JP6656970B2 - Steel carbon concentration measurement method, measurement device, and measurement program - Google Patents

Description

  The present invention relates to a method, a measuring device, and a measuring program for measuring carbon concentration of steel. More specifically, the present invention relates to a technique for measuring a carbon concentration suitable for measuring the concentration of a carbon element in a steel material used for, for example, piping of various plants.

  Steel materials used for pipes of various plants may deteriorate due to the temperature and internal pressure of liquids and gases flowing inside the pipes. For example, it is conceivable that segregation of precipitates causes a change in crystal structure and embrittlement, and it is important to determine the concentration distribution of elements in steel materials including precipitates in order to operate the steel materials stably. In particular, heat input to steel by welding may cause cracks due to aging near the weld. Carbon is an important element that has a correlation with tensile strength and the like, and it is important to examine the concentration of the carbon element in the weld.

  The carbon concentration of steel at the time of iron making is often determined by, for example, emission spectrometry using electric discharge (Non-Patent Document 1). However, in this method, unless ablation of a steel material having a diameter of about 1 cm is performed by a discharge, the discharge is not stable, and it is difficult to obtain a stable light emission intensity.

  On the other hand, a massive sample obtained by collecting a part of the molten steel and solidifying it was put into a sample holding section in a sample chamber in an inert gas atmosphere of the analyzer while being in a red-hot state, and pulsed laser light was applied to the surface of the sample. There is a steel component rapid analysis method in which fine particles generated by irradiation are conveyed to an ICP analyzer by an inert gas to analyze components (Patent Document 1).

  There is also a method of determining the carbon concentration in molten steel by irradiating a pulsed laser beam and setting the laser energy accurately using a method of performing emission analysis of plasma generated at the irradiation position (Patent Document 2).

JP-A-7-128237 JP 2013-36926 A

JIS G 1253 "Iron and steel-spark discharge emission spectroscopy"

  However, in the discharge analysis method of Non-Patent Document 1, it is difficult to detect a precipitate having a size of 1 mm or less because the analysis range is wide (in other words, the spatial resolution is large).

  Further, in the ICP analysis of Patent Document 1, it is necessary to dispose a steel material inside the analyzer, so that when a sample is collected from a member such as a pipe under test, the size of the sample may be limited. There is.

  Based on the above, it is considered that the method of irradiating the pulse laser beam is suitable for collecting and analyzing a sample from a member such as a pipe under test. However, in the method of Patent Document 2, a calibration curve is usually obtained using samples having the same composition. However, since some steels have a small number of steels having the same composition, various types of samples are required to obtain the calibration curve. Is difficult to prepare.

  Further, the method of Patent Document 2 is a method of measuring using molten steel. However, when a solid steel material is to be measured, the surface is shaved with the irradiation of the laser beam, and minute holes are generated. Then, since the spot diameter of the laser beam changes due to the formation of the hole, the light emission intensity changes. This is a phenomenon that is particularly conspicuous when measuring a minute area, and is one of the causes of a decrease in measurement accuracy.

  Therefore, an object of the present invention is to provide a method, a measuring device, and a measuring program of steel carbon concentration which can locally and quantitatively measure the concentration of carbon element in steel.

  In order to construct a technique for locally and quantitatively measuring the concentration of a carbon element in steel, the inventor analyzed the transition of the emission intensity of plasma light due to repetition of laser light irradiation on an object to be measured. .

  Here, the “steel” targeted by the present invention includes at least carbon steel (or ordinary steel) and rolled materials for general structures.

  The surface of carbon steel (S35C) as a test piece is repeatedly irradiated with laser light, and the change in plasma light emission intensity due to the repeated laser light irradiation (in other words, the increase in the number of irradiations) is experimentally measured. Verified.

  Specifically, there are a single pulse measurement, which is a method of measuring plasma emission once per laser light irradiation, and a method of measuring plasma emission once, twice laser irradiation with a time difference. For each of the double pulse measurements, the transition of the plasma light emission intensity with the increase in the number of laser beam irradiations was verified.

Regarding the single pulse measurement, irradiation laser energy E = 100 mJ, light receiving delay time t _g of a CCD (ICCD) camera with an intensifier = 1 μs, and exposure time t _w of the ICCD camera t _w = 10 μs were used as measurement conditions.

For the double pulse measurement, the first irradiation laser energy E ₁ = 50 mJ, the laser light irradiation interval IPD = 0.5 μs, the second irradiation laser energy E ₂ = 100 mJ, and the light reception delay time t _g of the ICCD camera = The exposure time t _w of the ICCD camera was set to 10 μs.

  Then, under the condition that the received emission spectrum is integrated 10 times, the transition of the emission intensity with respect to carbon C (I) 193.09 nm, which is a bright line (that is, an emission spectrum specific to the element), accompanying the increase in the number of laser beam irradiations is shown in FIG. As shown in FIG. In FIG. 5, "SP" indicates single pulse measurement, and "DP" indicates double pulse measurement.

  Since the same portion of the test piece is irradiated with the laser light, the more the irradiation is made, the more the trace of irradiation is generated, and the range where the laser light is irradiated becomes wider (in other words, the spot diameter of the laser light becomes larger). Emission intensity tends to gradually decrease overall.

  The results shown in FIG. 5 suggest that single-pulse measurement has higher emission intensity of carbon than double-pulse measurement and is more suitable for measurement of the concentration of carbon element.

  From the results shown in FIG. 5, the emission intensity of carbon was significantly reduced up to 100 times of laser light irradiation, and became constant thereafter.

  In order to consider the transition of the light emission intensity with the increase in the number of laser light irradiations, the depth of the irradiation mark at each irradiation number was measured.

