JP6638741B2 - Steel sheet with excellent delayed fracture resistance - Google Patents
Steel sheet with excellent delayed fracture resistance Download PDFInfo
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- JP6638741B2 JP6638741B2 JP2018001576A JP2018001576A JP6638741B2 JP 6638741 B2 JP6638741 B2 JP 6638741B2 JP 2018001576 A JP2018001576 A JP 2018001576A JP 2018001576 A JP2018001576 A JP 2018001576A JP 6638741 B2 JP6638741 B2 JP 6638741B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 76
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- 239000011575 calcium Substances 0.000 claims description 14
- 229910052790 beryllium Inorganic materials 0.000 claims description 6
- 229910052791 calcium Inorganic materials 0.000 claims description 5
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 4
- RFVVBBUVWAIIBT-UHFFFAOYSA-N beryllium nitrate Chemical compound [Be+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O RFVVBBUVWAIIBT-UHFFFAOYSA-N 0.000 claims description 4
- KQHXBDOEECKORE-UHFFFAOYSA-L beryllium sulfate Chemical compound [Be+2].[O-]S([O-])(=O)=O KQHXBDOEECKORE-UHFFFAOYSA-L 0.000 claims description 4
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Chemical compound [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 claims description 4
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 claims description 4
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 claims description 2
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- ABLZXFCXXLZCGV-UHFFFAOYSA-N Phosphorous acid Chemical compound OP(O)=O ABLZXFCXXLZCGV-UHFFFAOYSA-N 0.000 claims description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 2
- PBKYCFJFZMEFRS-UHFFFAOYSA-L beryllium bromide Chemical compound [Be+2].[Br-].[Br-] PBKYCFJFZMEFRS-UHFFFAOYSA-L 0.000 claims description 2
- 229910001621 beryllium bromide Inorganic materials 0.000 claims description 2
- YUOUKRIPFJKDJY-UHFFFAOYSA-L beryllium;diacetate Chemical compound [Be+2].CC([O-])=O.CC([O-])=O YUOUKRIPFJKDJY-UHFFFAOYSA-L 0.000 claims description 2
- VSGNNIFQASZAOI-UHFFFAOYSA-L calcium acetate Chemical compound [Ca+2].CC([O-])=O.CC([O-])=O VSGNNIFQASZAOI-UHFFFAOYSA-L 0.000 claims description 2
- 239000001639 calcium acetate Substances 0.000 claims description 2
- 229960005147 calcium acetate Drugs 0.000 claims description 2
- 235000011092 calcium acetate Nutrition 0.000 claims description 2
- YALMXYPQBUJUME-UHFFFAOYSA-L calcium chlorate Chemical compound [Ca+2].[O-]Cl(=O)=O.[O-]Cl(=O)=O YALMXYPQBUJUME-UHFFFAOYSA-L 0.000 claims description 2
- 239000001110 calcium chloride Substances 0.000 claims description 2
- 229910001628 calcium chloride Inorganic materials 0.000 claims description 2
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 2
- 239000000920 calcium hydroxide Substances 0.000 claims description 2
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims description 2
- 229940046413 calcium iodide Drugs 0.000 claims description 2
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- 239000001506 calcium phosphate Substances 0.000 claims description 2
- 229910000389 calcium phosphate Inorganic materials 0.000 claims description 2
- 235000011010 calcium phosphates Nutrition 0.000 claims description 2
- XPPKVPWEQAFLFU-UHFFFAOYSA-N diphosphoric acid Chemical compound OP(O)(=O)OP(O)(O)=O XPPKVPWEQAFLFU-UHFFFAOYSA-N 0.000 claims description 2
- ACVYVLVWPXVTIT-UHFFFAOYSA-N phosphinic acid Chemical compound O[PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-N 0.000 claims description 2
- 229940005657 pyrophosphoric acid Drugs 0.000 claims description 2
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 claims description 2
- 230000008021 deposition Effects 0.000 claims 2
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium atom Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 claims 1
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- 239000010960 cold rolled steel Substances 0.000 description 19
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 18
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Description
本発明は、耐遅れ破壊特性に優れた鋼板に関するものであり、詳細には、主として自動車、建材用の強度部材に好適な鋼板であって、耐遅れ破壊特性が要求される、引張り強度１１８０ＭＰａ（約１２０ｋｇｆ／ｍｍ２）以上を有する高張力鋼板に関するものである。 TECHNICAL FIELD The present invention relates to a steel sheet having excellent delayed fracture resistance, and more particularly, to a steel sheet suitable mainly for a strength member for automobiles and building materials, which is required to have delayed fracture resistance and has a tensile strength of 1180 MPa ( The present invention relates to a high-strength steel sheet having about 120 kgf / mm 2 or more.
従来、自動車用鋼板としては、その板厚の精度や平担度に関する要求から冷延鋼板が用いられているが、近年、自動車のＣＯ２排出量の低減及び安全性確保の観点から、自動車用鋼板の高強度化が図られている。
しかしながら、鋼材の強度を高めていくと、遅れ破壊という現象が生じやすくなることが知られており、この現象は強度の増大とともに激しくなり、特に引張り強さ１１８０ＭＰａ以上の高強度鋼で顕著となる。なお、遅れ破壊とは、高強度鋼材が静的な負荷応力（引張り強さ以下の負荷応力）を受けた状態で、ある時間が経過したとき、外見上はほとんど塑性変形を伴うことなく、突然脆性的な破壊が生じる現象である。
Conventionally, as automotive steel sheets, but the plate cold-rolled steel sheet from requests for accuracy and flat担度thickness is used, in recent years, in view of the reduction and safety CO 2 emissions of the automobile, automotive Higher strength of steel sheets has been achieved.
