High-strength wire rod for round link chain and preparation method therefor

Abstract

Disclosed in the present invention is a high-strength wire rod for a round link chain, comprising the following chemical components in percentage by mass: C: 0.20%-0.26%, Si: 0.10%-0.30%, Mn: 1.00%-1.30%, Cr: 0.40%-0.60%, Ni: 0.70%-0.90%, Cu≤0.10%, Mo: 0.20%-0.40%, Al: 0.025%-0.050%, O≤0.0020%, N≤0.0070%, H≤0.0001%, P≤0.015%, S≤0.010%, and B: 0.001%-0.005%. The advantages of the present invention are that, without adding additional devices and processes, the product purity is effectively improved, high hardenability, inherent fine grains, and good welding and carburizing properties are achieved, high strength and toughness are obtained after quenching and tempering, and the comprehensive performance is excellent.

Description

A high-strength circular link chain wire rod and its preparation method Technical Field

[0001] This invention belongs to the field of special steel production technology, and particularly relates to a high-strength circular link chain wire rod and its preparation method. Background Technology

[0002] Crane chains are connecting components used in lifting and running processes in hoisting machinery. They play a crucial role in improving crane operating efficiency and expanding the crane's working range. When selecting crane chains, different application scenarios and requirements can be considered. Currently, the quality of chain steel in China is still at a low to medium level, resulting in a low international market share. With the continuous development of lightweight materials, the development of high-strength chain steel has become the mainstream. Most manufacturers achieve high strength through high alloying, but this often results in poor weldability and higher production costs. While reducing alloy content can improve weldability, ensuring the chain's high strength becomes a new bottleneck. Summary of the Invention

[0003] The purpose of this invention is to solve the problem that existing wire rod steel for round link chains cannot simultaneously achieve high strength and weldability. It provides a high-strength wire rod for round link chains that does not require additional equipment or processes, effectively improves product purity, hardenability, fine grain structure, and good welding and carburizing properties. After quenching and tempering, it has high strength and toughness, and excellent overall performance.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A high-strength circular link chain wire rod has the following chemical composition and mass fraction: C: 0.20%–0.26%, Si: 0.10%–0.30%, Mn: 1.00%–1.30%, Cr: 0.40%–0.60%, Ni: 0.70%–0.90%, Cu≤0.10%, Mo: 0.20%–0.40%, Al: 0.025%–0.050%, O≤0.0020%, N≤0.0070%, H≤0.0001%, P≤0.015%, S≤0.010%, B: 0.001%–0.005%.

[0006] Furthermore, the chemical composition and mass fraction of the high-strength circular link chain wire rod include: C: 0.23%, Si: 0.25%, Mn: 1.05%, Cr: 0.50%, Ni: 0.75%, Cu: 0.02%, Mo: 0.25%, Al: 0.040%, P≤0.010%, S≤0.004%, B: 0.002%.

[0007] To further achieve the objectives of this invention, a method for preparing high-strength circular link chain wire rod is also provided, specifically comprising:

[0008] (1) When tapping steel in an electric arc furnace, the tapping conditions are C≥0.05%, P≤0.012%, and temperature is 1600~1650℃. The charging sequence during the tapping process includes deoxidizer → alloy → modified refining slag → lime. During the tapping process, 1.2~1.6kg / t of deoxidizer Al blocks, 5~8kg / t of lime, and 2~5kg / t of modified refining slag are added. By controlling the amount of C added during tapping and the amount of Al blocks added after the furnace, the initial oxygen content of the molten steel can be effectively reduced, preventing the molten steel from over-oxidizing and further reducing the space for inclusion formation.

[0009] (2) The initial Al content of the LF furnace is ≥0.020%, the final Al content is ≥0.025%, the amount of fluorite added is 0.5~0.6kg / t, the amount of diffusion deoxidizer added is 0.8~1.2kg / t, and the final S content is ≤0.010%. During the VD vacuum treatment, the ultimate vacuum time is ≥5min and the static stirring time is ≥15min. During the continuous casting of steel billets with a billet shape of 150*150mm, the superheat is 15~35℃, the casting speed is 2.00~2.20m / min, and the secondary cooling water adopts the weak cooling mode.

