A high-strength bending ratio HRB500E hot-rolled ribbed steel bar rolling method

Abstract

This invention discloses a method for rolling high-strength-yield-ratio HRB500E hot-rolled ribbed steel bars, comprising the following steps: S1, using a converter for smelting and nitrogen-enhanced continuous casting to obtain steel billets; S2, obtaining the measured nitrogen content of a single steel billet; S3, matching the steel billet to be rolled to a rolling production line with corresponding strength-yield-ratio reserves; S4, adjusting rolling strategies at different temperatures based on the measured nitrogen content (N) of the steel billets in different rolling production lines; S5, obtaining the predicted yield strength, predicted tensile strength, and predicted strength-yield-ratio using a pre-established mechanical property prediction model, adjusting the cooling bed temperature of the steel bars, and re-predicting performance until the predicted strength-yield-ratio meets the set requirements or reaches the predetermined process adjustment upper limit. The advantages of this invention are that it can stably control the product's strength-yield-ratio above 1.28, ensuring mechanical properties meet standards, reducing the alloy cost per ton of steel, and simultaneously improving production organization flexibility and process control capabilities.

Description

Technical Field

[0001] This invention relates to the field of intelligent production technology in iron and steel metallurgy, and in particular to a method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars. Background Technology

[0002] HRB500E high-strength seismic-resistant steel bars are widely used in major engineering projects such as high-rise buildings, bridges, and tunnels. The national standard GB 1499.2-2024 clearly requires that its yield strength be ≥500MPa, tensile strength be ≥630MPa, and strength-to-yield ratio be ≥1.25, while ensuring good plasticity and seismic performance.

[0003] Traditional HRB500E steel rebar production primarily relies on adding vanadium-nitrogen alloys to achieve precipitation strengthening. High vanadium content ensures that strength and yield strength ratio meet standards. However, vanadium is a precious metal, and the alloy's cost is high, significantly increasing steel rebar production costs. To reduce costs, the industry is gradually promoting a "nitrogen-increased, vanadium-reduced" process. This involves increasing the nitrogen content in the steel to promote V(C, N) precipitation, achieving strength standards with lower vanadium content.

[0004] However, the existing nitrogen enrichment and vanadium reduction processes still have the following technical problems:

[0005] First, the inherent performance differences between different rolling production lines have not been considered. Within the same plant, different bar production lines produce steel bars with the same composition but different cooling bed structures, rolling rhythms, and cooling paths, resulting in inherent differences in the strength-to-yield ratio of the produced steel bars. Production lines with walking beam cooling beds and slow rolling rhythms produce steel bars with slower heat dissipation after rolling, higher phase transformation temperatures, larger pearlite lamellar spacing, abnormally higher yield strength, and smaller strength-to-yield ratio margins. Conversely, production lines with fast rolling rhythms and strong cooling bed capabilities produce steel bars with greater phase transformation undercooling, finer microstructure, higher tensile strength, and more abundant strength-to-yield ratio reserves. Current production uses a uniform composition and process model, failing to utilize these production line differences for production organization optimization. This leads to a high likelihood of unqualified strength-to-yield ratios when high-nitrogen steel billets are rolled on production lines with low strength-to-yield ratio reserves.

[0006] Second, it is impossible to simultaneously achieve both strength-to-yield ratio and plasticity. In the nitrogen-increasing and vanadium-reducing process, increasing the nitrogen content enhances the precipitation effect, significantly increasing the yield strength, leading to a decrease in the strength-to-yield ratio; conversely, excessively low nitrogen content results in a decrease in the elongation of the steel bar, and the plasticity fails to meet the standards. Existing technologies mostly improve performance by adjusting the composition or the rolling process alone, failing to achieve synergistic optimization of strength-to-yield ratio and plasticity.

[0007] Third, process control is lagging and response to anomalies is slow. Current production mostly uses a fixed nitrogen supply scheme, which cannot dynamically adjust the subsequent rolling process according to the real-time nitrogen content fluctuations in converter smelting; performance testing is mostly offline and post-event testing, and by the time non-compliance is discovered, a batch of defective products has already been produced, resulting in a low production pass rate and poor fault tolerance.

