JP2014012876A - Method for suppressing hydrogen generation on steel material surface - Google Patents
Method for suppressing hydrogen generation on steel material surface Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 77
- 239000010959 steel Substances 0.000 title claims abstract description 77
- 239000000463 material Substances 0.000 title claims abstract description 76
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 63
- 239000001257 hydrogen Substances 0.000 title claims abstract description 63
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 61
- 238000000034 method Methods 0.000 title claims abstract description 20
- 239000002344 surface layer Substances 0.000 claims abstract description 26
- 239000007864 aqueous solution Substances 0.000 claims abstract description 16
- SOIFLUNRINLCBN-UHFFFAOYSA-N ammonium thiocyanate Chemical compound [NH4+].[S-]C#N SOIFLUNRINLCBN-UHFFFAOYSA-N 0.000 claims abstract description 14
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims 2
- 229910052742 iron Inorganic materials 0.000 claims 1
- 239000000654 additive Substances 0.000 abstract description 9
- 239000000243 solution Substances 0.000 abstract description 2
- 238000002474 experimental method Methods 0.000 description 25
- 239000000523 sample Substances 0.000 description 19
- 239000008151 electrolyte solution Substances 0.000 description 17
- 238000007254 oxidation reaction Methods 0.000 description 12
- 229910052751 metal Inorganic materials 0.000 description 9
- 239000002184 metal Substances 0.000 description 9
- 230000000996 additive effect Effects 0.000 description 8
- 239000013074 reference sample Substances 0.000 description 8
- 238000005259 measurement Methods 0.000 description 7
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 6
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 6
- 238000006722 reduction reaction Methods 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical class [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 1
- 229910021607 Silver chloride Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000001364 causal effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- -1 hydrogen ions Chemical class 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
Landscapes
- Preventing Corrosion Or Incrustation Of Metals (AREA)
Abstract
Description
本発明は、鋼材の強度低下を招く水素の侵入を抑制するための鋼材表面における水素発生を抑制する方法に関するものである。 The present invention relates to a method for suppressing hydrogen generation on the surface of a steel material for suppressing hydrogen intrusion that causes a reduction in strength of the steel material.
鉄鋼などの特定の金属は、ある使用環境において水素を含むと延性が失われ、強度が著しく低下する（非特許文献１参照）。この現象は、水素脆化と呼ばれている。多くの研究者は、この水素脆化に着目し、水素脆化に強い金属を開発してきた。例えば、表面にニッケルを濃化させた鋼材がある。ニッケルには水もしくは水素イオンの還元により金属表面に吸着した水素の再結合反応を促進し、外部環境に放出する効果がある。このため、鋼材表面にニッケルを濃化させると、吸着した水素が鋼材内部に侵入する量を低減することができる（非特許文献２参照）。 When certain metals such as steel contain hydrogen in a certain use environment, the ductility is lost and the strength is significantly reduced (see Non-Patent Document 1). This phenomenon is called hydrogen embrittlement. Many researchers have focused on this hydrogen embrittlement and have developed metals that are resistant to hydrogen embrittlement. For example, there is a steel material having nickel concentrated on the surface. Nickel has the effect of promoting the recombination reaction of hydrogen adsorbed on the metal surface by reduction of water or hydrogen ions and releasing it to the external environment. For this reason, when nickel is concentrated on the steel material surface, the amount of adsorbed hydrogen entering the steel material can be reduced (see Non-Patent Document 2).
また、水素脆化は、金属に水素が吸蔵された状態で応力が加わった時に生じることが知られている。ただし、一時的に金属に水素が吸蔵されても、長時間大気中に暴露されていたり、熱処理したりすることで金属中から水素を放出してしまえば、応力が加わっても水素脆化は起こらない。 Hydrogen embrittlement is known to occur when stress is applied in a state where hydrogen is occluded in a metal. However, even if hydrogen is temporarily occluded in the metal, if it is exposed to the atmosphere for a long time or if hydrogen is released from the metal by heat treatment, hydrogen embrittlement will occur even if stress is applied. Does not happen.