However, it is known that when the strength of a steel material is increased, a phenomenon called delayed fracture is likely to occur. This phenomenon becomes more severe as the strength increases, and is particularly remarkable in a high-strength steel having a tensile strength of 1180 MPa or more. . Delayed fracture is a condition in which a high-strength steel material is subjected to a static load stress (a load stress equal to or less than the tensile strength). This is a phenomenon in which brittle fracture occurs.
この遅れ破壊は、鋼板の場合、プレス加工により所定の形状に成形したときの残留応力と、このような応力集中部における鋼の水素脆性により生じるものであることが知られている。この水素脆性の起因となる水素は、ほとんどの場合、外部環境から鋼中に侵入し、それが拡散するものと考えられており、代表的には、鋼材の腐食に伴い侵入する水素が挙げられる。 In the case of a steel sheet, it is known that this delayed fracture is caused by residual stress when the steel sheet is formed into a predetermined shape by press working and by hydrogen embrittlement of steel in such a stress concentrated portion. In most cases, hydrogen that causes hydrogen embrittlement penetrates into steel from the external environment and is considered to diffuse, and typically, hydrogen that enters due to corrosion of steel is cited. .
高強度鋼板におけるこのような遅れ破壊を防止するために、例えば特許文献１に記載のように、鋼板の組織や成分を調整することにより、遅れ破壊感受性を弱める検討がなされている。しかしながら、このような手法を用いた場合には、外部環境から鋼板内部に侵入する水素量には変化がなく、遅れ破壊発生を遅らせることは可能であるとしても、遅れ破壊自体を抑制することはできない。すなわち、遅れ破壊を本質的に改善するためには、鋼板内部への水素侵入量自体を制御することが必要である。このような観点から、特許文献２には、冷延鋼板にＮｉ又はＮｉ基合金メッキを施すことにより、鋼板内部への水素侵入量を抑制することで遅れ破壊を抑制する技術が開示されている。また、特許文献３には、鋼板表面にＴｉなどの水素吸蔵性粒子を分散させた皮膜（めっき皮膜、化成処理皮膜など）を形成することで鋼板内部への水素の侵入を抑えることにより、遅れ破壊を抑制する技術が開示されている。
In order to prevent such delayed fracture in a high-strength steel sheet, for example, as described in
しかしながら、特許文献２に記載のようにＮｉ又はＮｉ基合金を電気メッキした場合、メッキ時に発生する水素が鋼板内に残存することで、遅れ破壊を引き起こすことが考えられる。さらに、鋼板表面にメッキしたままで、プレス加工に供した場合、メッキ層と鋼板との密着性が弱く、加工時にメッキ層が損傷し、目的とする効果が得られない可能性も高い。また、特許文献３に記載のように鋼板表面の皮膜で水素をトラップする手法では、腐食初期においては水素の侵入を抑制できるが、侵入する水素量が吸蔵能力を超えた場合に遅れ破壊を引き起こすことが考えられる。
また、自動車用鋼板として使用するためには、耐遅れ破壊特性だけでなく、優れた一次防錆性が必要とされる。
However, when Ni or a Ni-based alloy is electroplated as described in
In addition, for use as a steel sheet for automobiles, not only delayed fracture resistance, but also excellent primary rust resistance is required.
したがって本発明の目的は、以上のような従来技術の課題を解決し、主として自動車、建材用の強度部材に好適な引張り強度１１８０ＭＰａ以上を有する鋼板であって、耐遅れ破壊特性に優れ、さらに一次防錆性にも優れた鋼板を提供することにある。 Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a steel sheet having a tensile strength of 1180 MPa or more, which is suitable mainly for automobiles and strength members for building materials. An object of the present invention is to provide a steel sheet having excellent rust resistance.
本発明者らは、上記の課題を解決すべく、鋼板内に侵入する水素を抑制することにより遅れ破壊を防止する手段について、鋭意検討および研究を重ねた。その結果、冷延鋼板表面にＣａ塩、Ｂｅ塩の中から選ばれる１種以上の金属塩とＰ化合物を含む皮膜を形成することにより、鋼板への水素侵入量を大幅に抑制し、鋼板の遅れ破壊を効果的に抑制できることを見出した。また、同時に優れた一次防錆性を発揮できることも判った。
本発明は、以上のような知見に基づきなされたものであり、その要旨は以下のとおりである。
Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied and studied a means for preventing delayed fracture by suppressing hydrogen entering into a steel sheet. As a result, by forming a film containing at least one metal salt selected from Ca salts and Be salts and a P compound on the surface of the cold-rolled steel sheet, the amount of hydrogen intrusion into the steel sheet is significantly suppressed, and It has been found that delayed fracture can be effectively suppressed. It was also found that excellent primary rust prevention can be exhibited at the same time.
The present invention has been made based on the above findings, and the gist is as follows.
［1］引張り強度が１１８０ＭＰａ以上の冷延鋼板の表面に、Ｃａ塩、Ｂｅ塩の中から選ばれる１種以上の金属塩とＰ化合物を含有し、前記金属塩の金属（Ｃａ、Ｂｅ）換算での合計付着量が１０〜５００ｍｇ／ｍ２、前記Ｐ化合物のＰ換算での付着量が１０〜１０００ｍｇ／ｍ２である皮膜（Ａ）を有することを特徴とする耐遅れ破壊特性に優れた鋼板。
［2］上記［1］の鋼板において、さらに、皮膜（Ａ）の上層に膜厚が０．３μｍ以上４．０μｍ未満の有機樹脂層（Ｂ）を有することを特徴とする耐遅れ破壊特性に優れた鋼板。
［3］上記［1］又は［2］の鋼板において、皮膜（Ａ）における金属塩の金属（Ｃａ、Ｂｅ）換算での合計付着量が５０〜５００ｍｇ／ｍ２であることを特徴とする耐遅れ破壊特性に優れた鋼板。
[1] The surface of a cold-rolled steel sheet having a tensile strength of 1180 MPa or more contains at least one metal salt selected from Ca salts and Be salts and a P compound, and the metal salt is converted into metal (Ca, Be). Characterized in that it has a coating (A) having a total adhesion amount of 10 to 500 mg / m 2 and a P equivalent of the P compound of 10 to 1000 mg / m 2 , and is excellent in delayed fracture resistance. steel sheet.
