HRB500ce hot-rolled corrosion-resistant and anti-seismic steel bar and preparation method thereof

Abstract

The application discloses HRB500cE hot-rolled corrosion-resistant and anti-seismic steel bars and a preparation method thereof, and relates to the technical field of steel production. The volume content of the microstructure of the steel bar comprises the following: 38-41% of ferrite, ≤10% of pearlite, and the balance of bainite. By controlling the content of Cr, Ni and Cu, the steel bar oxidation can be prevented, and the corrosion resistance and mechanical properties of the steel bar are improved; by further controlling the content of Nb and V and the content of other elements, Nb-V compound carbonitride can prevent abnormal growth of austenite grains, play a role in refining ferrite grain in the cooling process of austenite transformation, and refine the pearlite interlamellar spacing, and a certain amount of bainite is obtained. Such organization design can guarantee the strength of the steel bar, improve the corrosion resistance of the steel bar, and does not reduce the ductility and plasticity of the steel bar, and effectively solves the problem that the strength and plasticity of high-strength corrosion-resistant HRB500cE steel bars are difficult to be considered.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and more specifically, to an HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar and its preparation method. Background Technology

[0002] HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars are a type of steel resistant to chloride ion corrosion, and are therefore widely used in the field of seawater corrosion protection technology. They can be used as raw materials for reinforced concrete structures such as coastal ports, wharves, and cross-sea bridges. Studies have shown that losses caused by steel corrosion are six times the combined losses from natural disasters such as floods, fires, hurricanes, and earthquakes. Therefore, the disasters and losses caused by steel corrosion are enormous. Furthermore, with my country's coastline exceeding 32,000 kilometers, and the increasing number of reinforced concrete structures such as coastal ports and cross-sea bridges, more building complexes face the severe challenge of chloride ion corrosion. In addition, it is often difficult to balance the strength and ductility of high-strength steel bars. When the strength of the steel bar increases, its ductility decreases accordingly, and vice versa. Therefore, providing a HRB500cE steel bar with higher strength, better corrosion resistance, and a balance between ductility and strength is urgently needed.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide an HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar and its preparation method.

[0005] This invention is implemented as follows:

[0006] In a first aspect, the present invention provides an HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar, wherein the elemental composition of the steel bar, by mass percentage, includes: C: 0.12-0.16 wt%, Si: 0.40-0.60 wt%, Mn: 1.00-1.35 wt%, Cr: 0.70-1.10 wt%, Cu: 0.30-0.60 wt%, Ni:

[0007] 0.30–0.60 wt%, Nb: 0.012–0.018 wt%, V: 0.070–0.085 wt%, Alt: 0.025–0.040 wt%, P≤0.035 wt%, S≤0.035 wt%, N≤0.010 wt%, O≤30 ppm, with the balance being Fe and unavoidable impurities.

[0008] The volumetric composition of the microstructure of the reinforcing steel bars includes: 38-41% ferrite, ≤10% pearlite, and the remainder is bainite.

[0009] Secondly, the present invention provides a method for preparing HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars as described in any of the foregoing embodiments, comprising continuously casting refined steel molten steel into a billet and hot-rolling the billet.

[0010] The hot rolling process involves heating the billet at high temperature for an extended period and then rolling it in a single line. The single-line rolling process is a multi-stage, weakly cooled, temperature-controlled rolling process.

[0011] The present invention has the following beneficial effects:

