Large-specification high-carbon steel wire rod and preparation method thereof

Abstract

The invention discloses a large-sized high-carbon steel wire rod and a preparation method thereof. The large-sized high-carbon steel wire rod comprises the following components in percentage by mass: 0.80%-0.84% of C, 0.10%-0.20% of Si, 0.55%-0.60% of Mn, less than or equal to 0.015% of P, 0.0030%-0.010% of S, 0.0010%-0.0020% of total oxygen, 0.0003%-0.0012% of Als, 0.0001%-0.0010% of Nb, 0.0004%-0.0010% of Co, 0.0002%-0.0010% of Mg, 0.0005%-0.0016% of (Nb + Mg) and the balance of iron and inevitable impurities. By optimizing the component proportion and adjusting the process parameters, the drawing performance requirements of users on large-specification high-carbon steel wire rods for steel wire ropes and the like are met.

Description

Technical Field

[0001] The invention relates to the technical field of materials and metallurgy, and more specifically, to a large-size high-carbon steel wire rod and a preparation method thereof. Background Art

[0002] Large-size high-carbon steel wire rods are widely used in the fields of steel wire ropes, etc. Among them, the organizational state of the wire rod is a key indicator affecting the drawing performance and stranding performance of large-size high-carbon steel wire rods.

[0003] A Chinese patent with application number 202311786832.6 discloses a high-carbon steel wire rod and a production method thereof, comprising: smelting high-carbon steel wire rod raw materials to obtain raw material smelting liquid; adding a preset weight portion of ferroniobium to the raw material smelting liquid to obtain a high-carbon steel wire rod smelting liquid; refining the high-carbon steel wire rod smelting liquid to obtain a high-carbon steel wire rod refined liquid; transferring the high-carbon steel wire rod refined liquid to a continuous casting machine, continuously casting the high-carbon steel wire rod refined liquid to obtain a square billet; sending the square billet into a heating furnace to heat the square billet; dephosphorizing the square billet using high-pressure water equipment; rolling and spinning the dephosphorized square billet to obtain a ring-shaped high-speed wire; transferring the ring-shaped high-speed wire to an air-cooled roller for controlled cooling to obtain a high-carbon steel wire rod. However, although this patent can achieve the purpose of reducing grain boundary cementite, it will greatly reduce production efficiency, lengthen production cycle, increase cost, and is not conducive to improving the market competitiveness of large-size high-carbon steel wire rods.

[0004] Therefore, there is an urgent need to develop a low-cost method for controlling the network cementite of large-size high-carbon steel wire rods to meet users' requirements for the drawing performance of wire rods. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and to provide a large-sized high-carbon steel wire rod and a preparation method thereof. By designing the chemical composition, optimizing the component ratio, and adjusting the process parameters, the large-sized high-carbon steel wire rod produced has only linear cementite precipitation, which meets the user's requirements for the drawing performance of large-sized high-carbon steel wire rods for purposes such as wire ropes.

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

[0007] A large-size high-carbon steel wire rod comprises the following components in mass percentage: C: 0.80%-0.84%, Si: 0.10%-0.20%, Mn: 0.55%-0.60%, P≤0.015%, S: 0.0030%-0.010%, total oxygen: 0.0010%-0.0020%, Als: 0.0003%-0.0012%, Nb: 0.0001%-0.0010%, Co: 0.0004%-0.0010%, Mg: 0.0002%-0.0010%, and (Nb+Mg): 0.0005%-0.0016%, and the balance is iron and unavoidable impurities.

[0008] The present invention also discloses a method for preparing the large-size high-carbon steel 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] During the wire rod rolling, the total furnace time of the continuous rolling billet is 150min-160min, the soaking section temperature is 1120°C-1150°C, and the soaking section insulation time of the continuous rolling billet is 40min-55min; the steel billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire laying in sequence.

[0010] Implementing the embodiments of the present invention will have the following beneficial effects:

[0011] The present invention designs an optimal component system and matches the alloy composition with smelting, continuous casting billet heating and rolling, rolling, cooling and other production processes, so that the wire rod has no completely closed or semi-closed cementite precipitation, only linear cementite precipitation, and the tensile strength is 1040MPa-1140MPa, and the cross-sectional shrinkage is 25%-35%. The metallographic structure of the wire rod includes 80%-95% of the troostite structure, the content of the troostite structure is ≤10%, and the level of the Widmanstatten structure is ≤1. It meets the drawing and plying requirements of users for products such as steel wire ropes. At the same time, the preparation method of the present invention has the characteristics of low production cost and strong process applicability, which is conducive to its production and promotion and application, and has significant social benefits. DETAILED DESCRIPTION

[0012] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0013] 1. Chemical composition and mechanical properties

[0014] The invention discloses an ultra-high strength high carbon steel wire rod, comprising the following components in mass percentage: C: 0.80%-0.84%, Si: 0.10%-0.20%, Mn: 0.55%-0.60%, P≤0.015%, S: 0.0030%-0.010%, total oxygen: 0.0010%-0.0020%, Als: 0.0003%-0.0012%, Nb: 0.0001%-0.0010%, Co: 0.0004%-0.0010%, Mg: 0.0002%-0.0010%, (Nb+Mg): 0.0005%-0.0016%, and the balance is iron and inevitable impurities.