  Specifically, after a laser beam is radiated a certain number of times using carbon steel (S35C) and a general structural rolled material SS400 having a similar chemical composition and mechanical properties, the bottom of the radiation mark and the periphery of the radiation mark are read with a reading microscope. The height difference was measured and defined as the irradiation mark depth. In this case, laser light irradiation was performed with a single pulse, and the irradiation laser energy was set to three conditions of 30 mJ, 100 mJ, and 150 mJ.

  With the increase in the number of laser beam irradiations, the depth of the irradiation mark (in other words, the ablation depth) increases linearly, and from the slope of a straight line that approximates the relationship between the number of laser light irradiations and the irradiation mark depth, Irradiation mark depth per irradiation (in other words, ablation ratio) was calculated for each irradiation laser energy.

  From the results shown in FIG. 6 in which the ablation ratios for each irradiation laser energy were arranged, it was found that the ablation ratio monotonically increased with the increase in the irradiation laser energy.

  From the results shown in FIG. 6, when the irradiation laser energy was 100 mJ and the single pulse measurement was performed, the irradiation mark depth was calculated at about 6.7 μm when the irradiation frequency at which the reduction ratio of the carbon emission intensity was changed was 100 times. Was.

  This depth is considered to roughly correspond to “surface roughness” after lathing (also referred to as “surface roughness”).

  Based on the above analysis results, the inventor has found that, for example, in a single pulse measurement in which the irradiation laser energy is 100 mJ, the reduction ratio of the light emission intensity becomes small after 100 times of irradiation, and the light emission intensity becomes stable. Since the irradiation mark depth at 100 irradiation times corresponds to the surface roughness, the sample surface is removed by laser light irradiation to a depth corresponding to the surface roughness of the sample (measurement target) surface (in other words, the sample It was found that the concentration of the carbon element in the sample can be accurately and quantitatively specified by using the emission spectrum after forming an irradiation mark on the surface) to calculate the emission intensity.

The method for measuring the carbon concentration of steel according to the present invention is based on the above findings, and the surface of the steel is removed to a depth of 5 to 10 μm by prior irradiation of the surface of the steel with laser light, and the surface is removed. The emission spectrum at the emission wavelength of the carbon element and the emission spectrum at the emission wavelength of the iron element, which are received by irradiating the pulsed laser beam to the set position, are respectively integrated to calculate the emission intensity of carbon and the emission intensity of iron Is calculated, and the ratio between the emission intensity of the carbon and the emission intensity of the iron is applied to a predetermined relational expression between the ratio of the emission intensity of the carbon and the emission intensity of the iron and the carbon concentration. The carbon concentration of steel is required.

Further, the apparatus for measuring the carbon concentration of steel of the present invention removes the surface of the steel to a depth of 5 to 10 μm by pre-irradiating the surface of the steel with laser light, and then applies a pulse to the position where the surface has been removed. Means for calculating the emission intensity of carbon by calculating the emission intensity of carbon by integrating the emission spectrum of the emission wavelength of the carbon element and the emission spectrum of the emission wavelength of the iron element, respectively, which are irradiated with laser light, Means for calculating the ratio between the emission intensity of carbon and the emission intensity of iron, and applying the ratio to a predetermined relational expression between the ratio of the emission intensity of carbon and the emission intensity of iron and the carbon concentration. Means for determining the carbon concentration of steel.

Further, the program for measuring the carbon concentration of steel according to the present invention removes the surface of the steel to a depth of 5 to 10 μm by pre-irradiating the surface of the steel with laser light, and then applies a pulse to the position where the surface has been removed. A process of calculating the emission intensity of carbon by calculating the emission intensity of carbon by integrating the emission spectrum of the emission wavelength of the carbon element and the emission spectrum of the emission wavelength of the iron element, respectively, which are irradiated and received with laser light; and A process of calculating a ratio between the emission intensity of carbon and the emission intensity of iron, and applying the ratio to a predetermined relational expression between the ratio of the emission intensity of carbon and the emission intensity of iron and the carbon concentration. The processing for obtaining the carbon concentration of steel is performed by a computer.

Therefore, according to the method, apparatus and program for measuring the carbon concentration of these steels, the surface of the steel to be measured is removed to a depth of 5 to 10 μm by pre-irradiating the steel to be measured with laser light. Since the emission spectrum is measured, the data at the stage where the light intensity of the emission spectrum greatly fluctuates in the initial stage of laser beam irradiation is not used, and the data at the stage where the light intensity of the emission spectrum is stable is used. Is done. In addition, it is possible to consistently perform the processes from removal to measurement with the same device without requiring a separate device to remove the steel surface layer.

  According to the measuring method, measuring device, and measuring program for the carbon concentration of these steels, the irradiation mark formed by the irradiation of the laser beam for removing the surface has a diameter of about 1 mm in a plan view. The carbon concentration is determined at intervals of about 1 mm when the irradiation marks are not overlapped, and at an interval smaller than 1 mm when the irradiation marks are overlapped.

  Further, according to the findings found by the inventor, when a relational expression between the emission intensity ratio and the carbon concentration used in the present invention is set, iron such as a rolled material for general structure or carbon steel is used. As long as the steel is a main component, a plurality of steel types of test pieces may be used. Furthermore, if both contain iron as the main component, the composition of the test piece used for setting the relational expression between the ratio of the luminescence intensity and the carbon concentration differs from the composition of the measurement object. Even so, the carbon concentration in the measurement object can be determined by the relational expression.

  Further, in the method and the apparatus for measuring the carbon concentration of steel according to the present invention, the steel may be steel in a welded portion of a steel material. In this case, the carbon concentration in the welded portion of the steel material is determined.

  In the method and apparatus for measuring the carbon concentration of steel according to the present invention, the inside of the spectroscope constituting the light receiving system of the emission spectrum may be replaced with an inert gas. In this case, light absorption in the vacuum ultraviolet wavelength region by oxygen molecules is reduced, and the emission intensity of carbon is increased.

