JP6963161B2 - Corrosion sensor for stainless steel and its manufacturing method - Google Patents

Description

The present invention is a corrosion sensor for stainless steel that measures the galvanic current flowing between the anode electrode and the cathode electrode, and a method for manufacturing the same.

An ACM type corrosion sensor (hereinafter referred to as an ACM sensor) has been developed (Non-Patent Document 1) as a corrosion sensor applying a galvanic pair of iron and silver. This is used for analysis of metal corrosiveness in the atmosphere, such as measurement and monitoring of metal corrosive factors in the atmospheric environment, and can measure the wetting time, the amount of adhesion equivalent to sea salt, etc., which are metal corrosive factors in the atmosphere. A high correlation can be obtained between the daily average amount of electricity of the sensor and the corrosion rate of the metal material (Non-Patent Document 2). Currently, ACM sensors are used in a wide range of technical fields, including monitoring of atmospheric metal corrosion factors, corrosion life analysis of metal materials, and anticorrosion measures.

Japanese Unexamined Patent Publication No. 2012-208088 Japanese Unexamined Patent Publication No. 2016-145744

Zairyo-to-Kankyo, 43, p. 550 (1994) Zairyo-to-Kankyo, 51, p. 398 (2002) Proceedings of the 42nd Corrosion and Anticorrosion Debate, p. 437 (1995) Corrosion Center News, p. 313 (2017)

Regarding the amount of sea salt equivalent, which is considered to be a metal corrosive factor in the environment, the amount of incoming sea salt particles measured by the gauze method and the wet candle method based on JIS Z 2382 is the same as that of iron and silver currently on the market. Galvanic paired ACM type corrosion sensors (hereinafter referred to as iron / silver vs. ACM sensors) can be used and they can be easily estimated from sensor output analysis.

In the case of the iron / silver vs. ACM sensor, the corrosion current of iron, which is the anode electrode, is measured, and the corrosion status of iron, which is the material of the anode electrode, is monitored and measured. However, the form of metal corrosion differs depending on the metal species. For example, in the atmosphere, iron generally takes a form of total corrosion, but stainless steel and aluminum often take a form of local corrosion such as pitting corrosion and crevice corrosion under the influence of sea salt. The water film formed on the metal surface cycles in a wet and dry state. That is, there is a limit to the corrosion monitoring of metal materials including alloys other than iron by substituting the iron / silver vs. ACM sensor for evaluation, and it is difficult to accurately analyze and judge the corrosion status. In this corrosion sensor consisting of galvanic pairs, by arranging the metal material for which corrosion information is to be obtained on the anode electrode, the corrosion information and corrosion status of the target metal can be monitored, and the corrosiveness of the actual environment can be easily and highly accurate. Can be evaluated at.

ACM sensors using metal types such as hot-dip galvanized steel sheets, aluminum, and copper as anode electrode substrates have been put into practical use. In the ACM sensor using ferritic stainless steel as the anode substrate, the sensor output has been confirmed at a relative humidity of 70% or less with MgCl2 attached (Non-Patent Document 3). Further, a corrosion monitoring sensor using stainless steel as an anode electrode and carbon as a cathode electrode has been proposed (Patent Document 1). However, these have not been put into practical use due to problems such as a smaller output than the iron / silver vs. ACM sensor. As the cathode electrode, a metal having an electrode potential noble rather than a metal type serving as the anode electrode is selected. However, when silver is used for the cathode electrode, the current output of the sensor decreases due to alteration of the silver electrode in a high salt concentration environment such as a coastal area. Further, it has been reported that a corrosion sensor using chemically stable carbon as a cathode electrode material can be used in a hydrogen sulfide environment (Non-Patent Document 4) for the purpose of preventing deterioration of the silver electrode due to sulfurization.

An object of the present invention is to provide a corrosion sensor for stainless steel and a method for manufacturing the same, which enables high-precision measurement by increasing the output of galvanic current.

As a result of diligent research to solve the above-mentioned problems, the present inventor has found that the galvanic current of the corrosion sensor for stainless steel can be increased with the following contents, and has achieved the present invention. An anode electrode portion made of a conductor containing a metal component, a cathode electrode portion made of a conductor containing a metal component different from the anode electrode portion, and an insulating portion formed between the anode electrode portion and the cathode electrode portion. The anode electrode portion has at least a corrosion promoting layer containing chromium carbide between the anode electrode portion and the cathode electrode portion.

