JPH0570788B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a quick and simple method for detecting phosphorus segregated areas by using a chemical reaction to reveal the distribution state of phosphorus in a metal material on a test paper. It is related to.

<Prior art and its problems> S, P,
Elements such as Mn, Si and C are locally concentrated and segregated,
It is known to have a significant impact on the quality of steel materials.

Conventionally, in steel works and the like, the determination of these centrally segregated areas has been carried out by the sulfur print test method. In this method, photographic paper impregnated with a sulfuric acid solution is pasted on the surface to be tested, and the generated hydrogen sulfide is detected on the paper.The distribution state of S in steel is two-dimensionally displayed on the test paper. I can get it out.

On the other hand, as a method for detecting segregated areas related to the sulfa print method, the present inventors selectively corrode the phosphorus segregated areas using a copper nitrate solution or silver nitrate solution, and then removed the phosphorus or iron occluded within the test paper. We have developed a phosphor printing method that detects the segregated site by coloring it, and have previously applied for it (Japanese Patent Applications No. 58-213497, No. 59-153799, No. 59-170227).
No. 59-174828, No. 59-180016).

Furthermore, the present inventors have found that when stainless steel is the target, the surface to be inspected cannot be sufficiently dissolved by the corrosive solution used in the sulfur print method or the phosphor print method. We have developed a new method for detecting dissolving phosphorus segregation areas and previously filed an application (Japanese Patent Application No. 182765-1982).

The latter method involves attaching a test sheet impregnated with an electrolytic solution to the surface to be tested, then anodically polarizing the test piece to dissolve it in a hyperpassive state, and then displaying the phosphorus that has permeated into the test sheet using a coloring reagent. This is a coloring method that allows phosphorus segregation areas in stainless steel to be detected clearly and with high resolution. However, when Fe is eluted in the Fe ²⁺ state (actively dissolved) during energization, the phosphorus coloring reagent is reduced and the entire surface becomes blue, making it impossible to detect phosphorus segregation areas. For this reason, it is necessary to change the elution form of Fe to Fe ³⁺ (hyperpassive dissolution), and this method cannot be applied to steel types that cannot be dissolved in the hyperpassive region. In other words, when stainless steel is electrolyzed in an oxidizing solution, Cr
Steel types with high content can be melted in the hyperpassive region, but
Conventional methods could not be applied to steel types with low Cr content because melting progresses in the active region.

<Objective of the Invention> The object of the present invention is to detect phosphorus segregated areas in metal materials, particularly stainless steel with a low Cr content, which can be detected on a test paper as easily as the conventional sulfa print method. The present invention provides a method.

<Structure of the Invention> According to the present invention, a solution containing an oxidizing agent is brought into contact with the surface to be tested of a metal material and held for a certain period of time, and then a test sheet is pasted on the surface to be tested. An electrolytic solution containing 0.1 to 20 wt% molybdate ions and an oxidizing agent is interposed between the test sheet and the test sheet, and a cathode plate is brought into contact with the test sheet,
There is provided a method for detecting a phosphorus segregated portion in a metal material, which comprises performing electrolysis using the test surface as an anode, peeling off the test sheet after electrolysis, and treating the test sheet with a reagent containing a reducing agent. Ru.

Hereinafter, the content of the present invention will be explained in detail.

When evaluating the internal defects of steel, the present inventors
Focusing on the importance of detecting phosphorus segregation sites, we have investigated a method for detecting phosphorus segregation sites in metal materials that can be applied to stainless steel with a low Cr content.

As a result, there is a gap between the surface of the metal material to be tested and the test sheet for printing the phosphorus segregation pattern.
After contacting a solution containing an oxidizing agent and holding it for a certain period of time, a test sheet is pasted on the surface to be tested, and at least 0.1 to 20 wt% of molybdate ions and the oxidizing agent are placed between the surface to be measured and the test sheet. It was discovered that the test surface could be dissolved in the hyperpassive region by intervening an electrolytic solution containing the phosphor and energizing it, and furthermore, by treating the phosphorus occluded in the sheet with a reagent containing a reducing agent, the phosphorus could be dissolved. It was found that segregation sites could be clearly detected with high resolution.

