JP4556861B2 - Round billet manufacturing method - Google Patents
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- JP4556861B2 JP4556861B2 JP2005361676A JP2005361676A JP4556861B2 JP 4556861 B2 JP4556861 B2 JP 4556861B2 JP 2005361676 A JP2005361676 A JP 2005361676A JP 2005361676 A JP2005361676 A JP 2005361676A JP 4556861 B2 JP4556861 B2 JP 4556861B2
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本発明は、Ｃを０．７〜１．５質量％、Ｃｒを０．９〜２．０質量％含有する高炭素クロム鋼の軸受用継目無鋼管の製造に供する、直径が１５０〜２５０mmの丸鋼片を製造する方法に関するものである。 The present invention is used for production of a seamless steel pipe for bearings of high carbon chromium steel containing 0.7 to 1.5% by mass of C and 0.9 to 2.0% by mass of Cr, and having a diameter of 150 to 250 mm. The present invention relates to a method of manufacturing a round steel piece.
高炭素クロム鋼の軸受用継目無鋼管素材は、「転炉又は電気炉→２次精錬→連続鋳造（矩形）→分塊」の工程を経て製造される。そして、その後、マンネスマン製管法等により継目無鋼管に加工される。 A seamless steel pipe material for bearings of high-carbon chromium steel is manufactured through a process of “converter or electric furnace → secondary refining → continuous casting (rectangular) → blocking”. And after that, it is processed into a seamless steel pipe by the Mannesmann pipe manufacturing method or the like.
ところで、高炭素クロム軸受鋼は高クロム鋼とは異なり、鋳造時の中心ポロシティが最終製品（本発明では継目無鋼管）の品質を悪化させることがない。従って、特許文献１に記載されているような、ポロシティ対策としての連続鋳造鋳片の扁平化はなされておらず、むしろ、分塊時における鋼片外面疵の低減を重視し、分塊性の良好な、正方形に近い形状の連続鋳造鋳片（扁平比Ｗ／Ｈ＜１．５）が使用されていた。
そして、このような正方形に近い形状の連続鋳造鋳片を用いて、高炭素クロム鋼の軸受用継目無鋼管の素材である、直径が１５０〜２５０mmの丸鋼片を製造する場合には、以下のＡ〜Ｃの対策が採られていた。 And when manufacturing a round steel piece with a diameter of 150 to 250 mm, which is a material of a seamless steel pipe for bearings of high carbon chromium steel, using a continuous cast slab having a shape close to a square, Measures A to C were taken.
Ａ．内面欠陥の対策
本特許発明が対象とする成分系の軸受鋼は、高Ｃ、高Ｃｒであり融点が低い。さらに、連続鋳造鋳片が矩形であったため、凝固が最も遅い中心部において、偏析が集中しやすい。偏析する元素のなかでも、Ｐは粒界に偏析して粒界の融点を低下させるとともにその強度も低下させる。
A. Countermeasures for Internal Defects The component bearing steels targeted by the present invention are high C, high Cr and have a low melting point. Furthermore, since the continuous cast slab was rectangular, segregation tends to concentrate in the central part where solidification is the slowest. Among the segregating elements, P segregates at the grain boundary to lower the melting point of the grain boundary and reduce its strength.
従って、このような連続鋳造鋳片を分塊圧延して継目無鋼管素材とする場合、その中心部の高温強度は低いものとなる。
マンネスマン製管法等では、穿孔時に素材の中心部が加工発熱により最も高温となるため、中心部の高温強度が低い素材の場合、中心部が穿孔時に溶融破断し、鋼管の内面に欠陥として残存してしまうことになる。
Therefore, when such a continuous cast slab is rolled into a seamless steel pipe material, the high-temperature strength at the center is low.
In the Mannesmann tube method, etc., the center part of the material becomes the highest temperature due to processing heat during drilling, so in the case of a material with low high-temperature strength in the center part, the center part melts and breaks during drilling and remains as a defect on the inner surface of the steel pipe. Will end up.
