A high-carbon steel wire rod with low microstructure anisotropy and its manufacturing process

Abstract

This invention discloses a high-carbon steel wire rod with low microstructure anisotropy and its production process. The chemical composition of the wire rod is as follows: [C] 0.60%–0.64%, [Si] 0.20%–0.30%, [Mn] 0.40%–0.50%, [Cr] 0.05%–0.13%, [P] ≤0.015%, [S] ≤0.010%, total oxygen 0.0010%–0.0030%, [Als] 0.0004%–0.0020%, [Nb] 0.0002%–0.0008%, [Mg] 0.0002%–0.0010%. The production process includes steel smelting and continuous casting, continuous casting billet heating and rolling, continuous rolling billet heating, wire rod rolling, and wire rod cooling. By controlling trace elements such as silicon, manganese, chromium, and magnesium, and by controlling the temperature compensation strain factor during the rolling process, the sorbitization rate of high carbon steel wire rod is ≥80%, the troostite structure is ≤5%, and the Widmanstätten structure is controlled below grade 0.5, thus meeting the user's quality requirements for the microstructure of high carbon steel wire rod.

Description

Technical Field

[0001] This invention relates to a high-carbon steel wire rod with low microstructure anisotropy and its manufacturing process, belonging to the field of wire rod technology. Background Technology

[0002] High-carbon steel wire rod has a wide range of applications in the metal products industry. This type of wire rod undergoes extensive processing during user operations, therefore users have strict requirements for its machinability. The microstructure of the wire rod is a crucial factor affecting its machinability.

[0003] Patent application number CN201910638740.0 discloses an ultra-fine, ultra-high-strength steel wire, a wire rod for ultra-fine, ultra-high-strength steel wire, and a method for producing the same. The chemical composition of the wire rod for ultra-fine, ultra-high-strength steel wire, by mass percentage, includes: C 0.90–0.96%, Si 0.12–0.30%, Mn 0.30–0.65%, Cr 0.10–0.30%, Al ≤ 0.004%, Ti ≤ 0.001%, Cu ≤ 0.01%, Ni ≤ 0.01%, S ≤ 0.01%, P ≤ 0.01%, O ≤ 0.0006%, N ≤ 0.0006%, with the remainder being Fe and unavoidable impurity elements. The inclusion size is ≤ 4 μm, and the average density of brittle inclusions is ≤ 2 inclusions / mm². 2 The aforementioned ultra-fine, ultra-high strength steel wire rod can be used as a base material for producing ultra-fine, ultra-high strength steel wire with a diameter of 50–60 μm and a tensile strength ≥4500 MPa. Furthermore, during the drawing process to produce ultra-fine, ultra-high strength steel wire, the continuous wire length can reach ≥300 km. The production method includes vacuum induction melting, remelting, forging, and rolling.

[0004] This patent focuses on ultra-fine, ultra-high-strength steel wire, wire rod for ultra-fine, ultra-high-strength steel wire, and their production methods, but fails to recognize the impact of Widmanstätten structure on the processing performance of high-carbon steel wire rod. The Widmanstätten structure of high-carbon steel wire rod exhibits anisotropy during deformation, easily leading to stress concentration in localized areas. This can cause micro-cracks to form during drawing or torsion, ultimately resulting in wire breakage. To meet users' requirements for the processing performance of high-carbon steel wire rod, there is an urgent need to develop technologies to control the Widmanstätten structure of high-carbon steel wire rod and improve its deformation performance. Summary of the Invention

[0005] The purpose of this invention is to provide a high-carbon steel wire rod with low microstructure anisotropy and its production process. Through the design of chemical composition and production process, the Widmanstätten structure of the high-carbon steel wire rod is controlled to be below grade 0.5, thus meeting the user's quality requirements for the microstructure of the high-carbon steel wire rod.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] This invention discloses a high-carbon steel wire rod with low microstructure anisotropy, the chemical composition of which is as follows by mass percentage: [C] 0.60%–0.64%, [Si] 0.20%–0.30%, [Mn] 0.40%–0.50%, [Cr] 0.05%–0.13%, [P] ≤0.015%, [S] ≤0.010%, total oxygen 0.0010%–0.0030%, [Als] 0.0004%–0.0020%, [Nb] 0.0002%–0.0008%, [Mg] 0.0002%–0.0010%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the Widmanstätten structure of the wire rod is below level 0.5.

[0009] Furthermore, the wire rod is predominantly composed of sorbite, with a sorbitization rate of ≥80% and a troostite content of ≤5%.

[0010] Furthermore, the wire rod is rolled to a specification of 8–11 mm.

