JPH10142154A - Method for analyzing nitrogen by emission spectroscopic analysis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To analyze the concentration of nitrogen quantitatively and with good accuracy in an emission spectroscopic analytical method for the surface of a solid which is formed of an iron and steel material and which is nitriding- treated. SOLUTION: A plurality of solid samples which are formed of stainless steel, into which nitrogen is introduced up to a prescribed depth from their surface at a uniform concentration and in which the concentration of nitrogen is different are used as standard samples. The luminous intensity of a spectral line which indicates nitrogen is measured by using the respective standard samples, the relationship between the luminous intensity and the concentration of the nitrogen by the respective standard samples is corrected on the basis of the content of iron in the standard samples, and a working curve is created. The accuracy of the working curve is high even on the side of a high concentration. While the working curve is used, the concentration of the nitrogen in every sample to be analyzed is determined quantitatively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a mechanical part formed of a steel material, and in particular, to a surface of which nitrogen or carbon has been introduced by heat treatment, using an emission spectrometer.

[0002]

2. Description of the Related Art Conventionally, nitrogen or carbon has been introduced (carburized and / or nitrided) into the surface of a mechanical part formed of a steel material in order to improve the mechanical properties of the mechanical part. . The amount of carbon and nitrogen present on the surface of the machine part by these treatments differs depending on the required mechanical properties, and it is confirmed that the surface after treatment has the carbon and nitrogen amounts according to the required properties. Confirmation is performed by analysis.

[0003] As a method for analyzing a solid surface formed of a steel material and carburized and / or nitrided, the following methods have been used.
Emission spectroscopy using a solid sample as an electrode is suitable. In emission spectroscopy of a solid sample, the surface of the solid sample is excited by a discharge between the solid sample and the counter electrode to emit light, and this is separated by a spectroscope to measure the wavelength and intensity of the spectral lines of each element. By doing so, qualitative and quantitative analysis of each element is performed.

In this emission spectroscopy, a calibration curve is prepared for each element to be analyzed by preparing a plurality of standard samples containing the element at various concentrations, and the calibration curve is used for each element. Perform quantitative analysis. Then, the concentration of each element in the standard sample is accurately measured by chemical analysis. In addition, since the mixing ratio of each element differs in steel materials according to steel types, it is preferable to prepare a standard sample using the same steel type as the solid sample to be analyzed. Further, it is preferable that the calibration curve is prepared from a plurality of standard samples within a range that can be sufficiently interpolated even when the content of the quantitative element is high. The standard sample needs to have a uniform composition up to the core.

[0005] In the nitriding treatment of a bearing race or the like, for example, 0.05 to 0.6% by weight of nitrogen is introduced into the surface in accordance with required performance. Therefore, in order to accurately quantify nitrogen on the surface of a raceway or the like, it is necessary to prepare a standard sample in which nitrogen is introduced at a high concentration of 0.6% by weight or more and prepare a calibration curve. However, bearing steels such as high-carbon chromium bearing steel and carburized steel have a low Cr content, and cannot contain high-concentration nitrogen at a uniform concentration up to the core.
That is, since only a standard sample into which low-concentration nitrogen is introduced can be prepared, a calibration curve extrapolating the high-concentration side is prepared.

[0006]

However, when such a calibration curve lacking reliability on the high concentration side is used, the surface of a solid sample formed of bearing steel and subjected to nitriding treatment is determined by emission spectroscopy. Nitrogen concentration cannot be quantitatively analyzed with high accuracy (especially on the high concentration side).

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. In the emission spectroscopic analysis of a solid surface formed of a steel material and subjected to nitriding treatment, the nitrogen concentration is accurately and quantitatively analyzed. The aim is to provide a method that can do this.

