Evaluation method of network cementite of wire rod for bridge cable

Abstract

The invention relates to an evaluation method for network cementite of a wire rod for a bridge cable, the quality of the wire rod is judged according to a network cementite score value, and the network cementite score value is equal to the product of the network cementite weight value, the network cementite size and the network cementite thickness. According to the method, the network cementite is comprehensively evaluated from the three dimensions of the number, the size and the thickness, the influence of the network cementite on use is evaluated more objectively, the detection precision and scientificity are improved, rapid pre-judgment and accurate control over the quality of the wire rod are achieved, the production cost is reduced, and the cable steel industry is promoted to develop towards high quality.

Description

Technical Field

[0001] The invention relates to an evaluation method for wire rod network cementite for bridge cables, belonging to the technical field of steel material performance evaluation. Background Art

[0002] As the core load-bearing component of bridges, bridge cables are widely used in the construction of long-span bridges. As the strength of steel wire used in bridge cables continues to increase, so too do the requirements for safety performance. Long-span bridges are subject to certain torsional stresses during construction and operation, making the torsional performance of cable wire a key technical indicator for measuring the safety level of bridge structures.

[0003] To meet torsion requirements, the raw wire rod must have a high degree of structural uniformity. The ideal structure for wire rod used in bridge cables is troostite, and should not contain bainite, network cementite, or martensite. As the strength level of steel wire increases, the carbon content of the wire rod increases, making it more difficult to control carbon segregation in the core, and it is very easy to form a network cementite structure during hot rolling and controlled cooling. Cementite precipitates along the original austenite grain boundaries, greatly reducing the grain boundary plasticity and deteriorating the wire rod's drawing properties and the torsional performance of the steel wire. Therefore, network cementite is a key indicator of the quality of wire rod used in bridge cables, directly determining whether the torsional performance of the steel wire produced using it can meet the requirements.

[0004] A comprehensive evaluation of network cementite is of great significance to the production of wire rod for cable steel. The industry generally uses YB / T 4412 "Evaluation Method for Network Cementite in High Carbon Steel Wire Rod" as a guide, and in actual production, the network cementite level is controlled to not exceed level 3. YB / T 4412 only evaluates whether the network cementite is closed and the amount of closure, ignoring the influence of its size and thickness. A large amount of production data shows that these two indicators are equally important to the performance of steel wire. Therefore, the existing network cementite evaluation method cannot truly reflect the control level of wire rod for bridge cables, and cannot accurately evaluate whether the torsional performance of galvanized steel wire made from the wire rod meets the relevant standards, which is not conducive to wire rod quality control. Summary of the Invention

[0005] The present invention provides an evaluation method for network cementite of wire rod for bridge cables, which improves the detection accuracy and scientificity, realizes rapid prediction and precise control of wire rod quality, reduces production costs, and promotes high-quality development of the cable steel industry.

[0006] The technical solution adopted by the present invention to solve its technical problem is: A method for evaluating wire rod network cementite for bridge cables, comprising the following steps: Step S1, cleaning, inlaying, grinding and polishing the cross section of the wire rod; Step S2, etching the wire rod treated in step S1 with a nitric acid alcohol solution until the wire rod clearly shows the metallographic structure of the steel; Step S3, observing the wire rod processed in step S2 under a metallographic microscope, performing a network cementite rating on the wire rod based on the microstructure and morphology characteristics of the network cementite, and classifying the wire rod according to the network cementite rating results and assigning a network cementite weight value; Step S4, continuing to measure the size of the network cementite in the wire rod after the treatment in step S2 under a metallographic microscope, taking the average value as the network cementite size of the wire rod, in units of μm; Step S5, measuring the thickness of the network cementite in the wire rod processed in step S2 under a scanning electron microscope to obtain the network cementite thickness in μm; Step S6, calculating the total score of the network cementite of the wire rod, the calculation formula is: score = network cementite weight value × network cementite size × network cementite thickness; Step S7, determining an evaluation system for the wire rod network cementite based on the score calculated in step S6; Furthermore, in step S1, the cross section of the wire rod is cleaned using ultrasonic waves; Furthermore, in step S2, the concentration of the nitric acid alcohol solution is 3%-4%, and the etching is performed for 3-5 seconds; Furthermore, in step S3, the wire rod is graded for network cementite according to the standard YB / T 4412, and the resolution magnification of the metallographic microscope used for observation is 500 times; Furthermore, in step S3, the wire rod is classified and a weight value is assigned to the network cementite: the network cementite of level 0-1 is classified as Class A, with a weight value of 1; the network cementite of level 2-3 is classified as Class B, with a weight value of 4; the network cementite of level 4 is classified as Class C, with a weight value of 8; Furthermore, in step S4, the size of each closed network cementite in the widest direction is measured. If the number of closed network cementite is less than 1, the size is 0. If 1 ≤ the number of closed network cementite ≤ 5, the average value is taken as the network cementite size. If the number of closed network cementite is greater than 5, the average value of the five largest network cementites is taken as the network cementite size. Furthermore, in step S4, the resolution magnification of the metallographic microscope used is 500 times; Furthermore, in step S5, the thickness of the network cementite in the wire rod is the maximum width of the network cementite on the observation surface; Furthermore, in step S5, the scanning electron microscope used has a resolution of 20,000 times; Furthermore, in step S7, the evaluation system of the wire rod network cementite is determined as follows: when 0≤score≤10, the wire rod network cementite is evaluated as excellent, and the number of twists of the produced galvanized steel wire is ≥20 times; when 10<score≤30, it is evaluated as good, and the number of twists of the produced galvanized steel wire is ≥12 times; when 30<score≤50, it is evaluated as qualified, and the number of twists of the produced galvanized steel wire is ≥8 times; when the score is >50, it is evaluated as unqualified and cannot be used for cable steel wire production.