  In the method and the apparatus for measuring the carbon concentration of steel according to the present invention, the irradiation of the pulsed laser light and the measurement of the emission spectrum measure the emission of the plasma once per laser light irradiation (that is, a single pulse). Method). In this case, the emission intensity of carbon is higher than in the case of the double pulse method.

  According to the method for measuring the carbon concentration of steel of the present invention, the measurement device, and the measurement program, since only the data of the stage where the light intensity of the emission spectrum by laser light irradiation is stable is used, the emission intensity of carbon and the emission of iron An error can be prevented from being included in the strength, and the carbon concentration can be accurately quantified, so that the reliability of the method for quantifying the carbon concentration can be improved.

  According to the method, the measuring device, and the measuring program for measuring the carbon concentration of steel of the present invention, the carbon concentration can be determined at intervals of about 1 mm or less than 1 mm. Can be improved.

  In the case of a steel containing iron as a main component, a plurality of steel types can be used as test pieces when setting a relational expression between the ratio of the luminescence intensity and the carbon concentration. The carbon concentration can be quantified even if the composition of the test piece used for the measurement differs from the composition of the measurement object. That is, since the main component is not restricted by the type of steel, the applicability and versatility of the method for quantifying the carbon concentration can be improved.

  The method and the apparatus for measuring the carbon concentration of steel according to the present invention provide valuable information on welds that are considered to easily undergo structural changes over time when the carbon concentration in steel welds is determined. Can be provided.

  The method and apparatus for measuring the carbon concentration of steel according to the present invention, when the inside of the spectrometer is replaced with an inert gas, reduce the light absorption by oxygen molecules to increase the emission intensity of carbon. , It is possible to accurately quantify the carbon concentration, and it is possible to lower the lower limit of detection of the carbon concentration, and as a result, the reliability and usefulness of the method for quantifying the carbon concentration Can be improved.

  The method and apparatus for measuring the carbon concentration of steel according to the present invention can increase the carbon emission intensity when the single pulse method is used as compared with the case of the double pulse method. And the lower limit of detection of the carbon concentration can be reduced, and the reliability and usefulness of the method for quantifying the carbon concentration can be improved. Become.

It is a flow chart which shows an example of an embodiment of a measuring method of carbon concentration of steel of the present invention. FIG. 3 is a functional block diagram of a steel carbon concentration measuring apparatus realized by the steel carbon concentration measuring program when the method for measuring carbon concentration of steel according to the embodiment is implemented using the steel carbon concentration measuring program. FIG. 2 is a schematic configuration diagram illustrating a configuration of an apparatus for performing laser beam irradiation and emission spectrum measurement before improvement. FIG. 2 is a schematic configuration diagram illustrating a configuration after improvement of a device that performs laser beam irradiation and emission spectrum measurement. FIG. 4 is a diagram showing a change in emission intensity of carbon with an increase in the number of times of laser light irradiation. It is a figure which shows the ablation depth per one laser beam irradiation according to irradiation laser energy in the case of the rolled material SS400 for general structures. FIG. 7 is a diagram showing a change in an emission spectrum depending on the presence or absence of nitrogen gas replacement inside a spectroscope. FIG. 4 is a diagram illustrating an intensity ratio concentration relational expression according to the first embodiment. It is a figure which shows the quantitative result of the carbon concentration in the welding part of the high chromium steel of Example 1.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

  FIGS. 1 to 4 and FIG. 7 show an embodiment of the measuring method, measuring device, and measuring program of the carbon concentration of steel according to the present invention.

In the method for measuring the carbon concentration of steel according to the present embodiment, the surface of the steel is removed to a depth of 5 to 10 μm by pre-irradiating the surface of the steel with laser light (S1), and a pulse is applied to the position where the surface has been removed. The emission spectrum of the emission wavelength of the carbon element and the emission spectrum of the emission wavelength of the iron element, which are irradiated and received by the laser beam, are respectively integrated to calculate the emission intensity of carbon and the emission intensity of iron (S2). , S3), the ratio between the emission intensity of carbon and the emission intensity of iron (S4) is applied to a predetermined relational expression between the ratio of the emission intensity of carbon to iron and the carbon concentration. Thereby, the carbon concentration of the steel is determined (S5) (see FIG. 1).

The apparatus for measuring the carbon concentration of steel according to the present embodiment is configured such that the surface of the steel is irradiated with the laser beam to a depth corresponding to the surface roughness of the steel, in other words, for example, by pre-irradiating the surface of the steel with the laser beam. The emission spectrum of the emission wavelength of the carbon element and the emission spectrum of the emission wavelength of the iron element, which are received after the surface of the steel has been removed to a depth of 10 μm and pulse laser light is applied to the position where the surface has been removed. A means for calculating the emission intensity of iron by calculating the emission intensity of carbon by integrating each of them, a means for calculating the ratio of the emission intensity of carbon and the emission intensity of iron, and the ratio is determined in advance. Means for obtaining the carbon concentration of the steel by applying a relational expression between the ratio of the emission intensity of carbon to the emission intensity of iron and the carbon concentration is provided. In addition to the irregularities on the steel surface, when the carbon concentration of the steel surface layer may change due to heat treatment or decarburization in the steel manufacturing process, or when the carbon contained in the machine tool at the time of cutting the test piece is added to the surface of the test piece, In the case of mixing, if the surface layer is removed by laser light irradiation up to the portion where the carbon concentration is changed, the carbon concentration can be obtained appropriately.

  The above-described method for measuring the carbon concentration of steel and the apparatus for measuring the carbon concentration of steel can also be implemented and realized by executing a program for measuring the carbon concentration of steel on a computer. Here, a case will be described in which a method for measuring the carbon concentration of steel is implemented by executing a program for measuring the carbon concentration of steel on a computer, and a measuring device for measuring the carbon concentration of steel is realized.

