Prestressed concrete sleeper reinforcing material hot-rolled wire rod and preparation method thereof

Abstract

The application discloses a kind of pre-stressed concrete sleeper reinforcing material hot-rolled wire rod and preparation method, belong to metallurgy, control cooling process technical field.The chemical composition and weight percentage of the hot-rolled wire rod are as follows: C:0.18-0.22%, Si:0.25-0.35%, Mn:0.60-0.70%, P≤0.035%, S≤0.035%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, O≤0.0080%, N≤0.0060%, the balance is iron and unavoidable impurities.The tensile strength of the hot-rolled wire rod is 500-550MPa, and the elongation after fracture is not less than 30%.There is no crack in the bending test (cold bending test 180°, bending core diameter is 1.0 times the sample diameter), and it has good mechanical properties.

Description

Technical Field

[0001] This invention relates to a hot-rolled wire rod as a reinforcement material for prestressed concrete railway sleepers and its preparation method, belonging to the fields of metallurgy and controlled cooling process technology. Background Technology

[0002] The static load strength and service life of concrete railway sleepers are closely related to their raw materials. To improve the load-bearing capacity and service life of prestressed concrete railway sleepers, the effective transfer of prestress between the reinforcing bars or wires and the concrete must be properly addressed during design and production. Cold-drawn reinforcing bars are typically used, and this is achieved through the rational arrangement of the amount and position of the reinforcing bars (wires). Scientific reinforcement (wire) design can both meet prestressing requirements and reduce consumption. Therefore, inventing a new material for reinforcing concrete railway sleeper components is urgently needed.

[0003] Patent application number CN200810152865.4 discloses the production process and specific implementation methods of indented steel strands for prestressed concrete, and patent application number CN202011476701.4 discloses a connection structure between a precast slab and a beam based on reinforced connections and its construction method. Existing technologies all disclose production processes or implementation methods for steel strands used in prestressed concrete. There are currently no publications on the preparation of reinforcement materials for prestressed concrete railway sleepers. Summary of the Invention

[0004] In view of the shortcomings of the prior art, this invention provides a hot-rolled wire rod as a reinforcement material for prestressed concrete railway sleepers and its preparation method. This invention develops a hot-rolled wire rod to effectively avoid brittle fracture failure of cold-drawn low-carbon steel wire prestressed concrete slab components when the strength safety factor is small. If there is a certain safety reserve after cracking and before failure, it can ensure that the component has some deformation (related to cracking) precursors before failure. This can be achieved by controlling the design reinforcement ratio of the component to be greater than the minimum reinforcement ratio. This wire rod is used as a reinforcement material for concrete railway sleepers. The prestressed concrete railway sleeper reinforcement material of this invention, when applied to concrete railway sleepers, requires strict requirements for the cleanliness of the molten steel, effective control of oxygen and nitrogen gases, good tensile strength uniformity, and ensures that the tensile strength matches the main reinforcement. Good wire rod surface quality and good cold bending performance are also required to ensure uniform stress distribution under load on the main reinforcement and improve the static load crack resistance of the sleeper.

[0005] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0006] In a first aspect, the present invention provides a hot-rolled wire rod as reinforcement material for prestressed concrete railway sleepers. The chemical composition and weight percentage of the hot-rolled wire rod are as follows: C: 0.18-0.22%, Si: 0.25-0.35%, Mn: 0.60-0.70%, P≤0.035%, S≤0.035%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, O≤0.0080%, N≤0.0060%, with the balance being iron and unavoidable impurities.

[0007] Furthermore, the microstructure of the hot-rolled wire rod is ferrite + pearlite; the tensile strength of the hot-rolled wire rod is 500-550 MPa, the elongation after fracture is not less than 30%, and no cracks are found in the bending test (cold bending test 180°, bending mandrel diameter is 1.0 times the sample diameter).

