JP7479794B2 - PC steel with excellent delayed fracture resistance and its manufacturing method - Google Patents
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- 229910000831 Steel Inorganic materials 0.000 title claims description 100
- 239000010959 steel Substances 0.000 title claims description 100
- 230000003111 delayed effect Effects 0.000 title claims description 46
- 238000004519 manufacturing process Methods 0.000 title claims description 17
- 239000000463 material Substances 0.000 claims description 58
- 230000032683 aging Effects 0.000 claims description 51
- 229910052799 carbon Inorganic materials 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 15
- 239000002184 metal Substances 0.000 claims description 11
- 229910052751 metal Inorganic materials 0.000 claims description 11
- 229910000734 martensite Inorganic materials 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 claims description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims 1
- 239000011513 prestressed concrete Substances 0.000 description 96
- 238000010438 heat treatment Methods 0.000 description 18
- 229910052739 hydrogen Inorganic materials 0.000 description 14
- 239000001257 hydrogen Substances 0.000 description 14
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 12
- 238000010791 quenching Methods 0.000 description 7
- 230000000171 quenching effect Effects 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- 238000005496 tempering Methods 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 239000004567 concrete Substances 0.000 description 6
- 239000011572 manganese Substances 0.000 description 6
- 229910000859 α-Fe Inorganic materials 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
- 239000011651 chromium Substances 0.000 description 5
- 239000010949 copper Substances 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 5
- 230000035882 stress Effects 0.000 description 5
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- 238000001816 cooling Methods 0.000 description 4
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- 238000009864 tensile test Methods 0.000 description 4
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- 229910001562 pearlite Inorganic materials 0.000 description 3
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- SOIFLUNRINLCBN-UHFFFAOYSA-N ammonium thiocyanate Chemical compound [NH4+].[S-]C#N SOIFLUNRINLCBN-UHFFFAOYSA-N 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
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- 238000005868 electrolysis reaction Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000000700 radioactive tracer Substances 0.000 description 2
- 230000003014 reinforcing effect Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
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- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 229910001294 Reinforcing steel Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000003679 aging effect Effects 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
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- 239000010703 silicon Substances 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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Description
本発明は、耐遅れ破壊特性に優れたＰＣ鋼材及びその製造方法に関する。 The present invention relates to PC steel with excellent delayed fracture resistance and a manufacturing method thereof.
ＰＣ鋼材は、コンクリートパイル、ポールおよび橋梁、建築等のプレストレストコンクリート（ＰＣ）に緊張を与える緊張材であり、ＰＣ鋼材としては、例えばＰＣ鋼棒やＰＣ鋼線、ＰＣ鋼より線などがある。
特に、ＰＣ鋼棒はコンクリートパイル、ポールおよび橋梁、建築等のプレストレストコンクリート（ＰＣ）構造物の補強用鋼材として広く使用されている。このようなＰＣ鋼棒はＪＩＳ Ｇ ３１０９「ＰＣ鋼棒」およびＪＩＳ Ｇ ３１３７「細径異形ＰＣ鋼棒」にて引張強さ、耐力、伸び、リラクセーション値が規格化されている。
ＰＣ鋼棒はコンクリート製品にプレストレスト力を作用するために常に引張応力が作用しており、プレストレストコンクリート構造物中の高強度ＰＣ鋼棒は長期間の使用中に、コンクリートのひび割れ部等から水分が侵入し、局部的に腐食が発生し、鋼中に水素が侵入することにより遅れ破壊を引き起こすことがある。このために高強度化に伴い、耐遅れ破壊特性が要求される。
PC steel members are tension members that provide tension to prestressed concrete (PC) in concrete piles, poles, bridges, buildings, etc., and examples of PC steel members include PC steel bars, PC steel wires, and PC steel strands.
In particular, PC steel bars are widely used as reinforcing steel materials for concrete piles, poles, and prestressed concrete (PC) structures such as bridges, buildings, etc. The tensile strength, yield strength, elongation, and relaxation values of such PC steel bars are standardized in JIS G 3109 "PC steel bars" and JIS G 3137 "Small diameter deformed PC steel bars."
Tensile stress is always applied to PC steel bars in order to apply prestressing force to concrete products, and during long-term use, moisture may penetrate high-strength PC steel bars in prestressed concrete structures through cracks in the concrete, causing localized corrosion and hydrogen to penetrate into the steel, which may lead to delayed fracture. For this reason, delayed fracture resistance is required along with increased strength.
耐遅れ破壊特性に優れたＰＣ鋼棒としては、例えば特許文献１及び２に、フェライトの平均面積率やフェライト粒のアスペクト比に着目した技術が記載されている。
また、特許文献３には、耐遅れ破壊特性に優れた高強度ボルトが記載されており、特許文献４及び５には、超高強度鋼や高強度ボルトの耐遅れ破壊特性を向上させるために、時効処理を行うことが記載されている。
As for PC steel bars having excellent delayed fracture resistance, for example, Patent Documents 1 and 2 describe technologies focusing on the average area ratio of ferrite and the aspect ratio of ferrite grains.
Furthermore, Patent Document 3 describes a high-strength bolt having excellent delayed fracture resistance, and Patent Documents 4 and 5 describe aging treatment in order to improve the delayed fracture resistance of ultra-high strength steel and high strength bolts.
本発明はこのような事情の下、従来とは異なる手法により、耐遅れ破壊特性に優れたＰＣ鋼材及びその製造方法を提供することを目的とする。 Under these circumstances, the present invention aims to provide a PC steel material with excellent delayed fracture resistance and a manufacturing method thereof, using a method different from conventional methods.
