A corrosion-resistant HRB500cE steel bar and its preparation method

Abstract

This invention discloses an HRB500cE corrosion-resistant steel bar and its preparation method. The chemical composition of the corrosion-resistant steel bar, by mass percentage, is: C 0.14-0.17%, Si 0.45-0.55%, Mn 1.05-1.15%, Cr 1.05-1.25%, Ti 0.07-0.13%, Ni 0.48-0.62%, Cu 0.35-0.45%, Nb 0.06-0.12%, N 0.015-0.020%, B 0.003-0.005%, P≤0.025%, S≤0.025%, and Si+Mn≤1.65%, Ti+Nb≥0.18%, Cr+Ni+Cu≥2.0%, with the balance being Fe and unavoidable impurities. The preparation method includes continuous casting and low-temperature controlled rolling and cooling processes. The corrosion-resistant steel bar provided by this invention has excellent performance and low production cost.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular to a corrosion-resistant HRB500cE steel bar and its preparation method. Background Technology

[0002] The steel industry is a vital pillar of my country's national economic development, influencing the development levels of various sectors including infrastructure construction, railway transportation, machinery manufacturing, aerospace, and national defense. Currently, my country's steel production has ranked first in the world for many years, making it a major steel producer. However, it still lags behind becoming a steel powerhouse, primarily due to the significant gap in steel quality compared to industrialized countries, with many mid-to-high-end steel products still in the research and development stage.

[0003] Steel reinforcement is one of the most widely used steel materials in my country, and it is widely used in industrial and civil buildings. However, for a long time, more than 60% of these industrial and civil buildings have used low-grade HRB335 steel bars as the main reinforcement material for concrete, while the use of higher-grade HRB500 steel bars is less than 10%, which seriously affects the service life of reinforced concrete buildings.

[0004] Reinforcing steel strength and corrosion resistance are two key indicators of the structural durability of reinforced concrete. Currently, all main reinforcement bars in concrete structures of major industrialized countries worldwide use HRB500 grade or higher corrosion-resistant and seismic-resistant steel bars, while the use of HRB335 grade steel bars is prohibited. In 2017, based on the domestic metallurgical technology level, my country issued GB / T 33953-2017 Corrosion-Resistant Steel Bars for Reinforced Concrete, which specifies the technical standards for eight grades of corrosion-resistant steel bars in two grades: HRB400 and HRB500. Domestic steel companies have also successively carried out research and development work on various grades.

[0005] Publication number CN105950989A discloses a corrosion-resistant steel bar and its production method. The disclosed chemical composition of the corrosion-resistant steel bar is: C 0.15~0.23%, Si 0.30~0.65%, Mn 0.90~1.60%, P≤0.030%, S≤0.020%, Cr1.40~2.50%, Cu 0.20~0.40%, Ti 0.010~0.025%, N≤0.015%, O≤0.0020%. The method uses an induction furnace → continuous casting → rolling process to produce the corrosion-resistant steel bar. The product exhibits outstanding strength and corrosion resistance, making it an excellent technical solution. However, this method uses an induction furnace as the smelting equipment, making it more suitable for small-scale production and difficult to promote industrially.

[0006] Publication number CN113528962A discloses corrosion-resistant steel bars and their production methods. The chemical composition is as follows: C 0.02–0.08%, Si≤1%, Mn≤1%, Cr 4–8%, Mo≤2%, Cu 0.3–0.6%, Ni≤2%, N≤0.02%, 0.03%<P≤0.05%, S≤0.01%, and Si+Mn≤1%, Cr+Mo 4–8.5%, Cu+Ni+P 0.5–2.5%, with the balance being iron. This corrosion-resistant steel bar exhibits excellent corrosion resistance through strict composition design; however, the high Cr and Mo content leads to higher production and usage costs, hindering large-scale application. Summary of the Invention

[0007] The purpose of this invention is to provide a high-efficiency, low-cost HRB500cE corrosion-resistant steel bar and its preparation method through reasonable composition and process design.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0009] A type of HRB500cE corrosion-resistant steel bar has the following chemical composition and mass percentage: C 0.14~0.17%, Si 0.45~0.55%, Mn 1.05~1.15%, Cr 1.05~1.25%, Ti 0.07~0.13%, Ni 0.48~0.62%, Cu 0.35~0.45%, Nb 0.06~0.12%, N 0.015~0.020%, B 0.003~0.005%, P≤0.025%, S≤0.025%, and Si+Mn≤1.65%, Ti+Nb≥0.18%, Cr+Ni+Cu≥2.0%, with the balance being Fe and unavoidable impurities.

