JP7333901B2 - Automotive steel plate - Google Patents
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- JP7333901B2 JP7333901B2 JP2018217190A JP2018217190A JP7333901B2 JP 7333901 B2 JP7333901 B2 JP 7333901B2 JP 2018217190 A JP2018217190 A JP 2018217190A JP 2018217190 A JP2018217190 A JP 2018217190A JP 7333901 B2 JP7333901 B2 JP 7333901B2
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Description
本発明は、自動車量鋼板に係り、更に詳細には、化成処理性に優れた自動車用鋼板に関する。 TECHNICAL FIELD The present invention relates to a steel sheet for automobiles, and more particularly to a steel sheet for automobiles having excellent chemical conversion treatability.
鋼板を製造する方法としては、天然資源である鉄鉱石を主な原料として高炉で製造する方法と、リサイクル資源である鉄スクラップを主な原料として電炉で製造する方法の二つの方法とがある。 There are two methods of manufacturing steel sheets: a method using iron ore, which is a natural resource, as the main raw material in a blast furnace, and a method using an electric furnace, using iron scrap, which is a recycled resource, as the main raw material.
高炉で鋼板を製造する場合は、鉄鉱石を溶かすエネルギーに加えて、鉄鉱石中に含まれる酸素を除去するために多くのコークスを使用する必要があり、二酸化炭素の排出量が多い。 When producing steel sheets in a blast furnace, in addition to the energy required to melt the iron ore, a large amount of coke must be used to remove the oxygen contained in the iron ore, resulting in a large amount of carbon dioxide emissions.
これに対し、電炉で製造する場合は、鉄スクラップを溶かして鋼板にするため、酸素を除去する必要がなく、高炉での鋼板の製造に比して二酸化炭素の排出量を大幅に削減できる。 On the other hand, when manufacturing steel sheets in an electric furnace, iron scrap is melted into steel sheets, so there is no need to remove oxygen, and carbon dioxide emissions can be greatly reduced compared to manufacturing steel sheets in a blast furnace.
上記電炉で製造した電炉材は、現在、主に建築土木用として利用されているが、自動車用鋼板にも用途を拡大することにより、国内における資源循環サイクルを可能とし、二酸化炭素の排出量をも削減できる。 The electric furnace materials manufactured by the above electric furnace are currently used mainly for construction and civil engineering, but by expanding their use to steel sheets for automobiles, it will be possible to recycle resources in Japan and reduce carbon dioxide emissions. can also be reduced.
しかし、上記電炉材は、鉄スクラップ材をその原料として用いるため、銅（Ｃｕ）、ニッケル（Ｎｉ）、スズ（Ｓｎ）などのトランプエレメントやクロム（Ｃｒ）などのスクラップ由来の元素を多く含有し、自動車用鋼板としては利用し難い。 However, since the electric furnace material uses iron scrap material as its raw material, it contains many tramp elements such as copper (Cu), nickel (Ni), tin (Sn) and scrap-derived elements such as chromium (Cr). , it is difficult to use as a steel sheet for automobiles.
すなわち、上記トランプエレメントは、自動車用鋼板に要求される、強度や成形性などの機械的特性の他、耐食性などの化学的安定性を低下させ、特に、鋼板の表面に存在する銅化合物は、耐食性を向上させるための化成処理性を低下させる。 That is, the tramp element reduces chemical stability such as corrosion resistance as well as mechanical properties such as strength and formability required for steel sheets for automobiles. Decrease the chemical conversion treatability for improving corrosion resistance.
鋼板の化成処理は、鋼板表面に形成される局部電池のアノード点から鉄を溶解させ、上記アノード点で発生した電子がカソード点で酸化剤を還元する反応によって、化成処理膜となる化合物を析出させて被膜を形成する処理であり、アノード点からの鉄の溶解反応が化成処理反応の駆動力となる。 In the chemical conversion treatment of a steel sheet, iron is dissolved from the anode point of the local battery formed on the surface of the steel sheet, and the electrons generated at the anode point reduce the oxidant at the cathode point. In this treatment, the dissolution reaction of iron from the anode point becomes the driving force of the chemical conversion treatment reaction.
