steel pipe are lowered. On the other hand, if it is less than the Ac 1 transformation point, the obtained cementite becomes excessively fine and the dispersion interval becomes narrow, so that the cut finish surface is lowered. For this reason, the rolling end temperature is limited to a temperature in the range of 900 ° C. to (Ac 1 transformation point). In addition, Preferably it is 850-750 degreeC.
また、900℃以下の温度域での累積縮径率が30％未満では、縮径圧延中にラメラー状パーライトの分断が十分に行われず、所望の球状化が達成できない。一方、900℃以下の温度域での累積縮径率が70％を超えると、セメンタイトの大きさが小さくなりすぎたり、加工硬化が大きくなりすぎたりして、冷間加工性が低下する。また、部品製造時の生産性が低下する。 Further, if the cumulative diameter reduction ratio in the temperature range of 900 ° C. or lower is less than 30%, the lamellar pearlite is not sufficiently divided during the diameter reduction rolling, and the desired spheroidization cannot be achieved. On the other hand, when the cumulative diameter reduction ratio in the temperature range of 900 ° C. or lower exceeds 70%, the size of cementite becomes too small or the work hardening becomes too large, resulting in a decrease in cold workability. In addition, productivity at the time of manufacturing parts is reduced.
上記した製造方法を素材鋼管に適用すれば、セメンタイトの平均粒径、隣接する各セメンタイト粒子の表面−表面間の平均距離が適正範囲である組織を有する高炭素鋼管が容易に得られる。
以下、実施例に基づいて、さらに本発明について説明する。
If the manufacturing method described above is applied to a material steel pipe, a high carbon steel pipe having a structure in which the average particle diameter of cementite and the average distance between the surfaces of adjacent cementite particles are in an appropriate range can be easily obtained.
Hereinafter, based on an Example, this invention is demonstrated further.
表1に示す組成を有する熱延鋼帯（板厚：7.0mm）に、連続的にロール成形し、略円筒状のオープン管とし、該オープン管の端部同士を電縫溶接する造管工程を施して、電縫鋼管（外径：89.1mmφ）とし、素材鋼管とした。
これら素材鋼管に、表２に示す条件で、縮径圧延を施し、製品鋼管とした。なお、一部の鋼管では、700℃×10hrの焼鈍処理、または925℃×15minの焼準処理を施し、従来例とした。従来例では、素材鋼管を40mmφに加工したのち上記した処理を施した。
A tube forming process in which hot rolled steel strips (sheet thickness: 7.0 mm) having the composition shown in Table 1 are continuously roll-formed to form a substantially cylindrical open pipe, and the ends of the open pipe are electro-welded. To make an electric resistance welded steel pipe (outer diameter: 89.1 mmφ).
These material steel pipes were subjected to reduction rolling under the conditions shown in Table 2 to obtain product steel pipes. Some steel pipes were annealed at 700 ° C. for 10 hours or normalized at 925 ° C. for 15 minutes to obtain conventional examples. In the conventional example, the above-mentioned treatment was performed after processing the raw steel pipe to 40 mmφ.
得られた鋼管について、組織観察を行うとともに、冷間加工性、焼入れ性、被削性を調査した。調査方法はつぎのとおりとした。
（１）組織観察
得られた製品鋼管から組織観察用試験片を採取し、管長手方向に垂直な断面（Ｃ断面）を研磨し、ナイタール腐食液で腐食したのち、走査型電子顕微鏡（倍率：2000倍）を用いて観察し、10視野以上でセメンタイト100個以上を含むように、撮像した。得られた写真を画像解析して、各セメンタイト粒の面積を求め、円相当径を算出して各粒の粒径とし、それらを算術平均して、その鋼管のセメンタイト粒の平均粒径ｄとした。また、得られた写真を画像解析して、各隣接するセメンタイト粒とセメンタイト粒との表面−表面間の距離を求め、算術平均して、その鋼管の隣接するセメンタイト粒とセメンタイト粒との表面−表面間の平均距離Ｌを算出した。
The obtained steel pipe was subjected to a structure observation and examined for cold workability, hardenability and machinability. The survey method was as follows.
(1) Microstructure observation A specimen for microstructural observation is collected from the obtained product steel pipe, a cross section (C cross section) perpendicular to the longitudinal direction of the pipe is polished, corroded with a nital corrosive liquid, and then a scanning electron microscope (magnification: 2000 times) and imaged to include 100 or more cementites in 10 fields of view or more. Image analysis of the obtained photograph, the area of each cementite grain was determined, the equivalent circle diameter was calculated to be the grain diameter of each grain, and they were arithmetically averaged, and the average grain diameter d of the cementite grains of the steel pipe did. In addition, the obtained photograph was image-analyzed to determine the distance between the surface and the surface of each adjacent cementite grain and cementite grain, and the arithmetic average was calculated as the surface of the cementite grain and the cementite grain adjacent to the steel pipe. The average distance L between the surfaces was calculated.
