JP4458610B2 - Hot-dip aluminized steel sheet with excellent high-temperature oxidation resistance - Google Patents
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Description
【０００１】
【産業上の利用分野】
本発明は、８５０℃以上の高温雰囲気に耐え得る構造材として使用され、耐高温酸化性及び高温強度に優れ、且つ室温での加工性も良好な溶融アルミニウムめっき鋼板に関する。
【０００２】
【従来の技術】
８００℃以上の高温雰囲気で優れた耐高温酸化性を示す材料として、Ｃｒを約１０質量％以上含有する各種ステンレス鋼が従来から使用されている。ステンレス鋼は，表層に生成するＣｒ系酸化物皮膜（不動態皮膜）の保護的作用によって優れた耐高温酸化性を示すものの、鋼材コストが高いことが欠点である。そこで、普通鋼を母材として鋼板表面に溶融アルミニウムめっきを施すことにより，耐高温酸化性を改善した溶融アルミニウムめっき鋼板が実用化されている。
たとえば、特開昭５６−１０２５２３号公報では、極低炭素Ｔｉ添加鋼をベースとして溶融アルミニウムめっきを施し、アルミニウムめっき鋼板としては比較的高温での耐高温酸化性を改善した溶融アルミニウムめっき鋼板を製造する方法が紹介されている。
【０００３】
特開昭５６−１０２５５６号公報では、５質量％までのＣｒを含有する極低炭素Ｔｉ添加鋼をベースとして溶融アルミニウムめっきを施すことにより耐熱性を改善しためっき鋼板が紹介されている。これらの溶融アルミニウムめっき鋼板は、８３０℃の高温雰囲気で良好な耐高温酸化性を呈することが実施例で紹介されている。
ステンレス鋼以外に無垢材として８５０℃を超える高温雰囲気で優れた耐高温酸化性を呈する材料としては、ＦｅにＡｌを含有させたＦｅ−Ａｌ合金が古くから知られている。
【０００４】
【発明が解決しようとする課題】
普通鋼を母材とした通常の溶融アルミニウムめっき鋼板の使用可能な温度は、高くても８３０℃程度に過ぎない。Ｃｒを５質量％程度まで添加した鋼板をベースにした溶融アルミニウムめっき鋼板は、僅かに耐高温酸化性が改善されるものの、８５０℃を超える高温雰囲気に曝されると短時間で異常酸化し、通常の使用に耐えられなくなる。
他方、Ｆｅ−Ａｌ合金は、耐高温酸化性に優れるものの、単純なＦｅ−Ａｌ二元系では構造材として十分な高温強度が得られない。Ｆｅ−Ａｌ合金のＡｌ含有量を増加させＦｅ3Ａｌ，ＦｅＡｌ等の規則合金を作ることにより高温強度を向上させることも可能であるが、これらの規則合金は室温での靭性に劣るため薄板材の製造が非常に困難である。
【０００５】
【課題を解決するための手段】
本発明は、このような問題を解消すべく案出されたものであり、無垢材としても８５０℃を超える高温雰囲気での使用に耐える優れた耐高温酸化性及び高温強度をもつと共に、室温での加工性にも優れ、ステンレス鋼に比較して安価な溶融アルミニウムめっき鋼板を得ることを目的とする。
本発明者等は、耐高温酸化性に優れた溶融アルミニウムめっき鋼板について種々調査検討した結果、Ｃ：０．０１質量％以下，Ｓｉ：０．０２〜２．０質量％，Ｍｎ：０．２４〜２．５質量％，Ｐ：０．０２質量％以下，Ａｌ：１〜１０質量％，Ｓ：０．０１０質量％以下，Ｎ：０．０１０質量％以下を含み、残部がＦｅと不可避的不純物からなる組成を基本組成にする鋼板を基材に使用するとき、８５０℃以上の高温雰囲気で十分使用に耐え得る耐高温酸化性及び高温強度が得られ、しかも室温での加工性も確保されることを見出した。
【０００６】
