JP4890492B2 - Method for producing alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance - Google Patents
Method for producing alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance Download PDFInfo
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本発明は、塗装焼付硬化性(BH性)、常温遅時効性、成形性を兼ね備えた合金化溶融亜鉛めっき鋼板の製造方法に関するものである。 The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet having paint bake hardenability (BH property), room temperature slow aging property, and formability.
本発明が係わる合金化溶融亜鉛めっき鋼板は、自動車、家庭電気製品、建物などに使用されるものである。 The alloyed hot-dip galvanized steel sheet according to the present invention is used for automobiles, household electrical appliances, buildings and the like.
溶鋼の真空脱ガス処理の進歩により、極低炭素鋼の溶製が容易になった現在、良好な加工性を有する極低炭素鋼板の需要は益々増加しつつある。この中でも、TiやNbを添加した極低炭素鋼板は極めて良好な加工性を有するが、更にこの添加量をC量とのバランスで調整することで塗装焼付硬化(BH)性を付与しつつ、PやMnやSiなどの固溶強化元素を添加して高強度化を図るなどした、高強度合金化溶融亜鉛めっき鋼板は重要な位置をしめつつある。しかしながら、BH鋼板はその発現機構として、固溶Cとプレス成型等で材料に導入された転位との相互作用を利用するため、プレス成型時のストレッチャーストレイン発生、即ち時効現象も起こりやすく、常温遅時効性との両立が技術的な課題である。 With the progress of vacuum degassing treatment of molten steel, it has become easy to melt ultra-low carbon steel. Now, the demand for ultra-low carbon steel sheet with good workability is increasing more and more. Among these, the ultra-low carbon steel sheet to which Ti or Nb is added has extremely good workability, and furthermore, by imparting paint bake hardening (BH) properties by adjusting the addition amount in balance with the C amount, High-strength alloyed hot-dip galvanized steel sheets, which have been strengthened by adding solid solution strengthening elements such as P, Mn, and Si, are becoming important. However, since the BH steel sheet uses the interaction between solid solution C and dislocations introduced into the material by press molding or the like as its manifestation mechanism, stretcher strain generation during press molding, that is, aging phenomenon easily occurs. Coexistence with delayed aging is a technical issue.
この両立を図るために、特許文献1のようなめっき鋼板の製造ラインにおける冷延板からの焼鈍−めっき浸漬−合金化などの熱履歴を制御する技術を始め、特許文献2のような最終の調質圧延量を調整する技術、また特許文献3のようなめっき鋼板に異周速調質圧延を施す技術など、固溶Cの量や状態、及び材料に導入する転位の量や状態の両面から種々の技術が検討されている。しかしながら、これらの従来技術は基本的に冷延板の焼鈍工程を含む熱処理とそれに続く調質圧延との組み合わせによるゼンジマー法や無酸化炉方式での合金化溶融亜鉛めっき製造プロセスを前提としたものである。
In order to achieve this coexistence, a technique for controlling the thermal history such as annealing-plating immersion-alloying from a cold-rolled sheet in a production line for a plated steel sheet as in
ところが近年、特許文献4のように冷延板を焼鈍した焼鈍済み冷延鋼板を用いて、これを電気加熱などで急速昇温して、めっき浸漬後に合金化熱処理することで合金化溶融亜鉛めっき鋼板を製造する新しい製造プロセスが開発されている。このプロセスは既存の冷延鋼板製造ラインを焼鈍ラインとして活用するため、続く合金化溶融亜鉛めっき鋼板製造ラインでは焼鈍する必要がない。しかしながら他方、一旦焼鈍済みの冷延鋼板を後者のラインで通板する際に、めっき不良につながる形状不良を防止するなどの目的で、前者の冷延鋼板製造ラインで調質圧延を施されると、後者のめっきラインでの最終の調質圧延と合わせて、計二度の調質圧延が材料に付与されることになる。ところで前者の調質圧延は、鋼板がその後加熱され、亜鉛めっき合金化熱処理を受けることを考えると、後者の最終の調質圧延とは鋼板に与える影響が異なる。このため前記の新プロセスにおける二回の調質圧延方法については、例えば特許文献5のような低炭素Alキルド鋼や、特許文献6のような複合組織の高強度鋼板の材質に関して、特に前者の中間での調質圧延の伸び率に着目した検討がなされている。しかしながら、この新めっきプロセスでの極低炭素鋼板の材質に関する検討、特にBH性と常温遅時効性の両立が求められる極低炭素焼付硬化鋼板における検討は見当たらない。 However, in recent years, an annealed cold-rolled steel sheet obtained by annealing a cold-rolled sheet as in Patent Document 4 is rapidly heated by electric heating or the like, and alloyed hot-dip galvanized by performing an alloying heat treatment after plating immersion. New manufacturing processes for manufacturing steel sheets have been developed. Since this process uses the existing cold-rolled steel sheet production line as an annealing line, it does not need to be annealed in the subsequent galvannealed steel sheet production line. However, on the other hand, when the annealed cold-rolled steel sheet is passed through the latter line, the former cold-rolled steel sheet production line is subjected to temper rolling for the purpose of, for example, preventing shape defects leading to plating defects. In combination with the final temper rolling in the latter plating line, a total of two temper rollings are applied to the material. By the way, the former temper rolling is different from the latter temper rolling in that the steel sheet is subsequently heated and subjected to a galvanizing alloying heat treatment. For this reason, with respect to the temper rolling method performed twice in the new process, for example, the former is particularly concerned with the material of the low carbon Al killed steel as in Patent Document 5 and the high-strength steel sheet with a composite structure as in Patent Document 6. Consideration has been made focusing on the elongation rate of temper rolling in the middle. However, there are no studies on the material of an ultra-low carbon steel sheet in this new plating process, particularly an ultra-low carbon bake-hardened steel sheet that requires both BH properties and room temperature slow aging properties.
上述のとおり、BH性と常温遅時効性の両立が求められる極低炭素焼付硬化鋼板における、前記の新めっきプロセスでの材質に関わる調質圧延方法に関する技術は見当たらない。しかしながら、BH性や時効性は調質圧延率の影響を強く受けること、更にそもそも、加工性の良好な極低炭素鋼板の調質圧延は、過度に行うと降伏強度の上昇や伸びの低下などまねくことなど、本発明が対象とする鋼板製造において、常温遅時効性を確保するのに必要最小限の調質圧延条件を明確にすることは、工業的に極めて重要である。 As described above, there is no technology relating to the temper rolling method related to the material in the new plating process in the ultra-low carbon bake-hardened steel sheet that requires both BH properties and room temperature slow aging properties. However, BH properties and aging properties are strongly affected by the temper rolling rate. Furthermore, temper rolling of extremely low carbon steel sheets with good workability in the first place increases yield strength and decreases elongation. It is industrially very important to clarify the minimum temper rolling conditions necessary to ensure normal temperature slow aging in the production of steel sheets targeted by the present invention, such as mimicking.
そこで、本発明は、焼鈍済み冷延鋼板を用いて、これを急速昇温して、めっき浸漬後に合金化熱処理することで合金化溶融亜鉛めっき鋼板を製造する新しい製造プロセスでの、BH性と常温遅時効性とを兼ね備えた、塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法を提供することを目的とするものである。 Therefore, the present invention uses an annealed cold-rolled steel sheet, rapidly raises the temperature, and heat treatment by alloying after plating soaking is performed in a new production process for producing an alloyed hot-dip galvanized steel sheet. It is an object of the present invention to provide a method for producing an alloyed hot-dip galvanized steel sheet that has both room temperature slow aging and excellent paint bake hardening performance.
