JP5277908B2 - Billet piercing and rolling method - Google Patents

Billet piercing and rolling method Download PDF

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JP5277908B2
JP5277908B2 JP2008303650A JP2008303650A JP5277908B2 JP 5277908 B2 JP5277908 B2 JP 5277908B2 JP 2008303650 A JP2008303650 A JP 2008303650A JP 2008303650 A JP2008303650 A JP 2008303650A JP 5277908 B2 JP5277908 B2 JP 5277908B2
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billet
piercing
rolling
tip
hole
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JP2010125493A (en
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拓也 長濱
宏太郎 藤澤
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JFE Steel Corp
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JFE Steel Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a piercing rolling method for a billet by which the occurrence of scratches on the inner surface at a distal end part of a seamless steel tube is prevented advantageously. <P>SOLUTION: In the piercing rolling method for a billet performing piercing rolling on the billet 10 after heating it, tapering work 20 is applied to the outer surface of the distal end part of the billet and a conical hole piercing work 40 is applied to the center of the distal end face thereof before performing piercing rolling. The conical hole is formed into a shape in which the depth of the hole is &gt;50 mm and the inlet diameter of the hole is larger than the depth of the hole. The tapering work is performed so as to satisfy expression (1): G0. 5Db&gt;D100&gt;D0&gt;Gt, wherein Db denotes the diameter of the billet 10 before the tapering work, D0 and D100 denote the diameters in the distal end position and in a position of 100 mm inside from the distal end position after tapering work, respectively, and Gt and G0. 5Db denote gaps between rolls in the distal end position of a plug of a piercer used for the piercing rolling and in a position 0.5&times;Db upstream from the distal end of the plug, respectively. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

本発明は、ビレット（継目無鋼管用素材）の穿孔圧延方法に関し、特に、ビレットを例えばマンネスマンピアサーのような穿孔圧延機にて穿孔圧延するときに被圧延材先端部に内面疵を発生し難くした、ビレットの穿孔圧延方法に関する。   The present invention relates to a piercing and rolling method for billets (materials for seamless steel pipes), and in particular, when a billet is pierced and rolled by a piercing and rolling machine such as a Mannesmann Piercer, an inner surface flaw is hardly generated at the tip of the material to be rolled. The present invention relates to a billet piercing and rolling method.

穿孔圧延機、例えばマンネスマンピアサーは、図１に示すようにロール軸方向の中央から両端に進むほどロール径が小さくなる形状（太鼓形状）のロール１，２を上下に交差配置（ただしロール軸は圧延方向に平行な面内にある）し、かつ、プラグ先端がロールバイト中央付近に位置しプラグ後端が圧延方向の下流側に位置するようにプラグ３を配置して構成され、そのロールバイト内に材料10を通して穿孔圧延が行われる。   As shown in FIG. 1, a piercing and rolling mill, for example, Mannesmann Piercer, has rolls 1 and 2 having a shape in which the roll diameter decreases (drum shape) as it goes from the center to the both ends in the roll axis direction. The plug 3 is arranged so that the tip of the plug is located near the center of the roll bite and the rear end of the plug is located downstream of the roll direction. The material 10 is pierced and rolled inside.

上記穿孔圧延の原理は、ロールバイト始端位置からプラグ先端位置にかけての圧延方向範囲（空揉み部４）で、回転鍛造（空揉み）によりビレット10の断面中心部を脆化させ、続いてプラグ先端位置からロールバイト終端位置にかけての圧延方向範囲（穿孔部５）で、前記脆化した断面中心部をプラグ３に押付けて穿孔し、管肉厚を決定するというものである。   The principle of the above piercing and rolling is that the center of the cross section of the billet 10 is embrittled by rotary forging (empty stagnation) in the rolling direction range (empty stagnation part 4) from the roll bite starting end position to the plug tip position. In the rolling direction range from the position to the end position of the roll bite (piercing part 5), the embrittled cross-sectional center part is pressed against the plug 3 and drilled to determine the tube thickness.

