CN114369760A

CN114369760A - Wire rod for stress corrosion resistant ultra-high strength steel strand and manufacturing method of steel strand

Info

Publication number: CN114369760A
Application number: CN202210014702.XA
Authority: CN
Inventors: 尹一; 刘祥; 廖德勇; 安绘竹; 徐曦
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2022-04-19
Anticipated expiration: 2042-01-07
Also published as: CN114369760B

Abstract

A wire rod for a stress corrosion resistant ultra-high strength steel strand and a manufacturing method of the steel strand are disclosed, wherein the steel comprises the following chemical components in percentage by weight: 0.90 to 1.00 percent of C, 0.80 to 1.10 percent of Si, 0.40 to 0.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.20 to 0.50 percent of Cr0.05 to 0.10 percent of V, 0.0008 to 0.0035 percent of B, and the balance of Fe and inevitable impurities. On the basis of a 1860MPa pre-stress steel strand wire rod, the invention effectively improves and optimizes the design of conventional alloy elements, improves the content of C, Si elements, reasonably adds metal elements Cr, V and B, adjusts the hot rolling controlled cooling and steel strand production processes, improves the steel wire drawing process and the steel strand stabilizing production process, and develops a stress corrosion resistant ultra-high strength steel strand which can be popularized and used.

Description

Wire rod for stress corrosion resistant ultra-high strength steel strand and manufacturing method of steel strand

Technical Field

The invention relates to the technical field of metallurgical production, in particular to a wire rod for an ultrahigh-strength stress corrosion resistant steel strand and a manufacturing method of the steel strand, which are mainly used for the ultrahigh-strength prestressed steel strand and can meet the requirement of the ultrahigh-strength prestressed steel strand on the level of 2300MPa-2400MPa on the stress corrosion resistance.

Background

The prestressed steel strand is mainly used for projects such as high-speed rails, bridges and large buildings, and has the characteristics of high strength, low relaxation and the like. At present, 1860 MPa-grade steel strands are generally adopted in China. Since the 90 s of the last century, the prestressed steel strand adopted in the field of engineering construction in China mainly takes SWRH82B wire rods as raw materials to manufacture 1860 grade steel strands, and the annual consumption is about 360-. With the improvement of the use function in recent years, the 1860 grade steel strand can not effectively meet the requirement of a large-span structure, and becomes a bottleneck problem restricting the development of a prestressed concrete structure. Meanwhile, in order to save steel and other resources and simplify the concrete structure, China is seeking to improve the tensile strength level of the steel strand, and 2300-2400MPa level steel strands are researched and developed. The adoption of the ultrahigh-strength prestressed steel strand can save the steel consumption, reduce the thickness of a concrete protective layer and reduce the self weight of the structure, has obvious technical and economic significance, meets the national requirements on energy conservation, emission reduction and green economy development, and is a future development trend. After the tensile strength grade of the steel strand is improved, the tension applied during tensioning is correspondingly improved, under the same environmental condition, the stress corrosion condition is severer than that of a 1860MPa grade steel strand, and the ultrahigh-strength steel strand is easier to generate stress corrosion damage. The ultrahigh-strength steel strand is produced by adopting conventional chemical components and a production process, and a stress corrosion test is difficult to be qualified. The tensile strength of the steel strand is improved, and the stress corrosion resistance of the steel strand must be improved. Therefore, aiming at the problem that the stress corrosion performance of the ultrahigh-strength steel strand is unqualified, the chemical composition design of the wire rod for the steel strand is improved, the production process of the wire rod is improved, the wire drawing process is improved in the production process of the steel strand, the temperature of a steel wire is reduced, the stabilizing treatment temperature is increased, shot blasting is carried out on the surface of the steel strand, the stress corrosion resistance performance of the ultrahigh-strength steel strand is improved, and the problem that the stress corrosion test of the ultrahigh-strength steel strand is unqualified is solved.

The common strength grade of the prestressed steel strand is 1860MPa, the common steel grade is SWRH82B, the content of C in the steel is 0.79-0.86%, the content of Si is 0.17-0.37%, the content of Mn is 0.60-0.90%, and 0.20-0.30% of Cr is added. Along with the improvement of the requirement on the strength level of the steel strand, the requirement on the 2300MPa-2240MPa level steel strand is provided. The steel type commonly used for the ultrahigh-strength steel strand at present is 92Si and the like, wherein the steel contains 0.90-0.95% of C, 0.80-1.10% of Si, 0.40-0.50% of Mn and 0.20-0.30% of Cr. When the strength of the steel strand is increased, the tensile force under tension is increased, and the breaking time in the stress corrosion test is reduced. Therefore, in addition to improving the strength of the steel strand, the ultrahigh-strength steel strand is developed to reduce the stress corrosion sensitivity and prevent the steel strand from rapidly breaking after stress corrosion.

