JP6505498B2 - Method of passivating stainless steel - Google Patents
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本発明は、ステンレス鋼の不動態化方法に関し、特に環境を考慮したステンレス鋼の不動態化方法に関するものである。 The present invention relates to a stainless steel passivating method, and more particularly to an environmentally friendly stainless steel passivating method.
ステンレス鋼の不動態化方法は、大きく分けて以下の３つの方法がある。
（１）硝酸その他の強力な酸化剤を含む溶液に浸漬する方法。
（２）酸素または、清浄な空気中における低温加熱による方法。
（３）酸化剤を含む溶液中における陽極分極による方法。
Passivation methods of stainless steel are roughly classified into the following three methods.
(1) A method of immersing in a solution containing nitric acid or other strong oxidizing agent.
(2) A method by low temperature heating in oxygen or clean air.
(3) A method by anodic polarization in a solution containing an oxidizing agent.
このうち、（１）の「強力な酸化剤を含む溶液に浸漬する方法」が一般的で、硝弗酸（約１重量％HF、３０重量％HNO３、残りH２O）、あるいは１０〜３０重量％の硝酸などの酸化性の強い溶液にステンレス鋼を浸漬し、あるいは浸漬とともに電解処理するようにしている。 Among them, (1) “method of immersing in a solution containing a strong oxidizing agent” is generally used, such as nitric hydrofluoric acid (about 1 wt% HF, 30 wt% HNO 3 , remaining H 2 O), or 10 to 10 wt% The stainless steel is immersed in a strongly oxidizing solution such as 30% by weight of nitric acid, or electrolytic treatment is performed with the immersion.
また、酸化性の強い溶液として、硝酸と塩酸の混合液を使用する方法が、特開昭５２−１０６３３３号公報に開示されている。硝酸を５〜４０重量％、塩酸を０．５〜２．０重量％含み、残り水およびインヒビタ０．１ｇ〜１０ｇ／ｌよりなる溶液を、５０〜７０℃に加熱して３０〜９０秒ステンレス鋼を浸漬するようにしたものである。 Moreover, the method of using the liquid mixture of nitric acid and hydrochloric acid as strong oxidizing solution is disclosed by Unexamined-Japanese-Patent No. 52-106333. A solution containing 5 to 40% by weight of nitric acid, 0.5 to 2.0% by weight of hydrochloric acid, and the remaining water and 0.1 g to 10 g / l of water is heated to 50 to 70 ° C. for 30 to 90 seconds. It is made to immerse steel.
ステンレス鋼表面に形成される不動態皮膜の構造はまだ充分には解明されていないが、本質的には、Cr2O3・nH２Oで表されるような、厚さが１０〜３０Åの均一で薄い化学的に安定な非晶質の酸化膜になっていると考えられている。硝弗酸や硝酸中での不動態化処理は、不動態皮膜中のCr元素の濃縮により、安定な不動態皮膜を形成させると考えられている。 The structure of the passive film formed on the stainless steel surface has not been fully elucidated yet, but essentially has a thickness of 10 to 30 Å, as represented by Cr 2 O 3 .nH 2 O It is believed to be a uniform, thin, chemically stable, amorphous oxide film. Passivation treatment in nitric hydrofluoric acid or nitric acid is considered to form a stable passive film by concentration of Cr element in the passive film.
これらの不動態化処理のうち弗化水素酸（ＨＦ）は労働安全衛生法施工令特定化学物質等第２種物質に指定されていること、および、硝酸との混合溶液においては窒素酸化物が発生するため、これらを用いない工程の開発が望まれていた。
Among these passivation treatments, hydrofluoric acid (HF) is designated as
更に、硝酸を使用した場合には、使用後の硝酸は苛性ソーダ等のアルカリ剤で中和してから廃棄する必要があり、この工程も省略することが望まれる。 Furthermore, when nitric acid is used, it is necessary to neutralize the used nitric acid with an alkali agent such as caustic soda and then discard it, and this step is also desirably omitted.
