JP7369063B2 - Method of appearance of prior austenite grain boundaries in alloy steel materials for machine structures - Google Patents

Method of appearance of prior austenite grain boundaries in alloy steel materials for machine structures Download PDF

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JP7369063B2
JP7369063B2 JP2020039246A JP2020039246A JP7369063B2 JP 7369063 B2 JP7369063 B2 JP 7369063B2 JP 2020039246 A JP2020039246 A JP 2020039246A JP 2020039246 A JP2020039246 A JP 2020039246A JP 7369063 B2 JP7369063 B2 JP 7369063B2
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意公男 谷
淳也 鈴木
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JATCO Ltd
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Description

本発明は、機械構造用合金鋼材の旧オーステナイト粒界の現出方法に関する。 The present invention relates to a method for revealing prior austenite grain boundaries in alloy steel materials for machine structures.

従来から、旧オーステナイト粒界を組織にもつ鋼材について、ピクリン酸を含有する腐食液を用いて旧オーステナイト粒界を現出させる方法が知られている。特許文献１には、ピクリン酸を含有する腐食液に鋼材を浸漬させることで鋼材の旧オーステナイト結晶粒界を現出させるエッチング方法が開示されている。 Conventionally, for steel materials having prior austenite grain boundaries in their structure, a method has been known in which prior austenite grain boundaries are exposed using a corrosive solution containing picric acid. Patent Document 1 discloses an etching method in which prior austenite grain boundaries of a steel material are exposed by immersing the steel material in a corrosive solution containing picric acid.

特開２００５－２４１６３５号公報Japanese Patent Application Publication No. 2005-241635

しかしながら、ピクリン酸はその性質上取り扱いが容易ではないため、ピクリン酸を用いることなく旧オーステナイト粒界を現出させる方法の開発が急務であった。 However, because picric acid is not easy to handle due to its nature, there was an urgent need to develop a method for revealing prior austenite grain boundaries without using picric acid.

本発明は、このような技術的課題に鑑みてなされたものであり、ピクリン酸を用いることなく、機械構造用合金鋼材の旧オーステナイト結晶粒界を現出させる方法を提供することを目的とする。 The present invention was made in view of such technical problems, and an object of the present invention is to provide a method for revealing prior austenite grain boundaries in alloy steel materials for mechanical structures without using picric acid. .

本発明のある態様によれば、しゅう酸と、界面活性剤と、を含有する腐食液を用いて電解腐食を行う、機械構造用合金鋼材の旧オーステナイト粒界の現出方法が提供される。 According to one aspect of the present invention, there is provided a method for revealing prior austenite grain boundaries in an alloy steel material for mechanical structures, which involves performing electrolytic corrosion using a corrosive solution containing oxalic acid and a surfactant.

上記態様によれば、ピクリン酸を用いることなく、機械構造用合金鋼材の旧オーステナイト粒界を現出させることができる。 According to the above aspect, the prior austenite grain boundaries of the alloy steel for machine structures can be exposed without using picric acid.

本発明の機械構造用合金鋼材の電解腐食に係る装置の概要図である。FIG. 1 is a schematic diagram of an apparatus for electrolytic corrosion of alloy steel materials for machine structures according to the present invention. 本発明の電解腐食方法のプロセス図である。FIG. 3 is a process diagram of the electrolytic corrosion method of the present invention. 本発明の電解腐食方法のプロセス図である。FIG. 3 is a process diagram of the electrolytic corrosion method of the present invention. 本発明による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。1 is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries according to the present invention. 本発明による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。1 is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries according to the present invention. 比較例による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。It is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries in a comparative example. 比較例による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。It is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries in a comparative example. 本発明による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。1 is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries according to the present invention. 本発明による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。1 is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries according to the present invention. 比較例による旧オーステナイト粒界現出結果を示す金属組織の光学顕微鏡写真である。It is an optical micrograph of a metal structure showing the appearance of prior austenite grain boundaries in a comparative example.

以下、添付図面を参照しながら本発明の実施形態について説明する。 Embodiments of the present invention will be described below with reference to the accompanying drawings.

［電解腐食装置］
まず、機械構造用合金鋼材の電解腐食に用いる電解腐食装置１００について説明する。 [Electrolytic corrosion equipment]
First, a galvanic corrosion apparatus 100 used for electrolytic corrosion of alloy steel materials for machine structures will be described.

図１に示すように、電解腐食装置１００は、容器１と、陽極２と、陰極３と、台座４と、電源装置５と、電線６，７と、を備える。 As shown in FIG. 1, the electrolytic corrosion apparatus 100 includes a container 1, an anode 2, a cathode 3, a pedestal 4, a power supply device 5, and electric wires 6 and 7.

容器１は、陰極３及び台座４を収容可能であるとともに、台座４を浸漬させる程度の腐食液を収容可能な大きさのものである。容器１は、例えば、ガラス製のビーカである。 The container 1 is large enough to accommodate the cathode 3 and the pedestal 4, and to contain enough corrosive liquid to immerse the pedestal 4. The container 1 is, for example, a glass beaker.

陰極３は、機械構造用合金鋼材の試験片Ｔを保持する台座４を載せられる大きさの受け皿部分３ａと、受け皿部分３ａと連結する部分であって電線７を介して電源装置５と接続する棒部３ｂと、を有する。本実施形態では、陰極３はステンレスである。ステンレスは、例えばＳＵＳ３０４である。 The cathode 3 includes a tray portion 3a having a size on which a pedestal 4 holding a test piece T of alloy steel for mechanical structure can be placed, and a portion connected to the tray portion 3a, and is connected to a power supply device 5 via an electric wire 7. It has a rod portion 3b. In this embodiment, the cathode 3 is made of stainless steel. The stainless steel is, for example, SUS304.

陽極２は、一端が電線６を介して電源装置５と接続するとともに、他端が試験片Ｔの表面と接触可能な部材である。本実施形態では、陽極２は銅である。 The anode 2 is a member whose one end is connected to the power supply device 5 via the electric wire 6 and whose other end can be brought into contact with the surface of the test piece T. In this embodiment, the anode 2 is copper.

陽極２と陰極３とを異種の金属にすることで、同種の金属とする場合と比べて陽極２－陰極３間に電位差が生じ、試験片Ｔの腐食を促進することができる。なお、陽極２及び陰極３は上記に限定されるものではなく、陽極２を白金、銅、ステンレスのうちから選択し、陰極３を白金、銅、ステンレスのうちから陽極２に選択した金属以外の金属を選択して用いても良い。費用面や腐食の効果を踏まえると、陽極２として銅を選択し、陰極３としてステンレスを選択するのがより好ましい。 When the anode 2 and the cathode 3 are made of different metals, a potential difference is generated between the anode 2 and the cathode 3 compared to when the anode 2 and the cathode 3 are made of the same metal, and corrosion of the test piece T can be accelerated. Note that the anode 2 and the cathode 3 are not limited to those mentioned above, and the anode 2 is selected from platinum, copper, and stainless steel, and the cathode 3 is made of a metal other than the metal selected for the anode 2 from among platinum, copper, and stainless steel. Any metal may be selected and used. Considering costs and corrosion effects, it is more preferable to select copper as the anode 2 and select stainless steel as the cathode 3.

台座４は、樹脂によって構成され、試験片Ｔを埋め込み可能な形状になっている。 The pedestal 4 is made of resin and has a shape in which the test piece T can be embedded.

電源装置５は、電圧や電流供給時間などを調整可能なものが用いられる。所定の時間及び所定の電圧で電気分解を実施するためである。 As the power supply device 5, one whose voltage, current supply time, etc. can be adjusted is used. This is to perform electrolysis for a predetermined time and at a predetermined voltage.

