JP3492155B2 - Method for analyzing oxygen in metals - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a technique belonging to the field of analyzing the amount of oxygen in a metal by an inert gas carrier melting-infrared absorption method, and pretreats the contamination of an oxide film formed on a metal surface. Without being concerned, the present invention relates to a method of separating oxygen in a metal into surface contamination oxygen and oxygen composed of oxide-based inclusions in the metal and analyzing the separated oxygen.

[0002]

2. Description of the Related Art Development of ultra-low oxygen steel and high-purity iron whose oxide morphology is controlled is in progress, and it is required to accurately quantify a minute amount of oxygen concentration of ppm (parts per million) level. ing. Therefore, it is necessary to remove the contamination such as the oxide film generated on the sample surface when analyzing the trace oxygen. An electrolytic polishing method or a chemical polishing method is used as a pretreatment method at the time of oxygen analysis for removing the contamination such as the oxide film.

The electropolishing method uses a non-aqueous solvent type electrolytic solution such as a 10% acetylsalicylic acid-1% tetramethylammonium chloride-methyl alcohol solution or a 4% sulfosalicylic acid-1% lithium chloride-methyl alcohol solution. This is a method of removing contaminants such as an oxide film generated on the sample surface. The chemical polishing method is a method of immersing a metal sample for analysis in a solution of hydrogen fluoride-hydrogen peroxide (HF-H ₂ O ₂ ) or the like to remove contamination such as an oxide film formed on the sample surface (for example, , Yasuhara and others: CAMP ISIJ,
10 (1997), p709).

However, the amount of oxygen present as surface oxides of these samples is not constant, and the amount of surface oxides removed varies depending on, for example, the polishing solution, polishing time, etc., so that the analysis values vary widely. Further, in the method of electrolytically polishing or chemically polishing the surface of the sample, pretreatment of the sample becomes complicated and it takes time.

As a method for solving the above problems, after polishing the surface of a steel sample with a grinder, a file, etc.,
In a method of measuring by extracting a trace amount of oxygen in the sample by heating, the sample after the grinding treatment is put in a carbon crucible and preheated at a temperature of 900 ° C. or higher and 1400 ° C. or lower to remove oxygen or an oxide film attached to the sample surface. There has been proposed a method for analyzing a trace amount of oxygen in steel, which is characterized by separating and analyzing oxygen in a metal composed of contaminated oxygen and oxide-based inclusions (JP-A-6-148170).

[0006]

However, when the amount of oxygen is analyzed by the above-mentioned method (Japanese Patent Laid-Open No. 6-148170), the oxide is different depending on the type, amount and particle size distribution of oxide inclusions. The first point is point D where oxygen starts to be generated from the system inclusions.
It was found that there was a problem that it was not possible to accurately analyze only the amount of oxygen generated from oxide-based inclusions, which was included in the amount of oxygen adhering to the surface and the amount of oxygen generated from iron oxides. .

The present invention has been made in order to solve the above-mentioned problems, and when analyzing the amount of oxygen in a metal, the oxide film formed on the metal surface is not contaminated, and the oxide film is not pretreated. It is an object of the present invention to provide a method for accurately separating and analyzing oxygen in a metal composed of oxygen contaminated with oxygen and oxide-based inclusions.

[0008]

The present inventor, when analyzing the amount of oxygen in a metal, does not pre-treat the contamination of the oxide film formed on the metal surface, but does not pre-treat the contaminated oxygen and the oxide in the metal. The research was repeated on the method of separating and analyzing into oxygen composed of system inclusions. As a result, in the method of analyzing the amount of oxygen in the metal, the polluted oxygen and the oxygen composed of the oxide-based inclusions in the metal are converted into the oxygen without pretreatment of the oxide film formed on the metal surface. In order to separate and analyze, we obtained new knowledge that the temperature rising conditions of the metal in the temperature range when decomposing contaminated oxides and the temperature range when decomposing oxide inclusions are important. The invention has been completed.

The present invention is intended to solve the above problems,
The summary is as described in the claims. That is, 1) Injecting a metal sample into a graphite crucible, heating and melting it, and vacuum-extracting the gas from the melting bath to analyze and carry out an inert gas transfer melting-infrared absorption method to change the total oxygen content in the metal into a plurality of waveforms. In the method of separating and analyzing , the addition of the metal sample is performed.
From the heat start point 0 to the first waveform appearance start point A and the first waveform peak appearance point B at a temperature rising rate of 20 ° C./s or less.
The method is characterized in that heating is performed and the temperature from the peak appearance point B of the first waveform to the end point C of the first waveform appearance is set to a constant temperature, and after the completion of appearance of the first waveform, the temperature is further raised to heat melting for analysis. Method for analyzing oxygen in metals.

