CN112375995B

CN112375995B - 400MPa grade corrosion-resistant steel bar and its production method

Info

Publication number: CN112375995B
Application number: CN202110051522.4A
Authority: CN
Inventors: 麻晗; 周云; 赵家七; 张宇; 陈焕德
Original assignee: Jiangsu Shagang Group Co Ltd; China Railway Design Corp; Jiangsu Shagang Iron and Steel Research Institute Co Ltd
Current assignee: Jiangsu Shagang Group Co Ltd; China Railway Design Corp; Jiangsu Shagang Iron and Steel Research Institute Co Ltd
Priority date: 2021-01-15
Filing date: 2021-01-15
Publication date: 2021-05-07
Anticipated expiration: 2041-01-15
Also published as: EP4279626A1; KR20230118953A; CN112375995A; WO2022151603A1; US20240068064A1; JP2024504120A; EP4279626A4; CN113186472B; CN113186472A

Abstract

本发明揭示了一种400MPa级耐蚀钢筋及其生产方法。钢筋化学成分包括：铬:9.5~10.4%，钼:1.0~1.2%，锰:0.3~0.6%，镍:0.01~1%，铜:0.01~0.5%，碳≤0.014%，氮≤0.004%，铌:0.01~0.05%，硅:0.2~0.6%，铬＋钼＋0.5锰＋0.35镍+0.25铜为11.1~12.2%，碳+氮+0.3硅+锰+1.8铌为0.4~0.8%，余量铁。微观组织为贝氏体和28%~40%铁素体；R_p0.2≥420MPa，Rm≥540MPa，A≥18%，Agt≥7.5%；模拟海洋环境腐蚀试验时，耐蚀性能提高45倍以上，自腐蚀电位正移0.4V且电流密度降低至1/65。The invention discloses a 400MPa grade corrosion-resistant steel bar and a production method thereof. The chemical composition of steel bars includes: chromium: 9.5~10.4%, molybdenum: 1.0~1.2%, manganese: 0.3~0.6%, nickel: 0.01~1%, copper: 0.01~0.5%, carbon≤0.014%, nitrogen≤0.004%, Niobium: 0.01~0.05%, silicon: 0.2~0.6%, chromium + molybdenum + 0.5 manganese + 0.35 nickel + 0.25 copper is 11.1~12.2%, carbon + nitrogen + 0.3 silicon + manganese + 1.8 niobium is 0.4~0.8% , the balance of iron. The microstructure is bainite and 28%~40% ferrite; R _p0.2 ≥420MPa, Rm≥540MPa, A≥18%, Agt≥7.5%; in the simulated marine environment corrosion test, the corrosion resistance is improved by 45 times Above, the self-corrosion potential was shifted by 0.4 V and the current density was reduced to 1/65.

Description

400 MPa-grade corrosion-resistant steel bar and production method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and relates to a 400 MPa-level corrosion-resistant steel bar and a production method of the 400 MPa-level corrosion-resistant steel bar.

Background

The reinforced concrete structure is the most widely applied structural form in infrastructure construction, the theoretical service life of the reinforced concrete structure is long, but in actual engineering, numerous cases of early failure of the reinforced concrete exist, so that the maintenance cost is increased, and the energy and resource waste is also caused. Through investigation, the coastal reinforced concrete structure is influenced by severe environments such as high chloride ion and sulfate content, high temperature and high humidity, and the like, so that after the coastal reinforced concrete structure is put into use for 10-15 years, serious corrosion damage generally occurs, and the theoretical service life of the coastal reinforced concrete structure is far short of the designed theoretical service life.

The concrete in the reinforced concrete structure belongs to a strong alkaline environment, and in the alkaline environment, the surface of the steel bar can be passivated to generate a layer of stable metal oxide passivation film. In the practical use of the reinforced concrete structure, the dissolution and repair of the passive film are theoretically in an approximately balanced state, so that the potentials of all positions on the surface of the steel bar are basically kept consistent, and the steel bar is ensured to be difficult to corrode or have a low corrosion rate. However, when the passive film on the surface of the steel bar is damaged by external erosion substances, for example, in a marine environment, when active chlorine ions on the passive film on the surface of the steel bar reach a certain concentration, the passive film is dissolved and repaired out of balance, the dissolution of the passive film is accelerated, and corrosion pits are formed, so that the steel bar matrix is exposed to erosion media, and finally, the reinforced concrete structure fails.

Although the measures of corrosion inhibitors, surface protective layers, cathodic protection, coating reinforcing steel bars and the like have a certain effect on prolonging the service life of the reinforced concrete structure at present, the measures are taken as the core of the reinforced concrete structure to improve the corrosion resistance of the matrix of the reinforcing steel bars, which is the key point for solving the problem of corrosion damage of the reinforced concrete structure.

Meanwhile, besides the corrosion resistance, the mechanical property, the welding property, the production and manufacturing cost and other aspects of the steel bar are also important aspects influencing the actual production and application of the steel bar. For example, stainless steel bars are a common steel bar type with better corrosion resistance, and the corrosion resistance can be greatly improved compared with common carbon steel bars by adding a large amount of alloy elements such as Cr, Ni, Mo and the like, and the corrosion resistance is remarkably excellent; however, the welding performance of the stainless steel bar is very poor due to the addition of a large amount of alloy elements, so that the welding construction cost of the stainless steel bar in actual construction is very high, and the risk of structural instability of a reinforced concrete structure due to poor welding exists; meanwhile, because a large amount of alloy elements are added into the stainless steel bars, the raw material cost and the production cost of the stainless steel bars are increased by times compared with those of common steel bars, so that the stainless steel bars are high in price and cannot be widely applied, and the social requirements for energy conservation and consumption reduction are not met; in addition, there is still controversy about whether macro-cell corrosion will occur when stainless steel bars and ordinary steel bars are lapped.

Therefore, how to simultaneously ensure the corrosion resistance, the mechanical property, the welding property and the cost is an important subject with remarkable social significance and economic effect in the research aspect of the corrosion-resistant steel bar.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention aims to provide a 400 MPa-grade corrosion-resistant steel bar which has excellent corrosion resistance, comprehensive mechanical property and welding property, can be prepared at lower material cost and process cost, and is suitable for being widely used in ocean engineering.

In order to achieve the above object, one embodiment of the present invention provides a 400 MPa-grade corrosion-resistant steel bar, which comprises the following chemical components by mass: 9.5 to 10.4% of Cr, 1.0 to 1.2% of Mo, 0.3 to 0.6% of Mn, 0.01 to 1.00% of Ni, 0.01 to 0.5% of Cu, 0.014% or less of C, 0.004% or less of N, 0.01 to 0.05% of Nb, 0.2 to 0.6% of Si, 0.004% or less of S, 0.003% or less of O, 0.01% or less of As, 0.01 to 0.03% of P, 11.1 to 12.2% of Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu, 0.4 to 0.8% of C + N +0.3Si + Mn +1.8Nb, and the balance of Fe and inevitable impurities.

Preferably, the chemical composition of the steel bar further comprises, by mass: 0.1 to 0.15% of V, 0.01 to 0.05% of Ti, 0.01 to 0.03% of Al, and 0.0005 to 0.0020% of B.

Furthermore, the microstructure of the steel bar is ferrite and bainite, wherein the ferrite accounts for 28% -40%.

Furthermore, the class A, B, C and D inclusions of the steel bar under the GB/T10561 standard are all less than or equal to 1.0 grade.

Furthermore, the yield strength of the steel bar is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the elongation after fracture is more than or equal to 18 percent, and the maximum force total elongation is more than or equal to 7.5 percent.

Preferably, the nominal diameter of the steel bar is 6-32 mm.

Preferably, when the nominal diameter of the steel bar is 6-10 mm, the steel bar is arranged into a coiled steel bar; when the nominal diameter of reinforcing bar is 12~32mm, the reinforcing bar setting is the straight bar reinforcing bar.

