A high-strength yield ratio HRB600E seismic-resistant steel bar and its preparation method

Abstract

This invention relates to a high-strength-to-yield ratio HRB600E seismic-resistant steel bar and its preparation method, belonging to the field of metallurgical technology. Its chemical composition is: C: 0.25–0.28%, Si: 0.55–0.75%, Mn: 1.32–1.38%, Cr: 0.28–0.32%, Ti: 0.08–0.12%, V: 0.06–0.10%, N: 0.015–0.020%, P≤0.025%, S≤0.025%, with the balance being Fe and unavoidable impurities. The preparation method includes converter smelting, LF refining, continuous casting, and controlled rolling and cooling processes. The HRB600E seismic-resistant steel bar alloy obtained by this invention has low cost, a yield strength of 620–660 MPa, a tensile strength of 780–840 MPa, and a strength-to-yield ratio of not less than 1.25, making it a low-cost, high-performance seismic-resistant building steel material.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a high-strength-yield-ratio HRB600E earthquake-resistant steel bar and its preparation method. Background Technology

[0002] In recent years, earthquakes and other geological disasters have occurred frequently around the world, causing significant losses to local countries and people. To improve the structural safety of buildings such as houses and factories, the proportion of earthquake-resistant steel reinforcement used is increasing. When a building is subjected to seismic wave impact or other external force impact, earthquake-resistant steel reinforcement can effectively delay the time of building fracture and prevent the building from collapsing in a short period of time, thereby improving the building's safety performance. Therefore, it requires high yield strength and a high strength-to-yield ratio.

[0003] In developing countries, lower-grade hot-rolled ribbed steel bars have long been used in construction. HRB335 steel bars account for over 60%, while HRB500 accounts for less than 10%, a significant gap compared to developed countries. Countries like the US, UK, Japan, and Germany rarely use HRB335 steel bars anymore; even when they do, it's only used for accent reinforcement, with higher-grade bars like HRB400 and HRB500 used for main reinforcement. HRB400 and HRB500 steel bars are highly sought after due to their higher yield strength and strength-to-yield ratio, resulting from the addition of alloying elements such as vanadium, niobium, titanium, and nitrogen.

[0004] Currently, in countries such as the United States, Canada, South Korea, Iran, and Japan, the usage of 400MPa grade steel bars has reached over 70%, and the usage of 600MPa grade steel bars has reached 15%. In countries such as Germany, France, and the United Kingdom, the proportion of 500MPa grade steel bars has reached over 70%, and the usage of 600MPa grade steel bars has reached over 40%. However, in developing countries, 600MPa grade steel bars are mostly in the initial stage and have not yet been practically applied.

[0005] Therefore, in the face of natural disasters such as earthquakes that may occur at any time, developing and promoting such steel bars is one of the important issues that researchers urgently need to address in order to prevent loss of property and life.

[0006] Publication number CN106636917A discloses a vanadium-containing high-strength hot-rolled earthquake-resistant steel bar (HRB600E) and its production method. Its chemical composition is: C 0.23–0.30%, Si 0.5–0.8%, Mn 1.20–1.60%, V 0.15–0.20%, P ≤0.035%, S ≤0.030%, N 0.015–0.025%. By controlling the V and N content in the steel, the formation and precipitation of fine V(C,N) particles are promoted. Strict control of steelmaking and rolling process parameters significantly improves the strength of the steel bar, and all indicators meet the requirements for earthquake-resistant steel bars, making it an excellent technical solution. However, the V content in this steel reaches ≥0.15wt%, resulting in high alloy costs, which is not conducive to large-scale promotion.

