Sampling method for controlling hot cutting allowance of steel plate sample

Abstract

The invention discloses a sampling method for controlling the hot cutting allowance of a steel plate sample, and aims to solve the problems of high material consumption and difficult transportation caused by the existing standard hot cutting allowance or detection distortion caused by insufficient allowance. The method is suitable for high-toughness low-welding-crack-sensitivity steel plates and super-thick steel plates for water-power engineering, and is implemented by four steps: determining an applicable steel plate range; dividing w / 4 and w / 2 sampling positions; dividing into four grades according to the thickness, and verifying and determining the side surface hot cutting allowance h1 and the end surface hot cutting allowance h2 by multiple methods; and thermally cutting the sample according to the allowance flame. The device can completely cover a heat affected zone, guarantees the detection authenticity, greatly reduces the material consumption, is suitable for multiple scenes, and is suitable for the detection of water-power engineering steel plates.

Description

Technical Field

[0001] This invention relates to the technical field of steel plate sample sampling methods, and in particular to a sampling method for controlling the hot cutting allowance of steel plate samples. Background Technology

[0002] In large-scale hydropower projects, core components of the water conveyance system, such as pressure pipes, branch pipes, and spiral casings, utilize high-strength, low-weld-crack-sensitivity medium-thick steel plates (24mm–150mm thick) such as SX610CF, SX780CF, and SX950CF. Key components of the turbine's guide vane mechanism, such as the seat ring plate, rotor center disc, and top cover flange, employ extra-thick steel plates (>100mm–350mm thick) such as SXQ500D-Z35 and SXQ355NC-Z35. These steel plates, as critical load-bearing materials, require strict heat treatment and control over chemical composition and non-metallic inclusions to ensure performance meets standards. Their physical and chemical properties directly determine the load-bearing capacity of the hydropower equipment and the safety of the power station's operation; therefore, they must undergo complete and qualified inspections before being put into use.

[0003] The current testing procedure for the physical and chemical properties of steel plates follows a fixed process: sample material is obtained from the steel plate by flame cutting → sample material is sent to the testing center → sample billet is machined → sample billet is processed into test specimen → test specimen size is inspected → performance test is conducted → report is issued → qualification is determined.

[0004] Among these aspects, controlling the hot cutting allowance of the sample is a crucial step. Appendix B of GB / T2975 clearly stipulates that when using the flame hot cutting method to take sample billets, the machining allowance from the cutting line of the sample billet to the edge of the sample (actually the test material) should not be less than the thickness or diameter of the steel product. However, this standard requirement faces insurmountable difficulties in actual production and inspection, becoming a core pain point restricting the efficiency and cost control of steel plates used in hydropower projects.

[0005] On the one hand, the hot cutting allowance specified in the standard leads to a huge consumption of steel plate material, resulting in extremely poor economic efficiency. Taking the SXQ355NC-Z35 extra-thick steel plate (rolled and trimmed dimensions: 3530mm longitudinal × 950mm transverse × 350mm thick) used for the top cover flange of the Tiantai pumped storage unit as an example, when taking samples according to the standard requirements: to test tensile, impact and other properties, the plate width must be within a certain range. w Take a rectangular sample at position / 4, measuring 100mm x 200mm x 350mm. Because the hot-cutting allowance must be no less than 350mm thick, the actual sample size needs to be enlarged to 800mm x 900mm x 350mm. To test the Z-direction tensile properties, the sample should be taken at the width of the plate. w A square sample measuring 100mm x 100mm x 350mm is taken from position / 2. After adding the hot-cutting allowance, the dimensions must reach 800mm x 800mm x 350mm. The original transverse width of this steel plate is only 950mm, which can only accommodate a sample of... w Sample at position / 4w There is no space available for sampling at position 2; if a single unit is required to complete the sampling, the steel plate needs to be lengthened by at least 1600mm, adding an extra 4.2t of weight; if three units are involved—steel mill self-inspection, main engine plant re-inspection, and owner sampling inspection—an additional 12.6t of weight is required, which is about 1.36 times the weight of the steel plate itself, significantly increasing manufacturing costs and failing to meet the requirements of engineering economics.

[0006] On the other hand, the selection of hot cutting allowance is caught in a dilemma: if the standard is strictly followed and sufficient allowance is left, in addition to material consumption, the large sample (such as a sample with a length of 800mm, a width of 900mm, and a thickness of 350mm) is heavy, difficult to transport, and has high shipping costs; if the hot cutting allowance is reduced in order to reduce costs and facilitate transportation, the heat-affected zone generated during the hot cutting process cannot be completely removed by subsequent machining, which will directly affect the authenticity of the performance of the blank and sample, resulting in the distortion of the test results of key indicators such as tensile strength and impact toughness, causing false detection and misjudgment, which may lead to qualified steel plates being judged as unqualified, resulting in waste of resources; or unqualified steel plates may flow into the project, posing a safety hazard to the operation of the power station.