Patent document CN111321352A discloses "a prestressed steel strand with strength of 2400MPa level and its production process" (CN111321352A), and the technical content disclosed by the patent document has the following problems: 1. chemical composition C of the wire rod: 0.88 to 1.02%, Si: 0.10% -1.30%, Mn: 0.30% -0.90%, P: less than or equal to 0.015 percent, S: less than or equal to 0.010 percent, Cr: 0.10-0.50%, V: 0.01-0.10%, Al: 0.01-0.08%, and the balance of Fe and inevitable impurities. The chemical composition has the advantages that the lower limit of the V content is controlled to be too low, meanwhile, the B element is not added, and the composition design is not specially carried out on the stress corrosion resistance of the steel strand; 2. through processes such as salt bath, the problem of overlarge performance difference of bad tissues and the poker due to uneven air cooling speed is solved, the rapid cooling and isothermal transformation of the wire rod are realized, and compared with the water bath adopted by the patent, the method has the differences of high cost, low yield, environmental pollution and the like; 3. the wire rod is subjected to drawing, stranding and stabilizing treatment, belongs to a conventional steel strand production process, has no special control method for stress corrosion, and has no measures for the stress corrosion resistance of the ultrahigh-strength steel strand compared with the processes of pickling and drying, low-temperature drawing, high-temperature stabilization, spraying of antirust liquid and the like.

In the patent document "vanadium-silicon composite microalloyed ultrahigh-strength wire rod and preparation process thereof" (CN103122437A), the disclosed technical content has the following problems: 1. chemical composition C of the wire rod: 0.85-0.95%, Si: 0.95% -1.10%, Mn: 0.50-0.60%, Cr: 0.20-0.35%, Ti: 0.01-0.05%, V: 0.11-0.15%, Al: 0.005-0.050%, and the balance of Fe and inevitable impurities. The carbon content of the chemical composition is low, and only steel strands below 2300MPa can be produced; 2. the preparation process sequentially comprises heating, rolling and controlled cooling, wherein the controlled cooling process adopts stelmor controlled cooling, and compared with the water bath adopted in the patent, the air cooling process has the problems of low cooling speed, uneven cooling and the like, and can cause low structure performance of the wire rod; 3. the wire rod is used for producing products such as ultrahigh-strength prestressed steel strands and galvanized steel strands, a production process control method of the steel strands is not specified, and measures aiming at the stress corrosion resistance of the ultrahigh-strength steel strands are not provided.

Disclosure of Invention

The invention aims to provide a wire rod for a stress corrosion resistant ultrahigh-strength steel strand and a manufacturing method of the steel strand, which are characterized in that on the basis of a 1860MPa prestressed steel strand wire rod, the conventional alloy element design is effectively improved and optimized, the C, Si element content is improved, metal elements Cr, V and B are reasonably added, the hot rolling and cooling control and steel strand production processes are adjusted, the steel wire drawing process and the steel strand stabilizing production process are improved, and the stress corrosion resistant ultrahigh-strength steel strand capable of being popularized and used is developed.

In order to achieve the purpose, the invention adopts the following technical scheme:

the wire rod for the stress corrosion resistant ultrahigh-strength steel strand comprises the following chemical components in percentage by weight: 0.90 to 1.00 percent of C, 0.80 to 1.10 percent of Si, 0.40 to 0.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.20 to 0.50 percent of Cr, 0.05 to 0.10 percent of V, 0.0008 to 0.0035 percent of B, and the balance of Fe and inevitable impurities.