[0010] (3) When heating the billet, the preheating section furnace temperature is ≤850℃, the first heating section furnace temperature is 900~1050℃, the second heating section furnace temperature is 950~1100℃, the soaking section furnace temperature is 1000~1100℃, the residual oxygen is ≤4%, and the billet spacing and empty step distance are controlled according to the actual production layout. The total heating time is ≤300min, the initial rolling temperature is 900~1000℃, the final rolling temperature is 800~900℃, the wire drawing temperature is 800~900℃, and after the wire rod is drawn, it is rapidly cooled to 700℃ at a cooling rate of 3.0~6.0℃ / s and then kept warm and cooled until it is coiled off the line.

[0011] Furthermore, in step (1), the electric furnace tapping conditions are: the C content of the tapped steel is 0.10%, the P content is 0.008%, and the temperature is 1630℃.

[0012] Furthermore, in step (1), 1.4 kg / t of deoxidizer Al blocks, 6 kg / t of lime, and 3 kg / t of modified refining slag are added during the electric furnace tapping process.

[0013] Further, in step (2), the initial Al content of the LF furnace is 0.030%, the final Al content is ≥0.035%, the amount of fluorite added is 0.6 kg / t, the diffusion deoxidizer is 1.0 kg / t, and the final S content is 0.004%.

[0014] Furthermore, in step (2), the superheat of the continuous casting process is 25°C and the casting speed is 2.20 m / min.

[0015] Furthermore, in step (3), during the billet heating process, the preheating section furnace temperature is ≤850℃, the first heating section furnace temperature is 950℃, the second heating section furnace temperature is 1000℃, and the soaking section furnace temperature is 1050℃.

[0016] Furthermore, in step (3), the total heating time is 230 min, the initial rolling temperature is 970℃, the final rolling temperature is 850℃, the wire drawing temperature is 830℃, and the wire rod is rapidly cooled to 700℃ at a cooling rate of 5.0℃ / s after wire drawing.

[0017] The mechanism of action of the component design in this invention is as follows:

[0018] As the most important element in steel, carbon directly affects the strength, plasticity, toughness and weldability of steel. In order to balance the weldability and strength-toughness of chain steel, the carbon content is designed to be in the range of 0.20 to 0.26%.

[0019] Mn can improve the strength of steel. While improving the strength of steel, it has a relatively small impact on plasticity. If the manganese content is too high, it will reduce the plasticity and weldability of steel. Therefore, the Mn content should be controlled within the range of 1.00 to 1.30%.

[0020] Cr can increase the hardenability of steel and has a secondary hardening effect. It can improve hardness and wear resistance without making the steel brittle, so that the steel has good comprehensive mechanical properties after quenching and tempering. The Cr content should be controlled within the range of 0.40 to 0.60%.

[0021] Ni has high strength, high toughness, good hardenability, high electrical resistance, and high corrosion resistance. On the one hand, it greatly improves the strength of steel, and on the other hand, it always keeps the toughness of steel at an extremely high level. Its brittleness temperature is extremely low. Taking into account cost, the Ni content range is designed to be 0.70% to 0.90%.

[0022] Mo in steel can improve hardenability and hot strength, improve the tempering resistance or tempering stability of steel, so that the chain can more effectively eliminate or reduce residual stress after tempering and improve plasticity. Therefore, the Mo content should be controlled within the range of 0.20-0.40%.

[0023] Nitrogen (N) can improve the strength of steel, but as the N content increases, plasticity and toughness decrease, weldability deteriorates, and cold brittleness increases. The N content should be controlled to ≤0.0070%.

[0024] H is a harmful element in steel. It dissolves into molten steel at high temperatures and accumulates during cooling, forming micropores, cracks, and brittle fractures, which deteriorate the plasticity, toughness, and fatigue strength of steel. The H content should be controlled to ≤0.0001%.