[0007] In summary, the hot cutting allowance requirements for steel plate samples specified in the existing GB / T2975 standard are seriously out of sync with the actual inspection needs of medium-thick and extra-thick steel plates used in hydropower projects. This results in problems such as high material consumption, high inspection costs, difficulty in implementation, and easy misjudgment of performance, and fails to meet the requirements of hydropower projects for efficient, cost-controllable, and reliable inspection of key steel plates. Summary of the Invention

[0008] The technical problem to be solved by this invention is that if the standard is strictly followed and sufficient allowance is left, in addition to the large material consumption, the transportation is difficult. If the hot cutting allowance is reduced, the performance authenticity of the blank and the sample will be affected.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a sampling method for controlling the hot cutting allowance of steel plate samples, comprising the following steps: S1. Determine the applicable steel plate range: high-strength and tough steel plates with low weld crack sensitivity and extra-thick steel plates; S2. Define the sampling locations; S21, Plate Width w / 4 position samples need to reserve hot cutting allowance to meet the sample and retest sample requirements for chemical composition analysis, metallographic test, transverse tensile test, longitudinal and transverse impact test, transverse 5% strain aging impact test, transverse bending test. S22, Plate Width w For samples at position / 2, a hot cutting allowance must be reserved to meet the requirements for sampling of blanks for Z-direction tensile tests and sampling of retest blanks; S23. For steel plate performance testing, the sample billet must have a hot-cutting allowance on the side of the sample billet that is ≥ h1. The hot cutting allowance on the end face of the sample blank must be ≥ h 2; S3, Create hot cutting allowance; S31. The calculation is based on the test values ​​of hot-cut samples of medium and high strength steel plates. S32. The sample thickness is divided into four grades: ≤100mm, >100mm~200mm, >200mm~300mm, and >300mm~350mm. Except for the ≤100mm grade, for each additional grade of thickness, the side hot cutting allowance is... h 1. Increase by 5mm; S33. Using the width of the heat-affected zone determined by the metallographic-hardness method as the base, multiply the average width of the heat-affected zone for each thickness by 5 and round it to the nearest integer to obtain the initial hot cutting allowance for the side of the blank. h 1; S34, Correcting the initial state h 1. The width of the heat-affected zone must be no less than three times the maximum width of the heat-affected zone determined by the metallographic-hardness method for that grade, and no less than the width of the heat-affected zone determined by the sequential impact test, and no less than twice the width of the heat-affected zone determined by the fine-tuning distance impact test. S35, Set the hot cutting allowance on the end face of the blank. h 2, and h 2< h 1; S4. Hot cutting test sample: on a steel plate w / 4、 w At position / 2, a sample was hot-cut using flame cutting, ensuring that the side of the sample was at least ≥ the hot-cut edge. h 1. The distance from the end face of the sample blank to the hot-cut edge is ≥ h 2. Preferably, in S21, the plate width w Recommended dimensions for sample testing at position / 4: Lateral length ≥ Total lateral requirement of sample blank + 2 × h 1. Longitudinal length ≥ Total longitudinal requirement of sample blank + 2 × h 2. The thickness is consistent with the steel plate to be sampled. Preferably, in S22, the plate width w Recommended dimensions for sample at position / 2: Lateral length ≥ Lateral requirement of Z-axis stretching sample + 2 × h 1. Longitudinal length ≥ Z-axis tensile blank longitudinal requirement + 2 × h 2. The thickness is consistent with the steel plate to be sampled. Preferably, in step S33, the metallographic-hardness method for determining the width of the heat-affected zone includes the following steps: taking samples along the hot-cut section of the sample, observing the changes in the microstructure and measuring the hardness distribution, taking the position where the hardness reaches a stable value as the boundary, measuring the width, and determining the width of the heat-affected zone. Preferably, in S34, the sequential tensile and impact test includes the following steps: sequentially cutting tensile and impact specimens at equal intervals along the hot-cut edge toward the base material and testing them, and determining the width of the heat-affected zone based on the position where the tensile properties and impact absorption energy reach a stable value. Preferably, in S34, the fine-tuning distance method for tensile and impact testing includes the following steps: finely adjusting the spacing along the hot-cut edge towards the base material to cut tensile and impact specimens and conduct tests, and accurately determining the width of the heat-affected zone at the position where the tensile properties and impact absorption energy reach a stable value. Preferably, in S4, the correction is performed. h Beforehand, the sampling center line and hot cutting boundary line need to be marked on the surface of the steel plate. Preferably, when the steel plate to be sampled is a high-strength, high-toughness, low-weld-crack-sensitivity steel plate, S31 should additionally refer to the metallographic-hardness test results of the hot-cut sample of the high-strength, high-toughness, low-weld-crack-sensitivity steel plate to adapt to its heat-affected zone characteristics after quenching and tempering. Preferably, when the steel plate to be sampled is an extra-thick steel plate series, the average heat-affected zone width calculation value in S33 needs to be corrected by referring to the characteristics of the heat-affected zone after normalizing or normalizing + tempering heat treatment. Preferably, after hot cutting, the cut edges of the sample should be inspected, and samples with cracks, missing corners, or excessive burrs should be discarded; for local defects, the hot cutting boundary should be redefined to ensure that the distance between the sample and the new boundary is consistent. h 1. h 2. Requirements.

