JP2008196046A - Steel for high strength reinforcing rod, high strength reinforcing rod, and method for producing them - Google Patents
Steel for high strength reinforcing rod, high strength reinforcing rod, and method for producing them Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 124
- 239000010959 steel Substances 0.000 title claims abstract description 124
- 230000003014 reinforcing effect Effects 0.000 title claims abstract description 36
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 239000000463 material Substances 0.000 claims abstract description 91
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 19
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 19
- 239000001257 hydrogen Substances 0.000 claims abstract description 19
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 16
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 12
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 11
- 239000000203 mixture Substances 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 4
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 3
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 3
- 229910052717 sulfur Inorganic materials 0.000 claims abstract 2
- 238000005452 bending Methods 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 19
- 238000001816 cooling Methods 0.000 claims description 15
- 238000005096 rolling process Methods 0.000 claims description 15
- 239000011150 reinforced concrete Substances 0.000 claims description 14
- 238000005098 hot rolling Methods 0.000 claims description 11
- 238000010276 construction Methods 0.000 claims description 7
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- 229910001294 Reinforcing steel Inorganic materials 0.000 claims description 6
- 239000000126 substance Substances 0.000 claims description 6
- 229910052787 antimony Inorganic materials 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 229910052721 tungsten Inorganic materials 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 238000003466 welding Methods 0.000 abstract description 17
- 238000000034 method Methods 0.000 abstract description 5
- 230000000717 retained effect Effects 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 13
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 9
- 230000002787 reinforcement Effects 0.000 description 8
- 238000009864 tensile test Methods 0.000 description 8
- 230000007423 decrease Effects 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000010953 base metal Substances 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 238000005496 tempering Methods 0.000 description 3
- 230000002411 adverse Effects 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 150000003568 thioethers Chemical class 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
Description
本発明は、例えば、鉄筋コンクリート構造物に用いられる剪断補強筋の素材として使用される高強度鉄筋用鋼材および高強度鉄筋、ならびにそれらの製造方法に関する。 The present invention relates to a steel material for high-strength reinforcing bars and high-strength reinforcing bars used as a material for shear reinforcing bars used in, for example, reinforced concrete structures, and methods for producing the same.
鉄筋コンクリート構造物を補強してその崩壊を防ぐために剪断補強筋が使用される。剪断補強筋を使用した鉄筋コンクリート構造物では、鉄筋コンクリート構造物が剪断変形する際に、剪断補強筋が伸びて塑性変形することにより、鉄筋コンクリート構造物の変形エネルギーが剪断補強筋に吸収され鉄筋コンクリート構造物の崩壊が防がれる。しかし、これまでの剪断補強筋は、伸び特性という点からは必ずしも十分なものではない。剪断補強筋は、曲げ加工により円形や角形等に成形されて製造されるものであり、伸び特性に優れると、曲げ加工が容易となり、加工性の面からも大きなメリットとなる。 Shear reinforcement is used to reinforce the reinforced concrete structure and prevent its collapse. In a reinforced concrete structure using shear reinforcement, when the reinforced concrete structure undergoes shear deformation, the shear reinforcement extends and plastically deforms, so that the deformation energy of the reinforced concrete structure is absorbed by the shear reinforcement and the reinforced concrete structure Collapse is prevented. However, conventional shear reinforcements are not always sufficient in terms of elongation characteristics. A shear reinforcing bar is manufactured by being formed into a circular shape or a square shape by bending, and if it has excellent elongation characteristics, it becomes easy to bend and is a great merit in terms of workability.
また、近年は、剪断補強筋を溶接して施工することで鉄筋コンクリート構造物を補強する、施工性のよい溶接閉鎖型の需要が高まっている。この溶接閉鎖型の剪断補強筋では、溶接後の強度・延性を低下させないことが大切であり、溶接部の継手伸びも重要な特性となる。通常、剪断補強筋の溶接では、フラッシュバット溶接やアプセットバット溶接と呼ばれる高能力、高生産性の抵抗溶接が利用される。ここで、フラッシュバット溶接とは、２本の棒鋼の端面どうしを接触させ２つの端面の間に大電圧をかけ、アークの接触と短絡を繰り返して端部に溶融部を形成し、最後にこの溶融部をアプセット（据え込み変形）により排出し、２本の棒鋼の端部に接合部を形成する溶接法である。また、アプセットバット溶接とは、完全に突き合わせられた２本の棒鋼の端面の間に大電圧をかけ、抵抗発熱により端部をアプセットし２本の棒鋼の端部に接合部を形成する溶接法である。 In recent years, there has been an increasing demand for a welded closed type with good workability that reinforces a reinforced concrete structure by welding a shear reinforcing bar. In this welded-type shear reinforcement, it is important not to lower the strength and ductility after welding, and the joint elongation of the welded portion is also an important characteristic. Usually, in the welding of shear reinforcement, high-capacity, high-productivity resistance welding called flash butt welding or upset butt welding is used. Here, the flash butt welding means that two end faces of steel bars are brought into contact with each other, a large voltage is applied between the two end faces, and arc contact and short circuit are repeated to form a melted part at the end. This is a welding method in which the molten part is discharged by upset (upsetting deformation) and a joining part is formed at the ends of two steel bars. Upset butt welding is a welding method in which a large voltage is applied between the two end faces of two steel bars that are completely butted, the ends are upset by resistance heat generation, and a joint is formed at the ends of the two steel bars. It is.
このような剪断補強筋に用いる鉄筋用鋼材として、圧延後に焼入れや焼き戻し等の熱処理を施さなくとも強度と延性に優れ、溶接しても母材と同等レベルの引張強度や延性を有する非調質鉄筋用鋼材が知られている（例えば、特許文献１、特許文献２、特許文献３参照。）。
特許文献1に記載の非調質鉄筋用鋼材は、Ｍｏ添加を必須とするため、コストが高いという問題がある。また、特許文献２に記載の高強度鉄筋用非調質鋼材は、Ｔｉを０．００３％以上含有するため、ＴｉＮの生成により靭性が低下する場合がある。 The steel material for non-tempered rebar described in Patent Document 1 has a problem of high cost because it requires the addition of Mo. Moreover, since the non-tempered steel material for high-strength reinforcing bars described in Patent Document 2 contains 0.003% or more of Ti, toughness may be reduced due to generation of TiN.
またこれらの鋼材については低温靭性について考慮されていないため、寒冷地での使用に際して割れが発生する恐れもある。 Moreover, since these steel materials are not considered about low temperature toughness, there exists a possibility that a crack may generate | occur | produce at the time of use in a cold district.
さらに、これらの鋼材は圧延ままでの高い強度−延性バランスの達成を目的としているが、熱間圧延後の線材冷却履歴等のばらつきを起因とする特性ばらつきが大きく、優れた特性を安定的に得ることが困難であるのが実情である。 Furthermore, these steel materials are intended to achieve a high strength-ductility balance in the as-rolled state, but there are large variations in properties caused by variations in the wire cooling history after hot rolling, etc. The reality is that it is difficult to obtain.
