JP7089751B2 - Simple measurement method and evaluation electrolyte for metal surface condition - Google Patents

Description

The present invention simply and quickly determines the strength of the oxide film existing near the surface of stainless steel, the strength of the passivation film formed by the surface modification treatment for improving corrosion resistance, and the degree of deterioration of corrosion resistance due to processing such as welding. The present invention relates to a simple method for measuring a metal surface condition that can be quantitatively and non-destructively measured, and an evaluation electrolytic solution used therein.

It is known that the oxygen-based film originally present on the surface of stainless steel and the passivation film formed by surface modification treatment such as pickling and electrolytic treatment are closely related to the corrosion resistance of stainless steel. For the evaluation of the corrosion resistance, official methods such as a salt spray test and a ferric chloride solution immersion test are widely adopted. These methods take several hours to more than half a day and are not non-destructive.

Even in the relatively simple spot test introduced in the stainless steel handbook, the required time is 5 minutes or more, and the stability and accuracy of the test including reproducibility are not sufficient. Also, electrochemical measurement with a reference electrode or the like is known, but it has many problems such as low applicability to a product manufacturing site or the like.

In response to these, the present inventor has previously invented a "simple method for measuring the passivation effect of a metal" (see Patent Document 1). This method is widely applied as a unique method for quickly and easily measuring the degree of passivation in the field, which was completely impossible in the past.

On the other hand, the present inventor has also evolved the passivation method, and for a passivation film having unparalleled strength and corrosion resistance, "Cleaning the surface of stainless steel and passivation treatment method" (see Patent Document 2). "Stainless steel having a fluorine-containing or fluorine-containing / oxygen-based film layer and its manufacturing method" (see Patent Document 3) and "Processing method of surface-modified stainless steel and surface-modified stainless steel" (Patent Document 4). See) invented.

Japanese Patent No. 1925460 Japanese Patent No. 3484525 Japanese Patent No. 4218000 Japanese Patent No. 4678612

Due to these daily advances, the function of the passivation film has improved, and high-performance and high-durability film with chlorine pitting corrosion resistance in addition to full-scale corrosion resistance is being widely applied. The precise evaluation of the dynamic film has a big problem that the conventional method using an electrolytic solution (also called a discrimination solution) lacks accuracy. That is, in order to accurately grasp the strength of the high-performance, high-performance passivation film, it was necessary to improve the discriminant solution used for the measurement.

There is an official method for evaluating the corrosion resistance of stainless steel materials as stipulated in the JIS method, but it is indispensable to have a discrimination method that can be applied to the work site with a stable method that anyone can carry out quickly and easily. There is an urgent need to develop a highly accurate passivation film strength evaluation method that is suitable for the sophistication of passivation films.

In addition, stainless steel materials cause deterioration of corrosion resistance due to the phenomenon of sensitization or formation of a chromium-deficient layer due to the heat effect during welding, but a method for easily measuring the degree of deterioration is also eagerly desired for practical use. Are at the same time.

The present invention is a method for simultaneously solving this situation, that is, a method for measuring the strength of which the corrosion resistance is enhanced by passivation and the degree of deterioration of the corrosion resistance caused by processing such as welding, and the measurement thereof. It proposes the electrolytic solution to be used.

In the present invention, a stainless steel subject to be measured is directly set as one pole, and a counter electrode made of the same material as the subject and in an activated state is via a holding member containing an electrolytic solution capable of dissolving the subject. This is a simple method for measuring the surface state of a metal by contacting it with the surface of the subject, measuring the potential difference between the two poles, and determining the surface state of the subject from the change in the potential difference. The surface condition of the subject includes the degree of immobilization and the degree of deterioration of corrosion resistance due to the influence of heat , and the content of the sulfate is adjusted by using an electrolytic solution containing sulfuric acid, chloride and sulfate . This is a simple method for measuring a metal surface state, characterized in that the measurement sensitivity can be adjusted by the above.

In the present invention, the subject of stainless steel to be measured is directly set as one pole, and the counter electrode, which is made of the same material as the subject and is in an activated state, is via a holding member containing an electrolytic solution capable of dissolving the subject. An electrolytic solution used in a simple method for measuring a metal surface state, which can be brought into contact with the surface of a subject, the potential difference between the two poles is measured, and the surface state of the subject can be determined from the change in the potential difference. It contains hydrochloric acid , sulfuric acid, chloride and sulfate , and the surface condition of the subject includes the degree of immobilization, the degree of deterioration of corrosion resistance due to thermal influence, and further, total corrosion resistance and chlorine pore corrosion resistance. It is an electrolytic solution characterized by being able to evaluate with high accuracy at the same time.

