Corrosion-resistant HRB400 threaded steel and preparation method thereof

Abstract

The application provides a kind of corrosion-resistant HRB400 threaded steel and a preparation method thereof, comprising the following components in percentage by mass: C: 0.20~0.30%, Si: 0.35~0.65%, Mn: 1.30~1.70%, V: 0.01~0.06%, P: ≤0.015%, S: ≤0.008%, Al: 0.005~0.040%, Ca: 0.0005~0.0040%, La+Ce: 0.0010~0.0100%, T.O: ≤0.0040%, and the balance is Fe and other inevitable impurities. Through the synergistic regulation of the above components and inclusion evolution, the corrosion resistance of HRB400 threaded steel in various chloride salt environments such as concrete pore solution, salt spray, dry-wet alternating, deicing salt and saline soil is effectively improved. ‑ The electrochemical test results show that the pitting potential of the corrosion-resistant HRB400 threaded steel prepared in the application is increased, the passivation current density is reduced, and the pitting corrosion resistance in Cl ‑ The pitting corrosion resistance in simulated concrete pore solution is significantly enhanced.

Description

Technical Field

[0001] This invention relates to the field of corrosion-resistant rebar technology, and particularly to a corrosion-resistant HRB400 rebar and its preparation method. Background Technology

[0002] HRB400 rebar is widely used in reinforced concrete structures such as bridges, ports, docks, cross-sea channels, marine engineering, de-icing and salt-resistant roads, buildings in saline-alkali areas, underground pipe corridors, and coastal industrial facilities; it is effective in applications involving load, localized stress concentration, and Cl. - Under the coupled effects of multiple factors such as intrusion, CO2 carbonization, alternating wet and dry conditions, temperature and humidity cycles, oxygen concentration differences, and concrete cracking, the alkaline environment inside the concrete gradually weakens, and the stability of the original passivation film on the surface of the reinforcing steel decreases; when Cl... - When the content reaches a certain level, the passivation film is destroyed, leading to the formation of pitting corrosion sources. After localized corrosion occurs in the reinforcing steel, the volume of corrosion products exceeds the volume of the original metal matrix. The resulting expansion stress further causes debonding at the steel-concrete interface, cracking and spalling of the protective layer, and accelerates the corrosion of the reinforcing steel. - The intrusion of oxygen causes pitting corrosion to develop into uneven corrosion, resulting in a reduction in cross-sectional area and stress concentration, which severely degrades the strength, plasticity, fatigue and bonding performance of the steel bars.

[0003] In related technologies, HRB400 rebar typically uses a C-Mn-Si composition design. During smelting, deoxidation, refining, and continuous casting, elongated MnS and / or irregular Al2O3 and other non-metallic inclusions inevitably form in the steel. During hot rolling, MnS readily elongates along the rolling direction, especially in Cl-containing... - Preferential dissolution in the environment, causing interfacial micro-region acidification and Cl- - Enrichment becomes a source of pitting corrosion initiation; the continuous distribution of MnS along the rolling direction also provides active channels for corrosion propagation, causing pitting corrosion to develop into grooves along the rolling direction, resulting in a sharp reduction in cross-section and severe stress concentration, leading to premature degradation of mechanical and bonding properties, thereby seriously threatening the long-term safe service of critical infrastructure in harsh chloride salt environments.

[0004] Therefore, there is an urgent need to provide a corrosion-resistant HRB400 rebar and its preparation method. Summary of the Invention

[0005] This invention provides a corrosion-resistant HRB400 rebar and its preparation method, which can solve the problem of insufficient protection of corrosion product film in existing HRB400 rebar in chlorine-containing environments.

[0006] In a first aspect, the present invention provides a corrosion-resistant HRB400 rebar, comprising, by weight percentage, the following components: C: 0.20~0.30%, Si: 0.35~0.65%, Mn: 1.30~1.70%, V: 0.01~0.06%, P: ≤0.015%, S: ≤0.008%, Al: 0.005~0.040%, Ca: 0.0005~0.0040%, La+Ce: 0.0010~0.0100%, TO: ≤0.0040%, with the balance being Fe and other unavoidable impurities.

[0007] More preferably, by mass percentage, it comprises the following components: C: 0.23~0.27%, Si: 0.45~0.55%, Mn: 1.45~1.60%, V: 0.02~0.04%, P: ≤0.010%, S: ≤0.005%, Al: 0.010~0.030%, Ca: 0.0010~0.0030%, La+Ce: 0.0030~0.0080%, TO: ≤0.0030%, with the balance being Fe and other unavoidable impurities.

[0008] More preferably, the mass percentages of O and Al satisfy the following relationship: .

[0009] More preferably, the mass percentages of Ca and S satisfy the following relationship: .

[0010] More preferably, the mass percentages of La, Ce, and S satisfy the following relationship: .

[0011] More preferably, the mass percentages of La, Ce, Ca, O, and S satisfy the following relationship: .

[0012] Secondly, embodiments of the present invention also provide a method for preparing the corrosion-resistant HRB400 rebar as described in any one of the above claims, the method comprising the following steps: (1) The iron source is mixed, smelted and refined under a protective atmosphere, and the C, Si, Mn, V, P and S elements are adjusted to the target content to obtain the basic molten steel; (2) Under a protective atmosphere, aluminum material is added to the base steel liquid for deoxidation treatment in order to control the total oxygen content and Al / O ratio in the steel to the target range; (3) Under a protective atmosphere, calcium-containing raw materials are added to the deoxidized molten steel to pre-modify the inclusions in order to control the Ca / S ratio to the target range; (4) Under a protective atmosphere, lanthanum and cerium-containing raw materials are added to the pre-modified molten steel to perform final modification of inclusions, so as to control the (La+Ce) / S ratio, La / Ce ratio and (La+Ce+Ca) / (O+S) ratio to the target range. (5) The final modified molten steel is cast into ingots under a protective atmosphere, and the ingots are forged and rolled in sequence. After cooling, the corrosion-resistant HRB400 rebar is obtained.

[0013] Preferably, in step (1), the iron source is pure iron, low-phosphorus and low-sulfur scrap steel or HRB400 base material; the smelting temperature is 1580~1600℃, and the refining time after the furnace charge is melted is 10~15min.

[0014] Preferably, in step (2), the aluminum raw material is an aluminum block or aluminum wire; the aluminum material is added in batches at 1580~1600℃ and stirred for 3~5 minutes for deoxidation treatment.

[0015] Preferably, in step (3), the calcium-containing raw material is a calcium-silicon alloy or a calcium-containing cored wire; preferably, the calcium-containing raw material is added at 1560~1580℃ and stirred for 3~8 minutes to pre-modify the inclusions.