[0010] The principle for selecting components and determining the content range in this invention is as follows:

[0011] (1) C is an important solid solution strengthening element and a Nb and Ti carbide forming element, but excessive carbon will seriously affect the weldability of steel bars and will also form Cr. 23 C6 large-particle brittle carbides severely reduce the toughness and corrosion resistance of steel, so the designed addition amount is 0.14-0.17%.

[0012] (2) The design incorporates 0.07-0.13% Ti, 0.06-0.12% Nb with Ti+Nb≥0.18% and 0.010-0.015% N as precipitation strengthening elements. During the low-temperature controlled rolling and cooling process, it ensures that sufficient amounts of Ti and Nb carbonitrides are finely dispersed and precipitated, which refines the grains and matrix structure and improves the strength and toughness of the steel. At the same time, Ti, as a strong deoxidizer, significantly reduces the oxygen content in the steel.

[0013] (3) Si is an important strengthening element that can significantly improve the strength of steel and the corrosion resistance of reinforcing bars. It can also effectively deoxidize when mixed with Mn. However, if the content is too high, it will not be conducive to the weldability and toughness of the material. Therefore, the Si content is designed to be 0.45-0.55%. In addition to deoxidizing with Si, Mn is also a solid S element. However, if the manganese content is too high, it will increase the brittleness of the steel and reduce the weldability. Therefore, the Mn content is designed to be 1.05-1.15%, and Si+Mn≤1.65%.

[0014] (4) Cr, Ni, and Cu can effectively increase the corrosion resistance of steel bars. Cr can increase the corrosion potential of the steel matrix and form a dense Cr2O3 protective film on the surface of the steel. In this invention, which is an atmospheric concrete corrosion-resistant steel bar, the Cr content is limited to 1.05-1.25% to save costs. Ni can change the corrosion potential of steel in the positive direction and increase the structural stability of steel. Together with Cr, it can significantly improve the corrosion resistance of steel. The Ni content is designed to be 0.48-0.62%. Cu forms a rust-proof barrier layer on the steel matrix, but excessive Cu will form intergranular interactions between crystals, which can easily cause cracks. In this invention, the Cu content is limited to 0.35-0.45%. At the same time, to ensure sufficient corrosion resistance, the Cr+Ni+Cu ratio is limited to ≥2.0%.

[0015] (5) Adding 0.003 to 0.005% B mainly strengthens the grain boundaries. The B element segregates at the grain boundaries, which reduces the segregation concentration of C atoms at the grain boundaries, effectively inhibits the precipitation of proeutectoid ferrite, improves the hardenability of bainite, and promotes the formation of bainite.

[0016] (6) P and S are harmful elements, and the design limits are P≤0.025% and S≤0.025%.

[0017] The room temperature microstructure of the HRB500cE corrosion-resistant steel bar described in this invention is ferrite + (17-22%) pearlite + (5-8%) bainite, with a grain size of 9-12.

[0018] The HRB500cE corrosion-resistant steel bar described in this invention has a yield strength of 540–580 MPa, a tensile strength of 680–740 MPa, a strength-to-yield ratio ≥1.26, an elongation after fracture A ≥18%, and a maximum force total elongation A gt ≥11%.

[0019] The HRB500cE corrosion-resistant steel bar of this invention has a specification of Φ32~40mm.

[0020] To achieve the above objectives, the present invention also provides a method for preparing HRB500cE corrosion-resistant steel bars, including continuous casting, low-temperature controlled rolling and controlled cooling processes.

[0021] The continuous casting process described in this invention is as follows: tundish temperature 1520~1540℃, immersion nozzle argon protection, casting speed 2.3~2.8m / min.

[0022] The low-temperature controlled rolling and cooling process described in this invention involves heating the billet to 1020–1100°C, holding it at that temperature for 2–4 hours, and then rolling it.