Further, in the week immersion corrosion test, the average weight loss corrosion rate of the steel bar is 0.05-0.1 g/(m)²H); in a salt spray corrosion test, the average weight loss corrosion rate of the steel bar is 0.01-0.04 g/(m)²·h)；

In simulated concrete pore liquid with chloride ion concentration more than or equal to 3mol/L, the self-corrosion potential of the steel bar is-0.1 to-0.15V, and the polarization resistance is 2500 to 3000 kOmega/cm²The self-corrosion current density is less than or equal to 0.13 mu A/cm²。

Preferably, the steel bar can be prepared by adopting a process route I and a process route II;

the first process route comprises a molten iron pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a billet continuous casting process, a hot continuous rolling process and a temperature-controlled cooling process which are sequentially carried out;

the second process route comprises a molten iron pre-desulfurization procedure, a converter smelting procedure, an LF furnace refining procedure, an RH furnace refining procedure, a billet continuous casting procedure, a hot continuous rolling procedure and a temperature control cooling procedure which are sequentially carried out.

Preferably, in the first process route: the tapping temperature of the converter smelting process is 1600-1660 ℃; in the AOD furnace refining process, high-carbon ferrochrome and ferromolybdenum are added into molten steel to carry out primary alloying on the molten steel, slagging is carried out after reduction, then manganese alloy is added, a steel ladle used for steel tapping is swept by argon for more than 5min before steel tapping, 20kg of aluminum ingot is added into the molten steel in the steel tapping process, the steel tapping temperature is 1630-1670 ℃, and the steel tapping C content is less than or equal to 0.01%; in the LF furnace refining process, after molten steel reaches a ladle of the LF furnace, slag is adjusted according to a scheme of adding 13-15 kg of lime and 4.0-6.5 kg of fluorite to each ton of molten steel, the white slag holding time is not less than 8min, the soft stirring time is 8-15 min, and the tapping temperature is 1600-1620 ℃; in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 1.2-1.6 m/min.

Preferably, in the second process route: in the converter smelting process, micro-carbon ferrochrome is added into molten steel in the tapping process to preliminarily alloy the molten steel, and the tapping temperature is 1700-1750 ℃; in the LF furnace refining process, the ladle of the LF furnace is subjected to whole-process bottom blowing with the argon flow of 80-160L/min, and the tapping temperature is 1560-1600 ℃; in the RH furnace refining process, after the RH furnace is vacuumized for 3min, oxygen is blown into the RH furnace, and the total oxygen blowing amount is 500-700 Nm³Then adding micro-carbon ferrochrome alloy into the molten steel to alloy the molten steel, and performing clean cycle treatment for more than 5min when the vacuum degree is less than 2mbar, wherein the tapping temperature is 1560-1600 ℃, and the tapping C content is less than or equal to 0.015 percent; in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 2.2-2.6 m/min.

Preferably, the first process route and the second process route are both:

in the hot continuous rolling process, a continuous casting billet is heated in a heating furnace at the heating temperature of 1100-1200 ℃ for 60-120 min, and then rolled into a straight threaded steel bar with the diameter of 12-32 mm, the initial rolling temperature is 1000-1100 ℃, and the finish rolling temperature is 850-950 ℃;

and during the temperature control cooling process, naturally cooling the rolled straight twisted steel bar on a cooling bed, wherein the temperature of the steel bar on the cooling bed is 860-920 ℃.

Preferably, the first process route and the second process route are both: in the hot continuous rolling process, a continuous casting blank is heated in a heating furnace at the heating temperature of 1080-1130 ℃ for 60-120 min, and then rolled into a coiled twisted steel bar with the diameter of 6-10 mm, the initial rolling temperature is 980-1030 ℃, the finish rolling temperature is 850-950 ℃, and the spinning temperature is 830-920 ℃.

Preferably, the first process route and the second process route both comprise an online pickling process and a packaging process which are sequentially performed after the temperature-controlled cooling process; in the on-line pickling process, the steel bar sequentially passes through the pickling tank, the passivation tank and the drying equipment, and the air nozzles of the pickling tank are distributed around the central line of the pickling tank.

Further, when two reinforcing bars are connected into a welding sample by electroslag pressure welding, a fracture point of the obtained welding sample in a tensile test is formed at the base metal of the two reinforcing bars.

Compared with the prior art, the invention has the beneficial effects that:

(1) on the premise of ultra-low carbon design, the respective contents and the association relations of Cr, Mo, Mn, Ni and Cu are reasonably designed, and the respective contents and the association relations of C, N, Si, Mn and Nb are reasonably designed, so that the steel bar has ferrite and bainite two-phase microstructure with a reasonable proportion, and the overall comprehensive performance of the steel bar is excellent; in particular, the mechanical properties of the steel bar are as follows: the yield strength is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the elongation after fracture is more than or equal to 18 percent, and the maximum force total elongation is more than or equal to 7.5 percent; the corrosion resistance is as follows: in a week immersion corrosion test and a salt spray corrosion test, the corrosion resistance is improved by more than 45 times compared with that of the common HRB400, in an electrochemical corrosion test, the positive displacement amplitude of the self-corrosion potential relative to the common HRB400 exceeds 0.4V, the polarization resistance is far higher than that of the common HRB400, and the self-corrosion current density is equal to 1/65 of the common HRB400 or even lower; the welding performance is as follows: the welding is easy, the welding point has a firm structure and is not easy to break, and the breaking point of the welding sample in the tensile test is formed at the base metal of the steel bar;

(2) under the condition of the chemical composition design scheme, the alloy can not only realize excellent corrosion resistance, comprehensive mechanical property and welding property, but also has low cost of alloy elements, saves energy and reduces consumption, can be prepared by a plurality of process routes, reduces the cost of the production process, is suitable for actual production and processing, and has higher social significance and economic effect.

In order to solve the technical problems in the prior art, the invention aims to provide a production method of a 400 MPa-grade corrosion-resistant steel bar, and the obtained steel bar has excellent corrosion resistance, comprehensive mechanical property and welding property, has lower material cost and process cost, and is suitable for being widely used in ocean engineering.

In order to achieve the above object, one embodiment of the present invention provides a method for producing a 400 MPa-level corrosion-resistant steel bar, the method comprising the steps of,

(1) making steel

The method comprises the following steps of sequentially carrying out molten steel smelting by adopting a molten iron pre-desulfurization process, a converter smelting process, an AOD furnace refining process and an LF furnace refining process, or sequentially carrying out molten steel smelting by adopting a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process and an RH furnace refining process, and continuously casting the obtained molten steel into a steel billet, wherein the steel billet comprises the following chemical components in percentage by mass: 9.5 to 10.4% of Cr, 1.0 to 1.2% of Mo, 0.3 to 0.6% of Mn, 0.01 to 1.00% of Ni, 0.01 to 0.5% of Cu, 0.014% or less of C, 0.004% or less of N, 0.01 to 0.05% of Nb, 0.2 to 0.6% of Si, 0.004% or less of S, 0.003% or less of O, 0.01% or less of As, 0.01 to 0.03% of P, 11.1 to 12.2% of Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu, 0.4 to 0.8% of C + N +0.3Si + Mn +1.8Nb, and the balance of Fe and inevitable impurities;

(2) controlled rolling and cooling

Heating the steel billet obtained in the step 1 in a heating furnace at 1100-1200 ℃ for 60-120 min, and then rolling the steel billet into a straight twisted steel bar with the diameter of 12-32 mm, wherein the initial rolling temperature is 1000-1100 ℃, and the finish rolling temperature is 850-950 ℃; naturally cooling the rolled straight twisted steel bar on a cooling bed, wherein the temperature of the steel bar on the cooling bed is 860-920 ℃;

or heating the steel billet obtained in the step 1 in a heating furnace at the heating temperature of 1080-1130 ℃ for 60-120 min, rolling the steel billet into a coiled twisted steel bar with the diameter of 6-10 mm, wherein the initial rolling temperature is 980-1030 ℃, the finish rolling temperature is 850-950 ℃, and the spinning temperature is 830-920 ℃; and then, the rolled coiled thread steel bar is cooled in a delayed stelmor cooling mode, and fans below the roller way are all closed.

Preferably, in step 1, the chemical composition of the steel billet further includes, in mass percent: 0.1 to 0.15% of V, 0.01 to 0.05% of Ti, 0.01 to 0.03% of Al, and 0.0005 to 0.0020% of B.