本発明者らは、上記の目標を達成するために、鋭意、研究を遂行し、以下に述べるような、従来にはない知見を得た。 The inventors of the present invention diligently conducted research to achieve the above-described goal, and obtained the following unprecedented knowledge as described below.
すなわち、新めっきプロセスにおけるめっき前後の調質圧延率に対して、加工性や常温遅時効性などの各種材質に及ぼす影響を調査し、BH性と常温遅時効性とを兼ね備えた、塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板を得ることができるめっき前後の二種の調質圧延の最適な付与比率の条件を見出したものである。 In other words, we investigated the effects of various properties such as workability and room temperature slow aging on the temper rolling ratio before and after plating in the new plating process, and the paint bake hardening that combines BH properties and room temperature slow aging. The present inventors have found out conditions for the optimum application ratio of two types of temper rolling before and after plating that can obtain an alloyed hot-dip galvanized steel sheet having excellent performance.
本発明は、このような思想と新知見に基づいて構築されたものであり、その発明の要旨とするところは以下のとおりである。 The present invention has been constructed on the basis of such ideas and new findings, and the gist of the present invention is as follows.
(1) 質量%で、
C :0.0014〜0.0025%、
Si≦0.5%、
Mn:0.03〜1.0%、
P :0.01〜0.15%、
S ≦0.015%、
Al:0.005〜0.1%、
N ≦0.0040%
を含有し、残部Feおよび不可避的不純物からなる組成のスラブを、Ar3変態点以上の温度で熱間圧延を行い、圧下率60〜95%の冷間圧延を施し、連続焼鈍ラインにて650℃〜Ac3変態点で焼鈍後に調質圧延を施して、一旦、焼鈍済み冷延鋼板を製造し、引き続き、連続溶融亜鉛めっきラインにて亜鉛めっき浴温度まで加熱してめっきした後、460〜600℃までの温度範囲で5〜15秒の合金化熱処理を行い、その後、再度調質圧延を施す、合金化溶融亜鉛めっき鋼板の製造プロセスにおいて、めっき前後の二種の調質圧延率の関係が、めっきをしない連続焼鈍ラインのみによって製造される冷延鋼板に施される調質圧延率を基準とした、次式で示す条件で行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
SP1+SP2≦SP0≦0.75×SP1+1.5×SP2
ここで、SP0は冷間圧延後に焼鈍ラインのみによって冷延鋼板を製造する際の、鋼板の遅時効性(鋼板に100℃で1時間の熱処理を施した後の引張時の降伏伸び≦0.3%)が確保される最小限の調質圧延率(%)、SP1とSP2は焼鈍ラインに引き続くめっきラインによって合金化溶融亜鉛めっき鋼板を製造する際の、めっき前後の各々の調質圧延率(%)を意味する。
(1) In mass%,
C: 0.0014 to 0.0025%,
Si ≦ 0.5%,
Mn: 0.03 to 1.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar3 transformation point, cold-rolled at a reduction rate of 60 to 95%, and 650 ° C. in a continuous annealing line. After temper rolling after annealing at the Ac3 transformation point, an annealed cold-rolled steel sheet is once manufactured, and then heated to a galvanizing bath temperature in a continuous hot-dip galvanizing line, followed by plating at 460-600 ° C. In the manufacturing process of the alloyed hot-dip galvanized steel sheet, which is subjected to alloying heat treatment for 5 to 15 seconds in the temperature range up to and then subjected to temper rolling again, the relationship between the two types of temper rolling ratio before and after plating, Alloyed molten zinc with excellent paint bake hardening performance, characterized by the following formula, based on the temper rolling ratio applied to cold-rolled steel sheets produced only by continuous annealing lines without plating Me Method of manufacturing a steel plate.
SP1 + SP2 ≦ SP0 ≦ 0.75 × SP1 + 1.5 × SP2
Here, SP0 is the slow aging property of a steel sheet when producing a cold-rolled steel sheet only by an annealing line after cold rolling (yield elongation at tension after subjecting the steel sheet to heat treatment at 100 ° C. for 1 hour ≦ 0. 3%) is the minimum temper rolling ratio (%), and SP1 and SP2 are the temper rolling ratios before and after plating when producing galvannealed steel sheets by the plating line following the annealing line. (%).
(2) さらに、質量%で、B:0.0001〜0.0040%を含有することを特徴とする前記(1)に記載の塗装焼付硬化性能に優れた冷延鋼板の製造方法。 (2) The method for producing a cold-rolled steel sheet having excellent paint bake hardening performance according to the above (1), further comprising B: 0.0001 to 0.0040% by mass%.
(3) 質量%で、
C :0.0014〜0.0030%、
Si≦0.5%、
Mn:0.03〜1.0%、
P :0.01〜0.15%、
S ≦0.015%、
Al:0.005〜0.1%、
N ≦0.0040%
を含有し、さらに
Ti:0.002〜0.015%
および
Nb:0.002〜0.015%
のうち1種または2種を
Ti+Nb=0.002〜0.015%
となるように含有し、残部Feおよび不可避的不純物からなる組成のスラブを、Ar3変態点以上の温度で熱間圧延を行い、圧下率60〜95%の冷間圧延を施し、連続焼鈍ラインにて650℃〜Ac3変態点で焼鈍後に調質圧延を施して、一旦、焼鈍済み冷延鋼板を製造し、引き続き、連続溶融亜鉛めっきラインにて亜鉛めっき浴温度まで加熱してめっきした後、460〜600℃までの温度範囲で5〜15秒の合金化熱処理を行い、その後、再度調質圧延を施す、合金化溶融亜鉛めっき鋼板の製造プロセスにおいて、めっき前後の二種の調質圧延率の関係が、めっきをしない連続焼鈍ラインのみによって製造される冷延鋼板に施される調質圧延率を基準とした、次式で示す条件で行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
SP1+SP2≦SP0≦0.75×SP1+1.5×SP2
ここで、SP0は冷間圧延後に焼鈍ラインのみによって冷延鋼板を製造する際の、鋼板の遅時効性(鋼板に100℃で1時間の熱処理を施した後の引張時の降伏伸び≦0.3%)が確保される最小限の調質圧延率(%)、SP1とSP2は焼鈍ラインに引き続くめっきラインによって合金化溶融亜鉛めっき鋼板を製造する際の、めっき前後の各々の調質圧延率(%)を意味する。
(3) In mass%,
C: 0.0014 to 0.0030%,
Si ≦ 0.5%,
Mn: 0.03 to 1.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
And further Ti: 0.002 to 0.015%
And Nb: 0.002 to 0.015%
1 type or 2 types of Ti + Nb = 0.002 to 0.015%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar3 transformation point, cold-rolled at a reduction ratio of 60 to 95%, and continuously annealed. After annealing at 650 ° C. to Ac3 transformation point, temper rolling is performed to once produce an annealed cold-rolled steel sheet, followed by heating to a galvanizing bath temperature in a continuous hot dip galvanizing line and then plating 460 In the manufacturing process of alloyed hot-dip galvanized steel sheet, which is subjected to alloying heat treatment for 5 to 15 seconds in a temperature range up to ~ 600 ° C and then subjected to temper rolling again, An alloy excellent in paint bake hardening performance, characterized in that the relationship is based on the temper rolling ratio applied to the cold-rolled steel sheet produced only by the continuous annealing line without plating, based on the conditions shown by the following formula Chemical dissolution Method of manufacturing a galvanized steel sheet.
