High corrosion resistance 500mpa grade chloride ion corrosion resistant steel bar and its production method

Abstract

The present application relates to a kind of high corrosion resistance 500MPa grade resistance to chloride ion corrosion reinforcing bar and its production method, belong to hot-rolled ribbed steel bar technical field.The present application is by optimizing alloy element content and proportion, improve the microstructure of steel, improve grain boundary cementite morphology or precipitation, improve the strength of steel without reducing even improving plasticity, improve the mechanical properties and corrosion performance of steel, obtain the reinforcing bar with excellent corrosion resistance, the mechanical properties of reinforcing bar are, Rp 0.2 ≥550MPa, Rm≥780MPa, A≥18%, Agt≥10.5%; When periodic infiltration corrosion test, relative corrosion rate is 60% or less;Meanwhile, the production cost of the reinforcing bar is lower, the process operability is strong, is suitable for enterprise mass popularization and use, and the performance of reinforcing bar meets 500MPa grade resistance to chloride ion corrosion standard.

Description

Technical Field

[0001] This invention belongs to the technical field of hot-rolled ribbed steel bars, specifically relating to a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar and its production method. Background Technology

[0002] With the rapid development of my country's national economy, the existing hot-dip galvanized anti-corrosion Q235B and Q345B structural steels and ordinary corrosion-resistant reinforcing bars can no longer meet the requirements for various steel applications demanding high corrosion resistance, long service life, and low cost. There is an urgent need to develop new energy-saving, environmentally friendly, and highly corrosion-resistant structural reinforcing bars. Therefore, while maintaining good corrosion resistance, adopting next-generation steel material production technologies to improve strength and enhance the overall performance of steel, the development of a new generation of economical corrosion-resistant reinforcing bars will inevitably replace traditional corrosion-resistant reinforcing bars.

[0003] my country is also accelerating the research and development of alloy corrosion-resistant steel bars, with Cu-P series and Cr 3-5wt.% alloy corrosion-resistant steel bars being developed. However, these corrosion-resistant steel bars can only meet the 400MPa level, which cannot meet the high strength requirements of construction. At the same time, their corrosion resistance is limited, with a relative corrosion rate of 60-70%, and their production cost is high, making it difficult to promote and use them on a large scale.

[0004] Traditional corrosion-resistant steel bars have limited applications and are difficult to promote on a large scale due to their high alloy content, low strength-to-yield ratio, poor plasticity, high price, and low corrosion resistance. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention provides a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar and its production method. By optimizing the content and ratio of alloying elements, the microstructure of the steel is improved, the morphology or precipitation of cementite at grain boundaries is improved, the strength of the steel is increased without reducing or even increasing its plasticity, and the mechanical and corrosion properties of the steel are improved, resulting in a steel bar with excellent corrosion resistance. The mechanical properties of the steel bar are Rp 0.2 ≥550MPa, Rm≥780MPa, A≥18%, Att≥10.5%; during the periodic immersion corrosion test, the relative corrosion rate is below 60%; at the same time, the production cost of this steel bar is low, the process is easy to operate, and it is suitable for large-scale promotion and use by enterprises. All properties of the steel bar meet the 500MPa grade chloride ion corrosion resistance standard.

[0006] A high corrosion-resistant 500MPa grade chloride ion corrosion-resistant steel bar, the chemical composition by mass percentage includes: C: 0.08-0.10%, Si: 0.45-0.55%, Mn: 1.1-1.3%, Cu: 0.5-0.55%, Cr: 1.0-1.1%, Ni: 0.50-0.55%, P: 0.02-0.03%, S: 0.008-0.01%, V: 0.05-0.08%, Ti≤0.1%, Al≤0.1%, with the balance being Fe and unavoidable impurities.

[0007] The high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar has a yield strength ≥550MPa, tensile strength ≥780MPa, elongation after fracture ≥18%, and total elongation under maximum force ≥10.5%.

[0008] The microstructure of the high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar is ferrite, pearlite and bainite, of which ferrite accounts for 28% to 40%.

[0009] The high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar has a grain size of 10-11.

[0010] The high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bars exhibited an average corrosion rate of 5.6473–5.9413 g / (m²) in a 72-hour accelerated immersion corrosion test. 2 •h), with a relative corrosion rate of no more than 60%.