この基本組成にＴｉ，Ｎｂ，Ｍｏ，Ｖの１種又は２種以上を合計で０．０１〜０．３質量％添加するとき、室温での加工性を大きく劣化させることなく高温強度が更に改善される。なお、Ｔｉ，Ｎｂ，Ｍｏ，Ｖの１種又は２種以上を含む鋼にあっては、Ｓｉ含有量は０．０１質量％以上２．０質量％以下であってもよい。
耐高温酸化性は、Ｌａ，Ｃｅ，Ｎｄ，Ｙの１種又は２種以上を合計で０．０１〜０．２質量％、或いはＣｒ：１〜８質量％を添加するとき一層向上する。また、構造材としてプレス加工する際の耐二次加工割れ性は、Ｂ：０．０００２〜０．００２質量％を添加することにより改善される。
【０００７】
【作用】
以下、本発明で基材に使用される高Ａｌ鋼板に含まれる合金成分，含有量等を説明する。
Ｃ：０．０１質量％以下
耐高温酸化性及び室温での加工性に悪影響を及ぼす合金成分であり、可能な限りＣ含有量を低くすることが好ましい。しかし、過度の脱炭は製造コストを上昇させる原因となるので、本発明においてはＣによる悪影響が現れない０．０１質量％を上限に設定した。
Ｓｉ：０．０１〜２．０質量％
耐高温酸化性及び高温強度の改善に有効な合金成分であり、０．０１質量％以上でＳｉの効果が顕著になる。しかし、２．０質量％を超える過剰量のＳｉが含まれると、室温での加工性及び耐二次加工割れ性が劣化する。
【０００８】
Ｍｎ：０．０５〜２．５質量％
高温強度の改善に有効な合金成分であり、０．０５質量％以上でＭｎの効果が顕著になる。しかし、２．５質量％を超える過剰量のＭｎが含まれると、室温での加工性及び耐二次加工割れ性が劣化する。
Ｐ：０．０２質量％以下
高温強度の改善に有効な合金成分であるが、粒界に偏析し室温及び低温での靭性に悪影響を及ぼす。靭性に及ぼすＰの影響は、Ｃ含有量を低減した成分系では顕著になる。この点、Ｐ含有量は可能な限り低いことが好ましく、本発明では上限を０．０２質量％に設定した。
【０００９】
Ａｌ：１〜１０質量％
耐高温酸化性の改善に必須の合金成分であり、８５０℃以上の高温雰囲気での使用に耐え得る耐高温酸化性を得るため１質量％以上のＡｌ含有量が必要である。耐高温酸化性の観点からはＡｌ含有量が多いほど好ましいが、１０質量％を超える過剰量のＡｌが含まれると非常に硬質で脆いＦｅ3Ａｌ規則合金が生成し、室温での加工性が大きく劣化する。
Ｓ：０．０１０質量％以下
耐高温酸化性及び室温での加工性に悪影響を及ぼす有害成分であり、可能な限りＳ含有量を低減することが好ましく、本発明ではＳ含有量の上限を０．０１０質量％に設定した。
Ｎ：０．０１０質量％以下
耐高温酸化性及び室温での加工性に悪影響を及ぼす有害成分であり、可能な限りＮ含有量を低減することが好ましく、本発明ではＮ含有量の上限を０．０１０質量％に設定した。
【００１０】
Ｔｉ，Ｎｂ，Ｍｏ，Ｖの１種又は２種以上：合計で０．０１〜０．３質量％
必要に応じて添加される合金成分であり、高温強度を向上させる作用を呈する。Ｔｉ，Ｎｂ，Ｍｏ，Ｖ等の添加により高温強度が改善されるメカニズムは必ずしも明確でないが，Ｔｉ，Ｎｂ，Ｍｏ，Ｖ等が鋼中のＳ，Ｃ，Ｎと結合して形成された硫化物，炭化物，炭窒化物等の析出物及びマトリックスに固溶したＴｉ，Ｎｂ，Ｍｏ，Ｖ等が転位の移動を規制するソリュートドラッグ効果によるものと推察される。Ｔｉ，Ｎｂ，Ｍｏ，Ｖ等の添加効果は、０．０１質量％以上で顕著になるが、０．３質量％を超えて添加しても高温強度を向上させる効果が飽和するばかりでなく、室温での加工性及び耐高温酸化性が劣化する。
【００１１】
Ｌａ，Ｃｅ，Ｎｄ，Ｙの１種又は２種以上：合計で０．０１〜０．２質量％
必要に応じて添加される合金成分であり、高温域で生成した保護的なＡｌ系酸化皮膜を緻密化し、耐高温酸化性を一層向上させる作用を呈する。Ｌａ，Ｃｅ，Ｎｄ，Ｙ等の添加効果は、０．０１質量％以上で顕著になるが、０．２質量％を超えて添加しても耐高温酸化性改善効果が飽和し、鋼材コストを上昇させる原因となる。
