JPH0353016A - Method for measuring depth of decarburized layer of steel products - Google Patents

Abstract

PURPOSE:To easily and accurately measure the depth of the decarburized layer of steel products by diagonally grinding the surface layer part of the steel products, detecting the carbon concn. of the ground surface by a glow discharge spectrochemical analysis and converting the detected concn. to the carbon concn. distribution in the thickness direction. CONSTITUTION:The surface layer part of a specimen material 10 of the steel products subjected to a decarburization treatment is diagonally ground over a depth d and a length L. This ground surface is then subjected to the glow discharge spectrochemical analysis, by which the carbon concn. of the ground surface is detected. The length l at which the carbon concn. changes to the specified value equal to the base iron is determined from the carbon concn. distribution curve of the ground surface obtd. in such a manner. The depth d0 of the decarburized layer is then determined from equation: d0=l.(d/L).

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for measuring the depth of a decarburized layer of a steel material, which is suitable for evaluating the depth of a decarburized layer of a steel material using a simple procedure.

[Conventional technology]

Decarburization of the surface layer of steel products treated at high temperatures through rolling, hot forging, heat treatment, etc. is unavoidable. The decarburized surface layer does not reach the desired hardness even after heat treatment, resulting in lower fatigue strength and poor wear resistance. Therefore, when treating steel materials at high temperatures, care is taken to prevent decarburization as much as possible. Therefore, it is important to measure the decarburization N depth of steel products, especially mechanical parts. Conventionally, this decarburized layer is
It was measured by microstructural examination using a mirror, hardness test, or chemical analysis test. In the measurement method using a microscopic structure test, as shown in JIs G 0558, a test piece of sea bream material is first cut, and the cut surface is etched to expose the structure. Next, the ffl weave is visually observed through a microscope, and the carbon concentration is determined from the area ratio of 7ela 7ite and barite in the steel, and the depth of the decarburized layer is measured. However, this measurement method
This is a visual sensory test, and the measurement values vary from person to person, so there is a problem with accuracy. Also, the carbon concentration is 0.8%
For hypereutectic steels that exceed 100%, the entire cross section of the sample changes to pearlite and there is no ferrite, making it difficult to measure the depth of the decarburized layer. In addition, in the measurement method using a hardness test, first, the test piece is cut perpendicular to its surface, and the cut surface is polished to serve as the surface to be polished. Next, conduct a Bitkers hardness test on the surface to be polished, measure the depth from the surface to the point where the hardness of the material is obtained, and determine the depth of the decarburized layer. However, in this measurement method, the materials to be measured are limited, mainly steel in the quenched or tempered state. Additionally, the measurement pitch when performing hardness tests is limited by the size of the indentation, which may result in insufficient measurement accuracy in the depth direction. In addition, in the measurement method using chemical analysis, after removing impurities from the sample surface, samples are taken from the sample surface as thinly as possible and at equal intervals, and an accurate carbon content transition curve is determined from the sample to determine the decarburized layer thickness. Measure the quality. however,
In this method, f! Because it is difficult to sample thin layers, it is not possible to measure the depth of very thin decarburized layers, and there is a measurement limit. In addition, electronic probe microanalyzer (EPMA)
A system is now being adopted that connects and controls the element with a computer, collects characteristic X-rays of elements at multiple points in two dimensions, and performs image (i) analysis to understand the element distribution state. It is possible to know the depth of the decarburized layer by knowing the distribution of carbon in the steel material.However, this system requires complex procedures such as scanning with an electronic probe and various calculations, so the testing process lacks speed. It is something.

[Problem to be solved by the invention]

As mentioned above, there was a problem in the past that there was no technology that could accurately measure the depth of the decarburized layer of steel materials using a simple procedure. The present invention has been made in order to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a method for measuring the depth of a decarburized layer of a steel material, which can accurately measure the depth of a decarburized layer of a steel material using a simple procedure. This is a topic.

[Means to accomplish the task]

When measuring the depth of the decarburized layer of a steel material, the present invention obliquely grinds the surface layer of the steel material, performs glow discharge spectroscopy analysis on the ground surface to detect the carbon concentration of the ground surface, and detects the carbon concentration of the ground surface. The above problem was achieved by converting the carbon concentration distribution in the depth direction from the steel surface to determine the depth of the decarburized layer.

