【発明の詳細な説明】[Detailed description of the invention]
この発明は化成処理性にすぐれた表面処理鋼板
に関する。
自動車用鋼板は一般に、実際使用に際してはブ
レス成形などの加工を行つた後、塗装下地処理と
しての化成処理（例えばリン酸塩処理）を施した
後その上に例えばカチオン電着塗装を施して最終
用途に使用されるが、前記電着塗装の塗膜が良好
な塗装耐食性を得るためには、まず下地処理にお
いて良好な化成皮膜を得ることが必要不可欠の条
件となる。この良好な化成皮膜を得るためには、
素材表面が化成皮膜結晶の核発生や成長を阻害し
ないような良好な状性（化成処理性にすぐれた性
状）を有していることが必要とされる。
さて、自動車用鋼板として用いられる冷延鋼板
は、従来は連続焼鈍における冷却を無酸化雰囲気
でのガスジエツトクール等の方法で行つていたの
で、化成処理皮膜の形成に有利とされるMn等の
表面濃化層が存在する等して化成処理性に極めて
すぐれた鋼板であつた。しかし最近、上記連続焼
鈍におけるヒートサイクルの合理化を図るため、
無酸化雰囲気でのガスジエツトクールに代えて水
冷または気水冷却の方法を採用する傾向にある。
この場合冷却過程が酸化性雰囲気となるため表面
に酸化膜が生成し、従つてこの酸化膜除去のため
の酸洗処理が必要となる。この酸洗処理を行つた
冷延鋼板は、上記Mn濃化層が除去されたり、ま
た酸洗残渣（水酸化鉄）の表面吸着等があつて化
成処理性が劣化してきている。
また冷延鋼板を自動車車体に用いる場合、車体
腐食が安全上大きな問題となるが、特に自動車外
板等で腐食の受け易い片面のみを耐食性にすぐれ
た例えばZnメツキ面もしくは、Zn−Ni合金メツ
キやFe−Zn合金メツキ面とし、他面を鋼板のま
まとして車体腐食の軽減を図るようにした片面メ
ツキ鋼板が用いられるようになつた。片面メツキ
鋼板としては電気メツキ法と溶融メツキ法の２種
類の製造方法があるが、電気メツキ法の場合は前
処理として酸洗が行われ、また多くの場合酸性浴
である電気メツキ浴中を経過するため酸洗効果を
受けるので非メツキ面の化成処理性は低下する。
また溶融メツキ法の場合は、高温状態で溶融メツ
キ浴中から出てくるため非メツキ面の酸化は避け
難く、このためメツキ終了後酸洗処理が必要とな
り同様に化成処理性は低下する。近年特にFe系
またはFe−Zn系合金電気メツキが一般的となり
つつあり、この場合酸性メツキ浴中に多量の
Fe3+イオンを含有しているため非メツキ面は酸
焼けピツテイング状態を呈しており、化成処理性
が極めて劣悪となつている。また電気Znメツキ
法によるものもあるが、この場合も高電流密度操
業の傾向が進むにつれて腐食性の強い塩化浴が使
用されるため、片面メツキ鋼板の非メツキ面側は
極度の溶解が起こり、このため同様に化成処理性
が極めて劣化している。また特にメツキ浴槽内で
の浸漬時間の長いたて型メツキ槽を用いた場合
は、よこ型メツキ槽の場合に比較して化成処理性
の劣化は極めて激しくなり、深刻な事態を生じる
に至つている。
本発明は上記の如く酸洗処理等を受けた冷延鋼
板または片面メツキ鋼板の非メツキ面の化成処理
性の劣化を解消すべくなされたものであつて、化
成処理性に劣る冷延鋼板表面性状を改善するとと
もに、化成処理反応速度の促進を図つた化成処理
性にすぐれた表面処理鋼板を提供しようとするも
のである。
化成処理性の劣化した冷延鋼板表面の改善を図
ることを目的として、冷延鋼板表面に金属Niを
0.3〜10mg／ｄm2付着させる方法が特開昭56−
116883号公報で開示されている。そしてこの発明
によれば確かにリン酸塩処理試験において化成処
理性（結晶サイズ、皮膜付着量）や塗装耐食性の
向上効果は得られる。しかしながら実際の化成処
理工程においては、オンラインで連続的処理が行
われており、このような工程で生産性を向上させ
るためには化成処理反応速度を高めてライン速度
をより一層高める必要があるので、化成処理性の
劣化した鋼板面の改善を図るとともに化成処理反
応速度の向上をも図り得る冷延鋼板が望まれてい
た。
本発明者らは上記に鑑み、良好な化成皮膜が得
られ、かつ、化成処理反応速度の向上を図り得る
化成処理性にすぐれた表面処理鋼板の開発を意図
して種々実験研究を重ねた。その結果、冷延鋼板
の表面に少量のＰを含有したNi−Ｐ合金を適正
量付着せしめることによつて、化成処理性の飛躍
的な向上が図り得るという新たな事実を知見し
た。
Ni−Ｐ合金を鋼板表面に付着させることによ
り化成処理性が良好となるメカニズムについては
未だ適確な解明は得られていないが、現段階では