この現象を防止するには、特許文献２に示された連続鋳造鋳片の組織調整が有効とされてきた。具体的には、連続鋳造鋳片を分塊圧延する時、または継目無鋼管素材を製管する時に１１００℃以上で均熱する時間（Hr）をＦＴとした場合、
[Ｃ]＋（[Ｐ]×１００）−ＦＴ／１０≦１．６
となる様、Ｃ、Ｐ、ＦＴを調整する方法である。
[C] + ([P] × 100) −FT / 10 ≦ 1.6
This is a method of adjusting C, P, and FT.
しかしながら、軸受鋼として要求される機械的性能を確保するため、Ｃの範囲はほぼ限定される。また、ＦＴでの調整も、分塊能率または製管能率の変動を生じさせるため、その範囲もほぼ一定とする必要があり、長時間側での条件とする傾向にある。
従って、品質を維持しながら生産性を向上するためには、低Ｐ化等の対策が要求される。
However, in order to ensure the mechanical performance required as bearing steel, the range of C is almost limited. In addition, since the adjustment with FT also causes fluctuations in the lump efficiency or tube production efficiency, the range needs to be substantially constant and tends to be a condition on the long time side.
Therefore, in order to improve productivity while maintaining quality, measures such as lowering P are required.
Ｂ．分塊加熱時の熱応力割れ対策
連続鋳片の扁平比が小さい、すなわち正方形に近い場合、常温から分塊可能な温度（１２３０℃）までの加熱過程に生じる熱応力により、分塊圧延時には中心部の応力が増大する。
B. Measures against thermal stress cracking when heating ingots When the flattening ratio of the continuous slab is small, that is, close to a square, it is the center of the slab rolling due to the thermal stress that occurs in the heating process from room temperature to the temperature at which it can be smashed (1230 ° C). The stress of the part increases.
さらに、連続鋳造鋳片には先に述べた偏析による中心部の強度低下や、高Ｃ鋼に特有の巨大炭化物が散在してそのまわりに応力集中を生じさせるので、耐割れ性を低減させる要因がある。 In addition, the continuous cast slab has a decrease in strength at the center due to segregation as described above, and a large carbide peculiar to high C steel is scattered and stress is concentrated around it. There is.
従って、熱応力を増加させる加熱条件とすると、これらの理由により加熱中に連続鋳造鋳片が割れてしまう。 Therefore, if it is set as the heating conditions which increase a thermal stress, a continuous cast slab will break during heating for these reasons.
この対策として、従来は、鋳造後直ちに分塊工場へ搬送して加熱を開始することで熱応力の発生を抑制する方法が採られていた。また、連続鋳造から分塊までに時間を要する場合は、中心部の偏析や、巨大な炭化物を拡散させるための均熱が必要であった。 As a countermeasure, conventionally, a method of suppressing the generation of thermal stress by transporting to a lump factory immediately after casting and starting heating has been adopted. Moreover, when time is required from continuous casting to agglomeration, segregation at the center and soaking for diffusing huge carbides are necessary.
Ｃ．製管加熱時の熱応力割れ対策
また、分塊比が不十分な場合は、継目無鋼管素材とした後も鋳片中心部の強度改善が十分に図れず、製管時の常温から製管可能な温度（１２３０℃）までの加熱過程において、前記Ｂと同じ理由による熱応力割れを生じさせる可能性がある。
C. Countermeasures against thermal stress cracking when heating pipes Also, if the split ratio is insufficient, the strength of the center part of the slab cannot be improved sufficiently even after the seamless steel pipe material is used, and pipes are manufactured from room temperature at the time of pipe making. In the heating process up to a possible temperature (1230 ° C.), there is a possibility of causing thermal stress cracking for the same reason as B.
この対策として、従来は連続鋳造鋳片を大型化し、分塊比を確保していた。 Conventionally, as a countermeasure, a continuous cast slab has been enlarged to ensure a mass ratio.
しかしながら、従来のＡ〜Ｃの対策では、以下のような問題があった。
先ず、Ａの内面欠陥の対策では、内面欠陥の安定化、および製造能力の拡大のための低Ｐ化により、コストアップとなる。
However, the conventional measures A to C have the following problems.
First, in the countermeasure against the inner surface defect of A, the cost is increased by stabilizing the inner surface defect and lowering the P for expanding the production capacity.