Ｃｒ：１〜８質量％
必要に応じて添加される合金成分であり、Ａｌと同様に保護的な酸化皮膜を生成し、耐高温酸化性の改善に有効に作用する。Ｃｒの添加効果は、５質量％以上のＡｌと複合添加する系では１質量％以上のＣｒ添加で発現する。しかし、８質量％を超える過剰量のＣｒ添加は、鋼材コストを上昇させる原因となる。
【００１２】
Ｂ：０．０００２〜０．００２質量％
必要に応じて添加される合金成分である。一般的にいって極低炭素鋼では、粒界に偏析するＣ量が少ないため十分な粒界強度が得られず、プレス加工等の強加工を受けた場合に二次加工割れと称されている粒界割れが発生することがある。この点、粒界に偏析しやすいＢを添加すると、粒界強度が向上し耐二次加工割れ性が改善される。耐二次加工割れ性の改善は、０．０００２質量％以上のＢ添加で顕著になるが、０．００２質量％を超える過剰量のＢを添加すると却って室温での加工性が劣化する。
【００１３】
以上のように成分調整された高Ａｌ鋼板は、通常の薄鋼板製造工程で製造できる。得られる高Ａｌ鋼板は、基本的には耐高温酸化性に優れた薄鋼板であるが、電縫鋼管用素材として使用するとき耐高温酸化性に優れた電縫鋼管も得られる。耐食性を改善するため、めっき原板としての使用も可能である。
高Ａｌ鋼板は、常法に従って溶融アルミニウムめっきされるが、溶融アルミニウムめっき浴への導入に先立ってプレＦｅめっきを施しておくと、ピンホール，不めっき等のめっき欠陥がなく密着性の高い溶融アルミニウムめっき層が形成される。電気Ｆｅめっき層を２ｇ／ｍ2以上の目付け量で形成するとき、めっき欠陥の抑制効果が顕著になる。なお、本明細書で言う「電気Ｆｅめっき層」は、Ｂ，Ｐ等を包含する意味で使用している。
【００１４】
【実施例１】
表１の組成をもつ溶鋼を高周波真空溶解炉で溶製し、３０ｋｇの鋼塊に鋳造した。得られた鋼塊を厚み３０ｍｍまで熱間鍛造した後、１２５０℃に加熱し、仕上げ温度９１０℃の熱間圧延により板厚３．２ｍｍの熱延鋼帯とした。
【００１５】
熱延鋼帯を酸洗して表面のスケールを除去した後、板厚１．０ｍｍまで冷間圧延した。次いで、８５０℃×均熱６０秒の短時間焼鈍を施した。
焼鈍材の表面にフラックスを塗布し、６８０℃に加熱した溶融アルミニウムめっき浴（Ａｌ−１０質量％Ｓｉ）中に浸漬し，溶融アルミニウムめっきを施した。冷却後に溶融アルミニウムめっき鋼板の断面を観察したところ、片面当り約１５〜２５μｍ程度の厚みで溶融アルミニウムめっき層が形成されていた。
【００１７】
溶融アルミニウムめっき鋼板から試験片を切り出し、引張試験，耐高温酸化性試験，高温強度試験，耐二次加工割れ性試験に供した。
引張試験では、圧延方向と平行に切り出したＪＩＳ５号引張試験片を用い、室温での引張性質を調査した。耐高温酸化性試験では、直径４５ｍｍの形状に打ち抜いた試験片を９００℃に加熱したマッフル炉に装入し、大気雰囲気中で１００時間保持した後の酸化増量を測定し、酸化増量で耐高温酸化性を評価した。高温強度試験では、平行部１０ｍｍ，標点間距離５０ｍｍの高温引張試験片を使用し、ＪＩＳ Ｇ０５６７に準じて測定した８００℃での降伏強さにより高温強度を評価した。耐二次加工割れ性試験では、絞り比２．５で試験片をカップ成形した後、ドライアイス，液体窒素等で冷却した冷媒中に１５分間保持し、６０度の円錐ポンチで押し広げ試験し、粒界割れが発生しない最低温度を耐二次加工割れ性の限界温度として評価した。
【００１８】
表２及び図１の調査結果にみられるように、Ａｌ含有量が１質量％未満の試験番号１，２では酸化増量が１００ｇ／ｍ2を超えているのに対し、Ａｌ含有量が１質量％以上になると酸化増量が２０ｇ／ｍ2以下となり非常に優れた耐高温酸化性が得られている。耐高温酸化性は、図１に示すようにＡｌ含有量１質量％を境として急激に変わり、Ａｌ含有量の増加に応じて向上しており、Ｃｒや希土類元素（ＲＥＭ）が共存するとき耐高温酸化性が一層向上していることが判る。