[0015] Specifically, the mechanism of action of each alloy component in the wire rod of the present invention is as follows:

[0016] Carbon: Carbon is the main element that controls the strength of the wire rod. If the carbon content of the wire rod is too low, it cannot meet the strength requirements of the user for the steel wire. If the content is too high, the strength of the steel wire will exceed the user's requirements; at the same time, a higher carbon content will increase the wire breakage rate during the drawing process of the wire rod, and the user's scrap rate will increase. Therefore, the carbon content in the present invention is controlled at 0.80% to 0.84%.

[0017] Silicon: Silicon is the main deoxidizing element in high carbon steel. Low silicon content will result in insufficient deoxidation of the molten steel; excessive silicon content in the steel will cause coarse silicate inclusions to appear in the steel, which is easy to cause cracks between the inclusions and the matrix during the wire rod processing process, resulting in cracking or breaking of the wire. Silicon increases the eutectoid transformation temperature of steel, causes pearlite to transform in the high temperature zone, and makes the pearlite structure of the wire rod coarse, which is not conducive to the complex deformation of the steel wire. Therefore, the silicon content in the present invention is controlled at 0.10% to 0.20%.

[0018] Manganese: Manganese is an element that improves the strength of the wire, so that the steel wire meets the user's tensile strength requirements; manganese has the effect of reducing the eutectoid transformation temperature of steel, refining the pearlite structure of the wire rod, and improving the coordinated deformation ability of the wire rod at different parts during the steel wire processing process. Therefore, the manganese content in the present invention is controlled at 0.55% to 0.60%.

[0019] Phosphorus: Phosphorus is easy to form band segregation in the wire rod, which reduces the coordinated deformation ability of different parts of the wire rod during the steel wire processing and causes cracking and breaking of the steel wire. Therefore, the phosphorus content in the present invention is controlled to be ≤0.015%.

[0020] Sulfur: A higher sulfur content in steel reduces the cold working performance of the wire rod and is prone to cause delamination and cracking of the wire rod during the wire processing process. Since MnS inclusions have good deformation ability, an appropriate amount of sulfur in the steel can reduce the harm of non-deformable inclusions in the steel and prevent the generation of micro cracks caused by inclusions. Therefore, the sulfur content in the present invention is controlled at 0.0030% to 0.010%.

[0021] Oxygen: When the oxygen content is low, the inclusions in the wire rod have a high melting point and poor deformation ability, and cracks are likely to appear between the inclusions and the matrix, which is not conducive to the processing of the steel wire; when the oxygen content is high, the inclusions in the steel are large in size, which is easy to cause micro cracks in the process of wire rod processing and cause the steel wire to crack. Therefore, the total oxygen content of the wire rod in the present invention is controlled at 0.0010% to 0.0020%.

[0022] Acid-soluble aluminum: 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 the deformation ability of the inclusions decreases, which is not conducive to the processing of the steel wire. When the acid-soluble aluminum content is high, the Al2O3 content of the inclusions in the steel increases, which is easy to cause cracking during the processing of the steel wire. Therefore, the acid-soluble aluminum content of the present invention is controlled at 0.0003% to 0.0012%.

[0023] Niobium: Niobium element uses undissolved compounds to hinder the coarsening of steel billet grains during the heating process of the steel billet, ensuring that the wire rod structure meets the requirements of steel wire processing. However, a higher niobium content causes severe work hardening of the wire rod during the steel wire processing process, and the coordinated deformation ability of different parts of the wire rod decreases, which easily leads to cracking and breaking of the steel wire. Therefore, the niobium content of the present invention is controlled at 0.0001% to 0.0010%.

[0024] Cobalt: Cobalt is dissolved in steel to improve its strength. However, the cobalt content in steel should not be too high to prevent the higher wire rod strength from reducing the drawing and deformation properties of the wire rod. Cobalt increases the precipitation temperature of proeutectoid ferrite, increases the transformation temperature of austenite to pearlite, inhibits the appearance of Widmanstätten structure in the wire rod, reduces the content of troostite in the wire rod, and improves the uniform deformation performance of the wire rod. Therefore, the cobalt content in the present invention is controlled at 0.0004% to 0.0010%.