このような穿孔圧延においては、疵が管内面の先端部（圧延時の先頭端部）に集中的に発生する傾向がある。この疵の発生機構は次のように考えられている。すなわち、図２に示すように、ビレット10（角スラブ→ビレット圧延材、あるいは直鋳ビレット）はその断面中心部に偏析15（角スラブ→ビレット圧延材では線状偏析、直鋳ビレットでは点状偏析）を有する。偏析15は、先端部に位置する部分が、穿孔圧延前の加熱で酸化する。空揉みの際、この酸化した偏析部分が起点となって先端部に割れが発生・進展する。この割れの内面の凹凸がプラグで圧下されて倒れ込み、管11の圧延先端部内面の疵50となる。   In such piercing and rolling, wrinkles tend to occur intensively at the tip of the inner surface of the pipe (the leading end during rolling). The generation mechanism of this wrinkle is considered as follows. That is, as shown in FIG. 2, billet 10 (square slab → billet rolled material or straight cast billet) is segregated at the center of the cross section 15 (linear segregation in square slab → billet rolled material, and spot shaped in direct cast billet. Segregation). In the segregation 15, the portion located at the tip is oxidized by heating before piercing and rolling. At the time of emptying, this oxidized segregation part is the starting point and cracks are generated and propagated at the tip part. The cracks on the inner surface of the crack are squeezed down by the plug and fall down, resulting in a flange 50 on the inner surface of the rolling tip of the tube 11.

上記のような疵発生の軽減対策として、図３に示すように、製鋼工程で偏析15を、穿孔箇所になるビレット10の断面中心部位から外れた位置にずらす方法（偏析をオフセットする方法；特許文献１参照）や、図４に示すように、コーンタイプピアサー（上下にコーン形状のロール21,22を配置した穿孔圧延機）を用いて、圧延中のせん断変形抑制により、凹凸倒れ込みの防止を図る方法（特許文献２参照）などが知られている。
特開平１０−１２８５１０号公報 特許第３０２１６６４号公報 As a countermeasure for reducing the occurrence of wrinkles as described above, as shown in FIG. 3, a method of shifting the segregation 15 to a position deviated from the central portion of the cross-section of the billet 10 that becomes a drilling site (method of offsetting segregation; patent) Reference 1) and as shown in Fig. 4, using cone type piercers (a piercing and rolling machine with cone-shaped rolls 21 and 22 arranged on the top and bottom) to prevent uneven collapse by suppressing shear deformation during rolling. A method (see Patent Document 2) is known.
JP-A-10-128510 Japanese Patent No. 3021664

しかし、上記の偏析をオフセットする方法では、管肉厚内部に偏析が残るため、品質上の不均一を招く。また、上記のコーンタイプピアサーを用いる方法では、ロール形状の変更やロール軸を圧延方向に対し傾斜させる設備が必要となり、投資が膨大となる。すなわち、従来の技術では継目無鋼管の先端部内面の疵発生を有利に防止するのは困難であるという課題が残されたままであった。   However, in the method of offsetting the above-mentioned segregation, segregation remains inside the tube thickness, resulting in non-uniform quality. In addition, the method using the cone type piercer requires a facility for changing the roll shape and tilting the roll shaft with respect to the rolling direction, resulting in an enormous investment. In other words, the conventional technique still has a problem that it is difficult to advantageously prevent the generation of flaws on the inner surface of the distal end portion of the seamless steel pipe.

発明者らは、前記課題を解決するための手段を鋭意検討し、以下に記される本発明をなした。
（請求項１）
ビレットを加熱し、穿孔圧延する方法において、前記穿孔圧延するより前に、前記ビレットの先端部に、外面へのテーパ加工および先端面中心へのコーン状孔あけ加工を施すにあたり、前記ビレットの、テーパ加工前の直径をＤ ｂ 、テーパ加工後の先端位置および該先端位置から１００ｍｍ内側の位置における直径をそれぞれＤ ０ 、Ｄ １００ とし、前記穿孔圧延に用いる穿孔圧延機の、プラグ先端位置および該プラグ先端位置から０．５×Ｄ ｂ だけ上流側の位置におけるロール間ギャップをそれぞれＧ ｔ 、Ｇ ０．５Ｄｂ として、下記式(1)が満足されるように、前記テーパ加工を行うことを特徴とするビレットの穿孔圧延方法。
記
Ｇ ０．５Ｄｂ ＞Ｄ １００ ＞Ｄ ０ ＞Ｇ ｔ ‥‥(1)
（請求項２）
前記コーン状孔の孔形状を、孔深さが５０ｍｍ超、孔入口径が前記孔深さ超の孔形状とすることを特徴とする請求項１に記載のビレットの穿孔圧延方法。 The inventors diligently studied the means for solving the above-mentioned problems and made the present invention described below.
(Claim 1)
In the method of heating and piercing and rolling the billet, before performing the piercing and rolling, the tip of the billet is subjected to taper processing to the outer surface and cone-shaped drilling processing to the center of the tip surface . tapered front of the diameter D b, and D 0, D 100, respectively diameters of 100mm inner position from the tip position and tip position after tapering, the piercing-rolling machine used in the piercing-rolling, the plug tip position and the each G t gaps between the rolls in only the upstream-side position 0.5 × D b from the plug tip position, as G 0.5 dB, so the following equation (1) is satisfied, characterized in that said tapered Billet piercing and rolling method.
Record
G 0.5Db > D 100 > D 0 > G t (1)
(Claim 2)
2. The billet piercing and rolling method according to claim 1, wherein a hole shape of the cone-shaped hole is a hole shape having a hole depth exceeding 50 mm and a hole inlet diameter exceeding the hole depth .