［腐食液］
次に、電解腐食に用いる腐食液について説明する。本実施形態に係る腐食液は、しゅう酸と、界面活性剤と、を含有する。腐食液は、電解腐食を行う対象の鋼材に応じて調製することができる。 [Corrosive liquid]
Next, the corrosive liquid used for electrolytic corrosion will be explained. The corrosive liquid according to this embodiment contains oxalic acid and a surfactant. The corrosive liquid can be prepared depending on the steel material to be electrolytically corroded.

本実施形態においては、電解腐食の対象鋼材として、機械構造用合金鋼材に分類される鋼材のうち、比較的耐腐食性が低い鋼材と、比較的耐腐食性が高い鋼材とを扱うことができる。比較的耐腐食性が低い鋼材の例としては、炭素（Ｃ）が０．２質量％、けい素（Ｓｉ）が０．９質量％、マンガン（Ｍｎ）が０．８質量％、クロム（Ｃｒ）が０．９質量％、残部が鉄（Ｆｅ）及び不可避的不純物の組成の鋼がある。比較的耐腐食性が高い鋼材の例としては、炭素（Ｃ）が０．２質量％、けい素（Ｓｉ）が０．２質量％、マンガン（Ｍｎ）が０．８質量％、クロム（Ｃｒ）が１．０質量％、残部が鉄（Ｆｅ）及び不可避的不純物の組成の鋼（いわゆるクロム鋼）がある。これらの機械構造用合金鋼材について、旧オーステナイト粒界を現出させるための腐食液の各成分を以下に説明する。 In this embodiment, steel materials classified as alloy steel materials for machine structures that have relatively low corrosion resistance and steel materials that have relatively high corrosion resistance can be treated as steel materials subject to galvanic corrosion. . Examples of steel materials with relatively low corrosion resistance include 0.2% by mass of carbon (C), 0.9% by mass of silicon (Si), 0.8% by mass of manganese (Mn), and 0.8% by mass of chromium (Cr). ) is 0.9% by mass, and the balance is iron (Fe) and unavoidable impurities. Examples of steel materials with relatively high corrosion resistance include 0.2% by mass of carbon (C), 0.2% by mass of silicon (Si), 0.8% by mass of manganese (Mn), and 0.8% by mass of chromium (Cr). ) is 1.0% by mass, and the balance is iron (Fe) and unavoidable impurities (so-called chromium steel). Regarding these alloy steel materials for machine structures, each component of the corrosive liquid for revealing prior austenite grain boundaries will be explained below.

＜しゅう酸＞
しゅう酸は、粒界の腐食を促進する物質として腐食液に含まれている。本実施形態では、しゅう酸二水和物として添加される。 <Oxalic acid>
Oxalic acid is contained in the corrosive solution as a substance that promotes corrosion of grain boundaries. In this embodiment, it is added as oxalic acid dihydrate.

しゅう酸の添加量が過多であると、鋼材組織が現出してしまう状態まで腐食が進行してしまう。一方、しゅう酸の添加量が過少であると、腐食は進まず、旧オーステナイト粒界を現出させることができない。 If the amount of oxalic acid added is too large, corrosion progresses to the point where the steel structure appears. On the other hand, if the amount of oxalic acid added is too small, corrosion will not proceed and prior austenite grain boundaries will not appear.

機械構造用合金鋼材のうち比較的耐腐食性の低い鋼材を電解腐食する場合、腐食反応を適切に進行させる観点から、しゅう酸二水和物を水１００ｃｍ3に対して０．０４～０．０６ｇ添加するのが好ましい。また、しゅう酸二水和物を水１００ｃｍ3に対して０．０５ｇ添加するのが、さらに好ましい。 When electrolytically corroding steel materials with relatively low corrosion resistance among alloy steel materials for machine structures, from the viewpoint of allowing the corrosion reaction to proceed appropriately, the amount of oxalic acid dihydrate per 100 cm 3 of water is 0.04 to 0. It is preferable to add 0.6g. Further, it is more preferable to add 0.05 g of oxalic acid dihydrate to 100 cm 3 of water.

機械構造用合金鋼材のうち比較的耐腐食性の高い鋼材を電解腐食する場合には、同様の観点から、しゅう酸二水和物を水１００ｃｍ3に対して０．０８～０．１２ｇ添加するのが好ましい。腐食反応を適切に進行させる観点では、しゅう酸二水和物を水１００ｃｍ3に対して０．１０ｇ添加するのが、さらに好ましい。 When electrolytically corroding steel materials with relatively high corrosion resistance among alloy steel materials for machine structures, from the same viewpoint, 0.08 to 0.12 g of oxalic acid dihydrate is added to 100 cm 3 of water. is preferable. From the viewpoint of appropriately advancing the corrosion reaction, it is more preferable to add 0.10 g of oxalic acid dihydrate per 100 cm 3 of water.

＜界面活性剤＞
界面活性剤は、粒界の腐食速度を調整する物質として腐食液に含まれる。本実施形態では、界面活性剤として、ドデシルベンゼンスルホン酸ナトリウムまたは中性洗剤を用いることができる。界面活性剤は、腐食反応を適切に進行させる観点から、水１００ｃｍ3に対して４ｇ含まれるのが好ましい。界面活性剤は、水１００ｃｍ3に対する含有量が４ｇ以上であっても腐食反応を適切に進行させる効果が頭打ちになるためである。なお、中性洗剤は、上記のものに限らず、イオン系界面活性剤を界面活性剤成分とする中性洗剤や、非イオン系界面活性剤を界面活性剤成分とする中性洗剤を用いることができる。 <Surfactant>
The surfactant is included in the corrosive solution as a substance that adjusts the corrosion rate of grain boundaries. In this embodiment, sodium dodecylbenzenesulfonate or a neutral detergent can be used as the surfactant. The surfactant is preferably contained in an amount of 4 g per 100 cm 3 of water from the viewpoint of allowing the corrosion reaction to proceed appropriately. This is because even if the content of the surfactant is 4 g or more per 100 cm 3 of water, the effect of promoting the corrosion reaction appropriately reaches a ceiling. Note that the neutral detergent is not limited to those mentioned above, but neutral detergents containing ionic surfactants as surfactant components or neutral detergents containing nonionic surfactants as surfactant components may be used. I can do it.

＜塩酸＞
機械構造用合金鋼材のうち比較的耐腐食性の高い鋼材を電解腐食させる場合には、しゅう酸と、界面活性剤とに加えて、さらに塩酸を含有する腐食液を用いる。塩酸を腐食液に添加するのは、不動態被膜を除去して鋼材の腐食を良好に進行させるためである。なお、機械構造用合金鋼材のうち比較的耐腐食性の低い鋼材を電解腐食させる場合には、腐食液に塩酸を添加しない。 <Hydrochloric acid>
When electrolytically corroding steel materials with relatively high corrosion resistance among alloy steel materials for machine structures, a corrosive solution containing hydrochloric acid in addition to oxalic acid and a surfactant is used. The reason why hydrochloric acid is added to the corrosive solution is to remove the passive film and promote corrosion of the steel material. Note that when electrolytically corroding steel materials with relatively low corrosion resistance among alloy steel materials for machine structures, hydrochloric acid is not added to the corrosive solution.

塩酸は、腐食性が高いため、添加量が過多であると鋼材組織が現出してしまう状態まで腐食が進行してしまう。そのため、塩酸は、腐食反応を適切に進行させる観点から、水１００ｃｍ3に対して０．５ｇ～２．００ｇ添加するのが好ましい。界面活性剤にドデシルベンゼンスルホン酸ナトリウムを用いる場合には、塩酸は、水１００ｃｍ3に対して１．００ｇ添加するのがさらに好ましい。また、界面活性剤に中性洗剤を用いる場合には、塩酸は、水１００ｃｍ3に対して１．５０ｇまたは２．００ｇ添加するのがさらに好ましい。 Since hydrochloric acid is highly corrosive, if it is added in an excessive amount, corrosion will progress to the point where the steel structure will appear. Therefore, it is preferable to add 0.5 g to 2.00 g of hydrochloric acid per 100 cm 3 of water from the viewpoint of promoting the corrosion reaction appropriately. When using sodium dodecylbenzenesulfonate as the surfactant, it is more preferable to add 1.00 g of hydrochloric acid per 100 cm 3 of water. Furthermore, when a neutral detergent is used as the surfactant, it is more preferable to add 1.50 g or 2.00 g of hydrochloric acid to 100 cm 3 of water.

