A method for distinguishing nitriding and nitrocarburizing heat treatments

Abstract

The present invention discloses a method for distinguishing between nitriding and nitrocarburizing heat treatments. A carbon element surface scan is performed on the white-bright layer region to obtain the color brightness of the white-bright layer and the carbon concentration curve of the white-bright layer. The sample treatment type is determined based on the color brightness of the white-bright layer and the carbon concentration curve, thereby distinguishing between nitriding and nitrocarburizing heat treatments. Specifically, based on the principle of electron probe, on a surface scan of an element, the color brightness of a region is proportional to the content of the element in that region. That is, the higher the color brightness at a location, the higher the content of the element at that location. Therefore, the color brightness difference between the white-bright layer and the substrate and the carbon concentration curve are used to determine whether the sample's heat treatment was nitriding or nitrocarburizing: if the color brightness of the white-bright layer is higher than that of the substrate and the carbon concentration curve shows a significant decrease, the sample can be determined to have been nitrocarburized; if the color brightness of the white-bright layer is consistent with that of the substrate and the carbon concentration curve is flat with no significant decrease, the sample can be determined to have been nitrided.

Description

Technical Field

[0001] The invention belongs to the field of automobile parts manufacturing and relates to a method for identifying nitriding and nitrocarburizing heat treatments. Background Art

[0002] Nitriding and nitrocarburizing are two surface-strengthening heat treatment processes for metal materials that share similar principles and processes. Parts treated with nitriding and nitrocarburizing exhibit high surface hardness, wear resistance, and corrosion resistance, significantly improving fatigue strength and service life. Compared to carburizing and carbonitriding, these processes offer advantages such as reduced deformation, aesthetically pleasing appearance, and superior high-temperature performance. Furthermore, nitriding and nitrocarburizing are becoming increasingly popular alternatives to carburizing and carbonitriding due to their low environmental impact, making them an increasingly popular alternative in the automotive parts industry.

[0003] Nitriding and nitrocarburizing heat treatment processes utilize surface strengthening media with similar compositions. Both processes produce a "white layer" of comparable hardness and thickness, no thicker than 0.05mm, on the surface of the workpiece. The thickness, density, and continuity of this layer are key indicators of process quality for both nitriding and nitrocarburizing processes. However, when developing and improving products, designers often need to assess the surface heat treatment process performance of similar products from other companies. Conventional testing methods, such as direct reading spectroscopy, metallography, and hardness testing, are unable to identify whether a workpiece has undergone nitriding or nitrocarburizing by analyzing the "white layer." Summary of the Invention

[0004] The purpose of the present invention is to solve the problem in the prior art that it is impossible to identify whether a workpiece has undergone a nitriding or nitrocarburizing heat treatment process by analyzing the white bright layer, and to provide a method for identifying nitriding and nitrocarburizing heat treatments.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention proposes a method for distinguishing nitriding and nitrocarburizing heat treatment, comprising the following steps:

[0007] Obtaining a white bright layer area of the processed sample according to the processed sample;

[0008] Process the white bright layer area to obtain the color brightness and carbon concentration curve of the white bright layer;

[0009] The sample treatment type is obtained according to the color brightness of the white bright layer and the carbon concentration curve of the white bright layer, so as to realize the identification of nitriding and nitrocarburizing heat treatment.

[0010] Preferably, the method for obtaining the sample treatment type according to the color brightness of the white bright layer and the carbon concentration curve of the white bright layer is as follows:

[0011] If the color brightness of the white bright layer is higher than that of the matrix outside the white bright layer, and the carbon concentration curve of the white bright layer decreases, the sample is treated by nitrocarburizing;

[0012] If the color brightness of the white bright layer is consistent with the color brightness of the matrix outside the white bright layer, and the carbon concentration curve of the white bright layer remains unchanged, the sample is nitrided.

[0013] Preferably, the thickness of the white bright layer region is less than 0.05 mm.

