JP5233271B2 - Steel pipe excellent in workability and manufacturing method thereof - Google Patents
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Description
本発明は、伸管、曲げ、ハイドロフォーミング等によって成形する構造用鋼管、配管等に適する加工性に優れた鋼管及びその製造方法に関する。 The present invention relates to a structural steel pipe formed by drawing, bending, hydroforming or the like, a steel pipe excellent in workability suitable for piping, and the like, and a method for manufacturing the same.
工程の省略及び部品点数の削減による自動車の製造コスト低減を目的として、鋼管から複雑な形状の部品を製造するハイドロフォーミング技術が開示されている（特許文献１を参照）。このようなハイドロフォーミング技術のメリットを十分に活用するためには、塑性異方性の指標であるｒ値（ランクフォード値）の高い鋼管が望ましく、ハイドロフォーミング用鋼管及びその製造方法が開示されている（特許文献２〜６を参照）。しかしながら、これらの鋼管は、いずれも鋼管を素管として該素管を加熱した後、比較的高温で縮径加工することによって鋼管の集合組織を制御してｒ値を高める方法であることから、製造設備が高価となり、製造コストが上昇するという問題点があった。 For the purpose of reducing the manufacturing cost of automobiles by omitting processes and reducing the number of parts, a hydroforming technique for manufacturing parts having a complicated shape from a steel pipe has been disclosed (see Patent Document 1). In order to fully utilize the merits of such hydroforming technology, a steel pipe having a high r value (Rankford value), which is an index of plastic anisotropy, is desirable, and a steel pipe for hydroforming and a method for manufacturing the same are disclosed. (See Patent Documents 2 to 6). However, since these steel pipes are methods of increasing the r value by controlling the texture of the steel pipe by heating the raw pipe as a raw pipe and then reducing the diameter at a relatively high temperature. There is a problem that the manufacturing equipment becomes expensive and the manufacturing cost increases.
一方、圧延方向及び圧延方向に直交する方向のｒ値が高い冷延鋼板を用いて造管した後、鋼管を熱処理する方法が開示されている（特許文献７を参照）。しかしながら、鋼管を製造する時、シーム溶接部において溶融した部分とＡｃ１変態点以上に再加熱されオーステナイトへ変態した部分のｒ値が低下し、加工性に劣るという問題点があった。さらに、この方法は素材となる冷間圧延鋼板の製造コストが高いので、鋼管の製造コストも上昇するという問題点があった。 On the other hand, a method of heat-treating a steel pipe after pipe forming using a cold rolled steel sheet having a high r value in a rolling direction and a direction orthogonal to the rolling direction is disclosed (see Patent Document 7). However, when manufacturing a steel pipe, there was a problem that the r value of the melted part in the seam welded part and the part reheated to the Ac1 transformation point or more and transformed to austenite was lowered, and the workability was inferior. Furthermore, this method has a problem that the manufacturing cost of the steel pipe also increases because the manufacturing cost of the cold-rolled steel sheet as the material is high.
一方、引張強度が３５０ＭＰａ以上であり、管軸方向及び円周方向のｒ値がともに１．３以上であって、管軸方向のｎ値「ｎ」と引張強度「ＴＳ[ＭＰａ]」がＴＳ＋３２８５×ｎ＞１０８２の関係を満たす加工性に優れた鋼管、及びその製造法として冷間圧延鋼板を素材として造管し、その後、加熱する方法が開示されている（特許文献８を参照）。しかしながら、鋼管を製造する時のシーム溶接部において溶融した部分とＡｃ１変態点以上に再加熱されオーステナイトへ変態した部分は、鋼管を単に加熱するだけではｒ値の向上は認められず、加工性に劣るという問題点があった。さらに、この方法は冷間圧延鋼板を素材として鋼管を製造し、該鋼管を加熱することによって鋼管の集合組織を制御してｒ値を高める方法であることから、素材となる冷間圧延鋼板の製造コストが高くなり、鋼管の製造コストも上昇するという問題点があった。
そこで、本発明は、このような従来の事情に鑑みて提案されたものであり、安価で加工性に優れた鋼管及びその製造方法を提供することを目的とする。 Then, this invention is proposed in view of such a conventional situation, and it aims at providing the cheap steel pipe excellent in workability, and its manufacturing method.
