HRB400E anti-seismic deformed steel bar as well as controlled cooling process and production method thereof

Abstract

The invention relates to the technical field of deformed steel bars, in particular to HRB400E anti-seismic deformed steel bars as well as a controlled cooling process and a production method thereof. The controlled cooling process comprises the following steps: S1, primary cooling: cooling a rolled steel bar at a cooling speed of not less than 15 DEG C / s until the surface temperature of the steel bar reaches 700-750 DEG C; s2, secondary cooling is conducted, specifically, the reinforcing steel bars continue to be cooled, the cooling speed is not lower than 30 DEG C / s, and cooling is conducted till the surface temperature of the reinforcing steel bars reaches 350-450 DEG C; s3, air cooling: performing air cooling on the reinforcing steel bar until the surface of the reinforcing steel bar is tempered to 600-650 DEG C; and S4, third-time cooling: continuously cooling the reinforcing steel bar at the cooling speed of not higher than 3 DEG C / s until the surface temperature of the reinforcing steel bar reaches room temperature. By reasonably controlling the cooling speed in the cooling process, the mechanical property of the material can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ribbed steel, and particularly relates to an HRB400E earthquake-resistant ribbed steel, its controlled cooling process and production method. Background Art

[0002] As the main material in concrete structures, the performance of steel bars directly affects the safety of building engineering structures. With the rapid economic development of our country, the consumption of steel bars in our country is still increasing year by year. At present, low-alloy steels (HRB335, HRB400, and HRB500) are mainly used as steel bars in our country. Among them, as the third-grade steel bar, HRB400 steel bars have relatively high strength requirements. The new national standard GB / T 1499.2—2018 "Steel for Reinforced Concrete - Part 2: Hot Rolled Ribbed Bars" stipulates that replacing HRB335 steel bars with HRB400 steel bars can save 10% - 15% of steel, enabling the whole society to achieve the same or better use effect with less high-quality steel, promoting the steel industry to improve the quality and use efficiency of steel, and having a huge effect on reducing the quantity of the whole society. Among them, the mechanical property standards of HRB400E earthquake-resistant ribbed steel bars are as follows: tensile strength ≥ 540 MPa; yield strength ≥ 400 MPa; uniform elongation at maximum force ≥ 9.0%; the ratio of tensile strength to yield strength (strength ratio) should not be less than 1.25, and the ratio of the measured yield strength value to the yield strength standard value (yield ratio) should not be greater than 1.30. The microstructure of HRB400E steel bars is mainly ferrite and pearlite, and it is stipulated that tempered martensite structure shall not appear on the base circle.

[0003] The patent document with the publication number CN113319121A discloses a production method of such an earthquake-resistant ribbed steel HRB400E, including: setting of a water-piercing device; controlled rolling: the reduction of the rolled piece in the roughing mill is 40 - 50%, the reduction in the intermediate rolling mill is 30 - 40%, and the reduction in the finishing mill is 10 - 20%; controlled cooling: according to the specifications of the finished ribbed steel HRB400E, two-stage water-piercing or three-stage water-piercing is adopted. After the rolled piece completes the first-stage pre-water-piercing in the intermediate rolling mill, the surface temperature of the rolled piece is reduced from 1020 - 1060 °C to 870 - 910 °C; after the rolled piece completes the second-stage water-piercing in the finishing mill, the surface temperature of the rolled piece is reduced from 950 - 1000 °C to 850 °C - 900 °C (or the second-stage water-piercing is omitted); after passing through the 18# rolling mill in the finishing mill, the third-stage water-piercing reduces the temperature of the rolled piece to 790 - 850 °C. In the prior art, products with a metallographic structure of F + P are obtained by two-stage continuous water-piercing or three-stage continuous water-piercing and controlling the temperature before and after water-piercing, and their mechanical properties still need to be improved. Summary of the Invention

[0004] The present invention aims to solve the above problems and provides an HRB400E earthquake-resistant ribbed steel with good mechanical properties, its controlled cooling process and production method.

