JP3370572B2 - Analysis method for oxide inclusion oxygen in metals by type - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of analyzing the oxygen content of oxygen-containing inclusions in metals such as iron and steel by an inert gas carrier melting / infrared absorption method or the like. The present invention relates to a method for analyzing oxide-based inclusion oxygen for each type of oxide-based inclusions in a metal. 2. Description of the Related Art Development of ultra-low oxygen steel and high-purity iron in which the form of oxides is controlled has been promoted, and it is necessary to accurately determine the concentration of a trace amount of oxygen at a ppm (parts per million) level. Is required. In particular, in bearing steels used under severe conditions, Al ₂ O ₃ , MgO · Al
Inclusions such as ₂ O ₃ tend to form large grains, which cause fatigue failure. For this reason, it is important to reduce the amount of inclusions in the product and control the form of the inclusions, and there is a demand for an accurate and rapid technique for analyzing the types of inclusions in low oxygen steel. Conventionally, methods for analyzing inclusions in steel include a method of collecting a test piece from a sample, observing the surface to be inspected under a microscope, and classifying the sample into A to C systems (JIS G0555), and mirror-polishing the sample surface. In addition, methods using instrumental analysis such as electron beam microanalysis have been performed. [0004] However, since these methods are measurement methods for a cross section of a sample, it is impossible to detect true inclusions that cause material destruction, measurement time is enormous, and sample adjustment such as polishing is required. There are problems such as complexity. [0005] As one solution to solve these problems,
Recently, an analysis method using an oxygen analyzer has been proposed (JP-A-6-148167). In this method, a sample is put into a graphite crucible, and then continuously heated at a constant heating rate, whereby oxygen from easily reduced oxides (FeO, MnO, etc.) in which a decomposition reaction occurs on a relatively low temperature side, and a relatively small amount. Non-reducible oxides (CaO, Al ₂ O ₃
Etc.) and oxygen from the gas using the gas extraction curve at the time of analysis. However, the method disclosed in JP-A-6-148167 is intended for a high oxygen content of 10% or more in steelmaking slag, and a trace amount of oxygen of several ppm order. When applied to a metal sample with a large amount, it is difficult to separate the waveforms because the peaks are small and the waveforms overlap each other, and it is clear that it cannot be applied to a metal sample with a trace amount of oxygen on the order of several ppm. became. This method separates oxygen from easily reduced oxides and oxygen from hardly reduced oxides, and cannot be applied to the analysis of oxygen by type of oxide-based inclusions. The present invention has been made to solve the above problems, and has as its object to provide a method for analyzing oxygen for each type of oxide-based inclusions in a metal. Means for Solving the Problems The present inventor has studied on a method for analyzing oxide-based inclusions in metals such as iron and steel by type. As a result, when conducting analysis by type of oxide in a metal sample with a trace amount of oxygen, it was found that the heating conditions of the metal in the temperature range where oxide-based inclusions are decomposed are important. The invention has been completed. [0010] The present invention has been made to solve the above problems, and the gist is as described in the claims. In other words, the gist is that a metal sample such as a steel sample is dropped into a graphite crucible under an inert gas atmosphere, heated and melted, and CO gas is extracted from the molten bath to reduce the amount of oxygen in the metal such as steel to a plurality. A method of separating and analyzing waveforms, and for each waveform emerging from a temperature of 900 ° C. or higher,
An analysis method for each type of oxide-based inclusion oxygen in metals such as steel, characterized by repeatedly analyzing the following temperature control pattern. [0011] heating from appearing starting point A _n of each wave to a peak appearance point B _n of each wave at 2 ° C. / sec or less of the heating rate. [0012] a constant temperature until the emergence end point C _n of each wave peak appearance point B _n of each wave. Heating is performed at a heating rate of 2 ° C./sec or less from the appearance end point C _n of each waveform to the appearance start point A _{n + 1 of the} next waveform. In the present invention, the method of analyzing gas or oxygen is not particularly limited as long as a metal sample is dropped into a graphite crucible in an inert gas atmosphere, heated and melted, and CO gas is extracted from the molten bath. Not something. A typical method is a so-called inert gas carrier melting / infrared absorption method. According to the study of the present inventors, the extraction temperature of the oxygen content of the oxide-based inclusions occurs in a temperature range of 900 ° C. or higher, and the CO gas generated in a temperature range of less than 900 ° C. is adsorbed on the surface of the metal sample. It can be regarded as being generated from oxygen and oxygen contaminated by the iron oxide film on the surface. From the above findings, the present invention does not particularly consider the waveform of the gas extraction curve generated at a temperature lower than 900 ° C. Target waveform. For example, there are various types of oxide inclusions in steel materials, such as Al ₂ O ₃ , SiO ₂ , CaO, MgO, and MnO. In addition, these exist not only as a single substance but also in various forms such as those in a composite form such as MgO.Al ₂ O ₃ . When analyzing the amount of oxygen in a metal by an inert gas carrier melting-infrared absorption method or the like, M