[0011] A production process for high-carbon steel wire rod with low microstructure anisotropy includes steel smelting and continuous casting, continuous casting billet heating and rolling, continuous rolling billet heating, wire rod rolling, and wire rod cooling.

[0012] Heating and rolling of continuous casting billets: The total time for heating the continuous casting billets in the furnace is 3.5 to 4.6 hours, the temperature of the soaking zone is controlled at 1210 to 1260℃, and the holding time in the soaking zone is 30 to 55 minutes; after heating, the continuous casting billets are continuously rolled, and the final rolling temperature is controlled at 940 to 1000℃.

[0013] Heating of continuously rolled billets: The total time of continuously rolled billets in the furnace is 140 to 160 minutes, and the temperature of the soaking zone is 1120 to 1150℃; the holding time in the soaking zone is 30 to 50 minutes.

[0014] Wire rod rolling: After continuous rolling billet heating, it undergoes roughing, intermediate rolling, pre-finishing, finishing rolling, and double-module rolling before wire rod production. The wire rod exiting the pre-finishing mill is at 950–1000℃, and the temperature compensation strain factor at the last stand of the pre-finishing mill is (1.1–2.6)*10. 13 s -1 The entry temperature into the finishing mill is 880℃~960℃, and the temperature compensation strain factor at the last stand of the finishing mill is (1.6~3.2)*10. 14 s -1 The temperature at the dual-module entry point is 890℃~940℃, and the temperature compensation strain factor at the last stand of the dual-module rolling mill is (4.5~9.9)*10. 14 s -1 The wire rod spinning temperature should be controlled between 890℃ and 920℃.

[0015] Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The cooling rate before the pearlite phase change is controlled at 10-15℃ / s, the cooling rate during the pearlite phase change is 0.5-1.0℃ / s, the phase change temperature is controlled at 610-650℃, and the cooling rate after the pearlite phase change is controlled at 2-6℃ / s.

[0016] Furthermore, the grain size of the continuously rolled steel billet is controlled at 45–80 μm.

[0017] Furthermore, the molten steel is smelted using a combination of molten iron and scrap steel, and then refined using an LF furnace. The LF furnace refining time for the molten steel is controlled at 30–50 min, and the refining temperature is controlled at 1450–1550 °C. Argon gas is used for stirring during the molten steel refining process, and the argon gas flow rate is controlled at 200–500 NL / min.

[0018] Furthermore, the cross-sectional dimensions of the continuously cast billet are (250~300)mm*(350~400)mm.

[0019] Furthermore, the proportion of scrap steel in the molten iron + scrap steel smelting process is 5% to 10%.

[0020] Compared with existing technologies, this invention controls the amount of trace elements such as silicon, manganese, chromium and magnesium, and controls the temperature compensation strain factor during the rolling process to achieve a sorbitization rate of ≥80% and a troostite structure of ≤5% for high-carbon steel wire rods, and Widmanstätten structure below grade 0.5, thus meeting the user's quality requirements for the microstructure of high-carbon steel wire rods. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0022] The chemical composition design principles of the wire rod described in this invention are as follows (by mass percentage):

[0023] The chemical composition of the wire rod applicable to this invention is as follows: [C] 0.60%–0.64%, [Si] 0.20%–0.30%, [Mn] 0.40%–0.50%, [Cr] 0.05%–0.13%, [P] ≤0.015%, [S] ≤0.010%, total oxygen 0.0010%–0.0030%, [Als] 0.0004%–0.0020%, [Nb] 0.0002%–0.0008%, [Mg] 0.0002%–0.0010%, with the balance being Fe and unavoidable impurities.

[0024] The finished wire rod is mainly composed of sorbite, with a sorbitization rate of ≥80% and a troostite content of ≤5%.

[0025] The rationale for setting the range of chemical composition of the wire rod in this invention is as follows.

[0026] Carbon: If the carbon content in the wire rod is too low, it will not meet the strength requirements of the user when drawing steel wire. If the carbon content is too high, the tensile strength of the wire rod will be too high, which will increase the wire breakage rate in the production process of high carbon steel wire. Therefore, the carbon content in this invention is controlled at 0.60% to 0.64%.

[0027] Silicon: Silicon is the main deoxidizing element in steel. Low silicon content will result in insufficient deoxidation of molten steel; excessive silicon content in steel will increase the precipitation temperature of proeutectoid ferrite and reduce the Widmanstätten structure. Therefore, the silicon content in this invention is controlled at 0.20% to 0.30%.

[0028] Manganese: Manganese is an element that improves the strength of wire rods. An appropriate amount of manganese in steel ensures that the wire rods produced meet the user's strength requirements. Manganese also lowers the precipitation temperature of proeutectoid ferrite, making it easier to increase the Widmanstätten structure. Therefore, the manganese content in this invention is controlled at 0.40% to 0.50%.