[0005] The technical solution for the present invention to solve the problem is as follows. First, a controlled cooling process for the production of HRB400E earthquake-resistant ribbed steel bars is provided, including the following steps:

[0006] S1. Primary cooling: Cool the rolled steel bars, with a cooling rate of not less than 15 °C / s until the surface temperature of the steel bars reaches 700 - 750 °C.

[0007] S2. Secondary cooling: Continue to cool the steel bars, with a cooling rate of not less than 30 °C / s until the surface temperature of the steel bars reaches 350 - 450 °C.

[0008] S3. Air cooling: Air-cool the steel bars until the surface of the steel bars is tempered to 600 - 650 °C.

[0009] S4. Tertiary cooling: Continue to cool the steel bars, with a cooling rate of not higher than 3 °C / s until the surface temperature of the steel bars reaches room temperature.

[0010] The inventor's research found that the cooling rate has a great influence on the metallography of the material. By reasonably controlling the cooling rate during the cooling process, a material with ideal strength and toughness properties can be obtained. It is speculated that the principle is as follows: First, the rolled steel bars are cooled continuously twice. Among them, in the first stage, the temperature is reduced to above the phase transformation temperature at a relatively moderate cooling rate, which can reduce the quenching stress and control the microstructure state of austenite, making the austenite grains refined; in the second stage, the temperature is reduced to the critical temperature at which the transformation to martensite begins at a relatively high cooling rate, which can quickly pass through the most unstable region of austenite and cause the transformation of austenite to martensite, so that the surface of the steel bars is quenched into martensite and retained austenite structure, and the core is still in the austenite state due to the high temperature. Secondly, air cooling is carried out, and the heat in the core diffuses and conducts to the surface, making the internal and external temperatures of the steel bars approach each other, and the retained austenite on the surface transforms into martensite, while the core is still in the austenite state. Finally, a relatively slow cooling rate can make the internal and external temperatures of the steel bars decrease simultaneously, reach the transformation temperature of austenite to ferrite and pearlite, cause the core to start to transform, and reduce the tissue stress generated during the phase transformation, avoiding deformation and cracking caused by excessive stress, and finally obtaining the ideal required material.

[0011] In step S1, it is speculated that too low a cooling rate will cause the starting temperatures of the ferrite and pearlite phase transformations of the material to increase, while too high a cooling rate will cause the material to reach the martensite start transformation temperature before it has time to obtain a refined austenite structure. As a preference of the invention, in step S1, the cooling rate is 15 - 60 °C / s. For example, it can be 15 °C / s, 20 °C / s, 25 °C / s, 30 °C / s, 35 °C / s, 40 °C / s, 45 °C / s, 50 °C / s, 55 °C / s, 60 °C / s. Among them, within this range, the larger the cooling rate, the finer the austenite grains. Further preference is given to 40 - 60 °C / s.

[0012] In step S2, it is speculated that too low a cooling rate will cause the austenite structure to be unstable, while too high a cooling rate will cause too large a temperature difference between the inside and outside of the steel bar, affecting subsequent air-cooling tempering. As a preference of the present invention, in step S2, the cooling rate is 30 - 100 °C / s. For example, it can be 30 °C / s, 40 °C / s, 50 °C / s, 60 °C / s, 70 °C / s, 80 °C / s, 90 °C / s, 100 °C / s. Among them, within this range, the larger the cooling rate, the smaller the austenite grains in the core. Further preference is given to 80 - 100 °C / s.

[0013] As a preference of the present invention, the cooling rate in step S2 is 1.5 - 2 times the cooling rate in step S1.

[0014] In step S4, within the cooling rate range not higher than 3 °C / s (usually 0.5 - 3 °C / s), the inventor has found through research that as the cooling rate increases, the pearlite lamellar spacing gradually decreases. Decreasing the pearlite lamellar spacing can improve both the strength and toughness of the steel. As a preference of the present invention, in step S4, the cooling rate is 2 - 3 °C / s. For example, it can be 2 °C / s, 2.5 °C / s, 3 °C / s, with preference given to 3 °C / s.