[0014] Preferably, the white bright layer area is processed by electron probe.

[0015] Preferably, the electron probe selects a standard sensitivity curve to perform carbon element scanning analysis to obtain the color brightness of the white bright layer and the carbon concentration curve of the white bright layer.

[0016] Preferably, the acceleration voltage of the electron probe is 15 kV, the electron beam current is 100 nA, and the test time is 20 s.

[0017] Preferably, the method for obtaining the processed sample is as follows:

[0018] The sample is cut, and the cut sample is cleaned and roughly ground to remove the cut marks of the cutting line; the roughly ground sample is cleaned in anhydrous ethanol and then blown dry to obtain a processed sample.

[0019] Preferably, the material of the sample is carbon steel or low carbon steel.

[0020] Preferably, the sample is cut using a wire cutting method.

[0021] Preferably, the coarsely ground sample is cleaned in anhydrous ethanol using an ultrasonic method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The method proposed in this paper distinguishes between nitriding and nitrocarburizing heat treatments. This method processes the white-bright layer region, obtains the color brightness and carbon concentration curves of the white-bright layer, and uses these curves to determine the sample treatment type, enabling identification of nitriding and nitrocarburizing heat treatments. This method addresses the existing issue of accurately determining whether a part has been nitrided or nitrocarburized, providing accurate data support for new product design and improvements to product quality. Furthermore, this method is not limited by sample shape or size, is simple to operate, and produces intuitive and reliable results.

[0024] Furthermore, by selecting the standard sensitivity curve method and performing a surface scanning analysis of the carbon content, a distribution image of the carbon content in the test area and a concentration curve as a straight line can be obtained.

[0025] Furthermore, the white bright layer area is processed by an electron probe because the electron probe can perform accurate quantitative analysis of elements, and the accuracy of carbon element analysis reaches 0.01%.

[0026] Furthermore, setting the acceleration voltage of the electron probe to 15 kV, the electron beam current to 100 nA, and the test time to 20 s can achieve the best efficiency and accuracy in carbon element analysis.

[0027] Furthermore, carbon steel or low carbon steel is used as a sample because its carbon content is between 0.05% and 1.0%, and the carbon content is distributed in a gradient, which can improve the analysis accuracy.

[0028] Furthermore, anhydrous ethanol is used for cleaning in order to easily remove fat-soluble substances on the surface of the sample that cannot be washed off with water; and anhydrous ethanol evaporates quickly, and the surface residues will evaporate immediately after cleaning.

[0029] Furthermore, wire cutting can be used to cut samples regardless of workpiece hardness, regardless of whether the material is conductive or semi-conductive. Furthermore, the kerf of wire cutting can be as narrow as 0.005mm, and only the workpiece contour is nested, resulting in high material utilization and significant savings.

[0030] Furthermore, the ultrasonic method is used to clean the coarsely ground samples. The cleaning speed is fast and the cleaning accuracy is high. It can effectively clean tiny dirt particles, maintain consistent cleanliness of the workpiece and cause no damage to the workpiece surface. There is no need for human hands to contact the cleaning liquid, and it is safe and reliable to clean deep holes, fine cracks and hidden places of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 The present invention is a flow chart of the method for identifying nitriding and nitrocarburizing heat treatment.

[0033] Figure 2 These are the scanning result diagrams of the present invention ((a) BSD image of nitrided part, (b) surface distribution of C element during nitriding treatment, (c) BSD image of nitrocarburized part, (d) surface distribution of C element during nitrocarburizing treatment).

[0034] Figure 3 This is the carbon element concentration curve of the nitriding treatment of the present invention.

[0035] Figure 4 This is the carbon element concentration curve of the nitrocarburizing treatment of the present invention.