しかしながら、上述したように、添加物を加えると、鋼材の所期の機能が得られない場合が発生する。例えば、鋼材は、チタンや硫黄などの添加物を加えると破断応力強度や耐食性が変化することが知られている（非特許文献３参照）。従って、金属への添加が可能な元素やこの添加量には制限があり、添加剤の添加による金属材料の水素脆化対策には限界があった。このため、鋼材などの金属に対する添加物の量を変えることなく、耐水素脆化特性を向上させる技術が重要となる。 However, as described above, when an additive is added, the intended function of the steel material may not be obtained. For example, steel materials are known to change in breaking stress strength and corrosion resistance when an additive such as titanium or sulfur is added (see Non-Patent Document 3). Therefore, there is a limit to the elements that can be added to the metal and the amount of this element added, and there has been a limit to measures for hydrogen embrittlement of the metal material by the addition of the additive. For this reason, a technique for improving the hydrogen embrittlement resistance without changing the amount of the additive to the metal such as steel is important.
本発明は、以上のような問題点を解消するためになされたものであり、鋼材における添加物の状態を変更することなく、鋼材における水素脆化が抑制できるようにすることを目的とする。 The present invention has been made to solve the above-described problems, and an object thereof is to suppress hydrogen embrittlement in a steel material without changing the state of an additive in the steel material.
本発明に係る鋼材表面における水素発生を抑制する方法は、鋼材を形成する第１工程と、チオシアン酸アンモニウム水溶液を鋼材の表面に接触させて鋼材の表面に表面層を形成する第２工程とを少なくとも備える。なお、表面層は、鉄の酸化物を含んでいる。また、表面層は、１０μｍ以上形成するとよい。 The method for suppressing hydrogen generation on the steel material surface according to the present invention includes a first step of forming the steel material, and a second step of forming a surface layer on the surface of the steel material by bringing the ammonium thiocyanate aqueous solution into contact with the surface of the steel material. At least. The surface layer contains iron oxide. Further, the surface layer is preferably formed with a thickness of 10 μm or more.
以上説明したように、本発明によれば、チオシアン酸アンモニウム水溶液の処理により鋼材表面に表面層を形成するようにしたので、鋼材における添加物の状態を変更することなく、鋼材における水素脆化が抑制できるようになるという優れた効果が得られる。 As described above, according to the present invention, the surface layer is formed on the surface of the steel material by the treatment with the ammonium thiocyanate aqueous solution, so that the hydrogen embrittlement in the steel material can be achieved without changing the state of the additive in the steel material. An excellent effect of being able to be suppressed is obtained.
以下、本発明の実施の形態について図を参照して説明する。図１は、本発明の実施の形態における鋼材表面における水素発生を抑制する方法を説明するためのフローチャートである。この方法は、まず、第１工程Ｓ１０１で、対象とする鋼材を形成する。次に、第２工程Ｓ１０２で、チオシアン酸アンモニウム水溶液を鋼材の表面に接触させて鋼材の表面に表面層を形成する。例えば、対象とする鋼材を、５０℃の２０％チオシアン酸アンモニウム水溶液に６０時間以上浸漬する。表面層は、鋼材の表面に接した状態で形成する。例えば、第１工程Ｓ１０１で形成した鋼材表面に自然酸化膜などが形成されている場合、これを除去して鋼材の表面を露出させてから、第２工程Ｓ１０２の処理を行えばよい。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining a method for suppressing hydrogen generation on the surface of a steel material in an embodiment of the present invention. In this method, first, a target steel material is formed in the first step S101. Next, in the second step S102, an aqueous solution of ammonium thiocyanate is brought into contact with the surface of the steel material to form a surface layer on the surface of the steel material. For example, the target steel material is immersed in a 20% aqueous ammonium thiocyanate solution at 50 ° C. for 60 hours or more. The surface layer is formed in contact with the surface of the steel material. For example, when a natural oxide film or the like is formed on the surface of the steel material formed in the first step S101, the second step S102 may be performed after removing the natural oxide film to expose the surface of the steel material.
