JP4146307B2 - Method for producing alloyed hot-dip galvanized steel sheet - Google Patents

Description

【００１０】
図２は、本発明における合金化溶融亜鉛メッキ鋼板のヒートパターンの実施形態を例示する図である。
まず、亜鉛メッキ浴へ入側の鋼板温度（Ｔin）でメッキ浴に浸漬してメッキを施した鋼板を、加熱炉にて、加熱炉出側の鋼板温度（Ｔ₁₁）まで加熱する。
その後、２つに分割された保熱炉内でメッキ鋼板は徐冷され、最初の保熱炉からＴ₁₂の温度で出た後に冷却装置にてＴ₁₂からＴ₂₁の温度に冷却される。
なお、この冷却は後述するように、メッキ構造を高度化するためのものであり、省略することもできる。
続いて、第２の保熱炉内で徐冷されて、Ｔ₂₂なる温度で出た後に冷却される。本発明においては、加熱手段および加熱速度は問わないが、設備がコンパクトで急速加熱が可能な誘導加熱装置を用いて、昇温速度を１０℃／s以上にすることが好ましい。
加熱炉における昇温速度を１０℃／s以上とすることにより、低温度域でのＦｅ−Ｚｎ合金化反応によるζ相の生成を抑制することができる。
【００１１】
本発明者らは、本発明における温度積分値（Ｓ）とメッキ層構造との関係を解析した結果、温度積分値（Ｓ）を５００≦Ｓ≦３０００を満足するようにヒートパターンを調整することによって、メッキ層をδ相単相主体の要求される製品特性を有する構造に近づけうることを見出した。
加熱炉出側の鋼板温度（Ｔ_１１）にて鋼板温度が最高到達温度に達した後、保熱炉にて徐冷する。
さらに、本発明においては、下記（A）式にて算出される温度積分値（Ｓ）が、５００≦Ｓ≦３０００を満足することを特徴とする。
Ｓの範囲を５００≦Ｓ≦３０００とするのは、Ｓが５００未満の場合は、δ相が減ってζ相が増加して摺動性が悪くなり、Ｓが３０００を超えるとδ相が減ってΓ_１相が増加してパウダリング性が悪くなるからである。
Ｓ＝（Ｔ_１１−Ｔ_０）×ｔ_１／２
+（（Ｔ_１１−Ｔ_０）+（Ｔ_１２−Ｔ_０））×ｔ_２／２
+（（Ｔ_１２−Ｔ_０）+（Ｔ_２１-Ｔ_０））×Δｔ／２
+（（Ｔ_２１−Ｔ_０）+（Ｔ_２２−Ｔ_０））×ｔ_３／２
+（Ｔ_２２−Ｔ_０）×ｔ_４／２・・・・（Ａ）
ここに、Ｔ_０ ：４２０（℃）、
Ｔ_１１：加熱炉出側の鋼板温度（℃）、
Ｔ_１２：保熱炉冷却帯入側の鋼板温度（℃）、
Ｔ_２１：保熱炉冷却帯出側の鋼板温度（℃）、
Ｔ_２２：保熱炉出側の鋼板温度（℃）、
ｔ_１ ：Ｔ_０から加熱炉出側までの処理時間（sec）、
ｔ_２ ：加熱炉出側から冷却帯入側までの処理時間（sec）、
Δｔ ：冷却帯入側から冷却帯出側までの処理時間（sec）、
ｔ_３ ：冷却帯出側から保熱炉出側までの処理時間（sec）、
ｔ_４ ：急冷帯入側からＴ_０までの処理時間（sec）
本実施形態においては、Ｆｅ濃度から温度積分値（Ｓ）を求め、通板速度（ＬＳ）から上記ｔ_１〜ｔ_４ を決定し、（Ｔ_１１−Ｔ_２２）を保熱炉の条件から決定し、これらの値とΔｔに基づいてＴ_１１およびＴ_２２を決定する。
なお、本実施形態では、保熱炉の中に冷却帯を設けているが、この冷却帯は必ずしも必要でなく、保熱炉の中に冷却帯を設けない場合には上記（Ａ）式におけるΔｔ＝０とすればよい。
次に、本発明における温度積分値の意味合いを以下に示す。
まず、合金メッキの拡散係数Ｄは下記（Ｂ）式、拡散距離Ｘは下記（Ｃ）式で表される。
Ｄ＝Ｄ_０×exp(-Ｑ／Ｒ・Ｔ)・・・（Ｂ）
Ｘ＝√（Ｄ・ｔ）・・・・（Ｃ）
ここに、Ｄ：拡散係数
Ｄ_０：定数
Ｑ：拡散の活性化エネルギー
Ｒ：気体定数
Ｔ：温度
Ｘ：拡散距離
ｔ：時間
上記（Ｂ）式をテイラー展開により近似すると、Ｄ∝（Ａ+Ｂ・Ｔ）となり、これを（Ｃ）式に代入することにより下記（Ｄ）式を得る。
Ｘ∝√（Ａ・ｔ+Ｂ・Ｔ・ｔ）・・・（Ｄ）
（Ｄ）式から、拡散距離（Ｘ）は合金メッキ中のＦｅ濃度を表すことができるとして、温度（Ｔ）と時間（ｔ）とを掛け合わせて積算した温度積分値は、合金メッキ中のＦｅ濃度と相関があることが分かる。
【００１２】
以下に、本発明における合金化条件の決定手順を例示する。
この合金化条件の決定方法は、前述の温度積分値（Ｓ）とメッキ層中のＦｅ％との関係式を求め、この式と温度積分値（Ｓ）を算出する理論式から、合金化度と加熱炉出側の鋼板温度（Ｔ₁₁）の相関式、Ｔ₁₁＝ｆ（合金化度（Ｆｅ％）、鋼種、付着量、鋼板速度、板厚）を導出し、各パラメータの変化に応じて常に最適な加熱炉出側の鋼板温度（Ｔ₁₁）を自動計算し、この最適な加熱炉出側の鋼板温度を維持するように加熱炉の入熱量を調整するものである。
【００１３】
＜データ採取＞
１）各種条件（鋼種、付着量、鋼板速度、板厚）毎に未アロイぎりぎり（定合金）になる温度積分値（Ｓ）を求めて、最適な加熱炉出側の鋼板温度に対する鋼種の影響係数を導出する。
２）加熱炉出側の鋼板温度を変化させることによって、温度積分値（Ｓ）とメッキ層中のＦｅ％（合金化度）との相関を求め、Ｓ＝ｆ（メッキ中Ｆｅ％）を導出する。