[0008]

To achieve the above object, the present invention provides a method for analyzing nitrogen by emission spectroscopy of a solid sample formed of a steel material and containing nitrogen.
A plurality of solid samples having a different nitrogen concentration, prepared from an alloy steel containing a large amount of r and having nitrogen introduced at a uniform concentration up to the core, are prepared as standard samples, and the emission intensity of a spectral line indicating nitrogen by each standard sample is prepared. Is measured, and a calibration curve showing the relationship between the luminescence intensity and the nitrogen concentration with respect to the iron content of each standard sample is created.Based on the calibration curve, the amount of nitrogen in the solid sample to be analyzed is determined. A method for analyzing nitrogen by emission spectroscopy is provided.

An alloy steel containing a large amount of Cr can contain a high concentration of nitrogen at a uniform concentration up to the core, so that a standard sample into which a high concentration of nitrogen is introduced can be prepared. Accordingly, since a calibration curve is created from a plurality of standard samples within a range that can be sufficiently interpolated even when the nitrogen concentration of the solid sample to be analyzed is high, a highly accurate calibration curve can be obtained. Therefore, by using this calibration curve, it is possible to accurately and quantitatively analyze the nitrogen concentration on the surface formed of bearing steel or the like and subjected to high concentration nitriding. That is, the present invention is particularly suitable for the case where the solid sample to be analyzed is formed of a steel material and the surface of which is subjected to a high concentration nitriding treatment.

[0010] Examples of the alloy steel containing a large amount of Cr include stainless steel, cold tool steel, and steel for hot molds. Super heat-resistant alloys (Co-base or Ni-base) having an alloy component of 50% or more are also C-based.
It contains a large amount of r. The solid sample used as the standard sample is prepared by melting such an alloy steel containing a large amount of Cr in a nitrogen atmosphere to dissolve nitrogen in the alloy steel at a predetermined ratio, and thereafter cooling (preferably, rapidly cooling). It can be obtained by:

Here, the Cr content of the alloy steel used is as follows:
It is preferably from 10 to 26% by weight. That is, as for the alloy steel used, the one containing more Cr can dissolve more nitrogen, but if the Cr content exceeds 26% by weight, it is difficult to obtain it cheaply (stainless steel can be obtained relatively cheaply). , Since the upper limit of the Cr content is 26% by weight). If the Cr content is less than 10% by weight, it is difficult to prepare a standard sample containing nitrogen at a concentration higher than or equal to the upper limit (for example, 0.6% by weight) of the nitrogen introduced into the surface of the bearing race ( It cannot be obtained stably in a short time).

The emission intensity of each element obtained by emission spectroscopy on a solid sample formed of a steel material is affected by the background iron content. The lower the content, the higher the emission intensity (the emission intensity indicates a concentration higher than the actual concentration). Therefore, for each of the standard samples, the relationship between the measured value of the emission intensity and the value obtained by correcting the chemical analysis value of the nitrogen concentration by the iron content (for example, the nitrogen content when iron is 100) is plotted. And a reference calibration curve (a calibration curve in which the relationship with the iron content of the standard sample is corrected) is obtained.

Further, since the iron content of the solid sample to be analyzed (analytical sample) is naturally different from the iron content (for example, 100) used as a reference when preparing the calibration curve,
The value obtained from the measured emission intensity of the analysis sample using the above-mentioned calibration curve is not an accurate nitrogen content because the iron content of the analysis sample is not taken into account. Therefore, unless the nitrogen content (temporary nitrogen content) specified by the calibration curve is corrected by the iron content of the analysis sample, a correct nitrogen content cannot be obtained.

Here, for the main components other than iron and nitrogen, the provisional element contents are determined in the same manner as in the case of the above-mentioned nitrogen, and the total of the provisional element contents for the main components other than iron and the provisional nitrogen are determined. By calculating the content by introducing the content into a predetermined mathematical formula, the correct nitrogen content can be calculated without accurately measuring the iron content of the analysis sample.