[0007] Publication No. CN113388781A discloses a method for producing HRB600E threaded steel bars from high-speed bar stock and the HRB600E threaded steel bars produced from high-speed bar stock. The chemical composition of the produced HRB600E threaded steel bars is: C 0.23–0.28%, Si 0.65–0.80%, Mn 1.25–1.45%, P ≤0.04%, S ≤0.035%, V 0.065–0.10%, Nb 0.008–0.02%, N 0.015–0.028%, B 0.0015–0.0035%, and Cr 0.1–0.2%. While the alloy content is low and the production cost is low, the nitrogen saturated solubility, calculated according to the disclosed composition system, is low, only about 0.010 wt%. Achieving the target value of 0.015–0.028 wt% presents significant production challenges and requires extremely high-level technological expertise, hindering widespread adoption. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention provides a high-strength yield ratio HRB600E seismic-resistant steel bar and its preparation method, the technical solution of which is as follows:

[0009] A high-strength yield ratio HRB600E seismic-resistant steel bar has the following chemical composition and mass percentage: C: 0.25-0.28%, Si: 0.55-0.75%, Mn: 1.32-1.38%, Cr: 0.28-0.32%, Ti: 0.08-0.12%, V: 0.06-0.10%, N: 0.015-0.020%, P≤0.025%, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0010] Furthermore, the steel bars are φ10~25mm in size; their microstructure, based on area percentage, consists of 50.2~51.7% ferrite, 5.5~6.9% bainite, and the remainder is pearlite.

[0011] Furthermore, the steel reinforcement has a yield strength ≥ 600 MPa, tensile strength ≥ 780 MPa, elongation after fracture A ≥ 18%, and a maximum total elongation Amax. gt ≥9%, strength-to-yield ratio ≥1.25.

[0012] The preparation method of the aforementioned high-strength yield ratio HRB600E seismic-resistant steel bar includes converter smelting, LF refining, continuous casting, and controlled rolling and controlled cooling processes; the controlled rolling and controlled cooling process includes primary rolling, intermediate rolling, recrystallization, finish rolling, and air cooling steps; wherein,

[0013] The initial rolling temperature is 1100–1130℃, the rolling speed is 2.5–6.5 m / s, and the rolling process consists of 6 passes.

[0014] The intermediate rolling temperature is 1000-1050℃, the rolling speed is 8.5-12.5m / s, and the rolling process consists of 6 passes.

[0015] Finishing temperature 900~930℃, rolling speed 14~18m / s, 6 passes;

[0016] After finishing rolling, the temperature is cooled to 580-630℃ by air, and finally air-cooled at a rate of 300-500℃ / min.

[0017] Furthermore, in the controlled rolling and cooling process, the continuously cast steel billet is heated in a furnace at 1150-1180℃ for 120-150 minutes before the initial rolling.

[0018] Furthermore, in the converter smelting process, the temperature of molten iron entering the furnace is ≥1280℃, and the molten iron contains 3.5~4.5wt% C, 0.4~0.6wt% Si, and 0.2~0.3wt% Mn.

[0019] Furthermore, in the converter smelting process, nitrogen is blown from the bottom throughout the process, and the carbon content in the molten steel at the end of the smelting process is ≥0.08wt%, and the temperature of the molten steel is 1640~1660℃. Slag addition is strictly prohibited during the tapping process. When 1 / 3 of the steel is tapped, high-carbon ferromanganese, high-carbon ferrochrome, ferrosilicon, and carbon powder are added to the ladle in sequence, and the addition is completed when 2 / 3 of the steel is tapped.

[0020] Furthermore, in the LF refining process, the ladle inlet temperature is ≥1560℃, nitrogen is introduced for soft blowing for 8-10 minutes, and the outlet temperature is 1550-1580℃.

[0021] Furthermore, in the LF refining process, the white residue, by weight percentage, comprises: CaO 55-60%, SiO2 12-14%, Al2O3 17-21%, TiO2 1.5-2.5%, MgO 6-7.5%, MnO+FeO <0.8%, P2O5 <0.06%, with the remainder being unavoidable impurities.

[0022] Furthermore, in the continuous casting process, the temperature of molten steel in the tundish is 1515–1530°C, argon gas protection is provided at the immersion nozzle, and the continuous casting speed is 1.35–1.45 m / min.

[0023] The beneficial effects of adopting the above technical solution are as follows:

[0024] In the composition design of this invention, strengthening elements such as 0.08–0.12 wt% Ti, 0.06–0.10 wt% V, and 0.015–0.020 wt% N are added. During solidification, the first precipitated TiN acts as heterogeneous nucleation sites, increasing the nucleation rate and refining the austenite grains. During controlled rolling and controlled cooling, the fine and dispersed precipitation of carbonitrides such as TiC, VN, and VC is controlled, refining the grains and pearlite structure, and improving the strength and plasticity of the steel. In the process design, air cooling is adopted to avoid the inconsistencies in macroscopic and microscopic metallographic structures caused by water cooling, ensuring uniform microstructure and properties.

