Wire rod for high-strength round-link chain and preparation method of wire rod

Abstract

The invention discloses a wire rod for a high-strength round-link chain. The wire rod comprises the following chemical components in percentage by mass: 0.20%-0.26% of C, 0.10%-0.30% of Si, 1.00%-1.30% of Mn, 0.40%-0.60% of Cr, 0.70%-0.90% of Ni, less than or equal to 0.10% of Cu, 0.20%-0.40% of Mo, 0.025%-0.050% of Al, less than or equal to 0.0020% of O, less than or equal to 0.0070% of N, less than or equal to 0.0001% of H, less than or equal to 0.015% of P, less than or equal to 0.010% of S and 0.001%-0.005% of B. The method has the advantages that extra equipment and procedures do not need to be added, the purity, high hardenability, essential fine grains and good welding and carburizing performance of the product are effectively improved, and the product has high obdurability and excellent comprehensive performance after quenching and tempering.

Description

Technical Field

[0001] The present invention belongs to the technical field of special steel production processes, and particularly relates to a wire rod for high-strength circular chain and a preparation method thereof. Background Art

[0002] Lifting chains are connecting pieces used in the hoisting, running and other links of lifting machinery. Lifting chains play an important role in improving the operation efficiency of cranes and expanding the operation range of cranes. When selecting lifting chains, they can be selected according to different application scenarios and requirements. At present, the quality of domestic chain steels is still at a medium and low level, resulting in a very low international market share of chain steels. With the continuous development of materials towards lightweight, the development of high-strength chain steels has become the mainstream. Most manufacturers achieve high strength through high alloying, but often have poor welding performance and relatively high production costs; although reducing the alloy content can improve the welding performance, ensuring the high strength of the chain has become a new bottleneck. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem that the existing wire rod steel for circular chains cannot balance high strength and welding performance, and provides a wire rod for high-strength circular chains, which does not require additional equipment and processes, effectively improves the product purity, high hardenability, fine-grained structure, good welding and carburizing performance, and has high strength and toughness after quenching and tempering, with excellent comprehensive performance.

[0004] In order to achieve the above purpose, the present invention adopts the following technical solutions: A wire rod for high-strength circular chain, its chemical composition and mass fraction 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%.

[0005] Further, the chemical composition and mass fraction of the wire rod for high-strength circular chain 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%.

[0006] In order to further achieve the purpose of the present invention, a preparation method of a wire rod for high-strength circular chain is also provided, specifically including: (1)During tapping from the electric furnace, the tapping conditions are C≥0.05%, P≤0.012%, and the temperature is 1600 - 1650°C. The feeding sequence during the tapping process includes deoxidizer → alloy → modified refining slag → lime. During the tapping process of the electric furnace, 1.2 - 1.6 kg / t of deoxidizer Al block, 5 - 8 kg / t of lime, and 2 - 5 kg / t of modified refining slag are added. By controlling the C content during the tapping of the electric furnace and the addition amount of Al block after the furnace, the initial oxygen content of the molten steel can be effectively reduced, preventing the overoxidation of the molten steel and further reducing the generation space of inclusions. (2)In the LF furnace, the initial Al≥0.020%, the final Al≥0.025%, the added amount of fluorite is 0.5 - 0.6 kg / t, the diffusion deoxidizer is 0.8 - 1.2 kg / t, and the final S≤0.010%; during the VD vacuum treatment process, the ultimate vacuum time≥5 min, the static stirring time≥15 min; during the continuous casting process of billets with a size of 150*150 mm, the superheat is 15 - 35°C, the drawing speed is 2.00 - 2.20 m / min, and the secondary cooling water adopts a weak cooling mode. (3)When heating the continuous casting billet, the furnace temperature in the preheating section ≤850°C, the furnace temperature in the first heating section is 900 - 1050°C, the furnace temperature in the second heating section is 950 - 1100°C, the soaking section furnace temperature is 1000 - 1100°C, the residual oxygen≤4%. According to the actual production arrangement, the billet spacing and the empty step distance in the furnace are controlled, the total heating time≤300 min, the rolling start temperature is 900 - 1000°C, the final rolling temperature is 800 - 900°C, the wire laying temperature is 800 - 900°C. After the wire laying of the wire rod, it is rapidly cooled at a cooling rate of 3.0 - 6.0°C / s to 700°C and then subjected to heat preservation and delayed cooling until it is coiled and unloaded.