According to the simple measuring method and the discriminant solution for the metal surface state according to the present invention, the surface state evaluation such as the superiority or inferiority determination of the passivation film and the corrosion resistance deterioration determination due to the heat effect can be completed in a short time and quantitatively. It can be said to be an epoch-making method that leads to quality control and process shortening at the site and R & D site.

It is a figure which shows the structure of the potential measuring apparatus used in Example 1 of this invention. It is a measurement result of Example 1 of this invention. It is a comparative example of Example 1 of the present invention, and is a measurement result using dilute sulfuric acid as a discriminant solution. It is a measurement result of Example 2 of this invention. It is a measurement result of Example 3 of this invention. It is a measurement result of Example 4 of this invention. It is an observation photograph of the surface state of the test piece of Example 5 of this invention. It is a measurement result of Example 5 of this invention. It is a photograph which shows the result of the JIS compliant ferric chloride pitting corrosion test.

In the present invention, the electrolytic solution having a composition for evaluation of total corrosion is retained by using a mixed acid containing hydrochloric acid and sulfuric acid or an aqueous solution containing chloride and sulfuric acid as a discriminant solution and containing the discriminating solution. Through a member (cloth or paper (eg, filter paper)), stainless steel to be the subject is used as one pole, and activated stainless steel of the same material as the subject is brought into contact as the counter electrode, and it is generated between the two poles. By measuring the potential difference, the presence or absence of a passivation film and the strength of the passivation film are quantitatively evaluated.

In addition, the electrolytic solution is a mixed acid of hydrochloric acid and sulfuric acid so that the acid resistance (total corrosion) and chlorine resistance (chlorine erosion resistance, stress corrosion cracking) of the material can be evaluated together, and the mixing ratio and chloride and sulfuric acid are used. By properly adjusting the amount of salt added, it is possible to quantitatively evaluate the strength of a highly functional and strong passivation film with chlorine erosion resistance as well as the conventional oxygen-based passivation film. There is.

Furthermore, by using this electrolytic solution, it is possible to evaluate the surface condition of the metal material itself without being disturbed by the oxide film (welding burn) formed on the surface of the welded material. In other words, it is an excellent method that can grasp the degree of decrease in corrosion resistance when affected by heat, in addition to determining the improvement in corrosion resistance due to passivation.

Conventionally, since an aqueous solution containing dilute sulfuric acid as a main component has been used for passivation degree measurement, the entire corrosion behavior has been the main evaluation target. In other words, while the passivation technology continues to evolve by imparting chlorine pitting corrosion resistance and stress corrosion cracking resistance, the electrolytic solution (also called the discrimination solution) used to measure the degree of passivation is totally corroded. Since the composition was for evaluation, it was not possible to evaluate the functionality of the evolving passivation film with high accuracy.

In addition, when measuring the weld heat-affected zone using an electrolytic solution containing the dilute sulfuric acid as the main component, welding burn (oxide film) or the like acts as an interfering factor, and the corrosion resistance of the material itself should be accurately grasped. Was difficult.

On the other hand, in the simple method for measuring the metal surface state and the electrolytic solution according to the present invention, a passivation film can be obtained by using a mixed acid containing hydrochloric acid and sulfuric acid or an aqueous solution containing chloride and sulfate as a discrimination solution. The strength can be evaluated quantitatively, and the degree of deterioration of corrosion resistance when affected by heat can also be grasped.

Regarding the electrolytic solution (discrimination solution) of the present invention, the composition of the components affects the measurement result to some extent, but magnesium chloride 0.01 to 58 wt%, sodium chloride 0.01 to 37 wt%, copper sulfate 0 to 30 wt%, hydrochloric acid 0.01 to 35 wt. It was possible to measure the degree of passivation by preparing in the range of% and 0.01 to 66 wt% sulfuric acid. In order to measure the degree of immobilization with higher accuracy, the range of magnesium chloride 0.1 to 30 wt%, sodium chloride 0.1 to 30 wt%, copper sulfate 0 to 15 wt%, hydrochloric acid 0.1 to 15 wt%, and sulfuric acid 0.1 to 35 wt% is available. The range of magnesium chloride 1 to 10 wt%, sodium chloride 1 to 20 wt%, copper sulfate 0 to 5 wt%, hydrochloric acid 1 to 10 wt%, and sulfuric acid 1 to 10 wt% is more preferable.