上述した処理により鋼材表面に生成した表面層は、腐食環境中におかれた鋼材の酸化反応を抑制し、結果として還元反応により発生する水素の生成量が減少するため、鋼材に添加物を加えることなく、鋼材中への水素侵入が抑制できるようになる。 The surface layer generated on the surface of the steel material by the above-described treatment suppresses the oxidation reaction of the steel material placed in the corrosive environment, and as a result, the amount of hydrogen generated by the reduction reaction decreases, so an additive is added to the steel material. Therefore, hydrogen intrusion into the steel material can be suppressed.
以下、上述した表面層の形成により、鋼材に対する水素侵入が抑制できることを示す実験（電気化学的水素透過法）について説明する。まず、実験の実施において用いた実験装置について図２を用いて説明する。この実験装置は、容器２０１と、実験対象の鋼材から構成された容器２０２と、容器２０３とを備える。容器２０２は、実験対象の鋼材より構成した円筒である。 Hereinafter, an experiment (electrochemical hydrogen permeation method) showing that hydrogen intrusion to the steel material can be suppressed by forming the surface layer described above will be described. First, the experimental apparatus used in the experiment will be described with reference to FIG. This experimental apparatus includes a container 201, a container 202 made of a steel material to be tested, and a container 203. The container 202 is a cylinder made of a steel material to be tested.
容器２０１には、チオシアン酸アンモニウム水溶液からなる第１電解質溶液２２１が収容されている。また、容器２０２には、０．２Ｍの水酸化ナトリウム水溶液からなる第２電解質溶液２３１が収容され、第２電解質溶液２３１には、第２参照電極２３２および対極２３３が浸漬されている。なお、容器２０２を、作用電極とする。この状態の容器２０２が、容器２０１の内部で第１電解質溶液２２１に浸漬されている。 The container 201 contains a first electrolyte solution 221 made of an ammonium thiocyanate aqueous solution. The container 202 contains a second electrolyte solution 231 made of a 0.2 M sodium hydroxide aqueous solution, and the second reference electrode 232 and the counter electrode 233 are immersed in the second electrolyte solution 231. The container 202 is a working electrode. The container 202 in this state is immersed in the first electrolyte solution 221 inside the container 201.
上記構成とすることで、実験対象の鋼材からなる容器２０２は、外側の面が、第１電解質溶液２２１に接触し、内側の面が、容器２０２内部の第２電解質溶液２３１に接触した状態となる。 With the above configuration, the container 202 made of the steel material to be tested has an outer surface in contact with the first electrolyte solution 221 and an inner surface in contact with the second electrolyte solution 231 inside the container 202. Become.
また、第１電解質溶液２２１には、塩橋２２２を介し、容器２０３に収容された飽和塩化カリウム水溶液からなる外部電解質溶液２２３が接続し、外部電解質溶液２２３に第１参照電極２２４が浸漬されている。第１参照電極２２４は、Ａｇ／ＡｇＣｌ電極である。 The first electrolyte solution 221 is connected to an external electrolyte solution 223 made of a saturated potassium chloride aqueous solution contained in the container 203 via the salt bridge 222, and the first reference electrode 224 is immersed in the external electrolyte solution 223. Yes. The first reference electrode 224 is an Ag / AgCl electrode.