[0025] In this invention, the solid solution strengthening ratios of Ti and V are 43.2% and 31.6%, respectively, while the precipitation strengthening ratios are 56.8% and 68.4%, with a grain size of 8-9. At room temperature, its microstructure is: F: 50.2-51.7%, B: 5.5-6.9%, with the remainder being P. This microstructure ensures both high yield strength and tensile strength, while also improving seismic performance, resulting in a strength-to-yield ratio greater than 1.25. Attached Figure Description

[0026] Figure 1 The image shows the microstructure of the Φ10mm steel bar in Example 1.

[0027] Figure 2 The image shows the microstructure of the Φ12mm steel bar in Example 1.

[0028] Figure 3 This is a microstructure diagram of the Φ15mm steel bar in Example 1. Detailed Implementation

[0029] The chemical composition and mass percentage of the high strength-to-yield ratio HRB600E seismic steel bar of this invention are as follows: C: 0.25-0.28%, Si: 0.55-0.75%, Mn: 1.32-1.38%, Cr: 0.28-0.32%, Ti: 0.08-0.12%, V: 0.06-0.10%, N: 0.015-0.020%, P≤0.025%, S≤0.025%, with the balance being Fe and unavoidable impurities.

[0030] The preparation method of the above-mentioned high-strength yield ratio HRB600E seismic-resistant steel bars includes converter smelting, LF refining, continuous casting, and controlled rolling and cooling processes. The specific steps are as follows:

[0031] (1) Converter smelting

[0032] ① Charging: 110-130 kg / t of scrap steel is charged into the top-and-bottom combined blowing converter. 钢 Then add 960-980 kg / t of molten iron. 钢 The molten iron temperature upon entering the furnace is ≥1280℃, and the molten iron contains 3.5~4.5wt% C, 0.4~0.6wt% Si, and 0.2~0.3wt% Mn.

[0033] ② Smelting: Place the oxygen lance and begin blowing, adding 20-30 kg / t 钢 Lime, 10-15 kg / t 钢 Lightly calcined dolomite, 1-3 kg / t 钢 Slag is made from iron ore and other materials, and nitrogen bottom blowing is maintained throughout the process. The final steel content of C in the smelting process is ≥0.08wt%, and the final temperature is 1640~1660℃.

[0034] ③ Tapping: Use a slag-blocking spout for tapping. Slag feeding is strictly prohibited. When 1 / 3 of the steel is tapped, add high-carbon ferromanganese, high-carbon ferrochrome, ferrosilicon, carbon powder and other alloy materials to the ladle in sequence according to the design composition. The addition is completed when 2 / 3 of the steel is tapped.

[0035] (2) LF Refining

[0036] ① Slag making: Control the ladle temperature at the station to ≥1560℃, lower the graphite electrode, and add lime, ferrosilicon powder, aluminum powder, dolomite, etc. to make white slag. According to the weight percentage, the white slag composition includes: CaO 55~60%, SiO2 12~14%, Al2O3 17~21%, TiO2 1.5~2.5%, MgO 6~7.5%, MnO+FeO<0.8%, P2O5<0.06%. The molten steel temperature at the end of slag making is 1580~1620℃.

[0037] ② Alloying: Add ferrotitanium, ferrovanadium, and ferrochromium nitride, test the bulk composition, and fine-tune to meet the requirements;

[0038] ③ Out of the station: Introduce nitrogen into the bottom of the ladle, gently blow for 8-10 minutes, and adjust the temperature to 1550-1580℃ before leaving the station.

[0039] (3) Continuous casting

[0040] ① Tundish metallurgy: The tundish has a built-in double baffle wall + filter + dam, and an external electromagnetic heating device to maintain the temperature of molten steel inside the ladle at 1515~1530℃;

[0041] ② Casting: Immersion nozzle argon protection, 2-machine 4-strand square billet casting machine, casting speed 1.35~1.45m / min, casting into rectangular billets with a cross section of 300mm×360mm.