[Effect]

The above-mentioned JIS method is used to measure the depth of the decarburized layer of steel materials.
There are various methods such as G0558, but the inventors came up with the idea of measuring the depth of the decarburized layer by glow discharge spectroscopy, regardless of these methods.Glow discharge spectroscopy generally measures the depth of the decarburized layer. It has been applied to continuous analysis in the depth direction. When vertically analyzing the plating layer in the depth direction using this analysis method, the maximum depth at which continuous analysis can be performed is approximately 100 μm. Therefore, the measurement depth may be insufficient for application to measuring the depth of the decarburized layer. Therefore, as a result of various studies, the inventors found that by diagonally grinding the surface layer of the sample material 10, the length d in the depth direction can be reduced to the length in the longitudinal direction, as shown by diagonal lines in FIG. It was found that the decarburized layer depth dO can be enlarged and understood by replacing it with . For example, if the specimen material is a steel bar, diagonal grinding is shown in Figure 2 (A).
If the test material is a thick steel plate, the second
Perform as shown in Figure (B). The diagonally cut ground surface is analyzed by glow discharge spectroscopy to detect the carbon concentration, and the distribution of the detected carbon concentration is determined. This carbon concentration distribution is obtained by converting the carbon concentration distribution in the depth direction to the distribution in the longitudinal direction, so by converting it in the depth direction, the depth of the decarburized layer can be determined from the concentration distribution. In addition, the decarburized layer is a layer in which the carbon concentration changes depending on the depth from the surface.On the other hand, since the carbon concentration is constant in sub-steel, the position where the carbon concentration is constant is at the depth of the decarburized layer. Correspondingly, the depth of the decarburized layer can be determined from the carbon concentration. For example, the detected carbon-containing Ji (corresponding to carbon concentration) is the first
When the distribution is as shown in the figure, the portion at °C where the carbon content changes corresponds to the decarburized layer, and the decarburized layer depth dO is determined from the following equation (1). do=1・(d/L)・
...(1) The present invention was created based on the above findings. In the present invention, unlike the above-mentioned EPMA, there is no need for the procedure of mirror polishing the specimen, and
Since it can be measured simply by diagonally cutting the surface layer and performing glow discharge spectroscopy with an electrode, it becomes possible to quantitatively measure the decarburized N depth using a convenient procedure for PJJ. In addition, the measurement accuracy is high because it can measure hypereutectoid steel without difficulty compared to the above-mentioned measurement method using a microscope. Note that, as mentioned above, the size of the discharge To[i and the angle of oblique grinding used in glow discharge spectroscopic analysis affect the measurement accuracy, so it is necessary to select the appropriate one. Therefore, the inventors obliquely ground the ends of the steel bars at various angles as shown in FIG. 3, and analyzed them using electrodes of various diameters D.
We investigated how much depth Δd corresponds to in the depth direction. The results of the survey are shown in Figure 4. This depth Δd determines the accuracy of the analysis, so use an electrode with a diameter or choose the angle of the grinding surface depending on the desired accuracy. Glow discharge spectroscopy analysis is performed on the ground surface using the above electrode, and the point to be measured is moved at an appropriate pitch to find a position where the concentration of carbon C is constant. The depth of the decarburized layer can be determined by converting it to .