Preferably, in step 1, if molten steel is smelted by sequentially performing the molten iron pre-desulfurization step, the converter smelting step, the AOD furnace refining step, and the LF furnace refining step, then: the tapping temperature of the converter smelting process is 1600-1660 ℃; in the AOD furnace refining process, high-carbon ferrochrome and ferromolybdenum are added into molten steel to carry out primary alloying on the molten steel, slagging is carried out after reduction, then manganese alloy is added, a steel ladle used for steel tapping is swept by argon for more than 5min before steel tapping, 20kg of aluminum ingot is added into the molten steel in the steel tapping process, the steel tapping temperature is 1630-1670 ℃, and the steel tapping C content is less than or equal to 0.01%; in the LF furnace refining process, after molten steel reaches a ladle of the LF furnace, slag is adjusted according to a scheme of adding 13-15 kg of lime and 4.0-6.5 kg of fluorite to each ton of molten steel, the white slag holding time is not less than 8min, the soft stirring time is 8-15 min, and the tapping temperature is 1600-1620 ℃; in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 1.2-1.6 m/min;

and if molten steel is smelted by sequentially adopting a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process and an RH furnace refining process, then: in the converter smelting process, micro-carbon ferrochrome is added into molten steel in the tapping process to preliminarily alloy the molten steel, and the tapping temperature is 1700-1750 ℃; in the LF furnace refining process, the ladle of the LF furnace is subjected to whole-process bottom blowing with the argon flow of 80-160L/min, and the tapping temperature is 1560-1600 ℃; in the RH furnace refining process, after the RH furnace is vacuumized for 3min, oxygen is blown into the RH furnace, and the total oxygen blowing amount is 500-700 Nm³Then adding micro-carbon ferrochrome alloy into the molten steel to alloy the molten steel when the vacuum degree is less than 2mbarCarrying out net circulation treatment for more than 5min, wherein the tapping temperature is 1560-1600 ℃, and the tapping C content is less than or equal to 0.015 percent; in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 2.2-2.6 m/min.

Preferably, the production method further comprises the step (3) of in-line acid washing:

sequentially passing the steel bar obtained in the step 2 through a pickling tank, a passivation tank and drying equipment to carry out online pickling, wherein the air nozzles of the pickling tank are distributed around the central line of the pickling tank; and (4) packaging the steel bars after the steel bars leave the drying equipment.

Furthermore, when the two steel bars prepared by the production method are connected into a welding sample by electroslag pressure welding, the fracture point of the obtained welding sample in a tensile test is formed at the base metal of the two steel bars.

Furthermore, the microstructure of the steel bar prepared by the production method is ferrite and bainite, wherein the ferrite accounts for 28% -40%.

Furthermore, the A-type, B-type, C-type and D-type inclusions of the steel bar prepared by the production method are less than or equal to 1.0 grade under the GB/T10561 standard.

Furthermore, the yield strength of the steel bar prepared by the production method is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the elongation after fracture is more than or equal to 18 percent, and the maximum force total elongation is more than or equal to 7.5 percent.

Furthermore, in the steel bar prepared by the production method, in the week immersion corrosion test, the average weight loss corrosion rate of the steel bar is 0.05-0.1 g/(m)²H); in a salt spray corrosion test, the average weight loss corrosion rate of the steel bar is 0.01-0.04 g/(m)²·h)；

Compared with the prior art, the invention has the beneficial effects that:

(2) based on the chemical composition design scheme, the alloy can not only realize excellent corrosion resistance, comprehensive mechanical property and welding property, but also has low cost of alloy elements, saves energy and reduces consumption, can be prepared by a plurality of process routes, reduces the cost of the production process, is suitable for actual production and processing, and has higher social significance and economic effect;

(3) in addition, on the premise of the chemical composition design scheme, the structure, the mechanical property, the corrosion resistance and the welding property of the steel bar can be further optimized by combining the process control in the rolling and cooling control, so that the comprehensive performance of the steel bar is further improved, the process operation in the hot continuous rolling process is simple, convenient and easy to control, and the smooth working condition of the actual production is ensured.

Detailed Description

The technical solution of the present invention is further described below with reference to specific embodiments, but the scope of protection claimed is not limited to the description.

< first embodiment >

The embodiment provides a corrosion-resistant steel bar, in particular to a hot-rolled ribbed steel bar, which comprises the following chemical components in percentage by mass: 9.5 to 10.4 percent of Cr, 1.0 to 1.2 percent of Mo, 0.3 to 0.6 percent of Mn, 0.01 to 1.00 percent of Ni, 0.01 to 0.50 percent of Cu, less than or equal to 0.014 percent of C, less than or equal to 0.004 percent of N, 0.01 to 0.05 percent of Nb, 0.2 to 0.6 percent of Si, less than or equal to 0.004 percent of S, less than or equal to 0.003 percent of O, less than or equal to 0.01 percent of As, 0.01 to 0.03 percent of P, and the balance of Fe and inevitable impurities.

And the chemical components of the steel bar also comprise Cr, Mo, Mn, Ni and Cu in percentage by mass: 11.1% or more Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu or less than 12.2%; and the mass percentage of C, N, Si, Mn and Nb is more than or equal to 0.4 percent and less than or equal to 0.3 percent and 0.8 percent and less than or equal to 0.8 percent.

The functions of the chemical components in the steel bar are explained as follows.

Cr: important corrosion-resistant elements can form an oxide passive film on the surface of the steel bar, thereby effectively preventing the steel bar from being oxidized and improving the corrosion resistance of a steel bar matrix; especially, when the corrosion inhibitor coexists with elements such as Mo, Ni and the like, the steel bar can obtain better corrosion resistance and avoid the occurrence of pitting corrosion; in addition, Cr can also improve the hardenability of the steel bar; in the chemical composition design of the invention, the Cr content is controlled to be 9.5-10.4%.

Mo: the addition of Mo element can passivate the surface of the steel bar and prevent the steel bar from pitting corrosion in chloride solution, thereby integrally improving the corrosion resistance of the steel bar in various environments; moreover, Mo has very obvious inhibiting effect on pearlite transformation, and simultaneously, Cr is combined with carbide to form an element, so that bainite can be promoted to be generated; in addition, Mo can promote grain refinement, and improve the hardenability and the heat strength of the steel bar; however, when the Mo content is too high, the oxidation resistance of the reinforcing steel bar may be deteriorated; in the chemical composition design of the invention, the content of Mo is controlled to be 1.0-1.2%.

Mn: the solid solution strengthening element can improve the strength of the wire rod and can be combined with a harmful element S to reduce the hot brittleness of the steel bar; and is also an important deoxidizer, desulfurizer and austenite forming element; however, when the Mn content is too high, the plasticity, impact toughness, welding properties, and the like of the steel bar are all reduced; in the chemical composition design of the invention, the content of Mn is controlled to be 0.3-0.6%.

Ni: important corrosion resisting elements enable the steel bar to have higher corrosion resisting capacity to acid-base environments and enable the steel bar to have higher antirust capacity and heat resisting capacity at high temperature; meanwhile, Ni element is an austenite forming element, so that the steel has a uniform austenite structure to improve corrosion resistance; in the chemical composition design of the invention, the Ni content is controlled to be 0.01-1.00%.

Cu: important corrosion resistant elements are beneficial to improving the corrosion resistance of the steel bar, however, when the content of Cu is too high, the plasticity of steel is reduced, and hot rolling cracking is caused; in the chemical composition design of the invention, the Cu content is controlled to be 0.01-0.50%.

C: austenite forming elements, and controlling the carbon content to be below the dissolution limit of ferrite, thereby improving the uniformity of the steel structure and the component distribution, reducing the potential difference between the regions in the steel bar, and reducing the corrosion rate, wherein in the chemical component design of the invention, the C content is controlled to be below 0.014%.

N: if the content of the austenite forming element is higher, the plasticity of the steel bar is reduced, and the proportion control of ferrite and bainite in the steel bar structure is not facilitated, and in the chemical composition design of the invention, the content of N is controlled to be less than 0.004%.

A microalloy strengthening element that can perform precipitation strengthening and grain refining strengthening in a rolling process (for example, a hot continuous rolling process described later); however, if the content of Nb is too high, the plasticity of the steel bar is reduced and the cost is increased; in the chemical composition design of the invention, the Nb content is controlled to be 0.01-0.05%.