特開２００１−１１５２７１号公報には、不動態化の工程で環境負荷の小さい過酸化水素を使用する方法が開示されている。これによると、被加工物を有機酸で研磨した後、硝酸又は過酸化酸水素を含む酸化性溶剤の液に浸漬して不動態化するようになっている。しかしながら、有機酸での研磨効果は一般的に弱く、不動態化処理に硝酸を使用しない限り充分な強度の不動態皮膜を形成することはできない。当該公報の実施例では硝酸溶液での不動態化処理の結果しか開示されていないので、出願人がクエン酸を用いて研磨したステンレス鋼の試料に対する過酸化水素の不動態化処理について実験した結果を、別途比較例として示す。 Japanese Patent Application Laid-Open No. 2001-115271 discloses a method of using hydrogen peroxide which has a small environmental load in the passivation process. According to this, after the workpiece is polished with an organic acid, it is immersed in a solution of an oxidizing solvent containing nitric acid or hydrogen peroxide to passivate it. However, the polishing effect with organic acids is generally weak, and a passivated film of sufficient strength can not be formed unless nitric acid is used for passivation treatment. Since the examples of this publication only disclose the results of passivation with nitric acid solution, applicants have experimented with hydrogen peroxide passivation on samples of stainless steel polished with citric acid. Is separately shown as a comparative example.
不動態化処理に過酸化水素と他の強い酸性溶液（例えば硫酸）を混合して使用する技術が、例えば特開平１１−２９３４８２号公報に開示されている。しかしながら上記したように、過酸化水素以外の強酸化性溶液を使用することは、後の処理に時間と費用を要するという欠点がある。 For example, Japanese Patent Application Laid-Open No. 11-293482 discloses a technique in which hydrogen peroxide and another strong acidic solution (for example, sulfuric acid) are mixed and used for passivation treatment. However, as mentioned above, the use of a strongly oxidizing solution other than hydrogen peroxide has the disadvantage that the later processing is time-consuming and expensive.
加えて、不動態皮膜は、不動態化処理そのものの方法はもちろん、不動態化処理の前段階での処理が不動態皮膜の特性に大きな影響を及ぼす点を考慮すると、不動態化処理を評価するとき、不動態化処理の各部にのみ注目するのではなく、全工程に注目する必要がある。 In addition, the passivation film is evaluated in consideration of the method of passivation treatment itself, considering that the treatment before the passivation treatment greatly affects the characteristics of the passivation film. When doing this, it is necessary to focus on the entire process, not just on each part of the passivation process.
本発明は上記従来の事情に鑑みて提案されたものであって、不動態化処理時に後処理の必要な強酸性の溶液を用いないステンレス鋼の不動態化処理を提供することを目的とするものである。 The present invention has been proposed in view of the above-described conventional circumstances, and it is an object of the present invention to provide passivation treatment of stainless steel which does not use a strongly acidic solution which requires post-treatment at the time of passivation treatment. It is a thing.
上記目的を達成するために、この発明は、まず、硫酸とリン酸の混合液中で被処理物を電解研磨し、その後、有機酸であるリンゴ酸、クエン酸、グルコノラクトン、酒石酸の内の１種と過酸化水素を含む溶液に所定の時間浸漬（無電解処理）処理することによって不動態膜を形成するようになっている。 In order to achieve the above object, according to the present invention, first, the object to be treated is electropolished in a mixture of sulfuric acid and phosphoric acid, and then organic acids such as malic acid, citric acid, gluconolactone and tartaric acid are used. A passive film is formed by immersion (electroless treatment) in a solution containing hydrogen peroxide and hydrogen peroxide for a predetermined time.
上記の方法を採用することによって、形成された不動態皮膜は耐塩化物孔食性の指標である孔食電位において、従前の硝酸溶液で不動態化した場合と同等あるいはそれ以上の品質の膜を形成することができ、しかも、廃液を下水等に廃棄しても環境に負荷のかからない効果がある。 By adopting the above-mentioned method, the formed passive film forms a film of the same or higher quality as that of the passivated solution with the conventional nitric acid solution at the pitting potential which is an index of chloride pitting resistance. In addition, even if the waste liquid is discarded to sewage etc., it has the effect of not affecting the environment.
本発明は被処理物のステンレス鋼を電解研磨し、その後有機酸（例えばリンゴ酸）と過酸化水素を含む溶液に浸漬することによってステンレス鋼表面を不動態化するようにしている。 The present invention is adapted to passivate the surface of stainless steel by electropolishing the stainless steel to be treated and then immersing it in a solution containing an organic acid (eg, malic acid) and hydrogen peroxide.
