A wire rod for 1100mpa grade cableway rope and a method for manufacturing the same

Abstract

The application discloses a 1100MPa-grade wire rod for cableway ropes and a preparation method thereof. The wire rod comprises the following components in percentage by mass: C: 0.79% to 0.85%, Si: 0.10% to 0.20%, Mn: 0.50% to 0.60%, P: 0.015% or less, S: 0.0030% to 0.010%, N: 0.0040% or less, total oxygen: 0.0010% to 0.0020%, Als: 0.0005% to 0.0020%, Nb: 0.0002% to 0.0010%, V: 0.0003% to 0.0010%, and (Nb+V): 0.0005% to 0.0015%, and the balance is iron and inevitable impurities. Through chemical component design, optimization of component proportion and adjustment of process parameters, the wire rod has good comprehensive mechanical properties and meets the performance requirements of the cableway ropes in the service process.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and more specifically, to a 1100MPa grade cableway wire rod and its preparation method. Background Technology

[0002] Cableway ropes are steel wire ropes with extremely high safety requirements. During service, they endure repeated tension, impact, and friction. To ensure the safety performance of cableway ropes, the wire rods need to have high deformation properties to meet the production and service performance requirements. 1100MPa strength grade cableway rope wire rods are widely used, and the stable service performance of these wire rods is crucial for the safe operation of cableway ropes.

[0003] Chinese invention patent CN102268596A discloses a high-carbon steel wire rod for producing fine steel wire. The chemical composition of this wire rod, by weight percentage, is as follows: [C]: 0.6%–0.88%, [Si]: 0.1%–1.0%, [Mn]: 0.3%–1.0%, [P]≤0.015%, [S]≤0.010%, [N]≤0.004%, [O]≤0.002%, [Al]≤0.002%, [Ti]≤0.002%, [Mg]≤0.001%, with other unavoidable impurities not exceeding 0.1%, and the remainder being iron. This patent focuses on the high-carbon steel wire rod for producing fine steel wire and does not describe wire rods for 1100MPa strength cableways or their production methods.

[0004] Because 1100MPa-grade ultra-high strength cableway ropes have a wide range of applications, there is an urgent need to develop a cableway rope wire rod that can improve its safe operation under repeated tension, impact and friction to meet the performance requirements of cableway ropes. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a 1100MPa grade cableway wire rod and its preparation method to meet the user's performance requirements for cableway ropes during service.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A 1100MPa grade cableway rope bar comprises the following components by mass percentage: C: 0.79%–0.85%, Si: 0.10%–0.20%, Mn: 0.50%–0.60%, P≤0.015%, S: 0.0030%–0.010%, N≤0.0040%, total oxygen: 0.0010%–0.0020%, Als: 0.0005%–0.0020%, Nb: 0.0002%–0.0010%, V: 0.0003%–0.0010%, and (Nb+V): 0.0005%–0.0015%, with the balance being iron and unavoidable impurities.

[0008] The present invention also discloses a method for preparing 1100MPa grade cableway wire rod as described above, comprising the following steps: converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, and wire rod cooling;

[0009] In the converter smelting process, scrap steel and molten iron are used as furnace charge, with the proportion of scrap steel being 5% to 10%; the oxygen activity of the molten steel after converter smelting is controlled at 60 ppm to 120 ppm.

[0010] In the LF refining process, the molten steel after being tapped from the converter smelting furnace is fed into the LF furnace for refining treatment. The refining temperature of the LF furnace is 1490℃~1540℃, and the refining time is 30min~50min.

[0011] In the continuous casting process, molten steel that has been refined by the LF is continuously cast to obtain a continuously cast billet.

[0012] In the continuous casting billet heating and rolling process, the continuous casting billet that comes off the production line in the continuous casting process is sent to a heating furnace for heating, and the heated continuous casting billet is continuously rolled, with a final rolling temperature of 880℃~980℃.

[0013] In the wire rod rolling process, the continuously rolled steel billet is heated in a heating furnace, and then sequentially undergoes roughing rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire drawing.

[0014] During the wire rod cooling process, the wire rod is cooled on an air-cooled roller conveyor after spinning to obtain the 1100MPa grade cableway wire rod.