  FIG. 2 shows an entire configuration of a computer 10 (in this embodiment, also a steel carbon concentration measuring apparatus 10) for executing the steel carbon concentration measuring program 17 of the present embodiment.

  The computer 10 (the carbon concentration measuring device 10 for steel) includes a control unit 11, a storage unit 12, an input unit 13, a display unit 14, and a memory 15, which are mutually connected by a signal line such as a bus. .

  The control unit 11 controls the entire computer 10 and performs calculations related to the measurement of the carbon concentration of the steel according to the steel carbon concentration measurement program 17 stored in the storage unit 12, and includes, for example, a CPU (Central Processing Unit). ).

  The storage unit 12 is a device capable of storing at least data and programs, and is, for example, a hard disk.

  The input unit 13 is an interface (that is, an information input mechanism) for giving at least an operator's command and various information to the control unit 11, and is, for example, a keyboard and a mouse. Note that a plurality of types of interfaces such as both a keyboard and a mouse may be provided as the input unit 13.

  The display unit 14 performs drawing and display of characters, graphics, images, and the like under the control of the control unit 11, and is, for example, a display.

  The memory 15 is a memory space which is a work area when the control unit 11 executes various controls and calculations, and is, for example, a RAM (Random Access Memory).

  In addition, the computer 10 can transmit and receive (ie, input and output) signals such as data and control commands to and from the computer 10 as necessary by using a signal line such as a bus or a wide area network line. The data server 18 may be connected.

  The control unit 11 of the computer 10 (hereinafter referred to as “steel carbon concentration measuring device 10”) is irradiated with a laser beam on the steel surface by executing a steel carbon concentration measuring program 17. After the surface of the steel is removed to a depth corresponding to the surface roughness of the steel, the position where the surface has been removed is irradiated with pulsed laser light, and the emission spectrum of the emission wavelength of the carbon element received and the iron element And an intensity calculator 11a for calculating the emission intensity of carbon by calculating the emission intensity of carbon by integrating the emission spectra of the emission wavelengths, and calculating the ratio between the emission intensity of carbon and the emission intensity of iron. And calculating the carbon concentration of the steel by applying the ratio to a predetermined relational expression between the ratio of the luminescence intensity of carbon and the luminescence intensity of iron and the carbon concentration. processing Constitute a carbon concentration calculating portion 11c carries out.

  In the present embodiment, the device shown in FIG. 4 is used to irradiate the measurement target with laser light. In the present embodiment, a steel carbon concentration measuring device 10 is incorporated in the device configuration shown in FIG. 4 as a control device (computer) that controls laser beam irradiation and emission spectrum measurement performed by the device. I have. However, the control device (computer) for controlling the laser beam irradiation and the emission spectrum measurement and the steel carbon concentration measurement device 10 may be provided separately.

  In the present invention, as a method of measuring the concentration of carbon element, rapid elemental analysis is possible, spatial resolution related to measurement and analysis is possible, a wide range of analysis is possible, and furthermore, the configuration of the apparatus is complicated. Laser-induced breakdown spectroscopy (LIBS: abbreviation for Laser-Induced Breakdown Spectroscopy) is used in consideration of the fact that measurement can be performed in an atmospheric pressure environment in which gasification is avoided.

  First, FIG. 3 shows an initial conventional device configuration assuming application to the present invention.

  Specifically, it is a Q switch Nd: YAG laser device (pulse width 7 to 10 ns, repetition 10 Hz), and irradiates the measurement object with the second harmonic. However, a pulse laser having a pulse width of 100 ns or less, such as a microchip laser or an excimer laser, may be used. In addition, by using a high-power continuous-wave laser to sweep the steel surface two-dimensionally at high speed and instantaneously irradiating laser light to one location, it is equivalent to irradiating pulsed laser light. It is considered possible to obtain the effect described above. Based on this, "pulse laser light" in the description of the configuration of the present invention has the same effect as irradiating pulse laser light, in addition to laser light itself which is a pure pulse wave. Laser light (and the mode of laser light irradiation) is included.

  Laser light emitted from the laser device 1 is focused on the surface of the measurement target 9 using the plano-convex lens 2 having a focal length of 250 mm.

  In addition, when the distance from the plano-convex lens 2 to the surface of the measurement object 9 is almost the same as the focal length of the plano-convex lens 2, irradiation marks generated when laser light irradiation is repeated become deep, and the irradiation area of the laser light becomes small. The distance from the plano-convex lens 2 to the surface of the measurement object 9 is set to 200 mm in order to avoid a large change due to the number of irradiations.

  When the laser beam was irradiated by the apparatus having the above specifications, the irradiation mark formed on the surface of the measurement target 9 became elliptical, and the major axis of the irradiation mark was about 1.0 mm and the minor axis was 0.5 mm. It was about.

  In the present invention in which the concentration analysis of the carbon element is performed by emission spectroscopy, for example, carbon C (I) 193.09, which is the wavelength of the analysis line described in JIS G 1253, is used as the bright line (that is, the wavelength of the analysis line). nm may be used.

  The plasma emission is received by using a bundle fiber 3, a spectroscope 4, and an ICCD (abbreviation of Image Intensifier Charge Coupled Device) camera 5. The width of the entrance slit of the spectroscope 4 is set to 50 μm.

  The delay pulse generator 6 is used to synchronize the irradiation of the laser beam by the laser device 1 with the exposure start time of the ICCD camera 5 to set the light reception delay time and the exposure time of the ICCD camera 5.

  In the apparatus shown in FIGS. 3 and 4, the measurement object 9 is placed on the XY stage 7 having two orthogonal axes and can be moved. It is not essential in the present invention that the measurement is carried out after being placed on 7).

