Detection method for impact toughness of reinforcing steel bar, application of detection method and preparation method of sample

Abstract

The invention provides a preparation method of a reinforcing steel bar impact sample, which is applied to a Charpy pendulum impact test method and comprises the following steps: S1, performing first milling treatment on a reinforcing steel bar with the maximum inner diameter of D1 along the length direction, and processing the reinforcing steel bar into a first square strip with the side length of the cross section of not less than 10mm; the steel bars comprise hot-rolled ribbed steel bars; s2, carrying out second milling treatment on the first square long strips, and processing the first square long strips into second square long strips with the cross section specification of 10mm * 10mm; and S3, controlling the length of the second square strip to be 55 mm, and processing a V-shaped notch in the surface of the second square strip to obtain the impact sample. The method is used for measuring the impact energy of the hot-rolled ribbed steel bar, machining and using of the steel bar in different environments can be guided according to the impact detection value, the quality safety and structural stability of engineering are guaranteed, early failure is reduced, and the maintenance cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of steel bar force detection, and specifically relates to a steel bar impact toughness detection method and application thereof, and a sample preparation method. Background Art

[0002] The GB 1499.2-2024 standard only specifies the specific requirements for the chemical composition, mechanical properties and microstructure of hot-rolled ribbed steel bars, but does not make any requirements for impact energy, nor does it provide instructions for the impact energy testing of hot-rolled ribbed steel bars.

[0003] Hot-rolled ribbed steel bars have excellent ductility, weldability, mechanical connectivity and anchoring properties. Their strength and plasticity are superior to ordinary steel bars. Due to their excellent properties, hot-rolled ribbed steel bars are widely used in high-strength building structures, such as large bridges, high-rise buildings, tunnels, etc., and often serve in harsh low-temperature environments.

[0004] However, metal materials such as steel bars tend to show higher brittleness at low temperatures. This is because as the temperature decreases, the bonding force between the atoms of the material increases, making it more difficult for the material to undergo plastic deformation when subjected to external forces, making it more likely to undergo brittle fracture. When the temperature drops to a certain level, the impact value of the steel bar will drop significantly. The ability of the steel bar to resist impact loads is weakened, making it more likely to undergo brittle fracture. Only hot-rolled ribbed steel bars with good impact toughness can have stable quality in this environment.

[0005] In summary, the lack of a method for measuring the impact energy of hot-rolled ribbed steel bars in common technologies results in insufficient stability of the service state of hot-rolled ribbed steel bars in low-temperature environments.

[0006] Based on this, it is necessary to provide a method for detecting the impact toughness of steel bars and its application, as well as a method for preparing samples, in order to alleviate or solve the above problems. Summary of the invention

[0007] The invention aims to solve the technical problem that the lack of a method for measuring the impact energy of hot-rolled ribbed steel bars in the above-mentioned common technologies makes the hot-rolled ribbed steel bars unstable and difficult to predict under service conditions in different environments. The invention provides a method for preparing a steel bar impact specimen, which is applied to a Charpy pendulum impact test method, comprising the steps of:

[0008] S1. A steel bar having a maximum inner diameter of D1 is first milled along the length direction and processed into a first square strip having a cross-sectional side length of not less than 10 mm; the steel bar comprises a hot-rolled ribbed steel bar;

[0009] S2. The first square strip is subjected to a second milling process to form a second square strip having a cross-sectional specification of 10mm*10mm;

[0010] S3. The length of the second square strip is controlled to be 55 mm, and a V-shaped notch is processed on the surface of the second square strip to obtain an impact specimen.

[0011] Furthermore, the step S1 includes: the steel bar with the maximum inner diameter of D1 is subjected to a first milling process along the length direction to be processed into a first square strip with a cross-sectional side length of 0.6D1-0.7D1 mm.

[0012] Furthermore, the step S2 includes: performing a second milling process on two adjacent faces of the first square strip from a vertical direction, and retaining an angle formed by the two adjacent faces to obtain the second square strip.

[0013] Furthermore, controlling the length of the second square strip to 55 mm in step S3 includes: cutting off the end of the second square strip and selecting a square sample with a length of 55 mm from the remaining portion.

[0014] Furthermore, in the step of selecting a square specimen with a length of 55 mm from the remaining part, three square specimens are cut with the midline of the remaining part in the length direction as the axis of symmetry.

[0015] Furthermore, the length of the end cut off is not less than 10 mm.

[0016] Furthermore, the step S3 of machining a V-shaped notch on the surface of the second square strip includes machining the V-shaped notch from the second milled surface, the depth of the V-shaped notch is 2 mm, and the bottom curvature radius is 0.25 mm.

[0017] Furthermore, the length H of the second square strip is 185-200 mm.

