JP3765412B2 - Direct heat treatment method for hot rolled wire rod - Google Patents

Direct heat treatment method for hot rolled wire rod Download PDF

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Publication number
JP3765412B2
JP3765412B2 JP2002184860A JP2002184860A JP3765412B2 JP 3765412 B2 JP3765412 B2 JP 3765412B2 JP 2002184860 A JP2002184860 A JP 2002184860A JP 2002184860 A JP2002184860 A JP 2002184860A JP 3765412 B2 JP3765412 B2 JP 3765412B2
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Prior art keywords
cooling
wire
wire rod
hot
heat treatment
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JP2004027286A (en
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達也 井上
義弘 橋本
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Sumitomo Electric Industries Ltd
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Sumitomo Electric Industries Ltd
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Description

【0001】
【発明の属する技術分野】
本発明は、熱間圧延線材の直接熱処理方法と、この熱処理方法で製造される高強度鉄筋用線材および熱間圧延線材の直接熱処理設備に関するものである。特に、剪断補強筋に好適な高強度鉄筋用非調質線材を得ることができる直接熱処理方法に関するものである。
【0002】
【従来の技術】
従来より、剪断補強筋に好適な高強度鉄筋として、次の技術が知られている。
▲1▼特開2001-181781号公報
この公報は、化学成分、ベイナイト分率、残留オーステナイト分率および表層スケール厚みを限定することで、溶接性に優れた高強度熱間圧延鋼材を示している。その鋼材の強度としては、降伏強度70kgf/mm2級のものが主に開示されている。
【0003】
▲2▼特開平10-121200号公報
合金成分を多種含有したフェライト・パーライト組織またはフェライト・パーライト・ベイナイトの組織の高強度せん断補強筋用鋼材が開示されている。
【0004】
▲3▼特開平11-293399号公報
非常に多種の合金成分を添加した溶接性の優れた化学成分の高強度らせん筋が開示されている。
【0005】
【発明が解決しようとする課題】
しかし、上記の従来技術では、次のような問題があった。
▲1▼強度を確保するために多種類の合金成分を多量に添加する必要があり、不経済である。熱間圧延線材の直接熱処理設備としてはステルモアープロセスが一般的である。このステルモアープロセスは空冷のため、特に13.0mmを越えるような太径線材では十分な冷却速度が得られず、多くの合金元素の添加が必要である。
【0006】
▲2▼非調質(焼き入れ・焼戻しを行わず)で降伏強度80kgf/mm2以上の太径高強度鉄筋の製造を安定して実施することは非常に難しく、オフラインでの焼鈍処理等が必要であった。特に、合金元素を多量に添加した鋼では、直接熱処理中の冷却速度ばらつきの影響を受けやすく、線材の長手方向の機械的性能が大きくばらつく。そのため、従来技術の製造方法(非調質処理)では安定して80kgf/mm2級の高強度鉄筋を製造するのは非常に困難であった。
【0007】
従って、本発明の主目的は、多量の合金元素を含むことなく、高強度の鋼線を得ることができる熱間圧延線材の直接熱処理方法を提供することにある。
【0008】
また、本発明の他の目的は、上記の熱処理方法により得られる高強度鉄筋用線材を提供することにある。
【0009】
さらに、本発明の他の目的は、高強度の鋼線を得ることができる熱間圧延線材の直接熱処理設備を提供することにある。
【0010】
【課題を解決するための手段】
本発明は、圧延後に圧延線材を冷媒に浸漬して冷却する際の条件を限定し、さらに冷媒から引き上げた後の放冷条件を特定することで上記の目的を達成する。
【0011】
すなわち、本発明熱間圧延線材の直接熱処理方法は、重量%でC:0.10〜0.30、Si:0.20〜2.00、Mn:0.30〜2.50、Cr:0.50〜1.50、Mo:0.01〜0.30を含み、残部が鉄と不可避的不純物とからなる鋼材を熱間圧延する工程と、熱間圧延後の線材をルーズコイル状に巻き取り、温水または気水混合冷媒の冷却槽に浸漬して5℃/秒以上の冷却速度で冷却する工程と、その後、線材を前記冷却槽から150℃〜450℃の線温で引き上げて大気中で放冷する工程とを具えることを特徴とする。