[2] The steel sheet of [1], further comprising an organic resin layer (B) having a thickness of 0.3 μm or more and less than 4.0 μm as an upper layer of the film (A). Excellent steel plate.
[3] The steel sheet according to [1] or [2], wherein the total amount of the metal salt in the coating (A) in terms of metal (Ca, Be) in the coating (A) is 50 to 500 mg / m 2. Steel sheet with excellent delayed fracture characteristics.
本発明の鋼板は、遅れ破壊が効果的に抑制される優れた耐遅れ破壊特性を有し、しかも優れた一次防錆性を有している。このため自動車や建材に高強度材を使用することができ、それらの重量削減が可能となる。 The steel sheet of the present invention has excellent delayed fracture resistance, in which delayed fracture is effectively suppressed, and also has excellent primary rust prevention. Therefore, high-strength materials can be used for automobiles and building materials, and their weight can be reduced.
本発明の耐遅れ破壊特性に優れた鋼板において、基質となる鋼板（素材鋼板）は、化学組成、金属組織、圧延方法などについては特に限定されるものではなく、任意のものとすることができるが、そのなかで、自動車分野や建材分野などにおいて用いられ、特に自動車分野などにおいて多く用いられる冷延鋼板が望ましく、なかでも大気腐食環境下で遅れ破壊発生の懸念が生じる引張り強度が１１８０ＭＰａ（約１２０ｋｇｆ／ｍｍ２）以上の高張力冷延鋼板であることが重要である。引張り強度が１１８０ＭＰａ未満の鋼板に対して本発明を適用し、表面に特定の金属塩とＰ化合物を含む皮膜を形成しても、当該鋼板の各種特性には影響はしないが、引張り強度の低い鋼板は本質的に遅れ破壊が生じにくいため、本発明に係る皮膜を形成することでコスト増加につながる。 In the steel sheet having excellent delayed fracture resistance according to the present invention, the steel sheet (base steel sheet) serving as a substrate is not particularly limited with respect to the chemical composition, metal structure, rolling method, and the like, and may be any. However, among them, cold-rolled steel sheets used in the field of automobiles and building materials, and particularly used in the field of automobiles and the like are desirable, and among them, a tensile strength of 1180 MPa (approximately 1180 MPa (approx. It is important that the steel sheet is a high-tensile cold-rolled steel sheet of 120 kgf / mm 2 ) or more. Applying the present invention to a steel sheet having a tensile strength of less than 1180 MPa and forming a film containing a specific metal salt and a P compound on the surface does not affect various properties of the steel sheet, but has a low tensile strength. Since a steel sheet is essentially resistant to delayed fracture, forming a film according to the present invention leads to an increase in cost.
なお、高強度冷延鋼板では、機械特性などの諸特性を向上させるために、例えば、Ｃ、Ｎなどの侵入型固溶元素やＳｉ、Ｍｎ、Ｐ、Ｃｒなどの置換型固溶元素の添加による固溶体強化、Ｔｉ、Ｎｂ、Ｖなどの炭・窒化物による析出強化、その他、Ｗ、Ｚｒ、Ｈｆ、Ｃｏ、Ｂ、希土類元素などの強化元素の添加といった化学組成的改質、再結晶の起こらない温度で回復焼きなましすることによる強化あるいは完全に再結晶させずに未再結晶領域を残す部分再結晶強化、ベイナイトやマルテンサイト単相化あるいはフェライトとこれら変態組織の複合組織化といった変態組織による強化、フェライト粒径をｄとしたときのHall-Petchの式：σ＝σ０+ｋｄ-1/2（式中σ：応力、σ０，ｋ：材料定数）で表される細粒化強化、圧延などによる加工強化といった組織的ないし構造的改質が、単独ないし複数組み合わせて行われているが、上述したように本発明において用いられる鋼板の化学組成および金属組織は特に限定されるものではなく、所定の引張り強度を有するものであれば、いかなる化学組成、金属組織を有するものでもよい。 In the case of high-strength cold-rolled steel sheets, for example, in order to improve various properties such as mechanical properties, for example, addition of interstitial solid solution elements such as C and N and substitution type solid solution elements such as Si, Mn, P and Cr are added. Solid solution strengthening, precipitation strengthening by carbon / nitride such as Ti, Nb, V, etc., chemical compositional reforming such as addition of strengthening elements such as W, Zr, Hf, Co, B, rare earth elements, recrystallization occurs Strengthening by recovery annealing at no temperature or partial recrystallization strengthening that leaves unrecrystallized region without complete recrystallization, single phase bainite or martensite, or composite structure of ferrite and these transformation structures And Hall-Petch equation when the ferrite grain size is d: σ = σ 0 + kd −1/2 (where σ: stress, σ 0 , k: material constant) Processing enhancement by rolling etc. However, as described above, the chemical composition and the metal structure of the steel sheet used in the present invention are not particularly limited, and a predetermined tensile strength can be obtained. As long as it has strength, it may have any chemical composition and metal structure.
