JP2011226993A - Method for detecting solidification structure of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting solidification structure of a type of steel which has relatively low differences in concentrations of solute elements due to segregation during solidification, particularly of a low-carbon steel which has a carbon concentration of 0.01 mass% or less.SOLUTION: After a cross section of a sample of steel cast slab is polished, the cross section of the sample is corroded to cause solidification structure of the steel to appear while applying supersonic waves of 30 kHz to 3 MHz to a corrosive liquid 15 in which microbubble-containing water is used as a solvent to subject the corrosive liquid 15 to water resonance. The sample is then washed and dried, and corroded holes formed in the cross section of the sample are filled with polishing powder. After transparent adhesive tape is stuck on the cross section of the sample to adhere the polishing powder in the corroded holes to the transparent adhesive tape, the transparent adhesive tape is removed and then stuck on a white mount.

Description

  The present invention relates to a method for detecting a solidified structure of steel.

  In the steel manufacturing process, detecting the solidification structure of the steel material (slab) after casting evaluates internal defects such as macro segregation such as crack occurrence of the slab and central segregation, and guarantees the quality of the subsequent process. Important to do. In addition, it is important to judge the abnormality of the casting process and the casting machine from the state of occurrence of these internal defects and correct and maintain them in an appropriate state to prevent the occurrence of internal defects. Furthermore, it is important to estimate the flow condition of the internal molten steel during solidification and the cooling rate of the slab from the inclination and interval of the dendritic structure called dendrites in order to optimize the operating conditions.

Observation of the steel structure by corrosion is roughly divided into the following two in principle.
(1) An electrochemical corrosion method using a potential difference due to a difference in solute concentration at each position in the sample.
(2) A chemical corrosion method using a chemical potential difference of crystal grains depending on phases having different chemical potentials and crystal orientations on the surface.

(1) is used to detect dendritic structures, internal cracks, and center segregation by utilizing, for example, concentration differences due to segregation of solute elements during solidification, and (2) is the chemistry of Fe ₃ C and ferrite. There are observation of pearlite structure using potential difference and macro corrosion using chemical potential difference due to surface orientation of coarse ferrite grains.

  Therefore, in order to detect the solidified structure of the slab, it is necessary to suppress the chemical corrosion of (2) and cause the electrochemical corrosion of (1).

  As a method for detecting a solidified structure of a slab, a method of corroding a sample surface using a corrosive liquid containing picric acid as a main component is generally implemented (Non-Patent Document 1). Further, an etch print method has been proposed as a method for recording the detected solidified structure (Patent Documents 1 to 4).

  Non-patent document 2 describes microbubbles that are important constituent elements of the present invention. Microbubbles are fine bubbles (in this specification, those having a diameter of 150 μm or less are referred to as microbubbles), and the internal gas is an atmosphere during the production of microbubbles, such as a mixed gas such as air, and other gases. Regardless of the type, etc., in addition to water purification and aquaculture, application and utilization in various industrial fields has been tried and attracted attention. Microbubbles can be used to clean interfaces such as removing various contaminants in water, impact pressure effects such as cell destruction in the medical field, and the ability to decompose refractory harmful substances. Examples include radical generation and oxidation, and physiological activity such as bioactivation that promotes safe and safe growth of the living body. Non-Patent Document 2 does not describe the application of microbubbles to the corrosion treatment of a solidified structure.

Japanese Patent Publication No. 64-2212 JP 61-170581 A Japanese Patent Laid-Open No. 1-227943 JP-A-7-198565

“Steel Handbook, Version III, Basics”, p. 205-208 (Japan Steel Association), published in 1981 by Maruzen Co., Ltd. "All about microbubbles, Hirofumi Taisei", 2006, published by Nihon Jitsugyo Publishing Co., Ltd.