[0015] The cooling form is not restricted. In some embodiments, for specimens with smaller dimensions, a Gleeble-3500 thermal simulation testing machine can be used to control the cooling rate. Its temperature range is from room temperature to 1450 °C, and the temperature control accuracy is ±1 °C. The cooling methods can be heat transfer cooling, compressed air cooling, and aerosol cooling.

[0016] In some embodiments, for specimens with larger dimensions, immersion cooling in a cooling medium can be used. The cooling rate can be achieved by adjusting the type of cooling medium, the flow rate of the cooling medium, the temperature of the cooling medium, and the concentration of the cooling medium. Commonly used cooling media include air, nitrogen, helium, water, brine, alkaline water, oil, polyalkylene glycol aqueous solution, sodium polyacrylate aqueous solution, polyvinyl alcohol aqueous solution, etc. The cooling medium is closely related to the temperature change of the material and the evolution law of the tissue field.

[0017] As preferred steps S1 and S2 of the present invention, a liquid is used as the cooling medium, and the liquid is one of oil, PAG quenching agent, and PAS quenching agent. The liquid cooling medium has a greater cooling capacity at high temperatures, a relatively fast cooling rate, a higher content of martensite transformed from supercooled austenite on the surface of the steel bar, and can improve the hardness of the material.

[0018] As a preference of the present invention, in step S4, a gas is used as the cooling medium, and the gas is at least one of air, nitrogen, and helium. The gas cooling medium has a smaller cooling rate in the low-temperature region, can reduce the tissue stress of the material, and reduce the tendency of deformation and cracking.

[0019] Secondly, another object of the present invention is to provide a production method for HRB400E earthquake-resistant ribbed steel bars, which sequentially includes a melting process, a controlled rolling process, and the controlled cooling process as described above.

[0020] Melting is to process raw materials through processes such as decarburization, dephosphorization, desulfurization, deoxidation, removal of harmful gases and non-metallic inclusions. The specific melting means is not limited and can be the same as the prior art.

[0021] Controlled rolling mostly uses hot rolling. The material is heated to the single-phase austenite temperature range for rolling. There is no tissue stress inside the raw material, and single-phase austenite belongs to the face-centered lattice and is easy to deform. By reasonably controlling the metal heating system, deformation system, and temperature system, hot plastic deformation can be combined with solid-state phase transformation to obtain a fine grain structure. Controlled rolling can refine austenite grains through two methods. One is the recrystallization after austenite processing, and the other is rolling below the recrystallization temperature in the austenite region. The recrystallization state affects the subsequent controlled cooling effect. Therefore, as a preference of the present invention, before controlled cooling, by controlling the process of controlled rolling, the austenite does not recrystallize or only partially recrystallizes, and the strengthening effect of deformation on austenite is retained or partially retained in the deformed austenite. The deformation strengthening and phase transformation strengthening effects are added together to further improve the mechanical properties of the material.

[0022] As a preference of the present invention, it specifically includes the following steps:

[0023] S1. Heat the steel billet to 1100 - 1200 °C and perform rough rolling with a deformation amount of 30% - 40%; by rough rolling in the recrystallization zone, the austenite is deformed to produce extremely fine austenite grains.

[0024] S2. After rough rolling, cool the surface temperature of the steel bar to 900 - 950 °C, and then perform medium rolling with a deformation amount of 60% - 65%; accumulate dislocation strengthening and fine grain strengthening through medium rolling in the non-recrystallization zone. Among them, the cooling rate is preferably 40 - 60 °C / s.

