JPH035549B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for analyzing nitrogen in metals. It is well known that gas components such as nitrogen in metals have various effects on the properties of metal materials, and it goes without saying that it is important to know their abundance. In recent years, advances in refining technology such as vacuum degassing have made it possible to actively control the amount of gas components in metals. Conversely, techniques have been developed to add nitrogen to improve strength and corrosion resistance. In order to accurately control the amount of gas components to a desired value in the production of such metals, it is extremely important to quickly (within 3 minutes) know the amount of gas components in the molten metal being refined. Conventional methods for gas analysis in metals include melting in an inert gas using an impulse furnace or high-frequency furnace as a heating source - gas chromatography separation - thermal conductivity method, but this method requires three steps in the determination itself. ~4
In addition, it takes a long time to pre-process the sample for quantification. In other words, in samples collected from molten metal, there is an oxide film on the surface that causes quantitative errors, so this must be removed by polishing or cutting the oxide part, and bulk samples cannot be analyzed as they are. Therefore, complicated pretreatment is required, such as cutting or shredding to collect a small sample of about 0.3 to 1 g, and then accurately weighing the collected sample, which is insufficient for rapid analysis. In addition to the other conventional nitrogen chemical analysis method, which requires the same sample preparation as the inert gas melting-gas chromatographic separation-thermal conductivity method,
Because sample dissolution and analysis operations require a long time,
Melting in inert gas. It takes much longer to quantify than the gas chromatographic separation-thermal conductivity method, so it cannot be used for process control. In addition, the present inventors previously irradiated metal with a narrowly focused electron beam in a high vacuum, melted only the irradiated part, stirred it to boiling, and extracted the gas contained in the molten part as neutral atoms and molecules. He also reported a method for local gas analysis in metals using a gas analyzer (Japanese Patent Application Laid-open No. 124795/1983). Although this method is a useful method that does not require cutting or weighing the sample, it takes some time to vacuum and is not suitable for rapid analysis for process control. In view of the current situation, the inventors of the present invention have conducted various studies, and as a result, have melted a part of a metal sample with an electron beam in a high vacuum and quantitatively determined the amount of nitrogen gas extracted from the melted part. When analyzing the nitrogen content in a metal sample, the sample is first introduced into a sample introduction section with a small volume (volume ratio of 1/30 or less compared to the high vacuum section), and then an exhaust pump (exhaust pump) independent of the high vacuum section After evacuating the atmosphere in the introduction section (with a capacity of 200/min or more), introduce the sample into the high vacuum section and evacuate the sample using the respective vacuum pumps while maintaining continuity between the sample introduction section and the high vacuum section. This allows the vacuum evacuation time from sample loading to electron beam irradiation under high vacuum to be shortened from the conventional several hours or tens of minutes to the order of tens of seconds, and the volume of the molten part can be reduced. Since it is determined with good reproducibility by the electron beam current, voltage, and irradiation time, it is possible to use a sample of a certain shape and obtain a calibration curve prepared in advance using a homogeneous sample with a known nitrogen content. Since the nitrogen quantitative value can be converted into nitrogen content, there is no need to perform operations such as cutting, polishing, and weighing the sample, and by combining this with a high-speed gas analyzer, the amount of nitrogen can be determined within 3 minutes. We found that it is possible to quantify Furthermore, by forming the valve that isolates the sample introduction part and the high vacuum part integrally with the sample moving mechanism, it is possible to eliminate the waiting time for opening and closing the valve and further shorten the analysis time. The present invention was made based on these findings, and its gist is as follows: 1. A part of a metal sample is melted by an electron beam in a high vacuum, and nitrogen extracted from the melted part is To quantify gas and analyze the nitrogen content in metal samples, the sample was placed in a sample introduction section isolated from the high vacuum section, and then evacuated to below 1 Torr using a vacuum pump independent of the high vacuum section exhaust pump. Afterwards, the sample is introduced into the high vacuum section, and with the sample introduction section connected to the high vacuum section, vacuum evacuation is further performed, and when the degree of vacuum becomes 5 × 10 ^-6 Torr or less, the sample is irradiated with an electron beam. A method for analyzing nitrogen in metals. 2. The ratio of the high vacuum section for irradiating a part of the metal sample with an electron beam, the vacuum pump for evacuating the high vacuum section, and the internal volume of the high vacuum section is 1/30 or less and 1 A sample introduction section with the following internal volume that can be freely connected to the high vacuum section and the atmosphere, a vacuum pump to evacuate the introduction section, and a sample transferred from the sample introduction section to the high vacuum section in high vacuum. This is an apparatus for analyzing nitrogen in metals, which is characterized by consisting of a mechanism for irradiation, an electron beam irradiation section, and a high-speed gas analyzer. Hereinafter, the present invention will be explained in detail based on drawings showing examples. FIGS. 1 and 2 are examples of the apparatus of the present invention for measuring nitrogen gas components in metals, with the former showing the state during sample insertion and the latter showing the state during analysis. After the metal sample 1 is attached to the mounting part 4 in the sample introduction part 3 through the sample inlet/outlet 2, the sample inlet/outlet 2 is closed, the valve 5 is opened, and the gas inside the sample introduction part 3 is removed using a vacuum pump (exhaust capacity). 200/min or more)