[0011] A production process for high corrosion resistance (500MPa grade) and chloride ion corrosion resistant steel bars includes the following steps:

[0012] (1) Converter roughing: High-quality scrap steel is used. The amount of copper-nickel alloy and nickel-iron is determined according to the amount of trace alloying elements collected in special scrap steel, and is added into the furnace with the scrap steel at the lower limit. The final slag basicity is controlled at R=2.8~3.2, and the final lance pressing time is >40s. Bottom blowing argon gas is used for stirring throughout the converter blowing process. Converter final control: the steel tapping C is controlled at 0.04%~0.05%, and the converter tapping temperature is controlled at 1640℃~1660℃. Bottom blowing argon gas is turned on 1~2 minutes in advance before tapping, and large volume stirring is used during the tapping process. Clean turnover steel ladle is used to ensure red ladle tapping. Double slag blocking is used with slag plug + slag cone, and the slag layer thickness in the ladle is <50mm.

[0013] (2) Refining: The composition is finely adjusted by using low-aluminum ferrosilicon, ferromanganese silicon, low-carbon ferrochrome, vanadium-nitrogen alloy, etc., and the addition is completed when the molten steel is 2 / 3 poured; deoxidation and alloying are carried out in the ladle; slag washing: lime and quartz sand are added with the steel stream during the tapping process. The lime and quartz sand are added when the steel is 1 / 3 poured, along with the alloy; the bottom blowing argon stirring is carried out throughout the tapping process, and the ladle is blown in the argon station for 3 minutes and then sampled;

[0014] (3) Rolling: The steel bars are obtained by rolling.

[0015] Further, in step (1), 6.1 to 6.3 kg / t of low-carbon ferrochrome is added to the converter roughing process, and in step (2), 11 to 12 kg / t of low-carbon ferrochrome is added to the refining process.

[0016] Further, in step (3), the rolling heating temperature is 1150℃~1200℃, and after holding for 100~120 minutes, hot continuous rolling is carried out. The initial rolling temperature is 1080~1140℃. During the rolling process, water quenching is controlled, the finishing rolling temperature is controlled at 950~1080℃, and the final rolling temperature is 930℃~1070℃.

[0017] Furthermore, in step (3), the temperature of the upper cooling bed is 900℃~1050℃, the post-rolling cooling method is slow cooling, and the cooling rate is controlled below 1℃ / s.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention optimizes the alloy composition system and smelting process. The entire converter blowing process employs bottom-blown argon stirring and a double slag-blocking system (slag plug + slag cone) to prevent excessive slag discharge. Slag is formed using lime and ferrosilicon powder, and the addition of fluorite ensures submerged arc refining. The liquidus temperature is controlled at 1515℃, the superheat at 30-40℃, and the casting speed ≥2.2m / min. The tundish working layer uses magnesia dry material with a baking temperature ≥1000℃. The tundish uses a stopper rod tundish or a quick-change sizing tundish. Long nozzles can be used from the ladle to the tundish, and a sealed cover is used on the tundish to reduce temperature drop and secondary oxidation.

[0020] This invention designs a new composition system, optimizing the content of elements such as Cu, Cr, Ni, and V, and considering the strengthening and corrosion resistance mechanisms of each element. This refines the grain size of the steel, improves the strength of the reinforcing steel, and ensures that all properties of the reinforcing steel meet the 500MPa chloride ion corrosion resistance standard. Employing a process of "high-temperature initial rolling + low-temperature finishing rolling + slow cooling after rolling," and rationally controlling the heating temperature, initial rolling temperature, finishing rolling temperature, cooling bed temperature, and cooling method, the steel structure is composed of ferrite, pearlite, and a small amount of bainite. This results in reinforcing steel with excellent strength, toughness, and corrosion resistance, solving the problem of simultaneously achieving corrosion resistance, mechanical properties, and cost in chloride ion corrosion-resistant reinforcing steel, fully meeting national standards. It possesses excellent corrosion resistance, comprehensive mechanical properties, and weldability, and can be manufactured with relatively low material and process costs, making it suitable for widespread use in marine engineering. Attached Figure Description

[0021] Figure 1 Prepared as in Example 1 Microstructure of chloride ion corrosion resistant steel bars;

[0022] Figure 2 Prepared for Example 2 Microstructure of chloride ion corrosion resistant steel bars;

[0023] Figure 3 Prepared as in Example 1 Corrosion morphology of chloride-resistant steel bars and ordinary steel bars after immersion in a 2% NaCl solution for 72 hours. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description of the invention will be given below with reference to the accompanying drawings, and several embodiments of the invention will be provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be more thorough and complete.