[0029] Chromium: Chromium in wire rod improves hardenability, refines the microstructure, and reduces the Widmanstätten grade. However, excessive chromium content leads to significant work hardening during processing, deteriorating machinability and increasing the likelihood of wire drawing or torsional fracture. Therefore, the chromium content in this invention is controlled at 0.05%–0.13%.

[0030] Phosphorus: Phosphorus tends to form banded segregation in wire rod, which reduces the cold working performance of the wire rod and causes cracking and breakage of the steel wire. Therefore, the phosphorus content in this invention is controlled at ≤0.015%.

[0031] Sulfur: High sulfur content in steel reduces the cold working performance of wire rod, therefore the sulfur content in this invention is controlled at ≤0.010%.

[0032] Oxygen: When the oxygen content in the wire rod is high, the inclusions in the steel are large, which easily leads to fracture during the deep processing of the wire rod. When the oxygen content in the wire rod is low, the inclusion components in the wire rod are located in the high melting point region, and the inclusions have poor deformation ability, which is not conducive to improving its deep processing capability; therefore, in this invention, the total oxygen content of the wire rod is controlled at 0.0010% to 0.0030%.

[0033] Acid-soluble aluminum: When the acid-soluble aluminum content is high, the Al2O3 content in the wire rod is high, the melting point of the inclusions is high, and the deformation ability of the inclusions is poor; when the acid-soluble aluminum content in the wire rod is too low, the melting point of the inclusions in the steel also increases, and the deep processing capability of the wire rod decreases. Therefore, the acid-soluble aluminum content in this invention is controlled at 0.0004% to 0.0020%.

[0034] Niobium: Niobium can inhibit grain growth in steel billets during heating, thereby refining the pearlite structure of the wire rod and increasing the precipitation temperature of the proeutectoid phase, thus suppressing the formation of Widmanstätten structure. However, a higher niobium content leads to a higher niobium carbonitride content in the steel, resulting in severe work hardening during wire processing and making the wire prone to cracking and breakage. Therefore, the niobium content in this invention is controlled at 0.0002% to 0.0008%.

[0035] Magnesium: Magnesium controls the type of inclusions in steel. Higher magnesium content leads to the formation of magnesium-aluminum spinel inclusions, reducing the machinability of the wire rod. Appropriate magnesium content improves the deformation properties of inclusions, which is beneficial for enhancing the wire rod's ability to undergo coordinated deformation. Therefore, the magnesium content in this invention is controlled at 0.0002% to 0.0010%.

[0036] The manufacturing process of the wire rod of this invention includes the following steps:

[0037] Steelmaking and continuous casting: Steel is smelted using a combination of molten iron and scrap steel, with the scrap steel proportion being 5%–10%. After smelting, the steel is refined using an LF furnace. The LF furnace refining time is controlled at 30–50 minutes, and the refining temperature is controlled at 1450℃–1550℃. Argon gas is used for stirring during the steel refining process, with the argon gas flow rate controlled at 200–500 NL / min. The cross-sectional dimensions of the continuously cast billet are (250–300) mm * (350–400) mm.

[0038] Heating and rolling of continuously cast billets: The total furnace time for heating the continuously cast billets is 3.5–4.6 hours. The temperature in the soaking zone is controlled at 1210–1260℃, and the holding time in the soaking zone is 30–55 minutes. After heating, the continuously cast billets are continuously rolled, and the final rolling temperature is controlled at 940–1000℃. The grain size of the continuously rolled billets is controlled at 45–80 μm.

[0039] Heating of continuously rolled billets: The total time of continuously rolled billets in the furnace is 140 to 160 minutes, and the temperature of the soaking zone is 1120 to 1150℃; through high-temperature diffusion of the billet, the segregation of elements such as carbon and manganese is reduced, and the grain size of the billet is controlled; the holding time of the soaking zone of the billet is 30 to 50 minutes.

[0040] Wire rod rolling: After continuous rolling, the billet is heated and then passes through roughing, intermediate rolling, pre-finishing, finishing rolling, and a double-module stage before the wire rod is produced. The wire rod exiting the pre-finishing rolling stage is at a temperature of 950–1000℃, and the temperature compensation strain factor for the last stand in the pre-finishing rolling stage is (1.1–2.6)*10. 13 s -1 The entry temperature into the finishing mill is 880–960℃, and the temperature compensation strain factor for the last stand of the finishing mill is (1.6–3.2)*10. 14 s -1 The temperature of the double-module mill is 890–940℃, and the temperature compensation strain factor of the last stand of the double-module mill is (4.5–9.9)*10. 14 s -1 The wire rod spinning temperature is controlled between 890 and 920℃. A higher spinning 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 rolling specification is 8–11 mm.

