JP4637681B2 - Steel bar manufacturing method - Google Patents
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本発明は、熱間圧延後の圧延材を冷却した後に切断して棒鋼を製造する方法に関するものである。 The present invention relates to a method for manufacturing a steel bar by cutting after cooling a rolled material after hot rolling.
棒鋼は、熱間圧延ラインで圧延して得られた圧延材を、圧延ライン終端に接して設けられた冷却床上で冷却した後、切断機（コールドシャー）で所望の長さに切断することで得られる。このとき圧延材の鋼種が例えば合金鋼や高炭素鋼の場合には、切断時に端面割れが発生し易い。そこで切断時の端面割れ発生を防止する技術として、本出願人は、例えば特許文献１の技術を先に提案した。この文献において本発明者は、被圧延材の材質に応じて最適切断温度を定めると共に、切断直前における被切断材の温度を測定し、この温度が前記最適切断温度より低い場合には、この最適切断温度まで被切断材を加熱した後、切断することを提案した。しかしこの技術では、切断機よりも上流側に被切断材を加熱するための装置を設ける必要があり、設備が複雑となる。また、この文献には、最適切断温度を被圧延材の材質に応じて定めるための具体的手段について開示していなかった。 A steel bar is obtained by cooling a rolled material obtained by rolling in a hot rolling line on a cooling bed provided in contact with the end of the rolling line, and then cutting it to a desired length with a cutting machine (cold shear). can get. At this time, when the steel type of the rolled material is, for example, alloy steel or high carbon steel, end face cracks are likely to occur during cutting. Thus, as a technique for preventing the occurrence of end face cracks at the time of cutting, the present applicant previously proposed the technique of Patent Document 1, for example. In this document, the inventor determines the optimum cutting temperature according to the material of the material to be rolled, measures the temperature of the material to be cut immediately before cutting, and if this temperature is lower than the optimum cutting temperature, this optimum It was proposed that the material to be cut was heated to the cutting temperature and then cut. However, in this technique, it is necessary to provide a device for heating the material to be cut upstream of the cutting machine, and the equipment becomes complicated. Further, this document does not disclose specific means for determining the optimum cutting temperature according to the material of the material to be rolled.
ところで上記特許文献１には、圧延材の切断温度は、通常では３００〜４００℃が最適であると記載しており、圧延材の鋼種が合金鋼や高炭素鋼の場合には、切断温度をより高くすればよいことを開示している。ところが上記特許文献１のように、被切断材を切断直前に加熱しない場合は、圧延材を高温で切断するために、熱間圧延後の圧延材を素早く切断機へ移動させる必要がある。そのため圧延材を素早く切断機へ移動させるには、冷却床のスペースを空けて冷却床での切断待ち時間を短縮する必要がある。しかし冷却床のスペースを空けるには、例えば熱間圧延間隔を長くするなど生産性を落とさなければならない。
本発明は、この様な状況に鑑みてなされたものであり、その目的は、熱間圧延後の圧延材を冷却した後に切断して棒鋼を製造するに当たり、生産性を低下させることなく、切断端面に割れが少ない棒鋼を製造できる方法を提供することにある。 The present invention has been made in view of such a situation, and its purpose is to cut the hot rolled material after cooling and cut it to produce a steel bar without cutting the productivity. An object of the present invention is to provide a method capable of producing a steel bar with less cracks at the end face.
本発明者らは、生産性を低下させることなく、切断端面に割れが少ない棒鋼を製造する方法について検討を重ねた。その結果、圧延材のＤｉ値に基づいて切断温度を定めて圧延材を切断してやれば、比較的低温で切断しても端面割れが発生しないこと、これにより生産性を落とすことなく圧延材を切断して棒鋼を製造できることを見出し、本発明を完成した。 The inventors of the present invention have repeatedly studied a method of manufacturing a steel bar with less cracks on the cut end face without reducing productivity. As a result, if the cutting temperature is determined based on the Di value of the rolled material and the rolled material is cut, end face cracks will not occur even if it is cut at a relatively low temperature, thereby cutting the rolled material without reducing productivity. As a result, it was found that steel bars could be manufactured, and the present invention was completed.
即ち、上記課題を解決することのできた本発明に係る棒鋼の製法とは、熱間圧延後の圧延材を冷却した後に切断して棒鋼を製造するに当たり、ＡＳＴＭで規定する前記圧延材のＤｉ値に基づいて切断温度を定めて切断する点に要旨を有する。 That is, the manufacturing method of the steel bar according to the present invention that has been able to solve the above-mentioned problem is that, after the hot-rolled rolled material is cooled and cut to produce the steel bar, the Di value of the rolled material specified by ASTM The point is that the cutting temperature is determined on the basis of the above and cutting is performed.