［電解腐食方法］
次に、電解腐食装置１００による鋼材の電解腐食の方法について説明する。 [Electrolytic corrosion method]
Next, a method of electrolytic corrosion of steel materials using the electrolytic corrosion apparatus 100 will be explained.

＜比較的耐腐食性が低い鋼材の電解腐食方法＞
図２は、機械構造用合金鋼材のうち比較的耐腐食性が低い鋼材の電解腐食方法のプロセス図である。 <Electrolytic corrosion method for steel materials with relatively low corrosion resistance>
FIG. 2 is a process diagram of a galvanic corrosion method for steel materials with relatively low corrosion resistance among alloy steel materials for machine structures.

まず、電解腐食対象の機械構造用合金鋼材から所定の大きさの切片を切取り、組織観察用の試験片Ｔを作成する（ステップＳ１）。 First, a section of a predetermined size is cut from a mechanical structural alloy steel material to be electrolytically corroded to create a test piece T for microstructural observation (step S1).

図１に示すように、作成した試験片Ｔは、一方の面が露出するように台座４に埋め込まれる。試験片Ｔは、台座４ごと陰極３の受け皿部３ａに置かれて、腐食液に浸漬される。試験片Ｔの露出面に陽極２を接触させて、電源装置５から所定の電圧及び時間で電流を流すことで、試験片Ｔを電解腐食する（ステップＳ２）。腐食液の界面活性剤にドデシルベンゼンスルホン酸ナトリウムを用いる場合には、電圧０．８～１．２Ｖで５～７秒間電流を流して試験片Ｔを電解腐食するのが好ましい。また、電圧１．０Ｖで５秒間電流を流すのが、さらに好ましい。 As shown in FIG. 1, the prepared test piece T is embedded in the pedestal 4 so that one surface is exposed. The test piece T, together with the pedestal 4, is placed on the tray portion 3a of the cathode 3 and immersed in the corrosive liquid. The test piece T is electrolytically corroded by bringing the anode 2 into contact with the exposed surface of the test piece T and applying a current at a predetermined voltage and time from the power supply device 5 (step S2). When sodium dodecylbenzenesulfonate is used as a surfactant in the corrosive solution, it is preferable to electrolytically corrode the test piece T by passing a current at a voltage of 0.8 to 1.2 V for 5 to 7 seconds. Further, it is more preferable to flow a current at a voltage of 1.0V for 5 seconds.

対して、腐食液の界面活性剤に中性洗剤を用いる場合には、電圧２．８～３．２Ｖで５～７秒間電流を流して試験片Ｔを電解腐食するのが好ましい。また、電圧３Ｖで５秒間電流を流すのが、さらに好ましい。 On the other hand, when a neutral detergent is used as a surfactant in the corrosive solution, it is preferable to electrolytically corrode the test piece T by passing a current at a voltage of 2.8 to 3.2 V for 5 to 7 seconds. Further, it is more preferable to flow a current at a voltage of 3V for 5 seconds.

電解腐食を実施後には、電解腐食により生成される腐食生成物のうち、試験片Ｔの表面に付着している腐食生成物を試験片Ｔから除去するために、試験片Ｔを容器１から取り出して表面を脱脂綿で拭う（ステップＳ３）。その後、試験片Ｔを、エタノールで洗浄し（ステップＳ４）、ドライヤーで乾燥させて（ステップＳ５）、試験片Ｔの表面を光学顕微鏡で観察する（ステップＳ６）。 After performing electrolytic corrosion, the test piece T is taken out from the container 1 in order to remove from the test piece T the corrosion products that adhere to the surface of the test piece T among the corrosion products generated by the electrolytic corrosion. and wipe the surface with absorbent cotton (step S3). Thereafter, the test piece T is washed with ethanol (step S4), dried with a dryer (step S5), and the surface of the test piece T is observed with an optical microscope (step S6).

光学顕微鏡観察の結果、試験片Ｔの表面に、ＪＩＳ Ｇ０５５１に規定される鋼－結晶粒度の顕微鏡試験方法（以下、ＪＩＳ Ｇ０５５１に規定される方法と称する。）にて旧オーステナイト粒界を測定できる程度に粒界が現出していれば（ステップＳ６ ＹＥＳ）、電解腐食を完了させる（ＥＮＤ）。 As a result of optical microscopic observation, prior austenite grain boundaries can be measured on the surface of the test piece T using the steel-crystal grain size microscopic test method specified in JIS G0551 (hereinafter referred to as the method specified in JIS G0551). If grain boundaries have appeared to a certain degree (step S6 YES), the electrolytic corrosion is completed (END).

本実施形態に係る電解腐食は、緩やかに進行するように設定される。そのため、鋼材の腐食が過度に進行して鋼材組織が現出してしまうことを防止できる。また、本実施形態に係る電解腐食方法は、上記一連のステップを完了後に再度繰り返し行うことができる腐食反応であるため、試験片Ｔに旧オーステナイト粒界が現出するまで複数回実施することができるものである。光学顕微鏡の観察の結果、粒界の現出が不鮮明であれば（ステップＳ６ ＮＯ）、１回目の電解腐食と同一の条件（腐食液・電圧・腐食時間）で電解腐食を繰り返す。電解腐食は、ＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できる程度に試験片Ｔの表面全面に旧オーステナイト粒界が現出するまで繰り返す。 The electrolytic corrosion according to this embodiment is set to proceed slowly. Therefore, it is possible to prevent the corrosion of the steel material from progressing excessively and the steel structure from appearing. Furthermore, since the galvanic corrosion method according to the present embodiment is a corrosion reaction that can be repeated again after completing the series of steps described above, it can be carried out multiple times until prior austenite grain boundaries appear in the test piece T. It is possible. If the appearance of grain boundaries is unclear as a result of observation with an optical microscope (step S6 NO), electrolytic corrosion is repeated under the same conditions as the first electrolytic corrosion (corrosive solution, voltage, corrosion time). The electrolytic corrosion is repeated until prior austenite grain boundaries appear on the entire surface of the test piece T to the extent that prior austenite grain boundaries can be measured by the method specified in JIS G0551.

ところで、上記方法では、ステップＳ３にて電解腐食により生成される電解腐食物を試験片Ｔから除去する。この工程を行う理由は以下の通りである。電解腐食を繰り返す場合、仮に試験片Ｔの表面に腐食生成物が付着したまま電解腐食を行うと、腐食生成物が付着した部分では、腐食生成物が付着していない部分よりも電解腐食が促進されて、鋼材組織まで現出するおそれがある。これに対して、本実施形態ではステップＳ３にて試験片Ｔの表面から腐食生成物を除去する。これによれば、腐食生成物の付着によって電解腐食が部分的に促進されることを防ぐことができる。したがって、試験片Ｔの表面全体を均一に電解腐食させて、試験片Ｔの表面全体に旧オーステナイト粒界を現出させることができる。 By the way, in the above method, electrolytic corrosion products generated by electrolytic corrosion are removed from the test piece T in step S3. The reason for performing this step is as follows. When electrolytic corrosion is repeated, if electrolytic corrosion is performed with corrosion products still attached to the surface of the test piece T, the electrolytic corrosion will accelerate in the areas where the corrosion products have adhered than in the areas where the corrosion products have not adhered. There is a risk that the structure of the steel material may be exposed. In contrast, in this embodiment, corrosion products are removed from the surface of the test piece T in step S3. According to this, it is possible to prevent electrolytic corrosion from being partially accelerated due to attachment of corrosion products. Therefore, the entire surface of the test piece T can be electrolytically corroded uniformly, and prior austenite grain boundaries can be made to appear on the entire surface of the test piece T.