Si: the solid solution strengthening element is solid-dissolved in ferrite, can inhibit the diffusion of the C element in austenite, delay the transformation of the ferrite and pearlite, and improve the yield strength and the tensile strength of the steel bar; however, if the content of Si is too high, the plasticity of steel is reduced, and the welding performance of the steel bar is deteriorated; in the chemical composition design of the invention, the content of Si is controlled to be 0.2-0.6%.

P: the strength and the corrosion resistance of the steel bar can be improved, but segregation is easy to occur in steel, and the mechanical property at low temperature is poor due to the fact that the content of P is too high, and in the chemical composition design, the content of P is controlled to be 0.01-0.03%.

Cr + Mo + 0.5Mn + 0.35Ni +0.25 Cu: the comprehensive control of corrosion resistance, plasticity and cost of the steel bar is very important, on one hand, an oxidation film on the surface of the steel bar has enough compactness, the corrosion resistance repair capability of a steel bar matrix is improved, the corrosion resistance of the steel bar oxidation film and the steel bar matrix is ensured, on the other hand, the condition that the proportion of ferrite in a steel bar tissue is low is avoided, the microstructure and proportion of the steel bar are favorably controlled to improve the plasticity of the steel bar and increase the elongation after fracture and the total elongation of maximum force, on the other hand, the addition of precious alloy elements is also reduced, the cost is reduced, and the engineering popularization, design and use are promoted.

C + N +0.3Si + Mn +1.8 Nb: the method is very important for the comprehensive control of the mechanical properties such as the strength and the plasticity of the steel bar, on one hand, the alloy elements can be ensured to fully play the roles of respective solid solution strengthening, precipitation strengthening, structure strengthening and the like, so that the strength of the steel bar is improved, on the other hand, the proportion of ferrite in the steel bar structure is prevented from being low, and the proportion of bainite in the steel bar structure is prevented from being high, namely, the respective proportions of ferrite and bainite in the steel bar structure are optimized, the plasticity of the steel bar is improved, and the elongation after fracture and the maximum force total elongation are increased, and in the chemical composition design of the invention, C + N +0.3Si + Mn +1.8Nb meets 0.4-0.8%.

In summary, compared with the prior art, in the design of the chemical components in the invention: (1) on the premise of ultra-low carbon design, the respective contents and the association relations of Cr, Mo, Mn, Ni and Cu are reasonably designed, and the respective contents and the association relations of C, N, Si, Mn and Nb are reasonably designed, so that the microstructure of the steel bar is ferrite and bainite, wherein the ferrite accounts for 28-40%, and the bainite accounts for 60-72%, and the steel bar has excellent corrosion resistance, comprehensive mechanical properties and welding performance, is excellent in overall comprehensive performance and is suitable for the use requirements of ocean engineering; (2) under the condition of the chemical composition design scheme, the alloy can not only realize excellent corrosion resistance, comprehensive mechanical property and welding property, but also has low cost of alloy elements, saves energy and reduces consumption, can be prepared by a plurality of process routes, reduces the cost of the production process, is suitable for actual production and processing, and has higher social significance and economic effect.

As mentioned above, the microstructure of the steel bar is ferrite and bainite, wherein the ferrite accounts for 28% -40%, and the bainite accounts for 60% -72%. Thus, the microstructure and the ferrite to bainite ratio thereof further affect the steel bar in two ways: on one hand, the mechanical properties are adopted, and the proper yield strength and good elongation rate including elongation after fracture and maximum force total elongation can be ensured by controlling the proportion of ferrite to bainite in the embodiment, so that good comprehensive mechanical properties are ensured; on the other hand, the corrosion resistance is ensured, a certain bainite structure proportion is ensured, and the corrosion resistance of the steel bar can be improved.

Specifically, in terms of mechanical properties, the steel bar is a steel bar with the strength of more than 400MPa, the yield strength is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the elongation after fracture is more than or equal to 18 percent, and the maximum total elongation is more than or equal to 7.5 percent.

In addition, the steel bar is well controlled in the aspect of inclusions, and particularly, the A-type, B-type, C-type and D-type inclusions of the steel bar under the GB/T10561 standard are not more than 1.0 grade, so that the toughness of the steel bar under the low-temperature condition can be improved, and the mechanical property of the steel bar is favorably ensured.

Further, in the aspect of corrosion resistance, in a periimmersion corrosion test and a salt spray corrosion test, the corrosion resistance of the steel bar is improved by more than 45 times compared with that of the common HRB 400. Specifically, in the week immersion corrosion test, the average weight loss corrosion rate of the steel bar is 0.05-0.1 g/(m)²H); in a salt spray corrosion test, the average weight loss corrosion rate of the steel bar is 0.01-0.04 g/(m)²·h)；

The specific method of the weekly leaching corrosion test is as follows: placing the treated sample in a week immersion test box, and carrying out the test according to a corrosion test method of YB/T4367 steel bars in a chloride ion environment, wherein the solution is 2.0 +/-0.05 (wt%) NaCl, the pH value is 6.5-7.2, the solution temperature is 45 +/-2 ℃, the drying temperature is 70 +/-10 ℃, and continuously carrying out the test to obtain the average weight loss corrosion rate at 168 hours.

The specific method of the adopted salt spray corrosion test comprises the following steps: and (3) placing the treated sample in a salt spray test box, carrying out the test according to a GB/T10125 artificial atmosphere corrosion test-salt spray corrosion test, wherein the solution is 2.0 +/-0.05 (wt%) NaCl, the pH value is 6.5-7.2, the solution temperature is 35 +/-2 ℃, continuously carrying out the test, and obtaining the average weight loss corrosion rate at 168 hours.

In the electrochemical corrosion test, under the condition of the simulated concrete pore liquid corrosion test with the chloride ion concentration more than or equal to 3 mol/L: the self-corrosion potential of the steel bar is-0.1 to-0.15V, and the forward shift amplitude of the steel bar relative to the common HRB400 is more than 0.4V; the polarization resistance of the steel bar is 2500-3000 k omega/cm²Far higher than the common HRB 400; the self-corrosion current density of the steel bar is less than or equal to 0.13 mu A/cm²1/65 equivalent to that of conventional HRB400 or even lower.

The specific method of the adopted electrochemical corrosion test comprises the following steps: the electrochemical test is executed according to GB/T24196-2009 'constant potential and potentiodynamic polarization measurement guide rule of metal and alloy corrosion electrochemical test method', a three-electrode system is adopted, a reference electrode is a saturated calomel electrode, an auxiliary electrode is a Pt sheet, and a test solution is simulated concrete pore liquid with chloride ion concentration more than or equal to 3 mol/L; the test scanning range of the polarization curve is-300-600 mV relative to the self-corrosion potential of the sample, and the scanning frequency is 1 mV/s; the scanning frequency range of the electrochemical impedance test is 105-10-2 Hz, and the amplitude of the alternating current excitation signal is +/-5 mV.

Therefore, in the aspect of corrosion resistance, the steel bar has excellent corrosion resistance, and under the condition of carrying out a corrosion performance test in a simulated seawater solution, all indexes are far superior to those of common deformed steel bars of the same grade.

In the aspect of welding performance, the steel bars are easy to weld, when two steel bars are connected into a welding sample by electroslag pressure welding, the welding point is firm in structure and not easy to break, and the breaking point of the welding sample in a tensile test is formed at the steel bar base metal instead of the welding point.

Preferably, in the embodiment, the nominal diameter of the steel bar is 6-32 mm.

When the nominal diameter of the steel bar is 6-10 mm, the steel bar is arranged into a coiled steel bar; when the nominal diameter of reinforcing bar is 12~32mm, the reinforcing bar setting is the straight bar reinforcing bar. Therefore, the requirements on the steel bar in ocean engineering can be met, and the comprehensive mechanical property and the corrosion resistance of the steel bar structure can be improved through the diameter design.

< second embodiment >

The embodiment provides a corrosion-resistant steel bar, in particular to a hot-rolled ribbed steel bar suitable for ocean engineering, which is mainly different from the first embodiment in that: the chemical composition is further added with one or more of 0.1-0.15% of V, 0.01-0.05% of Ti, 0.01-0.03% of Al and 0.0005-0.0020% of B, thereby further improving the performance of the steel bar.