[0007] Furthermore, in the step (1), the tapping conditions of the electric furnace are: the C content during tapping is 0.10%, the P content is 0.008%, and the temperature is 1630°C.

[0008] Furthermore, in the step (1), 1.4 kg / t of deoxidizer Al block, 6 kg / t of lime, and 3 kg / t of modified refining slag are added during the tapping process of the electric furnace.

[0009] Furthermore, in the step (2), the initial Al content in the LF furnace is 0.030%, the final Al≥0.035%, the added amount of fluorite is 0.6 kg / t, the diffusion deoxidizer: 1.0 kg / t, and the final S content is 0.004%.

[0010] Furthermore, in the step (2), the superheat during the continuous casting process is 25°C, and the drawing speed is 2.20 m / min.

[0011] Furthermore, in the step (3), during the heating process of the continuous casting billet, the furnace temperature in the preheating section ≤850°C, the furnace temperature in the first heating section is 950°C, the furnace temperature in the second heating section is 1000°C, and the soaking section furnace temperature is 1050°C.

[0012] Further, in the step (3), the total heating time is 230 min, the starting rolling temperature is 970 °C, the finishing rolling temperature is 850 °C, the wire laying temperature is 830 °C, and after the wire rod is laid, it is rapidly cooled to 700 °C at a cooling rate of 5.0 °C / s.

[0013] The mechanism of action of the composition design of the present invention is as follows: As the most important element in steel, C directly affects the strength, plasticity, toughness and welding performance of steel. To balance the welding performance and the matching of strength and toughness of chain steel, the designed content range of C is 0.20 - 0.26%; Mn can improve the strength of steel. While increasing the strength of steel, its influence on plasticity is relatively small. If the manganese content is too high, the plasticity and welding performance of steel will be reduced. Therefore, the controlled content range of Mn is 1.00 - 1.30%; Cr can increase the hardenability of steel and has the effect of secondary hardening, can improve hardness and wear resistance without making the steel brittle, and enables the steel to have better comprehensive mechanical properties after quenching and tempering. The controlled content range of Cr is 0.40 - 0.60%; The Ni element has high strength, high toughness, good hardenability, high resistance and high corrosion resistance. On the one hand, it strongly improves the strength of steel, and on the other hand, it always keeps the toughness of steel at an extremely high level, and its embrittlement temperature is extremely low. Considering the cost, the designed content range of Ni is 0.70 - 0.90%; Mo in steel can improve hardenability and thermal strength, improve the temper resistance or temper stability of steel, enable the chain to more effectively eliminate or reduce residual stress after tempering, and improve plasticity. Therefore, the controlled content range of Mo is 0.20 - 0.40%; N can improve the strength of steel, but with the increase of N content, plasticity and toughness decrease, weldability becomes poor, and cold brittleness increases. The controlled content of N is ≤0.0070%; H is a harmful element in steel. It dissolves into the molten steel at high temperature and aggregates to form micropores, cracks and brittle fractures when cooling and cannot escape in time, deteriorating the plasticity, toughness and fatigue strength of steel. The controlled content of H is ≤0.0001%; The main role of B in steel is to increase the hardenability of steel and improve its strength performance, but boron has a slight tendency to promote temper brittleness, so boron cannot completely replace molybdenum. The controlled content of B is 0.001 - 0.005%.

[0014] 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, reducing the cold brittleness tendency and aging tendency.

[0015] The mechanism of action of the smelting process of the present invention is as follows: By controlling the tapping carbon content of the electric furnace and the use of post-furnace Al-based deoxidizers, the initial oxygen content of the molten steel can be significantly reduced, preventing the overoxidation of the molten steel and further reducing the generation space of inclusions. To better remove inclusions, the LF furnace adopts the precipitation deoxidation + diffusion deoxidation process, controls the final Al content of the LF furnace, and ensures the static stirring time after the VD furnace vacuum treatment to promote the full floating of inclusions, achieving a gas N content ≤ 0.0070% and a gas H content ≤ 0.0001%.

[0016] The working mechanism of the rolling process of the present invention is as follows: Due to the high contents of chromium, molybdenum, nickel, and manganese in high-grade chain steel, the steel has high hardenability and good low-temperature toughness. Downstream users need to adopt spheroidizing annealing to reduce strength, improve plasticity, and enhance its cold working or drawing performance. Spheroidizing annealing is achieved through long-time high-temperature heating and holding, which transforms the lamellar or flaky carbides into dispersed spherical shapes, enabling the wire rod to obtain better cold deformation performance. Different original microstructures have different effects on the spheroidizing annealing effect.