[0015] Implementing the embodiments of the present invention will have the following beneficial effects:

[0016] This invention, through the design of an optimal composition system and the application of matching smelting, continuous casting billet heating and continuous rolling, and cooling processes, produces wire rods with excellent comprehensive mechanical properties and a tensile strength of 1050MPa–1150MPa. This meets the performance requirements of users for cableway ropes during service. Compared with currently industrially produced cableway rope wire rods, this invention reduces the cost of the wire rod alloy, enhances product competitiveness, and conserves alloy resources. It also improves the mechanical properties of the wire rod, enhancing its safe operation under repeated tension, impact, and friction. Furthermore, the preparation method of this invention features low production cost and strong process applicability, improving the comprehensive mechanical properties of cableway rope wire rods, which is beneficial for their production and widespread application, resulting in significant social benefits. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0018] I. Chemical composition and mechanical properties

[0019] This invention discloses a 1100MPa grade cableway rope bar, comprising the following components by mass percentage: C: 0.79%–0.85%, Si: 0.10%–0.20%, Mn: 0.50%–0.60%, P≤0.015%, S: 0.0030%–0.010%, N≤0.0040%, total oxygen: 0.0010%–0.0020%, Als: 0.0005%–0.0020%, Nb: 0.0002%–0.0010%, V: 0.0003%–0.0010%, and (Nb+V): 0.0005%–0.0015%, with the balance being iron and unavoidable impurities.

[0020] Specifically, the mechanism of action of each alloy component in the wire rod of this invention is as follows:

[0021] Excessive carbon content in wire rod will cause the cableway ropes processed from the rods to exceed the required strength range; simultaneously, higher strength will increase the breakage rate of the wire rods during cableway rope manufacturing, leading to a higher scrap rate for users. Insufficient carbon content in the wire rods will not meet the user's strength requirements for the wire ropes. Therefore, in this invention, the carbon content is controlled between 0.79% and 0.85%.

[0022] Silicon increases the eutectoid transformation temperature of steel and results in coarse pearlite structure in wire rods, which is detrimental to the complex deformation processes during cableway rope manufacturing. Silicon is a major deoxidizing element in high-carbon steel; excessive silicon content leads to coarse silicates and impurities after deoxidation, while insufficient silicon content results in inadequate deoxidation, thus reducing the deformation capacity of the wire rods during cableway rope manufacturing. Therefore, the silicon content in this invention is controlled at 0.10%–0.20%.

[0023] Manganese is an element that improves the strength of wire rod, which helps ensure that the steel wire processed from wire rod meets the tensile strength requirements of users. Manganese also lowers the eutectoid transformation temperature of steel, refines the pearlite structure of wire rod, and improves the deformation capacity during the processing of cable rope steel wire from wire rod. Therefore, the manganese content in this invention is controlled at 0.50% to 0.60%.

[0024] Phosphorus reduces the deformation capacity of wire rods during cable rope processing, causing cracking and breakage of the steel wires. Therefore, the phosphorus content in this invention is controlled to be no higher than 0.015%.

[0025] High sulfur content in steel reduces the cold working performance of wire rod. Since MnS inclusions have good deformability, an appropriate amount of sulfur in the steel can reduce the harmful effects of crystalline inclusions; therefore, the sulfur content in this invention is controlled at 0.0030%–0.010%.

[0026] The nitrogen content needs to be controlled to a low range to reduce the hardening effect during the cable rope processing and improve the deformation capacity of the steel wire. Therefore, in this invention, the nitrogen content is controlled to be no higher than 0.0040%.

[0027] When the oxygen content is low, the inclusions in the wire rod have poor deformation ability, which is not conducive to the processing of cable ropes; when the oxygen content in the wire rod is high, the inclusions in the steel are large in size and numerous, which easily leads to cracking and breakage during the processing of cable ropes. Therefore, in this invention, the total oxygen content of the wire rod is controlled at 0.0010% to 0.0020%.

[0028] When the acid-soluble aluminum content is high, large Al2O3 inclusions will appear in the steel; when the acid-soluble aluminum content in the wire rod is too low, the melting point of the inclusions in the steel is high, and cracks are prone to occur between the inclusions and the matrix during processing, leading to cracking and breakage of the cableway rope during processing. Therefore, the acid-soluble aluminum content of this invention is controlled at 0.0005% to 0.0020%.

[0029] Niobium can refine the pearlitic structure of wire rod by inhibiting grain growth in the billet during heating, thereby improving the deformation capacity of the wire rod during cable rope processing. However, a higher niobium content leads to a higher niobium carbonitride content in the steel, resulting in severe work hardening of the wire rod during wire processing, which easily leads to cracking and breakage of the wire. Therefore, the niobium content in this invention is controlled at 0.0002% to 0.0010%.