Specifically, in this embodiment, the chemical composition of the steel bar includes, by mass: 9.5 to 10.4% of Cr, 1.0 to 1.2% of Mo, 0.3 to 0.6% of Mn, 0.01 to 1.00% of Ni, 0.01 to 0.50% of Cu, 0.014% or less of C, 0.004% or less of N, 0.01 to 0.05% of Nb, 0.2 to 0.6% of Si, 0.004% or less of S, 0.003% or less of O, 0.01% or less of As, 0.01 to 0.03% of P, 0.1 to 0.15% of V, 0.01 to 0.05% of Ti, 0.01 to 0.03% of Al, 0.0005 to 0.0020% of B, and the balance Fe and inevitable impurities.

And the same as the first embodiment, the steel bar has the chemical composition that the mass percentages of Cr, Mo, Mn, Ni and Cu are as follows: 11.1% or more Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu or less than 12.2%; and the mass percentage of C, N, Si, Mn and Nb is more than or equal to 0.4 percent and less than or equal to 0.3 percent and 0.8 percent and less than or equal to 0.8 percent.

The effects of the elements of Cr, Mo, Mn, Ni, Cu, C, N, Nb, Si, P, etc. in the steel bar, and the design effects of Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu and C + N +0.3Si + Mn +1.8Nb are the same as in the first embodiment, and thus are not described in detail. The action of the optional elements V, Ti, Al and B in the present embodiment will be explained below.

V: the microalloy strengthening elements can precipitate V (C, N) compounds in a rolling process (such as a later hot continuous rolling process), have a certain precipitation strengthening effect, prevent austenite and ferrite grains from growing, and have a fine grain strengthening effect; however, if the content of V is too high, the plasticity of the steel bar is reduced and the cost is increased, and in the chemical composition design of the invention, the content of V is controlled to be 0.1-0.15%.

Ti: the affinity with C element is larger than that of Cr, so that the phenomenon that chromium carbide is precipitated to cause poor chromium at grain boundary can be avoided, and intergranular corrosion is effectively prevented; moreover, by adding a proper amount of Ti, TiOx and TiN which are distributed in a fine and dispersed manner can be formed in the steel plate; however, if the content of Ti is too high, the viscosity of molten steel is increased, which is not favorable for smelting the molten steel, and the size of TiOx formed is large, which deteriorates the toughness of the steel plate; in the chemical composition design of the invention, the Ti content is controlled to be 0.01-0.05%.

Al: the commonly used deoxidizer can improve the electrode potential of the steel bar matrix and improve the corrosion resistance; the growth of austenite grains can be prevented, and the strength of the steel bar is improved; however, if the Al content is too large, there is a possibility that oxides in the steel increase, which is detrimental to the weldability of the steel bar; in the chemical composition design of the invention, the Al content is controlled to be 0.01-0.03%.

B: the strengthening element has a remarkable effect on improving the strength of the steel bar, but the excessive content of B is not favorable for improving the intercrystalline corrosion resistance; in the chemical composition design of the invention, the content of B is controlled to be 0.0005-0.0020%.

In the embodiment, based on the selective addition of any one or more of V, Ti, Al and B, the performance of the steel bar is further improved on the basis of the first embodiment, and the steel bar has more excellent corrosion resistance, mechanical strength, plasticity and welding performance, thereby facilitating engineering construction and having a longer theoretical service life when used in ocean engineering.

< third embodiment >

The present embodiment provides a method for producing a corrosion-resistant reinforcing bar, which can be used for both the production and the preparation of the corrosion-resistant reinforcing bar of the first embodiment and the production and the preparation of the corrosion-resistant reinforcing bar of the second embodiment.

In this embodiment, the process route of the production method includes a molten iron pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, and a packaging process, which are performed in sequence. The production method is described in detail below in the order of steps.

(1) Step of steelmaking

In the step, molten steel is smelted by sequentially adopting a molten iron pre-desulphurization process, a converter smelting process, an AOD furnace refining process and an LF furnace refining process, and the obtained molten steel is continuously cast into a billet by adopting the billet continuous casting process.

It can be understood that when the production method is used for preparing the corrosion-resistant steel bar of the first embodiment, the chemical composition of the steel blank obtained in the step is consistent with that of the steel bar of the first embodiment, that is, the chemical composition of the steel blank comprises the following components in percentage by mass: 9.5 to 10.4% of Cr, 1.0 to 1.2% of Mo, 0.3 to 0.6% of Mn, 0.01 to 1.00% of Ni, 0.01 to 0.50% of Cu, 0.014% or less of C, 0.004% or less of N, 0.01 to 0.05% of Nb, 0.2 to 0.6% of Si, 0.004% or less of S, 0.003% or less of O, 0.01% or less of As, 0.01 to 0.03% of P, 11.1 to 12.2% of Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu, 0.4 to 0.8% of C + N +0.3Si + Mn +1.8Nb, and the balance of Fe and inevitable impurities; similarly, when the production method is used for preparing the corrosion-resistant steel bar of the second embodiment, the chemical composition of the steel blank obtained in this step is consistent with that of the steel bar of the second embodiment, that is, the chemical composition of the steel blank comprises, in mass percent: 9.5 to 10.4% of Cr, 1.0 to 1.2% of Mo, 0.3 to 0.6% of Mn, 0.01 to 1.00% of Ni, 0.01 to 0.50% of Cu, 0.014% or less of C, 0.004% or less of N, 0.01 to 0.05% of Nb, 0.2 to 0.6% of Si, 0.004% or less of S, 0.003% or less of O, 0.01% or less of As, 0.01 to 0.03% of P, 0.1 to 0.15% of V, 0.01 to 0.05% of Ti, 0.01 to 0.03% of Al, 0.0005 to 0.0020% of B, 11.1 to 12.2% of Cr + Mo + 0.35Ni +0.25Cu, 0.4 to 0.8% of C + N +0.3Si + Mn +1.8Nb, and the balance of Fe and inevitable impurities.

Further, the tapping temperature in the converter smelting process is 1600-1660 ℃, so that the effects of C removal and P removal are ensured, and the subsequent alloying is facilitated.

During the AOD furnace refining process, the high-carbon ferrochrome alloy and the ferromolybdenum alloy with lower cost are added into the molten steel to carry out primary alloying on the molten steel, slag is removed after reduction, the content of impurity elements such as P is reduced, then the manganese alloy is added, the primary alloying is completed while deoxidation is carried out, a steel ladle used for steel tapping is swept by argon for more than 5min before steel tapping, the secondary oxidation of the molten steel is reduced, 20kg of aluminum ingots are added into the molten steel during the steel tapping process, the steel tapping temperature is 1630-1670 ℃, the steel tapping C content is less than or equal to 0.01 percent, and the molten steel decarburization effect and the production rhythm are ensured.

In the LF furnace refining process, after the molten steel reaches a ladle of the LF furnace, slag is adjusted according to a scheme of adding 13-15 kg of lime and 4.0-6.5 kg of fluorite to each ton of molten steel, the white slag holding time is not less than 8min, the soft stirring time is 8-15 min, the tapping temperature is 1600-1620 ℃, and the molten steel deoxidation and desulfurization are gradually completed.

And in the square billet continuous casting process, continuously casting the molten steel discharged in the LF furnace refining process into a square billet, wherein carbon-free covering slag or ultra-low carbon covering slag is adopted to prevent the molten steel from being carburized, the continuous casting temperature is 1520-1560 ℃, the drawing speed is 1.2-1.6 m/min in the continuous casting process, and the continuous casting is ensured.

(2) Controlled rolling and cooling

In the step, the billet obtained in the step 1 is rolled into a steel bar with the nominal diameter of 6-32 mm through a hot continuous rolling process, and then a temperature control cooling process is carried out. The specific process scheme of the step is different according to the difference of the nominal diameter of the steel bar.

Specifically, for a steel bar with a nominal diameter of 12-32 mm, in the step: in the hot continuous rolling process, the billet obtained in the step 1 is heated in a heating furnace at the heating temperature of 1100-1200 ℃ for 60-120 min, the alloy elements are fully redissolved, the strengthening effect of the alloy elements is favorably exerted, and then the billet is rolled into a straight twisted steel bar with the diameter of 12-32 mm, the rolling temperature is 1000-1100 ℃, the finish rolling temperature is 850-950 ℃, so that austenite crystal grains are kept in a certain size; and then, during the temperature-controlled cooling process, naturally cooling the rolled straight twisted steel on a cooling bed, wherein the temperature of the steel on the cooling bed is 860-920 ℃, and ensuring the size and proportion control of subsequent ferrite and pearlite.

