JP2010138482A - Cold rolled steel sheet, hot dip galvannealed steel sheet, and method for producing them - Google Patents
Cold rolled steel sheet, hot dip galvannealed steel sheet, and method for producing them Download PDFInfo
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- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 14
- 239000008397 galvanized steel Substances 0.000 claims description 14
- 238000005097 cold rolling Methods 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 11
- 238000009749 continuous casting Methods 0.000 claims description 9
- 229910052717 sulfur Inorganic materials 0.000 claims description 9
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- 235000019982 sodium hexametaphosphate Nutrition 0.000 description 4
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- 150000001639 boron compounds Chemical class 0.000 description 1
- 150000001722 carbon compounds Chemical class 0.000 description 1
- DXHPZXWIPWDXHJ-UHFFFAOYSA-N carbon monosulfide Chemical class [S+]#[C-] DXHPZXWIPWDXHJ-UHFFFAOYSA-N 0.000 description 1
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- YLRAQZINGDSCCK-UHFFFAOYSA-M methanol;tetramethylazanium;chloride Chemical compound [Cl-].OC.C[N+](C)(C)C YLRAQZINGDSCCK-UHFFFAOYSA-M 0.000 description 1
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Abstract
Description
本発明は、自動車の外板等に使用される、軟質で加工後の形状均一性に優れた冷延鋼板と合金化溶融亜鉛めっき鋼板およびそれらの製造方法に関するものである。 TECHNICAL FIELD The present invention relates to a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet that are soft and excellent in shape uniformity after processing and are used for automobile outer plates and the like, and methods for producing them.
従来から、自動車の外装板としては、引張り強さが350MPa未満と軟質で、加工性に優れた冷延鋼板や合金化溶融亜鉛めっき鋼板が多く使用されている。例えば、軟質で加工性に優れた冷延鋼板としては、炭窒化物形成元素を含有する極低炭素鋼を熱間圧延し、熱延鋼板の段階で炭窒化物を生成させ、鋼中の固溶Cおよび固溶Nを低減させた後、冷間圧延および再結晶焼鈍を経て製造される冷延鋼板、いわゆるIF(Interstitial Free)鋼板が知られている。 Conventionally, cold rolled steel sheets and alloyed hot dip galvanized steel sheets, which are soft with a tensile strength of less than 350 MPa and excellent in workability, are widely used as exterior panels for automobiles. For example, as a cold-rolled steel sheet that is soft and excellent in workability, an ultra-low carbon steel containing a carbonitride-forming element is hot-rolled to produce carbonitride at the stage of the hot-rolled steel sheet, thereby A cold-rolled steel sheet, so-called IF (Interstitial Free) steel sheet, which is manufactured through cold rolling and recrystallization annealing after reducing dissolved C and solute N is known.
このようなIF鋼板のうち、炭窒化物形成元素としてTiを添加したIF鋼板は、特に深絞り性などの加工性に優れるという特徴がある。しかしながら、Tiは炭窒化物のみならず、微細な硫化物や炭硫化物を形成し、これらの微細析出物が再結晶および再結晶後の粒成長を阻害することがあるため、部分的に未再結晶粒が残存するという問題があった。部分的に未再結晶粒が残存すると局部的に降伏強度が高い領域が存在することになり、プレス加工後に形状不均一が生じることがあるため、好ましくない。また、合金化溶融亜鉛めっきを施す際に、鋼板表層部に未再結晶粒の残存部が存在すると、合金化速度にムラが生じ、外観ムラの原因ともなる。
これらの問題を解決する手法として、例えば、特許文献１には、溶融亜鉛めっき処理を行うに際し、鋼板表面に、炭素化合物、窒素化合物およびホウ素化合物の中から選択される１種または２種以上をC、N、B量として0.1〜1000mg/m2付着させ、かつ硫黄または硫黄化合物をS量として0.1〜1000mg/m2付着させた後、水素を含む非酸化性雰囲気で680℃以上の温度で焼鈍する方法が開示されている。
また、特許文献２には、スジムラと呼ばれる表面外観不均一を解決するために、連続鋳造直後のスラブをその表面温度が1000℃以上になるように保持して仕上圧延工程に導き、Ar3点以上の温度で仕上げる方法が開示されている。
さらに、特許文献３には、表面外観不均一を解決するために、鋼を連続鋳造してスラブとした後加熱し、表面温度が1000℃以上のスラブに酸素を含む酸化性ガスを吹付けた後、熱間圧延、酸洗、冷間圧延、焼鈍を行う方法が開示されている。
Among such IF steel sheets, IF steel sheets to which Ti is added as a carbonitride-forming element are particularly characterized by excellent workability such as deep drawability. However, Ti forms fine sulfides and carbon sulfides as well as carbonitrides, and these fine precipitates may hinder recrystallization and grain growth after recrystallization. There was a problem that recrystallized grains remained. If the non-recrystallized grains partially remain, a region having a high yield strength exists locally, and shape unevenness may occur after press working, which is not preferable. In addition, when alloyed hot dip galvanizing is performed, if a remaining portion of non-recrystallized grains is present in the surface layer portion of the steel sheet, unevenness occurs in the alloying speed, which may cause uneven appearance.
As a technique for solving these problems, for example, in Patent Document 1, when performing hot dip galvanizing treatment, one or more selected from a carbon compound, a nitrogen compound, and a boron compound are added to the steel sheet surface. C, N, B amount 0.1 to 1000 mg / m 2 adhered to as, and sulfur or after the sulfur compound to 0.1 to 1000 mg / m 2 is deposited as a S content, at a temperature above 680 ° C. in a non-oxidizing atmosphere containing hydrogen A method of annealing is disclosed.
Further, in Patent Document 2, in order to solve the uneven surface appearance called “straight unevenness”, the slab immediately after continuous casting is held at a surface temperature of 1000 ° C. or higher and led to the finishing rolling process, and Ar3 point or higher A method of finishing at the following temperature is disclosed.
Further, in Patent Document 3, in order to solve the uneven surface appearance, steel is continuously cast to form a slab and then heated, and an oxidizing gas containing oxygen is sprayed on a slab having a surface temperature of 1000 ° C. or higher. Thereafter, a method of performing hot rolling, pickling, cold rolling, and annealing is disclosed.
しかしながら、特許文献１に記載の方法では、硫黄または硫黄化合物をS量として0.1〜1000mg/m2付着させる工程が必要となり、生産性の低下やコストの増大を招くという問題がある。
特許文献２に記載の方法では、スラブの表面を溶削するなどして表面欠陥を防止する、いわゆるスラブ手入れを行うことができず、特に美麗な表面外観を要求される自動車外装板用途に用いるには不適当である。
さらに、特許文献３に記載の方法では、鋼板の両面で外観不均一を防止するためには、1000℃以上の高温のスラブを表裏反転させて酸化性のガスを吹付ける必要があり、実用的でない。
さらに、特許文献１〜３の技術には、プレス加工後の形状不均一を解決する方法については開示されていない。
However, the method described in Patent Document 1 requires a step of depositing 0.1 to 1000 mg / m 2 of sulfur or a sulfur compound as the amount of S, and there is a problem that the productivity is lowered and the cost is increased.
In the method described in Patent Document 2, so-called slab care that prevents surface defects by cutting the surface of the slab or the like cannot be performed, and it is used for an automobile exterior plate that requires a particularly beautiful surface appearance. Inappropriate for
Further, in the method described in Patent Document 3, in order to prevent uneven appearance on both sides of the steel sheet, it is necessary to invert the high-temperature slab of 1000 ° C. or higher and spray an oxidizing gas, which is practical. Not.
Furthermore, the techniques of Patent Documents 1 to 3 do not disclose a method for solving the non-uniform shape after press working.