上記電解研磨は、硫酸とリン酸の混合溶液中で、被処理物を正極として行われる。前記混合溶液としては、８５重量％のリン酸と、９８重量％の硫酸を用いた場合リン酸と硫酸の容量比が、５０〜９０％：１０〜５０％のものを用いる。電解研磨条件は、電流密度１〜２０Ａ／dm2、温度３０〜８０℃、時間３０秒〜６０分である。 The above-mentioned electrolytic polishing is performed in a mixed solution of sulfuric acid and phosphoric acid, with the object to be treated as a positive electrode. When 85% by weight of phosphoric acid and 98% by weight of sulfuric acid are used as the mixed solution, one having a volume ratio of phosphoric acid to sulfuric acid of 50 to 90%: 10 to 50% is used. The electropolishing conditions are a current density of 1 to 20 A / dm 2 , a temperature of 30 to 80 ° C., and a time of 30 seconds to 60 minutes.
上記電解研磨処理において、リン酸の濃度が５０％より小さいと光沢性が低下し、９０％より多いとコスト高となる。 In the above-mentioned electropolishing treatment, when the concentration of phosphoric acid is less than 50%, the gloss is lowered, and when it is more than 90%, the cost becomes high.
また、上記電解研磨処理は、温度３０〜８０℃の下で、電流密度１〜２０Ａ／dm2で、時間３０秒〜６０分で行われる。温度が３０℃より低いと試料表面の鉄分の溶解速度が充分ではなく被処理物の表面を充分にクロムリッチにすることができない。また８０℃より高いと雰囲気に硫酸臭が立ち込め、作業性に問題が生じる。電流密度が１Ａ／dm2より小さいと、鉄分の溶出が充分でなく、また、２０Ａ／dm2より大きいと、電流密度の均一性が低下することで研磨状態の品質の低下を招く。 Moreover, the said electropolishing process is performed by the time of 30 seconds-60 minutes by the current density of 1-20 A / dm < 2 > under the temperature of 30-80 degreeC. When the temperature is lower than 30 ° C., the dissolution rate of iron on the sample surface is not sufficient, and the surface of the object to be treated can not be made sufficiently chromium-rich. When the temperature is higher than 80 ° C., sulfuric acid odor enters the atmosphere, causing problems in workability. If the current density is less than 1 A / dm 2 , the elution of iron is not sufficient, and if it is more than 20 A / dm 2 , the uniformity of the current density is reduced, resulting in the deterioration of the quality of the polished state.
上記、温度、電流密度、電解処理時間の関係は、鉄分の溶出量が大きくなり過ぎない程度、また、少なすぎて後の無電解処理（不動態化処理）に支障を来たさないよう、相対的に決定される。 The above-mentioned relationship between temperature, current density, and electrolytic treatment time is such that the elution amount of iron does not become too large, or too little so as not to affect the later electroless treatment (passivation treatment), It is determined relatively.
上記無電解処理に使用する溶液の濃度と温度、更に浸漬時間は、より優れた特性の不動態を形成するためには、下記の範囲で相対的に決定される。 The concentration and temperature of the solution used for the above-mentioned electroless processing, and also the immersion time are relatively determined in the following range in order to form a better passivity.
すなわち、上記有機酸と過酸化水素の溶液中、有機酸の濃度は有機酸の種類を問わず０．５重量％以上である。０．５重量％より濃度が低いと酸化効果が充分ではなく、耐食性に優れた孔食電位の高い不動態皮膜を形成することはできない。有機酸の濃度の上限は限定されないが、１０重量％より高くなると、溶液のエッチング作用が強くなり電解研磨の光沢が低下する恐れがあること、作業後の排水処理の必要性が生じることなどの難点が出てくる（表５参照）。 That is, in the solution of the organic acid and hydrogen peroxide, the concentration of the organic acid is 0.5% by weight or more regardless of the type of the organic acid. If the concentration is lower than 0.5% by weight, the oxidation effect is not sufficient, and it is impossible to form a passivation film having high corrosion resistance and high pitting potential. The upper limit of the concentration of the organic acid is not limited, but when it is higher than 10% by weight, the etching action of the solution becomes strong and the gloss of the electropolishing may decrease, and the necessity of post-work drainage treatment arises, etc. There are difficulties (see Table 5).
上記有機酸と過酸化水素を含む溶液中、過酸化水素の濃度は０．９８重量％以上である。過酸化水素の濃度が０．９８重量％以下になると、酸化能力が劣ることになる。過酸化水素の濃度の上限は限定されないが、７．０重量％以上になると、溶液のｐHが低くなることで不働態化が不安定となるおそれがある（表４参照）。 The concentration of hydrogen peroxide in the solution containing the organic acid and hydrogen peroxide is 0.98% by weight or more. When the concentration of hydrogen peroxide is 0.98% by weight or less, the oxidation ability is inferior. Although the upper limit of the concentration of hydrogen peroxide is not limited, when it is 7.0% by weight or more, passivation may become unstable due to the decrease in pH of the solution (see Table 4).