2) Injecting a metal sample into a graphite crucible, heating and melting it, and extracting the gas from the melting bath by vacuum extraction for analysis. to a method of separating analysis, oxygen of the <br/> metal in metal according to claim 1, the contamination of the sample surface to the generated oxide film pretreated, characterized in that analyzed without removing Analysis method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with respect to the method of the present invention.

Contamination sources of oxygen on the metal surface are 1) oxygen adsorbed from the air, 2) when cutting the metal with a saw or grinding with a grinder to adjust the metal to a predetermined weight. It is oxygen as iron oxide, which is generated by the surface oxidation due to the rise in temperature. Among these, the latter iron oxides differ in the type and amount of oxides due to cutting, grinding temperature, time, etc., but when the types were investigated by Auger electron spectroscopy, Fe ₂ O ₃ ,
It was found to be composed of Fe ₃ O ₄ , FeO and the like.

In the graphite crucible used for the analysis of the amount of oxygen in the metal by the inert gas carrier melting-infrared absorption method, the MO
It is considered that a reaction of + C = M + CO (M: metal, O: oxygen, C: carbon) is occurring. The temperature at which iron oxide decomposes varies depending on the type of oxide and the CO partial pressure in the crucible, and is approximately 400 according to thermodynamic equilibrium calculation and measurement results.
Is in the range of to 1100 ° C. On the other hand, the thermodynamic equilibrium temperature of oxide-based inclusions depends on the type of oxide and CO in the crucible.
Although it cannot be generally discussed because it depends on the partial pressure, it is generally at a temperature higher than the decomposition temperature of iron oxides, but depending on the heating conditions of the metal, the reduction of oxide inclusions by carbon may cause the reduction of iron oxides. We have obtained a new finding that CO gas is generated even at a low temperature at which reduction occurs. The present invention skillfully utilizes this knowledge. FIG. 1 shows the extraction curves of oxygen extracted according to the type of oxide.
The waveform with the first peak is an extraction curve corresponding to the amount of oxygen adsorbed from the air and the amount of oxygen generated from iron oxide, and the waveform with the second peak is generated from oxide inclusions. It is an extraction curve corresponding to the amount of oxygen.

The two oxygen extraction curves do not overlap with each other, and the more they are separated from each other, the more accurately the amount of oxygen adsorbed from the air and the amount of oxygen generated from iron oxide and the amount of oxygen generated from oxide inclusions can be separated. It will be. The conditions for this are the contents described in claim 1 of the present application.

When the temperature at which the first waveform starts to occur is too fast, the first waveform and the second waveform are likely to overlap with each other, making it difficult to separate the waveforms. It is considered that the slower the temperature rising rate until the first waveform starts to be generated, the closer the condition to thermodynamic equilibrium is achieved, and the appearance temperature of the first waveform appearance start point A can be easily confirmed. However, 20 ° C./s or less is preferable from the viewpoint of analysis efficiency and easiness of determination of rising timing. When the material is continuously heated and melted at this heating rate, the amount of CO generated due to the reduction by carbon such as iron oxide is maximized. When the CO gas generation amount reaches the maximum value, the temperature is kept constant and the gas extraction is completed. The temperature from the peak appearance point B of the first waveform to the end point C of the first waveform appearance is kept constant because the amount of oxide inclusions in the metal is increased when the temperature is continuously raised during this period. The reason for this is to prevent the decomposition of oxide-based inclusions within the temperature or time during which the first waveform appears, although it depends on the size, composition, location, etc.

After the completion of the appearance of the first waveform, the temperature is further raised to rapidly decompose the oxide inclusions, and the second waveform, which is an oxygen extraction curve corresponding to the amount of oxide inclusions, is formed. Get it.

As described above, a total amount of oxygen in a metal is measured by an inert gas carrier melting-infrared absorption method in which a metal sample is placed in a graphite crucible, heated and melted, and a gas is extracted from the melting bath for analysis. When separating and analyzing multiple waveforms,
From the first waveform appearance start point A to the first waveform peak appearance point B, the temperature rising rate is 20 ° C./s or less, and from the first waveform peak appearance point B to the first waveform appearance end point C. After the completion of the appearance of the first waveform, the temperature is kept constant, and the temperature is further raised to heat and melt it for analysis, so that the oxygen in the metal is not contaminated on the surface without pretreatment of the contamination of the oxide film formed on the surface of the metal sample. It has become possible to accurately separate and analyze oxygen and oxygen composed of oxide-based inclusions in metals. The heating rate from the first waveform appearance starting point A to the peak appearance point B of the first waveform is appropriately 20 ° C./s or less, but 5 ° C./s or less is particularly preferable. The heating rate after the completion of appearance of the first waveform is not particularly limited, but a higher heating rate is preferable in terms of analysis efficiency.

