JP4005583B2 - Method for extracting oxide inclusions in metal - Google Patents

Description

  The present invention relates to a method for effectively extracting nonmetallic inclusions in metal, particularly oxide inclusions contained in steel materials.

  Non-metallic inclusions in metals, particularly oxide inclusions contained in steel materials, have a great influence on various properties of the materials such as strength, toughness, workability, and surface properties. For these reasons, it is of great concern to engineers who handle steel materials to evaluate the number and size of oxide inclusions in steel.

As one method for extracting oxide inclusions, an extraction method by acid decomposition (acid decomposition method) is known. This method is known as a method for extracting oxide inclusions, particularly Ai ₂ O ₃ and SiO ₂ and composite oxides mainly composed of these oxides. For example, Non-Patent Document 1 discloses an oxide system while heating an acidic solution. A method for extracting inclusions is shown. Moreover, as an acidic solution to be used, nitric acid aqueous solution (warm nitric acid method) and sulfuric acid sulfuric acid aqueous solution (warm sulfuric acid method) are mentioned. Among these, the warm nitric acid method is a method that is generally widely adopted as a method for extracting non-metallic inclusions in metal materials.

  FIG. 1 is an explanatory diagram showing a basic procedure in the warm nitric acid method. First, an aqueous nitric acid solution 2 and a sample 3 are placed in a beaker 1 [FIG. 1 (a)]. Next, the nitric acid aqueous solution 2 is heated by the heater 4 (for example, about 90 ° C.), the sample 3 is dissolved, and the oxide inclusions present in the sample 3 are eluted [FIG. 1 (b)]. The aqueous nitric acid solution 2 in which the elution of oxide inclusions has been completed is cooled and then filtered (membrane filter 5, filter base 6 and funnel 7), and the aqueous nitric acid solution 3 is stored in the flask 8 and remains as a residue on the membrane filter 5. Oxide inclusions are extracted [FIG. 1 (c)]. As the nitric acid aqueous solution 2 used, an aqueous solution obtained by adding a small amount of sulfuric acid [for example, 3 mL to 450 mL (milliliter) nitric acid aqueous solution] to nitric acid aqueous solution of nitric acid: water = 1: 3 is used.

In the warm nitric acid method as described above, when a normal steel material is used as a sample, Al ₂ O ₃ , SiO ₂ and composite oxides mainly composed of these can be extracted without problems. However, when a steel material having a high Si concentration is used, the SiO ₂ hydrate [SiO ₂ .nH ₂ O] is mainly used in the elution step of the oxide inclusions [FIG. 1 (b)]. (Hereinafter referred to as “SiO ₂ gel”). When such SiO ₂ gel occurs is not measured should be measured as originally SiO ₂ inclusions, there is a problem that the prevent extraction after inclusion analysis. In particular, in the case of Si killed steel containing SiO ₂ as the main component, the SiO ₂ gel is generated from the SiO ₂ inclusions in the steel, or it is not derived from the SiO ₂ inclusions and is generated in the melting process. In some cases, it may be difficult to determine whether it has been made. In any case, it becomes difficult to accurately grasp the form of inclusions in the steel. Such a situation is not limited to the case where nitric acid is used as the acidic solution (warm nitric acid method), and the same applies to the case where sulfuric acid is used (warm sulfuric acid method).

From the viewpoint of preventing the generation of the SiO ₂ gel as described above, for example, a technique as shown in Non-Patent Document 2 has also been proposed. In this technique, an alkali solution such as NaOH is added between the steps shown in FIGS. 1B and 1C and heated to dissolve and remove the SiO ₂ gel. Such a process is also suggested in Non-Patent Document 1. However, in the case of using an alkaline solution, unless sufficient attention is paid to the NaOH concentration and the heating temperature, the SiO ₂ inclusion to be originally extracted and the complex oxide system mainly composed of this are preferably dissolved. Will lead to no situation.