本発明者らは、以下の構成により上記課題が解決できることを見出した。 The inventors have discovered that the above problems can be solved by the following configuration:
＜１＞
質量％で、Ｃ：０．１０～０．６０％、Ｓｉ：１．０％以上を含有し、金属組織が焼戻しマルテンサイトであり、引張強さが１２００Ｎ／ｍｍ２以上であり、
遅れ破壊試験において一定の引張荷重を１００時間加えても破断しない最大の荷重を、遅れ破壊試験を行う前の引張強度で除した値を遅れ破壊強度比と定義した場合、この遅れ破壊強度比が０．９０以上である、ＰＣ鋼材。
＜２＞
質量％で、Ｃ：０．１０～０．６０％、Ｓｉ：１．０％以上を含有し、金属組織が焼戻しマルテンサイトであり、引張強さが１２００Ｎ／ｍｍ２以上であるＰＣ鋼材に対して、下記条件を満たすひずみ時効処理を行う、耐遅れ破壊特性に優れたＰＣ鋼材の製造方法。
付与する予ひずみ：塑性ひずみで０．２～０．６％
時効温度：２００～３００℃
時効時間：０．１～１００時間
<1>
In mass%, it contains C: 0.10 to 0.60%, Si: 1.0% or more, the metal structure is tempered martensite, and the tensile strength is 1200 N/ mm2 or more,
PC steel having a delayed fracture strength ratio of 0.90 or more, where the delayed fracture strength ratio is defined as the maximum load at which a constant tensile load is applied for 100 hours in a delayed fracture test without causing fracture, divided by the tensile strength before the delayed fracture test.
＜2＞
A method for producing PC steel material with excellent resistance to delayed fracture, comprising the steps of: (a) subjecting PC steel material to strain aging treatment that satisfies the following conditions; the PC steel material contains, by mass%, 0.10 to 0.60% C and 1.0% or more Si, has a tempered martensite metal structure, and has a tensile strength of 1,200 N/ mm2 or more.
Pre-strain applied: Plastic strain of 0.2 to 0.6%
Aging temperature: 200-300°C
Aging time: 0.1 to 100 hours
本発明によれば、従来とは異なる手法により、耐遅れ破壊特性に優れたＰＣ鋼材及びその製造方法を提供することができる。 The present invention provides PC steel with excellent delayed fracture resistance and a manufacturing method thereof, using a method different from conventional methods.
［ＰＣ鋼材］
本発明のＰＣ鋼材は、質量％で、Ｃ：０．１０～０．６０％、Ｓｉ：１．０％以上を含有し、金属組織が焼戻しマルテンサイトであり、引張強さが１２００Ｎ／ｍｍ２以上であり、遅れ破壊試験において一定の引張荷重を１００時間加えても破断しない最大の荷重を、遅れ破壊試験を行う前の引張強度で除した値を遅れ破壊強度比と定義した場合、この遅れ破壊強度比が０．９０以上である。
[PC steel]
The PC steel material of the present invention contains, by mass%, 0.10 to 0.60% C and 1.0% or more Si, has a metal structure of tempered martensite, and has a tensile strength of 1200 N/ mm2 or more. When the delayed fracture strength ratio is defined as the maximum load at which a constant tensile load is applied for 100 hours in a delayed fracture test without causing fracture, divided by the tensile strength before the delayed fracture test, the delayed fracture strength ratio is 0.90 or more.
本発明のＰＣ鋼材における化学成分について述べる。なお、各化学成分の組成の「％」は「質量％」である。 The chemical components of the PC steel material of the present invention will be described below. Note that the "%" in the composition of each chemical component is "mass %."
〔Ｃ（炭素）〕
本発明のＰＣ鋼材は、Ｃを０．１０～０．６０％含有する。Ｃは、焼入れ性を向上させる元素で、ＰＣ鋼材の強度と時効の効果に影響を及ぼす元素である。本発明のＰＣ鋼材は、所定の強度を得るためにＣを０．２５～０．４５％含有することが好ましく、０．３０～０．３６％含有することがより好ましい。
[C (carbon)]
The PC steel material of the present invention contains 0.10 to 0.60% C. C is an element that improves hardenability and affects the strength and aging effect of the PC steel material. In order to obtain a predetermined strength, the PC steel material of the present invention preferably contains 0.25 to 0.45% C, and more preferably contains 0.30 to 0.36% C.
〔Ｓｉ（ケイ素）〕
本発明のＰＣ鋼材は、Ｓｉを１．０％以上含有する。Ｓｉを１．０％以上含有することで、転位の粒界への集積を抑制し、耐遅れ破壊特性を向上させることができると考えられる。耐遅れ破壊特性の観点から、本発明のＰＣ鋼材におけるＳｉの含有率は、１．５％超であることが好ましく、１．６％以上であることがより好ましい。また、ＰＣ鋼材の素材の製造の観点から、本発明のＰＣ鋼材におけるＳｉの含有率は２．５％以下であることが好ましく、品質を安定させるために、２．０％以下であることがより好ましい。
[Si (silicon)]
The PC steel material of the present invention contains 1.0% or more of Si. It is believed that the inclusion of 1.0% or more of Si can suppress the accumulation of dislocations at grain boundaries and improve delayed fracture resistance. From the viewpoint of delayed fracture resistance, the Si content of the PC steel material of the present invention is preferably more than 1.5%, and more preferably 1.6% or more. In addition, from the viewpoint of the production of PC steel material, the Si content of the PC steel material of the present invention is preferably 2.5% or less, and in order to stabilize the quality, it is more preferably 2.0% or less.