【Example】

Embodiments of the present invention will be described below with reference to the drawings. In this example, a steel bar specimen 10 shown in No. 2 [J(A)] is analyzed using a glow random spectrometer 12 as shown in FIG. 5, and the depth of the decarburized layer is measured from the result. It is something. The glow discharge spectrometer 12 shown in FIG. 5 mainly includes a glow emission section 14, a spectroscopic section 16, a photometry section 18, and an analytical data processing section 20. The glow emitting section 14 is provided with a glow electrode 15 for causing the sample 24 of the test material 10 to glow discharge, and power is supplied between the glow electrode 15 and the sample 24 from a DC power source 22. ．． The glow light generated from the sample 24 by the glow discharge in the glow light emitting section l4 enters the spectroscopic section 16. The spectroscopic section 16 includes an entrance slit 26 that converts the incident glow light into slit light, a diffraction grating 28 that separates the slit light into elements, and a diffraction grating 28 that converts the separated glow light (spectrum) into slit light. It has an exit slit 30 and each photomultiplier tube 32 for detecting the light intensity (hereinafter referred to as spectral intensity) of each slit light. Note that this spectroscopic section 16 is provided with a vacuum pump 34 for maintaining its interior at a predetermined degree of vacuum. The photometry section 8 includes an attenuator 35 for setting the measurement response of each photomultiplier tube 32, an integration circuit fI436 for integrating the output signal of each photomultiplier tube 32 by a mirror integration circuit, and via an A/D converter 38 that converts the obtained spectral intensity data into digital data, and an interface 42,
It has a microcomputer 40 for setting the attenuator 35 according to analysis conditions and measurement groups, and an interface 42 for outputting converted spectral intensity data to the outside. The data processing unit 20 processes the output spectral intensity data using a pre-given calibration curve to determine, for example, carbon content (corresponding to carbon concentration). , CR the processed data
Display 4 displayed on T (cathode ray tube) or printer
4 is provided. The sample 24 of the test material 10 is held with a jig 50 as shown in FIG. 6 so that the ground surface faces parallel to the direction of movement of the electrode 15. This jig allows the glow electrode to be scanned horizontally across the grinding surface with high accuracy. When analyzing the sample 24 with the glow discharge spectrometer 12, first, a glow discharge is caused from the surface of the sample 24 in the glow emitting section 14. The glow discharge light enters the spectroscope 16 and is irradiated onto the diffraction grating 28 through the entrance slit 26. The diffraction grating 28 separates the glow discharge light,
Irradiate each exit slit 30. The exit slit 30 converts the irradiated light into slit light and enters the photoelectron intensifier fB g3 2. The photomultiplier tube 32 converts the spectral intensity of each spectral beam from the incident light into an electrical signal, and inputs the electrical signal to the integrator 36. The integrator 36 integrates the input signal to obtain spectral intensity data and transmits it to the A/D converter 38. The A/D converter 38 digitally processes the transmitted data and performs data processing via the interface 40. Enter the information in section 20. The data processing unit 20 quantifies elements from the input data and displays the content of each element on the display screen 44. Therefore, by horizontally scanning the ground surface of the sample 24 with the electrode 15, the distribution of carbon content on the ground surface is determined, for example, as shown in FIG. 1 above. In this distribution, the depth of the decarburized layer is measured from the position where the carbon content is constant and the equation (1) above. Next, an example of setting the decarburization layer depth for steel materials using the method of the present invention will be explained. In this case, the cross-sectional structure of the steel material to be measured is photo (1) and photo (2).
). Sample 1 of each steel material,
2 is a steel bar as shown in Figure 2 <A) above, and its diameter is 501 mm. Also, the length in the longitudinal direction of these samples 1 and 2 is 1001, and the height d in the depth direction is 1.0.
It was diagonally ground so that it was 1. Furthermore, the diameter of the electrode used for glow discharge was 1 inch. The results of glow discharge spectroscopic analysis of Sample 1 and Sample 2 under the above conditions are shown in Figures 7A and 7B. As shown in FIG. 7 (A>), in sample 1, the content (concentration) of carbon C gradually increases from the surface to a depth of 0.41 mm, and the content (concentration) of carbon C gradually increases from the surface to a depth of 0.41 mm.
It became flat when it exceeded 41. Therefore, in this sample 1, the depth of the decarburized layer can be determined to be 0.4nl'N from the surface. Further, as shown in FIG. 7(B), in sample 2, the content (concentration) of carbon C gradually increases from the surface of the sample to a position exceeding a depth of 0.31 mm. :
It became flat after exceeding In. Therefore, the depth of the decarburized layer in sample 2 is Q. It is determined that the number is 3nun. From this measurement example, it is understood that the depth of the decarburized layer can be measured with high accuracy by the present invention. In addition, in this analysis, the contents of other components can be detected at the same time as shown in FIGS. 7(A) and (B), and the data can be used effectively.

【Effect of the invention】

As explained above, according to the present invention, the extensive effect of being able to quantitatively and accurately measure the decarburization N depth of steel materials with a simple procedure can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view including a partial line diagram showing how to determine the decarburization NJ depth for explaining the principle of the present invention, and Fig. 2 (A)
, (B) is a perspective view of the main part showing an example of processing the sample material for measuring the depth of the decarburized layer, and Fig. 3 illustrates the influence of the grinding angle of the sample piece and the diameter of the electrode used on the measurement accuracy. FIG. 4 is a line diagram; FIG. 5 is a layout diagram including a partial block diagram showing the configuration of a glow discharge spectrometer according to an embodiment of the present invention; FIG. 7(A) and 7(B) are surface views showing the state of holding by the sample holder used in the device; FIGS. 7(A) and 7(B) show the depth of the decarburized layer by glow discharge spectroscopic analysis of steel using the present invention. This is a diagram showing an example. O... Test material, 2... Glow discharge spectrometer, 4... Glow-emitting part, 5... Electrode, 6... Spectroscopic part, 8... Photometry part, 0...・Data processing unit, 4...sample, 8...diffraction grating, 2...photomultiplier tube.

Claims (1)

[Claims] (1) When measuring the depth of the decarburized layer of a steel material, the surface layer of the steel material is obliquely ground, and the ground surface is analyzed by glow discharge spectroscopy to detect the carbon concentration of the ground surface. A method for measuring the depth of a decarburized layer in a steel material, the method comprising determining the depth of the decarburized layer by converting a carbon concentration distribution into a carbon concentration distribution in the depth direction from the surface of the steel material.