上記課題を解決することを目的とした本発明の要旨は以下の通りである。
（１） 鋼成分が質量％で、Ｃ：０．０３５〜０．３５０％、Ｓｉ：０．１３〜０．３４％、Ｍｎ：０．４０〜１．３５％、Ｐ：０．００６５〜０．０１５０％、Ｓ：０．００１６〜０．００４３％、Ａｌ：０．００２〜０．０３３％、Ｎ：０．００１９〜０．００４８％、Ｏ：０．００１９〜０．００３４％、残部鉄および不可避不純物からなる鋼管を素管として、該素管を冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に加熱して製造する鋼管において、シーム溶接部を含む鋼管全域で鋼管の軸方向のｒ値（ｒＬ）が１．２以上、鋼管の円周方向のｒ値（ｒＣ）が１．２以上で、且つ、前記鋼管の１／２板厚における板面の{１１１}のＸ線反射面ランダム強度比が２．０以上７．０以下、{１１０}のＸ線反射面ランダム強度比が１．０以上５．０以下、{１００}のＸ線反射面ランダム強度比が３．０以下であることを特徴とする加工性に優れた鋼管。
（２） 更に鋼成分が質量％で、Ｃｒ：０．２４％、Ｍｏ：０．２０％、Ｔｉ：０．０１１〜０．０１２％、Ｂ：０．００１０％、のいずれか１種以上を含むことを特徴とする前記（１）に記載の加工性に優れた鋼管。
（３） 請求項１または請求項２に記載の鋼成分からなり、シーム溶接部を含む素管を減面率１０％以上６０％以下、且つ減肉率１％以上となるように冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に３０秒以上加熱し、その後、冷却することを特徴とする加工性に優れた鋼管の製造方法。
（４） 前記素管を冷間で伸管加工する前に、Ａｃ３変態点以上の温度に加熱し、圧延することなく、冷却する工程を付加することを特徴とする前記（３）に記載の加工性に優れた鋼管の製造方法。
The gist of the present invention aimed at solving the above problems is as follows.
(1) Steel component is mass%, C: 0.035 to 0.350%, Si: 0.13 to 0.34%, Mn: 0.40 to 1.35%, P: 0.0065 to 0 0.150%, S: 0.0016-0.0043%, Al: 0.002-0.033%, N: 0.0019-0.0048%, O: 0.0019-0.0034%, balance iron And a steel pipe made of inevitable impurities, the steel pipe is cold drawn and then heated to a temperature range from Ac1 transformation point -70 ° C. to Ac1 transformation point. The steel pipe has an r-value (rL) in the axial direction of 1.2 or more, a steel pipe circumferential r-value (rC) of 1.2 or more, and a half-thickness of the steel pipe. The {111} X-ray reflecting surface random intensity ratio of the surface is 2.0 or more and 7.0 or less, the {110} X-ray reflecting surface Random intensity ratio of 1.0 or more and 5.0 or less, excellent workability, wherein the X-ray reflection surfaces random intensity ratio of {100} is 3.0 or less steel.
(2) Further, the steel component is mass%, and one or more of Cr: 0.24%, Mo: 0.20%, Ti: 0.011 to 0.012%, B: 0.0010%. The steel pipe excellent in workability as described in said (1) characterized by including.
(3) The steel component according to claim 1 or claim 2, wherein the raw pipe including the seam weld is cold so that the area reduction rate is 10% or more and 60% or less and the wall thickness reduction rate is 1% or more. A method for producing a steel pipe excellent in workability, characterized by heating the tube to a temperature range from Ac1 transformation point -70 ° C. to Ac1 transformation point for 30 seconds or more after cooling and then cooling.
(4) Before the tube is cold drawn, the step of heating to a temperature not lower than the Ac3 transformation point and cooling without rolling is added. A method of manufacturing steel pipes with excellent workability.