【0012】
また、本発明熱間圧延線材の直接熱処理設備は、鋼材を熱間圧延する圧延機構と、この圧延機構で熱間圧延後の線材をルーズコイル状に巻き取り、温水または気水混合冷媒の冷却槽に浸漬して冷却する冷却機構と、前記冷却槽から引き上げた線材を放冷する際、自然放冷よりも放冷速度を緩やかにする保温放熱機構とを有することを特徴とする。
【0013】
上述の工程を経ることで、安定して80kgf/mm2以上の強度を有する線材を得ることができる。従って、鉄筋用線材として最適な線材を得ることができる。
【0014】
また、本発明設備によれば、放冷速度を緩やかにすることができ、例えば5℃/秒未満の放冷速度を得ることができる。これにより、高強度の鉄筋用線材を得ることができる。
【0015】
以下、本発明をより詳しく説明する。まず、化学成分を限定した理由は次の通りである。
C:0.10〜0.30重量%
Cは強度を確保するのに必須の元素である。0.10%未満では十分な降伏強度を得ることが難しく、0.30%を超えると靭性や曲げ加工性が低下する。
【0016】
Si:0.20〜2.00重量%
Siは鋼材溶製時の脱酸に有効に作用すると共に、固溶強化元素として降伏強度の向上にも関与する元素である。このような効果を発揮するには0.20%以上の添加が必要である。逆に2.00%を超えると靭性や曲げ加工性が低下する。
【0017】
Mn:0.30〜2.50重量%
Mnは鋼材溶製時の脱酸に有効に作用すると共に、焼入れ性を高めて降伏強度の向上にも関与する元素である。このような効果を発揮するには0.30%以上の添加が必要である。逆に2.50%を超えると靭性や曲げ加工性が低下する。
【0018】
Cr:0.50〜1.50重量%
CrもMnと同様に強度を高めることに資する元素である。このような効果を発揮するには0.50%以上の添加が必要である。逆に1.50%を超えると向上効果が少なく経済性に乏しくなる。
【0019】
Mo:0.01〜0.30重量%
Moは焼入れ性を向上し、強度を向上することに資する元素である。このような効果を発揮するには0.01%以上の添加が必要である。逆に0.30%を超えると向上効果が少なく経済性に乏しくなる。
【0020】
次に、熱処理条件をより詳しく説明する。
熱間圧延工程において、仕上げ圧延の温度は800〜1050℃程度が好適である。仕上げ圧延を経た後、ルーズコイル状に線材を巻き取る。この巻き取り温度は750〜1000℃程度であるが、760〜840℃とすることが好ましい。巻き取り温度を760〜840℃とすることで、線材表面に生じるスケールを薄くすることができる。特に、スケールの厚みを安定して10μm以下に抑えることが可能である。高強度鉄筋は主鉄筋に溶接するような使用方法があり、巻き取り温度の調整により圧延直後の線材で発生する酸化スケールの薄肉化を行って溶接性を改善することができる。また、スケールの厚みは、巻き取り後、冷却槽に導入されるまでの間に大気に触れる時間にも影響を受ける。この大気に触れる時間は15秒以下が好適である。
【0021】
冷却槽における冷媒は、温水または温水と気体との気水混合冷媒を用いる。温水の温度は60〜100℃、気水混合冷媒の温度は60〜97℃が好適である。この冷却槽における冷却は5℃/秒以上の速度で行う。この冷却速度は、(冷却槽入口における線材温度−冷却槽出口における線材温度)/冷媒中に浸漬されている時間で求められる。通常、15〜20℃/秒程度の冷却速度が好適である。
【0022】
冷却槽から引き上げる際の線材温度は150〜450℃とする。このような温度で引き上げを行うのは、引き上げ後の線材の顕熱を用いて緩速冷却を行うためである。この温度調整は、冷媒種類、冷媒温度、冷却槽での浸漬時間(搬送速度)、線材の重なり程度などを適宜選択して調整する。冷却槽から引き上げる際の線材温度は、例えばサーモビジョンにより測定を行う。線材が密に重なった箇所と疎に配された箇所とでは線材温度にばらつきがあるが、この引き上げ時の温度はルーズコイル状線材の最高温度と最低温度の平均値で規定する。
【0023】
この線材温度のばらつきは150℃以下に抑えることが好ましい。温度ばらつきを抑制することで、線材長手方向にわたってほぼ均一な熱処理を施すことができ、線材長手方向に強度や曲げ加工性のばらつきが小さい線材を得ることができる。
【0024】
冷却槽から引き上げた線材は放冷する。その際、放冷速度を5℃/秒未満の緩やかな速度とする。これは、冷却槽から引き上げた際に線材に残る残熱を用いて熱処理を施すためである。通常、線材を搬送するコンベアの少なくとも上部をカバーで覆うことにより、緩やかな速度で放冷させることができる。カバーサイズを調整し、線材の覆われる範囲を調整することで放冷速度の調整ができる。もちろん、線材を搬送するコンベアの全周を覆う筒型のカバーとしても良い。また、必要に応じて、ヒーターなどの加熱手段を用いて放冷速度を緩やかに調整することも可能である。特に、冷媒温度が低い場合は線材の引き上げ温度が低く、線径の細いものは放冷しやすいため、放冷速度が速くなりすぎないように十分に保温を行う。この放冷速度は、(冷却槽出口における線材温度−線材集束機における線材温度)/冷却槽出口から線材集束機までの通過時間で求められる。
【0025】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。
図1は本発明熱処理方法に用いる直接熱処理設備の平面図、図2は本発明熱処理設備における冷却槽を中心とした構成図である。