[0025] The main role of boron in steel is to increase its hardenability and improve its strength properties. However, boron tends to promote temper brittleness. Therefore, boron cannot completely replace molybdenum. The boron content should be controlled at 0.001-0.005%.

[0026] Al is added to steel as a deoxidizer or alloying element. Its deoxidizing ability is stronger than that of silicon and manganese. The main role of Al in steel is to refine grains and fix nitrogen, thereby significantly improving the impact toughness of steel and reducing its tendency to brittleness and aging.

[0027] The working mechanism of the smelting process of this invention is as follows:

[0028] By controlling the carbon content at the tapping point of the electric arc furnace and the use of Al-based deoxidizers after the furnace, the initial oxygen content of the molten steel can be significantly reduced, preventing over-oxidation of the molten steel and further reducing the space for inclusion formation. In order to better remove inclusions, the LF furnace adopts a precipitation deoxidation + diffusion deoxidation process, controls the Al content at the end of the LF furnace, and ensures static stirring time after vacuum treatment in the VD furnace to promote the full flotation of inclusions, achieving a gas N content ≤0.0070% and a gas H content ≤0.0001%.

[0029] The rolling process mechanism of this invention is as follows:

[0030] High-grade chain steel, due to its higher chromium, molybdenum, nickel, and manganese content, exhibits high hardenability and good low-temperature toughness. Downstream users require spheroidizing annealing to reduce strength while increasing plasticity, thereby improving its cold working or drawing properties. Spheroidizing annealing involves prolonged high-temperature heating and holding, transforming layered or lamellar carbides into dispersed spherical shapes, resulting in better cold deformation performance of the wire rod. Different initial microstructures have varying effects on the spheroidizing annealing effect.

[0031] Compared with the prior art, the advantages of the technical solution of the present invention are as follows:

[0032] (1) In order to ensure that the wire rod obtains an independent bainite and martensite hot-rolled structure, the wire rod adopts a low-temperature rolling process. After the wire is rolled, it is first rapidly cooled and then slowly cooled. It passes through the ferrite and pearlite transformation zone to avoid the ferrite and pearlite transformation. After the wire rod temperature drops to the bainite transformation zone, a slow cooling process is used to ensure the bainite and martensite transformation.

[0033] (2) Through the rational design of chemical composition, the present invention enables the wire rod to have high purity, high hardenability, fine grains and good welding and carburizing properties. After quenching and tempering, it has high strength and toughness and excellent comprehensive performance.

[0034] (3) This invention achieves high toughness and high strength of the chain by reasonably controlling the carbon content and using high Ni, Cr, Mo and other alloys. No additional equipment or processes are required. The inclusions in the wire rod are rated A, B, C, D, and the coarse and fine series are all ≤1.5. The gas content of the wire rod is N≤70ppm and H≤1.0ppm. The cold bending performance of the wire rod is qualified. The tensile strength of the wire rod Rm≤1150MPa, the elongation A≥10%, and the reduction of area Z≥25%. After the wire rod is annealed, drawn, chained, quenched and tempered, the breaking tensile strength of the finished chain is ≥1000MPa and the elongation of the cross section is ≥20%, which meets the technical requirements of users for high-strength circular link chains. Attached Figure Description

[0035] Figure 1 is a rating table of coarse and fine series of impurities A, B, C, and D in the wire rod of the circular link chain in this invention;

[0036] Figure 2 shows the gas and tensile properties of the wire rod used for the circular link chain in this invention.