次のように考察される。すなわち、酸洗により鋼
板表面には水酸化鉄、水錆など化成処理性を阻害
する要因となる生成物が形成されているが、浴中
にFeより貴なNiイオンを適正量含有せしめて電
解すると、このNiが鋼板表面に分散して前記生
成物層より突出するような状態で析出することが
考えられる。従つて化成処理のときにこの析出
Niが化成結晶の核となつて働き、化成皮膜の結
晶成長の起点となつて、微細で、緻密な化成皮膜
の形成が期待できる。化成反応速度の増加がNi
中にＰを微量添加することにより見られる学術上
の理由は、明らかではないが、ひとつの仮設とし
て次のように考えられる。すなわち、Niは上記
の如き結晶核生成の働きをなし、またＰは化成処
理液中のリン酸と反応する際に自己触媒的な活性
点となつて化成処理反応速度を促進する作用をな
すものと推察される。
本発明は上記知見に基づいてなされたものであ
つて、その要旨とするところは、冷延鋼板表面上
に、Ｐを0.01〜1.0％含有したNi−Ｐ合金が１〜
３mg／m2未満付着していることを特徴とする化成
処理性にすぐれた表面処理鋼板にある。
次にNi−Ｐ合金の付着方法について説明する。
付着方法としては、電気メツキ（メツキ浴として
水溶液、非水溶液、溶融塩浴等のいずれでもよ
い）無電解メツキ、真空蒸着等いずれの方法を用
いてもよく、特に限定するものではない。しか
し、装置規模、操業コスト等の観点から、常法に
よる酸性水溶液を使用した電気メツキ法、もしく
は無電解メツキ法の適用が最も好ましい。
蒸気電気メツキ法、無電解メツキ法の一例を示
せば次の通りである。
電気メツキ層：
例えば次の浴組成からなる公知のワツト浴を
基本とした亜リン酸添加浴を用いるのが好まし
い。
浴組成：NiSO4・6H2O 240ｇ/
NiCl2・6H2O 45ｇ/
H3BO3 30ｇ/
温 度 60℃
電流密度 １〜10A／ｄm2
上記浴にH3PO3を0.1〜10ｇ/の範囲で変化
させて添加し、鋼板表面にＰ含有率を調整した
Ni−Ｐ合金を付着させる。またNi−Ｐ付着量
は電解時間×電流密度を適宜変えて調整する。
無電解メツキ法：
次の組成からなる浴を用いる。
浴組成：硫酸ニツケル 0.1M/
酒石酸ナトリウム 0.5M/
硫酸アンモニウム 0.5M/
PH ９
温 度 90℃
上記浴に次亜リン酸ナトリウムを0.01〜0.05
Ｍ／の範囲で変化させて添加し、Ni−Ｐ合金
中のＰ含有率を調整する。またNi−Ｐ付着量
は浸漬時間の制御により変化させて調整する。
次に本発明における各要件の数値の限定理由を
説明する。
Ni−Ｐ合金中のＰ含有率を0.01〜1.0％に限定
したのは、0.01％未満では化成処理反応速度の促
進効果が不十分であるからであり、1.0％を超え
ると溶解性の少ないNi−Ｐ成分が増えて化成処
理反応速度を逆に抑制するようになるからであ
る。Ｐが1.0％を超える場合においては、反応速
度が減少する理由としては、Ni−Ｐ合金の結晶
性成分と非晶質成分との中で、非晶質成分の比率
が高まるためと思われる。
またNi−Ｐ合金の付着量を１〜３mg／m2未満
に限定したのは、１mg／m2未満では付着量が少な
すぎて十分な化成処理性ならびに塗装耐食性の改
善効果が挙げられないからであり、また３mg／m2
以上と付着量を多くしても化成処理性の改善はそ
れほど進まない。
なお、本発明に基づく化成処理性に優れた表面
処理鋼板の構造は、常に鋼板の両面に対して適用
しなければならないというものでなく、片面につ
いてのみこの構造を採用し、他側の面は例えば異
なる構造のメツキ面とするというような形で実施
するも何ら差し支えなく、こうした形態も本発明
の表面処理鋼板の範ちゆうに属するものである。
次に実施例を掲げて本発明の効果を説明する。
実施例 １
アルミキルド連続鋳造鋳片を素材として厚さ
0.8mmに冷間圧延した後、これを連続焼鈍ライン
で焼鈍し、気水冷却（N2＋水）で室温まで冷却
した後酸洗を施したアルミキルド冷延鋼板に、無
電解メツキ法によりNi−Ｐ合金付着量ならびに
Ni−Ｐ合金中Ｐ含有率を本発明範囲内で種々に
変えてNi−Ｐ合金を付着せしめて本発明の例の
供試材２〜４、７，８，９を得た。
また比較のため、同様に焼鈍後気水冷却し酸洗
を施したアルミキルド冷延鋼板に本発明から外れ
た範囲のNi−Ｐ合金付着量またはNi−Ｐ合金中
Ｐ含有率でNi−Ｐ合金を付着せしめて比較例の
供試材１，５，６，１０を得た。また上記同様焼
鈍後気水冷却し酸洗を施したままの従来例の供試
材１１と焼鈍後従来の冷却方法に従つて無酸化雰
囲気のガスジエツトクールで冷却したままの従来