具体的には、前記切断温度をＴをとしたとき、前記Ｄｉ値が、２．８０インチ以上、３．２０インチ未満の場合には、下記（１）式を満足するように前記切断温度Ｔを定め、前記Ｄｉ値が、３．２０インチ以上、３．５０インチ未満の場合には、下記（２）式を満足するように前記切断温度Ｔを定め、前記Ｄｉ値が、３．５０インチ以上の場合には、前記切断温度を２６０℃以上として切断すればよい。
Ｔ≧２５０×Ｄｉ−６００ …（１）
Ｔ≧２００×Ｄｉ−４４０ …（２）
前記圧延材は、直径が特に６０ｍｍ以下の場合に上記製法を採用することが推奨される。
Specifically, when the cutting temperature is T, and the Di value is 2.80 inches or more and less than 3.20 inches, the cutting temperature T is set so as to satisfy the following expression (1). When the Di value is 3.20 inches or more and less than 3.50 inches, the cutting temperature T is determined so as to satisfy the following formula (2), and the Di value is 3.50 inches. In the above case, the cutting temperature may be set to 260 ° C. or higher.
T ≧ 250 × Di−600 (1)
T ≧ 200 × Di-440 (2)
It is recommended that the above rolling method is adopted when the rolled material has a diameter of 60 mm or less.
本発明の製法によれば、圧延材の切断温度をＡＳＴＭで規定する圧延材のＤｉ値に基づいて定めているため、切断温度を必要以上に高めて圧延材を切断しなくても端面割れを発生しない。従って加熱設備を設ける必要がなく、しかも生産性を低下させずに端面割れの少ない棒鋼を製造できる。 According to the manufacturing method of the present invention, since the cutting temperature of the rolled material is determined based on the Di value of the rolled material specified by ASTM, end face cracks can be generated without increasing the cutting temperature more than necessary and cutting the rolled material. Does not occur. Therefore, it is not necessary to provide heating equipment, and a steel bar with less end face cracks can be produced without reducing productivity.
圧延材の鋼種（例えば、合金鋼や高炭素鋼）が同じ場合でも、切断後の端面に割れを発生していることがあった。そこで本発明者らは、ＡＳＴＭで規定する圧延材のＤｉ値に注目し、該Ｄｉ値と切断温度の間に関係がないか調べた。その結果、後述する実施例から明らかなように、圧延材のＤｉ値と切断温度の間には関係があり、Ｄｉ値に基づいて圧延材の切断温度を定めて切断すれば、端面に割れが発生しないことが判明した。 Even when the steel type of the rolled material (for example, alloy steel or high carbon steel) is the same, cracks may occur on the end face after cutting. Therefore, the present inventors paid attention to the Di value of the rolled material specified by ASTM, and examined whether there is a relationship between the Di value and the cutting temperature. As a result, as will be apparent from the examples to be described later, there is a relationship between the Di value of the rolled material and the cutting temperature. It turns out that it does not occur.
Ｄｉ値に基づいて圧延材の切断温度を定めて切断すれば、端面に割れが発生しない理由については全てを解明できたわけではないが、圧延材のＤｉ値が大きい場合は、焼入れ性が高いため冷却床上での冷却時に過冷組織（例えば、ベイナイトやマルテンサイト）が生成し、切断するまでに圧延材が硬くなり過ぎることによると考えられる。そのためＤｉ値が大きい圧延材を切断する場合には、高温で切断すればよい。一方、圧延材のＤｉ値が小さい場合は、焼入れ性が低いため、冷却床で緩やかに冷却しても切断するまでに過冷組織は殆ど生成しないと考えられる。そのため切断するまでに時間がかかっても圧延材は硬くなりすぎず、低温で切断しても端面割れは発生しないと考えられる。このように圧延材のＤｉ値に基づいて切断温度を定めてこの温度で切断してやれば、端面割れが発生しない最適温度で切断できるため、例えば冷却床に無駄な空きスペースを作って圧延材の送り速度を大きくする必要はなくなり、生産性を高めることができる。 If the cutting temperature of the rolled material is determined based on the Di value and then cut, not all of the reasons why cracks do not occur on the end face have been clarified. However, when the Di value of the rolled material is large, the hardenability is high. It is considered that a supercooled structure (for example, bainite or martensite) is generated during cooling on the cooling bed and the rolled material becomes too hard before being cut. Therefore, what is necessary is just to cut | disconnect at high temperature, when cutting a rolling material with a large Di value. On the other hand, when the Di value of the rolled material is small, the hardenability is low. Therefore, it is considered that a supercooled structure is hardly generated until cutting even if it is slowly cooled in the cooling bed. Therefore, even if it takes time to cut, the rolled material does not become too hard, and it is considered that end face cracks do not occur even if cut at a low temperature. In this way, if the cutting temperature is determined based on the Di value of the rolled material and cutting is performed at this temperature, the cutting can be performed at the optimum temperature at which end face cracks do not occur. There is no need to increase the speed, and productivity can be increased.