Here, since the wavelength resolution is high, the emission line can be sufficiently approximated not by the Voigt function but by a Gaussian function. Therefore, the amplitude of the function when each emission line is multi-peak approximated by the Gaussian function is defined as the emission intensity. In addition, the half width of the function was fixed to 1.5 × 10 ⁻² mm for convergence of calculation.

  Then, the inventor performs measurement and analysis for verification using the apparatus having the configuration shown in FIG. 3 described above, and considers measuring the emission line of carbon in the vacuum ultraviolet wavelength range under an atmospheric pressure environment. In order to optimize the conditions for locally and quantitatively measuring the concentration of the carbon element in the steel as the object 9 (specifically, to increase the spectral intensity at the emission wavelength of carbon (C) in particular), FIG. The shown device configuration was improved as follows (see FIG. 4 for the improved device configuration).

  <Improvement 1> Instead of using the bundle fiber 3, a synthetic quartz glass lens 8 is used to receive and condense plasma emission. The material of the bundle fiber 3 is synthetic quartz, and the transmittance decreases at a wavelength of 190 nm or less. This is due to the fact that the transmittance of synthetic quartz in this wavelength range is lower than that of air. In order to prevent the luminescence intensity from attenuating, the distance from the plasma generation site to the detector (specifically, the ICCD camera 5; which can also be referred to as a light receiving device) is shortened, and an enlarged condensing system is constructed. Increase the amount of received light. In order to shorten the distance from the position where the plasma is generated to the spectroscope 4, the measurement object 9 is irradiated with laser light from a direction approximately 45 degrees with respect to the normal direction of the surface of the measurement object 9, and the laser beam is irradiated. Plasma emission is received from a direction at an angle of 90 degrees to the optical line of sight.

<Improvement 2> Since the light (vacuum ultraviolet) is absorbed by Schumann-Runge bands of oxygen molecules (O ₂ ) at a wavelength of 170 to 200 nm, the atmosphere inside the spectroscope 4 is replaced with an inert gas. Specifically, for example, a nitrogen (N ₂ ) gas can be used as the inert gas. By replacing the inside of the spectroscope 4 with an inert gas such as nitrogen gas, light absorption by oxygen molecules is reduced, and the emission intensity of carbon can be increased (see FIG. 7).

  <Improvement 3> In order to prevent ionization of the atmospheric gas (specifically, air) on the surface of the measurement object 9 due to the generation of plasma, the surface of the measurement object 9 (specifically, the irradiation point of the laser beam) ) Is injected with an inert gas. As the inert gas, specifically, for example, helium (He) gas can be used. In consideration of the injection of the inert gas, the irradiation of the laser beam, and the lens 8 of the light receiving system, the laser beam is irradiated from the direction of 45 degrees with respect to the normal direction of the surface of the measurement object 9 and the measurement object 9 is irradiated. Inert gas is injected from the surface normal direction. Injection of an inert gas such as helium gas onto the surface of the measurement object 9 prevents ionization of carbon dioxide contained in air, particularly when measurement is performed under low carbon concentration conditions. Can be accurately measured. Further, ionization of the atmospheric gas is prevented, and generation of continuous light having no wavelength dependence, which causes a background, is suppressed.

In the present embodiment, an apparatus having a configuration shown in FIG. 4 is used. In order to measure the ultraviolet region, a lens 8 made of synthetic quartz glass is used as a mechanism for receiving and condensing plasma emission (the above <Improvement 1>). Further, the emission line of carbon (that is, the wavelength of the analysis line; C (I) 193.09 nm) and the emission line of iron (the wavelength of the analysis line; 200.09 nm of Fe (II)) to be measured are in the vacuum ultraviolet region. In order to alleviate the attenuation of the emission line intensity in the atmosphere, the atmosphere inside the spectroscope 4 is replaced with nitrogen (N ₂ ) gas (the above <Improvement 2>). Also, single pulse measurement is performed.

  In addition, as a specific configuration for replacing the atmosphere inside the spectroscope 4 with an inert gas (nitrogen gas), for example, an inert gas is introduced from the back of the collimating mirror inside the spectroscope 4 and the gap between the slits is set. An example is to let the water flow out of the container.

  Then, as a procedure for implementing the method for measuring the carbon concentration of steel, first, a measurement object is irradiated with laser light in advance (S1).

  In the irradiation of the laser beam as the process of S1, the surface of the measurement object is removed to a depth corresponding to the surface roughness of the measurement object (that is, a steel material or a sample collected from the steel material) by ablation by laser light irradiation. (In other words, minute holes are formed as irradiation traces on the surface of the measurement object).

  Therefore, the depth of the surface of the measurement object removed by the preliminary irradiation of the laser light, in other words, the depth of the irradiation mark formed on the surface of the measurement object by the preliminary irradiation of the laser light is a specific depth. The depth is not limited, and is set as appropriate for each measurement object to a depth corresponding to the surface roughness of the measurement object (that is, a steel material or a sample collected from a steel material).

  The depth of the surface of the measurement object removed by the pre-irradiation of the laser light specifically corresponds to the surface roughness of the measurement object in a range of approximately 5 to 10 μm, for example, only as an example. The depth can be set appropriately.

  The method of irradiating the laser light as the pre-irradiation of the laser light is limited to specific contents as long as the surface of the measurement target can be removed to a depth corresponding to the surface roughness of the measurement target. Instead, appropriate contents are appropriately set in consideration of, for example, the performance of the device to be used.

  Specifically, for example, the laser energy is set in a range of about 30 to 150 mJ, the spot diameter of the laser light is set in a range of about 0.5 to 2 mm, and the number of laser light irradiations is set in a range of about 50 to 150 times. More specifically, the laser energy is set to about 100 mJ, the spot diameter of the laser light is set to about 1.0 mm, and the number of laser light irradiations is set to about 100 times. It is conceivable that the laser beam is continuously (in other words, fired) continuously applied.