本発明は、かかる事情に鑑み、深絞り性に優れたTi添加IF鋼板において、特殊な処理を施さずに、均一な外観とプレス加工後の形状均一性を得ることのできる冷延鋼板、合金化溶融亜鉛めっき鋼板およびそれらの製造方法を提供することを目的とする。 In view of such circumstances, the present invention is a Ti-added IF steel sheet excellent in deep drawability, a cold-rolled steel sheet and an alloy that can obtain a uniform appearance and shape uniformity after pressing without performing special treatment. An object of the present invention is to provide a galvannealed steel sheet and a method for producing the same.
発明者らは、上記問題点を解決するため、プレス加工後に表面欠陥として現出する欠陥の発生メカニズムと抑制対策について、鋭意研究調査を重ねた。
その結果、上記問題を生じる鋼板には、極表層に未再結晶粒が残存すること、そしてこれらの未再結晶粒を調査した結果、鋼板表面〜10μmの領域における析出物の析出状態に特徴があることを見出した。
本発明は、以上の知見に基づいてなされたものであり、その要旨は以下のとおりである。
［1］mass％で、C：0.0005〜0.01%、Si：0.2%以下、Mn：0.1〜1.5%、P：0.03%以下、S：0.005〜0.03%、Ti：0.02〜0.1%、Al：0.01〜0.05%、N： 0.005%以下であり、かつ、Ti*=（Ti%）−3.4×（N%）−1.5×（S%）−4×（C%）で示されるTi*を、0＜Ti*＜0.02を満たす範囲で含有し、残部はFeおよび不可避的不純物からなる成分組成を有し、鋼板両面における各表面から10 μｍまでの板厚表層部において、大きさ20nm未満の析出物に含まれるTi元素の該板厚表層部中での含有量（mass％）が、鋼板中の全Ti含有量（mass％）の9％以下であることを特徴とする冷延鋼板。
ただし、（Ti%）、（N%）、（S%）、（C%）は、それぞれTi、N、S、Cの含有量（mass％）を示す。
［２］前記［１］において、さらに、mass％で、Nb : 0.001〜0.01%、B : 0.0002〜0.0015%のうち、いずれか一種または二種を含有することを特徴とする冷延鋼板。
［３］前記［１］または［２］において、さらに、mass％で、Sb：0.03%以下を含有することを特徴とする冷延鋼板。
［４］前記［１］〜［３］のいずれかにおいて、鋼板各表面における板面に平行な方向の{100}面Ｘ線強度が、ランダム強度比で2.0未満であることを特徴とする冷延鋼板。
［５］前記［１］ないし［４］のいずれかに記載の冷延鋼板の表面に合金化溶融亜鉛めっき層を具えることを特徴とする合金化溶融亜鉛めっき鋼板。
［６］前記［１］ないし［３］のいずれかに記載の成分組成を有する鋼を連続鋳造によりスラブとし、該スラブに対して、加熱温度が1000℃以上1200℃未満で、かつ1000℃以上の温度域での加熱時間が3.0時間以下の条件で加熱し、スケール除去および粗圧延を施し、次いで、鋼板表面温度が（Ar3変態点−300℃）以上Ar3変態点以下の範囲となるよう冷却した後、仕上げ圧延終了時の鋼板表面温度がAr3変態点以上の温度となるように仕上げ圧延し、冷却し、650℃以上の温度で巻取り、次いで、酸洗、冷間圧延後、焼鈍を行うことを特徴とする冷延鋼板の製造方法。
［７］前記［１］ないし［３］のいずれかに記載の成分組成を有する鋼を連続鋳造によりスラブとし、該スラブに対して、加熱温度が1000℃以上1200℃未満で、かつ1000℃以上の温度域での加熱時間が3.0時間以下の条件で加熱し、スケール除去および粗圧延を施し、次いで、鋼板表面温度が（Ar3変態点−300℃）以上Ar3変態点以下の範囲となるよう冷却した後、仕上げ圧延終了時の鋼板表面温度がAr3変態点以上の温度となるように仕上げ圧延し、冷却し、650℃以上の温度で巻取り、次いで、酸洗、冷間圧延後、焼鈍し、溶融亜鉛めっきおよび合金化処理を行うことを特徴とする合金化溶融亜鉛めっき鋼板の製造方法。
なお、本明細書において、鋼の成分を示す％は、すべてmass％である。
In order to solve the above-mentioned problems, the inventors have conducted intensive research and investigation on the generation mechanism of the defects that appear as surface defects after press working and the countermeasures to suppress them.
As a result, unrecrystallized grains remain in the surface layer of the steel plate that causes the above problems, and as a result of investigating these unrecrystallized grains, the precipitation state of precipitates in the region of the steel sheet surface to 10 μm is characterized. I found out.
This invention is made | formed based on the above knowledge, The summary is as follows.
[1] In mass%, C: 0.0005 to 0.01%, Si: 0.2% or less, Mn: 0.1 to 1.5%, P: 0.03% or less, S: 0.005 to 0.03%, Ti: 0.02 to 0.1%, Al: 0.01 ˜0.05%, N: 0.005% or less, and Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%) <Ti * <0.02 is included, the balance is composed of Fe and inevitable impurities, and the deposit is less than 20 nm in the surface layer part of each sheet thickness from 10 μm to 10 μm on both surfaces of the steel sheet. A cold-rolled steel sheet, wherein the content (mass%) of the Ti element contained in the steel sheet is 9% or less of the total Ti content (mass%) in the steel sheet.
However, (Ti%), (N%), (S%), and (C%) indicate the contents (mass%) of Ti, N, S, and C, respectively.
[2] The cold-rolled steel sheet according to [1], further containing at least one of mass percentages of Nb: 0.001 to 0.01% and B: 0.0002 to 0.0015%.
[3] The cold-rolled steel sheet according to [1] or [2], further containing mass% and Sb: 0.03% or less.
[4] In any one of the above [1] to [3], the {100} plane X-ray intensity in the direction parallel to the plate surface on each surface of the steel plate is less than 2.0 in terms of a random intensity ratio. Rolled steel sheet.
[5] An alloyed hot dip galvanized steel sheet comprising an alloyed hot dip galvanized layer on the surface of the cold rolled steel sheet according to any one of [1] to [4].
[6] The steel having the component composition according to any one of [1] to [3] is formed into a slab by continuous casting, and the heating temperature is 1000 ° C. or higher and lower than 1200 ° C. and 1000 ° C. or higher. Heat in the temperature range of 3.0 hours or less under conditions of scale removal and rough rolling, and then cooling so that the steel sheet surface temperature is in the range of (Ar3 transformation point -300 ° C) to Ar3 transformation point Then, finish rolling so that the steel sheet surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point, cooling, winding at a temperature of 650 ° C or higher, and then pickling and cold rolling, followed by annealing. A method for producing a cold-rolled steel sheet, comprising:
[7] The steel having the component composition according to any one of [1] to [3] is made into a slab by continuous casting, and the heating temperature is 1000 ° C. or more and less than 1200 ° C. and 1000 ° C. or more with respect to the slab. Heat in the temperature range of 3.0 hours or less under conditions of scale removal and rough rolling, and then cooling so that the steel sheet surface temperature is in the range of (Ar3 transformation point -300 ° C) to Ar3 transformation point After that, finish rolling so that the steel sheet surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point, cooling, winding at a temperature of 650 ° C or higher, and then annealing after pickling and cold rolling. A method for producing an alloyed hot-dip galvanized steel sheet, characterized by performing hot-dip galvanizing and alloying treatment.
In addition, in this specification, all% which shows the component of steel is mass%.