  However, in the methods described in Patent Documents 1 to 4 and Non-Patent Document 1, a clear solidified structure can be detected in steel types having a relatively large concentration difference due to segregation of solute elements during solidification. It is difficult to detect solidified structure clearly in steel types with a relatively small concentration difference due to segregation, especially in low carbon steel with a carbon concentration of 0.01 mass% or less. It has become clear from the results. Further, in the methods described in Patent Documents 1 to 4 and Non-Patent Document 1, since the corrosion time is required for a long time, it is a problem to shorten the corrosion time.

  As described above, an object of the present invention is to provide a method for detecting a solidified structure more clearly, or a detection method capable of reducing the corrosion time when the clarity is the same. It is another object of the present invention to provide a method for detecting a solidified structure of a steel type having a relatively small concentration difference due to segregation of solute elements during solidification as described above, particularly a low carbon steel having a carbon concentration of 0.01 mass% or less. .

  A method for detecting a solidified structure of steel according to the present invention in accordance with the above object is a method for detecting a solidified structure of steel in which a sample cross section of a steel slab is ground and then corrodes the sample cross section. Solidified structure detection of steel characterized in that an ultrasonic wave of 30 kHz to 3 MHz is applied to a corrosive liquid using a water to cause the cross section of the sample to corrode and reveal a solidified structure of the steel while causing the corrosive liquid to resonate with water. Is the method. Thereby, an ultrasonic wave can be efficiently applied to the entire corrosive liquid, and a clear solidified structure can be detected.

  It is preferable that the ultrasonic wave is an ultrasonic wave having two or more different frequencies within a range of 30 kHz to 3 MHz. As a result, it is possible to efficiently apply ultrasonic waves to the entire corrosive liquid, and it is possible to detect a more solidified structure and shorten the corrosive time. Furthermore, it is preferable that the solvent contains picric acid. This makes it possible to reliably detect a solidified structure and shorten the corrosion time.

  After the sample cross section of the steel slab has been polished, the sample cross section is corroded by any of the methods described above, then washed and dried, and abrasive powder is embedded in the corrosion holes formed in the sample cross section. A transparent adhesive tape is applied to the cross section, and after the abrasive powder in the corrosion holes is adhered to the transparent adhesive tape, the transparent adhesive tape is peeled off, and then the transparent adhesive tape is applied onto a white mount. A method for detecting a solidified structure of steel is provided. According to this method, the clearly detected solidified tissue can be easily recorded.

  The steel slab may be steel having a carbon content of 0.01 mass% or less. It is possible to detect a solidified structure clearly for a steel type that is impossible with the conventional method.

  According to the present invention, ultrasonic waves can be efficiently applied to the entire corrosive liquid, and a clear solidified structure can be detected regardless of the degree of segregation of solute elements during solidification. Further, the corrosion time can be shortened as compared with the conventional case.

It is explanatory drawing which shows the electrochemical corrosion using the electrical potential difference by the solute concentration difference by each position in a sample. It is sectional drawing which shows embodiment of this invention.

  Conventionally, in detecting the solidified structure of steel, attempts have been made to use surfactants and corrosion aids in order to accelerate the reaction on the corroded surface and detect a clear solidified structure in a short time. For example, as described in Patent Document 2, a saturated aqueous solution of picric acid is used as a main corrosive solution, “Lypon F” (registered trademark) as a surfactant, and cupric chloride as a corrosion adjusting aid have been used. It was.

  However, when these materials are used, wastes accumulate on the corroded surface as the corrosion progresses, and the problem is that the corrosion is stagnated because the contact between the corroded surface and the corrosive liquid is hindered. For this reason, a clear solidified structure may not be obtained, or even if a clear solidified structure is obtained, a long time is required for the corrosion treatment.

  As a means for solving this problem, there has been performed a method in which ultrasonic vibration is applied to a corroding sample and a corrosive solution to remove and activate waste products on the corroded surface. However, when an ultrasonic wave is simply applied, the ultrasonic wave is highly linear and is transmitted in a one-dimensional manner. For example, when using a sample smaller than the ultrasonic wave transmission range, a corresponding effect can be obtained. When a sample that detects the solidification structure (for example, a large sample such as a continuous cast slab) is used, the ultrasonic vibration is not transmitted uniformly to the entire corroded surface but is transmitted locally (one-dimensional ultrasonic On the contrary, there is a defect that uneven corrosion tends to occur. In particular, when strong ultrasonic waves are applied locally, there is a drawback that erosion, that is, physical corrosion of the corroded surface easily occurs due to the cavity effect peculiar to ultrasonic waves.