[0025] Magnesium: Magnesium controls the oxygen content in steel and also controls the type of inclusions in steel. A higher magnesium content causes magnesium-aluminum spinel inclusions to appear in the steel, reducing the processing performance of the wire rod. An appropriate amount of magnesium content in steel improves the deformation performance of inclusions, expands the area with higher inclusion deformation, and is conducive to improving the coordinated deformation ability of the wire rod. Therefore, the magnesium content of the present invention is controlled at 0.0002% to 0.0010%.

[0026] In order to prevent the niobium and magnesium elements from not fully exerting their effects and to prevent excessive niobium and magnesium content from reducing the coordinated deformation capacity of the wire rod, the present invention controls the (Nb+Mg) content to within the range of 0.0005% to 0.0016%.

[0027] In a specific embodiment, the tensile strength of the wire rod is 1040 MPa to 1140 MPa, and the cross-sectional shrinkage is 25% to 35%.

[0028] In a specific embodiment, the metallographic structure of the wire rod includes 80% to 95% of troostite structure, the content of troostite structure is not more than 10%, and the level of Widmanstatten structure is not more than 1, measured by volume fraction.

[0029] 2. Production technology

[0030] The present invention also discloses a method for preparing a large-size high-carbon steel 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.

[0031] Further, the method specifically includes the following steps:

[0032] S1. In converter smelting, scrap steel and molten iron are used as furnace charge, and the mass percentage of scrap steel in the furnace charge is 5% to 15%; the oxygen activity of liquid steel after smelting is controlled at 100ppm to 200ppm.

[0033] In S2 and LF refining, the molten steel discharged from the converter enters the LF furnace for refining. The refining temperature of the LF furnace is 1450°C to 1560°C, and the refining time is 30min to 50min. Argon stirring is performed during refining, and the argon flow rate is 200NL / min to 500NL / min.

[0034] S3. During continuous casting, the molten steel treated by LF refining is continuously cast, and the cross-sectional size of the continuous casting billet is (250mm-300mm)×(350mm-400mm); the surface temperature of the edge of the continuous casting billet during the straightening process is 890℃-930℃, and the temperature of the corner of the continuous casting billet is 780℃-830℃. The continuous casting speed is 0.6m / min-0.8m / min, and the depth of the surface crack of the continuous casting billet is ≤1mm.

[0035] S4. During the heating and continuous rolling of the continuous casting billet, the total heating time of the continuous casting billet in the furnace is 3.5h~4.2h; the temperature of the soaking section is 1200℃~1260℃; the insulation time of the billet in the soaking section is 40min~50min; the continuous casting billet is continuously rolled after heating, and the final rolling temperature is 880℃~980℃; the austenite grain size of the continuously rolled billet is 35μm~80μm; the thickness of the decarburization layer on the surface of the continuously rolled billet is 500μm~1000μm, and the depth of the crack on the surface of the continuously rolled billet is ≤0.8mm.

[0036] S6. During wire rod rolling, the total furnace time of the continuous rolled billet is 150min-160min, the temperature of the soaking section is 1120℃-1150℃, and the insulation time of the soaking section of the continuous rolled billet is 40min-55min. The billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling and wire laying in sequence.

[0037] In a specific embodiment, the pre-finishing rolling temperature of the wire rod is 985℃~1005℃; the finishing rolling temperature is 890℃~930℃; the double module temperature is 880℃~940℃; and the wire rod spinning temperature is 900℃~940℃. The higher spinning temperature of the wire rod increases the cooling speed of the wire rod on the air-cooled roller, laying the foundation for controlling the final structure of the wire rod. The wire rod rolling specification is 8mm~10mm.

[0038] S6. During the cooling of the wire rod, the wire rod is cooled on an air-cooled roller after spinning, and the cementite precipitation start temperature of the wire rod is controlled to be 730℃~760℃, and the cooling rate of the wire rod is 5℃ / s~10℃ / s; the undercooling degree of the wire rod austenite to pearlite phase transformation is controlled to be 80℃~120℃, and the phase transformation time is 12s~18s; the wire rod coiling temperature is 350℃~500℃.

[0039] The following are specific embodiments

[0040] Examples 1-6

[0041] The chemical composition, preparation process and performance parameters of the wire rods of Examples 1-6 of the present invention are shown in Table 1.