[0025] Example 1

[0026] This invention provides a high-corrosion-resistant 500MPa grade chloride ion corrosion-resistant steel bar. Its chemical composition, by mass percentage, includes: C: 0.08%, Si: 0.50%, Mn: 1.25%, Cu: 0.55%, Cr: 1.1%, Ni: 0.55%, P: 0.02%, S: 0.008%, V: 0.05%, Ti≤0.1%, Al≤0.1%, with the balance being Fe and unavoidable impurities. This invention achieves this by controlling the content of alloying elements such as C, Si, Mn, Cu, Cr, Ni, P, and S.

[0027] Carbon (C) is a fundamental element in steel materials, and its strength can be improved through solid solution strengthening and carbide precipitation strengthening. Higher C content generally results in higher steel strength, but lower plasticity and toughness. Furthermore, considering weldability, this invention significantly reduces the C content compared to existing steel reinforcement (0.22–0.28%). Therefore, to ensure the comprehensive mechanical properties of steel, the C content should be minimized while still meeting the required strength. The C content in this invention is 0.08–0.10%.

[0028] Si (Si) acts as a solid solution strengthening agent, increasing the strength of steel and achieving a low yield strength ratio. However, excessive Si content significantly reduces the plasticity and toughness of the steel. Therefore, the Si content in this invention is between 0.45% and 0.55%. Mn (Mn) is a deoxidizer and desulfurizer, increasing the strength and hardenability of steel. It helps to improve the hardness and strength of ferrite and austenite in steel. It is also an element that forms carbides, but it reduces elongation and the yield strength ratio.

[0029] Excessive Mn content can lead to segregation and affect the stability of the microstructure. In this invention, the Mn content is 1.1–1.3%. V has precipitation strengthening and grain refinement strengthening effects, simultaneously improving the strength and toughness of the steel and ensuring its ductility. Generally, VN is added to enhance precipitation strengthening. VN alloy appears as black dots in the steel, providing both precipitation strengthening and solid solution strengthening. Simultaneously, alloying elements can also refine the grain structure, acting as austenite grain boundaries and inhibiting austenite growth. In this invention, V is 0.05–0.08%, saving costs.

[0030] Cr strengthens ferrite through solid solution strengthening, but relatively reduces ductility and toughness. Cr can also significantly increase the hardenability of steel, and has a high strengthening effect on low alloy steel, improving the strength, hardness, wear resistance, and corrosion resistance of steel. However, the tendency of steel to temper brittleness increases with increasing Cr content.

[0031] The addition of Cu is to precipitate Cu-containing precipitates, which has been considered an effective element for improving corrosion resistance. Moreover, based on considerations of weldability and cost, the Cr content of this invention is 1.0-1.1%, and the Cu content of this invention is 0.5-0.55%.

[0032] A production process for high corrosion resistance (500MPa grade) and chloride ion corrosion resistant steel bars includes the following steps:

[0033] (1) Converter roughing: Strictly charge 95 tons, use high-quality scrap steel to reduce impurities; determine the amount of copper-nickel alloy and nickel-iron to be added according to the amount of trace alloying elements recovered in special scrap steel, and add them into the furnace with the scrap steel at the lower limit; control the basicity of the final slag at R=2.8~3.2, and the final lance pressing time >40s; use bottom blowing argon gas to stir the entire converter blowing process; final control: control the steel tapping C at 0.04%~0.05%, strengthen the control of carbon-oxygen product, and strictly prevent the steel from over-oxidizing; control the converter tapping temperature between 1640℃ and 1660℃; use a steel ladle with good permeability of permeable bricks, turn on the bottom blowing argon gas 1~2 minutes before tapping, and stir the steel with a large volume of gas during the tapping process to ensure that the alloys are fully melted; use a clean turnover steel ladle to ensure that the steel is tapped from the ladle, and use a double slag blocking plug + slag blocking cone to prevent a large amount of slag from falling, and the slag layer thickness inside the ladle is <50mm;