各電極における電位制御，電流測定，および電位測定は、ポテンショスタット２０４および電圧測定部２０５を用いる。第１参照電極２２４は、電圧測定部２０５に接続し、第２参照電極２３２および対極２３３は、ポテンショスタット２０４に接続する。また、作用電極となる容器２０２は、ポテンショスタット２０４および電圧測定部２０５に接続する。ポテンショスタット２０４は、電位規制および電流測定手段となり、電圧測定部２０５は、容器２０２と第１参照電極２２４の端子間電圧測定手段となる。なお、容器２０１は、恒温水槽２０６により、例えば５０℃に保持されている。また、容器２０２は、栓として機能する支持台２０７の上に固定されている。 The potentiostat 204 and the voltage measuring unit 205 are used for potential control, current measurement, and potential measurement at each electrode. The first reference electrode 224 is connected to the voltage measurement unit 205, and the second reference electrode 232 and the counter electrode 233 are connected to the potentiostat 204. A container 202 serving as a working electrode is connected to a potentiostat 204 and a voltage measuring unit 205. The potentiostat 204 serves as a potential regulation and current measurement unit, and the voltage measurement unit 205 serves as a voltage measurement unit between the terminals of the container 202 and the first reference electrode 224. In addition, the container 201 is hold | maintained at 50 degreeC by the constant temperature water tank 206, for example. The container 202 is fixed on a support base 207 that functions as a stopper.
上述したように各電極を接続し、例えば、第１電解質溶液２２１に容器２０２を浸漬させることで，第１電解質溶液２２１に容器２０２を接触させる。この状態で、ポテンショスタット２０４により、第２参照極２３２を基準として容器２０２の電位を水素の酸化反応が進行する電印に規制した状態で、容器２０２と対極２３３との間に流れる電流を測定すると、第１電解質溶液２２１側から第２電解質溶液２３１側にかけて容器２０２を透過してきた水素が、容器２０２と第２電解質溶液２３１との界面において酸化されることによる電流の変化が、観測されるようになる。なお、電圧測定部２０５では、容器２０２と第１電解質溶液との界面における反応の状況を確認するために、容器２０２と第１参照電極２２４との間の電圧を測定する。 The electrodes are connected as described above, and the container 202 is brought into contact with the first electrolyte solution 221 by, for example, immersing the container 202 in the first electrolyte solution 221. In this state, the current flowing between the container 202 and the counter electrode 233 is measured by the potentiostat 204 in a state where the potential of the container 202 is regulated to the electric mark where the oxidation reaction of hydrogen proceeds with the second reference electrode 232 as a reference. Then, a change in current due to oxidation of the hydrogen that has permeated the container 202 from the first electrolyte solution 221 side to the second electrolyte solution 231 side at the interface between the container 202 and the second electrolyte solution 231 is observed. It becomes like this. The voltage measurement unit 205 measures the voltage between the container 202 and the first reference electrode 224 in order to confirm the reaction state at the interface between the container 202 and the first electrolyte solution.
上述した実験装置を用いた実験では、水素の侵入側となる第１電解質溶液２２１を、２０％のチオシアン酸アンモニウム水溶液とし、水素検出側となる第２電解質溶液２３１は、０．２Ｍの水酸化ナトリウム水溶液としている。また、試料となる容器２０２は、研磨紙で研磨することで、表面に形成されている酸化物などを除去した状態としている。なお、参照試料として、表面に形成されている自然酸化物などの表面酸化膜を除去していない鋼材（黒皮材）を用い、上記同様の実験を行った。 In the experiment using the experimental apparatus described above, the first electrolyte solution 221 on the hydrogen intrusion side is a 20% ammonium thiocyanate aqueous solution, and the second electrolyte solution 231 on the hydrogen detection side is 0.2 M hydroxide. Sodium aqueous solution. Further, the sample container 202 is polished with polishing paper to remove oxides formed on the surface. As a reference sample, a steel material (black skin material) from which a surface oxide film such as a natural oxide formed on the surface was not removed was used, and the same experiment was performed.