[0008] Therefore, there is an urgent need to develop a rolling method for HRB500E steel bars that is adapted to the nitrogen-increasing and vanadium-reducing process, can dynamically match production resources according to nitrogen content, stably control the strength-to-yield ratio, and take into account both plasticity and cost. Summary of the Invention

[0009] The purpose of this invention is to provide a method for rolling high-strength-yield ratio HRB500E hot-rolled ribbed steel bars, in order to solve the problems of large fluctuations in strength-yield ratio, insufficient production flexibility, and delayed abnormal response caused by nitrogen content fluctuations, specification differences, and inherent performance differences of rolling production lines in the production of existing nitrogen-enhanced and vanadium-reduced HRB500E steel bars.

[0010] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars includes the following steps: S1 is produced by converter smelting, nitrogen-enhancing alloys are added for nitrogen addition, and steel billets are obtained by continuous casting. S2, the nitrogen content of each continuously cast steel billet is tested to obtain the measured nitrogen content N of a single billet; S3, calculate the nitrogen content diversion threshold N based on the nominal diameter D of the steel bar to be rolled. limit Based on the measured nitrogen content N and the nitrogen content diversion threshold N limit Based on the comparison results, the steel billets to be rolled are matched to rolling production lines with corresponding strength-to-yield ratio reserves; S4, adjusting rolling strategies at different temperatures based on the measured nitrogen content (N) of steel billets in different rolling production lines; S5, before the finishing rolling is completed and the steel bars are placed on the cooling bed, obtain the measured nitrogen content N and the real-time cooling bed temperature T. b The model is input into a pre-established mechanical property prediction model to obtain the predicted yield strength ReL. pred Predicting tensile strength Rm pred and predict the yield strength ratio k pred When the predicted yield strength ratio k pred If the temperature is lower than the set target value, adjust the temperature of the steel bar on the cooling bed and re-predict the performance until the predicted strength-to-yield ratio meets the set requirements or reaches the predetermined upper limit of process adjustment.

[0011] Preferably, the vanadium mass fraction in the steel billet of step S1 is 0.050% to 0.060%, the nitrogen mass fraction is 170 to 230 ppm, and the niobium mass fraction is 0 to 0.020%, wherein the nitride alloy is selected from one or two of silicon manganese nitride and vanadium iron nitride.

[0012] Preferably, in step S3, the nitrogen content diversion threshold N limit Based on the nominal diameter D of the reinforcing bar, a linear or piecewise linear correction is performed, and the calculation relationship satisfies: N limit =N0+k×(D-D0); Wherein, N0 is the reference nitrogen content, D0 is the reference nominal diameter, and k is the specification correction factor, and the specification correction factor k increases as the nominal diameter D of the steel bar increases.

[0013] Preferably, in step S4, when the billet to be rolled is matched to the high-strength yield ratio reserve production line and its measured nitrogen content reaches the preset high-nitrogen threshold, a high-temperature homogenization rolling strategy is adopted. This high-temperature homogenization rolling strategy is an open-loop basic process setting, including: The temperature of the soaking zone of the heating furnace is controlled at 1180~1220℃; The descaling pressure at the roughing mill inlet shall be controlled to be no less than 18 MPa; The temperature of the steel bars on the cooling bed should be controlled at 980-1020℃; Turn on the pre-water cooling device before finishing rolling and control the inlet temperature of finishing rolling at 1000-1050℃.

[0014] Preferably, in step S4, when the billet to be rolled is matched to a low strength-to-yield ratio reserve production line and its measured nitrogen content is lower than a preset low nitrogen threshold, a low-temperature rolling strategy different from the high-temperature homogenization rolling strategy is adopted. The high-temperature homogenization rolling strategy includes: The temperature of the soaking zone of the heating furnace is controlled at 1120–1160℃; The temperature of the steel bars on the cooling bed is controlled at 920-960℃.

[0015] Preferably, in step S4, the strength-to-yield ratio reserve ρ is the difference between the strength-to-yield ratio of steel bars produced by steel billets with the same composition under the standard process of the corresponding production line and the minimum limit specified in GB 1499.2 standard; The high strength yield ratio reserve production line has a strength yield ratio reserve ρ≥0.04, which is a bar production line with fast rolling rhythm and strong cooling bed cooling capacity; The low strength-to-yield ratio reserve production line has a strength-to-yield ratio reserve ρ < 0.04, and is a bar production line with a walking beam cooling bed and a slow rolling rhythm.