[0016] Preferably, in step (4), the raw material containing lanthanum and cerium is a lanthanum-cerium master alloy or a lanthanum-cerium cored wire; preferably, the raw material containing lanthanum and cerium is added at 1550~1580℃ and the inclusions are finally modified by soft blowing argon gas for 5~15min.

[0017] Preferably, in step (5), the pouring temperature is 1530~1560℃.

[0018] Preferably, in step (5), during the forging process, the initial forging temperature is 1100~1150℃ and the final forging temperature is not lower than 850℃.

[0019] Preferably, in step (5), the initial rolling temperature is 980~1100℃ and the final rolling temperature is 850~950℃.

[0020] Preferably, in step (5), three rolling passes are preferred, with a total reduction rate of 60-70%.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: In this invention, by sequentially adding Al, Ca, La, and Ce elements to the base HRB400 rebar, and through synergistic control of the amount of each element added and the reaction process, stable composite inclusions are formed between La, Ce, and Ca and the S, O, and Al deoxidation products in the base steel. This promotes the transformation of elongated MnS and irregular composite oxide inclusions into fine, spherical, or near-spherical composite inclusions, thereby reducing the sensitivity to inclusion-induced pitting corrosion. Through the synergistic regulation of the above-mentioned components and inclusion evolution, the corrosion resistance of HRB400 rebar in Cl-containing steel is effectively improved. - The corrosion resistance of the HRB400 rebar prepared in this invention is demonstrated in various chloride-containing environments, including concrete pore fluid, salt spray, alternating wet and dry conditions, de-icing salt, and saline soil. Electrochemical testing results show that the pitting potential of the corrosion-resistant HRB400 rebar prepared in this invention is increased, and the passivation current density is decreased, particularly in chloride-containing environments. - The pitting resistance in simulated concrete pore fluid is significantly enhanced. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The microstructure of a corrosion-resistant HRB400 rebar provided in Embodiment 5 of the present invention is shown in the diagram; wherein, (a1) is a microstructure of ferrite and pearlite under an optical microscope, and (a2) is a microstructure of ferrite and pearlite under an electron microscope. Figure 2 The microstructure of a corrosion-resistant HRB400 rebar provided in Comparative Example 3 of this invention is shown in the diagram; (b1) is a microstructure of ferrite and pearlite under an optical microscope, and (b2) is a microstructure of ferrite and pearlite under an electron microscope. Figure 3 The inclusion morphology and elemental distribution diagram of a corrosion-resistant HRB400 rebar provided in Embodiment 1 of the present invention; Figure 4 This is a diagram showing the inclusion morphology and elemental distribution of a corrosion-resistant HRB400 rebar provided in Comparative Example 1 of the present invention. Figure 5 The images show the Fe 2p results of the surface corrosion product film of a corrosion-resistant HRB400 rebar provided in Example 8 and Comparative Example 1 of the present invention; where (a) is Example 8 and (b) is Comparative Example 1. Figure 6The above are O1s XPS peak results of the surface corrosion product film of a corrosion-resistant HRB400 rebar provided in Example 8 and Comparative Example 1 of the present invention; wherein, (a) is Example 8 and (b) is Comparative Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] As mentioned earlier, HRB400 rebar is mostly designed with a C-Mn-Si composition, inevitably resulting in the formation of non-metallic inclusions such as MnS, Al2O3, Al2O3-MnS composite inclusions, silicon manganese oxides, and small amounts of calcium aluminate inclusions. The composition, size, morphology, number density, and interface state between these inclusions and the steel matrix not only affect the plasticity and toughness of the rebar but also its performance in Cl-containing environments. - Localized corrosion behavior in the environment. Among them, MnS inclusions have strong rolling deformation ability and easily extend into long strips or bands along the rolling direction during hot rolling. Furthermore, there are differences in composition and electrochemical properties between the long strip-shaped MnS and the steel matrix, especially in Cl-containing environments. - It readily dissolves in the medium, causing acidification of nearby micro-regions and promoting Cl... - MnS accumulates at the interface between inclusions and the matrix, thereby destroying the local passivation film and inducing pitting corrosion. Simultaneously, the continuous or densely distributed MnS along the rolling direction provides a relatively continuous active channel for corrosion propagation, causing pitting pits to develop along the inclusion distribution direction. Al2O3 inclusions typically have high melting points, high hardness, and low plastic deformation capacity, making them difficult to deform synchronously with the steel matrix during rolling. However, irregular or angular Al2O3 inclusions easily form interfacial voids, microcracks, and localized stress concentrations. When MnS further precipitates on the Al2O3 surface, Al2O3-MnS composite inclusions can form. These composite inclusions combine the characteristics of hard oxide interface defects and preferential dissolution of sulfides, thus potentially becoming sensitive pitting corrosion initiation sites in chloride-containing environments. If the inclusions are large, have a high aspect ratio, or are clustered, their adverse effects on corrosion resistance and mechanical properties will be more pronounced, seriously threatening the long-term service safety of critical infrastructure in harsh chloride environments.

[0026] Based on this, embodiments of the present invention provide a corrosion-resistant HRB400 rebar, comprising the following components by weight percentage: C: Carbon is an important element for ensuring the strength of HRB400 rebar, promoting pearlite formation and improving steel strength. However, excessively high C content increases the proportion of pearlite, increasing the galvanic corrosion tendency between ferrite and pearlite, while reducing the steel's plasticity, toughness, and weldability. Therefore, considering both strength and corrosion resistance requirements, the C content in this invention is 0.20~0.30% (e.g., 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, or 0.30%).

[0027] Si: Silicon has deoxidation and solid solution strengthening effects, which can improve the strength of steel and improve the deoxidation effect of molten steel; however, excessive Si content may affect the surface quality of rolled material and have an adverse effect on the toughness of steel; therefore, the Si content in this invention is 0.35~0.65% (for example, it can be 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.52%, 0.55%, 0.58%, 0.60%, 0.62% or 0.65%).

[0028] Mn: Manganese can improve the strength, hot working properties, and structural stability of steel, and is an important strengthening element in HRB400 rebar. However, Mn easily combines with S to form MnS inclusions. MnS tends to extend along the rolling direction during hot rolling, and in Cl-containing areas... - It preferentially dissolves in the environment, triggering pitting corrosion initiation; therefore, the Mn content in this invention is 1.30~1.70% (for example, it can be 1.30%, 1.40%, 1.50%, 1.60% or 1.70%).