Aiming at the steel bar with the nominal diameter of 6-10 mm, in the step: in the hot continuous rolling process, the billet obtained in the step 1 is heated in a heating furnace at the heating temperature of 1080-1130 ℃, so that alloy elements can be fully dissolved, the furnace time is 60-120 min, and then the billet is rolled into a coiled twisted steel bar with the diameter of 6-10 mm, the initial rolling temperature is 980-1030 ℃, the finish rolling temperature is 850-950 ℃, the laying temperature is 830-920 ℃, so that austenite crystal grains are kept in a certain size; and then, in the temperature control cooling process, the rolled coiled twisted steel is cooled in a delayed Steyr-Mole mode, fans below the roller way are all closed, and ferrite and pearlite phase transformation is completed on the roller way.

(3) Packaging the mixture

And (4) packaging the cooled steel bars in the step (2) to be transported and put into engineering application.

Therefore, compared with the prior art, the production method of the embodiment has the beneficial effects that:

(1) the design of the chemical components of the steel bar is that on the premise of ultra-low carbon design, the respective contents and the association relations of Cr, Mo, Mn, Ni and Cu are reasonably designed, and the respective contents and the association relations of C, N, Si, Mn and Nb are reasonably designed, so that the microstructure of the prepared steel bar is ferrite and bainite, wherein the ferrite accounts for 28% -40%, and the bainite accounts for 60% -72%, and the steel bar has excellent corrosion resistance, comprehensive mechanical property and welding property, is excellent in overall comprehensive property and is suitable for the use requirements of ocean engineering;

(2) under the condition of the chemical composition design scheme, the process route is reasonable, especially the process control in controlled rolling and controlled cooling is reasonable, the overall comprehensive performance of the obtained steel bar is further optimized, the rolling process has no crack defects, the cost of alloy elements is low, the energy is saved, the consumption is reduced, the cost of the production process is reduced, the steel bar is suitable for actual production and processing, the process operation is simple and convenient and easy to control, the working condition of actual production is ensured to be smooth, and the steel bar has higher social significance and economic effect.

< fourth embodiment >

In this embodiment, the process route of the production method includes a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process, an RH furnace refining process, a billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, and a packaging process, which are sequentially performed. That is, the present embodiment differs from the aforementioned third embodiment only in that: the process comprises the steps of a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process, an RH furnace refining process and a square billet continuous casting process, namely a steelmaking step. The production method of the present embodiment will be described in detail below only with respect to the steel-making step.

(1) Step of steelmaking

In the step, molten steel is smelted by sequentially adopting a molten iron pre-desulphurization process, a converter smelting process, an LF furnace refining process and an RH furnace refining process, and the obtained molten steel is continuously cast into a billet by adopting the billet continuous casting process.

Further, during the smelting process of the converter, micro-carbon ferrochrome alloy is added into the molten steel in the tapping process to carry out preliminary alloying on the molten steel, the content of C in the molten steel is controlled from the alloy adding angle as far as possible, the efficiency is improved, the tapping temperature is 1700-1750 ℃, the dephosphorization effect is ensured, and preparation is made for subsequent smelting.

During the LF furnace refining process, the ladle of the LF furnace is subjected to whole-process bottom blowing with the argon flow of 80-160L/min, the tapping temperature is 1560-1600 ℃, the alloy in the ladle is guaranteed to be dissolved and homogenized, and the production rhythm control is facilitated.

In the RH furnace refining process, after the RH furnace is vacuumized for 3min, oxygen is blown into the RH furnace, and the total oxygen blowing amount is 500-700 Nm³And then adding micro-carbon ferrochrome alloy into the molten steel to alloy the molten steel, completing Cr alloying step by step, simultaneously reducing recarburization of the molten steel, and performing net circulation treatment for more than 5min when the vacuum degree is less than 2mbar, wherein the tapping temperature is 1560-1600 ℃, the tapping C content is less than or equal to 0.015 percent, and ensuring the decarburization effect.

And in the square billet continuous casting process, continuously casting the molten steel discharged in the LF furnace refining process into a square billet, wherein carbon-free covering slag or ultra-low carbon covering slag is adopted to prevent the molten steel from being carburized, the continuous casting temperature is 1520-1560 ℃, the drawing speed is 2.2-2.6 m/min in the continuous casting process, and the continuous casting is facilitated.

As mentioned above, the rolling and cooling control step in step 2 and the baling process in step 3 are the same as those in the third embodiment, and are not described again.

< fifth embodiment >

The embodiment provides a production method of corrosion-resistant steel bars, and the process route comprises a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process, an RH furnace refining process, a billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, an online acid pickling process and a packaging process which are sequentially carried out.

In this embodiment, the process from the molten iron pre-desulfurization process to the temperature-controlled cooling process may be specifically implemented by using the third embodiment, or may be implemented by using the fourth embodiment, that is, the online pickling process is added before the packaging process on the basis of the third embodiment or the fourth embodiment, and only the online pickling process is described below, and the rest will not be described again.

Specifically, in the online pickling process, namely after the temperature-controlled cooling process and before the packaging process, the reinforcing steel bars sequentially pass through the pickling tank, the passivation tank and the drying equipment, so that the online pickling of the reinforcing steel bars is realized. Wherein, the gas nozzle of the pickling tank is distributed around the central line of the pickling tank so as to enhance the pickling effect.

Examples 1 to 16 of the present invention are provided below to further explain the present invention. It is to be understood that the following are only some of the preferred embodiments of the present invention, and not all embodiments of the present invention, and that other embodiments based on the foregoing embodiments may be made without departing from the technical spirit of the present invention.

First, examples 1 to 16 and comparative examples 1 to 4 each provide a steel bar having a chemical composition as shown in table 1. Example 12 was carried out according to the first embodiment of the present invention, the remaining examples were carried out according to the second embodiment of the present invention, and comparative examples 1 to 4 did not satisfy any of the embodiments of the present invention.

[ Table 1]

The production methods of examples 1 to 8 adopt a process route including a molten iron pre-desulfurization process, a converter smelting process, an AOD furnace refining process, an LF furnace refining process, a billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, and an on-line pickling process, which are performed in this order, and each process is described below.

(1) The molten iron pre-desulfurization process: pre-desulfurizing the molten iron;

(2) a converter smelting process: the tapping temperature is 1600-1660 ℃;

(3) AOD furnace refining: adding high-carbon ferrochrome and ferromolybdenum to molten steel to preliminarily alloy the molten steel, slagging off after reduction, then adding manganese alloy, purging a steel ladle used for tapping for more than 5min before tapping, adding 20kg of aluminum ingot to the molten steel in the tapping process, wherein the tapping temperature is 1630-1670 ℃, and the tapping C content is less than or equal to 0.010%;

(4) and (3) refining in an LF furnace: after the molten steel reaches a ladle of an LF (ladle furnace), slag is adjusted according to a scheme that 13-15 kg of lime and 4.0-6.5 kg of fluorite are added into each ton of molten steel, the white slag holding time is not less than 8min, the soft stirring time is 8-15 min, and the tapping temperature is 1600-1620 ℃;

(5) a square billet continuous casting process: continuously casting the molten steel discharged in the LF furnace refining process into a square billet, wherein carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the casting speed is 1.2-1.6 m/min in the continuous casting process;

(6) a hot continuous rolling procedure: in the embodiments 1 to 4, a square billet is heated in a heating furnace at the heating temperature of 1100 to 1200 ℃ for 60 to 120min, and then rolled into a straight threaded steel bar with the diameter of 12 to 32mm, the initial rolling temperature is 1000 to 1100 ℃, and the finish rolling temperature is 850 to 950 ℃; in examples 5 to 8, a square billet is heated in a heating furnace at a heating temperature of 1080 to 1130 ℃ for 60 to 120min, and then rolled into a coiled twisted steel bar with a diameter of 6 to 10mm, wherein the initial rolling temperature is 980 to 1030 ℃, the finish rolling temperature is 850 to 950 ℃, and the spinning temperature is 830 to 920 ℃;

(7) temperature control cooling process: in the embodiments 1 to 4, the rolled straight twisted steel bar is naturally cooled on a cooling bed, and the temperature of the upper cooling bed is 860 to 920 ℃; in examples 5 to 8, the rolled coiled twisted steel is cooled in a delayed stelmor manner, and fans below the roller table are all turned off;

(8) an online acid washing process: the steel bar is sequentially subjected to pickling tank, passivation tank and drying equipment to realize the online pickling of the steel bar, wherein the air jet of the pickling tank surrounds the central line of the pickling tank and is then packaged.