SP1 + SP2 ≦ SP0 ≦ 0.75 × SP1 + 1.5 × SP2
Here, SP0 is the slow aging property of a steel sheet when producing a cold-rolled steel sheet only by an annealing line after cold rolling (yield elongation at tension after subjecting the steel sheet to heat treatment at 100 ° C. for 1 hour ≦ 0. 3%) is the minimum temper rolling ratio (%), and SP1 and SP2 are the temper rolling ratios before and after plating when producing galvannealed steel sheets by the plating line following the annealing line. (%).
(4) さらに、質量%で、B:0.0001〜0.0040%を含有することを特徴とする前記(3)に記載の塗装焼付硬化性能に優れた冷延鋼板の製造方法。 (4) The method for producing a cold-rolled steel sheet having excellent paint bake hardening performance according to (3), further comprising B: 0.0001 to 0.0040% by mass%.
以上詳述したように、本発明により、焼鈍済み冷延鋼板を用いて、これを急速昇温して、めっき浸漬後に合金化熱処理することで合金化溶融亜鉛めっき鋼板を製造する、新しいめっき鋼板製造プロセスによって、強度と加工性を兼ね備え、更にBH性と常温遅時効性をも兼ね備えた、塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法を提供することができる。この新しいプロセスは、既存の冷延鋼板製造ラインを活用することを前提としているため、生産効率が高く、他方、本発明により製造された鋼板は、使用に当たって今までの鋼板より板厚を減少でき、地球環境保全に寄与できる軽量化を可能にする鋼板であることから、本発明は工業的に価値の高い発明であると言える。 As described in detail above, according to the present invention, a new plated steel sheet is manufactured by using an annealed cold-rolled steel sheet, rapidly raising the temperature, and performing alloying heat treatment after plating immersion to produce an alloyed hot-dip galvanized steel sheet. According to the production process, it is possible to provide a method for producing an alloyed hot-dip galvanized steel sheet that has both strength and workability, and further has BH properties and room temperature slow aging properties and excellent in bake hardening performance. This new process is based on the premise that the existing cold-rolled steel plate production line is used, so that the production efficiency is high. On the other hand, the steel plate manufactured according to the present invention can reduce the plate thickness compared with the conventional steel plate. Since the steel sheet enables weight reduction that can contribute to global environmental conservation, it can be said that the present invention is an industrially valuable invention.
ここに、本発明において鋼組成および製造条件を上述のように限定する理由についてさらに説明する。 Here, the reason why the steel composition and production conditions are limited as described above in the present invention will be further described.
Cは製品のBH特性および常温遅時効性さらには加工性を決定する極めて重要な元素である。Cが0.0014%未満となると十分なBH性が発現しないほか、製造コストが著しく増加するので、その下限を0.0014%とする。一方、C量が0.0025%を超えると成形性の劣化を招き、また常温非時効性が確保されなくなるので、上限を0.0025%とする。高BH性と常温遅時効性とのバランスは、C量を0.0016〜0.0022%の範囲とすることがさらに好ましい。Ti、Nbを含有する場合には、固溶Cを確保しにくくなるのでCの上限を0.0030%とする。Ti、Nbを含有する場合には0.0017〜0.0024%がC量の好ましい範囲である。 C is an extremely important element that determines the BH characteristics, normal temperature slow aging property and workability of the product. When C is less than 0.0014%, sufficient BH properties are not exhibited, and the manufacturing cost is remarkably increased, so the lower limit is made 0.0014%. On the other hand, if the amount of C exceeds 0.0025%, the moldability is deteriorated and the non-aging property at room temperature is not ensured, so the upper limit is made 0.0025%. The balance between the high BH property and the room temperature slow aging is more preferably within the range of 0.0016 to 0.0022% of the C content. When Ti and Nb are contained, since it becomes difficult to ensure solid solution C, the upper limit of C is made 0.0030%. When Ti and Nb are contained, 0.0017 to 0.0024% is a preferable range of the C amount.
Siは安価に強度を増加させる元素として知られており、その添加量は狙いとする強度レベルに応じて変化するが、添加量が0.5%超となると降伏強度が上昇しすぎてプレス成形時に面歪が生じる。なお従来のゼンジマー法や無酸化炉方式でのめっき製造プロセスによる合金化溶融亜鉛めっき鋼板では、めっき密着性の低下や、合金化反応の遅延による生産性の低下などの問題から、Si量に制約が設けられることが多いが、本発明が対象とするめっき製造プロセスでは、後述するように、焼鈍済みの冷延鋼板をめっき浴温度まで加熱する際の表面酸化防止などの理由でNiめっきやNi−Feめっきなどのプレめっきが付与されるため、特段の制約を設ける必要はない。 Si is known as an element that increases strength at a low cost, and the amount of addition varies depending on the target strength level, but when the amount exceeds 0.5%, the yield strength increases too much and press forming is performed. Sometimes surface distortion occurs. In the case of alloyed hot-dip galvanized steel sheets produced by conventional Zenzimer and non-oxidizing furnace plating processes, the amount of Si is limited due to problems such as poor plating adhesion and reduced productivity due to the delay of the alloying reaction. However, in the plating manufacturing process targeted by the present invention, as described later, Ni plating and Ni are used for the purpose of preventing surface oxidation when heating an annealed cold-rolled steel sheet to the plating bath temperature. Since pre-plating such as -Fe plating is applied, it is not necessary to provide special restrictions.
MnはMnSを形成し熱延時のSによる耳割れを抑制したり、熱延板組織を微細にするので、0.03%以上添加する。さらに、Mnは降伏強度をあまり増加させずに強度を増加させる有効な固溶体強化元素であり、かつ化成処理性を改善したり、溶融亜鉛めっき性を改善する効果も有する。一方、Mn量が1.0%を超えると強度が高くなりすぎたり、亜鉛めっきの密着性が阻害されたりするのでその上限を1.0%とする。 Mn forms MnS, suppresses the ear cracking due to S during hot rolling, and makes the hot rolled sheet structure fine, so 0.03% or more is added. Furthermore, Mn is an effective solid solution strengthening element that increases the strength without significantly increasing the yield strength, and also has the effect of improving the chemical conversion treatment property and the hot dip galvanizing property. On the other hand, if the amount of Mn exceeds 1.0%, the strength becomes too high, or the adhesion of galvanization is inhibited, so the upper limit is made 1.0%.
PはSiと同様に安価に強度を上昇させる効果がある元素として知られており、0.01%以上でその効果が得られるが、強度を増加する必要がある場合にはさらに積極的に添加する。また、Pは熱延組織を微細にし、加工性を向上する効果も有する。ただし、添加量が0.15%を超えると、降伏強度が増加し過ぎてプレス時に面形状不良を引き起こす。さらに、連続溶融亜鉛めっき時に合金化反応が極めて遅くなり、生産性が低下する。また、2次加工性も劣化する。したがって、Pの上限値を0.15%とする。 P is known as an element that has the effect of increasing the strength at a low cost similarly to Si, and the effect can be obtained at 0.01% or more. However, when it is necessary to increase the strength, P is more actively added. To do. P also has the effect of making the hot-rolled structure fine and improving workability. However, if the addition amount exceeds 0.15%, the yield strength increases excessively, causing surface shape defects during pressing. Furthermore, the alloying reaction becomes extremely slow during continuous hot dip galvanizing, and productivity is lowered. Also, the secondary workability is deteriorated. Therefore, the upper limit value of P is set to 0.15%.
