JP6095046B2 - Weather-resistant steel and welded joint using the same - Google Patents
Weather-resistant steel and welded joint using the same Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 111
- 239000010959 steel Substances 0.000 title claims description 111
- 229910000859 α-Fe Inorganic materials 0.000 claims description 21
- 229910000870 Weathering steel Inorganic materials 0.000 claims description 11
- 229910002796 Si–Al Inorganic materials 0.000 claims description 6
- 229910001563 bainite Inorganic materials 0.000 claims description 6
- 229910052751 metal Inorganic materials 0.000 claims description 5
- 239000002184 metal Substances 0.000 claims description 5
- 239000000463 material Substances 0.000 description 23
- 229910018125 Al-Si Inorganic materials 0.000 description 14
- 229910018520 Al—Si Inorganic materials 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 14
- 230000007423 decrease Effects 0.000 description 10
- 239000011572 manganese Substances 0.000 description 10
- 239000000203 mixture Substances 0.000 description 10
- 229910052799 carbon Inorganic materials 0.000 description 8
- 238000003466 welding Methods 0.000 description 8
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 6
- 229910006639 Si—Mn Inorganic materials 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 238000005536 corrosion prevention Methods 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000010422 painting Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 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
- 240000008168 Ficus benjamina Species 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000004210 cathodic protection Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- -1 galvanization Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
Description
本発明は、橋梁、建築、海洋構造物、その他の構造物に用いる溶接性を考慮した耐候性鋼に関し、特に溶接後に生じるボンド部（以下ボンド部と称する）の靱性低下を防ぐことができる耐候性鋼に関する。また、本発明は、前述の耐候性鋼を用いた溶接継ぎ手に関し、特に、溶接部強度低下がなく良好なボンド部の靱性を持つ溶接継ぎ手に関する。 The present invention relates to a weather resistant steel considering weldability used for bridges, buildings, offshore structures, and other structures, and in particular, a weather resistance capable of preventing a decrease in toughness of a bond portion (hereinafter referred to as a bond portion) generated after welding. Related to steel. The present invention also relates to a welded joint using the above-mentioned weathering steel, and more particularly to a welded joint having a good bond portion toughness without a decrease in weld strength.
鋼材は自然環境中において不可逆的に腐食あるいは錆化してゆくため、鋼橋のような構造物では、適切な防錆防食の処置を講じる必要がある。鋼材の防錆防食法には、表面被覆、表面改質、電気防食、鋼材自体の改質など、多くの方法がある。そして、鋼材の代表的な防錆防食法には、塗装、耐候性鋼材、亜鉛メッキ、金属溶射が知られている。このうち、耐候性鋼材は、鋼材に適量の合金元素を添付することで、鋼材表面に緻密な錆層を形成させ、これが鋼材表面を保護することで、以降の錆の進展が抑止され、腐食速度が普通鋼に比べて低下する(非特許文献１)。
耐候性鋼材は、例えばＪＩＳ Ｇ ３１１４（ＩＳＯ ４９５２）に規定されており、現在搭載されている合金の組成元素には、マンガン、銅、クロムを必須元素とし、ニッケル、モリブデン、ニオブ、チタン、及びバナジウムを任意元素としている。
Since steel materials are irreversibly corroded or rusted in the natural environment, it is necessary to take appropriate rust and corrosion prevention measures for structures such as steel bridges. There are many methods for preventing rust and corrosion of steel materials, such as surface coating, surface modification, cathodic protection, and modification of steel materials themselves. As typical rust prevention and corrosion prevention methods for steel materials, painting, weathering steel materials, galvanization, and metal spraying are known. Among these, the weathering steel material attaches an appropriate amount of alloying elements to the steel material to form a dense rust layer on the surface of the steel material, which protects the steel material surface and prevents subsequent rust development and corrosion. The speed is lower than that of ordinary steel (Non-Patent Document 1).
For example, JIS G 3114 (ISO 4952) defines the weather-resistant steel material, and manganese, copper, and chromium are essential elements for the composition elements of currently mounted alloys, and nickel, molybdenum, niobium, titanium, and Vanadium is an optional element.
しかしながら、現在ＪＩＳに規定された耐候性鋼材では、任意元素や必須元素にトランプエレメントを含むため、鉄鋼材料のリサイクル使用の際に分離困難な不純物成分となると共に、昨今の金属価格の上昇期には合金の組成元素の調達が困難となり、鋼材の生産に支障を生ずるという課題があった。
そこで、本出願人は、特許文献１や非特許文献２に示すように、Ｆｅ―Ｍｎ―Ｓｉ−Ａｌを基本成分とした耐候性鋼（以下ではＡｌ-Ｓｉ鋼と称する）を開発している。この耐候性鋼はＡｌの組成が０．１から３．５質量％、Ｓｉの組成が０．３から３．５質量％含むことにより優れた耐候性を示すもので、微細粒鋼であることを特徴としている。
However, since the weather-resistant steel materials currently specified by JIS include trump elements as optional elements and essential elements, it becomes an impurity component that is difficult to separate when recycling steel materials, and during the recent rise of metal prices However, it has been difficult to procure elemental elements of the alloy, which has been a problem for the production of steel materials.