[0025] After medium rolling, the surface temperature of the steel bar is cooled to 850 - 900 °C, and then finish rolling is carried out with a deformation amount of 10% - 20%; through finish rolling in the two-phase region, the non-transformed γ grains are further elongated to form deformation bands, and the transformed α grains are compressed to form substructures. Among them, the cooling rate is preferably 40 - 60 °C / s.

[0026] Finally, another object of the present invention is to provide an HRB400E earthquake-resistant ribbed steel bar. After being processed by the above-mentioned controlled cooling process, the hardness of this tensile ribbed steel bar can reach 253 HV 10 , and the tensile strength can reach 633 MPa; after combining with the above-mentioned controlled rolling process, the hardness can reach 269 HV 10 , and the tensile strength can reach 648 MPa; it has good mechanical properties.

[0027] The composition of the ribbed steel bar is not restricted. As a preference of the present invention, in the ribbed steel bar, by mass, it includes 0.22% - 0.25% C, 0.40% - 0.50% Si, 1.35% - 1.45% Mn, 0.015% - 0.020% Ni, 0.015% - 0.025% Cu, 0.025% - 0.035% Cr, 0.010% - 0.020% V, S ≤ 0.020%, P ≤ 0.040%, and the balance is Fe.

[0028] The beneficial effects of the present invention:

[0029] 1. The present application provides a controlled cooling process for HRB400E earthquake-resistant ribbed steel bars, which improves the mechanical properties of the material by reasonably controlling the cooling rate during the cooling process.

[0030] 2. The present application provides a production method for HRB400E earthquake-resistant ribbed steel bars, which combines the controlled rolling process and the controlled cooling process, effectively combines the deformation strengthening and phase transformation strengthening of the material, and further improves the mechanical properties of the material.

[0031] 3. The present application provides an HRB400E earthquake-resistant ribbed steel bar, with a hardness that can reach 269 HV 10 , and a tensile strength that can reach 648 MPa, having good mechanical properties. Description of the Drawings

[0032] Figure 1 is the microstructural diagram of the material obtained in Example 1. Detailed Embodiments

[0033] The following are the detailed embodiments of the present invention, and the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0034] Example 1

[0035] An HRB400E earthquake-resistant ribbed steel bar is prepared through the following steps:

[0036] Take the intermediate billet after rough rolling of φ8mm coil bar, process it into a φ6mm×15mm specimen, and the chemical composition (mass fraction, %) determined by spectroscopic method is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe. Heat the specimen to 1050°C and hold for 5 minutes, then immediately carry out a controlled cooling process in a thermal simulation testing machine. The controlled cooling process is as follows:

[0037] S1. Primary cooling: Cool the rolled steel bar, with a cooling rate of 15°C / s, until the surface temperature of the steel bar reaches 700°C;

[0038] S2. Secondary cooling: Continue to cool the steel bar, with a cooling rate of 30°C / s, until the surface temperature of the steel bar reaches 400°C;

[0039] S3. Air cooling: Air cool the steel bar until the surface of the steel bar is tempered to 650°C;

[0040] S4. Tertiary cooling: Continue to cool the steel bar, with a cooling rate of 3°C / s, until the surface temperature of the steel bar reaches room temperature.

[0041] Cut the obtained material, after grinding and polishing, etch it with a 4% nitric acid alcohol solution by volume fraction, and observe the microstructure of the core of each specimen under an Axioplan2 Imaging Zeiss optical microscope and an FEI-Nova 400 scanning electron microscope, as Figure 1 shown, the core structure is mainly polygonal ferrite and pearlite.

[0042] Example 2

[0043] This example is basically the same as Example 1, and the difference is only that: the controlled cooling process is different, as follows:

[0044] S1. Primary cooling: Cool the rolled steel bar, with a cooling rate of 45°C / s, until the surface temperature of the steel bar reaches 700°C;

[0045] S2. Secondary cooling: Continue to cool the steel bar, with a cooling rate of 30°C / s, until the surface temperature of the steel bar reaches 400°C;

[0046] S3. Air cooling: Air cool the steel bar until the surface of the steel bar is tempered to 650°C;

[0047] S4. Tertiary cooling: Continue to cool the steel bars at a cooling rate of 3 °C / s until the surface temperature of the steel bars reaches room temperature.