[0007] Through the above technical solution, compared with the existing technology, the present invention has the following beneficial effects: 1. The evaluation method for network cementite in wire rods for bridge cables provided by the present invention introduces three quantitative dimensions: quantity, size, and thickness for comprehensive evaluation. This method more objectively assesses the impact of network cementite on usage and can produce a more realistic test value, which is of guiding significance for the classification and commissioning of wire rods. 2. The present invention provides a method for evaluating the network cementite in wire rods for bridge cables. Through extensive testing, a corresponding relationship between the "network cementite score" and the "number of torsional cycles of galvanized steel wire" has been established. This eliminates the need to first produce steel wire and then test torsional performance. Predictions can be made based on the wire rod metallographic score, shortening R&D cycles and reducing costs. 3. The evaluation method of network cementite in wire rod for bridge cables provided by the present invention establishes a direct relationship between "structure-performance-process", realizes rapid prediction and precise control of wire rod quality, reduces production costs, promotes technological upgrading of the industry, and drives the cable steel industry towards high-quality development. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be further described below with reference to the accompanying drawings and examples.

[0009] Figure 1 This is a metallographic microscope photograph of the network carbide of Example 1 provided by the present invention; Figure 2 This is a scanning electron microscope photograph of the network carbide of Example 1 provided by the present invention; Figure 3 This is a metallographic microscope photograph of the network carbide of Example 2 provided by the present invention; Figure 4 This is a scanning electron microscope photograph of the network carbide of Example 2 provided by the present invention. DETAILED DESCRIPTION

[0010] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "left side", "right side", "upper", "lower", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are intended only to facilitate the description of the present invention and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not indicate the importance of the components and therefore should not be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrative purposes only and do not limit the scope of protection of the present invention.

[0011] As explained in the background, traditional cementite network ratings are typically based solely on whether it is closed and the amount of closed cementite (such as the grading system in YB / T 4412). This is a single-morphological observation, a qualitative or semi-quantitative assessment that lacks a precise description of "quantity" and is subjective. Simply put, the current evaluation method dictates that a more closed network is considered to indicate more severe cementite precipitation along grain boundaries and a higher risk of brittleness, while an unclosed (intermittent) network is considered to have less impact on performance.

[0012] However, in actual working conditions, if the cementite network, while not completely closed, has extremely small and densely distributed pores (e.g., chain-like), it can still create a fragmented effect similar to a continuous network, reducing the continuity of the matrix. Furthermore, the greater the physical thickness of the cementite network, the more significant the decrease in plasticity. Therefore, it is necessary to consider the impact of the size and thickness of the cementite network to precisely control its unfavorable morphology, reduce the risk of steel wire fracture caused by microstructural defects during service, and ensure the safety of bridge structures.

[0013] In order to solve the above problems, the present application provides a method for evaluating wire rod network cementite for bridge cables, which specifically includes the following steps: Step S1, cleaning, inlaying, grinding and polishing the cross section of the wire rod; in this step, ultrasonic cleaning is used to clean the cross section of the wire rod.

[0014] Step S2: etching the wire rod treated in step S1 with a 3%-4% nitric acid alcohol solution for 3-5 seconds until the wire rod clearly shows the metallographic structure of the steel.