That is, in a method for analyzing nitrogen by emission spectroscopy of a solid sample formed of a steel material and containing nitrogen, a nitrogen sample formed of an alloy steel containing a large amount of Cr and having a uniform concentration of nitrogen introduced into the core. A plurality of solid samples having different concentrations are prepared as standard samples, and the emission intensity of a spectral line indicating nitrogen is measured by each of the standard samples, and the relationship between the emission intensity and the nitrogen concentration with respect to the iron content of each standard sample is shown. Create a calibration curve, based on this calibration curve, determine the temporary nitrogen content of the solid sample to be analyzed,
With respect to the main components other than iron and nitrogen of the solid sample to be analyzed, the provisional element contents are determined in the same manner as in the case of nitrogen, and the total of the provisional element contents of the main components other than iron (nitrogen ) And the provisional nitrogen content are calculated by introducing them into a predetermined mathematical formula. This method is preferable because the correct nitrogen content can be calculated without accurately measuring the iron content of the analysis sample.

Further, when a curved surface such as a bearing raceway surface that has been carburized and / or nitrided is directly subjected to quantitative analysis by emission spectroscopy, it is necessary to machine the treated surface into a flat surface. And / or a member having a curved surface subjected to a nitriding treatment is annealed in a vacuum, an inert gas, or a reducing gas to reduce the hardness to an HRC (Rockwell hardness) of 35 or less and then use a press machine. A pre-processing method for emission spectroscopy for processing into a flat surface is exemplified.

Further, in the pretreatment method, the annealing is performed by heating to a temperature at which austenitization can be performed by a high-frequency heating device, maintaining the temperature for a short time, and then cooling at a cooling rate of 3 to 5 ° C./sec. This is preferable because the hardness can be reduced to HRC 35 or less while the reduction rate of the nitrogen concentration on the surface due to the annealing treatment is suppressed to 5% or less.

[0018]

Embodiments of the present invention will be described below. [Creation of Calibration Curve for Nitrogen Analysis] As a standard sample for emission spectroscopy, eight kinds of disk-shaped materials (diameters) having a uniform composition up to the core and having the compositions of iron and main components shown in Table 1 below 30 mm, thickness 30 mm).

[0019]

[Table 1] Each standard sample was prepared by melting the SCR material () and various stainless steels (-) under a predetermined condition in a nitrogen atmosphere to thereby obtain a predetermined nitrogen content (0.01 to 0.01) in the steel.
(8 types of 0.41% by weight), quenched, and then solidified to obtain a disk having the above-mentioned shape.

The composition of the main components other than iron was measured by collecting a small amount of cuttings from a disk-shaped material and performing a wet chemical analysis specified in JIS. In addition, the iron content H
_Fe, the total amount of the major components other than the .SIGMA.H _EL Fe, .SIGMA.H
_{When MC} is the total content of the trace components, it is calculated by the following equation (1). Therefore, the iron content shown in Table 1 is obtained by adding the sum of the values C to N in Table 1 obtained by chemical analysis to ΔH
_EL was calculated by approximating ΣH _MC to 0 and using equation (1).

[0021]

(Equation 1) Further, for each of the standard samples, the nitrogen content A _N when the iron content was 100 was calculated from the iron content H _Fe calculated by the equation (1) and the nitrogen content H _N measured by chemical analysis. calculate. Here, the ratio _AN is represented by the following equation (2).

[0022]

(Equation 2) Then, the emission intensity of a spectral line indicating nitrogen is measured using each standard sample. By plotting the relationship between the measured emission intensity I and the ratio A _N for each standard sample, a calibration curve K _{N serving} as a reference for nitrogen is obtained. [Correction Based on Iron Content of Analytical Sample] Next, the emission intensity of a spectral line indicating nitrogen was measured for the analytical sample, and a ratio A _N (a value indicating a temporary nitrogen content) corresponding to the measured value I _BN was measured. Is determined using the calibration curve K _N, and the ratio A
_N is obtained as the same value when the emission intensity is the same regardless of the iron content of the analysis sample. Accordingly, the ratio A _N obtained from the measured value I _BN using the calibration curve K _N, not corrected according to the iron content of the analyzed sample when it is impossible to obtain a correct nitrogen content G _N. The correct nitrogen content G _N (% by weight) is expressed by the following equation (3).

[0023]

(Equation 3) Here, (H _Fe / 100) can be expressed by the following equation (8) from the above equation (1) through the following equations (4) to (7).