[0008] Secondly, the present invention provides a method for preparing hot-rolled wire rod as reinforcement material for prestressed concrete railway sleepers, including smelting and controlled rolling and cooling processes;

[0009] The smelting process is as follows: desulfurization → converter → LF refining → billet continuous casting;

[0010] The controlled rolling and cooling process is as follows: heating → high-pressure water descaling → controlled rolling and cooling.

[0011] Furthermore, the molten iron temperature before the converter is ≥1300℃, and the sulfur content (S) at the desulfurization station is ≤0.020wt%.

[0012] Furthermore, the converter smelting includes:

[0013] S1. First, scrap steel is fed into the oxygen top-and-bottom blowing converter, followed by molten iron. The scrap steel accounts for 10-12% by mass, and the molten iron accounts for 88-90%. Then, auxiliary materials lime and dolomite are added, with the following amounts per ton of steel: lime 40-50 kg / t, dolomite 28-32 kg / t. The heating process then begins, involving initial phosphorus removal and later sulfur removal. The converter's final carbon content is controlled at 0.10%-0.15 wt%, phosphorus ≤ 0.025 wt%, and the tapping temperature is 1680-1700℃. Slag addition is strictly prohibited. The converter is then tilted once to avoid excessive nitrogen content during initial blowing. Finally, the molten steel is poured into the ladle.

[0014] S2. Alloying of the ladle: When the steel is 1 / 4 to 1 / 3 full, lime, deoxidizer, and ferroalloy are added for alloying; argon blowing time ≥ 5 min, of which lime is 10-14 kg / t, deoxidizer is 0.06-0.09 kg / t; alloy addition per ton of steel: manganese silicon 8.8-9.3 kg / t, ferrosilicon 2.7-3.1 kg / t, deoxidizer 0.2-0.3 kg / t; then tap the ladle, slag must not be added during tapping; when adding slag, the amount of slag should be ≤ 30 mm.

[0015] S3. Static Argon Blowing: Static argon blowing time ≥ 8 min, pretreatment temperature 1640℃-1655℃, posttreatment temperature 1610℃-1625℃, after static argon blowing, feed 1kg-1.2kg / t of nitrogen-coated alloy wire at a feeding speed of 3m / s; clearance 450-500mm, slag thickness 35-40mm; and carbonized rice husks are prohibited after treatment before leaving the station.

[0016] Further, LF refining includes: inputting molten steel from the converter into the LF refining process; first, refining under slight positive pressure; adjusting the air damper before slag formation; then adding active lime, carbide slag, and ferrosilicon powder to create white slag; adding fluorite to dilute the slag; and then adding medium-carbon ferromanganese, ferrosilicon, and ferrosilicon for fine-tuning; soft blowing time ≥12 minutes; adding a covering agent to carbonize rice husks before removing from the furnace; this step requires white slag operation, controlling slag basicity and oxygen potential while ensuring slag fluidity; LF refining Time: 60-80 min; Full analysis temperature: 1635℃-1655℃; Alloy addition per ton of steel: 8.0-9.5 kg / t of active lime, 18-20 kg / furnace of carbide slag, 0.70-0.75 kg / t of ferrosilicon powder, 200-230 kg / furnace of fluorite, 0.24-0.30 kg / t of medium-carbon ferromanganese, 0.65-0.72 kg / t of ferromanganese, 2.10-2.20 kg / t of ferrosilicon, and 1.5-2.2 kg / t of carbonized rice husk.

[0017] Furthermore, the billet continuous casting includes: using electromagnetic stirring in the crystallizer and electromagnetic stirring at the end; a platform temperature of 1595±5℃; a tundish temperature of 1540℃-1550℃; maintaining a superheat of 20℃-30℃; protective casting throughout the process; using medium carbon steel protective slag in the crystallizer; ensuring the sprue is aligned; and having an insertion depth of 80-100mm; and maintaining a constant casting speed of 2.2-2.4m / min.

[0018] Furthermore, the heating process includes: a preheating section temperature of 880±50℃, a heating section temperature of 1080±50℃, a soaking section temperature of 1120±50℃, and a heating time of 2.5±0.5h.