[0041] Wire rod cooling: After wire drawing, the wire rod is cooled on an air-cooled roller conveyor. The cooling rate before the pearlitic phase transformation is controlled at 10-15℃ / s, the cooling rate during the pearlitic phase transformation is 0.5-1.0℃ / s, the phase transformation temperature is controlled at 610-650℃, and the cooling rate after the pearlitic phase transformation is controlled at 2-6℃ / s. After final cooling, the wire rod cord steel has a predominantly sorbitic structure with a sorbitization rate of 70%-85%, which is beneficial for wire drawing by users.

[0042] Examples of the present invention are described below.

[0043]

[0044]

[0045] 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 high-carbon steel wire rod with low structural anisotropy, characterized in that, The chemical composition of the wire rod, by mass percentage, is as follows: [C] 0.60%~0.64%, [Si] 0.20%~0.30%, [Mn] 0.40%~0.50%, [Cr] 0.05%~0.13%, [P]≤0.015%, [S]≤0.010%, total oxygen 0.0010%~0.0030%, [Als] 0.0004%~0.0020%, [Nb] 0.0002%~0.0008%, [Mg] 0.0002%~0.0010%, with the balance being Fe and unavoidable impurities. The production process includes steel smelting and continuous casting, continuous casting billet heating and rolling, continuous rolling billet heating, wire rod rolling, and wire rod cooling. Heating and rolling of continuous casting billets: The total time for heating the continuous casting billets in the furnace is 3.5 to 4.6 hours, the temperature of the soaking zone is controlled at 1210 to 1260℃, and the holding time in the soaking zone is 30 to 55 minutes; after heating, the continuous casting billets are continuously rolled, and the final rolling temperature is controlled at 940 to 1000℃. Heating of continuously rolled billets: The total time of continuously rolled billets in the furnace is 140 to 160 minutes, and the temperature of the soaking zone is 1120 to 1150℃; the holding time in the soaking zone is 30 to 50 minutes. Wire rod rolling: After continuous rolling billet heating, it undergoes roughing, intermediate rolling, pre-finishing, finishing rolling, and double-module rolling before wire rod production. The wire rod exiting the pre-finishing mill is at a temperature of 950–1000℃, and the temperature compensation strain factor at the last stand of the pre-finishing mill is (1.1–2.6)*10. 13 s -1 The entry temperature into the finishing mill is 880℃~960℃, and the temperature compensation strain factor at the last stand of the finishing mill is (1.6~3.2)*10. 14 s -1 The temperature at the dual-module entry point is 890℃~940℃, and the temperature compensation strain factor at the last stand of the dual-module rolling mill is (4.5~9.9)*10. 14 s -1 The wire rod spinning temperature should be controlled between 890℃ and 920℃. Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The cooling rate before the pearlite phase change is controlled at 10-15℃ / s, the cooling rate during the pearlite phase change is 0.5-1.0℃ / s, the phase change temperature is controlled at 610-650℃, and the cooling rate after the pearlite phase change is controlled at 2-6℃ / s.

2. The high-carbon steel wire rod with low microstructure anisotropy according to claim 1, characterized in that, The Widmanstätten structure of the wire rod is below grade 0.

5.

3. A high-carbon steel wire rod with low microstructure anisotropy according to claim 1, characterized in that, The wire rod is mainly composed of sorbite, with a sorbitization rate of ≥80% and a troostite content of ≤5%.

4. A high-carbon steel wire rod with low microstructure anisotropy according to claim 1, characterized in that, The wire rod is rolled to a diameter of 8-11 mm.

5. A high-carbon steel wire rod with low microstructure anisotropy according to claim 1, characterized in that, The grain size of the continuously rolled billet is controlled at 45–80 μm.

6. A high-carbon steel wire rod with low microstructure anisotropy according to claim 1, characterized in that, The molten steel is smelted using molten iron and scrap steel, and then refined using an LF furnace. The LF furnace refining time for the molten steel is controlled at 30-50 minutes, and the refining temperature is controlled at 1450-1550℃. Argon gas is used for stirring during the molten steel refining process, and the argon gas flow rate is controlled at 200-500 NL / min.

7. A high-carbon steel wire rod with low microstructure anisotropy according to claim 1, characterized in that, The cross-sectional dimensions of the continuously cast billet are (250~300) mm * (350~400) mm.

8. A high-carbon steel wire rod with low microstructure anisotropy according to claim 6, characterized in that, The proportion of scrap steel in the smelting of molten iron and scrap steel is 5% to 10%.

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