The invention according to claim 2 is characterized in that the corrosion promoting layer of the anode electrode portion contains a sensitized structure or undissolved chromium carbide.

The invention according to claim 3 is characterized in that the anode electrode portion contains 1.0% by mass or more of chromium carbide.

The invention according to claim 4 is characterized in that the cathode electrode portion is made of a conductor containing a carbon component.

The invention according to claim 5 comprises an anode forming step of forming an anode electrode portion having a corrosion promoting layer containing chromium carbide by heat-treating a base material made of stainless steel, and insulating the surface of the formed anode electrode portion. It is characterized by including an insulation forming step of forming a portion and a cathode forming step of laminating a conductive material containing a metal component different from that of the anode electrode portion on the surface of the formed insulating portion to form a cathode electrode portion. do.

The invention according to claim 6 is characterized in that, in the anode forming step, heat treatment is performed by heating at a temperature of 550 ° C. to 900 ° C. for a predetermined time.

The invention according to claim 7 is characterized in that, in the anode forming step, heat treatment is performed by irradiation with laser light.

The invention according to claim 8 comprises an insulation forming step of forming an insulating portion on the surface of an anode electrode portion formed of a base material made of stainless steel, and a conductive material containing a conductive component different from that of the anode electrode portion. Corrosion containing chromium carbide in the anode electrode portion by the cathode forming step of forming the cathode electrode portion and the heat treatment by irradiating the surface of the anode electrode portion between the anode electrode portion and the cathode electrode portion with laser light. it characterized by comprising a corrosion formation step of forming a promoting layer.

In the invention according to claim 9, the base material contains Cr 11.5% by mass or more, C 0.08% by mass or more, Ni 14.0% by mass or less, Si 1.0% by mass or less, and Mn 2.0% by mass or less. The balance is a stainless steel composed of Fe and unavoidable impurities.

According to the present invention, by providing an anode electrode portion having a corrosion promoting layer containing chromium carbide, it is possible to increase the output of galvanic current and perform high-precision measurement, and to monitor corrosion of stainless steel in indoor and outdoor atmospheric environments. It is possible to realize a corrosion sensor for stainless steel that can perform environmental corrosiveness evaluation and life prediction with high accuracy.

It is an enlarged schematic view of the electrode part cross section of the corrosion sensor for stainless steel. It is an enlarged schematic view of the cross section of an electrode part about another example of the corrosion sensor for stainless steel.

Hereinafter, embodiments according to the present invention will be described in detail. FIG. 1 is an enlarged schematic view showing a cross section of an electrode portion of a corrosion sensor for stainless steel according to the present invention. The corrosion sensor for stainless steel includes an anode electrode portion 1 made of a conductor containing a metal component, a cathode electrode portion 3 made of a conductor containing a metal component different from that of the anode electrode portion 1, and an anode electrode portion 1 and a cathode electrode portion 3. The anode electrode portion 1 has a corrosion promoting layer 1a containing chromium carbide. The anode electrode portion 1 is a portion where an oxidation reaction occurs on the electrode surface to generate electrons. In this example, a corrosion promoting layer containing chromium carbide on the entire electrode surface by heating stainless steel as a base material and heat-treating it. It forms 1a.

Examples of the stainless steel used for the anode electrode portion 1 include known materials such as austenite-based stainless steel, ferrite-based stainless steel, martensite-based stainless steel, austenite-ferrite two-phase stainless steel, and precipitation-hardened stainless steel.

The corrosion-promoting layer 1 is a layer in which the amount of chromium is reduced and a local chromium-deficient region is generated due to the inclusion of chromium carbide in stainless steel, and the corrosion resistance is remarkably lowered so that corrosion is easily promoted, and corrosion is promoted. As a result, galvanic current can easily flow and high output can be achieved. In order to promote corrosion, the content of chromium carbide is preferably 1.0% by mass or more.

Examples of the corrosion promoting layer 1a include a sensitized structure formed by heat-treating stainless steel. The sensitized structure is a metal structure in which chromium carbide, which is a chemically bonded stainless steel component, is deposited. The amount of chromium carbide deposited varies depending on the heating temperature / time and the stainless steel type. Further, for such a sensitized structure, for example, stepped, mixed, groove-shaped corrosion shape evaluation of grain boundary portion by metal structure observation method (JIS G 0571) by oxalic acid etching, sulfuric acid / ferric sulfate corrosion test ( Corrosion rate evaluation by JIS G 0572) or 65% nitric acid corrosion test (JIS G 0573), corrosion shape observation by sulfuric acid / copper sulfate corrosion test (JIS G 0575), or electrochemical by EPR test method (JIS G 0580) It can be specifically determined by the reactivation rate R _m.