[0019] Furthermore, the water pressure for the high-pressure water dephosphorization is ≥14MPa.

[0020] Furthermore, the controlled rolling and cooling includes: initial rolling temperature: 1180±20℃; first stand entry temperature: 1010±30℃; finishing rolling entry temperature: 900±20℃; wire drawing temperature: 920±20℃; air-cooled roller speed: head roller 0.30-0.40m / s; roller speed increase setting 3-5%.

[0021] Beneficial effects:

[0022] 1. This invention utilizes carefully selected raw materials, converter precipitation deoxidation process, non-metallic inclusion modification treatment technology, and continuous casting tundish metallurgy and protective casting technology to ensure the cleanliness of molten steel.

[0023] 2. This invention ensures the strength stability of wire rod through the Stellmore controlled rolling and cooling process.

[0024] 3. This invention can control the wire rod size accuracy to reach the B+ accuracy standard in GB / T14981.

[0025] 4. Using the hot-rolled wire rod of this invention as the reinforcement material for concrete sleepers can save 10-30% of steel and 25% of concrete compared to ordinary reinforced concrete, reducing the cost by about 10%. Detailed Implementation

[0026] To better explain and facilitate understanding of the present invention, a detailed description of the invention will be provided through specific embodiments.

[0027] These embodiments are provided so that the invention can be understood more clearly and thoroughly, and so that the scope of the invention can be fully conveyed to those skilled in the art.

[0028] Examples 1-5

[0029] This embodiment provides a method for preparing hot-rolled wire rods as reinforcement material for prestressed concrete railway sleepers. The hot-rolled wire rods as reinforcement material for prestressed concrete railway sleepers have the following chemical composition by weight percentage: C: 0.18-0.22%, Si: 0.25-0.35%, Mn: 0.60-0.70%, P≤0.035%, S≤0.035%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, O≤0.0080%, N≤0.0060%, with the balance being iron and unavoidable impurities.

[0030] The production process of this hot-rolled wire rod is as follows: smelting and controlled rolling and controlled cooling process.

[0031] The smelting process is as follows: desulfurization → converter → refining → billet continuous casting;

[0032] The controlled rolling and cooling process is as follows: heating → high-pressure water descaling → controlled rolling and cooling.

[0033] The specific process is as follows:

[0034] 1. The temperature of molten iron before the converter is ≥1300℃, the sulfur content at the desulfurization station is ≤0.020wt%, the charging amount is 173±2t / furnace, and the scrap steel requirement is ≤10 tons of reusable slag steel + cutting material.

[0035] 2. Converter smelting:

[0036] S1. First, scrap steel is fed into the oxygen top-and-bottom blowing converter, followed by molten iron. By mass percentage, scrap steel accounts for 12% and molten iron accounts for 88%. Then, auxiliary materials lime and dolomite are added. The auxiliary material addition amounts per ton of steel are: lime 40-50 kg / t and dolomite 28-32 kg / t. Then, the heating operation begins, with early P removal and mid-to-late S removal. The converter's final carbon content is controlled at 0.10%-0.15%, P ≤ 0.025%, and the tapping temperature is 1680-1700℃. Slag addition is strictly prohibited. Afterward, the furnace is turned over once to avoid spot blowing and prevent excessive nitrogen content. Finally, the molten steel is poured into the ladle.

[0037] S2. Alloying of steel ladle: When the steel is 1 / 4 to 1 / 3 full, lime, deoxidizer, and ferroalloy are added for alloying; argon blowing time ≥ 5 min, of which lime 10-14 kg / t, deoxidizer 0.06-0.09 kg / t; alloy addition per ton of steel: manganese silicon 9.3 kg / t, ferrosilicon 3.1 kg / t, deoxidizer 0.3 kg / t; then tap the ladle, slag must not be added during tapping; when adding slag, the amount of slag added should be ≤ 30 mm.