特許文献３に記載の非調質鉄筋用鋼材は、上記のコストや低温靭性の問題を解決できる優れた鋼材であるが、特許文献１、２に記載の鋼材と同様に延性のばらつきが大きく、曲げ加工を行なう際に折れが発生する場合があるという問題がある。 The steel material for non-tempered rebar described in Patent Document 3 is an excellent steel material that can solve the above-mentioned problems of cost and low temperature toughness, but has a large variation in ductility as with the steel materials described in Patent Documents 1 and 2, There is a problem in that bending may occur when bending is performed.
したがって本発明の目的は、このような従来技術の課題を解決し、降伏応力７８５ＭＰａ以上の高強度鉄筋用鋼材であって、延性のばらつきが小さく、しかも、低温靭性に優れ溶接しても母材と同等レベルの引張強度や延性を有する高強度鉄筋用鋼材および高強度鉄筋、ならびにそれらの製造方法を、低コストで提供することにある。 Therefore, the object of the present invention is to solve such problems of the prior art, and is a steel material for high-strength rebar having a yield stress of 785 MPa or more, having a small variation in ductility, and excellent in low-temperature toughness even when welded. The present invention is to provide a steel material for high-strength reinforcing bars and high-strength reinforcing bars having tensile strength and ductility at the same level as those described above, and a method for producing them.
このような課題を解決するための本発明の特徴は以下の通りである。 The features of the present invention for solving such problems are as follows.
第１の発明は、質量％でＣ：０．１５〜０．３０％を含有する鋼材の金属組織が、体積比率で８０％以上のベイナイト、残部フェライトおよび／またはマルテンサイトから構成され、鋼材中の残留水素濃度が０．３ｐｐｍ以下であることを特徴とする高強度鉄筋用鋼材。 In the first invention, the metal structure of the steel material containing C: 0.15 to 0.30% by mass% is composed of bainite, balance ferrite and / or martensite having a volume ratio of 80% or more, and in the steel material A high-strength steel material for reinforcing steel, characterized by having a residual hydrogen concentration of 0.3 ppm or less.
第２の発明は、鋼材が質量％で、Ｃ：０．１５〜０．３０％、Ｓｉ：０．０５〜１％、Ｍｎ：０．２〜２．５％、Ｐ：０．０３％以下、Ｓ：０．０３％以下、Ａｌ：０．０１〜１．０％、Ｎｂ：０．００１〜０．３％、Ｔｉ：０．００３％未満、Ｎ：０．００６０％未満、を含有し、残部がＦｅ及び不可避的不純物からなることを特徴とする第１の発明に記載の高強度鉄筋用鋼材。 2nd invention is steel materials by mass%, C: 0.15-0.30%, Si: 0.05-1%, Mn: 0.2-2.5%, P: 0.03% or less S: 0.03% or less, Al: 0.01-1.0%, Nb: 0.001-0.3%, Ti: less than 0.003%, N: less than 0.0060% The balance is made of Fe and inevitable impurities, and the steel material for high-strength reinforcing bars according to the first invention.
第３の発明は、鋼材がさらに、Ｂを含有し、該Ｂの含有量は、質量％で、鋼中のＮ量、Ｔｉ量との間に下記（１）式で示される関係が成り立つことを特徴とする第２の発明に記載の高強度鉄筋用鋼材。
０．０１００≧Ｂ（％）≧｛Ｎ（％）／１４−Ｔｉ（％）／２７｝×１１＋０．０００５・・・（１）
第４の発明は、鋼材がさらに、質量％で、Ｃｒ：０．１〜２．０％、Ｍｏ：０．０１〜１．０％、Ｖ：０．０１〜１．０％、Ｗ：０．０１〜１．０％、Ｎｉ：０．０１〜１．０％、Ｃｕ：０．０１〜１．０％、Ｃｏ：０．０１〜１．０％、Ｓｂ：０．００１０〜０．００５０％の中から選ばれる１種又は２種以上を含有することを特徴とする第２の発明または第３の発明に記載の高強度鉄筋用鋼材。
In the third invention, the steel material further contains B, and the content of B is mass%, and the relationship represented by the following formula (1) holds between the N content and the Ti content in the steel. A steel material for high-strength rebar as set forth in the second invention, characterized in that
0.0100 ≧ B (%) ≧ {N (%) / 14−Ti (%) / 27} × 11 + 0.0005 (1)
In the fourth aspect of the invention, the steel material is further in mass%, Cr: 0.1 to 2.0%, Mo: 0.01 to 1.0%, V: 0.01 to 1.0%, W: 0 0.01-1.0%, Ni: 0.01-1.0%, Cu: 0.01-1.0%, Co: 0.01-1.0%, Sb: 0.0010-0.0050 The steel material for high-strength reinforcing bars according to the second invention or the third invention, characterized by containing one or more selected from%.
第５の発明は、第２の発明ないし第４の発明のいずれかに記載の化学組成を有する鋼を、加熱温度：Ａｃ3点以上、圧延終了温度：Ａｒ3温度以上で熱間圧延し、その後５００℃〜８００℃の温度範囲を０．３℃／ｓ以上、２５℃／ｓ以下の冷却速度で冷却し、その後下記（２）式を満たす保持温度Ｔ（Ｋ）、保持時間ｔ（秒）での保持を行なうことを特徴とする高強度鉄筋用鋼材の製造方法。
Ｔ×ｌｏｇｔ≧１７００・・・（２）
第６の発明は、第１の発明ないし第４の発明のいずれかに記載の高強度鉄筋用鋼材に、鉄筋コンクリート施工に使用するための曲げ加工が施されていることを特徴とする高強度鉄筋。
A fifth invention is a steel having a chemical composition according to any one of the second aspect of the invention to fourth invention, the heating temperature of Ac 3 point or more, the rolling end temperature: hot rolling at Ar 3 temperature or above, Thereafter, the temperature range of 500 ° C. to 800 ° C. is cooled at a cooling rate of 0.3 ° C./s or more and 25 ° C./s or less, and then a holding temperature T (K) and a holding time t (second) satisfying the following expression (2). The method of manufacturing a steel material for high-strength reinforcing bars,
T × logt ≧ 1700 (2)
A sixth invention is a high-strength reinforcing bar characterized in that the high-strength reinforcing steel material according to any one of the first to fourth inventions is subjected to bending for use in reinforced concrete construction. .