[0042] Table 1 Chemical composition, preparation process and performance parameters of wire rods of Examples 1-6

[0043]

[0044]

[0045] According to the above results, the present invention designs the best component system, and matches the smelting, continuous casting billet heating and rolling, rolling, cooling and other production processes with the alloy composition, so that the wire rod has no completely closed or semi-closed cementite precipitation, only linear cementite precipitation, and the tensile strength is 1040MPa~1140MPa, and the cross-sectional shrinkage rate is 25%~35%. The metallographic structure of the wire rod includes 80%~95% of the troostite structure, the content of the troostite structure is ≤10%, and the level of the Widmanstatten structure is ≤1 level. It meets the drawing and plying requirements of users for products such as wire ropes. At the same time, the preparation method of the present invention has the characteristics of low production cost and strong process applicability, which is conducive to its production and promotion and application, and has significant social benefits.

[0046] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A large-size high-carbon steel wire rod, characterized in that: The following components are included in mass percentage: C: 0.80% ~ 0.84%, Si: 0.10% ~ 0.20%, Mn: 0.55% ~ 0.60%, P ≤ 0.015%, S: 0.0030% ~ 0.010%, total oxygen: 0.0010% ~ 0.0020%, Als: 0.0003% ~ 0.0012%, Nb: 0.0001% ~ 0.0010%, Co: 0.0004% ~ 0.0010%, Mg: 0.0002% ~ 0.0010%, and (Nb + Mg): 0.0005% ~ 0.0016%, and the balance is iron and unavoidable impurities.

2. The large-size high-carbon steel wire rod according to claim 1, characterized in that: The tensile strength of the wire rod is 1040MPa-1140MPa, and the cross-sectional shrinkage is 25%-35%.

3. The large-size high-carbon steel wire rod according to claim 1, characterized in that: Calculated by volume fraction, the metallographic structure of the wire rod includes 80% to 95% of troostite structure, the content of troostite structure is ≤10%, and the level of Widmanstatten structure is ≤1.

4. A method for preparing a large-size high-carbon steel wire rod as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Converter smelting, LF refining, continuous casting, continuous casting billet heating and rolling, wire rod rolling and wire rod cooling; During the wire rod rolling, the total furnace time of the continuous rolling billet is 150min-160min, the soaking section temperature is 1120°C-1150°C, and the soaking section insulation time of the continuous rolling billet is 40min-55min; the steel billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire laying in sequence.

5. The preparation method according to claim 4, characterized in that: In the converter smelting, scrap steel and molten iron are used as furnace charge, and the mass percentage of scrap steel in the furnace charge is 5% to 15%; the oxygen activity of the liquid steel after smelting is controlled at 100ppm to 200ppm.

6. The preparation method according to claim 4, characterized in that: In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment. The refining temperature of the LF furnace is 1450°C to 1560°C, and the refining time is 30min to 50min. Argon stirring is performed during the refining, and the argon flow rate is 200NL / min to 500NL / min.

7. The preparation method according to claim 4, characterized in that: During the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast, and the cross-sectional size of the continuous casting billet is (250mm-300mm)×(350mm-400mm); the surface temperature of the edge of the continuous casting billet during the straightening process is 890°C-930°C, and the temperature of the corner of the continuous casting billet is 780°C-830°C; the continuous casting pulling speed is 0.6m / min-0.8m / min, and the depth of the surface crack of the continuous casting billet is ≤1mm.

8. The preparation method according to claim 4, characterized in that: During the continuous casting billet heating and continuous rolling, the total furnace heating time of the continuous casting billet is 3.5h-4.2h; the soaking section temperature is 1200°C-1260°C; the billet soaking section insulation time is 40min-50min; the continuous casting billet is continuously rolled after heating, and the final rolling temperature is 880°C-980°C; the austenite grain size of the continuously rolled billet is 35μm-80μm; the decarburization layer thickness of the continuously rolled billet surface is 500μm-1000μm, and the crack depth of the continuously rolled billet surface is ≤0.8mm.

9. The preparation method according to claim 4, characterized in that: During the wire rod rolling, the wire rod exiting pre-finishing rolling temperature is 985°C to 1005°C; the wire rod entering finishing rolling temperature is 890°C to 930°C; the wire rod entering double module temperature is 880°C to 940°C; and the wire rod spinning temperature is 900°C to 940°C.

10. The preparation method according to claim 4, characterized in that: During the wire rod cooling, the wire rod is cooled on an air-cooled roller after spinning, and the cementite precipitation start temperature of the wire rod is controlled to be 730°C to 760°C, and the wire rod cooling rate is 5°C / s to 10°C / s; the undercooling degree of the wire rod austenite to pearlite phase transformation is controlled to be 80°C to 120°C, and the phase transformation time is 12s to 18s; the wire rod coiling temperature is 350°C to 500°C.

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