[0017] Compared with the prior art, the advantages of the technical solution of the present invention are specifically as follows: (1) In order to ensure that the wire rod obtains independent bainite and martensite hot-rolled microstructures, the wire rod adopts a low-temperature rolling process. After wire laying, it is first rapidly cooled and then slowly cooled, passing through the ferrite and pearlite transformation zones to avoid the occurrence of ferrite and pearlite transformations. After the wire rod temperature drops to the bainite transformation zone, a slow cooling process is adopted to ensure bainite and martensite transformations; (2) Through the reasonable design of chemical compositions, the wire rod of the present invention has high purity, high hardenability, fine-grained nature, and good welding and carburizing properties. After quenching and tempering, it has high strength and toughness and excellent comprehensive performance; (3) Through the reasonable control of carbon content and the adoption of a higher alloy design with Ni, Cr, Mo, etc., the present invention achieves high toughness and high strength of the chain without the need to add additional equipment and processes. The inclusion ratings of the wire rod for A, B, C, D coarse series and fine series are all ≤ 1.5, the gas N in the wire rod ≤ 70 ppm, H ≤ 1.0 ppm, the cold bending performance of the wire rod is qualified, the tensile strength Rm of the wire rod ≤ 1150 MPa, the elongation A ≥ 10%, and the reduction of area Z ≥ 25%. After the user anneals, draws, weaves the chain, and quenches and tempers the wire rod, the breaking tensile strength of the finished chain ≥ 1000 MPa, and the cross-sectional elongation ≥ 20%, meeting the technical index requirements of the user for high-strength round-link chains. Description of the Drawings

[0018] Figure 1 It is the rating table of inclusions A, B, C, D coarse series and fine series of the wire rod for round-link chains in the present invention; Figure 2 It is the gas and tensile property table of the wire rod for round-link chains in the present invention; Figure 3 This is the hot-rolled microstructure image of the wire rod for high-strength round-link chains in the embodiments of the present invention. Specific embodiments Embodiment

[0019] To make the present invention more clearly understood, the following further describes a wire rod for high-strength round-link chains and its preparation method according to the present invention with reference to the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] The preparation process of a wire rod for high-strength round-link chains includes: electric furnace → LF furnace → VD furnace → continuous casting → heating → rolling → cooling → coiling. By controlling measures such as 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 controlled cooling during the rolling process, see Figure 1 and Figure 2 , the inclusion ratings of the wire rod for both the A, B, C, D coarse series and the fine series are ≤ 1.5, the gas content of the wire rod is N ≤ 70 ppm, H ≤ 1.0 ppm, the cold bending performance of the wire rod is qualified, the tensile strength Rm of the wire rod is ≤ 1150 MPa, the elongation A ≥ 10%, and the reduction of area Z ≥ 25%.

[0021] In this embodiment, taking the wire rod for high-strength round-link chains as an example, the mass fractions of its main elements 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%.

[0022] The tapping conditions of the electric furnace are that the tapping C content is 0.10%, the P content is 0.008%, and the temperature is 1630 °C. The feeding sequence during tapping: deoxidizer → alloy → modified refining slag → lime. During the tapping process of the electric furnace, 1.4 kg / t of deoxidizer Al block, 6 kg / t of lime, and 3 kg / t of modified refining slag are added. By controlling the tapping C of the electric furnace and the addition amount of the post-furnace Al block, the initial oxygen content of the molten steel can be effectively reduced, preventing the overoxidation of the molten steel and further reducing the generation space of inclusions.

[0023] The initial Al content of the LF furnace is 0.030%, the final Al content ≥ 0.035%, the supplementary addition amount of fluorite is 0.6 kg / t, the diffusion deoxidizer: 1.0 kg / t, and the final S content is 0.004%. The VD vacuum treatment process: the ultimate vacuum time is 5 min, and the static stirring time is 15 min. The continuous casting process (billet type 150x150 mm): the superheat is 25 °C, the drawing speed is 2.20 m / min, and the secondary cooling water adopts a weak cooling mode.

[0024] During the continuous casting billet heating process, the furnace temperature in the preheating section is ≤850°C, the furnace temperature in the first heating section is 950°C, the furnace temperature in the second heating section is 1000°C, the furnace temperature in the soaking section is 1050°C, and the residual oxygen is ≤4%. Control the billet spacing and the empty step distance according to the actual production arrangement, and the total heating time is 230 min. The starting rolling temperature is 970°C, the finishing rolling temperature is 850°C, and the wire laying temperature is 830°C. After the wire rod is laid, it is rapidly cooled at a cooling rate of 5.0°C / s to 700°C and then subjected to heat preservation and delayed cooling until it is coiled and unloaded from the production line.

