JP2004083920A - Steel strip having excellent reddening resistance during high temperature oxidation and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet which has excellent press workability, corrosion resistance and spot weldability, allows perfect combustion and decomposition of films in a cathode-ray tube sealing step, can form the films having the good corrosion resistance similar to that of blackened films without the occurrence of hematite (red rust) and elimniates the need for blackening treatment after press working. <P>SOLUTION: A cold rolled steel strip or pickled and hot rolled steel strip of surface roughness 0.2 to 3 μm Ra is pretreated by preferably an aqueous acid solution or aqueous metal ion-containing solution and thereafter the film of a thickness 0.1 to 6 μm of an organic resin essentially consisting of C, H or C, H, O or C, H, O, and N is formed on its surface. <P>COPYRIGHT: (C)2004,JPO

Description

【００５９】
本例では、表面粗さ０．５　μｍ　Ｒａの冷延鋼帯に、連続ラインで、表２に示す前処理を施した後、その両面に樹脂液のロール塗装と焼き付けにより、厚み１．７　μｍ　のウレタン系有機樹脂被膜　（添加成分を含有せず）　を形成した。
【００６０】
表２に記載した各処理の条件は次の通りであった：
アルカリ脱脂：水酸化ナトリウム１％、６０℃、２秒浸漬；
湯洗：水温８０℃、２秒浸漬；
溶液▲１▼：硫酸１％、６０℃、２秒浸漬；
溶液▲２▼：硫酸ニッケル１０％　（ｐＨ　４）　、６０℃、２秒浸漬。
【００６１】
使用した樹脂液は、市販の水系ウレタン塗料用の樹脂液であり、塗装後の焼き付け条件は約１２０　℃の温度で１０秒間であった。焼き付け後、鋼帯を空冷し、コイルに巻いた。
【００６２】
得られた各鋼帯について、塗装性と赤変性を次にようして調査した。
塗装性
塗装焼き付けした素材の仕上がり外観を目視で観察し、塗りムラの有無を評価した。また、この素材をアルコールまたはトリクロロエチレンで超音波洗浄し、洗浄後に塗膜の脱落の有無を調べ、塗膜の密着性を評価した。
【００６３】
◎：塗りムラがなく、超音波洗浄で塗膜の脱落がない、
○：わずかに塗りムラが発生するが、ハジキではなく、超音波洗浄で塗膜の脱落がない、
×：ハジキが発生する著しい塗りムラとなり、超音波洗浄でも塗膜の脱落がある。
【００６４】
赤変性
塗装焼き付けした素材に大気中で４５０　℃×１２０　分の加熱処理を行い、加熱処理後の赤変　（葉状ヘマタイト発生）　の程度を顕微鏡および目視で評価した。
【００６５】
◎：全く赤変しない（目視でも顕微鏡でも赤変を認識できない）、
○：ほとんど赤変しない（目視では赤変をほとんど認識できない）、
△：わずかに赤変する（目視でごくわずかな赤変を認識できる）、
×：著しく赤変する（葉状ヘマタイトが粉状になっていて、目視でも明確に赤変を確認できる）。
【００６６】
【表２】

【００６７】
表２からわかるように、溶液▲１▼または▲２▼を用いて前処理を行うと、赤変性が改善され、溶液▲１▼と▲２▼の両方で前処理すると、赤変性がさらに改善される。従って、これらの前処理は高温酸化時の葉状マタイト　（赤錆）　の生成による赤変を防止する効果がある。アルカリ脱脂のみでは、葉状ヘマタイトの生成をまったく防止できない。塗装性はいずれの場合も良好である。
【００６８】
（実施例２）
実施例１と同様にして、前処理した冷延鋼帯にウレタン系有機樹脂被膜を形成した。使用した冷延鋼帯、前処理方法、および樹脂被膜厚みは実施例１と同様であった。表３には、実施例１と同様にして評価した塗装性と赤変性の試験結果も示す。
【００６９】
本例では、前処理は表３に示す手順で実施し、有機樹脂被膜としては、表３に示すように、
・有機樹脂のみ　（Ａ）　、
・カップリング剤Ｂを含有　（Ａ＋Ｂ）　、
・金属酸化物Ｃを含有　（Ａ＋Ｃ）　、
・カップリング剤Ｂと金属酸化物Ｃの両方を含有　（Ａ＋Ｂ＋Ｃ）　、
の４種類を形成した。
【００７０】
有機樹脂Ａは、参考例１と同じ市販の水系ウレタン系塗料用の樹脂液であり、カップリング剤Ｂはシランカップリング剤　（γ−グリシドキシプロピルトリメトキシシラン）　であり、金属酸化物Ｃはコロイダルシリカであった。添加量は、樹脂液中の全固形分に基づいて、Ｂが２０％、Ｃが３０％であった。
【００７１】
【表３】

【００７２】
表３から、有機樹脂被膜がカップリング剤Ｂまたは金属酸化物Ｃの一方を含有すると、赤変性　（葉状ヘマタイトの生成防止）　が改善され、ＢとＣの両方を含有すると赤変性がさらに改善されることがわかる。その結果、酸または酸性水溶液による前処理を行わない、アルカリ脱脂のみの鋼帯に有機樹脂被膜を形成した場合でも、赤変性が改善される。
【００７３】
赤変性が最も良好な◎であったサンプルについて、赤変性試験で加熱処理された試験片の表面被膜の状況をＸ線回折により調べた。その結果、Ｘ線回折図には、マグネタイト（Ｆｅ_３Ｏ_４）　および地鉄（Ｆｅ）に帰属される回折ピークのみが現れ、加熱処理でマグネタイト主体の被膜が生成したことが確認された。
【００７４】
（実施例３）
表２および３の試験Ｎｏ．１に記載のＡ＋Ｂ＋Ｃの有機樹脂被膜の条件に、さらに各種粒径のワックスを異なる量で添加して、有機樹脂被膜を形成した。
【００７５】
即ち、表面粗さ０．５　μｍ　Ｒａの冷延鋼帯を、アルカリ脱脂⇒湯洗⇒溶液▲１▼　（硫酸溶液）　塗布⇒湯洗の順で連続的に前処理した。その後、同じライン内で、樹脂液をロール塗装した後、実施例１と同様に焼き付けて、塗膜厚みの異なる鋼帯を得た。
【００７６】
使用した樹脂液は、参考例１で使用したのと同じウレタン系樹脂液であり、市販の水系塗料用樹脂液を利用した。この樹脂液に、ワックスに加えて、樹脂液中の全固形分に基づいて、参考例２と同じ種類および量で、シランカップリング剤とコロイダルシリカを添加した。
【００７７】
表４に、使用したワックスの粒径　（φ）　、有機樹脂被膜の厚み　（Ｔ）　、φ／Ｔの比、ワックス粒の面積率　（Ｄ）　、および深絞りである円筒絞り試験で評価したプレス加工性の結果を示す。
【００７８】
ワックス粒の面積率　（Ｄ）　は、有機樹脂被膜の表面を電子顕微鏡　（ＳＥＭ）　で観察した際に確認できるワックス粒の面積率である。
円筒絞り試験は、パンチ径５０　ｍｍ　、パンチ肩Ｒ　２　ｍｍ　、ダイス肩Ｒ　２　ｍｍ　、しわ押さえ力５００　ｋｇｆ　、絞り比１．８　で実施し、問題なく加工できる場合を○、割れる場合を×と評価した。
【００７９】
【表４】