例の供試材１２を得た。
ひきつづいて、これらの各供試材１〜１２を下
記に示す化成処理条件およびカチオン電着条件で
リン酸塩処理ならびにカチオン電着塗装を施し、
化成処理性、および塗装耐食性の良否を調査し
た。
化成処理条件
(イ)脱脂：フアインクリーナ4326T（商品名：日
本パカーライジングK.K製）
液温50℃、２分浸漬
(ロ)表面調査：パーコレンZT（商品名：日本パー
カーライジングK.K製）
20秒浸漬
(ハ)リン酸亜鉛処理：ボンデライトBT−3030
（商品名：日本パーカーライ
ジングK.K製）
液温50℃、２分間浸漬
電着塗装条件
(イ)塗料：エスビオ1000（神東塗料社製）のカチ
オン電着塗料
(ロ)電圧：250V、(ハ)浴温：30℃、(ニ)通電時間：
３分
なお化成処理性は、化成皮膜のフオスフオフイ
ライト（Ｐで示す）とホペイト（Ｈで示す）との
比P/P＋ＨをＸ線回析から求め、さらに走査型電
子顕微鏡により結晶の大きさを求め、さらに皮膜
付着量を重量法で求め、これらの値に基づいて評
価した。
また塗装耐食性は、電着塗膜にメツキ面に達す
る切れ目を２mm間隔でゴバン目状に入れたクロス
カツト部の塩水噴霧試験960時間後のセロテープ
剥離巾で評価した。
上記調査結果をまとめて第１表に示す。
The present invention relates to a surface-treated steel sheet with excellent chemical conversion treatment properties. In general, when steel sheets for automobiles are actually used, they are processed by press forming, etc., and then subjected to chemical conversion treatment (for example, phosphate treatment) as a base treatment for painting, and then, for example, cationic electrodeposition coating is applied thereon for the final treatment. In order to obtain good coating corrosion resistance of the electrodeposition coating, it is essential to first obtain a good chemical conversion coating in the surface treatment. In order to obtain this good chemical conversion coating,
The surface of the material is required to have good properties (properties that are excellent in chemical conversion treatment) so as not to inhibit nucleation and growth of chemical conversion coating crystals. Now, cold-rolled steel sheets used as steel sheets for automobiles have conventionally been cooled during continuous annealing using methods such as gas jet cooling in a non-oxidizing atmosphere. The steel sheet had extremely good chemical conversion treatment properties due to the presence of a surface concentration layer such as . However, recently, in order to rationalize the heat cycle in the above continuous annealing,
There is a tendency to use water cooling or air/water cooling instead of gas jet cooling in a non-oxidizing atmosphere.