図３の（ａ）に、表面に形成されている酸化物などを除去した鋼材による試料における実験時間に対する水素透過電流の変化を示した特性図を示す。実験開始直後に水素透過電流の上昇が見られたが、時間経過とともに減少し、６０時間程度でほぼ一定の電流値を示すようになった。なお、図３の（ｂ）は、表面に形成されている自然酸化物などの表面酸化膜を除去していない鋼材（黒皮材）による参照試料の実験結果である。 FIG. 3A is a characteristic diagram showing a change in the hydrogen permeation current with respect to the experiment time in a sample of a steel material from which oxides and the like formed on the surface are removed. An increase in the hydrogen permeation current was observed immediately after the start of the experiment, but it decreased with the passage of time and showed a substantially constant current value in about 60 hours. FIG. 3B shows experimental results of a reference sample made of a steel material (black skin material) from which a surface oxide film such as a natural oxide formed on the surface is not removed.
次に、実験後に、容器２０２を取り出し、断面観察を行った結果を図４に示す。図４（ａ）は実験前の表面酸化物が除去されている初期状態の試料、（ｃ）は実験後の試料の断面写真である。なお、図４の（ｂ）は、参照試料の実験後の断面写真である。 Next, FIG. 4 shows the result of taking out the container 202 and performing cross-sectional observation after the experiment. FIG. 4A is a sample in an initial state where the surface oxide before the experiment is removed, and FIG. 4C is a cross-sectional photograph of the sample after the experiment. FIG. 4B is a cross-sectional photograph of the reference sample after the experiment.
図４の（ａ）と図４の（ｃ）との実験前後で比較すると、実験前の試料表面には酸化被膜がほとんど存在していないが、８０時間実験を行った後の試料表面には、厚さ１０μｍ程度の比較的均一な表面層の生成が確認できる。この表面層は、上述した実験による鋼材表面における酸化反応により形成されたものであり、主に、鋼材を構成している鉄の酸化物から構成されている。また、表面層は、鉄の酸化物に加え、硫黄などが含まれていることも確認されている。 Comparing before and after the experiment of FIG. 4 (a) and FIG. 4 (c), there is almost no oxide film on the sample surface before the experiment, but on the sample surface after the 80-hour experiment. The formation of a relatively uniform surface layer having a thickness of about 10 μm can be confirmed. This surface layer is formed by an oxidation reaction on the steel material surface by the above-described experiment, and is mainly composed of an iron oxide constituting the steel material. It has also been confirmed that the surface layer contains sulfur and the like in addition to the iron oxide.
図３の（ａ）に示した水素透過電流の減少と図４の（ｃ）に示した表面層の生成との因果関係は明らかになっていないが、上記処理による酸化被膜からなる表面層が形成され、試料が溶解する酸化反応が抑制された結果、酸化反応で生成した電子を消費する還元反応である水素発生反応が抑制され、試料表面近傍に存在する水素が減少することにより水素透過電流が減少したのではないかと考えられる。また、表面層は、試料表面の全域にわたって均一に、厚さ１０μｍ程度に形成されており、このような厚い表面層が形成されたことも、図３の（ａ）に示した水素透過電流の減少の１要因と考えられる。 Although the causal relationship between the decrease in the hydrogen permeation current shown in FIG. 3A and the formation of the surface layer shown in FIG. As a result of the suppression of the oxidation reaction that forms and dissolves the sample, the hydrogen generation reaction, which is a reduction reaction that consumes the electrons generated in the oxidation reaction, is suppressed, and the hydrogen permeation current is reduced by reducing the hydrogen present near the sample surface. Is thought to have decreased. Further, the surface layer is uniformly formed to a thickness of about 10 μm over the entire surface of the sample, and the formation of such a thick surface layer is also due to the hydrogen permeation current shown in FIG. This is considered to be one factor for the decrease.