[0048] Example 3

[0049] This example is basically the same as Example 1, and the only difference is that the controlled cooling process is different as follows:

[0050] S1. Primary cooling: Cool the rolled steel bars at a cooling rate of 45 °C / s until the surface temperature of the steel bars reaches 700 °C;

[0051] S2. Secondary cooling: Continue to cool the steel bars at a cooling rate of 90 °C / s until the surface temperature of the steel bars reaches 400 °C;

[0052] S3. Air cooling: Air-cool the steel bars until the surface of the steel bars is tempered to 650 °C;

[0053] S4. Tertiary cooling: Continue to cool the steel bars at a cooling rate of 3 °C / s until the surface temperature of the steel bars reaches room temperature.

[0054] Example 4

[0055] This example is basically the same as Example 1, and the only difference is that the controlled cooling process is different as follows:

[0056] S1. Primary cooling: Cool the rolled steel bars at a cooling rate of 15 °C / s until the surface temperature of the steel bars reaches 700 °C;

[0057] S2. Secondary cooling: Continue to cool the steel bars at a cooling rate of 90 °C / s until the surface temperature of the steel bars reaches 400 °C;

[0058] S3. Air cooling: Air-cool the steel bars until the surface of the steel bars is tempered to 650 °C;

[0059] S4. Tertiary cooling: Continue to cool the steel bars at a cooling rate of 3 °C / s until the surface temperature of the steel bars reaches room temperature.

[0060] Example 5

[0061] This example is basically the same as Example 1, and the only difference is that the controlled cooling process is different as follows:

[0062] S1. Primary cooling: Cool the rolled steel bars at a cooling rate of 15 °C / s until the surface temperature of the steel bars reaches 700 °C;

[0063] S2. Secondary cooling: Continue to cool the steel bars at a cooling rate of 30 °C / s until the surface temperature of the steel bars reaches 400 °C;

[0064] S3. Air cooling: Air-cool the steel bars until the surface of the steel bars is tempered to 650 °C.

[0065] S4. Tertiary cooling: Continuously cool the steel bars at a cooling rate of 0.5 °C / s until the surface temperature of the steel bars reaches room temperature.

[0066] Example 6

[0067] An HRB400E earthquake-resistant deformed steel bar is prepared by the following steps:

[0068] Take the intermediate billet after rough rolling of φ8mm coil bars, process it into a φ6mm×15mm specimen, and the chemical composition (mass fraction, %) measured by spectroscopy is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe. Heat the specimen to 1050 °C and hold for 5 min, then immediately carry out a controlled cooling process. The controlled cooling process is as follows:

[0069] S1. Primary cooling: Put the rolled steel bars into a cooling medium for cooling. The cooling medium is L-AN32 total loss system oil at 60 °C. In the range of 700 - 1050 °C, the maximum cooling rate is 50 °C / s, and cool until the surface temperature of the steel bars reaches about 700 °C.

[0070] S2. Secondary cooling: Continuously cool the steel bars. The cooling medium is L-AN32 + 8% cooling rate adjustment additive at 80 °C. In the range of 400 - 700 °C, the maximum cooling rate is 99 °C / s, and cool until the surface temperature of the steel bars reaches about 400 °C.

[0071] S3. Air cooling: Take the steel bars out of the cooling medium and carry out air cooling until the surface of the steel bars is tempered to about 650 °C.

[0072] S4. Tertiary cooling: Continuously cool the steel bars. The cooling medium is air under forced circulation at 0.15 MPa. The maximum cooling rate is 2.8 °C / s, and cool until the surface temperature of the steel bars reaches room temperature.