Therefore, as shown in Patent Document 1 and Non-Patent Document 2, the present applicant has developed a weathering steel (hereinafter referred to as Al-Si steel) containing Fe-Mn-Si-Al as a basic component. . This weather-resistant steel shows excellent weather resistance when it contains Al of 0.1 to 3.5% by mass and Si of 0.3 to 3.5% by mass, and is a fine-grained steel. It is characterized by.
しかし、微細粒鋼は溶接を行うと熱影響部（以下ではＨＡＺ部と称する）で軟化が生じるという課題がある。ＨＡＺ部の軟化を防ぐためにはＣ量を増やすことが必要である（非特許文献３、４）。しかし、ＳｉとＭｎを含むＳｉ−Ｍｎ系の鉄鋼材料はＣ量を多くするとボンド部の靱性が低下する。図１に示すように、Ａｌ-Ｓｉ鋼ではＣ量が増えると、靱性（シャルピー吸収エネルギー）が低下している。このため、Ｃ量の高いＡｌ-Ｓｉ鋼では、ボンド部の靱性が低下し良好な溶接継ぎ手とならないという課題があった。 However, when fine-grained steel is welded, there is a problem that softening occurs in a heat-affected zone (hereinafter referred to as a HAZ zone). In order to prevent the softening of the HAZ part, it is necessary to increase the amount of C (Non-patent Documents 3 and 4). However, the Si-Mn steel material containing Si and Mn decreases the toughness of the bond portion when the C content is increased. As shown in FIG. 1, the toughness (Charpy absorbed energy) decreases as the C content increases in Al—Si steel. For this reason, in the Al-Si steel with a high C content, there is a problem that the toughness of the bond portion is lowered and a good weld joint is not obtained.
そこで、靱性（シャルピー吸収エネルギー）を向上させるためにはＣ量を少なくすることが有効であるが、他方で、Ｃ量が少ないＡｌ-Ｓｉ鋼では、溶接によりＨＡＺ部に軟化が生じる。このように、Ａｌ-Ｓｉ鋼の靱性を確保し溶接時の軟化を同時に防止することは困難である。このため現在に至るまで、溶接部強度低下がなく良好なボンド部の靱性を持つＡｌ-Ｓｉ鋼は知られていない。そこで、鋼橋のような構造物において、鋼材としてＡｌ-Ｓｉ鋼を用いる場合に、溶接継ぎ手の強度が充分に得られないため、耐候性鋼としての用途が限られるという課題があった。 Therefore, in order to improve toughness (Charpy absorbed energy), it is effective to reduce the amount of C. On the other hand, in the Al—Si steel having a small amount of C, softening occurs in the HAZ part by welding. Thus, it is difficult to ensure the toughness of the Al—Si steel and simultaneously prevent softening during welding. For this reason, to date, no Al—Si steel has been known that has no bond strength reduction and good bond toughness. Thus, in a structure such as a steel bridge, when Al—Si steel is used as the steel material, there is a problem that the use as a weather resistant steel is limited because sufficient strength of the welded joint cannot be obtained.
他方、特許文献２では、２質量％のＳｉで、Ａｌをほとんど含まない低炭素ベイナイト鋼（Ｆｅ-０．０５Ｃ―０．２Ｍｎ−０．２Ｓｉ）の厚板を作る時にはＢの添加が有効であるとされている。その理由は、Ｂが添加されると連続冷却変態（ＣＣＴ）図上のフェライト相が長時間側に移動するので、厚板中央部の冷却速度がベイナイト析出域のみを通るようになるためである。 On the other hand, in Patent Document 2, the addition of B is effective when making a thick plate of low carbon bainitic steel (Fe-0.05C-0.2Mn-0.2Si) containing 2% by mass of Si and hardly containing Al. It is said that there is. The reason is that when B is added, the ferrite phase on the continuous cooling transformation (CCT) diagram moves to the long time side, so that the cooling rate at the center of the thick plate passes only through the bainite precipitation region. .