＜比較的耐腐食性が高い鋼材の電解腐食方法＞
図３は、機械構造用合金鋼材のうち比較的耐腐食性が高い鋼材の電解腐食方法のプロセス図である。この方法は、図２の方法と比べて、電解腐食（ステップＳ１２）の最適条件が相違する。腐食液の界面活性剤にドデシルベンゼンスルホン酸ナトリウムを用いる場合には、電圧１．８～２．２Ｖで１５～２０秒間電流を流して試験片Ｔを電解腐食するのが好ましい。また、電圧２．０Ｖで２０秒間電流を流すのが、さらに好ましい。 <Electrolytic corrosion method for steel materials with relatively high corrosion resistance>
FIG. 3 is a process diagram of a galvanic corrosion method for steel materials with relatively high corrosion resistance among alloy steel materials for machine structures. This method differs from the method shown in FIG. 2 in the optimum conditions for electrolytic corrosion (step S12). When sodium dodecylbenzenesulfonate is used as a surfactant in the corrosive solution, it is preferable to electrolytically corrode the test piece T by passing a current at a voltage of 1.8 to 2.2 V for 15 to 20 seconds. Further, it is more preferable to flow a current at a voltage of 2.0V for 20 seconds.

対して、腐食液の界面活性剤に中性洗剤を用いる場合には、電圧を１．８～３．０Ｖにすることができ、電圧１．８～２．２Ｖで１５～２０秒間電流を流して試験片Ｔを電解腐食するのが好ましい。また、電圧２Ｖで２０秒間電流を流すのがさらに好ましい。上記の他にも、電解腐食（ステップＳ１２）を実施し試験片Ｔの表面を脱脂綿で拭った（ステップＳ１３）後に、試験片Ｔの表面をバフ研磨し（ステップＳ１４）、再度試験片Ｔの表面を脱脂綿で拭う（ステップＳ１５）工程を加える点でも、図２の方法と相違する。 On the other hand, when a neutral detergent is used as a surfactant in the corrosive liquid, the voltage can be set to 1.8 to 3.0V, and a current is applied for 15 to 20 seconds at a voltage of 1.8 to 2.2V. It is preferable to electrolytically corrode the test piece T. Further, it is more preferable to flow a current at a voltage of 2V for 20 seconds. In addition to the above, after carrying out electrolytic corrosion (step S12) and wiping the surface of the test piece T with absorbent cotton (step S13), the surface of the test piece T is buffed (step S14), and the surface of the test piece T is polished again. This method is also different from the method shown in FIG. 2 in that a step of wiping the surface with absorbent cotton (step S15) is added.

図３のステップＳ１１、Ｓ１３は図２のステップＳ１、Ｓ３に相当する。図３のステップＳ１５は図２のステップＳ３に相当する。図３のステップＳ１６～Ｓ１８は図２のステップＳ４～Ｓ６に相当する。そのため、これらの説明は割愛する。 Steps S11 and S13 in FIG. 3 correspond to steps S1 and S3 in FIG. 2. Step S15 in FIG. 3 corresponds to step S3 in FIG. Steps S16 to S18 in FIG. 3 correspond to steps S4 to S6 in FIG. Therefore, these explanations are omitted.

図３に示す方法で、バフ研磨の工程を加える理由は以下の通りである。比較的耐腐食性が高い鋼材の電解腐食する場合には、鋼材の不動態被膜を除去するために塩酸を添加する。但し、塩酸を添加した腐食液で電解腐食を行うと、試験片Ｔの表面には腐食ピットが生成される場合がある。試験片Ｔの表面に腐食ピットが生成されると、旧オーステナイト粒界の観察や測定に支障をきたすおそれがある。そこで、機械構造用合金鋼材のうち比較的耐腐食性が高い鋼材の電解腐食（言い換えれば、腐食液に塩酸を添加する場合の電解腐食）を行うときは、電解腐食を実施後に、バフ研磨によって試験片Ｔの表面を研磨し（ステップＳ１４）、再度試験片Ｔの表面を脱脂綿で拭う（ステップＳ１５）ことで、電解腐食により試験片Ｔに生成される腐食ピット及びバフ研磨で生じた粉末を除去する。これにより、ステップＳ１８での旧オーステナイト粒界の観察を良好に行うことができる。 The reason for adding the buffing step to the method shown in FIG. 3 is as follows. When electrolytically corroding a steel material that has relatively high corrosion resistance, hydrochloric acid is added to remove the passive film of the steel material. However, when electrolytic corrosion is performed using a corrosive solution containing hydrochloric acid, corrosion pits may be generated on the surface of the test piece T. If corrosion pits are generated on the surface of the test piece T, there is a possibility that observation and measurement of prior austenite grain boundaries will be hindered. Therefore, when performing galvanic corrosion (in other words, galvanic corrosion when hydrochloric acid is added to the corrosive solution) of steel materials with relatively high corrosion resistance among alloy steel materials for machine structures, after performing galvanic corrosion, buffing is performed. By polishing the surface of the test piece T (step S14) and wiping the surface of the test piece T again with absorbent cotton (step S15), corrosion pits generated on the test piece T due to electrolytic corrosion and powder generated during buffing are removed. Remove. Thereby, prior austenite grain boundaries can be well observed in step S18.

［作用効果］
続いて、これまで説明した実施形態の作用効果について説明する。 [Effect]
Next, the effects of the embodiments described so far will be described.

本実施形態によれば、機械構造用合金鋼材の旧オーステナイト粒界の現出方法として、しゅう酸と、ドデシルベンゼンスルホン酸ナトリウムまたは中性洗剤と、を含有する腐食液を用いて電解腐食を行う。これによれば、ピクリン酸を用いることなく、機械構造用合金鋼材の旧オーステナイト粒界を現出させることができる（請求項１に対応する効果）。 According to this embodiment, as a method for revealing prior austenite grain boundaries in alloy steel materials for machine structures, electrolytic corrosion is performed using a corrosive solution containing oxalic acid and sodium dodecylbenzenesulfonate or a neutral detergent. . According to this, the prior austenite grain boundaries of the alloy steel for mechanical structures can be exposed without using picric acid (effect corresponding to claim 1).

また、旧オーステナイト粒界が現出するまで電解腐食を複数回実施する。これによれば、緩やかに進行するように設定される電解腐食であって、一連のステップを終了した後に再度同じステップを繰り返すことができる腐食反応である電解腐食を複数回実施することにより、機械構造用合金鋼の旧オーステナイト粒界を現出させることができる（請求項２に対応する効果）。 Furthermore, electrolytic corrosion is performed multiple times until prior austenite grain boundaries appear. According to this, by performing electrolytic corrosion multiple times, which is a corrosion reaction that is set to progress slowly and can repeat the same step again after completing a series of steps, Prior austenite grain boundaries of structural alloy steel can be exposed (effect corresponding to claim 2).

また、電解腐食により生成される腐食生成物を機械構造用合金鋼材から除去する。これによれば、電解腐食を複数回行う場合、腐食生成物の付着によって電解腐食が部分的に促進されることを防ぐことができる。つまり、試験片Ｔの表面全体を均一に電解腐食させて、試験片Ｔの表面全体に旧オーステナイト粒界を現出させることができる（請求項３に対応する効果）。 Further, corrosion products generated by galvanic corrosion are removed from alloy steel materials for machine structures. According to this, when electrolytic corrosion is performed multiple times, it is possible to prevent the electrolytic corrosion from being partially accelerated due to attachment of corrosion products. That is, the entire surface of the test piece T can be electrolytically corroded uniformly, and prior austenite grain boundaries can be made to appear on the entire surface of the test piece T (effect corresponding to claim 3).