[0029] Vanadium (V) can form V(C,N) precipitates with C and N, which significantly improve the yield strength of steel through precipitation strengthening and grain refinement, enabling the steel to meet the HRB400 strength grade requirements. However, excessive V content will increase production costs and may lead to coarsening of the precipitates, weakening the strengthening effect. Therefore, the V content in this invention is 0.01~0.06% (for example, it can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05% or 0.06%).

[0030] P: Phosphorus is a harmful impurity element in steel. It tends to segregate at grain boundaries, reducing the toughness of steel and potentially increasing the corrosion sensitivity of grain boundaries and local areas. Therefore, the P content in this invention needs to be controlled to be ≤0.015%.

[0031] S: Sulfur is an important element affecting the chloride corrosion resistance of steel. Increased S content increases the number of MnS inclusions and makes inclusion modification more difficult; long, strip-shaped MnS... -Selective dissolution and pitting corrosion can easily occur in the environment; therefore, this invention controls S ≤ 0.008% and determines the amount of La, Ce and Ca added based on the actual S content.

[0032] Al: Aluminum is mainly used to complete the deoxidation of molten steel and control the residual oxygen content. If the Al content is too low, the residual oxygen content of the molten steel will be too high, and the subsequently added La and Ce will be easily consumed by excessive oxidation. When the Al content is too high, it may increase the number of Al2O3 inclusions. Therefore, in this invention, the Al content is controlled at 0.005~0.040% (for example, it can be 0.005%, 0.008%, 0.010%, 0.020%, 0.030% or 0.040%).

[0033] Ca: Calcium can pre-modify Al2O3 and Al2O3-MnS composite inclusions to reduce the irregularity and agglomeration tendency of the inclusions and regulate the precipitation behavior of subsequent sulfides. If the Ca content is too low, the modification effect of Al2O3 and Al2O3-MnS composite inclusions will be insufficient, while if the Ca content is too high, coarse CaS, calcium aluminate or Ca-containing composite inclusions may be formed, which will affect the stability of steel casting. Therefore, in this invention, the Ca content is controlled at 0.0005~0.0040% (for example, it can be 0.0005%, 0.0008%, 0.0010%, 0.0020%, 0.0030% or 0.0040%).

[0034] La+Ce: La and Ce can react with O, S, and existing inclusions, transforming elongated MnS and irregular oxide inclusions into spherical or near-spherical composite inclusions. If the total amount of La and Ce is insufficient, MnS and composite oxides cannot be sufficiently modified; if the total amount of La and Ce is excessive, coarse rare earth sulfides, oxides, or oxysulfides are easily formed. Therefore, this invention controls the total content of La and Ce to 0.0010~0.0100% (for example, it can be 0.0010%, 0.0030%, 0.0050%, 0.0080%, or 0.0100%), and adjusts the (La+Ce) / S ratio according to the S content, while simultaneously determining the actual amount of La and Ce added by combining La / Ce and (La+Ce+Ca) / (O+S).

[0035] TO: ≤0.0040%, with the balance being Fe and other unavoidable impurities; where TO represents the total oxygen content in the steel.

[0036] In this embodiment of the invention, by sequentially adding Al, Ca, La, and Ce elements to the base HRB400 rebar, and through synergistic control of the amount of each element added and the reaction process, stable composite inclusions are formed between La, Ce, and Ca and the S, O, and Al deoxidation products in the base steel. This promotes the transformation of elongated MnS and irregular composite oxide inclusions into fine, spherical, or near-spherical composite inclusions, thereby reducing the sensitivity to inclusion-induced pitting corrosion. Through the synergistic regulation of the above-mentioned components and inclusion evolution, the corrosion resistance of HRB400 rebar in Cl-containing steel is effectively improved. - The corrosion resistance of the HRB400 rebar prepared in this invention is demonstrated in various chloride-containing environments, including concrete pore fluid, salt spray, alternating wet and dry conditions, de-icing salt, and saline soil. Electrochemical testing results show that the pitting potential of the corrosion-resistant HRB400 rebar prepared in this invention is increased, and the passivation current density is decreased, particularly in chloride-containing environments. - The pitting resistance in simulated concrete pore fluid is significantly enhanced.

[0037] According to some preferred embodiments, the composition, by mass percentage, includes the following components: C: 0.23~0.27% (e.g., 0.23%, 0.24%, 0.25%, 0.26%, or 0.27%), Si: 0.45~0.55% (e.g., 0.45%, 0.46%, 0.48%, 0.50%, 0.52%, 0.53%, or 0.55%), Mn: 1.45~1.60% (e.g., 1.45%, 1.48%, 1.50%, 1.52%, 1.55%, 1.58%, or 1.60%), V: 0.02~0.04% (e.g., 0.02%, 0.03%, or 0.04%), P: ≤0.01 0%, S: ≤0.005%, Al: 0.010~0.030% (e.g., 0.010%, 0.015%, 0.018%, 0.020%, 0.022%, 0.025%, 0.028% or 0.030%), Ca: 0.0010~0.0030% (e.g., 0.0010%, 0.0020% or 0.0030%), La+Ce: 0.0030~0.0080% (e.g., 0.0030%, 0.0040%, 0.0050%, 0.0060%, 0.0070% or 0.0080%), Total Oxygen (TO): ≤0.0030%, balance being Fe and other unavoidable impurities.

[0038] In this embodiment of the invention, by further controlling the content of the above-mentioned components within the above-mentioned range, it is beneficial to form a stable synergistic reaction between La, Ce, Ca and S, O and Al deoxidation products in steel, promote the transformation of long strip-shaped MnS and irregular composite oxide inclusions into fine, spherical or near-spherical composite inclusions, reduce the sensitivity of inclusion-induced pitting corrosion, and significantly improve the performance of HRB400 rebar in Cl-containing steel. - Resistance to pitting and corrosion in various chloride salt environments, such as concrete pore fluid, salt spray, alternating wet and dry conditions, de-icing salt, and saline soil.

[0039] According to some preferred embodiments, the mass percentages of O and Al satisfy the following relationship: O represents the total oxygen content (TO) in the steel.

[0040] In this embodiment of the invention, by further controlling the ratio of O and Al elements, the degree of Al deoxidation can be synergistically matched with the total oxygen content in the steel. If the Al / O ratio is too low, La and Ce will be easily consumed excessively by residual oxygen. If the ratio is too high, more Al2O3 inclusions may be formed. Therefore, this invention controls the Al / O ratio to 3.00~16.00 (for example, it can be 3, 5, 6, 8, 10, 12, 15 or 16).

[0041] According to some preferred embodiments, the mass percentages of Ca and S satisfy the following relationship: .