上記有機酸と過酸化水素を含む溶液への浸漬時間は、有機酸+過酸化水素の各成分の濃度が最も低い溶液（有機酸０．５重量％、過酸化水素０．９８重量％）で３０分以上である。３０分より短いと優れた不動態皮膜を形成するに至らない。浸漬時間の上限はないが、例えば５時間といった長時間になると、作業性および、コストの面での障害が生じることになる（表２参照）。 The immersion time in the solution containing the organic acid and hydrogen peroxide is the solution with the lowest concentration of each component of organic acid + hydrogen peroxide (0.5 wt% organic acid, 0.98 wt% hydrogen peroxide) 30 minutes or more. If it is shorter than 30 minutes, an excellent passive film can not be formed. There is no upper limit of immersion time, but if it is a long time such as 5 hours, for example, problems in workability and cost will occur (see Table 2).
＜実施例１＞（研磨方法）
まず、ステンレス鋼を不動態化するについて、その前処理として、電解研磨をすることが有効である。このことを立証するアノード分極曲線を図１に示す。電流が立ち上がっている電位が孔食電位である。また、以下のすべての実験において（図１〜図９）、５サンプルの平均値を示している。
Example 1 (Polishing method)
First, for passivating stainless steel, it is effective to perform electropolishing as a pretreatment. An anodic polarization curve that demonstrates this is shown in FIG. The potential at which the current is rising is the pitting potential. Moreover, in all the following experiments (FIGS. 1-9), the average value of 5 samples is shown.
ステンレス鋼（ＳＵＳ３０４、以下すべて同じ）をバフ研磨（No.４００）の後に８重量％のリンゴ酸に２５℃で２時間浸漬して、不動態化処理した試料１は０mV近辺の孔食電位でしかない。また、電解研磨のみの試料２も２００mV近辺の孔食電位でしかない。更に、バフ研磨（No.４００）の後８重量％のリンゴ酸と０．９８重量％の過酸化水素を含む溶液に２５℃で2時間浸漬した試料３は、４００mV以下の孔食電位でしかない。電解研磨後８重量％のリンゴ酸に２５℃で2時間浸漬した試料４は４００mVを少し越えた孔食電位でしかない。電解研磨後０．９８％重量％の過酸化水素の溶液に２５℃で２時間浸漬した試料５は、８５０ｍV付近の孔食電位であった。
A stainless steel (SUS 304, all the same below) was buffed (No. 400) and then immersed in 8 wt% malic acid for 2 hours at 25 ° C., and the passivated
これらに対して電解研磨後、８重量％のリンゴ酸と０．９８重量％の過酸化水素を含む溶液に２５℃で２時間浸漬した試料６（本願発明）は１０００mVを超える孔食電位を示した。 On the other hand, Sample 6 (invention of the present invention) immersed in a solution containing 8% by weight of malic acid and 0.98% by weight of hydrogen peroxide for 2 hours at 25 ° C. after electropolishing shows a pitting potential exceeding 1000 mV. The
以上のことより、前処理としての研磨の種類は電解研磨が重要であり、その後の無電解処理液として、リンゴ酸のみ（試料４）、あるいは過酸化水素のみ（試料５）では不十分であり、リンゴ酸に少なくとも０．９８重量％の過酸化水素を添加した溶液を用いるのが最適であることが理解できる。 From the above, it is important to use electro-polishing as the type of polishing as pretreatment, and it is insufficient with only malic acid (sample 4) or hydrogen peroxide alone (sample 5) as the subsequent electroless treatment solution. It can be seen that it is best to use a solution of at least 0.98% by weight hydrogen peroxide in malic acid.
なお、上記の電解研磨はすべてバフ研磨(♯４００)後に８５重量％のリン酸と、９８重量％の硫酸を用いてリン酸と硫酸の容量比が、７５％：２５％である電解浴で、温度４５℃、電圧８Vで６分間行われている。また、孔食電位は、２５℃で３．５重量％の脱気NaCl溶液中で測定されている。 In the above electrolytic polishing, 85% by weight of phosphoric acid and 98% by weight of sulfuric acid are used after buffing (# 400), and the volume ratio of phosphoric acid to sulfuric acid is 75%: 25%. The temperature is 45 ° C., and the voltage is 8 V for 6 minutes. The pitting potential is also measured in 3.5 wt% degassed NaCl solution at 25 ° C.