また、機械構造用合金鋼材はクロム鋼である場合には、腐食液は、さらに塩酸を含有する。これによれば、比較的耐腐食性が高い鋼材であるクロム鋼を電解腐食するにあたり、不動態被膜を除去して、鋼材の腐食を良好に進行させることができる（請求項４，５に対応する効果）。 Moreover, when the alloy steel material for machine structures is chromium steel, the corrosive liquid further contains hydrochloric acid. According to this, when electrolytically corroding chrome steel, which is a steel material with relatively high corrosion resistance, the passive film can be removed and corrosion of the steel material can progress favorably (corresponding to claims 4 and 5). effect).

また、機械構造用合金鋼材はクロム鋼であって、腐食液はさらに塩酸を含有する場合、電解腐食により機械構造用合金鋼材に生成される腐食ピットを除去する。これによれば、旧オーステナイト粒界の観察を良好に行うことができる（請求項６に対応する効果）。 Further, when the alloy steel material for machine structure is chromium steel and the corrosive liquid further contains hydrochloric acid, corrosion pits generated in the alloy steel material for machine structure due to electrolytic corrosion are removed. According to this, prior austenite grain boundaries can be observed satisfactorily (effect corresponding to claim 6).

本発明の実施形態に係る方法と、当該方法との比較用の方法とで、機械構造用合金鋼材の腐食を行い、旧オーステナイト粒界の現出について評価を行った。 A mechanical structural alloy steel material was corroded using a method according to an embodiment of the present invention and a method for comparison with the method, and the appearance of prior austenite grain boundaries was evaluated.

［評価方法］
後述する［実施例及び比較例］に示す腐食方法と条件と腐食液とで、鋼材の試験片Ｔの腐食を実施後、光学顕微鏡により試験片Ｔの表面を観察し、旧オーステナイト粒界の現出結果を評価した。旧オーステナイト粒界の現出結果の評価は、ＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できる程度に試験片Ｔの表面全面に旧オーステナイト粒界が現出した場合をＡと評価し、試験片Ｔの表面に旧オーステナイト粒界が部分的にしか現出していないためＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できない場合をＢと評価し、試験片Ｔの表面に旧オーステナイト粒界が確認できずＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できない場合をＣと評価した。つまり、現出結果の評価がＡの場合のみ、ＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できる。 [Evaluation method]
After corroding a steel specimen T using the corrosion method, conditions, and corrosive liquid shown in [Examples and Comparative Examples] described below, the surface of the specimen T was observed using an optical microscope to determine the appearance of prior austenite grain boundaries. The results were evaluated. The appearance of prior austenite grain boundaries is evaluated as A when prior austenite grain boundaries appear on the entire surface of the test piece T to the extent that prior austenite grain boundaries can be measured using the method specified in JIS G0551. However, if the prior austenite grain boundaries are only partially exposed on the surface of the test piece T, and therefore the prior austenite grain boundaries cannot be measured using the method specified in JIS G0551, it is evaluated as B. The case where the prior austenite grain boundary could not be confirmed and the prior austenite grain boundary could not be measured by the method specified in JIS G0551 was evaluated as C. That is, only when the evaluation of the appearance result is A, prior austenite grain boundaries can be measured by the method specified in JIS G0551.

［実施例及び比較例］
＜比較的耐腐食性が低い鋼材の腐食＞
機械構造用合金鋼のうち比較的耐腐食性が低い鋼材である、炭素（Ｃ）が０．２質量％、けい素（Ｓｉ）が０．９質量％、マンガン（Ｍｎ）が０．８質量％、クロム（Ｃｒ）が０．９質量％、残部が鉄（Ｆｅ）及び不可避的不純物の組成の鋼（以下、鋼Ａと称する）の腐食方法について、本発明の実施例、比較例、及び参考例を以下に示す。 [Examples and comparative examples]
<Corrosion of steel materials with relatively low corrosion resistance>
A steel material with relatively low corrosion resistance among alloy steels for machine structures, containing 0.2% by mass of carbon (C), 0.9% by mass of silicon (Si), and 0.8% by mass of manganese (Mn). %, chromium (Cr) is 0.9 mass %, the balance is iron (Fe), and the corrosion method of steel (hereinafter referred to as steel A) has a composition of unavoidable impurities. Examples, comparative examples, and A reference example is shown below.

＜実施例１＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．０５ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧１Ｖ、腐食時間５秒の条件での電解腐食を旧オーステナイト粒界の現出状態を見ながら５回行った（５回で旧オーステナイト粒界が現出した）。 <Example 1>
The container 1 of the electrolytic corrosion apparatus 100 contains a corrosive solution prepared at room temperature with a composition of 0.05 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water, and the anode 2 is made of copper and the cathode 3 is made of copper. Using stainless steel, electrolytic corrosion was performed 5 times under the conditions of a set voltage of 1 V and a corrosion time of 5 seconds while observing the appearance of prior austenite grain boundaries (prior austenite grain boundaries appeared after 5 times).

＜実施例２＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．０５ｇ、中性洗剤４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、設定電圧を３Ｖにした以外は実施例１と同様にして電解腐食を行った。 <Example 2>
Example 1 except that the container 1 of the electrolytic corrosion apparatus 100 contained a corrosive liquid having a composition of 0.05 g of oxalic acid, 4.00 g of neutral detergent, and 100 cm 3 of water prepared at room temperature, and the set voltage was set to 3V. Electrolytic corrosion was carried out in the same manner.

＜比較例１＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．１０ｇ、塩酸１．００ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２をステンレスに、陰極３をステンレスにして、設定電圧２Ｖ、腐食時間２０秒の条件での電解腐食を、実施例１に合わせて５回行った。 <Comparative example 1>
The container 1 of the electrolytic corrosion apparatus 100 contains a corrosive solution prepared at room temperature with a composition of 0.10 g of oxalic acid, 1.00 g of hydrochloric acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water, and the anode 2 is made of stainless steel. Next, the cathode 3 was made of stainless steel, and electrolytic corrosion was performed five times in accordance with Example 1 under the conditions of a set voltage of 2 V and a corrosion time of 20 seconds.

＜比較例２＞
電解腐食装置１００の陽極２をステンレスにして、設定電圧を３Ｖにした以外は実施例１と同様にして電解腐食を行った。 <Comparative example 2>
Electrolytic corrosion was carried out in the same manner as in Example 1 except that the anode 2 of the electrolytic corrosion apparatus 100 was made of stainless steel and the set voltage was 3V.

＜比較例３＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸１０．０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧３Ｖの条件での電解腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 3>
In the container 1 of the electrolytic corrosion apparatus 100, a corrosive solution having the composition of 10.0 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water prepared at room temperature is stored, the anode 2 is made of copper, and the cathode 3 is made of copper. Stainless steel was used and electrolytic corrosion was performed at a set voltage of 3V. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例４＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸１０．０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧１０Ｖの条件での電解腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 4>
In the container 1 of the electrolytic corrosion apparatus 100, a corrosive solution having the composition of 10.0 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water prepared at room temperature is stored, the anode 2 is made of copper, and the cathode 3 is made of copper. Stainless steel was used and electrolytic corrosion was performed under the condition of a set voltage of 10V. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例５＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．１０ｇ、塩酸１．００ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３を銅にして、設定電圧２Ｖ、腐食時間２０秒の条件での電解腐食を実施例１に合わせて５回行った。 <Comparative example 5>
The container 1 of the electrolytic corrosion apparatus 100 contains a corrosive solution prepared at room temperature with a composition of 0.10 g of oxalic acid, 1.00 g of hydrochloric acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water, and the anode 2 is made of copper. Next, the cathode 3 was made of copper, and electrolytic corrosion was performed five times as in Example 1 under the conditions of a set voltage of 2 V and a corrosion time of 20 seconds.

＜比較例６＞
電解腐食装置１００の陰極３を銅にした以外は実施例１と同様にして電解腐食を行った。 <Comparative example 6>
Electrolytic corrosion was carried out in the same manner as in Example 1 except that the cathode 3 of the electrolytic corrosion apparatus 100 was made of copper.