  As described above, when ultrasonic vibration is applied directly to the corroding sample and the corrosive liquid, even if a clear solidified structure is obtained, uneven corrosion of the sample is generated, or a clear solidified structure is obtained by erosion. In some cases, the corrosion treatment time could not be shortened.

  In order to solve the above problems, the present inventors have studied a method of applying an ultrasonic wave that suppresses uneven corrosion and erosion of a sample and obtains a clear solidified structure. As a result, the inventors have conceived that microbubbles are included in the corrosive liquid.

  It is known that when an ultrasonic wave is applied to an aqueous solution (corrosive liquid) containing microbubbles, the aqueous solution enters a water resonance state when the ultrasonic frequency and the diameter of the microbubbles are in a resonance relationship.

  When the aqueous solution is in a water resonance state, the present inventors transmit ultrasonic waves almost uniformly to the entire corroded surface of the sample in the corrosion tank, that is, transmit ultrasonic waves three-dimensionally, and the entire corrosive liquid and the sample As a result, it was newly conceived that a clear solidified structure can be stably obtained, and the corrosion unevenness and erosion of the sample can be suppressed.

  Microbubble generation methods, which are important constituent elements of the present invention, include shearing of bubbles, ultrasonic waves, electrolysis, chemical reaction, and the like, but the operational effects of the present invention do not depend on the microbubble generation method. For example, in a shearing method in which microbubbles are generated by swirling an aqueous solution and air at an ultra-high speed, a hollow portion is formed at the swirling portion by swirling the propeller in the pump. The part is cut by turning to generate microbubbles.

  The minimum visible diameter of the microbubbles is about 150 μm, and it is generally difficult to visually confirm the presence of the microbubbles. However, the microbubbles immediately after the generation are generally considered to have a diameter of about 150 μm or less. As the diameter increases, bubbles tend to rise remarkably in the liquid, and bubbles of about 150 μm tend to rise in the liquid, and the lifetime of microbubbles (existence period in the liquid) is considered to be shortened. Therefore, it is preferable that at least the diameter of the microbubble is mainly 150 μm or less. The inventors obtained a suitable effect when the diameter of the microbubbles was set to 106 μm or less. In addition, since the gas inside a microbubble can melt | dissolve in a liquid, generally the minimum diameter immediately after microbubble generation is assumed to be about 0.01 micrometer.

  Here, the diameter (for example, 106 micrometers or less) of the above-mentioned microbubble was defined as follows. Using a sieve described in JIS Z8801-1 (for example, nominal opening 106 μm), the liquid containing microbubbles is passed through the sieve, and the diameter of the microbubbles in the liquid after passing through the sieve is less than the size of the nominal opening (106 μm). Defined below). The nominal openings (unit: μm) of JIS Z8801-1 include, for example, 150, 125, 106, 90, and 75, and can be appropriately selected. In addition, the maximum diameter of the microbubbles may be controlled by creating a sieve with an arbitrary nominal opening. Also, without using the above sieves, adjust the bubble shearing conditions, ultrasonic application conditions, electrolysis conditions, chemical reaction conditions, etc. of the microbubble generator so that the presence of bubbles is almost invisible. It can be determined that the microbubbles having a diameter of 150 μm or less are mainly used. Further, the concentration of microbubbles (pieces / mL) may be measured with a commercially available device (particle counter, bubble distribution measuring device, etc.).

  Concentration (number / mL) of microbubbles is such that when water containing microbubbles is generated by passing water not containing microbubbles through a microbubble generator, the initial concentration in water is at least about 20 (number / mL). When microbubbles of less than about 100 (pieces / mL) were generated and a corrosive solution using water containing these microbubbles as a solvent was used, an effect was obtained in the experiments of the present inventors.