Sは0.015%超では、熱間割れの原因となったり、加工性を劣化させるので0.15%を上限とする。 If S exceeds 0.015%, it causes hot cracking and deteriorates workability, so 0.15% is made the upper limit.
Alは脱酸調整およびTiを添加しない場合にはNの固定に使用するが、0.005%未満ではその効果が不十分である。一方、Al量が0.1%超になるとコストアップを招いたり、表面性状の劣化を招くのでその上限を0.1%とする。 Al is used for deoxidation adjustment and fixing N when Ti is not added, but if it is less than 0.005%, its effect is insufficient. On the other hand, if the Al content exceeds 0.1%, the cost is increased or the surface properties are deteriorated, so the upper limit is made 0.1%.
Nはあまり多いと多量のTi、Nb、Alが必要になったり、加工性が劣化したりするので0.0040%を上限値とする。 If N is too large, a large amount of Ti, Nb, and Al becomes necessary, and workability deteriorates, so 0.0040% is made the upper limit.
Bは2次加工脆化の防止に有効であるほか、AlやTiでNを固定するよりも再結晶温度が低くなるので、必要に応じて0.0040%以下添加する。しかし、Bが0.0001%未満ではその効果が発現しないので、0.0001%を下限とする。 B is effective in preventing secondary work embrittlement, and the recrystallization temperature is lower than fixing N with Al or Ti, so 0.0040% or less is added as necessary. However, if B is less than 0.0001%, the effect is not exhibited, so 0.0001% is made the lower limit.
Ti、NbはN、C、Sの一部を固定することにより、常温遅時効性を確保する役割を有する。さらには、熱延板の結晶粒を微細化し、製品板の加工性を良好にするので必要に応じてTi、Nbの1種又は2種を添加する。Ti、Nbがそれぞれ0.002%未満ではその添加効果が現れないのでこれを下限値とする。一方、Ti、Nbの添加量が多すぎると十分なBH性が発現しにくいばかりではなく、再結晶温度が著しく上昇したり、亜鉛めっきの密着性も阻害される。従って、Ti、Nbの上限をいずれも0.015%、Ti+Nbの上限を0.015%とする。より好ましくはTi:0.004〜0.010%、Nb:0.003〜0.009%、Ti+Nb=0.004〜0.010%である。 Ti and Nb have a role of securing a slow aging property at room temperature by fixing a part of N, C, and S. Furthermore, since the crystal grains of the hot-rolled plate are refined and the workability of the product plate is improved, one or two of Ti and Nb are added as necessary. If Ti and Nb are each less than 0.002%, the effect of addition does not appear, so this is the lower limit. On the other hand, if the addition amount of Ti and Nb is too large, not only the sufficient BH property is hardly exhibited, but also the recrystallization temperature is remarkably increased, and the adhesion of galvanization is also inhibited. Therefore, the upper limits of Ti and Nb are both 0.015%, and the upper limit of Ti + Nb is 0.015%. More preferably, Ti is 0.004 to 0.010%, Nb is 0.003 to 0.009%, and Ti + Nb = 0.004 to 0.010%.
これらを主成分とする鋼にCu、Sn、Zn、Mo、W、Cr、Niを合計で1%以下含有しても構わない。 You may contain 1% or less of Cu, Sn, Zn, Mo, W, Cr, and Ni in the steel which has these as a main component in total.
次に、製造条件の限定理由について述べる。
熱間圧延に供するスラブは特に限定するものではない。すなわち、連続鋳造スラブや薄スラブキャスターなどで製造したものであればよい。また、鋳造後に直ちに熱間圧延を行う連続鋳造−直接圧延(CC−DR)のようなプロセスにも適合する。
Next, the reasons for limiting the manufacturing conditions will be described.
The slab used for hot rolling is not particularly limited. That is, what was manufactured with the continuous casting slab, the thin slab caster, etc. should just be used. It is also compatible with processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.
熱延の仕上温度は製品板の加工性を確保するという観点からAr3変態点以上とする必要がある。 The hot rolling finishing temperature needs to be not less than the Ar3 transformation point from the viewpoint of ensuring the workability of the product plate.
熱延後の冷却は、限定するものではないが、特に優れた加工性を必要とする場合には、圧延後1.5秒以内に冷却を開始し、巻取温度までの平均冷却速度を30℃/s以上とすることが望ましい。 Although cooling after hot rolling is not limited, when particularly excellent workability is required, cooling is started within 1.5 seconds after rolling, and the average cooling rate up to the coiling temperature is set to 30. It is desirable to set it to at least ° C / s.
巻取温度は特に限定しないが、TiやBを添加しないときには650〜800℃とすることが望ましい。これによってAlNの形成、成長が促され良好な成形性が確保される。TiやBを添加する際にはNは巻取前に固定されるので巻取温度は室温から800℃とすればよい。巻取温度の上限が800℃であることは、コイル両端部での材質劣化に起因する歩留低下を防止すること、また、熱延組織の粗大化を防止する観点から決定される。 The coiling temperature is not particularly limited, but is preferably 650 to 800 ° C. when Ti or B is not added. This promotes the formation and growth of AlN and ensures good moldability. When adding Ti or B, N is fixed before winding, so the winding temperature may be from room temperature to 800 ° C. The upper limit of the coiling temperature of 800 ° C. is determined from the viewpoint of preventing a decrease in yield due to material deterioration at both ends of the coil and preventing the hot rolled structure from becoming coarse.
冷間圧延は、通常の条件でよく、焼鈍後の深絞り性を確保する目的からその圧延率は、60%以上とする。圧下率を95%超とすると加工性が劣化してしまうのでこれを上限とする。 Cold rolling may be performed under normal conditions, and the rolling rate is set to 60% or more for the purpose of ensuring deep drawability after annealing. If the rolling reduction exceeds 95%, workability deteriorates, so this is the upper limit.
連続焼鈍ラインの焼鈍温度は、650℃以上Ac3変態点以下とする。焼鈍温度が650℃未満では、再結晶が完了せず、加工性が劣悪となる。一方、焼鈍温度がAc3変態点超では、変態によって加工性の低下を招く。焼鈍後の冷却および熱処理条件は、特別に限定するものではないが、通常、650℃以上の温度から熱処理温度までの範囲を40℃/s以上で冷却し、連続焼鈍ラインでの生産性を低下させない温度域として、280〜450℃で120秒以上行うことが好ましく、280〜380℃の範囲で150秒以上熱処理を行うのがより好ましい。なお、このラインの冷却の際に、水やミスト冷却を行うと鋼板表面がスケール生成するため、鋼板を熱処理後に酸洗する場合があるが、本発明はこの酸洗の有無に何ら影響するものではない。 The annealing temperature of a continuous annealing line shall be 650 degreeC or more and Ac3 transformation point or less. When the annealing temperature is less than 650 ° C., recrystallization is not completed, and the workability is deteriorated. On the other hand, when the annealing temperature exceeds the Ac3 transformation point, the workability is lowered due to the transformation. Cooling and heat treatment conditions after annealing are not particularly limited, but usually the temperature from 650 ° C. or higher to the heat treatment temperature is cooled at 40 ° C./s or more to reduce productivity in the continuous annealing line. As a temperature range not to be performed, it is preferable to carry out at 280-450 degreeC for 120 second or more, and it is more preferable to heat-process in the range of 280-380 degreeC for 150 second or more. In addition, when water or mist cooling is performed during cooling of this line, the steel sheet surface generates scale, so the steel sheet may be pickled after heat treatment, but the present invention has no influence on the presence or absence of this pickling. is not.