[0042] In this embodiment of the invention, an appropriate amount of Ca can pre-modify Al2O3 inclusions, thereby reducing their sharp angles and agglomeration tendency. It can also react with S to regulate the precipitation behavior of sulfides, thus providing a relatively stable inclusion basis for La and Ce treatment. The Ca content and the total La+Ce content need to be synergistically controlled in conjunction with the S, O, and Al content in the steel. Furthermore, by controlling the Ca / S ratio, the appropriate degree of pre-modification of sulfur-containing inclusions and Al2O3-MnS composite inclusions by Ca can be achieved. If the Ca / S ratio is too low, the pre-modification is insufficient; if the Ca / S ratio is too high, coarse CaS or Ca-containing composite inclusions may form, which is detrimental to subsequent rare earth modification. Therefore, this invention controls the Ca / S ratio to 0.30~0.80 (for example, it can be 0.30, 0.40, 0.50, 0.60, 0.70, or 0.80).

[0043] According to some preferred embodiments, the mass percentages of La, Ce, and S satisfy the following relationship: .

[0044] In this embodiment of the invention, the addition of La and Ce composite rare earth elements improves the cleanliness of molten steel, refines inclusions, and alters the morphology of sulfides. La and Ce have a strong affinity for oxygen and sulfur. When added in appropriate amounts, they can react with O, S, and existing oxides in the molten steel, transforming some elongated MnS and irregular oxides into smaller, relatively regular spherical or near-spherical La-Ce-OS, La-Ce-S, or rare earth composite inclusions. Spherical or near-spherical inclusions are less prone to severe elongation deformation during hot rolling, which helps reduce interface defects between inclusions and the steel matrix and reduces local electrochemical inhomogeneity around inclusions, thereby inhibiting pitting corrosion initiation from the root. To fully leverage the modification advantages of La and Ce, in this embodiment of the invention, the La / Ce ratio is further controlled to 0.50~2.00 (for example, it can be 0.50, 0.80, 1.0, 1.5 or 2.00). This is beneficial for optimizing the phase composition and stability of rare earth composite inclusions, avoiding the excessive amount of a single rare earth element that would lead to a single type of inclusion or an increased tendency for growth, and ensuring the consistency and controllability of the inclusion modification effect.

[0045] Meanwhile, the control effect of rare earth inclusions depends not only on the total amount and ratio of La and Ce added, but also on factors such as the S content, total oxygen content, Al deoxidation degree, Ca treatment state, La / Ce ratio, rare earth addition sequence, and soft blowing time after addition. If the residual oxygen content in the steel is high, the added La and Ce may preferentially react with oxygen, resulting in insufficient effective rare earth for sulfide modification; if the S content is high and the amount of La and Ce added is insufficient, the original MnS is difficult to be fully modified, and a large number of long strip-shaped sulfides may still be retained after rolling; conversely, if the amount of La and Ce added exceeds the range that O and S in the steel can reasonably consume, coarse rare earth oxygen sulfides, rare earth sulfides, or agglomerated inclusions may be formed. These coarse inclusions are difficult to remove by flotation and may form interface defects in subsequent rolling, becoming new pitting corrosion initiation sites. Therefore, in this embodiment of the invention, the ratio of (La+Ce) / S is further controlled so that it can accurately reflect the matching relationship between the total content of La and Ce and the content of S in the steel. This ratio is controlled between 0.75 and 2.50 (for example, it can be 0.75, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25 or 2.50), preferably between 1.25 and 2.00, and more preferably between 1.50 and 1.70. This helps to ensure that La and Ce can fully modify MnS and other sulfur-containing inclusions, transforming them into fine, spherical or near-spherical rare earth composite inclusions, while effectively avoiding the formation of coarse or agglomerated inclusions due to excessive rare earth. Thus, while optimizing the morphology and distribution of inclusions, the risk of pitting corrosion induced by inclusions is minimized, and the corrosion resistance of HRB400 rebar in harsh chloride salt environments is significantly improved.

[0046] According to some preferred embodiments, the mass percentages of La, Ce, Ca, O, and S satisfy the following relationship: .

[0047] Considering that controlling only (La+Ce) / S is insufficient to fully reflect the degree to which La and Ce are consumed by oxides during deoxidation, and also fails to reflect the pre-modification effect of Ca on Al2O3 and MnS composite inclusions; for HRB400 rebar treated with Al deoxidation and Ca, it is also necessary to consider the deoxidation state reflected by Al / O, the calcium-sulfur matching relationship reflected by Ca / S, and the overall matching degree between the active inclusion modification elements (La, Ce, Ca) and the total oxygen and sulfur in the steel. Therefore, in this embodiment of the invention, by further controlling the ratio of (La+Ce+Ca) / (O+S), a comprehensive consideration of La, Ce, and Ca can be achieved, avoiding the control deviation caused by focusing only on sulfide modification while ignoring oxide consumption. This achieves a comprehensive measurement of the matching relationship between the modification of oxides and sulfides by La, Ce, and Ca and the actual O and S content. If the ratio is too low, the oxides and sulfides will not be sufficiently modified; if the ratio is too high, coarse or agglomerated composite inclusions are easily formed. Therefore, this invention controls the ratio of (La+Ce+Ca) / (O+S) to 0.80~2.20 (for example, it can be 0.80, 1.00, 1.20, 1.50, 1.80, 2.00, or 2.20).

[0048] In summary, in this embodiment of the invention, by synergistically controlling the proportional relationships between (La+Ce) / S, La / Ce, Ca / S, Al / O, and (La+Ce+Ca) / (O+S), the addition amounts of La, Ce, and Ca can be precisely matched with the deoxidation state of S, O, and Al in the steel. This avoids incomplete inclusion modification due to insufficient addition and reduces the risk of forming coarse or agglomerated inclusions due to excessive addition. These proportions are interrelated and mutually restrictive; any significant deviation from a reasonable range may lead to insufficient inclusion modification or the formation of new coarse composite inclusions, thus failing to effectively suppress pitting corrosion. After the above-mentioned proportional synergistic control, the inclusions in the steel are transformed from elongated MnS and irregular Al2O3-MnS composite inclusions into fine, spherical or near-spherical La-Ce-Ca-OS, La-Ce-OS, La-Ce-Mn-S or Ca-Al-OS composite inclusions. Among them, the average size of the inclusions is ≤2.5 μm, the maximum size is ≤8 μm, the aspect ratio is ≤3, the proportion of spherical or near-spherical inclusions is ≥70%, and the number of elongated MnS inclusions is reduced by ≥50% compared with steel not controlled according to the proportion of the present invention. This significantly reduces the sensitivity of inclusion-induced pitting corrosion from the root cause and greatly improves the corrosion resistance of HRB400 rebar in harsh chloride salt environments.