次に、Ｂの分塊加熱時の熱応力割れ対策では、鋳造から分塊までの時間的制約により、工程の自由度が低下する。
また、Ｃの製管加熱時の熱応力割れ対策では、分塊比確保のための連続鋳造鋳片の大型化が必要となり、中心部偏析、熱応力増大につながる。
Next, in the measure against thermal stress cracking at the time of heating the B block, the degree of freedom of the process is lowered due to the time restriction from casting to the block.
Further, in order to prevent thermal stress cracking when heating the pipe made of C, it is necessary to increase the size of the continuous cast slab in order to secure a mass ratio, leading to segregation at the center and increased thermal stress.
本発明が解決しようとする問題点は、従来のＡの対策ではコストがアップし、また、Ｂの対策では工程の自由度が低下し、さらに、Ｃの対策では中心部に偏析が発生し、熱応力が増大するという点である。 The problems to be solved by the present invention are that the cost of the conventional measure A is increased, the measure of measure B is reduced in the degree of freedom of the process, and the measure C is segregated at the center, That is, the thermal stress increases.
本発明の丸鋼片の製造方法は、
Ｃを０．７〜１．５質量％、Ｃｒを０．９〜２．０質量％含有する高炭素クロム鋼の軸受用継目無鋼管の素材である、直径が１５０〜２５０mmの丸鋼片を、連続鋳造した矩形状鋳片を熱間で分塊圧延して製造するに際し、コストアップ、工程の自由度低下、中心部偏析、熱応力増大という問題を解決するために、
矩形状鋳片の長辺長さをＷ（mm）、短辺長さをＨ（mm）とし、丸鋼片の直径をＤ（mm）とした場合に、
連続鋳造によって得た下記（１）〜（３）式の条件を満足する長辺、短辺、扁平比を有する矩形状鋳片を、下記（４）式の条件を満足する分塊比で分塊圧延して丸鋼片を製造することを最も主要な特徴としている。
２．５≦Ｗ／Ｈ≦３．５ ・・・（１）
１．２≦Ｈ／Ｄ ・・・（２）
Ｗ／Ｄ≦４．５ ・・・（３）
６．５≦（Ｈ×Ｗ）／（π×（Ｄ／２）２） ・・・（４）
The method for producing the round steel slab of the present invention is as follows.
A round steel slab having a diameter of 150 to 250 mm, which is a material of a high-carbon chromium steel seamless steel pipe containing 0.7 to 1.5% by mass of C and 0.9 to 2.0% by mass of Cr. In order to solve the problems of increased cost, reduced process freedom, segregation in the center, and increased thermal stress when manufacturing a continuous cast rectangular slab by hot rolling.
When the long side length of the rectangular slab is W (mm), the short side length is H (mm), and the diameter of the round steel piece is D (mm),
A rectangular slab having a long side, a short side, and a flatness ratio satisfying the conditions of the following formulas (1) to (3) obtained by continuous casting is divided at a lump ratio satisfying the condition of the following formula (4). The most important feature is the production of round steel pieces by lump rolling.
2.5 ≦ W / H ≦ 3.5 (1)
1.2 ≦ H / D (2)
W / D ≦ 4.5 (3)
6.5 ≦ (H × W) / (π × (D / 2) 2 ) (4)
本発明により、低Ｐ化、連続鋳造から分塊圧延までの時間制約、鋳片大型化の弊害を緩和し、低コスト、高能率で、少なくとも分塊圧延時に発生するビレット外面疵が生じないようにし、鋼管の表面品質の優れた継目無鋼管を得ることができる、軸受用継目無鋼管素材を製造できるという利点がある。 According to the present invention, low P, time restriction from continuous casting to ingot rolling, and adverse effects of slab enlargement are alleviated, so that billet outer surface flaws generated at least during ingot rolling do not occur at low cost and high efficiency. In addition, there is an advantage that a seamless steel pipe material for bearings can be manufactured, which can obtain a seamless steel pipe with excellent surface quality of the steel pipe.