連続焼鈍ラインの焼鈍及び熱処理に引き続き、通常ライン内に併設されている、調質圧延機によるめっき前の調質圧延率は、本発明において重要である。しかしながらこの量は後述するように、めっき後に付与される最終の調質圧延率と合わせて、最適な組み合わせが存在するため、ここで単独に圧延率を規定するものではない。例えば、この後のめっきラインでの通板性が確保される場合には、この焼鈍ラインでのめっき前調質圧延は、省略すら可能である。他方これに対し、このラインが最終工程となる冷延鋼板の場合には、時効によるプレス成型時のストレッチャーストレインの防止、即ち常温遅時効性を確保するために、この調質圧延は必須である。但し、必要以上の過度な調質圧延は、材料をいたずらに加工硬化させ、降伏強度の上昇や伸びの低下につながることから、通常、遅時効性が確保される最小の調質圧延率が選定される。具体的には鋼組成に応じて1〜2%の調質圧延が施されている。 Following the annealing and heat treatment of the continuous annealing line, the temper rolling ratio before plating by the temper rolling mill provided in the normal line is important in the present invention. However, as will be described later, there is an optimum combination of this amount together with the final temper rolling ratio applied after plating, so the rolling ratio is not stipulated here alone. For example, when the plate-passability in the subsequent plating line is ensured, the pre-plating temper rolling in the annealing line can be omitted. On the other hand, in the case of a cold-rolled steel sheet in which this line is the final process, this temper rolling is indispensable to prevent stretcher strain at the time of press molding due to aging, that is, to ensure room temperature slow aging. is there. However, excessive temper rolling more than necessary can cause the material to be hardened and hardened, leading to an increase in yield strength and a decrease in elongation. Therefore, the minimum temper rolling rate that normally ensures delayed aging is selected. Is done. Specifically, 1-2% temper rolling is applied depending on the steel composition.
この後に通板する連続溶融亜鉛めっきラインでは、前記のとおり、まず、焼鈍済みの冷延鋼板をめっき浴温度まで加熱する際の表面酸化防止などの理由で、NiめっきやNi−Feめっきなどのプレめっきを付与した後に、めっきするために鋼板をめっき浴温度まで加熱する。このめっき量としては0.2〜2g/m2程度が望ましいが、プレめっきの方法は電気めっき、浸漬めっき、スプレーめっきの何れでもよい。またその加熱方法は短時間処理でき生産性の高い電気加熱で行われることが望ましい。次に、亜鉛浴中に浸漬し、ワイピング後に更に昇温して、めっき合金化のために熱処理を行う。この条件は460〜600℃で5〜15秒とする。460℃未満や5秒未満では合金化が十分に生じないため摺動性が悪化し、600℃を超えたり15秒を超えると合金化が進みすぎてパウダリング性が悪くなる。 In the continuous hot-dip galvanizing line that passes after this, as described above, first, for the purpose of preventing surface oxidation when heating the annealed cold-rolled steel sheet to the plating bath temperature, Ni plating, Ni-Fe plating, etc. After applying the pre-plating, the steel sheet is heated to the plating bath temperature for plating. The plating amount is preferably about 0.2 to 2 g / m 2, but the pre-plating method may be any of electroplating, immersion plating, and spray plating. In addition, it is desirable that the heating method be performed by electric heating that can be processed in a short time and has high productivity. Next, it is immersed in a zinc bath, further heated after wiping, and heat-treated for forming a plating alloy. This condition is 460 to 600 ° C. and 5 to 15 seconds. If it is less than 460 ° C. or less than 5 seconds, alloying does not occur sufficiently, so that the slidability deteriorates. If it exceeds 600 ° C. or exceeds 15 seconds, alloying proceeds too much and the powdering properties deteriorate.
合金化後の鋼板には、表面調整や形状調整のためにラインの最終段階で再度、調質圧延が施されるが、このめっき後の調質圧延率は、前記の連続焼鈍ラインにおけるめっき前の調質圧延率と合わせて、本発明で最も重要である。そこでこの二種の調質圧延率の要件に関しては、本発明に至った実験によって、以下に詳細に説明する。 The steel sheet after alloying is subjected to temper rolling again at the final stage of the line for surface adjustment and shape adjustment. The temper rolling ratio after plating is the same as that before plating in the continuous annealing line. The temper rolling ratio is the most important in the present invention. Therefore, the requirements for these two types of temper rolling ratio will be described in detail below by experiments that have led to the present invention.
表1に示す本発明の鋼を用いて、スラブ加熱温度1200℃、仕上温度920℃、巻取温度720℃で熱間圧延し、4.0mm厚の鋼帯とした。酸洗後、80%の圧下率の冷間圧延を施し0.8mm厚の冷延板とし、次いで連続焼鈍ラインにて780℃で焼鈍した。この焼鈍板にめっき前調質圧延率として0〜1.5%の種々の調質圧延を付与し、連続溶融めっきラインにてめっき後に550℃で10秒の合金化処理し、再度、めっき後調質圧延率として0.5〜2%の種々の調質圧延を付与した。そして、このめっき鋼板の降伏応力と常温遅時効性、及びBH量を調査した。ここで引張試験はJIS Z 2201記載の5号試験片をJIS Z 2241記載の方法で行い、BH量はJIS G 3135の附属書Aに規定の方法で、また常温遅時効性は、試験前の試験片に100℃で1時間の熱処理を施した後の引張時の降伏伸びで評価し、0.3%以下のものを遅時効性が確保されているとした。試験結果を鋼Aについては図1で、鋼Bについては図2でまとめる。 Using the steel of the present invention shown in Table 1, it was hot-rolled at a slab heating temperature of 1200 ° C., a finishing temperature of 920 ° C., and a winding temperature of 720 ° C. to obtain a steel strip having a thickness of 4.0 mm. After pickling, cold rolling with a reduction rate of 80% was performed to obtain a cold rolled sheet with a thickness of 0.8 mm, and then annealed at 780 ° C. in a continuous annealing line. This tempered sheet was subjected to various temper rolling of 0 to 1.5% as a pre-plating temper rolling ratio, subjected to alloying treatment at 550 ° C. for 10 seconds after plating in a continuous hot dipping line, and again after plating. Various temper rolling of 0.5-2% was given as a temper rolling rate. And the yield stress of this plated steel plate, normal temperature slow aging property, and BH amount were investigated. Here, the tensile test is performed on the No. 5 test piece described in JIS Z 2201 by the method described in JIS Z 2241. The BH amount is the method specified in Annex A of JIS G 3135. The test piece was evaluated by the yield elongation at the time of tension after the heat treatment at 100 ° C. for 1 hour. The test results are summarized in FIG. 1 for steel A and in FIG. 2 for steel B.