しかし、銅化合物を含む鋼片では、製造時の加熱処理によって表面の鉄が選択的に酸化されて酸化鉄となり、銅化合物は上記酸化物に溶け込めず排出されるため、酸化鉄の生成と共に銅化合物が濃縮されて粗大化して鋼板の表面が銅化合物で覆われてしまう。
したがって、銅化合物を含む鋼片は、化成処理の反応を駆動するアノ－ド点が減少し、鉄の溶解反応が進まないため、化成処理性が低下する。
However, in steel billets containing copper compounds, the iron on the surface is selectively oxidized by heat treatment during production to become iron oxide, and the copper compounds are not dissolved in the oxide and are discharged. The compound is concentrated and coarsened, and the surface of the steel sheet is covered with the copper compound.
Therefore, the slab containing a copper compound has a reduced anodic point that drives the chemical conversion reaction, and the dissolution reaction of iron does not proceed, resulting in a decrease in chemical conversion treatability.
特許文献１の特開平８－２２５８８８号公報には、化成処理性を向上させる硫黄とリンの含有量と、耐食性を向上させる銅化合物の含有量とを所望の関係にすることで耐食性と化成処理性とを両立できる旨が記載されている。 In Japanese Patent Laid-Open No. 8-225888 of Patent Document 1, the content of sulfur and phosphorus that improves the chemical conversion treatability and the content of the copper compound that improves the corrosion resistance are in a desired relationship to improve corrosion resistance and chemical conversion treatment. It is stated that it can be compatible with sexuality.
また、特許文献２の特開２０１５－９８６２０号公報には、銅の含有量を０．０５％未満にすることで化成処理性を向上させた自動車用鋼板が記載されている。 Further, Japanese Patent Application Laid-Open No. 2015-98620 of Patent Document 2 describes a steel sheet for automobiles in which the copper content is less than 0.05% to improve the chemical convertibility.
しかしながら、硫黄の含有量が多い鋼板はスポット溶接が困難であり、特許文献１に記載の鋼板は自動車用鋼板には適さない。また、特許文献２に記載の鋼板は、銅の含有量を少なくすることが必須であるため、上記鉄スクラップ材を原料とする電炉材は使用できない。 However, steel sheets with a high sulfur content are difficult to spot weld, and the steel sheet described in Patent Document 1 is not suitable for automotive steel sheets. In addition, since the steel sheet described in Patent Document 2 must have a low copper content, it cannot be used as an electric furnace steel made from the iron scrap material.
本発明は、このような従来技術の有する課題に鑑みてなされたものであり、その目的とするところは、電炉材を利用可能な化成処理性に優れる自動車用鋼板を提供することにある。 The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a steel sheet for automobiles that can be used with an electric furnace and has excellent chemical conversion treatability.
本発明者は、上記目的を達成すべく鋭意検討を重ねた結果、化成処理反応においてカソード点なって化成処理膜の生成サイトとなる、鋼板表面に露出した銅化合物粒子の粒径を小さくすると共に、残留スケールを所定量以下にすることにより、上記目的が達成できることを見出し、本発明を完成するに至った。 As a result of extensive studies to achieve the above object, the present inventors have found that the grain size of the copper compound particles exposed on the surface of the steel sheet, which becomes the cathode point in the chemical conversion reaction and becomes the site for forming the chemical conversion film, is reduced. The inventors have found that the above object can be achieved by reducing the residual scale to a predetermined amount or less, and have completed the present invention.
即ち、上記課題は、本発明の下記（１）～（３）により解決される。
（１）鉄（Ｆｅ）を９８．３０質量％以上９９．３６質量％以下、
銅（Ｃｕ）を０．１０質量％以上０．５０質量％以下、
残部不可避不純物を含み、
粒径が０．０３μｍ以上の表面の残留スケールの個数が１００，８００個／ｍｍ２以下であり、
粒径が０．０３μｍ以上の表面に露出した銅化合物粒子が、２１，６００個／ｍｍ２～１２０，０００個／ｍｍ２であり、その最大粒径が２μｍ以下であることを特徴とする化成処理用自動車鋼板。
（２）上記銅化合物粒子が、粒径が０．１μｍ以下である銅化合物粒子を８０個数％以上含むことを特徴とする上記第（１）項に記載の化成処理用自動車用鋼板。
（３）銅化合物粒子の最大粒径が２μｍ未満であることを特徴とする上記第（１）項又は上記第（２）項に記載の化成処理用自動車用鋼板。
That is, the above problems are solved by the following (1) to (3) of the present invention.