発明者らは、鋳片の扁平比増による、下記(1)、(2)の利点に着目し、軸受用継目無鋼管素材への適用を考えた。
(1) Ｐの中心偏析を低減することで、粒界溶融状の内面欠陥を抑制できること。
(2) 分塊加熱時の熱応力分布を改善して中心部の応力を抑制することで、分塊圧延時の鋳片割れを防止できること。
The inventors paid attention to the following advantages (1) and (2) due to the increase in the flatness ratio of the slab, and considered application to a seamless steel pipe material for bearings.
(1) By reducing the center segregation of P, it is possible to suppress inner surface defects in the form of grain boundary fusion.
(2) By suppressing the stress at the center by improving the thermal stress distribution during mass heating, it is possible to prevent slab cracking during mass rolling.
しかしながら、鋳片の扁平比増により丸ビレット分塊時にビレット外面に折れ込みや皺などの疵が生じやすくなる。 However, an increase in the flatness ratio of the slab tends to cause wrinkles such as folding and wrinkles on the outer surface of the billet when the round billet is agglomerated.
そこで、発明者らは、前記の疵を抑制しつつ、要求するビレット径に分塊圧延できる連続鋳造鋳片の短辺、長辺長さを規定することとした。
また、製管工程での素材加熱時の熱応力割れ防止する観点から分塊比も規定することにした。
Therefore, the inventors have decided to define the short side and long side length of a continuous cast slab that can be subjected to ingot rolling to the required billet diameter while suppressing the wrinkles.
Moreover, it decided to prescribe | regulate a lump ratio from a viewpoint of preventing the thermal stress crack at the time of the raw material heating in a pipe making process.
すなわち、本発明は、連続鋳造で製造した矩形状鋳片を分塊圧延して丸鋼片とし、継目無鋼管素材として使用する製造プロセスにおいて用いる方法である。
そして、その場合、軸受に使用される継目無鋼管のサイズは比較的小径であり、その素材の丸鋼片の直径Ｄはφ１５０〜２５０（mm）が一般的である。
That is, the present invention is a method used in a manufacturing process in which a rectangular cast slab produced by continuous casting is subjected to block rolling into round steel pieces and used as a seamless steel pipe material.
In this case, the size of the seamless steel pipe used for the bearing is relatively small, and the diameter D of the round steel piece of the material is generally φ150 to 250 (mm).
従って、前記範囲の直径の素材を分塊圧延するために使用する矩形状の連続鋳造鋳片の短辺長さをＨ（mm）、長辺の長さＷを（mm）とした場合に、連続鋳造鋳片の形状（短辺、長辺長さ）、前記継目無鋼管素材の寸法（直径）、の組み合わせ、およびその鋳片を分塊圧延する際の分塊比を適正化することにより、低コストで製造能率の向上が図れる継目無鋼管素材の製造方法を見出した。 Accordingly, when the short side length of the rectangular continuous cast slab used for the rolling of the material having the diameter in the above range is H (mm) and the long side length W is (mm), By optimizing the combination of the shape (short side, long side length) of the continuous cast slab, the dimension (diameter) of the seamless steel pipe material, and the shard ratio when the slab is rolled The present inventors have found a method for producing a seamless steel pipe material that can improve production efficiency at low cost.
すなわち、本発明の丸鋼片の製造方法は、Ｃを０．７〜１．５質量％、Ｃｒを０．９〜２．０質量％含有する高炭素クロム鋼の軸受用継目無鋼管の素材である、直径が１５０〜２５０mmの丸鋼片を、連続鋳造した矩形状鋳片を熱間で分塊圧延して製造する方法であって、矩形状鋳片の長辺長さをＷ（mm）、短辺長さをＨ（mm）とし、丸鋼片の直径をＤ（mm）とした場合に、連続鋳造によって得た下記（１）〜（３）式の条件を満足する長辺、短辺、扁平比を有する矩形状鋳片を、下記（４）式の条件を満足する分塊比で分塊圧延して丸鋼片を製造することを特徴としている。
２．５≦Ｗ／Ｈ≦３．５ ・・・（１）
１．２≦Ｈ／Ｄ ・・・（２）
Ｗ／Ｄ≦４．５ ・・・（３）
６．５≦（Ｈ×Ｗ）／（π×（Ｄ／２）２） ・・・（４）
That is, the method for producing a round steel slab of the present invention is a material for a seamless steel pipe for bearings of high carbon chromium steel containing 0.7 to 1.5% by mass of C and 0.9 to 2.0% by mass of Cr. Is a method of producing a round steel slab having a diameter of 150 to 250 mm by hot-rolling a rectangular slab continuously cast, and the long side length of the rectangular slab is W (mm ), When the short side length is H (mm) and the diameter of the round steel piece is D (mm), the long side satisfying the conditions of the following formulas (1) to (3) obtained by continuous casting, A round slab is produced by rolling a rectangular slab having a short side and a flatness ratio at a sizing ratio satisfying the condition of the following formula (4).