以上のように、本発明によれば、安価で加工性に優れた鋼管を伸管、曲げ、ハイドロフォーミングなどで加工する構造用鋼管、配管等に適用することにより、安全性が著しく向上するとともに工程の省略及び部品点数の削減による製造コストの低減が可能となり、資源の有効利用が可能となる。 As described above, according to the present invention, by applying an inexpensive and excellent workability steel pipe to a structural steel pipe, piping, etc. processed by drawing, bending, hydroforming, etc., the safety is remarkably improved. Manufacturing costs can be reduced by omitting processes and reducing the number of parts, and resources can be used effectively.
以下に、本発明の加工性に優れた鋼管及びその製造方法について詳細に説明する。
本発明者らは、鋼管を素管として該素管を加熱した後、直ちに縮径加工するような高価な製造設備を必要とすることなく、また、高価な冷間圧延鋼板を素材として造管することなく、安価に製造可能できる、シーム溶接部も含めた全域で加工性に優れた鋼管について鋭意検討を行った。その結果、鋼管を素管として、素管を減面率１０％以上６０％以下、且つ減肉率１％以上となるように冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に３０秒以上加熱し、その後、冷却することによって、鋼管の１／２板厚における板面の{１１１}のＸ線反射面ランダム強度比が２．０以上７．０以下、{１１０}のＸ線反射面ランダム強度比が１．０以上５．０以下、{１００}のＸ線反射面ランダム強度比が３．０以下とすることが可能となり、シーム溶接部を含む鋼管全域で鋼管の軸方向のｒ値（ｒＬ）及び鋼管の円周方向のｒ値（ｒＣ）を高くして、曲げ加工やハイドロフォーミングなどの加工性を向上させることを見出し、本発明を完成するに至った。
Below, the steel pipe excellent in the workability of this invention and its manufacturing method are demonstrated in detail.
The inventors of the present invention do not need an expensive manufacturing facility that uses a steel pipe as a raw pipe and heats the raw pipe and then immediately reduces the diameter, and also uses an expensive cold-rolled steel sheet as a raw material. Steel pipes that can be manufactured inexpensively and that have excellent workability throughout the entire seam welded area, including seam welds, were intensively studied. As a result, the steel pipe was used as a raw pipe, and the raw pipe was cold-drawn so that the area reduction rate was 10% or more and 60% or less and the thickness reduction ratio was 1% or more, and then the Ac1 transformation point from -70 ° C to Ac1. By heating to the temperature range of the transformation point for 30 seconds or more and then cooling, the X-ray reflecting surface random intensity ratio of {111} of the plate surface at 1/2 plate thickness of the steel pipe is 2.0 or more and 7.0 or less. , {110} X-ray reflection surface random intensity ratio can be 1.0 or more and 5.0 or less, and {100} X-ray reflection surface random intensity ratio can be 3.0 or less, including a seam weld. The present invention has been completed by increasing the axial r value (rL) of the steel pipe and the circumferential r value (rC) of the steel pipe to improve workability such as bending and hydroforming. It came to do.
すなわち、本発明の特徴は、鋼管を素管として、該素管を冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に加熱して製造する鋼管において、シーム溶接部を含む鋼管円周方向全域で特定の集合組織を形成させることによってｒＬ、ｒＣを高くし、加工性を向上させる鋼管であること、並びにその製造方法として、素管を特定の減面率及び減肉率で冷間の伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に加熱し、その後、冷却することにある。 That is, a feature of the present invention is that in a steel pipe manufactured using a steel pipe as a raw pipe, the raw pipe is cold-drawn and then heated to a temperature range from Ac1 transformation point -70 ° C. to Ac1 transformation point. By forming a specific texture in the entire circumferential direction of the steel pipe including the welded portion, it is a steel pipe that increases rL and rC and improves workability. And after cold-drawing at a thinning rate, the temperature is from the Ac1 transformation point -70 ° C. to the temperature range of the Ac1 transformation point, followed by cooling.