以上のことから、前述した実施の形態における方法により、鋼材に水素が侵入しにくくなる表面を作製することができる。なお、対象とする鋼材をチオシアン酸アンモニウム水溶液中に浸漬した後、一時的に侵入した水素を放出するため、３０℃程度の温度条件で、１６８時間程度大気中に放置しておくとよい（非特許文献４参照）。ここで、水素浸入の抑制効果をより発揮させるためには、チオシアン酸アンモニウム水溶液の処理前に、鋼材表面の自然酸化膜などをより完全に除去し、鋼材自身が完全に露出した状態とすることよりよい。 From the above, the surface in which hydrogen hardly enters the steel material can be produced by the method in the above-described embodiment. In addition, after dipping the target steel material in an ammonium thiocyanate aqueous solution, it is good to leave it in the atmosphere for about 168 hours under a temperature condition of about 30 ° C. in order to release hydrogen that has invaded temporarily (non- (See Patent Document 4). Here, in order to further exert the effect of suppressing hydrogen intrusion, before the treatment with the ammonium thiocyanate aqueous solution, the natural oxide film etc. on the surface of the steel material is more completely removed so that the steel material itself is completely exposed. Better.
図３の（ｂ）に示すように、参照試料では、実験前から、表面に表面酸化膜が存在しているために、試料と比較して水素透過電流量が少ないが、時間と共に電流量が増加する傾向が見られる。また、図４の（ｂ）に示すように、参照試料では、図４の（ｃ）の試料と比較して、形成されている被膜の厚さが不均一で、局所的に膜厚が非常に薄い部分が存在することが分かる。 As shown in FIG. 3B, in the reference sample, since the surface oxide film exists on the surface from before the experiment, the amount of hydrogen permeation current is small compared to the sample. There is an increasing trend. Further, as shown in FIG. 4B, the reference sample has a non-uniform thickness of the formed film compared to the sample of FIG. It can be seen that there are thin parts.
更に、図５の表面写真や図６の表面ＳＥＭ（走査型電子顕微鏡）画像でも、実験後の試料と参照試料とを比較すると、参照試料の表面では、酸化被膜が不均一に生成していることが確認できる。なお、図５において、（ａ）は、参照試料であり、（ｂ）は、試料である。また、図６において、（ａ）は、試料であり、（ｂ）は、参照試料である。 Furthermore, in the surface photograph of FIG. 5 and the surface SEM (scanning electron microscope) image of FIG. I can confirm that. In FIG. 5, (a) is a reference sample, and (b) is a sample. In FIG. 6, (a) is a sample, and (b) is a reference sample.
図３の（ａ）と図３の（ｂ）との水素透過電流の変化に関する傾向の違いも、試料の場合には、実験初期には清浄な鋼材表面が露出しているために鋼材の酸化などの反応と、この反応に伴う水素の発生が非常に起こりやすいが、当該反応が鋼材表面において均一に進行することから酸化皮膜も均一に形成され、一定の厚さまで表面層が成長すると鋼材の酸化反応が表面層により阻害され、水素透過電流が減少すると考えられる。 3 (a) and FIG. 3 (b), the difference in tendency regarding the change in the hydrogen permeation current is also due to the oxidation of the steel material because the clean steel surface is exposed at the beginning of the experiment in the case of the sample. And the generation of hydrogen associated with this reaction is very easy to occur, but since the reaction proceeds uniformly on the surface of the steel material, the oxide film is formed uniformly, and when the surface layer grows to a certain thickness, It is considered that the oxidation reaction is inhibited by the surface layer and the hydrogen permeation current is reduced.