It is considered that a reaction of O + C = M + CO (M: metal, O: oxygen, C: carbon) occurs. The temperature at which the oxide decomposes depends on the type of the oxide and the partial pressure of CO in the crucible, and the respective reaction temperatures can be estimated or measured based on thermodynamic equilibrium calculations and actual measurement results. The present inventor has obtained a new finding that the decomposition temperature of an oxide is greatly affected by the heating conditions of a sample, regardless of the type of oxide, when performing analysis such as inert gas transport melting-infrared absorption method. Was. In other words, the lower the heating rate, the closer the reaction temperature to the calculated equilibrium value, the better the separation of the gas extraction curve for each type of oxide, and conversely, the higher the heating rate, the higher the gas temperature for each oxide type. The separability of the extraction curve deteriorates. The present invention is based on this finding and applied to the analysis of oxide inclusions by gas analysis of metal samples. FIG. 1 shows an example of the gas extraction curve obtained by the method of the present invention. For example, assuming that n kinds of oxide-based inclusions are contained in the sample, n peaks are obtained in the form of a first peak and a second peak in the order of oxides that are easily reduced. These gas extraction curves do not overlap each other, and the more they are separated from each other, the more accurately each oxide can be extracted. The conditions for this are the contents of the present invention. When a metal sample having an extremely low oxygen content is analyzed by an inert gas carrier melting / infrared absorption method or the like, the influence of the amount of surface contaminating oxygen, which makes the total oxygen content, cannot be ignored. Analysis is performed by removing the surface contamination oxygen by polishing using a chemical polishing method, but the effect of the surface contamination has not yet been completely removed. However, iron oxides and hydroxides such as FeO, Fe ₃ O ₄ , and FeOOH that constitute the surface contaminating layer can be decomposed at a relatively low temperature at the rate of temperature rise of the sample during oxygen analysis. is there. Before analyzing the amount of oxygen composed of oxide-based inclusions, the temperature at which the above-mentioned contaminant oxygen on the metal surface is separated and removed is less than 900 ° C., and the temperature at which only oxygen derived from oxide-based inclusions is extracted and analyzed. Is set to 900 ° C. or higher for this reason. If the temperature at which each peak starts to be generated is too high, the temperature range of the reaction between the first oxide and the second oxide becomes too close, and it becomes difficult to separate the waveforms. In addition, it is considered that the slower the temperature rise rate, the closer to the thermodynamic equilibrium condition, but the analysis by type of oxide is performed considering the work efficiency and the ease of confirming the appearance temperature at the waveform appearance start point. For this purpose, it is necessary that the heating rate be 2 ° C./sec or less. As the sample is continuously heated and melted at this rate of heating, the oxide-based inclusions in the sample are eventually reduced to carbon by carbon reduction.
The amount of O gas generation becomes maximum. When the amount of generated CO gas becomes maximum, the temperature is kept constant and the CO gas extraction is completed. To hold the temperature to each waveform appearing end point C _n constant from the peak appearance point B _n of each wave, when between this keeps continuously heated, the amount of other inclusions in the sample, the size ,
This is to prevent the decomposition of the (n + 1) -th oxide-based inclusion within the temperature or time during which the waveform of the certain n-th inclusion appears, although it differs depending on the composition and the location. Next, after the appearance of the n-th waveform is completed,
The temperature is further increased to obtain a second waveform which is a gas extraction curve corresponding to the (n + 1) -th oxide-based inclusion amount. This heating method is repeated, and finally, n waveforms extracted from the n kinds of oxide-based inclusions present in the sample at the end of the analysis are obtained. By confirming the appearance position of the waveform of each oxide that has been artificially created in advance, the oxide-based inclusions in the sample can be identified from the obtained waveform. Further, the respective oxygen amounts of the oxide-based inclusions in the sample can be obtained from each waveform. As described above, a method in which a metal sample is dropped into a graphite crucible, heated and melted, CO gas is extracted from the molten bath, and the amount of oxygen in the metal is separated into a plurality of waveforms and analyzed. Then, for each waveform appearing from a temperature of 900 ° C. or higher, it is possible to accurately separate and analyze oxide-based inclusions in a sample by repeating the following temperature control pattern while analyzing the same. Now you can. The heat from the appearance starting point A _n of each wave to a peak appearance point B _n of each wave at 2 ° C. / sec or less of the heating rate. [0025] a constant temperature until the emergence end point C _n of each wave peak appearance point B _n of each wave. From the appearance end point C _n of each waveform to the appearance start point A _{n + 1 of the} next waveform, heating is performed at a heating rate of 2 ° C./sec or less. The heating method up to 900 ° C. is not particularly limited, but from the viewpoint of avoiding adverse effects on the whole analysis, the heating up to 900 ° C. is preferably performed at a heating rate of 2 ° C./sec or less. . Next, examples of the present invention will be described with reference to Table 1 together with comparative examples. In each example, the amount of oxygen in the metal was measured by dropping a metal sample into a graphite crucible under an inert gas atmosphere, heating and melting, and extracting and analyzing CO gas from the molten bath. Is analyzed. [Table 1] Comparative Example 1 is an analysis of carbon steel for machine structural use. As shown in FIG. 3, the metal sample was analyzed at a heating rate of 1 ° C./sec from the start of heating to the end of analysis. It is difficult to separate peaks for each oxide, and the total oxygen content is 12.