[0030] Vanadium dissolves into steel to increase its strength. However, the vanadium content in the steel should not be too high to prevent the high strength of the wire rod from reducing its drawing performance. Vanadium can inhibit grain growth in the billet during heating, thereby refining the pearlite structure of the wire rod and improving its uniform deformation ability during cable rope processing. Therefore, the vanadium content in this invention is controlled between 0.0003% and 0.0010%.

[0031] The present invention further sets the total content of Nb and V within the range of 0.0005% to 0.0015%, which is beneficial to ensure the processing performance of wire rod and prevent excessive carbide precipitation, which would lead to excessive work hardening during wire rod drawing.

[0032] In one specific embodiment, the tensile strength of the 1100MPa grade cable rope wire rod of the present invention is 1050MPa to 1150MPa.

[0033] In one specific embodiment, the oxygen content at the interface between the wire rod matrix and the iron oxide scale is 3.0% to 6.5%, and the iron content is 76.5% to 80.5%.

[0034] II. Production Process Technology

[0035] The present invention also discloses a method for preparing 1100MPa grade cableway wire rod as in any embodiment of the present invention, comprising the following steps: converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, and wire rod cooling.

[0036] Furthermore, the specific steps include:

[0037] S1. In converter smelting, scrap steel and molten iron are used as furnace charge, with the proportion of scrap steel being 5% to 10%; the oxygen activity of the molten steel after converter smelting is controlled at 60ppm to 120ppm.

[0038] In S2 and LF refining, the molten steel after being tapped from the converter is fed into the LF furnace for refining. The refining temperature in the LF furnace is 1490℃~1540℃, and the refining time is 30min~50min.

[0039] In one specific embodiment, the size of the molten steel inclusions at the LF inlet position is ≤60μm, the size of the molten steel inclusions at the LF outlet position is ≤50μm, and the size of the molten steel inclusions at the tundish position is ≤40μm.

[0040] S3. In continuous casting, molten steel that has been refined by LF is continuously cast to obtain a continuously cast billet.

[0041] In one specific embodiment, the cross-sectional dimensions of the continuously cast billet are (250-300) mm × (350-400) mm.

[0042] S4. In the continuous casting billet heating and rolling process, the continuous casting billet that comes off the continuous casting line is sent to a heating furnace for heating, and the heated continuous casting billet is rolled continuously. The final rolling temperature is 880℃~980℃.

[0043] In one specific embodiment, during the heating and rolling of the continuously cast billet, the total time in the furnace for heating the continuously cast billet is 3.8h to 4.7h; the temperature of the soaking zone is 1170℃ to 1220℃, and the holding time is 30min to 50min; the cross-sectional dimensions of the continuously rolled billet are (140 to 180)mm × (140 to 180)mm.

[0044] S5. In the wire rod rolling process, the continuously rolled steel billet is heated in a heating furnace, and then successively passes through rough rolling, intermediate rolling, pre-finishing rolling, finish rolling, and wire drawing.

[0045] In one specific embodiment, during wire rod rolling, the wire rod is produced from square billets. The total furnace time for the billet is 150-170 minutes, the soaking temperature is 1100-1150°C, and the soaking time is 30-50 minutes. The billet heating process takes place in the austenitic high-temperature region, with a carbon content of 1.25%-1.5% at the austenite-cementite interface. High-temperature diffusion in the billet reduces the segregation of elements such as carbon and manganese. After heating, the billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling before wire rod extrusion. The wire rod exiting the pre-finishing rolling mill is at 980-1000°C; entering the finishing rolling mill at 890-930°C; entering the double-module rolling mill at 910-940°C; and the wire rod extrusion temperature is 900-930°C. The higher wire rod extrusion temperature increases the cooling rate of the wire rod on the air-cooled roller conveyor, laying the foundation for controlling the final microstructure of the wire rod. The wire rod is rolled to a diameter of 8mm to 11mm.

[0046] S6. During the wire rod cooling process, the wire rod is cooled on the air-cooled roller conveyor after spinning to obtain 1100MPa grade wire rod for cableway ropes.

[0047] In one specific embodiment, during the wire rod cooling process, the wire rod is cooled on an air-cooled roller conveyor after wire drawing. The phase transformation temperature of the wire rod is controlled at 600℃~650℃. When the phase transformation time on the air-cooled line is 5s~8s, the pearlite content of the wire rod is ≥40%; when the phase transformation time is 15s~18s, the pearlite content is 85%~95%. After final cooling, the cord steel wire rod is mainly composed of sorbite structure, which is beneficial for the user's wire drawing.