【００８０】
表４から、ワックスのφ／Ｔ比が　０．５〜５の範囲内で、ワックスの面積率が２〜２０％の範囲内であると、鋼帯は深絞り可能な優れたプレス加工性を示すことがわかる。
【００８１】
（実施例４）
表面粗さの異なる各種の冷延鋼帯を、参考例１の表２の試験Ｎｏ．７に従って、アルカリ脱脂⇒湯洗⇒溶液▲１▼（硫酸溶液）　塗布⇒溶液▲２▼（硫酸ニッケル溶液）　塗布⇒湯洗の順で連続処理した。その後、同じライン内で、樹脂液をロール塗装した後、実施例１と同様に焼き付けて、鋼帯表面に有機樹脂被膜を形成した。
【００８２】
使用した樹脂液は、ウレタン系樹脂液またはウレタン系とアクリル系の混合樹脂液であり、市販の水系塗料用樹脂液を利用した。一部の樹脂液には、金属酸化物としてシリカゾルを添加した。
【００８３】
表５に、冷延鋼帯の表面粗さ（Ｒａ）、樹脂種、樹脂被膜厚み（Ｔ）　およびＴ／Ｒａの比を示す。
これらの鋼帯のプレス加工性、スポット溶接性、耐食性、および被膜燃焼性を、次のようにして調査した。これらの試験結果も表５に併記する。
【００８４】
プレス加工性
アンコイラーを備えたプレス加工設備を使用し、コイル巻きされた鋼帯をメジャーロールで送りだしながら、打ち抜きと曲げ加工金型または絞り加工金型によるプレス加工を行なった。
【００８５】
従来材以外の試験では、このプレス加工時の材料の送り出し時のメジャーロールでの滑りや、打ち抜き加工されたブランクの剥離性（重ねた状態で搬送されたブランクが密着して剥がれず、複数枚のブランクが重なったままプレス加工機に搬送されてしまうかどうか）により、プレス加工性を次のように評価した。
【００８６】
○：メジャーロールで材料を送り出す際に滑りを起こさずに所定の長さの材料を送り出すことができ、打ち抜き加工後のブランクの剥離性が良好で、一連のプレス加工工程において全く問題が発生しない；
△：メジャーロールで材料を送り出す際の滑りはないが、打ち抜き加工後に複数枚のブランクがプレス加工機に搬送されるトラブルが発生する傾向がある；
×：メジャーロールで材料を送り出す際に滑りが発生し、一連のプレス加工工程を安定して操業できない。
【００８７】
スポット溶接性
実際の使用条件は素材ユーザー毎に多少の差があるため、平均的な条件として、下記の条件でスポット溶接を行い、溶接の状態　（無通電の有無、チリの発生、大きさ、連続打点時の電極チップの損耗等）　を調べた。
【００８８】
チップ：上下共、先端形状は５ｍｍ径の球頭、純Ｃｕ製
荷重：　５ｋｇｆ
電流：　６００　Ａ
サイクル：６サイクル
○：１００００　打点以上　（正常に通電してナゲットを形成し、チップの損耗が少なく、良好に溶接できる打点数）　、
△：５０００〜１００００　打点、
×：５０００打点未満で正常な溶接ができなくなる。
【００８９】
耐食性
鋼帯を５０　ｍｍ　×１００　ｍｍの大きさに切断して得た試験片を、表面に一般的な鋼板用防錆油（鉱油系）を塗布してから標準的な条件下で脱脂洗浄した後、大気暴露試験に供した。大気暴露試験は、雨などで試験片が濡れない環境で３０日間実施した。３０日後の試験片の錆発生状況により、次のように耐食性を判定した。
【００９０】
○：錆が全く発生しない、
△：やや点錆が発生
×：かなりの錆が発生。
【００９１】
観察期間を３０日までとしたのは、高温酸化されるインナー磁気シールド等のの生産工程では、何らかの事故が無い限りは、それ以上の保管期間を必要としないこと、大気暴露試験の環境が、実際の使用現場の環境より腐食性の高い状態であることから、３０日間の観察期間で妥当とであると判断できたからである。
【００９２】
被膜燃焼性
上記と同じ試験片の表面に一般的な鋼板用防錆油（鉱油系）を塗布してから、冷延鋼板が脱脂しうる範囲で可及的に短い脱脂洗浄時間で脱脂洗浄を行った。その後、大気雰囲気で４５０　℃に４０分間加熱した。この加熱条件は、ブラウン管の封着工程を想定して設定したものである。加熱後の試験片の表面の樹脂の残存を、ＥＰＭＡによる分析で判定した。また、上記加熱処理中のガス発生量を経時的に測定し、封着工程中にガスの発生が終了するかどうかを確認すると共に、ガスサンプルをＴＧ−ＭＳ　法およびＰｙｒｏ−ＧＣ−ＭＳ法により分析して、Ｓ、Ｃｌ、Ｆ等を含有する腐食性ガスの発生の有無についても調べ、次のように判定した。
【００９３】
○：上記条件での加熱処理後に樹脂が残存せず、加熱処理中にガスの発生が終了し、かつ腐食性ガスの発生がなかった場合、
×：樹脂の残存が認められるか、加熱処理中にガスの発生が終了しなかったか、または腐食性ガスが発生した場合。
【００９４】
【表５】

【００９５】
表５からわかるように、鋼帯の表面粗さが０．２　μｍ　Ｒａより小さいとプレス加工性が劣化し、３μｍ　Ｒａより大きいと耐食性が劣化する。スポット溶接性は、Ｔ／Ｒａ比が２．５　より大きくなると低下し始め、４より大きくなると著しく悪くなる。Ｔ／Ｒａ比が０．４　より小さいと、耐食性が低下しはじめ、特にＴ／Ｒａ比が０．２　未満であると耐食性が著しく低下する。
【００９６】
本発明に従って、有機樹脂被膜に金属酸化物を含有させると、実施例１に示したように高温酸化時の赤変性が改善されるが、本例で調べた特性に関して、金属酸化物が特性を阻害することはなかった。
【００９７】
（実施例５）
表６に示す組成（残部：Ｆｅおよび不可避不純物）の低炭アルミキルド鋼ａ〜ｅを用いて、熱間圧延と冷間圧延により、表面粗さ　０．５μｍ　Ｒａ、厚み０．１５　ｍｍ　の冷延鋼帯を得た。この冷延鋼帯を連続焼鈍設備にてＮ_２雰囲気で８００　℃×５秒保持の熱処理により焼鈍した。
【００９８】
この冷延鋼帯を、表２の試験Ｎｏ．３に従って、アルカリ脱脂⇒湯洗の手順で前処理した。各処理条件は実施例１と同様であった。
前処理した冷延鋼帯の両面に、実施例１と同様にして厚み１．７　μｍ　のウレタン系有機樹脂被膜を形成して、鋼帯を作製した。
【００９９】
こうして得られた鋼帯の試験片に対し、ブラウン管の封着工程を模して、大気中４５０　℃に１２０　分間加熱する熱処理を施し、熱処理後のスケールの密着性をセロテープ（Ｒ）　での剥離試験により次の基準で評価した。また、外観の赤変性を上記実施例１と同様の基準で評価した。それらの結果も表６に併せて示す。
【０１００】
スケールの密着性
○：スケールの密着が良好で、全く剥離しない、
△：わずかに剥離する場合がある、
×：層間剥離が発生し、スケールがフィルム状に剥離する。
【０１０１】
【表６】