[0012] This invention provides an HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar and its preparation method. By controlling the contents of Cr, Ni, and Cu, oxidation of the steel bar can be prevented, improving its corrosion resistance. Simultaneously, Ni and Cu also enhance the mechanical properties of the steel bar. Further control of the contents of Nb and V, as well as other elements, allows strain energy to induce the precipitation of Nb-V composite carbonitrides at the austenite grain boundaries during hot rolling, acting as a pinning agent. This prevents abnormal austenite grain growth during heating and controls austenite recrystallization during rolling, thus mitigating austenite degradation. Recrystallization leads to grain growth and refinement of austenite grains. Simultaneously, the further precipitation of Nb-V composite carbonitrides results in fine polygonal ferrite grains during the cooling process of austenite transformation, which also contributes to refining the ferrite grain size. This significantly refines the ferrite grain size in the steel reinforcement and reduces the pearlite lamellar spacing. At the same time, a certain amount of bainite is obtained, which can ensure the strength and corrosion resistance of the steel reinforcement without reducing its ductility and plasticity. This effectively solves the problem of balancing strength and plasticity in high-strength and corrosion-resistant HRB500cE steel reinforcement. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 An electron microscope image of the HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar provided in Embodiment 1 of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0017] HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars are an improved version of HRB500E steel, resistant to chloride ion corrosion. Compared to HRB500E steel, HRB500cE steel exhibits superior corrosion resistance. Therefore, to ensure its excellent performance, its elemental composition and proportions are more complex, and the process control requires higher precision. However, with the increase in reinforced concrete structures such as coastal ports and cross-sea bridges, the demand for HRB500cE steel with seawater corrosion resistance is also increasing. Therefore, reducing the cost of HRB500cE steel while improving its mechanical and corrosion resistance properties has been a persistent goal in this field.

[0018] In a first aspect, the present invention provides an HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar, wherein the elemental composition of the steel bar, by mass percentage, includes: C: 0.12-0.16 wt%, Si: 0.40-0.60 wt%, Mn: 1.00-1.35 wt%, Cr: 0.70-1.10 wt%, Cu: 0.30-0.60 wt%, Ni:

[0019] 0.30–0.60 wt%, Nb: 0.012–0.018 wt%, V: 0.070–0.085 wt%, Alt: 0.025–0.040 wt%, P≤0.035 wt%, S≤0.035 wt%, N≤0.010 wt%, O≤30 ppm, with the balance being Fe and unavoidable impurities.

[0020] Carbon is an effective strengthening element and an austenite-forming element, playing a role in solid solution strengthening. It can also form more pearlite in steel, further improving the strength of the steel. C can reduce the potential difference between different areas inside the steel bar, thereby reducing the corrosion rate.

[0021] Nitrogen is beneficial to the pitting corrosion resistance of steel; however, carbonitrides enriched at grain boundaries are prone to intergranular corrosion, reducing the corrosion resistance of steel. Therefore, it is necessary to control the ratio of nitrogen to carbon and the precipitation process of carbonitrides. Furthermore, carbonitrides can also reduce the plasticity of reinforcing steel, making the combined control of nitrogen and carbon content in reinforcing steel even more crucial. This invention, by controlling the C and N content within the aforementioned ranges, can balance the strength and plasticity of reinforcing steel, while simultaneously working with other alloying elements to improve the corrosion resistance of the reinforcing steel.

[0022] Silicon primarily enhances the strength of reinforcing bars through solid solution strengthening. It is also a deoxidizing element in steel and a ferrite-forming element. However, excessive Si content can reduce the plasticity of steel and deteriorate the weldability of reinforcing bars.

[0023] Manganese is a weak carbide-forming element. In smelting, it plays a role in deoxidation and eliminating the effects of sulfur. It can also lower the transformation temperature of austenite and refine ferrite grains, which is beneficial to improving the strength and toughness of steel bars. In addition, it can strengthen ferrite through solid solution and combine with harmful element sulfur to reduce the hot brittleness of steel bars. However, when the Mn content is too high, the plasticity, impact toughness, and weldability of steel bars will all decrease.

[0024] Chromium can form a dense chromium oxide film in steel, effectively preventing oxidation of the reinforcing steel and improving the corrosion resistance of the steel matrix. In addition, chromium is also an important element in the formation of ferrite and carbides, significantly affecting the microstructure and properties of the reinforcing steel. When the chromium content is too high, a large amount of bainite is easily formed in the reinforcing steel, affecting its ductility and plasticity. Therefore, the chromium content needs to be controlled within a certain range to ensure that the reinforcing steel contains a certain amount of bainite without affecting its ductility and plasticity.

[0025] Nickel, copper, and chromium are all major corrosion-resistant elements in steel bars. Nickel has strong resistance to acid and alkali corrosion, which can improve the strength of steel bars while maintaining their plasticity and toughness. Copper has good resistance to atmospheric corrosion and can also improve the strength and toughness of steel bars.

[0026] Vanadium primarily refines austenite grains and improves strength and toughness by precipitating fine V(C,N) structures that pin the austenite grain boundaries.