[0048] The following are specific embodiments.

[0049] Examples 1-6

[0050] The chemical composition, preparation process, and performance parameters of the wire rods in Examples 1-6 of this invention are shown in Table 1.

[0051] Table 1. Chemical composition, preparation process, and performance parameters of wire rods from Examples 1-6

[0052]

[0053]

[0054] Based on the above results, it can be seen that the present invention has carried out a large number of systematic experimental studies on alloy element screening and proportioning, converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, and wire rod cooling process design optimization. Finally, the composition system and manufacturing process that can meet the purpose of the present invention were determined, and a wire rod for cableway rope with a tensile strength of up to 1050MPa to 1150MPa was obtained.

[0055] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing 1100MPa grade cableway wire rod, characterized in that, 1100MPa grade cableway wire rods comprise the following components by weight percentage: C: 0.79%~0.85%, Si: 0.10%~0.20%, Mn: 0.50%~0.60%, P≤0.015%, S: 0.0030%~0.010%, N≤0.0040%, total oxygen: 0.0010%~0.0020%, Als: 0.0005%~0.0020%, Nb: 0.0002%~0.0010%, V: 0.0003%~0.0010%, and (Nb+V): 0.0005%~0.0015%, with the balance being iron and unavoidable impurities; The preparation method of the 1100MPa grade cableway rope wire rod includes the following steps: converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, and wire rod cooling; In the converter smelting process, scrap steel and molten iron are used as furnace charge, with the scrap steel ratio being 5% to 10%; the oxygen activity of the molten steel after converter smelting is controlled at 60 ppm to 120 ppm. In the LF refining process, the molten steel after being tapped from the converter smelting furnace is fed into the LF furnace for refining treatment. The refining temperature of the LF furnace is 1490℃~1540℃, and the refining time is 30min~50min. In the continuous casting process, the molten steel refined by the LF is continuously cast to obtain a continuously cast billet. In the continuous casting billet heating and rolling process, the continuous casting billet that comes off the production line in the continuous casting process is sent to a heating furnace for heating, and the heated continuous casting billet is continuously rolled, with a final rolling temperature of 880℃~980℃. In the aforementioned wire rod rolling process, the continuously rolled steel billet is heated in a heating furnace, and then sequentially undergoes roughing rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire drawing. In the wire rod cooling process, after the wire rod is spun, it is cooled on an air-cooled roller conveyor to obtain the 1100MPa grade cableway wire rod. In the wire rod cooling process, after the wire rod is spun, it is cooled on the air-cooled roller conveyor. The phase change temperature of the wire rod is controlled at 600℃~650℃. When the phase change time of the wire rod on the air-cooled line is 5s~8s, the pearlite content of the wire rod is ≥40%; when the phase change time is 15s~18s, the pearlite content is 85%~95%.

2. The preparation method according to claim 1, characterized in that, The tensile strength of the wire rod is 1050MPa to 1150MPa.

3. The preparation method according to claim 1, characterized in that, The oxygen content at the interface between the base and the iron oxide scale of the wire rod is 3.0% to 6.5%, and the iron content is 76.5% to 80.5%.

4. The preparation method according to claim 1, characterized in that, In the LF refining process, the size of inclusions in the molten steel at the LF inlet is ≤60μm, the size of inclusions in the molten steel at the LF outlet is ≤50μm, and the size of inclusions in the molten steel at the tundish is ≤40μm.

5. The preparation method according to claim 1, characterized in that, In the continuous casting billet heating and rolling process, the total furnace heating time for the continuous casting billet is 3.8h to 4.7h; the soaking temperature is 1170℃ to 1220℃, and the holding time is 30min to 50min.

6. The preparation method according to claim 1, characterized in that, In the aforementioned wire rod rolling process, the total furnace time for the billet is 150-170 minutes, the soaking temperature is 1100-1150℃, and the holding time in the soaking section is 30-50 minutes. The billet heating process takes place in the austenitic high-temperature region, with a carbon content of 1.25%-1.5% at the austenitic-cementite interface. After heating, the billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling before wire rod production. The wire rod exiting the pre-finishing rolling mill is 980-1000℃; entering the finishing rolling mill is 890-930℃; entering the double-module rolling mill is 910-940℃; and the wire rod production temperature is 900-930℃.

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