本発明によれば、特殊な処理を施さずに、均一な外観を有し、かつ、プレス加工後の形状均一性に優れた冷延鋼板および合金化溶融亜鉛めっき鋼板が得られる。 According to the present invention, a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet having a uniform appearance and excellent shape uniformity after press working can be obtained without performing special treatment.
以下に、本発明の詳細を説明する。
従来の自動車の外装板用のＴｉ添加ＩＦ鋼板の集合組織は、板面に平行な方向に{111}面が多く形成されることが知られている。しかしながら、前述したように、このような集合組織を有する合金化溶融亜鉛めっき鋼板では外観ムラが生じることがあり、冷延鋼板および合金化溶融亜鉛めっき鋼板ではプレス加工後の形状不均一が生じる場合がある。
そこで、このような外観ムラやプレス加工後の形状不均一が生じる鋼板について詳細に調査した。その結果、上記問題が生じる鋼板には、板厚表層部、具体的には鋼板表面から10 μｍ程度までの表層部に部分的に未再結晶粒が残存すること、さらには、これらの未再結晶粒は{100}面を主とする方位であることを知見した。また、これらの{100}面を主体とする未再結晶粒が表層付近に残存した場合には、プレス加工後の形状不均一のみならず、合金化処理時に合金化速度が局部的に異なるため外観ムラが生じることもわかった。
上記知見を受けて、本発明者らは、次に、表層付近に未再結晶粒が残存する原因を詳細に検討した。その結果、未再結晶粒が残存する部分には大きさが20nm未満のごく微細なＴｉを含む析出物が多く存在することがわかった。このような微細な析出物は、自動車外装板用鋼板に施される一般的な焼鈍条件では固溶せずに残存し、いわゆるピン止め効果によって{111}面再結晶粒の粒界移動を妨げるため、再結晶が容易に進まず、{100}面を主とする方位の未再結晶粒が残存するものと考えられる。
そこで、このような問題を解決するために、様々な製造条件での実験を繰返し実施して種々の鋼板を得、得られた鋼板について表層付近の状態を調査した。そうしたところ、特定の組成の鋼では、表層付近に{100}面の未再結晶粒が多く残存せず、合金化溶融亜鉛めっき鋼板における外観ムラや、冷延鋼板および合金化溶融亜鉛めっき鋼板のプレス加工後形状不均一が生じないことを見出した。そして、この鋼板の板厚最表層付近、具体的には鋼板両面の表面から10μmまでの領域では、20nm未満の析出物量が低減されていた。そこで、外観ムラやプレス加工後形状不均一が生じない好適な条件を定量化するため、大きさが20nm未満の析出物に含まれるTi元素の含有量を算出し、鋼板中の全Ti含有量に対する割合を求めたところ、その割合が9％以下であれば、鋼板表面での、板面に平行な方向の{100}面Ｘ線強度がランダム強度比で2.0未満となり、その結果、外観ムラやプレス加工後形状不均一の発生を低減できることが明らかになった。なお、鋼板表面でのＸ線強度は、概ね表面から10μmまでの領域を測定している。
なお、大きさ20nm未満の析出物に含まれるTiの量は、以下の方法により測定することができる。
試料を電解液中で所定量電解した後、試料片を電解液から取り出して分散性を有する溶液中に浸漬する。次いで、この溶液中に含まれる析出物を、孔径20nmのフィルタを用いてろ過する。この孔径20nmのフィルタをろ液と共に通過した析出物が大きさ20nm未満である。次いで、ろ過後のろ液に対して、誘導結合プラズマ（ICP）発光分光分析法、ICP質量分析法、および原子吸光分析法等から適宜選択して分析し、大きさ20nm未満の析出物に含まれるTi含有量（mass％）を求める。
以上より、均一な外観とプレス加工後の形状均一性を得るために、本発明では、鋼板両面の各表面から10μmまでの領域での、大きさ20nm未満の析出物に含まれるTi元素の含有量（mass％）は、鋼板中の全Ti含有量（mass％）の9%以下とする。
また、板面に平行な方向の{100}面Ｘ線強度が、ランダム強度比で2.0未満であることが望ましい。2.0以上では、表層未再結晶の残存量が多く、プレス加工後の形状均一性が損なわれる場合がある。
Details of the present invention will be described below.
It is known that the texture of conventional Ti-added IF steel plates for automobile exterior plates has many {111} surfaces formed in a direction parallel to the plate surface. However, as described above, appearance irregularities may occur in an alloyed hot-dip galvanized steel sheet having such a texture, and non-uniform shapes after press working may occur in cold-rolled steel sheets and alloyed hot-dip galvanized steel sheets. There is.
Therefore, the steel sheet in which such uneven appearance and non-uniform shape after press working were investigated in detail. As a result, in the steel plate in which the above problem occurs, non-recrystallized grains partially remain in the plate thickness surface portion, specifically, the surface layer portion from the steel plate surface to about 10 μm. The crystal grains were found to be oriented mainly in the {100} plane. In addition, when these non-recrystallized grains mainly composed of {100} face remain in the vicinity of the surface layer, not only the shape non-uniformity after press working but also the alloying speed locally differs during the alloying process. It was also found that uneven appearance occurred.
In view of the above findings, the present inventors then examined in detail the cause of the remaining non-recrystallized grains in the vicinity of the surface layer. As a result, it was found that there were many precipitates containing very fine Ti having a size of less than 20 nm in the portion where unrecrystallized grains remained. Such fine precipitates remain undissolved under the general annealing conditions applied to steel plates for automobile exterior plates, and hinder the grain boundary migration of {111} recrystallized grains by the so-called pinning effect. Therefore, it is considered that recrystallization does not proceed easily and unrecrystallized grains mainly oriented in the {100} plane remain.
Therefore, in order to solve such a problem, experiments under various production conditions were repeatedly performed to obtain various steel plates, and the state of the surface layer of the obtained steel plates was investigated. As a result, in the steel of a specific composition, many unrecrystallized grains of {100} face do not remain in the vicinity of the surface layer, the appearance irregularity in the galvannealed steel sheet, the cold rolled steel sheet and the galvannealed steel sheet It was found that non-uniform shape does not occur after pressing. In the vicinity of the outermost layer thickness of the steel sheet, specifically, in the region from the surface of both surfaces of the steel sheet to 10 μm, the amount of precipitates of less than 20 nm was reduced. Therefore, in order to quantify suitable conditions that do not cause uneven appearance and non-uniform shape after pressing, the content of Ti element contained in precipitates with a size of less than 20 nm was calculated, and the total Ti content in the steel sheet As a result, when the ratio is 9% or less, the {100} plane X-ray intensity in the direction parallel to the plate surface on the steel sheet surface is less than 2.0 in terms of the random intensity ratio. It has been clarified that the occurrence of non-uniform shapes after pressing can be reduced. Note that the X-ray intensity on the surface of the steel sheet is measured in a region approximately 10 μm from the surface.
The amount of Ti contained in the precipitate having a size of less than 20 nm can be measured by the following method.
After the sample is electrolyzed in a predetermined amount in the electrolytic solution, the sample piece is taken out of the electrolytic solution and immersed in a solution having dispersibility. Next, the precipitate contained in the solution is filtered using a filter having a pore diameter of 20 nm. The precipitate that has passed through the filter having a pore diameter of 20 nm together with the filtrate has a size of less than 20 nm. Next, the filtrate after filtration is appropriately selected from inductively coupled plasma (ICP) emission spectrometry, ICP mass spectrometry, atomic absorption spectrometry, etc. and analyzed, and is contained in precipitates having a size of less than 20 nm. Find the Ti content (mass%).