このような高強度冷延鋼板の組成としては、例えば、Ｃ：０．１〜０．４mass％、Ｓｉ:０〜２．５mass％、Ｍｎ：１〜３mass％、Ｐ：０〜０．０５mass％、Ｓ：０〜０．００５mass％、残部がＦｅおよび不可避的不純物であるもの、これにＣｕ、Ｔｉ、Ｖ、Ａｌ、Ｃｒなどの１種又は２種以上を添加したもの、などを例示できるが、勿論これらに限定されるものではない。 As a composition of such a high-strength cold-rolled steel sheet, for example, C: 0.1 to 0.4 mass%, Si: 0 to 2.5 mass%, Mn: 1 to 3 mass%, P: 0 to 0.05 mass% , S: 0 to 0.005 mass%, the balance being Fe and unavoidable impurities, and the addition of one or more of Cu, Ti, V, Al, Cr, and the like thereto. Of course, it is not limited to these.
また、高強度冷延鋼板として商業的に入手可能なものとしては、例えば、ＪＦＥ−ＣＡ１１８０、ＪＦＥ−ＣＡ１３７０、ＪＦＥ−ＣＡ１４７０、ＪＦＥ−ＣＡ１１８０ＳＦ、ＪＦＥ−ＣＡ１１８０Ｙ１、ＪＦＥ−ＣＡ１１８０Ｙ２(以上、ＪＦＥスチール（株）製）、ＳＡＦＣ１１８０Ｄ（新日鐵住金（株）製）などが非限定的に例示できる。
また、基質となる冷延鋼板の板厚も特に限定されないが、例えば、０．８〜２．５ｍｍ程度、より好ましくは１．２〜２．０ｍｍ程度のものが適当である。
Examples of commercially available high-strength cold-rolled steel sheets include, for example, JFE-CA1180, JFE-CA1370, JFE-CA1470, JFE-CA1180SF, JFE-CA1180Y1, JFE-CA1180Y2 (JFE-CA1180Y2). )) And SAFC1180D (manufactured by Nippon Steel & Sumitomo Metal Corporation).
The thickness of the cold-rolled steel sheet serving as a substrate is not particularly limited, but is, for example, about 0.8 to 2.5 mm, more preferably about 1.2 to 2.0 mm.
本発明に係る耐遅れ破壊性に優れた鋼板は、上記したような冷延鋼板の表面に、Ｃａ塩、Ｂｅ塩の中から選ばれる１種以上の金属塩とＰ化合物を含有する皮膜（Ａ）を有する。
Ｃａ塩、Ｂｅ塩としては、例えば、硝酸カルシウム、水酸化カルシウム、塩化カルシウム、酢酸カルシウム、硫酸カルシウム、ヨウ化カルシウム、リン酸カルシウム、塩素酸カルシウム、硫酸ベリリウム、硝酸ベリリウム、酢酸ベリリウム、臭化ベリリウムなどが挙げられ、これらの1種以上を含有することができる。
また、Ｐ化合物としては、リン酸、ピロリン酸、ホスホン酸、次亜リン酸などが挙げられ、これらの1種以上を含有することができる。
The steel sheet excellent in delayed fracture resistance according to the present invention comprises a film (A) containing at least one metal salt selected from Ca salts and Be salts and a P compound on the surface of the cold-rolled steel sheet as described above. ).
Examples of the Ca salt and Be salt include calcium nitrate, calcium hydroxide, calcium chloride, calcium acetate, calcium sulfate, calcium iodide, calcium phosphate, calcium chlorate, beryllium sulfate, beryllium nitrate, beryllium acetate, beryllium bromide and the like. And may contain one or more of these.
Further, examples of the P compound include phosphoric acid, pyrophosphoric acid, phosphonic acid, hypophosphorous acid, and the like, and one or more of these compounds can be contained.
皮膜（Ａ）中での金属塩の金属（Ｃａ、Ｂｅ）換算での合計付着量は１０〜５００ｍｇ／ｍ２とする。付着量が１０ｍｇ／ｍ２未満では、水素発生量を低下させる効果が小さく、耐遅れ破壊特性を発揮することができない。この観点から付着量の好ましい下限は５０ｍｇ／ｍ２である。一方、５００ｍｇ／ｍ２を超える付着量であっても耐遅れ破壊特性のための機能が低下することはないが、コスト高となるため好ましくない。
また、皮膜（Ａ）中でのＰ換算でのＰ化合物の付着量は１０〜１０００ｍｇ／ｍ２とする。付着量が１０ｍｇ／ｍ２未満では、鋼板との反応層の形成が十分でないため、長期にわたる耐遅れ破壊特性の向上が見られない。一方、１０００ｍｇ／ｍ２を超える付着量であっても耐遅れ破壊特性のための機能が低下することはないが、コスト高となるため好ましくない。
The total adhesion amount of the metal salt in the film (A) in terms of metal (Ca, Be) is 10 to 500 mg / m 2 . If the amount of adhesion is less than 10 mg / m 2 , the effect of lowering the amount of generated hydrogen is small, and the delayed fracture resistance cannot be exhibited. From this viewpoint, a preferable lower limit of the amount of adhesion is 50 mg / m 2 . On the other hand, even if the amount exceeds 500 mg / m 2 , the function for the delayed fracture resistance does not decrease, but it is not preferable because the cost increases.
Further, the amount of the P compound attached in the film (A) in terms of P is 10 to 1000 mg / m 2 . When the amount of adhesion is less than 10 mg / m 2 , the formation of a reaction layer with the steel sheet is not sufficient, so that the improvement of the delayed fracture resistance over a long period of time is not seen. On the other hand, even if the adhesion amount exceeds 1000 mg / m 2 , the function for the delayed fracture resistance does not decrease, but it is not preferable because the cost increases.