本発明のＰＣ鋼材の化学成分は、上記したＣとＳｉ以外の残部はＦｅ及び不可避的不純物（例えばＣｕなど）であってもよいし、更に別の元素を含んでいてもよい。
本発明のＰＣ鋼材が含んでもよい元素としては、Ｃ及びＳｉ以外の鉄鋼主要５元素であるＭｎ、Ｐ、及びＳが挙げられる。また、例えば、Ｎｉ、Ｃｒ、Ｔｉ、及びＢなどを含んでもよい。
The chemical composition of the PC steel material of the present invention may be such that the balance other than the above-mentioned C and Si is Fe and unavoidable impurities (such as Cu), and may further contain other elements.
The PC steel material of the present invention may contain elements such as Mn, P, and S, which are the five main steel elements other than C and Si. In addition, the PC steel material may contain, for example, Ni, Cr, Ti, B, etc.
〔Ｍｎ（マンガン）〕
Ｍｎは、製鋼段階における脱酸剤として好ましい元素であり、本発明のＰＣ鋼材においては、組織をマルテンサイトとするために焼入れ性を向上させる元素としても作用する。Ｍｎの含有率は、強度を確保するために、０．１％以上添加することが好ましい。また、機械的性質の観点から、２．０％以下が好ましく、０．５～１．０％であることがより好ましく、０．６～０．９％であることが更に好ましい。
[Mn (manganese)]
Mn is a preferred element as a deoxidizer in the steelmaking stage, and in the PC steel material of the present invention, it also acts as an element that improves hardenability by making the structure martensite. In order to ensure strength, the Mn content is preferably 0.1% or more. From the viewpoint of mechanical properties, the Mn content is preferably 2.0% or less, more preferably 0.5 to 1.0%, and even more preferably 0.6 to 0.9%.
〔Ｐ（リン）〕
Ｐは、機械的性質や耐遅れ破壊性を損なう元素で、一般的なＰＣ鋼材においてもその含有量が０．０３％以下であることが規定されている。本発明のＰＣ鋼材においてもより少ないほうが好ましい。Ｐの含有率は、０．０３％以下であることが好ましく、０．０２％以下であることがより好ましい。
[P (phosphorus)]
P is an element that impairs mechanical properties and delayed fracture resistance, and its content is regulated to be 0.03% or less in general PC steel materials. The lower the content, the better in the PC steel material of the present invention. The P content is preferably 0.03% or less, and more preferably 0.02% or less.
〔Ｓ（硫黄）〕
Ｓは、機械的性質や耐遅れ破壊性を損なう元素で、一般的なＰＣ鋼材においてもその含有量が０．０３％以下であることが規定されている。本発明のＰＣ鋼材においてもより少ないほうが好ましい。Ｓの含有率は、０．０３％以下であることが好ましく、０．０１％以下であることがより好ましい。
[S (sulfur)]
S is an element that impairs mechanical properties and delayed fracture resistance, and its content is regulated to be 0.03% or less in general PC steel materials. The lower the content, the better in the PC steel material of the present invention. The S content is preferably 0.03% or less, and more preferably 0.01% or less.
〔Ｃｕ（銅）〕
Ｃｕは、製鋼上不可避的不純物であり、脆性の原因となるので、一般的なＰＣ鋼材においてもその含有量が０．３％以下であることが規定されている。本発明のＰＣ鋼材においてもより少ないほうが好ましく、Ｃｕの含有率は、質量％で０．３％以下であることが好ましく、０．１５％以下であることがより好ましい。
[Cu (copper)]
Cu is an unavoidable impurity in steelmaking and causes brittleness, so its content in general PC steel is regulated to be 0.3% or less. In the PC steel of the present invention, the lower the content, the better, and the Cu content is preferably 0.3% or less, and more preferably 0.15% or less, by mass%.
〔Ｎｉ（ニッケル）〕
Ｎｉは、焼入れ性や耐遅れ破壊性を改善する元素であるが、経済性に優れないので、１．５％を上限に必要に応じて添加してもよい。
[Ni (nickel)]
Ni is an element that improves hardenability and delayed fracture resistance, but is not economically advantageous, so it may be added, if necessary, up to an upper limit of 1.5%.
〔Ｃｒ（クロム）〕
Ｃｒは、焼入れ性を改善する元素であるが、多量に添加すると熱処理時に溶解し難い炭化物を形成するので、その添加量は、２．０％以下にすることが好ましい。
[Cr (Chromium)]
Cr is an element that improves hardenability, but if added in a large amount, it forms carbides that are difficult to dissolve during heat treatment, so the amount of Cr added is preferably 2.0% or less.
〔Ｔｉ（チタン）〕
Ｔｉは、微細炭窒化物を形成し、結晶粒微細化効果により、機械的性質を改善する元素である。０．０５％以上添加しても効果がないので、０．０５％以下の範囲で、必要に応じて添加してもよい。
[Ti (Titanium)]
Ti is an element that forms fine carbonitrides and improves mechanical properties by refining crystal grains. Since there is no effect when added in an amount of 0.05% or more, Ti may be added in a range of 0.05% or less as necessary.
〔Ｂ（ホウ素）〕
Ｂは、極微量で焼入れ性や耐遅れ破壊性を改善する元素である。０．０００５％以上で効果が得られるため、この範囲で添加してもよい。
[B (boron)]
B is an element that improves hardenability and delayed fracture resistance even in a very small amount. Since the effect can be obtained at 0.0005% or more, B may be added within this range.