（２）冷間加工性
得られた製品鋼管から、JIS 11号Ａ引張試験片（GL：50mm）を採取し、JIS Z 2241に準拠して引張試験を実施し、引張強さTS、伸びElを求めた。伸びElが40％以上である場合を「冷間加工性に優れる」と評価し、○とした。それ以外は×とした。
（３）焼入れ性
得られた製品鋼管から試験材（長さ：300mm）を採取し、該採取した試験材に、JIS G 0559に準拠して高周波誘導加熱装置を用いて、表面温度が1000℃になるように加熱したのち、管外面に水を噴射して焼入れた。なお、加熱条件は、周波数：10kHz、誘導加熱コイル送り速度：20mm/sとした。焼入れした試験材から試験片を採取し、ビッカース硬度計（荷重：4.9N）で板厚方向の断面硬さ分布を測定し、Ｃ含有量に応じた限界硬さ以上となる領域の深さを求め、有効硬化層深さとした。管の外表面から肉厚の95％以上の範囲において、限界硬さ以上の硬さを確保できるものを「焼入れ性に優れる」と評価し、○とした。それ以外は×とした。
(2) Cold workability JIS No. 11 A tensile test specimen (GL: 50 mm) was taken from the obtained product steel pipe and subjected to a tensile test in accordance with JIS Z 2241. Tensile strength TS, elongation El Asked. A case where the elongation El was 40% or more was evaluated as “excellent in cold workability”, and was evaluated as ◯. Otherwise, it was set as “x”.
(3) Hardenability Test material (length: 300mm) is sampled from the obtained product steel pipe, and the sample temperature is 1000 ° C using a high frequency induction heating device in accordance with JIS G 0559. After heating, the water was jetted onto the outer surface of the tube and quenched. The heating conditions were a frequency: 10 kHz and an induction heating coil feed rate: 20 mm / s. Take a test piece from the quenched test material, measure the cross-sectional hardness distribution in the thickness direction with a Vickers hardness tester (load: 4.9N), and determine the depth of the region that is greater than the limit hardness according to the C content. The effective hardened layer depth was obtained. Those having a hardness of more than the limit hardness within the range of 95% or more of the wall thickness from the outer surface of the tube were evaluated as “Excellent hardenability” and indicated as “Good”. Otherwise, it was set as “x”.
（４）被削性
得られた製品鋼管に、管内面溝切加工（V溝加工）を実施した。加工の条件は下記のとおりとした。
回転数：100rpm
送り速度：0.3mm／rev
V溝切り込み深さ：１mm
チップ：超硬チップ
この加工を100本の製品鋼管に行ったのち、バイト（工具）を交換し、工具の状況を観察した。バイト切損、刃先欠損、切削仕上面の異常がない場合は○、ある場合は×として評価した。
(4) Machinability Pipe inner surface grooving (V-grooving) was performed on the obtained product steel pipe. The processing conditions were as follows.
Rotation speed: 100rpm
Feeding speed: 0.3mm / rev
V groove depth of cut: 1mm
Insert: Carbide insert After this processing was performed on 100 product steel pipes, the tool (tool) was replaced and the condition of the tool was observed. Evaluation was made as ◯ when there was no cutting tool breakage, cutting edge deficiency, or abnormal cutting surface, and x when there was any.
得られた結果を表３に示す。 The obtained results are shown in Table 3.
本発明例はいずれも、焼鈍処理を施した従来例と同等以上の伸びを示し、冷間加工性に優れ、さらに焼準処理を施した従来例と同等以上の焼入性を示し、高周波焼入れ性に優れ、さらに、焼準処理を施した従来例と同等以上の工具摩耗、切削仕上げ面の表面性状を示す、被削性に優れた高炭素鋼管となっている。一方、本発明の範囲を外れる比較例は、冷間加工性が低下しているか、焼入れ性が低下しているか、被削性が低下しているか、あるいは冷間加工性、高周波焼入れ性、被削性のいずれもが低下している。 Each example of the present invention exhibits an elongation equal to or higher than that of the conventional example subjected to the annealing treatment, is excellent in cold workability, and further exhibits a hardenability equal to or higher than that of the conventional example subjected to the normalizing treatment. It is a high carbon steel pipe excellent in machinability, and further exhibiting tool wear equivalent to or better than that of the conventional example subjected to the normalizing treatment and surface properties of the cut finish surface. On the other hand, comparative examples that are outside the scope of the present invention are cold workability, hardenability is lowered, machinability is lowered, or cold workability, induction hardenability, All of the machinability is reduced.