本発明において、Ｃａ塩、Ｂｅ塩の中から選ばれる１種以上の金属塩とＰ化合物を含有する皮膜（Ａ）を形成することにより耐遅れ破壊特性が向上する理由は必ずしも明らかではないが、以下のような機構によるものと考えられる。
乾湿腐食環境の乾燥過程において、鋼板表面のｐＨは低下する。その結果、腐食反応のカソードでの水素発生量が増加し、鋼板内に侵入する水素量が増加して遅れ破壊の原因となる。一方、Ｃａ、Ｂｅは溶解した際に溶液のｐＨを上昇させることが知られている。上述の構成成分を含む皮膜が表層に存在することで界面のｐＨ低下を抑制し、水素発生量が減少していると考えられる。そのため、鋼板内部への水素侵入量が低下し、結果的に耐遅れ破壊特性が向上するものと考えられる。
In the present invention, the reason why the delayed fracture resistance is improved by forming a film (A) containing one or more metal salts selected from Ca salts and Be salts and a P compound is not necessarily clear, It is thought to be due to the following mechanism.
During the drying process in a wet and dry corrosive environment, the pH of the steel sheet surface decreases. As a result, the amount of hydrogen generated at the cathode of the corrosion reaction increases, and the amount of hydrogen entering the steel sheet increases, causing delayed fracture. On the other hand, it is known that Ca and Be increase the pH of a solution when dissolved. It is considered that the presence of the film containing the above-described constituent components in the surface layer suppresses a decrease in pH at the interface and reduces the amount of generated hydrogen. Therefore, it is considered that the amount of hydrogen entering into the steel sheet is reduced, and as a result, the delayed fracture resistance is improved.
さらに、皮膜（Ａ）がＰ化合物を含むことにより、鋼板表面と反応層を形成するため、強固な皮膜とすることができる。上述したようにＣａ塩やＢｅ塩は、腐食過程での水素侵入量の低下に効果があるが、それら単独では溶解性が高く、腐食試験の湿潤時に皮膜が溶出してしまい、長期にわたる耐遅れ破壊特性の向上効果が見られないが、Ｐ化合物を含有することで、長期にわたって優れた耐遅れ破壊特性が得られる。同時に、鋼板表面に強固な皮膜を形成することで、優れた一次防錆性を得ることができる。 Furthermore, since the film (A) contains a P compound and forms a reaction layer with the steel sheet surface, a strong film can be obtained. As described above, Ca salts and Be salts are effective in reducing the amount of hydrogen intrusion during the corrosion process, but they alone have high solubility, and the film is eluted when wet in the corrosion test, resulting in a long-term delay resistance. Although the effect of improving the fracture characteristics is not seen, by including the P compound, excellent delayed fracture resistance can be obtained over a long period of time. At the same time, by forming a strong film on the surface of the steel sheet, excellent primary rust prevention can be obtained.
冷延鋼板表面の皮膜（Ａ）の形成方法については特に限定されないが、例えば、上述の構成成分（金属塩、Ｐ化合物）を含む表面処理液を冷延鋼板の表面にコーティングした後加熱乾燥させる方法が挙げられる。
冷延鋼板表面にコーティングする表面処理液は、溶媒（水及び／又は有機溶剤）に上述した構成成分（金属塩、Ｐ化合物）を溶解又は分散させることにより調製することができる。
The method of forming the film (A) on the surface of the cold-rolled steel sheet is not particularly limited. For example, the surface treatment liquid containing the above-mentioned components (metal salt, P compound) is coated on the surface of the cold-rolled steel sheet and then heated and dried. Method.
The surface treatment liquid for coating the surface of the cold-rolled steel sheet can be prepared by dissolving or dispersing the above-described components (metal salt, P compound) in a solvent (water and / or an organic solvent).
表面処理液を冷延鋼板表面にコーティングする方法としては、塗布方式、浸漬方式、スプレー方式のいずれでもよく、塗布方式ではロールコーター（３ロール方式、２ロール方式など）、スクイズコーター、ダイコーターなどのいずれの塗布手段を用いてもよい。また、スクイズコーターなどによる塗布処理、浸漬処理、スプレー処理の後に、エアナイフ法やロール絞り法により塗布量の調整、外観の均一化、膜厚の均一化を行うことも可能である。 The method of coating the surface treatment liquid on the surface of the cold-rolled steel sheet may be any of an application method, an immersion method, and a spray method. In the application method, a roll coater (three-roll method, two-roll method, etc.), a squeeze coater, a die coater, etc. Any of the application means may be used. Further, after the coating, dipping, and spraying with a squeeze coater or the like, adjustment of the coating amount, uniform appearance, and uniform film thickness can be performed by an air knife method or a roll drawing method.
上記のように表面処理液をコーティングした後、通常、水洗することなく加熱乾燥を行うが、処理後に水洗を行ってもよい。コーティングした表面処理液を加熱乾燥する方法は任意であり、例えば、ドライヤー、熱風炉、高周波誘導加熱炉、赤外線炉などの手段を用いることができる。この加熱乾燥処理は、到達板温で４０〜３００℃、望ましくは４０〜１６０℃の範囲で行うことが好ましい。加熱乾燥温度が４０℃未満では、乾燥時間が長くなり、皮膜ムラとなる恐れがある。一方、加熱乾燥温度が高くなると、焼鈍工程で制御した材質を変化させることで強度が低下するなど、本来の高強度鋼板としての機能が減少する恐れがある。このような観点から短時間の熱処理時間であることが好ましく、温度範囲は３００℃以下であることが好ましい。 After the surface treatment liquid is coated as described above, heating and drying are usually performed without washing with water, but washing with water may be performed after the treatment. The method of heating and drying the coated surface treatment liquid is arbitrary, and for example, a means such as a dryer, a hot air oven, a high frequency induction heating oven, an infrared oven, or the like can be used. This heating and drying treatment is preferably performed at a temperature of the ultimate plate temperature of 40 to 300 ° C, preferably 40 to 160 ° C. When the heating and drying temperature is lower than 40 ° C., the drying time is prolonged, and there is a possibility that the film becomes uneven. On the other hand, when the heating and drying temperature is increased, the function as an original high-strength steel sheet may be reduced, for example, the strength is reduced by changing the material controlled in the annealing step. From such a viewpoint, the heat treatment time is preferably short, and the temperature range is preferably 300 ° C. or less.
