JPH09166590A - Rapid determining method for trace carbon in steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To analyze a trace quantity of carbon in steel with high accuracy without requiring complicated preparation and operation by using copper as a combustion improver, using a high frequency heating device as a heating means, setting the surface area of a sample to a specific value or less to the weight of the sample, and heating for a fixed time. SOLUTION: A sample 1, the surface area of which is 4cm<2> or less per 1g in sample weight, is put in a magnetic boat 3 along with 0.7g of a copper combustion improver 2, and the magnetic boat 3 is inserted in a combustion pipe 4 installed at the central part of a high frequency coil 5. Oxygen gas is led into the combustion pipe 4. The lead-out port of oxygen gas is connected to a detector 6 to detect the carbon quantity of gas in the combustion pipe 4. While leading in oxygen gas at the rate of 2.5 lit./min., heating is applied for 20-60 seconds at high frequency of 18MHz with output of 2.3Kw to extract carbon. A contaminated carbon signal and a steel carbon signal are separated by the detector for measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analytical method for rapidly and accurately quantifying a trace amount of carbon in a steel sample.

[0002]

2. Description of the Related Art In recent years, in the steel manufacturing industry, ultra-low carbon steels have been manufactured in which the carbon concentration in the steels has been made as low as possible and the deep drawability has been improved, as the quality of the products has increased. In these manufacturing processes, it is necessary to grasp the carbon concentration in a short time for process control and quality control, and rapid analysis of trace carbon is urgently required. In order to meet this demand, an analytical method that can accurately measure a minute amount of carbon, at the same time avoids complicated operations and can quickly obtain a result on site is indispensable.

In a method for analyzing carbon in steel, a sample is heated and melted together with a combustion improver in an oxygen stream to burn carbon and convert it into carbon monoxide and carbon dioxide carbon dioxide gas for extraction, which is then infrared-absorbed. Method and the coulometric titration method to detect the amount of carbon and there is a combustion analysis method. Copper, tin, or a mixture of tin and tungsten is used as the combustion improver.

A problem in the analysis of a trace amount of carbon is carbon adhering to the surface of the sample, and if it is mixed with carbon in steel, the measured value will be disturbed. On the sample surface, organic carbon such as hydrocarbons floating in the atmosphere may be attached or carbon dioxide gas may be adsorbed. Organic carbon can be removed to some extent by washing with an organic solvent, but the adsorbed carbon dioxide gas can hardly be removed.

The carbon adhering to the surface of the sample in this way is said to be contaminated carbon, but this contaminated carbon is in a very small amount and can be ignored if the carbon content in the steel is large. However, if the amount of carbon in the steel is very small, it cannot be ignored, and the amount of contaminated carbon must be separated to obtain the true amount of carbon in steel.

Conventionally, there are three measures to deal with this problem. The first is a measure to avoid sample contamination from the time of sampling. For example, in Japanese Patent Laid-Open No. 3-71057, after collecting molten steel with a vacuum sampler, all pretreatment operations such as crushing the sampler and cutting the sample are performed in an airtight chamber purged with an inert gas. An analyzer is described which connects the airtight chamber and the quantitative analyzer in an airtight state. However, this is a large-scale facility and is not practical.

The second is a measure for measuring carbon in steel after removing contaminating carbon. Carbon in steel is extracted as carbon monoxide or carbon dioxide as carbon dioxide by heating and melting in an oxygen stream in the presence of a combustion improver.
Carbon in steel is not extracted even in an oxygen stream unless there is a combustion improver and the degree of heating reaches the melting of the sample. on the other hand,
Contaminant carbon can be removed as carbon oxide gas by heating in the presence of oxygen.

Based on the above idea, JIS G 12
In No. 11, the preheating method is specified. In this method, an electric resistance heating furnace is used as a heating means, and the sample is heated in advance at 420 ° C. ± 10 ° C. for 5 to 10 minutes in the atmosphere to remove the contaminated carbon. After this, a combustion improver is added and combustion heating is performed in an oxygen stream to extract carbon in steel as carbon oxide gas and send it to the detector. By this method, carbon in steel having a content of 3 ppm to 100 ppm can be accurately analyzed.

However, this method requires a time for preheating, and further requires an operation of taking out the sample from the furnace once and adding a combustion improver between the preheating and the subsequent combustion heating.
This is not suitable for process control analysis because the time required for analysis becomes long. Also, in preheating, it is necessary to maintain the heating temperature within a narrow range, and it is necessary to use an electric resistance heating furnace that can control the temperature inside the furnace, but this furnace has a high frequency of replacement of the core tube and heating element. However, it is not suitable for practical use in the field.