本発明のＰＣ鋼材の金属組織は、焼戻しマルテンサイトを主体とし、体積率で５％未満の未溶解フェライトや３％未満の未変態オーステナイトを含んでも良い。 The metal structure of the PC steel material of the present invention is mainly composed of tempered martensite, and may contain less than 5% by volume of undissolved ferrite and less than 3% by volume of untransformed austenite.
本発明のＰＣ鋼材の引張強さは１２００Ｎ／ｍｍ２以上であり、１４２０Ｎ／ｍｍ２以上であることが好ましい。また、本発明のＰＣ鋼材の引張強さは、１６００Ｎ／ｍｍ２以下であることが好ましい。 The tensile strength of the PC steel material of the present invention is 1200 N/ mm2 or more, and preferably 1420 N/ mm2 or more. Also, the tensile strength of the PC steel material of the present invention is preferably 1600 N/ mm2 or less.
本発明のＰＣ鋼材の遅れ破壊強度比は０．９０以上である。
ここで、「遅れ破壊強度比」とは、遅れ破壊試験において一定の引張荷重を１００時間加えても破断しない最大の荷重を、遅れ破壊試験を行う前の引張強度で除した値である。
本発明のＰＣ鋼材の遅れ破壊強度比は０．９３以上が好ましく、０．９４以上がより好ましく、０．９５以上が更に好ましい。
The PC steel material of the present invention has a delayed fracture strength ratio of 0.90 or more.
Here, the "delayed fracture strength ratio" is a value obtained by dividing the maximum load at which a certain tensile load is applied for 100 hours in a delayed fracture test without causing fracture by the tensile strength before the delayed fracture test.
The delayed fracture strength ratio of the PC steel material of the present invention is preferably 0.93 or more, more preferably 0.94 or more, and even more preferably 0.95 or more.
本発明のＰＣ鋼材は、種々の用途に用いることができる。例えば、コンクリート構造物の補強筋として使用することで、補強筋の遅れ破壊に伴うコンクリート構造物の破壊を防止することが可能となる。
本発明のＰＣ鋼材の形状は特に限定されず、引張強度と耐遅れ破壊特性が要求される任意の用途に使用するのに適した形状とすることができる。
本発明のＰＣ鋼材の具体的な態様の例としては、ＰＣ鋼棒、ＰＣ鋼線及びＰＣ鋼より線が挙げられる。
ＰＣ鋼棒については、前述のとおり、日本工業規格（ＪＩＳ） Ｇ ３１０９「ＰＣ鋼棒」およびＪＩＳ Ｇ ３１３７「細径異形ＰＣ鋼棒」にて、公称断面積、単位質量、引張強さ、耐力、伸び、リラクセーション値などが規格化されている。
ＰＣ鋼線については、ＪＩＳ Ｇ ３５３６「ＰＣ鋼線及びＰＣ鋼より線」にて、公称断面積、単位質量、引張強さ、耐力、伸び、リラクセーション値などが規格化されている。
The PC steel material of the present invention can be used for various purposes. For example, by using it as a reinforcing bar of a concrete structure, it becomes possible to prevent the destruction of the concrete structure due to delayed fracture of the reinforcing bar.
The shape of the PC steel material of the present invention is not particularly limited, and it can be in any shape suitable for use in any application requiring tensile strength and delayed fracture resistance.
Specific examples of the PC steel material of the present invention include a PC steel bar, a PC steel wire, and a PC steel strand.
As described above, the nominal cross-sectional area, unit mass, tensile strength, yield strength, elongation, relaxation value, etc. of PC steel bars are standardized in Japanese Industrial Standards (JIS) G 3109 "PC steel bars" and JIS G 3137 "Small diameter deformed PC steel bars."
For PC steel wires, the nominal cross-sectional area, unit mass, tensile strength, yield strength, elongation, relaxation value, etc. are standardized in JIS G 3536 "PC steel wires and PC steel strands."
本発明のＰＣ鋼材は、以下に説明する耐遅れ破壊特性に優れたＰＣ鋼材の製造方法（本発明のＰＣ鋼材の製造方法）により製造することができる。 The PC steel material of the present invention can be manufactured by the manufacturing method of PC steel material with excellent delayed fracture resistance described below (the manufacturing method of PC steel material of the present invention).
［耐遅れ破壊特性に優れたＰＣ鋼材の製造方法］
本発明は、質量％で、Ｃ：０．１０～０．６０％、Ｓｉ：１．０％以上を含有し、金属組織が焼戻しマルテンサイトであり、引張強さが１２００Ｎ／ｍｍ２以上であるＰＣ鋼材に対して、下記条件を満たすひずみ時効処理を行う、耐遅れ破壊特性に優れたＰＣ鋼材の製造方法にも関するものである。
付与する予ひずみ：塑性ひずみで０．２～０．６％
時効温度：２００～３００℃
時効時間：０．１～１００時間
[Manufacturing method for PC steel with excellent delayed fracture resistance]
The present invention also relates to a method for producing PC steel material with excellent delayed fracture resistance, which comprises subjecting PC steel material containing, by mass%, 0.10 to 0.60% C and 1.0% or more Si, having a tempered martensite metal structure, and having a tensile strength of 1200 N/mm2 or more to a strain aging treatment that satisfies the following conditions:
Pre-strain applied: Plastic strain of 0.2 to 0.6%
Aging temperature: 200-300°C
Aging time: 0.1 to 100 hours
耐遅れ破壊特性に優れたＰＣ鋼材とは、具体的には、前述の遅れ破壊強度比が０．９０以上であるＰＣ鋼材である。
本発明のＰＣ鋼材の製造方法は、上記のように、質量％で、Ｃ：０．１０～０．６０％、Ｓｉ：１．０％以上を含有し、金属組織が焼戻しマルテンサイトであり、引張強さが１２００Ｎ／ｍｍ２以上であるＰＣ鋼材に対して、特定のひずみ時効処理を行うものである。
Specifically, PC steel having excellent delayed fracture resistance is a PC steel having the above-mentioned delayed fracture strength ratio of 0.90 or more.