＜比較例７＞
常温下で作製したしゅう酸１０．０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液（比較例３，４の腐食液と同一の腐食液）に浸漬させて、液浸腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 7>
It was immersed in a corrosive liquid (same corrosive liquid as those used in Comparative Examples 3 and 4) prepared at room temperature with a composition of 10.0 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water. Corroded. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例８＞
常温下で作製したしゅう酸０．１０ｇ、塩酸１．００ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液（比較例１，５の腐食液と同一の腐食液）に浸漬させて、液浸腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 8>
Immersed in a corrosive liquid (same corrosive liquid as the corrosive liquid of Comparative Examples 1 and 5) prepared at room temperature and having a composition of 0.10 g of oxalic acid, 1.00 g of hydrochloric acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water. Then, immersion corrosion was performed. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例９＞
常温下で作製したしゅう酸０．０５ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液（実施例１，比較例２，６の腐食液と同一の腐食液）に浸漬させて、液浸腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 9>
It was immersed in a corrosive solution (same corrosive solution as those used in Example 1, Comparative Examples 2 and 6) prepared at room temperature and having a composition of 0.05 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water. Then, immersion corrosion was performed. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜参考例１＞
常温下で作製したピクリン酸４．００ｇ、しゅう酸０．１０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液に６００秒浸漬させて、液浸腐食を行った（従来から知られている旧オーステナイト粒界の現出方法）。 <Reference example 1>
Immersion corrosion was performed by immersing for 600 seconds in a corrosive solution prepared at room temperature with a composition of 4.00 g of picric acid, 0.10 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water. Known methods of appearance of prior austenite grain boundaries).

［比較的耐腐食性が低い鋼材の腐食結果］
上記した実施例、比較例、参考例の結果を第１表に示す。 [Corrosion results of steel materials with relatively low corrosion resistance]
Table 1 shows the results of the above examples, comparative examples, and reference examples.

Figure 0007369063000001
Figure 0007369063000001

第１表に示すように、評価試験を行った結果、実施例１，実施例２では、ピクリン酸を用いた方法の参考例１と同程度に、試験片Ｔの表面全面に旧オーステナイト粒界が現出した（評価Ａ）。図４Ａは、実施例１の条件による旧オーステナイト粒界現出結果を示す鋼Ａの組織の光学顕微鏡写真である。図４Ｂは、実施例２の条件による旧オーステナイト粒界現出結果を示す鋼Ａの組織の光学顕微鏡写真である。このように、実施例１，実施例２の条件による電解腐食によれば、ピクリン酸を用いることなく、鋼Ａの旧オーステナイト粒界を現出させることができる。 As shown in Table 1, as a result of the evaluation test, in Examples 1 and 2, prior austenite grain boundaries were formed on the entire surface of the test piece T to the same extent as in Reference Example 1 using the method using picric acid. appeared (rating A). FIG. 4A is an optical micrograph of the structure of Steel A showing the appearance of prior austenite grain boundaries under the conditions of Example 1. FIG. 4B is an optical micrograph of the structure of Steel A showing the appearance of prior austenite grain boundaries under the conditions of Example 2. As described above, according to the electrolytic corrosion under the conditions of Examples 1 and 2, the prior austenite grain boundaries of Steel A can be exposed without using picric acid.

また、比較例１，比較例２，比較例５，比較例６に示すように、陽極２と陰極３とが同種の金属である場合では、旧オーステナイト粒界は、部分的にしか現出しない（評価Ｂ）か、確認することができない（評価Ｃ）ことが分かる。例えば、図４Ｃは、比較例６の条件による旧オーステナイト粒界現出結果を示す鋼Ａの組織の光学顕微鏡写真である。図４Ｃに示すように、陽極２と陰極３とが銅（同種の金属）であると、他の条件が実施例１と同一であっても、旧オーステナイト粒界を部分的にしか現出させることができないことがわかる。実施例１，実施例２，比較例１，比較例２，比較例５，比較例６の結果より、陽極２と陰極３とは、異なる金属である方が良いことが分かる。 Furthermore, as shown in Comparative Example 1, Comparative Example 2, Comparative Example 5, and Comparative Example 6, when the anode 2 and the cathode 3 are made of the same type of metal, the prior austenite grain boundaries appear only partially. (Evaluation B) or cannot be confirmed (Evaluation C). For example, FIG. 4C is an optical micrograph of the structure of Steel A showing the appearance of prior austenite grain boundaries under the conditions of Comparative Example 6. As shown in FIG. 4C, when the anode 2 and the cathode 3 are made of copper (same metal), the prior austenite grain boundaries only partially appear even if the other conditions are the same as in Example 1. I know that I can't do it. From the results of Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 5, and Comparative Example 6, it can be seen that it is better for the anode 2 and the cathode 3 to be made of different metals.

また、比較例３，比較例４に示すように、陽極２と陰極３とが異なる金属であっても、電圧を高く設定し、しゅう酸の含有量が実施例１，実施例２よりも過剰な場合には、旧オーステナイト粒界を確認することができない（評価Ｃ）ことがわかる。例えば、図４Ｄは、しゅう酸の含有量が過剰な腐食液を用いた条件による旧オーステナイト粒界現出結果を示す鋼Ａの組織の光学顕微鏡写真である。図４Ｄに示すように、この場合には鋼材組織が現出するまで腐食が進んでおり、旧オーステナイト粒界を確認することができない。 In addition, as shown in Comparative Examples 3 and 4, even if the anode 2 and the cathode 3 are made of different metals, the voltage is set high and the content of oxalic acid is higher than in Examples 1 and 2. It can be seen that in such cases, prior austenite grain boundaries cannot be confirmed (evaluation C). For example, FIG. 4D is an optical micrograph of the structure of Steel A showing the appearance of prior austenite grain boundaries under conditions using a corrosive solution containing excessive oxalic acid. As shown in FIG. 4D, in this case, corrosion has progressed until the steel structure appears, and prior austenite grain boundaries cannot be confirmed.

また、比較例７，比較例８，比較例９，参考例１に示すように、ピクリン酸を含有する腐食液を用いた液浸腐食（参考例１）でなければ、ＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できる程度に試験片Ｔの表面全面に旧オーステナイト粒界を現出させることができないことが分かる。ピクリン酸を含有しない腐食液による液浸腐食では、実施例１と同一の腐食液による液浸腐食（比較例９）であっても、また、粒界腐食を促進する成分（しゅう酸、塩酸）が実施例１の腐食液よりも多い腐食液（比較例７，比較例８）であっても、いずれも試験片Ｔの表面全面に旧オーステナイト粒界を現出させることができない（評価Ｃ）ことが分かる。 In addition, as shown in Comparative Example 7, Comparative Example 8, Comparative Example 9, and Reference Example 1, unless it is liquid immersion corrosion using a corrosive solution containing picric acid (Reference Example 1), it is specified in JIS G0551. It can be seen that prior austenite grain boundaries cannot be made to appear over the entire surface of test piece T to the extent that prior austenite grain boundaries can be measured by this method. In immersion corrosion using a corrosive solution that does not contain picric acid, even in immersion corrosion using the same corrosive solution as in Example 1 (Comparative Example 9), components that promote intergranular corrosion (oxalic acid, hydrochloric acid) Even if the corrosive liquid is larger than the corrosive liquid of Example 1 (Comparative Example 7, Comparative Example 8), prior austenite grain boundaries cannot be made to appear on the entire surface of the test piece T in either case (evaluation C) I understand that.

このことから、本実施形態に係る実施例１，実施例２の方法によれば、ピクリン酸を用いることなく、機械構造用合金鋼材である鋼Ａの旧オーステナイト粒界を現出させることができる。 From this, according to the methods of Examples 1 and 2 according to the present embodiment, the prior austenite grain boundaries of Steel A, which is an alloy steel material for machine structures, can be exposed without using picric acid. .