上記の実験例はリンゴ酸以外の他の有機酸を使用することについての可能性をも類推させることになり、以下に示す実施例でそのことが実証されている。 The above experimental example is also to infer the possibility of using other organic acids other than malic acid, which is demonstrated in the examples given below.
＜実施例２＞（無電解処理の時間）
次に、無電解処理（リンゴ酸と過酸化水素を含む溶液への浸漬）時間を確認する実験をし、図２にそのアノード分極曲線を示す。
Example 2 (Time of Electroless Treatment)
Next, an experiment was conducted to confirm the time of electroless treatment (immersion in a solution containing malic acid and hydrogen peroxide), and the anodic polarization curve is shown in FIG.
ステンレス鋼を上記試料６と同様の条件でバフ研磨と電解研磨をし、８重量％のリンゴ酸と０．９８重量％過酸化水素を含む溶液に２５℃で、０．５時間、1時間、２時間浸漬した試料についての孔食電位は、いづれも１１００mV程度で差異はないが、電解研磨のみの試料の孔食電位は２００mVと低いことが理解できる。
The stainless steel was buffed and electropolished under the same conditions as the
表１はリンゴ酸以外の有機酸でも良好な結果が得られることを示している。すなわち、８重量％の有機酸（クエン酸、グルコノラクトン、酒石酸）に０．９８重量％の過酸化水素を含む溶液に２５℃で、時間を変えて、試料６と同じ条件で前処理（バフ研磨＋電解研磨）した試料を浸漬したときの各試料の孔食電位を測定した結果を示すものである。いずれの有機酸でも０．５時間以上の浸漬時間で１０００mV以上の孔食電位を得ることができる。 Table 1 shows that good results are obtained with organic acids other than malic acid. That is, pre-treatment was carried out under the same conditions as sample 6 (at 25 ° C. for a solution containing 8 wt% organic acid (citric acid, gluconolactone, tartaric acid) and 0.98 wt% hydrogen peroxide) The result of having measured the pitting potential of each sample at the time of immersing the sample which buffed + electropolished) is shown. With any organic acid, a pitting potential of 1000 mV or more can be obtained by immersion time of 0.5 hours or more.
更に、図３は前記前処理（バフ研磨＋電解研磨）後の試料を過酸化水素０．９８重量％でリンゴ酸の濃度を０．５重量％とした溶液に２５℃で、０．５時間、1時間、２時間、浸漬した試料についてのアノード分極曲線を示すものである。いずれも孔食電位は１１００mV前後を示し、実用には充分であることが理解できる。 Furthermore, FIG. 3 shows that the sample after the above pretreatment (buffing + electropolishing) is a solution of 0.98% by weight of hydrogen peroxide and 0.5% by weight of malic acid at 25 ° C. for 0.5 hours. 1 shows anodic polarization curves for samples immersed for 1 hour and 2 hours. In any case, the pitting potential is around 1100 mV, which is understood to be sufficient for practical use.
表２はリンゴ酸を含む有機酸について、前記前処理（バフ研磨、電解研磨）後の試料を過酸化水素０．９８重量％で有機酸の濃度を０．５重量％とした溶液に、２５℃で、０．５時間、１時間、２時間、浸漬した試料についての孔食電位を示すものである。いづれも１１００mV前後の値を示しており、実用には充分といえる。 Table 2 shows the results of the pretreatment (buffing, electropolishing) of the organic acid containing malic acid in a solution of 0.98% by weight of hydrogen peroxide and 0.5% by weight of organic acid. The pitting potential is shown for a sample immersed for 0.5 hours, 1 hour, 2 hours at ° C. Both show values around 1100 mV, which is sufficient for practical use.
また、孔食電位の測定条件は実施例１と同じである。 Moreover, the measurement conditions of pitting potential are the same as Example 1.
＜実施例３＞（無電解処理の温度）
図４は８重量％リンゴ酸と０．９８重量％過酸化水素を含む溶液に２時間浸漬した無電解処理の温度条件を見出すためのアノード分極曲線を示すものである。５℃での孔食電位は、試料によるバラツキが多少見られるが９７０mVであり、実用的には充分であるといえる。１５℃を超えると孔食電位が１０００mVを超えるようになり試料間のバラツキも少なく充分といえる。
Example 3 (Temperature of Electroless Treatment)
FIG. 4 shows an anodic polarization curve for finding the temperature conditions of electroless treatment immersed in a solution containing 8% by weight of malic acid and 0.98% by weight of hydrogen peroxide for 2 hours. The pitting potential at 5 ° C. is 970 mV although some variation depending on the sample is observed, and it can be said that it is practically sufficient. When the temperature exceeds 15 ° C., the pitting potential exceeds 1000 mV, and it can be said that the variation among samples is small.