[0042] (4) Controlled rolling and controlled cooling

[0043] ① Heating of steel billets: Place the continuously cast steel billets in a heating furnace at 1150~1180℃ and hold for 120~150min;

[0044] ② Controlled rolling and controlled cooling: The process is as follows: primary rolling → intermediate rolling → recrystallization → finish rolling → air cooling.

[0045] The initial rolling temperature is 1100–1130℃, the rolling speed is 2.5–6.5 m / s, and the rolling process consists of 6 passes.

[0046] The intermediate rolling temperature is 1000-1050℃, the rolling speed is 8.5-12.5m / s, and the rolling process consists of 6 passes.

[0047] Finishing temperature 900~930℃, rolling speed 14~18m / s, 6 passes;

[0048] After finishing rolling, the temperature is cooled to 580-630℃ by air, and finally air-cooled at a rate of 300-500℃ / min.

[0049] The chemical composition and specifications of the HRB600E seismic-resistant steel bars obtained in Examples 1-6 are shown in Table 1; the parameter control of each process is shown in Tables 2-5; and the specifications and mechanical properties of the steel bars are shown in Table 6.

[0050] Table 1. Chemical composition (wt%) and specifications (mm) of the reinforcing steel bars in each embodiment.

[0051] 1 10～15 0.25 0.55 1.36 0.015 0.015 0.30 0.09 0.10 0.016 2 16～25 0.25 0.55 1.38 0.018 0.017 0.32 0.10 0.09 0.018 3 16～25 0.28 0.58 1.32 0.020 0.022 0.28 0.08 0.08 0.015 4 10～25 0.26 0.63 1.36 0.016 0.010 0.28 0.12 0.06 0.019 5 10～15 0.26 0.72 1.34 0.018 0.016 0.29 0.12 0.06 0.020 6 16～25 0.27 0.75 1.33 0.016 0.019 0.29 0.11 0.08 0.020 7 10～15 0.26 0.60 1.35 0.018 0.018 0.29 0.11 0.07 0.018 8 16～25 0.28 0.66 1.37 0.017 0.021 0.31 0.10 0.09 0.019

[0052] Table 2. Converter smelting process parameters for each embodiment

[0053]

[0054] Table 3. Parameters of LF refining and continuous casting processes in each embodiment

[0055]

[0056]

[0057] Table 4. White residue composition (wt%) in the LF refining process of each embodiment.

[0058] 1 58.1 13.9 18.6 1.7 6.5 0.5 0.03 2 56.4 13.5 19.2 2.4 7.2 0.6 0.04 3 55.0 14.0 20.1 2.3 7.5 0.4 0.03 4 57.2 13.0 20.0 1.5 7.0 0.7 0.05 5 57.5 12.1 21.0 2.1 6.8 0.3 0.03 6 59.2 12.0 19.0 1.9 6.9 0.5 0.02 7 60.0 12.8 17.0 2.5 6.7 0.4 0.04 8 56.6 14.0 20.3 2.0 6.0 0.6 0.03

[0059] In Table 4, the rest are unavoidable impurity elements.

[0060] Table 5. Parameters of controlled rolling and controlled cooling processes in each embodiment

[0061]

[0062] Table 6. Mechanical properties of steel bars in each embodiment

[0063]

[0064]

[0065] Figures 1-3 In the microstructure, white represents polygonal ferrite, black represents bainite, and gray represents pearlite. The microstructure of Φ10mm, Φ12mm, and Φ15mm steel bars in Example 1, by area percentage, contains 50.2–51.7% ferrite, 5.5–6.9% bainite, and the remainder is pearlite. The microstructures of the steel bars in other examples are similar and are therefore omitted.