【００１９】
室温引張試験での伸びは、Ａｌ，Ｓｉ，Ｍｎの含有量が多くなるに従って低下する傾向が示された。Ａｌが１０質量％を超える試験番号８，Ｓｉが２．０質量％を超える試験番号１１及びＭｎが２．５質量％を超える試験番号１４では、伸びが２０％を下回り、延性に劣っていた。０．０１質量％を超える過剰量のＣを含む試験番号１５においても、延性に劣っていた。
Ｔｉ，Ｎｂ，Ｍｏ，Ｖの１種又は２種以上を含む試験番号１６〜２２，２４，２５では，２８Ｎ／ｍｍ 2 以上の高い高温強度が示されたものの，合計量が０．３質量％を超える試験番号２０では室温での延性及び耐二次加工割れ性に劣っていた。
また、Ｂを含む試験番号２４をＢ無添加以外はほぼ同じ組成をもつ試験番号１６と比較すると、耐二次加工割れ性の限界温度が試験番号１６で−７０℃であるのに対し、試験番号２４では−１１０℃と良好な値を示した。
【００２０】
【実施例２】
表３の組成に成分に調整した溶鋼を連続鋳造して得た鋼塊を、加熱温度１２５０℃，仕上げ温度９００℃，巻取り温度５５０℃の条件で熱間圧延し、板厚３．０ｍｍの熱延鋼帯を製造した。熱延鋼帯を酸洗した後、板厚１．０ｍｍまで冷間圧延し、インライン焼鈍タイプの連続式溶融アルミニウムめっきラインに通板して８５０℃×均熱６０秒の焼鈍を施し、次いで両面当たり８０ｇ／ｍ2の付着量で溶融アルミニウムめっきした。なお、本発明鋼Ｄでは、溶融アルミニウムめっきに先立って片面当り２ｇ／ｍ2の電気Ｆｅ−Ｂプレめっき層を形成した。
【００２２】
得られた冷延鋼帯の引張性質，耐高温酸化性，高温強度及び耐二次加工割れ性を実施例１と同様に調査した。また、コイルのトップ部及びエンド部で発生しがちなめっき欠陥を調査し、めっき欠陥の発生量をコイル全体に対する重量割合で表しためっき不良率を求めた。
表４の調査結果にみられるように、Ａｌ含有量が少ない比較鋼Ａでは、９００℃での酸化増量が１００ｇ／ｍ2を超える非常に大きな値を示した。これに対し、本発明で規定した組成をもつ本発明鋼Ｂ〜Ｄは、９００℃での酸化増量が少なく、他の特性に関しても良好な値を示した。更に、Ａｌ含有量がほぼ等しい本発明鋼Ｃと本発明鋼Ｄとを比較すると、溶融アルミニウムめっきに先立ちＦｅ−Ｂめっき層を形成しておくことによりめっき不良率が低減されていることが判る。
【００２４】
【発明の効果】
以上に説明したように、本発明の溶融アルミニウムめっき鋼板は、耐高温酸化性に優れ、高温強度及び室温での加工性も良好で、高温構造用材として従来から使用されているステンレス鋼よりも安価である。このような高温特性及び加工性を利用し、自動車や各種燃焼機器の部材等、広範な分野に使用される溶融アルミニウムめっき鋼板が提供される。
【図面の簡単な説明】
【図１】 耐高温酸化性に及ぼすＡｌ含有量の影響を表したグラフ[0001]
[Industrial application fields]
The present invention relates to a hot-dip aluminized steel sheet that is used as a structural material that can withstand a high-temperature atmosphere of 850 ° C. or higher, is excellent in high-temperature oxidation resistance and high-temperature strength, and has good workability at room temperature.