[0016] Preferably, in step S5, the mechanical property prediction model is based at least on the measured nitrogen content N and the upper cooling bed temperature T. b As input variables, and built using historical production data, the model includes: ReL pred =A0+A1×N+A2×T b ; Rm pred =B0+B1×N+B2×T b ; k pred =Rm pred / ReLpred ; Where A0, A1, A2, B0, B1, and B2 are model parameters; Furthermore, the model parameters satisfy: A1 > 0, A2 < 0, B1 > 0, B2 < 0, and |A2| > |B2|.

[0017] Preferably, the mechanical property prediction model in step S5 is implemented using a lookup table correction method, specifically: the reference yield strength ReL under the reference working condition is predetermined. ref Compared with the reference tensile strength Rm ref The benchmark operating condition is the benchmark nitrogen content N. ref =200ppm, reference upper cooling bed temperature T ref =1000℃; During online calculations, the strength correction is calculated using the following formula: ΔReL=α N ×(N N ref ) / 10+α T ×(T b T ref ) / 10; ΔRm=β N ×(N N ref ) / 10+β T ×(T b T ref ) / 10; In the formula, α N α is the correction factor for nitrogen content on yield strength, with a value ranging from 4 to 6 MPa / 10 ppm; T β is the correction factor for the yield strength based on the upper cooling bed temperature, with a value ranging from -2.0 to -1.0 MPa / 10℃; N β is a correction factor for nitrogen content against tensile strength, with a value ranging from 3 to 5 MPa / 10 ppm; T The temperature of the upper cooling bed is a correction factor for tensile strength, with a value range of -1.5 to -0.5 MPa / 10℃; The formula for calculating the predicted intensity is: ReL pred =ReL ref +ΔReL; Rm pred =Rm ref +ΔRm; Among them, the benchmark yield strength ReL ref The tensile strength is 550~570MPa, and the reference tensile strength Rm is... ref It is 705~725MPa.

[0018] Preferably, the baseline strength and correction coefficients are obtained in the following way: collect historical production data of the target production line within 1 to 3 months, screen the furnace batches with upper cooling bed temperature of 990 to 1010℃ and measured nitrogen content of 195 to 205ppm, take the average value of their mechanical properties as the baseline strength, obtain each correction coefficient through multiple linear regression, and update the baseline strength and correction coefficients every 1 to 3 months.

[0019] Preferably, in step S5, the adjustment amount of the upper cooling bed temperature is determined according to the following rules: When the difference between the predicted strength-to-yield ratio and the preset qualified threshold is ≤0.03, the temperature is increased by 15℃ in a single adjustment. When the difference is greater than 0.03, the temperature will be increased by 30℃ in a single adjustment. The cumulative increase will not exceed 30°C.

[0020] In summary, the present invention has the following beneficial effects: 1. Improve the stability of the strength-to-yield ratio: By utilizing the inherent strength-to-yield ratio reserves of different rolling lines for dynamic diversion, high-nitrogen billets can be preferentially allocated to more favorable rolling conditions, thus solving the problem of the decrease in strength-to-yield ratio caused by high nitrogen from the production organization level.

[0021] 2. Reduce dependence on high vanadium content: This invention achieves satisfactory mechanical properties even with low vanadium content by increasing nitrogen and reducing vanadium content, combined with rolling line matching and hot rolling process optimization. When the vanadium mass fraction is about 0.055% and the nitrogen content is 215ppm, different strategies can be used on different rolling lines to obtain a strength-to-yield ratio of 1.27 to 1.29.

[0022] 3. Reduce performance fluctuations caused by differences in rolling lines: This invention no longer considers all production lines to have the same performance, but instead establishes a reserve database of rolling line strength-to-yield ratio, transforming the equipment capabilities of existing different bar production lines into performance resources that can be used for production scheduling.