In this case, since the cooling process creates an oxidizing atmosphere, an oxide film is formed on the surface, and therefore a pickling treatment is required to remove this oxide film. Cold-rolled steel sheets subjected to this pickling treatment have deteriorated chemical conversion treatment properties due to the removal of the Mn-enriched layer and surface adsorption of pickling residues (iron hydroxide). In addition, when cold-rolled steel sheets are used in automobile bodies, body corrosion becomes a major safety problem.In particular, one side of the automobile exterior plate, which is susceptible to corrosion, is coated with a highly corrosion-resistant surface such as Zn plating or Zn-Ni alloy plating. Single-sided plated steel plates, which have a Fe-Zn alloy plated surface and the other side left as a steel plate, have come to be used to reduce car body corrosion. There are two manufacturing methods for single-sided plated steel sheets: electroplating and hot-dip plating. In the case of electroplating, pickling is performed as a pretreatment, and in most cases, the electroplating process is carried out in an acidic electroplating bath. As the process progresses, the chemical conversion treatment property of the non-plated surface decreases as it is subjected to the pickling effect.
Furthermore, in the case of the melt plating method, since the material comes out of the melt plating bath in a high temperature state, oxidation of the non-plated surface is difficult to avoid, and therefore, pickling treatment is required after the plating is completed, and chemical conversion treatability is similarly reduced. In recent years, electroplating of Fe-based or Fe-Zn-based alloys has become particularly popular, and in this case, a large amount of metal is used in the acid plating bath.
Because it contains Fe 3+ ions, the non-plated surface exhibits acid pitting, resulting in extremely poor chemical conversion treatment properties. There is also an electric Zn plating method, but in this case too, as the trend toward high current density operation progresses, a highly corrosive chloride bath is used, so the non-plated side of the single-sided plated steel sheet undergoes extreme melting. For this reason, the chemical conversion treatment properties are also extremely deteriorated. In addition, especially when using a vertical plating tank with a long immersion time in the plating bath, the deterioration of chemical conversion properties will be much more severe than in the case of a horizontal plating tank, which may lead to a serious situation. There is. The present invention has been made in order to eliminate the deterioration in chemical conversion treatability of the non-plated surface of a cold rolled steel sheet or single-sided plated steel sheet that has been subjected to pickling treatment etc. as described above. It is an object of the present invention to provide a surface-treated steel sheet with improved chemical conversion properties and improved chemical conversion treatment properties, which promotes the reaction rate of chemical conversion treatment. Metallic Ni is applied to the surface of cold rolled steel sheets with the aim of improving the surface of cold rolled steel sheets with deteriorated chemical conversion treatability.
A method for depositing 0.3 to 10mg/ dm2 was published in 1982.
It is disclosed in Publication No. 116883. According to the present invention, the effect of improving chemical conversion treatment properties (crystal size, coating amount) and coating corrosion resistance can be obtained in the phosphate treatment test. However, in the actual chemical conversion process, processing is carried out continuously online, and in order to improve productivity in such a process, it is necessary to increase the chemical conversion reaction rate and further increase the line speed. There has been a desire for a cold-rolled steel sheet that can improve the surface of a steel sheet with deteriorated chemical conversion treatment properties and also improve the reaction rate of chemical conversion treatment. In view of the above, the present inventors have conducted various experimental studies with the intention of developing a surface-treated steel sheet with excellent chemical conversion treatment properties that can provide a good chemical conversion coating and improve the chemical conversion reaction rate. As a result, we discovered a new fact that by depositing an appropriate amount of Ni--P alloy containing a small amount of P on the surface of a cold-rolled steel sheet, chemical conversion treatment properties can be dramatically improved. Although the mechanism by which chemical conversion treatment properties are improved by adhering a Ni-P alloy to the surface of a steel sheet has not yet been clearly elucidated, the following is considered at this stage. In other words, products such as iron hydroxide and water rust are formed on the surface of the steel sheet by pickling, which inhibits chemical conversion properties. Then, it is considered that this Ni is dispersed on the surface of the steel sheet and precipitated in a state that protrudes from the product layer. Therefore, this precipitation occurs during chemical conversion treatment.