  Further, according to the knowledge of the present inventors, in a configuration in which the water containing the generated microbubbles is supplied again to the microbubble generator and passed therethrough, the passing time of the microbubble generator (for example, more than 1 times the water capacity of the water tank) When the concentration was adjusted to 100 (pieces / mL) or more by adjusting the amount of time required to pass through the liquid, a clearer and easier-to-view solidified structure was obtained. On the other hand, when the concentration is too high, the liquid passing time becomes longer, and the microbubble generator becomes large and it becomes difficult to supply the microbubbles by adjusting the number. Therefore, when the expression of microbubble effect and workability are taken into consideration, the initial concentration in water is preferably 100 / mL to 5000 / mL.

  In the research of the present inventors, when applying ultrasonic waves to an aqueous solution (water, corrosive liquid, etc.) containing microbubbles as the solvent of the corrosive liquid, the ultrasonic liquid is resonated with water, and the frequency of the ultrasonic waves to be applied. In the case of an aqueous solution (water, corrosive liquid, etc.) containing microbubbles having a diameter of 150 μm or less or 0.01 to 106 μm, 30 kHz to 3 MHz is appropriate, the aqueous solution liquid surface greatly vibrates, and water resonates. I found out. At this time, it is more effective to apply ultrasonic waves having two or more different frequencies (for example, one ultrasonic frequency is twice or more the other ultrasonic frequency).

  As described above, the present inventors have found that the inclusion of microbubbles in the solvent of the corrosive liquid can realize improvement in the clarity of the solidified structure (or shortening of the etching time) and suppression of corrosion unevenness and erosion. .

The reason why this effect is manifested is considered to be as follows because the solidified structure is clearly etched by the corrosion reaction generally indicated by Fe + 2H ⁺ → Fe ²⁺ + H ₂ at the corrosion interface. In contrast to the H ₂ gas generated at the corrosion interface that inhibits the corrosion reaction, the microbubbles promote the removal of the H ₂ gas bubbles to substantially accelerate the corrosion reaction. The moving micro bubbles are uniformly dispersed in the corrosive liquid, and the supply of H ⁺ ions to the corrosive interface is promoted by promoting the replacement of the corrosive liquid at the corrosive interface with the dispersion and removal of the H ₂ gas bubbles. , Etc.

As shown in FIG. 1, the corrosion reaction proceeds by a local cell (local cell) composed of a segregation part 1 (anode) and a non-segregation part 2 (cathode). In the segregation part 1 (anode), Fe is Fe. ^A reaction in which H ⁺ ions become hydrogen gas (H ₂ ) occurs in the non-segregated portion 2 (cathode). Here, Fe ²⁺ ions locally concentrate in the segregation part 1, but Fe ²⁺ ions diffuse and dilute from the segregation part 1 due to the uniform diffusion effect of microbubbles, while hydrogen gas (H _{2) in the} non-segregation part _2. ) Is generated and the corrosion reaction is difficult to proceed, it can be understood that hydrogen gas (H ₂ ) is easily removed by the combined coalescence of micro bubbles and hydrogen gas (H ₂ ) bubbles, and this phenomenon uses micro bubbles. This is considered to be the reason for shortening the time for etching the solidified structure and improving the clarity.

The reason why the method of applying the ultrasonic wave to the corrosive liquid containing water containing microbubbles and resonating the corrosive liquid with water is effective in detecting the solidified structure of steel is that the single effect of the corrosive liquid containing microbubbles described above is used. In addition, the following reasons can be considered. That is, the microbubbles dispersed in the liquid vibrate due to water resonance, and the corrosion liquid and the sample vibrate uniformly and three-dimensionally to promote the removal of waste from the corrosion interface and the activation of the corrosion interface (Fe This is to promote diffusion promotion of ²⁺ ions from the segregation part, promotion of removal of hydrogen gas (H ₂ ) bubbles), and the like.