[0010] This invention provides a sampling method for controlling the hot cutting allowance of steel plate samples, which has the following beneficial effects.

[0011] 1. The logic for creating the hot cutting allowance is verified through multiple methods and calculated in stages to ensure the hot cutting allowance on the side. h 1. It simultaneously meets the requirements of 3 times the maximum heat-affected zone width of the metallographic-hardness method, 2 times the heat-affected zone width of the sequential impact test, and 2 times the heat-affected zone width of the fine-tuning distance impact test, completely covering the heat-affected zone generated by flame cutting and avoiding interference from heat-affected zone residues on the sample performance. Whether it is medium-thick or extra-thick steel plate, the test results of key indicators such as tensile strength, impact toughness, and Z-direction resistance to lamellar tearing can accurately reflect the performance of the steel plate base material, effectively eliminating the risk of qualified steel plates being misjudged as unqualified or unqualified steel plates entering the project due to insufficient hot cutting allowance, providing reliable testing assurance for the safety of key components in hydropower projects.

[0012] 2. Compared to the requirement in GB / T2975 that the hot cutting allowance should not be less than the steel plate thickness, this invention designs the hot cutting allowance in four grades according to the steel plate thickness. h 1, and each gear h 1 is much smaller than the corresponding steel plate thickness. For example, the side hot-cutting allowance for a 350mm thick steel plate according to this invention.h 1 is only 30mm, w The dimensions of the hot-cut sample at position / 4 are only 350mm (length) × 450mm (width) × 350mm (thickness); if the standard specifies that the hot-cut allowance width should not be less than the steel plate thickness, i.e., not less than 350mm, then... w The minimum dimensions of the hot-cut sample at position / 4 are 800mm long × 900mm wide and 350mm thick. Therefore, this invention significantly reduces the manufacturing cost of steel plates, while also reducing the weight and volume of the sample for transportation, lowering transportation difficulty and costs, and balancing technical rationality and engineering economy. Attached Figure Description

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the sample material, blank, specimen, side hot cutting allowance, and end hot cutting allowance in an embodiment of the present invention.

[0014] Figure 2 The width of the plate in the embodiment of the present invention w / 4 position hot cutting test material sampling diagram.

[0015] Figure 3 This is a schematic diagram of the sequential method for taking tensile, impact, and metallographic blanks in an embodiment of the present invention.

[0016] Figure 4 This is a schematic diagram of sampling for tensile, impact, and metallographic blanks using the fine-tuning distance method in an embodiment of the present invention.

[0017] Figure 5 This is a schematic diagram of the hardness gradient curve in an embodiment of the present invention.

[0018] Figure 6 This is a schematic diagram of the width of the heat-affected zone in an embodiment of the present invention.

[0019] Figure 7 This is a regression analysis diagram showing the relationship between sample thickness and heat-affected zone width in an embodiment of the present invention.

[0020] Figure 8 This is a regression analysis diagram showing the relationship between the thickness of the high-strength sample and the width of the heat-affected zone in an embodiment of the present invention.

[0021] Figure 9 This is a regression analysis diagram showing the relationship between the thickness of high-strength and ultra-high-strength samples and the width of the heat-affected zone in embodiments of the present invention.

[0022] Figure 10 This is a microstructure diagram of the hot-cut area of ​​the SX780CF sample in an embodiment of the present invention. Detailed Implementation

[0023] A sampling method for controlling the hot cutting allowance of steel plate samples is applicable to steel plates of the following series: SX610CF, SX780CF, SX950CF, SXQ355N, SXQ500D, and SXQ550D, as specified in Q / CTG 24 "Technical Conditions for High Strength, Toughness and Low Welding Crack Sensitivity Steel Plates for Hydropower Projects", Q / CTG ×× "Technical Conditions for High Strength, Toughness and Low Welding Crack Sensitivity Steel Plates for Hydropower Projects", and Q / CTG 25 "Technical Conditions for Extra-Thick Steel Plates for Hydropower Units". Other grades of steel plates can refer to this method for implementation.