As described above, the method for manufacturing PC steel material of the present invention involves carrying out a specific strain aging treatment on PC steel material that contains, by mass%, C: 0.10 to 0.60%, Si: 1.0% or more, has a tempered martensite metal structure, and has a tensile strength of 1200 N/ mm2 or more.
本発明のＰＣ鋼材の製造方法に用いられる特定のひずみ時効処理を行う前のＰＣ鋼材を、「ひずみ時効処理前のＰＣ鋼材」とも呼ぶ。
ひずみ時効処理前のＰＣ鋼材についての化学成分、金属組織、引張強さは、前述した本発明のＰＣ鋼材と同様である。
The PC steel material before the specific strain aging treatment used in the PC steel material manufacturing method of the present invention is also called "PC steel material before strain aging treatment."
The chemical composition, metal structure, and tensile strength of the PC steel material before strain aging treatment are the same as those of the PC steel material of the present invention described above.
ひずみ時効処理前のＰＣ鋼材は、公知の方法により入手することができる。
例えば、質量％で、Ｃ：０．１０～０．６０％、Ｓｉ：１．０％以上を含有する鋼材（焼き入れ可能な鋼材であり、例えば、フェライトとパーライトからなる金属組織を有する鋼材）に対して、焼き入れ、及び焼き戻しを行うことで、金属組織を焼戻しマルテンサイトとし、かつ引張強さを１２００Ｎ／ｍｍ２以上に調節することができる。
上記焼き入れ及び焼き戻しについての条件は特に限定されない。
焼き入れの際の加熱温度は、フェライトとパーライトからオーステナイトへの変態が開始する温度であるＡｃ１点以上であることが好ましく、例えば８５０～９５０℃とすることが挙げられる。
焼き入れの際の加熱方法及び加熱速度は特に限定されない。
加熱方法としては、例えば、誘導性の加熱、通電による抵抗加熱（例えば、放射電熱を利用した炉加熱）などが挙げられる。
焼き入れの際の冷却方法、冷却温度及び冷却速度は、焼入れ可能な範囲であれば特に限定されない。
焼き戻しの際の加熱温度は、焼き戻しができる温度であれば特に限定されないが、例えば、低温焼戻し脆性が生じない４００℃以上、かつ、逆変態が起こらない６５０℃以下で実施することが好ましい。
焼き戻しの際の加熱方法、加熱速度及び時間は特に限定されないが、所望の強度となるように、温度と時間を調整する必要がある。
The PC steel material before strain aging treatment can be obtained by a known method.
For example, by quenching and tempering a steel material containing, by mass%, C: 0.10 to 0.60% and Si: 1.0 % or more (a steel material that can be hardened, for example, a steel material having a metal structure consisting of ferrite and pearlite), the metal structure can be made into tempered martensite and the tensile strength can be adjusted to 1200 N/mm2 or more.
The conditions for the above quenching and tempering are not particularly limited.
The heating temperature during quenching is preferably equal to or higher than the Ac1 point, which is the temperature at which transformation from ferrite and pearlite to austenite begins, and may be, for example, 850 to 950°C.
The heating method and heating rate during quenching are not particularly limited.
Examples of the heating method include inductive heating and resistance heating by passing electricity (for example, furnace heating using radiant heat).
The cooling method, cooling temperature and cooling rate during quenching are not particularly limited as long as they are within the ranges that allow quenching.
The heating temperature during tempering is not particularly limited as long as the tempering is possible, but it is preferable to perform the tempering at a temperature of 400°C or higher at which low-temperature temper brittleness does not occur and 650°C or lower at which reverse transformation does not occur.
The heating method, heating rate and time during tempering are not particularly limited, but it is necessary to adjust the temperature and time so as to obtain the desired strength.
以下、ひずみ時効処理について説明する。 The strain aging treatment is explained below.
〔付与する予ひずみ〕
付与する予ひずみは、塑性ひずみで０．２～０．６％であり、好ましくは０．３～０．６％である。
付与する予ひずみが塑性ひずみで０．２％未満では、固着される転位量が少ない（応力緩和も大きい）ため、耐遅れ破壊特性を向上させることができない。また、付与する予ひずみが塑性ひずみで０．６％超では、転位が増殖しすぎるため、固着されない転位が残り、耐遅れ破壊特性を向上させることができない。
ひずみを付与する方法は特に限定されず、公知の方法でひずみ時効処理前のＰＣ鋼材に０．２～０．６％の引張塑性ひずみを与えることができる。ひずみの付与は、例えば、端部を掴んで引張加工する方法やピンチロール間で挟んで連続的に張力を与える方法、段ロールを用いて連続的に曲げ加工する方法などにより行うことができる。
ひずみを付与する際の温度は、時効温度以下に限定される。例えば、冷間加工では２００℃以下、加工とひずみ時効を同時に行う場合は、時効温度（２００～３００℃）で行ってもよい。
[Prestrain to be applied]
The prestrain applied is a plastic strain of 0.2 to 0.6%, preferably 0.3 to 0.6%.