  In addition, the depth of the surface of the steel removed by pre-irradiation of laser light, in addition to the depth corresponding to the surface roughness, the surface of the carburized or decarburized steel surface where the carbon concentration differs from the base metal, When the carbon concentration changes under the influence of such a surface treatment, it is conceivable that the thickness is affected by the influence of the surface treatment.

  Next, the measurement target is irradiated with pulsed laser light (S2).

  The irradiation of the laser beam as the process of S2 is for performing elemental analysis by laser-induced breakdown spectroscopy.

  The irradiation of the pulse laser light as the processing of S2 is performed subsequent to the irradiation of the laser light as the processing of S1, and the irradiation of the laser light as the processing of S1 and the irradiation of the laser light as the processing of S2 are the same apparatus ( In the present embodiment, this is performed by the device shown in FIG.

  However, the type of the laser beam irradiated in the pre-irradiation as the process of S1 and the type of the laser beam irradiated in the measurement irradiation as the process of S2 may be different. For example, a continuous wave laser beam may be irradiated in the pre-irradiation as the process of S1, and a pulse laser beam may be irradiated in the measurement irradiation as the process of S2.

  Irradiation of the pulsed laser beam as the process of S2 is performed on a portion of the measurement target whose surface has been removed in the process of S1 (in other words, a minute hole formed on the surface as an irradiation mark). Done. That is, the irradiation of the laser beam as the process of S1 and the irradiation of the laser beam as the process of S2 are performed on the same portion of the measurement target.

  Then, the plasma emission generated on the surface (irradiation mark) of the measurement object 9 is guided to the spectroscope 4 via the synthetic quartz glass as the condensing lens 8, and the spectroscope 4 analyzes the plasma light. The emission spectrum of the emission wavelength of carbon (C), which is the element, and the emission spectrum of the emission wavelength of iron (Fe) are separated.

  Further, the emission spectrum of the emission wavelength of carbon (C) and the emission spectrum of the emission wavelength of iron (Fe) separated by the spectroscope 4 are received by the detector (specifically, the ICCD camera 5).

  The detector (ICCD camera 5) outputs the emission spectra of carbon (C) and iron (Fe) for the emission of plasma generated on the surface of the object 9 to be measured to the carbon concentration measuring device 10 for steel. You. Here, the signal output from the detector and corresponding to the emission spectrum is referred to as “spectral data”.

  As the emission wavelength of carbon (the wavelength of the emission line and the analysis line), for example, C (I) 193.09 nm, C (I) 156.14 nm, or C (I) 165.81 nm may be used. It is considered that, for example, Fe (II) of 200.09 nm, Fe (II) of 193.19 nm, or Fe (II) of 193.25 nm is used as the emission wavelength (wavelength of the emission line and the analysis line) of iron. Can be

  In addition, the processing from the irradiation of the pulse laser beam as the processing in S2 to the output of the spectrum data is performed in consideration of the number of times required for calculating the emission intensity by integrating the emission spectrum in the processing in S3. This is performed an appropriate number of times.

  The number of times from the irradiation of the pulse laser beam as the processing of S2 to the output of the spectrum data (and the number of times of integrating the emission spectrum when calculating the emission intensity in the processing of S3) is specifically, for example, only an example. For example, it can be set to about 50 times.

  Then, in the process of S2, emission spectra of carbon (C) and iron (Fe) corresponding to each of the multiple irradiations of the pulsed laser light are output from the detector as spectrum data.

  Next, the emission intensity is calculated (S3).

  In the process of S3, the emission spectrum obtained by the process of S2 is integrated to calculate the emission intensity.

  Specifically, the spectrum data output from the detector in the process of S2 is input to the measuring device 10 for carbon concentration of steel, and the intensity calculation unit 11a of the control unit 11 integrates the emission spectrum of carbon (C). Then, the emission intensity of carbon is calculated, and the emission spectrum of iron (Fe) is integrated to calculate the emission intensity of iron.

  Then, the emission intensity of carbon (C) and the emission intensity of iron (Fe) calculated by the intensity calculator 11a are stored in the memory 15.

  Next, the ratio between the emission intensity of carbon and the emission intensity of iron is calculated (S4).

  Specifically, the emission ratio of carbon (C) and the emission intensity of iron (Fe) stored in the memory 15 in the process of S3 are read by the intensity ratio calculation unit 11b of the control unit 11, and the emission intensity of iron is read. Is calculated.

  Then, the calculated value of the ratio of the emission intensity of carbon to the emission intensity of iron is stored in the memory 15 by the intensity ratio calculation unit 11b.

  Next, the concentration of the carbon element in the measurement object is calculated (S5).

  In the process of S5, the ratio between the emission intensity of carbon and the emission intensity of iron calculated in the process of S4 is a predetermined <ratio between emission intensity of carbon and emission intensity of iron> and <carbon concentration>. (Referred to as “intensity ratio concentration relational expression”; that is, a calibration curve for obtaining carbon concentration), the carbon concentration (specifically, steel) of the object to be measured (specifically, steel) : Weight%) is calculated.

  The intensity ratio concentration relational expression is obtained by measuring a pulse laser beam after performing pre-irradiation of a laser beam on each of a plurality of test pieces having at least a known carbon concentration as a chemical component in the same manner as in the processing of S1 to S4 described above. Irradiation is performed to calculate the emission intensity, and the ratio between the emission intensity of carbon and the emission intensity of iron is calculated, whereby the <carbon concentration (known)>, <the emission intensity of carbon and the emission intensity of iron, No.> ratio is prepared.