[0027] During the heating and rolling process of steel billets, niobium forms niobium carbonitride with carbon and nitrogen, which segregates at the austenite grain boundaries, effectively inhibiting austenite recrystallization. As a second phase particle, it prevents austenite grain growth and plays a role in grain refinement and strengthening, thereby improving the strength and toughness of steel bars. At the same time, the addition of Nb promotes the precipitation of fine Nb-V composite carbonitrides, further enhancing the strength and toughness matching of steel bars.

[0028] Furthermore, by controlling the content of nickel, copper, chromium, vanadium, and niobium, this invention enables the use of relatively less nickel, copper, and chromium to achieve the main anti-corrosion effect, while the fine-grain strengthening effect of vanadium and niobium composite reduces the raw material formulation cost of steel bars.

[0029] A small amount of aluminum can refine the grains and improve toughness. It also has antioxidant and corrosion-resistant properties. When used in combination with chromium and silicon, it can improve the high-temperature corrosion resistance of steel bars.

[0030] By controlling the elemental composition of the reinforcing steel within the aforementioned range, the resulting microstructure comprises: 38-41% ferrite, ≤10% pearlite, and the remainder bainite. Due to the low pearlite content and the 38-41% ferrite content, the microstructure of the reinforcing steel contains approximately 50% bainite, thus ensuring its strength. Furthermore, the ferrite content ensures the steel's plasticity; the combination of these two factors results in excellent yield strength, elongation after fracture, and total elongation at maximum force. Additionally, controlling the bainite content also enhances the steel's corrosion resistance.

[0031] In an optional embodiment, the elemental composition of the reinforcing steel, by mass percentage, includes: C: 0.12–0.16 wt%, Si: 0.40–0.60 wt%, Mn: 1.00–1.35 wt%, Cr: 0.70–1.10 wt%, Cu: 0.30–0.45 wt%, Ni: 0.30–0.45 wt%, Nb: 0.012–0.018 wt%, V: 0.070–0.080 wt%, Alt: 0.025–0.040 wt%, P ≤ 0.035 wt%, S ≤ 0.035 wt%, N ≤ 0.010 wt%, O ≤ 30 ppm, with the balance being Fe and unavoidable impurities. Further optimizing the elemental composition of the reinforcing steel within the above ranges allows for the simultaneous acquisition of HRB500cE hot-rolled corrosion-resistant and earthquake-resistant reinforcing steel with both good mechanical properties and corrosion resistance.

[0032] In an optional implementation, the yield strength R of the hot-rolled corrosion-resistant and earthquake-resistant steel bar eL ≥540MPa, tensile strength R m ≥850MPa, elongation A≥20.0%, total elongation at maximum force A gt ≥9.5%, R 0 m / R 0 eL ≥1.35, R 0 eL / R eL ≤1.18, average corrosion rate ≤4.1 g / m 2 •h, with a relative corrosion rate ≤67% compared to HRB500E steel reinforcement.

[0033] In an optional embodiment, the volume content of the microstructure of the hot-rolled corrosion-resistant and earthquake-resistant steel bar includes: 40-41% ferrite, ≤8% pearlite, the balance being bainite, and a grain size of 9.5 or higher.

[0034] In order to improve the performance of steel bars in all aspects, in addition to controlling the elemental composition of the steel bars, the manufacturing process also needs to be controlled in order to ensure that the elemental composition can form the expected bainite content, ferrite content and pearlite content.

[0035] In a second aspect, the present invention provides a method for preparing reinforcing bars as described in any of the foregoing embodiments, comprising continuously casting refined molten steel into a billet and hot rolling the billet.

[0036] The hot rolling process involves heating the billet at high temperature for an extended period and then rolling it in a single line. The single-line rolling process is a multi-stage, weakly cooled, temperature-controlled rolling process.

[0037] In some embodiments, to clearly illustrate the preparation method of the HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar of the present invention, the following steps are included:

[0038] S01, Steel smelting

[0039] In an optional implementation, the steelmaking process includes smelting molten iron in a converter to obtain molten steel, and then sending the molten steel to an argon station for argon blowing and LF refining to obtain refined molten steel.

[0040] The purpose of steelmaking is to ensure that the content of each element in the refined steel is within the range required by the steel grade. Therefore, in order to achieve the above goal, the steelmaking process can be adjusted according to the specific conditions of each furnace of steel. The following is a preferred steelmaking scheme provided by the present invention, which can quickly and accurately adjust the components in the steel to the range required by the steel grade.