[0034] (2) Low-aluminum ferrosilicon, ferromanganese silicomanganese, low-carbon ferrochrome, vanadium-nitrogen alloy, etc. are used and added when the molten steel is 2 / 3 full; 6.1-6.3 kg / t of low-carbon ferrochrome is added to the converter and 11-12 kg / t of low-carbon ferrochrome is added to the refining process. Deoxidation and alloying are carried out in the ladle; slag washing: lime and quartz sand are added with the steel stream during the tapping process, and the timing of addition is when 1 / 3 of the steel is tapped, added together with the alloy; the bottom blowing argon stirring is carried out throughout the tapping process, and the ladle is blown into the argon station for 3 minutes for sampling.

[0035] (3) Rolling: The heating temperature is controlled at 1150℃~1200℃, and after holding at that temperature for 100~120 minutes, hot continuous rolling is carried out. The initial rolling temperature is 1120~1140℃, the finishing rolling temperature is 1000~1020℃, and the final rolling temperature is 1020℃~1040℃. No water quenching is performed during the rolling process. The upper cooling bed temperature is 1020℃~1050℃, and the post-rolling cooling method is slow cooling, with the cooling rate controlled below 1℃ / s.

[0036] The embodiment obtained The reinforcing steel has a yield strength of 550 MPa, a tensile strength of 790 MPa, an elongation after fracture ≥19%, and a total elongation at maximum force ≥11%. The microstructure of the reinforcing steel obtained in this embodiment is shown in the figure below. Figure 1 As shown, the microstructure of the reinforcing steel consists of ferrite, pearlite, and bainite, with ferrite accounting for 35%–40%. The grain size of the reinforcing steel is grade 10, and in a 72-hour immersion accelerated corrosion test, the average corrosion rate is 5.8298 g / (m²). 2 The relative corrosion rate is not greater than 60%. The steel bars obtained in this example and ordinary steel bars were immersed in a 2% NaCl solution for 72 hours. The corrosion morphology of the corrosion samples is shown in the following figures. Figure 3 As shown.

[0037] Example 2

[0038] This invention provides a high-corrosion-resistant 500MPa grade chloride ion corrosion-resistant steel bar. Its chemical composition, by mass percentage, includes: C: 0.08%, Si: 0.50%, Mn: 1.25%, Cu: 0.55%, Cr: 1.1%, Ni: 0.55%, P: 0.02%, S: 0.008%, V: 0.05%, Ti≤0.1%, Al≤0.1%, with the balance being Fe and unavoidable impurities. This invention achieves this by controlling the content of alloying elements such as C, Si, Mn, Cu, Cr, Ni, P, and S.

[0039] A production process for high corrosion resistance (500MPa grade) and chloride ion corrosion resistant steel bars includes the following steps:

[0040] (1) Converter roughing: Strictly charge 95 tons, use high-quality scrap steel to reduce impurities; determine the amount of copper-nickel alloy and nickel-iron to be added according to the amount of trace alloying elements recovered in special scrap steel, and add them into the furnace with the scrap steel at the lower limit; control the final slag basicity at R=2.8~3.2, and the final lance pressing time>40s; use bottom blowing argon gas to stir the entire converter blowing process; final control: control the steel tapping C at 0.04%~0.05%, strengthen the control of carbon-oxygen product, and strictly prevent the steel from over-oxidizing; control the converter tapping temperature between 1640℃ and 1660℃; use a steel ladle with good permeability using permeable bricks, turn on the bottom blowing argon gas 1-2 minutes before tapping, and use a large volume of stirring during the tapping process to ensure that the alloys are fully melted; use a clean turnover steel ladle to ensure that the steel is tapped from the ladle, and use a double slag blocking plug + slag blocking cone to prevent a large amount of slag from falling, and the slag layer thickness inside the ladle is <50mm;

[0041] (2) Low-aluminum ferrosilicon, ferromanganese silicomanganese, low-carbon ferrochrome, vanadium-nitrogen alloy, etc. are used and added when the molten steel is 2 / 3 full; 6.1-6.3 kg / t of low-carbon ferrochrome is added to the converter, and 11-12 kg / t of low-carbon ferrochrome is added during refining. Deoxidation and alloying are carried out in the ladle; slag washing: lime and quartz sand are added with the steel stream during the tapping process, and the timing of addition is when 1 / 3 of the steel is tapped, added together with the alloy; the bottom blowing argon stirring is carried out throughout the tapping process, and the ladle is blown into the argon station for 3 minutes for sampling.