[0036] Figure 5 This is the standard working curve for carbon element testing of the present invention. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0039] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0040] In the description of the embodiments of the present invention, it should be noted that if the terms "upper," "lower," "horizontal," "inner," etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the inventive product is typically placed when in use. These terms are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0041] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0042] The present invention is described in further detail below with reference to the accompanying drawings:

[0043] The present invention proposes a method for distinguishing nitriding and nitrocarburizing heat treatment, such as Figure 1 As shown, the following steps are included:

[0044] S1. Obtaining a white bright layer area of the processed sample according to the processed sample;

[0045] The material of the standard specimen is carbon steel or mild steel.

[0046] The processed sample is obtained by cutting the sample, cleaning the cut sample, and roughly grinding it to remove the cutting line marks; then, the roughly ground sample is washed in anhydrous ethanol and blown dry to obtain the processed sample. The sample is cut using a wire cutting method, and the roughly ground sample is cleaned using an ultrasonic method in anhydrous ethanol.

[0047] S2. Perform carbon element scanning analysis on the white bright layer area to obtain the color brightness and carbon concentration curve of the white bright layer;

[0048] The white-bright layer was analyzed using an electron probe. Specifically, a standard sensitivity curve was selected for the electron probe, and a carbon element scanning analysis was performed to obtain the color brightness and carbon concentration curves of the white-bright layer. The electron probe had an accelerating voltage of 15kV, an electron beam current of 100nA, and a test time of 20s. The thickness of the white-bright layer was less than 0.05mm.

[0049] S3. Obtain the sample treatment type based on the color brightness of the white bright layer and the carbon concentration curve of the white bright layer to achieve identification of nitriding and nitrocarburizing heat treatment.

[0050] The method for obtaining the sample treatment type based on the color brightness of the white bright layer and the carbon concentration curve of the white bright layer is as follows:

[0051] If the color brightness of the white bright layer is higher than that of the matrix outside the white bright layer, and the carbon concentration curve of the white bright layer decreases, the sample is treated by nitrocarburizing;

[0052] If the color brightness of the white bright layer is consistent with the color brightness of the matrix outside the white bright layer, and the carbon concentration curve of the white bright layer remains unchanged, the sample is nitrided.

[0053] The present invention utilizes a 1720 type electron probe, which can perform accurate quantitative element analysis, with a carbon analysis accuracy of 0.01%, which meets the requirements of the present invention. The present invention selects multiple standard samples for chemical spectroscopy, uses the mapping analysis mode of the electron probe, sets appropriate test parameters, selects an area containing a white bright layer, selects a standard sensitivity curve method, and performs a surface scanning analysis of the carbon element, obtaining a distribution image and a concentration gradient curve of the carbon element content in the test area, such as Figure 2 and Figure 3As shown. According to the principle of electron probe microscopy, the color brightness of a region on a surface scan of an element is proportional to the element's content in that region. That is, the higher the color brightness at a location, the higher the element's content at that location. Therefore, the difference in color brightness between the white layer and the carbon element in the matrix can be used to determine whether the sample's heat treatment method was nitriding or nitrocarburizing.

[0054] Select one sample each from the nitriding and nitrocarburizing heat treatments, cut the cross section using wire cutting, and metallographically polish. Place the sample in a beaker of anhydrous ethanol, perform ultrasonic cleaning, remove surface dirt, and then place it in the electron probe sample chamber. Select the Mapping analysis mode, find the white bright layer in the electron probe image observation window, frame the area containing the white bright layer, select the standard sensitivity curve, and perform a surface scanning analysis of the carbon element. The color change surface scanning analysis results of the carbon element content in the framed area are obtained. The results are as follows: Figure 2 As shown, (a) is the BSD image of the nitrided part, and (b) is the surface distribution of the C element after nitriding treatment. A straight line from the outside to the inside is taken on the surface scanning analysis result (the length of the straight line is about 0.05mm), and the carbon concentration change on the straight line is read, as shown in the figure. Figure 2 (c) is the BSD diagram of the nitrocarburized part, and (d) is the surface distribution of C element in the nitrocarburized process. The carbon content of the two samples at different distances from the surface is shown in Fig. Figure 3 、 Figure 4 Compare with Table 1. Figure 2 (b) and Figure 3 ,as well as Figure 2 (d) in Figure 4 The color and brightness of the white layer on the surface of the nitrided sample are basically the same as that of the substrate, and the carbon concentration curve is flat. The color and brightness of the white layer on the surface of the nitrocarburized sample are significantly higher than that of the substrate, and the carbon concentration curve decreases significantly from the surface to the inside, indicating obvious carbon increase. Therefore, this method can be effectively used to identify parts that have been nitrided or nitrocarburized.