【０１０２】
表６から、鋼組成が、本発明の好適態様に従って、下記条件：
［Ｓｉ］≧０．０２、０．２５≦［Ｓｉ］＋［Ａｌ］≦０．５５、０．０５≦［Ａｌ］−［Ｓｉ］≦０．３
の全てを満たすと、高温酸化時に密着性がよく、マグネタイト主体の酸化鉄被膜（スケール）　が生成することがわかる。
【０１０３】
【発明の効果】
本発明により、従来は、酸素雰囲気の調整が可能な特殊な熱処理炉を使用した黒化被膜の形成によって初めて可能であった、高温時の耐赤変性を、有機樹脂被膜の形成という簡便な手段で鋼帯に付与することができる。それにより、プレス加工を支障なく実施でき、プレス加工後も十分な耐食性を示すと同時に、高温酸化時には、有害なガスを発生させずに樹脂被膜が完全に燃焼分解され、葉状ヘマタイトの生成を防止して、黒化被膜に似たマグネタイト主体の酸化被膜が形成され、鋼帯にはその後の酸化に耐える高温耐食性が付与される。
【０１０４】
従って、本発明の鋼帯は、従来はプレス加工後に黒化処理を必要としていた用途に特に有用であり、費用のかかる黒化処理が不要となるので、経済的効果が高い。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a magnetite-based iron oxide coating that is dense and has good adhesion during high-temperature oxidation, and prevents red discoloration due to the formation of red foliate hematite that is brittle and easily falls off. The present invention relates to an excellent steel strip and a method for producing the same.
[0002]
[Problems to be solved by the invention]
When a cold-rolled steel strip or an acid-washed hot-rolled steel strip is exposed to a high temperature in the atmosphere or in an atmosphere having a high oxygen concentration, red rust occurs and the surface turns red. The identity of this red rust is the hematite (Fe₂O₃) Which grows upright from the surface of the steel strip and has a thickness or diameter of about 1 μm in a leaf-like or needle-like form (hereinafter, referred to as leaf-like hematite).
[0003]
Foliate hematite is very brittle and easily falls off the steel strip surface. Therefore, the formation of leaf-like hematite is not preferable in terms of the corrosion resistance of the steel strip, but the formation of leaf-like hematite may be unacceptable depending on the use of the steel strip. For example, in the case of a steel strip used in an environment where a vacuum is required, such as inside a TV CRT, foliated hematite easily absorbs gas, which hinders securing a necessary degree of vacuum and adversely affects the performance of the CRT. May give. Furthermore, if the dropped leaf-like hematite fragments adhere to the electron gun in the cathode ray tube, there is a risk of damaging the electron gun, thereby affecting the life of the cathode ray tube.
[0004]
On the other hand, the manufacture of a cathode ray tube includes a sealing process in which an electron gun and other necessary parts are incorporated therein, and then a joint portion of the divided glass tubes is fused. This sealing is performed by heating at a temperature of about 450 ° C. for 30 minutes to 2 hours in an air atmosphere. Therefore, the components incorporated inside the cathode ray tube are also heated under the same conditions, and if the components are made of steel, the surface is inevitably exposed to high-temperature oxidation.
[0005]
If foliated hematite is generated by high-temperature oxidation in the sealing step, as described above, the performance and life of the cathode ray tube is adversely affected, so steel components incorporated in the cathode ray tube, such as an inner magnetic shield, a frame, and a shadow mask, Before being incorporated into a cathode ray tube, a heat treatment is performed in advance in a weakly oxidizing high-temperature atmosphere (about {550-590 ° C.}) to obtain a magnetite (Fe₃O₄) A predominantly dense black iron oxide coating is formed on the surface. Thereby, even if the film is heated to a temperature of about 450 ° C. in the atmosphere in the subsequent sealing step, the blackened film becomes a barrier and is not oxidized any more, thereby preventing the formation of leaf-like hematite.
[0006]
However, since the blackening treatment is performed not on the steel strip itself but on the processed member after the press working, it is performed by a cathode ray tube manufacturer {a steel strip user}. Even if the steel strip is previously subjected to a blackening treatment, the blackened coating is exfoliated at the time of pressing, so that the effect of preventing leaf-like hematite is lost. For this reason, the user installs a dedicated small heat treatment facility and performs the blackening process after the press working, which increases the cost.
[0007]
Therefore, in order to eliminate the need for a blackening treatment, a steel strip excellent in resistance to reddening at the time of high-temperature oxidation, which can reliably prevent the formation of leaf-like hematite even when exposed to high-temperature oxidation conditions, is desired. .
[0008]
Conventionally, in order to prevent red discoloration due to the formation of foliated hematite during high-temperature oxidation, for example, as in the above-described blackening treatment, it must be oxidized in a special heat treatment furnace that controls the oxygen concentration, There were no other preventive measures.
[0009]
[Means for Solving the Problems]
The present inventors, if an organic resin film is formed on a steel strip in advance, even if the steel strip is exposed to a high temperature under oxidizing conditions such as in the air, the oxygen concentration near the steel strip surface due to the combustion decomposition of the organic resin is reduced. It has been found that needle-like or leaf-like hematite is less likely to be generated because it is relatively low, an oxide film mainly composed of magnetite is generated stably, and high-temperature oxidation resistance is maintained. In other words, the steel strip on which the organic resin coating is formed is prevented from reddening due to the formation of leaf-like hematite during high-temperature oxidation, and after high-temperature oxidation, a magnetite-based iron oxide coating is formed on the steel strip surface, and has excellent high-temperature oxidation resistance. Demonstrate.
[0010]
The present invention provides a steel strip having a surface roughness of {0.2 to 3 μm} Ra on at least one surface of which a thickness of an organic resin consisting essentially of C, H or C, H, O or C, H, O, N is about 0.1. It is a steel strip having a resistance to reddening during high-temperature oxidation characterized by having a coating of about 6 μm.
[0011]
The strip may further include one or more of the following features:
A ratio (T / Ra) of the thickness T of the organic resin film to the surface roughness Ra of the steel strip is {0.2 to 4.0};
The organic resin coating is (a) 2 to 50% by mass of at least one coupling agent, and (b) {2 to 80% by mass of SiO₂, Fe₃O₄, Fe₂O₃, Ni-O, Zr-O, Cr₂O₃And Al₂O₃At least one metal oxide selected from the group consisting of:
The organic resin film contains wax dispersed in the film, the ratio {(φ / T)} of the particle diameter φ of the wax to the thickness T of the organic resin film is {0.5 to 5}, and the content of the wax is When the surface area of the wax is 2 to 20% when the coating surface is observed with a microscope,
[0012]
The organic resin is to be decomposed by heating at 450 ° C. or less in the atmosphere;
Amount of metal of Ni, Cr or Fe or an alloy containing the metal as a main component on the base of the organic resin film {0.1 to 20} g / m²Having a plating film of
-The content of Si and Al {(% by mass)} in the steel strip is as follows:
[Si] ≧ 0.02, 0.25 ≦ [Si] + [Al] ≦ 0.55, 0.05 ≦ [Al] − [Si] ≦ 0.35
Meet.
[0013]
According to the present invention, the thickness of the organic resin consisting essentially of C, H or C, H, O or C, H, O, or N is provided on at least one surface of the cold-rolled steel strip or the pickled hot-rolled steel strip. Also provided is a method for producing a steel strip having excellent resistance to reddening during high-temperature oxidation, characterized by forming a coating having a thickness of 0.1 to 6 μm６.
[0014]
Also in this method, the T / Ra ratio, the organic resin coating, and the steel strip composition can have the above characteristics.
Preferably, prior to forming the coating on the steel strip, (1) an acid selected from hydrochloric acid, sulfuric acid, nitric acid and a mixed acid of two or more of these acids, and (2) {Ni, Co, Fe, Zr , Sb, V, Mo, W, or an acidic solution containing ions of at least one metal selected from the group consisting of Sb, V, Mo, and W.
[0015]
Alternatively or additionally, the cold-rolled steel strip or the pickled hot-rolled steel strip is plated with a metal made of Ni, Cr or Fe or an alloy containing the metal as a main component before forming the coating. , Adhesion amount: 0.1 to 20 g / m²May be formed.
[0016]
The present invention also provides a steel strip excellent in high-temperature oxidation resistance obtained by heating the above-described steel strip in an oxidizing atmosphere and burning and decomposing an organic resin.
The steel strip according to the present invention, which has excellent resistance to reddening during high-temperature oxidation, can be used as a processing material for various applications. For example, conventional steel strips such as inner magnetic shields for TV cathode-ray tubes, frames, shadow masks, etc. This is particularly useful in a field where a process of imparting high-temperature oxidation resistance, which is called a blackening process, is performed later, and a high-cost blackening process can be omitted.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The steel strip having excellent resistance to reddening at the time of high-temperature oxidation according to the present invention has essentially a C, H or C, H, O or C, It is formed of a coating of organic resin composed of H, O, and N with a thickness of {0.1 to 6 μm}. This organic resin coating protects the steel strip and imparts corrosion resistance to the steel strip until it is first oxidized at high temperature. When the steel strip is first oxidized at high temperature, the organic resin film is burned and decomposed, and a coating mainly composed of magnetite and having excellent high-temperature oxidation resistance is formed on the surface of the steel strip.
[0018]
The thickness of the steel strip is preferably in the range of 0.05 to 3.0 mm from the viewpoint of required strength and workability. The steel composition of the steel strip can be selected according to the application so as to have the properties required for the application. For example, the steel strip for the inner magnetic shield preferably has excellent magnetic properties.
[0019]
However, in order to prevent the formation of scales that lead to the generation of leaf-like hematite during high-temperature oxidation, it is preferable that the Si and Al contents {(% by mass)} in the steel composition of the steel strip satisfy the following conditions:
[Si] ≧ 0.02, 0.25 ≦ [Si] + [Al] ≦ 0.55, 0.05 ≦ [Al] − [Si] ≦ 0.35
This composition can be obtained, for example, by a killed steel to which ferrosilicon and aluminum are added. The Si and Al contents preferably satisfy the following conditions:
[Si] ≧ 0.05, 0.30 ≦ [Si] + [Al] ≦ 0.50, 0.10 ≦ [Al] − [Si] ≦ 0.30.
[0020]
Si and Al easily react with oxygen to form oxides. When this oxide is preferentially formed on the steel strip surface, the oxygen supplied to the steel strip surface decreases, and the formation of iron oxide coating (scale) mainly composed of magnetite instead of hematite, which has a large amount of oxygen, is suppressed. Encourage. For that purpose, the range of 0.25 to 0.55% in terms of the total amount of [Si] + [Al] is appropriate. If it is less than 0.25%, the effect of suppressing the formation of leaf-like hematite is insufficient, and if it exceeds 0.55%, a scale mainly composed of magnetite is formed, but its adhesion is reduced.
[0021]
Further, even if one of Si and Al alone is added, a sufficient effect cannot be obtained, and both Si and Al must be added, and Si ≧ 0.02%, 0.05% ≦ When the condition of [Al]-[Si] ≦ 0.35% is satisfied, the scale becomes a proper magnetite-based scale.
[0022]
By using a steel composition that satisfies this condition, the scale generated in the cathode ray tube attaching step can be controlled mainly by magnetite. However, the addition of a coupling agent and / or a metal oxide to the resin film described later, and the pretreatment Alternatively, a higher effect can be obtained by using it together with the undercoating treatment.
[0023]
In order to impart corrosion resistance to the steel strip, it is desirable that the organic resin film completely fills the steel strip surface by filling the unevenness of the steel strip surface. Therefore, a coating having a thickness of 0.1 μm or more is required. On the other hand, it is desirable that the organic resin film be completely decomposed by combustion during high-temperature oxidation depending on the use. For example, in the case of an inner magnetic shield used in a cathode ray tube, if the organic resin film is not completely decomposed and removed in the sealing process, the remaining film burns during the heat treatment in the next degassing process to generate gas, and It impairs air efficiency and lowers the vacuum of the CRT. The thickness of the resin coating is set to 6 μm or less so that the resin can be completely burned and decomposed by heating at about 450 ° C. in the atmosphere for about 40 minutes in the sealing step. The thickness of the resin film is preferably {0.2 to 4 μm}, more preferably 0.3 to 3 μm.
[0024]
If the surface roughness of the steel strip exceeds 3 μm Ra, the thickness of the resin coating required to fill the surface irregularities increases. If the resin film cannot completely fill the surface irregularities, the corrosion resistance is reduced, and the generation of rust cannot be prevented. On the other hand, if the coating is too thick in order to completely cover the surface irregularities, in the case of use in a cathode ray tube, not only the amount of generated gas in the sealing step increases, but also as described above, even after the sealing step. There is a high possibility that the film remains to inhibit the deaeration efficiency. Therefore, in a steel strip having a surface roughness of more than 3 μm こ と が Ra, it is difficult to control the coating thickness so as to achieve both corrosion resistance and deaeration efficiency.
[0025]
If the surface roughness of the steel strip is small, the thickness of the resin film required to fill the surface irregularities can be small. However, when the surface roughness is smaller than 0.2 μm Ra, the material is excessively slipped or adhered, which adversely affects the press working. In the press working step, a coil-shaped material is unwound, sent out by a measure roll, cut into an appropriate length, and then blanked by punching. If the material slides too much at this time, a slip occurs between the measure roll and the material, and the material cannot be cut to an accurate length. Further, in a more general tandem press method, punched blanks are stacked, transported to a press working place, peeled one by one, and pressed. At this time, if the materials are in close contact with each other, a plurality of materials are pressed together, so that the mold is damaged or cannot be processed into a prescribed shape.
[0026]
For the above reasons, the surface roughness of the steel strip is {0.2-3 μm} Ra, which is preferably 0.2-2 μm Ra, more preferably {0.3-1 μm Ra.
The thickness (T) 厚 み of the organic resin film is preferably correlated with the surface roughness (Ra) of the steel strip. In order to fill the surface irregularities and secure the corrosion resistance, it is effective to set the T / Ra ratio to 0.2 ° or more, particularly 0.4 ° or more. On the other hand, when the ratio of T / Ra was too large, it was found that spot welding was hindered. Since spot welding is often used for assembling a steel strip after pressing, it is desirable that the steel strip has spot weldability. If the organic resin film is too thick, the welding current may not flow (no current welding failure), or the electric resistance of the surface may be too high, causing abnormal heat generation and damaging the welding tip. The spot weldability starts to decrease when the T / Ra ratio exceeds 2.5 °, and particularly deteriorates when the T / Ra ratio exceeds 4.0 °. Therefore, the T / Ra ratio is preferably in the range of {0.2 to 4.0}, and more preferably in the range of {0.4 to 2.5}.
[0027]
The organic resin film is a film of an organic resin consisting essentially of C, H or C, H, O or C, H, O, N, and therefore does not generate corrosive gas when decomposed by combustion. This organic resin film has a film strength and adhesion so as not to be peeled off in a press working step, and is relatively short-time when heated to 450 ° C. in the air so as to be removed in a cathode ray tube sealing step. What decomposes by combustion is good.
[0028]
Examples of suitable organic resins include urethane resins, acrylic resins, polyester resins, polyolefin resins, polystyrene resins, polyamide resins, and the like.
[0029]
The organic resin coating comprises (a) {a total of 2 to 50% of at least one coupling agent, and (b)} a total of 80% or less of SiO₂, Fe₃O₄, Fe₂O₃, Ni-O, Zr-O, Cr₂O₃And Al₂O₃It is preferable to further contain one or both of at least one metal oxide selected from the group consisting of: Thereby, the red discoloration resistance during high-temperature oxidation of the steel strip is further improved. Although the coupling agent and the metal oxide are effective independently, it is more effective when both are used in combination.
[0030]
The coupling agent is an organometallic compound in which a hydrolyzable organic group is bonded to a metal, and preferentially reacts with and binds to the steel strip surface. Conventionally, the coupling agent has been used to ensure the adhesion between the organic resin film and the substrate, but the present inventors have found that if the organic resin film contains an appropriate amount of the coupling agent, the above-mentioned foliar hematite Was found to suppress the generation of. This is presumed that the metal element contained in the coupling agent coats the steel strip surface, thereby blocking the supply of excess oxygen during high-temperature oxidation and suppressing the formation of leaf-like hematite.
[0031]
The coupling agent may be any of a silane coupling agent, a titanium coupling agent, an aluminum coupling agent, and a zirconium coupling agent, and two or more types may be used in combination. When the content of the coupling agent in the organic resin film is 2% or less, the above-described effects cannot be substantially obtained. When the content of the coupling agent exceeds 50%, the viscosity of the resin liquid used for forming the film increases. The preferred content of the coupling agent is 3 to 25%.
[0032]
Adding a metal oxide to the organic resin coating means that when applying the organic resin coating to the surface of the galvanized steel strip, silica {eg, colloidal silica) is added for the purpose of improving corrosion resistance in a low temperature range. Has been done. The present inventors have found that, when not only silica but also a metal oxide is dispersed in an appropriate amount in an organic resin film, formation of foliated hematite during high-temperature oxidation is suppressed. In the process of burning and burning the organic resin film during high-temperature oxidation, the metal oxide in the film remains and gradually covers the steel strip surface. As a result, it is presumed that the production of leaf-like hematite is suppressed on the steel strip surface without excessive oxygen being supplied. As described above, the metal oxide in the coating does not decompose during combustion at a high temperature and remains on the surface of the steel strip in a state of the metal oxide, and adheres firmly.
[0033]
As the metal oxide, SiO₂, Fe₃O₄, Fe₂O₃, Ni-O, Zr-O, Cr₂O₃And Al₂O₃At least one selected from the group consisting of: This metal oxide is preferably used in the form of sol or submicron fine particles. The content of the metal oxide in the resin film is 2 to 80%. If the amount is less than 2%, the above-described effect cannot be substantially obtained. If the amount of the metal oxide is more than 80%, the viscosity of the resin liquid used for forming the film becomes too high, and the adhesion of the film decreases. The negative effects of the come out. The preferred content of the metal oxide is 5 to 50%.
[0034]
The organic resin film may contain wax dispersed in the film in order to provide the steel strip with excellent press workability capable of deep drawing. In this case, the wax has a particle diameter φ (μm) and a thickness T (μm) of the organic resin film {(φ / T)} satisfying the relation of {0.5 ≦ φ / T ≦ 5}. Use When the φ / T ratio exceeds 5, the wax is too large relative to the thickness of the coating, and the wax is liable to fall off, so that not only the effect of improving the press workability is not obtained, but also the corrosion resistance is lowered due to the wax falling off. On the other hand, when the φ / T ratio is smaller than 0.5 °, the wax is too small, and the effect of improving the press workability by adding the wax is not substantially obtained. The φ / T ratio is preferably in the range of 1-3.
[0035]
The content of the wax is such that the area ratio occupied by the wax when the coating surface is observed with an electron microscope is 2 to 20%. If the area ratio is less than 2%, the effect of improving the press workability is small, and if it exceeds 20%, the material becomes slippery, and it becomes difficult to handle the material as when Ra is too small. The area ratio of the wax is preferably in the range of 5 to 15%.
[0036]
The wax is preferably made of C, H or C, H, O or C, H, O, N for the same reason as the resin. Preferred waxes are synthetic waxes such as polyethylene waxes, fatty acid amide waxes, and petroleum-based waxes such as paraffin wax.
[0037]
The organic resin film may be colored with a coloring agent. The colorant is selected from those which do not generate corrosive gases when burned.
The organic resin film may be formed on only one side of the base steel strip, but is preferably formed on both sides.
[0038]
Next, the method for producing a steel strip according to the present invention will be described.
Base steel strip
Prepare a cold rolled steel strip or pickled hot rolled steel strip to be the base material. The cold-rolled steel strip is manufactured by passing a hot-rolled coil through a continuous cold rolling mill and cold-rolling the strip to almost a target thickness. By using the surface dull roll as the rolling roll, the surface of the steel strip can be dulled during cold rolling, and the surface roughness can be adjusted to a predetermined value within the range of {0.2 to 3 μm} Ra.
[0039]
The surface roughness of the steel strip can also be adjusted by performing temper rolling later. When the surface roughness is desired to be relatively large, the surface roughness can be given by shot blasting or the like.
[0040]
It is preferable that the cold-rolled material is annealed in order to recrystallize and grow grains of the rolled structure expanded into a fibrous shape by cold rolling. Thereby, the magnetic properties of the cold-rolled steel strip are improved. The annealing method may be either box annealing or continuous annealing. Generally, this annealing is carried out with N to prevent oxidation of the steel strip surface.₂Or N₂+ H₂The annealing temperature is usually in the range of {500 to 900} ° C.
[0041]
Finally, for the purpose of flattening the steel strip in the case of annealing and eliminating the stretcher strain and / or adjusting the surface roughness, temper rolling can be finally performed. In the case of the inner magnetic shield material, since the temper rolling reduces the magnetic properties, it is desirable to perform as little as possible or not.
[0042]
In the case of a hot-rolled steel strip, a pickled steel strip is used to remove a surface oxide film generated by hot rolling. The surface roughness of the hot-rolled steel strip can be adjusted, for example, by the surface roughness of the finishing roll.
[0043]
It is preferable to form an organic resin film after pre-treating the base steel strip in advance. Thereby, red discoloration due to the formation of leaf-like hematite during high-temperature oxidation can be further prevented. The reason is presumed as follows.
[0044]
Generally, the steel surface is microscopically non-uniform, and there are portions that are easily oxidized and portions that are hardly oxidized, so that the high-temperature oxidation reaction also proceeds microscopically non-uniformly. As a result, an oxide film having a non-uniform thickness is formed, and at the same time, foliate hematite grows, and the appearance becomes red rust and dusty. As described above, the foliated hematite easily falls off, for example, adversely affecting the life of the CRT.
[0045]
If the steel surface is microscopically uniform by pre-treatment, the high-temperature oxidation reaction will proceed microscopically uniformly, and the relatively mild oxidation environment generated by the combustion decomposition of the resin will produce more foliated hematite. It is effectively prevented, and a black magnetite-based coating is easily formed.
[0046]
In order to obtain this effect, the pretreatment includes (1) an acid selected from hydrochloric acid, sulfuric acid, nitric acid and a mixed acid of two or more of these acids, or (2) {Ni, Co, Fe, Zr, Sb, V , Mo, W, or an acidic solution containing ions of at least one metal selected from the group consisting of Mo and W.
[0047]
(1) The pretreatment with the acid (1) removes inactive portions on the surface of the steel strip and makes it uniform. On the other hand, in the pretreatment with an acidic solution containing metal ions in (2) above, active portions are repaired with metal ions and the surface is made uniform. Both (1) and (2) are effective in a single treatment, but the effect is further improved if both are used together. In that case, any of (1) and (2) may be performed first, and there is no need to wash with water, but washing with water is also possible.
[0048]
The pretreatment is performed by applying the solution of (1) or (2) to a steel strip. Application can be performed by any convenient method, such as dipping, spraying, roll coating, etc., but the simplest is dipping. The temperature of the treatment solution used for the pretreatment is preferably room temperature to about 85 ° C., and the concentration of the treatment solution is (0.2) to 3% in the case of the acid (1), and (2) the acid solution containing the metal ion of (2). In this case, the range of $ 0.2 to 50% is appropriate. The solution (2) may be, for example, an aqueous solution of a metal sulfate, hydrochloride or nitrate, and it is preferable to add an acid as needed to adjust the solution pH to a range of 2 to 5. In the case of dip coating, the dipping time is preferably from 1 second or less to about 10 seconds.
[0049]
The pretreated steel strip can form an organic resin coating after or without washing with water. Washing with water after the pretreatment may improve the effect of suppressing the formation of leaf-like hematite in the sealing step, particularly when both pretreatments (1) and (2) are used in combination. In any case, it is more effective to wash the steel strip with hot water {for example, 60 to 90 ° C.}.
[0050]
The above pretreatment is preferably performed after the steel strip is first degreased with an alkali. Alkaline degreasing removes oil and dirt adhering to the steel strip surface, and makes it easier for the resin to adhere to the steel strip surface. Therefore, the adhesion of the formed organic resin film is enhanced. However, since alkali degreasing hardly affects the high-temperature oxidation reaction, the generation of leaf-like hematite can be prevented even if alkali degreasing is omitted. Since the pretreatment is an acidic treatment, when the alkali degreasing is performed, the steel strip is thereafter washed with water and then the pretreatment is performed. Note that if alkali degreasing is performed after the above pretreatment, the effect of the pretreatment is lost, so that alkali degreasing is performed before the pretreatment.
[0051]
In order to make the surface of the steel strip microscopically uniform, metal plating may be applied to the surface of the steel strip as a base treatment instead of the above pretreatment. When metal plating is applied to the underlayer, the non-uniformity of the steel strip surface is improved, and the steel strip surface is covered with metal, so that the same effect as containing a coupling agent or a metal oxide in the coating can be obtained. Yes, the formation of leaf-like hematite can be effectively suppressed.
[0052]
When the metal plating is performed as the base treatment, the pretreatment described above is not necessary, but the pretreatment can be performed after the plating.
As the metal plating, plating of a metal composed of Ni, Cr or Fe or an alloy containing the metal as a main component can be used, and the plating adhesion amount is {0.1 to 20} g / m.²Is suitably within the range. This base plating film is preferably formed by electroplating, but other plating methods such as electroless plating are also possible. Unlike the Ni plating described as the prior art, no annealing is performed after this metal plating.
[0053]
Formation of organic resin film
An organic resin film having a thickness of {0.1 to 6 μm} is formed on a steel strip. The organic resin film is preferably formed by applying and baking a resin solution according to a conventional method. However, depending on the resin, other drying methods such as photocuring and room temperature drying can be employed. The resin liquid may be a solvent type or an aqueous type, and may be a solution type, a dispersion type or an emulsion type. From an environmental point of view, it is preferable to use an aqueous resin solution.
[0054]
When the organic resin film contains one or both of the above-described coupling agent and metal oxide, and / or wax, these additional components are added to the resin solution in an appropriate amount, respectively, and dissolved or dispersed. .
[0055]
The application of the resin liquid is often performed by roll application from the viewpoint of production efficiency and control of the film thickness, but other application methods such as curtain flow application, spray application, and dipping can also be adopted. The baking is performed at a temperature necessary for curing the coating according to the type of the resin.
[0056]
It is preferable from the viewpoint of operation efficiency that the above-mentioned respective processing steps are continuously performed {on one line} for the base steel strip.
[0057]
【Example】
(Example 1)
Using the composition shown in Table 1 (remainder: Fe and unavoidable impurities), a cold-rolled steel strip having a thickness of 0.15 mm was produced by hot rolling and cold rolling. This cold-rolled steel strip is subjected to N₂After annealing by heat treatment at 800 ° C. for 5 seconds in an atmosphere, temper rolling was performed. By changing the rolls used for the temper rolling and the rolling conditions, cold rolled steel strips having different surface roughness were produced.
[0058]
[Table 1]