The production methods of examples 9 to 16 adopt a process route including a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process, an RH furnace refining process, a billet continuous casting process, a hot continuous rolling process, a temperature-controlled cooling process, and an on-line pickling process, which are performed in this order, and each process will be described below.

(1) The molten iron pre-desulfurization process: pre-desulfurizing molten iron, wherein S is less than or equal to 0.001% after desulfurization, and the slagging rate is more than or equal to 95%;

(2) a converter smelting process: adding micro-carbon ferrochrome alloy into the molten steel in the tapping process to primarily alloy the molten steel, wherein the tapping temperature is 1700-1750 ℃;

(3) refining in an LF furnace; carrying out whole-process bottom blowing in a ladle of the LF furnace at the argon flow rate of 80-160L/min, wherein the tapping temperature is 1560-1600 ℃;

(4) RH furnace refining process: after vacuumizing the RH furnace for 3min, blowing oxygen into the RH furnace, wherein the total oxygen blowing amount is 500-700 Nm³Then adding micro-carbon ferrochrome alloy into the molten steel to alloy the molten steel, and performing clean cycle treatment for more than 5min when the vacuum degree is less than 2mbar, wherein the tapping temperature is 1560-1600 ℃, and the tapping C content is less than or equal to 0.015 percent;

(5) a square billet continuous casting process: continuously casting the molten steel discharged in the LF furnace refining process into a square billet, wherein carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the casting speed is 2.2-2.6 m/min in the continuous casting process;

(6) a hot continuous rolling procedure: in examples 9 to 12, a square billet is heated in a heating furnace at a heating temperature of 1100 to 1200 ℃ for 60 to 120min, and then rolled into a straight twisted steel bar with a diameter of 12 to 32mm, the initial rolling temperature is 1000 to 1100 ℃, and the finish rolling temperature is 850 to 950 ℃; in examples 13 to 16, a square billet is heated in a heating furnace at a heating temperature of 1080 to 1130 ℃ for 60 to 120min, and then rolled into a coiled twisted steel bar with a diameter of 6 to 10mm, wherein the initial rolling temperature is 980 to 1030 ℃, the finish rolling temperature is 850 to 950 ℃, and the spinning temperature is 830 to 920 ℃;

(7) temperature control cooling process: in examples 9 to 12, the rolled straight twisted steel bar was naturally cooled on a cooling bed at 860 to 920 ℃; in examples 13 to 16, the rolled coiled reinforcing steel bar was cooled in a delayed stelmor manner, and the fans below the roller bed were all turned off;

The production methods adopted in comparative examples 1 to 4 are the traditional process routes of converter smelting, square billet continuous casting, hot continuous rolling and cooling bed, wherein in the hot continuous rolling process, the heating temperature in a heating furnace is 1210 to 1290 ℃, the rolling temperature is 1090 to 1170 ℃, the temperature in an upper cooling bed is more than or equal to 1100 ℃, and the steel is naturally cooled on the cooling bed.

The reinforcing steel bars of examples 1 to 16 and comparative examples 1 to 4 were sampled and tested for mechanical properties according to the same test method, and the mechanical properties of each example and comparative example are shown in table 2.

As can be seen from Table 2, the mechanical properties of the examples 1 to 16 are obviously superior to those of the comparative examples 1 to 4, the requirements of 400 MPa-level anti-seismic steel bars are met, the yield strength is greater than or equal to 420MPa, the tensile strength is greater than or equal to 540MPa, the elongation after fracture is greater than or equal to 18%, and the maximum total elongation is greater than or equal to 7.5%.

[ Table 2]

For the steel bars of examples 1 to 16 and comparative examples 1 to 4, the immersion corrosion test, the salt spray corrosion test and the electrochemical corrosion test were performed in the same manner, and the test results are shown in table 3.

The adopted electrochemical corrosion test comprises the following specific steps: the electrochemical test is executed according to GB/T24196-2009 'constant potential and potentiodynamic polarization measurement guide rule of metal and alloy corrosion electrochemical test method', a three-electrode system is adopted, a reference electrode is a saturated calomel electrode, an auxiliary electrode is a Pt sheet, and a test solution is simulated concrete pore liquid with chloride ion concentration more than or equal to 3 mol/L; the test scanning range of the polarization curve is-300-600 mV relative to the self-corrosion potential of the sample, and the scanning frequency is 1 mV/s; the scanning frequency range of the electrochemical impedance test is 105-10-2 Hz, and the amplitude of the alternating current excitation signal is +/-5 mV.

[ Table 3]

As can be seen from Table 3, the corrosion resistance of the steel bars in the examples 1 to 16 is greatly superior to that of the comparative examples 1 to 4, and the average weight-loss corrosion rate of the steel bars in the week immersion corrosion test is 0.05 to 0.1 g/(m)²H); in a salt spray corrosion test, the average weight loss corrosion rate of the steel bar is 0.01-0.04 g/(m)²H), the corrosion resistance is improved by more than 45 times compared with that of the common HRB 400; in an electrochemical corrosion test, in a simulated concrete pore liquid with the chloride ion concentration of more than or equal to 3 mol/L: the self-corrosion potential of the steel bar is-0.1 to-0.15V, and the forward shift amplitude of the steel bar relative to the common HRB400 is more than 0.4V; the polarization resistance of the steel bar is 2500-3000 k omega/cm²Far higher than the common HRB 400; the self-corrosion current density of the steel bar is less than or equal to 0.13 mu A/cm²1/65 equivalent to that of conventional HRB400 or even lower.

Furthermore, the steel bars of examples 1 to 16 are sampled to carry out inclusion detection and microstructure detection, the A-type, B-type, C-type and D-type inclusions under the GB/T10561 standard are less than or equal to 1.0 grade, and the microstructure is ferrite and bainite, wherein the proportion of the ferrite is 28-40%, and the proportion of the bainite is 60-72%.

In addition, the steel bars of examples 1 to 16 were respectively sampled and subjected to welding tests by electroslag pressure welding, and tensile tests were performed on the welded samples according to the room temperature test method standard of the part 1 of the tensile test of the GBT228.1-2010 metal material, and it was found that the fracture points of the welded samples in the tensile tests were formed at the steel bar base metal, but not at the welded points, and the obtained steel bars were excellent in welding performance.

It should be understood that although the present description refers to embodiments, not every embodiment contains only a single technical solution, and such description is for clarity only, and those skilled in the art should make the description as a whole, and the technical solutions in the embodiments can also be combined appropriately to form other embodiments understood by those skilled in the art.

The detailed description set forth above is merely a specific description of possible embodiments of the present invention and is not intended to limit the scope of the invention, which is intended to include within the scope of the invention equivalent embodiments or modifications that do not depart from the technical spirit of the present invention.

Claims

1. The 400 MPa-grade corrosion-resistant steel bar is characterized by comprising the following chemical components in percentage by mass: 9.5 to 10.4% of Cr, 1.0 to 1.2% of Mo, 0.3 to 0.6% of Mn, 0.01 to 1.00% of Ni, 0.01 to 0.5% of Cu, 0 to 0.014% of C, 0.004% of N, 0.01 to 0.05% of Nb, 0.2 to 0.6% of Si, 0.004% of S, 0.003% of O, 0.01% of As, 0.01 to 0.03% of P, 11.1 to 12.2% of Cr + Mo + 0.5Mn + 0.35Ni +0.25Cu, 0.4 to 0.8% of C + N +0.3Si + Mn +1.8Nb, and the balance of Fe and inevitable impurities; the elongation after fracture of the steel bar is more than or equal to 18 percent; in the week immersion corrosion test, the average weight loss corrosion rate of the steel bar is 0.05-0.1 g/(m)²·h)。

2. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein the steel bar further comprises the following chemical components in percentage by mass: 0.1 to 0.15% of V, 0.01 to 0.05% of Ti, 0.01 to 0.03% of Al, and 0.0005 to 0.0020% of B.

3. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein the microstructure of the steel bar is ferrite and bainite, and the ferrite accounts for 28% -40%.

4. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein class A, class B, class C and class D inclusions of the steel bar under the GB/T10561 standard are all less than or equal to 1.0 grade.

5. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein the yield strength of the steel bar is more than or equal to 420MPa, the tensile strength of the steel bar is more than or equal to 540MPa, and the maximum force total elongation of the steel bar is more than or equal to 7.5%.

6. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein the nominal diameter of the steel bar is 6-32 mm.

7. The 400 MPa-grade corrosion-resistant steel bar according to claim 6, wherein when the nominal diameter of the steel bar is 6-10 mm, the steel bar is arranged into a coiled steel bar; when the nominal diameter of reinforcing bar is 12~32mm, the reinforcing bar setting is the straight bar reinforcing bar.

8. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein the average weight-loss corrosion rate of the steel bar in a salt spray corrosion test is 0.01-0.04 g/(m)²·h)；

9. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein the steel bar can be prepared by adopting a process route I and a process route II;

10. The 400MPa grade corrosion resistant steel bar according to claim 9, wherein in the first process route:

the tapping temperature of the converter smelting process is 1600-1660 ℃;

in the AOD furnace refining process, high-carbon ferrochrome and ferromolybdenum are added into molten steel to carry out primary alloying on the molten steel, slagging is carried out after reduction, then manganese alloy is added, a steel ladle used for steel tapping is swept by argon for more than 5min before steel tapping, 20kg of aluminum ingot is added into the molten steel in the steel tapping process, the steel tapping temperature is 1630-1670 ℃, and the steel tapping C content is less than or equal to 0.010%;

in the LF furnace refining process, after molten steel reaches a ladle of the LF furnace, slag is adjusted according to a scheme of adding 13-15 kg of lime and 4.0-6.5 kg of fluorite to each ton of molten steel, the white slag holding time is not less than 8min, the soft stirring time is 8-15 min, and the tapping temperature is 1600-1620 ℃;

in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 1.2-1.6 m/min.

11. The 400MPa grade corrosion resistant steel bar of claim 9, wherein in the second process route:

in the converter smelting process, micro-carbon ferrochrome is added into molten steel in the tapping process to preliminarily alloy the molten steel, and the tapping temperature is 1700-1750 ℃;

in the LF furnace refining process, the ladle of the LF furnace is subjected to whole-process bottom blowing with the argon flow of 80-160L/min, and the tapping temperature is 1560-1600 ℃;

in the RH furnace refining process, after the RH furnace is vacuumized for 3min, oxygen is blown into the RH furnace, and the total oxygen blowing amount is 500-700 Nm³Then adding micro-carbon ferrochrome alloy into the molten steel to alloy the molten steel, and performing clean cycle treatment for more than 5min when the vacuum degree is less than 2mbar, wherein the tapping temperature is 1560-1600 ℃, and the tapping C content is less than or equal to 0.015 percent;

in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 2.2-2.6 m/min.

12. The 400MPa grade corrosion resistant steel bar according to claim 9, wherein the first process route and the second process route are both:

13. The 400MPa grade corrosion resistant steel bar according to claim 9, wherein the first process route and the second process route are both:

in the hot continuous rolling process, a continuous casting blank is heated in a heating furnace at the heating temperature of 1080-1130 ℃ for 60-120 min, and then rolled into a coiled twisted steel bar with the diameter of 6-10 mm, the initial rolling temperature is 980-1030 ℃, the finish rolling temperature is 850-950 ℃, and the spinning temperature is 830-920 ℃.

14. The 400 MPa-grade corrosion-resistant steel bar according to claim 9, wherein the first process route and the second process route both comprise an online pickling process and a packaging process which are sequentially performed after the temperature-controlled cooling process;

in the on-line pickling process, the steel bar sequentially passes through the pickling tank, the passivation tank and the drying equipment, and the air nozzles of the pickling tank are distributed around the central line of the pickling tank.

15. The 400 MPa-grade corrosion-resistant steel bar according to claim 1, wherein when two steel bars are connected into a welding sample by electroslag pressure welding, a fracture point of the obtained welding sample in a tensile test is formed at a base material of the two steel bars.

16. A production method of 400 MPa-level corrosion-resistant steel bars is characterized by comprising the following steps,

(1) making steel

(2) controlled rolling and cooling

or heating the steel billet obtained in the step 1 in a heating furnace at the heating temperature of 1080-1130 ℃ for 60-120 min, rolling the steel billet into a coiled twisted steel bar with the diameter of 6-10 mm, wherein the initial rolling temperature is 980-1030 ℃, the finish rolling temperature is 850-950 ℃, and the spinning temperature is 830-920 ℃; and then cooling the rolled coiled thread steel bar by adopting Stelmor, and completely closing a fan below the roller way.

17. The method for producing 400MPa grade corrosion-resistant steel bar according to claim 16, wherein in step 1, the chemical composition of the steel billet further comprises, in mass percent: 0.1 to 0.15% of V, 0.01 to 0.05% of Ti, 0.01 to 0.03% of Al, and 0.0005 to 0.0020% of B.

18. The method for producing 400MPa grade corrosion resistant steel bar according to claim 16, wherein in step 1, if molten steel smelting is performed by sequentially adopting a molten iron pre-desulfurization process, a converter smelting process, an AOD furnace refining process and an LF furnace refining process, then: the tapping temperature of the converter smelting process is 1600-1660 ℃; in the AOD furnace refining process, high-carbon ferrochrome and ferromolybdenum are added into molten steel to carry out primary alloying on the molten steel, slagging is carried out after reduction, then manganese alloy is added, a steel ladle used for steel tapping is swept by argon for more than 5min before steel tapping, 20kg of aluminum ingot is added into the molten steel in the steel tapping process, the steel tapping temperature is 1630-1670 ℃, and the steel tapping C content is less than or equal to 0.01%; in the LF furnace refining process, after molten steel reaches a ladle of the LF furnace, slag is adjusted according to a scheme of adding 13-15 kg of lime and 4.0-6.5 kg of fluorite to each ton of molten steel, the white slag holding time is not less than 8min, the soft stirring time is 8-15 min, and the tapping temperature is 1600-1620 ℃; in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 1.2-1.6 m/min;

and if molten steel is smelted by sequentially adopting a molten iron pre-desulfurization process, a converter smelting process, an LF furnace refining process and an RH furnace refining process, then: in the converter smelting process, micro-carbon ferrochrome is added into molten steel in the tapping process to preliminarily alloy the molten steel, and the tapping temperature is 1700-1750 ℃; in the LF furnace refining process, the ladle of the LF furnace is subjected to whole-process bottom blowing with the argon flow of 80-160L/min, and the tapping temperature is 1560-1600 ℃; in the RH furnace refining process, after the RH furnace is vacuumized for 3min, oxygen is blown into the RH furnace, and the total oxygen blowing amount is 500-700 Nm³Then adding micro-carbon ferrochrome alloy into the molten steel to alloy the molten steel, and performing clean cycle treatment for more than 5min when the vacuum degree is less than 2mbar, wherein the tapping temperature is 1560-1600 ℃, and the tapping C content is less than or equal to 0.015 percent; in the square billet continuous casting process, carbon-free casting powder or ultra-low carbon casting powder is adopted, the continuous casting temperature is 1520-1560 ℃, and the drawing speed in the continuous casting process is 2.2-2.6 m/min.

19. The method for producing 400MPa grade corrosion resistant steel bar according to claim 16, further comprising the steps of,

(3) on-line acid washing

20. The method for producing 400MPa grade corrosion resistant steel bar according to claim 16, wherein when two steel bars prepared by the method are connected into a welding sample by electroslag pressure welding, a fracture point of the welding sample in a tensile test is formed at a base material of the two steel bars.