しかしながら、Ａｌ-Ｓｉ鋼では、フェライトフォーマーであるＡｌやＳｉを低炭素ベイナイト鋼よりも多量に含むため、低炭素ベイナイト鋼（Ｆｅ-０．０５Ｃ―０．２Ｍｎ−０．２Ｓｉ）と同じようにＢを添加しただけでは、初析フェライトや粒界フェライトの生成を防ぐことはできないことが、理論的に判明している。 However, since Al-Si steel contains a larger amount of ferrite former Al and Si than low-carbon bainite steel, it is the same as low-carbon bainite steel (Fe-0.05C-0.2Mn-0.2Si). It has been theoretically found that the addition of B to cannot prevent the formation of pro-eutectoid ferrite and grain boundary ferrite.
本出願人が開発したＡｌ-Ｓｉ鋼では、ＨＡＺ部の軟化を抑えるためにＣ量を高くすることが必要であった。しかし、Ｃ量が増えるとボンド部での靱性が低下し、良好な靱性を持つ溶接継ぎ手が得られなかった。そこで、本発明では、ボンド部の靱性及び強度がともに満足できる耐候性鋼及び溶接継ぎ手を提供することを目的とする。 In the Al—Si steel developed by the present applicant, it is necessary to increase the C content in order to suppress softening of the HAZ part. However, when the amount of C increases, the toughness at the bond portion decreases, and a welded joint having good toughness cannot be obtained. Accordingly, an object of the present invention is to provide a weather resistant steel and a welded joint that can satisfy both the toughness and strength of the bond portion.
本発明の耐候性鋼は、Ｆｅ-Ｍｎ-Ｓｉ-Ａｌ系の耐候性鋼であって、質量％で表して、Ａｌを０．１−３．５、Ｓｉを０．５７−０．６０、Ｍｎを０．４−２．５、Ｃを０．１１−０．２１、Ｂを０．０００４−０．００３５、含有し、残部がＦｅ及び不可避成分からなることを特徴とする。
本発明の耐候性鋼において、好ましくは、Ａｌを０．７−１．２、含有するとよい。耐候性鋼を製造する場合に、Ａｌを０．９５質量％を中心に、±０．２５質量％の許容範囲を設けて、製造歩留まりを高めるものである。本発明の耐候性鋼において、好ましくは、Ａｌを０．６０−０．６３、含有するとよい。
本発明の耐候性鋼において、好ましくは、Ｍｎを１．３５−１．６５、含有するとよい。耐候性鋼を製造する場合に、Ｍｎを１．５０質量％を中心に、±１０％の許容範囲を設けて、製造歩留まりを高めるものである。
本発明の耐候性鋼において、好ましくは、Ｃを０．１２−０．１７、含有するとよい。耐候性鋼を製造する場合に、Ｃを０．１２−０．１７質量％含有すると、ボンド部のシャルピー衝撃値として１００Ｊ以上の靱性値を確保でき、かつボンド部の硬さがヴィッカース硬さ（Ｈｖ）で２９７以上となる。
本発明の耐候性鋼において、好ましくは、Ｂを０．０００７−０．００２９、含有するとよい。耐候性鋼を製造する場合に、Ｂを０．０００７−０．００２９質量％含有すると、ボンド部のシャルピー衝撃値として１００Ｊ以上の靱性値を確保でき、かつボンド部の硬さがヴィッカース硬さ（Ｈｖ）で２９７以上となる。
The weather-resistant steel of the present invention is a Fe-Mn-Si-Al-based weather-resistant steel, expressed in terms of mass%, with Al 0.1-3.5, Si 0.57-0.60 , the Mn 0.4-2.5, 0.11-0.21 and C, B and 0.0004-0.0035, containing, the balance being Fe and inevitable components.
In the weather resistant steel of the present invention, it is preferable to contain 0.7 to 1.2 Al. When producing weathering steel, an allowable range of ± 0.25% by mass is provided centering on 0.95% by mass of Al, thereby increasing the production yield. In the weather resistant steel of the present invention, preferably, Al is contained in an amount of 0.60-0.63.
The weather resistant steel of the present invention preferably contains 1.35 to 1.65 Mn. When manufacturing weathering steel, an allowable range of ± 10% is provided with Mn at the center of 1.50% by mass to increase the manufacturing yield.
In the weather resistant steel of the present invention, it is preferable to contain 0.12-0.17 of C. When producing weather resistant steel, if 0.12 to 0.17% by mass of C is contained, a toughness value of 100 J or more can be secured as the Charpy impact value of the bond part, and the hardness of the bond part is Vickers hardness ( Hv) is 297 or more.
In the weather resistant steel of the present invention, 0.0007-0.0029 B is preferably contained. When producing weather-resistant steel, if B is contained in an amount of 0.0007-0.0029 mass%, a toughness value of 100 J or more can be secured as the Charpy impact value of the bond portion, and the hardness of the bond portion is Vickers hardness ( Hv) is 297 or more.