【0026】
図1に示すように、鋼材は圧延機構を通って仕上げ圧延機10で圧延され、仕上げ水冷帯11に導入される。次に、圧延された線材は巻き取り機12に導入され、ルーズコイル状に巻き取ってコンベアで冷却槽20に搬送される。
【0027】
この冷却槽20は、図2に示すように、内部に冷媒となる温水21が貯留されると共に、線材100をルーズコイル状のまま搬送するチェーンコンベア23を有するものである。冷却槽20に貯留された温水21は、バッファータンク24に排出され、同タンク24を出た温水は循環ポンプ25により配管26を介して冷却ノズル27から噴射されることにより冷却槽20に戻るよう循環される。冷却ノズル27につながる配管の途中には、常温空気を導入する空気導入管28が合流され、空気の供給量を調整することで空気と温水の混合割合を調整し、気水混合冷媒を噴射することができる。この気水混合冷媒の噴射量は、バルブ29の開閉程度により調整することができる。
【0028】
図3は冷却ノズル周辺の模式説明図である。この冷却ノズル27は、ルーズコイル状で搬送される線材100の両端側、つまり線材同士の重なりが密になった箇所を集中的に冷却できるような位置に配置されている。冷却ノズル27は、冷却槽20の長手方向(線材搬送方向)に複数並列されており、各ノズル27のバルブ29を調整することで、冷却槽20の長手方向において、線材100の冷却程度を調整することができる。例えば、線材温度の高い熱処理開始側(図2の左側)と線材温度が低くなる熱処理終了側(図2の右側)とでは冷却程度が異なるため、熱処理開始側のノズル27は空気の混合比を下げ、熱処理終了側のノズル27は空気の混合比を上げた気水混合冷媒を噴射するように冷却を行うことが好ましい。
【0029】
このような冷却槽20を出た線材はコンベア30で保温放熱機構に導入される。本例では、コンベア上に30cmの間隔をあけて長さ5mでルーズコイルの直径より若干大きい幅の鋼板を2枚搬送方向に並べて保温カバー40(図2参照)とした。この保温カバー40により、緩やかな放冷速度に調整することができる。
【0030】
(試験例1)
以上の直接熱処理設備を用いて以下のように線材の製造を行った。
重量%で、C:0.17、Si:0.90、Mn:1.50、Cr:0.90、Mo:0.03、残部がFeと不可避的不純物からなる鋼材を熱間圧延し、ルーズコイル状に巻き取って冷却槽に導入する。冷却槽で所定の熱処理を行い、さらに冷却槽から引き上げた線材を放冷して線材を得た。得られた線材について、平均降伏強度と降伏強度の標準偏差とを求めた。各試験条件と評価結果を表1に示す。
【0031】
【表1】

Figure 0003765412
【0032】
この表に示すように、引き上げ温度を150〜450℃とし、冷却速度を5℃/秒以上としたものは高い降伏強度が得られている。中でも、線材長手方向の温度差(ルーズコイル状線材の重複程度の違いによる温度差)が150℃以下であるものはより好ましい結果が得られている。さらに、保温カバーを用いたものは、安定して5℃/秒未満の放冷速度が得られ、高強度の線材が得られている。
【0033】
(試験例2)
次に、試験例1と同様の化学成分の鋼材を用い、巻き取り温度を変えて得られた線材のスケールの厚みと溶接性の関係について評価してみた。ここでの線材の製造条件は、仕上げ温度:1000℃、冷媒温度:98℃、冷却速度:25℃/秒、放冷速度:3.5℃/秒、保温カバー:有りである。評価結果を表2に示す。
【0034】
【表2】
Figure 0003765412
【0035】
表2から明らかなように、スケールの厚みを10μm以下にした線材は溶接性に優れることがわかる。
【0036】
【発明の効果】
以上説明したように、本発明熱処理方法によれば、強度と溶接性に優れた線材を得ることができる。特に、13mm以上の太径でも高強度の線材を得ることができる。また、本発明熱処理設備は、安定して緩やかな放冷速度を得ることができ、強度に優れた線材を製造することができる。さらに、スケールの厚みが10μm以下の線材は溶接性に優れ、鉄筋用線材としての有効利用が期待される。
【図面の簡単な説明】
【図1】直接熱処理設備の平面図である。
【図2】本発明熱処理設備における冷却槽を中心とした構成図である。
【図3】図2のA-A断面模式図である。
【符号の説明】
10 仕上げ圧延機
11 仕上げ水冷帯
12 巻き取り機
20 冷却槽
21 温水
23 チェーンコンベア
24 バッファータンク
25 循環ポンプ
26 配管
27 冷却ノズル
28 空気導入管
29 バルブ
30 コンベア
40 保温カバー
100 線材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct heat treatment method for hot-rolled wire, a high-strength rebar wire manufactured by this heat treatment method, and a direct heat treatment facility for hot-rolled wire. In particular, the present invention relates to a direct heat treatment method capable of obtaining a high-strength non-heat treated wire suitable for a reinforcing reinforcing bar.