第７の発明は、第２の発明ないし第４の発明のいずれかに記載の化学組成を有する鋼を、加熱温度：Ａｃ3点〜１２５０℃、圧延終了温度：Ａｒ3温度以上で熱間圧延し、その後５００℃〜８００℃の温度範囲を０．３℃／ｓ以上、２５℃／ｓ以下の冷却速度で冷却し、その後下記（２）式を満たす保持温度Ｔ（Ｋ）、保持時間ｔ（秒）での保持を行ない、しかる後に曲げ加工を施し、鉄筋コンクリート施工に使用する鉄筋とすることを特徴とする、高強度鉄筋の製造方法。
Ｔ×ｌｏｇｔ≧１７００・・・（２）
A seventh invention is a steel having a chemical composition according to any one of the second aspect of the invention to fourth invention, the heating temperature of Ac 3 point to 1250 ° C., rolling end temperature: hot rolling at Ar 3 temperature or above Then, the temperature range of 500 ° C. to 800 ° C. is cooled at a cooling rate of 0.3 ° C./s or more and 25 ° C./s or less, and then the holding temperature T (K) and the holding time t satisfying the following expression (2) A method for producing a high-strength reinforcing bar, characterized in that holding is performed in (seconds), and thereafter bending is performed to form a reinforcing bar used for reinforced concrete construction.
T × logt ≧ 1700 (2)
本発明によれば、強度・延性が高く、延性特性のばらつきが小さく、溶接した場合の母材伸びや溶接継手伸びに優れた鋼材を、高価な合金元素を添加することなく低コストで製造できる。また低温靭性に優れた高強度鉄筋用鋼材、さらには高強度鉄筋を製造できる。 According to the present invention, a steel material having high strength and ductility, small variation in ductility characteristics, and excellent base material elongation and weld joint elongation when welded can be manufactured at low cost without adding an expensive alloy element. . Moreover, the steel material for high strength rebar excellent in low temperature toughness, and also the high strength rebar can be manufactured.
本発明者らは、まず、非調質であっても強度と延性に優れ、しかも、溶接しても母材と同等レベルの引張強度や延性をもつ非調質鉄筋用鋼材を製造するために種々の実験・研究を行った。その際に、焼入れ・焼きもどしを行わずに圧延のままで降伏強度が７８５ＭＰａ以上、引張強度９３０ＭＰａ以上、母材伸び（ＥＬ）８％以上、溶接継手伸び５％以上、曲げ加工時破断なし、という強度と延性を兼ね備えた機械的性質を有する非調質鉄筋用鋼材を製造することを目標とした。また、低温靭性として、母材の０℃でのシャルピー衝撃値（ｕＥ０）が８０Ｊ以上であることを目標とした。そして、非調質鉄筋用鋼材において、溶接後の強度や延性の低下を防止するには、接合部付近の溶接熱影響部（ＨＡＺ）の軟化抑制が効果的であること、また、Ｔｉの含有量を少なくし、ＴｉＮの生成抑制により低温靭性の劣化を防止することが効果的であることを見出した。しかし一方で、製造した鋼材の延性特性、特に「絞り値」のばらつきが大きく、曲げ加工を行なう際に、折れが発生する場合があり、この点を改良すべく検討を重ねた。 In order to produce a steel material for non-tempered rebar, which has excellent strength and ductility even if it is non-tempered, and has the same level of tensile strength and ductility as that of the base metal even if it is welded. Various experiments and research were conducted. In that case, the yield strength is 785 MPa or more, the tensile strength is 930 MPa or more, the base material elongation (EL) is 8% or more, the weld joint elongation is 5% or more, and there is no fracture at the time of bending without rolling and tempering. The goal was to produce a steel for non-tempered rebar with mechanical properties that had both strength and ductility. Further, the low-temperature toughness was set such that the Charpy impact value (uE0) of the base material at 0 ° C. was 80 J or more. And in steel materials for non-tempered rebar, in order to prevent the strength and ductility after welding, it is effective to suppress softening of the weld heat affected zone (HAZ) in the vicinity of the joint, and Ti content It was found that it is effective to reduce the amount and prevent the deterioration of low temperature toughness by suppressing the formation of TiN. However, on the other hand, the ductility characteristics of the manufactured steel material, especially the “drawing value”, varies greatly, and bending may occur when bending is performed, and studies were made to improve this point.
本発明者らは、鋼中の残留水素と鋼材の引張特性との関係に着目し、種々調査を行なった。その結果、鋼中には０．５〜１．５ｐｐｍ程度の水素が残留しており、これが鋼材の延性に著しい悪影響を及ぼしていることを見出した。すなわち、残留水素の低減に伴い、引張特性、中でも曲げ加工性への影響が大きい絞り値の絶対値が上昇し、ばらつきが低減して、引張特性が大幅に改善されることが確認できた。そして、鋼材中の水素含有量と引張試験時の絞り値との関係を調査し、鋼中の水素含有量を０．３ｐｐｍ以下に制御することで、引張試験時に３５％以上の高い絞り値を達成し、高いレベルで安定した曲げ加工性を達成しうることを見出し、本発明を完成した。鋼材の圧延後に所定の温度で所定の時間、保持を行なうことで、鋼材中の水素含有量を低下させることができる。高温で保持を行なえば、保持時間を短縮できるが、鋼材を加熱することなく圧延後に所定の期間放置することも有効であり、高温保持を行なわない場合には本発明の鋼材は非調質鋼材に分類できる。 The present inventors conducted various investigations paying attention to the relationship between residual hydrogen in steel and the tensile properties of steel. As a result, it was found that about 0.5 to 1.5 ppm of hydrogen remained in the steel, which had a significant adverse effect on the ductility of the steel material. That is, as the residual hydrogen was reduced, it was confirmed that the absolute value of the drawing value, which has a great influence on the tensile properties, especially the bending workability, increased, the variation was reduced, and the tensile properties were greatly improved. And by investigating the relationship between the hydrogen content in the steel and the drawing value during the tensile test, and controlling the hydrogen content in the steel to 0.3 ppm or less, a high drawing value of 35% or more during the tensile test is achieved. And the present invention has been completed by finding that a stable bending workability can be achieved at a high level. By holding at a predetermined temperature for a predetermined time after rolling the steel material, the hydrogen content in the steel material can be reduced. If holding at high temperature, the holding time can be shortened, but it is also effective to leave the steel material for a predetermined period after rolling without heating, and in the case of not holding the high temperature, the steel material of the present invention is a non-tempered steel material Can be classified.
本発明の高強度鉄筋用鋼材は、質量％でＣ：０．１５〜０．３０％を含有する鋼材であり、金属組織が、体積比率で８０％以上のベイナイト、残部フェライトおよび／またはマルテンサイトから構成され、鋼材中の残留水素濃度が０．３ｐｐｍ以下であるものである。このような鋼材を用いることで、降伏強度が７８５ＭＰａ以上、母材伸び（ＥＬ）８％以上、絞り値３５％以上を達成できる。 The steel material for high-strength reinforcing bars of the present invention is a steel material containing C: 0.15 to 0.30% by mass%, and has a metal structure of 80% or more by volume ratio of bainite, remaining ferrite and / or martensite. The residual hydrogen concentration in the steel material is 0.3 ppm or less. By using such a steel material, it is possible to achieve a yield strength of 785 MPa or more, a base material elongation (EL) of 8% or more, and a drawing value of 35% or more.