Further, as the corrosion promoting layer 1, a layer containing unsolid solution chromium carbide in stainless steel can also be mentioned. The undissolved chromium carbide means the M23C6 type chromium carbide component produced by the heat treatment of quenching and tempering, and includes Cr23C6, Cr7C3 and the like. Even if the stainless steel does not contain the above-mentioned sensitized structure, the structure in which unsolidified chromium carbide is precipitated acts as a corrosion promoting layer. As with the sensitized structure, undissolved chromium carbide precipitation reduces the amount of chromium in the steel or causes a local chromium deficiency region in the steel, resulting in a decrease in the corrosion resistance of the stainless steel.

As described above, in the present invention, the chromium carbide is an MC-type carbide containing chromium as a main component, and includes M23C6 type undissolved chromium carbide produced by heat treatment.

The cathode electrode portion 3 is a portion where a reduction reaction occurs on the electrode surface and electrons are lost. In order to allow a galvanic current to flow between the anode electrode portion 1 and the anode electrode portion 1, the cathode electrode portion 3 has a more noble potential different from the metal component contained in the anode electrode portion 1 under the condition that an electrochemical reaction occurs. It is necessary to include the conductive component that becomes. Specific examples thereof include a combination with a conductive carbon component or a metal component such as silver, gold, or platinum.

The insulating portion 2 electrically insulates between the anode electrode portion 1 and the cathode electrode portion 3. In this example, the insulating portion 2 is laminated on the electrode surface of the anode electrode portion 1 serving as a substrate, the cathode electrode portion 3 is laminated on the upper surface of the insulating portion 2, and the anode electrode portion 1 and the cathode electrode portion 3 are in an insulated state. It is set. The insulating portion 3 is not particularly limited as long as it is a non-conductive material, and examples thereof include a resin material and a ceramic material.

FIG. 2 is an enlarged schematic view showing a cross section of an electrode portion in another embodiment of the present invention. In this example, stainless steel is used for the anode electrode portion 4 as in the example shown in FIG. 1, but the corrosion promoting layer 4a is formed at a portion serving as a flow path for the galvanic current flowing between the anode electrode portion 4 and the cathode electrode portion 3. Has been done. Specifically, the corrosion promoting layer 4a is formed so as to surround the outer periphery of the insulating portion 2, and as will be described later, the corrosion promoting layer is formed on the electrode surface by heat-treating the electrode surface by irradiating the corresponding portion with a laser. It can be formed locally and accurately. Then, as in the example shown in FIG. 1, the corrosion sensor can be configured by forming the cathode electrode portion 3 on the upper surface of the insulating portion 2.

In the examples shown in FIGS. 1 and 2, the structure is such that the anode electrode portion, the insulating portion, and the cathode electrode portion are laminated, but other structures are possible and are not particularly limited.

In the method for manufacturing a corrosion sensor for stainless steel according to the present invention, an anode forming step of forming an anode electrode portion having a corrosion promoting layer containing chromium carbide by heat-treating a base material made of stainless steel, and an anode electrode portion formed. It is possible to include an insulation forming step of forming an insulating portion on the surface of the anode electrode portion and a cathode forming step of laminating a conductive material containing a metal component different from that of the anode electrode portion on the surface of the formed insulating portion to form a cathode electrode portion. preferable.

The anode forming step is a step in which the stainless steel becomes a sensitized structure by heat treatment or unsolidified chromium carbide is precipitated to form a corrosion promoting layer, and the base material made of stainless steel is heated at a temperature of 550 ° C to 900 ° C. It is preferable to heat in the region to heat-treat.

For the heat treatment, it is preferable to use an electric furnace, and the electric furnace includes a batch type, a continuous type, and the like, but is not particularly limited. In order to avoid the oxide film layer formed on the surface of the stainless steel during the heat treatment as much as possible and to simplify the next polishing step, the heat treatment in an inert gas such as argon or a nitrogen gas atmosphere is preferable. The heating time is the time required for the stainless steel to be uniformly heat-treated, and is not particularly limited. The heating time can be calculated by estimating the amount of heat input from the size of the processing material and the shape of the electric furnace.