[0041] Preferably, the converter smelting adopts conventional top-and-bottom combined blowing oxygen converter smelting, with argon gas blowing throughout the steel tapping process. When the converter has tapped 1 / 4 of the steel, aluminum, silicon, manganese, chromium, copper, and nickel sources, along with scrap steel, are added sequentially to the molten steel for deoxidation and alloying. The molten steel is then sent to the argon station for argon blowing. This not only allows for the adjustment of the content of some alloying elements in the molten steel beforehand, but also ensures a more uniform composition and temperature of the molten steel.

[0042] Preferably, in order to improve the yield of various raw material alloys and achieve uniform alloy distribution, the argon blowing time at the argon station is greater than or equal to 6 minutes.

[0043] The silicon source can be ferrosilicon and / or silicomanganese. When the silicon source is ferrosilicon and silicomanganese, silicomanganese should be added to the molten steel first, followed by ferrosilicon. Additionally, silicomanganese can also be used as a manganese source to adjust the manganese content in the molten steel. The chromium source can be ferrochrome, and the copper and nickel sources can be copper plates and nickel plates, or their corresponding alloys as raw materials.

[0044] Molten steel exiting the argon station is sent to the LF furnace for refining via a ladle. In an optional implementation, during the LF refining process, the mass ratio of lime to molten steel is 3–6 kg / t, and the mass ratio of fluorite to molten steel is 0.5–1 kg / t. The addition of lime and fluorite is for slag formation during the LF smelting process, and also assists in desulfurization and deoxidation during the refining process.

[0045] Preferably, after adding lime and fluorite, the slag is slag-forming by electrolysis for 8–15 minutes.

[0046] Preferably, after the electrolytic slag is completed, a deoxidizer is added to produce white slag, and niobium source and vanadium source are added to adjust the element content in the molten steel. When the temperature of the refined molten steel is 1600℃, a calcium wire of 100-150m is fed and the soft blowing argon time is greater than or equal to 10min to obtain refined molten steel.

[0047] S02, continuous casting

[0048] The refined steel obtained from S01 is continuously cast into multiple billets. In an optional embodiment, during the continuous casting process, the temperature of the molten steel during continuous pouring in the tundish is 1520–1560°C, and the casting speed is 2.2–3.0 m / min. By controlling the above continuous casting parameters, the continuous casting process can be ensured to proceed smoothly, avoiding leakage due to excessively high molten steel temperature and preventing agglomeration in the crystallizer due to excessively low molten steel temperature.

[0049] S03, hot rolled

[0050] The billet obtained after continuous casting of SO2 is heated and rolled. The heated rolling includes single-line rolling after high-temperature long heating of the billet. The single-line rolling is multi-stage weak cooling temperature control rolling.

[0051] In an optional embodiment, during the high-temperature, long-duration heating process, the billet spends more than 120 minutes in the furnace, and the heating rate is 15–20 °C / s. Preferably, the temperature of the soaking zone in the furnace is 1140–1180 °C.

[0052] High-temperature, prolonged heating can fully dissolve the alloying elements in steel bars. However, the heating temperature of the billet should not be too high. Excessive heating temperature will not only cause coarse grains and damage the mechanical properties of the material, but also cause overheating of the crystals. Therefore, controlling the heating time and temperature of the billet within the above range can ensure the full dissolution of alloying elements without causing adverse effects.

[0053] Preferably, in order to ensure that the parameters of the above-mentioned high-temperature long heating process meet the above requirements, it can be achieved by controlling the temperature of the heating furnace. For example, the temperature of the heating section of the heating furnace is 990 to 1110°C.

[0054] Preferably, the heating section of the heating furnace includes a first heating section and a second heating section, wherein the temperature of the first heating section is 990–1030°C and the temperature of the second heating section is 1070–1110°C.

[0055] After the billet is heated in the heating furnace, it enters the rolling mill for single-line rolling. The single-line rolling adopts multi-stage weak cooling temperature control rolling. In an optional embodiment, multi-stage weak cooling temperature control rolling includes roughing, intermediate rolling, pre-finishing rolling and finishing rolling of the heated billet. Roughing, intermediate rolling and pre-finishing rolling are pre-rolling processes. The rolled piece obtained after pre-finishing rolling is an intermediate billet. Then, the intermediate billet is controlled-cooled and finished rolled to obtain the finished rolled piece.