Ni acts as a nucleus for chemical conversion crystals, and serves as a starting point for crystal growth of chemical conversion coatings, so it is expected that fine and dense chemical conversion coatings will be formed. Ni increases the chemical reaction rate.
The scientific reason for adding a small amount of P to the material is not clear, but one hypothesis is as follows. In other words, Ni functions as crystal nucleation as described above, and P acts as an autocatalytic active site when reacting with phosphoric acid in the chemical conversion treatment solution, thereby promoting the chemical conversion reaction rate. It is assumed that. The present invention has been made based on the above findings, and its gist is that a Ni-P alloy containing 0.01 to 1.0% P is applied on the surface of a cold-rolled steel sheet.
A surface-treated steel sheet with excellent chemical conversion treatment properties characterized by an adhesion of less than 3 mg/m 2 . Next, a method of adhering the Ni--P alloy will be explained.
The deposition method may be any method such as electroplating (the plating bath may be an aqueous solution, non-aqueous solution, molten salt bath, etc.), electroless plating, or vacuum deposition, and is not particularly limited. However, from the viewpoint of equipment scale, operating cost, etc., it is most preferable to apply a conventional electroplating method using an acidic aqueous solution or an electroless plating method. An example of the steam electroplating method and the electroless plating method is as follows. Electroplated layer: For example, it is preferable to use a phosphorous acid-added bath based on the known Watt bath having the following bath composition. Bath composition: NiSO 4・6H 2 O 240g/ NiCl 2・6H 2 O 45g/ H 3 BO 3 30g/ Temperature 60℃ Current density 1～10A/dm 2 Add 0.1～10g/ of H 3 PO 3 to the above bath P content was adjusted on the steel plate surface by adding P content by varying the range.
Deposit Ni-P alloy. Further, the amount of Ni--P deposited is adjusted by appropriately changing the electrolysis time x current density. Electroless plating method: A bath with the following composition is used. Bath composition: Nickel sulfate 0.1M/ Sodium tartrate 0.5M/ Ammonium sulfate 0.5M/ PH 9 Temperature 90℃ Add 0.01~0.05% of sodium hypophosphite to the above bath.
The P content in the Ni-P alloy is adjusted by adding it by changing it within the range of M/. Further, the amount of Ni--P deposited is adjusted by changing it by controlling the immersion time. Next, the reasons for limiting the numerical values of each requirement in the present invention will be explained. The reason why the P content in the Ni-P alloy was limited to 0.01 to 1.0% is that if it is less than 0.01%, the effect of accelerating the chemical conversion reaction rate is insufficient, and if it exceeds 1.0%, Ni has low solubility. This is because the -P component increases and conversely suppresses the chemical conversion reaction rate. When P exceeds 1.0%, the reason why the reaction rate decreases is considered to be that the ratio of the amorphous component increases between the crystalline component and the amorphous component of the Ni--P alloy. In addition, the amount of Ni-P alloy deposited was limited to 1 to less than 3 mg/m 2 because if the amount is less than 1 mg/m 2 , the amount of deposit is too small and sufficient improvement effect on chemical conversion treatment and paint corrosion resistance cannot be achieved. and 3 mg/m 2
Even if the amount of adhesion is increased as above, the chemical conversion treatment property will not improve much. Note that the structure of the surface-treated steel sheet with excellent chemical conversion properties based on the present invention does not always have to be applied to both sides of the steel sheet, but this structure is adopted only for one side, and the other side is For example, there is no problem in implementing the plated surface with a different structure, and such a form also falls within the scope of the surface-treated steel sheet of the present invention. Next, the effects of the present invention will be explained with reference to Examples. Example 1 Thickness using aluminum killed continuous cast slab as material