Furthermore, the following findings were obtained regarding the passive film that forms on the surface of stainless steel.

That is, when steel with a high Cr content (mainly 16% or more) is immersed in an electrolytic solution containing an oxidizing agent, a passive film is immediately formed on the surface metal. This film is dense and stable, so it is difficult to break, and upon anodic polarization, it gradually turns into a hyperpassive film, and dissolution proceeds in the hyperpassive region.

On the other hand, steel types with low Cr content (mainly less than 16%,
16Cr steel, etc.), the passive film that is formed is unstable, so the film formation and dissolution are repeated. Therefore, when electricity is applied, Fe is eluted as Fe ²⁺ , and the eluted Fe ²⁺ reduces the molybdate reagent.
The entire surface becomes blue.

Therefore, the present inventors believed that active solvents could be suppressed by forming a stable film in advance on steel types with low Cr content, and as a result of various studies,
It was found that when a solution containing a strong oxidizing agent was brought into contact with the test surface, a stable passive film was formed, and that only hyperpassive dissolution proceeded by energization.

Here, the solution containing the oxidizing agent used is nitric acid,
In addition to chromic acid and hydrogen peroxide, there are solutions containing metal ions such as Ce ⁴⁺ and Fe ³⁺ , and oxidizing solutions that do not affect the coloration of phosphorus can be used. When using nitric acid, the concentration of nitric acid is preferably 0.5N or more.
Furthermore, when Ce ⁴⁺ is used, the concentration of Ce ⁴⁺ is preferably 0.01 mol/or more. Nitric acid or Ce ⁴⁺
The reason why the concentrations of are set to 0.5N and 0.01 mol/or higher, respectively, is that a stable oxide film will not be formed if the concentration is less than 0.5N or 0.01 mol/. Note that other oxidizing agents may be used as long as they have the same oxidizing power as the above solution.

There are various ways in which the oxidizing solution can be used as a film forming agent.

The first method is to prepare a water-containing sheet, impregnate the sheet with the above-mentioned solution, and then apply this wet sheet to the surface to be inspected, and leave the wet sheet attached for a certain period of time.

The second method is to use a dried sheet and the above-mentioned solution, in which the dried sheet is pasted on the surface to be tested and the acid solution is impregnated between the sheet and the surface to be tested.

The third type is a dry sheet in which a sheet is impregnated with a solution containing the oxidizing agent, dried, and the reagent is supported within the sheet. When using this dry sheet, it is sufficient to attach the dry sheet to the surface to be inspected and to impregnate water or an acid solution between the sheet and the surface to be inspected.

Alternatively, the solution may be brought into contact with the test surface by coating or the like without using any sheet at all.

The sheet used to form the film may be made of wood, cloth, synthetic resin, leather, or any other material that can support an oxidizing solution, but filter paper or the like is usually used.

As described above, when an oxidizing solution is brought into contact with the surface to be tested, a stable passive film is formed. After the film is formed, printing can be performed by electrolyzing the surface to be tested as an anode. That is, a test sheet is pasted on the surface to be tested, and at least 0.1~
An electrolytic solution containing 20 wt% molybdate ions and an oxidizing agent is interposed, and a cathode plate is brought into contact with the test sheet, and electrolysis is performed using the test surface as an anode. After electrolysis, the test sheet is peeled off, and then the test sheet is removed. The test sheet is treated with a reagent containing a reducing agent to develop color.
The cathode plate used here is aluminum, platinum,
Any conductive material can be used, such as copper, stainless steel, and graphite plates.

The test sheet to be used may be anything that can support the electrolyte, such as wood or synthetic resin, but it is preferable to fill one side of a high-quality paper with a powdered inorganic compound, and then apply a gelatin solution on top of it. Good test sheet. For example, using high-quality paper made of hydrophilic pulp fibers, one side of the paper is filled with a powdered inorganic compound such as barium sulfate, white titanium, talc, clay, etc. to fill in the voids in the fiber layer and smooth the surface. It's a good idea to leave it there. Similarly to the test sheet, the sheet impregnated with or adsorbed with the oxidizing agent solution can also be made of the above materials.