[0024] Sample material: A representative portion of the material obtained by flame cutting from a steel plate. This portion of material should meet the requirements for the location, orientation, size, and quantity of the performance test sample blanks, as detailed in the following document. Figure 1 As shown.

[0025] Sample blank: A blank cut from the sample by machining or other methods, with a small machining allowance or no machining allowance on some surfaces, or subsequently heat-treated under appropriate conditions for the preparation of the sample. See [link to sample blank]. Figure 1 As shown.

[0026] Side hot cutting allowance: When cutting samples from steel plates using the flame hot cutting method, to avoid the hot cutting affecting the test results, there should be sufficient distance between the side of the sample and the hot cutting edge. h 1. See Figure 1 As shown.

[0027] End face hot cutting allowance: When cutting test samples from steel plates using the flame hot cutting method, to avoid the hot cutting affecting the test results, the end face of the sample should be at a sufficient distance from the hot cutting edge. h 2, see Figure 1 As shown.

[0028] The longitudinal and transverse dimensions of the hot-cut steel plate test material should meet the following requirements.

[0029] a) Board width w / 4 Position Specimen Size: Sufficient hot cutting allowance should be reserved, and the sample size should meet the requirements for chemical composition, metallography, transverse tensile, longitudinal and transverse impact, transverse 5% strain aging impact, transverse bending and other test sample sizes, as well as retest sample sizes.

[0030] b) Board width w / 2 Position sample size: Sufficient hot cutting allowance should be reserved, and the requirements for sampling blanks for Z-direction tensile performance test and retest sampling blanks should be met.

[0031] c) Recommended board width w Hot cutting test material at position / 4 (see Figure 2 (as shown) Dimensions, board width w The dimensions of the hot-cut test specimens at position / 2 are shown in Table 1.

[0032] Table 1. Dimensions of Hot Cutting Specimens

[0033] The method for creating the hot cutting allowance for steel plate samples is as follows.

[0034] a) The calculation is based on the test values ​​of hot-cut samples of medium and high strength steel plates such as SX610CF, SXQ355N series, SXQ500D series, and SXQ550D series; b) Based on the thickness of the sample, it is divided into four grades: ≤100mm, >100mm~200mm, >200mm~300mm, and >300mm~350mm; c) Except for the first grade, for each additional grade of sample thickness, the hot cutting allowance... h 1. Increase by 5mm; d) Hot cutting allowance h 1. The calculation base is based on the wider heat-affected zone determined by the metallographic-hardness method; e) Multiply the average heat-affected zone width determined by the metallographic-hardness method for each thickness of the sample by 5, and round it to the nearest integer as the hot cutting allowance for that thickness. h 1; f) Hot cutting allowance h 1. It should be no less than 3 times the width of the maximum heat-affected zone determined by the metallographic-hardness method for that grade; g) Hot cutting allowance h 1. It should not be less than the width of the heat-affected zone determined by the results of the impact test of the impact specimens obtained by the sequential method; h) Hot cutting allowance h 1. It should be no less than twice the width of the heat-affected zone determined by the impact test results obtained using the fine-tuning distance method; i) Hot cutting allowance h 2 Appropriately smaller than h 1.

[0035] Hot cutting allowance for steel plate samples h The calculation process is shown in Table 2.

[0036] Hot cutting allowance for the steel plate sample h 1. h 2. See Table 3.

[0037] Table 2 Hot Cutting Remaining Material h 1. Calculation

[0038] Table 3 Hot Cutting Remaining Material

[0039] The sampling method for controlling the hot cutting allowance of steel plate samples has been applied in the testing of spiral casing steel plates, seat ring plates, fixed guide vane steel plates, tongue plates, and top cover flange steel plates of pumped-storage units in Shitai, Zhangye, and Songyang. Application results demonstrate that this method not only accurately reflects the performance and quality of the steel plates but also significantly reduces material consumption, improves testing efficiency, and yields substantial economic benefits.

[0040] Example 1 The steel plate samples of SX610CF, SX780CF, SX950CF, SXQ355N series, SXQ500D series, and SXQ550D series were entrusted to a professional institution with CNAS and CMA qualifications and experience in testing and inspecting hydropower steel plates. The sampling billet, billet processing, sample inspection, and testing were carried out in accordance with the following requirements.