[0002]
[Prior art]
Conventionally, the following techniques are known as high-strength reinforcing bars suitable for shear reinforcing bars.
(1) Japanese Unexamined Patent Publication No. 2001-181781 This publication shows a high-strength hot-rolled steel material excellent in weldability by limiting chemical components, bainite fraction, retained austenite fraction and surface scale thickness. . As the strength of the steel material, those with a yield strength of 70 kgf / mm 2 class are mainly disclosed.
[0003]
{Circle around (2)} JP 10-121200 A steel material for high strength shear reinforcement with ferrite / pearlite structure or ferrite / pearlite / bainite structure containing various alloy components is disclosed.
[0004]
(3) Japanese Patent Application Laid-Open No. 11-293399 A high strength spiral of a chemical component having excellent weldability to which a great variety of alloy components are added is disclosed.
[0005]
[Problems to be solved by the invention]
However, the above prior art has the following problems.
(1) It is necessary to add a large amount of various kinds of alloy components in order to ensure strength, which is uneconomical. As a direct heat treatment facility for hot-rolled wire rods, a steermore process is generally used. Since this Stealmore process is air-cooled, a sufficient cooling rate cannot be obtained especially with a large-diameter wire exceeding 13.0 mm, and it is necessary to add many alloy elements.
[0006]
(2) It is very difficult to stably manufacture large diameter high strength rebars with a yield strength of 80kgf / mm 2 or more with non-tempering (without quenching and tempering). It was necessary. In particular, a steel to which a large amount of alloying element is added is easily affected by variations in the cooling rate during direct heat treatment, and the mechanical performance in the longitudinal direction of the wire varies greatly. Therefore, it has been very difficult to stably produce a high strength reinforcing bar of 80 kgf / mm 2 class by the conventional manufacturing method (non-refining treatment).
[0007]
Therefore, a main object of the present invention is to provide a direct heat treatment method for hot-rolled wire rods that can obtain a high-strength steel wire without containing a large amount of alloy elements.