If the pre-strain applied is less than 0.2% in terms of plastic strain, the amount of dislocations that are fixed is small (stress relaxation is also large), and therefore delayed fracture resistance cannot be improved.If the pre-strain applied is more than 0.6% in terms of plastic strain, dislocations increase too much, and dislocations that are not fixed remain, and therefore delayed fracture resistance cannot be improved.
The method of applying strain is not particularly limited, and a tensile plastic strain of 0.2 to 0.6% can be applied to the PC steel material before strain aging treatment by a known method. The application of strain can be performed, for example, by a method of pulling the PC steel material by gripping the end portion, a method of applying continuous tension by clamping the PC steel material between pinch rolls, or a method of continuously bending the PC steel material using corrugated rolls.
The temperature at which strain is applied is limited to the aging temperature or lower. For example, in cold working, the temperature is 200° C. or lower, and in the case where working and strain aging are carried out simultaneously, the temperature may be the aging temperature (200 to 300° C.).
〔時効温度〕
時効温度は、２００～３００℃であり、好ましくは２２０～２８０℃であり、より好ましくは２４０～２６０℃であり、さらに好ましくは２５０℃である。時効温度が２５０℃の場合に、応力緩和が最小、すなわち可動転位が最も少ない状態になる。
時効温度が２００℃未満では、炭素の拡散が不十分で固着されず、３００℃超では、固着が外れやすく、回復により転位が減少してしまうため、強度が低下してしまう。
時効温度に加熱する際の加熱方法及び加熱速度は特に限定されない。
[Aging temperature]
The aging temperature is 200 to 300° C., preferably 220 to 280° C., more preferably 240 to 260° C., and further preferably 250° C. When the aging temperature is 250° C., the stress relaxation is minimized, that is, the number of mobile dislocations is minimized.
If the aging temperature is less than 200°C, carbon diffusion is insufficient and carbon is not fixed, whereas if the aging temperature exceeds 300°C, carbon is easily released from the fixed state and dislocations are reduced by recovery, resulting in a decrease in strength.
The heating method and heating rate when heating to the aging temperature are not particularly limited.
〔時効時間〕
時効時間は、０．１～１００時間であるが、温度の影響を受けるためその目安として、公知である焼戻しパラメータ（Ｐ）が、１００００≦Ｐ≦１２０００となる範囲で実施することが好ましい。
Ｐ＝Ｔ×（Ｃ＋ｌｏｇｔ）
Ｔは温度（Ｋ）を表し、ｔは時間（ｈ）を表し、Ｃは化学成分による定数を表す。Ｃは下記式を用いて算出する。
Ｃ＝２１．３－５．８×（炭素の含有率（質量％））
時効時間は、０．１～１００時間であることが好ましく、０．１～２時間であることがより好ましく、２時間であることが更に好ましい。
[Statute of Limitations]
The aging time is 0.1 to 100 hours, but since it is affected by temperature, it is preferable to carry out the aging within a range where the known tempering parameter (P) is 10,000≦P≦12,000 as a guideline.
P = T x (C + log t)
T represents temperature (K), t represents time (h), and C represents a constant depending on the chemical components. C is calculated using the following formula.
C = 21.3 - 5.8 x (carbon content (mass%))
The aging time is preferably 0.1 to 100 hours, more preferably 0.1 to 2 hours, and even more preferably 2 hours.
本発明のＰＣ鋼材の製造方法で製造したＰＣ鋼材は、トレーサー水素量で表される格子欠陥量が、ひずみ時効を行うことにより、ひずみ時効を行う前に対して、１０％以上低減されていることが好ましい。 The PC steel material manufactured by the PC steel material manufacturing method of the present invention preferably has a lattice defect amount, represented by the amount of tracer hydrogen, that is reduced by 10% or more by strain aging compared to the amount before strain aging.
以下に、実施例に基づいて本発明を更に詳細に説明するが、本発明の範囲は以下に示す実施例により限定的に解釈されない。 The present invention will be described in more detail below with reference to examples, but the scope of the present invention should not be interpreted as being limited to the examples shown below.
＜ひずみ時効処理前のＰＣ鋼棒の作製＞
下記表１に示した化学成分（残部Ｆｅ及び不可避的不純物）の熱間圧延され組織がフェライトとパーライトからなる鋼線材を用いた。この鋼線材を出発材として、デスケーリング、伸線加工を行い、φ（直径）５ｍｍに形状を整えた、伸線材を作製した。作製した伸線材を高周波誘導加熱と水冷を組み合わせて、連続焼入れを行い、続いて所定の強度になるように高周波誘導加熱により焼戻しを行った。このようにして、ひずみ時効処理前のＰＣ鋼棒を作製した。
なお、すべての実施例及び比較例のＰＣ鋼棒の金属組織は１００％焼戻しマルテンサイトであった。
<Preparation of PC steel bar before strain aging treatment>
A hot-rolled steel wire having a structure consisting of ferrite and pearlite and having the chemical composition (balance Fe and unavoidable impurities) shown in Table 1 below was used. Using this steel wire as a starting material, descaling and wire drawing were performed to produce a drawn wire material shaped to a diameter of 5 mm. The produced drawn wire material was subjected to continuous quenching by combining high-frequency induction heating and water cooling, and then tempered by high-frequency induction heating to a predetermined strength. In this manner, a PC steel bar before strain aging treatment was produced.
