JPS6321137B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for determining oxygen. Oxygen in steel has a large effect on the mechanical properties of steel, and this effect varies greatly depending on the state of existence of oxygen in the steel, that is, the type and amount of each oxide in the steel. It is extremely useful to know the amount of oxygen in each state of existence. It is also useful to determine the amount of oxygen in iron oxide on the steel surface in order to know the oxidation status of the steel surface. However, the vacuum melting method and inert gas melting method conventionally used to quantify oxygen in steel have the following drawbacks. In other words, since the steel sample is melted at a single temperature and carbon monoxide is generated and extracted using graphite, it is not possible to separate the iron oxide oxygen on the surface of the sample from the oxygen in the sample, resulting in a total amount of oxygen. I can only get it. Furthermore, the quantitative value varies greatly depending on the amount of iron oxide on the sample surface. On the other hand, it was heated to 700℃ in hydrogen gas in advance.
There is a known method of reducing and removing oxides on the sample surface by heating for 10 minutes and then quantifying oxygen using a vacuum melting method (Igida et al., Nippon Kokan Giho, No. 41,
(pages 1-9). However, even in this method, the amount of oxygen in the iron oxide on the surface of the sample cannot be determined, only the total amount of oxygen in the sample can be determined, and furthermore, some oxides may be decomposed during the reduction of the surface. In addition, methods for chemically separating and quantifying oxides in steel samples by electrolysis, acid dissolution, or halogen-alcohol solution are known (Narita, Tetsu to Hagane, Vol. 60, No. 13, 1820). ~1826 pages).
However, this method has the disadvantage that it causes errors in quantitative values due to the dissolution of extremely fine oxides during extraction and separation and filtration leakage during filtration, and requires complicated operations and requires skill. The inventors of the present invention have conducted various studies in view of the current situation, and have found that by using hydrogen gas with a sufficiently low dew point for oxygen extraction, the oxygen in iron oxide on the sample surface can be removed for quantitative purposes at temperatures above 170°C. The reduction and extraction rate is sufficient; the extraction rate increases with increasing heating extraction temperature; below 550°C, the extraction of oxygen inside the sample is negligible; therefore, 170°C
We found that in the temperature range from ℃ to 550℃, it is possible to extract and quantify only the oxygen of iron oxide on the sample surface. In addition, only the iron oxide oxygen on the sample surface was
The thermal stability of each oxide in the sample against hydrogen gas when extracted at a heating extraction temperature range of ℃ to 550℃ and then heated to a higher temperature is not the same and decomposes at different temperatures depending on the type of oxide. We found that oxygen can be extracted and quantified as water. In addition, the water adhering to the sample surface is significantly desorbed at temperatures above 50°C.
I found out that it can be removed by The present invention has been made based on the above findings, and its gist is that when heating a steel sample in a hydrogen stream, the heating extraction temperature is set at 170°C to 550°C.
A method of extracting and quantifying by setting the required temperature within the range of ℃ to generate the oxygen of iron oxide on the surface of the sample as water, and then further increasing the temperature at each decomposition temperature of the oxide in the sample. A method for quantifying oxygen is characterized in that the oxygen of the oxide is generated as water while being allowed to stay or passed through the temperature, and the extracted and quantitatively determined water is extracted. In the present invention, water is mainly composed of water and also contains small amounts of carbon monoxide and carbon dioxide, which are produced by reaction with carbon, etc. in a steel sample, particularly at high temperatures. The present invention will be described in detail below. First, in the present invention, the temperature range for heating and extracting oxygen from iron oxide on the surface of a steel sample is set to 170°C to 550°C based on the following experiment. In addition, in the following experiments, the sample was a steel material that was cut with a saw blade or drill and sieved with a JIS standard sieve to obtain a constant particle size of 100 to 200 mesh.The hydrogen gas flow rate was 200 ml/min, the dew point was -61℃, and the temperature was heated. The extraction time was 2 hours. Since the dew point of hydrogen gas has a large effect on the heating extraction temperature and quantitative accuracy, it is desirable to keep it as low and constant as possible. FIG. 1 shows the results of quantifying the oxygen content of iron oxide on the surface of steel samples A and B, whose compositions are shown in Table 1, in a hydrogen stream at different heating extraction temperatures.
In FIG. 1, the horizontal axis is the heating extraction temperature, and the vertical axis is the quantitative value of oxygen, where a is the quantitative result for sample A, and b is the quantitative result for sample B. 1st
As shown in the figure, at temperatures below 170°C, the reaction rate of oxygen extraction from iron oxide on the sample surface is extremely low, making it unsuitable for quantitative purposes. Therefore, for the determination of iron oxide oxygen on the sample surface, it is necessary to set the heating extraction temperature to 170°C or higher. Also, as shown in Figure 1, below 550°C, only the iron oxide and oxygen on the sample surface are extracted and quantified without being affected by the oxide decomposition reaction inside the sample, whereas above 550°C, alloying elements are extracted and quantified. As the oxides of Si and Mn begin to decompose, the oxygen of these oxides is extracted and quantified together with the iron oxide oxygen on the sample surface, which causes an error in quantifying only the iron oxide oxygen on the sample surface. Therefore, in quantifying iron oxide oxygen on the sample surface, it is necessary to set the heating extraction temperature to 550°C or less. Based on the above findings, a temperature range of 170°C to 550°C is optimal for quantifying oxygen in iron oxide on the sample surface.