[0008]
Another object of the present invention is to provide a high-strength reinforcing steel wire obtained by the above heat treatment method.
[0009]
Furthermore, another object of the present invention is to provide a direct heat treatment facility for hot-rolled wire rods that can obtain a high-strength steel wire.
[0010]
[Means for Solving the Problems]
The present invention achieves the above-mentioned object by limiting the conditions for cooling the rolled wire rod immersed in a coolant after rolling, and further specifying the cooling conditions after being pulled up from the coolant.
[0011]
That is, the direct heat treatment method of the hot-rolled wire of the present invention includes C: 0.10 to 0.30, Si: 0.20 to 2.00, Mn: 0.30 to 2.50, Cr: 0.50 to 1.50, Mo: 0.01 to 0.30 in weight%, and the balance Is a process of hot rolling a steel material consisting of iron and inevitable impurities, and winding the wire after hot rolling into a loose coil shape and immersing it in a cooling bath of hot water or air-water mixed refrigerant at 5 ° C / second or more And a step of pulling the wire from the cooling bath at a line temperature of 150 ° C. to 450 ° C. and allowing to cool in the air.
[0012]
Moreover, the direct heat treatment equipment for hot rolled wire rod of the present invention comprises a rolling mechanism for hot rolling a steel material, and winding the wire rod after hot rolling in this rolling mechanism into a loose coil shape to cool hot water or air-water mixed refrigerant. It has a cooling mechanism that cools by being immersed in a tank, and a heat-retaining and heat-dissipating mechanism that makes the cooling rate slower than natural cooling when the wire pulled up from the cooling tank is allowed to cool.
[0013]
By passing through the above-mentioned process, a wire having a strength of 80 kgf / mm 2 or more can be obtained stably. Therefore, an optimal wire can be obtained as a reinforcing bar wire.
[0014]
Moreover, according to the facility of the present invention, the cooling rate can be moderated, and for example, a cooling rate of less than 5 ° C./second can be obtained. Thereby, a high intensity | strength wire for reinforcing bars can be obtained.
[0015]
Hereinafter, the present invention will be described in more detail. First, the reason for limiting the chemical components is as follows.
C: 0.10 to 0.30% by weight
C is an essential element for ensuring strength. If it is less than 0.10%, it is difficult to obtain sufficient yield strength, and if it exceeds 0.30%, toughness and bending workability are deteriorated.
[0016]
Si: 0.20 to 2.00% by weight
Si is an element that effectively acts on deoxidation at the time of melting steel, and is also an element involved in improving yield strength as a solid solution strengthening element. In order to exhibit such an effect, addition of 0.20% or more is necessary. On the other hand, if it exceeds 2.00%, toughness and bending workability deteriorate.
[0017]
Mn: 0.30 to 2.50% by weight
Mn is an element that effectively acts on deoxidation at the time of melting steel, and also contributes to the improvement of yield strength by improving hardenability. In order to exhibit such an effect, addition of 0.30% or more is necessary. On the other hand, if it exceeds 2.50%, the toughness and bending workability deteriorate.
[0018]
Cr: 0.50 to 1.50% by weight
Cr, like Mn, is an element that contributes to increasing the strength. In order to exhibit such an effect, addition of 0.50% or more is necessary. On the other hand, if it exceeds 1.50%, the improvement effect is small and the economy is poor.
[0019]
Mo: 0.01-0.30% by weight
Mo is an element that contributes to improving hardenability and strength. In order to exhibit such an effect, addition of 0.01% or more is necessary. On the other hand, if it exceeds 0.30%, the improvement effect is small and the economy is poor.
[0020]
Next, the heat treatment conditions will be described in more detail.
In the hot rolling step, the finish rolling temperature is preferably about 800 to 1050 ° C. After finishing rolling, the wire is wound into a loose coil shape. The winding temperature is about 750 to 1000 ° C., but preferably 760 to 840 ° C. By setting the winding temperature to 760 to 840 ° C., the scale generated on the surface of the wire can be thinned. In particular, the thickness of the scale can be stably suppressed to 10 μm or less. There is a usage method in which a high-strength reinforcing bar is welded to the main reinforcing bar, and the weldability can be improved by thinning the oxide scale generated in the wire immediately after rolling by adjusting the winding temperature. The thickness of the scale is also affected by the time of exposure to the atmosphere after being wound up and before being introduced into the cooling bath. The time for exposure to the atmosphere is preferably 15 seconds or less.