＜比較的耐腐食性が高い鋼材の腐食＞
次に、機械構造用合金鋼材のうち比較的耐腐食性が高い鋼材である炭素（Ｃ）が０．２質量％、けい素（Ｓｉ）が０．２質量％、マンガン（Ｍｎ）が０．８質量％、クロム（Ｃｒ）が１．０質量％、残部が鉄（Ｆｅ）及び不可避的不純物の組成の鋼（以下、鋼Ｂと称する。鋼Ｂはいわゆるクロム鋼である。）について、本発明の実施例、比較例、及び参考例を以下に示す。 <Corrosion of steel materials with relatively high corrosion resistance>
Next, carbon (C), which is a steel material with relatively high corrosion resistance among alloy steel materials for machine structures, is 0.2% by mass, silicon (Si) is 0.2% by mass, and manganese (Mn) is 0.2% by mass. Regarding steel with a composition of 8% by mass, 1.0% by mass of chromium (Cr), the balance being iron (Fe), and unavoidable impurities (hereinafter referred to as steel B. Steel B is a so-called chromium steel), this book Examples, comparative examples, and reference examples of the invention are shown below.

＜実施例３＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．１０ｇ、塩酸１．００ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧２Ｖ、腐食時間２０秒の条件での電解腐食を旧オーステナイト粒界の現出状態を見ながら５回行った（５回で旧オーステナイト粒界が現出した。）。 <Example 3>
The container 1 of the electrolytic corrosion apparatus 100 contains a corrosive solution prepared at room temperature with a composition of 0.10 g of oxalic acid, 1.00 g of hydrochloric acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water, and the anode 2 is made of copper. Next, the cathode 3 was made of stainless steel, and electrolytic corrosion was performed 5 times under the conditions of a set voltage of 2 V and a corrosion time of 20 seconds while observing the state of appearance of prior austenite grain boundaries (prior austenite grain boundaries appeared after 5 times). did.).

＜実施例４＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．１０ｇ、塩酸１．５０ｇ、中性洗剤４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧３Ｖ、腐食時間２０秒の条件での電解腐食を旧オーステナイト粒界の現出状態を見ながら５回行った（５回で旧オーステナイト粒界が現出した。）。 <Example 4>
In the container 1 of the electrolytic corrosion apparatus 100, a corrosive solution prepared at room temperature with a composition of 0.10 g of oxalic acid, 1.50 g of hydrochloric acid, 4.00 g of neutral detergent, and 100 cm 3 of water was stored, and the anode 2 was made of copper. The cathode 3 was made of stainless steel, and electrolytic corrosion was performed five times under conditions of a set voltage of 3 V and a corrosion time of 20 seconds while observing the appearance of prior austenite grain boundaries (prior austenite grain boundaries appeared after five times). ).

＜比較例１０＞
電解腐食装置１００の陽極２をステンレスにした以外は実施例３と同様にして電解腐食を行った。 <Comparative example 10>
Electrolytic corrosion was carried out in the same manner as in Example 3 except that the anode 2 of the electrolytic corrosion apparatus 100 was made of stainless steel.

＜比較例１１＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．０５ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２をステンレスに、陰極３をステンレスにして、設定電圧３Ｖ、腐食時間５秒の条件での電解腐食を実施例３，４に合わせて５回行った。 <Comparative example 11>
In the container 1 of the electrolytic corrosion apparatus 100, a corrosive solution prepared at room temperature with a composition of 0.05 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water was placed, the anode 2 was made of stainless steel, and the cathode 3 was made of stainless steel. Stainless steel was used, and electrolytic corrosion was performed five times in accordance with Examples 3 and 4 under the conditions of a set voltage of 3 V and a corrosion time of 5 seconds.

＜比較例１２＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸１０．０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧３Ｖの条件での電解腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 12>
In the container 1 of the electrolytic corrosion apparatus 100, a corrosive solution having the composition of 10.0 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water prepared at room temperature is stored, the anode 2 is made of copper, and the cathode 3 is made of copper. Stainless steel was used and electrolytic corrosion was performed at a set voltage of 3V. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例１３＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸１０．０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３をステンレスにして、設定電圧１０Ｖの条件での電解腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 13>
In the container 1 of the electrolytic corrosion apparatus 100, a corrosive solution having the composition of 10.0 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water prepared at room temperature is stored, the anode 2 is made of copper, and the cathode 3 is made of copper. Stainless steel was used and electrolytic corrosion was performed under the condition of a set voltage of 10V. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例１４＞
電解腐食装置１００の陰極３を銅にした以外は実施例３と同様にして電解腐食を行った。 <Comparative example 14>
Electrolytic corrosion was carried out in the same manner as in Example 3 except that the cathode 3 of the electrolytic corrosion apparatus 100 was made of copper.

＜比較例１５＞
電解腐食装置１００の容器１に、常温下で作製したしゅう酸０．０５ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液を収容し、陽極２を銅に、陰極３を銅にして、設定電圧１Ｖ、腐食時間５秒の条件での電解腐食を実施例３，４に合わせて５回行った。 <Comparative Example 15>
The container 1 of the electrolytic corrosion apparatus 100 contains a corrosive solution prepared at room temperature with a composition of 0.05 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water, and the anode 2 is made of copper and the cathode 3 is made of copper. Using copper, electrolytic corrosion was carried out five times in total under the conditions of a set voltage of 1 V and a corrosion time of 5 seconds in accordance with Examples 3 and 4.

＜比較例１６＞
常温下で作製したしゅう酸１０．０ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液（比較例１２，１３の腐食液と同一の腐食液）に浸漬させて、液浸腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 16>
It was immersed in a corrosive liquid (same corrosive liquid as those used in Comparative Examples 12 and 13) prepared at room temperature with a composition of 10.0 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water. Corroded. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例１７＞
常温下で作製したしゅう酸０．１０ｇ、塩酸１．００ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液（実施例３，比較例１０，比較例１４の腐食液と同一の腐食液）に浸漬させて、液浸腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 17>
A corrosive liquid prepared at room temperature with a composition of 0.10 g of oxalic acid, 1.00 g of hydrochloric acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm3 of water (same as the corrosive liquid of Example 3, Comparative Example 10, and Comparative Example 14) Immersion corrosion was carried out by immersing it in a corrosive solution (corrosive liquid). The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜比較例１８＞
常温下で作製したしゅう酸０．０５ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成の腐食液（比較例１１，１５の腐食液と同一の腐食液）に浸漬させて、液浸腐食を行った。腐食時間及び腐食回数は、変更しても現出結果が変わらなかったため、表記を省略している。 <Comparative example 18>
It was immersed in a corrosive liquid (the same corrosive liquid as those used in Comparative Examples 11 and 15) prepared at room temperature with the composition of 0.05 g of oxalic acid, 4.00 g of sodium dodecylbenzenesulfonate, and 100 cm 3 of water. Corroded. The corrosion time and the number of corrosion times are omitted because the appearance results did not change even if they were changed.

＜参考例２＞
ピクリン酸４．００ｇ、ドデシルベンゼンスルホン酸ナトリウム４．００ｇ、水１００ｃｍ3の組成で６０℃の腐食液に３００秒浸漬させて、液浸腐食を行った（従来から知られている旧オーステナイト粒界の現出方法）。 <Reference example 2>
Immersion corrosion was performed by immersing the composition of 4.00 g of picric acid, 4.00 g of sodium dodecylbenzene sulfonate, and 100 cm of water in a corrosive solution at 60°C for 300 seconds. method of appearance).

［比較的耐腐食性が高い鋼材の腐食結果］
上記した実施例、比較例、参考例の結果を第２表に示す。 [Corrosion results of steel materials with relatively high corrosion resistance]
Table 2 shows the results of the above examples, comparative examples, and reference examples.