両図共に、横軸にめっき前調質圧延率(%)を、縦軸にめっき後調質圧延率(%)をとり、各条件でのめっき鋼板の時効後降伏伸び(時効後YP−El)と降伏応力(YP)の程度から、材質を3種に分類して示した。なおYPの大小は、各鋼を冷間圧延後に焼鈍ラインのみによって冷延鋼板として製造する際に、鋼板の遅時効性が確保される最小限の調質圧延率(SP0)を施した時の、冷延鋼板の降伏応力(YP0)で分類した。ちなみにこの値は鋼AではSP0が1.5%で192MPa、鋼BではSP0が2.0%で203MPaであった。
なお、SP0の技術的意味について説明すると、極低炭素鋼板のBH性は、固溶Cと転位の相互作用を利用したものであるため、鋼組成と調質圧延率の関係は、冷延鋼板や従来のめっき鋼板(ゼンジマー法や無酸化炉法)のような調質圧延が一回のみ施される場合でも、鋼組成に応じてSP0が選定されています。一般的に固溶Cを有する鋼板は、調質圧延率を増すことにより、時効性は改善されますが、硬質化(YPの上昇、Elの劣化)すると共にBH量も低下するため、遅時効性が担保される最低の調質圧延率(SP0)を施すことは、同業者にとってはよく知られた技術である。
In both figures, the horizontal axis represents the temper rolling ratio before plating (%), the vertical axis represents the temper rolling ratio after plating (%), and the yield elongation after aging of the coated steel sheet under each condition (YP-El after aging). ) And yield stress (YP), the materials are classified into three types. Note that the size of YP is that when each steel is manufactured as a cold-rolled steel sheet only by an annealing line after cold rolling, when a minimum temper rolling rate (SP0) that ensures the delayed aging of the steel sheet is applied. And classified by the yield stress (YP0) of the cold-rolled steel sheet. By the way, this value was 192 MPa at 1.5% SP0 for steel A and 203 MPa at 2.0% SP0 for steel B.
The technical meaning of SP0 will be explained. Since the BH property of the ultra-low carbon steel sheet is based on the interaction between solute C and dislocation, the relationship between the steel composition and the temper rolling ratio is SP0 is selected according to the steel composition even when temper rolling is applied only once, such as conventional steel plates (Zenzimer method and non-oxidizing furnace method). In general, a steel plate with solute C is improved in aging by increasing the temper rolling ratio, but is hardened (increased YP, deteriorated El) and also decreases the amount of BH. Applying the minimum temper rolling ratio (SP0) that guarantees the property is a technique well known to those skilled in the art.
図1及び図2で×の条件は、時効後YP−Elが遅時効性の指標である0.3%を超えたものであり、調質圧延率として不十分な条件である。一方、△の条件は遅時効性は満足するものの、YPが上述の冷延鋼板の降伏応力(YP0)を超えており、冷延鋼板よりも材質が硬質となる条件である。よって、この二種の条件に挟まれた○の条件では、遅時効性を満足し、且つ、冷延鋼板よりも軟質な鋼板が得られる。なお、図1と図2の○の条件は異なっているが、これは各鋼の鋼組成の違いに起因した、SP0が異なることによるものであり、SP0を基準とすると、遅時効性を満足する条件は次の(1)式で、降伏応力を満足する条件は次の(2)式として、統一的に規定される。
SP1+2×SP2≦(4/3)×SP0・・・・(1)
SP1+SP2≦SP0・・・・(2)
よって(1)(2)式を共に満足する条件は以下の(3)式によって示すことが出来る。
SP1+SP2≦SP0≦0.75×SP1+1.5×SP2・・・・(3)
ここで、SP0は、冷間圧延後に焼鈍ラインのみによって冷延鋼板を製造する際の、鋼板の遅時効性(鋼板に100℃で1時間の熱処理を施した後の引張時の降伏伸び≦0.3%)が確保される最小限の調質圧延率(%)、SP1とSP2は焼鈍ラインに引き続くめっきラインによって合金化溶融亜鉛めっき鋼板を製造する際の、めっき前後の各々の調質圧延率(%)を意味する。
なお、図1と図2の図中に太枠の三角形の領域で示すのが、この式の示す条件であり、両図共に○の条件を規定していることが確認される。なお、この条件で製造しためっき鋼板のBH量は全て30MPa以上であり、本条件は本発明が要件とする、焼付硬化性も具備した遅時効性と加工性に優れためっき鋼板の製造条件ということができる。
1 and 2 indicate that the post-aging YP-El exceeds 0.3%, which is an indicator of slow aging, and is insufficient for the temper rolling ratio. On the other hand, the condition of Δ is a condition that although the delayed aging is satisfied, YP exceeds the yield stress (YP0) of the cold-rolled steel sheet, and the material is harder than the cold-rolled steel sheet. Therefore, under the condition of ○ sandwiched between these two types of conditions, a steel plate that satisfies the slow aging property and is softer than the cold-rolled steel plate can be obtained. In addition, although the conditions of (circle) of FIG. 1 and FIG. 2 differ, this is because it is based on the difference in SP0 resulting from the difference in the steel composition of each steel, and when SP0 is used as a standard, late aging is satisfied. The condition for satisfying this is the following equation (1), and the condition for satisfying the yield stress is uniformly defined as the following equation (2).
SP1 + 2 × SP2 ≦ (4/3) × SP0 (1)
SP1 + SP2 ≦ SP0 (2)
Therefore, the conditions satisfying both the expressions (1) and (2) can be expressed by the following expression (3).
SP1 + SP2 ≦ SP0 ≦ 0.75 × SP1 + 1.5 × SP2 (3)
Here, SP0 is the slow aging property of the steel sheet when the cold-rolled steel sheet is produced only by the annealing line after cold rolling (yield elongation at tension after subjecting the steel sheet to heat treatment at 100 ° C. for 1 hour ≦ 0 0.3%) is the minimum temper rolling rate (%), SP1 and SP2 are temper rolling before and after plating when producing alloyed hot-dip galvanized steel sheet by the plating line following the annealing line It means rate (%).
In FIG. 1 and FIG. 2, a thick triangular region indicates the condition indicated by this equation, and it is confirmed that the condition of ○ is defined in both figures. In addition, the BH amount of the plated steel sheet manufactured under these conditions is all 30 MPa or more, and this condition is a manufacturing condition of the plated steel sheet excellent in delayed aging and workability, which is required by the present invention and also has bake hardenability. be able to.
さらに、式について追加説明すると、本発明鋼に対し、これを冷延鋼板として製造する場合に最適な調質圧延率(連続焼鈍ラインで遅時効性が確保される最小の調質圧延:SP0を施す)で製造した鋼板材質(YP0)を基準として、同鋼を本発明のプロセスにより合金化溶融亜鉛めっき鋼板として製造する場合の種々の調質圧延率(連続焼鈍ライン=めっき前に調質圧延:SP1を施し、更にその後の連続合金化溶融亜鉛めっきライン=めっき後に調質圧延:SP2を施す)で得られる鋼板材質(YP)の大きさを比較して、これがYP0よりも小さくなる条件(図1、図2の○と△の境界)と、そもそもめっき鋼板で遅時効性が担保されるべき条件(図1、図2の×と○の境界)とから、二種の調質圧延率の条件として実験的に式を決定したものである。ここで図1、図2の比較から分かるようにこの条件は鋼種A,Bで異なる。しかし、これは鋼種A,Bは最適なSP0がそもそも異なることに由来したもので、ここで各SP0を基準とすることで、上記の式(3)で統一的に条件を規定できるため、これを本発明の条件とした。具体的には、式(1)が図1、図2の×と○の境界から上側(○側)を示し、式(2)が△と○の境界から下側(○側)を示す条件である。図中の境界線はこの式(1)、(2)を用いて、図1の鋼AではSP0を1.5%とし、図2の鋼BではSP0を2.0%として計算した結果であり、実験的に決定された異なる○の条件が、式(3)で統一的に表されていることが分かるように各図中に併記してある。 Further, the formula will be further explained. The temper rolling ratio (minimum temper rolling with which slow aging is ensured in the continuous annealing line: SP0) is optimum when the steel of the present invention is manufactured as a cold-rolled steel sheet. Various temper rolling rates (continuous annealing line = temper rolling before plating) when the steel is produced as an alloyed hot-dip galvanized steel sheet by the process of the present invention based on the steel sheet material (YP0) manufactured in : SP1 and further continuous alloying hot dip galvanizing line = temper rolling after plating: SP2 is compared to compare the size of steel plate material (YP), and this is smaller than YP0 ( Two types of temper rolling ratios based on the boundary between ○ and △ in Fig. 1 and Fig. 2) and the conditions (the boundary between X and ○ in Fig. 1 and Fig. 2) that should ensure delayed aging in the first place. Experimentally determined as the condition of Those were. Here, as can be seen from the comparison between FIG. 1 and FIG. 2, this condition differs between steel types A and B. However, this is because the steel types A and B are derived from the fact that the optimum SP0 is different in the first place. By using each SP0 as a reference here, the condition can be uniformly defined by the above equation (3). Was defined as a condition of the present invention. Specifically, the expression (1) indicates the upper side (O side) from the boundary between X and O in FIGS. 1 and 2, and the expression (2) indicates the lower side (O side) from the boundary between Δ and O. It is. The boundary line in the figure is the result of calculation using the formulas (1) and (2), with SP0 being 1.5% for steel A in FIG. 1 and SP0 being 2.0% for steel B in FIG. There are different experimentally determined conditions of ○, which are also shown in each figure so that it can be seen that they are uniformly expressed in equation (3).