(1) 98.30% by mass or more and 99.36% by mass or less of iron (Fe),
0.10% by mass or more and 0.50% by mass or less of copper (Cu),
Including residual inevitable impurities,
The number of residual scales on the surface with a particle size of 0.03 μm or more is 100,800/mm 2 or less,
21,600/mm 2 to 120,000/mm 2 of copper compound particles exposed on the surface having a particle size of 0.03 μm or more, and a maximum particle size of 2 μm or less. Automotive steel sheet for processing.
(2) The automotive steel sheet for chemical conversion treatment according to item (1) above, wherein the copper compound particles contain 80% by number or more of copper compound particles having a particle size of 0.1 μm or less.
(3) The automotive steel sheet for chemical conversion treatment according to item (1) or item (2) above, wherein the maximum particle size of the copper compound particles is less than 2 μm.
本発明によれば、化成処理においてカソード点となる鋼板表面に露出した銅化合物粒子の粒径を２μｍ以下にすると共に、残留スケールを所定量以下にしたため、化成処理性に優れた鋼板を提供することができる。 According to the present invention, the grain size of the copper compound particles exposed on the surface of the steel sheet, which becomes the cathode point in chemical conversion treatment, is set to 2 μm or less, and the residual scale is set to a predetermined amount or less, thereby providing a steel sheet excellent in chemical conversion treatability. be able to.
＜自動車用鋼板＞
本発明の自動車用鋼板について詳細に説明する。
上記鋼板は、その表面に露出した銅化合物粒子の最大粒径が２μｍ以下であり、かつ表面の残留スケールの個数が１６０，０００個／ｍｍ２以下である。
<Automotive steel plate>
The automotive steel sheet of the present invention will be described in detail.
In the steel sheet, the maximum grain size of copper compound particles exposed on the surface is 2 μm or less, and the number of residual scales on the surface is 160,000/mm 2 or less.
上記銅化合物粒子は、鋼板中の鉄（Ｆｅ）よりも電位が高く、鋼板表面に露出する微細な銅化合物粒子は、化成処理においてカソード点となって化成処理性を向上させる。 The copper compound particles have a higher potential than iron (Fe) in the steel sheet, and the fine copper compound particles exposed on the surface of the steel sheet serve as cathode points in the chemical conversion treatment to improve the chemical conversion treatability.
ここで、化成処理の反応について説明する。
化成処理反応は、鋼板の表面に形成される局部電池により駆動される。
すなわち、図１に示すように、鋼板の表面のアノード点では、下地のＦｅの溶解反応が起こることで電子が発生し、カソード点では、上記アノード点で発生した電子により酸化剤の還元反応が起こる。そして、化成処理液が酸性溶液である場合は、水素イオンが還元されて鋼板表面近傍のｐＨが上昇し、これに伴って表面に化成処理膜を形成する化合物が析出する。
Here, the chemical conversion reaction will be described.
The chemical conversion reaction is driven by a local cell formed on the surface of the steel sheet.
That is, as shown in FIG. 1, at the anode point on the surface of the steel sheet, electrons are generated by the dissolution reaction of the underlying Fe, and at the cathode point, the electrons generated at the anode point cause the reduction reaction of the oxidant. happen. When the chemical conversion treatment liquid is an acidic solution, the hydrogen ions are reduced to raise the pH in the vicinity of the steel sheet surface, and along with this, a compound that forms a chemical conversion film on the surface is deposited.
粗大な銅化合物粒子が鋼板の表面を広く覆うと、アノード点で発生した電子が粗大な銅化合物粒子の中央部まで行きわたらず、カソード点となる銅化合物粒子とアノード点との境界近傍でしか上記還元反応が起こらないため、銅化合物粒子の周縁しか化成処理膜で覆うことができず、化成処理性が低下してしまう。 When the surface of the steel sheet is widely covered with coarse copper compound particles, the electrons generated at the anode point do not reach the center of the coarse copper compound particles, and are limited to the vicinity of the boundary between the copper compound particles serving as the cathode point and the anode point. Since the reduction reaction does not occur, only the periphery of the copper compound particles can be covered with the chemical conversion treatment film, resulting in deterioration in chemical conversion treatability.