[0038] S3, Static Argon Blowing: The molten steel after exiting the furnace in S2 is fed into the argon station for argon blowing treatment. The static argon blowing time is ≥8min. The temperature before treatment is 1640℃-1655℃, and the temperature after treatment is 1610℃-1625℃. After static argon blowing, 1kg-1.2kg / t of nitrogen-coated alloy wire is fed at a feeding speed of 3m / s. The clearance is 500mm, and the slag thickness is 40mm. It is forbidden to add carbonized rice husks after treatment, and then the steel leaves the station.

[0039] 3. LF Furnace Refining: Molten steel from the converter is fed into the LF furnace for refining. Initially, a slightly positive pressure operation is used. Before slag formation, the damper is adjusted. If the requirements are not met when energized, adjustments must be made before energizing. During this process, large-scale argon blowing is prohibited to prevent nitrogen absorption. Then, active lime, carbide slag, ferrosilicon powder, and other auxiliary materials are added to create white slag. Fluorite is added to dilute the slag, followed by the addition of medium-carbon ferromanganese, ferrosilicon, and ferrosilicon for fine-tuning. Soft blowing time is ≥12 minutes to ensure sufficient static blowing time and argon blowing effect. Before removal from the furnace, a covering agent is added to carbonize rice husks, and then the slag is discharged. This step requires white slag operation, controlling slag basicity and oxygen content while ensuring slag fluidity. The refining time for LF is 60-80 minutes, and the full analysis temperature is 1635℃-1655℃. The alloy addition per ton of steel is as follows: ferrosilicon powder 0.70-0.75 kg / t, medium carbon ferromanganese 0.24-0.30 kg / t, ferromanganese 0.65-0.72 kg / t, and ferrosilicon 2.10-2.20 kg / t. The auxiliary material addition per ton of steel is as follows: active lime 8.0-9.5 kg / t, fluorite 230 kg / furnace, carbide slag 20 kg / furnace, and carbonized rice husk 1.5-2.2 kg / t. During the process, the molten steel is monitored in real time, and the alloy is finely adjusted to ensure that the composition of the molten steel meets the standard requirements.

[0040] 4. Continuous casting of billets: Molten steel from the refining furnace is fed into the billet continuous casting process; electromagnetic stirring in the crystallizer and at the end are used; the electromagnetic stirring current in the crystallizer is 240A, frequency 5Hz, forward and reverse rotation; the electromagnetic stirring current at the end is 250A, frequency 6Hz, continuous; the platform temperature is 1595±5℃, the tundish temperature is 1540℃-1550℃, the superheat is maintained at 20℃-30℃, and the entire process is protected during casting; medium carbon steel protective slag is used in the crystallizer; in addition, the sprue must be aligned, and the sprue insertion depth is controlled at 80-100mm; the constant casting speed is 2.2m / min-2.4m / min, and the billets are cast to a fixed length of 150mm×150mm and removed from the line; the billet cutting adopts a combination of automatic and manual methods.

[0041] 5. Heating process: The billet from the continuous casting line is hoisted into the pusher-type heating furnace. The entire heating process is controlled at 880±50℃ in the preheating section, 1080±50℃ in the heating section, and 1120±50℃ in the soaking section. The heating time is 2.5±0.5h, and then the billet is taken out of the furnace.

[0042] 6. Rolling process: The billet heated in the heating furnace is first subjected to high-pressure water descaling, followed by rough rolling, intermediate rolling, and finish rolling in sequence, and then wire cutting. The wired wire is transported off the line via the Steyrmo air-cooling line, integrated into coils, and after the ends are trimmed, it is packaged to obtain the finished steel product.

[0043] 7. The rolling temperature and cooling rate of the entire rolling process are specifically controlled as follows: Initial rolling temperature: 1180±20℃; First stand entry temperature: 1010±30℃; Finishing mill entry temperature: 900±20℃; Wire drawing temperature: 920±20℃; Air-cooled roller speed: Head roller 0.30m / s; Roller speed increase set at 3-5%.

[0044] The chemical composition (wt%) of the steels in Examples 1-5 is shown in Table 1.