The metal structure of the PC steel bars in all of the Examples and Comparative Examples was 100% tempered martensite.
＜ひずみ時効処理＞
作製したひずみ時効処理前のＰＣ鋼棒に対して、下記表１に示すひずみ量（全ひずみ及び塑性ひずみ）を付与し、下記表１に示す時効温度及び時効時間でひずみ時効処理を行った。
ひずみ付与においては、引張試験によって応力ひずみ曲線を見ながら下降伏点後までひずみが加わった後に除荷した。
なお、引張試験時の荷重変化と伸びの関係から、上降伏点あるいは下降伏点に相当する荷重を求めた。
時効加熱方法については、予め炉を時効温度に加熱しておいて、そこに予ひずみ付与後の試験片を投入することで行った。
<Strain aging treatment>
The prepared PC steel bars before strain aging treatment were given the strain amounts (total strain and plastic strain) shown in Table 1 below, and were subjected to strain aging treatment at the aging temperature and for the aging time shown in Table 1 below.
In applying strain, the stress-strain curve was observed in a tensile test, and the strain was applied up to the lower yield point, after which the load was removed.
The load corresponding to the upper yield point or the lower yield point was determined from the relationship between the load change and the elongation during the tensile test.
The aging heating method was performed by heating a furnace to the aging temperature in advance and placing the test piece after the prestraining was applied therein.
＜遅れ破壊試験＞
試験片に対し、
溶液：０．１ｍｏｌ／Ｌ ＮａＯＨ＋５．０ ｇ／Ｌ ＮＨ４ＳＣＮ、
溶液温度：３０℃、
電流密度：１００Ａ／ｍ２
の条件で陰極電解法による水素チャージと、負荷応力０．２０σＢ～０．９５σＢの一定弾性応力負荷を同時に行う。σＢは引張強度である。
また、４８～９６時間の水素チャージ後溶液交換を行うことで、それ以後も試験片内部の水素を平衡状態に保つことができる。
１００時間経過後も破断しなかったものについては未破断材とし、応力除荷と同時に水素チャージも終了した。
<Delayed fracture test>
For the test piece,
Solution: 0.1 mol/L NaOH + 5.0 g/L NH4SCN ,
Solution temperature: 30° C.
Current density: 100A/ m2
Under the condition above, hydrogen charging by cathodic electrolysis and constant elastic stress loading of 0.20σ B to 0.95σ B are simultaneously performed, where σ B is the tensile strength.
In addition, by replacing the solution after 48 to 96 hours of hydrogen charging, the hydrogen inside the test piece can be kept in equilibrium thereafter.
Those that did not break even after 100 hours were regarded as unbroken specimens, and hydrogen charging was terminated at the same time as the stress was removed.
＜引張強度＞
図１に示す全長３００ｍｍの試験片を用いて、両端の３０ｍｍを掴み部、中央部８０ｍｍを標点距離として、ひずみ時効処理前の引張特性を確認した。引張試験時の最大荷重を試験片の断面積（２．５×２．５×π＝１９．６ｍｍ２）で除して引張強さをそれぞれ求め、４本の平均値をひずみ時効処理前の引張強度とした。その結果、ひずみ時効処理前の引張強度は１４７０Ｎ／ｍｍ２であった。
また、試験片の一部は、所定の時効条件を施したのち、遅れ破壊試験を実施せず引張試験で最大荷重を求めた。
<Tensile strength>
Using a test piece with a total length of 300 mm as shown in Figure 1, the tensile properties before strain aging treatment were confirmed with 30 mm at both ends as gripping parts and 80 mm at the center as the gauge length. The maximum load during the tensile test was divided by the cross-sectional area of the test piece (2.5 x 2.5 x π = 19.6 mm2 ) to determine the tensile strength, and the average value of the four pieces was taken as the tensile strength before strain aging treatment. As a result, the tensile strength before strain aging treatment was 1470 N/ mm2 .
In addition, some of the test pieces were subjected to predetermined aging conditions, and then the maximum load was determined in a tensile test without carrying out a delayed fracture test.
＜格子欠陥量の測定＞
ひずみ時効処理後のＰＣ鋼棒より試験片を切り出し、無負荷で、
溶液：０．１ｍｏｌ／Ｌ ＮａＯＨ＋５．０ ｇ／Ｌ ＮＨ４ＳＣＮ、
溶液温度：３０℃、
電流密度：１００Ａ／ｍ２
チャージ時間：２４ｈ
の条件で陰極電解法による水素チャージを行った。
水素チャージ後の試験片を、アルゴンガス中で１００℃／ｈの速度で加熱しながら、試験片から放出される水素をガスクロマトグラフ法で検出する昇温脱離分析を行った。その結果、本発明のＰＣ鋼材の製造方法で製造したＰＣ鋼棒であるサンプルＮｏ．１について、ひずみ時効しないものの水素量は、３．２６ｐｐｍであり、ひずみ時効材の水素量は２．８４ｐｐｍであった。
なお、ひずみ時効処理後のＰＣ鋼棒からの試験片は、図２に示すように、ひずみ時効処理後のＰＣ鋼棒の中央部８０ｍｍの中央部３０ｍｍを切り出して作成した。
<Measurement of Lattice Defect Amount>
Test pieces were cut out from the PC steel bars after strain aging treatment, and
Solution: 0.1 mol/L NaOH + 5.0 g/L NH4SCN ,
Solution temperature: 30° C.