In order to shorten the time required for the analysis, a method of using a combustion improver from the beginning and performing analysis while flowing oxygen has also been proposed. For example, in Japanese Patent Laid-Open No. 6-123690, it is possible to switch the gas introduced into the heating part of the sample, first introduce an inert gas to remove contaminating carbon, and then switch to oxygen gas to change carbon in steel. It is described that is extracted as carbon oxide gas and detected. In this case, it is not necessary to maintain the preheating at a low temperature, a high-frequency heating device can be used as the heating means, and heating and combustion can be completed in a short time. However, a small amount of oxygen mixed in the inert gas acts on the decarburization of carbon in the steel and reduces the accuracy of analysis. Therefore, it is necessary to completely replace the inside of the system with an inert gas atmosphere after analysis in an oxygen stream. That is,
It takes time to prepare before measurement, and is not suitable for process control analysis or the like in which many samples must be rapidly and repeatedly analyzed.

Thirdly, there is a measure for separating and measuring when detecting carbon oxide gas. Contaminating carbon is extracted before the steel sample is melted while the sample is being heated. Therefore, contaminant carbon is detected prior to carbon in steel. For example, in Japanese Patent Laid-Open No. 3-37566, a sample and a combustion improver are put into a sample container, a lid is put on the sample container, the opening ratio is set to 30% or less, and the sample container is inserted into an oxygen atmosphere and heated from 1100 ° C. to 1400 ° C. A method for detecting gas is described. Because of the lid, the temperature rise of the sample becomes gentle, and the carbon oxide gas detected before the sample reaches 1100 ° C is due to contaminated carbon, and the carbon oxide gas detected thereafter is carbon in steel. It is due to. However, in this method, whether or not the contaminated carbon and the carbon in the steel can be clearly separated is greatly influenced by the heating rate of the sample, and the analysis accuracy varies depending on the sample container and the lid. In addition, since the heating temperature cannot be higher than 1400 ° C., an electric resistance heating furnace must be used, and like the preheating method, the core tube and heating element are frequently replaced, which is not suitable for practical use in the field. .

[0012]

As described above, when trying to analyze a trace amount of carbon in steel with high accuracy, the analysis time becomes long or complicated operation is required, and it is used for process analysis and quality control analysis. There was no suitable analytical method available.

The present invention has been made to solve this problem, and an object thereof is to analyze a trace amount of carbon in steel rapidly and with high accuracy without requiring complicated preparations and operations.

[0014]

[Means for Solving the Problem] The means for achieving this object is to heat and burn a steel sample in an oxygen stream by using a combustion improver, and use the carbon component in the sample as carbon oxide gas to obtain the carbon oxide gas concentration. In the combustion analysis method of carbon in steel for obtaining the carbon content from the sample, copper is used as a combustion improver, a high frequency heating device is used as a heating means, and the surface area of the sample is 1% by weight of the sample.
A rapid determination method for a trace amount of carbon in steel, in which the carbon content in the steel is 4 cm ² or less and the heating time is 20 seconds or more and within 1 minute to separate carbon in the steel from contaminating carbon.

Copper, tin, a mixture of tungsten and tin, etc. are generally used as the combustion improver. In the method of the present invention, when copper is used, the contamination carbon and the carbon in the steel can be separated in the shortest time. Be seen.

The high frequency heating device is used as the heating means in order to utilize the fact that the high frequency current is mainly induced on the surface of the sample and therefore the heating is performed on the surface layer of the sample. Further, in the high-frequency heating apparatus, unlike the electric resistance heating furnace, it is not necessary to replace the core tube or the heating element, and maintenance is easy. Furthermore, rapid heating is easy and the sample can be completely burned in a short time.

In the high frequency heating, heating is performed on the surface layer of the sample as described above, the temperature is raised from the surface layer and then the temperature inside the sample is increased by heat transfer. It is necessary to remove polluting carbon. By making the surface area smaller than the weight of the sample, the melting of the sample is delayed, and the contamination carbon and the carbon in steel are easily separated. Further, if the sample surface area is small, the amount of contaminated carbon is so small that the separation becomes easier.

The surface area of the sample is 4 cm ² per 1 g of the sample weight.
In the case of a trace amount of carbon steel having a carbon content of 100 ppm or less, contamination carbon and carbon in steel can be sufficiently separated and measured in a heating time of 1 minute or less.

If the output of high frequency is increased, the total carbon can be extracted in a short heating time, but if the extraction time is too short, the extraction of carbon in steel will start before the extraction of contaminated carbon is completed, and the separation of both Will be difficult. Therefore, it is necessary to heat for 20 seconds or more to extract the total amount of carbon.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Quartz tube with an inner diameter of 6 mm made of ultra-low carbon molten steel
Cut the rod-shaped steel sample sucked up using
The surface is 1.1g in weight without pretreatment such as surface polishing.
Product is 1.5 cm ^TwoA sample of was obtained.