表３はリンゴ酸を含む他の有機酸（クエン酸、グルコノラクトン、酒石酸）での上記同様の実験の結果の孔食電位を示すものである。５℃では上記リンゴ酸の場合と同様,試料間のバラツキはあるものの、充分実用に耐える孔食電位を示している。いずれの有機酸も５℃でも孔食電位は１０００mV前後を示し、更に１５℃以上で１０００mVを超え、バラツキもなく充分に実用に耐える値を得た。前処理としてのバフ研磨と電解研磨は実施例１の試料６と同様の条件であり、孔食電位の測定条件も実施例１と同じである。
Table 3 shows the pitting potential as a result of the same experiment with other organic acids (citric acid, gluconolactone, tartaric acid) containing malic acid. At 5 ° C., as in the case of malic acid described above, although there is variation among samples, it shows a pitting potential sufficiently durable for practical use. The pitting potential was about 1000 mV at 5 ° C. in any of the organic acids, and further exceeded 1000 mV at 15 ° C. or more. The buffing and the electropolishing as pretreatments are the same conditions as the
＜実施例４＞（過酸化水素濃度）
図５は、無電解処理に使用するリンゴ酸と過酸化水素を含む溶液における過酸化水素の濃度を０．９８重量％〜7.0重量％の間で変えたときの各試料の孔食電位を示すものである。過酸化水素を添加しない場合は、図１の試料４、あるいは図５（リンゴ酸８wt％）に示すように４８０mV程度の孔食電位しか示さないが、過酸化水素の僅かな添加によって、孔食電位は飛躍的に高くなることが理解できる。過酸化水素の濃度が高いほど孔食電位も高いとは言えるが、過酸化水素の濃度の変化に対して孔食電位が際立って変化するわけではなく、過酸化水素の割合を過剰に増やす必要はないといえる。尚、リンゴ酸の濃度は８重量％であり処理温度は２５℃、浸漬時間は２時間である。
<Example 4> (hydrogen peroxide concentration)
FIG. 5 shows the pitting potential of each sample when the concentration of hydrogen peroxide in the solution containing malic acid and hydrogen peroxide used for the electroless processing is varied between 0.98 wt% and 7.0 wt%. It is a thing. When hydrogen peroxide is not added, pitting potential is only about 480 mV as shown in
表４は、リンゴ酸を含む、他の有機酸（クエン酸、グルコノラクトン、酒石酸）の孔食電位を纏めたものであり、リンゴ酸と同様の効果を得ることができた。 Table 4 summarizes the pitting potentials of other organic acids (citric acid, gluconolactone, tartaric acid) including malic acid, and could obtain the same effect as malic acid.
前処理としてのバフ研磨と電解研磨は実施例１の試料６と同様の条件であり、孔食電位の測定条件も実施例１と同じである。
The buffing and the electropolishing as pretreatments are the same conditions as the
＜実施例５＞（有機酸の量）
図１の試料６は、リンゴ酸が８重量％の1種類のアノード分極曲線しか示されていない。そこで、リンゴ酸の量の下限を見極めるため、リンゴ酸の量を変化させた場合のアノード分極曲線を図６に示す。リンゴ酸の量が０．５重量％でも孔食電位は１１００mV近くを呈している。リンゴ酸の上限は特に限定されないが、量が多いと廃液処理上の問題が生じることになる。
Example 5 (amount of organic acid)
表５は、リンゴ酸を含む他の有機酸（クエン酸、グルコノラクトン、酒石酸）の孔食電位を纏めたものであり、リンゴ酸と同様、いずれの有機酸も下限は０．５重量％であることが理解できる。 Table 5 summarizes the pitting potentials of other organic acids (citric acid, gluconolactone, tartaric acid) containing malic acid. As with malic acid, the lower limit of any organic acid is 0.5% by weight. It can be understood that
前処理としてのバフ研磨と電解研磨は実施例１の試料６と同様の条件であり、孔食電位の測定条件も実施例１と同じである。
The buffing and the electropolishing as pretreatments are the same conditions as the
＜硝酸処理との比較１＞（塩分濃度）
図７は、硝酸溶液で無電解処理した試料と、有機酸としてリンゴ酸を用いたときの本願発明にかかる試料との濃度の異なるNaCl溶液中でのアノード分極曲線を示すものであり、図７(a)は硝酸処理の試料、図７(b)は本願発明に係る試料で、NaCl濃度は図中に記しているように３．５重量％から飽和濃度までの溶液である。硝酸処理は30重量％の硝酸に２５℃、２時間浸漬した試料を用いた。本願発明の試料は８重量％のリンゴ酸と０．９８重量％の過酸化水素を含む溶液に２５℃で２時間浸漬した試料を用いた。
<Comparison with
FIG. 7 shows anodic polarization curves in NaCl solutions of different concentrations of a sample electrolessly treated with a nitric acid solution and a sample according to the present invention when malic acid is used as an organic acid. (a) is a nitric acid-treated sample, FIG. 7 (b) is a sample according to the present invention, and the NaCl concentration is a solution from 3.5% by weight to a saturated concentration as indicated in the figure. The nitric acid treatment used the sample immersed in 30 weight% nitric acid at 25 ° C. for 2 hours. The sample of the present invention was a sample immersed in a solution containing 8% by weight of malic acid and 0.98% by weight of hydrogen peroxide at 25 ° C. for 2 hours.