[0023] The low-temperature controlled rolling and cooling process described in this invention is as follows: the initial rolling temperature is 930-980℃, and 6 passes are rolled; the intermediate rolling temperature is 830-900℃, and 6 passes are rolled; the finishing rolling temperature is 750-800℃, and 6 passes are rolled; after finishing rolling, the temperature is rapidly cooled to 470-540℃ by water, and then placed in a cooling bed for air cooling.

[0024] The technical solution of this invention has the following advantages:

[0025] When designing the composition, the content of various elements is limited according to their combined effects to make the composition system more comprehensive. For example, the composite addition of Ti, Nb, and N significantly increases the precipitation strengthening effect; limiting the Si+Mn content can ensure metallurgical deoxidation and sulfur fixation while avoiding toughness loss; limiting the Cr+Ni+Cu content ensures sufficient corrosion resistance; and adding B can strengthen grain boundaries and promote the formation of bainite.

[0026] A low-temperature controlled rolling and cooling process is designed to ensure microstructure refinement and sufficient bainite formation. Lower billet heating temperatures prevent complete dissolution of NbN and TiN, hindering austenite grain coarsening. Low-temperature rolling in the austenite+ferrite dual-phase region transforms the microstructure from deformed austenite into fine, equiaxed ferrite grains and pearlite without substructure, significantly improving the steel's strength and toughness. Post-rolling rapid water cooling to the bainite formation region not only inhibits the growth of precipitated carbonitrides but also allows some supersaturated austenite to form bainite, further enhancing the steel's strength.

[0027] Through reasonable composition and process design, the room temperature microstructure of the corrosion-resistant steel bar of this invention is ferrite + (17-22%) pearlite + (5-8%) bainite, with a grain size of 9-12, a yield strength of 540-580 MPa, a tensile strength of 680-740 MPa, a strength-to-yield ratio ≥1.26, an elongation after fracture A ≥18%, and a maximum force total elongation A gt ≥11%, which is superior to the performance of HRB500cE in the national standard. Attached Figure Description

[0028] Figure 1 The metallographic structure of the corrosion-resistant steel bar in Example 1 is shown.

[0029] Figure 2 The metallographic structure of the corrosion-resistant steel bar in Example 2 is shown.

[0030] Figure 3The metallographic structure of the corrosion-resistant steel bar in Example 3 is shown.

[0031] Figure 4 The metallographic structure of the corrosion-resistant steel bar in Example 4 is shown.

[0032] Figure 5 The metallographic structure of the corrosion-resistant steel bar in Example 5 is shown.

[0033] Figure 6 The metallographic structure of the corrosion-resistant steel bar in Example 6 is shown. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to specific embodiments.

[0035] A type of HRB500cE corrosion-resistant steel bar has the following chemical composition by mass percentage: C 0.14-0.17%, Si 0.45-0.55%, Mn 1.05-1.15%, Cr 1.05-1.25%, Ti 0.07-0.13%, Ni 0.48-0.62%, Cu 0.35-0.45%, Nb 0.06-0.12%, N 0.015-0.020%, B 0.003-0.005%, P≤0.025%, S≤0.025%, and Si+Mn≤1.65%, Ti+Nb≥0.18%, Cr+Ni+Cu≥2.0%, with the balance being Fe and unavoidable impurities.

[0036] The production method of HRB500cE corrosion-resistant steel bars includes the following steps:

[0037] (1) Continuous casting

[0038] ① Tundish metallurgy: The tundish has a built-in double baffle wall + filter + dam, and an external electromagnetic induction heating device to maintain the temperature of molten steel inside the ladle at 1520~1540℃;

[0039] ② Casting: Immersion-type argon gas protection for the sprue, casting on a 6-strand square billet casting machine with a casting speed of 2.3~2.8m / min, casting into small square billets with a cross section of 150mm×150mm.