[0041] Flame hot cutting was used on SX610CF, SX780CF, SX950CF, SXQ355N series, SXQ500D series, and SXQ550D series steel plates manufactured by multiple steel mills to cut the steel plates across the width of the plates. w Samples were taken at position / 4 (abbreviated as / 4) w / 4 Sample), if the steel plate has Z-axis performance requirements, the sample width should be increased. w Take a sample at position / 2 (abbreviated as / 2) w / 2 samples).

[0042] like Figure 3 As shown.

[0043] Using the sequential method w / 4 samples t / 4 is 1mm away from the hot-cut edge. The transverse tensile test blanks are taken in sequence by machining, including tensile test 1, tensile test 2, tensile test 3 (18mm×18mm×115mm, 2mm interval), and the number of tensile test blanks is determined according to whether the test results have reached stability.

[0044] exist w / 4 samples t The / 4' position is 1mm away from the hot-cut edge. The transverse impact test sample blank is punched 1' (12mm×12mm×170mm) by machining. The V-shaped notch of the impact sample is not close to the hot-cut edge.

[0045] When in w / 4 samples t When taking the impact sample blank at position / 4' and punching 1', t The impact sample blank 1 taken at position / 4 has a V-shaped notch near the hot cut edge.

[0046] exist w / 4 samples tThe metallographic test sample blank (16mm × 16mm) was taken from the hot-cut edge at position / 3. (×16mm).

[0047] like Figure 4 As shown.

[0048] Using the fine-tuning distance method w / 4 samples t / 4 positions are 1mm, 3mm, and 5mm away from the hot-cut edge, respectively. Transverse tensile test blanks are taken by machining for tensile I, tensile II, and tensile III (18mm×18mm×115mm, 2mm intervals).

[0049] Using the fine-tuning distance method w / 4 samples t The / 4' position is 1mm, 3mm, and 5mm away from the hot-cut edge, respectively. Transverse impact test blanks of punch I, punch II, and punch III (12mm×12mm×58mm, 2mm apart) are machined. The V-shaped notch of the impact test specimen is close to the hot-cut edge (the distance is not equal).

[0050] exist w / 4 samples t The metallographic test sample blank (16mm × 16mm) was taken from the hot-cut edge at position / 3. (×16mm).

[0051] exist w / 4 The test samples were prepared according to the standards of GB / T 4160, GB / T 232, GB / T 20066, etc., and were machined to take transverse 5% strain aging impact, bending test blanks and chemical composition analysis samples respectively.

[0052] exist w / 2 The Z-direction tensile test specimens were machined according to GB / T 5313 standard.

[0053] remove Figure 3 , Figure 4 In addition to the dimensions of the tensile, impact, and metallographic test specimens already marked, a machining allowance of 1mm to 2mm should be left on each machined surface of the remaining 5% strain aged impact, bending, and Z-direction tensile test specimens.

[0054] remove Figure 3 , Figure 4 In addition to the marked distances between the tensile, impact, and metallographic test specimen blanks and the hot-cut edge, the distances between the remaining surfaces of the tensile, impact, and metallographic test specimen blanks and the machined surfaces of the remaining test specimen blanks and the hot-cut edge are ≥30mm.

[0055] The 18mm×18mm×115mm tensile test specimen blank was machined into a diameter of 10mm / 16mm. For the 105mm tensile specimens, the distances from the hot-cut edge of the No. 1, No. 2, and No. 3 tensile specimens of the sample blank taken in sequence are 5mm, 25mm, and 45mm, respectively.

[0056] The distances from the hot-cut edge of tensile specimens I, II, and III, taken using the fine-tuning distance method, were 5mm, 7mm, and 9mm, respectively.

[0057] The 12mm×12mm×58mm impact test blank was machined into 10mm×10mm×55mm impact specimens. The distances from the hot-cut edge of the No.1, No.2, and No.3 impact specimens of the blank were taken in sequence and were 2mm, 16mm, and 30mm respectively. If the V-shaped notch was close to the hot-cut edge, the distances from the bottom of the V-shaped notch to the hot-cut edge were 4mm, 18mm, and 32mm respectively.

[0058] The distances from the hot-cut edge of impact specimens I, II, III, and IV, taken using the fine-tuning distance method, were 2mm, 4mm, 6mm, and 8mm, respectively, and the distances from the bottom of the V-shaped notch to the hot-cut edge were 4mm, 6mm, 8mm, and 10mm, respectively.

[0059] The 16mm×16mm×16mm metallographic blank was machined into 15mm×15mm×15mm metallographic specimens (with the hot cut edge retained). The remaining 5% strain-aged impact, bending, Z-direction tensile specimens and chemical composition analysis samples met the relevant standard requirements. The specimen shape, size and surface roughness were inspected and qualified.