[0049] This invention also provides a method for preparing the corrosion-resistant HRB400 rebar as described in any one of the above claims, the method comprising the following steps: (1) The iron source is mixed, smelted and refined under a protective atmosphere, and the C, Si, Mn, V, P and S elements are adjusted to the target content to obtain the basic molten steel; (2) Under a protective atmosphere, aluminum material is added to the base steel liquid for deoxidation treatment in order to control the total oxygen content and Al / O ratio in the steel to the target range; (3) Under a protective atmosphere, calcium-containing raw materials are added to the deoxidized molten steel to pre-modify the inclusions in order to control the Ca / S ratio to the target range; (4) Under a protective atmosphere, lanthanum and cerium-containing raw materials are added to the pre-modified molten steel to perform final modification of inclusions, so as to control the (La+Ce) / S ratio, La / Ce ratio and (La+Ce+Ca) / (O+S) ratio to the target range. (5) The final modified molten steel is cast into ingots under a protective atmosphere, and the ingots are forged and rolled in sequence. After cooling, the corrosion-resistant HRB400 rebar is obtained.

[0050] In this embodiment of the invention, pure iron, low-phosphorus and low-sulfur scrap steel, or HRB400 base material are used as the iron source. The content of C, Si, Mn, and V elements is adjusted by carbon raisers or graphite, FeSi, FeMn, and FeV, respectively. P and S are controlled within the target range in principle through raw material selection and dephosphorization and desulfurization treatment, and are not deliberately added as alloying elements. FeP or FeS is used for trace correction only when preparing composition gradient test steel and the analytical value is lower than the design value. At the same time, considering that some Si will be introduced into the subsequent Ca-Si alloy, the Si content of the base steel liquid is reserved according to the target value. After charging, the vacuum induction furnace is evacuated to a vacuum level not exceeding 10 Pa, and then heated. After the furnace charge is completely melted, vacuum refining is continued for 10-15 min. After refining, the vacuum is stopped, and Ar is backfilled into the furnace to 0.02-0.04 MPa. Sampling and fine-tuning of C, Si, Mn, V, P, and S are completed under a protective atmosphere to obtain the base steel liquid. The inclusions were modified in stages according to the sequence of Al deoxidation, Ca pretreatment and La+Ce posttreatment. First, the dissolved oxygen in the molten steel was reduced to the target level by Al. Then, an appropriate amount of Ca was used to pre-modify Al2O3 and Al2O3-MnS composite inclusions. Finally, La-Ce composite rare earth was added to allow La and Ce to react further with O, S and the original inclusions in the steel to form La-Ce-OS, La-Ce-S, La-Ce-Al-O, La-Ce-Ca-OS or La-Ce-Mn-S type composite inclusions.

[0051] Through the aforementioned staged treatment, elongated MnS and irregular oxide inclusions can be transformed into small, dispersed, spherical or near-spherical composite inclusions. This reduces the aspect ratio of the inclusions, decreases the electrochemical inhomogeneity between the inclusions and the steel matrix, and inhibits pitting corrosion initiation at its source. Furthermore, the fine, dispersed, and regularly morphologically regular La-Ce-Ca composite inclusions help reduce interfacial defects between the inclusions and the steel matrix, promote uniform deposition of corrosion products on the steel surface, improve the continuity and stability of the corrosion product film, and effectively inhibit Cl... - The migration of O2 and H2O to the steel matrix interface. Thus, without significantly increasing the content of precious alloying elements, this invention can significantly improve the chloride corrosion resistance of HRB400 rebar by synergistically controlling the proportions of trace amounts of La, Ce, Ca with S, O, and Al, while maintaining its strength, plasticity, and production cost advantages.

[0052] According to some preferred embodiments, in step (1), the iron source is pure iron, low phosphorus and low sulfur scrap steel or HRB400 base material; the smelting temperature is 1580~1600℃ (for example, it can be 1580℃, 1590℃ or 1600℃), and the refining time after the furnace charge is melted is 10~15min (for example, it can be 10min, 11min, 12min, 13min, 14min or 15min).

[0053] According to some preferred embodiments, in step (2), the aluminum raw material is an aluminum block or aluminum wire; the aluminum material is added in batches at 1580~1600℃ (for example, it can be 1580℃, 1590℃ or 1600℃) and stirred for 3~5min (for example, it can be 3min, 4min or 5min) for deoxidation treatment.

[0054] According to some preferred embodiments, in step (3), the calcium-containing raw material is a calcium-silicon master alloy or a calcium-containing cored wire; the calcium-containing raw material is added at 1560~1580℃ (for example, it can be 1560℃, 1570℃ or 1580℃) and stirred for 3~8min (for example, it can be 3min, 4min, 5min, 6min, 7min or 8min) to pre-modify the inclusions.

[0055] According to some preferred embodiments, in step (4), the raw material containing lanthanum and cerium is a lanthanum-cerium master alloy or a lanthanum-cerium cored wire; the raw material containing lanthanum and cerium is added at 1550~1580℃ (for example, it can be 1550℃, 1560℃, 1570℃ or 1580℃), and the inclusions are finally modified by soft blowing argon gas for 5~15min (for example, it can be 5min, 8min, 10min, 12min or 15min).

[0056] In this embodiment of the invention, specifically, the base molten steel is first controlled at the target temperature. Al blocks or Al wire are added in batches under Ar protection. After weak electromagnetic stirring for 3-5 minutes, the mixture is allowed to stand for 3-5 minutes and samples are taken for analysis. The deoxidation endpoint should simultaneously meet the target range requirements for total oxygen content (TO) and Al / O. If the target is not met, a small amount of Al is added according to the analysis results, and the standing and sampling steps are repeated. After Al deoxidation is completed, prolonged high vacuum treatment is not performed to avoid burn-off of subsequently added Ca, La, and Ce elements. Subsequently, the molten steel is cooled to a suitable temperature, and a Ca-Si master alloy is added or a Ca-containing cored wire is fed. When using block Ca-Si alloy, it must be pressed into the molten steel to a depth of about 1 / 2 to 2 / 3 below the surface of the molten steel under Ar protection. After Ca treatment, weak electromagnetic stirring or soft blowing of Ar is used for 3-8 minutes to ensure that the Ca / S ratio in the steel is within the target range. The Si in the base composition has been pre-adjusted by FeSi. The Si introduced by the Ca-Si alloy is included in the final Si content, and no additional large amount of Si is added after Ca treatment. Finally, after the Ca treatment is completed and the composition and temperature of the molten steel are stable, a La-Ce master alloy is added or a La-Ce cored wire is fed in at the set temperature. The alloy is then pressed into the molten steel to a depth of about 1 / 2 to 2 / 3 under Ar protection. The amount of La and Ce added is calculated based on the measured S, O and Ca contents to ensure that the ratios of (La+Ce) / S, La / Ce and (La+Ce+Ca) / (O+S) all meet the specified range. After addition, Ar is gently blown for 5 to 15 minutes, and then allowed to stand for 2 to 5 minutes. During this process, strong stirring, prolonged high vacuum and long waiting time should be avoided to reduce the oxidation loss of rare earth elements and the agglomeration of inclusions, thereby completing the staged modification treatment of inclusions in the molten steel.