The invention aims to meet the requirements of the ultrahigh-strength steel strand on improving the tensile strength and resisting stress corrosion cracking on the aspects of component design and alloy element selection, improves and optimizes the conventional alloy element design, improves the C, Si element content, reasonably adds metal elements Cr, V and B, adjusts the hot rolling and cooling control and steel strand production processes, improves the steel wire drawing process and the steel strand stabilizing production process and develops the stress corrosion resisting ultrahigh-strength steel strand which can be popularized and used on the basis of the 1860MPa steel strand wire rod. The design reason of the chemical components of the steel grade is as follows:

c is a chemical element for ensuring the strength and the structure of the wire rod, the carbon content is not less than 0.90 percent for ensuring the strength of the product, the proportion of cementite is increased, and simultaneously, the carbon content is not more than 1.00 percent for controlling the segregation of a continuous casting billet, controlling the structure, improving the plasticity of the wire rod and preventing the network cementite of a crystal boundary.

Si exists in a solid solution state in steel, can improve the hardenability of the steel, refines the interlayer spacing of pearlite pieces, has extremely strong strengthening effect, and simultaneously has the effect of inhibiting the formation of a net-shaped carburized body so as to better ensure the strength of a wire rod and control the structure. In addition, increasing the Si content reduces the speed of cementite spheroidization during the steel strand stabilization process, reducing strength loss.

Mn can improve the hardenability of steel, can refine a wire rod structure and a lamellar structure, and improves the strength and the plasticity, but the low-temperature structure is generated when the Mn content is too high, and the wire rod drawing performance is reduced, so the Mn content is controlled to be 0.40-0.50%.

P and S are harmful elements which can reduce the plasticity and toughness of the steel, so that the smaller the content, the better.

Cr can improve the hardenability of steel, refine the interlayer spacing of pearlite pieces, improve the strength of wire rods and improve the stress corrosion performance of steel strands. However, the Cr content is controlled to be 0.20-0.50% because the Cr content is too high, the low-temperature structure is generated, and the drawing performance of the wire rod is reduced.

V refines crystal grains, reduces the segregation of crystal boundary elements, forms a submicron V compound with C, N to be separated out during phase change, and can effectively improve the strength of the wire rod. Secondly, the V element can inhibit the precipitation of high-carbon steel grain boundary network cementite. Meanwhile, the V element is combined with the N element and the C element in the steel, so that the strain aging of the steel wire during drawing is reduced, and the stress corrosion resistance of the steel strand is improved. Therefore, the strength and the stress corrosion resistance of the steel strand can be improved by adding 0.05 to 0.10 percent of V element, and the stress corrosion resistance of the steel strand is improved.

B exists in a solid solution state in steel, and can improve the hardenability of the steel, refine the interlayer spacing of pearlite plates and improve the strength of a wire rod. Meanwhile, the B is combined with N in steel, so that the strain aging of the steel wire during drawing is reduced, and the stress corrosion resistance of the steel strand is improved. Therefore, the addition of 0.0008 to 0.0035 percent of the B element can improve the strength and the stress corrosion resistance of the steel strand and improve the stress corrosion resistance of the steel strand.

The manufacturing method of the stress corrosion resistant ultrahigh strength steel strand comprises the following steps:

1) smelting steel for a wire rod by a converter, and LF refining, wherein because the steel is low in P, S content and high in carbon content, low-S molten iron is selected during smelting, slag stopping and tapping are performed, Ar is blown from the top in a tank, and a reduction slag is refined by an LF furnace, so that the molten steel is uniform in component and low in inclusion content; the liquid steel has poor fluidity and large solidification shrinkage, and the drawing speed is controlled to be not more than 0.6m/min during continuous casting; because Si-containing steel has poor thermal conductivity and is easy to crack and burn, the total furnace time is not less than 4h and the temperature is 1200-1250 ℃ when the billet is heated before continuous rolling and cogging; the heating temperature of the steel billet in the wire plant is 1050-;

2) the steel drawing coefficient is controlled during the rolling of the wire rod, the surface quality is ensured, the water cooling and air cooling flow is controlled according to different specifications, the spinning temperature is 910 +/-15 ℃, an online water bath cooling and water outlet slow cooling process is adopted to replace the conventional off-line salt bath or lead bath process, the water bath cooling speed can reach more than 15 ℃/s, the sorbite rate of the wire rod is ensured to be more than 90 percent, the sorbite interlayer spacing is less than 120nm, the slow cooling process is adopted after the water bath, the cooling speed is less than 1 ℃/s, the low-temperature tissue of the wire rod is avoided, the uniform deformation of the wire rod in the drawing process is ensured, and the stress corrosion performance of the steel strand is improved;