[0060] Test the samples on suitable equipment (instruments) according to the relevant operating procedures. The test items, test standards, test equipment and instruments and their models are shown in Table 4.

[0061] Table 4 Test Items, Test Standards, Equipment, Instruments and Models

[0062] The width of the heat-affected zone is determined by the metallographic-hardness method. This involves analyzing the changes in the microstructure and observing the changes in the hardness gradient value of the heat-affected zone to determine its width, and then marking the width of the heat-affected zone on the microstructure photograph.

[0063] Samples were taken from SX610CF, SX780CF, SX950CF, SXQ355N series, SXQ500D series, and SXQ550D series steel plates for testing. Taking the SX780CF sample (200mm long x 340mm wide x 130mm thick) as an example, the hardness gradient values ​​are shown in Table 5, and the hardness gradient curve is shown in [the table / chart / etc.]. Figure 5 As shown, the width of the heat-affected zone is shown in the figure. Figure 6 As shown.

[0064] Table 5 Hardness gradient values

[0065] The test results of steel plates of SX610CF, SX780CF, SX950CF, SXQ355N series, SXQ500D series and SXQ550D series are shown in Tables 6 to 12.

[0066] Table 6. Test Results of SX610CF Samples

[0067] Table 6. Test results of SX610CF sample (continued)

[0068] Table 7. Test Results of SX780CF Sample

[0069] Table 7 SX780CF Sample Test Results (Continued)

[0070] Table 8. Test Results of SX950CF Sample

[0071] Table 8. Test results of SX950CF sample (continued)

[0072] Table 9. Test Results of SXQ355N Series Samples

[0073] Table 9. Test results of SXQ355N series samples (continued)

[0074] Table 10 SXQ500D Series Sample Test Results

[0075] Table 11. Test Results of SXQ550D Series Samples

[0076] Analyzing the data in Tables 6 to 11, the typical values ​​of the heat-affected zone width for the three sampling methods are shown in Table 12.

[0077] Table 12 Test methods and width of heat-affected zone

[0078] As can be seen from Table 12: The metallographic-hardness test results of SXQ355NC-Z35 sample with a thickness of 330mm showed that the maximum width of the heat-affected zone was 6.2mm.

[0079] The results of the sequential sampling tensile test verified that the width of the heat-affected zone was ≤25mm, and the results of the impact test verified that the width of the heat-affected zone was ≤16mm.

[0080] The results of tensile testing on SX610CF specimens with a thickness of 70mm using the fine-tuning distance method verified that the width of the heat-affected zone was ≤7mm. The results of impact testing on SX500D-Z35 specimens with a thickness of 235mm verified that the maximum width of the heat-affected zone was ≤10mm.

[0081] Analyzing the test data in Tables 6, 8, 9, 10, and 11, the impact test value of specimen No. 1 with the V-shaped notch near the hot-cut edge was significantly reduced, indicating that the test results of the impact specimen with the V-shaped notch near the hot-cut edge are easily affected.

[0082] Test samples with different longitudinal and transverse dimensions were hot-cut on three steel plates of grades SX610CF and SX950CF respectively. The comparison of the impact test values ​​of sample 1 is shown in Table 13.

[0083] As shown in Table 13, for the same steel plate, within a certain range of sample size, increasing the longitudinal and transverse dimensions of the sample did not reduce the degree of heat-affected zone, but it did not increase the degree of heat-affected zone by increasing the longitudinal and transverse dimensions of the sample.

[0084] Table 13 Sample dimensions and impact test values ​​of sample No. 1

[0085] Table 14 shows the thickness of the hot-cut specimen and the width of the heat-affected zone determined by the metallographic-hardness method. Regression analysis is shown in [Table 14]. Figure 7 As shown.

[0086] From Table 14, Figure 7 It can be seen that the greater the thickness of the sample, the longer the hot cutting time, and the greater the heat input intensity, the greater the trend of the width of the heat-affected zone of the sample determined by the metallographic-hardness method.

[0087] Table 14 Sample thickness and heat-affected zone width

[0088] Table 14 Sample thickness and heat-affected zone width (continued)

[0089] Table 15 shows the thickness of medium-high strength, high strength, and ultra-high strength specimens and the width of the heat-affected zone determined by the metallographic-hardness method. Regression analysis is shown in […]. Figure 8 , Figure 9 As shown.

[0090] Taking SX780CF sample (200mm long × 340mm wide × 130mm thick) as an example, the metallographic test results show the microstructure of the hot-cut area as follows: Figure 10 As shown.