[0024]

(Equation 4) Multiply both sides by (100 / H _Fe )

[0025]

(Equation 5) Transform the right side,

[0026]

(Equation 6) H _Fe on both sides,

[0027]

(Equation 7) Transforming this equation,

[0028]

(Equation 8) When this is substituted into the above equation (3), the following equation (9) is obtained.

[0029]

(Equation 9) Here, equation (9), the second term on the right side of the denominator is, using a calibration line K _EL criteria for each major component other than iron obtained in the same manner as the aforementioned nitrogen, of the element emission intensity I _EL
In corresponds to the sum of the temporary content A _EL of the element identified, since .SIGMA.H _MC can be approximated to zero, it is represented by the following equation (10).

[0030]

(Equation 10)Therefore, the main elements other than nitrogen must be
Calibration curve K_ELIs prepared, and the emission intensity I of the analysis sample is_EL
Is measured, and each calibration curve K_ELFrom the provisional content A of the element_EL
And further, a provisional nitrogen content A_NAlso specified
Then, A_ELAnd A _NIs introduced into the above equation (10) to calculate
If the exact nitrogen content G of the analytical sample is_NIs calculated.

In this way, accurate nitrogen of the analysis sample can be obtained.
Content G_NIs calculated.
Calibration curve K_NAnd calibration of other major elements contained in the analytical sample
Line K _ELObtained by the same emission spectrometer
Data obtained from research institutes in advance, and
Input to a data processor connected to the emission spectrometer
This can save time and effort.

The main components other than nitrogen (C, Si, M
In the determination of n, Ni, Cr, Cu, Mo, etc., the true element concentration can be finally determined from the equation corresponding to the equation (10) in the same manner as in the above-described determination of nitrogen. [Determination of nitrogen in analytical sample on site] Next, Table 2 below
The steel materials (S
In UJ2), the same disk-shaped molded product as the standard sample was prepared, and its surface was subjected to nitriding treatment under predetermined conditions to prepare a solid sample (analytical sample) to be analyzed.

[0033]

[Table 2]This analysis sample was applied to an emission spectrometer to obtain a spectrometer indicating nitrogen.
Luminous intensity I of torr line_BNIs measured, the emission spectroscopy
In the data processing device connected to the device, the measured value I _BNFrom
Calibration curve K input_NProvisional nitrogen
Rate A_NIs specified. In addition, major other than nitrogen and iron
Emission intensity I of each spectral line showing the element _ELMeasure
Other than nitrogen previously input in the data processing device.
Calibration curve K of main elements_ELFrom the provisional content A of each element_ELBut
Specified. In addition, the temporary content of major elements other than iron
Summation A_EL(Temporary nitrogen content A_NIs calculated)
This sum ΣA_ELAnd provisional nitrogen content A_NAnd by
From equation (10), the true nitrogen content G_NIs calculated.

In this embodiment, the standard samples shown in Table 1 and were used as standardized samples, and the calibration curve was calibrated due to the change over time in the analyzer, and then the measurement was performed. Further, here, in order to examine the nitrogen concentration distribution in the depth direction, the analysis surface of the analysis sample was ground to a predetermined depth by a plane polishing machine, subjected to finish polishing by a Belter polishing machine, and then subjected to an analyzer. Simultaneously, with respect to an analysis sample having the same composition and the same composition, which was simultaneously nitrided, chips of the analysis sample were collected at the same depths as described above, and the nitrogen content of the chips was determined according to JIS 122
The measurement was performed by performing a wet chemical analysis in accordance with Example 8.
These results are shown graphically in FIG.

As can be seen from this graph, the analysis values obtained by the emission spectroscopy and the chemical analysis values are almost the same, and it can be seen that the correct nitrogen content can be analyzed by the method of this embodiment. [Pretreatment method for emission spectral analysis of bearing raceway surface] The analysis sample of emission spectral analysis needs to have at least a flat analysis target surface, and when directly analyzing the actual bearing raceway surface, Perform pre-processing to make a plane. An embodiment of this preprocessing will be described below.