Ｄｉ値に基づいて切断温度を定めるに当たっては、具体的には、前記切断温度をＴをとしたとき、前記Ｄｉ値が２．８０インチ以上、３．２０インチ未満の場合には、下記（１）式を満足するように前記切断温度Ｔを定め、
Ｔ≧２５０×Ｄｉ−６００ …（１）
前記Ｄｉ値が、３．２０インチ以上、３．５０インチ未満の場合には、下記（２）式を満足するように前記切断温度Ｔを定め、
Ｔ≧２００×Ｄｉ−４４０ …（２）
前記Ｄｉが、３．５０インチ以上の場合には、前記切断温度を２６０℃以上（特に２８０℃以上）として切断すればよい。
In determining the cutting temperature based on the Di value, specifically, when the cutting temperature is T, and the Di value is 2.80 inches or more and less than 3.20 inches, the following (1 The cutting temperature T is determined so as to satisfy the formula
T ≧ 250 × Di−600 (1)
When the Di value is 3.20 inches or more and less than 3.50 inches, the cutting temperature T is determined so as to satisfy the following expression (2),
T ≧ 200 × Di-440 (2)
When the Di is 3.50 inches or more, the cutting temperature may be set to 260 ° C. or higher (particularly 280 ° C. or higher).
上記切断温度Ｔは、好ましくは、前記Ｄｉ値が２．８０インチ以上、３．５０インチ未満の場合に、下記（３）式を満足するように定めることが推奨される。
Ｔ≧（６００／７）×Ｄｉ−４０ …（３）
なお、前記Ｄｉ値が、２．８０インチ未満の場合の前記切断温度Ｔは特に限定されず、室温程度以上とすればよい。
The cutting temperature T is preferably determined so as to satisfy the following expression (3) when the Di value is 2.80 inches or more and less than 3.50 inches.
T ≧ (600/7) × Di-40 (3)
The cutting temperature T when the Di value is less than 2.80 inches is not particularly limited, and may be about room temperature or higher.
本発明において、上記Ｄｉ値は、ＡＳＴＭ（米国材料試験協会）の「Ａ−２５５」に準じて算出した値を用いる。即ち、圧延材のＤｉ値は、圧延材に含まれる合金成分量に応じて下記（ａ）式から算出できる。
Ｄｉ＝Ｆ（Ｃ）×Ｆ（Ｍｎ）×Ｆ（Ｓｉ）×Ｆ（Ｎｉ）×Ｆ（Ｃｒ）×Ｆ（Ｍｏ）×Ｆ（Ｃｕ）×Ｆ（Ｖ） …（ａ）
ここで、
Ｆ（Ｓｉ）＝１．００＋０．７×［Ｓｉ］
Ｆ（Ｎｉ）＝１．００＋０．３６３×［Ｎｉ］
Ｆ（Ｃｒ）＝１．００＋２．１６×［Ｃｒ］
Ｆ（Ｍｏ）＝１．００＋３．００×［Ｍｏ］
Ｆ（Ｃｕ）＝１．００＋０．３６５×［Ｃｕ］
Ｆ（Ｖ）＝１．００＋１．７３×［Ｖ］
であり、上記Ｆ（Ｃ）とＦ（Ｍｎ）は、Ｃ量またはＭｎ量に応じて下記式を用いる。
［Ｃ］≦０．３９質量％の場合
Ｆ（Ｃ）＝０．５４×［Ｃ］
０．３９質量％＜［Ｃ］≦０．５５質量％の場合
Ｆ（Ｃ）＝０．１７１＋０．００１×［Ｃ］＋０．２６５×［Ｃ］2
０．５５質量％＜［Ｃ］≦０．６５質量％の場合
Ｆ（Ｃ）＝０．１１５＋０．２６８×［Ｃ］−０．０３８×［Ｃ］2
０．６５質量％＜［Ｃ］≦０．７５質量％の場合
Ｆ（Ｃ）＝０．１４３+０．２×［Ｃ］
０．７５質量％＜［Ｃ］の場合
Ｆ（Ｃ）＝０．０６２＋０．４０９×［Ｃ］−０．１３５×［Ｃ］2
［Ｍｎ］≦１．２０質量％の場合
Ｆ（Ｍｎ）＝３．３３３３×［Ｍｎ］＋１．００
１．２０質量％＜［Ｍｎ］の場合
Ｆ（Ｍｎ）＝５．１０×［Ｍｎ］−１．１２
なお、上記式中、［ ］は、圧延材に含まれる各元素の量（質量％）を示している。
In the present invention, as the Di value, a value calculated according to ASTM (American Society for Testing and Materials) “A-255” is used. That is, the Di value of the rolled material can be calculated from the following equation (a) according to the amount of alloy components included in the rolled material.