The temperature rising rate from the start of heating the metal sample to the first waveform appearance start point A is not particularly limited, but the first waveform appearance start which may vary depending on the type of the metal to be analyzed. If it becomes possible to empirically understand the appearance time or the temperature of the point A, it is preferable that the rate of temperature increase is high in view of analysis efficiency and the like. Usually, the temperature at the first waveform appearance starting point A is often 400 ° C. or higher. Therefore, 4
Up to about 00 ° C, the heating rate may be 20 ° C / s or more.

[0019]

EXAMPLES Next, examples of the present invention will be described in Table 1 together with comparative examples. In each example, a metal sample was dropped in the graphite crucible,
The amount of oxygen in the metal is analyzed by an inert gas carrier melting-infrared absorption method in which the material is heated and melted, and a gas is extracted from the melting bath for analysis.

In Comparative Example 1, 1 g of a bearing steel sample was used as HF-H ₂ O.
₂ After soaking in the solution, the heating start point 0 of the sample shown in FIG.
From the peak appearance point B of the first waveform to 30 ° C
/ S, the first waveform appearance end point C from the peak appearance point B of the first waveform was 30 ° C./s, and after the first waveform appearance end point C was analyzed at 50 ° C./s. It is difficult to separate the first waveform corresponding to the amount of oxygen generated from surface-attached oxygen and iron oxide and the second waveform corresponding to the amount of oxygen generated from oxide-based inclusions, and the total amount of oxygen is 4.1 ppm. there were. Example 1 of the present invention is the same bearing steel as Comparative Example 1, and the bearing steel sample 1g
Without pretreatment, the temperature rising rate between the heating start point 0 and the peak appearance point B of the first waveform shown in FIG.
s, the temperature rising rate from the peak appearance point B of the first waveform to the first waveform appearance end point C is 0 ° C./s, the first waveform appearance end point C
After that, analysis was performed at a heating rate of 50 ° C./s. The oxygen amount corresponding to the first waveform was 1.8 ppm, the oxygen amount corresponding to the second waveform was 3.1 ppm, and the total amount was 4.9 ppm. From this, assuming that the oxygen content of oxide-based inclusions in the bearing steel of Comparative Example 1 is 3.1 ppm (total oxygen content of Comparative Example 1).
-(Amount of oxygen in the second waveform of Example 1) = 4.1-3.1 =
It becomes 1.0 ppm. Therefore, it is presumed that the oxygen amount of 1.0 ppm could not be sufficiently removed even by chemical polishing with the HF-H ₂ O ₂ solution and remained.

In Comparative Example 2, 1 g of carbon steel for machine structure was used as a non-aqueous solvent electrolyte of 4% sulfosalicylic acid-1% lithium chloride-methyl alcohol solution, electrolytic potential of 1 V, 500 mA.
After electropolishing under conditions of current of 4 minutes and electrolysis time of 4 minutes, ultrasonic cleaning was performed in a methanol solution for 8 minutes, and then oxygen analysis was performed. The heating rate between the heating start point 0 and the first waveform peak appearance point B of the sample shown in FIG. 2 is 50 ° C./s, and the first waveform peak appearance point B to the first waveform appearance end point C is also 50. ℃ /
s, after the first waveform appearance end point C, analysis was performed at 60 ° C./s. As in Comparative Example 1, it is difficult to separate the first waveform corresponding to the amount of oxygen generated from surface-adhered oxygen or iron oxide and the second waveform corresponding to the amount of oxygen generated from oxide-based inclusions. The amount was 8.4 ppm.

Example 2 of the present invention is an analysis of the same carbon steel for machine structure as Comparative Example 2. No pretreatment of the metal sample was performed. The heating rate from the heating start point 0 of the sample shown in FIG. 1 to the first waveform peak appearance point B is 10 ° C./s,
From the first waveform peak appearance point B to the first waveform appearance end point C
Was 0 ° C./s, and the temperature rising rate after the first waveform appearance end point C was 70 ° C./s. The amount of oxygen corresponding to the first waveform is 2.5 ppm, and the amount of oxygen corresponding to the second waveform is 7.3 pp
m, and the total was 9.8 ppm. Therefore, similarly to the above, it is estimated that 8.4-7.3 = 1.1 ppm remained without being removed even by electrolytic polishing. As described above, it is difficult to completely remove contaminants such as an oxide film generated on the sample surface by various pretreatments before analysis.
Even with the same pretreatment method, the total oxygen amount was not constant and the analysis values varied.