図４は、本発明に用いる温度積分値（Ｓ）とメッキ中Ｆｅ％との関係を例示する図である。
なお、下記の▲１▼式〜▲６▼式におけるa〜ｚは定数である。
図４において、目付（メッキ付着量）40-50mg/ｍ²のsulc材の温度積分値（Ｓ）とメッキ中Ｆｅ％は相関があり、これから近似式を求めることによって▲１▼式を導出する。
Ｆｅ％＝ｆ（Ｓ） ・・・・▲１▼
この▲１▼式を用いることによって、合金メッキ中の目標Ｆｅ濃度に応じて、前記温度積分値（Ｓ）を下記▲１▼´式により決定することができる。
Ｓ＝ｆ（Ｆｅ％） ・・・・▲１▼´
３）実績データより、保熱炉出側の鋼板温度（Ｔ₂₂）の予測式を導出する。
図４の実績データに基づいて重回帰計算により求めた加熱炉出側の鋼板温度（Ｔ₁₁）と保熱炉出側の鋼板温度（Ｔ₂₂）の差は▲２▼式となった。
Ｔ₁₁−Ｔ₂₂＝ｆ（通板速度, 板厚） ・・・▲２▼
尚、保熱炉内での冷却では、通常５〜３０℃程度冷却されるが、この部分の温度降下代Ｔ₁₂−Ｔ₂₁は、Ｔ₁₁−Ｔ₂₂の中に含めて温度パターンを決めることも可能である。
【００１４】
＜データ解析＞
４）温度積分値（Ｓ）の理論式である前述の（Ａ）式に図４の実績値を代入した下記▲３▼式に、前記▲１▼´式および▲２▼式を代入することによって、Ｓ＝ｆ（加熱炉出側の鋼板温度、通板速度、板厚）を導出し、▲４▼式を得ることができる。
Ｓ＝ｆ（通板速度, Ｔ₁₁, Ｔ₂₂） ・・・▲３▼
Ｔ₁₁＝f (通板速度, 板厚, Ｆｅ％)・・・▲４▼
メッキ浴出側の鋼板温度（Ｔ₀）の値によって温度積分値（Ｓ）の値は変わらないが、例えば、メッキ浴入側の鋼板温度（Ｔin）が１０℃低い場合には、温度積分値（Ｓ）+５００〜+１０００の範囲で高くすることによって、メッキ浴出側の鋼板温度が目標値からずれた場合でも適正な合金メッキ層を生成することができる。
この理由は、侵入する鋼板の表面温度が下がると、生成するアルミバリアー層の厚みが増加するためにバリアー層の消滅が若干遅れ、Ｆｅ濃度が低下する。このため、Ｆｅの拡散を促進させるために温度積分値を高くする必要があるものと考えられる。
【００１５】
５）図５に示すように、目付（メッキ付着量）とＦｅ％には一次式の相関があることから加熱炉出側の鋼板温度に対する付着量の影響項を求めて▲１▼´式のＦｅ％をＦｅ％＋α・Δ目付けと書き直すことにより▲５▼式を得ることができる。
Ｔ₁₁＝f (通板速度, 板厚, Ｆｅ％, 付着量) ・・・▲５▼
６）▲５▼式に１）で求めた最適な加熱炉出側の鋼板温度に対する鋼種の影響係数を追加することによって、▲６▼式を得ることができる。
Ｔ₁₁＝f (通板速度, 板厚, Ｆｅ％, 付着量, 鋼種) ・・・▲６▼
この▲６▼式によって、前記決定した温度積分値（Ｓ）に基づいて、前記加熱炉出側の鋼板温度（Ｔ₁₁）を決定し、鋼板の板厚および／または通板速度、目付量、合金化度（Ｆｅ濃度）、鋼種が変化しても該加熱炉出側の鋼板温度（Ｔ₁₁）を維持するように加熱炉の入熱量を調整することができる。
以下に、本発明を実施する際の制御フローを示す。
まず、計算機１により、鋼種、鋼板サイズ、付着量上下限値、合金化度区分を計算機２へ伝送する。
次に、計算機２により、ＩＨ出側板温制御式にて通板速度（ＬＳ）影響項以外を計算し制御装置に伝送する。
制御装置では、前記通板速度（ＬＳ）影響項を加味してＩＨ出側板温を算出し、ＩＨ出力電力を決定するとともに、ＩＨ入出板温設定値・実績値、電力実績値等を計算機２に伝送する。
次に、計算機２により、ＩＨ出側板温実績値（Ｔ₁₁）と計算機２の計算によるＩＨ出側板温設定値の差から合金化品質を判定するとともに、ＩＨ入出板温設定値・実績値・電力実績値等を計算機１に伝送する。
計算機１では、計算機２による品質判定NGのコイルを自動保留するとともに、各実績値をデータベースに保存する。
【００１６】
メッキ浴入側の鋼板温度（Ｔin）から加熱炉出側の鋼板温度（Ｔ₁₁）までの時間（ｔ₀）が１５秒以下であることが好ましい。
メッキ浴入側の鋼板温度（Ｔin）から加熱炉出側の鋼板温度（Ｔ₁₁）までの時間（ｔ₀）を１５秒以下とすることによって、メッキ浴中で生成するＡｌバリアー層が残存している状態で加熱炉出側の鋼板温度を４９５℃以上に到達させることができるので、低温域でのＦｅ−Ｚｎ合金化反応によるζ相の生成を抑制することができる。
また、本実施形態においてはＴ₀＝４２０（℃）としているが、理想的には、４９５℃以上でＡｌバリアー層が消滅してから温度積分値（Ｓ）の積算を開始することにより、さらに高精度なメッキ構造の制御を行うことができる。
本発明においては、保熱炉から出た鋼板の冷却速度は問わないが、４℃／sec以上の冷却速度で急冷することが好ましい。
保熱炉から出た鋼板を４℃／sec以上の冷却速度で急冷することによって、
Γ₁相の析出を回避し、耐パウダリング性をさらに向上させることができる。
従来の製造プロセスにおいては、保熱炉における鋼板温度はほぼ一定に保たれていたが、本発明においては、保熱炉にて図２におけるＴ₁₂からＴ₂₁まで冷却することにより、鋼板への入熱量を抑制して鋼板からメッキ層へのＦｅの拡散量を抑制させるとともに、Ｔ₂₁からＴ₂₂まではメッキ層内だけでＦｅを拡散させることによって、Γ₁相成長の抑制およびζ相→δ相化を促進しδ相単相化が可能となる。