[0042] (3) Rolling: The heating temperature is controlled at 1150℃~1200℃, and after holding at that temperature for 100~120 minutes, hot continuous rolling is carried out. The initial rolling temperature is 1100~1120℃, the finishing rolling temperature is 990℃~1030℃, and the final rolling temperature is 1000℃~1040℃. Pre-water piercing is performed during the rolling process, the upper cooling bed temperature is 1000℃~1050℃, and the post-rolling cooling method is slow cooling, with the cooling rate controlled below 1℃ / s.

[0043] The embodiment obtained The reinforcing steel has a yield strength of 570 MPa, a tensile strength of 800 MPa, an elongation after fracture ≥20%, and a total elongation at maximum force ≥11.8%. The microstructure of the reinforcing steel obtained in this embodiment is shown below. Figure 2 As shown, the microstructure of the reinforcing steel consists of ferrite, pearlite, and bainite, with ferrite accounting for 33%–37%. The grain size of the reinforcing steel is grade 10.5. In a 72-hour accelerated corrosion immersion test, the average corrosion rate was 5.6473 g / (m²). 2 •h), with a relative corrosion rate of no more than 60%.

[0044] Example 3

[0045] This invention provides a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar. Its chemical composition, by mass percentage, includes: C: 0.08%, Si: 0.55%, Mn: 1.3%, Cu: 0.5%, Cr: 1.0%, Ni: 0.55%, P: 0.02%, S: 0.008%, V: 0.08%, Ti≤0.1%, Al≤0.1%, with the balance being Fe and unavoidable impurities.

[0046] A production process for high corrosion resistance (500MPa grade) and chloride ion corrosion resistant steel bars includes the following steps:

[0047] (1) Converter roughing: Strictly charge 95 tons, use high-quality scrap steel to reduce impurities; determine the amount of copper-nickel alloy and nickel-iron to be added according to the amount of trace alloying elements recovered in special scrap steel, and add them into the furnace with the scrap steel at the lower limit; control the final slag basicity at R=2.8~3.2, and the final lance pressing time>40s; use bottom blowing argon gas to stir the entire converter blowing process; final control: control the steel tapping C at 0.04%~0.05%, strengthen the control of carbon-oxygen product, and strictly prevent the steel from over-oxidizing; control the converter tapping temperature between 1640℃ and 1660℃; use a steel ladle with good permeability using permeable bricks, turn on the bottom blowing argon gas 1-2 minutes before tapping, and use a large volume of stirring during the tapping process to ensure that the alloys are fully melted; use a clean turnover steel ladle to ensure that the steel is tapped from the ladle, and use a double slag blocking plug + slag blocking cone to prevent a large amount of slag from falling, and the slag layer thickness inside the ladle is <50mm;

[0048] (2) Low-aluminum ferrosilicon, ferromanganese silicomanganese, low-carbon ferrochrome, vanadium-nitrogen alloy, etc. are used and added when the molten steel is 2 / 3 full; 6.1-6.3 kg / t of low-carbon ferrochrome is added to the converter, and 11-12 kg / t of low-carbon ferrochrome is added during refining. Deoxidation and alloying are carried out in the ladle; slag washing: lime and quartz sand are added with the steel stream during the tapping process, and the timing of addition is when 1 / 3 of the steel is tapped, added together with the alloy; the bottom blowing argon stirring is carried out throughout the tapping process, and the ladle is blown into the argon station for 3 minutes for sampling.

[0049] (3) Rolling: The heating temperature is controlled at 1150℃~1200℃, and after holding at that temperature for 100~120 minutes, hot continuous rolling is carried out. The initial rolling temperature is 1140~1160℃, the finishing rolling temperature is 1050℃~1080℃, and the final rolling temperature is 1040℃~1070℃. No water quenching is performed during the rolling process. The upper cooling bed temperature is 1010℃~1040℃, and the post-rolling cooling method is slow cooling, with the cooling rate controlled below 1℃ / s.