[0023] 4. Achieve pre-prediction and online adjustment: By predicting the performance of steel bars before they are cooled on the cooling bed, the traditional "offline detection - discovery of non-conformity - post-processing" is transformed into "online prediction - real-time adjustment - re-prediction", which improves the fault tolerance under abnormal working conditions. Under the condition of 220ppm nitrogen content, the strength-to-yield ratio is improved from the predicted critical state to the final 1.267 through online temperature control adjustment.

[0024] 5. Improve production organization flexibility: Even if high-nitrogen billets cannot always be scheduled to high-reserve rolling lines due to production scheduling reasons, low-reserve rolling lines can be compensated through differentiated rolling strategies, thereby reducing dependence on fixed production routes. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below. These embodiments do not constitute a limitation on the present invention.

[0026] In this embodiment of the invention, the calibration values ​​of the strength-to-yield ratio reserve ρ for each production line within the plant area are as follows: 5-bar production line ρ≈0.05, 6-bar production line ρ≈0.045, belonging to the first category of high strength-to-yield ratio reserve production lines; 7-bar production line ρ≈0.015, 8-bar production line ρ≈0.01, belonging to the second category of low strength-to-yield ratio reserve production lines. All embodiments and comparative examples adopt the production process of converter smelting-continuous casting-hot rolling, and the steel bar performance testing is performed in accordance with GB 1499.2-2024 standard.

[0027] Comparative Example 1 (Traditional High Vanadium Process) Steelmaking composition: Vanadium mass fraction 0.075%, nitrogen mass fraction 90ppm, no niobium added. Rolling scheme: φ25mm steel bars are rolled on a 7-bar production line using standard process: heating furnace soaking zone temperature 1150℃, upper cooling bed temperature 950℃. Performance test results: yield strength 540MPa, tensile strength 685MPa, strength-to-yield ratio 1.26, maximum force total elongation Att=18.5%, performance is qualified, but the cost of vanadium alloy per ton of steel is high.

[0028] Comparative Example 2 (Nitrogen-enhanced and vanadium-reduced splitless process) Steelmaking composition: Vanadium mass fraction 0.055%, nitrogen mass fraction 215ppm, no niobium added. Rolling scheme: φ25mm steel bars are rolled on a 7-bar production line, using the same standard process as Comparative Example 1. Performance test results: Yield strength 580MPa, tensile strength 705MPa, strength-to-yield ratio 1.21, maximum force total elongation Att=17.0%. The strength-to-yield ratio is lower than the standard minimum limit, therefore it is unqualified.

[0029] Comparative Example 3 (High-Temperature Homogenization without Closed-Loop Control) Steelmaking composition: Vanadium mass fraction 0.055%, nitrogen mass fraction 215ppm, no niobium added. Rolling scheme: φ25mm steel bars are rolled on a 7-bar production line, employing a high-temperature homogenization strategy: soaking zone temperature 1200℃, descaling pressure 20MPa, upper cooling bed temperature 1000℃, no online closed-loop control. Performance test results: Yield strength 568MPa, tensile strength 718MPa, strength-to-yield ratio 1.264, just reaching the lower limit of acceptable quality, with insufficient margin, prone to non-compliance under production fluctuations.

[0030] Example 1 (Dynamic flow splitting process in production line) Steelmaking composition: Vanadium mass fraction 0.055%, Nitrogen mass fraction 215ppm, no niobium added. Rolling scheme: φ25mm steel bar, calculated downflow threshold N. limit=200 + 0.5 × (25 - 25) = 200 ppm; Measured nitrogen content 215 ppm ≥ 200 ppm, allocated to 6-bar production line (Type I production line) for rolling, using standard process: heating furnace soaking zone temperature 1150℃, upper cooling bed temperature 950℃. Performance test results: yield strength 560 MPa, tensile strength 725 MPa, strength-to-yield ratio 1.29, maximum force total elongation Att = 17.5%, all performances are qualified. Compared with Comparative Example 2, under the same composition, only by production line diversion, the strength-to-yield ratio increased by 0.08, verifying the significant effect of production line matching.