鋼管を素管として、該素管を冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に加熱して製造する鋼管において、曲げ加工やハイドロフォーミングなどの加工性を向上させるためには、シーム溶接部を含む鋼管全域でｒＬ、ｒＣがそれぞれ１．２以上である必要がある。一般的にｒ値が高くなると加工性は向上することが知られているが、シーム溶接部を含めて円周方向全域でｒＬ及びｒＣが高くなる場合、ｒＬ及びｒＣが１．２以上であれば、曲げ加工やハイドロフォーミングなどの加工性が十分であることを見出した。なお、４５゜方向のｒ値（ｒＤ）は加工性に大きな効果をおよぼさないので特に問わないが、このような鋼管の製造条件において、ｒＤは１．２未満となる。 For steel pipes that are manufactured by using a steel pipe as a raw pipe, and after the pipe is cold-drawn and then heated to a temperature range from Ac1 transformation point -70 ° C to Ac1 transformation point, workability such as bending and hydroforming In order to improve the above, it is necessary that rL and rC are 1.2 or more in the entire steel pipe including the seam weld. In general, it is known that workability improves as the r value increases. However, when rL and rC increase in the entire circumferential direction including the seam weld, rL and rC should be 1.2 or more. For example, it has been found that workability such as bending and hydroforming is sufficient. The r value (rD) in the 45 ° direction is not particularly limited because it does not have a significant effect on the workability. However, under such steel pipe manufacturing conditions, rD is less than 1.2.
鋼管のｒＬの測定方法については、先ず、鋼管からＪＩＳ Ｚ ２２０１に準拠して、管軸方向を長手方向として１２号円弧状試験片を採取し、試験片平行部に標点をマーキングして標点間の距離を測定する。次に、標点間の中央部にひすみゲージを幅方向に貼付した後、伸び計を取り付けて引張試験機で１０％の引張ひずみを与え、標点距離の変化とひずみゲージにより測定した幅方向のひずみ変化からｒＬを算出した。 Regarding the measurement method of rL of steel pipes, first, in accordance with JIS Z 2201, a No. 12 arc-shaped specimen is taken with the pipe axis direction as the longitudinal direction, and a test mark is marked on the parallel part of the specimen. Measure the distance between points. Next, after applying a strain gauge to the center between the gauge points in the width direction, attach an extensometer, give a tensile strain of 10% with a tensile tester, and change the gauge distance and the width measured with the strain gauge. RL was calculated from the strain change in the direction.
鋼管のｒＣの測定方法については、先ず、鋼管を切断してプレス等で平板状とし、円周方向を長手としてＪＩＳ Ｚ ２２０１の１３Ｂ号試験片を採取し、試験片平行部に標点をマーキングして標点距離ならびに試験片平行部の板厚及び板幅を測定した。次に、試験片に伸び計を取り付けて、引張試験機にて１０％の引張ひずみを与え、引張ひずみ導入前後の試験片の板幅及び標点間距離からｒＣを算出した。 Regarding the measurement method of rC of steel pipe, first cut the steel pipe and make it flat with a press etc., sample the JIS Z 2201 No. 13B test piece with the circumferential direction as the longitudinal direction, and mark the test mark on the parallel part of the test piece Then, the gauge distance and the plate thickness and plate width of the parallel part of the test piece were measured. Next, an extensometer was attached to the test piece, 10% tensile strain was applied with a tensile tester, and rC was calculated from the plate width of the test piece before and after introduction of the tensile strain and the distance between the gauge points.