[0050] The embodiment obtained The reinforcing steel has a yield strength of 555 MPa, a tensile strength of 780 MPa, an elongation after fracture ≥21%, and a total elongation at maximum force ≥13%. The microstructure of the reinforcing steel consists of ferrite, pearlite, and bainite, with ferrite accounting for 36%–40%. The grain size of the reinforcing steel is grade 10.5. In a 72-hour accelerated corrosion immersion test, the average corrosion rate was 5.8610 g / (m³). 2 •h), with a relative corrosion rate of no more than 60%.

[0051] Example 4

[0052] This invention provides a high-corrosion-resistant 500MPa grade chloride ion corrosion-resistant steel bar. Its chemical composition, by mass percentage, includes: C: 0.08%, Si: 0.50%, Mn: 1.2%, Cu: 0.5%, Cr: 1.0%, Ni: 0.55%, P: 0.02%, S: 0.008%, V: 0.05%, Ti≤0.1%, Al≤0.1%. The balance is Fe and unavoidable impurities. This invention achieves this by controlling the content of alloying elements such as C, Si, Mn, Cu, Cr, Ni, P, and S.

[0053] A production process for high corrosion resistance (500MPa grade) and chloride ion corrosion resistant steel bars includes the following steps:

[0054] (1) Converter roughing: Strictly charge 95 tons, use high-quality scrap steel to reduce impurities; determine the amount of copper-nickel alloy and nickel-iron to be added according to the amount of trace alloying elements recovered in special scrap steel, and add them into the furnace with the scrap steel at the lower limit; control the basicity of the final slag at R=2.8~3.2, and the final lance pressing time >40s; use bottom blowing argon gas to stir the entire converter blowing process; final control: control the steel tapping C at 0.04%~0.05%, strengthen the control of carbon-oxygen product, and strictly prevent the steel from over-oxidizing; control the converter tapping temperature between 1640℃ and 1660℃; use a steel ladle with good permeability of permeable bricks, turn on the bottom blowing argon gas 1~2 minutes before tapping, and stir the steel with a large volume of gas during the tapping process to ensure that the alloys are fully melted; use a clean turnover steel ladle to ensure that the steel is tapped from the ladle, and use a double slag blocking plug + slag blocking cone to prevent a large amount of slag from falling, and the slag layer thickness inside the ladle is <50mm;

[0055] (2) Low-aluminum ferrosilicon, ferromanganese silicomanganese, low-carbon ferrochrome, vanadium-nitrogen alloy, etc. are used and added when the molten steel is 2 / 3 full; 6.1-6.3 kg / t of low-carbon ferrochrome is added to the converter, and 11-12 kg / t of low-carbon ferrochrome is added during refining. Deoxidation and alloying are carried out in the ladle; slag washing: lime and quartz sand are added with the steel stream during the tapping process, and the timing of addition is when 1 / 3 of the steel is tapped, added together with the alloy; the bottom blowing argon stirring is carried out throughout the tapping process, and the ladle is blown into the argon station for 3 minutes for sampling.

[0056] (3) Rolling: The heating temperature is controlled at 1150℃~1200℃, and after holding at this temperature for 100~120 minutes, hot continuous rolling is carried out. The initial rolling temperature is 1080~1000℃, the finishing rolling temperature is 950℃~970℃, and the final rolling temperature is 930℃~950℃. Pre-water piercing is performed during the rolling process, the upper cooling bed temperature is 900℃~920℃, and the post-rolling cooling method is slow cooling, with the cooling rate controlled below 1℃ / s.

[0057] The embodiment obtained The reinforcing steel has a yield strength of 585 MPa, a tensile strength of 810 MPa, an elongation after fracture ≥18%, and a total elongation at maximum force ≥10.5%. The microstructure of the reinforcing steel consists of ferrite, pearlite, and bainite, with ferrite accounting for 28%–32%. The grain size of the reinforcing steel is grade 11. In a 72-hour accelerated corrosion immersion test, the average corrosion rate was 5.9413 g / (m³). 2 •h), with a relative corrosion rate of no more than 60%.

