JP5439799B2 - Rapid analysis method for acid-soluble aluminum in steel - Google Patents

Description

  The present invention relates to a method for analyzing acid-soluble aluminum (Al) in steel, and more particularly, to a method that allows simple, accurate and rapid analysis.

  Al in steel exists in the state of solid solution Al, nitrided Al, and oxidized Al. When the steel is dissolved with acid, the solid solution Al dissolved in the acid together with Al in the nitrided Al is called acid-soluble Al (sol.Al), and the Al in the oxidized Al not dissolved in the acid is acid-insoluble Al. It is called (insol.Al) and both are separated by acid dissolution of steel. sol.Al is used to improve the properties of thin steel plates for automobiles, thick steel plates for shipbuilding, electromagnetic steel plates, etc., but insol.Al has little effect on properties due to its small amount, so in many cases sol.Al is being analyzed.

  As a method for analyzing sol.Al in steel, an atomic absorption analysis method according to JIS G1257 (1994) in Non-Patent Document 1 is known as a standard method. However, in this method, operations such as collection of chips from a steel sample, weighing, and filtration and separation are complicated, and it may take a long time to obtain an analysis result.

Therefore, as a simple and rapid method for analyzing sol.Al in steel, for example, Patent Document 1 proposes an emission analysis method that can analyze a steel sample as it is. In this analysis method, a steel sample is caused to emit light by repeated discharge, the emission spectrum intensity of Al is measured for each discharge, the frequency distribution of the emission spectrum intensity is obtained, and sol.Al and insol.Al are determined from the frequency distribution. Quantified by form.
Japanese Standards Association "JIS Handbook Metal Analysis Steel" (2007) Japanese Patent Publication No.55-15657

  However, in the emission analysis method described in Patent Document 1, since a single discharge mark has a size of several tens of microns, when fine insol.Al coexists with sol.Al in the part, the obtained Al Since the emission spectrum of the same is also the sum of the two, sol.Al and insol.Al cannot be clearly distinguished in the frequency distribution, and sufficient analysis accuracy cannot be obtained.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method that can quickly and accurately analyze sol.Al in steel.

  The inventors have conducted intensive studies on a method for simply and accurately analyzing sol.Al in steel, and have found the following.

  1) For example, if a sample in which Al nitride is not precipitated and only solute Al and oxidized Al are present in an electrolyte solution, such as a steel sample that rapidly solidifies molten steel, is dissolved in the electrolyte solution. Al, that is, sol.Al in steel can be eluted.

  2) If the concentration ratio of Al to the comparative element is determined instead of the concentration of Al eluted in the electrolyte, and corrected by the content of the comparative element in the steel sample obtained by another method, it is simple and quick. In addition, the content of sol.Al in steel can be determined. Here, the comparative element is an additive metal element other than Al or Fe, which is a metal element existing in a solid solution state in a steel sample.

  The present invention has been made based on the above knowledge, and after electrolyzing a steel sample in which Al nitride is not precipitated in an electrolytic solution, the electrolytic solution is analyzed, and based on the result of the analysis, Calculate the concentration ratio of Al to the comparative element, and multiply the calculated concentration ratio of Al by the content of the comparative element in the steel sample. Provide analytical methods.

  In the analysis method of the present invention, it is preferable to analyze after adding an aqueous chelating agent solution to the electrolytic solution after electrolysis to make the comparative element and Al a water-soluble chelate. At this time, as the chelating agent aqueous solution, for example, an ethylenediaminetetraacetate aqueous solution can be used.

  According to the analysis method of the present invention, sol.Al in steel can be quickly and easily analyzed accurately and accurately. In addition, the method of the present invention does not require skill in the work, and therefore has an advantage that even an inexperienced analysis engineer can implement it.

  As described above, Al in steel is divided into solid solution Al and precipitated Al such as precipitates and inclusions such as Al nitride and Al oxide. When such a steel sample in which Al is present is electrolyzed using a commonly used non-aqueous solvent electrolyte, the solid solution Al elutes together with other elements such as Fe, Cr, Ni, etc. in the electrolyte, Precipitated Al present as Al nitride or Al oxide adheres to the sample surface as an undissolved residue. At this time, it is considered that the residue is attached to the surface of the sample because of electrical attraction. Therefore, by electrolyzing an unprecipitated steel sample of Al nitride, solid solution Al, that is, sol.Al, can be eluted in the electrolytic solution, and if the content of Al eluted in the electrolytic solution is measured Therefore, the exact content of sol.Al in the steel can be known from the amount of electrolysis of the sample.