本発明の鋼板は、上記皮膜（Ａ）の上層に有機樹脂層（Ｂ）を形成することができる。この有機樹脂層（Ｂ）は、腐食因子のバリア層となり、腐食を抑制する。
この有機樹脂層（Ｂ）の膜厚は０．３μｍ以上４．０μｍ未満とする。膜厚が０．３μｍ未満では、バリア層による耐食性向上効果が十分に得られない。一方、膜厚が４．０μｍ以上では導電性が低下し、溶接性が劣る。
有機樹脂層（Ｂ）を構成する有機樹脂としては、ウレタン系樹脂、エポキシ系樹脂、エチレン樹脂（ポリオレフィン樹脂）、アルキド樹脂、アクリル系樹脂、ポリエステル樹脂、ポリブタジエン樹脂、アミノ樹脂、フェノール樹脂、フッ素樹脂、シリコン樹脂などが挙げられ、これらのうちの１種を単独で又は２種以上を混合して使用することができる。
In the steel sheet of the present invention, an organic resin layer (B) can be formed on the film (A). The organic resin layer (B) becomes a barrier layer of corrosion factor, inhibit corrosion.
The thickness of the organic resin layer (B) is 0.3 μm or more and less than 4.0 μm. If the thickness is less than 0.3 μm, the effect of improving the corrosion resistance by the barrier layer cannot be sufficiently obtained. On the other hand, when the film thickness is 4.0 μm or more, the conductivity is reduced and the weldability is poor.
Examples of the organic resin constituting the organic resin layer (B) include urethane resin, epoxy resin, ethylene resin (polyolefin resin), alkyd resin, acrylic resin, polyester resin, polybutadiene resin, amino resin, phenol resin, and fluorine resin. , Silicon resin, etc., and one of these can be used alone or in combination of two or more.
有機樹脂層（Ｂ）を形成するには、有機樹脂を溶媒（水及び／又は有機溶剤）に溶解及び／又は分散させた処理液（樹脂溶液）を皮膜（Ａ）が形成された鋼板表面にコーティングした後、加熱乾燥させる方法が採られる。
有機樹脂を含む処理液をコーティングする方法としては、塗布方式、浸漬方式、スプレー方式のいずれでもよく、塗布方式ではロールコーター（３ロール方式、２ロール方式など）、スクイズコーター、ダイコーターなどのいずれの塗布手段を用いてもよい。また、スクイズコーターなどによる塗布処理、浸漬処理、スプレー処理の後に、エアナイフ法やロール絞り法により塗布量の調整、外観の均一化、膜厚の均一化を行うことも可能である。コーティングした処理液を加熱乾燥する方法は任意であり、例えば、ドライヤー、熱風炉、高周波誘導加熱炉、赤外線炉等の手段を用いることができる。
In order to form the organic resin layer (B), a treatment liquid (resin solution) obtained by dissolving and / or dispersing an organic resin in a solvent (water and / or organic solvent) is applied to the surface of the steel sheet on which the film (A) is formed. After coating, a method of drying by heating is adopted.
The method of coating the treatment liquid containing the organic resin may be any of a coating method, a dipping method, and a spray method. The coating method may be any of a roll coater (three-roll method, two-roll method, etc.), a squeeze coater, a die coater, and the like. May be used. Further, after the coating, dipping, and spraying with a squeeze coater or the like, adjustment of the coating amount, uniform appearance, and uniform film thickness can be performed by an air knife method or a roll drawing method. The method of heating and drying the coated treatment liquid is arbitrary, and for example, a means such as a dryer, a hot air oven, a high-frequency induction heating oven, an infrared oven, or the like can be used.
有機樹脂層（Ｂ）の膜厚は、皮膜断面を観察し、任意視野の複数箇所（例えば、３箇所）で有機樹脂層の厚さ（皮膜（Ａ）の表面から有機樹脂層の表面までの厚さ）を測定し、それらの平均値を膜厚とする。断面加工の方法は、特に限定されないが、例えばＦＩＢ加工などが採ることができる。 The thickness of the organic resin layer (B) is determined by observing the cross section of the film and measuring the thickness of the organic resin layer (from the surface of the film (A) to the surface of the organic resin layer) at a plurality of locations (for example, three places) in an arbitrary field of view. Thickness), and the average value thereof is defined as the film thickness. The method for processing the cross section is not particularly limited, and for example, FIB processing or the like can be employed.
［実施例１］
素材鋼板として、Ｃ：０．１９１mass％、Ｓｉ：０．４mass％、Ｍｎ：１．５６mass％、Ｐ：０．０１１mass％、Ｓ：０．００１mass％、残部Ｆｅおよび不可避的不純物からなる成分を有し、引張り強度が１５２０ＭＰａ、板厚が１．５ｍｍの冷延鋼板（冷間圧延ままの鋼板）を用いた。
[Example 1]
As a material steel sheet, there are components composed of C: 0.191% by mass, Si: 0.4% by mass, Mn: 1.56% by mass, P: 0.011% by mass, S: 0.001% by mass, the balance being Fe and unavoidable impurities. Then, a cold-rolled steel sheet (steel sheet as cold-rolled) having a tensile strength of 1520 MPa and a thickness of 1.5 mm was used.