[0059]
In this example, a cold-rolled steel strip having a surface roughness of 0.5 μm Ra was subjected to a pretreatment shown in Table 2 on a continuous line, and then rolled and baked with a resin liquid on both sides to obtain a thickness of 1.7. A μm urethane-based organic resin film {(containing no added component)} was formed.
[0060]
The conditions for each treatment described in Table 2 were as follows:
Alkaline degreasing: Sodium hydroxide 1%, immersion at 60 ° C for 2 seconds;
Hot water washing: immersion in water at 80 ° C for 2 seconds;
Solution (1): sulfuric acid 1%, immersion at 60 ° C for 2 seconds;
Solution (2): Nickel sulfate 10% {(pH 4)}, immersion at 60 ° C for 2 seconds.
[0061]
The resin liquid used was a resin liquid for a commercially available water-based urethane paint, and the baking conditions after coating were at a temperature of about 120 ° C. for 10 seconds. After baking, the steel strip was air-cooled and wound on a coil.
[0062]
The coatability and reddening of each of the obtained steel strips were examined as follows.
Paintability
The finished appearance of the baked material was visually observed, and the presence or absence of coating unevenness was evaluated. Further, this material was subjected to ultrasonic cleaning with alcohol or trichloroethylene, and after the cleaning, it was checked whether or not the coating film had fallen off, and the adhesion of the coating film was evaluated.
[0063]
：: No coating unevenness, no loss of coating film by ultrasonic cleaning,
：: coating unevenness is slightly generated, but not cissing, and there is no falling off of the coating film by ultrasonic cleaning.
×: Remarkable coating unevenness with repelling is generated, and the coating film is detached even by ultrasonic cleaning.
[0064]
Red denaturation
The coated and baked material was subjected to heat treatment at 450 ° C. × 120 ° in the air, and the degree of red discoloration (generation of leaf-like hematite) after the heat treatment was evaluated with a microscope and visually.
[0065]
：: no redness (redness cannot be recognized visually or under a microscope),
○: Almost no red discoloration (almost no red discoloration can be visually recognized),
Δ: Slight red discoloration (a slight red discoloration can be visually recognized),
X: Discoloration is remarkably red (the leaf-like hematite is powdery, and red discoloration can be clearly confirmed visually).
[0066]
[Table 2]