また、温度積分値（Ｓ）が、例えば、表２に示すような、前記合金メッキ中の目標Ｆｅ濃度に応じた値になったときに、前記保熱炉の間に設置した冷却装置により鋼板の冷却を開始することによって、メッキ層構造の制御をさらに高度化することができる。
【表２】

【００１７】
【実施例】
下記の条件にて実施した本発明の実施例を表３〜表５に示す。
＜実施条件＞
・設備構成：亜鉛メッキ浴？スクレーパ？加熱炉（ＩＨ炉）？保熱炉＃1（電気ヒータ） -GCB（保熱帯間にあるガス冷却）？保熱炉＃2（電気ヒータ）-気水冷却-付け量測定 器
・鋼種：ＩＦ鋼（Ｃ：30ppm以下＋Ti+Nb）
・板幅：６００〜１８８０ｍｍ
表３は本発明の実施例を示す。温度積分値（Ｓ）の値が本発明範囲である５００≦Ｓ≦３０００の範囲内であるため、パウダリング性および摺動性とも良好であり、Ｆｅ（％）のバラツキは±１％程度であった。
一方、従来は、鋼種、サイズ、目標Ｆｅ％において良好だった条件（LS、合金化炉温、合金化出側板温）を記録しておき、それと全く同じ条件になるよう手動で条件変更を行っていたため、上記操業条件への移行前後で、Ｆｅ（％）のバラツキは最大±３％程度になることもあったため、本発明によって著しく合金メッキの品質を安定化させることができることが確認された。
表４は、操業中に条件が変化した（異なる鋼板を繋いだ）時に所定の条件に変更する場合における本発明の実施例を示す。
操業中にライン速度や板厚が変化しても目標とするＦｅ％が変わらなければ温度積分値（Ｓ）の値が一定となるように操業することによってパウダリング性と摺動性の双方を良好に保つことができる。
また、操業中に目標とするＦｅ％や目付け量が変化する場合には、温度積分値（Ｓ）の値がそのＦｅ％と目付け量に応じた値になるように合金化処理の温度パターンを変更することによってパウダリング性と摺動性の双方を良好に保つことができる。
表５は、合金化までの時間、加熱速度、冷却速度が本発明の好ましい範囲を満足する発明例と満足しない比較例を示す。
比較例は、入熱量が大き過ぎるとＦｅ濃度が増加しパウダリング性がやや劣っており、加熱速度が好ましい範囲である１０℃/秒未満だとζ相が増えて摺動性がやや悪くなっている。
また、冷却速度が好ましい範囲である４℃/秒未満の場合には、Γ₁相が増加してパウダリング性がやや悪くなった。
【表３】

【表４】

【表５】

【００１８】
【発明の効果】
本発明によれば、鋼板の加熱温度と加熱時間を掛け合わせて合計した温度積分値に基づいて合金化処理の温度パターンを決定することによって、メッキ層構造およびＦｅ濃度を制御して、表面摺動性と耐パウダリング性を両立させ、所定の品質を持ったＡＳ製品の作り分けを安定して行うことができる製造方法を提供することができ、産業上有用な著しい効果を奏する。
【図面の簡単な説明】
【図１】 本発明における合金化溶融亜鉛メッキ鋼板の製造プロセスを例示する図である。
【図２】 本発明における合金化溶融亜鉛メッキ鋼板のヒートパターンの実施形態を例示する図である。
【図３】 溶融亜鉛メッキ鋼板の合金メッキ層の構造を示す図である。
【図４】 本発明に用いる温度積分値（Ｓ）とメッキ中Ｆｅ％との関係を例示する図である。
【図５】 本発明に用いる目付（メッキ付着量）とＦｅ％との関係を例示する図である。との関係を例示する図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet in which a steel sheet plated in a galvanizing bath is heated and subjected to an alloying treatment.
[0002]
[Prior art]
Alloyed hot-dip galvanized steel sheet (hereinafter referred to as AS) is used in various applications such as home appliances because of its excellent corrosion resistance, weldability, paintability, and coating film adhesion. Demand for rust-proof steel sheets for bodies is increasing.
Since the quality of plating for AS is greatly affected by the alloying conditions, manufacturing conditions that control the plating structure and have both slidability and powdering resistance are indispensable, and various proposals have been made in the past. Yes.
