A method for displaying phosphorus element distribution of a cord steel

Abstract

The present application belongs to the field of steel material metallographic detection, and particularly relates to a display method of phosphorus element distribution of cord steel. The present application provides a phosphorus element distribution etchant solution which is composed of sodium bisulfite, calcium bisulfite and distilled water, wherein the concentration of sodium bisulfite is 1.2-1.4 g / mL, and the concentration of calcium bisulfite is 0.03-0.06 g / mL. The display method of phosphorus element distribution of cord steel comprises the following steps: preparing a cord steel metallographic sample, immersing the polished surface of the metallographic sample into the etchant solution for etching, observing the etched surface of the sample under an optical microscope, and observing the bright yellow linear strip as the phosphorus segregation area. The stability research shows that the etchant solution of the present application has high stability and does not need to be prepared and used immediately; the energy spectrum component analysis result shows that the etchant of the present application can clearly and reliably display the distribution of phosphorus element in the cord steel, and provides efficient, convenient and reliable detection technical support for the research of phosphorus element distribution of cord steel wire rod.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus element segregation detection and analysis technology in steel, and specifically relates to a method for displaying the distribution of phosphorus element in cord steel. Background Technology

[0002] Phosphorus (P) is generally considered a harmful element in steel. While phosphorus can increase the strength and hardness of steel, it significantly reduces its plasticity and impact toughness. Especially at low temperatures, it makes steel significantly brittle, a phenomenon known as "cold brittleness." Cold brittleness worsens the cold workability and weldability of steel; the higher the phosphorus content, the greater the cold brittleness. Therefore, the phosphorus content in steel is strictly controlled, especially in high-strength cord steel wire rods used for cold drawing. Due to selective crystallization, the phosphorus content in steel is not uniformly distributed. Literature suggests that phosphorus is distributed in bands along the rolling direction, indicating uneven distribution. The uniformity of phosphorus distribution directly affects the mechanical properties, corrosion resistance, and processing performance of the material. Therefore, clearly and completely displaying the distribution of phosphorus in steel is of significant practical importance.

[0003] Currently, metallographic examination is the primary method for detecting phosphorus segregation and its distribution, which relies heavily on specialized phosphorus segregation etching solutions. However, existing etching methods for phosphorus segregation (such as the methods recommended in GB / T13298) involve numerous reagents, complex procedures, and fail to clearly and completely reveal the distribution morphology of phosphorus. For example, traditional Klemm reagents and their derivatives typically require the use of a mixture of bisulfite and thiosulfate (such as sodium thiosulfate), and some systems require additional additives to adjust performance. This results in a large variety of reagents and cumbersome formulations. Furthermore, some etching solutions used for detecting phosphorus segregation in steel billets require the introduction of persulfate, ferric chloride, or strong acids (hydrochloric acid, nitric acid, sulfuric acid), further increasing raw material procurement costs and preparation difficulty, hindering large-scale industrial application.

[0004] Secondly, thiosulfates are prone to hydrolysis, forming black silver sulfide precipitates or elemental sulfur precipitates, which cause the etching solution to become turbid. This not only interferes with the clarity of observation of phosphorus segregation areas but also leads to unstable corrosion rates, making precise control difficult and requiring frequent fresh preparation and use, thus reducing detection efficiency. Furthermore, some multi-component etching solutions are easily oxidized and discolored, becoming ineffective after short-term storage, further increasing detection costs and operational complexity.

[0005] Furthermore, the low ionic strength of a single sodium bisulfite system results in insufficient color contrast for low-phosphorus content and slight phosphorus segregation regions in low-phosphorus steel and microalloyed steel, making it difficult to clearly distinguish phosphorus-enriched areas from the matrix structure. In contrast, some systems containing strong acids or oxidants exhibit excessively vigorous corrosion, easily causing over-corrosion of the sample matrix, damaging the original material morphology, blurring the boundaries of phosphorus segregation regions, and even masking phosphorus segregation characteristics, thus hindering accurate display of phosphorus distribution. Additionally, some corrosive solutions can undergo non-selective reactions with pearlite, ferrite, and other structures in the material, interfering with the observation and judgment of phosphorus segregation.

[0006] Furthermore, some etching solutions use strong acids to adjust the acidity, resulting in high corrosiveness. This not only easily damages testing equipment but also poses a potential threat to the personal safety of operators. Simultaneously, the strong acid system's etching effect on the sample surface is intense, easily causing pitting and over-etching, damaging the sample and rendering it unusable, thus increasing testing costs. Moreover, the waste liquid from etching solutions containing strong acids and strong oxidants is difficult to treat and easily causes environmental pollution, which does not meet the development requirements of green production.