[0021]
As the refrigerant in the cooling tank, hot water or an air-water mixed refrigerant of hot water and gas is used. The temperature of the hot water is preferably 60 to 100 ° C, and the temperature of the air / water mixed refrigerant is preferably 60 to 97 ° C. Cooling in this cooling tank is performed at a rate of 5 ° C./second or more. This cooling rate is obtained by ((wire temperature at cooling tank inlet−wire temperature at cooling tank outlet) / time immersed in refrigerant). Usually, a cooling rate of about 15 to 20 ° C./second is suitable.
[0022]
The wire temperature when pulling up from the cooling tank is set to 150 to 450 ° C. The reason why the pulling is performed at such a temperature is to perform slow cooling using the sensible heat of the wire after the pulling. This temperature adjustment is performed by appropriately selecting the refrigerant type, the refrigerant temperature, the immersion time (conveying speed) in the cooling tank, the overlapping degree of the wires, and the like. The wire temperature at the time of pulling up from the cooling bath is measured by, for example, thermovision. There are variations in the wire temperature between the places where the wires are densely overlapped and the places where they are sparsely arranged, but the temperature at the time of this pulling is defined by the average value of the maximum temperature and the minimum temperature of the loose coil wire.
[0023]
This variation in wire temperature is preferably suppressed to 150 ° C. or less. By suppressing the temperature variation, a substantially uniform heat treatment can be performed over the longitudinal direction of the wire, and a wire with less variation in strength and bending workability in the longitudinal direction of the wire can be obtained.
[0024]
The wire pulled up from the cooling tank is allowed to cool. At that time, the cooling rate is set to a moderate rate of less than 5 ° C / second. This is because heat treatment is performed using the residual heat remaining in the wire when it is pulled up from the cooling bath. Usually, by covering at least the upper part of the conveyor which conveys a wire with a cover, it can cool at a moderate speed | rate. The cooling rate can be adjusted by adjusting the cover size and adjusting the area covered with the wire. Of course, it is good also as a cylindrical cover which covers the perimeter of the conveyor which conveys a wire. Further, if necessary, the cooling rate can be gradually adjusted by using a heating means such as a heater. In particular, when the refrigerant temperature is low, the wire pulling temperature is low, and those with a small wire diameter are easy to cool, so the temperature is sufficiently kept so that the cooling rate does not become too fast. The cooling rate is obtained by ((wire temperature at cooling tank outlet−wire temperature at wire focusing machine) / passing time from cooling tank outlet to wire focusing machine.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 is a plan view of a direct heat treatment facility used in the heat treatment method of the present invention, and FIG. 2 is a configuration diagram centering on a cooling tank in the heat treatment facility of the present invention.
[0026]
As shown in FIG. 1, the steel material is rolled by a finishing mill 10 through a rolling mechanism and introduced into a finishing water cooling zone 11. Next, the rolled wire is introduced into the winder 12, wound into a loose coil, and conveyed to the cooling tank 20 by a conveyor.
[0027]
As shown in FIG. 2, the cooling tank 20 has a chain conveyor 23 in which hot water 21 serving as a refrigerant is stored, and the wire 100 is conveyed in a loose coil shape. The hot water 21 stored in the cooling tank 20 is discharged to the buffer tank 24, and the hot water leaving the tank 24 returns to the cooling tank 20 by being injected from the cooling nozzle 27 through the piping 26 by the circulation pump 25. Circulated. In the middle of the pipe connected to the cooling nozzle 27, an air introduction pipe 28 for introducing room temperature air is joined, and the mixing ratio of air and hot water is adjusted by adjusting the air supply amount, and the air-water mixed refrigerant is injected. be able to. The injection amount of the air / water mixed refrigerant can be adjusted by the degree of opening and closing of the valve 29.