Current density: 100A/ m2
Charge time: 24 hours
Hydrogen charging was carried out by cathodic electrolysis under the following conditions.
The hydrogen-charged test specimen was heated in argon gas at a rate of 100°C/h, and the hydrogen released from the test specimen was detected by gas chromatography. As a result, for sample No. 1, which is a PC steel bar manufactured by the PC steel material manufacturing method of the present invention, the hydrogen content of the non-strain-aged material was 3.26 ppm, and the hydrogen content of the strain-aged material was 2.84 ppm.
The test specimens from the PC steel bars after strain aging treatment were prepared by cutting out a central 30 mm portion of a central 80 mm portion of the PC steel bars after strain aging treatment, as shown in FIG.
下記表１中の化学成分の含有量の単位は「質量％」である。 The units of content of chemical components in Table 1 below are "mass %."
下記表１中遅れ破壊試験の判定は、以下の基準で行った。
◎：大幅に改善されている
〇：改善されている
×：改善されていない
The delayed fracture test results in Table 1 below were judged according to the following criteria.
◎: Significantly improved 〇: Improved ×: Not improved
表１に示したように、本発明のＰＣ鋼材の製造方法で製造したＰＣ鋼棒は、遅れ破壊強度比が０．９０以上であった（サンプルＮｏ．１、３、及び４）。特に、サンプルＮｏ．１は、遅れ破壊強度比が０．９５であり、最も優れた耐遅れ破壊特性を示した。
また、本発明のＰＣ鋼材の製造方法で製造したＰＣ鋼棒は、トレーサー水素量で表される格子欠陥量が、ひずみ時効を行うことにより、ひずみ時効を行う前に対して、１０％以上低減された（ひずみ時効前の水素量３．２６ｐｐｍ、ひずみ時効後の水素量２．８４ｐｐｍ）。
As shown in Table 1, the PC steel bars manufactured by the PC steel bar manufacturing method of the present invention had a delayed fracture strength ratio of 0.90 or more (samples No. 1, 3, and 4). In particular, sample No. 1 had a delayed fracture strength ratio of 0.95, and showed the most excellent delayed fracture resistance.
Furthermore, the amount of lattice defects, represented by the amount of tracer hydrogen, of the PC steel rod manufactured by the PC steel manufacturing method of the present invention was reduced by 10% or more by strain aging compared to before strain aging (hydrogen amount before strain aging: 3.26 ppm, hydrogen amount after strain aging: 2.84 ppm).
Claims (1)
付与する予ひずみ：塑性ひずみで０．２～０．６％
時効温度：２００～３００℃
時効時間：０．１～１００時間 A method for manufacturing PC steel material with excellent resistance to delayed fracture, which comprises, by mass%, C: 0.10 to 0.60%, Si: 1.0% to 2.5% , Mn: 0.1% to 2.0% , P: 0.03% or less, S: 0.03% or less, Cu: 0.3% or less, Ni: up to 1.5%, Cr: 2.0% or less, Ti: 0.05% or less, the balance being iron and unavoidable impurities , and which has a metal structure of tempered martensite and a tensile strength of 1,200 N/ mm2 or more, is subjected to strain aging treatment that satisfies the following conditions.
Pre-strain applied: Plastic strain of 0.2 to 0.6%
Aging temperature: 200-300°C
Aging time: 0.1 to 100 hours
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| JP2002173739A (en) | 2000-12-01 | 2002-06-21 | Nippon Steel Corp | High strength steel having excellent hydrogen embrittlement resistance |
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| WO2011111873A1 (en) | 2010-03-11 | 2011-09-15 | 新日本製鐵株式会社 | High-strength steel and high-strength bolt with excellent resistance to delayed fracture, and manufacturing method therefor |
| WO2011111872A1 (en) | 2010-03-11 | 2011-09-15 | 新日本製鐵株式会社 | High-strength steel and high-strength bolt with excellent resistance to delayed fracture, and manufacturing method therefor |
| JP2014043612A (en) | 2012-08-27 | 2014-03-13 | Nippon Steel & Sumitomo Metal | High strength steel excellent in delayed fracture resistance |
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| JP3279086B2 (en) * | 1994-08-18 | 2002-04-30 | 住友金属工業株式会社 | Machine structural steel with excellent delayed fracture resistance |
| JPH08120399A (en) * | 1994-10-25 | 1996-05-14 | Sumitomo Metal Ind Ltd | Steel for machine structure excellent in delayed fracture resistance |
| JPH08209289A (en) * | 1995-02-06 | 1996-08-13 | Sumitomo Metal Ind Ltd | Steel for machine structural use excellent in delayed fracture resistance |
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| JP2002173739A (en) | 2000-12-01 | 2002-06-21 | Nippon Steel Corp | High strength steel having excellent hydrogen embrittlement resistance |
| JP2002194481A (en) | 2000-12-21 | 2002-07-10 | Nippon Steel Corp | High strength steel having excellent hydrogen embrittlement resistance |
| WO2011111873A1 (en) | 2010-03-11 | 2011-09-15 | 新日本製鐵株式会社 | High-strength steel and high-strength bolt with excellent resistance to delayed fracture, and manufacturing method therefor |
| WO2011111872A1 (en) | 2010-03-11 | 2011-09-15 | 新日本製鐵株式会社 | High-strength steel and high-strength bolt with excellent resistance to delayed fracture, and manufacturing method therefor |
| JP2014043612A (en) | 2012-08-27 | 2014-03-13 | Nippon Steel & Sumitomo Metal | High strength steel excellent in delayed fracture resistance |
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