本発明の鋼板は、鋼板表面に露出した銅化合物粒子の最大粒径が２μｍ以下であり、鋼板の表面に微細なカソード点を有する。上記銅化合物粒子の最大粒径は、２μｍ未満であることが好ましく、さらに１．５μｍ以下であることが好ましく、１．０μｍ以下であることがより好ましい。 In the steel sheet of the present invention, the maximum grain size of the copper compound particles exposed on the steel sheet surface is 2 μm or less, and the surface of the steel sheet has fine cathode points. The maximum particle size of the copper compound particles is preferably less than 2 μm, more preferably 1.5 μm or less, and more preferably 1.0 μm or less.
銅化合物粒子が微細であることで、従来、化成処理性を低下させるとされていた銅化合物を含んでいても、鉄（Ｆｅ）よりも電位が高いので、銅化合物粒子と該銅化合物粒子に隣接するアノード点とで微細な局部電池を形成して鋼板全体を覆う緻密な化成処理膜を形成できる。
上記銅化合物としては、銅硫化物や銅ニッケル合金を挙げることができる。
Because the copper compound particles are fine, even if they contain copper compounds that are conventionally believed to reduce chemical conversion treatability, the potential is higher than that of iron (Fe), so the copper compound particles and the copper compound particles Adjacent anode points form fine local cells to form a dense chemical conversion treatment film covering the entire steel sheet.
Examples of the copper compound include copper sulfides and copper-nickel alloys.
また、本発明の鋼板は、残留スケールの個数が１６０，０００個／ｍｍ２以下である。
残留スケールの個数が上記範囲であることで、化成処理膜の密着性が向上すると共に化成処理性が向上する。
In addition, the number of residual scales in the steel sheet of the present invention is 160,000/mm 2 or less.
When the number of residual scales is within the above range, the adhesion of the chemical conversion treatment film is improved and the chemical conversion treatability is improved.
残留スケールは、地鉄との界面で剥離し易く、残留スケールが多くなるとスケール上に形成された化成処理膜の密着性が低下してしまう。 The residual scale is easily peeled off at the interface with the base iron, and when the residual scale increases, the adhesion of the chemical conversion treatment film formed on the scale decreases.
残留スケールの個数が１６０，０００個／ｍｍ２以下であることで、化成処理反応が速やかに進み、緻密な化成処理膜が形成される。 When the number of residual scales is 160,000/mm 2 or less, the chemical conversion reaction proceeds rapidly, forming a dense chemical conversion film.
上記銅化合物粒子やスケールの粒径は、鋼板表面のＳＥＭ像から、特性Ｘ線をエネルギーで分光して鋼板表面を構成する元素を同定し、上記ＳＥＭ像を２値化して測定できる。
本発明においては、５μｍ×５μｍの視野を５０視野観察して各視野の粒径０．０３μｍ以上の銅化合物粒子及び粒径０．０３μｍ以上のスケール粒子の個数を求めた。
The particle size of the copper compound particles and the scale can be measured by analyzing the energy of the characteristic X-rays from the SEM image of the steel sheet surface, identifying the elements constituting the steel sheet surface, and binarizing the SEM image.
In the present invention, 50 visual fields of 5 μm×5 μm were observed, and the number of copper compound particles with a particle size of 0.03 μm or more and scale particles with a particle size of 0.03 μm or more in each field of view was determined.
また、本発明において粒径とは、粒子の長径と短径の平均値（（長径＋短径）／２）をいい、銅化合物粒子については１つのカソード点を形成一塊の銅化合物粒子群を粒子径とした。
上記銅化合物粒子群は単一の粒子で形成されていてもよく、微細な粒子が凝集して一塊となった粒子群であってもよい。
In the present invention, the particle size refers to the average value of the major axis and minor axis of the particle ((major axis + minor axis) / 2), and for copper compound particles, one cathode point is formed. Particle diameter.