[Table] Furthermore, as shown in FIG. 1, the oxides inside the sample each have different thermal stability, so each oxide is decomposed at a different temperature, and oxygen is extracted and quantified as water. Therefore, after setting the heating extraction temperature to a required temperature within the range of 170°C to 550°C to extract and quantify the oxygen in iron oxide on the sample surface, the temperature is further increased to over 550°C to remove the oxygen contained in the steel sample. The amount of oxygen in each oxide can be determined separately by allowing the various oxides to remain at each decomposition temperature or passing through these temperatures. FIG. 2 shows an example of the fractional quantification of oxygen, and is the result of quantification for steel sample C whose composition is shown in Table 1. Second
In the figure, the horizontal axis is the heating extraction time, the vertical axis on the left is the amount of oxygen extracted per unit time, the vertical axis on the right is the heating extraction temperature, c is the heating extraction curve of oxygen extracted and quantified as water, and d is the heating extraction curve of oxygen extracted as water and quantified. This is the heating extraction temperature.
In this experiment, the temperature was raised from room temperature at 400deg/hr and held at 400°C for 2 hours to quantify the iron oxide oxygen on the sample surface, and then the temperature was raised at 200deg/hr to 700°C.
The sample was held for 2 hours and the oxygen in MnO inside the sample was quantified. Then, increase the temperature at 200deg/hr and hold at 1000℃ for 2hr.
After holding and quantifying the oxygen in SiO ₂ in the sample, the temperature was further increased at 100 deg/hr to quantify the oxygen in TiO ₂ in the sample. As shown in Fig. 2, the heating extraction temperature is kept at the decomposition temperature of each oxide in the sample, and after the oxygen in the oxides has been extracted as water and quantified, the temperature is continued to rise and the next By repeating the process of retaining the sample at the decomposition temperature of the oxide, extracting and quantifying oxygen, the oxygen in the sample can be determined separately for each oxide. In addition, in quantifying the oxygen of each oxide, either the heating extraction temperature is maintained at a point near the decomposition temperature of the oxide, and the oxygen of the oxide is extracted and quantified, or the oxygen of the oxide is determined based on the component composition. If the temperature range for decomposition is clear, oxygen from the oxide may be extracted and quantified while increasing the temperature at a constant rate and passing the decomposition temperature of the oxide. Next, the procedure for quantifying oxygen by the method of the present invention will be described. FIG. 3 is an example of an apparatus for carrying out the method of the present invention. In the figure, reference numeral 1 denotes a furnace core tube made of a refractory material such as quartz, which is inserted into a heating furnace 3 equipped with a temperature control section 2 . A finely cut steel sample is charged into a sample crucible 4 made of a refractory material such as beryllia and inserted into the reactor core tube 1, and then a hydrogen gas source 5 is introduced.
Impurities (particularly water) are sufficiently removed from the hydrogen gas in the gas purification section 6, the flow rate is controlled at a constant flow rate in the flow rate control section 7, and the hydrogen gas is introduced into the core tube 1, and the temperature of the heating furnace 3 is raised by the temperature control section 2. Part or all of the water generated and extracted from the oxygen of the steel sample is introduced into the analyzer 8 together with hydrogen gas for quantitative determination. As the analyzer 8, for example, a gas analyzer such as a mass spectrometer or a moisture meter can be used. In this case, as mentioned above, the water adhering to the sample surface is
All of the moisture is desorbed during heating to 150℃, so if you drain the moisture on the sample surface out of the system in advance by, for example, switching the gas flow path, you can reduce the background during measurement and improve quantitative accuracy. Is possible. Furthermore, at temperatures above about 1000°C, some of the oxygen is extracted as carbon monoxide or carbon dioxide due to the presence of carbon in the steel sample, so measurements must take this into account. However, there is no problem in quantifying iron oxide oxygen on the sample surface. Next, the effects of the present invention will be illustrated more specifically by Examples. Example 1 Steel samples D and E, whose compositions are shown in Table 2, were finely cut to give 1 g of each sample by changing the sample grain size.
Table 3 shows the results of quantifying the iron oxide oxygen on the surface of the sample using the apparatus shown in FIG. The hydrogen gas flow rate at this time was 300ml/min.
The dew point was -62°C, the heating extraction temperature was 500°C, the heating extraction time was 1 hr, and a moisture meter using Karl Fischer titration was used as the analyzer. As shown in Table 3, as the sample particle size becomes finer, that is, as the surface area per sample weight increases, the amount of iron oxide oxygen on the sample surface increases. It became clear that the amount could be quantified with high accuracy.