本発明の溶接継手は、上記の耐侯性鋼を使用した溶接継手であって、ボンド部の金属組織の主相が、ベイナイト相であり、フェライト相が０．１％以下の体積分率であることを特徴とする。
本発明の溶接継手において、好ましくは、ボンド部の硬さがヴィッカース硬さ（Ｈｖ）で２３７以上、かつ、室温（２０℃）でのシャルピー吸収エネルギーが６０Ｊ以上であるとよい。
本発明の溶接継手において、好ましくは、ボンド部の硬さがヴィッカース硬さ（Ｈｖ）で２９７以上、かつ、室温（２０℃）でのシャルピー吸収エネルギーが１００Ｊ以上であるとよい。
The welded joint of the present invention is a welded joint using the above weather-resistant steel, wherein the main phase of the metal structure of the bond portion is a bainite phase and the ferrite phase has a volume fraction of 0.1% or less. It is characterized by that.
In the welded joint of the present invention, preferably, the hardness of the bond portion is 237 or more in terms of Vickers hardness (Hv), and the Charpy absorbed energy at room temperature (20 ° C.) is 60 J or more.
In the welded joint of the present invention, preferably, the bond portion has a Vickers hardness (Hv) of 297 or more and a Charpy absorbed energy at room temperature (20 ° C.) of 100 J or more.
Ａｌは耐食性を向上させる元素であるが、靱性と溶接性を劣化させる元素であり、３．５％を超えて添加できない。したがって、Ａｌの組成は０．１から３．５質量％が望ましく、特に好ましくは０．７−１．２質量％がよい。 Al is an element that improves corrosion resistance, but is an element that deteriorates toughness and weldability and cannot be added in excess of 3.5%. Therefore, the Al composition is desirably 0.1 to 3.5% by mass, particularly preferably 0.7 to 1.2% by mass.
Ｓｉは耐食性を向上させる元素であるが、靱性と溶接性を劣化させる元素であり、３．５％を超えて添加できない。したがって、Ｓｉの組成は０．３から３．５質量％が望ましく、特に好ましくは０．１５−０．６５質量％がよい。 Si is an element that improves corrosion resistance, but is an element that deteriorates toughness and weldability and cannot be added in excess of 3.5%. Therefore, the composition of Si is desirably 0.3 to 3.5% by mass, and particularly preferably 0.15-0.65% by mass.
Ｍｎは強度を向上させる元素であるが、２．５％を超えると延性と溶接性を劣化させる。したがって、Ｍｎの組成は０．４から２．５質量％が望ましく、特に好ましくは１．３５−１．６５質量％がよい。 Mn is an element that improves the strength, but if it exceeds 2.5%, ductility and weldability deteriorate. Therefore, the composition of Mn is desirably 0.4 to 2.5% by mass, particularly preferably 1.35 to 1.65% by mass.
Ｃは引張強度を高める元素であり、０．１１質量％以上であれば、Ｓｉ−Ｍｎ系の鉄鋼材料では、５９０ＭＰａ以上の溶接継ぎ手の引張強度を得ることができる。しかし、Ｃ量が高くなるとボンド部の靱性が低下する。５９０ＭＰａ級鋼のボンド部のシャルピー衝撃値である６０Ｊ以上の靱性値を確保するためには０．２１質量％以下のＣ量とする。更に、炭素鋼で５９０ＭＰａ以上の引張強度となるのはＨｖが２００以上であるので、Ｈｖが２３７以上であれば５９０ＭＰａ以上の引張強度を確保できる。特に好ましくは、Ｃを０．１２−０．１７質量％、含有すると、ボンド部のシャルピー衝撃値として１００Ｊ以上の靱性値を確保でき、かつボンド部の硬さがヴィッカース硬さ（Ｈｖ）で２９７以上となる。 C is an element that enhances the tensile strength. When the content is 0.11% by mass or more, the tensile strength of a welded joint of 590 MPa or more can be obtained in a Si—Mn steel material. However, when the amount of C increases, the toughness of the bond portion decreases. In order to secure a toughness value of 60 J or more which is the Charpy impact value of the bond portion of 590 MPa class steel, the C amount is 0.21 mass% or less. Further, the carbon steel has a tensile strength of 590 MPa or more because Hv is 200 or more. Therefore, if Hv is 237 or more, a tensile strength of 590 MPa or more can be secured. Particularly preferably, when 0.12 to 0.17% by mass of C is contained, a toughness value of 100 J or more can be secured as the Charpy impact value of the bond portion, and the bond portion has a Vickers hardness (Hv) of 297. That's it.