Claims (7)
Ｃ：0.25〜0.60％、 Si：0.01〜2.0％、
Mn：0.2〜3.0％、 Al：0.001〜0.1％、
Ｐ：0.001〜0.05％、 Ｓ：0.0001〜0.02％、
Ｎ：0.0010〜0.0100％、 Ｂ：0.0003〜0.0050％、
Ca：0.0001〜0.0050％
を含み、残部Feおよび不可避的不純物からなる組成と、基地相がフェライト相で、該基地相中にセメンタイト粒子が微細分散した組織を有し、前記セメンタイト粒子の平均粒径ｄが0.1μm以上0.5μm未満で、かつ隣接するセメンタイト粒子の表面−表面間の平均距離Ｌが0.5〜10μmであることを特徴とする冷間加工性、被削性および焼入れ性に優れた高炭素鋼管。 % By mass
C: 0.25 to 0.60%, Si: 0.01 to 2.0%,
Mn: 0.2-3.0%, Al: 0.001-0.1%,
P: 0.001 to 0.05%, S: 0.0001 to 0.02%,
N: 0.0010 to 0.0100%, B: 0.0003 to 0.0050%,
Ca: 0.0001 to 0.0050%
The base phase is a ferrite phase and the cementite particles are finely dispersed in the matrix phase, and the cementite particles have an average particle diameter d of 0.1 μm or more and 0.5 μm. A high carbon steel pipe excellent in cold workability, machinability and hardenability, characterized in that the average distance L between the surfaces of adjacent cementite particles is less than μm and is 0.5 to 10 μm.
Ｃ：0.25〜0.60％、 Si：0.01〜2.0％、
Mn：0.2〜3.0％、 Al：0.001〜0.1％、
Ｐ：0.001〜0.05％、 Ｓ：0.0001〜0.02％、
Ｎ：0.0010〜0.0100％、 Ｂ：0.0003〜0.0050％、
Ca：0.0001〜0.0050％
を含み、残部Feおよび不可避的不純物からなる組成を有する鋼管とし、
前記縮径圧延を、Ac３変態点以上に加熱・均熱したのち、圧延終了温度：900℃〜（Ac１変態点）とし、900℃以下の温度域での累積縮径率：30〜70％である縮径圧延とすることを特徴とする冷間加工性、被削性および焼入れ性に優れた高炭素鋼管の製造方法。 A high carbon steel pipe is used as a raw steel pipe, and the raw steel pipe is heated and soaked, and then subjected to reduced diameter rolling to obtain a product steel pipe.
C: 0.25 to 0.60%, Si: 0.01 to 2.0%,
Mn: 0.2-3.0%, Al: 0.001-0.1%,
P: 0.001 to 0.05%, S: 0.0001 to 0.02%,
N: 0.0010 to 0.0100%, B: 0.0003 to 0.0050%,
Ca: 0.0001 to 0.0050%
And a steel pipe having a composition consisting of the balance Fe and inevitable impurities,
After the diameter reduction rolling is heated and soaked to the Ac 3 transformation point or higher, the rolling end temperature is set to 900 ° C. to (Ac 1 transformation point), and the cumulative diameter reduction rate in the temperature range of 900 ° C. or less is 30 to 70. A method for producing a high carbon steel pipe excellent in cold workability, machinability and hardenability, characterized in that it is reduced diameter rolling.
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Cited By (6)
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|---|---|---|---|---|
| JP2012224900A (en) * | 2011-04-19 | 2012-11-15 | Jfe Steel Corp | Super high strength electric resistance welded steel pipe for hollow member excellent in workability and low temperature toughness, and method for manufacturing the same |
| KR101568503B1 (en) | 2013-12-20 | 2015-11-11 | 주식회사 포스코 | Hot rolled steel sheet having excellent anti-crack property, steel pipe using the same and method for manufacturing thereof |
| WO2018139671A1 (en) * | 2017-01-30 | 2018-08-02 | 新日鐵住金株式会社 | Steel pipe for underbody components of automobiles, and underbody component of automobiles |
| JP7560721B2 (en) | 2020-08-31 | 2024-10-03 | 日本製鉄株式会社 | Seamless steel pipes used as materials for bearing parts |
| WO2022215548A1 (en) * | 2021-04-08 | 2022-10-13 | 日本製鉄株式会社 | Hot-stretch-reduced electric resistance welded pipe |
| JP7160235B1 (en) * | 2021-04-08 | 2022-10-25 | 日本製鉄株式会社 | Hot shrinking ERW pipe |
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