[0007] Existing corrosive solutions generally suffer from numerous technical defects in practical applications, making it difficult to meet the high-efficiency, accurate, and safe requirements of industrial-scale batch testing. Therefore, it is necessary to develop a method for displaying phosphorus element distribution that is simple in formulation, highly safe, stable, highly accurate, and environmentally friendly. Summary of the Invention

[0008] The present invention aims to provide a method for displaying the distribution of phosphorus in cord steel.

[0009] The present invention first provides a corrosive solution for displaying phosphorus element distribution, which is composed of sodium bisulfite (NaHSO3), calcium bisulfite (Ca(HSO3)2) and distilled water.

[0010] In the corrosive solution, the concentration of sodium bisulfite is 1.2~1.4 g / mL, and the concentration of calcium bisulfite is 0.03~0.06 g / mL.

[0011] The present invention further provides a method for displaying the phosphorus element distribution in cord steel, comprising the following steps:

[0012] (1) Preparation of metallographic specimens of cord steel;

[0013] (2) Immerse the polished surface of the metallographic sample in the etchant solution for etching;

[0014] (3) Observe the corrosion surface of the sample under an optical microscope. The bright yellow linear bands are the phosphorus segregation areas. The distribution, quantity, and size of the bright yellow linear phosphorus elements can be recorded.

[0015] This invention does not have special requirements for the sample preparation method of metallographic specimens. For example, the following method can be used: Take a 20-30 mm long cord steel wire sample, and cut it again parallel to the rolling direction at 2 / 3 of the wire diameter. Proper cooling should be performed during cutting to avoid overheating. The cut specimens are then inlaid, and then coarsely and finely ground with metallographic sandpaper until the width of the longitudinal specimen is approximately equal to the diameter of the transverse specimen. The finely ground specimens are then mechanically polished. After polishing to a mirror finish, they are immediately cleaned with degreased cotton under running water, and then immediately etched.

[0016] Specifically, the sample can be removed when the polished surface turns yellowish-black, and the etching time is approximately 30 to 50 seconds.

[0017] Furthermore, the height of the corrosive solution is approximately 5–10 mm.

[0018] Furthermore, during corrosion, air bubbles should be prevented from forming. The sample can be shaken, but it should not touch the bottom of the petri dish.

[0019] Furthermore, immediately after corrosion is complete, rinse with clean water, then rinse with anhydrous alcohol, and finally dry with a hair dryer.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention uses only three raw materials—sodium bisulfite, calcium bisulfite, and distilled water—to prepare a phosphorus element distribution etching solution. The composition is extremely simple, the raw materials are readily available, and the procurement cost is low. Compared to traditional multi-component etching systems containing thiosulfates, the etching solution prepared in this invention exhibits excellent stability, is less prone to precipitation, and provides a gentle and controllable etching process, effectively preventing over-etching of the sample. By introducing calcium ions to adjust the ionic strength of the solution, this invention significantly improves the color contrast between the phosphorus segregation region and the matrix, achieving clear phosphorus element distribution even for low-phosphorus steels. Furthermore, this etching solution system has a mild acidity, contains no strong acids or volatile reagents, is highly safe, causes minimal damage to the sample, and has simple waste disposal, making it more suitable for industrial-scale batch testing needs.

[0022] In addition, the sample preparation is simple, requiring only conventional sample preparation methods similar to those used in metallographic testing of non-metallic inclusions, which metallographic testing personnel can quickly learn to operate.

[0023] The preparation process of the etching solution is safe and simple. It can be completed by dissolving the three reagents and stirring them thoroughly. Compared with the existing phosphorus segregation etching solution that requires six or seven reagents and contains strong acid, the preparation process is greatly simplified. The etching method after sample polishing is basically the same as the method of using 4% nitric acid alcohol solution to etch and observe the metallographic structure of ordinary metallographic samples. It is in line with the routine operating habits of inspection personnel and can be operated proficiently without additional training.

[0024] The distribution morphology of phosphorus can be observed with a conventional microscope without the need for other special testing equipment. Furthermore, the phosphorus distribution area after corrosion has a significant color difference and strong contrast with the normal area, and the morphology is clear and complete, making it easy to quickly identify and distinguish.

[0025] This invention requires no special equipment and can be carried out smoothly in a conventional metallographic laboratory. The obtained phosphorus element distribution morphology is clear, reliable, and easy to distinguish. It can provide efficient, convenient, and reliable detection technology support for the study of phosphorus element distribution in cold-drawn cord steel wire, effectively making up for the shortcomings of existing technologies. Attached Figure Description

[0026] The phosphorus distribution morphology of LX72A cord steel wire is as follows: Figures 1-3 As shown, the results are verified in [the document / reference needed]. Figure 4 :

[0027] Figure 1 Phosphorus distribution morphology of LX72A cord steel wire sample in Example 1 (×50).

[0028] Figure 2 Phosphorus distribution morphology of LX72A cord steel wire sample in Example 1 (×100).