  However, the non-aqueous solvent-based electrolyte is an organic solvent mainly composed of methanol, has high volatility, and has a capacity of several hundred ml. Therefore, it is not easy to measure the Al content in the electrolyte. Therefore, the concentration ratio of Al to other comparative elements eluted in the electrolyte is calculated, and the content ratio of sol.Al is calculated by multiplying this concentration ratio by the content ratio of the comparative element in the steel sample measured by other methods. If required, an appropriate amount of electrolytic solution is sufficient, so that simple and rapid analysis is possible.

  In order to analyze Al and comparative elements in the electrolytic solution, it is preferable to dry the nonaqueous solvent electrolytic solution and replace it with an aqueous solution. This is because it is generally very difficult to measure a metal component by directly introducing a non-aqueous solvent into the analyzer.

  However, in the non-aqueous solvent electrolyte after electrolysis, the eluted Al exists as a non-aqueous solvent-soluble complex, and if it is made into an aqueous solution in this state, a precipitate may be formed. There may be a problem (for example, it takes time until the output from the analyzer becomes stable and becomes measurable due to precipitation). Therefore, it is desirable to change the nonaqueous solvent-soluble complex of Al to a water-soluble complex before drying the nonaqueous solvent electrolyte. Specifically, before drying the electrolytic solution, an aqueous solution of a chelating agent is added to the electrolytic solution, and Al or a comparative element in the electrolytic solution is complexed as a water-soluble chelate. Replace with aqueous solution and analyze. By complexing Al and comparative elements in this way, it is possible to prevent the occurrence of precipitation due to aqueous solution and clogging of the solution introduction tube of the analyzer, which can be performed quickly and accurately. Become. As a chelating agent for complexing, ethylenediaminetetraacetate (EDTA) having a strong affinity for metal elements is most suitable. In addition, 1,2-cyclohexanediaminetetraacetic acid (CyDTA), 1,2- Dihydroxy-3,5-benzenedisulfonic acid, disodium salt (Tiron) and the like can also be used.

  As described above, a non-aqueous solvent-based electrolyte is used as the electrolyte, and this electrolyte is composed of a water-insoluble chelating agent, a supporting electrolyte, and an organic solvent (methanol), such as Al eluted in the electrolyte. These metal elements form a complex with this chelating agent. When an aqueous solution of a chelating agent containing a water-soluble chelating agent having a high complex-forming ability is mixed with an electrolytic solution containing this non-water-soluble chelating complex (the same as the above-mentioned non-aqueous solvent-soluble complex), the metal element becomes a water-soluble metal complex. Is replaced by When methanol as a solvent is evaporated in this state, there is an advantage that the substance remaining later can be easily converted into an aqueous solution. Examples of the water-insoluble chelating agent used in the non-aqueous solvent electrolyte include acetylacetone, maleic anhydride, triethanolamine, methyl salicylate, and salicylic acid. Further, as the supporting electrolyte, tetramethylammonium chloride, lithium chloride and the like are suitable.

  Various conditions for electrolysis are not particularly limited, and are appropriately designed depending on the complex forming ability of the water-insoluble chelating agent with respect to the element of interest and the stability of Al oxide. In addition, as described above, it is sufficient for the analysis of the electrolytic solution to have an appropriate amount of the electrolytic solution, but considering the case of drying at room temperature, the amount is preferably 5 ml or less, more preferably 1 ml or less. . Furthermore, when collecting the electrolytic solution in a state where Al oxide is adhered to the steel sample, the timing of collection is appropriately set depending on the type of steel, the electrolysis conditions, and the like. In particular, it is preferable to collect the electrolyte during energization from the viewpoint of the strength of the attractive force at which Al oxide is electrically attached to the steel sample. When collecting the electrolyte after energization, the rest of the steel sample may be immersed in the electrolyte, but generally the upper layer of the electrolyte has a low concentration of dissolved metal, so the final elemental analyzer In consideration of sensitivity and the like, it is preferable to remove the remainder of the steel sample from the electrolytic solution and then stir or collect the electrolytic solution from the lower layer.

  The method for analyzing the electrolytic solution after electrolysis is not particularly limited, but inductively coupled plasma emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry are suitable. .

  As a comparative element eluted in the electrolytic solution, it is a main component in a steel sample and exists in a solid solution state, such as Fe in the case of carbon steel and Fe, Cr or Ni in the case of stainless steel. It is desirable to select a metal element that does not form precipitates or inclusions, or has a very small proportion even if formed. In addition, it is not restricted to said example, If it is a metallic element to which the amount more than a certain amount was added, it can utilize as a comparative element. A plurality of metal elements may be used as comparative elements. For example, in the case of stainless steel, select two or more elements of Fe, Cr and Ni, and make the concentration of the comparative elements in the electrolyte solution the total concentration of those elements, then compare in the steel sample obtained by another method The present invention can be applied if the content of elements is the total content of these elements.