This inorganic compound also has the effect of improving the opacity of the paper surface and the contrast of the coloring layer. In order to obtain a clear printed image, it is important to bring the surface to be inspected and the surface of the test sheet into close contact with each other through the electrolyte and to prevent the electrolyte from spreading. By fixing gelatin, polyvinyl alcohol, starch, etc., a test sheet with excellent adhesion can be obtained, and bleeding of printed images due to electrolyte diffusion can also be suppressed.

Preferably, a water-absorbing material such as a filter paper sufficiently impregnated with an electrolytic solution is inserted between the test sheet and the cathode plate. This is to replenish the test sheet with the electrolyte contained in filter paper or the like. Although electrolysis can be performed using the test sheet alone, by using the above-mentioned impregnated filter paper in combination, a sufficient amount of electrolysis can be obtained on the surface to be tested. Any material other than filter paper may be used as long as it can be impregnated with the electrolyte, such as absorbent cotton, fibrous materials such as cloth, gel materials, leather, etc.

The electrolytic solution contained in the test sheet is preferably a solution containing a phosphorus coloring reagent and an oxidizing agent, preferably 0.5
~7N nitric acid with 0.1~20wt% molybdate ions added is good.

The first reason for using an oxidizing agent is to cause phosphorus eluted from the phosphorus segregation area to react with molybdate ions, which are coloring reagents, and it is necessary to oxidize phosphoric acid to orthophosphoric acid. The second reason is to maintain dissolution in the overpassive region, and to suppress dissolution of the film during energization.

In addition, the reason for adding molybdate salts such as ammonium molybdate to the electrolytic solution is to immediately precipitate eluted phosphorus as phosphomolybdic acid (molybdenum yellow) and suppress the diffusion of phosphoric acid radicals occluded in the test paper. This is because the printed image can be prevented from bleeding.

Examples of reagents that can be used as the molybdate include sodium molybdate, lithium molybdate, magnesium molybdate, calcium molybdate, and potassium molybdate.

It is preferable that the concentration of nitric acid added here is 0.5-7N and the concentration of molybdate ion is 0.1-20wt%.If the acid concentration is outside this range or if the molybdate ion concentration is less than 0.1wt%, molybdenum yellow This is because the formation is insufficient, and when the molybdate ion concentration exceeds 20 wt%, the molybdate itself develops color, making it impossible to identify the phosphorus segregation area.

As an oxidizing agent to replace nitric acid, the same solution as the oxidizing agent-containing solution for film formation can be used, and in addition to chromic acid and hydrogen peroxide, it also contains metal ions such as Ce ⁴⁺ and Fe ³⁺ . Solution can be used.

There are various ways to use the test sheet as a material for detecting phosphorus segregation.

The first is oxidizing agents, especially 0.5-7N nitric acid and 0.1
an aqueous solution containing ~20wt% molybdate ions;
This method uses a dried test sheet. When using this solution, a dry sheet is attached to the surface to be tested, the aqueous solution is interposed between the sheet and the surface by spraying, coating, etc., and electricity is applied. The solution may be an aqueous solution or an alcohol solution.

The second method is to impregnate the sheet with the above solution and use it as a wet sheet. This wet sheet may be attached to the surface to be tested and energized.

The third test sheet is a dry sheet impregnated with a solution containing molybdate ions and dried to support the reagent within the test sheet. When using this dry sheet, attach the dry sheet to the surface to be tested, and add an oxidizing agent between the sheet and the surface to be tested, especially 0.5
~7N nitric acid solution may be included so that the concentration of molybdate ions falls within the above-mentioned range.

As mentioned above, by interposing an oxidizing agent and molybdate ions between the surface to be inspected and the test sheet,
When dissolved by electrolysis, phosphorus is eluted from the test surface and is occluded in the test sheet as molybdenum yellow. By immersing this test sheet in a solution containing a reducing agent, the phosphorus becomes molybdenum blue and exhibits a blue color. This allows the phosphorus segregation area to be determined.