According to the present invention, it is possible to determine the surface state of stainless steel quickly, easily and with high accuracy. Moreover, since it requires an extremely fine stainless steel surface and can be carried out non-destructively and quantitatively, it is significantly superior in time and accuracy to conventional methods at work sites, R & D sites, etc. It becomes a thing.

Specifically, there are multiple methods for surface modification treatment of stainless steel, such as pickling and electrolysis, and the method (process) to be selected naturally depends on the conditions, environment, storage conditions after treatment, etc. The mode of the passivation film formed varies. Further, when stainless steel is affected by heat during welding, problems such as deterioration of corrosion resistance occur. However, if the method of the present invention is used, the state of the stainless steel surface, that is, passivation, can be performed quickly, easily and quantitatively. Since the strength of the film (corrosion resistance) and the deterioration of corrosion resistance (degree of sensitization) can be evaluated, it can be greatly utilized for process control, quality control, plant maintenance, and the like.

Hereinafter, a simple method for measuring a metal surface state and an electrolytic solution for evaluation according to the present invention will be described with reference to Examples 1 to 5.

Example 1
An aqueous solution containing 10 wt% magnesium chloride, 20 wt% sodium chloride, 5 wt% hydrochloric acid, and 5 wt% sulfuric acid was prepared as an electrolytic solution (discrimination solution) used for evaluating the passive film formed on the surface of stainless steel.

Through a holding member (cloth or paper (eg, filter paper)) impregnated with this discriminant solution, the stainless steel to be the subject is used as one pole, and the material is the same as that of the subject and is in an active state (polished with emery paper). The potential measurement was carried out using the other pole as the counter electrode. The apparatus configuration is as shown in FIG. 1, and the transition of the potential difference generated between the two poles is recorded by the electrometer 4 in FIG. The measurement results are shown in Fig. 2, and it is possible to capture clear differences between the material received from the material manufacturer (AS) and the material received with our ultra-passivation film.

On the other hand, the result of the same measurement using dilute sulfuric acid, which is a conventional discriminant solution, is shown in FIG. The superiority of the passivation has not been clearly determined. This is because the conventional liquid has a composition for discriminating an oxygen-based passivation film, so that the chlorine resistance newly added to the ultra-passivation film cannot be evaluated with high accuracy. I'm guessing the cause.

Here, the ultra-passivation film is a passivation film that has a special effect in preventing stress corrosion cracking, which is a drawback peculiar to austenite-based stainless steel. It is formed by electrolytic treatment using "CC (manufactured by Chemical Yamamoto Co., Ltd.)".

Example 2
The strength of various passivation films was measured using the composition discrimination solution described in Example 1. For these passivation films, the oxygen-based passivation films,'super passivation films'and'ultra-passivationfilms', which the inventor has developed so far, were used. In addition, the same measurement was performed on the received material (AS) and the sample in which the received material was activated (polished with emery paper), and the order of strength was evaluated. Specifically, the strength of the passivation film can be determined by the time for holding the film potential of 0.2 V or more, and the longer the holding time, the stronger the passivation film.

The measurement results are shown in FIG. 4 and Table 1. The receiving material (AS) is determined to be slightly passivated, as shown by the dashed line results. When the receiving material is activated (polished with emery paper), the film potential becomes almost zero, indicating that there is no passivation film. On the other hand, all of the samples subjected to the immobilization treatment by electrolysis showed higher strength than the AS material. As shown in Table 1, the order of the film strength was quantitatively determined in the order of oxygen system <AC system <NEO system <SCC system (compared to our products).

Table 1 summarizes the 0.2 V maintenance time KT (0.2) in FIG. 4 as the passivation film strength.

Here, the super passivation film is a film in which a fluorine-based passivation film is combined with an oxygen-based passivation film and has excellent chlorine erosion resistance, and is formed by an electrolytic treatment using a fluorine-containing neutral electrolytic solution. The ultra-passivation film is a stronger film in which boron is further incorporated into the composition of the super-passivation film.

Example 3
Similarly, the strength of the passivation film was measured for the SUS304-2B material ordered from a plurality of material manufacturers using the composition discrimination solution described in Example 1.

As shown in the measurement results in FIG. 5, the materials ordered from the three companies (Company A, B, C) are all SUS304-2B materials, but the strength of the passivation film formed on the surface is slight. It turns out that they are different. When these materials are activated (emery paper polishing), the generated membrane potential becomes zero and no passivation film exists. Next, when the activated sample is passivated, the 0.2 V retention time is greatly extended, so it can be clearly understood that the activated sample is strongly passivated.