Exhaust at 6. The reading of the vacuum gauge 7 in the introduction section 3 is
After confirming that the temperature is 1 Torr or less, the shaft drive unit 8 drives the shaft 9 to move the flange 10 fixed to the shaft to connect the sample introduction unit 3 with the high vacuum unit 11 and to transfer the sample 1. Install it at a predetermined electron beam irradiation position. The high vacuum section 11 is previously evacuated to a high vacuum of 1×10 ^-6 Torr or less by the high vacuum evacuation pump 13 via the valve 12. Since the degree of vacuum deteriorates, the high vacuum section vacuum gauge 14 returns to 5×10 ^-6 Torr.
Wait while exhausting the air until the following is shown. After confirming that the pressure is below the required level, the sample 1 is irradiated with an electron beam from the electron beam source 15 at a constant voltage, beam current, and irradiation time to locally melt the sample and extract it from the melted part into a high vacuum. The amount of nitrogen gas is quantified using a high-speed gas analyzer 16. The volume of the melted part is ±1% if each of the above conditions is kept constant within ±1%.
The accuracy is constant. Therefore, without weighing, the nitrogen quantitative value can be converted into nitrogen content using a calibration curve prepared in advance using a homogeneous sample with a known nitrogen content. In addition, especially for homogeneous samples that do not contain pores, the results obtained by irradiating two or three points at positions 3 mm or more apart are within a relative error of ±5%, and using the average of these results is reliable. Highly accurate analytical values can be obtained. After the analysis is completed, the shaft drive section 8 drives the shaft 9 again to return the sample to the sample introduction section 3, isolate the sample introduction section 3 and the high vacuum section 11, close the valve 5, and then open the leak valve 17. The Ar gas in the gas source 18 is introduced into the sample introduction section 3 to bring it to atmospheric pressure, and the inlet/outlet port 2 is opened to take out the sample, and if necessary, another sample is attached. The size of the sample inlet/outlet is 50 mm, taking into account the diameter of the sample to be inserted (10 to 40 mmφ) and the volume of the introduction section 3.
It is appropriate to set the diameter to 100 mmφ. Sample introduction part 3
1 or less and 1/ of the volume of the high vacuum section 11
30 or less, but considering only the time required to reach vacuum, it is desirable to make the volume of the introduction section 3 as small as possible, but considering the shape of the sample to be inserted, a certain volume is required. By connecting the sample introduction section 3 and the high vacuum section 11, the residual gas pressure in the sample introduction section 3 can be reduced to a degree of vacuum (5×10 ^-6 Torr) that allows electron beam irradiation. This was set as a necessary condition that the time required to reach this point could be sufficiently short. It is desirable to drive the shaft 9 when the degree of vacuum in the introduction section 3 is less than 1 Torr, and if the above-mentioned volume ratio condition is satisfied, the sample introduction section 3 and the pre-evacuated high vacuum section 11 are The degree of vacuum is better than that of the introduction part by the connection, and the low vacuum and large volume pump part 6 is isolated by closing the valve 5 at the same time as the connection.
This was done in order to shorten the analysis time by irradiating the sample with the electron beam almost at the same time as the sample is set at the irradiation position. When connected when the vacuum is lower than 1 Torr, the large volume high vacuum section 11 becomes a low vacuum, so the time to evacuate it again to a high vacuum capable of electron beam irradiation of 5×10 ^-6 Torr or less is extended. Ru. The reason for setting it below 5×10 ^-6 Torr is to prevent abnormal discharge during electron beam irradiation and reduce noise during analysis. The shaft drive section 8 has a system in which a shaft 9 that moves linearly within the high vacuum section 11 is driven from the outside via a bellows using an electric motor and a rack-and-pinion mechanism. The flange 10 is provided with a surface that receives the O-ring in a part of the sample introduction section 3, so that when the sample is located in the introduction section 3, the high vacuum section 11 and the introduction section 3 are vacuum-isolated. The structure was designed to be The electron beam source 15 has an accelerating voltage of 10 to 100 kV and a beam current of 5 to 100 kV.
It is best to use one that can be set within a range of 50 mA, including the irradiation time, with an accuracy of ±1%.
As the high-speed gas analyzer 16, a device such as a quadrupole mass spectrometer that can track partial pressure changes over a short period of time (approximately 1 sec) when the melt is extracted into a high vacuum and evacuated by a vacuum pump is used. Good. After the analysis, the sample was returned to the sample introduction section 3 and argon gas was introduced into it to bring it to atmospheric pressure. Other inert gases such as He may be used instead of Ar gas. Hereinafter, the effects of the present invention will be explained in more detail with reference to Examples. Example: After melting low carbon steel in a converter, degassing is performed using an RH degassing device, and 25 mm is removed every 5 minutes after the start of degassing.
A cylindrical sample of φ×(70±3) mm was taken, and after cooling with water, the amount of nitrogen was analyzed using the apparatus shown in FIG. 1 according to the procedure described above. The equipment used has an inlet volume of approximately 0.6, a high vacuum part volume of approximately 24, a 250/min oil rotary pump as the inlet vacuum evacuation pump, and a 330/sec turbo molecular pump as the high vacuum pump. A pump and a 250/min oil rotary pump were used. Electron beam irradiation conditions are acceleration voltage 30kV, beam current
At 20 mA and irradiation time of 1 sec, irradiation was performed at 3 points on the side of the cylinder at 3 mm intervals on the same sample.
The average was taken as the nitrogen quantitative value. The quantitative nitrogen value was converted into the nitrogen content using a calibration curve prepared in advance using steel of the same shape and known nitrogen content. The quantitative results are shown in Table 1.