  Then, a function approximating the plurality of combination data is estimated, and the estimated function is set as an intensity ratio concentration relational expression.

  The function and the approximation method for approximating the combination data described above are not limited to a specific function form or method. A function form considered to be obtained is appropriately selected, or a method capable of calculating the parameters of such a function is appropriately selected. Note that the regression line (that is, calibration curve) of the above combination data is a monotonically increasing curve.

  The number of combined data of <carbon concentration (known)> and <ratio of carbon emission intensity to iron emission intensity> (referred to as “relational expression setting data”) for setting the intensity ratio concentration relational expression is Although not limited to a specific number, it is preferable that the number is at least such that the approximation processing (regression analysis) of the relational expression setting data by the regression equation can be performed well.

  Further, it is preferable that test pieces having various carbon concentrations are prepared and used as test pieces used for preparing the relational expression setting data, and are at least assumed as the carbon concentrations in the measurement object. It is preferable that a carbon concentration covering the range is prepared and used.

  Here, according to the knowledge found by the inventor, for example, a steel having iron as a main component such as a rolled material for general structure SS400 or carbon steel (S25C, S35C, S45C, S50C, or S55C, etc.) is used. The steel type test piece may be used to prepare the relational expression setting data so that one strength ratio concentration relational expression may be estimated, and a common (in other words, regardless of the type of steel to be measured) Then, the carbon concentration may be calculated by one) intensity ratio concentration relational expression. That is, in the present invention, if both have iron as a main component, the composition of the test piece used for estimating the intensity ratio concentration relational expression as a calibration curve differs from the composition of the measurement object. Even so, the carbon concentration in the measurement object can be calculated by the intensity ratio concentration relational expression. However, the irradiation and measurement of laser light for preparing the relational expression setting data for setting the intensity ratio concentration relational expression as a calibration curve, and the irradiation and measurement of laser light on the measurement target are performed under the same conditions. (Specifically, for example, laser energy, spot diameter, etc.) are required.

  On the other hand, for example, an alloy not containing iron as a main component, such as a nickel-based alloy, is not suitable as a test piece for preparing data for setting relational expressions. This is considered to be due to the fact that the shape of the obtained spectrum of the alloy containing no iron as a main component is significantly different from the shape of the obtained spectrum of the alloy containing iron as a main component such as carbon steel.

  According to the findings found by the inventor, oxidation is further prevented because the data for setting the relational expression includes data having an extremely low carbon concentration (that is, the carbon concentration is close to 0 (zero)). If measures are taken, pure iron may be used as the test piece.

  In the present embodiment, the intensity ratio concentration relational expression is defined in advance in the steel carbon concentration measurement program 17, and the carbon emission intensity and the carbon emission intensity stored in the memory 15 in the processing of S4 by the carbon concentration calculation unit 11c. The value of the ratio with the light emission intensity is read, and the value of the ratio is substituted into the intensity ratio concentration relational expression to calculate the carbon concentration of the measurement object.

  Then, the control unit 11 displays the carbon concentration of the measurement object (specifically, steel) on the display unit 14 or saves the carbon concentration in the storage unit 12 as a data file, The processing relating to the measurement of the carbon concentration is terminated.

  According to the method for measuring the carbon concentration of steel, the measuring device, and the measurement program configured as described above, the surface of the steel to be measured is removed to a depth corresponding to the surface roughness of the steel to be measured. Since the emission spectrum is measured at the stage, the data at the stage where the light intensity of the emission spectrum greatly fluctuates in the early stage of the laser beam irradiation is not used, and only the data at the stage where the intensity of the emission spectrum is stable is used. It is possible to accurately determine the carbon concentration by preventing errors in the light emission intensity of carbon and the light emission intensity of iron, and to improve the reliability as a method of determining the carbon concentration. .

  According to the method for measuring the carbon concentration of steel, the measuring device, and the measurement program configured as described above, the spot diameter of the laser light applied to the measurement target is further adjusted, so that the surface of the measurement target is adjusted. Since the size of the irradiation mark can be reduced to, for example, about 1 mm or smaller, it is possible to measure a predetermined range of the measurement object at, for example, about 1 mm or smaller intervals, and to measure with a good spatial resolution. It becomes possible to measure the surface distribution of the carbon concentration in the object.

  Further, according to the findings found by the inventor, when setting the relational expression between the ratio of the luminescence intensity and the carbon concentration used in the present invention, iron such as a rolled material for general structure and carbon steel is mainly used. In the case of steel as a component, a plurality of steel types can be used as a test piece. Further, if both of them are mainly composed of iron, the relational expression between the ratio of the luminescence intensity and the carbon concentration is expressed as Even if the composition of the test piece used for setting and the composition of the measurement object are different, the carbon concentration in the measurement object can be quantified by the above-mentioned relational expression, that is, if iron is the main component, the steel type Since there is no restriction, it is possible to improve applicability and versatility as a method for quantifying the carbon concentration.

  Although the above-described embodiment is an example of a preferred embodiment when carrying out the present invention, the embodiment of the present invention is not limited to the above-described embodiment, and the present invention is not limited thereto without departing from the gist of the present invention. The invention can be implemented in various modifications.

  For example, in the above-described embodiment, the device shown in FIG. 4 is used to irradiate the measurement target with laser light. However, the device configuration shown in FIG. Although this is a preferred mode in that the apparatus is used and that the atmosphere inside the spectroscope 4 is replaced with an inert gas (for example, nitrogen gas), the apparatus configuration that can be used in the present invention is as follows. The invention is not limited to the one shown in FIG. 4, but may be any other one that can be measured as laser-induced breakdown spectroscopy. For example, the XY stage 7 in the device configuration shown in FIG. 4 may not be provided. If the total length is short, instead of concentrating the emission of plasma with a quartz lens, a fiber made of synthetic quartz may be used to bring the fiber close to the emission point and transmit the emission to a spectroscope. In addition, if the sensitivity is sufficient, the replacement of the inert gas inside the spectrometer may be omitted, and if the sensitivity is insufficient, the space from the spectrometer to the emission point may be reduced to a container or tube. The sensitivity can be expected to be improved by replacing the inside with an inert gas.