[0028]
FIG. 3 is a schematic explanatory view around the cooling nozzle. The cooling nozzle 27 is arranged at a position where the both ends of the wire rod 100 conveyed in a loose coil shape, that is, a portion where the overlapping of the wire rods is densely cooled. A plurality of cooling nozzles 27 are juxtaposed in the longitudinal direction of the cooling tank 20 (wire transport direction), and the degree of cooling of the wire 100 is adjusted in the longitudinal direction of the cooling tank 20 by adjusting the valve 29 of each nozzle 27. can do. For example, the heat treatment start side (left side in FIG. 2) where the wire temperature is high and the heat treatment end side (right side in FIG. 2) where the wire temperature is low differ in the degree of cooling. The nozzle 27 on the heat treatment end side is preferably cooled so as to inject the air-water mixed refrigerant with an increased air mixing ratio.
[0029]
The wire that exits the cooling tank 20 is introduced into the heat-retaining and heat-dissipating mechanism by the conveyor 30. In this example, two heat-insulating steel plates having a length of 5 m and a width slightly larger than the diameter of the loose coil are arranged on the conveyor in the conveying direction to form a heat insulating cover 40 (see FIG. 2). This heat retaining cover 40 can be adjusted to a moderate cooling rate.
[0030]
(Test Example 1)
The wire was manufactured as follows using the direct heat treatment equipment described above.
By weight percent, C: 0.17, Si: 0.90, Mn: 1.50, Cr: 0.90, Mo: 0.03, the remainder of the steel material consisting of Fe and inevitable impurities is hot-rolled and wound into a loose coil to form a cooling bath Introduce. A predetermined heat treatment was performed in the cooling bath, and the wire pulled up from the cooling bath was allowed to cool to obtain a wire. About the obtained wire, the average yield strength and the standard deviation of the yield strength were determined. Table 1 shows the test conditions and the evaluation results.
[0031]
[Table 1]
Figure 0003765412
[0032]
As shown in this table, a high yield strength is obtained when the pulling temperature is 150 to 450 ° C. and the cooling rate is 5 ° C./second or more. Among them, more preferable results are obtained when the temperature difference in the longitudinal direction of the wire (temperature difference due to the difference in the degree of overlap of the loose coiled wire) is 150 ° C. or less. Further, the one using the heat insulating cover stably obtains a cooling rate of less than 5 ° C./second, and a high strength wire is obtained.
[0033]
(Test Example 2)
Next, the steel material having the same chemical composition as in Test Example 1 was used, and the relationship between the thickness of the scale of the wire obtained by changing the winding temperature and weldability was evaluated. The manufacturing conditions of the wire here are: finishing temperature: 1000 ° C., refrigerant temperature: 98 ° C., cooling rate: 25 ° C./second, cooling rate: 3.5 ° C./second, and heat insulation cover: provided. The evaluation results are shown in Table 2.
[0034]
[Table 2]
Figure 0003765412
[0035]
As is apparent from Table 2, it can be seen that a wire rod having a scale thickness of 10 μm or less is excellent in weldability.
[0036]
【The invention's effect】
As described above, according to the heat treatment method of the present invention, a wire rod having excellent strength and weldability can be obtained. In particular, a high-strength wire can be obtained even with a large diameter of 13 mm or more. Moreover, the heat treatment equipment of the present invention can stably and slowly obtain a cooling rate, and can produce a wire having excellent strength. Furthermore, a wire with a scale thickness of 10 μm or less is excellent in weldability and is expected to be effectively used as a wire for reinforcing bars.
[Brief description of the drawings]
FIG. 1 is a plan view of a direct heat treatment facility.
FIG. 2 is a configuration diagram centering on a cooling tank in the heat treatment facility of the present invention.
3 is a schematic cross-sectional view taken along the line AA in FIG.