[0018] The present invention also provides a method for testing the impact toughness of hot-rolled ribbed steel bars, which is applied to the impact specimens as described in any one of the above.

[0019] The present invention also provides an application of the above-mentioned method for detecting the impact toughness of hot-rolled ribbed steel bars in the selection of hot-rolled ribbed steel bars under different temperature environments.

[0020] Compared with the prior art, the present invention has at least the following advantages:

[0021] The present invention provides a method for preparing a steel bar impact specimen, which is used for the impact energy determination of hot-rolled ribbed steel bars. The impact toughness of the hot-rolled ribbed steel bars can be characterized by testing and recording in combination with "GB / T 229-2020 Charpy Pendulum Impact Test Method for Metallic Materials". The impact test value can be used to guide the processing and use of steel bars in different environments (for example, when the temperature impact value is less than 27J, it indicates that the steel bar has poor toughness at this temperature and is prone to brittle fracture during processing. It is not recommended to process and use the same batch of steel bars in this temperature environment), thereby ensuring the quality and safety of the project and the structural stability, reducing early failures and reducing maintenance costs.

[0022] The present invention obtains an impact specimen with a specification of 10*10*55mm that meets the requirements of the specimen of "GB / T 229-2020 Charpy Pendulum Impact Test Method for Metallic Materials" through a first milling process and a second milling process. This processing method can ensure that the sample is close to the 1 / 2 and 1 / 4 positions of the steel bar, and the impact toughness detected is sufficiently representative. The surface of the hot-rolled ribbed steel bar usually has two longitudinal ribs and transverse ribs evenly distributed along the length direction, which need to be processed (such as rolling, grinding, etc.). The above-mentioned treatment will change the organizational structure of the surface layer of the material, and may also introduce surface defects (such as oxide scale, rust, etc.). These factors will affect the impact toughness of the surface, making it difficult for the impact energy value of the surface sample to accurately reflect the overall performance of the material. The core sampling will cause large fluctuations in the impact energy value due to the difference in the metallographic structure of the surface, one quarter and the core, so its representativeness is relatively low, and the impact value of the near-surface position pattern better represents the impact toughness of the material itself. Therefore, the sampling method in the present invention avoids the misleading impact toughness accuracy and representativeness caused by sampling in other parts, so as to hit the most indicative impact toughness value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0024] Figure 1 This is a schematic diagram of the operation of the first milling process in one embodiment of the present invention, wherein the oblique solid line portion is the first square strip;

[0025] Figure 2 This is a schematic diagram of the second milling process in one embodiment of the present invention, wherein the dotted lines in the four corners are the second square strips;

[0026] Figure 3This is a physical picture of a second square strip obtained by a second milling process in one embodiment of the present invention;

[0027] Figure 4 It is an impact specimen notch double-blade broaching machine used in one embodiment of the present invention;

[0028] Figure 5 This is a physical picture of the impact specimen prepared in one embodiment of the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0031] When numerical ranges are given in the embodiments, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any method, device and material of the prior art similar or equivalent to the method, device and material in the embodiments of the present invention can also be used to implement the present invention.

[0032] GB / T 229-2020 Charpy Pendulum Impact Test Method for Metallic Materials is the testing standard for metal impact toughness in traditional technology, including the following steps: In the steel bar impact test, the specific application of the Charpy pendulum impact test is as follows:

[0033] Sample preparation: First, it is necessary to prepare steel sample according to standard size and process a notch of specified shape (such as U-shaped or V-shaped notch) on the sample. The size and notch shape of the sample should comply with the requirements of relevant standards (such as GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method") to ensure the accuracy and comparability of the test results.

[0034] Test process: Place the prepared sample on the support of the impact tester, then lift the pendulum and let it fall freely to impact the sample. The absorbed work (i.e. impact absorption energy) of the sample is calculated by measuring the height difference of the pendulum before and after the impact. This value reflects the toughness of the steel bar under impact load.

[0035] Result analysis: Based on the test results, the impact performance of the steel bar can be evaluated. The larger the impact absorbed energy value, the better the toughness of the steel bar and the stronger its resistance to impact loads. In addition, the influence of different factors on the impact performance of steel bars can also be analyzed, such as material composition, heat treatment process, processing method, etc.

[0036] The Charpy impact test is a test method used to evaluate the toughness of materials under impact loads. It determines the brittleness and toughness of a material by measuring the energy absorbed by the specimen when it breaks. This test is widely used in the research and quality control of materials such as metals and plastics, especially the impact toughness determination of metal materials. Among them, plates usually have large cross-sectional dimensions and uniform material, which makes them ideal specimens for the Charpy impact test. Through standardized sampling and preparation processes, representative and comparable test results can be obtained.