The copper compound particle group may be formed of a single particle, or may be a particle group in which fine particles aggregate to form a lump.
上記鋼板は表面に露出した銅化合物粒子の最大粒径が２μｍ以下であり、上記銅化合物粒子のうち、粒径が０．１μｍ以下の銅化合物粒子を８０個数％以上含むことが好ましい。
銅化合物粒子の粒径が小さいことで、均一かつ緻密な化成処理膜を形成できる。
In the steel sheet, the maximum particle size of the copper compound particles exposed on the surface is 2 μm or less, and the copper compound particles preferably contain 80% by number or more of the copper compound particles having a particle size of 0.1 μm or less.
A uniform and dense chemical conversion treatment film can be formed because the particle size of the copper compound particles is small.
また、上記鋼板は、銅化合物粒子を、８００個／ｍｍ２以上２００，０００個／ｍｍ２以下有することが好ましい。単位面積当たりの銅化合物粒子の数が上記範囲内であることで、化成処理性が向上する。 Moreover, the steel sheet preferably has copper compound particles of 800/mm 2 or more and 200,000/mm 2 or less. When the number of copper compound particles per unit area is within the above range, the chemical conversion treatability is improved.
銅化合物粒子が８００個／ｍｍ２未満では、化成処理膜を形成する化合物の析出点が少なく、化成処理性が低下することがあり、２００，０００個／ｍｍ２を超えるとアノード点が少なく、化成処理性が低下することがある。 When the number of copper compound particles is less than 800/mm 2 , the number of precipitation points of the compound forming the chemical conversion treatment film is small, and the chemical conversion treatability may be deteriorated. Chemical convertibility may deteriorate.
上記化成処理としては、リン酸被膜処理や、メッキなど鋼板の耐食性を向上させる処理を挙げることができる。 Examples of the chemical conversion treatment include a phosphoric acid coating treatment and a treatment for improving the corrosion resistance of the steel sheet, such as plating.
上記鋼板は、上記カソード点を形成する銅や銅化合物の他、炭素（Ｃ）、ケイ素（Ｓｉ）マンガン（Ｍｎ）クロム（Ｃｒ）などを含むことができる。 The steel plate may contain carbon (C), silicon (Si), manganese (Mn), chromium (Cr), etc., in addition to copper and copper compounds forming the cathode point.
これら元素の含有量は、それぞれ、炭素（Ｃ）が０．００５質量％～０．２５質量％、ケイ素（Ｓｉ）が０．０１質量％～１．６０質量％、マンガン（Ｍｎ）が０．０１質量％～１．６０質量％、クロム（Ｃｒ）が０．０１質量％～１．６０質量％、銅が０．１０質量％～０．５０質量％であることが好ましい。 The contents of these elements are 0.005% to 0.25% by mass for carbon (C), 0.01% to 1.60% by mass for silicon (Si), and 0.01% to 1.60% by mass for manganese (Mn). 01% to 1.60% by weight, 0.01% to 1.60% by weight of chromium (Cr), and 0.10% to 0.50% by weight of copper.
上記元素は、上記元素はスクラップ材から混入し易い元素であり、上記元素を化成処理におけるカソード点とすることで、スクラップ材を用いた電炉材の化成処理性を向上させることが可能である。 The above elements are elements that are likely to be mixed from scrap materials, and by using the above elements as cathode points in chemical conversion treatment, it is possible to improve chemical conversion treatability of electric furnace materials using scrap materials.
＜自動車用鋼板の製造方法＞
本発明の自動車用鋼板は、加熱した鋼片を大気に所定時間曝し、粗圧延前にデスケーリングを行い、銅化合物脆化現象を避けた温度で圧延することで作製できる。
<Manufacturing method of automotive steel sheet>
The steel sheet for automobiles of the present invention can be produced by exposing a heated steel slab to the atmosphere for a predetermined period of time, performing descaling before rough rolling, and rolling at a temperature that avoids embrittlement of copper compounds.