2.5 ≦ W / H ≦ 3.5 (1)
1.2 ≦ H / D (2)
W / D ≦ 4.5 (3)
6.5 ≦ (H × W) / (π × (D / 2) 2 ) (4)
本発明の丸鋼片の製造方法は、軸受として使用される高炭素クロム鋼の継目無鋼管素材に関するものであるので、Ｃ、Ｃｒは以下の範囲を前提としている。 Since the method for manufacturing a round steel slab according to the present invention relates to a high-carbon chromium steel seamless steel pipe material used as a bearing, C and Cr are based on the following ranges.
Ｃ：
Ｃは軸受鋼としての強度、耐摩耗性を確保するために必要である。しかしながら、その含有量が０．７質量％未満であると軸受鋼に必要な機械的性質が得られない。一方、１．５質量％を超えると、靭性、熱処理時の耐割れ性が悪化する。そこで、本発明では、Ｃの含有量が０．７〜１．５質量％のものを対象とした。
C:
C is necessary to ensure the strength and wear resistance of the bearing steel. However, if the content is less than 0.7% by mass, the mechanical properties necessary for the bearing steel cannot be obtained. On the other hand, when it exceeds 1.5 mass%, toughness and crack resistance during heat treatment are deteriorated. Therefore, in the present invention, the C content is 0.7 to 1.5% by mass.
Ｃｒ：
ＣｒはＣと同様に軸受鋼としての強度、耐摩耗性を確保するために必要である。しかしながら、その含有量が０．９質量％未満であると軸受鋼に必要な機械的性質が得られない。一方、２．０質量％を超えると靭性、熱処理時の耐割れ性が悪化する。そこで、本発明では、Ｃｒの含有量が０．９〜２．０質量％のものを対象とした。
Cr:
Cr, like C, is necessary to ensure the strength and wear resistance of the bearing steel. However, if the content is less than 0.9% by mass, the mechanical properties required for the bearing steel cannot be obtained. On the other hand, if it exceeds 2.0% by mass, the toughness and crack resistance during heat treatment will deteriorate. Therefore, in the present invention, the Cr content is 0.9 to 2.0% by mass.
本発明では、ＣとＣｒ以外の元素については特に限定しないが、以下の元素に関しては、軸受鋼として使用するためには以下の範囲とすることが望ましい。
Ｓｉ：
Ｓｉは溶鋼の脱酸および、強度を確保するため含有させる。しかしながら、その含有量が少ないとそれらの効果が得られない。一方、過剰に含有させると介在物の増加をまねく。従って、その範囲は０．１５質量％以上、０．７質量％以下とすることが望ましい。
In the present invention, elements other than C and Cr are not particularly limited, but the following elements are preferably set in the following ranges for use as bearing steel.
Si:
Si is contained in order to ensure deoxidation and strength of the molten steel. However, if the content is small, those effects cannot be obtained. On the other hand, inclusion in excess causes an increase in inclusions. Therefore, the range is desirably 0.15 mass% or more and 0.7 mass% or less.
Ｍｎ：
Ｍｎを含有させると、靱性を劣化させることなく強度を向上させることができる。しかしながら、その含有量が少ないとそれらの効果が得られない。一方、過剰に含有させると、偏析を助長し、逆に靱性が劣化する場合がある。従って、その範囲は０．２０％以上、１．１５質量％以下とすることが望ましい。
Mn:
When Mn is contained, the strength can be improved without deteriorating toughness. However, if the content is small, those effects cannot be obtained. On the other hand, if it is contained excessively, segregation is promoted, and toughness may deteriorate on the contrary. Therefore, the range is desirably 0.20% or more and 1.15% by mass or less.