[0037] Figure 3 is an image of the hot-rolled microstructure of high-strength circular link chain wire rod in an embodiment of the present invention. Detailed Implementation

[0038] Example 1

[0039] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a high-strength circular link chain wire rod and its preparation method. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0040] The preparation process of a high-strength circular link chain wire rod includes: electric furnace → LF furnace → VD furnace → continuous casting → heating → rolling → cooling → coiling. By controlling the deoxidation system of the electric furnace, the refining process of the LF furnace, the matching of continuous casting process parameters, and the controlled rolling and cooling of the rolling process, as shown in Figures 1 and 2, the inclusion ratings of the wire rod (A, B, C, D, coarse and fine series) are all ≤1.5, the gas content of the wire rod is N≤70ppm and H≤1.0ppm, the cold bending performance of the wire rod is qualified, and the tensile strength Rm≤1150MPa, elongation A≥10%, and reduction of area Z≥25%.

[0041] In this embodiment, taking high-strength circular link chain wire rod as an example, its main element mass fractions are: C: 0.23%, Si: 0.25%, Mn: 1.05%, Cr: 0.50%, Ni: 0.75%, Cu: 0.02%, Mo: 0.25%, Al: 0.040%, P≤0.010%, S≤0.004%, B: 0.002%.

[0042] The electric arc furnace (EAF) tapping conditions are as follows: carbon (C) content is 0.10%, phosphorus (P) content is 0.008%, and the temperature is 1630℃. The charging sequence during tapping is: deoxidizer → alloy → modified refining slag → lime. During EAF tapping, 1.4 kg / t of deoxidizer (Al blocks), 6 kg / t of lime, and 3 kg / t of modified refining slag are added. By controlling the amount of carbon added during tapping and the amount of Al blocks added after the furnace, the initial oxygen content of the molten steel can be effectively reduced, preventing over-oxidation and further reducing the space for inclusion formation.

[0043] The initial Al content in the LF furnace is 0.030%, the final Al content is ≥0.035%, the amount of fluorite added is 0.6 kg / t, the diffusion deoxidizer is 1.0 kg / t, and the final S content is 0.004%. The VD vacuum treatment process includes: ultimate vacuum time of 5 min and static stirring time of 15 min. The continuous casting process (150x150mm billet): superheat 25℃, casting speed 2.20 m / min, and weak cooling mode for the secondary cooling water.

[0044] During the billet heating process, the preheating zone temperature is ≤850℃, the first heating zone temperature is 950℃, the second heating zone temperature is 1000℃, and the soaking zone temperature is 1050℃. The residual oxygen is ≤4%. The billet spacing and idle step distance are controlled according to actual production. The total heating time is 230 minutes. The initial rolling temperature is 970℃, the final rolling temperature is 850℃, and the wire drawing temperature is 830℃. After wire drawing, the wire rod is rapidly cooled to 700℃ at a cooling rate of 5.0℃ / s, and then held at that temperature for delayed cooling until it is coiled and removed from the production line.

[0045] Figure 3 shows the hot-rolled microstructure of the high-strength circular link chain wire rod prepared using the method described in this embodiment. To ensure that the wire rod obtains independent bainitic and martensitic hot-rolled microstructures, a low-temperature rolling process is adopted. After wire drawing, the wire rod is first rapidly cooled and then slowly cooled to pass through the ferrite-pearlite transformation zone, avoiding the ferrite-pearlite transformation. After the wire rod temperature drops to the bainitic transformation zone, a slow cooling process is used to ensure the bainitic-martensitic transformation. This invention achieves the product index requirements for high-strength circular link chain wire rod through composition design and optimized smelting and rolling processes, without requiring additional equipment or processes. The steel has high hardenability and good low-temperature toughness. This method is simple, practical, and widely applicable, and has good promotional and reference value for improving product quality.

[0046] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A high-strength wire rod for circular link chains, characterized in that: The chemical composition and mass fraction of the wire rod include: C: 0.20%–0.26%, Si: 0.10%–0.30%, Mn: 1.00%–1.30%, Cr: 0.40%–0.60%, Ni: 0.70%–0.90%, Cu≤0.10%, Mo: 0.20%–0.40%, Al: 0.025%–0.050%, O≤0.0020%, N≤0.0070%, H≤0.0001%, P≤0.015%, S≤0.010%, B: 0.001%–0.005%.