[0015] Step S3, observing the wire rod processed in step S2 under a metallographic microscope with a resolution of 500 times, and performing a network cementite rating on the wire rod based on the microstructure and morphology of the network cementite in accordance with standard YB / T 4412. The wire rod is then classified and assigned a network cementite weight value based on the network cementite rating results. This step also provides specific classification and weight value allocation. Network cementite levels 0-1 are classified as Class A, with a weight value of 1; network cementite levels 2-3 are classified as Class B, with a weight value of 4; network cementite level 4 is classified as Class C, with a weight value of 8.

[0016] Step S4, continue to measure the size of the network cementite in the wire rod after the treatment in step S2 under a metallographic microscope, and take the average value as the network cementite size of the wire rod, in μm; the metallographic microscope with a resolution of 500 times is still used in this step.

[0017] Regarding the selection of the network cementite size, the size of the widest direction of each closed network cementite is first measured separately. In order to improve the accuracy, the size requirements are set according to the number of closed network cementites. Specifically, if the number of closed network cementites is less than 1, the size is 0. If 1≤the number of closed network cementites≤5, the average value is taken as the network cementite size. If the number of closed network cementites is greater than 5, the average value of the 5 largest network cementites is taken as the network cementite size.

[0018] Continuing with step S5, the thickness of the network cementite in the wire rod processed in step S2 is measured under a scanning electron microscope with a resolution of 20,000 times, and the maximum width of the network cementite on the observation surface is obtained as the thickness in μm.

[0019] As the biggest innovation of this application, the core demands of the standard need to be revised next, that is, to re-establish the comprehensive scoring model, fully considering the background on which this application is based, through continuous experiments and repeated verification by users, the design of each influencing weight in the total score of the wire rod network cementite is taken as 1, then the calculation formula for the total score of the network cementite of the wire rod in step S6 is: score = network cementite weight value × network cementite size × network cementite thickness.

[0020] Step S7: Determine an evaluation system for the wire rod network cementite based on the score calculated in step S6. The evaluation system for the wire rod network cementite is as follows: when 0 ≤ score ≤ 10, the wire rod network cementite is evaluated as excellent, and the number of twists of the produced galvanized steel wire is ≥ 20 times; when 10 < score ≤ 30, the wire rod network cementite is evaluated as good, and the number of twists of the produced galvanized steel wire is ≥ 12 times; when 30 < score ≤ 50, the wire rod network cementite is evaluated as qualified, and the number of twists of the produced galvanized steel wire is ≥ 8 times; and when the score is greater than 50, the wire rod network cementite is evaluated as unqualified and cannot be used for cable steel wire production.

[0021] Obviously, the evaluation system finally determined by this application also establishes a corresponding relationship between the network cementite score and the number of galvanized steel wire twists. This is because the number of galvanized steel wire twists is a key indicator for measuring the toughness and fracture resistance of the steel wire. The more severe the cementite network, the greater the risk of cracking along the network interface when the steel wire is twisted, and the lower the number of twists. Therefore, it is very necessary to establish a corresponding relationship between the number of galvanized steel wire twists, so as to quickly and accurately determine whether the torsional performance of the galvanized steel wire made from the wire rod meets the relevant standards.

[0022] In order to verify whether the above evaluation system plays a positive role in wire rod quality control, this application provides Example 1 and Example 2.

[0023] Example 1

[0024] Scoring of wire rod network cementite for bridge cables includes the following steps: In the first step, a cross section of the wire rod is taken for inlaying, grinding and polishing; In the second step, the wire rod treated in the first step is etched with 4% nitric acid alcohol solution for 4 seconds until the visible structure of the steel appears; Step 3, Figure 1 As shown in the figure, under a 500x metallographic microscope, the wire rod after the second step treatment was graded for network cementite according to YB / T 4412. The network cementite level is 3, classified as Class B, and its weight value is 4; The fourth step is to measure the size of the network cementite of the wire rod after the second step treatment under a 500x metallographic microscope. The size of the network cementite is 23 μm. Step 5. Figure 2 As shown in the figure, the wire rod after the second step treatment was magnified to 20,000 times under a scanning electron microscope, and the thickness of the network cementite was measured to be 0.27 μm; Step 6: Calculate the network cementite score of the cable steel wire rod. The total score = 4 × 23 × 0.27 = 24.84. Track the user experience. The number of twists of the produced galvanized steel wire is 16-32 times. Step 7, 10<total score≤30, the wire rod network cementite is evaluated as good, meeting the bridge cable steel wire production standard of torsion number ≥12 times.