[0055] Table 1 Carbon content of two samples at different distances from the surface (mass fraction, %)

[0056]

[0057] The present invention proposes a method for distinguishing nitriding and nitrocarburizing heat treatment, which comprises the following steps:

[0058] 1) Establish a standard working curve for carbon element

[0059] The materials used for nitriding and nitrocarburizing are typically medium-carbon or low-carbon steels, with carbon contents ranging from 0.05% to 1.0%. Therefore, a set of standard samples with a carbon content gradient similar to the matrix structure and composition of the sample being tested is selected to improve analytical accuracy. The spectroscopic standard samples used in this invention are four pieces from the GSB H40072-94 series and the YSB S11273 b-2007GCr15. See Table 2 for detailed information.

[0060] Table 2 Standard values of C content of standard samples (mass fraction, %)

[0061]

[0062] like Figure 5 As shown, an electron probe is used to measure the X-ray intensity of a standard sample set. A linear intensity-content standard working curve is drawn based on the intensity of the standard sample's Kα X-rays and their carbon content. This standard curve allows analysis of the sample's carbon content and distribution, yielding accurate results.

[0063] 2) Sample preparation

[0064] Wire-cut samples are taken. Based on the size of the electron probe sample chamber, the sample length is required to be ≤30mm, the width is ≤30mm, and the height is ≤20mm. After cleaning, the sample is coarsely ground on a grinding wheel to remove the wire-cut cut marks. 320#, 600#, and 1000# sandpaper are used for grinding. The test surface is polished with 1μm diamond and 0.05μm alumina until there are no obvious scratches. Ultrasonic cleaning is performed in anhydrous ethanol for 1-3 minutes, then air-dried. The sample is quickly placed in the electron probe sample chamber for analysis and testing. After cleaning, the sample is coarsely ground on a grinding wheel to remove the wire-cut cut marks. 320#, 600#, and 1000# sandpaper are used for grinding. The test surface is polished with 1μm diamond and 0.05μm alumina. Ultrasonic cleaning is performed in anhydrous ethanol for 1-3 minutes, then air-dried. The sample is quickly placed in the electron probe sample chamber for analysis and testing.

[0065] 3) Carbon element surface scanning

[0066] After the electron probe is stable, select the Mapping analysis mode, choose C as the element to be measured, and set the electron probe operating conditions to: 15kV acceleration voltage, 100nA electron beam current, beam spot size min, and 20s test time. Under these conditions, the efficiency and accuracy of carbon analysis are optimized. Find the bright white layer in the electron probe image observation window, frame the area containing the bright white layer, select the standard sensitivity curve, and perform a surface scanning analysis of the carbon element. The color change surface scanning analysis results of the carbon content in the framed area and a straight line carbon concentration curve from the surface inward are obtained.

[0067] 4) Result determination

[0068] The heat treatment method of the sample is determined to be nitriding or nitrocarburizing based on the color brightness difference between the white bright layer and the matrix and the carbon concentration curve: if the color brightness of the white bright layer is higher than that of the matrix and the carbon concentration curve has a significant decrease, it can be determined that the sample is nitrocarburizing treated; if the color brightness of the white bright layer is consistent with that of the matrix and the carbon concentration curve is flat without a significant decrease, it can be determined that the sample is nitriding treated.