For example, Japanese Patent Laid-Open No. 6-256857 discloses a temperature increase rate of 20 ° C./s or more by high frequency induction heating after galvanizing in a zinc plating bath in which 0.1 to 0.2% of Al is added to a steel plate. After the steel sheet temperature reaches 490 to 550 ° C., it is held for 5 to 10 s, and then cooled to room temperature at a cooling rate of 20 ° C./s or more, so that the processability of the δ ₁ phase single phase type is achieved. An excellent method for producing a galvannealed steel sheet is disclosed.
[0003]
In order to manufacture AS that has both surface slidability and powdering resistance required for steel plates for automobiles that are severely processed, the plating layer is controlled and the ζ and Γ phases are both thin. That is, a δ single-phase plated layer structure is ideal.
However, as disclosed in, for example, Japanese Patent Laid-Open No. 6-256857, such control of the plated layer structure cannot be realized only by setting the heating rate and cooling rate after plating within a specific range.
[0004]
[Patent Document 1]
JP-A-6-256857 Publication
[Problems to be solved by the invention]
The present invention solves the problems of the prior art as described above, controls the plating layer structure, achieves both surface slidability and powdering resistance, and makes AS products with a predetermined quality. It is an object of the present invention to provide a production method that can be performed stably.
Specifically, it is necessary to adjust the Fe concentration in the alloy plating according to the intended use of the steel sheet. For example, in a member that requires good slidability, it is necessary to design a high Fe concentration and good powdering properties. In a member that requires the above, it is necessary to set the Fe concentration low.
For example, in a member that emphasizes pressability such as a side panel, the Fe concentration is 12 to 13%, and in a member that emphasizes the appearance such as a fender, powdering properties are required, so the Fe concentration needs to be approximately 10%. .
This Fe concentration (average value) during alloy plating is a factor that determines the plating layer structure, and is a factor that delicately controls product characteristics even within the same phase.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has been made as a result of intensive studies on the production conditions of AS, and based on a temperature integrated value obtained by multiplying the heating temperature and the heating time of the steel sheet, By controlling the temperature pattern of the heat treatment, it is possible to control the plating layer structure and Fe concentration to stabilize the production of AS products with specified quality while achieving both surface slidability and powdering resistance. The gist of the present invention is as follows, as described in the claims.
[0007]
(1) In a method for producing an alloyed hot-dip galvanized steel sheet, in which a steel sheet plated in a galvanizing bath is heated and alloyed,
The temperature integral value (S) calculated by the following equation (A) satisfies 500 ≦ S ≦ 3000, and after reaching the maximum temperature at the steel plate temperature (T ₁₁ ) on the heating furnace exit side, in the process of cooling in the heat furnace to _{T 0} after gradually cooled to _{T 22,} 10.5 wt% target Fe concentration in the alloy plating, 11.0 wt%, 11.5 wt%, 12.0 wt% When the temperature integrated value (S) corresponding to the temperature is reached, cooling is started with a cooling device provided between the heat-retaining furnaces, the temperature is cooled to T _{12 to} T ₂₁ , and then the heat is maintained until T ₂₂ , and then T ₀ A method for producing an alloyed hot-dip galvanized steel sheet, which is cooled to a low temperature.
_{S = (T 11 -T 0)} × t 1/2
_{+ ((T 11 -T 0)} + (T 12 -T 0)) × t 2/2
+ ((T ₁₂ −T ₀ ) + (T ₂₁ −T ₀ )) × Δt / 2
_{+ ((T 21 -T 0)} + (T 22 -T 0)) × t 3/2
_{+ (T 22 -T 0) ×} t 4/2 ···· (A)
Here, T ₀ : 420 (° C.),
T ₁₁ : Steel sheet temperature (° C.) on the heating furnace exit side,
T ₁₂ : Steel plate temperature (° C.) on the inlet side of the cooling zone in the heat insulation furnace,
T ₂₁ : steel plate temperature (° C.) on the cooling zone exit side of the heat-retaining furnace,
T ₂₂ : Steel plate temperature (° C.) on the exit side of the heat insulation furnace,
t _1: processing time from _{T 0} to the heating furnace exit side (sec),
t ₂ : treatment time (sec) from the heating furnace exit side to the cooling zone entry side,
Δt: Processing time (sec) from the cooling zone entry side to the cooling zone exit side,
t ₃ : treatment time (sec) from the cooling zone exit side to the heat insulation furnace exit side,
t ₄ : Processing time (sec) from the quenching zone entry side to T ₀
(2) Production of alloyed hot-dip galvanized steel sheet according to (1), wherein a heat insulation furnace divided into a first heat insulation furnace and a second heat insulation furnace is used as the heat insulation furnace Method.
(3) Based on the determined temperature integrated value (S), the steel plate temperature (T ₁₁ ) on the heating furnace exit side is determined, and the steel plate temperature (T ₁₁ ) on the heating furnace exit side is adjusted. The manufacturing method of the galvannealed steel plate as described in (1) or (2).
(4) The alloyed hot-dip galvanized steel sheet according to (3), wherein the determined steel plate temperature (T ₁₁ ) on the outlet side of the heating furnace is corrected according to the steel type and / or plating adhesion amount of the steel plate. Manufacturing method.
[0008]
(5) The integrated temperature galvanized steel sheet according to any one of (1) to (4) , wherein the temperature integral value is corrected by the steel sheet temperature (Tin) on the plating bath entrance side. Production method.
(6) When the degree of alloying (Fe concentration) is constant, the steel plate temperature (T ₁₁ ) on the heating furnace exit side is determined so that the temperature integrated value (S) is constant, and the target Fe concentration changes. When the temperature pattern for performing the alloying process is controlled by determining the steel plate temperature (T ₁₁ ) on the heating furnace exit side based on the temperature integrated value (S) corresponding to the target Fe concentration. (1) The manufacturing method of the galvannealed steel plate as described in any one of (1) thru | or (5) .