Examples of the reducing agent include, in addition to stannous chloride, hydroquinone, hydrazine sulfate, ascorbic acid, and the like. When using stannous chloride, it is preferable to use a solution with a stannous chloride concentration of 0.1 to 20 wt% and hydrochloric acid of 0.5 to 6N.

The concentration of stannous chloride was set to 0.1 to 20 wt% because
Less than 0.1wt%, the reducing power is insufficient, and 20wt%
This is because if it exceeds %, no effect on the reducing power will be seen even if more is added. The reason why the hydrochloric acid concentration was set to 0.5 to 6N is that if it is less than 0.5N, there is a problem that molybdic acid itself is reduced, and if it exceeds 6N, salt vapor will be generated and the working environment will deteriorate. Note that other reducing agents may be used as long as they have the same reducing power as above.

<Example> Next, the present invention will be specifically explained using examples.

Example 1 SUS-410 stainless steel (Cr: 13wt%, P:
After polishing the cross-section of the solidified and segregated part of a continuous cast piece (0.028 wt%) with Enamely paper #150 and wiping off the dirt on the surface to be examined with absorbent cotton, the surface was covered with a wet sheet containing 4.5N nitric acid aqueous solution. It was pasted on the inspection surface. After leaving the sheet as it is for 10 minutes and peeling it off from the surface to be tested, a wet test sheet impregnated with an aqueous solution containing 6wt% ammonium molybdate-4.5N nitric acid was pasted onto the surface to be tested. The surface to be tested was electrolyzed using a constant current method (current density 3 mA/cm ² ). Ten
After 5 minutes, the test sheet was peeled off from the surface to be tested and immersed in a 7wt% stannous chloride-4N hydrochloric acid aqueous solution for 5 minutes.
Washed well. The print result is shown in FIG.

Example 2 The cross section of the solidified and segregated part of a continuous slab of SUS-410 stainless steel was polished with #150 emery paper, and after wiping off the dirt on the test surface with a degreased surface, a sheet was attached to the test surface. did. This sheet was wetted with an aqueous solution containing 1wt% potassium dichromate-2N nitric acid, left for about 15 minutes, then peeled off, and a dry sheet containing ammonium molybdate and cerium nitrate (ammonium molybdate 1.2
g/m ² , cerium ammonium nitrate 0.4 g/m ² )
Attached. After uniformly moistening this test sheet using absorbent cotton impregnated with 4N nitric acid, the surface to be tested was electrolyzed using a galvanostatic method (current density: 5 mA/cm ² ).
After 5 minutes, the test sheet was peeled off from the surface to be tested and 7wt%
It was immersed in a stannous chloride-4N hydrochloric acid aqueous solution for 5 minutes and then washed with water. The print result is shown in FIG.

Example 3 SUS-420 stainless steel (Cr: 13wt%, P:
After polishing the cross section of the solidified and segregated part of the continuous cast piece (0.03wt%) with emery paper #150 and thoroughly wiping off the dirt on the test surface with absorbent cotton, apply cerium ammonium nitrate (0.5g/m2) to the test surface. ² ) A dry sheet containing the following ingredients was attached. This sheet was evenly wetted using a degreased surface impregnated with 4N sulfuric acid, left for about 20 minutes, then peeled off, and a test sheet was pasted on the surface to be tested.
This test sheet was uniformly moistened using absorbent cotton impregnated with an aqueous solution containing 6 wt% ammonium molybdate-3N nitric acid, and then the surface to be tested was electrolyzed by a galvanostatic method (current density 3 mA/cm ² ). After 15 minutes, the test sheet was peeled off from the surface to be tested and 7wt% stannous chloride was added.
After being immersed in a 4N hydrochloric acid aqueous solution for 5 minutes, it was thoroughly washed with water. The print result is shown in FIG.