Figure 0007369063000002
Figure 0007369063000002

第２表に示すように、評価試験を行った結果、実施例３，実施例４では、ピクリン酸を用いた方法の参考例２と同程度に試験片Ｔの表面全面に旧オーステナイト粒界が現出した（評価Ａ）。図５Ａは、実施例３の条件による旧オーステナイト粒界現出結果を示す鋼Ｂの組織の光学顕微鏡写真である。図５Ｂは、実施例４の条件による旧オーステナイト粒界現出結果を示す鋼Ｂの組織の光学顕微鏡写真である。このように、実施例３，実施例４の条件による電解腐食によれば、ピクリン酸を用いることなく、鋼Ｂの旧オーステナイト粒界を現出させることができる。 As shown in Table 2, as a result of the evaluation test, in Examples 3 and 4, prior austenite grain boundaries were present on the entire surface of the test piece T to the same extent as in Reference Example 2 using the method using picric acid. Appeared (rating A). FIG. 5A is an optical micrograph of the structure of Steel B showing the appearance of prior austenite grain boundaries under the conditions of Example 3. FIG. 5B is an optical micrograph of the structure of Steel B showing the appearance of prior austenite grain boundaries under the conditions of Example 4. As described above, according to the electrolytic corrosion under the conditions of Examples 3 and 4, the prior austenite grain boundaries of Steel B can be exposed without using picric acid.

また、比較例１０，比較例１１，比較例１４，比較例１５に示すように、陽極２と陰極３とが同種の金属である場合では、旧オーステナイト粒界は部分的にしか現出しない（評価Ｂ）か、確認することができない（評価Ｃ）ことが分かる。例えば、図５Ｃは、比較例１０の条件による旧オーステナイト粒界現出結果を示す鋼Ｂの組織の光学顕微鏡写真である。図５Ｃに示すように、陽極２と陰極３とが銅（同種の金属）であると、他の条件が実施例３と同一であっても、旧オーステナイト粒界を部分的にしか現出させることができないことがわかる。実施例３，実施例４，比較例１０，比較例１１，比較例１４，比較例１５の結果より、陽極２と陰極３とは、異なる金属である方が良いことが分かる。 Furthermore, as shown in Comparative Example 10, Comparative Example 11, Comparative Example 14, and Comparative Example 15, when the anode 2 and the cathode 3 are made of the same type of metal, the prior austenite grain boundaries only partially appear ( It can be seen that either the evaluation is B) or it cannot be confirmed (Evaluation C). For example, FIG. 5C is an optical micrograph of the structure of Steel B showing the appearance of prior austenite grain boundaries under the conditions of Comparative Example 10. As shown in FIG. 5C, when the anode 2 and the cathode 3 are made of copper (same type of metal), the prior austenite grain boundaries only partially appear even if the other conditions are the same as in Example 3. I know that I can't do it. From the results of Example 3, Example 4, Comparative Example 10, Comparative Example 11, Comparative Example 14, and Comparative Example 15, it can be seen that it is better for the anode 2 and the cathode 3 to be made of different metals.

また、比較例１２，比較例１３に示すように、陽極２と陰極３とが異なる金属であっても、電圧を高く設定し、しゅう酸の含有量が実施例３，実施例４よりも過剰で、塩酸を含有しない腐食液では、旧オーステナイト粒界を確認することができない（評価Ｃ）ことがわかる。 In addition, as shown in Comparative Examples 12 and 13, even if the anode 2 and the cathode 3 are made of different metals, the voltage is set high and the content of oxalic acid is higher than in Examples 3 and 4. It can be seen that prior austenite grain boundaries cannot be confirmed with a corrosive solution that does not contain hydrochloric acid (rating C).

また、比較例１６，比較例１７，比較例１８，参考例２に示すように、ピクリン酸を含有する腐食液を用いた液浸腐食（参考例２）でなければ、ＪＩＳ Ｇ０５５１に規定される方法にて旧オーステナイト粒界を測定できる程度に試験片Ｔの表面全面に旧オーステナイト粒界を現出させることができないことが分かる。ピクリン酸を含有しない腐食液による液浸腐食では、実施例３と同一の腐食液による液浸腐食（比較例１７）であっても、また、粒界腐食を促進する成分（しゅう酸、塩酸）が実施例３の腐食液よりも多い腐食液（比較例１６，比較例１７）であっても、いずれも試験片Ｔの表面全面に旧オーステナイト粒界を現出させることができない（評価Ｃ）ことが分かる。 In addition, as shown in Comparative Example 16, Comparative Example 17, Comparative Example 18, and Reference Example 2, unless it is immersion corrosion using a corrosive solution containing picric acid (Reference Example 2), the It can be seen that prior austenite grain boundaries cannot be made to appear over the entire surface of test piece T to the extent that prior austenite grain boundaries can be measured by this method. In immersion corrosion using a corrosive solution that does not contain picric acid, even in immersion corrosion using the same etchant as in Example 3 (Comparative Example 17), components that promote intergranular corrosion (oxalic acid, hydrochloric acid) Even if the corrosive liquid is larger than the corrosive liquid of Example 3 (Comparative Example 16, Comparative Example 17), prior austenite grain boundaries cannot be made to appear on the entire surface of the test piece T (evaluation C). I understand that.

このことから、本実施形態に係る実施例３，実施例４の方法によれば、ピクリン酸を用いることなく、機械構造用合金鋼材である鋼Ｂの旧オーステナイト粒界を現出させることができる。 From this, according to the methods of Examples 3 and 4 according to the present embodiment, the prior austenite grain boundaries of Steel B, which is an alloy steel material for machine structures, can be exposed without using picric acid. .

Claims (6)

しゅう酸と、界面活性剤と、を含有する腐食液を用いて電解腐食を行う、機械構造用合金鋼材の旧オーステナイト粒界の現出方法。 A method for revealing prior austenite grain boundaries in alloy steel materials for mechanical structures, which involves electrolytic corrosion using a corrosive solution containing oxalic acid and a surfactant. 請求項１に記載の機械構造用合金鋼材の旧オーステナイト粒界の現出方法であって、
前記電解腐食を複数回実施する、
ことを特徴とする機械構造用合金鋼材の旧オーステナイト粒界の現出方法。 A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures according to claim 1, comprising:
carrying out the electrolytic corrosion multiple times;
A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures, characterized by: 請求項１または２に記載の機械構造用合金鋼材の旧オーステナイト粒界の現出方法であって、
前記電解腐食により生成される腐食生成物を前記機械構造用合金鋼材から除去する、
ことを特徴とする機械構造用合金鋼材の旧オーステナイト粒界の現出方法。 A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures according to claim 1 or 2, comprising:
removing corrosion products generated by the galvanic corrosion from the mechanical structural alloy steel material;
A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures, characterized by: 請求項１から３のいずれかひとつに記載の機械構造用合金鋼材の旧オーステナイト粒界の現出方法であって、前記機械構造用合金鋼材はクロム鋼である、
ことを特徴とする機械構造用合金鋼材の旧オーステナイト粒界の現出方法。 4. A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures according to any one of claims 1 to 3, wherein the alloy steel material for machine structures is chromium steel.
A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures, characterized by: 請求項４に記載の機械構造用合金鋼材の旧オーステナイト粒界の現出方法であって、
前記腐食液は、さらに塩酸を含有する、
ことを特徴とする機械構造用合金鋼材の旧オーステナイト粒界の現出方法。 A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures according to claim 4, comprising:
The corrosive liquid further contains hydrochloric acid.
A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures, characterized by: 請求項５に記載の機械構造用合金鋼材の旧オーステナイト粒界の現出方法であって、
前記電解腐食により前記機械構造用合金鋼材に生成される腐食ピットを除去する、
ことを特徴とする機械構造用合金鋼材の旧オーステナイト粒界の現出方法。 A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures according to claim 5, comprising:
removing corrosion pits generated in the mechanical structural alloy steel material due to the galvanic corrosion;
A method for revealing prior austenite grain boundaries in an alloy steel material for machine structures, characterized by:
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