[0056] Preferably, the initial rolling temperature for rough rolling is 990–1030℃. Temperatures that are too high or too low will negatively impact the temperature control rolling process and deformation control of the cast billet. Increased rolling temperature leads to increased deformation, making recrystallization more likely. By controlling the initial rolling temperature within the above range, the uniformity of the austenite structure after hot deformation is affected by both the deformation amount and the rolling temperature. Increased deformation and higher rolling temperature are beneficial for the uniform distribution of austenite.

[0057] The roughing, intermediate rolling and pre-finishing rolling processes can be carried out using existing rolling methods to obtain intermediate billets. Since the temperature of the steel bars will continue to rise during the rolling process, in order to better control the microstructure of the steel bars during the finishing rolling process, the intermediate billets need to be cooled and temperature controlled before finishing rolling to prevent the temperature of the intermediate billets from being too high, which would cause unfavorable microstructures to grow during the rolling process.

[0058] Preferably, the cooling rate of the intermediate billet before finishing rolling is 5-15℃ / s, and the starting temperature of finishing rolling is 960-1000℃. More preferably, the starting temperature of finishing rolling is 960-980℃.

[0059] By controlling the cooling rate of the intermediate billet within the aforementioned range before finishing rolling and performing finishing rolling at the aforementioned starting temperature, the adverse effects of temperature rise on the microstructure of the reinforcing steel can be offset. This prevents excessively high temperatures in the intermediate billet from causing austenite grain growth within the microstructure, or excessively low temperatures from causing microstructure transformation and precipitation of secondary cementite. This invention fully utilizes controlled rolling and controlled cooling combined with the precipitation strengthening and grain refinement effects of Nb-V composite precipitation forming carbonitrides to obtain HRB500cE hot-rolled corrosion-resistant and earthquake-resistant reinforcing steel with superior microstructure and properties.

[0060] Preferably, the cooling rate of the intermediate billet before finishing rolling is controlled by controlling the amount of water passing through the water purifier before finishing rolling. For example, in some embodiments, both sets of water purifiers before finishing rolling must be put into operation, and the amount of water in the second set of water purifiers is controlled to be greater than that in the first set of water purifiers, with a difference of 10-20%. By increasing the amount of water before finishing rolling, more cooling capacity is provided to the billet.

[0061] To control the high bainite content in the steel bars, for example, the water volume of the first set of water-feeding devices before finishing rolling can be controlled to be 80-90%, and the water volume of the second set of water-feeding devices can be 100%.

[0062] Preferably, after the intermediate billet is finished and a finished steel section is obtained, the finished steel section needs to be controlled-cooled before it can be sent to a cooling bed for further cooling to ensure that the final steel reinforcement morphology meets the requirements. Specifically, the cooling rate of the finished steel section is less than or equal to 1.5℃ / s, and the temperature of the finished steel section on the cooling bed is 950~990℃.

[0063] To ensure slow cooling of the steel bars after finishing rolling, only the first two sets of water purifiers are opened, while the remaining four sets are completely closed. Furthermore, the water volume of the last set is 15-25% lower than that of the first set. By using a gradually decreasing cooling water volume to cool the finished steel bars, the slow cooling of the finished steel bars is achieved, which is conducive to the morphological transformation of the bainite structure in the microstructure.

[0064] For example, the water volume of the first set of water purifiers after finishing rolling is 100%, and the water volume of the second set of water purifiers is 80%.

[0065] After cooling to the upper cooling bed temperature at the above cooling rate, the finished rolled part is sent to the cooling bed for cooling. By controlling the high upper cooling bed temperature and the low cooling rate, the composition and proportion of each phase in the microstructure of the steel bar can be precisely controlled.

[0066] Example 1

[0067] This embodiment provides an HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar, whose elemental composition by mass percentage includes: C: 0.16wt%, Si: 0.52wt%, Mn: 1.21wt%, Cr: 0.79wt%, Cu: 0.40wt%, Ni: 0.40wt%, Nb: 0.016wt%, V: 0.073wt%, Alt: 0.031wt%, P: 0.019wt%, S: 0.009wt%, N: 0.0080wt%, O ≤ 30ppm, with the balance being Fe and unavoidable impurities.