【table】

【table】

[Table] Example 2 Steel samples D, E, and F, whose compositions are shown in Table 2, were finely cut to give a sample grain size of 100 to 200 mesh, and 2 g of each was taken using the apparatus whose example is shown in Figure 3. Table 4 shows the results of quantification of the sample according to its presence state and the results of extraction, separation and quantification using the conventional iodine-methanol method. In Table 4, the oxygen in the sample is the total amount of oxygen in MnO, SiO ₂ and TiO ₂ . The hydrogen gas flow rate at this time was 200ml/min.
The dew point is -61℃, and the heating conditions are higher than room temperature.
Raise the temperature at 400deg/hr, hold at 400℃ for 2.5hr, quantify the iron oxide oxygen on the sample surface, and then increase the temperature to 100deg/hr.
_The temperature was raised _at It was extracted and quantified using a mass spectrometer as an analyzer. As shown in Table 4, oxygen exists in various states in steel samples, and in conventional methods, errors occur in quantitative values due to dissolution of ultrafine oxides during extraction and separation and filtration leakage during filtration. It has become clear that according to the method of the present invention, the amount of oxygen for each oxide can be determined with high accuracy. In this example, MnO, SiO ₂ ,
Although the method of the present invention has been described with respect to the fractional determination of oxygen in TiO ₂ , it goes without saying that the method of the present invention can also be applied to the determination of oxygen in other oxides such as Al ₂ O ₃ .

[Brief explanation of drawings]

Figure 1 is a diagram showing changes in the quantitative value of oxygen in a steel sample with respect to heating extraction temperature, Figure 2 is a heating extraction curve for each steel sample depending on the state of oxygen present, and Figure 3 is an apparatus for carrying out the method of the present invention. FIG. 2 is a block diagram showing an example. DESCRIPTION OF SYMBOLS 1... Furnace core tube, 2... Temperature control section, 3... Heating furnace, 4... Sample crucible, 5... Hydrogen gas source, 6...
... Gas purification section, 7 ... Flow rate control section, 8 ... Analyzer.

Claims (1)

[Claims] 1. When heating a steel sample in a hydrogen stream, the heating extraction temperature is set to a required temperature within the range of 170°C to 550°C to generate oxygen in iron oxide on the surface of the sample as water. A method for quantifying oxygen, which is characterized by extracting and quantifying oxygen. 2. When heating a steel sample in a hydrogen stream, the heating extraction temperature is set to a required temperature within the range of 170°C to 550°C to generate oxygen from iron oxide on the surface of the sample as water, which is extracted, and then further raised. 1. A method for quantifying oxygen, which comprises heating the sample and allowing the sample to remain at each decomposition temperature of the oxide, or passing through the temperature to generate oxygen in the oxide as water, extracting the water, and quantifying each.