In addition, regardless of which extraction method is used, extraction equipment such as beakers, membrane filters, and funnels [see FIG. 1] generally uses acid-resistant and inexpensive glass products. It has SiO ₂ as the main component, and in the melting step or extraction step, a part of this glass may be mixed in the solution, and another problem is that it prevents the inclusion analysis after extraction. is there.
"Iron and Steel Handbook IV (Third Edition)", edited by the Japan Iron and Steel Institute, published October 30, 1975, Maruzen, pp. 329-330 "Iron and Steel" Volume 55 (1969), Maekawa et al., Page 393

The present invention has been made to solve such problems in the prior art, and the object thereof is to prevent the generation of SiO ₂ gel which hinders analysis after extraction of oxide inclusions as much as possible. It is an object of the present invention to provide a method that can eliminate SiO ₂ mixed in in the filtration / extraction step as much as possible.

The method of the present invention that has been able to solve the above-mentioned problems is that the nitric acid solution or sulfuric acid solution is heated to 50 ° C. or higher in advance when extracting oxide inclusions in a metal sample by the warm nitric acid method or the warm sulfuric acid method. Therefore, the present invention has a gist in that a metal sample is poured into this solution and dissolved, and oxide inclusions are filtered and extracted. In carrying out this method, the oxide inclusions preferably contain at least SiO ₂ .

In this method, it is preferable that the material of the device in contact with the solution does not contain SiO ₂ in the dissolving step and the subsequent filtration and extraction step of oxide inclusions. Further, as a material not containing SiO _2, polytetrafluoroethylene.

In the present invention, since the nitric acid solution or sulfuric acid solution used for extraction of oxide inclusions is heated to 50 ° C. or higher in advance, the generation of SiO ₂ gel that hinders inclusion analysis can be prevented as much as possible. It was.

In order to achieve the above-mentioned object, the present inventors studied the generation process of SiO ₂ gel and the mixing route of SiO ₂ from other than the inclusions in the steel. As a result, it was found that the generation of SiO ₂ gel was caused by the heating method of the solution, and the mixed SiO ₂ was caused by the material of the equipment. Hereinafter, the operation and effect of the present invention will be described in more detail while explaining how the present invention was completed.

The SiO ₂ gel is generated when a steel material sample having a high Si concentration is immersed in a nitric acid solution and heated to 90 ° C. However, when the sample is put into the nitric acid solution, if the nitric acid solution is heated to a predetermined temperature in advance and the sample is put into the heated nitric acid solution, the amount of generated SiO ₂ gel can be reduced as much as possible. There was found.

  FIG. 2 is an explanatory diagram showing the basic procedure of the method of the present invention. First, the nitric acid aqueous solution 2 is put into the beaker 1, the nitric acid aqueous solution is heated (at 50 ° C. or higher) by the heater 4 [FIG. 2A], and the sample 3 is put into the heated nitric acid aqueous solution. And the sample 3 is melt | dissolved by the nitric acid aqueous solution 2, and the oxide type inclusion which exists in the sample 3 is eluted [FIG.2 (b)]. The aqueous nitric acid solution 2 after dissolution and elution is cooled and filtered (membrane filter 5, filter base 6 and funnel 7), the aqueous nitric acid solution 3 is stored in the flask 8, and oxide inclusions as residues on the membrane filter 5. [FIG. 2 (c)].

When a steel sample containing 1% by mass of Si is put into a nitric acid solution, the state of generation of SiO ₂ gel when the temperature when the nitric acid solution is preheated (hereinafter referred to as “preheating”) is varied. Shown in Table 1 below. At this time, the evaluation criteria of the generation state of the SiO ₂ gel are as follows.

(Generation status of SiO ₂ gel)
×: It was confirmed that SiO ₂ gel was visually observed in the beaker, the funnel, or the filter.
Δ: Although it cannot be visually confirmed that SiO ₂ gel is generated, when the residue on the filter is checked with a microscope, generation of SiO ₂ gel is confirmed and cannot be distinguished from oxide inclusions. It is difficult to measure the number of objects and analyze the composition.
○: When the residue on the filter is observed with a microscope, generation of SiO ₂ gel is confirmed, but it is easy to distinguish from inclusions, and it is difficult to measure the number of inclusions and to analyze the composition.
◎: even by observing the remaining debt on the filter under a microscope, SiO ₂ gel is not observed.