上記のような鋼材として、下記に示す成分組成のものを用いることが好ましい。 As the steel material as described above, it is preferable to use one having the following component composition.
以下に本発明の鋼材の成分の限定理由を説明する。以下の説明において％で示す単位は、特に記載がある場合以外は全て質量％である。 The reasons for limiting the components of the steel material of the present invention will be described below. In the following description, all units shown in% are% by mass unless otherwise specified.
Ｃは、目的とする強度を確保するために０．１５％以上は必要である。しかし、０．３０％を超えて添加すると溶接性や延性が劣化するため０．３０％以下とする。 C is required to be 0.15% or more in order to ensure the intended strength. However, if added over 0.30%, weldability and ductility deteriorate, so the content is made 0.30% or less.
残留水素は、その濃度が０．３ｐｐｍ超であると、引張試験時に３５％以上の高い絞り値を達成できなくなり、高いレベルで安定した曲げ加工性を達成し得なくなる。よって、鋼材中の残留水素量は、０．３ｐｐｍ以下とする。 If the concentration of residual hydrogen is more than 0.3 ppm, a high drawing value of 35% or more cannot be achieved during a tensile test, and stable bending workability cannot be achieved at a high level. Therefore, the residual hydrogen amount in the steel material is set to 0.3 ppm or less.
本発明の鋼材では、前記したＣ、残留水素以外の元素の含有量は、後述する体積比率で８０％以上のベイナイト、残部フェライトおよび／またはマルテンサイトから構成される金属組織を得られれば特に限定されるものではないが、以下に示すように各元素の含有量が調整されていることが、特に好ましい。 In the steel material of the present invention, the content of elements other than C and residual hydrogen described above is particularly limited as long as a metal structure composed of bainite, remaining ferrite and / or martensite is 80% or more by volume ratio described later. However, it is particularly preferable that the content of each element is adjusted as described below.
Ｓｉは、鋼の脱酸及び強化のために添加できるが０．０５％未満では効果が少ないため０．０５％以上添加する。しかし、１％を超えて添加すると継手曲げ性を低下させるため１％以下とすることが好ましい。 Si can be added for deoxidation and strengthening of steel, but if it is less than 0.05%, the effect is small, so 0.05% or more is added. However, if added over 1%, the joint bendability is lowered, so it is preferably made 1% or less.
Ｍｎは、焼入性を確保し目標の強度を得るために０．２％以上添加することが好ましい。しかし、２．５％を超えて添加すると延性や溶接性の劣化を招くため２．５％以下とすることが好ましい。 Mn is preferably added in an amount of 0.2% or more in order to ensure hardenability and obtain a target strength. However, if added over 2.5%, ductility and weldability are deteriorated, so 2.5% or less is preferable.
Ｎｂは、鋼中に微細な炭窒化物を形成し、母材の強度上昇とともに、溶接熱影響部軟化抑制に有効な元素である。析出炭窒化物がＴｉＮと比較してもさらに微細であるため、靭性への悪影響も小さい。しかし、０.００１％未満の添加では十分な効果が得られず、０.３％を超えるとＮｂ炭窒化物であっても溶接熱影響部の靭性劣化が著しくなるため、Ｎｂ含有量は０.００１〜０.３％とすることが好ましい。 Nb is an element that forms fine carbonitrides in steel and is effective in suppressing softening of the weld heat affected zone as the strength of the base material increases. Since the precipitated carbonitride is finer than TiN, the adverse effect on toughness is small. However, if the addition is less than 0.001%, a sufficient effect cannot be obtained, and if it exceeds 0.3%, even if Nb carbonitride is used, the toughness deterioration of the weld heat affected zone becomes remarkable, so the Nb content is 0%. It is preferable to set it as 0.001 to 0.3%.
Ａｌは、鋼の脱酸のために添加できるが、０．０１％以下ではその効果が少ないため０．０１％を超える量を添加する。しかし、１．０％以上添加すると継手曲げ性を低下させるため１．０％未満とすることが好ましい。 Al can be added for deoxidation of steel, but if it is 0.01% or less, its effect is small, so an amount exceeding 0.01% is added. However, if added in an amount of 1.0% or more, the joint bendability is lowered, so the content is preferably less than 1.0%.
Ｔｉは、Ｎを固定し粗大な窒化物（ＴｉＮ）を生成するので靭性低下を促進する。よって、本発明の鋼材においては、ＴｉＮは析出しないこと、あるいは、ＴｉＮが析出する場合は、その粒径の最大径を１０μｍ以下とすることが望ましい。そのためには、Ｔｉは基本的に添加しないことが望ましく、含有されたとしてもその含有量は０．００３％未満ととすることが好ましい。 Since Ti fixes N and produces coarse nitrides (TiN), it promotes a decrease in toughness. Therefore, in the steel material of the present invention, TiN does not precipitate, or when TiN precipitates, it is desirable that the maximum particle size be 10 μm or less. For that purpose, it is desirable not to add Ti basically, and even if it is contained, its content is preferably less than 0.003%.
Ｐは、鋼材を脆化し、母材と溶接後の延性、および低温靭性を劣化させる。Ｐは基本的に含有しないことが望ましいが、不可避不純物として含有されたとしてもその含有量は０．０３％以下であることが好ましい。 P embrittles the steel material and degrades the base metal and the ductility after welding and the low temperature toughness. Although it is desirable not to contain P fundamentally, even if it contains as an unavoidable impurity, it is preferable that the content is 0.03% or less.
Ｓは、鋼中でＭｎなどの金属と結合して粗大な硫化物を形成し、母材と溶接後の延性、および低温靭性を劣化させる。Ｓは基本的に含有しないことが望ましいが、不可避不純物として含有されたとしてもその含有量は０．０３％以下であることが好ましい。 S combines with metals such as Mn in steel to form coarse sulfides, and deteriorates the base metal and ductility after welding and low temperature toughness. Although it is desirable not to contain S fundamentally, even if it contains as an unavoidable impurity, it is preferable that the content is 0.03% or less.
Ｎは、不可避的不純物であり、０．００６０％を超えて含有された場合、溶接時にＴｉＮ、ＶＮ等の粗大な析出物を形成し、溶接継手の引張強度及び曲げ性を低下させるため、０．００６０％未満とすることが好ましい。 N is an unavoidable impurity, and when it is contained in excess of 0.0060%, coarse precipitates such as TiN and VN are formed during welding, and the tensile strength and bendability of the welded joint are reduced. It is preferable to be less than .0060%.
さらに、Ｂを添加することが望ましい。 Furthermore, it is desirable to add B.