[0067]
As can be seen from Table 2, pretreatment with solution (1) or (2) improves reddening, and pretreatment with both solutions (1) and (2) further improves reddening. Is done. Therefore, these pretreatments have the effect of preventing red discoloration due to the formation of foliar matite {(red rust)} during high temperature oxidation. Alkaline degreasing alone cannot prevent the formation of foliate hematite at all. The paintability is good in each case.
[0068]
(Example 2)
In the same manner as in Example 1, a urethane-based organic resin film was formed on the pretreated cold-rolled steel strip. The cold rolled steel strip used, the pretreatment method, and the thickness of the resin film were the same as in Example 1. Table 3 also shows the test results of paintability and reddening evaluated in the same manner as in Example 1.
[0069]
In this example, the pretreatment was performed according to the procedure shown in Table 3, and as the organic resin film, as shown in Table 3,
・ Only organic resin {(A)},
-Contains coupling agent B {(A + B)},
-Contains metal oxide C {(A + C)},
Containing both coupling agent B and metal oxide C {(A + B + C)},
4 types were formed.
[0070]
The organic resin A is the same resin solution for a commercially available water-based urethane paint as in Reference Example 1, the coupling agent B is a silane coupling agent {(γ-glycidoxypropyltrimethoxysilane)}, and the metal oxide C Was colloidal silica. The amount of addition was 20% for B and 30% for C based on the total solids in the resin solution.
[0071]
[Table 3]