（請求項３）
前記テーパ加工およびコーン状孔あけ加工は、前記加熱後前記穿孔圧延前に、ビレット先端部加工目標形状の孔型を有する金型を用いて前記ビレットの先端部をプレスすることにより行うことを特徴とする請求項１または２に記載のビレットの穿孔圧延方法。
（請求項４）
請求項１〜３のいずれか１項に記載されたビレットの穿孔圧延方法を用いて製造されてなる継目無鋼管。 (Claim 3)
The taper processing and cone-shaped drilling are performed by pressing the tip of the billet using a die having a hole shape of a billet tip processing target shape after the heating and before the piercing and rolling. The billet piercing and rolling method according to claim 1 or 2 .
(Claim 4)
A seamless steel pipe manufactured by using the billet piercing and rolling method according to any one of claims 1 to 3 .

本発明によれば、継目無鋼管の品質上の不均一を招かずに、また膨大な設備投資を要さずに、管内面先端部の疵発生を防止することができる。   ADVANTAGE OF THE INVENTION According to this invention, the generation | occurrence | production of the flaw of a pipe inner surface front-end | tip part can be prevented, without causing the nonuniformity in quality of a seamless steel pipe, and without requiring huge equipment investment.

本発明では、ビレットを加熱し、穿孔圧延する。ビレットの加熱温度は通常の操業における加熱温度でよい。穿孔圧延に用いる穿孔圧延機は、図１のマンネスマンピアサー、図４のコーンタイプピアサーのいずれであってもよいが、設備コスト節約の点で、マンネスマンピアサーが好ましい。
本発明では、穿孔圧延するより前（加熱の前、あるいは加熱後穿孔圧延前）に、図５に示すように、ビレット10の先端部（穿孔圧延時に先頭になる部位）に、外面へのテーパ加工20、および先端面中心へのコーン状孔あけ加工40を施す。テーパ加工20によるテーパ形状は、いうまでもなく先細り形状である。また、コーン状孔あけ加工40による孔形状は、いうまでもなく先広がり形状である。 In the present invention, the billet is heated and pierced and rolled. The heating temperature of the billet may be the heating temperature in normal operation. The piercing and rolling machine used for piercing and rolling may be either the Mannesmann piercer of FIG. 1 or the cone type piercer of FIG. 4, but the Mannesmann piercer is preferable from the viewpoint of equipment cost saving.
In the present invention, before piercing-rolling (before heating or before piercing-rolling after heating), as shown in FIG. 5, the tip of billet 10 (portion leading to piercing-rolling) is tapered to the outer surface. Processing 20 and cone-shaped drilling 40 in the center of the tip surface are performed. Needless to say, the taper shape by the taper processing 20 is a tapered shape. Needless to say, the shape of the hole formed by the cone-shaped drilling process 40 is a divergent shape.

テーパ加工20を施したことにより、ビレット先端部に対する空揉みが軽減され、先端部が空揉み部４（図１参照）を通過する際に、断面中心部の偏析（先端部の偏析は加熱時に酸化されている）を起点とした割れの発生・進展が効果的に防止される。したがって、先端部の断面中心部位には、穿孔部５（図１参照）でプラグ３による圧下で倒れ込むべき内面凹凸を有する割れの発生・進展が抑制されている。   By applying the taper process 20, air stagnation with respect to the billet tip is reduced, and when the tip passes through the air stagnation part 4 (see FIG. 1), segregation at the center of the cross section (segregation at the tip is caused by heating). Occurrence and development of cracks starting from (oxidized) is effectively prevented. Therefore, the generation / progress of cracks having inner surface irregularities that should fall down under the pressure of the plug 3 at the perforated portion 5 (see FIG. 1) is suppressed at the central portion of the cross section of the tip portion.