From the above, in order to obtain a uniform appearance and shape uniformity after press working, in the present invention, the content of Ti element contained in precipitates having a size of less than 20 nm in the region of 10 μm from each surface of both surfaces of the steel plate The amount (mass%) is 9% or less of the total Ti content (mass%) in the steel sheet.
Further, the {100} plane X-ray intensity in the direction parallel to the plate surface is desirably less than 2.0 in terms of the random intensity ratio. If it is 2.0 or more, the remaining amount of unrecrystallized surface layer is large, and the shape uniformity after pressing may be impaired.
次に、本発明の成分組成の限定理由について説明する。
C：0.0005〜0.01%
Cは、固溶強化元素であり、降伏強度の上昇に寄与し、面内剛性の向上には有利であるが、優れた深絞り性を得るためには、極力低減することが好ましい。しかし、0.0005%未満では、結晶粒径が著しく粗大化して降伏強度が大きく低下するため、面内剛性が低下して腰折れなどの欠陥が発生しやすくなる。また、脱炭コストの増大を招く。よって、0.0005%を下限とする。一方、Cを多量に含有すると鋼中でのTi炭化物量が増加し、表層部での析出物量が増加して、板面に平行な方向の{100}面を主とする方位の未再結晶粒の残存量が増大するため、0.01%を上限とする。
Next, the reason for limiting the component composition of the present invention will be described.
C: 0.0005-0.01%
C is a solid solution strengthening element and contributes to an increase in yield strength and is advantageous for improving the in-plane rigidity. However, in order to obtain excellent deep drawability, C is preferably reduced as much as possible. However, if it is less than 0.0005%, the crystal grain size becomes extremely coarse and the yield strength is greatly reduced, so that the in-plane rigidity is lowered and defects such as hip breakage tend to occur. Moreover, the decarburization cost increases. Therefore, 0.0005% is set as the lower limit. On the other hand, if a large amount of C is contained, the amount of Ti carbide in the steel increases, the amount of precipitates in the surface layer increases, and the non-recrystallized orientation mainly of the {100} plane parallel to the plate surface. Since the residual amount of grains increases, 0.01% is made the upper limit.
Si:0.2%以下
Siは、比較的加工性を劣化することなく固溶強化により鋼を強化するのに有用な元素であるが、焼鈍時に表面に濃化して溶融亜鉛めっき性を著しく阻害するため、0.2%以下とする。
Si: 0.2% or less
Si is an element useful for strengthening steel by solid solution strengthening without relatively degrading workability, but it concentrates on the surface during annealing and significantly impairs hot dip galvanization, so it is 0.2% or less. To do.
Mn:0.1〜1.5%
Mnは、固溶強化元素として鋼強度を増大させる。鋼板剛性確保のため、0.1%以上の添加が必要である。所望の強度を得るために適宜添加することができるが、過剰な添加は加工性を阻害するため、1.5%以下とする。
Mn: 0.1-1.5%
Mn increases the steel strength as a solid solution strengthening element. Addition of 0.1% or more is necessary to secure the steel plate rigidity. Although it can be added as appropriate in order to obtain a desired strength, excessive addition inhibits workability, so it is made 1.5% or less.
P：0.03%以下
Pは固溶強化元素であり、鋼の強化と降伏強度向上には有効である。しかし、過度に添加すると、熱間、冷間割れの原因となるばかりでなく、溶融亜鉛めっきの合金化反応を阻害するため、0.03%以下とする。
P: 0.03% or less
P is a solid solution strengthening element and is effective in strengthening steel and improving yield strength. However, if added excessively, it not only causes hot and cold cracking, but also inhibits the alloying reaction of hot dip galvanizing, so it is made 0.03% or less.
S：0.005〜0.03%
Sは本発明において重要な元素である。Sは通常、不可避的不純物として鋼中に存在し、極力低減すべきものとされるが、本発明では敢えてその存在量を0.005%以上確保する。すなわち、0.005%未満では、連続鋳造後に生成するTiSが微細となり、熱延でのスラブ再加熱時に部分的に再固溶しやすくなるため、後工程で微細なTiSなどの析出物を比較的多量に析出する部位が生じ、表層に局部的に{100}方位の未再結晶粒を残存させる原因となる。このような微細析出物の影響を低減するため、0.005%以上とする。好ましくは0.010%以上である。一方0.03%超えでは、鋼板製造時の熱間割れが生じ易くなり、生産性が阻害されるとともに表面性状を劣化させる。よって、0.03%以下とする。
S: 0.005-0.03%
S is an important element in the present invention. S is usually present in steel as an unavoidable impurity and should be reduced as much as possible. In the present invention, S is intentionally secured in an amount of 0.005% or more. In other words, if it is less than 0.005%, TiS produced after continuous casting becomes fine, and it becomes easy to partially re-solidify during slab reheating in hot rolling, so a relatively large amount of fine TiS precipitates are produced in the subsequent process. This causes a site to precipitate in the surface layer, which causes unrecrystallized grains of {100} orientation to remain locally on the surface layer. In order to reduce the influence of such fine precipitates, the content is made 0.005% or more. Preferably it is 0.010% or more. On the other hand, if it exceeds 0.03%, hot cracking is likely to occur during the production of the steel sheet, which impedes productivity and deteriorates the surface properties. Therefore, it is set to 0.03% or less.
Ti：0.02〜0.1%、Ti*=（Ti%）−3.4×（N%）−1.5×（S%）−4×（C%）を、0＜Ti*＜0.02
Tiは本発明における最も重要な元素のひとつである。Tiは、鋼中のC，N，Sを析出物として固定することにより、加工性向上効果を有する。0.02%未満では、このような効果を得ることができない。一方、Tiを0.1%を超えて添加してもそれ以上の効果が望めないばかりでなく、板内部に異常組織の形成を招き、加工性を低下させる。
また、前述したように、鋼中のTiは、鋼中のC、N、Sと析出物を形成するため、これらの成分に対して、当量以上添加することにより、加工性を向上させることができる。そのためには、下記（１）式で示されるTi*を0より大きくする必要がある。一方で、固溶Tiを過剰に存在させると、焼鈍時の雰囲気によっては表層部で窒化が生じ、微細なTiNを生成する場合があり、この微細なTiNは表層において{100}方位の未再結晶粒残存を助長するため好ましくない。鋼板両面の表面から10μmまでの領域での、20nm未満のTiを含む微細析出物量を低減し、板面に平行な方向の{100}面Ｘ線強度をランダム強度比で2.0未満とするには、Ti*を0.02未満とする必要がある。
Ti*=（Ti%）−3.4×（N%）−1.5×（S%）−4×（C%）・・・（１）
ただし、（Ti%）、（N%）、（S%）、（C%）は、それぞれTi、N、S、Cの含有量（mass％）を示す。
Ti: 0.02 to 0.1%, Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%), 0 <Ti * <0.02
Ti is one of the most important elements in the present invention. Ti has an effect of improving workability by fixing C, N, and S in the steel as precipitates. If it is less than 0.02%, such an effect cannot be obtained. On the other hand, adding more than 0.1% of Ti not only can not expect further effects, but also leads to the formation of an abnormal structure inside the plate, thereby reducing workability.
In addition, as described above, Ti in steel forms precipitates with C, N, and S in steel, so adding these elements in an equivalent amount or more can improve workability. it can. For that purpose, it is necessary to make Ti * shown by the following formula (1) larger than 0. On the other hand, if excessive solute Ti is present, depending on the atmosphere during annealing, nitridation may occur in the surface layer portion, and fine TiN may be generated. This fine TiN is not re-recovered in the {100} orientation on the surface layer. This is not preferable because it promotes the remaining of crystal grains. To reduce the amount of fine precipitates containing Ti of less than 20nm in the region from the surface of both sides of the steel plate to 10μm, and to make the {100} plane X-ray intensity in the direction parallel to the plate surface less than 2.0 by random intensity ratio , Ti * should be less than 0.02.
Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%) (1)
However, (Ti%), (N%), (S%), and (C%) indicate the contents (mass%) of Ti, N, S, and C, respectively.
Al：0.01〜0.05%
Alは脱酸剤として添加する元素であり、0.01%以上必要であるが、多量に添加してもより一層の脱酸効果は得られないので、0.05%以下とする。
Al: 0.01-0.05%
Al is an element added as a deoxidizing agent and needs to be 0.01% or more. However, even if it is added in a large amount, a further deoxidizing effect cannot be obtained.
N： 0.005%以下
Nは少ないほど加工性には有利であるので、少ないほど望ましい。0.005％を超えて、過剰に添加すると、成形性の著しい低下と固溶Ti量の低下につながるので、上限を0.005％とする。
N: 0.005% or less
The smaller N, the better the workability, so the smaller N is desirable. If over 0.005% is added in excess, it leads to a significant decrease in formability and a decrease in the amount of dissolved Ti, so the upper limit is made 0.005%.
さらに、本発明では、次の添加元素からいずれか一種または二種を添加することが好ましい。
Nb : 0.001〜0.01%
NbはTiと同様炭窒化物を形成して加工性を向上させるのに有利な元素である。特に、前述した（１）式のTi*が0.005未満の場合には添加することが望ましく、加工性向上効果を得るためには、0.001%以上添加する必要がある。しかし、0.01%を超えて添加すると、結晶粒が微細化され、深絞り性などの加工性を劣化させる場合がある。よって、添加する場合は、0.001％以上0.01%以下とする。
B : 0.0002〜0.0015%
B は軟質IF鋼板の粒界強化に有効な元素であり、耐二次加工脆性が必要とされる場合に0.0002%以上添加すると効果的である。しかし、過剰に添加すると、鋼板製造時の表面性状を劣化させる恐れがあるため、0.0015%以下とする。
Furthermore, in this invention, it is preferable to add any 1 type or 2 types from the following additional elements.
Nb: 0.001 ~ 0.01%
Nb, like Ti, is an element advantageous for forming a carbonitride and improving workability. In particular, it is desirable to add Ti * in the above formula (1) when it is less than 0.005. In order to obtain the workability improvement effect, it is necessary to add 0.001% or more. However, if added over 0.01%, the crystal grains are refined, and workability such as deep drawability may be deteriorated. Therefore, when adding, it shall be 0.001% or more and 0.01% or less.
B: 0.0002-0.0015%
B is an element effective for strengthening the grain boundary of the soft IF steel sheet, and it is effective to add 0.0002% or more when secondary work embrittlement resistance is required. However, if added in excess, there is a risk of deteriorating the surface properties during the production of the steel sheet, so 0.0015% or less.
さらに、本発明では、Sbを0.03%以下の範囲で添加することが好ましい。
Sb：0.03％以下
Sbは鋼板表面の酸化あるいは窒化抑制剤として添加される元素であり、主に粒界に偏析して効果を発揮するため微量添加され、酸化あるいは窒化による熱処理中の析出物生成を抑制することで、鋼板表面組織微細化を軽減する。ただし、0.03%超えで添加すると、加工性を損なう場合がある。よって、添加する場合は、0.03%以下とする。
Furthermore, in the present invention, it is preferable to add Sb in a range of 0.03% or less.
Sb: 0.03% or less
Sb is an element added as an oxidation or nitridation inhibitor on the steel sheet surface. It is added in a small amount mainly to segregate at the grain boundaries and exert its effect, and suppresses the formation of precipitates during heat treatment due to oxidation or nitridation. , Reduce the surface structure refinement of the steel sheet. However, if added over 0.03%, workability may be impaired. Therefore, when adding, it is 0.03% or less.
残部はFeおよび不可避的不純物である。 The balance is Fe and inevitable impurities.
次に、本発明の冷延鋼板の製造方法について説明する。 Next, the manufacturing method of the cold rolled steel sheet of this invention is demonstrated.
本発明の冷延鋼板は、上記のような成分組成を有する鋼を連続鋳造によりスラブとし、該スラブに対して、加熱温度が1000℃以上1200℃未満で、かつ1000℃以上の温度域での加熱時間が3.0時間以下の条件で加熱し、スケール除去および粗圧延を施し、次いで、鋼板表面温度が（Ar3変態点−300℃）以上Ar3変態点以下の範囲となるよう冷却した後、仕上げ圧延終了時の表面温度がAr3変態点以上の温度となるように仕上げ圧延し、冷却し、650℃以上の温度で巻取り、次いで、酸洗、冷間圧延、洗浄し、焼鈍を行うことにより得られる。また、合金化溶融亜鉛めっき処理鋼板を得る場合は、上記焼鈍まで同様に行った後、溶融亜鉛めっきおよび合金化処理を行う。 The cold-rolled steel sheet of the present invention is a slab obtained by continuous casting of steel having the above component composition, and the heating temperature is 1000 ° C. or more and less than 1200 ° C. and a temperature range of 1000 ° C. or more. Heating is performed under conditions of heating time of 3.0 hours or less, scale removal and rough rolling are performed, and then cooling is performed so that the steel sheet surface temperature is within the range of (Ar3 transformation point -300 ° C) to Ar3 transformation point, and then finish rolling. Finished and rolled so that the surface temperature at the end is equal to or higher than the Ar3 transformation point, cooled, wound at a temperature of 650 ° C or higher, then pickled, cold rolled, washed, and annealed. It is done. Moreover, when obtaining an alloying hot dip galvanized steel sheet, after carrying out similarly to the said annealing, hot dip galvanization and alloying process are performed.
加熱温度が1000℃以上1200℃未満で、かつ1000℃以上の温度域での加熱時間が3.0時間以下の条件でスラブ加熱
熱間圧延工程で上記条件でスラブを加熱する。加熱温度が1000℃未満では、圧延温度が低下して仕上げ圧延後の鋼板表面温度をAr3変態点以上とすることが困難である。一方、加熱温度が1200℃を超えると、連続鋳造時に生成したTiMnSなどのTiを含有する硫化物が短時間で多く固溶し、後に続く工程において大きさ20nm未満の微細析出物が多く生成するため、好ましくない。
さらに、加熱温度が1200℃未満であっても、長時間保持すると、Tiを含有する硫化物の固溶が進むため好ましくない。よって、1000℃以上の温度域での加熱時間は3.0時間以下とする。
The slab is heated under the above conditions in the slab heating hot rolling step under the condition that the heating temperature is 1000 ° C. or more and less than 1200 ° C. and the heating time in the temperature range of 1000 ° C. or more is 3.0 hours or less. When the heating temperature is less than 1000 ° C., the rolling temperature is lowered, and it is difficult to set the steel sheet surface temperature after finish rolling to the Ar3 transformation point or higher. On the other hand, when the heating temperature exceeds 1200 ° C., many sulfides containing Ti such as TiMnS produced during continuous casting are dissolved in a short time, and many fine precipitates having a size of less than 20 nm are produced in the subsequent process. Therefore, it is not preferable.
Furthermore, even if the heating temperature is less than 1200 ° C., holding for a long time is not preferable because the solid solution of sulfide containing Ti proceeds. Therefore, the heating time in the temperature range of 1000 ° C. or higher is set to 3.0 hours or shorter.