[0002]
[Prior art]
Conventionally, various stainless steels containing about 10% by mass or more of Cr have been used as materials exhibiting excellent high-temperature oxidation resistance in a high-temperature atmosphere of 800 ° C. or higher. Although stainless steel exhibits excellent high-temperature oxidation resistance due to the protective action of a Cr-based oxide film (passive film) formed on the surface layer, it has a disadvantage of high steel material cost. Therefore, a hot dip galvanized steel sheet having improved high-temperature oxidation resistance by applying hot dip aluminum plating to the steel sheet surface using plain steel as a base material has been put into practical use.
For example, in Japanese Patent Application Laid-Open No. 56-102523, hot-dip aluminum-plated steel sheet with improved low-temperature oxidation resistance at a relatively high temperature is manufactured by applying hot-dip aluminum plating based on ultra-low carbon Ti-added steel. How to do is introduced.
[0003]
Japanese Unexamined Patent Publication No. 56-102556 introduces a coated steel sheet having improved heat resistance by applying hot-dip aluminum plating based on an ultra-low carbon Ti-added steel containing up to 5% by mass of Cr. It is introduced in the Examples that these hot-dip aluminized steel sheets exhibit good high-temperature oxidation resistance in a high-temperature atmosphere of 830 ° C.
As a material other than stainless steel that exhibits excellent high temperature oxidation resistance in a high temperature atmosphere exceeding 850 ° C. as a solid material, an Fe—Al alloy containing Fe in Al has been known for a long time.
[0004]
[Problems to be solved by the invention]
The usable temperature of a normal hot-dip aluminized steel sheet made of ordinary steel as a base material is only about 830 ° C. at the highest. Although the hot-dip galvanized steel sheet based on the steel sheet to which Cr is added to about 5% by mass is slightly improved in high temperature oxidation resistance, it is abnormally oxidized in a short time when exposed to a high temperature atmosphere exceeding 850 ° C., Unusable for normal use.
On the other hand, the Fe—Al alloy is excellent in high-temperature oxidation resistance, but a simple Fe—Al binary system cannot provide sufficient high-temperature strength as a structural material. It is possible to improve the high temperature strength by increasing the Al content of the Fe-Al alloy and making ordered alloys such as Fe 3 Al, FeAl, etc., but these ordered alloys are inferior in toughness at room temperature, so a thin plate material Is very difficult to manufacture.
[0005]
[Means for Solving the Problems]
The present invention has been devised to solve such problems, and has excellent high-temperature oxidation resistance and high-temperature strength that can withstand use in a high-temperature atmosphere exceeding 850 ° C. as a solid material, and at room temperature. The object is to obtain a hot-dip aluminized steel sheet that is also excellent in workability and is less expensive than stainless steel.
As a result of various investigations and studies on the hot-dip galvanized steel sheet excellent in high-temperature oxidation resistance, the present inventors have found that C: 0.01% by mass or less, Si: 0.02 to 2.0% by mass, Mn: 0.24 -2.5% by mass, P: 0.02% by mass or less, Al: 1-10% by mass, S: 0.010% by mass or less, N: 0.010% by mass or less, with the balance being inevitable with Fe When a steel sheet having a basic composition composed of impurities is used as a base material, high-temperature oxidation resistance and high-temperature strength that can sufficiently withstand use in a high-temperature atmosphere of 850 ° C. or higher are obtained, and workability at room temperature is also ensured. I found out.
[0006]
When one or more of Ti, Nb, Mo, and V is added to this basic composition in a total amount of 0.01 to 0.3% by mass, the high temperature strength is further improved without greatly degrading the workability at room temperature. Is done. In addition, in steel containing 1 type or 2 types or more of Ti, Nb, Mo, and V, Si content may be 0.01 mass% or more and 2.0 mass% or less.
High-temperature oxidation resistance is further improved when one or more of La, Ce, Nd, and Y are added in a total amount of 0.01 to 0.2% by mass, or Cr: 1 to 8% by mass. Moreover, the secondary work cracking resistance at the time of press working as a structural material is improved by adding B: 0.0002 to 0.002 mass%.