硝酸処理の試料では、NaCl濃度が２0重量％を超えると孔食電位が８００mVを下回り、２５％あるいは飽和濃度になると３００mV以下に下がっている。これに対して、本願発明品は飽和濃度になっても１０００mV以上の孔食電位を維持しており、本願発明の優位性が証明されている。 In the nitric acid-treated sample, the pitting potential falls below 800 mV when the NaCl concentration exceeds 20% by weight, and falls to 300 mV or less when it becomes 25% or the saturation concentration. On the other hand, the product of the present invention maintains a pitting potential of 1000 mV or more even at the saturation concentration, demonstrating the superiority of the present invention.
表６はリンゴ酸以外の有機酸（クエン酸、グルコノラクトン、酒石酸）での孔食電位をリンゴ酸とともに、纏めたものであり、いずれもリンゴ酸と同様、硝酸による無電解処理より優れた効果を得ることができた。 Table 6 shows the pitting potentials of organic acids other than malic acid (citric acid, gluconolactone, tartaric acid) together with malic acid, all of which are similar to malic acid and superior to electroless treatment with nitric acid I was able to get an effect.
＜硝酸処理との比較２＞（塩水浸漬時間）
図８は、硝酸溶液で無電解処理した試料と本願発明にかかる試料とを孔食電位測定前に空気を通気した３．５重量％NaCl溶液中に異なる時間（日数）保持し、その後脱気した３．５重量％NaCl溶液中で孔食電位を測定したときのアノード分極曲線を示すものである。図８(a)は硝酸処理の試料、図８(b)は有機酸としてリンゴ酸を用いた場合の本願発明に係る試料である。硝酸での処理条件、及び本願発明での処理条件は図７の場合と同じである。孔食電位の測定前の３．５重量％の通気NaCl溶液中での保持日数により孔食電位が低下すれば、不動態皮膜が劣化したことを意味する。
<Comparison with
FIG. 8 shows that a sample electrolessly treated with a nitric acid solution and a sample according to the present invention are held for a different time (days) in a 3.5 wt% NaCl solution which is aerated with air before measurement of pitting potential, and thereafter degassing The anodic polarization curve when the pitting potential is measured in the 3.5 wt% NaCl solution is shown. FIG. 8 (a) is a nitric acid-treated sample, and FIG. 8 (b) is a sample according to the present invention when malic acid is used as the organic acid. The treatment conditions with nitric acid and the treatment conditions in the present invention are the same as in FIG. A decrease in pitting potential due to the number of days of retention in a 3.5 wt% aerated NaCl solution prior to measurement of pitting potential means that the passive film has deteriorated.
しかし、硝酸処理の試料および本願発明の試料とも１００日を経過しても１０００mV以上の孔食電位を維持しており、処理皮膜の劣化は認められない。したがって両者の処理効果は同等であるが、硝酸のような強酸を使用しない点で本願発明の試料の優位性が立証できることになる。 However, both the nitric acid-treated sample and the sample of the present invention maintain a pitting potential of 1000 mV or more after 100 days, and no deterioration of the treated film is observed. Therefore, although the processing effects of the two are equivalent, the superiority of the sample of the present invention can be proved in that no strong acid such as nitric acid is used.