[0091] Table 15 Sample Strength Grade and Heat-Affected Zone Width

[0092] Table 15 Sample Strength Grade and Heat-Affected Zone Width (Continued)

[0093] From Table 15, Figures 8-10 It can be known that: The microstructures of the high-strength steel plate samples from the SXQ355N series, SX610CF, SXQ500D series, and SXQ550D series are F (ferrite) + P (pearlite), B (bainite), B+F, and B+P+F, respectively. During the hot cutting process, hardened martensite (M) is generated at the cut edge, and a small amount of M also appears in the hot cutting transition zone. The hardness and strength of the matrix microstructures F+P, B, B+F, and B+P+F differ greatly from that of M. Therefore, hot cutting has a significant thermal impact on the high-strength steel plate samples, and the width of the thermally affected zone of the samples is also relatively large.

[0094] The matrix structures of the high-strength and ultra-high-strength steel plate samples of SX780CF and SX950CF are S (tempered celestite) + B and M + B, respectively. During the hot cutting process, hardened M is generated at the hot cut edge, and a small amount of M also appears in the hot cutting transition zone. The hardness and strength of the matrix structures S + B and M + B are not significantly different from M. Therefore, hot cutting has a small thermal effect on the high-strength and ultra-high-strength steel plate samples, and the width of the heat-affected zone of the samples is also small.

[0095] Record the hot cutting process of the test material, including the grade, dimensions (longitudinal × transverse × thickness), ambient temperature, gas type, hot cutting gun model, flame temperature, and the temperature measured immediately after hot cutting at the edge of the hot cutting opening and at the geometric center of the rolled surface of the test material. The specific records of the process are shown in Table 16.

[0096] Table 16 Hot Cutting Record of Samples

[0097] Table 16 Hot Cutting Records of Samples (Continued)

[0098] As can be seen from Table 16: The significant difference in the hot-cut temperature of the test samples recorded by the two steel mills may be related to the timing of the temperature measurement.

[0099] When hot cutting the sample, the lower the ambient temperature, the greater the tendency to produce hardened material (M), and the greater the tendency for the heat-affected zone width of the sample to increase.

[0100] The temperature at the geometric center of the rolled surface of the sample after hot cutting is below 170℃, which is much lower than the tempering temperature of the steel plate after quenching.

[0101] The temperature of the hot cut opening recorded by H Steel Plant after hot cutting of the sample was 415℃~514℃, which had a slight low-temperature tempering effect on the area near the hot cut opening of the sample.

[0102] The width of the heat-affected zone (HAZ) was determined using the metallographic-hardness method. Tensile and impact specimens were then tested using a sequential method and a fine-tuning distance method to verify the actual HAZ width. After in-depth analysis of factors such as the longitudinal and transverse dimensions of the specimens, thickness, strength grade, and hot-cutting temperature, we found that: If the sample size is within the normal sampling range, increasing the longitudinal and transverse dimensions of the sample will not reduce the width of the heat-affected zone.

[0103] The greater the sample thickness, the wider the heat-affected zone tends to be; conversely, the smaller the sample thickness, the narrower the heat-affected zone tends to be.

[0104] Hot cutting has a significant thermal impact on medium and high strength steel plate samples such as SXQ355N series, SX610CF, SXQ500D series, and SXQ550D series, and the width of the thermally affected zone of the samples is also relatively large.

[0105] Hot cutting has a relatively small thermal impact on high-strength and ultra-high-strength steel plate samples such as SX780CF and SX950CF, and the width of the thermally affected zone of the samples is also relatively small.

[0106] The lower the ambient temperature during hot cutting of the sample, the larger the trend of the width of the heat-affected zone of the sample; conversely, the higher the ambient temperature during hot cutting of the sample, the smaller the trend of the width of the heat-affected zone of the sample.

[0107] The test results of the impact specimen with the V-shaped notch near the hot-cut edge are significantly reduced.

[0108] The actual width of the heat-affected zone is greater than the width of the heat-affected zone determined by the metallographic-hardness method.

[0109] The tensile test specimens were obtained using the sequential method to verify the results, and the actual width of the heat-affected zone did not exceed 25 mm.

[0110] The impact test specimens were obtained using a sequential method to verify the results, and the actual width of the heat-affected zone did not exceed 16 mm.

[0111] The results of the tensile test specimens were verified using the fine-tuning distance method. The actual width of the heat-affected zone did not exceed 7 mm (for a plate thickness of 70 mm).

[0112] The impact test specimens were verified using the fine-tuning distance method, and the actual width of the heat-affected zone did not exceed 10 mm (plate thickness 235 mm).

[0113] The accuracy of the heat-affected zone width determined by the fine-tuning distance method is higher than that determined by the sequential method.