さらに、コーン状孔あけ加工40を施したことにより、プラグ３による肉厚圧下が軽減し、それに伴うせん断変形が低減する。したがって、穿孔部５での割れ内面の凹凸倒れ込みは軽減される。
上記の割れ発生・進展抑制作用および割れ内面の凹凸倒れ込み軽減作用によって、管の先端部における内面の疵発生が効果的に防止されるわけである。 Furthermore, the cone-shaped drilling process 40 is performed, so that the wall thickness reduction by the plug 3 is reduced, and the accompanying shear deformation is reduced. Therefore, the uneven fall of the inner surface of the crack in the perforated portion 5 is reduced.
The above-described crack generation / development suppressing action and the depression / protrusion collapse reducing action on the inner surface of the crack effectively prevent the occurrence of wrinkles on the inner surface at the tip of the pipe.

本発明では、製鋼工程での偏析オフセットは必要ないから、継目無鋼管の品質上の不均一にはつながらない。また、ビレット先端部をテーパ加工およびコーン状孔あけ加工するための設備投資は僅少で済む。
本発明において、テーパ加工20による加工形状は、図６に示すように、ビレット10の、テーパ加工前の直径をＤｂ、テーパ加工後の先端位置および該先端位置から１００ｍｍ内側の位置における直径をそれぞれＤ０、Ｄ１００とし、前記穿孔圧延に用いる穿孔圧延機の、プラグ先端位置および該プラグ先端位置から０．５×Ｄｂだけ上流側の位置におけるロール１，２間ギャップをそれぞれＧｔ、Ｇ０．５Ｄｂとして、次式、
Ｇ０．５Ｄｂ＞Ｄ１００＞Ｄ０＞Ｇｔ ‥‥(1)
が満足されるテーパ加工形状とするのが好適である。式(1)において、Ｄ１００＞Ｄ０は、テーパ加工形状が先細り形状であるから当然のことである。また、Ｄ０＞Ｇｔとしたのは、Ｄ０≦Ｇｔであると、ビレット先端部が空揉み不十分（すなわち断面中心部の脆化が不十分）な状態のままプラグ３先端に衝突し、プラグ３の損傷を招くおそれがあるからである。また、Ｇ０．５Ｄｂ＞Ｄ１００としたのは、Ｇ０．５Ｄｂ≦Ｄ１００であると、ビレット先端がロールバイトをまだ通過し終わっていない非定常圧延の状態で、ロール１，２の空揉み関与領域が噛み込み側ロール端部にまで及んで、穿孔圧延機にかかる負荷が大きくなりすぎるおそれがあるからである。 In the present invention, no segregation offset is required in the steel making process, and this does not lead to uneven quality of the seamless steel pipe. Moreover, the capital investment for tapering and cone-shaped drilling of the billet tip is minimal.
In the present invention, as shown in FIG. 6, the processing shape by the taper processing 20 is that the diameter of the billet 10 before taper processing is D b , the tip position after taper processing, and the diameter at a position 100 mm inside from the tip position. D 0 and D 100 respectively, and the gap between the rolls 1 and 2 at the position upstream of the plug tip position and 0.5 × D b from the plug tip position of the piercing mill used for the piercing rolling is G t , As G 0.5Db ,
G 0.5Db > D 100 > D 0 > G t (1)
It is preferable to have a tapered shape that satisfies the above. In the formula (1), D 100 > D 0 is natural because the tapered shape is a tapered shape. Also, D 0 > G t is set so that when D 0 ≦ G t , the billet tip collides with the tip of the plug 3 while the billet tip is insufficiently hollowed (that is, the embrittlement at the center of the cross section is insufficient). This is because the plug 3 may be damaged. Further, G 0.5Db > D 100 is set such that G 0.5Db ≦ D 100 is an unsteady rolling state in which the billet tip has not yet passed through the roll bite and the rolls 1 and 2 are empty. This is because the stagnation-related region extends to the end of the biting side roll, and the load applied to the piercing and rolling mill may become too large.