[0072]
From Table 3, it can be seen that when the organic resin film contains either the coupling agent B or the metal oxide C, the red modification {(prevention of foliar hematite formation)} is improved, and when both B and C are contained, the red modification is further improved. You can see that As a result, even if an organic resin film is formed on a steel strip only subjected to alkali degreasing without performing pretreatment with an acid or an acidic aqueous solution, reddening is improved.
[0073]
With respect to the sample having the best red discoloration, the state of the surface coating of the test piece heat-treated in the red discoloration test was examined by X-ray diffraction. As a result, the magnetite (Fe₃O₄) Only diffraction peaks attributed to and ground iron (Fe) appeared, and it was confirmed that a film mainly composed of magnetite was formed by the heat treatment.
[0074]
(Example 3)
Test Nos. In Tables 2 and 3 The organic resin film of A + B + C described in 1 was further added with different amounts of wax having various particle sizes to form an organic resin film.
[0075]
That is, a cold-rolled steel strip having a surface roughness of 0.5 μm Ra was pretreated continuously in the order of alkali degreasing → water washing → solution (1) (sulfuric acid solution) coating⇒water washing. Thereafter, in the same line, the resin solution was roll-coated and baked in the same manner as in Example 1 to obtain steel strips having different coating film thicknesses.
[0076]
The resin solution used was the same urethane resin solution as used in Reference Example 1, and a commercially available resin solution for water-based paint was used. A silane coupling agent and colloidal silica were added to this resin solution in the same type and amount as in Reference Example 2, based on the total solid content in the resin solution, in addition to the wax.
[0077]
Table 4 shows the particle size of the wax used (φ), the thickness of the organic resin film (T), the ratio of φ / T, the area ratio of the wax particles (D), and the press evaluated by the deep drawing cylindrical drawing test. The results of workability are shown.
[0078]
The area ratio of wax particles {(D)} is the area ratio of wax particles that can be confirmed when the surface of the organic resin film is observed with an electron microscope {(SEM)}.
The cylindrical drawing test was performed with a punch diameter of 50 mm, a punch shoulder R of 2 mm, a die shoulder of 2 mm, a wrinkle holding force of 500 kgf, and a drawing ratio of 1.8 mm. evaluated.
[0079]
[Table 4]