3) after pickling and phosphating the wire rod, carrying out heat preservation at 250 ℃ for 3-7h for artificial aging at 200 ℃ to discharge hydrogen atoms remained and absorbed in steel after rolling the wire rod and in pickling, and improving the stress corrosion resistance; the steel wire drawing adopts the water cooling and air cooling of a winding drum, the temperature of the steel wire is reduced, and the temperature of a steel wire outlet does not exceed 120 ℃; the steel wire does not produce strain aging and dislocation plugging, hydrogen atom aggregation is prevented, and the stress corrosion resistance is improved;

4) because the content of Si in the steel is increased, the spheroidization speed of cementite in the stabilizing treatment process of the steel strand is reduced, and the strength loss is reduced, the heating temperature can be increased to 430-440 ℃ during the stabilizing treatment of the steel strand, the stress corrosion resistance of the steel strand is improved, and the tensile strength of the steel strand can meet the requirement of ultrahigh strength. In addition, before the steel strand is packaged, the surface is uniformly sprayed with antirust liquid, so that the stress corrosion resistance of the steel strand is further improved. The minimum value of the fracture time of the steel strand stress corrosion test is more than or equal to 2.5h, and the median value is more than or equal to 5.5 h.

The section of the continuous casting billet is 280 mm multiplied by 380mm²The square billet is about 8m in length.

The microstructure of the wire rod is mainly sorbite, the sorbite content is more than 90%, the inter-lamellar spacing is less than 120nm, low-temperature structures such as netlike cementite and martensite are avoided, the tensile strength is 1400-1450MPa, the tensile strength of the steel strand is guaranteed to reach 2300-2400MPa, and the reduction of area is more than or equal to 25%.

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

1) the steel strand stress corrosion resistance is improved by optimizing chemical components and adding Cr, V and B elements to prevent the strain aging generated in the drawing process of the steel wire and simultaneously reducing the strength loss of the steel strand during the stabilizing heating by adding Si element, and the stabilizing heating temperature is improved to improve the stress corrosion resistance of the steel strand while ensuring the strength. The stress corrosion resistance of the steel strand is further improved by controlling the steel wire drawing process and spraying the antirust liquid.

2) According to the invention, through reasonable optimization of each element component, the stable control of the components during smelting is ensured, and the rolling cooling process is adjusted to obtain the wire rod with more excellent performance. The steel strand processed by the wire rod through the process is subjected to stress corrosion performance test, and the stress corrosion performance test shows that: the steel strand produced by the wire rod for the 2300-plus-2400 MPa grade steel strand has the stress corrosion performance reaching the standard requirement, the shortest time standard requirement of the stress corrosion test is 2 hours, the actual time is 2.5-3.0 hours, and the median standard requirement is more than 5 hours, and the actual time is 5.5-6.0 hours.

Drawings

FIG. 1 is a microstructure view (500X) of the wire rod of the present invention;

FIG. 2 is a longitudinal microstructure (500X) of the steel wire in the steel strand according to the present invention.

Detailed Description

The following examples are intended to illustrate the invention in detail, and are intended to be a general description of the invention, and not to limit the invention.

The following are the production processes corresponding to the respective chemical components of the examples and comparative examples of the present invention. Wherein, table 1 shows the specific component design of the comparative example and the wire rod example of the invention, table 2 shows the controlled cooling process of the hot rolling production of the comparative example and the wire rod example of the invention, table 3 shows the mechanical property test results of the comparative example and the wire rod example of the invention, table 4 shows the production process of the steel strand of the comparative example and the example of the invention, table 5 shows the mechanical properties of the steel strand of the comparative example and the example of the invention, and table 6 shows the stress corrosion property test results of the comparative example and the example of the invention.

TABLE 1 Steel grade chemical composition (wt%)

TABLE 2 controlled Cooling Process conditions

TABLE 3 mechanical property test results of wire rod

TABLE 4 Steel wire production process

Specification mm	Wire drawing speed m/s	The temperature of the stabilized heating is lower	Rust inhibitor
				Comparative example	2.0-3.0	390-410	Is not sprayed
Example 1	1.5-2.5	430-440	Spraying of paint
				Example 2	1.5-2.5	430-440	Spraying of paint
Example 3	1.5-2.5	430-440	Spraying of paint

TABLE 5 test results of stranded wire properties

TABLE 6 stress Corrosion test results

Aiming at the problem of stress corrosion cracking of the 2300MPa-2400 grade steel strand, the invention improves the production process of the wire rod by improving the chemical composition design of the wire rod for the steel strand, improves the wire drawing process in the production process of the steel strand, reduces the temperature of the steel wire, improves the stabilizing treatment temperature, performs shot blasting on the surface of the steel strand and other measures, improves the stress corrosion resistance of the ultrahigh-strength steel strand, and solves the problem of unqualified stress corrosion test of the ultrahigh-strength steel strand.