加熱した鋼片を大気に曝すと鋼片の表面が酸化してスケールが生じる。
このとき、鋼片中の銅化合物は上記スケール中に溶け込めないため、スケールから排斥されて地鉄とスケールとの間に液相の層を形成する。そして、上記液相の層が生成することで、スケールと地鉄との密着性が低下し、後述するデスケーリング工程においてスケールが剥がれ易くなり、残留スケールの個数が１６０，０００個／ｍｍ２以下にすることができる。
When a heated steel slab is exposed to the atmosphere, the surface of the steel slab is oxidized to form scales.
At this time, since the copper compound in the steel billet cannot dissolve in the scale, it is expelled from the scale and forms a liquid phase layer between the base iron and the scale. Then, due to the formation of the liquid phase layer, the adhesion between the scale and the base iron is reduced, and the scale is easily peeled off in the descaling process described later, and the number of residual scales is 160,000/mm 2 or less. can be
上記鋼片を大気に曝す時間は、１～５分であることが好ましい。
１分未満では、上記銅を含む液相の層が充分形成されずスケールの剥離性が低下してスケールが残り易くなり、５分を超えると鋼片が冷えて粗圧延が困難になることがある。
The time for exposing the billet to the atmosphere is preferably 1 to 5 minutes.
If the time is less than 1 minute, the copper-containing liquid phase layer is not sufficiently formed, and scale releasability is lowered, and scale tends to remain. be.
そして、上記液相の層を生成させた後、粗圧延工程前にデスケーリングを行う。粗圧延工程前にデスケーリングを行うことで、銅化合物を含む液相と共にスケールを除去することができ、粗圧延工程において上記銅化合物を含む液相が地鉄表面に引き伸ばされて粗大化することが防止される。 After forming the liquid phase layer, descaling is performed before the rough rolling step. By performing descaling before the rough rolling process, the scale can be removed together with the copper compound-containing liquid phase, and in the rough rolling process, the copper compound-containing liquid phase is stretched on the surface of the base iron and coarsened. is prevented.
その後、鋼片の銅化合物脆化現象を避けた温度、具体的には、粗圧延出側の温度が９６０℃以上１０００℃以下で圧延する。
デスケーリング工程において残存した銅化合物が液相の状態のまま圧延を行うと、図２に示すように、液相の銅化合物が鋼片のオーステナイト粒界に押し込まれて粗大化するが、上記温度範囲で粗圧延を行うことで、地鉄表面に残存する銅化合物粒子が微細化されて、鋼板表面に露出する銅化合物粒子の最大粒径を２μｍ以下にすることができる。
Thereafter, the steel slab is rolled at a temperature that avoids copper compound embrittlement, specifically, at a temperature of 960° C. or more and 1000° C. or less on the delivery side of rough rolling.
If the copper compound remaining in the descaling process is rolled in a liquid phase state, the liquid phase copper compound is forced into the austenite grain boundaries of the steel billet and coarsens as shown in FIG. By performing rough rolling within this range, the copper compound particles remaining on the surface of the base steel are refined, and the maximum particle size of the copper compound particles exposed on the steel sheet surface can be made 2 μm or less.
上記デスケーリング工程と粗圧延工程とは、交互に複数回行うことが好ましい。粗圧延工程中に生じたスケールを逐次除去することで、上記スケールから排斥された銅化合物が地鉄のオーステナイト粒界に押し込まれて粗大化することを防止できる。 It is preferable that the descaling process and the rough rolling process are alternately performed a plurality of times. By successively removing the scale generated during the rough rolling step, it is possible to prevent the copper compounds expelled from the scale from being pushed into the austenite grain boundaries of the base iron and becoming coarse.
以下、本発明を実施例により詳細に説明するが、本発明は下記実施例に限定されるものではない。 EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.
下記表１に示す鋼片を加熱し、表２に示す条件で圧延して自動車用鋼板を作製した。 The steel slabs shown in Table 1 below were heated and rolled under the conditions shown in Table 2 to produce steel sheets for automobiles.
作製した鋼板の表面ＳＥＭ像を画像解析し、銅化合物粒子の最大粒径、０．２μｍ以下の銅化合物粒子の割合及び０．１μｍ以下の銅化合物粒子の割合を計測した。 A surface SEM image of the produced steel plate was subjected to image analysis, and the maximum particle size of copper compound particles, the ratio of copper compound particles of 0.2 μm or less, and the ratio of copper compound particles of 0.1 μm or less were measured.