Example 4 The cross section of the solidified and segregated part of a continuous slab of SUS-410 stainless steel was polished with #150 emery paper, and the dirt on the test surface was thoroughly wiped off with absorbent cotton, and then the test piece was immersed in a 6N nitric acid solution. did. After 15 minutes, remove the test piece, wash it thoroughly with water, and apply 6wt on the surface to be tested.
A wet test sheet impregnated with an aqueous solution containing % ammonium molybdate - 4.5N nitric acid is pasted on the surface to be tested, and the surface to be tested is subjected to the galvanostatic method (current density
Electrolysis was carried out at 4 mA/cm ² ). After 10 minutes, the test sheet was peeled off from the surface to be tested, immersed in a 7wt% stannous chloride-4N hydrochloric acid aqueous solution for 10 minutes, and then thoroughly washed with water. The print result is shown in FIG.

Example 5 After polishing the cross section of the solidified and segregated part of a continuously cast SUS410 stainless steel slab with #150 emery paper and wiping off the dirt on the test surface with absorbent cotton, the test piece was
Immersed in 6N nitric acid solution. After 15 minutes, the test piece was taken out and thoroughly washed with water, and then a wet test sheet impregnated with an aqueous solution containing 6wt% ammonium molybdate-4.5N nitric acid was attached to the test surface. Constant potential method (+1200mV vs
SCE). After 20 minutes, the test sheet was peeled off from the surface to be tested, immersed in a 7wt% stannous chloride-4N hydrochloric acid aqueous solution for 10 minutes, and then thoroughly washed with water. The print result is shown in FIG.

Comparative Example 1 The cross section of the solidified and segregated part of a continuously cast piece of SUS-410 stainless steel was polished with emery paper #400, and after wiping off the dirt on the test surface with a degreased surface, ammonium molybdate was applied to the test surface. Dry test sheet containing (ammonium molybdate 1.2g/m ² )
Attached. After uniformly moistening this test sheet using absorbent cotton impregnated with 3N nitric acid, the surface to be tested was electrolyzed using a galvanostatic method (current density: 5 mA/cm ² ).
After 10 minutes, the test sheet was peeled off from the surface to be tested and 7wt%
After being immersed in a stannous chloride-4N hydrochloric acid aqueous solution for 5 minutes, it was thoroughly washed with water. The print result is shown in FIG.

<Effects of the Invention> According to the method for detecting phosphorus segregated areas of the present invention, since the electrolytic method is applied to the pre-corrosion of the test surface, it is possible to arbitrarily increase the amount of dissolution on the test surface, and the phosphorus content can be increased. Phosphorus segregation areas can be detected even in low-quality samples.

Since the electrolysis method is extremely simple, it can be easily implemented at actual work sites as a method for detecting the central segregation of large steel ingots and continuous slabs.

In particular, in stainless steel with a low Cr content, which has been difficult to detect in the past, the formation of a hyperpassive film by preliminary treatment before electrolysis makes the detection effect of phosphorus segregation areas remarkable.

In addition, it can be easily and efficiently used to detect segregated portions of steel materials on-site, such as in factories, and can be recorded and stored, making it extremely convenient.

[Brief explanation of the drawing]

FIGS. 1 to 6 are printed photographs of metal structures, that is, phosphorus segregation areas of steel materials. Figures 1 and 2
3, 4, and 5 are print photographs of phosphorus segregated areas obtained in Examples 1, 2, 3, 4, and 5, respectively. FIG. 6 is a phosphor print photograph obtained in Comparative Example 1 using the conventional phosphor print method.

Claims (1)

[Claims] 1. After bringing a solution containing an oxidizing agent into contact with the surface to be tested of the metal material and holding it for a certain period of time, a test sheet is pasted on the surface to be tested, and at least 0.1 to 20wt is placed between the surface to be tested and the test sheet. % of an electrolytic solution containing molybdate ions and an oxidizing agent, a cathode plate is brought into contact with the test sheet, electrolysis is performed using the test surface as an anode, and after electrolysis, the test sheet is peeled off, and then the test is carried out. A method for detecting phosphorus segregation in a metal material, the method comprising treating a sheet with a reagent containing a reducing agent.