鋼板表面温度が（Ar3変態点−300℃）以上Ar3変態点以下の範囲となるよう冷却
加熱されたスラブに対して、スケール除去および粗圧延を施した後、仕上げ圧延を行う前に表面温度が（Ar3変態点−300℃）以上Ar3変態点以下の範囲となるよう冷却する。
通常の製造方法では、熱間圧延工程における仕上げ圧延後に冷却することでフェライト変態が始まる。しかし、本発明では、仕上げ圧延前に鋼板表面を冷却して表面温度を一旦Ar3変態点以下とする。このように仕上げ圧延前に所定の温度まで表面を冷却することで、表層部のみはフェライト変態を開始してTiを含む析出物が生成し始め、20nm以上のサイズに成長しやすくなる。その結果、20nm未満の析出物量が低減され、{100}面の未再結晶粒が多く残存することなく、均一な外観を有し、かつ、プレス加工後の形状均一性に優れた冷延鋼板が得られることになる。
なお、仕上げ圧延中に、表層部は、板厚中央からの復熱および加工発熱によって温度上昇する。
仕上げ圧延前の表面温度が低すぎると、仕上げ圧延終了時の表面温度がAr3変態点以下となり表層部に加工フェライト組織が生成し均一性が損なわれるため、仕上げ圧延前の表面温度は（Ar3変態点−300℃）以上とする必要がある。
このように仕上げ圧延前に表面を一旦冷却して表面温度を制御することは、本発明の製造方法において特に重要な要件であり、特徴である。
仕上げ圧延前に表面を冷却する方法としては、例えば、通常スケール除去に用いられる高圧水噴射装置などを用いて、表面が適切な温度域となるよう冷却することができる。
なお、Ar3変態点は以下のようにして求めることができる。各組成の鋼を100〜1200℃の温度に加熱し、その後冷却しながら温度と体積変化を測定することによりオーステナイト→フェライト変態による体積膨張が生じる温度（Ar3変態点）を得ることができる。
The surface temperature of the slab cooled and heated so that the steel sheet surface temperature is in the range of Ar3 transformation point to Ar3 transformation point is less than the Ar3 transformation point, and after surface removal before rough rolling. Cool so that it is in the range of (Ar3 transformation point-300 ° C) to Ar3 transformation point.
In a normal manufacturing method, the ferrite transformation starts by cooling after finish rolling in the hot rolling process. However, in the present invention, the surface of the steel sheet is cooled to the Ar3 transformation point or less once before the finish rolling. Thus, by cooling the surface to a predetermined temperature before finish rolling, only the surface layer portion starts ferrite transformation and precipitates containing Ti start to be formed, and it becomes easy to grow to a size of 20 nm or more. As a result, the amount of precipitates of less than 20 nm is reduced, a large number of non-recrystallized grains on the {100} plane do not remain, a uniform appearance, and a cold rolled steel sheet with excellent shape uniformity after press working Will be obtained.
During finish rolling, the temperature of the surface layer portion increases due to recuperation from the center of the plate thickness and processing heat generation.
If the surface temperature before finish rolling is too low, the surface temperature at the end of finish rolling will be below the Ar3 transformation point, and the processed ferrite structure will be generated in the surface layer and the uniformity will be impaired. Point -300 ° C) or higher.
Thus, it is a particularly important requirement and a feature in the manufacturing method of the present invention to control the surface temperature by once cooling the surface before finish rolling.
As a method for cooling the surface before finish rolling, for example, a high-pressure water injection device usually used for scale removal can be used to cool the surface so as to be in an appropriate temperature range.
The Ar3 transformation point can be obtained as follows. By heating the steel of each composition to a temperature of 100 to 1200 ° C. and then measuring the temperature and volume change while cooling, a temperature (Ar3 transformation point) at which volume expansion due to austenite → ferrite transformation occurs can be obtained.
仕上げ圧延終了時の鋼板の表面温度がAr3変態点以上の温度となるように仕上げ圧延し、冷却
仕上げ圧延終了時の鋼板表面温度がAr3変態点を下回ると、鋼板表層部に加工フェライト組織が生成し、均一性が損なわれる。このため、仕上げ圧延終了時の鋼板表面温度がAr3変態点以上となるように、制御する必要がある。
仕上げ圧延終了後に鋼板表面温度がAr3変態点以上に長時間保持されると、成長した比較的粗大な析出物が再固溶して、20nm未満の微細析出物量が増加するため好ましくない。そのため、鋼板表面温度がAr3変態点以上の温度で仕上げ圧延が終了した後、ただちに冷却してフェライト変態を促進することが好ましい。冷却開始までの許容時間は、好ましくは1秒以内である。
Finished rolling so that the surface temperature of the steel plate at the end of finish rolling is equal to or higher than the Ar3 transformation point, and when the surface temperature of the steel plate at the end of cooling finish rolling falls below the Ar3 transformation point, a processed ferrite structure is formed in the surface layer of the steel plate. And the uniformity is impaired. For this reason, it is necessary to control so that the steel plate surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point.
If the surface temperature of the steel sheet is maintained at a temperature higher than the Ar3 transformation point for a long time after the finish rolling, the grown relatively coarse precipitates are re-dissolved and the amount of fine precipitates of less than 20 nm increases, which is not preferable. Therefore, it is preferable that the steel sheet surface temperature is equal to or higher than the Ar3 transformation point, and after finishing rolling is finished, the steel sheet is immediately cooled to promote the ferrite transformation. The allowable time until the start of cooling is preferably within 1 second.
650℃以上で巻取り
冷却後、650℃以上で巻取る。巻取り温度が650℃を下回ると、析出物の成長速度が小さくなり、20nm未満の微細析出物量が増加する。巻取り温度の上限は特に規定するものではないが、高すぎると表層のスケールが成長して表面欠陥の原因となりやすいため、800℃未満とすることが望ましい。
Winding and cooling at 650 ° C or higher, then winding at 650 ° C or higher. When the coiling temperature is lower than 650 ° C., the growth rate of precipitates is reduced, and the amount of fine precipitates less than 20 nm is increased. The upper limit of the coiling temperature is not particularly specified, but if it is too high, the scale of the surface layer tends to grow and cause surface defects.
巻取り後、酸洗、冷間圧延、洗浄した後、焼鈍を行う。または、焼鈍後、溶融亜鉛めっき、合金化処理を行う。
巻き取り後、酸洗、冷間圧延および焼鈍を施す。酸洗、冷間圧延および焼鈍条件は特に限定する必要は無く、常法に従えばよい。
例えば巻き取り後の鋼板は、表面に生成したスケールを除去するために酸洗し、次いで冷間圧延を行うが、冷間圧延率（冷間圧延圧下率）は自動車用外板を製造する際に通常行われている50％〜90％程度とすればよい。なお、冷間圧延率は加工性（ｒ値）向上の観点からは70％以上とするのが望ましい。次いで、冷間圧延後の鋼板は、圧延油の脱脂や汚れを除くため洗浄した後、再結晶焼鈍される。なお、焼鈍温度は、Ａｃ３変態点を超えると加工性（ｒ値）が低下しやすいため、Ａｃ３変態点以下とすることが好ましい。なお、下限温度は、700℃程度とすることが、再結晶焼鈍を行う上で好ましい。焼鈍後、表面粗度の調整などのため調質圧延を行うことが好ましい。この際、調質圧延の圧延率（伸長率）は、0.5％〜1.5％程度とすることが好ましい。
また、合金化溶融亜鉛めっき鋼板とする際は、焼鈍まで上記冷延鋼板の場合と同様に行い、引き続き溶融亜鉛めっきおよび合金化処理を行う。なお、焼鈍前に軽酸洗を行ってもよい。溶融亜鉛めっき条件、合金化条件は特に限定する必要は無く、常法に従えばよい。
また、合金化処理後、冷延鋼板の場合と同様に、表面粗度の調整などのため調質圧延を行うことが好ましい。
以上により、加工後の形状均一性に優れた冷延鋼板が得られる。
After winding, pickling, cold rolling, washing, and annealing. Alternatively, after annealing, hot dip galvanization and alloying treatment are performed.