ボンド部のシャルピー吸収エネルギーは溶接部のＢ量によって変化する。Ｃ量が０．１６質量％でＢが０．００４質量％以下の溶接継ぎ手では、５９０ＭＰａ級の鉄鋼材料のボンド部よりも低いシャルピー吸収エネルギーとなる。また、Ｃ量が０．１６質量％でＢが０．００３５質量％以上の継ぎ手は５９０ＭＰａ級の鉄鋼材料のボンド部よりも低いシャルピー吸収エネルギーとなる。このため、Ｂの範囲は０．０００４質量％以上、０．００３５質量％以下であることが望ましい。
特に好ましくは、Ｂを０．０００７−０．００２９質量％、含有するとボンド部のシャルピー衝撃値として１００Ｊ以上の靱性値を確保でき、かつボンド部の硬さがヴィッカース硬さ（Ｈｖ）で２９７以上となる。
The Charpy absorbed energy of the bond part varies depending on the B amount of the weld part. In a welded joint having a C content of 0.16% by mass and B of 0.004% by mass or less, Charpy absorbed energy is lower than that of a bond part of a 590 MPa class steel material. Further, a joint having a C content of 0.16% by mass and B of 0.0035% by mass or more has lower Charpy absorbed energy than a bond part of a 590 MPa class steel material. For this reason, the range of B is desirably 0.0004 mass% or more and 0.0035 mass% or less.
Particularly preferably, when B is contained in an amount of 0.0007 to 0.0029% by mass, a toughness value of 100 J or more can be secured as the Charpy impact value of the bond portion, and the hardness of the bond portion is 297 or more in terms of Vickers hardness (Hv). It becomes.
Ａｌ-Ｓｉ鋼では、フェライトフォーマーであるＡｌやＳｉ多量に含むため、ボンド部の靭性を低下するフェライト相の生成は避けられないが、上述のようにＢを添加することによりボンド部のフェライト相の生成を抑制することが可能であり、ボンド部の靭性を改善することが可能となる。Ｂの範囲を０．０００４質量％以上、０．００３５質量％以下にした発明鋼を使用した溶接継ぎ手では、ボンド部の金属組織の主相がベイナイト相であり、フェライト相が０．１％以下の金属組織を有するので、溶接継ぎ手に必要とされる靭性が確保できる。 Since Al-Si steel contains a large amount of Al and Si, which are ferrite formers, it is inevitable to produce a ferrite phase that lowers the toughness of the bond part. However, by adding B as described above, ferrite in the bond part is produced. The generation of the phase can be suppressed, and the toughness of the bond portion can be improved. In the welded joint using the invention steel in which the range of B is 0.0004 mass% or more and 0.0035 mass% or less, the main phase of the metal structure of the bond portion is a bainite phase and the ferrite phase is 0.1% or less. Therefore, the toughness required for the welded joint can be ensured.
本発明に拠るＡｌ-Ｓｉ鋼のボンド部の組織は従来の耐候性鋼に比較し、図３に示すようにフェライトが少ない組織が得られた。図２に示す従来の耐候性鋼では白く見える粒界フェライトの割合が４７％と多い。これに対し本発明に拠るＡｌ-Ｓｉ鋼のボンド部の粒界フェライトの割合は０．１％以下と少なくなり優れたボンド靱性を有す。更に、ＨＡＺ軟化を防ぐためにＣ量を０．１１質量％から０．２１質量％まで高めた本発明によるＡｌ-Ｓｉ鋼のボンド靱性は、従来の耐候性鋼のボンド靱性よりも改善され（図４）、この特性を利用することにより良好な溶接継ぎ手を提供できる。 The structure of the bond part of the Al—Si steel according to the present invention was a structure with less ferrite as shown in FIG. 3 as compared with the conventional weathering steel. In the conventional weathering steel shown in FIG. 2, the ratio of grain boundary ferrite that appears white is as high as 47%. On the other hand, the proportion of intergranular ferrite in the bond part of the Al—Si steel according to the present invention is as low as 0.1% or less and has excellent bond toughness. Furthermore, the bond toughness of the Al—Si steel according to the present invention, in which the C content is increased from 0.11% by mass to 0.21% by mass in order to prevent HAZ softening, is improved over the bond toughness of the conventional weathering steel (see FIG. 4) By utilizing this characteristic, a good weld joint can be provided.