[0073] Example 7

[0074] An HRB400E earthquake-resistant deformed steel bar is prepared by the following steps:

[0075] Take the intermediate billet after rough rolling of φ8mm coil bars, process it into a φ6mm×15mm specimen, and the chemical composition (mass fraction, %) measured by spectroscopy is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe.

[0076] The specimen is heated to 1150 °C and rough rolled with a deformation of 38.8%. After rough rolling, the steel bar is cooled by water through cooling, with the water temperature at 30 °C, the water pressure at 0.6 MPa, and it comes out after 0.3 s, and the surface temperature of the steel bar is cooled to 930 °C. Then medium rolling is carried out with a deformation of 63.5%. After medium rolling, the steel bar is cooled by water through cooling, with the water temperature at 30 °C, the water pressure at 0.6 MPa, and it comes out after 0.3 s, and the surface temperature of the steel bar is cooled to 850 °C. Then finish rolling is carried out with a deformation of 11.2%.

[0077] Then an accelerated cooling process is immediately carried out, and the accelerated cooling process is as follows:

[0078] S1. Primary cooling: The rolled steel bar is put into a cooling medium for cooling. The cooling medium is L-AN32 total loss system oil at 60 °C. In the temperature range of 700 - 1050 °C, the maximum cooling rate is 50 °C / s, and it is cooled until the surface temperature of the steel bar reaches about 700 °C;

[0079] S2. Secondary cooling: The steel bar is continuously cooled. The cooling medium is L-AN32 + 8% cooling rate adjustment additive at 80 °C. In the temperature range of 400 - 700 °C, the maximum cooling rate is 99 °C / s, and it is cooled until the surface temperature of the steel bar reaches about 400 °C;

[0080] S3. Air cooling: The steel bar is taken out from the cooling medium and air cooled until the surface of the steel bar is tempered to about 650 °C;

[0081] S4. Tertiary cooling: The steel bar is continuously cooled. The cooling medium is air with forced circulation under 0.15 MPa, and the maximum cooling rate is 2.8 °C / s, and it is cooled until the surface temperature of the steel bar reaches room temperature.

[0082] Example 8

[0083] An HRB400E earthquake-resistant deformed steel bar is prepared through the following steps:

[0084] Take the intermediate billet after rough rolling of a φ8 mm coil bar and process it into a φ6 mm × 15 mm specimen. The chemical composition (mass fraction, %) measured by spectrometry is: 0.23 C, 0.48 Si, 1.39 Mn, 0.018 S, 0.031 P, 0.019 Ni, 0.021 Cu, 0.031 Cr, 0.013 V, and the balance is Fe.

[0085] Heat the specimen to 1150°C and perform rough rolling with a deformation of 38.8%. After rough rolling, place the steel bar in a cooling medium for cooling. The cooling medium is L-AN32 total loss system oil at 60°C, with a maximum cooling rate of 50°C / s, and cool until the surface temperature of the steel bar reaches 930°C. Then perform intermediate rolling with a deformation of 63.5%. After intermediate rolling, place the steel bar in a cooling medium for cooling. The cooling medium is L-AN32 total loss system oil at 60°C, with a maximum cooling rate of 50°C / s, and cool until the surface temperature of the steel bar cools to 850°C. Then perform finish rolling with a deformation of 11.2%.

[0086] Then immediately carry out the controlled cooling process, and the controlled cooling process is as follows:

[0087] S1. Primary cooling: Place the rolled steel bar in a cooling medium for cooling. The cooling medium is L-AN32 total loss system oil at 60°C. In the range of 700 - 1050°C, the maximum cooling rate is 50°C / s, and cool until the surface temperature of the steel bar reaches about 700°C;

[0088] S2. Secondary cooling: Continue to cool the steel bar. The cooling medium is L-AN32 + 8% cooling rate adjustment additive at 80°C. In the range of 400 - 700°C, the maximum cooling rate is 99°C / s, and cool until the surface temperature of the steel bar reaches about 400°C;

[0089] S3. Air cooling: Take the steel bar out of the cooling medium and perform air cooling until the surface of the steel bar is tempered to about 650°C;

[0090] S4. Tertiary cooling: Continue to cool the steel bar. The cooling medium is air with forced circulation at 0.15 MPa, and the maximum cooling rate is 2.8°C / s, and cool until the surface temperature of the steel bar reaches room temperature.