After winding, pickling, cold rolling and annealing are performed. Pickling, cold rolling, and annealing conditions are not particularly limited, and may be performed in accordance with ordinary methods.
For example, the steel sheet after winding is pickled to remove the scale formed on the surface, and then cold-rolled, and the cold rolling rate (cold rolling reduction rate) is the same as that for manufacturing an automobile outer plate. Usually, it may be about 50% to 90%. The cold rolling rate is preferably 70% or more from the viewpoint of improving workability (r value). Next, the cold-rolled steel sheet is cleaned to remove the degreasing and dirt of the rolling oil, and then recrystallized and annealed. In addition, since the workability (r value) tends to decrease when the annealing temperature exceeds the Ac3 transformation point, the annealing temperature is preferably set to be equal to or lower than the Ac3 transformation point. The lower limit temperature is preferably about 700 ° C. in performing recrystallization annealing. After annealing, it is preferable to perform temper rolling for adjusting the surface roughness. At this time, the rolling rate (elongation rate) of temper rolling is preferably about 0.5% to 1.5%.
Moreover, when setting it as an alloying hot-dip galvanized steel plate, it carries out similarly to the case of the said cold-rolled steel plate until annealing, and performs hot-dip galvanization and an alloying process continuously. In addition, you may perform light pickling before annealing. Hot dip galvanizing conditions and alloying conditions need not be particularly limited, and may be in accordance with conventional methods.
Further, after the alloying treatment, it is preferable to perform temper rolling for the adjustment of the surface roughness and the like as in the case of the cold-rolled steel sheet.
As described above, a cold-rolled steel sheet having excellent shape uniformity after processing can be obtained.
以下に本発明による効果を具体的に示す。
まず、表1に示す成分組成からなる溶鋼を、真空脱ガス処理後、連続鋳造によりスラブとした。次いで上記スラブを加熱し、スケール除去後、板厚40mmまで粗圧延した。次いで、スケール除去装置で鋼板表層を冷却した後、3.5ｍｍ厚まで仕上げ圧延し、巻取り温度700℃でコイルに巻き取った。なお、この時のスラブの加熱条件、仕上げ圧延前の冷却後の鋼板表層温度、仕上げ圧延温度を表2に示す。
次いで、巻取り後の鋼板を酸洗後、0.70mmまで冷間圧延（冷間圧延率：80％）して供試材とし、前処理として脱脂、酸洗した後、溶融亜鉛めっきラインで焼鈍、溶融亜鉛めっき処理、合金化処理、伸長率1.0%の調質圧延を行い、合金化溶融亜鉛めっき鋼板を得た。また、一部の鋼板については、冷延鋼板の特性を評価するため、焼鈍後、伸長率1.0%の調質圧延のみの処理を行い、冷延鋼板を得た。なお、前記焼鈍時の雰囲気は水素を含む非酸化性ガスとし、各供試材の焼鈍温度はAc3変態点以下である840℃とした。溶融亜鉛めっき処理は、Alを0.12%含む460℃亜鉛めっき浴を用いて、浸入板温460℃、浸漬時間3秒にて行った。合金化処理は、めっき後、N2ガスワイパーを用いて亜鉛付着量を片面当たり60g/m2に調整し、510℃で20秒で行った。
The effect by this invention is shown concretely below.
First, molten steel having the composition shown in Table 1 was made into a slab by continuous casting after vacuum degassing treatment. Next, the slab was heated, scale-removed, and then roughly rolled to a plate thickness of 40 mm. Next, the steel sheet surface layer was cooled with a scale removing device, and then finish-rolled to a thickness of 3.5 mm and wound on a coil at a winding temperature of 700 ° C. Table 2 shows the heating conditions of the slab at this time, the surface temperature of the steel sheet after cooling before finish rolling, and the finish rolling temperature.
Next, the steel sheet after winding is pickled and cold-rolled to 0.70 mm (cold rolling rate: 80%) as a test material, degreased and pickled as pretreatment, and then annealed in a hot-dip galvanizing line Then, hot dip galvanizing treatment, alloying treatment, and temper rolling with an elongation of 1.0% were performed to obtain an alloyed hot dip galvanized steel sheet. In addition, in order to evaluate the properties of the cold-rolled steel sheets, some of the steel sheets were subjected to only temper rolling with an elongation of 1.0% after annealing to obtain cold-rolled steel sheets. The atmosphere during the annealing was a non-oxidizing gas containing hydrogen, and the annealing temperature of each test material was 840 ° C., which is lower than the Ac 3 transformation point. The hot dip galvanizing treatment was performed using a 460 ° C. zinc plating bath containing 0.12% Al at an intrusion plate temperature of 460 ° C. and an immersion time of 3 seconds. The alloying treatment was carried out at 510 ° C. for 20 seconds after the plating by adjusting the zinc adhesion amount to 60 g / m 2 per side using an N 2 gas wiper.
上記の製造方法により得られた冷延鋼板および合金化溶融亜鉛鋼板に対して、鋼板両面の表面から10 μｍまでの表層部における大きさ20nm未満の析出物に含まれるTi元素の含有量、{100}面Ｘ線ランダム強度比、機械的特性および加工後形状均一性を下記の方法により測定、評価した。また、合金化溶融亜鉛鋼板に対しては、上記に加え、さらに外観も評価した。得られた結果を表３に示す。 For the cold-rolled steel sheet and galvannealed steel sheet obtained by the above production method, the content of Ti element contained in precipitates having a size of less than 20 nm in the surface layer part from the surface of both surfaces of the steel sheet to 10 μm, { 100} plane X-ray random intensity ratio, mechanical characteristics and post-processing shape uniformity were measured and evaluated by the following methods. In addition to the above, the appearance was further evaluated for the galvannealed steel sheet. The obtained results are shown in Table 3.
鋼板両面の表面から10 μｍまでの表層部における大きさ20nm未満の析出物に含まれるTi元素の含有量
得られた冷延鋼板および合金化溶融亜鉛めっき鋼板について、溶融亜鉛めっき鋼板はめっき層を塩酸で剥離した後、試料寸法が3cm×4cmとなる大きさに切断し、10％AA系電解液（10vol％アセチルアセトン-1mass％塩化テトラメチルアンモニウム-メタノール）中で、電流密度20mA/cm2で定電流電解した。電解は、鋼板両面同時に行い、電解厚みは片面あたり表層から10μmまでとした。
電解後の、表面に析出物が付着している試料片を電解液から取り出して、ヘキサメタリン酸ナトリウム水溶液（500mg/l）（以下、SHMP水溶液と称す）中に浸漬し、超音波振動を付与して、析出物を試料片から剥離しSHMP水溶液中に抽出した。次いで、析出物を含むSHMP水溶液を孔径20nmのフィルタを用いてろ過し、ろ過後のろ液に対してICP発光分光分析装置を用いて分析し、ろ液中のTiの絶対量を測定した。次いで、Tiの絶対量を電解重量で除して、大きさ20nm未満の析出物に含まれるTiの含有量（mass％）を得た。なお、電解重量は、析出物剥離後の試料に対して重量を測定し、電解前の試料重量から差し引くことで求めた。
なお、表３に示す含有量は、上記にて求めた両面の含有量を平均した値である。
The content of Ti element contained in precipitates with a size of less than 20 nm in the surface layer part from the surface of both sides of the steel plate to 10 μm About the obtained cold-rolled steel plate and alloyed hot-dip galvanized steel plate, after stripping with hydrochloric acid, was cut to a size of the sample size is 3cm × 4cm, 10% AA electrolytic solution (10 vol% acetylacetone -1Mass% tetramethylammonium chloride - methanol), at a current density of 20 mA / cm 2 Constant current electrolysis. The electrolysis was performed simultaneously on both sides of the steel sheet, and the electrolysis thickness was from the surface layer to 10 μm per side.