以上のような熱延の後の各工程、酸洗、冷延、焼鈍、熱処理、調質圧延(めっき前)、亜鉛めっき、合金化処理、調質圧延(めっき後)は各々独立した工程であってもかまわないし、部分的に連続している工程でもかまわない。生産効率から考えれば、全て連続化していることが理想である。 Each process after hot rolling as described above, pickling, cold rolling, annealing, heat treatment, temper rolling (before plating), galvanizing, alloying treatment, temper rolling (after plating) are independent processes. There may be a process that is partially continuous. From the viewpoint of production efficiency, it is ideal that everything is continuous.
次に本発明を実施例にて説明する。なお、実施例はSi,Mn,Pと言った固溶強化元素の量を調整して、引張強さが340MPa以上となるJIS G 3135記載のSPFC340H相当の材質を有する鋼板のみで示したが、本発明は固溶元素量を調整することで引張強さを270〜440MPaに調整することが可能なものである。 Next, the present invention will be described with reference to examples. In addition, although the Example showed only the steel plate which has the material equivalent to SPFC340H of JIS G3135 description which adjusts the quantity of the solid solution strengthening element called Si, Mn, and P, and tensile strength becomes 340 Mpa or more, In the present invention, the tensile strength can be adjusted to 270 to 440 MPa by adjusting the amount of the solid solution element.
<実施例1>
表2に示す本発明の鋼を溶製し、スラブ加熱温度1200℃、仕上温度920℃、巻取温度680℃で熱間圧延し、3.5mm厚の鋼帯とした。酸洗後、81%の圧下率の冷間圧延を施し0.65mm厚の冷延板とした。次いでこれを、連続焼鈍ラインにて加熱温度750℃で焼鈍後、冷却速度60℃/sで冷却し、270℃にて180秒の熱処理を行った後、種々の調質圧延率で調質圧延を施し、冷延鋼板を得た。さらにこの冷延鋼板を素材としてNiプレめっき後、昇温し亜鉛浴に浸漬し、これをワイピングした後に、550℃で10秒の合金化処理後、再度、種々の調質圧延率で調質圧延を施した。そしてこれらを冷延鋼板ままの材質と比較した。
<Example 1>
The steel of the present invention shown in Table 2 was melted and hot-rolled at a slab heating temperature of 1200 ° C., a finishing temperature of 920 ° C., and a winding temperature of 680 ° C. to form a steel strip having a thickness of 3.5 mm. After pickling, cold rolling was performed at a rolling reduction of 81% to obtain a cold rolled sheet having a thickness of 0.65 mm. Next, after annealing at a heating temperature of 750 ° C. in a continuous annealing line, cooling at a cooling rate of 60 ° C./s, heat treatment at 270 ° C. for 180 seconds, and then temper rolling at various temper rolling rates. And cold-rolled steel sheet was obtained. Further, after Ni pre-plating using this cold-rolled steel sheet as a raw material, the temperature was raised and immersed in a zinc bath. Rolled. And these were compared with the material as a cold-rolled steel plate.
結果を表3に示す。ここで冷延鋼板の欄は、各鋼を冷間圧延後に焼鈍ラインのみによって冷延鋼板として製造する際に、鋼板の遅時効性が確保される最小限の調質圧延率(SP0)とその時のYP(YP0)である。これに対し、めっき鋼板の欄は焼鈍済み冷延鋼板を素材としてめっき鋼板を製造した場合の、めっき前後の二種の調質圧延率(SP1、SP2)とその材質である。これによると、本発明条件を満たす調質圧延率のものは、遅時効性があり、めっき鋼板のYPが冷延鋼板のYP(YP0)よりも低く、またBH量も安定して30MPa以上あることから、良好な材質が得られている。これに対し、二種の調質圧延率が足りないものは遅時効性が担保されておらす、逆に過剰なものは冷延鋼板に比して硬質となっており、BH量や伸びも劣化している。 The results are shown in Table 3. Here, the column of cold-rolled steel sheet indicates the minimum temper rolling rate (SP0) at which the slow aging property of the steel sheet is ensured when each steel is manufactured as a cold-rolled steel sheet only by an annealing line after cold rolling, and at that time YP (YP0). On the other hand, the column of the plated steel sheet shows two types of temper rolling ratios (SP1, SP2) before and after plating and the material when the plated steel sheet is manufactured using an annealed cold-rolled steel sheet. According to this, the temper rolling ratio satisfying the present invention has delayed aging, YP of the plated steel sheet is lower than YP (YP0) of the cold-rolled steel sheet, and the BH amount is stably 30 MPa or more. Therefore, a good material is obtained. On the other hand, the two types of temper rolling ratios that are not sufficient ensure delayed aging, and conversely, excessive ones are harder than cold-rolled steel sheets, and the amount of BH and elongation are also high. It has deteriorated.
<実施例2>
表4に示す組成を有する鋼を溶製し、スラブ加熱温度1200℃、仕上温度920℃、巻取温度680℃で熱間圧延し、4.5mm厚の鋼帯とした。酸洗後、82%の圧下率の冷間圧延を施し0.8mm厚の冷延板とした。次いでこれを、連続焼鈍ラインにて加熱温度780℃で焼鈍後、冷却速度45℃/sで冷却し、300℃にて180秒の熱処理を行った後、種々の調質圧延率で調質圧延を施し、冷延鋼板を得た。さらにこの冷延鋼板を素材としてNiプレめっき後、昇温し亜鉛浴に浸漬し、これをワイピングした後に、530℃で12秒の合金化処理後、再度、種々の調質圧延率で調質圧延を施した。そしてこれらを冷延鋼板ままの材質と比較した。
<Example 2>
Steel having the composition shown in Table 4 was melted and hot-rolled at a slab heating temperature of 1200 ° C., a finishing temperature of 920 ° C., and a winding temperature of 680 ° C. to obtain a steel strip having a thickness of 4.5 mm. After pickling, cold rolling with a reduction rate of 82% was performed to obtain a cold-rolled sheet having a thickness of 0.8 mm. Next, after annealing at a heating temperature of 780 ° C. in a continuous annealing line, cooling at a cooling rate of 45 ° C./s, heat treatment at 300 ° C. for 180 seconds, and temper rolling at various temper rolling rates And cold-rolled steel sheet was obtained. Furthermore, after Ni pre-plating using this cold-rolled steel sheet as a raw material, the temperature was raised and immersed in a zinc bath. Rolled. And these were compared with the material as a cold-rolled steel plate.