[0031] Example 2 (High-Temperature Homogenization Process for Second Type of Production Line) Steelmaking composition: Vanadium mass fraction 0.055%, nitrogen mass fraction 215ppm, no niobium added. Rolling scheme: Due to production constraints, φ25mm steel bars need to be rolled on the 7-bar production line. The measured nitrogen content is ≥210ppm. A high-temperature homogenization strategy is implemented: heating furnace soaking zone temperature 1200℃, rough rolling descaling pressure 20MPa, and upper cooling bed temperature 1000℃. Performance test results: yield strength 565MPa, tensile strength 715MPa, strength-to-yield ratio 1.27, maximum force total elongation Att=17.2%, all performances are qualified. Compared with Comparative Example 2, under the same production line and composition, the strength-to-yield ratio is increased by 0.06 through differentiated temperature control, meeting the standard requirements.

[0032] Example 3 (Production of Small-Diameter Steel Bars) Steelmaking composition: Vanadium mass fraction 0.052%, Nitrogen mass fraction 195ppm, no niobium added. Rolling scheme: Producing φ16mm steel bars, specification correction factor k=0.4, calculated flow threshold N. limit =200+0.4×(16-25)=196.4ppm; The actual nitrogen content is 195ppm<196.4ppm, so it is allocated to the 8-bar production line (second-class production line) for rolling, using standard process. Performance test results: yield strength 550MPa, tensile strength 695MPa, strength-to-yield ratio 1.26, maximum force total elongation Agt=18.0%, performance is qualified.

[0033] Example 4 (Large-scale extreme working conditions) Steelmaking composition: Vanadium mass fraction 0.058%, Nitrogen mass fraction 205ppm, Niobium mass fraction 0.015%. Rolling scheme: Producing φ32mm steel bars, specification correction coefficient k=0.6, calculate the diversion threshold N. limit=200+0.6×(32-25)=204.2ppm; The measured nitrogen content of 205ppm is slightly higher than the threshold. Due to production constraints, the rolling is limited to a 7-bar production line. A high-temperature homogenization strategy is implemented: heating furnace soaking zone temperature 1200℃, rough rolling descaling pressure 20MPa, pre-water cooling before finishing rolling, finishing rolling inlet temperature 1020℃, and upper cooling bed temperature 1000℃. Performance test results: yield strength 555MPa, tensile strength 715MPa, strength-to-yield ratio 1.29, maximum force total elongation Agt=17.8%, grain size 9.5 grade, all performances are qualified. Mechanism explanation: High-temperature heating promotes complete solid solution of vanadium and niobium, and the high-temperature upper cooling bed delays the precipitation process, making the precipitated phase coarser, effectively reducing the plateau effect of yield strength; at the same time, pre-water cooling before finishing rolling refines the austenite grains, improves tensile strength, and ultimately achieves a significant increase in strength-to-yield ratio.

[0034] Example 5 (Verification of Online Closed-Loop Control) Steelmaking composition: Vanadium mass fraction 0.055%, nitrogen mass fraction 220ppm, no niobium added. Rolling scheme: φ25mm steel bars are rolled on a 7-bar production line, initially using a high-temperature homogenization process, with an initial upper cooling bed temperature of 990℃. During the rolling process, the online prediction module collects data and calculates the predicted yield strength as 573.5MPa, the predicted tensile strength as 721.4MPa, and the predicted strength-to-yield ratio as 1.258 < 1.26, automatically triggering an adjustment command to increase the upper cooling bed temperature by 15℃ to 1005℃. Performance test results after adjustment: yield strength 562MPa, tensile strength 712MPa, strength-to-yield ratio 1.267, meeting the standard requirements and verifying the effectiveness of online closed-loop control.

[0035] Example 6 (Two-parameter model calibration and verification) Historical data (composition range: V=0.052~0.058%, N=190~210ppm) of 50 heats of HRB500E steel bars continuously produced on the 7-bar production line were selected. Heats with an upper cooling bed temperature of 1000±10℃ were screened, and the baseline value was obtained: baseline nitrogen content N. ref =200ppm, based on the upper cooling bed temperature T ref =1000℃, reference yield strength ReL ref =562MPa, reference tensile strength Rm ref =712MPa. Multiple linear regression was performed on the samples deviating from the baseline operating condition to obtain the correction coefficient: α N =5.0MPa / 10ppm (yield), β N =4.2MPa / 10ppm (tensile strength); α T =-1.5MPa / 10℃ (yield), β T = -1.0MPa / 10℃ (tensile strength).