Through the analysis to super strength steel strand wires stress corrosion cracking reason, each element is to the influence of steel strand wires stress corrosion sensibility, and alloy element is to restraining the effect of high carbon steel wire strain ageing and reducing stress corrosion cracking sensibility, confirm to adopt high carbon high silicon steel, improve the Si content, through adding Cr, V, B element, adopt water bath and slow cooling technology production wire rod, adopt after pickling stoving, reduce the steel wire temperature, improve steel strand wires production tempering temperature, improve the stabilization treatment temperature, measures such as steel strand wires surface shot-blasting, when improving steel strand wires intensity, improve super strength steel strand wires anti stress corrosion performance, solve the unqualified problem of super strength steel strand wires stress corrosion test. The invention is based on solving the problem of stress corrosion of the ultrahigh-strength prestressed steel strand, is applied to the industries such as steel strands for prestressed concrete, railways, highways and the like, has excellent mechanical property, stress corrosion resistance and economy and has wide market prospect.

Claims

1. The wire rod for the stress corrosion resistant ultrahigh-strength steel strand is characterized in that the steel comprises the following chemical components in percentage by weight: 0.90 to 1.00 percent of C, 0.80 to 1.10 percent of Si, 0.40 to 0.50 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.20 to 0.50 percent of Cr, 0.05 to 0.10 percent of V, 0.0008 to 0.0035 percent of B, and the balance of Fe and inevitable impurities.

2. The method for manufacturing the stress corrosion resistant ultrahigh-strength steel strand is characterized in that the steel strand is prepared by using the wire rod for the stress corrosion resistant ultrahigh-strength steel strand as claimed in claim 1, and the method comprises the following steps:

1) smelting steel for a wire rod by a converter, LF refining, and controlling the drawing speed to be not more than 0.6m/min during continuous casting; the total furnace-in time of heating the steel billet before continuous rolling and cogging is not less than 4 hours, and the temperature is 1200-1250 ℃; heating the billet of the wire rod factory to 1050-1100 ℃;

2) the spinning temperature is 910 +/-15 ℃, an online water bath cooling and water outlet slow cooling process is adopted, the water bath cooling speed is more than 15 ℃/s, and the slow cooling speed is less than 1 ℃/s;

3) carrying out heat preservation at 200-250 ℃ for 3-7h for artificial aging after pickling and phosphorizing the wire rod, and conventionally cooling the steel wire by adopting water cooling and air cooling of a winding drum in the drawing process to reduce the temperature of the steel wire, wherein the temperature of a die outlet of the steel wire is not more than 120 ℃;

4) and (3) increasing the heating temperature to 430-440 ℃ during the stabilizing treatment of the steel strand, and uniformly spraying an antirust liquid on the surface of the steel strand before the steel strand is packaged.

3. The method for manufacturing a steel wire using a wire rod for a stress corrosion resistant ultra high strength steel strand as set forth in claim 2, wherein said slab section is 280 x 380mm²The square billet is about 8m in length.

4. The method for manufacturing the steel wire by using the wire rod for the stress corrosion resistant ultrahigh-strength steel strand according to claim 2, wherein the content of sorbite in a microstructure of the wire rod is more than 90%, the inter-lamellar spacing is less than 120nm, no netlike cementite or martensite exists, the tensile strength is 1400-1450MPa, and the reduction of area is not less than 25%.

5. The method for manufacturing a steel wire by using the wire rod for the stress corrosion resistant ultrahigh-strength steel strand as claimed in claim 1 or 4, wherein the tensile strength of the steel strand is 2300-2400 MPa.

6. The method for manufacturing the steel wire by using the wire rod for the stress corrosion resistant ultrahigh-strength steel strand according to claim 2, wherein the minimum value of the fracture time of the steel strand in the stress corrosion test is more than or equal to 2.5 hours, and the median value of the fracture time of the steel strand is more than or equal to 5.5 hours.