[0068] This embodiment also provides a method for preparing HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars, including the following steps:

[0069] S01, Steel smelting

[0070] Molten iron is added to a conventional top-and-bottom combined oxygen converter for converter smelting. Argon gas is blown throughout the steel tapping process. When the converter taps 1 / 4 of the steel, aluminum blocks, ferrosilicon, ferromanganese silicon, ferrochrome, copper plates, nickel plates and scrap steel are added to the molten steel in sequence for deoxidation and alloying. Then the ladle is sent to the argon station for argon blowing for 10 minutes.

[0071] Molten steel from the argon station is sent to the LF furnace for refining via a ladle. Slag is added at a ratio of 500 kg lime and 100 kg fluorite. After slag is energized and heated for 10 minutes, a deoxidizer is added to create white slag. Simultaneously, ferroniobium, vanadium-nitrogen alloy, and other alloys are added to fine-tune the composition. Once the composition and temperature reach 1600℃, 100 m of pure calcium wire is fed, and argon is blown softly for 12 minutes to obtain refined molten steel.

[0072] S02, continuous casting

[0073] The refined molten steel obtained from S01 was continuously cast into multiple billets. The temperature of the molten steel during continuous casting in the tundish was 1550℃, the specific water flow rate of the continuous casting machine was 1.6L / t, and the casting speed was 2.5m / min.

[0074] S03, hot rolled

[0075] The slab obtained after continuous casting of SO2 is heated and rolled. The slab spends 120 minutes in the heating furnace, and the heating rate is 15℃ / s. The temperature of the first heating section of the heating furnace is 1000℃, the temperature of the second heating section is 1100℃, and the temperature of the soaking section is 1160℃.

[0076] After the billet is heated in the heating furnace, it enters the rolling mill for rough rolling, intermediate rolling, pre-finish rolling and finish rolling in sequence. Rough rolling, intermediate rolling and pre-finish rolling are pre-rolling processes. The rolled piece obtained after pre-finish rolling is the intermediate billet. Then the intermediate billet is controlled-cooled and then finished rolled to obtain the finish rolled piece.

[0077] The roughing rolling temperature is 1025℃. After pre-finishing rolling, the intermediate billet is cooled to the finishing rolling temperature of 980℃ at a cooling rate of 10℃ / s, and then finished rolling is performed. After finishing rolling, the finished rolled part is obtained. The cooling rate of the finished rolled part is controlled at 0.8℃ / s, and it is cooled to the temperature of 990℃ on the cooling bed. The finished rolled part is then sent to the cooling bed.

[0078] The HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars provided in this embodiment were observed under an electron microscope, and the results were as follows: Figure 1 The results are shown. (From...) Figure 1 It is known that the microstructure of steel bars is mainly composed of ferrite and bainite, with a small amount of pearlite.

[0079] Examples 2-5 and Comparative Examples 1-5 are prepared using methods similar to those of Example 1, except that the elemental ratios are different (as shown in Table 1) and the parameters for the hot rolling step are different (as shown in Table 2). In the tables, S refers to the examples and D refers to the comparative examples.

[0080] Table 1. Elemental composition (wt%) of HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars.

[0081] C Mn S P Si Cr Ni Cu V Nb Alt N S1 0.16 1.21 0.009 0.019 0.52 0.79 0.40 0.40 0.073 0.016 0.031 0.0080 S2 0.12 1.16 0.001 0.011 0.51 0.80 0.39 0.40 0.085 0.017 0.035 0.0050 S3 0.12 1.10 0.008 0.017 0.51 0.79 0.39 0.40 0.085 0.015 0.026 0.0046 S4 0.14 1.19 0.002 0.012 0.53 0.79 0.42 0.38 0.080 0.013 0.039 0.0035 S5 0.15 1.25 0.009 0.018 0.54 0.79 0.40 0.42 0.070 0.017 0.021 0.0088 D1 0.16 1.20 0.009 0.018 0.51 0.80 0.40 0.41 0.075 0.010 0.035 0.0060 D2 0.15 1.18 0.008 0.017 0.52 0.79 0.42 0.39 0.080 0.002 0.025 0.0084 D3 0.07 1.25 0.008 0.018 0.54 0.99 0.45 0.45 0.085 0.015 0.038 0.0035 D4 0.14 1.24 0.008 0.017 0.52 1.20 0.45 0.45 0.085 0.016 0.038 0.0045 D5 0.14 1.24 0.008 0.017 0.52 1.00 0.45 0.45 0.002 0.035 0.038 0.0045

[0082] Table 2 Hot Rolling Process Parameters

[0083]

[0084] Experimental Example 1

[0085] The performance of the HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars provided in Examples 1-5 and Comparative Examples 1-5 was tested, and the results are shown in Tables 3 and 4.