FIG. 1 shows a situation in which a sample is heated and melted to extract carbon. The sample 1 was put in a porcelain boat 3 together with 0.7 g of the copper combustion improver 2, and was inserted into a combustion tube 4 installed at the center of the high frequency coil 5, and oxygen gas was introduced into the combustion tube 4.
The outlet of oxygen gas is connected to the detector 6, and the carbon content of the gas in the combustion tube is measured by this detector.

While introducing oxygen gas at a rate of 2.5 liters / minute, carbon was extracted by heating at a high frequency of 18 MHz and an output of 2.3 kW.

The signal intensity of the detected carbon is shown in FIG.
The signal that appeared 10 seconds after the start of heating is the signal of contaminated carbon, and the signal that appeared nearly 20 seconds later was the signal of carbon in steel. The peaks drawn by both signals are clearly separated, and the amount of polluted carbon and the amount of carbon in steel can be measured separately.
Using the calibration curve, the carbon concentration in the steel was calculated from the area of the peaks drawn by the subsequent signals to obtain 20.4 ppm.

A suitable sample weight is about 1 g,
The method of the present invention can be applied to a sample of about 0.3 g to 2 g.

The higher the frequency of the high frequency used for heating is, the more preferable it is, but about MHz is sufficient.

As the combustion improver, copper which does not melt until the extraction of the polluted carbon is finished is preferable, and tin melts at a low temperature and covers the surface of the sample, so that the extraction of the polluted carbon is delayed and the separation from the carbon in the steel becomes slightly difficult. .

In the above measurement, the detection signal intensity curve when the burner is changed from copper to a mixture of tin and tungsten is shown in FIG.
Shown in The peak of the signal of polluted carbon that appeared 10 seconds after the start of heating overlaps the peak of the signal of carbon in steel that appeared nearly 20 seconds after the heating, and it is impossible to separate and accumulate the respective intensities.

FIG. 4 shows a detection signal intensity curve when the high frequency output is increased and carbon is extracted in a time of less than 20 seconds in an attempt to excessively shorten the extraction time. Also in this case, separation is difficult.

[0029]

EXAMPLE An ultra-low carbon molten steel was sucked up into a rod-shaped sample by changing the diameter of the tube, and the rod-shaped sample was cut into an appropriate length, and the carbon concentration in the steel was measured for a sample of about 1 g in which the surface area was changed. For the measurement, the same steel type was measured 5 times, the average value was used as the measured value, and the relative reproducibility Cv was obtained from the standard deviation σ for evaluation, and the value measured by the preheating method according to JIS G 1211 described above was standardized. As a value, the difference from this was obtained and evaluated.

Table 1 shows other measurement conditions, measurement results, and evaluation results.

[0031]

[Table 1]

In the examples of the invention, the reproducibility Cv was 2% to 3%, but in the comparative examples, there was a large variation of 5% to 8%. As for the comparative example, N0.6 and 7 have a specific surface area larger than 4.0 cm ² / g, N0.8 uses tungsten and tin as a combustion improver, and N0.9 increases the high frequency output and the heating time is less than 20 seconds. It is what

Also, the relative value of the difference from the standard value was within 3% in the examples, but was as large as 4% to 11% in the comparative examples.

[0034]

As described above, according to the present invention, in a combustion analysis method for carbon in steel, a trace amount of carbon steel sample having a surface area of 4 cm ² or less per 1 g is heated by high frequency by using copper as a combustion improver. Heat for 20 seconds to 1 minute. Since the surface contaminant carbon is removed before the sample melts, the carbon in the steel separates and is accurately measured even if the analysis time is short. Moreover, the equipment can be easily maintained and maintained, which is suitable for process analysis and quality control analysis. As described above, the effect of the present invention, which realizes an analysis method that shortens the analysis time and has high accuracy and is easy to maintain, is great.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a sample heating unit for explaining the method of the present invention.

FIG. 2 is a curve diagram of carbon signal intensity in which polluted carbon and carbon in steel are separated by the method of the present invention.

FIG. 3 is a curve diagram of a carbon signal intensity in which a pollutant carbon and carbon in steel are insufficiently separated due to an inappropriate use of a combustion improver.

FIG. 4 is a curve diagram of a carbon signal intensity in which separation of polluted carbon and carbon in steel is insufficient by heating too rapidly.

[Explanation of symbols]

 1 sample 2 copper burner 3 porcelain boat 4 combustion tube 5 high frequency coil 6 detector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takanori Akiyoshi, 1-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Tadashi Mochizuki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (1)

[Claims] A steel sample is heated and burned in an oxygen stream by using a combustion improver, and a carbon component in the sample is used as a carbon oxide gas. As a burner in a combustion analysis method for obtaining a carbon content rate from the concentration of the carbon oxide gas. Using copper, using a high-frequency heating device as the heating means, and setting the surface area of the sample to 4 cm ² or less per 1 g of sample weight, and separating the carbon in the steel from the contaminated carbon within the heating time of 20 seconds or more and 1 minute Characteristic rapid determination method of trace carbon in steel.