Di = F (C) * F (Mn) * F (Si) * F (Ni) * F (Cr) * F (Mo) * F (Cu) * F (V) (a)
here,
F (Si) = 1.00 + 0.7 × [Si]
F (Ni) = 1.00 + 0.363 × [Ni]
F (Cr) = 1.00 + 2.16 × [Cr]
F (Mo) = 1.00 + 3.00 × [Mo]
F (Cu) = 1.00 + 0.365 × [Cu]
F (V) = 1.00 + 1.73 × [V]
The above F (C) and F (Mn) use the following formulas depending on the amount of C or the amount of Mn.
[C] ≦ 0.39 mass% F (C) = 0.54 × [C]
When 0.39 mass% <[C] ≦ 0.55 mass% F (C) = 0.171 + 0.001 × [C] + 0.265 × [C] 2
In the case of 0.55 mass% <[C] ≦ 0.65 mass% F (C) = 0.115 + 0.268 × [C] −0.038 × [C] 2
When 0.65% by mass <[C] ≦ 0.75% by mass F (C) = 0.143 + 0.2 × [C]
In the case of 0.75 mass% <[C] F (C) = 0.062 + 0.409 × [C] −0.135 × [C] 2
[Mn] ≦ 1.20 mass% F (Mn) = 3.3333 × [Mn] +1.00
When 1.20% by mass <[Mn] F (Mn) = 5.10 × [Mn] −1.12
In the above formula, [] indicates the amount (% by mass) of each element contained in the rolled material.
また、上記切断温度とは、切断機で圧延材を切断するときにおける圧延材の温度であり、この温度は例えば熱放射温度計で測定して確認できる。こうした温度計は、切断機よりも上流側に設けておき、切断位置における圧延材の温度をチェックすればよい。 The cutting temperature is the temperature of the rolled material when the rolled material is cut with a cutting machine, and this temperature can be confirmed by measuring with a thermal radiation thermometer, for example. Such a thermometer may be provided upstream of the cutting machine and the temperature of the rolled material at the cutting position may be checked.
圧延材のＤｉ値に基づいて圧延材の切断温度を調整するには、例えば熱間圧延後の圧延材を切断するまでの時間を調整すればよく、切断温度を高めるには、冷却床における圧延材の送り速度を大きくし、切断温度を低めるには、冷却床における圧延材の送り速度を小さくすればよい。圧延材の送り速度を大きくするには、冷却床を空けた状態とすればよい。また、切断温度を高めるには、冷却床の上方にカバーを設置して冷却床を覆ったり、切断温度を低めるには、冷却床にブロワー等の風冷装置を設置して強制冷却してもよい。 In order to adjust the cutting temperature of the rolled material based on the Di value of the rolled material, for example, the time until the rolled material after hot rolling is cut may be adjusted. To increase the cutting temperature, rolling in the cooling bed is performed. In order to increase the feed rate of the material and lower the cutting temperature, the feed rate of the rolled material in the cooling bed may be reduced. In order to increase the feed rate of the rolled material, the cooling bed may be left open. Also, to increase the cutting temperature, install a cover above the cooling floor to cover the cooling floor, or to lower the cutting temperature, install an air cooling device such as a blower on the cooling floor for forced cooling. Good.