After the electrolysis, remove the sample piece with deposits on the surface from the electrolyte and immerse it in an aqueous solution of sodium hexametaphosphate (500 mg / l) (hereinafter referred to as the SHMP aqueous solution) to apply ultrasonic vibration. The precipitate was peeled off from the sample piece and extracted into an aqueous SHMP solution. Subsequently, the SHMP aqueous solution containing the precipitate was filtered using a filter having a pore diameter of 20 nm, and the filtrate after filtration was analyzed using an ICP emission spectroscopic analyzer, and the absolute amount of Ti in the filtrate was measured. Next, the absolute amount of Ti was divided by the electrolytic weight to obtain the Ti content (mass%) contained in the precipitate having a size of less than 20 nm. In addition, the electrolysis weight was calculated | required by measuring a weight with respect to the sample after deposit peeling, and subtracting from the sample weight before electrolysis.
In addition, content shown in Table 3 is the value which averaged content of both surfaces calculated | required above.
{100}面Ｘ線ランダム強度比
板面に垂直な方向の{100}面Ｘ線強度は逆極点図法により測定した。表面での{100}面Ｘ線強度は、試験片を洗浄、乾燥したのちに、一方、板厚中心部での板面に垂直な方向の{100}面Ｘ線強度は、試験片の片面をシュウ酸により化学研磨して、板厚中心部を表面に露出させた後、測定を行った。合金化溶融亜鉛めっき鋼板の表面での{100}面Ｘ線強度は、試験片を10%塩酸にて酸洗して合金化めっき層を除去し、洗浄、乾燥したのち同様に測定した。Ｘ線源には白色Ｘ線を用い、{100}面Ｘ線の検出にはGe半導体検出器を用いた。また同時に、選択配向のない、結晶方位が不規則な分布をするランダム試料の{100}面Ｘ線強度（ランダム強度）を測定した。ランダム強度比は、ランダム試料の{100}面Ｘ線強度に対する実試験片の{100}面Ｘ線強度の比により算出した。
{100} plane X-ray random intensity The {100} plane X-ray intensity in the direction perpendicular to the specific plate surface was measured by reverse pole figure projection. The {100} plane X-ray intensity on the surface is measured after the test piece is cleaned and dried, while the {100} plane X-ray intensity in the direction perpendicular to the plate surface at the center of the thickness is measured on one side of the test piece. Was chemically polished with oxalic acid to expose the central portion of the plate thickness on the surface, and then the measurement was performed. The {100} plane X-ray intensity on the surface of the alloyed hot-dip galvanized steel sheet was measured in the same manner after the specimen was pickled with 10% hydrochloric acid to remove the alloyed plating layer, washed and dried. White X-rays were used as the X-ray source, and a Ge semiconductor detector was used to detect {100} plane X-rays. At the same time, the {100} plane X-ray intensity (random intensity) of a random sample with no selective orientation and an irregular distribution of crystal orientation was measured. The random intensity ratio was calculated by the ratio of the {100} plane X-ray intensity of the actual test piece to the {100} plane X-ray intensity of the random sample.
機械的特性
成形性は、引張特性とｒ値の機械的特性により評価した。引張特性は、ＪＩＳＺ 2201記載の５号試験片に加工した後、ＪＩＳＺ 2241記載の試験方法に従って行った。また平均ｒ値は、15％の引張予歪を与えた後、3点法にて測定し、鋼板の１方向に対して、90°方向、45°方向、０°方向のｒ値の平均=(r(0°)+2×ｒ(45°)+r(90°))/4として求めた。
Mechanical properties Formability was evaluated by tensile properties and r-value mechanical properties. Tensile properties were measured according to the test method described in JISZ 2241 after being processed into a No. 5 test piece described in JISZ 2201. The average r value was measured by a three-point method after applying a tensile pre-strain of 15%, and the average r value in the 90 ° direction, 45 ° direction, and 0 ° direction with respect to one direction of the steel sheet = It was determined as (r (0 °) + 2 × r (45 °) + r (90 °)) / 4.
加工後形状均一性
加工後形状均一性評価は、圧延直角方向に伸び率5%の歪みを付与した後、砥石がけを行い、形状不均一を可視化して、不均一の認められるものを×、認められないものを○とした。
Post-working shape uniformity Post-working shape uniformity evaluation is performed by giving a 5% strain in the direction perpendicular to the rolling direction, then grinding the wheel, visualizing the shape non-uniformity, x, Items that were not recognized were marked as ◯.
めっき後外観
合金化溶融亜鉛めっきを施したものについては、外観ムラの有無を観察し、ムラの生じたものを×、ムラなく均一な外観であったものを○とした。
Appearance of the alloyed hot-dip galvanized after plating was observed for the presence or absence of unevenness in appearance.
成分組成が本発明範囲内で、かつ表面から10 μｍまでの表層部における、大きさ20nm未満の析出物に含まれるTi元素の含有量が鋼板中に含有する全Ti量の9％以下である本発明例は、板面に平行な方向の{100}面Ｘ線強度がランダム強度比で2.0未満であり、深絞り性の指標である平均r値が1.5以上であり、加工後の形状均一性に優れ、かつ外観がムラがなく均一で自動車外装板用途に適した性能を有していた。
一方、比較例では、平均r値、加工後形状均一性、外観のいずれかが劣り、自動車外装板用途に適した性能を満足しなかった。
The component composition is within the range of the present invention, and in the surface layer portion from the surface to 10 μm, the content of Ti element contained in the precipitate having a size of less than 20 nm is 9% or less of the total amount of Ti contained in the steel plate. In the example of the present invention, the {100} plane X-ray intensity in the direction parallel to the plate surface is less than 2.0 in terms of random intensity ratio, the average r value that is an index of deep drawability is 1.5 or more, and the shape after processing is uniform It had excellent performance, uniform appearance and uniform performance suitable for automotive exterior panels.
On the other hand, in the comparative example, any one of the average r value, the processed post-process uniformity, and the appearance was inferior, and the performance suitable for the automobile exterior plate application was not satisfied.
本発明の鋼板は、自動車の外板を中心に、優れた成形後表面品質を必要とする各種電気機器、自動車などの部品に対して好適に使用できる。 The steel sheet of the present invention can be suitably used for various parts such as automobiles and automobiles that require excellent post-molding surface quality, centering on automobile outer plates.
Claims (7)
ただし、（Ti%）、（N%）、（S%）、（C%）は、それぞれTi、N、S、Cの含有量（mass％）を示す。 In mass%, C: 0.0005 to 0.01%, Si: 0.2% or less, Mn: 0.1 to 1.5%, P: 0.03% or less, S: 0.005 to 0.03%, Ti: 0.02 to 0.1%, Al: 0.01 to 0.05% , N: 0.005% or less, and Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%) Ti * is expressed as 0 <Ti * <Contains in a range satisfying 0.02, the remainder has a composition composed of Fe and unavoidable impurities, and is contained in precipitates with a size of less than 20 nm in the plate thickness surface layer portion up to 10 μm from each surface on both surfaces of the steel plate A cold-rolled steel sheet characterized in that the content (mass%) of Ti element in the surface layer portion of the Ti element is 9% or less of the total Ti content (mass%) in the steel sheet.
However, (Ti%), (N%), (S%), and (C%) indicate the contents (mass%) of Ti, N, S, and C, respectively.
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