Ｂは焼入性を向上させる元素であり、母材の強度上昇を特に必要とする場合には、添加が有効である。しかし、０．０１００％を超えて添加しても焼入性向上効果が飽和し、溶接性が劣化する原因にもなるため０．０１００％以下とすることが好ましい。また、強度上昇効果を得るためには、Ｂが鋼中に固溶している必要がある。しかし、鋼中に固溶Ｎが存在する場合には鋼中のＢはＢＮの形成に消費され、ＢＮとしてＢが鋼中に存在する場合には、焼き入れ性の向上に寄与しない。しかしＴｉが存在すると、その存在量に応じて鋼中のＮをＴｉＮとして固定し、ＴｉＮとなったＮはＢＮの形成に寄与しなくなる。したがって、Ｂを添加する場合にはＢＮの形成に消費される以上の量を添加する必要があり、鋼中のＢ量とＮ量とＴｉ量との間に下記（１）式で示される関係が成り立つことが特に好ましい。
０．０１００≧Ｂ（％）≧｛Ｎ（％）／１４−Ｔｉ（％）／２７｝×１１＋０．０００５・・・（１）
尚、上記（１）式の各元素記号は質量％での各元素の含有量である。
B is an element that improves hardenability, and addition is effective when it is particularly necessary to increase the strength of the base material. However, even if added over 0.0100%, the effect of improving hardenability is saturated and the weldability is deteriorated, so 0.0100% or less is preferable. Moreover, in order to obtain the strength increasing effect, B needs to be dissolved in the steel. However, when solid solution N is present in the steel, B in the steel is consumed for the formation of BN, and when B is present in the steel as BN, it does not contribute to improvement of the hardenability. However, when Ti is present, N in the steel is fixed as TiN according to the amount of Ti present, and N that has become TiN does not contribute to the formation of BN. Therefore, when adding B, it is necessary to add more than is consumed for the formation of BN, and the relationship expressed by the following formula (1) between the B content, the N content and the Ti content in the steel. It is particularly preferable that
0.0100 ≧ B (%) ≧ {N (%) / 14−Ti (%) / 27} × 11 + 0.0005 (1)
In addition, each element symbol of said (1) Formula is content of each element in the mass%.
以下の元素は、鋼材の強度・延性のバランス向上に有効であり、必要に応じて１種または２種以上を選択して添加することができる。 The following elements are effective for improving the balance between strength and ductility of the steel material, and one or more elements can be selected and added as necessary.
Ｃｒは、焼入性を高める元素であり、強度を上昇させるために含有されていてもよく、０．１％以上とすることが好ましい。しかし、２．０％を超えて添加すると焼入性が過大となり延性や溶接性を劣化させるため添加する場合は２．０％以下とすることが好ましい。 Cr is an element that enhances hardenability and may be contained in order to increase the strength, and is preferably 0.1% or more. However, if added over 2.0%, the hardenability becomes excessive and the ductility and weldability are deteriorated.
Ｍｏは、焼入性を高めるとともに、組織を改善して延性を向上させるために含有されていてもよく、０．０１％以上とすることが好ましい。しかし１．０％を超えて添加するとコストが上昇し、また、溶接性が劣化する原因となるため添加する場合は１．０％以下とすることが好ましい。 Mo may be contained in order to improve hardenability and improve the structure to improve ductility, and is preferably 0.01% or more. However, if added over 1.0%, the cost increases, and weldability deteriorates. Therefore, when added, the content is preferably made 1.0% or less.
Ｖは、鋼材の焼き入れ性を向上させるとともに炭窒化物の形成により母材の強度を上昇させ、さらに溶接熱影響部軟化抑制にも有効な元素である。０.０１％未満の添加では十分な効果が得られず、１．０％を超えると著しく溶接熱影響部の靭性を劣化させるため、Ｖを添加する場合は、０．０１％以上、１．０％以下とすることが好ましい。 V is an element that improves the hardenability of the steel material, increases the strength of the base material by forming carbonitrides, and is also effective for suppressing softening of the weld heat affected zone. If less than 0.01% is added, a sufficient effect cannot be obtained, and if it exceeds 1.0%, the toughness of the weld heat affected zone is remarkably deteriorated. It is preferable to make it 0% or less.
Ｗは、焼入れ性を向上させる元素である。強度の確保が必要な場合に０．０１％以上添加することができるが、高価であることに加えて、過剰に添加すれば溶接性を劣化させるため、添加する場合は１．０％以下とすることが好ましい。 W is an element that improves hardenability. When it is necessary to ensure strength, it can be added in an amount of 0.01% or more, but in addition to being expensive, if excessively added, the weldability is deteriorated. It is preferable to do.
Ｎｉは、焼入性を向上させる元素である。強度の確保が必要な場合に０．０１％以上添加することができるが、高価であることに加えて、過剰に添加すれば溶接性を劣化させるため、添加する場合は１．０％以下とすることが好ましい。 Ni is an element that improves hardenability. When it is necessary to ensure strength, it can be added in an amount of 0.01% or more, but in addition to being expensive, if excessively added, the weldability is deteriorated. It is preferable to do.
Ｃｕは、焼入性を高め、フェライト相を析出強化することにより強度を向上させる元素である。強度を確保する必要のある場合に添加することができるが、０．０１％未満では効果が不十分であり、１．０％を超えると熱間加工性や溶接性を阻害するため、添加する場合は０．０１％〜１．０％とすることが好ましい。 Cu is an element that improves the hardenability and improves the strength by precipitation strengthening of the ferrite phase. It can be added when it is necessary to ensure strength, but if it is less than 0.01%, the effect is insufficient, and if it exceeds 1.0%, hot workability and weldability are hindered. In such a case, the content is preferably 0.01% to 1.0%.
Ｃｏは、焼入性を向上させ強度の向上に有効な元素である。強度の確保が必要な場合に０．０１％以上添加することができるが、過剰に添加しても効果が飽和するため、添加する場合は１．０％以下とすることが好ましい。 Co is an element that improves hardenability and is effective in improving strength. If it is necessary to ensure strength, it can be added in an amount of 0.01% or more, but the effect is saturated even if it is added excessively.
Ｓｂは、熱間圧延前の加熱時のオーステナイト粒径粗大化を抑制するとともに、加熱時の表層脱炭を抑制する作用を有しており、熱間圧延時の加熱温度の上昇が必要な場合に添加することができる。０．００１０％未満の添加では十分な効果が得られず、一方、０．００５０％を超えて添加すると効果が飽和するとともに熱間加工性および低温靭性の低下をもたらずため、添加する場合は０．００１０％以上、０．００５０％以下とすることが好ましい。 Sb has the effect of suppressing austenite grain size coarsening during heating before hot rolling and suppressing surface layer decarburization during heating, and when heating temperature increase during hot rolling is required Can be added. When adding less than 0.0010%, a sufficient effect cannot be obtained. On the other hand, when adding over 0.0050%, the effect is saturated and hot workability and low temperature toughness are not lowered. Is preferably 0.0010% or more and 0.0050% or less.
上記以外の残部は、Ｆｅ及び上記以外の不可避的不純物からなることが好ましい。 The balance other than the above is preferably composed of Fe and inevitable impurities other than the above.