冷延鋼板の表面に付着した油をトルエン−エタノールの混合液で超音波脱脂した。コーティング法では、表１に示す各配合成分（金属塩、Ｐ化合物）を水（純水）に溶解させて皮膜形成用の表面処理液を調製し、この表面処理液を鋼板表面に塗布した後、高周波誘導加熱炉で加熱乾燥を実施し、発明例及び比較例の鋼板を得た。皮膜中の各金属成分の付着量は、蛍光Ｘ線により、既知の各金属成分付着量の鋼板を標準板として用いることで測定した。
以上のようにして得られた各鋼板について、以下に示す手法で耐遅れ破壊特性と一次防錆性を評価した。その結果を、皮膜構成とともに、表１に示す。なお、皮膜を形成しない鋼板（比較例であるNo.１）についても同様の特性評価を行った。
The oil adhering to the surface of the cold-rolled steel sheet was ultrasonically degreased with a mixture of toluene and ethanol. In the coating method, each component (metal salt, P compound) shown in Table 1 is dissolved in water (pure water) to prepare a surface treatment liquid for forming a film, and the surface treatment liquid is applied to the steel sheet surface. Then, heating and drying were performed in a high-frequency induction heating furnace to obtain steel sheets of invention examples and comparative examples. The adhesion amount of each metal component in the coating was measured by X-ray fluorescence using a steel plate with a known adhesion amount of each metal component as a standard plate.
The steel sheets obtained as described above were evaluated for delayed fracture resistance and primary rust prevention by the following method. The results are shown in Table 1 together with the film configuration. In addition, the same property evaluation was also performed on a steel sheet having no coating (No. 1 which is a comparative example).
・耐遅れ破壊特性の評価
発明例及び比較例の鋼板をそれぞれ幅３５ｍｍ×長さ１００ｍｍにせん断し、幅が３０ｍｍになるまで研削加工を施し、試験片を作製した。図1に示すように、この試験片１をＵ字形状に曲げて、ボルト２とナット３で拘束して試験片形状を固定し、遅れ破壊評価用試験片を得た。このようにして作製した遅れ破壊評価用試験片に対し、米国自動車技術会で定めたＳＡＥ Ｊ２３３４に規定された、乾燥・湿潤・塩水浸漬の工程からなる複合サイクル腐食試験（図２参照）を、最大２０サイクルまで実施した。各サイクルの塩水浸漬の工程前に目視により割れの発生の有無を調査し、割れ発生サイクル数を測定した。また、本試験は、各鋼板３検体ずつ実施し、その平均値をもって評価を行った。評価は割れ発生サイクル数から、以下の基準により評価した。なお、表１中に示しているが、皮膜を付与しない比較例の場合は４サイクルであったことから、◎、○を好適範囲とした。表１中の割れサイクル数２０以上とは、本実施例の結果では、割れが発生しなかったことを示す。
◎：１５サイクル以上
○：１０サイクル以上１５サイクル未満
×：１０サイクル未満
-Evaluation of delayed fracture resistance The steel sheets of the invention examples and the comparative examples were each sheared to a width of 35 mm x a length of 100 mm, and subjected to grinding until the width became 30 mm, thereby producing test pieces. As shown in FIG. 1, the
◎: 15 cycles or more ○: 10 cycles or more and less than 15 cycles ×: less than 10 cycles
・一次防錆性の評価
発明例及び比較例の鋼板をそれぞれ５０ｍｍ×５０ｍｍのサイズにせん断し、この試験片に対して上記の複合サイクル腐食試験（図２参照）を実施し、１サイクル後の赤錆発生面積率から、以下の基準により評価した。
○：赤錆発生面積率５０％未満
×：赤錆発生面積率５０％以上
-Evaluation of primary rust prevention properties The steel sheets of the invention examples and the comparative examples were each sheared to a size of 50 mm x 50 mm, and the above-described composite cycle corrosion test (see Fig. 2) was performed on the test pieces. From the red rust occurrence area rate, evaluation was made according to the following criteria.
：: Red rust occurrence area rate less than 50% ×: Red rust
表１において、No.３、５〜１３の発明例は皮膜中にＣａ塩とＰ化合物を、No.１４〜１９の発明例は皮膜中にＢｅ塩とＰ化合物を、それぞれ本発明の範囲で含有するものであるが、いずれの発明例も優れた耐遅れ破壊特性と一次防錆性が得られている。 In Table 1, the invention examples of Nos. 3, 5 to 13 include Ca salt and P compound in the film, and the invention examples of Nos. 14 to 19 include Be salt and P compound in the film, respectively, within the scope of the present invention. However, all of the inventive examples have excellent delayed fracture resistance and primary rust prevention.
［実施例２］
実施例１と同様の冷延鋼板を素材鋼板とし、この冷延鋼板の表面に付着した油をトルエン−エタノールの混合液で超音波脱脂した。コーティング法では、表２及び表３に示す各配合成分（金属塩、Ｐ化合物）を水（純水）に溶解させて皮膜形成用の表面処理液を調製し、この表面処理液を鋼板表面に塗布した後、高周波誘導加熱炉で加熱乾燥を実施して第一層皮膜を形成した。この皮膜中の各金属成分の付着量は、蛍光Ｘ線により、既知の各金属成分付着量の鋼板を標準板として用いることで測定した。
[Example 2]
The same cold-rolled steel sheet as in Example 1 was used as a material steel sheet, and oil adhering to the surface of the cold-rolled steel sheet was ultrasonically degreased with a mixed solution of toluene and ethanol. In the coating method, each component (metal salt, P compound) shown in Tables 2 and 3 is dissolved in water (pure water) to prepare a surface treatment liquid for forming a film, and this surface treatment liquid is applied to the steel sheet surface. After the application, heating and drying were performed in a high-frequency induction heating furnace to form a first layer film. The adhesion amount of each metal component in this film was measured by X-ray fluorescence using a steel plate having a known adhesion amount of each metal component as a standard plate.