[0080]
From Table 4, when the φ / T ratio of the wax is in the range of 0.5 to 5 and the area ratio of the wax is in the range of 2 to 20%, the steel strip has excellent press workability that can be deep drawn. You can see
[0081]
(Example 4)
Various cold-rolled steel strips having different surface roughness were used as test Nos. In Table 2 of Reference Example 1. According to No. 7, alkali degreasing → water washing → solution (1) (sulfuric acid solution) coating → solution (2) (nickel sulfate solution) coating → hot water washing were successively performed in this order. Thereafter, in the same line, the resin solution was roll-coated, and baked in the same manner as in Example 1 to form an organic resin film on the surface of the steel strip.
[0082]
The resin solution used was a urethane-based resin solution or a mixed resin solution of a urethane-based resin and an acrylic resin, and a commercially available resin solution for water-based paint was used. Silica sol was added as a metal oxide to some resin liquids.
[0083]
Table 5 shows the surface roughness (Ra), resin type, resin coating thickness (T) of the cold-rolled steel strip, and the ratio of T / Ra.
The press workability, spot weldability, corrosion resistance, and film flammability of these steel strips were investigated as follows. Table 5 also shows the results of these tests.
[0084]
Press workability
Using a press machine equipped with an uncoiler, punching and press working with a bending mold or drawing mold were performed while feeding the coiled steel strip with a major roll.
[0085]
In tests other than the conventional material, slipping on the measure roll when sending out the material during this press working, and peeling property of the punched blank (blanks conveyed in a stacked state did not come into close contact and peeled, The press workability was evaluated as follows according to whether the blanks were conveyed to a press machine with overlapping).
[0086]
：: A predetermined length of material can be sent out without causing slippage when sending out the material by the measure roll, the blank has good releasability after punching, and no problem occurs in a series of press working steps. ;
Δ: There is no slippage when the material is sent out by the measure roll, but there is a tendency that a trouble occurs in which a plurality of blanks are transported to the press machine after the punching process;
×: Slip occurs when the material is fed out by the measure roll, and a series of press working steps cannot be stably operated.
[0087]
Spot weldability
The actual conditions of use vary slightly depending on the material user. Therefore, as an average condition, spot welding is performed under the following conditions, and the welding conditions (whether or not there is no electricity, generation of dust, size, Of the electrode tip, etc.) was examined.
[0088]
Tip: Top and bottom, ball tip of 5mm diameter, pure Cu
Load: $ 5kgf
Current: {600} A
Cycle: 6 cycles
：: 10,000 or more dots (the number of dots that can be welded satisfactorily by forming a nugget with normal energization and by reducing chip wear)
Δ: 5000-10000 ° RBI,
X: Normal welding cannot be performed with less than 5000 spots.
[0089]
Corrosion resistance
A test piece obtained by cutting a steel strip to a size of 50 mm x 100 mm is coated with a general rust-preventive oil for steel sheets (mineral oil) and then degreased and washed under standard conditions. And subjected to an atmospheric exposure test. The air exposure test was carried out for 30 days in an environment where the test piece was not wet by rain or the like. Corrosion resistance was determined as follows according to the state of rusting of the test specimen after 30 days.
[0090]
：: no rust is generated,
Δ: Some spot rusting occurred
×: considerable rust occurred.
[0091]
The observation period was limited to 30 days because, in the production process of inner magnetic shields and the like that are oxidized at high temperatures, no additional storage period is required unless there is any accident. This is because the condition was more corrosive than the environment of the actual use site, and it was determined that the observation period of 30 days was appropriate.
[0092]
Film flammability
After applying a general rust-preventive oil for steel sheets (mineral oil system) to the surface of the same test piece as above, degreasing and washing were performed with a degreasing and washing time as short as possible as long as the cold-rolled steel sheet could be degreased. Thereafter, the substrate was heated at 450 ° C. for 40 minutes in an air atmosphere. The heating conditions are set on the assumption of a cathode ray tube sealing step. Residual resin on the surface of the test piece after heating was determined by EPMA analysis. In addition, the amount of gas generated during the heat treatment was measured with time, and it was confirmed whether or not gas generation was completed during the sealing step, and the gas sample was subjected to TG-MS and Pyro-GC-MS. The analysis was performed to determine whether or not a corrosive gas containing S, Cl, F, and the like was generated, and the determination was made as follows.
[0093]
：: When no resin remains after the heat treatment under the above conditions, generation of gas ends during the heat treatment, and no corrosive gas is generated,
×: Residual resin was observed, gas generation was not completed during heat treatment, or corrosive gas was generated.
[0094]
[Table 5]