(7) the bath furnace exit side of the steel plate temperature from the inlet side of a steel sheet temperature (Tin) _{(T 11)} until the time _{(t 0)} is equal to or less than 15 seconds (1) to (6 The manufacturing method of the galvannealed steel plate as described in any one of 1) .
(8) Any one of (1) to (7), wherein a rate of temperature increase from the steel plate temperature on the plating bath exit side to the steel plate temperature (T ₁₁ ) on the furnace exit side is 10 ° C./sec or more A method for producing an alloyed hot-dip galvanized steel sheet according to claim 1.
(9) The alloyed hot-dip galvanized steel sheet according to any one of (1) to (8), wherein the steel sheet exited from the heat-retaining furnace is rapidly cooled at a cooling rate of 4 ° C./sec or more. Manufacturing method.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a diagram illustrating a manufacturing process of an alloyed hot-dip galvanized steel sheet according to the present invention.
From the left in FIG. 1, the steel sheet annealed in the annealing furnace is immersed in a molten zinc bath (pot) and plated on the surface, and then heated to the maximum temperature in the heating furnace, followed by heat retention. An alloyed hot-dip galvanized steel sheet (hereinafter referred to as “AS”) is produced by slow cooling in a furnace and quenching in a cooling zone. In this case, it may be forcibly cooled temporarily in a heat insulating furnace.
The right side of FIG. 1 illustrates the heat pattern in the AS manufacturing process.
First, when entering the plating bath (pot), an Fe—Al alloy phase (Al barrier layer) is first generated, which becomes a barrier for the alloying reaction of Fe and Zn. The steel plate that has exited the plating bath (pot) is cooled in the process of controlling the amount of plating, and then heated to the maximum temperature in a heating furnace. During this heating process, the δ phase precipitates and the initial phase of the Fe—Zn alloy is determined. At this time, alloying is started by causing an outburst phenomenon that breaks through the Al barrier layer due to the volume expansion of the deposited δ phase.
Next, diffusion of Fe and Zn occurs in the process of slow cooling in the heat-retaining furnace, and a δ phase grows mainly on the crystal grain boundary of the steel sheet, thereby determining the plating layer structure.
As shown in FIG. 3, the AS plating layer structure is a Γ phase, δ phase, and ζ phase with high Fe% from the steel plate side. Since the ζ phase is soft and has high sliding resistance, it is formed into a foil shape by external force. It is easy to peel off, and the Γ phase is brittle, and when shear stress is applied, it is easily peeled off in powder form, so that so-called powdering is likely to occur.
Table 1 shows the Fe-Zn alloy phase and its characteristics.
[Table 1]

[0010]
FIG. 2 is a diagram illustrating an embodiment of the heat pattern of the galvannealed steel sheet according to the present invention.
First, the steel plate plated by immersion in the plating bath at the steel plate temperature (Tin) on the entry side into the galvanizing bath is heated to the steel plate temperature (T ₁₁ ) on the heating furnace exit side in a heating furnace.
Thereafter, the plated steel sheet is gradually cooled in the heat-retaining furnace divided into two parts, and after it comes out from the first heat-retaining furnace at a temperature of T ₁₂ , it is cooled to a temperature of T ₁₂ to T _{21 by} a cooling device.
As will be described later, this cooling is for upgrading the plating structure and can be omitted.
Then, being gradually cooled in the second retaining heat furnace, is cooled after it exits at T ₂₂ becomes temperature. In the present invention, the heating means and the heating rate are not limited, but it is preferable to set the heating rate to 10 ° C./s or more by using an induction heating apparatus that is compact and capable of rapid heating.
By setting the temperature rising rate in the heating furnace to 10 ° C./s or more, the formation of the ζ phase due to the Fe—Zn alloying reaction in a low temperature region can be suppressed.
[0011]
As a result of analyzing the relationship between the temperature integrated value (S) and the plating layer structure in the present invention, the inventors adjust the heat pattern so that the temperature integrated value (S) satisfies 500 ≦ S ≦ 3000. Thus, the present inventors have found that the plating layer can be made close to a structure having required product characteristics mainly composed of a δ phase.
After the steel plate temperature reaches the maximum temperature at the steel plate temperature (T ₁₁ ) on the heating furnace exit side, it is gradually cooled in a heat retaining furnace.
Furthermore, in the present invention, the temperature integrated value (S) calculated by the following equation (A) satisfies 500 ≦ S ≦ 3000.
The range of S is 500 ≦ S ≦ 3000. When S is less than 500, the δ phase decreases and the ζ phase increases and the slidability deteriorates. When S exceeds 3000, the δ phase decreases. This is because the Γ ₁ phase increases and the powdering property deteriorates.
_{S = (T 11 -T 0)} × t 1/2
_{+ ((T 11 -T 0)} + (T 12 -T 0)) × t 2/2
+ ((T ₁₂ −T ₀ ) + (T ₂₁ −T ₀ )) × Δt / 2
_{+ ((T 21 -T 0)} + (T 22 -T 0)) × t 3/2
_{+ (T 22 -T 0) ×} t 4/2 ···· (A)
Here, T ₀ : 420 (° C.),
T ₁₁ : Steel sheet temperature (° C.) on the heating furnace exit side,
T ₁₂ : Steel plate temperature (° C.) on the inlet side of the heat- retaining furnace cooling zone,
T _21: Honetsuro cooling home use side of the steel sheet temperature (° C.),
T ₂₂ : Steel plate temperature (° C.) on the exit side of the heat insulation furnace,
t ₁ : Processing time (sec) from T ₀ to heating furnace exit side,
t ₂ : treatment time (sec) from the heating furnace exit side to the cooling zone entry side,
Δt: Processing time (sec) from the cooling zone entry side to the cooling zone exit side,
t ₃ : treatment time (sec) from the cooling zone exit side to the heat insulation furnace exit side,
t ₄ : Processing time (sec) from the quenching zone entry side to T ₀
In the present embodiment, the temperature integrated value (S) is obtained from the Fe concentration, the above-mentioned t ₁ to t ₄ are determined from the plate passing speed (LS), and (T ₁₁ -T ₂₂ ) is determined from the conditions of the heat insulation furnace. Then, T ₁₁ and T ₂₂ are determined based on these values and Δt.