Ｐ：
Ｐは不純物であり、先に述べたように中心部に偏析して粒界強度を低下させる。従って、その範囲は０．０５０質量％以下とすることが望ましい。
P:
P is an impurity and segregates at the center as described above to lower the grain boundary strength. Therefore, the range is desirably 0.050% by mass or less.
Ｓ：
Ｓは不純物であり、鋼の熱間加工性を劣化させる。そのため、Ｓの含有量は０．０２５質量％以下と、低いほうが望ましい。
S:
S is an impurity and degrades the hot workability of steel. Therefore, the S content is preferably as low as 0.025% by mass or less.
また、本発明では以下のように、連続鋳造鋳片の長辺、短辺、扁平比、及び分塊圧延の分塊比を規定している。 In the present invention, the long side, the short side, the flatness ratio, and the block ratio of the block rolling are specified as follows.
Ｗ／Ｈ：
Ｗ／Ｈは、連続鋳造鋳片の横断面の扁平さをあらわす指標であり、本発明では、２．５〜３．５の範囲とする。
その理由は、Ｗ／Ｈが２．５未満の場合、中心部のＰ偏析に起因する粒界強度の低下が認められ、製管時に内面欠陥を発生させるからである。一方、Ｗ／Ｈが３．５を超えた場合は、連続鋳造鋳片が扁平すぎるために、丸鋼片への分塊圧延時に外面の形状不良や、長辺部の皺等が生じやすくなって、丸鋼片の形状、外面品質を悪化させるからである。
W / H:
W / H is an index representing the flatness of the cross section of the continuously cast slab, and in the present invention, it is in the range of 2.5 to 3.5.
The reason is that when W / H is less than 2.5, a decrease in grain boundary strength due to P segregation at the center is recognized, and an internal surface defect is generated during pipe production. On the other hand, when W / H exceeds 3.5, the continuous cast slab is too flat, and it is likely to cause shape defects on the outer surface, flaws on the long side portion, etc. during the partial rolling to round steel pieces. This is because the shape and outer surface quality of the round bar are deteriorated.
Ｈ／Ｄ：
Ｈ／Ｄは、連続鋳造鋳片の短辺と分塊後の丸鋼片の直径Ｄの比であり、短辺のみに着目した分塊比を意味し、本発明では、１．２以上とする。
その理由は、Ｈ／Ｄが１．２未満の場合、丸鋼片の直径Ｄに対して連続鋳造鋳片の短辺が短すぎるため、表面の圧延効果が小さく、鋳片段階での短辺の表面性状がそのまま丸鋼片に残存して、丸鋼片の外面品質を悪化するからである。なお、Ｈ／Ｄは、作用としてその上限値を決定する必要は無く、前記Ｗ／Ｈと、下記Ｗ／Ｄにておのずと上限値は制約される。
H / D:
H / D is the ratio of the short side of the continuous cast slab to the diameter D of the round steel slab after the ingot, meaning the ingot ratio focusing only on the short side. To do.
The reason is that when H / D is less than 1.2, the short side of the continuous cast slab is too short with respect to the diameter D of the round steel slab, so the rolling effect on the surface is small, and the short side at the slab stage This is because the surface texture of the steel remains as it is in the round steel piece and deteriorates the outer surface quality of the round steel piece. In addition, it is not necessary to determine the upper limit of H / D as an action, and the upper limit is constrained by the W / H and the following W / D.
Ｗ／Ｄ：
Ｗ／Ｄは、連続鋳造鋳片の長辺と分塊後の丸鋼片の直径Ｄの比であり、長辺のみに着目した分塊比を意味し、本発明では、４．５以下とする。
その理由は、Ｗ／Ｄが４．５を超えると、丸鋼片の直径Ｄに対して長辺が長くなりすぎるため、分塊圧延時に皺疵や形状不良が生じやすく、丸鋼片の外面品質を悪化するからである。Ｗ／Ｄは、作用としてその下限値を決定する必要は無く、前記Ｗ／ＨとＨ／Ｄにておのずと下限値は制約される。
W / D:
W / D is the ratio of the long side of the continuous cast slab to the diameter D of the round steel piece after the ingot, meaning the ingot ratio focusing only on the long side. In the present invention, it is 4.5 or less. To do.