次いで、第一層皮膜の上層に第二層皮膜として有機樹脂層を形成した。有機樹脂層用には下記Ａ１〜Ａ４の有機樹脂を用い、いずれかの有機樹脂を含む処理液をロール方式による塗布法で塗布した後、到達板温が１２０℃となるようにインダクションヒーターで加熱することで有機樹脂層を形成した。
Ａ１：エポキシ樹脂（ジャパンエポキシレジン（株）製、商品名：ｊＥＲ１００９）
Ａ２：ポリオレフィン樹脂（東邦化学工業（株）製、商品名：ＨＹＴＥＣ Ｓ−３１２１）
Ａ３：ウレタン樹脂（メーカー名：第一工業製薬(株)製 型番：スーパーフレックスＥ−２０００）
Ａ４：フッ素樹脂（旭硝子（株）製、商品名：ルミフロン ＬＦ５５２）
また、有機樹脂層の膜厚の測定は、ＦＩＢ加工により得られた断面をＳＥＭ観察し、任意視野の３箇所で有機樹脂層の厚さ（第一層皮膜面から有機樹脂層の表面までの厚さ）を測定し、それらの平均値を膜厚とした。
Next, an organic resin layer was formed as a second layer film on the first layer film. For the organic resin layer, an organic resin of the following A1 to A4 is used, and a treatment liquid containing any one of the organic resins is applied by a coating method using a roll method, and then heated by an induction heater so that the reached plate temperature becomes 120 ° C. Thus, an organic resin layer was formed.
A1: Epoxy resin (product name: jER1009, manufactured by Japan Epoxy Resin Co., Ltd.)
A2: polyolefin resin (manufactured by Toho Chemical Industry Co., Ltd., trade name: HYTEC S-3121)
A3: Urethane resin (manufacturer: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., model number: Superflex E-2000)
A4: Fluororesin (made by Asahi Glass Co., Ltd., trade name: Lumiflon LF552)
The thickness of the organic resin layer was measured by observing the cross section obtained by FIB processing with a SEM, and measuring the thickness of the organic resin layer (from the first layer coating surface to the surface of the organic resin layer at three points in an arbitrary field of view). Thickness) was measured, and the average value thereof was defined as the film thickness.
以上のようにして得られた各鋼板について、以下に示す手法で耐遅れ破壊特性、一次防錆性及び導電性を評価した。その結果を、皮膜構成とともに、表２及び表３に示す。なお、皮膜を形成しない鋼板（比較例であるNo.１）についても同様の特性評価を行った。
・耐遅れ破壊特性の評価
発明例及び比較例の鋼板に対して実施例１と同様の試験条件と評価基準で試験を実施した。
The steel sheets obtained as described above were evaluated for delayed fracture resistance, primary rust prevention and electrical conductivity by the following methods. The results are shown in Tables 2 and 3 together with the film configuration. In addition, the same property evaluation was also performed on a steel sheet having no coating (No. 1 which is a comparative example).
-Evaluation of delayed fracture resistance A test was performed on the steel sheets of the invention examples and the comparative examples under the same test conditions and evaluation criteria as in Example 1.
・一次防錆性の評価
発明例及び比較例の鋼板に対して実施例１と同様の試験を実施し、１サイクル後の赤錆発生面積率から、以下の基準により評価した。
◎：赤錆発生面積率５％未満
○：赤錆発生面積率５％以上２０％未満
×：赤錆発生面積率２０％以上
・導電性の評価
溶接性の指標として導電性を評価した。発明例および比較例の鋼板の試験片について、三菱化学アナリテック（株）製「ロレスタＧＰ ＡＳＰ端子」を用い表面抵抗値を測定し、表面抵抗値が１０−４Ω以下となる割合（％）により、以下の判定基準で評価した。
○：８０％以上
×：８０％未満
-Evaluation of primary rust prevention properties The same test as in Example 1 was performed on the steel sheets of the invention examples and the comparative examples, and the red rust occurrence area ratio after one cycle was evaluated according to the following criteria.
：: Red rust generation area rate less than 5% ○: Red rust generation area rate 5% or more and less than 20% ×: Red rust generation area rate 20% or more Conductivity evaluation Conductivity was evaluated as an index of weldability. With respect to the test pieces of the steel sheets of the invention examples and the comparative examples, the surface resistance was measured using “Loresta GP ASP terminal” manufactured by Mitsubishi Chemical Analytech Co., Ltd., and the ratio (%) at which the surface resistance became 10 −4 Ω or less was obtained. Was evaluated according to the following criteria.
：: 80% or more ×: less than 80%
表２において、No.３、５〜８、１０、１１、１３〜２５の発明例は皮膜中にＣａ塩とＰ化合物を、No.２６〜３１の発明例は皮膜中にＢｅ塩とＰ化合物を、それぞれ本発明の範囲で含有し、かつ上層に本発明条件を満たす有機樹脂層を有するものであるが、いずれの発明例も優れた耐遅れ破壊特性と一次防錆性、さらには導電性が得られている。 In Table 2, the invention examples of Nos. 3, 5 to 8, 10, 11, and 13 to 25 have Ca salt and P compound in the film, and the invention examples of Nos. 26 to 31 have Be salt and P compound in the film. Is contained within the scope of the present invention, and has an organic resin layer that satisfies the conditions of the present invention as an upper layer.Each of the inventive examples has excellent delayed fracture resistance and primary rust prevention properties, and furthermore, has excellent conductivity. Has been obtained.
１ 試験片
２ ボルト
３ ナット
1
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