In the present embodiment, a cooling zone is provided in the heat insulation furnace, but this cooling zone is not always necessary. In the case where no cooling zone is provided in the heat insulation furnace, the above formula (A) is used. Δt = 0 may be set.
Next, the meaning of the temperature integral value in the present invention is shown below.
First, the diffusion coefficient D of the alloy plating is expressed by the following formula (B), and the diffusion distance X is expressed by the following formula (C).
D = D ₀ × exp (−Q / R · T) (B)
X = √ (D · t) (C)
Where D: diffusion coefficient
D ₀ : Constant
Q: Activation energy of diffusion
R: Gas constant
T: Temperature
X: Diffusion distance
t: Time When the above equation (B) is approximated by Taylor expansion, D∝ (A + B · T) is obtained. By substituting this into equation (C), the following equation (D) is obtained.
X∝√ (A ・ t + B ・ T ・ t) (D)
From the equation (D), it is assumed that the diffusion distance (X) can represent the Fe concentration in the alloy plating, and the temperature integrated value obtained by multiplying the temperature (T) and the time (t) is integrated. It can be seen that there is a correlation with the Fe concentration.
[0012]
Below, the determination procedure of the alloying conditions in this invention is illustrated.
This alloying condition is determined by obtaining a relational expression between the above-mentioned temperature integrated value (S) and Fe% in the plating layer, and calculating the degree of alloying from a theoretical formula for calculating this expression and the temperature integrated value (S). And the steel plate temperature (T ₁₁ ) on the outlet side of the heating furnace, T ₁₁ = f (degree of alloying (Fe%), steel type, adhesion amount, steel plate speed, plate thickness) is derived, and according to changes in each parameter Thus, the optimum steel sheet temperature (T ₁₁ ) on the heating furnace outlet side is always automatically calculated, and the heat input amount of the heating furnace is adjusted so as to maintain the optimum steel sheet temperature on the heating furnace outlet side.
[0013]
<Data collection>
1) Obtain the temperature integral value (S) that is unalloyed (constant alloy) for each condition (steel type, adhesion amount, steel plate speed, plate thickness), and influence the steel type on the optimum steel plate temperature on the heating furnace exit side. Deriving coefficients.
2) By changing the steel plate temperature on the exit side of the heating furnace, the correlation between the temperature integrated value (S) and the Fe% (alloying degree) in the plating layer is obtained, and S = f (Fe% in plating) is derived. To do.
FIG. 4 is a diagram illustrating the relationship between the temperature integrated value (S) used in the present invention and Fe% during plating.
In the following formulas (1) to (6), a to z are constants.
In FIG. 4, there is a correlation between the temperature integrated value (S) of the sulc material having a basis weight (plating adhesion amount) of 40-50 mg / m ² and Fe% during plating, and the formula (1) is derived by obtaining an approximate expression therefrom. .
Fe% = f (S) ... (1)
By using this equation (1), the temperature integrated value (S) can be determined by the following equation (1) 'according to the target Fe concentration during alloy plating.
S = f (Fe%) (1)
3) A prediction formula for the steel plate temperature (T ₂₂ ) on the heat insulation furnace exit side is derived from the actual data.
Difference on the basis of the actual data of Figure 4 multiple regression calculated by the determined heating furnace exit side of the steel sheet temperature (T ₁₁₎ and the heat retaining furnace exit side of the steel sheet temperature (T ₂₂₎ was the ▲ 2 ▼ expression.
T ₁₁ -T ₂₂ = f (plate speed, plate thickness) ... (2)
In the heat insulation furnace, the temperature is usually about 5 to 30 ° C. The temperature drop allowance T ₁₂ -T ₂₁ in this part is included in T ₁₁ -T ₂₂ to determine the temperature pattern. Is also possible.
[0014]
<Data analysis>
4) Substituting the above formulas (1) and (2) into the following formula (3) in which the actual value of FIG. 4 is substituted into the formula (A), which is the theoretical formula of the temperature integral value (S). Thus, S = f (steel plate temperature on the heating furnace exit side, plate passing speed, plate thickness) can be derived, and equation (4) can be obtained.
S = f (feeding speed, T ₁₁ , T ₂₂ ) (3)
T ₁₁ = f (plate feed speed, plate thickness, Fe%) ... (4)
Although the value of the temperature integrated value (S) does not change depending on the steel plate temperature (T ₀ ) on the plating bath exit side, for example, when the steel plate temperature (Tin) on the plating bath entrance side is 10 ° C. lower, the temperature integrated value (S) By making it high in the range of + 500- + 1000, an appropriate alloy plating layer can be produced even when the steel plate temperature on the plating bath exit side deviates from the target value.
The reason for this is that when the surface temperature of the invading steel sheet is lowered, the thickness of the formed aluminum barrier layer is increased, so that the disappearance of the barrier layer is slightly delayed and the Fe concentration is lowered. For this reason, it is considered that the temperature integrated value needs to be increased in order to promote the diffusion of Fe.
[0015]
5) As shown in FIG. 5, since there is a linear relationship between the basis weight (plating adhesion amount) and Fe%, the influence term of the adhesion amount on the steel plate temperature on the heating furnace exit side is obtained and the formula (1) ' By rewriting Fe% as Fe% + α · Δ basis weight, the formula (5) can be obtained.