本発明で切断対象とする圧延材の直径は特に限定されないが、特に圧延材の直径が小さい場合に本発明の方法を採用することが推奨される。例えば直径が６０ｍｍ以下（特に４５ｍｍ以下）の細径圧延材を切断して棒鋼を製造する際に、本発明の方法を採用することが好ましい。直径が６０ｍｍ以下の細径棒鋼では、圧延材の直径が小さいため、熱間圧延後の冷却時において冷却速度の影響を大きく受け、徐冷しても過冷組織が発生し易い。そのため圧延材が硬くなり過ぎて切断時に端面割れが発生し易いからである。 The diameter of the rolled material to be cut in the present invention is not particularly limited, but it is recommended to adopt the method of the present invention particularly when the diameter of the rolled material is small. For example, it is preferable to employ the method of the present invention when a steel bar is produced by cutting a thin rolled material having a diameter of 60 mm or less (particularly 45 mm or less). In the case of a thin steel bar having a diameter of 60 mm or less, since the diameter of the rolled material is small, it is greatly affected by the cooling rate at the time of cooling after hot rolling, and a supercooled structure is likely to occur even if it is gradually cooled. Therefore, the rolled material becomes too hard and end face cracks are likely to occur during cutting.
本発明で切断対象とする圧延材の種類は特に限定されないが、例えば機械構造用合金鋼［ＪＩＳ Ｇ ４０５３；例えば、マンガン鋼（ＳＭｎ）、マンガンクロム鋼（ＳＭｎＣ）、クロム鋼（ＳＣｒ）、クロムモリブデン鋼（ＳＣＭ）、ニッケルクロム鋼（ＳＮＣ）、ニッケルクロムモリブデン鋼（ＳＮＣＭ）など］やばね鋼（ＪＩＳ Ｇ ４８０１；ＳＵＰ）、高炭素クロム軸受鋼（ＪＩＳ Ｇ ４８０５；ＳＵＪ）などからなる圧延材は、焼入れ性が高いため、熱間圧延後の冷却時に過冷組織を生成し易く、切断時に端面に割れを発生し易いが、本発明の方法を採用すれば切断端面に割れを生じさせることなく切断できる。 The type of rolled material to be cut in the present invention is not particularly limited. For example, alloy steel for mechanical structure [JIS G 4053; for example, manganese steel (SMn), manganese chromium steel (SMnC), chromium steel (SCr), chromium Rolling material made of molybdenum steel (SCM), nickel chromium steel (SNC), nickel chromium molybdenum steel (SNCM), etc.], spring steel (JIS G 4801; SUP), high carbon chromium bearing steel (JIS G 4805; SUJ), etc. Because of its high hardenability, it is easy to generate a supercooled structure during cooling after hot rolling, and it is easy to generate cracks at the end face during cutting, but if the method of the present invention is adopted, it will cause cracks at the cut end face. It can cut without.
以下、本発明を実施例によって更に詳細に説明するが、下記実施例は本発明を限定する性質のものではなく、前・後記の趣旨に適合し得る範囲で適当に変更して実施することも可能であり、それらはいずれも本発明の技術的範囲に含まれる。 Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.
表１に示す成分組成の鋼材をφ３５ｍｍに熱間圧延し、冷却床上で冷却した後、切断機（コールドシャー）で切断して棒鋼を得た。このとき熱間圧延で得られた圧延材を切断工程へ移す時間を制御して切断時における圧延材の温度を下記表２に示す温度に調整した。なお、表１には、ＡＳＴＭ（米国材料試験協会）の「Ａ−２５５」に準じて算出したＤｉ値を併記した。Ｄｉ値は、圧延材に含まれる合金成分量に応じて上記（ａ）式から算出した。また、切断機で圧延材を切断するときにおける圧延材の温度は、切断機に備えられた熱放射温度計で測定した。 Steel materials having the composition shown in Table 1 were hot-rolled to 35 mm, cooled on a cooling bed, and then cut with a cutting machine (cold shear) to obtain a bar steel. At this time, the time for moving the rolled material obtained by hot rolling to the cutting step was controlled, and the temperature of the rolled material at the time of cutting was adjusted to the temperature shown in Table 2 below. In Table 1, the Di values calculated according to ASTM (American Society for Testing and Materials) “A-255” are also shown. The Di value was calculated from the above equation (a) according to the amount of alloy components contained in the rolled material. Moreover, the temperature of the rolling material when cutting a rolling material with a cutting machine was measured with the thermal radiation thermometer with which the cutting machine was equipped.