Further, the heat treatment can be performed by irradiating with laser light. By irradiating the surface of a base material made of stainless steel with laser light and performing heat treatment, it is possible to form a corrosion promoting layer at a depth of several mm at the irradiated portion. In the laser processing machine used for laser light irradiation, the laser is emitted from the oscillator and is irradiated to the material through the reflecting mirror and the condenser lens, and there are semiconductor laser, carbon dioxide gas laser, YAG laser, fiber laser, etc. Is not particularly limited. The laser output, defocus, feed rate, etc. may be adjusted to the appropriate conditions for the processing machine to be used. As the assist gas, it is preferable to use an inert gas such as argon gas in order to avoid the formation of an oxide film on the surface of the base material.

Known stainless steel can be used as the base material. Specifically, Cr is 11.5% by mass or more, C is 0.08% by mass or more, Ni is 14.0% by mass or less, and Si is 1.0% by mass. Hereinafter, stainless steel containing 2.0% by mass or less of Mn and having a composition in which the balance is composed of Fe and unavoidable impurities is preferable.

In the anode forming step, it is preferable to polish the surface of the substrate after the heat treatment to completely remove the oxide film on the surface of the substrate. It is desirable to remove the sensor at a depth of 1 mm or more because the output of the sensor is reduced or the performance quality of the output difference of each sensor is affected. Examples of the removing method include wet polishing and blasting.

In the insulation forming step, a non-conductive material such as a resin material or a ceramic material is described in Patent Document 2, which is a known method such as an inkjet method, a screen printing method, a plating method, a vapor deposition method, or a manufacturing method combining these methods. An insulating portion can be formed by laminating on the surface of the substrate on which the anode electrode portion is formed by using the manufacturing method. In particular, the screen printing method is preferable in order to realize mass production, stable quality and low cost.

In the cathode forming step, a conductive material containing a metal component is prepared by using known methods such as an inkjet method, a screen printing method, a plating method, a vapor deposition method, a manufacturing method combining these methods, and a manufacturing method described in Patent Document 2. Therefore, the cathode electrode portion can be formed by laminating on the surface of the substrate on which the insulating portion is formed. In particular, the screen printing method is preferable in order to realize mass production, stable quality and low cost. As the conductive material containing a metal component, for example, a carbon simple substance such as graphite or graphite, or a resin printing paste containing a carbon component such as these carbon powders can be used.

Further, in the insulation forming step and the cathode forming step, the insulating portion and the cathode electrode portion can be formed at the same time by attaching a sheet body made of a resin film in which a metal vapor deposition layer is laminated on the substrate of the anode electrode portion.

In the above-mentioned example, the corrosion promoting layer is formed in the anode forming step, but the corrosion promoting layer can also be formed by post-treatment by using the heat treatment by irradiating the laser beam. For example, an insulation forming step of forming an insulating portion on the surface of an anode electrode portion formed of a base material made of stainless steel, and a cathode forming of a cathode electrode portion of a conductive material containing a conductive component different from that of the anode electrode portion. The present invention includes a step and a corrosion forming step of forming a corrosion promoting layer containing chromium carbide on the anode electrode portion by irradiating the surface of the anode electrode portion between the anode electrode portion and the cathode electrode portion with laser light and heat-treating the surface. This makes it possible to easily manufacture corrosion sensors having various structures according to the installation conditions.

Examples of the present invention will be specifically described below.

The stainless steel having the chemical composition shown in Table 1 was melted in vacuum to prepare a stainless steel plate having a thickness of 2 mm through hot forging, hot rolling, and cold rolling. This was cut into a length of 80 mm, a width of 80 mm, and a thickness of 2 mm to obtain a test piece, heated in a tubular electric furnace at 650 ° C. for 1 hour in a nitrogen gas atmosphere, taken out from the electric furnace, and slowly cooled at room temperature. Next, after polishing the surface of this test piece, it was cut out on a substrate for an anode electrode having a length of 64 mm, a width of 64 mm, and a thickness of 0.8 mm.

Prepare ME-990J # MBN (manufactured by Henkel Able Stick Japan Co., Ltd.) as the material of the insulating part and C-990J # 585 (manufactured by Henkel Able Stick Japan Co., Ltd.) as the material of the cathode electrode part, and use a screen printing machine. An insulating film and a cathode electrode were laminated on the surface of the substrate by screen printing with silver paste to prepare an ACM sensor as a corrosion sensor for stainless steel. The insulating film, the printed shape of the electrodes, the printing paste material, and the paste curing conditions were the same as those previously reported (Non-Patent Document 1).