鋼管のｒ値を高めるためには集合組織を制御する必要がある。すなわち、ｒＣ及びｒＬを高くして優れた加工性を得るためには、鋼管の１／２板厚における板面の{１１１}のＸ線反射面ランダム強度比が２．０以上７．０以下、{１１０}のＸ線反射面ランダム強度比が１．０以上５．０以下、{１００}のＸ線反射面ランダム強度比が３．０以下であることが必要である。これらのランダム強度比が規定する範囲内でない場合、ｒＣ及びｒＬをそれぞれ１．２以上にすることができない。特定の方位のみランダム強度比を高めると、他の方位のランダム強度比が低くなるので、それぞれの方位のランダム強度比について、その上限を規定した。 In order to increase the r value of the steel pipe, it is necessary to control the texture. That is, in order to obtain excellent workability by increasing rC and rL, the {111} X-ray reflecting surface random intensity ratio of the plate surface at 1/2 plate thickness of the steel pipe is 2.0 or more and 7.0 or less. , {110} has an X-ray reflection surface random intensity ratio of 1.0 to 5.0, and {100} has an X-ray reflection surface random intensity ratio of 3.0 or less. If these random intensity ratios are not within the specified range, rC and rL cannot be 1.2 or more, respectively. When the random intensity ratio is increased only in a specific orientation, the random intensity ratio in the other orientation is lowered. Therefore, the upper limit is defined for the random intensity ratio in each orientation.
各方位のＸ線ランダム強度比はＸ線回折によって測定した。すなわち、鋼管から弧状試験片を切り出して、これをプレスして平板としてＸ線解析を行った。また弧状試験片から平板とするときは試験片加工による結晶回転の影響を避けるため、極力低ひずみで行うものとし、加工により導入されるひずみ量の上限を１０％以下で行った。 The X-ray random intensity ratio in each direction was measured by X-ray diffraction. That is, an arc-shaped test piece was cut out from the steel pipe, and this was pressed to perform X-ray analysis as a flat plate. In addition, in order to avoid the influence of crystal rotation due to the processing of the test piece when the arc-shaped test piece is used as a flat plate, it was performed with as low a strain as possible, and the upper limit of the strain amount introduced by the processing was 10% or less.
このようにして得られた板状の試料について、機械研磨や化学研磨などによって板厚中心付近まで研磨し、バフ研磨によって鏡面に仕上げた後、電解研磨や化学研磨によってひずみを除去すると同時に、板厚中心層が測定面となるように調整する。なお、鋼板の板厚中心層に偏析帯が観察される場合には、板厚の３／８〜５／８の範囲で偏析帯のない場所を測定すればよい。さらにＸ線測定が困難な場合、ＥＢＳＰ法によって測定しても差し支えない。 The plate-like sample thus obtained is polished to the vicinity of the center of the plate thickness by mechanical polishing, chemical polishing, etc., finished to a mirror surface by buffing, and then strain is removed by electrolytic polishing or chemical polishing. Adjust the thickness center layer to be the measurement surface. In addition, when a segregation zone is observed in the thickness center layer of the steel plate, a place without a segregation zone may be measured in the range of 3/8 to 5/8 of the plate thickness. Further, when X-ray measurement is difficult, measurement by the EBSP method may be performed.
次に、鋼管の製造条件について説明する。素管は減面率１０％以上６０％以下、且つ減肉率１％以上となるように冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に３０秒以上加熱し、その後、冷却する必要がある。 Next, the manufacturing conditions of the steel pipe will be described. The tube is cold-drawn so that the area reduction rate is 10% or more and 60% or less and the wall thickness reduction rate is 1% or more, and then the temperature range from Ac1 transformation point to 70 ° C to Ac1 transformation point is 30 seconds or more. It needs to be heated and then cooled.
素管の減面率が１０％未満の場合、十分な結晶回転が起こらず、熱処理後の再結晶集合組織が特定の方位に制御できないため、Ｃ及びＬ方向のｒ値が高くならない。また、減面率が６０％を超えると冷間加工時に破断するため、減面率は６０％以下と制限した。なお、減面率は、（伸管加工前の断面積−伸管加工後の断面積）／（伸管加工前の断面積）で表すものとする。 When the area reduction ratio of the tube is less than 10%, sufficient crystal rotation does not occur, and the recrystallized texture after the heat treatment cannot be controlled to a specific orientation, so the r values in the C and L directions do not increase. Further, if the area reduction rate exceeds 60%, the area is reduced during cold working, so the area reduction rate is limited to 60% or less. The area reduction ratio is expressed by (cross-sectional area before tube drawing-cross-sectional area after tube drawing) / (cross-sectional area before tube drawing).