T ₁₁ = f (plate speed, plate thickness, Fe%, adhesion amount) ・ ・ ・ ▲ 5 ▼
6) The formula (6) can be obtained by adding the influence coefficient of the steel type to the optimum steel plate temperature on the outlet side of the heating furnace obtained in 1) to the formula (5).
T ₁₁ = f (plate speed, plate thickness, Fe%, adhesion amount, steel type) ・ ・ ・ ▲ 6 ▼
From this equation (6), based on the determined temperature integral value (S), the steel plate temperature (T ₁₁ ) on the heating furnace exit side is determined, and the steel plate thickness and / or plate passing speed, basis weight, Even if the degree of alloying (Fe concentration) and the steel type change, the heat input of the heating furnace can be adjusted so as to maintain the steel sheet temperature (T ₁₁ ) on the heating furnace exit side.
Below, the control flow at the time of implementing this invention is shown.
First, the computer 1 transmits the steel type, the steel plate size, the upper and lower limits of adhesion amount, and the alloying degree classification to the computer 2.
Next, the computer 2 calculates the terms other than the plate speed (LS) influence term by the IH outlet side plate temperature control formula, and transmits them to the control device.
In the control device, the IH outlet side plate temperature is calculated in consideration of the term of influence of the plate passing speed (LS), the IH output power is determined, and the IH input / output plate temperature set value / actual value, actual power value, etc. Transmit to.
Next, the computer 2 determines the alloying quality from the difference between the IH outlet side plate temperature actual value (T ₁₁ ) and the IH outlet side plate temperature set value calculated by the computer 2, and the IH I / O plate temperature set value / actual value / The actual power value is transmitted to the computer 1.
In the computer 1, the coil for quality determination NG by the computer 2 is automatically suspended and each actual value is stored in a database.
[0016]
The time (t ₀ ) from the steel plate temperature (Tin) on the plating bath entrance side to the steel plate temperature (T ₁₁ ) on the heating furnace exit side is preferably 15 seconds or less.
By setting the time (t ₀ ) from the steel plate temperature (Tin) on the plating bath entrance side to the steel plate temperature (T ₁₁ ) on the heating furnace exit side to 15 seconds or less, the Al barrier layer generated in the plating bath remains. Since the steel plate temperature on the exit side of the heating furnace can be reached to 495 ° C. or higher in the state of being heated, the formation of ζ phase due to the Fe—Zn alloying reaction in a low temperature region can be suppressed.
In this embodiment, T ₀ = 420 (° C.), but ideally, by starting the integration of the temperature integral value (S) after the Al barrier layer disappears at 495 ° C. or higher, It is possible to control the plating structure with high accuracy.
In the present invention, the cooling rate of the steel sheet coming out of the heat-retaining furnace is not limited, but it is preferable to rapidly cool at a cooling rate of 4 ° C./sec or more.
By rapidly cooling the steel sheet from the heat-retaining furnace at a cooling rate of 4 ° C / sec or more,
The precipitation of the Γ ₁ phase can be avoided and the powdering resistance can be further improved.
In the conventional manufacturing process, the steel plate temperature in the heat-retaining furnace was kept almost constant, but in the present invention, by cooling from T ₁₂ to T ₂₁ in FIG. The amount of heat input is suppressed to suppress the diffusion amount of Fe from the steel sheet to the plating layer, and from T ₂₁ to T ₂₂ , Fe is diffused only in the plating layer, thereby suppressing the Γ ₁ phase growth and the ζ phase → The δ phase can be promoted and the δ phase can be converted into a single phase.
Further, when the temperature integral value (S) becomes a value corresponding to the target Fe concentration during the alloy plating as shown in Table 2, for example, the steel plate is cooled by a cooling device installed between the heat insulation furnaces. By starting the cooling, the control of the plating layer structure can be further enhanced.
[Table 2]

[0017]
【Example】
Examples of the present invention implemented under the following conditions are shown in Tables 3 to 5.
<Conditions for implementation>
・ Equipment configuration: zinc plating bath? Scraper? Heating furnace (IH furnace)? Thermal furnace # 1 (Electric heater) -GCB (gas cooling in the tropical zone)? Thermal insulation furnace # 2 (electric heater)-Air / water cooling-Amount measurement device / steel grade: IF steel (C: 30ppm or less + Ti + Nb)
・ Plate width: 600 ~ 1880mm
Table 3 shows examples of the present invention. Since the value of the temperature integrated value (S) is within the range of 500 ≦ S ≦ 3000, which is the range of the present invention, the powdering property and the sliding property are good, and the variation of Fe (%) is about ± 1%. there were.
On the other hand, in the past, the conditions (LS, alloying furnace temperature, alloying outlet side plate temperature) that were good in the steel type, size, and target Fe% were recorded, and the conditions were changed manually so that the conditions were exactly the same. Therefore, before and after the transition to the above operating conditions, the variation in Fe (%) was sometimes about ± 3% at the maximum, so it was confirmed that the quality of the alloy plating can be remarkably stabilized by the present invention. .
Table 4 shows an embodiment of the present invention in the case of changing to a predetermined condition when the condition is changed during operation (different steel plates are connected).
Even if the line speed or plate thickness changes during operation, if the target Fe% does not change, the temperature integrated value (S) is operated so that the powdering and sliding properties are both constant. Can keep good.
In addition, when the target Fe% and the basis weight change during operation, the temperature pattern of the alloying process is set so that the value of the temperature integrated value (S) becomes a value corresponding to the Fe% and the basis weight. By changing, both powdering property and sliding property can be kept good.
Table 5 shows invention examples in which the time to alloying, heating rate, and cooling rate satisfy the preferred range of the present invention, and comparative examples that do not satisfy it.