As is clear from this result, in order to reduce the amount of generated SiO ₂ gel, the preheating temperature needs to be at least 50 ° C., preferably 60 ° C. or more. The upper limit of the preheating temperature is not particularly limited. However, if the temperature exceeds 90 ° C., the sample may be bumped when a high-temperature solution is added, which is not safe for work. From this point of view, the preheating temperature is preferably 90 ° C. or lower, more preferably 80 ° C. or lower.

The reason why the generation of SiO ₂ gel can be reduced as much as possible by preheating the solution to which the sample is charged has not been clarified, but probably the Si in the steel and the water in the solution There is a temperature at which reaction is likely to occur, and if it is heated rapidly above this temperature, it will be difficult to form hydrates.

Next, the present inventors investigated the influence of equipment materials such as beakers and funnels on the generation of SiO ₂ . When the materials of the beaker 1, the filter base 6 and the funnel 7 shown in FIGS. 1 and 2 are all made of glass (the material of the membrane filter 5 is made of nylon), all or a part of these materials are made of a heat-resistant poly. When tetrafluoroethylene (PTFE: Teflon (registered trademark)) is used, the series of operations (blank test) shown in FIG. The number of inclusion particles having a major axis of 20 μm or more containing SiO ₂ was measured with a micro analyzer (Electron Probe X-ray Micro Analyzer: EPMA). The results are shown in Table 2 below.

From this result, we could consider as follows. If the steel material is not dissolved, there should normally be no residue on the filter. However, it was found that when at least one of the beaker, the filter base and the funnel is made of glass, particles containing SiO ₂ are detected. In contrast, when all of the beaker, funnel, and filter base were made of PTFE, particles containing SiO ₂ were not detected. In addition, about the flask in which a waste liquid enters, since the solution did not contact by the time a residue was extracted on a filter, it was judged that it may be glass.

In the above description, the case where nitric acid is used as the acidic solution for dissolving and extracting the sample has been described. However, the situation where SiO ₂ gel is generated is the same when sulfuric acid is used. That is, even when sulfuric acid was used as the solution for dissolution, it was confirmed that the same effect as described above could be obtained if the solution was preheated (50 ° C. or higher).

In addition, as the metal material to be used in the present invention, a steel material that is expected to contain at least SiO ₂ is optimal, but is not limited to a steel material, and can be applied to, for example, a copper alloy or a nickel alloy. . In addition, it is not necessarily limited to those containing SiO _2, and from the viewpoint of confirming the presence or absence, even a metal material that is expected to mainly contain Al ₂ O ₃ as an oxide-based inclusion contained. Applicable.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and any design changes in accordance with the gist of the preceding and following descriptions are technical aspects of the present invention. It is included in the range.

Example 1
C: 0.01%, Mn: 0.1%, P: 0.005%, S: 0.005%, Al; 0.01%, and iron 50k containing other inevitable impurities are experimentally dissolved. Made and cast. Since this iron material is Al killed steel, the composition of the inclusions produced is mainly Al ₂ O ₃ . Twelve acid-dissolved samples (25 g) were cut out from the center of the steel ingot.

The cut sample was dissolved in the manner shown in FIG. 2 to extract inclusions. After dissolution, nitric acid (HNO ₃ ): 250 mL (milliliter) was added with water to 700 mL, and 10 mL of sulfuric acid was added to a 2 L capacity beaker. A 25-g steel sample was put into this and melt | dissolved. A membrane filter having a pore diameter of 1 μm was used as a membrane filter used for filtration. The residue on the filter was analyzed by EPMA, and the number of inclusions containing Ai ₂ O ₃ or SiO _{2 and} having a major axis of 20 μm or more was counted. At this time, as a comparative example, an example in which glass is used for a beaker, a funnel, a filter stand, etc., or preheating is performed by a method in which preheating is not performed before the sample is put into the solution (the method shown in FIG. 1). Although it went, the example which used glass for the shift | offset | difference of one or more of a beaker, a funnel, and a filter stand was investigated. These results are collectively shown in Table 3 below.