[0091] Comparative Example 1

[0092] Take the intermediate billet after rough rolling of φ8mm wire rod and process it into a φ6mm×15mm specimen. The chemical composition (mass fraction, %) determined by spectroscopic method is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe. Heat the specimen to 1050°C and hold for 5 min, then immediately carry out the controlled cooling process in a thermal simulation testing machine. The controlled cooling process is as follows:

[0093] Cool the steel bar at a cooling rate of 3°C / s until the surface temperature of the steel bar reaches room temperature.

[0094] Comparative Example 2

[0095] An HRB400E earthquake-resistant threaded steel bar is prepared by the following steps:

[0096] Take the intermediate billet after rough rolling of φ8mm wire rod and process it into a φ6mm×15mm specimen. The chemical composition (mass fraction, %) determined by spectroscopic method is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe. Heat the specimen to 1050°C and hold for 5 min, then immediately carry out a controlled cooling process in a thermal simulation testing machine. The controlled cooling process is as follows:

[0097] S1. Primary cooling: Cool the rolled steel bar, with a cooling rate of 30°C / s, until the surface temperature of the steel bar reaches 400°C;

[0098] S2. Air cooling: Air cool the steel bar until the surface of the steel bar is tempered to 650°C;

[0099] S3. Secondary cooling: Continue to cool the steel bar, with a cooling rate of 3°C / s, until the surface temperature of the steel bar reaches room temperature.

[0100] Comparative Example 3

[0101] An HRB400E earthquake-resistant ribbed steel bar is prepared through the following steps:

[0102] Take the intermediate billet after rough rolling of φ8mm wire rod and process it into a φ6mm×15mm specimen. The chemical composition (mass fraction, %) determined by spectroscopic method is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe. Heat the specimen to 1050°C and hold for 5 min, then immediately carry out a controlled cooling process in a thermal simulation testing machine. The controlled cooling process is as follows:

[0103] S1. Primary cooling: Cool the rolled steel bar, with a cooling rate of 15°C / s, until the surface temperature of the steel bar reaches 700°C;

[0104] S2. Secondary cooling: Continue to cool the steel bar, with a cooling rate of 30°C / s, until the surface temperature of the steel bar reaches 400°C;

[0105] S3. Tertiary cooling: Continue to cool the steel bar, with a cooling rate of 3°C / s, until the surface temperature of the steel bar reaches room temperature.

[0106] Comparative Example 4

[0107] An HRB400E earthquake-resistant ribbed steel bar is prepared through the following steps:

[0108] Take the intermediate billet after rough rolling of φ8mm wire rod and process it into a φ6mm×15mm specimen. The chemical composition (mass fraction, %) measured by spectroscopy is: 0.23C, 0.48Si, 1.39Mn, 0.018S, 0.031P, 0.019Ni, 0.021Cu, 0.031Cr, 0.013V, and the balance is Fe. Heat the specimen to 1050°C and hold for 5 minutes, then immediately conduct a controlled cooling process in a thermal simulation testing machine. The controlled cooling process is as follows:

[0109] S1. Primary cooling: Cool the rolled steel bar at a cooling rate of 15°C / s until the surface temperature of the steel bar reaches 700°C;

[0110] S2. Secondary cooling: Continue to cool the steel bar at a cooling rate of 30°C / s until the surface temperature of the steel bar reaches 400°C;

[0111] S3. Air cooling: Air cool the steel bar until the surface temperature of the steel bar reaches room temperature.