The reason for this is that when W / D exceeds 4.5, the long side becomes too long with respect to the diameter D of the round steel piece, so that wrinkles and shape defects are liable to occur during the ingot rolling. This is because the quality deteriorates. It is not necessary to determine the lower limit value of W / D as an action, and the lower limit value is constrained by W / H and H / D.
なお、従来、扁平比の小さな正方形に近い連続鋳造鋳片からの分塊圧延では、単なる断面積の比で管理することが可能であったが、連続鋳造鋳片を扁平化する本発明においては、前記Ｈ／ＤやＷ／Ｄの管理は必須である。 In addition, conventionally, in the ingot rolling from a continuous cast slab close to a square with a small flatness ratio, it was possible to manage with a simple cross-sectional area ratio, but in the present invention for flattening the continuous cast slab The management of the H / D and W / D is essential.
（Ｈ×Ｗ）／（π×（Ｄ／２）２）：
（Ｈ×Ｗ）／（π×（Ｄ／２）２）は、前記のように長辺と短辺を規定した連続鋳造鋳片を丸鋼片に分塊圧延する場合の分塊比を意味する。
この分塊比は、６．５以上とする。分塊比が６．５未満の場合、中心部の凝固組織の分塊による改善が十分なされないからである。
(H × W) / (π × (D / 2) 2 ):
(H × W) / (π × (D / 2) 2 ) means the block ratio when the continuous cast slab with the long side and the short side defined above is subjected to block rolling into round steel pieces. To do.
This chunk ratio is 6.5 or more. This is because when the mass ratio is less than 6.5, the improvement due to the mass of the solidified tissue in the center is not sufficiently achieved.
以下、本発明の効果を確認するために行った実験結果の一例について説明する。
実験は、鋳型の長辺、短辺を変更して連続鋳造した種々の矩形鋳片を、種々の分塊比で丸鋼片に分塊圧延し、その後マンネスマン法により継目無鋼管とした場合の、夫々の条件と、丸鋼片の外面品質、継目無鋼管の内外面品質を評価した。
鋳型の長辺、短辺、夫々の条件や分塊比等を下記表１に、その結果を下記表２に示す。
Hereinafter, an example of the results of experiments conducted to confirm the effects of the present invention will be described.
In the experiment, various rectangular slabs that were continuously cast by changing the long side and short side of the mold were slab-rolled into round steel slabs at various sizing ratios, and then seamless steel pipes were formed by the Mannesmann method. Each condition, the outer surface quality of the round steel slab, and the inner and outer surface quality of the seamless steel pipe were evaluated.
The long side and short side of the mold, the respective conditions and the lump ratio, etc. are shown in Table 1 below, and the results are shown in Table 2 below.
上記表１において、Ｎｏ．３，４，１０，１１が本発明例で、その他はグレーで示した条件が本発明例の範囲を外れた比較例である。 In Table 1 above, no. 3, 4, 10, and 11 are examples of the present invention, and the others are comparative examples in which the conditions shown in gray are out of the scope of the examples of the present invention.
表２より明らかなように、長辺、短辺、扁平比、および分塊比が本発明の条件を充足する矩形鋳片を分塊圧延して丸鋼片を製造する本発明例では、いずれも、分塊圧延時にビレット外面疵が発生せず、丸鋼片の外面品質は良好であり、製管時に内面疵も発生せず、鋼管の内面品質も良好であった。 As is clear from Table 2, in the present invention example in which a round slab is manufactured by split-rolling a rectangular slab whose long side, short side, flatness ratio, and block ratio satisfy the conditions of the present invention, However, the billet outer surface flaws did not occur at the time of the ingot rolling, the outer surface quality of the round steel pieces was good, the inner surface flaws did not occur at the time of pipe making, and the inner surface quality of the steel pipe was also good.
一方、扁平比（Ｗ／Ｈ）のみが本発明の条件を充足しない（小さい）、比較例Ｎｏ．１，５〜８，１２〜１４，１９，２０では、製管時に内面疵が発生し、内面品質が悪化した。 On the other hand, only the flatness ratio (W / H) does not satisfy the conditions of the present invention (small). In 1,5-8,12-14,19,20, the inner surface flaw generate | occur | produced at the time of pipe making, and the inner surface quality deteriorated.