Using a steel material (SCr420) having the composition shown in Table 3 below (the composition of main components other than iron),
An inner ring of a single row deep groove ball bearing (manufactured by Nippon Seiko Co., Ltd., nominal number 6206) having a 0 mm outer diameter of 62 mm and a thickness of 16 mm was prepared, and this was held at 940 ° C. for 5 hours in a carbon atmosphere, followed by oil quenching. Thereafter, carburizing treatment was performed by tempering at 160 ° C. for 1 hour. Further, the inner ring similarly prepared was subjected to carbonitriding by holding in an atmosphere of carbon and nitrogen at 940 ° C. for 5 hours, oil quenching, and then tempering at 160 ° C. for 1 hour.

[0037]

[Table 3] The carburized or carbonitrided inner ring is cut into an appropriate size, and is reduced in vacuum (process A), in Ar gas (process B), and in a reducing gas (mixed gas of Ar: H ₂ = 1: 1). during in either atmosphere (process C), a ₁ transformation point (72
(3 ° C.) for 30 minutes at a temperature lower by 30 to 50 ° C., and then softened by gradually cooling at a rate of 1 ° C./min.
In any of the treatments A to C, the softened material obtained had a Rockwell hardness of about HRC30, and the track surface could be easily processed into a flat surface by bending it with a hand press.

The inner ring sample having the flat raceway surface was subjected to emission spectroscopy to measure the carbon concentration distribution and the nitrogen concentration distribution in the depth direction of the raceway surface. For comparison, chips were taken at predetermined depths from the raceway surface of the same inner ring that was simultaneously carburized or carbonitrided, and subjected to chemical analysis in accordance with JIS1228 to obtain accurate carbon concentration distribution and The nitrogen concentration distribution was measured. These results are shown in FIGS. Note that “chemical value” in the figure means an analytical value obtained by chemical analysis.

FIG. 2 shows the measurement results of the carbon concentration distribution of the carburized inner ring, FIG. 3 shows the measurement results of the carbon concentration distribution of the carbonitrided inner ring, and FIG. 4 shows the measurement results of the carbonitrided inner ring. 7 is a graph showing the measurement results of the nitrogen concentration distribution of the sample. From these graphs, the results of the emission spectroscopy using the analysis sample planarized by each pretreatment method in this embodiment almost match the chemical values, and it is understood that each of the above pretreatment methods is appropriate. [Changes in Nitrogen Reduction Rate and Hardness Due to Annealing Conditions] Using the steel material (SUJ2) having the composition shown in Table 4 below (the composition of main components other than iron), the same disk-shaped molded product as described above was produced. Then, carbonitriding was performed under the condition of maintaining the temperature at 840 ° C. for 4 hours, and tempering was performed at 180 ° C. for 1 hour. This sample was annealed under the following conditions 1-4.

[0040]

[Table 4] (Condition 1) A sample is placed in a high-frequency furnace capable of maintaining temperature,
Heated rapidly to 950 ° C (austenitizing temperature) (heating rate 1 ° C / sec or more, preferably 2 ° C / sec or more)
Thereafter, the temperature is maintained at 950 ° C. for 20 seconds. Then, 950
The sample is transferred to an electric furnace maintained at a temperature of 0 ° C., and is cooled rapidly at 10 ° C./sec by flowing a nitrogen gas into the sample.

(Condition 2) The heating conditions in the high-frequency furnace are the same as those in (Condition 1), but after holding at 950 ° C. for 20 seconds, do not transfer to the electric furnace. / Sec.

(Condition 3) Heating conditions in the high-frequency furnace and up to transfer to the electric furnace are the same as in (Condition 1), but the cooling rate in the electric furnace is 3 ° C./sec.

(Condition 4) Heating conditions in the high-frequency furnace and up to transfer to the electric furnace are the same as in (Condition 1), but the cooling rate in the electric furnace is 1 ° C./sec.

Then, the nitrogen concentration on the sample surface before the annealing treatment and the nitrogen concentration on the sample surface after the annealing treatment were measured, and the nitrogen reduction rate by the annealing treatment was calculated. Further, the Rockwell hardness HRC of the sample surface after the annealing treatment was measured. The above results are shown in Table 4 below.