[0045] C and S analyses and gas content (wt%) are shown in Table 2.

[0046] The steel smelting processes of Examples 1-5 are shown in Table 3.

[0047] The rolling process of the steel in Examples 1-5 is shown in Table 4.

[0048] The physical properties of the wire rods in Examples 1-5 are shown in Table 5.

[0049] The wire rod dimensions for Examples 1-5 are shown in Table 6.

[0050] Table 1. Chemical composition (wt%) of the steel in each embodiment.

[0051]

[0052] Table 2. C, S analysis and gas content (wt%)

[0053]

[0054] Table 3. Smelting processes of steel in each embodiment.

[0055]

[0056]

[0057] Table 4 Rolling process of steel in each embodiment

[0058]

[0059] Table 5 Physical properties of wire rod in each embodiment

[0060]

[0061]

[0062] Table 6. Wire rod dimensions for each embodiment

[0063]

[0064] The hot-rolled wire rods prepared in Examples 1-5 have a tensile strength of 500-550 MPa, an elongation of ≥30%, and show no cracks in a 180° cold bending test (d=a). Non-metallic inclusions are classified as A-grade ≤1.5, B-grade ≤1.0, C-grade ≤1.5, and D-grade ≤1.0. Oxygen and nitrogen content is low (O content ≤0.0080%, N content ≤0.0060%). The metallographic structure consists of ferrite and pearlite with a grain size ≥8.5. The dimensional accuracy of the wire rods meets or exceeds GB / T14981 Grade B accuracy.

[0065] This invention utilizes hot-rolled wire rods as reinforcement material to prepare prestressed concrete sleepers. The sleepers are anchored using a pre-tensioning method, relying on self-anchoring through bond strength. To increase anchoring capacity, indented steel wires are used, relying on surface deformation to increase friction between the steel and concrete interfaces, thus strengthening the bond. The reasonable reinforcement quantity and wire placement allow for a gradual stress release, reducing the probability of sleeper cracks while minimizing damage to the concrete meshing teeth and the bond strength between the steel wire and concrete, thereby reducing the loss of static load crack resistance. This meets the requirements for high track stability, high speed, and high capacity transport, and increases the service life of the sleepers.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hot-rolled wire rod as reinforcement material for prestressed concrete railway sleepers, characterized in that, The chemical composition and weight percentage of the hot-rolled wire rod are as follows: C: 0.18-0.22%, Si: 0.25-0.35%, Mn: 0.60-0.70%, P≤0.035%, S≤0.035%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, O≤0.0080%, N≤0.0060%, with the balance being iron and unavoidable impurities; The microstructure of the hot-rolled wire rod is ferrite + pearlite; the tensile strength of the hot-rolled wire rod is 500-550 MPa, the elongation after fracture is not less than 30%, there are no cracks in the bending test, and the non-metallic inclusions are grade A ≤1.5, grade B ≤1.0, grade C ≤1.5, grade D ≤1.0, O content ≤0.0080%, and N content ≤0.0060%. The method for preparing hot-rolled wire rod, the raw material for prestressed concrete sleeper reinforcement, includes smelting and controlled rolling and cooling processes. The smelting process is as follows: desulfurization → converter → LF refining → billet continuous casting; The controlled rolling and cooling process is as follows: heating → high-pressure water descaling → controlled rolling and cooling; The converter smelting includes: S1. First, scrap steel is fed into the oxygen top-and-bottom blowing converter, followed by molten iron. The weight percentage of scrap steel is 10-12%, and molten iron is 88-90%. Then, auxiliary materials lime and dolomite are added, with the following amounts per ton of steel: lime 40-50 kg / t, dolomite 28-32 kg / t. The heating process then begins, involving initial phosphorus removal and later sulfur removal. The converter's final carbon content is controlled at 0.10%-0.15 wt%, phosphorus ≤ 0.025 wt%, and the tapping temperature is 1680-1700℃. Slag addition is strictly prohibited. The converter is then tilted once to avoid excessive nitrogen content during initial blowing. Finally, the molten steel is poured into the ladle. S2. Alloying of the ladle: When the steel is 1 / 4 to 1 / 3 full, lime, deoxidizer, and ferroalloy are added for alloying; argon blowing time ≥ 5 min, of which lime is 10-14 kg / t, deoxidizer is 0.06-0.09 kg / t; alloy addition per ton of steel: manganese silicon 8.8-9.3 kg / t, ferrosilicon 2.7-3.1 kg / t, deoxidizer 0.2-0.3 kg / t; then tap the ladle, slag must not be added during tapping; when adding slag, the amount of slag should be ≤ 30 mm. S3. Static Argon Blowing: Static argon blowing time ≥ 8 min, pretreatment temperature 1640℃-1655℃, posttreatment temperature 1610℃-1625℃, after static argon blowing, feed 1kg-1.2kg / t of nitrogen-coated alloy wire at a feeding speed of 3m / s; clearance 450-500mm, slag thickness 35-40mm; and carbonized rice husks are prohibited after treatment before leaving the station.