[0007]
[Action]
Hereinafter, the alloy component, content, etc. contained in the high Al steel plate used for the base material in the present invention will be described.
C: 0.01% by mass or less C is an alloy component that adversely affects high-temperature oxidation resistance and workability at room temperature, and the C content is preferably as low as possible. However, excessive decarburization causes an increase in production cost, and therefore, in the present invention, the upper limit is set to 0.01% by mass at which no adverse effect due to C appears.
Si: 0.01-2.0 mass%
It is an alloy component effective for improving high-temperature oxidation resistance and high-temperature strength, and the effect of Si becomes remarkable at 0.01% by mass or more. However, when an excessive amount of Si exceeding 2.0% by mass is contained, workability at room temperature and resistance to secondary work cracking deteriorate.
[0008]
Mn: 0.05 to 2.5% by mass
It is an alloy component effective for improving the high-temperature strength, and the effect of Mn becomes remarkable at 0.05% by mass or more. However, when an excessive amount of Mn exceeding 2.5% by mass is contained, workability at room temperature and resistance to secondary work cracking deteriorate.
P: 0.02 mass% or less Although it is an alloy component effective for improving the high temperature strength, it segregates at the grain boundary and adversely affects the toughness at room temperature and low temperature. The effect of P on toughness becomes significant in a component system with a reduced C content. In this respect, the P content is preferably as low as possible. In the present invention, the upper limit is set to 0.02% by mass.
[0009]
Al: 1 to 10% by mass
It is an alloy component essential for improving high-temperature oxidation resistance, and an Al content of 1% by mass or more is necessary to obtain high-temperature oxidation resistance that can withstand use in a high-temperature atmosphere of 850 ° C. or higher. From the viewpoint of resistance to high-temperature oxidation, it is preferable that the Al content is large. However, when an excessive amount of Al exceeding 10% by mass is contained, a very hard and brittle Fe 3 Al ordered alloy is formed, and the workability at room temperature is improved. Deteriorates greatly.
S: 0.010% by mass or less It is a harmful component that adversely affects high-temperature oxidation resistance and processability at room temperature, and it is preferable to reduce the S content as much as possible. Was set to 0.010 mass%.
N: 0.010% by mass or less It is a harmful component that adversely affects high-temperature oxidation resistance and processability at room temperature, and it is preferable to reduce the N content as much as possible. Was set to 0.010 mass%.
[0010]
One or more of Ti, Nb, Mo and V: 0.01 to 0.3% by mass in total
It is an alloy component added as necessary, and exhibits the effect of improving the high temperature strength. The mechanism by which high temperature strength is improved by the addition of Ti, Nb, Mo, V, etc. is not necessarily clear, but sulfides formed by combining Ti, Nb, Mo, V, etc. with S, C, N in steel Presumably, precipitates such as carbides and carbonitrides and Ti, Nb, Mo, V, and the like dissolved in the matrix are due to a solution drag effect that restricts the movement of dislocations. The effect of addition of Ti, Nb, Mo, V, etc. becomes prominent at 0.01% by mass or more, but even if added over 0.3% by mass, the effect of improving the high temperature strength is saturated, Workability at room temperature and high-temperature oxidation resistance deteriorate.
[0011]
One or more of La, Ce, Nd, Y: 0.01 to 0.2% by mass in total
It is an alloy component that is added as necessary, and has a function of densifying a protective Al-based oxide film generated in a high temperature range and further improving high-temperature oxidation resistance. The effect of addition of La, Ce, Nd, Y, etc. becomes prominent at 0.01% by mass or more, but even if added over 0.2% by mass, the effect of improving high-temperature oxidation resistance is saturated and the steel material cost is reduced. Causes it to rise.
Cr: 1 to 8% by mass
It is an alloy component added as necessary, and forms a protective oxide film similarly to Al, and effectively acts to improve high-temperature oxidation resistance. The effect of adding Cr is manifested by adding 1% by mass or more of Cr in a system in which 5% by mass or more of Al is added in combination. However, addition of an excessive amount of Cr exceeding 8% by mass causes an increase in steel material cost.