[0086] The yield strength was tested using GB / T 228.1 method, the tensile strength was tested using GB / T 228.1 method, the total elongation at maximum force was tested using GB / T 228.1 method, and the corrosion rate was tested using YB / T 4367 method.

[0087] Table 3 Performance of HRB500cE Hot-Rolled Corrosion-Resistant and Earthquake-Resistant Steel Bars

[0088] Table 4 Microstructure of HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars

[0089] Diameter (mm) Ferrite (%) Bainite (%) Pearlite (%) Grain size (grade) S1 25 38 54 8 10.0 S2 25 39 56 5 9.5 S3 28 39 56 5 9.5 S4 28 40 52 8 9.5 S5 36 41 51 8 9.5 D1 25 35 55 10 9.5 D2 25 36 49 15 9.5 D3 28 48 44 8 9.0 D4 32 35 60 5 9.5 D5 25 39 56 5 9.0

[0090] As shown in Tables 3 and 4, the steel bars provided in Examples 1 to 5 of the present invention have excellent comprehensive performance. They not only have good strength, with yield strength exceeding 540 MPa and tensile strength between 850 and 885 MPa, but also have a large total elongation at maximum force and good ductility. At the same time, the steel bars in Examples 1 to 5 of the present invention also have good corrosion resistance and a low corrosion rate. Compared with ordinary HRB500E steel bars, the relative corrosion rate is even smaller.

[0091] Comparative Examples 1 and 2 altered the Nb content and the temperature of the soaking zone during hot rolling, resulting in a significant decrease in the mechanical properties of the reinforcing steel. Comparative Example 3 reduced carbon content and shortened furnace time during hot rolling, also significantly reducing the mechanical properties of the reinforcing steel. Comparative Example 4 altered the Cr content, achieving high strength and corrosion resistance, but significantly decreasing ductility. Comparative Example 5 altered the V and Nb contents, again achieving high strength and corrosion resistance, but significantly decreasing ductility.

[0092] In summary, the HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar and its preparation method provided by the present invention have at least the following advantages:

[0093] 1) By controlling the elemental composition, a low-carbon alloy system with chromium, nickel, copper, aluminum, niobium and vanadium is adopted. Through niobium and vanadium composite strengthening, as well as high-temperature long heating and multi-stage weak controlled cooling technology, the steel bars have excellent corrosion resistance and comprehensive mechanical properties. The overall comprehensive performance is excellent and it is suitable for the use of engineering in chloride ion corrosion environment.

[0094] 2) Under the above chemical composition design scheme, the use of high temperature long heating, high temperature rolling, high temperature cooling bed and cooling rate control technology reduces manufacturing cost while reducing alloy cost, and further optimizes the overall comprehensive performance of the obtained steel bars, which is suitable for actual production and processing. The process operation is simple and easy to control, ensuring the smooth operation of actual production, and has higher social significance and economic effect.