減肉率が１％未満の場合、熱処理後の再結晶集合組織が特定の方位に制御できないため、Ｃ及びＬ方向のｒ値が高くならない。減肉率を１％以上にするためには、冷間での伸管加工時に鋼管内部にプラグを差込み、板厚を制御する方法が望ましい。なお、減肉率は、（伸管加工前の肉厚−伸管加工後の肉厚）／（伸管加工前の肉厚）で表すものとする。 When the thinning ratio is less than 1%, the recrystallized texture after the heat treatment cannot be controlled to a specific orientation, and therefore the r values in the C and L directions do not increase. In order to make the thickness reduction rate 1% or more, a method of controlling the plate thickness by inserting a plug into the steel pipe at the time of cold drawing is desirable. The thickness reduction rate is expressed as (thickness before tube drawing-thickness after tube drawing) / (wall thickness before tube drawing).
冷間で伸管加工した後、加熱温度がＡｃ１変態点−７０℃未満の場合、再結晶が十分に進行しないので狙いとする再結晶集合組織が得られず、Ｃ及びＬ方向のｒ値が高くならない。加熱温度がＡｃ１変態点を超えると、オーステナイト変態が起こり、狙いとする集合組織が得られず、Ｃ及びＬ方向のｒ値が高くならない。また、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に加熱する際、３０秒未満であると、再結晶が十分に進行せず、特定の再結晶集合組織が得られないのでＣ及びＬ方向のｒ値が高くならない。鋼管を加熱した後の冷却は空冷或いは水冷でも構わない。 When the heating temperature is less than Ac1 transformation point −70 ° C. after cold drawing, the target recrystallization texture cannot be obtained because the recrystallization does not proceed sufficiently, and the r values in the C and L directions are It will not be high. When the heating temperature exceeds the Ac1 transformation point, austenite transformation occurs, the targeted texture cannot be obtained, and the r values in the C and L directions do not increase. Further, when heating to a temperature range from Ac1 transformation point -70 ° C. to Ac1 transformation point, if it is less than 30 seconds, recrystallization does not proceed sufficiently, and a specific recrystallization texture cannot be obtained. The r value in the direction does not increase. The cooling after heating the steel pipe may be air cooling or water cooling.
冷間で伸管加工する前にＡｃ３変態点以上の温度に加熱し、圧延することなく、冷却することによってシーム溶接部を含めた鋼管の集合組織がランダム化され、その後の冷間での伸管加工と熱処理によってさらに高いｒ値が得られる。加熱温度がＡｃ３変態点未満では集合組織のランダム化が不十分となるので、加熱温度の上限をＡｃ３変態点未満とした。また、素管を加熱し、圧延した場合、表面形状が劣化し、加工性が劣化するために、圧延せずに冷却する。冷却は、空冷あるいは水冷のどちらでも構わない。 Prior to cold drawing, the texture of the steel pipe including the seam weld is randomized by heating to a temperature above the Ac3 transformation point and cooling without rolling, and the subsequent cold drawing. Higher r values can be obtained by tube processing and heat treatment. If the heating temperature is less than the Ac3 transformation point, the randomization of the texture becomes insufficient. Therefore, the upper limit of the heating temperature is set to be less than the Ac3 transformation point. In addition, when the raw tube is heated and rolled, the surface shape deteriorates and the workability deteriorates, so that cooling is performed without rolling. Cooling may be either air cooling or water cooling.