次に、本発明の鋼材の金属組織について説明する。本発明の鋼材の金属組織は、実質的にベイナイト組織からなる。実質的にベイナイト組織からなるとは、本発明の作用効果を無くさない限り、ベイナイト以外の組織を含有するものが、本発明の範囲に含まれることを意味する。ベイナイト以外の組織を含有すると、強度と延性のバランスが低下するため、ベイナイト以外の組織は少ないほど望ましい。しかし、ベイナイト以外の組織の割合が低い場合は影響が無視できるため、ベイナイトの体積比率が８０％以上であればよい。ベイナイト以外の組織を含有する場合は、フェライトおよび／またはマルテンサイトから構成されるものとする。島状マルテンサイトやフェライトを含有する場合には、トータルの体積比率で島状マルテンサイトおよびフェライトの割合はそれぞれ１０％未満であることが望ましい。 Next, the metal structure of the steel material of the present invention will be described. The metal structure of the steel material of the present invention substantially consists of a bainite structure. The expression “substantially consisting of a bainite structure” means that a structure containing a structure other than bainite is included in the scope of the present invention unless the effects of the present invention are lost. When a structure other than bainite is contained, the balance between strength and ductility is lowered, so the smaller the structure other than bainite, the better. However, since the influence can be ignored when the proportion of the structure other than bainite is low, the volume fraction of bainite may be 80% or more. When a structure other than bainite is contained, it is composed of ferrite and / or martensite. When island-like martensite and ferrite are contained, the ratio of island-like martensite and ferrite is preferably less than 10% in the total volume ratio.
本発明の鋼材は、上記の成分組成を有する鋼を用い、加熱温度：Ａｃ3点〜１２５０℃、圧延終了温度：Ａｒ3温度以上で熱間圧延を行い、その後５００℃〜８００℃の温度範囲を０．３℃／ｓ以上、２５℃／ｓ以下の冷却速度で冷却を行ない、さらにその後、下記（２）式を満足する温度、および時間で保持する工程を経ることで、ベイナイトの体積比率が８０％以上の組織を有し、残留水素濃度が０．３ｐｐｍ以下であって、強度と延性バランスに優れ、特性ばらつきも小さい高強度鉄筋用鋼材として製造することができる。
Ｔ×ｌｏｇｔ≧１７００・・・（２）
但し、Ｔは保持温度（Ｋ）、ｔは保持時間（秒）である。
The steel material of the present invention uses steel having the above-described composition, and is subjected to hot rolling at a heating temperature: Ac 3 point to 1250 ° C., a rolling end temperature: Ar 3 temperature or higher, and then a temperature range of 500 ° C. to 800 ° C. Is cooled at a cooling rate of 0.3 ° C./s or more and 25 ° C./s or less, and then is maintained at a temperature and time satisfying the following formula (2), whereby the volume ratio of bainite Can be manufactured as a steel material for high-strength reinforcing bars with a structure of 80% or more, a residual hydrogen concentration of 0.3 ppm or less, an excellent balance between strength and ductility, and small variation in properties.
T × logt ≧ 1700 (2)
However, T is holding temperature (K) and t is holding time (second).
加熱温度をＡｃ3点以上とした理由は、Ａｃ3点未満の温度では加熱後に引き続いて行われる圧延において加工性が悪化することと、鋼のミクロ組織中に伸長したフェライトが残留して伸びが低下することによるものである。なお、１２５０℃を超える加熱の場合、オーステナイト粒の粗大化にともなって延性が低下し、また、熱料原単位の上昇にもつながる場合があるので、加熱温度は１２５０℃以下とする。 The reason why the heating temperature is set to Ac 3 point or higher is that when the temperature is less than Ac 3 point, the workability deteriorates in the subsequent rolling after heating, and the elongated ferrite remains in the microstructure of the steel. This is due to the decline. In addition, in the case of heating exceeding 1250 ° C., the ductility decreases as the austenite grains become coarser, and the heating unit may increase, so the heating temperature is set to 1250 ° C. or less.
熱間圧延においては、通常、丸棒または異形形状に圧延して、棒鋼または異形棒鋼の鉄筋用鋼材とする。 In hot rolling, the steel bar is usually rolled into a round bar or a deformed shape to form a steel bar for a steel bar or a deformed bar steel.
熱間圧延後５００℃以上、８００℃以下の温度範囲内を０．３℃／ｓ以上、２５℃／ｓ以下の冷却速度で冷却する理由は、０．３℃／ｓ未満の冷却では組織中にフェライトが、また２５℃／ｓ超の冷却速度では島状マルテンサイトの組織分率が増加し、強度と伸びのバランスが低下するからである。 The reason for cooling within a temperature range of 500 ° C. or higher and 800 ° C. or lower after hot rolling at a cooling rate of 0.3 ° C./s or more and 25 ° C./s or less is that in the structure when cooling at less than 0.3 ° C./s This is because ferrite has a structure rate of island martensite at a cooling rate of more than 25 ° C./s, and the balance between strength and elongation decreases.
冷却後、上記（２）式を満足する温度、および時間で保持する。鋼中の残留水素の放出挙動は、温度と時間との関数の形で表すことが可能であり、保持温度により必要な保持時間は異なっている。上記（２）式を満足する保持温度（Ｋ）−保持時間（秒）の履歴を経ることで、目標とする鋼中の残留水素濃度０．３ｐｐｍ以下の鋼材を得ることが可能となる。 After cooling, the temperature is maintained at a temperature and time satisfying the above expression (2). The release behavior of residual hydrogen in steel can be expressed as a function of temperature and time, and the required holding time varies depending on the holding temperature. By passing through a history of holding temperature (K) −holding time (seconds) that satisfies the above formula (2), it is possible to obtain a steel material having a target residual hydrogen concentration of 0.3 ppm or less in steel.
上記（２）式を満足させるためには、例えば１５０℃で５時間の熱処理（Ｔ×ｌｏｇｔ＝１８００≧１７００）をすることや、あるいは平均気温２０℃で２０日間保持する（Ｔ×ｌｏｇｔ＝１８２８≧１７００）など、種々の方法が可能である。１００〜４５０℃の温度域で３０分以上保持することが、一つの目安である。ただし、保持温度を４５０℃以上にすると、ベイナイトおよびマルテンサイトの焼戻しが進行しすぎて、強度が低下するため、上記（２）式におけるＴは４５０℃以下とする。好ましくは４００℃以下である。気温の高い場所で鋼材を保管する場合は、加熱の工程が不要であり、鋼材製造後の保管期間の管理のみで本発明を実施することが可能である。 In order to satisfy the above formula (2), for example, heat treatment at 150 ° C. for 5 hours (T × logt = 1800 ≧ 1700), or holding at an average temperature of 20 ° C. for 20 days (T × logt = 1828) Various methods are possible, such as ≧ 1700). One guideline is to maintain the temperature in the temperature range of 100 to 450 ° C. for 30 minutes or more. However, if the holding temperature is set to 450 ° C. or higher, tempering of bainite and martensite proceeds excessively and the strength decreases, so T in the above formula (2) is set to 450 ° C. or lower. Preferably it is 400 degrees C or less. When the steel material is stored in a place where the temperature is high, the heating process is unnecessary, and the present invention can be implemented only by managing the storage period after the steel material is manufactured.