[0040] (2) Low-temperature controlled rolling and cooling

[0041] ① Heating of steel billets: Place the continuously cast steel billets in a heating furnace at 1020~1100℃ and hold for 2~4 hours;

[0042] ② Rolling: The process is as follows: primary rolling → intermediate rolling → finish rolling → water cooling. The primary rolling temperature is controlled at 930-980℃, with 6 passes; the intermediate rolling temperature is controlled at 830-900℃, with 6 passes; the finish rolling temperature is controlled at 750-800℃, with 6 passes; after finish rolling, the temperature is rapidly cooled to 470-540℃ by water cooling, and then placed in a cooling bed for air cooling.

[0043] Examples 1-6

[0044] The chemical composition and specifications of the HRB500cE corrosion-resistant steel bars in each embodiment are shown in Table 1.

[0045] The production process parameters of HRB500cE corrosion-resistant steel bars in each embodiment are shown in Table 2.

[0046]

[0047]

[0048] The metallographic structures of the HRB500cE corrosion-resistant steel bars in each embodiment are shown below. Figures 1-6 In the image, the white particles represent the matrix ferrite, the gray precipitates represent pearlite, and the black precipitates represent bainite. Figures 1-6 It can be seen that its microstructure is ferrite + (17-22%) pearlite + (5-8%) bainite; the grain size is 9-12.

[0049] The mechanical properties of HRB500cE corrosion-resistant steel bars in each embodiment are shown in Table 3.

[0050]

[0051] As shown in Table 3, the HRB500cE corrosion-resistant steel bar provided by this invention has a yield strength of 540-580 MPa, a tensile strength of 680-740 MPa, an elongation after fracture A≥18%, and a maximum force total elongation Amax. gt With a strength-to-yield ratio ≥11%, a strength-to-yield ratio ≥1.26, and a yield-to-yield ratio ≤1.16, all performance indicators are superior to the requirements of GB / T 33953-2017 "Corrosion-resistant steel bars for reinforced concrete", making it one of the preferred materials for corrosion-resistant steel bars in construction.

Claims

1. A corrosion-resistant steel bar of HRB500cE, characterized in that: The chemical composition of the steel reinforcement, by mass percentage, is: C 0.14–0.17%, Si 0.45–0.55%, Mn 1.05–1.15%, Cr 1.05–1.25%, Ti 0.07–0.13%, Ni 0.48–0.62%, Cu 0.35–0.45%, Nb 0.06–0.12%, N 0.015–0.020%, B The steel bar contains 0.003–0.005% Fe, P ≤ 0.025% P, S ≤ 0.025% P, and Si + Mn ≤ 1.65%, Ti + Nb ≥ 0.18%, Cr + Ni + Cu ≥ 2.0%, with the balance being Fe and unavoidable impurities; the steel bar is prepared by a low-temperature controlled rolling and cooling process; the steel bar has a yield strength of 540–580 MPa, a tensile strength of 680–740 MPa, a strength-to-yield ratio ≥ 1.26, an elongation after fracture A ≥ 18%, and a maximum force total elongation A gt ≥11%; the steel bars are Φ32~40mm in size.

2. The HRB500cE corrosion-resistant steel bar according to claim 1, characterized in that: The room temperature microstructure of the steel bars is ferrite + (17-22%) pearlite + (5-8%) bainite, with a grain size of 9-12.

3. The method for preparing HRB500cE corrosion-resistant steel bars according to claim 1 or 2, characterized in that, This includes continuous casting and cryogenic controlled rolling and cooling processes.

4. The method for preparing HRB500cE corrosion-resistant steel bars according to claim 3, characterized in that, The continuous casting process includes: tundish temperature of 1520–1540℃, argon gas protection at the immersion nozzle, and casting speed of 2.3–2.8 m / min.

5. The method for preparing HRB500cE corrosion-resistant steel bars according to claim 3, characterized in that, The low-temperature controlled rolling and cooling process involves heating the billet to 1020–1100℃, holding it at that temperature for 2–4 hours, and then rolling it through primary rolling, intermediate rolling, and finish rolling.

6. The method for preparing HRB500cE corrosion-resistant steel bars according to claim 5, characterized in that, The low-temperature controlled rolling and cooling process involves controlling the initial rolling temperature to 930–980°C, the intermediate rolling temperature to 830–900°C, and the finishing rolling temperature to 750–800°C. After finishing rolling, the temperature is rapidly cooled in water to 470–540°C, and then placed in a cooling bed for air cooling.

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