2. The high-strength circular link chain wire rod according to claim 1, characterized in that: The chemical composition and mass fraction of the high-strength circular link chain wire rod include: C: 0.23%, Si: 0.25%, Mn: 1.05%, Cr: 0.50%, Ni: 0.75%, Cu: 0.02%, Mo: 0.25%, Al: 0.040%, P≤0.010%, S≤0.004%, B: 0.002%.

3. A method for preparing high-strength circular link chain wire as described in claim 1 or 2, characterized in that: (1) When tapping steel in an electric arc furnace, the tapping conditions are C≥0.05%, P≤0.012%, and temperature is 1600~1650℃. The charging sequence during the tapping process includes deoxidizer → alloy → modified refining slag → lime. During the tapping process, 1.2~1.6kg / t of deoxidizer Al blocks, 5~8kg / t of lime, and 2~5kg / t of modified refining slag are added. By controlling the amount of C added during tapping and the amount of Al blocks added after the furnace, the initial oxygen content of the molten steel can be effectively reduced, preventing the molten steel from over-oxidizing and further reducing the space for inclusion formation. (2) The initial Al content of the LF furnace is ≥0.020%, the final Al content is ≥0.025%, the amount of fluorite added is 0.5~0.6kg / t, the amount of diffusion deoxidizer added is 0.8~1.2kg / t, and the final S content is ≤0.010%. During the VD vacuum treatment, the ultimate vacuum time is ≥5min and the static stirring time is ≥15min. During the continuous casting of steel billets with a billet shape of 150*150mm, the superheat is 15~35℃, the casting speed is 2.00~2.20m / min, and the secondary cooling water adopts the weak cooling mode. (3) When heating the billet, the preheating section furnace temperature is ≤850℃, the first heating section furnace temperature is 900~1050℃, the second heating section furnace temperature is 950~1100℃, the soaking section furnace temperature is 1000~1100℃, the residual oxygen is ≤4%, and the billet spacing and empty step distance are controlled according to the actual production layout. The total heating time is ≤300min, the initial rolling temperature is 900~1000℃, the final rolling temperature is 800~900℃, the wire drawing temperature is 800~900℃, and after the wire rod is drawn, it is rapidly cooled to 700℃ at a cooling rate of 3.0~6.0℃ / s and then kept warm and cooled until it is coiled off the line.

4. The method for preparing high-strength circular link chain wire rod according to claim 3, characterized in that: In step (1), the conditions for tapping steel in the electric furnace are: the C content is 0.10%, the P content is 0.008%, and the temperature is 1630℃.

5. The method for preparing high-strength circular link chain wire rod according to claim 3, characterized in that: In step (1), 1.4 kg / t of deoxidizer Al blocks, 6 kg / t of lime, and 3 kg / t of modified refining slag are added during the electric furnace tapping process.

6. The method for preparing high-strength circular link chain wire according to claim 3, characterized in that: In step (2), the initial Al content of the LF furnace is 0.030%, the final Al content is ≥0.035%, the amount of fluorite added is 0.6 kg / t, and the diffusion deoxidizer is: 1.0 kg / t, final sulfur content 0.004%.

7. The method for preparing high-strength circular link chain wire rod according to claim 3, characterized in that: In step (2), the superheat of the continuous casting process is 25°C and the casting speed is 2.20 m / min.

8. The method for preparing high-strength circular link chain wire according to claim 3, characterized in that: In step (3), during the billet heating process, the furnace temperature in the preheating section is ≤850℃, the furnace temperature in the first heating section is 950℃, the furnace temperature in the second heating section is 1000℃, and the furnace temperature in the soaking section is 1050℃.

9. The method for preparing high-strength circular link chain wire rod according to claim 3, characterized in that: In step (3), the total heating time is 230 min, the initial rolling temperature is 970℃, the final rolling temperature is 850℃, the wire drawing temperature is 830℃, and the wire rod is rapidly cooled to 700℃ at a cooling rate of 5.0℃ / s after wire drawing.

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