[0057] In this embodiment of the invention, if La and Ce are added too early, the rare earth elements are prone to oxidation and burn-off during subsequent refining or steel transfer, or they may preferentially react with incompletely removed oxides and be ineffectively consumed. If strong argon blowing or prolonged stirring is performed after La and Ce treatment, it will increase the tendency for secondary oxidation of rare earth elements and collision and agglomeration of inclusions. Therefore, La and Ce must be added after Al deoxidation and Ca pretreatment are completed, and the composition and temperature of the molten steel are relatively stable. By precisely controlling the addition temperature, addition method, soft blowing intensity, soft blowing time, and settling time, the effective yield of La and Ce and the stability of composite inclusion modification can be improved.

[0058] According to some preferred embodiments, in step (5), the pouring temperature is 1530~1580℃ (for example, it can be 1530℃, 1540℃, 1550℃, 1560℃, 1570℃ or 1580℃), preferably 1540~1560℃; during the forging process, the initial forging temperature is 1100~1150℃ (for example, it can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃ or 1150℃). The final forging temperature is not lower than 850℃; during the rolling process, the initial rolling temperature is 980~1100℃ (for example, it can be 980℃, 990℃, 1000℃ or 1100℃), and the final rolling temperature is 850~950℃ (for example, it can be 850℃, 880℃, 900℃, 920℃ or 950℃); preferably, it is a three-pass rolling process with a total reduction rate of 60~70% (for example, it can be 60%, 62%, 65%, 68% or 70%).

[0059] In this embodiment of the invention, after sampling the final composition, the temperature of the molten steel is adjusted to the target range, and it is poured uniformly into a steel ingot mold preheated to 200-300°C under Ar gas protection. The pouring process should be continuous to avoid slag entrapment and secondary oxidation. After the steel ingot has completely solidified and cooled, it is demolded, and surface defects are removed. Subsequently, the steel ingot is heated to 1150-1200°C and held for 1.0-1.5 hours for forging. The forging adopts a two-way or higher upsetting process, with a total forging ratio of not less than 3, and is forged into a rolled steel billet with a thickness of 20±1 mm. After forging, it is air-cooled to room temperature. Finally, the forged steel billet is heated to 1150-1250°C and held for 1.0-2.0 hours, and the initial rolling temperature is controlled for rolling. As a preferred embodiment, this invention employs a three-pass rolling process: the billet is held at 1200℃ for 1.5 hours, then cooled in the furnace to 1000℃ and descaled, followed by rolling. Specific process parameters are: first pass reduction of 30.0%, rolling temperature 1000±20℃; second pass reduction of 28.6%, rolling temperature 950±20℃; third pass reduction of 30.0%, rolling temperature 900±20℃. The total reduction across the three passes is controlled at 60%–70%, and the final rolling temperature is controlled at 900±20℃. After rolling, the billet is air-cooled to room temperature to obtain HRB400 rebar. If the initial rolling temperature, final rolling temperature, deformation amount, and cooling rate are not properly controlled, significant ferrite-pearlite banded structures, grain coarsening, or continuous pearlite distribution may form, exacerbating electrochemical differences between microstructures. In this case, even if inclusions have been effectively modified, severe microstructure inhomogeneity may still provide a continuous expansion channel for localized corrosion. Therefore, by combining inclusion modification with controlled rolling process, it is beneficial to obtain HRB400 rebar with fine grains, uniform distribution of ferrite and pearlite, and no obvious banded structure.

[0060] In summary, through the above-mentioned component design, proportion control, and preparation methods, inclusions in steel can be mainly transformed into La-Ce-Ca-OS, La-Ce-OS, La-Ce-S, La-Ce-Al-O, or La-Ce-Mn-S type composite inclusions. The average size of the inclusions is no greater than 2.5 μm, the maximum size is no greater than 8.0 μm, the aspect ratio is no greater than 3, and the proportion of spherical or near-spherical inclusions is no less than 70%. Through inclusion refinement, spheroidization, and dispersion, this invention can reduce the sensitivity to inclusion-induced pitting corrosion and improve the continuity and stability of the corrosion product film while maintaining the yield strength, tensile strength, and plasticity of HRB400 rebar. This improves the performance of the rebar in marine atmospheres, port terminals, de-icing salt roads, chloride-contaminated concrete, saline soil, and dry-wet cycle Cl-containing environments. - Corrosion resistance in the environment.

[0061] To more clearly illustrate the technical solution and advantages of the present invention, the following describes in detail a corrosion-resistant HRB400 rebar and its preparation method through several embodiments.