[0112] Mechanical property testing

[0113] Conduct mechanical property tests on the materials obtained in the examples and comparative examples:

[0114] According to GB / T231.1—2018 "Metallic materials—Brinell hardness test—Part 1: Test method", use a HV-1000B type Vickers hardness tester to test its hardness. The load weight is 10 kg, the holding time is 10 s, randomly select 7 points to measure the hardness of the specimen, remove the maximum and minimum values in the data, and take the average value. The test results are shown in Table 1 below.

[0115] Process the material into a 5mm standard tensile specimen with a gauge length of 25mm, 2 parallel specimens in each group. According to GB / T228.1—2021 "Metallic materials—Tensile testing—Part 1: Method of test at room temperature", conduct a room temperature tensile test on a WE-300 type tensile testing machine, and measure its tensile strength, yield strength, elongation after fracture, and total elongation at maximum force. The test results are shown in Table 1 below.

[0116] Table 1.

[0117]

[0118] As shown in Table 1, by comparing Example 1 with Comparative Examples 1 to 4, it can be seen that the controlled cooling technical solution of this application can achieve the effect of improving the mechanical properties of the material, and the technical solution of this application is an overall technical solution. Missing any step will affect the mechanical properties of the final material.

[0119] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A controlled cooling process for the production of HRB400E earthquake-resistant ribbed steel bars, characterized in that: It includes the following steps: S1. Primary cooling: Cool the rolled steel bars. The cooling rate is not less than 15 °C / s until the surface temperature of the steel bars reaches 700 - 750 °C. S2. Secondary cooling: Continue to cool the steel bars. The cooling rate is not less than 30 °C / s until the surface temperature of the steel bars reaches 350 - 450 °C. S3. Air cooling: Air-cool the steel bars until the surface of the steel bars is tempered to 600 - 650 °C. S4. Tertiary cooling: Continue to cool the steel bars. The cooling rate is not higher than 3 °C / s until the surface temperature of the steel bars reaches room temperature.

2. The controlled cooling process for the production of HRB400E earthquake-resistant ribbed steel bars according to claim 1, characterized in that: In step S1, the cooling rate is 40 - 60 °C / s.

3. The controlled cooling process for producing HRB400E earthquake-resistant ribbed steel bars according to claim 1, characterized in that: In step S2, the cooling rate is 80 - 100 °C / s.

4. A controlled cooling process for producing HRB400E earthquake-resistant ribbed steel bars according to claim 1, characterized in that: In step S4, the cooling rate is 2 - 3 °C / s.

5. The controlled cooling process for producing HRB400E earthquake-resistant deformed steel bars according to claim 1, characterized in that: In steps S1 and S2, a liquid is used as the cooling medium, and the liquid is one of oil, PAG quenching agent, and PAS quenching agent.

6. The controlled cooling process for producing HRB400E earthquake-resistant ribbed steel bars according to claim 1, characterized in that: In step S4, a gas is used as the cooling medium, and the gas is at least one of air, nitrogen, and helium.

7. A production method of HRB400E earthquake-resistant deformed steel bars, characterized in that: It sequentially includes a melting process, a controlled rolling process, and the controlled cooling process according to any one of claims 1 - 6.

8. A production method of HRB400E earthquake-resistant ribbed steel bars according to claim 7, characterized in that: The controlled rolling process includes the following steps: Heat the steel billet to 1100 - 1200 °C and perform rough rolling with a deformation amount of 30% - 40%; after rough rolling, cool the surface temperature of the steel bars to 900 - 950 °C, and then perform medium rolling with a deformation amount of 60% - 65%; after medium rolling, cool the surface temperature of the steel bars to 850 - 900 °C, and then perform finish rolling with a deformation amount of 10% - 20%.

9. The production method of an HRB400E earthquake-resistant ribbed steel bar according to claim 8, characterized in that: The cooling rates are independently 40 - 60 °C / s respectively.

10. An HRB400E earthquake-resistant threaded steel bar produced by the production method according to any one of claims 7 - 9.

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