表７はリンゴ酸以外の有機酸（クエン酸、グルコノラクトン、酒石酸）についての実験をリンゴ酸とともに、纏めたものであり、いずれもリンゴ酸と同様の効果を得ることができた。 Table 7 shows the experiment about organic acids other than malic acid (citric acid, gluconolactone, tartaric acid) together with malic acid, and it is what was able to obtain the same effect as malic acid in all.
＜従来技術との比較＞
ここで本願発明と関連する従来の処理技術であるクエン酸で研磨後、過酸化水素に浸漬する不動態化処理と本願発明の処理との違いについて確認した実験を図９に示す。
<Comparison with prior art>
Here, FIG. 9 shows an experiment confirmed about the difference between the passivating treatment in which the substrate is immersed in hydrogen peroxide after polishing with citric acid, which is a conventional treatment technique related to the present invention, and the treatment of the present invention.
バフ研磨(♯４００)したステンレス鋼素材を４５℃の２0重量％クエン酸に３０分浸漬して表面を研磨し、更に４５℃の４．０重量％過酸化水素に１時間浸漬した試料と、実施例１と同じ条件で電解研磨し、８重量％リンゴ酸と０．９８重量％過酸化水素を含む溶液で無電解処理（２５℃、２時間）した試料を３．５重量％のNaCl溶液中でアノード分極したときの孔食電位の比較を図９に示す。 A sample obtained by immersing a buffed (# 400) stainless steel material in 20 wt% citric acid at 45 ° C. for 30 minutes to polish the surface and further dipping it in 4.0 wt% hydrogen peroxide at 45 ° C. for 1 hour, A 3.5 wt% NaCl solution was electropolished under the same conditions as Example 1, and a sample electrolessly treated (25 ° C., 2 hours) with a solution containing 8 wt% malic acid and 0.98 wt% hydrogen peroxide A comparison of pitting potentials when anodic polarization is performed in is shown in FIG.
クエン酸処理の試料はせいぜい３００mＶの孔食電位であるのに対して、本願発明に掛かる試料は１０００mV以上の孔食電位を示した。加えて実施例１と同じ条件で電解研磨し、３０重量％の硝酸で無電解処理した試料についても同様に実験したが、本願発明の試料と孔食電位の値は同等である。したがって、両者の皮膜の性能はほぼ同等と考えられるが、硝酸が強酸であり危険かつ廃液処理が必要という観点からは本願発明の優位性が強調できることになる。 The sample subjected to the present invention exhibited a pitting potential of 1000 mV or more, while the sample subjected to the citric acid treatment had a pitting potential of at most 300 mV. In addition, the same experiment was performed on a sample which was electropolished under the same conditions as in Example 1 and subjected to an electroless treatment with 30% by weight of nitric acid, but the value of the pitting potential was the same as the sample of the present invention. Therefore, although the performances of both films are considered to be almost equal, the superiority of the present invention can be emphasized from the viewpoint that nitric acid is a strong acid and it is dangerous and waste liquid treatment is necessary.
従って、単純に不動態化処理（無電解処理）にクエン酸などの有機酸を用いるというだけの発想では充分ではなく、その前処理に電解研磨を用いるということ、およびリンゴ酸などの有機酸に若干の過酸化水素を添加することが極めて重要であることが理解できる。 Therefore, the idea of simply using an organic acid such as citric acid for passivation treatment (electroless treatment) is not sufficient, and that electropolishing is used for its pretreatment, and organic acids such as malic acid It can be appreciated that the addition of some hydrogen peroxide is very important.
以上説明したように、本発明は不動態化処理に廃棄処理が不要なリンゴ酸を含む有機酸と過酸化水素を用いることができるので、環境保全の観点、コスト低減の観点からの利点が大きく、産業上の利用可能性は極めて大きい。
As described above, since the present invention can use an organic acid containing malic acid and hydrogen peroxide which do not need to be disposed of for passivation processing, the advantages from the viewpoint of environmental protection and cost reduction are significant. The industrial applicability is extremely large.
Claims (3)
上記電解研磨された被処理物を、有機酸であるリンゴ酸、クエン酸、グルコノラクトン、酒石酸の内の１種と過酸化水素を含む溶液に浸漬するステップ
を備えたことを特徴とするステンレス鋼の不動態化方法。 The step of immersing the object to be processed, which is steps and the electrolytic polishing to electrolytic polishing an object to be processed, malic acid is an organic acid, citric acid, gluconolactone, a solution containing one and hydrogen peroxide of the tartaric acid passivation method of stainless steel, comprising the.
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