本発明の耐候性鋼によれば、鉄鋼材料のリサイクル使用の際に分離困難な不純物成分となるトランプエレメントを含まないため、鉄鋼材料のリサイクル使用が容易にできる。また、本発明の耐候性鋼によれば、溶接を行っても熱影響部で軟化が生じにくいと共に、靱性（シャルピー吸収エネルギー）を良好に保持できる。そこで、本発明の耐候性鋼によれば、ボンド部の靱性を高く維持して、良好な溶接継ぎ手となるため、橋梁のような鋼構造物の防錆防食用として最適である。 According to the weather-resistant steel of the present invention, since the trump element that is an impurity component that is difficult to separate when the steel material is recycled is not included, the steel material can be easily recycled. Moreover, according to the weather-resistant steel of the present invention, softening hardly occurs in the heat-affected zone even when welding is performed, and toughness (Charpy absorbed energy) can be favorably maintained. Therefore, according to the weather resistant steel of the present invention, since the toughness of the bond portion is maintained high and a good welded joint is obtained, it is optimal for rust and corrosion prevention of steel structures such as bridges.
[実施例１]
表１は目標組成をＡｌは０．６質量％、Ｓｉを０．６質量％、Ｍｎを１．５０質量％とし、Ｃ量は０．１０質量％から０．２０質量％まで０．０２質量％ずつ増加させ、Ｂを添加しない比較鋼と、同じ目標組成でＢ添加した開発鋼の成分の分析値とシャルピー吸収エネルギーを示したものである。比較鋼ではＣ量が０．１０質量％（分析値：０．１１質量％）から０．２０質量％の範囲では、シャルピー吸収エネルギーの値は最大９９．２Ｊ、最小２１．５Ｊであり、Ｃ量を変えても１００Ｊ以下のシャルピー吸収エネルギーしか得られない。開発鋼では、Ｃ量を０．１０（分析値：０．１１質量％）から０．２０質量％（分析値：０．２１質量％）の範囲では、シャルピー吸収エネルギーの値は最大１９９．７Ｊ、最小８１．２Ｊであった。Ｂを添加した開発鋼のシャルピー吸収エネルギーとＢを添加しない比較鋼のそれとを同じＣ量で比較した結果を図４に示す。０．１０質量％Ｃの時には開発鋼のシャルピー吸収エネルギーは比較鋼の２．０倍、０．１２質量％Ｃの時には２．４倍、０．１４質量％Ｃの時には４．３倍、０．１６質量％Ｃの時には４．７倍、０．１８質量％Ｃの時には４．６倍、０．２０質量％Ｃの時には３．８倍となり、開発鋼では比較鋼に対しシャルピー吸収エネルギーが大きく改善されている。
[Example 1]
Table 1 shows that the target composition is 0.6 mass% for Al, 0.6 mass% for Si, 1.50 mass% for Mn, and 0.02 mass for C content from 0.10 mass% to 0.20 mass%. It shows the analytical values and Charpy absorbed energy of the comparative steel without B added and the developed steel added with B with the same target composition. In the comparative steel, when the C content is in the range of 0.10% by mass (analytical value: 0.11% by mass) to 0.20% by mass, the Charpy absorbed energy value is 99.2 J at the maximum and 21.5 J at the minimum. Even if the amount is changed, only Charpy absorbed energy of 100 J or less can be obtained. In the developed steel, when the C content is in the range of 0.10 (analytical value: 0.11 mass%) to 0.20 mass% (analytical value: 0.21 mass%), the Charpy absorbed energy value is a maximum of 199.7 J The minimum was 81.2 J. FIG. 4 shows the result of comparing the Charpy absorbed energy of the developed steel to which B is added with that of the comparative steel to which B is not added with the same C amount. The Charpy absorbed energy of the developed steel is 2.0 times that of the comparative steel at 0.10% by mass C, 2.4 times at 0.12% by mass C, 4.3 times at 0.14% by mass C, 0 When it is .16 mass% C, it is 4.7 times, when it is 0.18 mass% C, it is 4.6 times, and when it is 0.20 mass% C, it is 3.8 times. Greatly improved.