[0095]
As can be seen from Table 5, if the surface roughness of the steel strip is smaller than 0.2 μm Ra, the press workability is deteriorated, and if it is larger than 3 μm Ra, the corrosion resistance is deteriorated. The spot weldability begins to decrease when the T / Ra ratio is greater than 2.5 °, and becomes significantly worse when the T / Ra ratio is greater than 4. When the T / Ra ratio is less than 0.4 °, the corrosion resistance starts to decrease. In particular, when the T / Ra ratio is less than 0.2 °, the corrosion resistance significantly decreases.
[0096]
When the metal oxide is contained in the organic resin film according to the present invention, the reddening at the time of high-temperature oxidation is improved as shown in Example 1. It did not inhibit.
[0097]
(Example 5)
Cold rolling with a surface roughness of {0.5 μm {Ra} and a thickness of 0.15 mm} was performed by hot rolling and cold rolling using low-carbon aluminum killed steels a to e having the compositions shown in Table 6 (remainder: Fe and unavoidable impurities). A steel strip was obtained. This cold rolled steel strip is N₂Annealing was performed by heat treatment at 800 ° C. for 5 seconds in an atmosphere.
[0098]
This cold-rolled steel strip was subjected to Test No. According to 3, pretreatment was carried out by the procedure of alkaline degreasing → water washing. Each processing condition was the same as in Example 1.
A 1.7-μm-thick urethane-based organic resin film was formed on both surfaces of the pretreated cold-rolled steel strip in the same manner as in Example 1 to produce a steel strip.
[0099]
The test piece of the steel strip thus obtained was subjected to a heat treatment of heating at 450 ° C. for 120 minutes in the air to simulate the sealing process of a cathode ray tube, and the adhesion of the scale after the heat treatment was peeled off with a cellophane tape (R). The test was evaluated according to the following criteria. Further, the redness of the appearance was evaluated based on the same criteria as in Example 1 above. The results are also shown in Table 6.
[0100]
Scale adhesion
：: Good adhesion of scale, no peeling at all,
Δ: May peel slightly,
×: Delamination occurs, and the scale peels in a film shape.
[0101]
[Table 6]

[0102]
From Table 6, it can be seen that the steel composition, according to a preferred embodiment of the present invention, has the following conditions:
[Si] ≧ 0.02, 0.25 ≦ [Si] + [Al] ≦ 0.55, 0.05 ≦ [Al] − [Si] ≦ 0.3
It can be seen that, when all of the conditions are satisfied, the adhesion is good at the time of high-temperature oxidation, and an iron oxide film (scale) mainly composed of magnetite is formed.
[0103]
【The invention's effect】
According to the present invention, the resistance to reddening at high temperatures, which was conventionally possible only by forming a blackening film using a special heat treatment furnace capable of adjusting the oxygen atmosphere, is a simple means of forming an organic resin film. Can be applied to the steel strip. As a result, the press working can be carried out without any trouble, while exhibiting sufficient corrosion resistance even after the press working, and at the time of high-temperature oxidation, the resin film is completely burned and decomposed without generating harmful gas, preventing the formation of leaf-like hematite As a result, a magnetite-based oxide film similar to the blackened film is formed, and the steel strip is given high-temperature corrosion resistance to withstand subsequent oxidation.
[0104]
Therefore, the steel strip of the present invention is particularly useful in applications where blackening treatment was conventionally required after press working, and costly blackening treatment is not required, so that the economic effect is high.

Claims (15)

At least one surface of a steel strip having a surface roughness of {0.2-3 μm} Ra having a thickness of {0.1-6 μm} of an organic resin consisting essentially of C, H or C, H, O or C, H, O, N A steel strip having excellent resistance to reddening during high-temperature oxidation, characterized by having: The steel strip according to claim 1, wherein a ratio (T / Ra) of the thickness T of the organic resin film to the surface roughness Ra of the steel strip is {0.2 to 4.0}. The organic resin coating comprises (a) a total of 2 to 50% by mass of at least one coupling agent, and (b) a total of _{2 to} 80% by mass of SiO ₂ , Fe ₃ O ₄ , Fe ₂ O ₃ , and Ni—O. The steel strip according to claim 1, comprising one or both of at least one metal oxide selected from the group consisting of Zr—O, Zr—O, Cr ₂ O ₃ and Al ₂ O ₃ . The organic resin film contains wax dispersed in the film, the ratio {(φ / T)} of the particle size φ of the wax to the thickness T of the organic resin film is {0.5 to 5}, and the content of the wax is determined by an electron microscope. The steel strip according to any one of claims 1 to 3, wherein the amount of the wax occupied by the wax is 2 to 20% when the surface of the coating is observed with the steel strip. The steel strip according to any one of claims 1 to 4, wherein the organic resin decomposes and decomposes when heated at 450 ° C or lower in the atmosphere. The metal coating made of Ni, Cr or Fe or an alloy containing the metal as a main component has a plating film having an adhesion amount of 0.1 to 20 g / m ^{2 on} a base of the organic resin film. The steel strip described in the above. The Si and Al contents (% by mass) of the steel strip are as follows:
[Si] ≧ 0.02, 0.25 ≦ [Si] + [Al] ≦ 0.55, 0.05 ≦ [Al] − [Si] ≦ 0.35
The steel strip according to any one of claims 1 to 6, which satisfies the following. At least one surface of the cold-rolled steel strip or the pickled hot-rolled steel strip is coated with an organic resin essentially consisting of C, H or C, H, O or C, H, O, N to a thickness of {0.1 to 6 μm}. A method for producing a steel strip having excellent resistance to reddening during high-temperature oxidation. The method for producing a steel strip according to claim 8, wherein the ratio (T / Ra) of the thickness T of the organic resin film to the surface roughness Ra of the steel strip is {0.2 to 4.0}. Before forming the coating on the steel strip, (1) an acid selected from hydrochloric acid, sulfuric acid, nitric acid and a mixed acid of two or more of these acids; and (2) an acid selected from Ni, Co, Fe, Zr, Sb, The method for producing a steel strip according to claim 8 or 9, wherein a pretreatment for applying one or both of an acidic solution containing ions of at least one metal selected from V, Mo, and W is performed. The cold-rolled steel strip or the pickled hot-rolled steel strip is plated with a metal composed of Ni, Cr or Fe or an alloy containing the metal as a main component before the coating is formed, and the adhesion amount is 0.1 to 20 g. The method for producing a steel strip according to any one of claims 8 to 10, wherein a plating film of / m ² is formed. The organic resin coating comprises (a) a total of 2 to 50% by mass of at least one coupling agent, and (b) a total of _{2 to} 80% by mass of SiO ₂ , Fe ₃ O ₄ , Fe ₂ O ₃ , and Ni—O. , Zr-O, at least one metal oxide selected from _Cr 2 _{O 3} and _Al 2 _{O 3,} containing one or both of the method for producing a steel strip according to any of claims 8-11. The organic resin film contains wax dispersed in the film, the ratio {(φ / T)} of the particle size φ of the wax to the thickness T of the organic resin film is {0.5 to 5}, and the content of the wax is determined by an electron microscope. The method for producing a steel strip according to any one of claims 8 to 12, wherein the area ratio of the wax occupied when the surface of the coating film is observed at 2 to 20% is 2 to 20%. The method for producing a steel strip according to any one of claims 8 to 13, wherein the organic resin is decomposed by combustion at a temperature of 450 ° C or lower in the atmosphere. A steel strip excellent in high-temperature oxidation resistance, obtained by heating the steel strip according to any one of claims 1 to 7 in an oxidizing atmosphere to burn and decompose the organic resin.