[0058] Table 1 compares the 72-hour corrosion rates of the 500MPa grade chloride ion corrosion-resistant steel bars prepared in Examples 1-4 with those of ordinary steel bars. Table 2 shows the mechanical properties of the 500MPa grade chloride ion corrosion-resistant steel bars prepared in Examples 1-4. As can be seen from Tables 1 and 2, the 500MPa grade chloride ion corrosion-resistant steel bars prepared using the method of this invention exhibit a slower corrosion rate and higher yield strength and tensile strength.

[0059]

[0060] Table 1

[0061]

[0062] Table 2.

Claims

1. A production process for high corrosion resistance (500MPa grade) chloride ion corrosion resistant steel bars, characterized in that, The chemical composition, by mass percentage, includes: C: 0.08~0.10%, Si: 0.45~0.55%, Mn: 1.1~1.3%, Cu: 0.5~0.55%, Cr: 1.0~1.1%, Ni: 0.50~0.55%, P: 0.02~0.03%, S: 0.008~0.01%, V: 0.05~0.08%, Ti≤0.1%, Al≤0.1%, with the balance being Fe and unavoidable impurities; Includes the following steps: (1) Converter roughing: High-quality scrap steel is used. The amount of copper-nickel alloy and nickel-iron is determined according to the amount of trace alloying elements collected in special scrap steel, and is added into the furnace with the scrap steel at the lower limit. The final slag basicity is controlled at R=2.8~3.2, and the final lance pressing time is >40s. Bottom blowing argon gas is used for stirring throughout the converter blowing process. Converter final control: the steel tapping C is controlled at 0.04%~0.05%, and the converter tapping temperature is controlled at 1640℃~1660℃. Bottom blowing argon gas is turned on 1~2 minutes in advance before tapping, and large volume stirring is used during the tapping process. Clean turnover steel ladle is used to ensure red ladle tapping. Double slag blocking is used with slag plug + slag cone, and the slag layer thickness in the ladle is <50mm. (2) Refining: The composition is finely adjusted by using low-aluminum ferrosilicon, ferromanganese silicomanganese, low-carbon ferrochrome, and vanadium-nitrogen alloy. The addition is completed when the molten steel is 2 / 3 of the way through. Deoxidation and alloying are carried out in the ladle. Slag washing: Lime and quartz sand are added with the steel stream during the tapping process. The timing of adding lime and quartz sand is when 1 / 3 of the steel is tapped, and they are added together with the alloy. The bottom blowing argon stirring is carried out throughout the tapping process. The ladle is blown in the argon station for 3 minutes and then sampled. (3) Rolling: Rolling to obtain steel bars; In step (3), the heating temperature during the rolling process is 1150℃~1200℃. After holding the temperature for 100~120 minutes, hot continuous rolling is carried out. The initial rolling temperature is 1080~1140℃. Water quenching is controlled during the rolling process. The finishing rolling temperature is controlled at 950~1080℃, and the final rolling temperature is 930℃~1070℃. In step (3), the temperature of the upper cooling bed during the rolling process is 900℃~1050℃, and the cooling method after rolling is slow cooling with a cooling rate controlled below 1℃ / s.

2. The production process of a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar according to claim 1, characterized in that, The high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar has a yield strength ≥550MPa, tensile strength ≥780MPa, elongation after fracture ≥18%, and total elongation under maximum force ≥10.5%.

3. The production process of a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar according to claim 1, characterized in that, The microstructure of the high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar is ferrite, pearlite and bainite, of which ferrite accounts for 28%~40%.

4. The production process of a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar according to claim 1, characterized in that, The high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar has a grain size of 10~11.

5. The production process of a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar according to claim 1, characterized in that, The high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bars exhibited an average corrosion rate of 5.6473~5.9413 g / (m²) in a 72-hour accelerated immersion corrosion test. 2 •h), with a relative corrosion rate of no more than 60%.

6. The production process of a high corrosion resistance 500MPa grade chloride ion corrosion resistant steel bar according to claim 1, characterized in that, In step (1), 6.1~6.3 kg / t of low-carbon ferrochrome is added to the converter roughing process, and in step (2), 11~12 kg / t of low-carbon ferrochrome is added to the refining process.

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