Then, the concentration K _Al of the Al in the electrolytic solution and the concentration K _M of the comparative element M are measured, and the concentration ratio (K _Al / K _M ) is calculated. By multiplying the content C _M of the comparative element M in the steel, the content C _Al [= (K _Al / K _M ) × C _M ] of sol.Al in the steel is obtained. At this time, as a method for obtaining the content of the comparative element in the steel sample, a spark discharge emission spectroscopic analysis method [JIS G1253 (2002)], a fluorescent X-ray analysis method [JIS G1256 (1997)], and the above ICP- A method of subtracting the total content of elements other than comparative elements obtained by AES or ICP-MS from 100% by mass is appropriate.

At the casting stage after deoxidation in the steel making process, a disk and pin integrated steel sample shown in Appendix 1 Fig. 2a) of JIS G0417 (1999) was collected using an immersion probe. Since this steel sample was rapidly solidified, no Al nitride was precipitated. The pin portion (hereinafter referred to as pin sample) of this integrated steel sample was subjected to the analysis of the present invention example, and the disk portion was subjected to the analysis of the comparative example. Further, the disc portion was separately analyzed by the method of JIS G1253 (2002), and the total content of elements other than Fe was subtracted from 100% by mass to calculate the _Fe content C _Fe .
(Example of the present invention)
First, the surface of the pin sample is lightly polished using a belt polishing apparatus. Subsequently, using the electrolytic device 6 schematically shown in FIG. 1, in a beaker 3 in about 40 ml of 10% AA-based electrolyte 5 (10% by volume acetylacetone-1% by mass tetramethylammonium chloride-methanol). The pin sample 1 is connected to the anode of the constant current power source 4 and the electrode 2 is connected to the cathode of the constant current power source 4, and about 0.03 g of the pin sample 1 is subjected to constant current electrolysis. About 1 ml of the electrolyte solution 5 in which the pin sample 1 is immersed is put into another beaker containing 0.4 ml of a 0.1 mol / l EDTA aqueous solution as an aqueous chelating agent solution. Next, about 20 ml of pure water was further added to the beaker, and after sufficient stirring, the Al concentration K _Al and the Fe concentration K _Fe were measured by ICP-MS to calculate (K _Al / K _Fe ). . The concentration ratio (K _Al / K _Fe ) was multiplied by the _Fe content C _Fe described above to obtain the content of sol.Al in the steel sample.
(Comparative example)
First, the surface of the disk part is polished to remove the oxide layer, then drilled from the disk surface to the back surface with a drilling machine, and using the generated chips, sol according to Annex 15 of JIS G1257 (1994) The content of .Al was determined. However, the sample weighed 0.5 g.

  FIG. 2 shows the relationship between the sol.Al content according to the present invention example and the sol.Al content according to the comparative example. It can be seen that the content of sol.Al is in good agreement.

  Further, FIG. 3 shows the analysis time in the present invention example and the comparative example, but the present invention example is a complicated process such as sample weighing, filtration, residue decomposition, and a time-consuming process such as a constant volume / cooling process. Therefore, it can be seen that the analysis time is shorter than that of the comparative example, and the method is simple and quick.

It is a figure which shows typically an example of the electrolyzer used for the analysis method of this invention. It is a figure which shows the relationship between content of sol.Al by the example of this invention, and content of sol.Al by a comparative example. It is a figure which shows the analysis time in this invention example and a comparative example.

Explanation of symbols

1-pin sample
2 electrodes
3 beakers
4 Constant current power supply
5 Electrolyte
6 Electrolyzer

Claims (2)

After electrolysis of a steel sample in which Al nitride is not precipitated in a non-aqueous solvent electrolyte containing a non-water-soluble chelating agent, a chelating agent aqueous solution containing a water-soluble chelating agent is added to the non-aqueous solvent-based electrolyte , and a comparative element And Al as a water-soluble chelate, each concentration was analyzed, and based on the result of the analysis, the concentration ratio of Al to the comparative element in the non-aqueous solvent electrolyte was calculated, and the calculated Al The content ratio of the comparative element in the steel sample obtained by using any one of the spark discharge emission spectrometry method, the fluorescent X-ray analysis method, the inductively coupled plasma emission spectrometry method, and the inductively coupled plasma mass spectrometry method. A rapid analysis method for acid-soluble Al (sol.Al) in steel characterized by multiplying by; the comparative element is an additive metal element other than Al or Fe, and exists in a solid solution state in a steel sample. It is a metallic element. 2. The rapid analysis method for sol.Al in steel according to claim 1 , wherein the chelating agent aqueous solution is an ethylenediaminetetraacetate aqueous solution.

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