[0036] Verification: The measured nitrogen content was 220 ppm, and the upper cooling bed temperature was 990℃. Substituting these values ​​into the calculation, we get ΔReL = 5.0 × (220 - 200) / 10 + (-1.5) × (990 - 1000) / 10 = 11.5 MPa, ΔRm = 4.2 × (220 - 200) / 10 + (-1.0) × (990 - 1000) / 10 = 9.4 MPa; the predicted yield strength was 573.5 MPa, the predicted tensile strength was 721.4 MPa, and the predicted strength-to-yield ratio was 1.258. Actual measured values: yield strength 569 MPa, tensile strength 720 MPa, strength-to-yield ratio 1.263. The strength error is less than 5 MPa, and the strength-to-yield ratio error is less than 0.01. The model accuracy meets the requirements.

[0037] Example 7 (Fault Tolerance Verification of Extreme Working Condition Model) Steelmaking composition: Vanadium mass fraction 0.058%, Nitrogen mass fraction 230ppm, Niobium mass fraction 0.015%. Rolling scheme: Producing φ32mm steel bars, 7-bar production line, initial upper cooling bed temperature 1020℃. Online prediction: Substituting into the model, the calculated ΔReL=5.0×(230-200) / 10+(-1.5)×(1020-1000) / 10=12MPa, ΔRm=4.2×3+(-1.0)×2=10.6MPa; predicted yield strength 574MPa, predicted tensile strength 722.6MPa, predicted strength-to-yield ratio 1.259<1.26. The system automatically increases the upper cooling bed temperature by 20℃ to the process upper limit of 1040℃, and after recalculation, the predicted strength-to-yield ratio rises back to 1.265. Performance test results: yield strength 566MPa, tensile strength 718MPa, strength-to-yield ratio 1.268, grain size grade 9.5. All performance parameters are qualified, verifying the reliability of the model under high nitrogen and large-scale extreme working conditions.

[0038]

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars, characterized in that, Includes the following steps: S1 is produced by converter smelting, nitrogen-enhancing alloys are added for nitrogen addition, and steel billets are obtained by continuous casting. S2, the nitrogen content of each continuously cast steel billet is tested to obtain the measured nitrogen content N of a single billet; S3, calculate the nitrogen content diversion threshold N based on the nominal diameter D of the steel bar to be rolled. limit Based on the measured nitrogen content N and the nitrogen content diversion threshold N limit Based on the comparison results, the steel billets to be rolled are matched to rolling production lines with corresponding strength-to-yield ratio reserves; S4, adjusting rolling strategies at different temperatures based on the measured nitrogen content (N) of steel billets in different rolling production lines; S5, before the finishing rolling is completed and the steel bars are placed on the cooling bed, obtain the measured nitrogen content N and the real-time cooling bed temperature T. b The model is input into a pre-established mechanical property prediction model to obtain the predicted yield strength ReL. pred Predicting tensile strength Rm pred and predict the yield strength ratio k pred When the predicted yield strength ratio k pred If the temperature is lower than the set target value, adjust the temperature of the steel bar on the cooling bed and re-predict the performance until the predicted strength-to-yield ratio meets the set requirements or reaches the predetermined upper limit of process adjustment.

2. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: The steel billet in step S1 has a vanadium mass fraction of 0.050% to 0.060%, a nitrogen mass fraction of 170 to 230 ppm, and a niobium mass fraction of 0 to 0.020%. The nitriding alloy is selected from one or two of silicon manganese nitride and vanadium iron nitride.

3. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: In step S3, the nitrogen content diversion threshold N limit Based on the nominal diameter D of the reinforcing bar, a linear or piecewise linear correction is performed, and the calculation relationship satisfies: N limit =N0+k×(D-D0); Wherein, N0 is the reference nitrogen content, D0 is the reference nominal diameter, and k is the specification correction factor, and the specification correction factor k increases as the nominal diameter D of the steel bar increases.

4. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: In step S4, when the steel billet to be rolled is matched to the high-strength yield ratio reserve production line and its measured nitrogen content reaches the preset high-nitrogen threshold, a high-temperature homogenization rolling strategy is adopted. The high-temperature homogenization rolling strategy includes: The temperature of the soaking zone of the heating furnace is controlled at 1180~1220℃; The descaling pressure at the roughing mill inlet shall be controlled to be no less than 18 MPa; The temperature of the steel bars on the cooling bed should be controlled at 980-1020℃; Turn on the pre-water cooling device before finishing rolling and control the inlet temperature of finishing rolling at 1000-1050℃.

5. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: In step S4, when the steel billet to be rolled is matched to the low strength-to-yield ratio reserve production line and its measured nitrogen content is lower than the preset low nitrogen threshold, a low-temperature rolling strategy different from the high-temperature homogenization rolling strategy is adopted. The high-temperature homogenization (low-temperature) rolling strategy includes: The temperature of the soaking zone of the heating furnace is controlled at 1120–1160℃; The temperature of the steel bars on the cooling bed is controlled at 920-960℃.

6. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: In step S4, the strength-to-yield ratio reserve ρ is the difference between the strength-to-yield ratio of steel bars produced by steel billets with the same composition under the standard process of the corresponding production line and the minimum limit specified in GB1499.2 standard; The high strength yield ratio reserve production line has a strength yield ratio reserve ρ≥0.04, which is a bar production line with fast rolling rhythm and strong cooling bed cooling capacity; The low strength-to-yield ratio reserve production line has a strength-to-yield ratio reserve ρ < 0.04, and is a bar production line with a walking beam cooling bed and a slow rolling rhythm.

7. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: In step S5, the mechanical property prediction model is based at least on the measured nitrogen content N and the upper cooling bed temperature T. b As input variables, and built using historical production data, the model includes: ReL pred =A0+A1×N+A2×T b ; Room pred =B0+B1×N+B2×T b ; k pred =Rm pred / ReL pred ; Where A0, A1, A2, B0, B1, and B2 are model parameters; Furthermore, the model parameters satisfy: A1 > 0, A2 < 0, B1 > 0, B2 < 0, and |A2| > |B2|.

8. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: The mechanical property prediction model in step S5 is implemented using a lookup table correction method, specifically: the reference yield strength ReL under the reference working condition is determined in advance. ref Compared with the reference tensile strength Rm ref The benchmark operating condition is the benchmark nitrogen content N. ref =200ppm, reference upper cooling bed temperature T ref =1000℃; During online calculations, the strength correction is calculated using the following formula: ΔReL=a N ×(N N ref ) / 10+a T ×(T b T ref ) / 10; ΔRm=β N ×(N N ref ) / 10+β T ×(T b T ref ) / 10; In the formula, α N α is the correction factor for nitrogen content on yield strength, with a value ranging from 4 to 6 MPa / 10 ppm; T β is the correction factor for the yield strength based on the upper cooling bed temperature, with a value ranging from -2.0 to -1.0 MPa / 10℃; N The nitrogen content is a correction factor for tensile strength, with a value ranging from 3 to 5 MPa / 10 ppm; β T The temperature of the upper cooling bed is a correction factor for tensile strength, with a value range of -1.5 to -0.5 MPa / 10℃; The formula for calculating the predicted intensity is: ReL pred =ReL ref +ΔReL; Rm pred =Rm ref +ΔRm; Among them, the benchmark yield strength ReL ref The tensile strength is 550~570MPa, and the reference tensile strength Rm is... ref It is 705~725MPa.

9. A method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 8, characterized in that: The baseline strength and correction coefficients are obtained as follows: historical production data of the target production line within 1 to 3 months are collected, furnace batches with cooling bed temperature of 990 to 1010℃ and measured nitrogen content of 195 to 205ppm are selected, and the average mechanical property test value is taken as the baseline strength. The correction coefficients are obtained through multiple linear regression, and the baseline strength and correction coefficients are updated every 1 to 3 months.

10. The method for rolling high-strength yield ratio HRB500E hot-rolled ribbed steel bars according to claim 1, characterized in that: In step S5, the adjustment amount of the upper cooling bed temperature is determined according to the following rules: When the difference between the predicted strength-to-yield ratio and the preset qualified threshold is ≤0.03, the temperature is increased by 15℃ in a single adjustment. When the difference is greater than 0.03, the temperature will be increased by 30℃ in a single adjustment. The cumulative increase will not exceed 30°C.

Images