また、調整直後の化成処理液（標準条件）と、繰り返し使用して劣化した交換直前の化成処理液（劣化条件）とを用いて化成処理を行い、形成された被膜を観察した。
評価結果を鋼板の製造条件と共に表２に示す。
◎： 劣化条件の化成処理液でも結晶サイズが５．５μｍ未満。
○： 劣化条件の化成処理液での結晶サイズが５．５μｍ以上９μｍ以下。
△： 劣化条件の化成処理液での結晶サイズが９μｍを超える。
×： 標準条件の化成処理液での結晶サイズが９μｍを超える。
In addition, chemical conversion treatment was performed using a chemical conversion treatment solution immediately after preparation (standard conditions) and a chemical conversion treatment solution deteriorated by repeated use just before replacement (degraded conditions), and films formed were observed.
The evaluation results are shown in Table 2 together with the steel sheet production conditions.
⊚: The crystal size is less than 5.5 µm even with a chemical conversion treatment solution under deteriorated conditions.
◯: The crystal size in the chemical conversion treatment solution under deteriorated conditions is 5.5 μm or more and 9 μm or less.
Δ: The crystal size exceeds 9 μm in the chemical conversion treatment solution under deteriorated conditions.
x: The crystal size exceeds 9 μm in the chemical conversion treatment solution under standard conditions.
実施例２の鋼板の表面ＳＥＭ像を図３、該鋼板に形成した化成処理膜の表面ＳＥＭ像を図４に示す。銅化合物粒子の最大粒径が２μｍ以下の実施例２は、緻密な化成処理膜を形成でき、自動車用鋼板として利用できることが確認された。
また、比較例３の鋼板の表面ＳＥＭ像を図５に示す。比較例３は鋼板表面に図５中、まるで囲んだ箇所に膜状の銅化合物が残存しており、化成処理性が低下した。
FIG. 3 shows a surface SEM image of the steel plate of Example 2, and FIG. 4 shows a surface SEM image of the chemical conversion treatment film formed on the steel plate. It was confirmed that Example 2, in which the maximum particle size of the copper compound particles was 2 μm or less, could form a dense chemical conversion film and could be used as a steel sheet for automobiles.
Moreover, the surface SEM image of the steel plate of Comparative Example 3 is shown in FIG. In Comparative Example 3, a film-like copper compound remained on the surface of the steel sheet in the area that was completely enclosed in FIG.
Claims (3)
銅（Ｃｕ）を０．１０質量％以上０．５０質量％以下、
残部不可避不純物を含み、
粒径が０．０３μｍ以上の表面の残留スケールの個数が１００，８００個／ｍｍ２以下であり、
粒径が０．０３μｍ以上の表面に露出した銅化合物粒子が、２１，６００個／ｍｍ２～１２０，０００個／ｍｍ２であり、その最大粒径が２μｍ以下であることを特徴とする化成処理用自動車鋼板。 98.30% by mass or more and 99.36% by mass or less of iron (Fe),
0.10% by mass or more and 0.50% by mass or less of copper (Cu),
Including residual inevitable impurities,
The number of residual scales on the surface with a particle size of 0.03 μm or more is 100,800/mm 2 or less,
21,600/mm 2 to 120,000/mm 2 of copper compound particles exposed on the surface having a particle size of 0.03 μm or more, and a maximum particle size of 2 μm or less. Automotive steel sheet for processing.
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| JP2000355734A (en) | 1999-06-15 | 2000-12-26 | Nippon Steel Corp | High burring hot rolled steel sheet excellent in fatigue characteristic and its production |
| JP2006124773A (en) | 2004-10-28 | 2006-05-18 | Sumitomo Metal Ind Ltd | Hot rolled steel strip and its production method |
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| JP2000355734A (en) | 1999-06-15 | 2000-12-26 | Nippon Steel Corp | High burring hot rolled steel sheet excellent in fatigue characteristic and its production |
| JP2006124773A (en) | 2004-10-28 | 2006-05-18 | Sumitomo Metal Ind Ltd | Hot rolled steel strip and its production method |
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