[0095] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hot-rolled corrosion-resistant and earthquake-resistant steel bar of HRB500cE, characterized in that, The elemental composition of steel bars, by mass percentage, includes: C: 0.12~0.16wt%, Si: 0.40~0.60wt%, Mn: 1.00~1.35wt%, Cr: 0.70~1.10wt%, Cu: 0.30~0.45wt%, Ni: 0.30~0.45wt%, Nb: 0.012~0.018wt%, V: 0.070~0.080wt%, Alt: 0.025~0.040wt%, P≤0.035wt%, S≤0.035wt%, N≤0.010wt%, O≤30ppm, with the balance being Fe and unavoidable impurities; The volumetric composition of the microstructure of the steel reinforcement includes: 38-41% ferrite, ≤10% pearlite, and the balance being bainite; The method for preparing the steel bar includes: hot rolling a cast billet; the hot rolling process includes single-line rolling of the cast billet after high-temperature long heating, wherein the single-line rolling is multi-stage weak cooling temperature-controlled rolling. The multi-stage weak cooling temperature control rolling includes pre-rolling the heated billet into an intermediate billet, and then controlling the cooling of the intermediate billet before precision rolling to obtain a precision rolled part; The process of pre-rolling the billet into an intermediate billet includes rough rolling, intermediate rolling and pre-finish rolling of the billet, wherein the initial rolling temperature of the rough rolling is 990~1030℃; The cooling rate of the intermediate billet before finishing rolling is 5~15℃ / s, and the starting temperature of finishing rolling is 960~1000℃. The method for controlling the cooling rate of the intermediate billet before finishing rolling is as follows: control the water volume of the two sets of water purifiers before finishing rolling, with the water volume of the first set of water purifiers being 80-90% and the water volume of the second set of water purifiers being 100%. After the intermediate billet finishes rolling, the cooling rate of the finished rolled part is less than or equal to 1.5℃ / s, and the temperature of the cooling bed on the finished rolled part is 950~990℃.

2. The HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar according to claim 1, characterized in that, The yield strength R of the steel reinforcement eL ≥540MPa, tensile strength R m ≥850MPa, elongation A≥20.0%, total elongation at maximum force A gt ≥9.5%, R 0 m / R 0 eL ≥1.35, R 0 eL / R eL ≤1.18, average corrosion rate ≤4.1 g / m 2 •h, with a relative corrosion rate ≤67% compared to HRB500E steel bars.

3. The HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bar according to claim 1, characterized in that, The volumetric composition of the microstructure of the steel reinforcement includes: 40-41% ferrite, ≤8% pearlite, with the balance being bainite, and a grain size of 9.5 or higher.

4. A method for preparing HRB500cE hot-rolled corrosion-resistant and earthquake-resistant steel bars as described in any one of claims 1 to 3, characterized in that, This includes continuously casting refined molten steel into billets by proportional smelting, and hot rolling the billets; The hot rolling process includes subjecting the billet to high-temperature long-term heating followed by single-line rolling, wherein the single-line rolling is a multi-stage weak cooling temperature-controlled rolling process.

5. The preparation method according to claim 4, characterized in that, The finishing rolling temperature is 960~980℃.

6. The preparation method according to claim 4 or 5, characterized in that, During the high-temperature long-term heating process, the billet spends more than 120 minutes in the heating furnace, and the heating rate is 15~20℃ / s.

7. The preparation method according to claim 6, characterized in that, The temperature of the soaking zone of the heating furnace is 1140~1180℃; the temperature of the heating zone of the heating furnace is 990~1110℃.

8. The preparation method according to claim 7, characterized in that, The heating section of the heating furnace includes a first heating section and a second heating section. The temperature of the first heating section is 990~1030℃, and the temperature of the second heating section is 1070~1110℃.

9. The preparation method according to claim 4, characterized in that, The preparation of the refined steel includes smelting molten iron in a converter to obtain molten steel, and then sending the molten steel to an argon station for argon blowing and LF refining. Argon gas is blown throughout the entire process of smelting in the converter. When the converter has tapped 1 / 4 of the steel, aluminum source, silicon source, manganese source, chromium source, copper source, nickel source and scrap steel are added to the molten steel in sequence for deoxidation and alloying. Then the molten steel is sent to the argon station for argon blowing. The argon blowing time at the argon station is greater than or equal to 6 minutes.

10. The preparation method according to claim 9, characterized in that, In the LF refining process, the mass ratio of lime to molten steel is 3~6 kg / t, and the mass ratio of fluorite to molten steel is 0.5~1 kg / t. After adding lime and fluorite, electrolyze the slag for 8-15 minutes. After the electrolytic slag is completed, a deoxidizer is added to produce white slag, and niobium source and vanadium source are added to adjust the element content in the molten steel. When the temperature of the refined molten steel is 1600℃, calcium wire is fed for 100~150m, and the soft blowing argon time is greater than or equal to 10min.

11. The preparation method according to claim 4, characterized in that, During the continuous casting process, the temperature of the molten steel during continuous casting in the tundish is 1520~1560℃, and the casting speed is 2.2~3.0m / min.

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