[0012]
B: 0.0002 to 0.002 mass%
It is an alloy component added as necessary. Generally speaking, in ultra-low carbon steel, sufficient grain boundary strength cannot be obtained due to the small amount of C segregated at the grain boundary, and it is called secondary cracking when subjected to strong processing such as press working. Intergranular cracking may occur. In this respect, when B which is easily segregated at the grain boundary is added, the grain boundary strength is improved and the secondary work cracking resistance is improved. The improvement in secondary work cracking resistance becomes remarkable when B is added in an amount of 0.0002% by mass or more. However, when an excessive amount of B exceeding 0.002% by mass is added, the workability at room temperature deteriorates.
[0013]
The high Al steel plate whose components are adjusted as described above can be manufactured by a normal thin steel plate manufacturing process. The obtained high Al steel sheet is basically a thin steel sheet excellent in high temperature oxidation resistance, but when used as a material for an ERW steel pipe, an ERW steel pipe excellent in high temperature oxidation resistance can also be obtained. In order to improve the corrosion resistance, it can be used as a plating plate.
High Al steel sheets are hot-dip aluminum plated in accordance with conventional methods, but if pre-Fe plating is performed prior to introduction into the hot-dip aluminum plating bath, there will be no plating defects such as pinholes and non-plating and high adhesion will be achieved. An aluminum plating layer is formed. When the electric Fe plating layer is formed with a basis weight of 2 g / m 2 or more, the effect of suppressing plating defects becomes remarkable. In addition, the “electric Fe plating layer” referred to in the present specification is used to include B, P, and the like.
[0014]
[Example 1]
Molten steel having the composition shown in Table 1 was melted in a high-frequency vacuum melting furnace and cast into a 30 kg steel ingot. The obtained steel ingot was hot forged to a thickness of 30 mm, heated to 1250 ° C., and hot rolled with a finishing temperature of 910 ° C. to form a hot rolled steel strip having a thickness of 3.2 mm.
[0015]
The hot-rolled steel strip was pickled to remove the surface scale, and then cold-rolled to a thickness of 1.0 mm. Subsequently, short-time annealing of 850 ° C. × soaking for 60 seconds was performed.
Flux was applied to the surface of the annealed material and immersed in a molten aluminum plating bath (Al-10% by mass Si) heated to 680 ° C. to perform molten aluminum plating. When the cross section of the hot dip aluminum plated steel sheet was observed after cooling, a hot dip aluminum plating layer was formed with a thickness of about 15 to 25 μm per side.
[0017]
Test pieces were cut out from the hot-dip aluminized steel sheet and subjected to a tensile test, a high temperature oxidation resistance test, a high temperature strength test, and a secondary work crack resistance test.
In the tensile test, the tensile properties at room temperature were investigated using a JIS No. 5 tensile test piece cut out parallel to the rolling direction. In the high-temperature oxidation resistance test, a test piece punched into a shape of 45 mm in diameter was placed in a muffle furnace heated to 900 ° C., and the amount of increase in oxidation after being kept in the atmosphere for 100 hours was measured. Oxidizing properties were evaluated. In the high-temperature strength test, a high-temperature strength test piece having a parallel portion of 10 mm and a distance between gauge points of 50 mm was used, and the high-temperature strength was evaluated based on the yield strength at 800 ° C. measured according to JIS G0567. In the secondary work cracking resistance test, the test piece was cup-shaped at a draw ratio of 2.5, then held in a refrigerant cooled with dry ice, liquid nitrogen, etc. for 15 minutes, and then spread and tested with a 60-degree conical punch. The lowest temperature at which no intergranular cracking occurred was evaluated as the limit temperature for secondary work cracking resistance.
[0018]
As can be seen from the investigation results in Table 2 and FIG. 1, in
[0019]
The elongation in the room temperature tensile test tended to decrease as the content of Al, Si, and Mn increased. In test number 8 in which Al exceeds 10% by mass, test number 11 in which Si exceeds 2.0% by mass, and test number 14 in which Mn exceeds 2.5% by mass, the elongation was less than 20% and the ductility was poor. . Even in
In test numbers 16 to 22, 24, and 25 containing one or more of Ti, Nb, Mo, and V, a high temperature strength of 28 N / mm 2 or more was shown, but the total amount was 0.3 mass%. In test number 20 exceeding, the ductility at room temperature and the secondary work cracking resistance were inferior.
In addition, when test number 24 containing B is compared with test number 16 having almost the same composition except that B is not added, the limit temperature for secondary work cracking resistance is -70 ° C. in test number 16 and No. 24 showed a good value of −110 ° C.