[0037] In addition to plates, the Charpy impact test is also widely used to determine the impact toughness of other metal materials such as steel sections, round steel, etc. These materials may need to consider more factors when preparing specimens, such as sampling location, to ensure the accuracy and comparability of the test results.

[0038] Specifically, the middle of the round steel is usually the part with the largest diameter and the most uniform material, so the sampling position is relatively clear and easy to locate and cut. When sampling in the middle, since the shape and size of the round steel are relatively regular, it is easier to control the cutting accuracy and sample shape during processing, thereby reducing the processing difficulty, reducing material waste caused by improper sampling position, and improving experimental efficiency.

[0039] In comparison, plates usually retain edge sampling. During the production process of rolling, heat treatment, etc., the material of the edge and the center of the plate may be different. The edge may be affected by more factors such as work hardening and different cooling rates, resulting in different toughness. In certain specific applications, such as bridges, buildings, ships, etc., the edge of the plate may be directly exposed to the external environment or subjected to greater stress. Therefore, understanding the toughness of the edge is crucial to ensure the safety of the structure. By understanding the toughness of the plate edge, more accurate data support can be provided for the design, thereby optimizing the structural design and improving the overall performance of the product.

[0040] However, the above sampling method cannot be applied to the hot-rolled ribbed steel bars of the present invention. The surface of the hot-rolled ribbed steel bars usually has two longitudinal ribs and transverse ribs evenly distributed along the length direction, which need to be processed (such as rolling, grinding, etc.). The above processing will change the organizational structure of the surface layer of the material, and may also introduce surface defects (such as scale, rust, etc.). These factors will affect the impact toughness of the surface, making it difficult for the impact energy value of the surface sample to accurately reflect the overall performance of the material. The core sampling will cause large fluctuations in the impact energy value due to the difference in the metallographic structure of the surface, one quarter and the core, so its representativeness is relatively low, and the impact value of the near-surface position sample better represents the impact toughness of the material itself.

[0041] In order to solve the problems existing in the above sampling method, the present invention provides a method for preparing a steel bar impact specimen, which is characterized by comprising the steps of:

[0042] S1. A steel bar with a maximum inner diameter of D1 is subjected to a first milling process along the length direction to be processed into a first square strip with a cross-sectional side length of not less than 10 mm; the steel bar includes a hot-rolled ribbed steel bar.

[0043] The cross section of hot-rolled ribbed steel bars is usually circular with specific rib patterns on the surface. These rib patterns consist of two longitudinal ribs and transverse ribs evenly distributed along the length.

[0044] Hot rolled ribbed steel bars are mainly composed of iron, carbon, silicon, manganese, phosphorus, sulfur and other elements.

[0045] Step S1 includes: a steel bar having a maximum inner diameter of D1 is subjected to a first milling process along a length direction to be processed into a first square strip having a cross-sectional side length of 0.6D1-0.7D1 mm.

[0046] Since the steel bar matrix is ​​approximately circular (such as Figure 1 As shown, where D1 is the inner diameter of the steel bar, the maximum processed side length is D1*√2 / 2, so the present invention determines that the cross-sectional processed side length L of the first square strip is 0.6D1-0.7D1mm.

[0047] Exemplarily, the first milling process can be performed by a CNC lathe.

[0048] S2. Perform a second milling process on the first square strip to form a second square strip with a cross-sectional specification of 10 mm*10 mm.

[0049] Step S2 includes: performing a second milling process on two adjacent faces of the first square strip, so that the second square strip obtained by the process retains the angle formed by the two adjacent faces.

[0050] In some embodiments, the length of the second square strip may be 185-200 mm.

[0051] Exemplarily, the physical image of the second square strip is as follows: Figure 3 Shown

[0052] S3. The length of the second square strip is controlled to be 55 mm, and a V-shaped notch is processed on the surface of the second square strip to obtain an impact specimen.

[0053] Controlling the length of the second square strip to 55 mm in step S3 includes: cutting off the end of the second square strip and selecting a square sample with a length of 55 mm from the remaining portion.

[0054] Exemplarily, the length of the end cut is not less than 10 mm.

[0055] In some embodiments, three square samples may be cut with the midline of the remaining portion in the length direction as the axis of symmetry.

[0056] The step S3 of machining the V-shaped notch on the surface of the second square strip includes machining the V-shaped notch from the second milled surface, the depth of the V-shaped notch is 2 mm, and the bottom curvature radius is 0.25 mm.

[0057] In some embodiments, the Figure 4 The impact specimen notch shown is machined on a double-blade broaching machine with a V-shaped notch on the second milling plane.