2. The hot-rolled wire rod used as reinforcement material for prestressed concrete railway sleepers according to claim 1, characterized in that, The temperature of molten iron before the converter is ≥1300℃, and the sulfur content (S) at the desulfurization station is ≤0.020wt%.

3. The hot-rolled wire rod used as reinforcement material for prestressed concrete railway sleepers according to claim 1, characterized in that, LF refining includes: inputting molten steel from the converter into the LF refining process; first, refining under slight positive pressure, adjusting the air damper before slag formation; then adding active lime, carbide slag, and ferrosilicon powder to create white slag; adding fluorite to dilute the slag; and then adding medium-carbon ferromanganese, ferrosilicon, and ferrosilicon for fine-tuning; soft blowing time ≥12 minutes; adding a covering agent to carbonize rice husks before removing from the furnace; this step requires white slag operation, controlling slag basicity and oxygen potential while ensuring slag fluidity; LF refining time 6 minutes. 0min-80min, full analysis temperature 1635℃-1655℃; alloy addition per ton of steel: active lime 8.0-9.5kg / t, carbide slag 18-20kg / furnace, ferrosilicon powder 0.70-0.75kg / t, fluorite 200-230kg / furnace, medium carbon ferromanganese 0.24-0.30kg / t, ferromanganese 0.65-0.72kg / t, ferrosilicon 2.10-2.20kg / t, carbonized rice husk 1.5-2.2kg / t.

4. The hot-rolled wire rod used as reinforcement material for prestressed concrete railway sleepers according to claim 1, characterized in that, The billet continuous casting includes: using electromagnetic stirring in the crystallizer and electromagnetic stirring at the end; platform temperature of 1595±5℃; tundish temperature of 1540℃-1550℃; superheat maintained at 20℃-30℃; protective casting throughout the process; medium carbon steel protective slag used in the crystallizer; sprue must be aligned; sprue insertion depth of 80-100mm; constant casting speed of 2.2-2.4m / min.

5. The hot-rolled wire rod used as reinforcement material for prestressed concrete railway sleepers according to claim 1, characterized in that, The heating process includes: a preheating section temperature of 880±50℃, a heating section temperature of 1080±50℃, and a soaking section temperature of 1120±50℃; the heating time is 2.5±0.5h.

6. The hot-rolled wire rod used as reinforcement material for prestressed concrete railway sleepers according to claim 1, characterized in that, The water pressure for high-pressure water dephosphorization is ≥14MPa.

7. The hot-rolled wire rod used as reinforcement material for prestressed concrete railway sleepers according to claim 1, characterized in that, The controlled rolling and cooling includes: initial rolling temperature: 1180±20℃; first stand entry temperature: 1010±30℃; finishing rolling entry temperature: 900±20℃; wire drawing temperature: 920±20℃; air-cooled roller speed: head roller 0.30-0.40m / s; roller speed increase setting 3-5%.

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