In Comparative Example 3, the bearing steel was not subjected to pretreatment such as chemical polishing as in Comparative Example 1 and electrolytic polishing as in Comparative Example 2, but the heating starting point of the sample in FIG. The temperature rising rates of the appearance point B and the first waveform peak appearance point B to the first waveform appearance end point C were analyzed at 50 ° C./s, and 50 ° C./s after C. The first waveform corresponding to the amount of oxygen generated from surface-attached oxygen and iron oxide and the second waveform corresponding to the amount of oxygen generated from oxide inclusions could not be separated and completely overlapped as shown in FIG. . Example 3 is the same bearing steel as Comparative Example 3, and the bearing steel sample 1g was not pretreated, and the heating start point 0 of the sample shown in FIG.
The temperature rising rate is 5 ° C./s, the peak appearance point B of the first waveform
Therefore, the first waveform appearance end point C was analyzed at 0 ° C./s, and the temperature after the first waveform appearance end point C was analyzed at 100 ° C./s.
The amount of oxygen corresponding to the first waveform was 2.3 ppm, the amount of oxygen corresponding to the second waveform was 2.2 ppm, and the total amount was 4.5 ppm. From this, it is now assumed that the oxygen content of oxide-based inclusions in the bearing steel of Comparative Example 3 is 2.2 ppm (Comparative Example 3
Total oxygen amount) − (oxygen amount of the second waveform of Example 3) = 4.
It becomes 9-2.2 = 2.7 ppm. Therefore, it is considered that the oxygen amount of 2.7 ppm corresponds to the oxygen amount generated from surface-adhered oxygen and iron oxide.

Examples 1 to 3 are examples of the present invention. The first waveform corresponding to the amount of oxygen generated from surface-attached oxygen and iron oxide and the second waveform corresponding to the amount of oxygen generated from oxide inclusions could be clearly separated. In addition, when several identical steel types were repeatedly analyzed, there was almost no variation in the analytical values.

As described above, according to the analysis method of the present invention, the amount of contaminated oxygen generated from the surface-attached oxygen of a metal or iron oxide can be obtained without pretreatment such as chemical polishing or electrolytic polishing of a sample. And the amount of oxygen generated from oxide inclusions can be accurately separated and quantified.

[0026]

[Table 1]

[0027]

As described above, the oxygen in the metal is not contaminated by the pretreatment of the oxide film formed on the metal surface by the analysis method of the present invention, and the surface contamination oxygen and the oxide-based inclusions in the metal are included. It became possible to separate and analyze into oxygen composed of.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an oxygen extraction curve of an example of the present invention.

FIG. 2 is an explanatory diagram showing an oxygen extraction curve of a comparative example.

FIG. 3 is an explanatory diagram showing an oxygen extraction curve of a comparative example.

[Explanation of symbols]

A ... Temperature or time at which oxygen starts to be generated from surface-attached oxygen or iron oxide B ... Maximum peak appearance point C ... Temperature or time at which generation of oxygen from surface-attached oxygen or iron oxide is completed D ... Oxide-based intervention Temperature or time when oxygen starts to be generated from an object E ... Temperature or time when generation of oxygen from an oxide inclusion is completed

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 33/20 G01J 3/42 G01N 21/35

Claims (2)

(57) [Claims] 1. An inert gas carrier melting-infrared absorption method in which a metal sample is placed in a graphite crucible, heated and melted, and a gas is extracted from the melting bath by vacuum extraction to analyze the total oxygen content in the metal in a plurality of waveforms. a method of separating analysis, the gold
From the heating start point 0 of the genus sample to the first waveform appearance start point A and the first waveform peak appearance point B are heated at a temperature rising rate of 20 ° C./s or less, and the first waveform peak appearance point B is obtained. To a first waveform appearance end point C is kept at a constant temperature, and after completion of the appearance of the first waveform, the temperature is further raised to heat, melt, and analyze the oxygen in the metal. 2. An inert gas carrier melting-infrared absorption method in which a metal sample is placed in a graphite crucible, heated and melted, and a gas is extracted from the melting bath by vacuum extraction to analyze the total oxygen content in the metal in a plurality of waveforms. In the method for separating and analyzing the metal sample according to claim 1, wherein the contamination of the oxide film formed on the surface of the metal sample is analyzed without being pretreated and removed. Oxygen analysis method.