鋼管の化学成分については特に規定しない。通常の構造用鋼管、自動車用鋼板に使用される材料であれば、鋼成分にかかわらず所定の効果を発揮する。鋼成分によってＡｃ１変態点が異なるので、熱処理条件を設定する際、Ａｃ１変態点を測定する必要がある。Ａｃ１変態点はフォ−マスター試験等によって測定することが可能である。 The chemical composition of steel pipes is not specified. If it is the material used for the normal structural steel pipe and the steel plate for automobiles, a predetermined effect is exhibited regardless of the steel components. Since the Ac1 transformation point differs depending on the steel component, it is necessary to measure the Ac1 transformation point when setting the heat treatment conditions. The Ac1 transformation point can be measured by a Formaster test or the like.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明は、下記実施例に限定されるものではなく、本発明の趣旨に適合し得る範囲で適宜変更を加えて実施することも可能であり、それらは何れも本発明の技術的範囲に含まれる。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and is implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.
本実施例では、先ず、鋼管サイズが６３．５φ×２．２ｍｍｔになるように冷間加工前の母管を準備して、伸管加工を行い、その後、熱処理した鋼管を表１〜表３に示す。なお、表１には、鋼管の化学成分を示し、表２には、鋼管の製造条件を示し、表３には、鋼管の機械的性質を示した。伸管前の熱処理は９５０℃加熱のノルマを施した。鋼管の加工性の評価は以下の方法で行った。すなわち、鋼管に１０ｍｍφのスクライブドサークルを転写して、内圧と軸押し量を制御して、円周方向への張り出し成形を行った。バースト直前での最大拡管率を示す部位（拡管率＝成形後の最大周長／母管の周長）の軸方向のひずみと円周方向のひずみを測定した。この２つのひずみの比ρと最大拡管率をプロットして、ρ＝−０．５となる拡管率Ｒｅをもってハイドロフォームの成形性指標とした。 In this embodiment, first, a mother pipe before cold working is prepared so that the steel pipe size is 63.5φ × 2.2 mmt, pipe drawing is performed, and then the heat-treated steel pipe is shown in Tables 1 to 3 below. Shown in Table 1 shows the chemical composition of the steel pipe, Table 2 shows the manufacturing conditions of the steel pipe, and Table 3 shows the mechanical properties of the steel pipe. The heat treatment before drawing was performed with a 950 ° C. heating normal. The workability of the steel pipe was evaluated by the following method. That is, a scribed circle of 10 mmφ was transferred to the steel pipe, the internal pressure and the axial push amount were controlled, and overhanging was performed in the circumferential direction. Strain in the axial direction and strain in the circumferential direction of the portion showing the maximum tube expansion rate immediately before the burst (tube expansion rate = maximum circumferential length after molding / circumferential length of the mother tube) were measured. The ratio ρ of the two strains and the maximum pipe expansion ratio are plotted, and the pipe expansion ratio Re at which ρ = −0.5 is used as the formability index of the hydroform.
表３から明らかなように、Ｎｏ．１〜７の鋼管（本発明例）は、何れも良好な集合組織とｒ値を有し、ハイドロフォーム加工時の最大拡管率が高く、良好な加工性を有する。これに対して、Ｎｏ．８〜１３の鋼管（比較例）は、具備すべき条件が適切でなく、加工性が劣る。具体的に、Ｎｏ．８の鋼管は、減面率が低いため、ｒ値が低く最大拡管率が低い。Ｎｏ．９の鋼管は、減面率が高すぎるため、伸管加工時に破断した。Ｎｏ．１０の鋼管は、減肉率が小さいため、ｒ値が低く最大拡管率が低い。Ｎｏ．１１の鋼管は、熱処理温度が低いため、ｒ値が低く最大拡管率が低い。Ｎｏ．１２の鋼管は、熱処理温度が高いため、ｒ値が低く最大拡管率が低い。Ｎｏ．１３の鋼管は、熱処理時間が短いため、ｒ値が低く最大拡管率が低い。Ｎｏ．１４の鋼管は、伸管加工前の熱処理において加熱後に圧延を行ったために、表面性状が劣化し、最大拡管率が低く、加工性が劣化した。 As is apparent from Table 3, No. The steel pipes 1 to 7 (examples of the present invention) all have a good texture and an r value, have a high maximum tube expansion ratio during hydroforming, and have good workability. In contrast, no. The steel pipes of 8 to 13 (comparative examples) are not suitable for the conditions to be provided and are inferior in workability. Specifically, no. Since the steel pipe No. 8 has a low area reduction rate, the r value is low and the maximum pipe expansion rate is low. No. The steel pipe No. 9 was broken at the time of drawing because the area reduction rate was too high. No. Since the steel pipe No. 10 has a small thickness reduction rate, the r value is low and the maximum pipe expansion rate is low. No. Since the steel tube No. 11 has a low heat treatment temperature, the r value is low and the maximum tube expansion rate is low. No. Since the steel pipe No. 12 has a high heat treatment temperature, the r value is low and the maximum tube expansion ratio is low. No. Since the steel pipe No. 13 has a short heat treatment time, the r value is low and the maximum pipe expansion rate is low. No. Since the steel pipe No. 14 was rolled after heating in the heat treatment before drawing, the surface properties were deteriorated, the maximum tube expansion ratio was low, and the workability was deteriorated.