上記以外の製造工程は特に限定されず、通常の鉄筋の製造工程を用いることができる。 The manufacturing process other than the above is not particularly limited, and a normal manufacturing process for reinforcing bars can be used.
以上説明した製造方法により、本発明の鉄筋用鋼材を製造できるが、本発明の鉄筋用鋼材を、鉄筋コンクリート施工に用いるためには、適宜曲げ加工を施す必要がある。本発明の鉄筋用鋼材は、残留水素濃度が０．３ｐｐｍ以下に抑制されているので、曲げ加工性への影響が大きい絞り値の絶対値が大きく、かつ、そのばらつきも小さいので、曲げ加工時に折れることがない。 Although the steel material for reinforcing bars of the present invention can be manufactured by the manufacturing method described above, in order to use the steel material for reinforcing bars of the present invention for reinforced concrete construction, it is necessary to appropriately perform bending. In the steel material for reinforcing bars of the present invention, since the residual hydrogen concentration is suppressed to 0.3 ppm or less, the absolute value of the drawing value having a large influence on the bending workability is large and the variation thereof is small. It won't break.
本発明の高強度鉄筋用鋼材に曲げ加工を施した本発明の高強度鉄筋は、延性に富んでおり、鉄筋コンクリート施工時に折損することもない。 The high-strength reinforcing bar of the present invention obtained by bending the steel material for high-strength reinforcing bar of the present invention is rich in ductility and does not break during reinforced concrete construction.
さらに、本発明の高強度鉄筋用鋼材は、溶接継手の延性についても優れているので、本発明の高強度鉄筋に溶接を施した鉄筋についても、鉄筋コンクリート施工時の折損が防止されたものとなる。 Furthermore, since the steel material for high-strength reinforcing bars of the present invention is also excellent in ductility of welded joints, breakage at the time of reinforced concrete construction is prevented even for the reinforcing bars welded to the high-strength reinforcing bars of the present invention. .
表１に示す化学成分の鋼（鋼種Ａ〜Ｌ）を溶製鋳造してビレットとし、表２に示す各温度に加熱して、各圧延終了温度で完了する圧延を行い、表２に示す冷却速度で５００℃〜８００℃の温度範囲を冷却したのち、種々の温度で種々の時間保持して、直径１３ｍｍの異形棒鋼を製造した（Ｎｏ．１〜１８）。なお、加熱温度はいずれもＡｃ3点以上であり、圧延終了温度はいずれもＡｒ3温度以上である。 Steels of the chemical components shown in Table 1 (steel types A to L) are melt cast to form billets, heated to the temperatures shown in Table 2 and rolled to complete at each rolling end temperature, and the cooling shown in Table 2 After cooling the temperature range of 500 ° C. to 800 ° C. at a speed, the steel bar having a diameter of 13 mm was produced by holding at various temperatures for various times (No. 1 to 18). The heating temperature is either Ac 3 points or more, the finish rolling temperature is either Ar 3 temperature or more.
製造した各棒鋼について顕微鏡観察により組織とその体積比率を調べ、鋼材中の残留水素濃度を測定した。 The structure and volume ratio of each manufactured steel bar were examined by microscopic observation, and the residual hydrogen concentration in the steel material was measured.
また、母材の特性を調べるために引張試験を行ない、降伏強度（ＹＳ）、引張強度（ＴＳ）、母材伸び（ＥＬ）を測定した。 In addition, a tensile test was performed in order to investigate the characteristics of the base material, and the yield strength (YS), tensile strength (TS), and base material elongation (EL) were measured.
また、引張試験において絞り値も測定した。各棒鋼について２０箇所ずつ測定して絞り値の標準偏差を求めた。 The drawing value was also measured in the tensile test. The standard deviation of the drawing value was determined by measuring 20 points for each bar.
次に、図１に示すように節１０ａ、２０ａをそれぞれ有する２本の異形棒鋼１０、２０をアプセットバット溶接して溶接継手を作製し、これを引張試験に供して溶接継手伸び（溶接部を含む棒鋼そのものを引張試験した際の全伸びの値）を測定するとともに破断位置を確認した。破断位置は、溶接部近傍について０．５ｍｍピッチでビッカース硬さを測定して、図１に示すような長手方向の硬さプロファイルを求め、母材硬さより硬さが大きい部分を溶接部、母材硬さよりも硬さが小さい部分を軟化部として、破断位置がいずれの部分であるかを評価した。
Next, as shown in FIG. 1, two deformed bar steels 10 and 20 each having
次に、母材の曲げ特性を調べるために、異形棒鋼を長さ５００ｍｍに切断した後、公称直径の１倍の曲げ直径で１８０°まで曲げた後、これを９０°まで曲げ戻す曲げ−曲げ戻し試験を行い、異形棒鋼１０本中の折損本数の割合（破断率）を算出することにより曲げ加工性を評価した。 Next, in order to examine the bending characteristics of the base material, the deformed steel bar is cut into a length of 500 mm, bent to 180 ° with a bending diameter that is one times the nominal diameter, and then bent back to 90 °. A return test was performed, and bending workability was evaluated by calculating the ratio (breakage rate) of the number of breaks in 10 deformed steel bars.
さらに、低温靭性として、母材の０℃でのシャルピー衝撃値（ｕＥ０）を測定した。 Further, as the low temperature toughness, the Charpy impact value (uE0) of the base material at 0 ° C. was measured.
結果を表２に併せて示す。なお、表２には、上記の硬さプロファイルにおいて最小の硬さをＨＡＺビッカース硬さとして併記する。 The results are also shown in Table 2. In Table 2, the minimum hardness in the above-mentioned hardness profile is also shown as HAZ Vickers hardness.
降伏強度が７８５ＭＰａ以上、引張強度９３０ＭＰａ以上、母材伸び（ＥＬ）８％以上、母材絞り値平均が４０％以上、絞り値標準偏差が１０以下を、延性のばらつきの小さい鋼材として評価した。溶接継手伸び５％以上、曲げ加工時破断率０％を本発明の鋼材に必要な特性とした。そして、シャルピー衝撃値（ｕＥ０）が８０J以上の物を良好とした。 Yield strength of 785 MPa or more, tensile strength of 930 MPa or more, base material elongation (EL) of 8% or more, base material drawing value average of 40% or more, and drawing value standard deviation of 10 or less were evaluated as steel materials having a small variation in ductility. The welded joint elongation of 5% or more and the breaking rate at the time of bending were set to 0% for the steel material of the present invention. And the thing whose Charpy impact value (uE0) is 80J or more was considered good.