After cold rolling to 0.8 mm, this was annealed on a continuous annealing line, cooled to room temperature with air water cooling (N 2 + water), and then pickled. -P alloy adhesion amount and
Test materials 2 to 4, 7, 8, and 9 of examples of the present invention were obtained by depositing Ni-P alloys while varying the P content in the Ni-P alloy within the range of the present invention. For comparison, Ni-P alloy was applied to an aluminium-killed cold-rolled steel sheet that had been similarly annealed, air-water cooled, and pickled. was attached to obtain comparative sample materials 1, 5, 6, and 10. Similarly to the above, the conventional specimen 11 was still air-water cooled and pickled after annealing, and the conventional specimen 11 was cooled by gas jet cooling in a non-oxidizing atmosphere according to the conventional cooling method after annealing. Sample material 12 was obtained. Subsequently, each of these test materials 1 to 12 was subjected to phosphate treatment and cationic electrodeposition coating under the chemical conversion treatment conditions and cationic electrodeposition conditions shown below,
The quality of chemical conversion treatment and paint corrosion resistance was investigated. Chemical conversion treatment conditions (a) Degreasing: Fine Cleaner 4326T (product name: Nippon Parker Rising KK), solution temperature 50℃, immersion for 2 minutes (b) Surface investigation: Percolene ZT (product name: Nippon Parker Rising KK) 20 seconds Immersion (c) Zinc phosphate treatment: Bonderite BT-3030
(Product name: Nippon Parker Rising KK) Liquid temperature: 50℃, immersion for 2 minutes Electrodeposition coating conditions (a) Paint: Esbio 1000 (manufactured by Shinto Toyo Co., Ltd.) cationic electrodeposition paint (b) Voltage: 250V, (ha) ) Bath temperature: 30℃, (d) Current application time:
3 minutes Chemical conversion treatment properties are determined by determining the ratio P/P+H of phosphofluorite (indicated by P) and hopite (indicated by H) in the chemical conversion coating from X-ray diffraction, and then determining the crystal size using a scanning electron microscope. was determined, and the amount of film adhesion was determined gravimetrically, and evaluation was made based on these values. The corrosion resistance of the coating was evaluated by measuring the peeling width of the cellophane tape after 960 hours of a salt spray test on a cross-cut area in which cuts reaching the plating surface were made at 2 mm intervals in the electrodeposited coating. The above survey results are summarized in Table 1.
【表】
第１表の化成皮膜外観の〇印は良好なものを示
す。
第１表に見る通り、比較例１はNi−Ｐ合金付
着量が少ないため結晶粗大、皮膜にムラ・スケ発
生、塗膜剥離巾大、比較例５はNi−Ｐ付着量が
過多のために化成処理製の改善効果が低下し付着
量が少なく、皮膜にムラ・スケが発生、剥離巾が
大、比較例６はＰ含有量が少なすぎたため所望速
さの化成処理反応速度が得られず、付着量も不十
分で、塗膜剥離巾が大、比較例10はＰ含有量が多
すぎたために化成処理反応速度が低下し、皮膜付
着量が極めて少なく、塗膜剥離巾が大で、いずれ
も化成処理性および塗装耐食性が不良であつた。
これに対し本発明例の２ ３ ４、７ ８ ９は
いずれもNi−Ｐ合金付着量およびNi−Ｐ合金中
のＰ含有率が本発明範囲で適正であつたために化
成処理反応速度が速く、適正な皮膜付着量が得ら
れ、結晶の大きさも微細で、皮膜外観もムラ・ス
ケが全く無く、良好な化成処理性を示すとともに
塗膜剥離巾も12mm以下と良好な塗装耐食性を示し
た。
また従来例11は酸洗を行つた冷延板であるため
表面性状が不良で、従つて化成皮膜結晶も粗大で
皮膜外観もムラ・スケが発生し化成処理が不良で
あり、かつ塗膜剥離巾も大で塗装耐食性も不良で
あつた。これに対し従来例12は焼鈍後の冷却を無
酸化雰囲気で行つた酸洗なしの冷延鋼板であるた
め化成処理性、塗装耐食性のいずれも極めて良好
であつた。
実施例 ２
実施例１と同様に焼鈍後気水冷却で常温まで冷
却した後酸洗を施した厚さ0.8mmのアルミキルド
冷延鋼板に、無電解メツキ法によりNi−Ｐ合金
中のＰ含有率を０〜10％の範囲で種々に変化させ
てNi−Ｐ合金をそれぞれ2.5mg／m2で付着させた
供試材を、実施例１に示したと同様の条件でリン
酸亜鉛による化成処理を施し、その際の化成処理
反応終了時間（化成皮膜の生成量が飽和するまで
に要した時間）をそれぞれ測定した。前記測定結
果を第１図に示す。第１図はNi−Ｐ合金中のＰ
含有率（重量％）と化成処理反応終了時間との関
係を特性曲線Ｐで示した図である。
図に見る通り、Ｐ含有率が0.01〜1.0％の本発
明範囲のＰ含有率の供試材はすべて化成処理反応
終了時間が１〜12分程度と極めて化成処理反応速
度が速い。
以上の説明から明らかなように、本発明の表面
処理鋼板は、酸洗を行わない従来の冷延鋼板なみ
のすぐれた化成処理性を備え、かつカチオン電着
塗装系の塗装においてすぐれた塗装耐食性を有す
る塗膜を得ることを可能とする許りでなく、化成
処理反応速度が速いという実用上極めて有利な性
質を兼ね備えている。従つて特に自動車用鋼板と