また、コーン状孔加工40の孔形状は、図５のように孔深さをｌ、孔入口径をＤhで表すとして、ｌ＞５０ｍｍ（より好ましくは、１００ｍｍ＞ｌ＞５０ｍｍ）、Ｄh＞ｌ（なお、当然ながらＤ０＞Ｄhである）、を満たすものとすることが好ましい。こうすることで、通常のプラグを用いる場合に、凹凸倒れ込み軽減作用の効果が、より大きくなる。
また、テーパ加工20およびコーン状孔あけ加工40は、加熱後穿孔圧延前の段階で、例えば図７に示すように、ビレット先端部加工目標形状（テーパ加工20とコーン状孔あけ加工40の双方の加工目標形状の合成形状）の孔型32を設けた金型30を用いてビレット10の先端部をプレスする（好ましくは１回だけプレスする）方法で行うことが、他の加工方法（加熱前の冷間での切削や金型プレスなど、あるいは加熱後穿孔圧延前の熱間であっても金型プレスではない方法）に比べて、効率、省エネルギー、設備コストなどの面で有利なので、好ましい。 Further, the hole shape of the cone-shaped hole machining 40 is l> 50 mm (more preferably, 100 mm>l> 50 mm) and Dh> l, where the hole depth is represented by l and the hole inlet diameter is represented by Dh as shown in FIG. (Of course, D 0 > Dh) is preferably satisfied. By doing so, the effect of reducing the unevenness collapse becomes greater when a normal plug is used.
Further, the taper processing 20 and the cone-shaped drilling 40 are performed at the stage after heating and before piercing and rolling, for example, as shown in FIG. Other processing methods (heating) can be performed by pressing the tip of the billet 10 (preferably pressing only once) using a mold 30 provided with a hole mold 32 having a composite shape of the processing target shape). Compared to previous cold cutting, die press, or hot press before piercing and rolling, it is advantageous in terms of efficiency, energy saving, equipment cost, etc. preferable.

また、本発明の継目無鋼管は、本発明のビレットの穿孔圧延方法を用いて製造されたものであるから、管先端部内面に疵を有さないものである。   Moreover, since the seamless steel pipe of the present invention is manufactured using the billet piercing and rolling method of the present invention, the inner surface of the pipe tip portion does not have wrinkles.

表１に示す形態のビレット（断面円形状、断面中心部に偏析あり）を、表１に示す条件で、加熱→穿孔圧延（マンネスマンピアサーで圧延）し、あるいは、加熱→先端部テーパ加工およびコーン状孔あけ加工（図７のように金型でプレス加工、プレスは１回）→穿孔圧延（マンネスマンピアサーで圧延）し、管（継目無鋼管）を得た。得られた管について、先端から管長手方向に３００ｍｍ入った位置までの範囲の内面を、ファイバースコープで観察し、疵の有無を調べた結果を表１に示す。   Billet (circular cross section, with segregation in the center of the cross section) shown in Table 1 is heated to piercing and rolling (rolling with Mannesmann Piercer) under the conditions shown in Table 1, or heated to tip taper processing and cone A hole (seamless steel pipe) was obtained by punching (rolling with a Mannesmann Piercer) → punching (pressing with a mold as shown in FIG. 7, pressing once) → punching and rolling (rolling with a Mannesmann Piercer). Table 1 shows the results obtained by observing the inner surface of the obtained tube from the tip to a position 300 mm in the longitudinal direction of the tube with a fiber scope and examining the presence or absence of wrinkles.

表１より、本発明例では、管先端部内面の疵発生が抑制されたことがわかる。   From Table 1, it can be seen that in the example of the present invention, generation of wrinkles on the inner surface of the tube tip portion was suppressed.

Figure 0005277908
Figure 0005277908

穿孔圧延の原理を示す説明図である。It is explanatory drawing which shows the principle of piercing-rolling. 管先端部内面疵の発生機構を示す説明図である。It is explanatory drawing which shows the generation | occurrence | production mechanism of a pipe tip part inner surface flaw. 従来技術の１例を示す説明図である。It is explanatory drawing which shows an example of a prior art. 従来技術の１例を示す説明図である。It is explanatory drawing which shows an example of a prior art. 本発明に用いるビレットの先端部加工形状を示す概略図である。It is the schematic which shows the front-end | tip part process shape of the billet used for this invention. 本発明に用いるビレットの好適な先端部加工形状を示す説明図である。It is explanatory drawing which shows the suitable front-end | tip part process shape of the billet used for this invention. 本発明に用いるビレットの好適な先端部加工方法の１例を示す説明図である。It is explanatory drawing which shows an example of the suitable tip part processing method of the billet used for this invention.