From this result, we could consider as follows. In this example, since the Si concentration of the molten steel was relatively low, no SiO ₂ gel was generated regardless of the presence or absence of preheating and the heating temperature. Of these, No. Examples of 1 to 7 and 12 are examples in which PTFE is used for all of the beaker, the funnel, and the filter base, but no SiO ₂ is detected, and it can be seen that the inclusion is only Al ₂ O ₃ system. .

In contrast, no. In 8-11, glass was used in one or more of the beaker, funnel, and filter base, but these detected SiO _{2 that} could not be produced in the steel, and the dissolution / extraction process It was thought that it had been mixed in.

Example 2
C: 0.01%, Mn: 0.1%, P: 0.005%, S: 0.005%, Al; 0.01%, and 50 kg of iron containing other inevitable impurities are experimentally dissolved. Made and cast. Since this iron material is Si killed steel, the composition of the inclusions produced is mainly composed of SiO ₂ . Twelve acid-dissolved samples (25 g) were cut out from the center of the steel ingot.

Using the cut sample, dissolution, extraction, and inclusion measurement were performed in the same manner as in Example 1. Nitric acid (HNO ₃ ): 250 mL of water was added to 700 mL, and 10 mL of sulfuric acid was added to a 2 L beaker. A 25-g steel sample was put into this and melt | dissolved. A filter having a pore size of 1 μm was used as the filter. At this time, as a comparative example, an example in which glass is used for a beaker, a funnel, a filter base, etc., or a preheating is performed by a method in which preheating is not performed before the sample is put into a solution (the method shown in FIG. 1). Although it went, the example which used glass for the shift | offset | difference of one or more of a beaker, a funnel, and a filter stand was investigated. These results are collectively shown in Table 4 below.

From this result, we could consider as follows. In this example, the Si concentration of the molten steel is relatively high, so 24, No. having a preheating temperature of less than 50 ° C In 13 and 14, SiO ₂ gel was generated, and it was impossible to measure inclusions on the filter.

In contrast, no. In the case of 15 to 23, since the dissolved solution was heated to 50 ° C. or higher before putting the sample, there was no generation of SiO ₂ gel or the amount was extremely small, and inclusions on the filter could be measured. It was possible. Of these, No. Examples of 20 to 23 are examples in which glass is used in one or more of the beaker, the funnel, and the filter base. The number of detected SiO ₂ inclusions is larger than that of 15-19. This was thought to be because SiO ₂ mixed in the melting and extracting steps was added to the number of inclusions originally present in the steel.

It is explanatory drawing which shows the basic procedure in a warm nitric acid method. It is explanatory drawing which shows the basic procedure of this invention method.

Explanation of symbols

1 Beaker 2 Nitric acid aqueous solution 3 Sample 4 Heater 5 Membrane filter 6 Filter base 7 Funnel 8 Flask

Claims (4)

  In extracting the oxide inclusions in the metal sample by the warm nitric acid method or the warm sulfuric acid method, the nitric acid solution or the sulfuric acid solution is heated to 50 ° C. or more in advance, and then the metal sample is put into this solution to be dissolved. A method for extracting oxide inclusions in a metal, comprising filtering and extracting oxide inclusions. The extraction method according to claim 1, wherein the oxide inclusions contain at least SiO ₂ . The extraction method according to claim 1 or 2, wherein, in the dissolving step and the subsequent filtration and extraction step of oxide inclusions, the material of the device in contact with the solution does not contain SiO ₂ . The extraction method according to claim 3, wherein the material of the device is polytetrafluoroethylene.

Images