[0062] Example 1: The corrosion-resistant HRB400 rebar contains the following components by weight percentage (wt.%): C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0015%, Ce: 0.0015%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities; among which, the total content of La+Ce is 0.0030%, A=(La+Ce) / S is 0.75, B=La / Ce is 1.00, D=Ca / S is 0.50, F=Al / O is 11.11, and E=(La+Ce+Ca) / (O+S) is 0.86; (1) The iron source (HRB400 base material, with the following specific composition: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, TO: 0.0018%, with the balance being Fe) was placed in a vacuum induction furnace, evacuated to a vacuum level not exceeding 10 Pa, heated to 1580℃ and completely melted, then vacuum refined for 15 min, and backfilled with argon gas to 0.03 MPa. Under this atmosphere, samples were taken for testing, and the C, Si, Mn, V, P and S elements were adjusted to the target content using graphite, FeSi, FeMn and FeV to obtain the base steel liquid; (2) The base steel liquid is controlled at 1580℃. Under the protection of argon, aluminum material (aluminum block) is added in batches for deoxidation treatment. After weak electromagnetic stirring for 5 minutes, it is left to stand for 5 minutes and then sampled to control the total oxygen content and Al / O ratio in the steel to the target range. (3) Reduce the temperature of the deoxidized molten steel to 1570℃. Under the protection of argon, press the calcium-containing raw material (calcium-silicon alloy) into the molten steel to a depth of 1 / 2 below the surface of the molten steel. Use weak electromagnetic stirring for 5 minutes to pre-modify the inclusions in order to control the Ca / S ratio to the target range. (4) After the pre-modification is completed and the composition and temperature of the molten steel are stable, at 1570°C under an argon protective atmosphere, the raw material containing lanthanum and cerium (lanthanum-cerium master alloy) is pressed into the molten steel to a depth of 1 / 2 below the surface of the molten steel. Argon is used for soft blowing for 10 minutes, and then it is left to stand for 5 minutes to carry out the final modification of the inclusions, so as to control the (La+Ce) / S ratio, La / Ce ratio and (La+Ce+Ca) / (O+S) ratio to the target range. (5) Adjust the temperature of the final modified molten steel to 1550℃ and pour it into the steel ingot mold at 250℃ at a uniform speed under the protection of argon. Keep the pouring process continuous and avoid slag entrapment and secondary oxidation. After the steel ingot is completely solidified and cooled, demold it to obtain the steel ingot. After cleaning the defects on the surface of the steel ingot, heat the steel ingot to 1170℃ and hold it for 1.0h. The initial forging temperature is 1120℃ and the final forging temperature is not lower than 850℃. Use two-way upsetting and drawing to make the total forging ratio not lower than 3 and forge it into a rolled steel billet with a thickness of 20±1 mm. Then air cool it to room temperature. The forged steel billet was heated to 1200℃ and held for 1.5 h, then furnace cooled to 1000℃ and descaled before undergoing three-pass rolling. The first pass rolled the billet from 20 mm to 14 mm (30.0% reduction) at 1000℃; the second pass rolled it from 14 mm to 10 mm (28.6% reduction) at 950℃; and the third pass rolled it from 10 mm to 7 mm (30.0% reduction) at 900℃. The total reduction was 65.0%, and the final rolling temperature was controlled at 900℃. After rolling, the billet was air-cooled to room temperature to obtain corrosion-resistant HRB400 rebar.

[0063] Example 2: Example 2 is basically the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0020%, Ce: 0.0020%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. Specifically, the total La+Ce content is 0.0040%, A = (La+Ce) / S is 1.00, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 1.03.

[0064] Example 3: Example 3 is basically the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0025%, Ce: 0.0025%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. Specifically, the total La+Ce content is 0.0050%, A = (La+Ce) / S is 1.25, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 1.21.

[0065] Example 4: Example 4 is basically the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0030%, Ce: 0.0030%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. The total La+Ce content is 0.0060%, A=(La+Ce) / S is 1.50, B=La / Ce is 1.00, D=Ca / S is 0.50, F=Al / O is 11.11, and E=(La+Ce+Ca) / (O+S) is 1.38.

[0066] Example 5: Example 5 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0034%, Ce: 0.0034%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. The total La+Ce content is 0.0068%, A = (La+Ce) / S is 1.70, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 1.52.

[0067] Example 6: Example 6 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0040%, Ce: 0.0040%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. Specifically, the total La+Ce content is 0.0080%, A = (La+Ce) / S is 2.0, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 1.72.

[0068] Example 7: Example 7 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0045%, Ce: 0.0045%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. The total La+Ce content is 0.0090%, A = (La+Ce) / S is 2.25, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 1.90.

[0069] Example 8: Example 8 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0050%, Ce: 0.0050%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. Specifically, the total La+Ce content is 0.0100%, A = (La+Ce) / S is 2.50, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 2.07.

[0070] Comparative Example 1: Comparative Example 1 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, TO: 0.0018%, with no added La and Ce, and the balance being Fe and other unavoidable impurities. Specifically, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La + Ce + Ca) / (O + S) is 0.34.

[0071] Comparative Example 2: Comparative Example 2 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0005%, Ce: 0.0005%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. Specifically, the total La+Ce content is 0.0010%, A = (La+Ce) / S is 0.25, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 0.52.

[0072] Comparative Example 3: Comparative Example 3 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0010%, Ce: 0.0010%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. Specifically, the total La+Ce content is 0.0020%, A = (La+Ce) / S is 0.50, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 0.69.

[0073] Comparative Example 4: Comparative Example 4 is essentially the same as Example 1, except that, by mass percentage (wt.%), the corrosion-resistant HRB400 rebar contains the following components: C: 0.24%, Si: 0.50%, Mn: 1.50%, V: 0.03%, P: 0.005%, S: 0.0040%, Al: 0.0200%, Ca: 0.0020%, La: 0.0055%, Ce: 0.0055%, TO: 0.0018%, with the balance being Fe and other unavoidable impurities. The total La+Ce content is 0.0110%, A = (La+Ce) / S is 2.75, B = La / Ce is 1.00, D = Ca / S is 0.50, F = Al / O is 11.11, and E = (La+Ce+Ca) / (O+S) is 2.24.

[0074] Comparative Example 5: Comparative Example 5 is basically the same as Example 1, except that in steps (2), (3) and (4), the base molten steel is controlled at 1580°C and in an argon protective atmosphere, aluminum material (aluminum block), calcium-containing raw material (calcium-silicon alloy) and lanthanum and cerium-containing raw material (lanthanum-cerium intermediate alloy) with the same content as in Example 1 are stirred weakly with electromagnetic stirring for 30 minutes and then allowed to stand for 5 minutes to obtain modified molten steel.

[0075] Electrochemical tests were conducted on the corrosion-resistant HRB400 rebar (hereinafter referred to as samples) prepared in the examples and comparative examples. The test results are shown in Table 1.

[0076] The electrochemical tests were conducted in a mixed solution of saturated Ca(OH)2 and 1.0 wt.% NaCl to simulate the pore fluid environment of Cl---containing concrete. Pitting potential and passivation current density tests were performed using electrochemical polarization curve fitting. Specifically: First, a 10×10×3 mm block sample was cut, copper wire was soldered to the sample, and then it was sealed with epoxy resin, leaving one sample surface as the working surface. Next, the working surface was successively polished with 240#, 400#, 800#, 1500#, and 2000# SiC sandpaper, then rinsed and dried with deionized water and anhydrous ethanol. Finally, electrochemical tests were conducted using a DH7006 electrochemical workstation. All experiments were performed in a three-electrode system, using a platinum sheet as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode. To ensure the accuracy of the test results, all electrochemical tests were repeated at least three times. The passivation behavior of rebar was studied using a PDP. The test range started from -250 mV and scanned towards the anodic region at a scan rate of 1 mV / s. When the anodic current density reached 1 mA / cm², the passivation was investigated. 2 Stop scanning when the time is right.