符号の説明Explanation of symbols

１ ロール（太鼓形状のロールを上に配置したもの）
２ ロール（太鼓形状のロールを下に配置したもの）
３ プラグ
４ 空揉み部
５ 穿孔部
10 ビレット（継目無鋼管用素材、被圧延材）
11 管（継目無鋼管）
15 偏析
20 テーパ加工
21 ロール（コーン形状のロールを上に配置したもの）
22 ロール（コーン形状のロールを下に配置したもの）
30 金型
32 ビレット先端部加工目標形状の孔型
40 コーン状孔あけ加工
50 疵 1 roll (a drum-shaped roll placed on top)
2 rolls (a drum-shaped roll placed below)
3 Plug 4 Empty part 5 Perforated part
10 Billet (material for seamless steel pipe, rolled material)
11 pipe (seamless steel pipe)
15 Segregation
20 Taper processing
21 roll (cone-shaped roll placed on top)
22 roll (cone-shaped roll placed below)
30 mold
32 Hole shape with billet tip machining target shape
40 Cone drilling
50 疵

Claims (4)

ビレットを加熱し、穿孔圧延する方法において、前記穿孔圧延するより前に、前記ビレットの先端部に、外面へのテーパ加工および先端面中心へのコーン状孔あけ加工を施すにあたり、前記ビレットの、テーパ加工前の直径をＤ ｂ 、テーパ加工後の先端位置および該先端位置から１００ｍｍ内側の位置における直径をそれぞれＤ ０ 、Ｄ １００ とし、前記穿孔圧延に用いる穿孔圧延機の、プラグ先端位置および該プラグ先端位置から０．５×Ｄ ｂ だけ上流側の位置におけるロール間ギャップをそれぞれＧ ｔ 、Ｇ ０．５Ｄｂ として、下記式(1)が満足されるように、前記テーパ加工を行うことを特徴とするビレットの穿孔圧延方法。
記
Ｇ ０．５Ｄｂ ＞Ｄ １００ ＞Ｄ ０ ＞Ｇ ｔ ‥‥(1) In the method of heating and piercing and rolling the billet, before performing the piercing and rolling, the tip of the billet is subjected to taper processing to the outer surface and cone-shaped drilling processing to the center of the tip surface . tapered front of the diameter D b, and D 0, D 100, respectively diameters of 100mm inner position from the tip position and tip position after tapering, the piercing-rolling machine used in the piercing-rolling, the plug tip position and the each G t gaps between the rolls in only the upstream-side position 0.5 × D b from the plug tip position, as G 0.5 dB, so the following equation (1) is satisfied, characterized in that said tapered Billet piercing and rolling method.
Record
G 0.5Db > D 100 > D 0 > G t (1) 前記コーン状孔の孔形状を、孔深さが５０ｍｍ超、孔入口径が前記孔深さ超の孔形状とすることを特徴とする請求項１に記載のビレットの穿孔圧延方法。   2. The billet piercing and rolling method according to claim 1, wherein a hole shape of the cone-shaped hole is a hole shape having a hole depth exceeding 50 mm and a hole inlet diameter exceeding the hole depth. 前記テーパ加工およびコーン状孔あけ加工は、前記加熱後前記穿孔圧延前に、ビレット先端部加工目標形状の孔型を有する金型を用いて前記ビレットの先端部をプレスすることにより行うことを特徴とする請求項１または２に記載のビレットの穿孔圧延方法。 The taper processing and cone-shaped drilling are performed by pressing the tip of the billet using a die having a hole shape of a billet tip processing target shape after the heating and before the piercing and rolling. The billet piercing and rolling method according to claim 1 or 2 . 請求項１〜３のいずれか１項に記載されたビレットの穿孔圧延方法を用いて製造されてなる継目無鋼管。 A seamless steel pipe manufactured by using the billet piercing and rolling method according to any one of claims 1 to 3 .
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JP5459347B2 (en) 2012-04-18 2014-04-02 新日鐵住金株式会社 Round billet for seamless metal pipe and method for producing seamless metal pipe
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JPS5372763A (en) * 1976-12-10 1978-06-28 Nippon Steel Corp Method and apparatus for forming center hole during making seamless steel pipe
JPS61162217A (en) * 1985-01-11 1986-07-22 Sumitomo Metal Ind Ltd Production of seamless metal pipe and billet for seamless metallic pipe
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