[0025] The hot-rolled microstructure diagram of the wire rod for high-strength round-link chains prepared by the method in this embodiment is as Figure 3 shown. In order to ensure that the wire rod obtains independent bainite and martensite hot-rolled microstructures, the wire rod adopts a low-temperature rolling process. After wire laying, it is first rapidly cooled and then slowly cooled, passing through the ferrite and pearlite transformation zones to avoid the occurrence of ferrite and pearlite transformations. After the wire rod temperature drops to the bainite transformation zone, a slow cooling process is adopted to ensure bainite and martensite transformations. Through composition design, optimized smelting and rolling processes, the present invention meets the product index requirements of the wire rod for high-strength round-link chains, without the need to add additional equipment and processes. The steel has high hardenability and good low-temperature toughness. This method is simple, highly practical and applicable, and has good promotion and reference significance for improving product quality.

[0026] In addition to the above embodiments, the present invention may have other implementation manners. Any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A wire rod for high-strength round-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 wire rod for high-strength round-link chains according to claim 1, characterized in that: The chemical composition and mass fraction of the wire rod for high-strength round-link chains 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 preparation method of the wire rod for high-strength round-link chains according to claim 1 or 2, characterized in that: (1) When tapping steel from the electric furnace, the tapping conditions are C ≥ 0.05%, P ≤ 0.012%, and the temperature is 1600 - 1650°C. The charging sequence during the tapping process of the electric furnace includes deoxidizer → alloy → modified refining slag → lime. During the tapping process of the electric furnace, 1.2 - 1.6 kg / t of deoxidizer Al block, 5 - 8 kg / t of lime, and 2 - 5 kg / t of modified refining slag are added. By controlling the C content during the tapping of the electric furnace and the addition amount of Al block after the furnace, the initial oxygen content of the molten steel can be effectively reduced, preventing the overoxidation of the molten steel and further reducing the generation space of inclusions; (2) In the LF furnace, the initial Al ≥ 0.020% and the final Al ≥ 0.025%. The amount of supplementary fluorite added is 0.5 - 0.6 kg / t, and the amount of diffusion deoxidizer is 0.8 - 1.2 kg / t. The final S ≤ 0.010%; during the VD vacuum treatment process, the ultimate vacuum time ≥ 5 min and the static stirring time ≥ 15 min; during the continuous casting of the billet with a billet shape of 150*150 mm, the superheat is 15 - 35°C, the drawing speed is 2.00 - 2.20 m / min, and the secondary cooling water adopts a weak cooling mode; (3) When heating the billet, the furnace temperature in the preheating section ≤ 850°C, the furnace temperature in the first heating section is 900 - 1050°C, the furnace temperature in the second heating section is 950 - 1100°C, the furnace temperature in the soaking section is 1000 - 1100°C, the residual oxygen ≤ 4%. According to the actual production arrangement, control the billet spacing and idle step distance in the furnace. The total heating time ≤ 300 min, the rolling start temperature is 900 - 1000°C, the final rolling temperature is 800 - 900°C, the wire laying temperature is 800 - 900°C. After the wire rod is laid, it is rapidly cooled to 700°C at a cooling rate of 3.0 - 6.0°C / s and then subjected to heat preservation and delayed cooling until it is coiled and taken offline.

4. The preparation method of the wire rod for high-strength round-link chains according to claim 3, characterized in that: In the step (1), the conditions for tapping steel from the electric furnace are as follows: the C content in the tapped steel is 0.10%, the P content is 0.008%, and the temperature is 1630 °C.

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

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

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

8. The method for preparing wire rods for high-strength round-link chains according to claim 3, characterized in that: In the step (3), during the heating process of the continuous casting billet, the furnace temperature in the preheating section ≤ 850 °C, the furnace temperature in the first heating section is 950 °C, the furnace temperature in the second heating section is 1000 °C, and the furnace temperature in the soaking section is 1050 °C.

9. The method for preparing wire rods for high-strength round-link chains according to claim 3, characterized in that: In the step (3), the total heating time is 230 min, the rolling start temperature is 970 °C, the final rolling temperature is 850 °C, the wire laying temperature is 830 °C, and after the wire rods are laid, they are rapidly cooled to 700 °C at a cooling rate of 5.0 °C / s.

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