[0077] Table 1 As shown in Table 1, under the condition that B=La / Ce, D=Ca / S, and F=Al / O remain consistent, as A=(La+Ce) / S and E=(La+Ce+Ca) / (O+S) increase, the pitting potential of rebar generally shows a trend of first increasing and then decreasing, while the passivation current density generally shows a trend of first decreasing and then increasing. When A is below 0.75 and E is below 0.80, the improvement effect on pitting resistance is limited due to insufficient addition of La and Ce. When A is 0.75~2.50 and E is 0.80~2.20, the corrosion resistance is better than that of Comparative Example 1 without the addition of La and Ce. Among them, Example 5, with A of 1.70 and E of 1.52, exhibited the best pitting corrosion resistance. Compared with Comparative Example 1, its pitting potential shifted positively by 0.80 V, and its passivation current density decreased by approximately 26.1%. When A was further increased to 2.75 and E to 2.24, the pitting potential of Comparative Example 4 decreased to 0.10 V, and its passivation current density increased to 3.28 × 10⁻⁶ V. -5 A / cm 2 This indicates that excessive addition of La and Ce may lead to the formation of coarse or agglomerated rare earth oxides, sulfides, and oxysulfides, thereby weakening the modification effect of inclusions and the stabilization effect of the passivation film.

[0078] Furthermore, in combination Figure 1 and Figure 2It can be seen that the microstructures of Example 5 and Comparative Example 3 are both ferrite and pearlite. The addition of appropriate amounts of La and Ce did not change the microstructure type of the steel, but the pearlite content increased. Figure 3 and Figure 4 As can be seen, the inclusions in Example 1 are spherical or near-spherical, and elements such as La, Ce, Si, and Mn were detected; while the inclusions in Comparative Example 1 are mainly long strips of MnS extending along the rolling direction. Spherical or near-spherical rare earth composite inclusions can reduce interface defects and local stress concentration between the inclusions and the steel matrix, thereby reducing the pitting corrosion sensitivity caused by the selective dissolution of MnS. Meanwhile, due to… Figure 5 and Figure 6 As can be seen from the above, compared with Comparative Example 1, the Fe content in the surface corrosion product film of Example 8 is significantly lower. 3+ / Fe 2+ Related components and O 2- OH - The relevant components are more clearly defined, indicating that the La and Ce composite treatment that satisfies the multi-element ratio is beneficial to promoting the formation of corrosion products such as oxides and hydroxy oxides, improving the continuity and stability of the corrosion product film, and thus enhancing the steel's resistance to Cl content. - Resistance to pitting corrosion in the environment.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A corrosion-resistant HRB400 rebar, characterized in that, It contains the following components by mass percentage: C: 0.20~0.30%, Si: 0.35~0.65%, Mn: 1.30~1.70%, V: 0.01~0.06%, P: ≤0.015%, S: ≤0.008%, Al: 0.005~0.040%, Ca: 0.0005~0.0040%, La+Ce: 0.0010~0.0100%, TO: ≤0.0040%, with the balance being Fe and other unavoidable impurities.

2. The rebar according to claim 1, characterized in that, It contains the following components by mass percentage: C: 0.23~0.27%, Si: 0.45~0.55%, Mn: 1.45~1.60%, V: 0.02~0.04%, P: ≤0.010%, S: ≤0.005%, Al: 0.010~0.030%, Ca: 0.0010~0.0030%, La+Ce: 0.0030~0.0080%, TO: ≤0.0030%, with the balance being Fe and other unavoidable impurities.

3. The rebar according to claim 1 or 2, characterized in that, The mass percentages of O and Al satisfy the following relationship: 。 4. The rebar according to claim 3, characterized in that, The mass percentages of Ca and S satisfy the following relationship: 。 5. The rebar according to claim 4, characterized in that, The mass percentages of La, Ce, and S satisfy the following relationship: 。 6. The rebar according to claim 5, characterized in that, The mass percentages of La, Ce, Ca, O, and S satisfy the following relationship: 。 7. A method for preparing corrosion-resistant HRB400 rebar according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: (1) The iron source is mixed, smelted and refined under a protective atmosphere, and the C, Si, Mn, V, P and S elements are adjusted to the target content to obtain the basic molten steel; (2) Under a protective atmosphere, aluminum material is added to the base steel liquid for deoxidation treatment in order to control the total oxygen content and Al / O ratio in the steel to the target range; (3) Under a protective atmosphere, calcium-containing raw materials are added to the deoxidized molten steel to pre-modify the inclusions in order to control the Ca / S ratio to the target range; (4) Under a protective atmosphere, lanthanum and cerium-containing raw materials are added to the pre-modified molten steel to perform final modification of inclusions, so as to control the (La+Ce) / S ratio, La / Ce ratio and (La+Ce+Ca) / (O+S) ratio to the target range. (5) The final modified molten steel is cast into ingots under a protective atmosphere, and the ingots are forged and rolled in sequence. After cooling, the corrosion-resistant HRB400 rebar is obtained.

8. The preparation method according to claim 7, characterized in that, In step (1), the iron source is pure iron, low-phosphorus and low-sulfur scrap steel, or HRB400 base material; The melting temperature is 1580~1600℃, and the refining time after the furnace charge is melted is 10~15min.

9. The preparation method according to claim 7, characterized in that, In step (2), the aluminum raw material is aluminum block or aluminum wire; aluminum material is added in batches at 1580~1600℃ and stirred for 3~5 minutes for deoxidation treatment; In step (3), the calcium-containing raw material is a calcium-silicon alloy or a calcium-containing cored wire; preferably, the calcium-containing raw material is added at 1560~1580℃ and stirred for 3~8 minutes to pre-modify the inclusions; In step (4), the raw material containing lanthanum and cerium is a lanthanum-cerium master alloy or a lanthanum-cerium cored wire; preferably, the raw material containing lanthanum and cerium is added at 1550~1580℃ and the inclusions are finally modified by soft blowing argon gas for 5~15min.

10. The preparation method according to claim 7, characterized in that, In step (5), the pouring temperature is 1530~1560℃; During the forging process, the initial forging temperature is 1100~1150℃, and the final forging temperature is not lower than 850℃; During the rolling process, the initial rolling temperature is 980~1100℃, and the final rolling temperature is 850~950℃; The preferred rolling process is three-pass rolling, with a total reduction rate of 60-70%.

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