[0025] Example 2

[0026] Scoring of wire rod network cementite for bridge cables includes the following steps: In the first step, a cross section of the wire rod is taken for inlaying, grinding and polishing; In the second step, the wire rod treated in the first step is etched with 3% nitric acid alcohol solution for 5 seconds until the visible structure of the steel appears; Step 3, Figure 3As shown in the figure, under a 500x metallographic microscope, the wire rod after the second step treatment was graded for network cementite according to YB / T 4412. The network cementite level was 4, classified as Class C, and its weight value was 8. The fourth step is to measure the size of the network cementite of the wire rod after the second step treatment under a 500x metallographic microscope. The size of the network cementite is 20 μm. Step 5. Figure 4 As shown, the wire rod after the second step treatment was magnified to 20,000 times under a scanning electron microscope, and the thickness of the network cementite was measured to be 0.52 μm; Step 6: Calculate the network cementite score of the cable steel wire rod. The total score = 8 × 20 × 0.52 = 83.2. Step 7: If the score is >50, the wire rod network cementite is evaluated as unqualified and cannot be used in the production of wire rod for bridge cable steel wire.

[0027] In summary, the evaluation method for network cementite of wire rod for bridge cables provided in this application, after application, solves the problem that the existing standards are incomplete in the evaluation of network cementite of wire rod for bridge cables and cannot accurately guide the quality control of wire rod. It plays an important role in the formulation of the best production process, plays a positive role in the quality control of wire rod, and helps to achieve the production of high-quality wire rod for cable steel.

[0028] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such, will not be interpreted in an idealized or overly formal sense.

[0029] The meaning of "and / or" in this application means that both situations where each exists alone or both exist at the same time are included.

[0030] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0031] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for evaluating wire rod network cementite for bridge cables, characterized by: The specific steps include: Step S1, cleaning, inlaying, grinding and polishing the cross section of the wire rod; Step S2, etching the wire rod treated in step S1 with a nitric acid alcohol solution until the wire rod clearly shows the metallographic structure of the steel; Step S3, observing the wire rod processed in step S2 under a metallographic microscope, performing a network cementite rating on the wire rod based on the microstructure and morphology characteristics of the network cementite, and classifying the wire rod according to the network cementite rating results and assigning a network cementite weight value; Step S4, continuing to measure the size of the network cementite in the wire rod after the treatment in step S2 under a metallographic microscope, taking the average value as the network cementite size of the wire rod, in units of μm; Step S5, measuring the thickness of the network cementite in the wire rod processed in step S2 under a scanning electron microscope to obtain the network cementite thickness in μm; Step S6, calculating the total score of the network cementite of the wire rod, the calculation formula is: score = network cementite weight value × network cementite size × network cementite thickness; Step S7: Determine the evaluation system of the wire rod network cementite according to the score calculated in step S6.

2. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S1, the cross section of the wire rod is cleaned using ultrasonic waves.

3. The evaluation method of wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S2, the concentration of the nitric acid alcohol solution is 3%-4%, and the etching time is 3-5 seconds.

4. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S3, the wire rod is graded for network cementite according to the standard YB / T 4412, and the resolution magnification of the metallographic microscope used for observation is 500 times.

5. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S3, the wire rod is classified and the network cementite weight value is assigned as follows: the network cementite level 0-1 is classified into Class A, and its weight value is 1; the network cementite level 2-3 is classified into Class B, and its weight value is 4; the network cementite level 4 is classified into Class C, and its weight value is 8.

6. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S4, the size of each closed network cementite in the widest direction is measured. If the number of closed network cementites is less than 1, the size is 0. If 1≤the number of closed network cementites≤5, the average value is taken as the network cementite size. If the number of closed network cementites is greater than 5, the average value of the five largest network cementites is taken as the network cementite size.

7. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S4, the resolution magnification of the metallographic microscope used is 500 times.

8. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S5, the thickness of the cementite network in the wire rod is the maximum width of the cementite network on the observation surface.

9. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S5, the scanning electron microscope used has a resolution of 20,000 times.

10. The method for evaluating wire rod network cementite for bridge cables according to claim 1, characterized in that: In step S7, the evaluation system of the wire rod network cementite is determined as follows: when 0≤score≤10, the wire rod network cementite is evaluated as excellent, and the number of twists of the produced galvanized steel wire is ≥20 times; when 10<score≤30, it is evaluated as good, and the number of twists of the produced galvanized steel wire is ≥12 times; when 30<score≤50, it is evaluated as qualified, and the number of twists of the produced galvanized steel wire is ≥8 times; when the score is >50, it is evaluated as unqualified and cannot be used for cable steel wire production.

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