Claims

1. A sampling method for controlling the hot cutting allowance of steel plate samples, characterized in that, Includes the following steps: S1. Determine the applicable steel plate range: high-strength and tough steel plates with low weld crack sensitivity and extra-thick steel plates; S2. Define the sampling locations; S21, Plate Width w / 4 position samples need to reserve hot cutting allowance to meet the sample and retest sample requirements for chemical composition analysis, metallographic test, transverse tensile test, longitudinal and transverse impact test, transverse 5% strain aging impact test, transverse bending test. S22, Plate Width w For samples at position / 2, a hot cutting allowance must be reserved to meet the requirements for sampling of blanks for Z-direction tensile tests and sampling of retest blanks; S23. For steel plate performance testing, the sample billet must have a hot-cutting allowance on the side of the sample billet that is ≥ h 1. The hot cutting allowance on the end face of the sample blank must be ≥ h 2; S3, Create hot cutting allowance; S31. The calculation is based on the test values ​​of hot-cut samples of medium and high strength steel plates. S32. The sample thickness is divided into four grades: ≤100mm, >100mm~200mm, >200mm~300mm, and >300mm~350mm. Except for the ≤100mm grade, for each additional grade of thickness, the side hot cutting allowance is... h 1. Increase by 5mm; S33. Using the width of the heat-affected zone determined by the metallographic-hardness method as the base, multiply the average width of the heat-affected zone for each thickness by 5 and round it to the nearest integer to obtain the initial hot cutting allowance for the side of the blank. h 1; S34, Correcting the initial state h 1. The width of the heat-affected zone must be no less than three times the maximum width of the heat-affected zone determined by the metallographic-hardness method for that grade, and no less than the width of the heat-affected zone determined by the sequential impact test, and no less than twice the width of the heat-affected zone determined by the fine-tuning distance impact test. S35, Set the hot cutting allowance on the end face of the blank. h 2, and h 2< h 1; S4. Hot cutting test sample: on a steel plate w / 4、 w At position / 2, a sample was hot-cut using flame cutting, ensuring that the side of the sample was at least ≥ the hot-cut edge. h 1. The distance from the end face of the sample blank to the hot-cut edge is ≥ h 2。 2. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: In S21, the plate width w Recommended dimensions for sample testing at position / 4: Lateral length ≥ Total lateral requirement of sample blank + 2 × h 1. Longitudinal length ≥ Total longitudinal requirement of sample blank + 2 × h 2. The thickness is consistent with the steel plate to be sampled.

3. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: In S22, the plate width w Recommended dimensions for sample at position / 2: Lateral length ≥ Lateral requirement of Z-axis stretching sample + 2 × h 1. Longitudinal length ≥ Z-axis tensile blank longitudinal requirement + 2 × h 2. The thickness is consistent with the steel plate to be sampled.

4. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: In S33, the metallographic-hardness method for determining the width of the heat-affected zone includes the following steps: taking samples along the hot-cut section of the sample, observing the changes in the microstructure and measuring the hardness distribution, taking the position where the hardness reaches a stable value as the boundary, measuring the width, and determining the width of the heat-affected zone.

5. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: In S34, the sequential tensile and impact test includes the following steps: taking tensile and impact specimens at equal intervals along the hot-cut edge toward the base material and testing them, and determining the width of the heat-affected zone based on the position where the tensile properties and impact absorption energy reach a stable value.

6. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: In S34, the fine-tuning distance method for tensile and impact testing includes the following steps: finely adjusting the spacing along the hot-cut edge towards the base material to cut tensile and impact specimens and conduct tests, and accurately determining the width of the heat-affected zone at the position where the tensile properties and impact absorption energy reach a stable value.

7. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: In S4, the correction h Beforehand, the sampling center line and hot cutting boundary line need to be marked on the surface of the steel plate.

8. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: When the steel plate to be sampled is a high-strength, high-toughness, low-weld-crack-sensitivity steel plate, the metallographic-hardness test results of the hot-cut sample of the high-strength, high-toughness, low-weld-crack-sensitivity steel plate should be additionally referenced in S31 to adapt to the characteristics of its heat-affected zone after quenching and tempering.

9. The sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: When the steel plate to be sampled is an extra-thick steel plate series, the average heat-affected zone width calculation value in S33 needs to be corrected by referring to the characteristics of the heat-affected zone after normalizing or normalizing + tempering heat treatment.

10. A sampling method for controlling the hot cutting allowance of steel plate samples according to claim 1, characterized in that: After hot cutting, the cut edges of the sample must be inspected, and samples with cracks, missing corners, or excessive burrs should be discarded. For local defects, the hot cutting boundary needs to be redefined to ensure that the distance between the sample and the new boundary is consistent. h 1. h 2. Requirements.

Images