本発明の鋼管は、安価で加工性に優れているので、伸管、曲げ、ハイドロフォーミングなどで加工する構造用鋼管や配管などに広く適用することができる。 Since the steel pipe of the present invention is inexpensive and excellent in workability, it can be widely applied to structural steel pipes and pipes processed by drawing, bending, hydroforming and the like.
Claims (4)
Ｃ：０．０３５〜０．３５０％、
Ｓｉ：０．１３〜０．３４％、
Ｍｎ：０．４０〜１．３５％、
Ｐ：０．００６５〜０．０１５０％、
Ｓ：０．００１６〜０．００４３％、
Ａｌ：０．００２〜０．０３３％、
Ｎ：０．００１９〜０．００４８％、
Ｏ：０．００１９〜０．００３４％、
残部鉄および不可避不純物からなる鋼管を素管として、該素管を冷間で伸管加工した後、Ａｃ１変態点−７０℃からＡｃ１変態点の温度範囲に加熱して製造する鋼管において、シーム溶接部を含む鋼管全域で鋼管の軸方向のｒ値（ｒＬ）が１．２以上、鋼管の円周方向のｒ値（ｒＣ）が１．２以上で、且つ、
前記鋼管の１／２板厚における板面の{１１１}のＸ線反射面ランダム強度比が２．０以上７．０以下、{１１０}のＸ線反射面ランダム強度比が１．０以上５．０以下、{１００}のＸ線反射面ランダム強度比が３．０以下であることを特徴とする加工性に優れた鋼管。 Steel component is mass%,
C: 0.035 to 0.350%,
Si: 0.13-0.34%,
Mn: 0.40 to 1.35%,
P: 0.0065 to 0.0150%,
S: 0.0016 to 0.0043%,
Al: 0.002 to 0.033%,
N: 0.0019 to 0.0048%,
O: 0.0019 to 0.0034%,
In a steel pipe manufactured by heating a steel pipe made of the remaining iron and inevitable impurities as a raw pipe and then cold-drawing the raw pipe to a temperature range of Ac1 transformation point -70 ° C. to Ac1 transformation point. In the entire steel pipe including the portion, the r value (rL) in the axial direction of the steel pipe is 1.2 or more, the r value (rC) in the circumferential direction of the steel pipe is 1.2 or more , and
{111} X-ray reflecting surface random intensity ratio of {111} of the plate surface at 1/2 plate thickness of the steel pipe is 2.0 to 7.0, and {110} X-ray reflecting surface random intensity ratio is 1.0 to 5 2.0 or less, excellent workability, characterized in der Rukoto X-ray reflection surfaces random intensity ratio of 3.0 or less for {100} steel.
Ｃｒ：０．２４％、Ｍｏ：０．２０％、Ｔｉ：０．０１１〜０．０１２％、Ｂ：０．００１０％、のいずれか１種以上を含むことを特徴とする請求項１に記載の加工性に優れた鋼管。 Furthermore, the steel component is mass%,
It contains any one or more of Cr: 0.24%, Mo: 0.20%, Ti: 0.011-0.012%, B: 0.0010%. Steel pipe with excellent workability.
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