[0069] The method proposed in this paper addresses the difficulty in accurately determining whether a part has been nitrided or nitrocarburized. This method provides accurate data support for new product design and the improvement and enhancement of product quality. The advantages of this method are that it is not limited by sample shape or size; it can be tested after metallographic polishing and dust removal of a cross-section. No sample corrosion is required, making the method simple to use and providing intuitive and reliable results. Nitriding and nitrocarburizing are two surface-strengthening heat treatments for metal materials that share similar principles and processes, employing surface strengthening media with similar compositions. Parts treated with both nitriding and nitrocarburizing develop a white layer on the surface with comparable hardness and a thickness of no more than 0.05 mm. After nitriding, the white layer on the workpiece surface incorporates only nitrogen, and the carbon content of the white layer is the same as that of the substrate. Nitrocarburizing, on the other hand, incorporates both nitrogen and carbon, resulting in a significantly higher carbon content in the white layer than in the substrate. Based on this difference, the present invention determines the heat treatment process of a sample by detecting the carbon content difference between the white layer and the substrate. According to the principle of electron probe microscopy, the color brightness of a region on a surface scan of an element is proportional to the content of that element in that region. That is, the higher the color brightness at a location, the higher the content of that element at that location. Therefore, the color brightness difference between the white layer and the matrix and the carbon concentration curve are used to determine whether the sample's heat treatment method is nitriding or nitrocarburizing. If the color brightness of the white layer is basically the same as that of the matrix, and the carbon concentration curve is flat with no significant decrease, the sample can be determined to have been nitrided. If the color brightness of the white layer is higher than that of the matrix, and the carbon concentration curve shows a significant decrease, the sample can be determined to have been nitrocarburized.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for distinguishing nitriding and nitrocarburizing heat treatments, characterized in that: The steps include: Obtaining a white bright layer area of the processed sample according to the processed sample; Process the white bright layer area to obtain the color brightness and carbon concentration curve of the white bright layer; Obtain the sample treatment type based on the color brightness of the white bright layer and the carbon concentration curve of the white bright layer to achieve identification of nitriding and nitrocarburizing heat treatment; The method for obtaining the color brightness of the white bright layer and the carbon concentration curve of the white bright layer is as follows: Find the white bright layer in the electron probe image observation window, frame the area containing the white bright layer, select the standard sensitivity curve, perform a surface scanning analysis of the carbon element, and obtain the color brightness and carbon concentration curve of the white bright layer; The method for obtaining the sample treatment type based on the color brightness of the white bright layer and the carbon concentration curve of the white bright layer is as follows: If the color brightness of the white bright layer is higher than that of the matrix outside the white bright layer, and the carbon concentration curve of the white bright layer decreases, the sample is treated by nitrocarburizing; If the color brightness of the white bright layer is consistent with the color brightness of the matrix outside the white bright layer, and the carbon concentration curve of the white bright layer remains unchanged, the sample is nitrided.

2. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 1, characterized in that: The thickness of the white bright layer area is less than 0.05 mm.

3. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 1, characterized in that: The white bright layer area was processed using an electron probe.

4. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 3, characterized in that: The electron probe selects the standard sensitivity curve to perform carbon element scanning analysis to obtain the color brightness and carbon concentration curve of the white bright layer.

5. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 3, characterized in that: The accelerating voltage of the electron probe is 15 kV, the electron beam current is 100 nA, and the test time is 20 s.

6. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 1, characterized in that: The method for obtaining the processed samples is as follows: The sample is cut, and the cut sample is cleaned and roughly ground to remove the cut marks of the cutting line; the roughly ground sample is cleaned in anhydrous ethanol and then blown dry to obtain a processed sample.

7. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 6, characterized in that: The material of the sample is carbon steel or low carbon steel.

8. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 6, characterized in that: The specimens were cut using the wire cutting method.

9. The method for distinguishing nitriding and nitrocarburizing heat treatment according to claim 6, characterized in that: The coarsely ground samples were cleaned in anhydrous ethanol using ultrasonic method.

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