  The reason why the effect is further improved by applying ultrasonic waves having two or more different frequencies is presumed to be that there are a plurality of vibration modes and the bias of fine vibrations at the corrosion interface is reduced. Furthermore, there is a diameter of microbubbles that resonates according to the frequency of the ultrasonic wave, and by adopting two or more frequencies, the number of resonating microbubbles increases, and the corrosive liquid and sample vibrate more strongly. It is considered that a clearer solidified structure was obtained.

  As explained above, when microbubbles are used, it is clear that the clarity of the solidified structure obtained by corrosion is improved compared to the case where microbubbles are not used. As for the corrosive liquid, the corrosive liquid mainly composed of picric acid provides the most stable and clear solidified structure. Further, “Lypon F” (registered trademark) as a surfactant and cupric chloride as a corrosion control aid may be added to a corrosive solution containing picric acid.

  Further, the operational effects of the microbubbles of the present invention are not impaired even when used in combination with conventionally used surfactants and corrosion control aids, and do not impair the respective operational effects. However, the use of surfactants and corrosion control aids not only increases costs but also may complicate the treatment of waste liquid after corrosion, and may be combined as appropriate according to the application and situation.

  As a means for recording a solidified structure, it is possible to polish a cross section of a substantially rectangular parallelepiped slab (sample) where the solidified structure is to be detected, corrode the sample cross section for a predetermined time by the above method, and then take a photograph. The recording may be performed by the following method that has been conventionally used. That is, pulling up the sample that has corroded the cross section, cleaning and drying the sample, embedding the abrasive powder in the corrosion hole formed in the sample cross section, sticking the transparent adhesive tape to the sample cross section, and transparently adhering the abrasive powder in the corrosion hole In this method, after the tape is adhered, the tape is peeled off, and then the tape is stuck on the white mount.

  By exposing the solidified structure using the above-described corrosive liquid according to the present invention, a clear solidified structure is photographed on the sample corroded surface after washing and drying of the sample and the white mount with the transparent adhesive tape attached thereto. It can be taken and recorded on a white mount.

  Further, according to the present invention, since corrosion of the corroded surface of the sample can be promoted, a steel type having a relatively small difference in concentration due to segregation of solute elements during solidification, which has conventionally been impossible to clearly detect a solidified structure, for example, A clear solidified structure can be detected even in a low carbon steel having a carbon concentration of 0.01 mass% or less.

  As for the method of applying ultrasonic waves to the corrosive liquid containing microbubbles, as shown in FIG. 2A, vibration devices 12 and 13 are installed outside the tank 11 containing the corrosive liquid, and the tank wall 14 is interposed. An ultrasonic wave is applied to the internal corrosive liquid 15 or the vibration devices 12 and 13 are immersed directly in the internal corrosive liquid 15 in the tank 11 as shown in FIG. Sound waves may be applied. However, in the case of FIG. 2B, since the vibration devices 12 and 13 may be corroded by the corrosive liquid 15, the vibration devices 12 and 13 are accommodated in a stainless steel case or covered with a corrosion-resistant resin. It is necessary to take measures such as The installation positions of the vibration devices 12 and 13 need only be within a range in which ultrasonic waves can be applied to a part of the corrosive liquid 15, and when a part of the system is in a resonance state, micro vibrations are three-dimensionally chained to Resonant state. In this way, normal application of ultrasonic waves can only give local vibration, whereas when ultrasonic waves of a specific frequency are applied to an aqueous solution containing microbubbles, water can be applied uniformly to the entire system. It is a feature of resonance.

  The present invention is not limited to the above-described embodiments, and can be changed without changing the gist of the present invention. For example, some or all of the above-described embodiments and modifications are possible. The method of detecting the solidified structure of steel of the present invention by combining the above is also included in the scope of the present invention.

  Next, examples carried out for confirming the effects of the present invention will be described.