[0058] Impact specimens Figure 5 As shown, its specifications are 10*10*55mm. The standard V-shaped impact specimen after the above processing is tested and recorded in accordance with "GB / T 229-2020 Metal Material Charpy Pendulum Impact Test Method" to characterize the impact toughness of the hot-rolled ribbed steel bars.

[0059] The present invention provides a method for testing the impact toughness of a hot-rolled ribbed steel bar, which is applied to any one of the above impact specimens.

[0060] The present invention also provides an application of the above-mentioned method for detecting the impact toughness of hot-rolled ribbed steel bars in the selection of hot-rolled ribbed steel bars under different temperature environments.

[0061] The impact test value can be used to guide the processing and use of steel bars in different environments. For example, when the temperature impact value is less than 27J, it indicates that the steel bar has poor toughness at this temperature and is prone to brittle fracture during processing. It is not recommended to process and use the same batch of steel bars in this temperature environment.

[0062] According to the appearance characteristics of hot-rolled ribbed steel bars, the present invention proposes a method for detecting the impact toughness of hot-rolled ribbed steel bars. A standard V-shaped impact specimen is processed by CNC lathe, size determination, milling surface processing, grinding and cutting, and notching. Then, according to the relevant requirements of GB / T 229-2020, the impact energy at different temperatures can be detected, so as to characterize the toughness of batches of steel bars under different temperature environments.

[0063] In order to facilitate those skilled in the art to further understand the present invention, examples are given below:

[0064] Example 1

[0065] The invention provides a method for detecting the impact toughness of a hot-rolled ribbed steel bar, the steps of which include sample preparation - plane milling - grinding - cutting - V-notching - impact testing according to GB / T 229-2020 - recording the impact energy value.

[0066] The present invention is further described below by specific embodiments 1 to 3:

[0067] Embodiments 1 to 3 are HRB400E hot-rolled ribbed steel bars of three specifications of ∮16mm, ∮28mm, and ∮40mm. Three 200mm long steel bars are respectively taken and processed into a group of three 10*10*55mm standard V-shaped impact specimens by the present invention to perform impact energy detection at different temperatures.

[0068]

[0069] The impact energy detected by the method of the present invention can accurately characterize the impact toughness of the hot-rolled ribbed steel bars. The impact energy values ​​of the tested specifications at -20°C are all ≥27J, indicating that the toughness is sufficient and the steel bars of the same batch can be safely processed and used in a -20°C environment. If the detected impact energy value is less than 27J, the processing and use of the steel bars under this temperature condition should be carefully considered, as brittle fracture of the steel bars is likely to occur.

[0070] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a steel bar impact specimen, characterized in that: The Charpy pendulum impact test method includes the following steps: S1. A steel bar having a maximum inner diameter of D1 is first milled along the length direction and processed into a first square strip having a cross-sectional side length of not less than 10 mm; the steel bar comprises a hot-rolled ribbed steel bar; S2. The first square strip is subjected to a second milling process to form a second square strip having a cross-sectional specification of 10mm*10mm; S3. The length of the second square strip is controlled to be 55 mm, and a V-shaped notch is processed on the surface of the second square strip to obtain an impact specimen.

2. The preparation method according to claim 1, characterized in that: The step S1 includes: performing a first milling process on the steel bar with a maximum inner diameter of D1 along the length direction to process the steel bar into a first square strip with a cross-sectional side length of 0.6D1-0.7D1 mm.

3. The preparation method according to claim 1, characterized in that: The step S2 includes: performing a second milling process on two adjacent faces of the first square strip from a vertical direction, and retaining the angle formed by the two adjacent faces to obtain the second square strip.

4. The preparation method according to claim 3, characterized in that: Controlling the length of the second square strip to 55 mm in step S3 includes: cutting off the end of the second square strip and selecting a square sample with a length of 55 mm from the remaining portion.

5. The preparation method according to claim 4, characterized in that: In the step of selecting a square specimen with a length of 55 mm from the remaining portion, three square specimens are cut with the midline of the remaining portion in the length direction as the axis of symmetry.

6. The preparation method according to claim 4, characterized in that: The length of the end cut off is not less than 10 mm.

7. The preparation method according to claim 3, characterized in that: The step S3 of machining the V-shaped notch on the surface of the second square strip includes machining the V-shaped notch from the second milled surface, the depth of the V-shaped notch is 2 mm, and the bottom curvature radius is 0.25 mm.

8. The preparation method according to claim 1, characterized in that: The length H of the second square strip is 185-200 mm.

9. A method for testing the impact toughness of hot-rolled ribbed steel bars, characterized in that: An impact test specimen according to any one of claims 1 to 8 is used.

10. Application of the method for testing the impact toughness of hot-rolled ribbed steel bars as claimed in claim 9 in selecting hot-rolled ribbed steel bars under different temperature environments.

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