[実施例２]
Ｓｉ−Ｍｎ系の微細粒鋼では溶接部の軟化防止のためには０．１６質量％以上のＣが必要である(非特許文献１)。そこで溶接部の軟化を防止するために、目標組成をＣは０.１６質量％、Ａｌは０．６質量％、Ｓｉは０．６質量％、Ｍｎは１．５０質量％とし、Ｂを０．０００６質量％、０．０００８質量％、０．００１０質量％、０．００１６質量％、０．００３０質量％、０．００５０質量％とした開発鋼を試作し、シャルピー吸収エネルギーを調べた。表２は開発鋼の成分の分析値とシャルピー吸収エネルギーを示したものである。Ｂを添加しないものは表1の比較鋼６に相当している。Ｂ添加量に対するシャルピー吸収エネルギーの変化を図５に示す。Ｂが０．００１２質量％から０．００１６質量％付近でシャルピー吸収エネルギーは最大値（１４２．２Ｊ）を示す。この範囲よりＢが少なくなると吸収エネルギーは低下する。またこの範囲よりＢが多くなってもシャルピー吸収エネルギーは低下している。
[Example 2]
In the Si-Mn based fine-grained steel, 0.16% by mass or more of C is necessary to prevent softening of the welded portion (Non-patent Document 1). Therefore, in order to prevent softening of the weld zone, the target composition is 0.16 mass% for C, 0.6 mass% for Al, 0.6 mass% for Si, 1.50 mass% for Mn, and B is 0 mass%. Developed steels with .0006 mass%, 0.0008 mass%, 0.0010 mass%, 0.0016 mass%, 0.0030 mass%, and 0.0050 mass% were made as prototypes, and Charpy absorbed energy was examined. Table 2 shows the analytical values and Charpy absorbed energy of the components of the developed steel. The steel to which B is not added corresponds to the comparative steel 6 in Table 1. The change in Charpy absorbed energy with respect to the amount of B added is shown in FIG. When B is 0.0012% by mass to 0.0016% by mass, the Charpy absorbed energy shows a maximum value (142.2J). When B is less than this range, the absorbed energy decreases. Further, even if B is larger than this range, the Charpy absorbed energy is lowered.
[実施例３]
市販の５９０ＭＰａ級鋼と同等以上の強度を持つためにはＣ量は０．１０質量％以上が必要である。そこで、目標組成をＣは０.１０質量％、Ａｌは０．６質量％、Ｓｉは０．６質量％、Ｍｎは１．５０質量％とし、Ｂを０．０００６質量％、０．００１２質量％、０．００３０質量％、０．００６０質量％とした開発鋼を試作し、シャルピー吸収エネルギーを調べた。開発鋼の成分とシャルピー吸収エネルギーを表３に示す。Ｂを添加しないものは表１の比較鋼３に相当している。シャルピー吸収エネルギーの結果を図６に示す。Ｂが０．０００７質量％から０．００１３質量％付近でシャルピー吸収エネルギーは最大値（１９２．７Ｊ）を示す。この値よりＢが少なくなるとシャルピー吸収エネルギーは低下し、この値よりＢが多くなるとシャルピー吸収エネルギーは低下している。
[Example 3]
In order to have a strength equal to or higher than that of commercially available 590 MPa class steel, the amount of C needs to be 0.10% by mass or more. Therefore, the target composition is 0.10 mass% for C, 0.6 mass% for Al, 0.6 mass% for Si, 1.50 mass% for Mn, and 0.0006 mass%, 0.0012 mass for B. %, 0.0030 mass%, and 0.0060 mass% of the developed steel were made on a trial basis and the Charpy absorbed energy was examined. Table 3 shows the composition and Charpy absorbed energy of the developed steel. The material to which B is not added corresponds to the comparative steel 3 in Table 1. The result of Charpy absorbed energy is shown in FIG. When B is in the vicinity of 0.0007% by mass to 0.0013% by mass, the Charpy absorbed energy shows the maximum value (192.7J). When B is less than this value, Charpy absorbed energy is reduced, and when B is more than this value, Charpy absorbed energy is reduced.
[実施例４]
比較鋼のボンド部の組織の一例として比較鋼６の組織を図２に示す。白く見える粗大な粒界フェライトが見られる。この粗大な粒界フェライトの体積分率は４７％であった。これに対し、開発鋼のボンド部の組織の一例として開発鋼６の組織を図３に示す。開発鋼では粗大な粒界フェライト組織は認められず微細組織が認められた。比較鋼のように白く見える粒界フェライトの体積分率は０．１％と少なくなっている。比較鋼のボンド部では粗大な粒界フェライトが多く存在する部分から破壊が生じるのでシャルピー吸収エネルギーは低くなる。これに対し、開発鋼のボンド部では粒界フェライトが微細で、かつ、量が少ないので破壊の基点になることはなく、シャルピー吸収エネルギーは高くなる。
[Example 4]
As an example of the structure of the bond portion of the comparative steel, the structure of the comparative steel 6 is shown in FIG. Coarse grain boundary ferrite appears white. The volume fraction of the coarse grain boundary ferrite was 47%. On the other hand, the structure of the developed steel 6 is shown in FIG. 3 as an example of the structure of the bond portion of the developed steel. In the developed steel, no coarse grain boundary ferrite structure was observed, and a fine structure was observed. The volume fraction of grain boundary ferrite that appears white like the comparative steel is as low as 0.1%. In the bond portion of the comparative steel, the Charpy absorbed energy is low because the fracture occurs from the portion where there are many coarse grain boundary ferrites. On the other hand, since the grain boundary ferrite is fine and small in the bond portion of the developed steel, it does not become the starting point of fracture, and the Charpy absorbed energy increases.