  As a corrosive solution, a solidified structure of steel was detected for Examples 1 to 18 of the present invention using an aqueous solution in which 20 g / L of picric acid was added to water containing microbubbles. Further, in part (Invention Examples 13 to 15), either or both of cupric chloride 5 g / L and surfactant “Lypon F” (registered trademark) 20 g / L were added to the corrosive liquid. It was. The initial temperature of the corrosive liquid was 25 ° C., and the corrosion time was 30 to 90 minutes. As test materials, an ultra-low carbon steel for automobiles having a carbon concentration of 0.001 mass%, a low-carbon steel sheet for cold rolling with 0.01 mass%, and a medium carbon steel sheet for thick plates with 0.1 mass% were used. The diameter of the microbubble was adjusted to 106 μm or less (0.01 to 106 μm) in the initial state through the sieve. The application of ultrasonic waves was performed by installing two kinds of ultrasonic oscillators of 38 kHz and 100 kHz, which were obtained stably as a result of prior experiments, on the outer wall of the corrosion tank.

  The concentration of microbubbles generated (pieces / mL) is generally 20 (pieces / mL) to 100 (pieces / mL) by adjusting the flow time of the microbubble generator and the operating conditions of the microbubble generator. Experiments were performed under two conditions, when adjusted to less than 100 and when set to 100 to 1000 (pieces / mL).

  In addition, as a conventional example, normal water not containing microbubbles is used as a solvent for a corrosive solution, and corroded under the same components as in the present invention, corrosive solution, steel type, corrosion time, and no ultrasonic wave applied, and solidified structure Relative evaluation was performed on the intelligibility. Specifically, the solidification structure appearance situation of the conventional example corresponding to the present invention example was compared, ◎: the present invention example improved very clearly compared to the conventional example, ○: the present invention example compared to the conventional example △: The example of the present invention improved slightly more clearly than the conventional example, x: The example of the present invention was equivalent or unclear to the conventional example. The size of the specimen was H100 to 300 mm × W500 to 750 mm in terms of the size of the corroded surface, and the thickness was t50 to 100 mm. Table 1 shows the result list.

  Inventive Examples 1 to 3 use ultra-low carbon steel for automobiles having a carbon concentration of 0.001 mass% as a test material, and microbubbles having a diameter of 0.01 to 106 μm in an initial state of 100 to 1000 (pieces / piece mL) The corrosive solution obtained by adding 20 g / L of picric acid to an aqueous solvent containing two kinds of ultrasonic waves of 38 kHz and 100 kHz, or one of them, is caused to corrode for 30 minutes in a state of water resonance to form a solidified structure. This is an example. Compared with the conventional example in which a solidified structure is revealed only with a normal corrosive solution, the clarity of the solidified structure is improved in any case, and in particular, when two types of ultrasonic waves of 38 kHz and 100 kHz are superimposed and applied, the solidification is achieved. The organization became very clear.

  Examples 4 to 6 of the present invention use an ultra-low carbon steel for automobiles having a carbon concentration of 0.001 mass% as a test material, and microbubbles having a diameter of 0.01 to 106 μm in an initial state of 100 to 1000 (pieces / piece). mL) The corrosive solution obtained by adding 20 g / L of picric acid to an aqueous solvent containing two kinds of ultrasonic waves of 38 kHz and 100 kHz or one of them to cause water resonance and corroding for 90 minutes. This is an example. The same results as those of Invention Examples 1 to 3 were obtained.

  Inventive Examples 7 to 9 use a low-carbon steel sheet for cold rolling having a carbon concentration of 0.01 mass% as a test material, and microbubbles having a diameter of 0.01 to 106 μm in an initial state of 100 to 1000 (pieces / piece). mL) In a state where two kinds of ultrasonic waves of 38 kHz and 100 kHz are applied to a corrosive solution obtained by adding 20 g / L of picric acid to an aqueous solvent containing water and resonated with water, it is corroded for 30 to 90 minutes to reveal a solidified structure. This is an example. Compared with the conventional example in which the solidified structure appeared only with a normal corrosive solution, the solidified structure was improved very clearly in each case.