The substrate was electrolyzed in a methanol solution of maleic anhydride, insoluble components were recovered with a 0.2 μm membrane filter, and the amount of chromium carbide precipitated was measured from this weight. The recovered insoluble component was investigated by measuring the diffraction pattern with an X-ray diffraction analyzer. In addition, a 65% nitric acid corrosion test method (JIS G 0573) for stainless steel was performed on a part of the substrate.

In order to investigate the current output value of the created ACM sensor in a simulated environment, a constant temperature and humidity test was performed according to the following procedure. While keeping the ACM sensor warm at 50 ° C. on a hot plate, 10 g / m ^{2 of} droplets of artificial seawater was adhered to the comb-shaped electrode portion of the ACM sensor and dried. This was installed in a constant temperature and humidity chamber, and the galvanic current of the ACM sensor flowing between the anode electrode and the cathode electrode at 25 ° C and 50% relative humidity was measured at 2-minute intervals with a non-resistive ammeter. .. A stable sensor current value was measured 2 hours after the start of measurement, and the results are shown in Example 1 of Table 1.

The test piece having a length of 80 mm, a width of 80 mm, and a thickness of 2 mm used in Example 1 was heated at 900 ° C. for 5 minutes in an electric furnace in a nitrogen gas atmosphere, then taken out from the electric furnace and slowly cooled at room temperature. Next, the same processing as in Example 1 was carried out to prepare a substrate for an anode electrode, and an ACM sensor using the substrate as an anode electrode was prepared. The prepared sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Example 2 of Table 1.

Using the stainless steel having the chemical composition shown in Table 1, a stainless steel plate having a thickness of 2 mm was prepared in the same manner as in Example 1. This test piece was heat-treated at 650 ° C. for 1 hour, then air-cooled, polished, and cut to prepare a substrate for an anode electrode, and then an ACM sensor using the substrate as an anode electrode was prepared. Similar to Example 1, the prepared ACM sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a metallographic structure observation by a oxalic acid etching test method (JIS G 0571) of stainless steel. These results are shown in Example 3 of Table 1.

From the stainless steel plate having a thickness of 2 mm in Example 1, a substrate for an anode electrode having a length of 64 mm, a width of 64 mm, and a thickness of 0.8 mm was cut out. An ACM sensor having a substrate as an anode electrode was created. Similar to Example 1, the prepared ACM sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Comparative Example 1 of Table 1.

From the stainless steel plate having a thickness of 2 mm in Example 3, a substrate for an anode electrode having a length of 64 mm, a width of 64 mm, and a thickness of 0.8 mm was cut out. An ACM sensor having a substrate as an anode electrode was created. Similar to Example 1, the prepared ACM sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a metallographic structure observation by a oxalic acid etching test method (JIS G 0571) of stainless steel. These results are shown in Comparative Example 2 in Table 1.

The stainless steel having the chemical composition shown in Table 1 was subjected to vacuum melting, hot forging, hot rolling, and cold rolling in the same manner as in Example 1 to prepare a stainless steel plate having a thickness of 2 mm. From this stainless steel plate, a substrate for an anode electrode having a length of 64 mm, a width of 64 mm, and a thickness of 0.8 mm was cut out. An ACM sensor having a substrate as an anode electrode was created. Similar to Example 1, the prepared ACM sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Comparative Example 3 of Table 1.

A commercially available iron / silver pair ACM sensor in which the anode electrode substrate is carbon steel was subjected to a constant temperature and humidity test after adhering sea salt in the same manner as in Example 1, and the results are shown in Comparative Example 4 in Table 1.