[0045]

[Table 5] The “processing time” in Table 5 indicates the time required from the start of heating up to the end of cooling.

Further, these results are shown in the relationship between the cooling rate and the nitrogen reduction rate, and the cooling rate and the Rockwell hardness HRC.
FIG. 5 is a graph showing the relationship with. In the bearing inner ring (Nippon Seiko Co., Ltd., nominal number 6206) having the above shape,
If the hardness after annealing is HRC 35 or less, it can be easily processed into a flat surface. On the basis of this, as can be seen from the graph of FIG. 5, the cooling rate is preferably 5 ° C./sec or less. . In addition, since there is a management criterion for maintaining the nitrogen concentration of the bearing inner ring with an accuracy of 5% or less, as clear from the graph of FIG. 5, the cooling rate is 3 ° C./sec or more to clear this. Is preferred.

Therefore, the cooling rate should be 3-5 ° C./sec.
(The range of L in FIG. 5), the reduction rate of the nitrogen concentration on the surface due to the annealing treatment is suppressed to 5% or less.
It is preferable because the hardness can be HRC35 or less.

Further, by using a high-frequency furnace, heating to the austenitizing temperature can be performed in a short time, so that the influence of the pretreatment can be reduced.
Note that, as described above, the pretreatment method for flattening a curved surface such as a bearing raceway surface is not limited to only the nitrogen concentration and the carbon concentration by emission spectroscopy. Of course, the present invention is also applied to the case where each element in other steel materials is analyzed by emission spectroscopy.

[0049]

As described above, according to the present invention,
In emission spectroscopy of a solid formed of a steel material and containing nitrogen, the nitrogen concentration on a highly nitrided surface can be quantitatively analyzed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a graph comparing the nitrogen concentration distribution in the depth direction of a surface subjected to nitriding treatment when measured by a method according to an embodiment of the present invention and when measured by chemical analysis.

FIG. 2 shows the results of measurement of the carbon concentration distribution of a carburized inner ring subjected to pretreatment by annealing under various conditions to obtain a flat surface for an emission spectroscopic analysis sample by emission spectroscopy, and the same carburized inner ring. 5 is a graph showing the result of measuring the carbon concentration distribution of the sample by chemical analysis.

FIG. 3 shows that the inner ring that has been carbonitrided has been subjected to pretreatment by annealing under various conditions, and has been subjected to the same carburizing treatment as the result of measuring the carbon concentration distribution of a flat surface for an emission spectroscopic analysis sample by emission spectrometry. It is a graph which shows the result of having measured carbon concentration distribution about an inner ring by chemical analysis.

FIG. 4 shows that the inner ring subjected to carbonitriding was subjected to pretreatment by annealing under various conditions, and was subjected to the same carburizing treatment as a result of measuring the nitrogen concentration distribution of a flat surface for an emission spectroscopic analysis sample by emission spectrometry. It is a graph which shows the result of having measured nitrogen concentration distribution about an inner ring by chemical analysis.

FIG. 5 shows the relationship between the cooling rate of the annealing treatment and the nitrogen reduction rate of the surface due to the annealing treatment when the carbonitrided sample is subjected to the annealing treatment, and the relationship between the cooling rate of the annealing treatment and the annealing treatment of the surface. It is a graph which shows the relationship with Rockwell hardness HRC.

Claims (1)

[Claims] 1. A method for analyzing nitrogen by emission spectroscopy of a solid sample formed of a steel material and containing nitrogen, the nitrogen being formed of an alloy steel containing a large amount of Cr and having a uniform concentration of nitrogen introduced into the core. A plurality of solid samples having different concentrations are prepared as standard samples, and the emission intensity of a spectral line indicating nitrogen is measured by each of the standard samples, and the relationship between the emission intensity and the nitrogen concentration with respect to the iron content of each standard sample is shown. A method for analyzing nitrogen by emission spectroscopy, comprising preparing a calibration curve and quantifying nitrogen in a solid sample to be analyzed based on the calibration curve.