化学成分が本発明の第１の発明の範囲内であるＮｏ．１〜１７、１９の鋼材のうち、圧延後の冷却速度が０．３℃／ｓよりも低いＮｏ.１２およびＮｏ.１５、さらにはＮ量が０．００７０％と高く、Ｂ量がＢ（％）≧｛Ｎ（％）／１４−Ｔｉ（％）／２７｝×１１＋０．０００５を満足しない鋼Ｊを用いたＮｏ．１６、およびＮｂ量が０．００１％に満たない鋼Ｋを用いたＮｏ．１７はそれぞれ鋼中ミクロ組織のフェライト含有率が高く、本発明で規定した、体積比率で８０％以上のベイナイトを満足しない。そのため、表２に示すように、降伏強度（ＹＳ）が目標値に達していない。また、引張強度（ＴＳ）も低い。 No. whose chemical component is within the scope of the first invention of the present invention. Among steel materials 1 to 17 and 19, No. 12 and No. 15 whose cooling rate after rolling is lower than 0.3 ° C./s, N amount is as high as 0.0070%, and B amount is B ( %) ≧ {N (%) / 14-Ti (%) / 27} × 11 + 0.0005 16 and No. using steel K with Nb content less than 0.001%. No. 17 has a high ferrite content in the microstructure in the steel, and does not satisfy bainite of 80% or more by volume ratio defined in the present invention. Therefore, as shown in Table 2, the yield strength (YS) does not reach the target value. Also, the tensile strength (TS) is low.
一方、圧延後の冷却速度が２５℃／ｓよりも高いＮｏ.１３は鋼中ミクロ組織のマルテンサイト含有率が高く、曲げ加工時に破断を生じるサンプルが存在した。 On the other hand, No. 13 whose cooling rate after rolling was higher than 25 ° C./s had a high martensite content in the microstructure in the steel, and there was a sample that broke during bending.
圧延後の保持温度Ｔ（Ｋ）と保持時間ｔ（秒）とがＴ×ｌｏｇｔ≧１７００の関係を満足しない、Ｔ×ｌｏｇｔが１７００未満であるＮｏ．１４、１５、１９では、鋼中の残留水素濃度が高く、引張試験時の絞り値の平均値が低く、標準偏差が大きく、ばらつきが大きい。さらに、Ｎｏ．１４、１５、１９では、曲げ加工時には折損も認められた。 The holding temperature T (K) after rolling and the holding time t (seconds) do not satisfy the relationship of T × logt ≧ 1700, and T × logt is less than 1700. In 14, 15, and 19, the residual hydrogen concentration in the steel is high, the average value of the drawing value during the tensile test is low, the standard deviation is large, and the variation is large. Furthermore, no. In 14, 15, and 19, breakage was also observed during bending.
鋼組成が本発明の範囲外となる鋼Ｌを用いたＮｏ．１８では、溶接後の伸びが十分に得られず、また曲げ試験時に全ての鋼材に折損を発生した。 No. using steel L whose steel composition falls outside the scope of the present invention. In No. 18, the elongation after welding was not sufficiently obtained, and all steel materials were broken during the bending test.
これに対して、本発明の規定を満足するＮｏ．１〜１１では、ＹＳ、ＴＳ、母材伸び、絞り値（平均値、標準偏差）、溶接継手伸び、曲げ加工時破断率とも、それぞれ、目標とする値が得られ、溶接割れの発生も無かった。また低温靭性も良好であった。 In contrast, No. 1 satisfying the provisions of the present invention. 1 to 11, YS, TS, base material elongation, drawing value (average value, standard deviation), weld joint elongation, and fracture rate during bending are obtained as target values, and there is no occurrence of weld cracks. It was. The low temperature toughness was also good.
中でもＮｏ．１〜Ｎｏ．９は、熱間圧延前の加熱温度が１２５０℃よりも高いＮｏ.１０、およびＴｉ量が０．００３％よりも高い鋼Ｉを用いたＮｏ．１１と比較してもさらに優れた絞り値とシャルピー衝撃値を達成した。 Among these, No. 1-No. No. 9 is No. 10 in which the heating temperature before hot rolling is higher than 1250 ° C, and No. 10 using Steel I in which the Ti content is higher than 0.003%. Compared to 11, the aperture value and Charpy impact value were further improved.
１０、２０ 異形棒鋼
１０ａ、２０ａ 節
10, 20
Claims (7)
０．０１００≧Ｂ（％）≧｛Ｎ（％）／１４−Ｔｉ（％）／２７｝×１１＋０．０００５・・・（１） The steel material further contains B, and the content represented by the following formula (1) is established between the N content and the Ti content in the steel in mass%. 2. A steel material for high-strength reinforcing steel as described in 2.
0.0100 ≧ B (%) ≧ {N (%) / 14−Ti (%) / 27} × 11 + 0.0005 (1)
Ｔ×ｌｏｇｔ≧１７００・・・（２） The steel having the chemical composition according to any one of claims 2 to 4, the heating temperature: Ac 3 point to 1250 ° C., rolling end temperature: hot rolling at Ar 3 temperature or above, then 500 ° C. to 800 ° C. Is cooled at a cooling rate of 0.3 ° C./s or more and 25 ° C./s or less, and then held at a holding temperature T (K) and a holding time t (second) satisfying the following expression (2). The manufacturing method of the steel material for high-strength reinforcing steel characterized by the above-mentioned.
T × logt ≧ 1700 (2)
Ｔ×ｌｏｇｔ≧１７００・・・（２） The steel having the chemical composition according to any one of claims 2 to 4, the heating temperature: Ac 3 point to 1250 ° C., rolling end temperature: hot rolling at Ar 3 temperature or above, then 500 ° C. to 800 ° C. Is cooled at a cooling rate of 0.3 ° C./s or more and 25 ° C./s or less, and then held at a holding temperature T (K) and a holding time t (second) satisfying the following expression (2). A method for producing a high-strength reinforcing bar, characterized in that it is subjected to bending after that to form a reinforcing bar for use in reinforced concrete construction.
T × logt ≧ 1700 (2)
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Cited By (11)
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| JP2008196045A (en) * | 2007-01-17 | 2008-08-28 | Jfe Steel Kk | Manufacturing method of steel for high strength reinforcement |
| JP2011174137A (en) * | 2010-02-24 | 2011-09-08 | Jfe Steel Corp | Method for manufacturing steel material for reinforcing bar |
| WO2013035848A1 (en) * | 2011-09-09 | 2013-03-14 | 新日鐵住金株式会社 | Medium carbon steel sheet, quenched member, and method for manufacturing medium carbon steel sheet and quenched member |
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| Publication number | Publication date |
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| JP5205820B2 (en) | 2013-06-05 |
| JP2008196045A (en) | 2008-08-28 |
| JP5092554B2 (en) | 2012-12-05 |
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