[Explanation of symbols]
10 Finishing mill
11 Finished water cooling zone
12 Winder
20 Cooling tank
21 Hot water
23 Chain conveyor
24 Buffer tank
25 Circulation pump
26 Piping
27 Cooling nozzle
28 Air inlet pipe
29 Valve
30 conveyor
40 Thermal insulation cover
100 wire rod

Claims (6)

重量%でC:0.10〜0.30、Si:0.20〜2.00、Mn:0.30〜2.50、Cr:0.50〜1.50、Mo:0.01〜0.30を含み、残部が鉄と不可避的不純物とからなる鋼材を熱間圧延する工程と、
熱間圧延後の線材をルーズコイル状に巻き取り、温水または気水混合冷媒の冷却槽に浸漬しながら、ルーズコイル状に巻き取られた線材の重なりが密になった箇所を集中的に冷却して、線材の密度差に起因する冷却槽引き上げ時の線材温度のばらつきが 150 ℃以内となるように調整して5℃/秒以上の冷却速度で冷却する工程と、
その後、線材を前記冷却槽から150℃〜450℃の線温で引き上げて5 / 秒未満の冷却速度にて放冷する工程とを具えることを特徴とする熱間圧延線材の直接熱処理方法。
Hot rolling of steel materials containing C: 0.10 to 0.30, Si: 0.20 to 2.00, Mn: 0.30 to 2.50, Cr: 0.50 to 1.50, Mo: 0.01 to 0.30 with the balance being iron and inevitable impurities And a process of
Winding the wire rod after hot rolling into a loose coil shape and immersing it in a cooling bath of hot water or air / water mixed refrigerant while intensively cooling the place where the overlap of the wire rod wound in the loose coil shape is dense And adjusting the wire temperature variation when pulling up the cooling bath due to the difference in wire density to be within 150 ° C and cooling at a cooling rate of 5 ° C / second or more,
Thereafter, the direct method for heat treating a hot rolled wire rod, characterized in that it comprises the step of cooling the wire at a cooling rate of less than the from the cooling bath and pulled up at a linear temperature of 150 ~450 ℃ 5/ sec .
前記放冷する工程は、線材の少なくとも上部をカバーで覆って行うことを特徴とする請求項 1に記載の熱間圧延線材の直接熱処理方法。2. The method for direct heat treatment of a hot-rolled wire rod according to claim 1 , wherein the step of cooling is performed by covering at least an upper portion of the wire rod with a cover . ルーズコイル状に巻き取った際の巻き取り温度が720〜920℃であることを特徴とする請求項 1 または 2に記載の熱間圧延線材の直接熱処理方法。3. The method for direct heat treatment of a hot-rolled wire rod according to claim 1 or 2 , wherein a winding temperature when wound in a loose coil shape is 720 to 920 ° C. 前記巻き取り温度がThe winding temperature is 760760 ~ 840840 ℃であることを特徴とする請求項C. 3Three に記載の熱間圧延線材の直接熱処理方法。A method for directly heat-treating a hot-rolled wire described in 1. 鋼材を熱間圧延する圧延機構と、
この圧延機構で熱間圧延後の線材をルーズコイル状に巻き取り、温水または気水混合冷媒の冷却槽に浸漬して冷却する冷却機構と、
前記冷却槽から引き上げた線材を放冷する際、自然放冷よりも放冷速度を緩やかにする保温放熱機構とを有し、
前記冷却機構は、冷却槽中で線材の重なりが密になった箇所を集中的に冷却できる位置に配置される冷却ノズルを備えていることを特徴とする熱間圧延線材の直接熱処理設備。
A rolling mechanism for hot rolling steel materials;
A cooling mechanism that winds the wire rod after hot rolling in this rolling mechanism into a loose coil shape, and cools by immersing it in a cooling tank of hot water or air-water mixed refrigerant,
When the wire rod pulled up from the cooling tank is allowed to cool, it has a heat-retaining and heat-dissipating mechanism that makes the cooling rate slower than natural cooling .
The said cooling mechanism is provided with the cooling nozzle arrange | positioned in the position which can cool intensively the location where the overlapping of the wire became dense in a cooling tank, The direct heat processing equipment of the hot rolling wire characterized by the above-mentioned.
請求項1〜4のいずれかに記載の熱処理方法で製造した高強度鉄筋用線材であって、
圧延直後の線材のスケール厚さが10μm以下であることを特徴とする高強度鉄筋用線材。
A high-strength reinforcing steel wire manufactured by the heat treatment method according to any one of claims 1 to 4,
A wire rod for high-strength reinforcing bars, characterized in that the scale thickness of the wire rod immediately after rolling is 10 μm or less.
JP2002184860A 2002-06-25 2002-06-25 Direct heat treatment method for hot rolled wire rod Expired - Fee Related JP3765412B2 (en)

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