  Inventive Examples 10 to 12 use a medium carbon steel plate for thick plates having a carbon concentration of 0.1 mass% as a test material, and microbubbles having a diameter of 0.01 to 106 μm in an initial state of 100 to 1000 (pieces / piece). mL) In a state where two kinds of ultrasonic waves of 38 kHz and 100 kHz are applied to a corrosive solution obtained by adding 20 g / L of picric acid to an aqueous solvent containing water and resonated with water, it is corroded for 30 to 90 minutes to reveal a solidified structure. This is an example. Compared with the conventional example in which the solidified structure appeared only with a normal corrosive solution, the solidified structure became clear in all cases. However, the improvement allowance depends on the time, and when the corrosion time is as long as 90 minutes as in Example 12 of the present invention, the difference from the conventional example is not so large. This is because the solidified structure generally tends to appear as the carbon concentration increases, and the solidified structure tends to appear as the corrosion time increases. Therefore, the conventional example corresponding to Example 12 of the present invention. However, since the corrosion time is as long as 90 minutes, it seems that the solidified structure has come out sufficiently under the conventional corrosion conditions. In other words, the effect of the present invention is more easily exhibited in steel types that are less likely to have a solidified structure, such as steel having a carbon content of 0.01 mass% or less.

  Inventive Examples 13 to 15 are examples in which either or both of 5 g / L of cupric chloride and a surfactant “Lypon F” (registered trademark) 20 g / L were added to the corrosive liquid of the present invention. In either case, the clarity of the solidified tissue was greatly improved as compared with the conventional examples corresponding to each case.

  On the other hand, Examples 16 to 18 of the present invention are examples in which the concentration of microbubbles in the initial state is as low as 20 / mL or more and less than 100 / mL, although the corrosive liquid contains microbubbles. Although the clarity was not inferior to that of, improvement cost was very small. That is, in the present invention example containing microbubbles in the corrosive liquid, the clarity of the solidified structure revealed compared to the comparative example not containing microbubbles was improved, but the effect of the present invention was sufficiently exhibited. This means that it is more preferable to adjust and control the concentration of microbubbles so that a sufficient water resonance state is obtained.

  On the other hand, Comparative Examples 1 to 3 are examples in which ultrasonic waves were applied to a corrosive solution that did not contain microbubbles. In any case, corrosion was uneven and overall clarity was not improved.

  As described above, the present invention is a solidified structure of a steel type in which the concentration difference due to segregation of solute elements during solidification, which is difficult to detect the solidified structure, particularly a low carbon steel having a carbon concentration of 0.01 mass% or less. Can be detected clearly, which is extremely useful in the industry.

DESCRIPTION OF SYMBOLS 1 Segregation part 2 Non-segregation part 11 Tank 12, 13 Ultrasonic oscillator 14 Tank wall 15 Corrosion liquid

Claims (5)

  In a method for detecting a solidified structure of steel that corrodes the sample cross section after polishing the sample cross section of the steel slab, an ultrasonic wave of 30 kHz to 3 MHz is applied to a corrosive solution using water containing microbubbles as a solvent. A method for detecting a solidified structure of steel, wherein the solidified structure of the steel is revealed by corroding the cross section of the sample while causing the corrosive liquid to resonate with water.   2. The method for detecting a solidified structure of steel according to claim 1, wherein the ultrasonic waves are ultrasonic waves having two or more different frequencies within a range of 30 kHz to 3 MHz.   The method for detecting a solidified structure of steel according to claim 1 or 2, wherein the solvent contains picric acid.   After the sample cross section of the steel slab is polished, the sample cross section is corroded by the method according to any one of claims 1 to 3, and then washed and dried, and polished to the corrosion holes formed in the sample cross section. After embedding powder, sticking a transparent adhesive tape to the sample cross section, adhering the abrasive powder in the corrosion hole to the transparent adhesive tape, peeling off the transparent adhesive tape, and then attaching the transparent adhesive tape on a white mount A method for detecting a solidified structure of steel, characterized by comprising:   The method for detecting a solidified structure of steel according to any one of claims 1 to 4, wherein the steel slab is steel having a carbon content of 0.01 mass% or less.

Images