The commercially available iron / silver pair ACM sensor shown in Comparative Example 4 had a sensor current value of 11 μA in a constant temperature and humidity test. The amount of chromium carbide deposited on the stainless steel substrate of Example 1 was 3.1% by mass, and the metal structure was a martensite structure in which martensite leaves were observed in austenite grains of about 20 μm. It showed a high corrosion amount of 5 g / m2 / h. Since the corrosion amount of 0.4 g / m2 / h or more was determined to be a sensitized structure in the nitric acid corrosion test, it was considered that the substrate had a sensitized structure and a corrosion promoting layer was formed. The generated sensor output was confirmed to have a current value of 10 μA, which is equivalent to that of Comparative Example 4. The substrate of Example 2 had a low corrosion amount of 0.1 g / m2 / h or less in the nitric acid corrosion test and could not be judged as a sensitized structure, but the chromium carbide precipitation amount was 2.3% by mass, and unsolidified carbonization was performed. It was considered that a corrosion-promoting layer was formed in which the chromium component in the steel was reduced due to the chromium precipitation and the corrosion resistance was significantly reduced. The current value of the created sensor was as high as 5 μA. Example 3 is an austenitic stainless steel, and the amount of chromium carbide deposited on the substrate is less than 1.0% by mass. However, in the oxalic acid etching test, clear groove-like corrosion was observed at the austenitic grain boundary, which was observed. , It can be judged as a sensitized structure, and it is considered that a corrosion promoting layer is formed. The generated sensor output was also as high as 6 μA. Comparative Example 1 and Comparative Example 2 are stainless steel plates having the same chemical composition as in Example 1 and Example 3, respectively, but because they are not heat-treated, the amount of chromium carbide is 0.1% by mass and the structure is sensitized. No corrosion-promoting layer is formed on the anode substrate, and the sensor current value is extremely low. The ACM sensor made of ferritic stainless steel shown in Comparative Example 3 obtained a current value close to that of Non-Patent Document 3, but the current value was 1/20 of that of Example 1.

In the ACM sensor of Example 1, an ACM sensor was prepared by using an epoxy resin-based carbon paste (carbon component content: about 80%) instead of the silver paste for the cathode electrode portion, and it was referred to as Example 4. Similar to Example 1, the prepared ACM sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Example 4 of Table 2.

Example 5 was an ACM sensor in which a platinum plating layer of 0.5 μm was formed by wet plating on the surface of the cathode electrode of the ACM sensor of Example 1 as in Patent Document 2. Similar to Example 1, the prepared ACM sensor was subjected to a constant temperature and humidity test, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Example 5 of Table 2.

The stainless steel plate having a thickness of 2 mm used in Example 1 was heated in a tubular electric furnace at a temperature of 550 ° C. for 30 minutes in a nitrogen gas atmosphere, then taken out from the electric furnace and slowly cooled at room temperature. Next, in the same manner as in Example 1, an ACM sensor was prepared using the heat-treated test piece as a substrate for an anode electrode. A carbon paste was used for the cathode electrode portion of the sensor as in Example 4. The prepared ACM sensor was subjected to a constant temperature and humidity test in the same manner as in Example 1, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Example 6 of Table 2.

The stainless steel plate having a thickness of 2 mm used in Example 1 was heated in a tubular electric furnace at a temperature of 900 ° C. for 30 minutes in a nitrogen gas atmosphere, then taken out from the electric furnace and slowly cooled at room temperature. Next, in the same manner as in Example 1, an ACM sensor was prepared using the heat-treated test piece as a substrate for an anode electrode. A carbon paste was used for the cathode electrode portion of the sensor as in Example 4. The prepared ACM sensor was subjected to a constant temperature and humidity test in the same manner as in Example 1, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Example 7 of Table 2.

The stainless steel plate having a thickness of 2 mm used in Example 1 was heated in a tubular electric furnace at a temperature of 400 ° C. for 30 minutes in a nitrogen gas atmosphere, then taken out from the electric furnace and slowly cooled at room temperature. Next, in the same manner as in Example 1, an ACM sensor was prepared using the heat-treated test piece as a substrate for an anode electrode. A carbon paste was used for the cathode electrode portion of the sensor as in Example 4. The prepared ACM sensor was subjected to a constant temperature and humidity test in the same manner as in Example 1, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Comparative Example 5 of Table 2.

The stainless steel plate having a thickness of 2 mm used in Example 1 was heated in a tubular electric furnace at a temperature of 1050 ° C. for 30 minutes in a nitrogen gas atmosphere, then taken out from the electric furnace and slowly cooled at room temperature. Next, in the same manner as in Example 1, an ACM sensor was prepared using the heat-treated test piece as a substrate for an anode electrode. A carbon paste was used for the cathode electrode portion of the sensor as in Example 4. The prepared ACM sensor was subjected to a constant temperature and humidity test in the same manner as in Example 1, and the substrate was subjected to a chromium carbide amount measurement and a 65% nitric acid corrosion test method for stainless steel (JIS G 0573). These results are shown in Comparative Example 6 of Table 2.