圧延材の切断端面を光学顕微鏡を用いて１００倍で観察し、割れの発生の有無を観察した。切断端面を観察したときに、１ｍｍ以上の割れが発生している場合を「割れ発生あり」とし、１ｍｍ未満の場合には「割れ発生なし」とした。サンプル数は１０個とし、下記基準で端面割れを評価した。評価結果を下記表２に示す。
＜評価基準＞
○：全てのサンプルで割れ発生なし
△：割れ発生ありのサンプルが１個
×：割れ発生ありのサンプルが２個以上（不合格）
The cut end surface of the rolled material was observed at a magnification of 100 using an optical microscope, and the presence or absence of cracks was observed. When the cut end face was observed, a case where a crack of 1 mm or more was generated was regarded as “cracking occurred”, and when it was less than 1 mm, “cracking occurred”. The number of samples was 10, and end face cracks were evaluated according to the following criteria. The evaluation results are shown in Table 2 below.
<Evaluation criteria>
○: No cracking occurred in all samples Δ: One sample with cracking ×: Two or more samples with cracking (failed)
上記表２から明らかなように、Ｄｉ値と切断温度には良好な関係があり、Ｄｉ値に基づいて切断温度を定めて切断すれば、端面割れの少ない棒鋼を製造できる。特にＤｉ値が小さい圧延材を切断する際には、低温で切断しても端面割れが発生しないため、冷却床のスペースを空けることなく生産性を高めることができる。 As is clear from Table 2 above, there is a good relationship between the Di value and the cutting temperature. If the cutting temperature is determined based on the Di value and cutting is performed, a steel bar with few end face cracks can be produced. In particular, when cutting a rolled material having a small Di value, end face cracks do not occur even when cut at a low temperature, so that productivity can be increased without leaving a space for the cooling bed.
なお、鋼種Ｄを１５０℃または２００℃で、或いは鋼種Ｅを２００℃で切断した場合には、切断状態によっては端面割れが発生することがあった（表２中の△）。即ち、切断機のバイトの切れやすさが悪かったり、上刃と下刃の調整が不良の場合に、端面割れが発生することがあった。 When steel type D was cut at 150 ° C. or 200 ° C., or steel type E was cut at 200 ° C., end face cracks may occur depending on the cutting state (Δ in Table 2). That is, end face cracking may occur when the cutting tool of the cutting machine is not easily cut or the upper blade and the lower blade are poorly adjusted.
Claims (3)
ＡＳＴＭで規定する前記圧延材のＤｉ値に基づいて切断温度を定めて切断することを特徴とする棒鋼の製法。 In manufacturing a steel bar by cutting after cooling the rolled material after hot rolling,
A method for producing a bar steel, characterized in that a cutting temperature is determined based on a Di value of the rolled material defined by ASTM.
前記Ｄｉ値が、２．８０インチ以上、３．２０インチ未満の場合には、下記（１）式を満足するように前記切断温度Ｔを定め、
前記Ｄｉ値が、３．２０インチ以上、３．５０インチ未満の場合には、下記（２）式を満足するように前記切断温度Ｔを定め、
前記Ｄｉ値が、３．５０インチ以上の場合には、前記切断温度を２６０℃以上として切断する請求項１に記載の製法。
Ｔ≧２５０×Ｄｉ−６００ …（１）
Ｔ≧２００×Ｄｉ−４４０ …（２） When the cutting temperature is T,
When the Di value is 2.80 inches or more and less than 3.20 inches, the cutting temperature T is determined so as to satisfy the following formula (1):
When the Di value is 3.20 inches or more and less than 3.50 inches, the cutting temperature T is determined so as to satisfy the following expression (2),
The manufacturing method according to claim 1, wherein when the Di value is 3.50 inches or more, the cutting temperature is 260 ° C or more.
T ≧ 250 × Di−600 (1)
T ≧ 200 × Di-440 (2)
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| JPH02221325A (en) * | 1989-02-22 | 1990-09-04 | Kobe Steel Ltd | Production of softened steel bar |
| JPH03240918A (en) * | 1990-02-15 | 1991-10-28 | Nippon Steel Corp | Production of wide flange shape excellent in refractoriness and reduced in yield ratio |
| JP2002126940A (en) * | 2000-10-25 | 2002-05-08 | Nippon Steel Corp | Method for shearing steel bar |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH02221325A (en) * | 1989-02-22 | 1990-09-04 | Kobe Steel Ltd | Production of softened steel bar |
| JPH03240918A (en) * | 1990-02-15 | 1991-10-28 | Nippon Steel Corp | Production of wide flange shape excellent in refractoriness and reduced in yield ratio |
| JP2002126940A (en) * | 2000-10-25 | 2002-05-08 | Nippon Steel Corp | Method for shearing steel bar |
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