結果を表5に示す。本発明の成分の鋼を用いて、更に本発明の調質圧延率を施しためっき鋼板は、高強度でありながら加工性が優れており、また30MPa以上のBH量と遅時効性を兼備していることがわかる。 The results are shown in Table 5. The plated steel sheet that has been subjected to the temper rolling ratio of the present invention using the steel of the present invention is excellent in workability while having high strength, and also has a BH amount of 30 MPa or more and delayed aging. You can see that
Claims (4)
C :0.0014〜0.0025%、
Si≦0.5%、
Mn:0.03〜1.0%、
P :0.01〜0.15%、
S ≦0.015%、
Al:0.005〜0.1%、
N ≦0.0040%
を含有し、残部Feおよび不可避的不純物からなる組成のスラブを、Ar3変態点以上の温度で熱間圧延を行い、圧下率60〜95%の冷間圧延を施し、連続焼鈍ラインにて650℃〜Ac3変態点で焼鈍後に調質圧延を施して、一旦、焼鈍済み冷延鋼板を製造し、引き続き、連続溶融亜鉛めっきラインにて亜鉛めっき浴温度まで加熱してめっきした後、460〜600℃までの温度範囲で5〜15秒の合金化熱処理を行い、その後、再度調質圧延を施す、合金化溶融亜鉛めっき鋼板の製造プロセスにおいて、めっき前後の二種の調質圧延率の関係が、めっきをしない連続焼鈍ラインのみによって製造される冷延鋼板に施される調質圧延率を基準とした、次式で示す条件で行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
SP1+SP2≦SP0≦0.75×SP1+1.5×SP2
ここで、SP0は冷間圧延後に焼鈍ラインのみによって冷延鋼板を製造する際の、鋼板の遅時効性(鋼板に100℃で1時間の熱処理を施した後の引張時の降伏伸び≦0.3%)が確保される最小限の調質圧延率(%)、SP1とSP2は焼鈍ラインに引き続くめっきラインによって合金化溶融亜鉛めっき鋼板を製造する際の、めっき前後の各々の調質圧延率(%)を意味する。 % By mass
C: 0.0014 to 0.0025%,
Si ≦ 0.5%,
Mn: 0.03 to 1.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar3 transformation point, cold-rolled at a reduction rate of 60 to 95%, and 650 ° C. in a continuous annealing line. After temper rolling after annealing at the Ac3 transformation point, an annealed cold-rolled steel sheet is once manufactured, and then heated to a galvanizing bath temperature in a continuous hot-dip galvanizing line, followed by plating at 460-600 ° C. In the manufacturing process of the alloyed hot-dip galvanized steel sheet, which is subjected to alloying heat treatment for 5 to 15 seconds in the temperature range up to and then subjected to temper rolling again, the relationship between the two types of temper rolling ratio before and after plating, Alloyed molten zinc with excellent paint bake hardening performance, characterized by the following formula, based on the temper rolling ratio applied to cold-rolled steel sheets produced only by continuous annealing lines without plating Me Method of manufacturing a steel plate.
SP1 + SP2 ≦ SP0 ≦ 0.75 × SP1 + 1.5 × SP2
Here, SP0 is the slow aging property of a steel sheet when producing a cold-rolled steel sheet only by an annealing line after cold rolling (yield elongation at tension after subjecting the steel sheet to heat treatment at 100 ° C. for 1 hour ≦ 0. 3%) is the minimum temper rolling ratio (%), and SP1 and SP2 are the temper rolling ratios before and after plating when producing galvannealed steel sheets by the plating line following the annealing line. (%).
C :0.0014〜0.0030%、
Si≦0.5%、
Mn:0.03〜1.0%、
P :0.01〜0.15%、
S ≦0.015%、
Al:0.005〜0.1%、
N ≦0.0040%
を含有し、さらに
Ti:0.002〜0.015%
および
Nb:0.002〜0.015%
のうち1種または2種を
Ti+Nb=0.002〜0.015%
となるように含有し、残部Feおよび不可避的不純物からなる組成のスラブを、Ar3変態点以上の温度で熱間圧延を行い、圧下率60〜95%の冷間圧延を施し、連続焼鈍ラインにて650℃〜Ac3変態点で焼鈍後に調質圧延を施して、一旦、焼鈍済み冷延鋼板を製造し、引き続き、連続溶融亜鉛めっきラインにて亜鉛めっき浴温度まで加熱してめっきした後、460〜600℃までの温度範囲で5〜15秒の合金化熱処理を行い、その後、再度調質圧延を施す、合金化溶融亜鉛めっき鋼板の製造プロセスにおいて、めっき前後の二種の調質圧延率の関係が、めっきをしない連続焼鈍ラインのみによって製造される冷延鋼板に施される調質圧延率を基準とした、次式で示す条件で行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
SP1+SP2≦SP0≦0.75×SP1+1.5×SP2
ここで、SP0は冷間圧延後に焼鈍ラインのみによって冷延鋼板を製造する際の、鋼板の遅時効性(鋼板に100℃で1時間の熱処理を施した後の引張時の降伏伸び≦0.3%)が確保される最小限の調質圧延率(%)、SP1とSP2は焼鈍ラインに引き続くめっきラインによって合金化溶融亜鉛めっき鋼板を製造する際の、めっき前後の各々の調質圧延率(%)を意味する。 % By mass
C: 0.0014 to 0.0030%,
Si ≦ 0.5%,
Mn: 0.03 to 1.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
And further Ti: 0.002 to 0.015%
And Nb: 0.002 to 0.015%
1 type or 2 types of Ti + Nb = 0.002 to 0.015%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar3 transformation point, cold-rolled at a reduction ratio of 60 to 95%, and continuously annealed. After annealing at 650 ° C. to Ac3 transformation point, temper rolling is performed to once produce an annealed cold-rolled steel sheet, followed by heating to a galvanizing bath temperature in a continuous hot dip galvanizing line and then plating 460 In the manufacturing process of alloyed hot-dip galvanized steel sheet, which is subjected to alloying heat treatment for 5 to 15 seconds in a temperature range up to ~ 600 ° C and then subjected to temper rolling again, An alloy excellent in paint bake hardening performance, characterized in that the relationship is based on the temper rolling ratio applied to the cold-rolled steel sheet produced only by the continuous annealing line without plating, based on the conditions shown by the following formula Chemical dissolution Method of manufacturing a galvanized steel sheet.
SP1 + SP2 ≦ SP0 ≦ 0.75 × SP1 + 1.5 × SP2
Here, SP0 is the slow aging property of a steel sheet when producing a cold-rolled steel sheet only by an annealing line after cold rolling (yield elongation at tension after subjecting the steel sheet to heat treatment at 100 ° C. for 1 hour ≦ 0. 3%) is the minimum temper rolling ratio (%), and SP1 and SP2 are the temper rolling ratios before and after plating when producing galvannealed steel sheets by the plating line following the annealing line. (%).
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