By using the electrolytic solution (discrimination solution) and the measuring method according to the present invention, not only the measurement of the passivated subject but also the strength of the oxygen-based passivation film possessed by the material itself can be grasped with high accuracy. Turned out to be possible.

Example 4
In such discriminant measurement, we want to make the difference between the untreated material and the treated material look large, and we want to accurately grasp how much the difference in the passivation degree occurs depending on the processing conditions, for example, the processing voltage and the processing time. Alternatively, there is a need to complete the measurement in a short time. In order to make such measurement sensitivity adjustment possible, it was effective to additionally add copper sulfate to the electrolytic solution (discrimination solution).

FIG. 6 is a measurement result when the discrimination liquid (A) used in Examples 1 to 3 and the discrimination liquid (B, C) in which copper sulfate is added to the discrimination liquid are used. When the discriminant solution (A) containing no copper sulfate is used, the measurement time is about 40 seconds, whereas with the discriminant solution (B and C) to which copper sulfate is added, the measurement time can be shortened. There is. In this example, the copper sulfate content was 1.0 wt% and 2.0 wt%, but the measurement sensitivity could be adjusted arbitrarily within the range of 0.01 to 10 wt% copper sulfate content.

Example 5
Similarly, the surface condition of the heat-affected zone of the stainless steel welded portion was evaluated using the composition determination liquid described in Example 1.

FIG. 7 (photograph) is a welded test piece, and numbers 1 to 4 in the figure indicate a portion where the surface condition of stainless steel is measured by the method of the present invention.

The measurement results are summarized in FIG. 8, and as shown in FIG. 7, the degree of passivation is significantly lower in the vicinity 1 of the weld line than in the vicinity 2 of the weld line. That is, it can be determined that the corrosion resistance is deteriorated. This indicates that the Cr-deficient layer is formed and sensitized due to the heat effect during welding, and the tendency becomes stronger near the welding line. In addition, as a result of performing the same surface condition measurement after performing our original passivation treatment on the test piece, the holding time of 0.2V or more in both the vicinity 3 of the weld line and the periphery 4 has increased remarkably. It can be seen that the degree of passivation is improved. This measurement result shows that the passivation of the same level as that of the general part is achieved by our passivation technology even for the part that has been sensitized by the heat.

When a JIS-compliant ferric chloride pitting test was carried out on the same test piece, pitting corrosion occurred as shown in FIG. 9 (photograph), and the locations where the pitting corrosion occurred were concentrated near the weld line (). (Left half of FIG. 9). On the other hand, it can be seen that no pitting corrosion occurs in the region subjected to the electrolysis treatment of our company and the region has high corrosion resistance (right half of FIG. 9).

The measurement results of this method and the results of JIS-compliant corrosion resistance evaluation are in good agreement, and it was confirmed that the present invention is an extremely effective method that can easily and non-destructively evaluate the surface state of a metal.

1 Subject 2 Filter paper 3 Electrode 4 Electrometer

Claims (2)

The subject of stainless steel to be measured is directly set as one pole, and the counter electrode, which is made of the same material as the subject and is in an activated state, is subjected to the above-mentioned subject via a holding member containing an electrolytic solution capable of dissolving the subject. It is a simple method for measuring the surface state of a metal that can be brought into contact with the surface, the potential difference between the two poles is measured, and the surface state of the subject can be determined from the change in the potential difference.
An electrolytic solution containing hydrochloric acid, sulfuric acid, chloride and sulfate was used as the electrolytic solution.
The surface state of the subject includes the degree of passivation and the degree of deterioration of corrosion resistance due to the influence of heat.
A simple method for measuring a metal surface state, characterized in that the measurement sensitivity can be adjusted by adjusting the content of the sulfate . The subject of stainless steel to be measured is directly set as one pole, and the counter electrode, which is made of the same material as the subject and is in an activated state, is subjected to the above-mentioned subject via a holding member containing an electrolytic solution capable of dissolving the subject. An electrolytic solution used in a simple method for measuring the surface state of a metal, which is in contact with a surface, measures the potential difference between the two poles, and can determine the surface state of the subject from the change in the potential difference.
Contains hydrochloric acid , sulfuric acid, chloride and sulfate,
The surface state of the subject includes the degree of passivation and the degree of deterioration of corrosion resistance due to the influence of heat, and is characterized in that the entire surface corrosion resistance and chlorine pitting corrosion resistance can be evaluated at the same time with high accuracy. Electrolyte.

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