Claims

1. A high-strength yield ratio HRB600E seismic-resistant steel bar, characterized in that, The chemical composition and mass percentage of the steel bars are as follows: C: 0.25-0.28%, Si: 0.55-0.75%, Mn: 1.32-1.38%, Cr: 0.28-0.32%, Ti: 0.08-0.12%, V: 0.06-0.10%, N: 0.015-0.020%, P≤0.025%, S≤0.025%, with the balance being Fe and unavoidable impurities; The steel bars are φ10~25mm in size; their microstructure, based on area percentage, consists of 50.2~51.7% ferrite, 5.5~6.9% bainite, and the remainder is pearlite. The method for preparing the reinforcing steel bars includes converter smelting, LF refining, continuous casting, and controlled rolling and cooling processes; the controlled rolling and cooling process includes primary rolling, intermediate rolling, recrystallization, finish rolling, and air cooling steps; wherein, The initial rolling temperature is 1100–1130℃, the rolling speed is 2.5–6.5 m / s, and the rolling process consists of 6 passes. The intermediate rolling temperature is 1000-1050℃, the rolling speed is 8.5-12.5m / s, and the rolling process consists of 6 passes. Finishing temperature 900~930℃, rolling speed 14~18m / s, 6 passes; After finishing rolling, the temperature is cooled to 580-630℃ by air, and finally air-cooled at a rate of 300-500℃ / min.

2. The high-strength yield ratio HRB600E seismic-resistant steel bar according to claim 1, characterized in that, The steel reinforcement has a yield strength ≥600MPa, tensile strength ≥780MPa, elongation after fracture A ≥18%, and maximum total elongation Amax. gt ≥9%, strength-to-yield ratio ≥1.

25.

3. The method for preparing high-strength yield-to-weight ratio HRB600E seismic-resistant steel bars according to claim 1 or 2, characterized in that, It includes converter smelting, LF refining, continuous casting, and controlled rolling and cooling processes; the controlled rolling and cooling process includes primary rolling, intermediate rolling, recrystallization, finish rolling, and air cooling steps; wherein, The initial rolling temperature is 1100–1130℃, the rolling speed is 2.5–6.5 m / s, and the rolling process consists of 6 passes. The intermediate rolling temperature is 1000-1050℃, the rolling speed is 8.5-12.5m / s, and the rolling process consists of 6 passes. Finishing temperature 900~930℃, rolling speed 14~18m / s, 6 passes; After finishing rolling, the temperature is cooled to 580-630℃ by air, and finally air-cooled at a rate of 300-500℃ / min.

4. The method for preparing high-strength yield-to-weight ratio HRB600E seismic-resistant steel bars according to claim 3, characterized in that, In the controlled rolling and cooling process, the continuously cast steel billet is heated in a furnace at 1150-1180℃ and held for 120-150 minutes before the initial rolling.

5. The method for preparing high-strength yield ratio HRB600E seismic-resistant steel bars according to claim 3, characterized in that, In the converter smelting process, the temperature of molten iron entering the furnace is ≥1280℃, and the molten iron contains 3.5~4.5wt% C, 0.4~0.6wt% Si, and 0.2~0.3wt% Mn.

6. The method for preparing high-strength yield ratio HRB600E seismic-resistant steel bars according to claim 5, characterized in that, The converter smelting process is carried out with bottom-blowing nitrogen throughout. The carbon content in the molten steel at the end of the smelting process is ≥0.08wt%, and the steel temperature is 1640~1660℃. Slag addition is strictly prohibited during the tapping process. When 1 / 3 of the steel is tapped, high-carbon ferromanganese, high-carbon ferrochrome, ferrosilicon, and carbon powder are added to the ladle in sequence, and the addition is completed when 2 / 3 of the steel is tapped.

7. The method for preparing high-strength yield-to-weight ratio HRB600E seismic-resistant steel bars according to claim 6, characterized in that, In the LF refining process, the ladle inlet temperature is ≥1560℃, nitrogen is introduced for soft blowing for 8-10 minutes, and the outlet temperature is 1550-1580℃.

8. The method for preparing high-strength yield ratio HRB600E seismic-resistant steel bars according to claim 7, characterized in that, The LF refining process, by weight percentage, comprises the following white slag components: CaO 55-60%, SiO2 12-14%, Al2O3 17-21%, TiO2 1.5-2.5%, MgO 6-7.5%, MnO+FeO <0.8%, P2O5 <0.06%, with the remainder being unavoidable impurities.

9. The method for preparing high-strength yield ratio HRB600E seismic-resistant steel bars according to any one of claims 3-8, characterized in that, In the continuous casting process, the temperature of molten steel in the tundish is 1515–1530℃, argon gas protection is provided at the immersion nozzle, and the continuous casting speed is 1.35–1.45 m / min.

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