これに対し、黒皮材を使用した参照試料の場合には実験前から酸化物が鋼材表面に形成されているため、実験初期の水素透過電流は、試料の場合と比較して非常に少ない。しかし、実験前から存在する表面酸化膜は、試料表面に実験により形成された表面層と比較して厚みや被覆状況が不均一であると推定され、局所的に酸化反応が進行しやすい領域が発生することが予想される。このような場合には、例えば、腐食電流の集中に伴う孔蝕の発生や比表面積の増大、あるいは酸化皮膜の不均一な膜厚に起因する膜内の応力による皮膜へのクラックの発生などにより酸化反応に伴う水素透過電流が徐々に増加していると考えられる。 On the other hand, in the case of the reference sample using the black skin material, since the oxide is formed on the steel material surface before the experiment, the hydrogen permeation current at the initial stage of the experiment is very small compared to the case of the sample. However, the surface oxide film existing before the experiment is presumed to be uneven in thickness and coverage compared to the surface layer formed by experiment on the sample surface, and there is a region where the oxidation reaction is likely to proceed locally. It is expected to occur. In such a case, for example, pitting corrosion due to concentration of corrosion current, increase in specific surface area, or generation of cracks in the film due to stress in the film due to uneven film thickness of the oxide film, etc. It is thought that the hydrogen permeation current accompanying the oxidation reaction is gradually increasing.
このように、表面酸化膜が不均一に存在すると、局所的に酸化反応と還元反応がそれぞれ起こりやすい場所ができてしまい、均一な表面層を作製するのは難しい。このため、表面酸化膜を除去し、この後で、チオシアン酸アンモニウム水溶液の処理により表面層を生成させることが重要であることと推察される。 Thus, when the surface oxide film exists unevenly, a place where an oxidation reaction and a reduction reaction are likely to occur locally is created, and it is difficult to produce a uniform surface layer. For this reason, it is presumed that it is important to remove the surface oxide film and thereafter form a surface layer by treatment with an ammonium thiocyanate aqueous solution.
以上に説明したように、本発明によれば、チオシアン酸アンモニウム水溶液の処理により、鋼材表面に表面層を形成するようにしたので、腐食環境中におかれた鋼材の酸化反応を抑制し、結果として還元反応により発生する水素の生成量が減少し、金属中への水素侵入を抑制できるようになる。この結果、鋼材における添加物の状態を変更することなく、鋼材自体の特性を維持した状態で、鋼材における水素脆化が抑制できるようになる。 As described above, according to the present invention, the surface layer is formed on the surface of the steel material by the treatment with the ammonium thiocyanate aqueous solution, so that the oxidation reaction of the steel material placed in the corrosive environment is suppressed. As a result, the amount of hydrogen generated by the reduction reaction is reduced, so that hydrogen intrusion into the metal can be suppressed. As a result, hydrogen embrittlement in the steel material can be suppressed while maintaining the characteristics of the steel material itself without changing the state of the additive in the steel material.
なお、本発明は以上に説明した実施の形態に限定されるものではなく、本発明の技術的思想内で、当分野において通常の知識を有する者により、多くの変形および組み合わせが実施可能であることは明白である。 The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.
Claims (3)
チオシアン酸アンモニウム水溶液を前記鋼材の表面に接触させて前記鋼材の表面に表面層を形成する第２工程と
を少なくとも備えることを特徴とする鋼材表面における水素発生を抑制する方法。 A first step of forming a steel material;
And a second step of forming a surface layer on the surface of the steel material by bringing an aqueous solution of ammonium thiocyanate into contact with the surface of the steel material. A method for suppressing hydrogen generation on the surface of the steel material.
前記表面層は、鉄の酸化物を含んでいることを特徴とする鋼材表面における水素発生を抑制する方法。 In the method of suppressing hydrogen generation on the steel material surface according to claim 1,
The said surface layer contains the oxide of iron, The method of suppressing the hydrogen generation | occurrence | production on the steel material surface characterized by the above-mentioned.
前記表面層は、１０μｍ以上形成することを特徴とする鋼材表面における水素発生を抑制する方法。 In the method for suppressing hydrogen generation on the steel material surface according to claim 1 or 2,
The method for suppressing hydrogen generation on the surface of a steel material, wherein the surface layer is formed to have a thickness of 10 μm or more.
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