また、長辺、短辺、扁平比、分塊比の何れか２つの条件が本発明の条件を充足しない、比較例Ｎｏ．２，９，１５〜１８では、分塊圧延時にビレット外面疵が発生して丸鋼片の外面品質が悪化したり、製管時に内面疵が発生して内面品質が悪化した。 Further, Comparative Example No. 1 in which any two conditions of the long side, the short side, the flatness ratio, and the lump ratio do not satisfy the conditions of the present invention. In Nos. 2, 9, 15 to 18, billet outer surface flaws occurred at the time of the ingot rolling and the outer surface quality of the round steel pieces deteriorated, or inner surface flaws occurred at the time of pipe making, and the inner surface quality deteriorated.
本発明は、上記の実施例に示したものに限られるものではなく、各請求項に記載した技術的思想の範囲内で適宜実施態様を変更しても良いことはいうまでもない。 The present invention is not limited to those shown in the above embodiments, and it goes without saying that the embodiments may be appropriately changed within the scope of the technical idea described in each claim.
Claims (1)
矩形状鋳片の長辺長さをＷ（mm）、短辺長さをＨ（mm）とし、丸鋼片の直径をＤ（mm）とした場合に、
連続鋳造によって得た下記（１）式、（２）式、（３）式の条件を満足する長辺、短辺、扁平比を有する矩形状鋳片を、下記（４）式の条件を満足する分塊比で分塊圧延して丸鋼片を製造することを特徴とする丸鋼片の製造方法。
２．５≦Ｗ／Ｈ≦３．５ ・・・（１）
１．２≦Ｈ／Ｄ ・・・（２）
Ｗ／Ｄ≦４．５ ・・・（３）
６．５≦（Ｈ×Ｗ）／（π×（Ｄ／２）２） ・・・（４）
A round steel slab having a diameter of 150 to 250 mm, which is a material of a high-carbon chromium steel seamless steel pipe containing 0.7 to 1.5% by mass of C and 0.9 to 2.0% by mass of Cr. , A method of manufacturing a continuously cast rectangular slab by hot rolling and manufacturing,
When the long side length of the rectangular slab is W (mm), the short side length is H (mm), and the diameter of the round steel piece is D (mm),
A rectangular slab having a long side, a short side, and a flatness ratio that satisfies the conditions of the following formulas (1), (2), and (3) obtained by continuous casting satisfies the conditions of the following formula (4): A method of manufacturing a round steel slab, characterized in that a round steel slab is manufactured by performing a slabbing with a sizing ratio.
2.5 ≦ W / H ≦ 3.5 (1)
1.2 ≦ H / D (2)
W / D ≦ 4.5 (3)
6.5 ≦ (H × W) / (π × (D / 2) 2 ) (4)
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| JPS61140301A (en) * | 1984-12-12 | 1986-06-27 | Kawasaki Steel Corp | Manufacture of round billet for seamless stainless steel pipe by skew rolling |
| JP2001105001A (en) * | 1999-10-13 | 2001-04-17 | Sumitomo Metal Ind Ltd | BLOOMING METHOD OF Cr STEEL CONTINUOUSLY CAST BLOOM FOR SEAMLESS STEEL PIPE |
| JP3487234B2 (en) * | 1999-08-23 | 2004-01-13 | 住友金属工業株式会社 | Manufacturing method of high carbon steel slab for seamless steel pipe |
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| JPS61140301A (en) * | 1984-12-12 | 1986-06-27 | Kawasaki Steel Corp | Manufacture of round billet for seamless stainless steel pipe by skew rolling |
| JP3487234B2 (en) * | 1999-08-23 | 2004-01-13 | 住友金属工業株式会社 | Manufacturing method of high carbon steel slab for seamless steel pipe |
| JP2001105001A (en) * | 1999-10-13 | 2001-04-17 | Sumitomo Metal Ind Ltd | BLOOMING METHOD OF Cr STEEL CONTINUOUSLY CAST BLOOM FOR SEAMLESS STEEL PIPE |
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