[比較例１]
比較鋼１から９は、目標組成をＡｌは０．６質量％、Ｓｉを０．６質量％、Ｍｎを１．５０質量％とし、Ｂを添加せずに、Ｃ量を０．０６質量％から０．２４質量％まで０．０２質量％ずつ増加させたものである。比較鋼の成分と硬さ及びシャルピー吸収エネルギーを表４に示す。Ｃの増加に伴い、シャルピー吸収エネルギーが減少し０．１５質量％Ｃ（分析値）以上では４０Ｊ以下となっている。Ｃ量が少なくなると硬さが増えるが、逆に、シャルピー吸収エネルギーは低下している。０．１質量％Ｃ量のボンド部のＨｖは２１６．９となり、５９０ＭＰａ級鋼と同等である。より高強度とするにはＣ量をこの値より高くする必要があるが、０．１２質量％を超える範囲ではＨｖは２６１．０以上となるものの、シャルピー吸収エネルギーが７９．９Ｊ以下の値となる。したがって、比較鋼では、強度と靭性の両方（Ｈｖが２３７以上、かつ、室温（２０℃）で６０Ｊ以上のボンド靱性）を満足する溶接継手を作ることはできない。
[Comparative Example 1]
Comparative steels 1 to 9 have a target composition of 0.6 mass% for Al, 0.6 mass% for Si, 1.50 mass% for Mn, and 0.06 mass% for C without adding B. It is increased by 0.02% by mass from 0.24% by mass to 0.24% by mass. Table 4 shows the components, hardness, and Charpy absorbed energy of the comparative steel. As C increases, Charpy absorbed energy decreases, and it is 40 J or less at 0.15 mass% C (analytical value) or more. Hardness increases as the amount of C decreases, but conversely, Charpy absorbed energy decreases. The Hv of the 0.1 mass% C bond portion is 216.9, which is equivalent to 590 MPa grade steel. In order to obtain higher strength, the C amount needs to be higher than this value. However, in the range exceeding 0.12% by mass, Hv is 261.0 or more, but Charpy absorbed energy is 79.9 J or less. Become. Therefore, the comparative steel cannot make a welded joint that satisfies both strength and toughness (Hv is 237 or more and bond toughness of 60 J or more at room temperature (20 ° C.)).
開発鋼について、硬さとシャルピー吸収エネルギーの関係を求めた結果を表５に示す。開発鋼では、引張強度が５９０ＭＰａ級鋼以上を満足するための硬さＨｖが２３７以上となり、かつ、室温（２０℃）で６０Ｊ以上のボンド部靱性を持つ溶接継手を作ることができた。 Table 5 shows the results of determining the relationship between hardness and Charpy absorbed energy for the developed steel. In the developed steel, a weld joint having a hardness Hv of 237 or more for satisfying a tensile strength of 590 MPa class steel or more and having a bond part toughness of 60 J or more at room temperature (20 ° C.) was able to be produced.
本発明のＡｌ-Ｓｉ鋼を使用すれば、溶接で生じるＨＡＺ軟化とボンド靱性低下の両方を同時に抑えた溶接継ぎ手の作製が可能となり、優れた耐候性を持った各種の鋼構造物を製作することができる。また、従来、塗装や表面処理が不可欠であった溶接用鋼材による鋼構造物を本発明鋼に置き換えることにより、メンテナンスフリーの鋼構造物となり、建設費及び維持管理費コストの低減化が図られる。
By using the Al-Si steel of the present invention, it becomes possible to produce a welded joint that simultaneously suppresses both HAZ softening and bond toughness degradation caused by welding, and produces various steel structures having excellent weather resistance. be able to. In addition, by replacing steel structures made of welding steel, which conventionally required painting and surface treatment, with steels of the present invention, they become maintenance-free steel structures, and construction costs and maintenance costs can be reduced. .
Claims (9)
Ａｌを０．１−３．５、
Ｓｉを０．５７−０．６０、
Ｍｎを０．４−２．５、
Ｃを０．１１−０．２１、
Ｂを０．０００４−０．００３５、
含有し、残部がＦｅ及び不可避成分からなることを特徴とする耐侯性鋼。 Fe-Mn-Si-Al-based weathering steel, expressed in mass%,
Al 0.1-3.5,
0.57-0.60 Si,
Mn 0.4-2.5,
C is 0.11-0.21 ,
B is 0.0004-0.0035,
Containing weather resistant steel, wherein the balance consists of Fe and inevitable components.
The weld joint according to claim 7, wherein the bond portion has a Vickers hardness (Hv) of 297 or more, and a Charpy absorbed energy at room temperature (20 ° C) of 100 J or more. Welded joints.
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