して実用価値の極めて高い鋼板である。[Table] In Table 1, the chemical conversion coating appearance marked with a circle indicates a good appearance. As shown in Table 1, Comparative Example 1 had a small amount of Ni-P alloy deposited, resulting in coarse crystals, unevenness and scattering of the film, and large peeling of the coating, while Comparative Example 5 had an excessive amount of Ni-P deposited. The improvement effect of chemical conversion treatment decreased, the amount of adhesion was small, unevenness and sagging occurred on the film, and the peeling width was large. In Comparative Example 6, the desired chemical conversion reaction rate could not be obtained because the P content was too low. In Comparative Example 10, the chemical conversion reaction rate decreased because the P content was too high, the amount of film deposited was extremely small, and the width of paint film peeling was large. Both had poor chemical conversion treatment properties and paint corrosion resistance.
On the other hand, in Inventive Examples 234 and 789, the Ni-P alloy deposition amount and the P content in the Ni-P alloy were appropriate within the range of the present invention, so the chemical conversion reaction rate was fast. Appropriate coating weight was obtained, the crystal size was fine, the coating had no unevenness or scratches, and it showed good chemical conversion treatment properties, as well as coating peeling width of 12 mm or less, which showed good paint corrosion resistance. In addition, since Conventional Example 11 is a cold-rolled plate that has been pickled, the surface quality is poor, and the chemical conversion coating crystals are coarse and the coating appearance is uneven and uneven, resulting in poor chemical conversion treatment, and the coating peels off. The width was large and the corrosion resistance of the coating was poor. On the other hand, Conventional Example 12 was a cold-rolled steel sheet that was cooled in a non-oxidizing atmosphere after annealing and was not pickled, so both chemical conversion treatment properties and paint corrosion resistance were extremely good. Example 2 As in Example 1, a 0.8 mm thick aluminum killed cold rolled steel sheet was annealed and then cooled to room temperature by air-water cooling and then pickled, and the P content in the Ni-P alloy was determined by electroless plating. The test materials were coated with Ni-P alloys at 2.5 mg/m 2 with various changes in the range of 0 to 10%, and were chemically treated with zinc phosphate under the same conditions as shown in Example 1. The completion time of the chemical conversion treatment reaction (the time required until the amount of chemical conversion film produced was saturated) was measured. The measurement results are shown in FIG. Figure 1 shows P in Ni-P alloy.
FIG. 3 is a diagram showing the relationship between content (wt%) and chemical conversion reaction completion time using a characteristic curve P. As shown in the figure, all of the sample materials with a P content within the range of the present invention, which is 0.01 to 1.0%, had extremely fast chemical conversion reaction rates, with a chemical conversion reaction completion time of about 1 to 12 minutes. As is clear from the above description, the surface-treated steel sheet of the present invention has excellent chemical conversion treatment properties comparable to conventional cold-rolled steel sheets without pickling, and has excellent paint corrosion resistance in cationic electrodeposition coating. It not only makes it possible to obtain a coating film having a chemical conversion treatment, but also has the extremely advantageous property of having a high reaction rate for chemical conversion treatment. Therefore, it is a steel sheet with extremely high practical value, especially as a steel sheet for automobiles.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は、Ni−Ｐ合金中のＰ含有率と化成処
理反応終了時間との関係を示した図である。
FIG. 1 is a diagram showing the relationship between the P content in the Ni-P alloy and the chemical conversion reaction completion time.