1 ppm was shown. In Example 1 of the present invention, the same carbon steel for mechanical structure as in Comparative Example 1 was analyzed. As shown in FIG. 2, the peak appearance point B of the first waveform from the heating start point O of the metal sample was obtained. The heating rate during this period was 1 ° C./sec, and the heating rate from the peak appearance point B of the first waveform to the end point C of the first waveform was 0 ° C./sec. Next, the heating rate from the end point C of the first waveform to the second peak appearance point E was again set to 1 ° C./s.
ec, and the rate of temperature increase from the peak appearance point E of the second waveform to the end point F of the second waveform was 0 ° C./sec. Further, the heating rate was again set to 1 ° C./sec from the end point of the second waveform, but no gas extraction was observed thereafter until the end of the analysis. The oxygen value of the first waveform is 1.8 pp
m, the oxygen value of the second waveform was 10.3 ppm, for a total of 12.1 ppm. When calculating oxides that react at these temperatures from the equilibrium calculation, the first waveform is SiO ₂ ,
The second waveform represents Al ₂ O ₃ . In addition, the results obtained by examining the composition ratio of the oxide composition with an X-ray microanalyzer were appropriate. Comparative Example 2 is an analysis of bearing steel.
As shown in FIG. 3, the sample was analyzed at a heating rate of 1 ° C./sec from the start of heating to the end of analysis. It was difficult to separate the peak for each oxide, and the total oxygen content was 3.8 ppm. In Example 2, the same bearing steel as in Comparative Example 2 was analyzed. As shown in FIG. 4, the rate of temperature rise from the heating start point O of the sample to the peak appearance point B of the first waveform was 1 point. ° C / sec,
From the peak appearance point B of the first waveform to the end point C of the first waveform
The heating rate up to 0 ° C./sec. Next, the heating rate from the end point C of the first waveform to the second peak appearance point E is again set to 1 ° C./sec, and from the peak appearance point E of the second waveform to the end point F of the second waveform. Was set to 0 ° C./sec. Next, from the end point F of the second waveform, the heating rate is again set to 1 ° C./sec, and from the third peak appearance point H, the heating rate is set to 0 ° C./sec. After that, the temperature was raised again to 1 ° C./sec, but no gas extraction was observed until the end of the analysis. The oxygen value of the first waveform is 1.1 pp
m, the oxygen value of the second waveform was 1.4 ppm, and the oxygen value of the third waveform was 1.3 ppm, for a total of 3.8 ppm. When the oxides reacting at these temperatures are calculated from the equilibrium calculation, the first waveform is SiO ₂ and the second waveform is Al
₂ O ₃ and the third waveform shows CaO. This result was appropriate from the result of examining the composition ratio of the oxide composition by an X-ray microanalyzer. Comparative Example 3 is an analysis of a bearing steel of a different steel type from Comparative Example 2. When the rate of temperature rise from the start to the end of the analysis was analyzed at 1 ° C./sec, the waveform could not be separated as shown in FIG. 3, and the total oxygen content was 3.9 ppm. Example 3 is the same bearing steel as Comparative Example 3 analyzed by this method. As shown in FIG. 5, the heating rate between the heating start point O of the sample and the peak appearance point B of the first waveform is 1 ° C./sec, and the temperature rise rate of the first waveform from the peak appearance point B of the first waveform. The heating rate up to the end point C was set at 0 ° C./sec. Next, the heating rate from the end point C of the first waveform to the second peak appearance point E is again set to 1 ° C./sec, and from the peak appearance point E of the second waveform to the end point F of the second waveform. Was set to 0 ° C./sec. Next, from the end point F of the second waveform to the peak appearance point H of the third waveform, the heating rate is again set to 1 ° C./sec, and the end point of the third waveform from the peak appearance point H of the third waveform. The heating rate up to I was 0 ° C./sec, and the heating rate was 1 ° C./sec again from the third waveform end point I. Thereafter, the heating rate was 0 ° C./sec from the peak appearance point K of the fourth waveform. As sec, the heating rate was set to 1 ° C./sec again from the end point L of the fourth waveform, but no gas extraction was observed thereafter until the end of the analysis. The oxygen value of the first waveform is 0.9 ppm, and the oxygen value of the second waveform is 1.1 pp.