[0029] Figure 3 Phosphorus distribution morphology of LX72A cord steel wire sample in Example 1 (×200).

[0030] Figure 4 Phosphorus distribution morphology of LX72ALX72A cord steel wire sample in Example 2 (×200).

[0031] Figure 5 Energy dispersive spectroscopy (EDS) analysis of LX72A cord steel wire samples. Detailed Implementation

[0032] The present invention will be described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. Unless otherwise stated, the experimental methods, detection methods, and preparation methods disclosed in the present invention all adopt conventional techniques in this technical field. Unless otherwise specified, the reagents and materials involved in the embodiments are all commercially available products.

[0033] Example 1

[0034] A method for displaying the phosphorus distribution in cord steel

[0035] 1. Sample preparation

[0036] 1.1 Take a 20-30 mm long sample of cord steel wire and cut it again parallel to the rolling direction. The cutting position is 2 / 3 of the wire diameter. Appropriate cooling should be performed during cutting to avoid overheating.

[0037] 1.2 The cut samples are inlaid, and then coarse and fine grinding is performed using metallographic sandpaper until the width of the longitudinal sample is basically equal to the diameter of the transverse sample.

[0038] 1.3 After fine grinding, the sample was mechanically polished. After polishing to a mirror finish, it was immediately cleaned with degreased cotton under running water and then immediately corroded.

[0039] 2. Reagent preparation

[0040] Preparation of corrosive agent: Dissolve 135g of NaHSO3 powder, 4g of Ca(HSO3)2 powder, and 100ml of distilled water, and stir thoroughly to prepare a phosphorus segregation detection corrosive agent solution.

[0041] 3. Corrosion methods

[0042] 3.1 Pour the corrosive solution into the petri dish, with the corrosive solution level approximately 5–10 mm.

[0043] 3.2 Immerse the polished surface of the sample in the etchant for 30-50 seconds until the polished surface turns yellowish-black.

[0044] 3.3 During corrosion, prevent the formation of bubbles. The sample can be shaken, but the sample should not touch the bottom of the petri dish.

[0045] 3.4 After corrosion is complete, rinse immediately with clean water, then rinse with anhydrous alcohol, and then dry with a hair dryer.

[0046] 4. Observation Methods

[0047] 4.1 The magnification for observation under an optical microscope is ≥50×.

[0048] 4.2 Observe the corroded surface of the sample under a microscope under magnification, ensuring that the field of view covers the entire polished and corroded surface of the sample. The bright yellow linear bands observed are the phosphorus segregation areas (see Appendix). Figures 1-3 It can record information such as the distribution, quantity, and thickness of bright yellow linear phosphorus elements.

[0049] Example 2

[0050] After the corrosive solution prepared in Example 1 was left to stand for 24 hours, steps 3 and 4 of Example 1 were repeated. It was found that bright yellow linear bands could still be clearly observed on the corroded surface of the sample (see Example 1). Figure 4 This indicates that the corrosive solution is relatively stable and does not need to be prepared and used immediately.

[0051] Example 3

[0052] Energy dispersive spectroscopy (EDS) component analysis and result verification: The sample with bright yellow linear bands on the corroded surface from Example 1 was placed in a scanning electron microscope and subjected to EDS for component analysis. Analysis revealed that the phosphorus content in the bright yellow linear band area ranged from 0.13% to 0.28% (the EDS component detection method is qualitative or semi-quantitative, and the measured results are not precise values), while no phosphorus was detected in the normal area. Figure 5 Electron microscopy and energy dispersive spectroscopy analysis confirmed that the bright yellow linear bands observed during microscopic examination after the sample was corroded were the phosphorus segregation regions.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A corrosive solution for displaying phosphorus elemental distribution, characterized in that, It is composed of sodium bisulfite, calcium bisulfite and water.

2. The etchant solution for displaying phosphorus elemental distribution according to claim 1, characterized in that, In the corrosive solution, the concentration of sodium bisulfite is 1.2~1.4 g / mL, and the concentration of calcium bisulfite is 0.03~0.06 g / mL.

3. A method for displaying the phosphorus element distribution in tire cord steel, characterized in that, Includes the following steps: (1) Preparation of metallographic specimens of cord steel; (2) Immerse the polished surface of the metallographic sample in the etchant solution described in claim 1 or 2 for etching; (3) Observe the corrosion surface of the sample under an optical microscope. The bright yellow linear bands are the phosphorus segregation areas.

4. The method for displaying the phosphorus distribution in tire cord steel according to claim 3, characterized in that, In step (2), the sample can be removed once the polished surface turns yellowish-black due to corrosion.

5. The method for displaying the phosphorus distribution in tire cord steel according to claim 3, characterized in that, The corrosion time in step (2) is 30 to 50 seconds.

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