In the comparative example, if the heat input is too large, the Fe concentration increases and the powdering property is slightly inferior, and if the heating rate is less than 10 ° C./second, which is the preferred range, the ζ phase increases and the slidability becomes slightly worse. ing.
Further, when the cooling rate was less than 4 ° C./second which is a preferable range, the Γ ₁ phase increased and the powdering property was slightly deteriorated.
[Table 3]

[Table 4]

[Table 5]

[0018]
【The invention's effect】
According to the present invention, the plating layer structure and the Fe concentration are controlled by determining the temperature pattern of the alloying treatment based on the integrated temperature value obtained by multiplying the heating temperature and the heating time of the steel sheet, and the surface slide is controlled. It is possible to provide a manufacturing method that can achieve both stability and powdering resistance and can stably produce AS products having a predetermined quality, and has a remarkable industrially useful effect.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a production process of an alloyed hot-dip galvanized steel sheet according to the present invention.
FIG. 2 is a diagram illustrating an embodiment of a heat pattern of the galvannealed steel sheet according to the present invention.
FIG. 3 is a view showing a structure of an alloy plating layer of a hot dip galvanized steel sheet.
FIG. 4 is a diagram illustrating the relationship between a temperature integrated value (S) used in the present invention and Fe% during plating.
FIG. 5 is a diagram illustrating the relationship between the basis weight (plating adhesion amount) and Fe% used in the present invention. It is a figure which illustrates the relationship with.

Claims (9)

In the manufacturing method of the alloyed hot-dip galvanized steel sheet in which the steel sheet plated in the galvanizing bath is heated and alloyed,
The temperature integral value (S) calculated by the following equation (A) satisfies 500 ≦ S ≦ 3000, and after reaching the maximum temperature at the steel plate temperature (T ₁₁ ) on the heating furnace exit side, in the process of cooling in the heat furnace to _{T 0} after gradually cooled to _{T 22,} 10.5 wt% target Fe concentration in the alloy plating, 11.0 wt%, 11.5 wt%, 12.0 wt% When the temperature integrated value (S) corresponding to the temperature is reached, cooling is started with a cooling device provided between the heat-retaining furnaces, the temperature is cooled to T _{12 to} T ₂₁ , and then the heat is maintained until T ₂₂ , and then T ₀ A method for producing an alloyed hot-dip galvanized steel sheet, which is cooled to a low temperature.
_{S = (T 11 -T 0)} × t 1/2
_{+ ((T 11 -T 0)} + (T 12 -T 0)) × t 2/2
+ ((T ₁₂ −T ₀ ) + (T ₂₁ −T ₀ )) × Δt / 2
_{+ ((T 21 -T 0)} + (T 22 -T 0)) × t 3/2
_{+ (T 22 -T 0) ×} t 4/2 ···· (A)
Here, T ₀ : 420 (° C.),
T ₁₁ : Steel sheet temperature (° C.) on the heating furnace exit side,
T ₁₂ : Steel plate temperature (° C.) on the inlet side of the cooling zone in the heat insulation furnace,
T ₂₁ : steel plate temperature (° C.) on the cooling zone exit side of the heat-retaining furnace,
T ₂₂ : Steel plate temperature (° C.) on the exit side of the heat insulation furnace,
t ₁ : Processing time (sec) from T ₀ to heating furnace exit side,
t ₂ : treatment time (sec) from the heating furnace exit side to the cooling zone entry side,
Δt: Processing time (sec) from the cooling zone entry side to the cooling zone exit side,
t ₃ : treatment time (sec) from the cooling zone exit side to the heat insulation furnace exit side,
t _4: processing time from the rapid cooling zone entry side to _{T 0} (sec)   The method for producing an alloyed hot-dip galvanized steel sheet according to claim 1, wherein a heat insulation furnace divided into a first heat insulation furnace and a second heat insulation furnace is used as the heat insulation furnace. Billing based on said determined temperature integrated value (S), to determine the heating furnace exit side of the steel sheet temperature (T _11), and adjusting the heating furnace exit side of the steel sheet temperature (T ₁₁₎ The manufacturing method of the galvannealed steel plate of Claim 1 or Claim 2. Method for producing alloyed hot-dip galvanized steel sheet according to claim 3, characterized in that said determined furnace outlet side of the steel sheet temperature (T _11), corrected in accordance with the steel grade and / or coating weight of the steel plate .   The method for producing an alloyed hot-dip galvanized steel sheet according to any one of claims 1 to 4, wherein the temperature integrated value is corrected by a steel sheet temperature (Tin) on the plating bath entrance side. When the degree of alloying (Fe concentration) is constant, the steel plate temperature (T ₁₁ ) on the heating furnace exit side is determined so that the temperature integrated value (S) is constant, and when the target Fe concentration changes, The temperature pattern for performing the alloying process is controlled by determining a steel plate temperature (T ₁₁ ) on the heating furnace exit side based on a temperature integrated value (S) corresponding to a target Fe concentration. The manufacturing method of the galvannealed steel plate as described in any one of Claim 1 thru | or 5. The time (t ₀ ) from the steel plate temperature (Tin) on the plating bath entrance side to the steel plate temperature (T ₁₁ ) on the heating furnace exit side is 15 seconds or less. A method for producing an alloyed hot-dip galvanized steel sheet according to claim 1. The heating rate from the steel plate temperature on the plating bath outlet side to the steel plate temperature (T ₁₁ ) on the heating furnace outlet side is 10 ° C./sec or more. The manufacturing method of the galvannealed steel plate described in 1.   The method for producing an alloyed hot-dip galvanized steel sheet according to any one of claims 1 to 8, wherein the steel sheet from the heat-retaining furnace is rapidly cooled at a cooling rate of 4 ° C / sec or more. .

Images