  FIG. 8 shows an example of the estimation of the intensity ratio concentration relational expression performed to verify the validity of the measurement of the carbon concentration of steel according to the present invention, and the quantification of the carbon concentration performed using the estimated intensity ratio concentration relational expression. This will be described with reference to FIG.

  In this embodiment, first, pure iron having a known carbon concentration, rolled material for general structure SS400, and carbon steel are used as the test pieces, and the ratio of the light emission intensity of carbon to the light emission intensity of iron for each test piece is used. Was calculated.

  Then, a relational expression between <carbon concentration (calculation)> and <ratio of emission intensity of carbon and emission intensity of iron> (that is, relational expression of intensity ratio concentration) is estimated, and a monotonic increase shown in FIG. The curve was estimated. The circles in FIG. 8 are plots of the relational expression setting data obtained in the present embodiment.

  The relation formula of the intensity ratio concentration estimated in the present embodiment is as the following Expression 1.

In Equation 1, I is the ratio between the emission intensity of carbon and the emission intensity of iron, x is the carbon concentration, and I ₀ , A, and B are constants determined by exponential function approximation. In the example shown in FIG. 8, _I0 = 0.45, A = -0.37, and B = 0.20.

  Further, the carbon concentration in the welded portion of the high chromium steel (fire SCMV28) was quantified using the estimated strength specific concentration relational expression, and the results shown in FIG. 9 were obtained. In addition, the result shown in FIG. 9 is a carbon concentration at each measurement position when the carbon concentration at three locations is determined at 1 mm intervals.

  The carbon concentration of the welding material used here is unknown because it has not been chemically analyzed, but the typical value shown in the manufacturer's catalog was 0.06% by weight. Since the welded portion has almost the same composition as the welding material, this value is considered to correspond to the average value of the carbon concentration of the welded portion.

  From the results shown in FIG. 9, the carbon concentration of the weld determined by the present invention is almost consistent with the typical value of 0.06% by weight of the carbon concentration of the welding material. It was confirmed that this method was appropriate as a technique for measuring the carbon concentration, and that the carbon concentration of steel could be measured with good spatial resolution.

  The method for measuring the carbon concentration of steel, the measuring device, and the measurement program according to the present invention can perform, for example, the determination of the carbon concentration in steel with high accuracy and high spatial resolution. It has high utility value in fields such as soundness evaluation of components.

10 Carbon concentration measurement device for steel 17 Measurement program for carbon concentration in steel

Claims (9)

The surface of the steel is preliminarily irradiated with laser light to remove the surface of the steel to a depth of 5 to 10 μm, and the position where the surface is removed is irradiated with pulsed laser light to receive the emission wavelength of the carbon element. The emission spectrum of the iron element and the emission spectrum of the iron element are respectively integrated to calculate the emission intensity of the carbon and the emission intensity of the iron, and the ratio between the emission intensity of the carbon and the emission intensity of the iron is calculated as follows: A method for measuring the carbon concentration of the steel, wherein the carbon concentration of the steel is determined by applying to a relational expression between a predetermined ratio of the emission intensity of carbon and the emission intensity of iron and the carbon concentration. .   The method according to claim 1, wherein the steel is steel in a welded portion of a steel material.   2. The method for measuring the carbon concentration of steel according to claim 1, wherein the inside of the spectroscope constituting the light receiving system of the emission spectrum is replaced with an inert gas.   The method for measuring the carbon concentration of steel according to claim 1, wherein the irradiation of the pulsed laser light and the measurement of the emission spectrum are of a type in which the emission of plasma is measured once per laser light irradiation. After the surface of the steel has been removed to a depth of 5 to 10 μm by pre-irradiation of the surface of the steel with laser light, the position where the surface has been removed is irradiated with pulsed laser light to receive light emission of the carbon element. Means for calculating the emission intensity of carbon by integrating the emission spectrum of the wavelength and the emission spectrum of the emission wavelength of the iron element, respectively, and calculating the emission intensity of the iron, and the emission intensity of the carbon and the emission intensity of the iron Means for calculating the ratio, and means for determining the carbon concentration of the steel by applying the ratio to a relational expression between the ratio of the predetermined emission intensity of carbon and the emission intensity of iron and the carbon concentration. A carbon concentration measuring device for steel, comprising:   The measuring device for carbon concentration of steel according to claim 5, wherein the steel is steel in a welded portion of a steel material.   6. The measuring apparatus according to claim 5, wherein the inside of the spectroscope constituting the light receiving system of the emission spectrum is replaced with an inert gas.   The apparatus for measuring the carbon concentration of steel according to claim 5, wherein the irradiation of the pulsed laser light and the measurement of the emission spectrum are of a type in which the emission of the plasma is measured once per laser light irradiation. After the surface of the steel has been removed to a depth of 5 to 10 μm by pre-irradiation of the surface of the steel with laser light, the position where the surface has been removed is irradiated with pulsed laser light to receive light emission of the carbon element. A process of calculating the emission intensity of carbon by integrating the emission spectrum of the wavelength and the emission spectrum of the emission wavelength of the iron element, respectively, and calculating the emission intensity of the iron, and the emission intensity of the carbon and the emission intensity of the iron The process of calculating the ratio, and the process of determining the carbon concentration of the steel by applying the ratio to a relational expression between the ratio of the predetermined emission intensity of carbon and the emission intensity of iron and the carbon concentration. A program for measuring the carbon concentration of steel, which is performed by a computer.

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