m, the oxygen value of the third waveform is 0.7 ppm,
The oxygen value of the fourth waveform is 1.2 ppm, for a total of 3.9 ppm.
Met. When the oxides reacting at these temperatures are calculated from the equilibrium calculation, the first waveform is SiO ₂ and the second waveform is A
l ₂ O ₃ , the third waveform is MgO, the fourth waveform is CaO
Is shown. This result also indicates that the composition ratio of the oxide composition is X
The results were also appropriate based on the results of investigation with a line microanalyzer. Comparative Example 4 is a case where the rate of temperature rise was set to 3 ° C./sec, which was faster than the method of the present invention, among the heating conditions of the method of the present invention. Despite using the same bearing steel as in Example 3,
As shown in FIG. 6, the separability of the waveforms was poor, and the waveforms could not be separated into two waveforms, and the oxygen value of each oxide-based inclusion could not be determined. Examples 1 to 3 are examples of the present invention. In each case, the waveform of each CO gas derived from the included oxide-based inclusions can be clearly separated, and the oxide-based inclusions can be separated. Oxygen analysis for each type was performed. Each of the above embodiments has a 90
This is oxygen from oxide inclusions extracted at 0 ° C. or higher, and is a value obtained by analyzing the true oxygen value in a metal sample for each type of oxide inclusion. As described above, by applying the analysis method according to the method of the present invention to oxygen analysis by an inert gas melting and transporting-infrared absorption method, the accuracy of the oxygen-based inclusion oxygen in the metal sample can be determined for each type. Well separated and analyzed. As described above, according to the analysis method of the present invention, oxygen-based inclusion oxygen in a metal sample can be separated for each type of oxide-based inclusion without any trouble. It became possible to analyze. The present invention is an extremely useful invention that meets the needs of the industry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing an oxygen extraction curve according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing an oxygen extraction curve of Example 1 of the present invention. FIG. 3 is an explanatory diagram showing oxygen extraction curves of Comparative Examples 1, 2 and 3. FIG. 4 is an explanatory diagram showing an oxygen extraction curve of Example 2 of the present invention. FIG. 5 is an explanatory diagram showing an oxygen extraction curve of Example 3 of the present invention. FIG. 6 is an explanatory diagram showing an oxygen extraction curve of Comparative Example 4. By inclusion of A _n ... sample [EXPLANATION OF SYMBOLS] are reacted, the end of the n-th point of the waveform appears B _n ... th n-th peak appearance point C _n ... n-th waveforms of Point A: Point where the first waveform appears due to the reaction of the inclusions in the sample B ... Peak appearance point C of the first waveform C ... End point D of the first waveform D ... Second waveform appearance point E ... peak appearance point F of the second waveform F ... end point G of the second waveform H ... third waveform appearance point H ... peak appearance point I of the third waveform ... end point J of the third waveform ... fourth Waveform appearance point K: Peak appearance point L of the fourth waveform L: End point of the fourth waveform

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 33/20 G01N 31/00 G01N 31/12

Claims (1)

(57) [Claims 1] A metal sample is dropped into a graphite crucible under an inert gas atmosphere, heated and melted, and CO gas is extracted from the molten bath to reduce the amount of oxygen in the metal. And analyzing the waveforms appearing from a temperature of 900 ° C. or higher by repeating the following temperature control pattern repeatedly. Analysis method by type of oxygen. Peak appearance point B of each waveform from appearance start point _An of each waveform
Heat up to _n at a heating rate of 2 ° C./sec or less. From the peak appearance point _Bn of each waveform to the appearance end point C of each waveform
_{Let n} be a constant temperature. From the appearance end point C _n of each waveform to the appearance start point A of the next waveform
Heat up to _{n + 1} at a heating rate of 2 ° C./sec or less.