Using a semiconductor laser machine, the comb-shaped electrode portion, which is the anode electrode portion of the ACM sensor having the same configuration as that of Comparative Example 2, was irradiated with laser light and locally heat-treated. The irradiation conditions were scanning with a laser output of 200 W, a defocus amount of 15 mm, and a feed rate of 1000 mm / min, and an argon gas was used as the assist gas, and the processing was performed in an argon gas atmosphere. The irradiation angle of the laser beam was 60 degrees, and the ACM sensor was cooled to 5 ° C. The heat-treated ACM sensor was subjected to the same constant temperature and humidity test as in Example 1. Further, the metallographic structure of the cross section near the anode electrode portion of the ACM sensor was observed by the oxalic acid etching test method (JIS G 0571) of stainless steel. The results are shown in Example 8 of Table 2.

The current output of the sensor in which the cathode electrode of the ACM sensor of Example 1 was carbon (Example 4) or platinum (Example 5) was the same value as that of Comparative Example 4. Also in Example 6 or 7, the sensor current value was close to that of Comparative Example 4. In Example 8, a groove-like structure, which is a sensitized structure, was confirmed in the anode electrode portion to a depth of about 0.2 mm from the surface layer, and a local corrosion promoting layer was formed in the anode electrode portion by laser processing. rice field. Further, the sensor current value was 5 μA, which was significantly increased as compared with Comparative Example 2 shown in Table 1, which was considered to be the effect of the corrosion promoting layer formed on the anode electrode portion. In Comparative Example 5 and Comparative Example 6, the heat treatment temperature was 400 ° C. or 1050 ° C., which was outside the range of the present invention, no sensitized structure was confirmed, and the amount of chromium carbide precipitated was less than 1.0% by mass. As a result, the sensor. The current value was also low.

1 Anode electrode part 1a Corrosion promotion layer 2 Insulation part 3 Cathode electrode part 4 Anode electrode part 4a Corrosion promotion layer

Claims (9)

An anode electrode portion made of a conductor containing a metal component, a cathode electrode portion made of a conductor containing a conductive component different from the anode electrode portion, and an insulating portion formed between the anode electrode portion and the cathode electrode portion. A corrosion sensor for stainless steel, wherein the anode electrode portion has at least a corrosion promoting layer containing chromium carbide between the anode electrode portion and the cathode electrode portion. The corrosion sensor for stainless steel according to claim 1, wherein the corrosion promoting layer of the anode electrode portion contains a sensitized structure or undissolved chromium carbide. The corrosion sensor for stainless steel according to claim 1 or 2, wherein the anode electrode portion contains 1.0% by mass or more of chromium carbide. The corrosion sensor for stainless steel according to any one of claims 1 to 3, wherein the cathode electrode portion is made of a conductor containing a carbon component. An anode forming step of forming an anode electrode portion having a corrosion promoting layer containing chromium carbide by heat-treating a base material made of stainless steel, and an insulating forming step of forming an insulating portion on the surface of the formed anode electrode portion. A method for manufacturing a corrosion sensor for stainless steel, which comprises a cathode forming step of laminating a conductive material containing a conductive component different from that of the anode electrode portion on the surface of the formed insulating portion to form a cathode electrode portion. .. The method for manufacturing a corrosion sensor for stainless steel according to claim 5, wherein in the anode forming step, heat treatment is performed by heating at a temperature of 550 ° C. to 900 ° C. for a predetermined time. The method for manufacturing a corrosion sensor for stainless steel according to claim 5, wherein in the anode forming step, heat treatment is performed by irradiation with a laser beam. An insulation forming step of forming an insulating portion on the surface of an anode electrode portion formed of a base material made of stainless steel, and a cathode forming step of forming a cathode electrode portion with a conductive material containing a conductive component different from that of the anode electrode portion. A corrosion forming step of forming a corrosion promoting layer containing chromium carbide on the anode electrode portion by irradiating the surface of the anode electrode portion between the anode electrode portion and the cathode electrode portion with laser light and heat-treating the anode electrode portion. A method for manufacturing a corrosion sensor for stainless steel, which comprises. The base material contains Cr 11.5% by mass or more, C 0.08% by mass or more, Ni 14.0% by mass or less, Si 1.0% by mass or less, and Mn 2.0% by mass or less, and the balance is composed of Fe and unavoidable impurities. The method for manufacturing a corrosion sensor for stainless steel according to any one of claims 5 to 8, wherein the material is stainless steel.

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