[Table] After analysis using the method of the present invention, a part of the unmelted part of the sample was cut, polished, and weighed, and the results of nitrogen quantitative determination using the conventional inert gas melting-gas chromatography separation-thermal conductivity detection method are also included. Shown. It is clear that the results are in good agreement with the conventional method. The time required to obtain the above analytical values using the method of the present invention was approximately 120 seconds in each case. Therefore,
By the method of the present invention, the effect of RH degassing can be quickly grasped, and the RH degassing operation can be controlled for a sufficient time, which not only improves the properties of the material but also contributes to energy saving. It's large.

[Brief explanation of drawings]

Figures 1 and 2 show an example of the device of the present invention for analyzing nitrogen in metals;
The latter shows the state at the time of analysis. 1...metal sample, 2...sample inlet/outlet, 3...
...Sample introduction part, 4...Sample mounting part, 5...Valve, 6
... Vacuum exhaust pump, 7 ... Vacuum gauge, 8 ... Shaft drive section, 9 ... Shaft, 10 ... Flange, 11 ... High vacuum section, 12 ... Valve, 13 ... Exhaust pump, 14 ... ...Vacuum gauge, 15...Electron beam source, 16...High speed gas analyzer, 17...Leak valve, 18...Gas source.

Claims (1)

[Claims] 1. When a part of a metal sample is melted by an electron beam in a high vacuum and the nitrogen gas extracted from the melted part is quantified and the nitrogen content in the metal sample is analyzed, the sample is After placing the sample in the sample introduction section that is isolated from the high vacuum section, the sample is evacuated to 1 Torr or less using a vacuum pump independent of the high vacuum section exhaust pump, and then the sample is introduced into the high vacuum section and the sample introduction section is separated from the high vacuum section. A method for analyzing nitrogen in metals, which is characterized by further evacuation in a conductive state, and irradiating the sample with an electron beam when the degree of vacuum reaches 5 x 10 ^-6 Torr or less. 2 The ratio of the high vacuum section for irradiating a part of the metal sample with an electron beam, the vacuum pump for evacuating the high vacuum section, and the internal volume of the high vacuum section is 1/30 or less and 1 or less A sample introduction section with an inner volume of An apparatus for analyzing nitrogen in metals, comprising a mechanism, an electron beam irradiation section, and a high-speed gas analyzer. 3. An apparatus for analyzing nitrogen in metals according to claim 2, characterized in that a valve for isolating the sample introduction section and the high vacuum section is formed integrally with the sample moving mechanism.