[0020]
[Example 2]
A steel ingot obtained by continuously casting molten steel adjusted to the composition shown in Table 3 was hot-rolled under the conditions of a heating temperature of 1250 ° C., a finishing temperature of 900 ° C., and a winding temperature of 550 ° C. Hot rolled steel strip was produced. After pickling the hot-rolled steel strip, it is cold-rolled to a thickness of 1.0 mm, passed through a continuous hot-dip aluminum plating line of in-line annealing type, and annealed at 850 ° C. × soaking for 60 seconds, then both sides Hot dip aluminum plating was performed at an adhesion amount of 80 g / m 2 per unit. In the steel D of the present invention, an electric Fe—B pre-plated layer of 2 g / m 2 per side was formed prior to hot-dip aluminum plating.
[0022]
The tensile properties, high-temperature oxidation resistance, high-temperature strength, and secondary work cracking resistance of the obtained cold-rolled steel strip were investigated in the same manner as in Example 1. Moreover, the plating defect which tends to generate | occur | produce in the top part and end part of a coil was investigated, and the plating defect rate which represented the generation amount of the plating defect with the weight ratio with respect to the whole coil was calculated | required.
As can be seen from the results of the investigation in Table 4, the comparative steel A having a small Al content showed a very large value in which the increase in oxidation at 900 ° C. exceeded 100 g / m 2 . On the other hand, the inventive steels B to D having the composition defined in the present invention had a small amount of increase in oxidation at 900 ° C., and showed good values for other characteristics. Furthermore, when the present invention steel C and the present invention steel D having substantially the same Al content are compared, it can be seen that the defective plating rate is reduced by forming the Fe-B plating layer prior to the hot dip aluminum plating. .
[0024]
【The invention's effect】
As described above, the hot dip aluminized steel sheet of the present invention has excellent high temperature oxidation resistance, high temperature strength and good workability at room temperature, and is less expensive than stainless steel conventionally used as a high temperature structural material. It is. By utilizing such high temperature characteristics and workability, a hot dip galvanized steel sheet used in a wide range of fields such as automobiles and various combustion equipment members is provided.
[Brief description of the drawings]
FIG. 1 is a graph showing the effect of Al content on high-temperature oxidation resistance.
Claims (5)
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| JP2000085710A JP4458610B2 (en) | 2000-03-27 | 2000-03-27 | Hot-dip aluminized steel sheet with excellent high-temperature oxidation resistance |
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| JP2000085710A JP4458610B2 (en) | 2000-03-27 | 2000-03-27 | Hot-dip aluminized steel sheet with excellent high-temperature oxidation resistance |
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| EP2767601B1 (en) * | 2013-02-14 | 2018-10-10 | ThyssenKrupp Steel Europe AG | Cold rolled steel flat product for deep drawing applications and method for its production |
| EP2767602B1 (en) | 2013-02-14 | 2019-04-17 | ThyssenKrupp Steel Europe AG | Cold rolled steel flat product for deep drawing applications and method for its production |
| CN104894493A (en) * | 2014-03-07 | 2015-09-09 | 安徽省宁国市华达耐磨材料有限公司 | Novel super-high manganese steel and modification treatment thereof |
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| JPS56102556A (en) * | 1980-01-22 | 1981-08-17 | Nisshin Steel Co Ltd | Aluminum plated steel sheet with superior heat resistance |
| JPS63213658A (en) * | 1987-03-02 | 1988-09-06 | Sumitomo Metal Ind Ltd | Aluminum-plated steel sheet excellent in heat resistance |
| JPH07173594A (en) * | 1993-12-16 | 1995-07-11 | Nisshin Steel Co Ltd | Hot-dip aluminum plated cr-containing steel sheet for exterior |
| DE19634524A1 (en) * | 1996-08-27 | 1998-04-09 | Krupp Ag Hoesch Krupp | Lightweight steel and its use for vehicle parts and facade cladding |
| JPH111750A (en) * | 1997-06-06 | 1999-01-06 | Nippon Steel Corp | Catalyst support alloy for exhaust system, and its production |
| JP4418072B2 (en) * | 2000-01-17 | 2010-02-17 | 新日本製鐵株式会社 | Manufacturing method of high tension hot-dip aluminized steel sheet |
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