High-strength steel wire rod for lifting round-link chain and spheroidizing annealing method of high-strength steel wire rod

Abstract

The invention discloses a wire rod for a high-strength lifting round-link chain. The wire rod comprises the following main elements in percentage by mass: 0.21% < = omega [C] < = 0.26%, 0.10% < = omega [Si] < = 0.30%, 1.00% < = omega [Mn] < = 1.30%, 0.40% < = omega [Cr] < = 0.60%, 0.60% < = omega [Ni] < = 0.90%, omega [Cu] < = 0.10%, 0.20% < = omega [Mo] < = 0.40%, 0.025% < = omega [Al] < = 0.050%, omega [O] < = 0.0020%, omega [N] < = 0.0070%, omega [H] < = 0.0001%, omega [P] < = 0.015%, omega [S] < = 0.010% and 0.001% < The steel wire rod has the advantages that the steel wire rod has a high spheroidizing rate and proper annealing hardness and hardness dispersion difference, the toughness is high after quenching and tempering, and the comprehensive performance is excellent.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel production and preparation, and in particular relates to a wire rod for a high-strength lifting round link chain and a spheroidizing annealing method thereof. Background Art

[0002] Lifting chains are connectors used in lifting equipment such as hand hoists and electric hoists. High-grade chain steel combines high strength with high toughness, weldability, wear resistance, and fatigue properties. Common preparation processes for high-grade chain steel include spheroidizing annealing of the wire rod base material, drawing, pickling, chain braiding, welding, straightening, and heat treatment. Spheroidizing annealing is a crucial step in the chain steel manufacturing process. It not only imparts sufficient plasticity to the material for cold forming, but also spheroidizes the carbides in the steel, transforming them from flake or mesh forms into spheres. These carbides are then evenly dispersed throughout the ferrite matrix, providing a favorable structural foundation for subsequent heat treatment. Spheroidizing annealing also eliminates residual stress within the material, stabilizes its structural structure, reduces dimensional change and deformation during subsequent tempering and use, and improves the dimensional accuracy and stability of parts.

[0003] At present, in the spheroidizing annealing process of wire rod for lifting round link chain, the spheroidizing rate is low, the annealing hardness and hardness dispersion are large, the strength and toughness after quenching and tempering are limited, and the overall performance is greatly reduced. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of low spheroidization rate and poor comprehensive performance of existing steel for lifting chains, and to provide a high-strength wire rod for lifting round link chains, which does not require additional equipment and processes, is simple and efficient, and has a high spheroidization rate and suitable annealing hardness and hardness dispersion, high strength and toughness after quenching and tempering, and excellent comprehensive performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A high-strength wire rod for a lifting round link chain, wherein main elements and mass fractions thereof include: 0.21%≤ω[C]≤0.26%, 0.10%≤ω[Si]≤0.30%, 1.00%≤ω[Mn]≤1.30%, 0.40%≤ω[Cr]≤0.60%, 0.60%≤ω[Ni]≤0.90%, ω[Cu]≤0.10%, 0.20%≤ω[Mo]≤0.40%, 0.025%≤ω[Al]≤0.050%, ω[O]≤0.0020%, ω[N]≤0.0070%, ω[H]≤0.0001%, ω[P]≤0.015%, ω[S]≤0.010%, and 0.001%≤ω[B]≤0.005%.

[0006] In order to further achieve the purpose of the present invention, a spheroidizing annealing method for wire rod for high-strength lifting round link chain is also provided, which specifically includes: the hood annealing furnace adopts N2 purging protection, the furnace table baking temperature is 200℃*1h, after the air tightness test and pre-purging are completed, the heating hood is placed, the annealing curve is 6h slowly heated to 700~720℃ to ensure uniform and slow heating, the insulation section is kept warm for 10h, and cooled to below 500℃ for 7h, the cooling rate is controlled to ≤30℃ / h, and the cooling hood is replaced for cooling.

[0007] Furthermore, the bell-type furnace annealing operation steps are: material rack preparation → loading → furnace loading → lifting and locking the inner cover → air tightness test → N2 pre-purge → selection of annealing curve → buckle the heating cover → ignition → heating and annealing → lifting the heating cover → buckle the cooling cover → cooling → lifting the cooling cover → loosening and lifting the inner cover → unloading → unloading → transfer.

[0008] Furthermore, the spheroidizing annealing temperature is set to be lower than 726°C.

[0009] Furthermore, when determining the spheroidizing annealing temperature, the sample is processed into a cylindrical shape with a diameter of φ6±0.06 mm and a length of 25±0.1 mm. Both ends are ground flat to ensure good contact. The surface roughness of the sample is Ra1.60. The sample is heated from room temperature to 1000°C at a rate of 3K / min. The temperature and expansion amount are simultaneously recorded, and an expansion curve or a differential curve is drawn. The peak or inflection point of the differential curve corresponds to the start / end temperature of the phase transition. The measured phase transition point AC1 temperature is 726°C, and the AC3 temperature is 827°C. A temperature lower than the critical temperature of AC1 is used as the spheroidizing annealing temperature.

[0010] Furthermore, the replacement interval of the cooling cover shall not exceed 1 hour, and the heating cover shall not be lifted away when there is no cooling cover.

[0011] Furthermore, after annealing, the metallographic structure of the wire rod is ferrite + spheroidize, the spheroidization rate is ≥95%, the depth of the decarburized layer of the wire rod is ≤0.05mm, the microhardness of the wire rod is ≤187HV, and the microhardness difference between the core and the surface is ≤5HV.

[0012] Furthermore, after annealing, the wire rod is braided into a chain and quenched and tempered, the finished chain has a breaking tensile strength of ≥1100MPa and a cross-sectional elongation of ≥20%, meeting the technical index requirements of high-strength lifting round link chains.

[0013] The mechanism of the present invention is as follows: Mechanism of Spheroidizing Annealing: Cementite spheroidization can be achieved primarily through two methods. One is subcritical spheroidizing annealing, which involves the spontaneous transformation of lamellar pearlite into spherical pearlite through diffusion of carbon and iron atoms when the material is held below the AC1 temperature without undergoing a phase transformation. Due to the significant difference in carbon content between pearlite and ferrite, carbon diffusion cannot achieve equilibrium during spheroidizing annealing, resulting in a very slow spheroidization of pearlite. The spheroidization of bainite and martensite, on the other hand, is a process in which granular carbides precipitate from the supersaturated α phase. Bainite and martensite are metastable structures with numerous defects such as dislocations and subgrained structures, resulting in numerous carbide nucleation sites. Consequently, the spheroidization rate of bainite and martensite is rapid, resulting in a uniformly distributed spheroidized structure within a short period of time. Therefore, despite the same spheroidizing annealing process, the spheroidization of bainite and martensite is superior to that of pearlite. The spheroidization process primarily involves the splitting of lamellar layers into fragments and the spheroidization growth of the fragments. Another method is critical spheroidizing annealing, which utilizes the principle of divorced eutectoid to heat the annealing temperature to above AC1 temperature and keep it warm. During the cooling process, spherical cementite is precipitated by divorced eutectoid.

[0014] Furthermore, pearlite spheroidization occurs through a carbon diffusion process involving dissolution and deposition, causing the lamellae of cementite to initially segment and then gradually grow into spherical shapes. This carbon diffusion process involves a dynamic equilibrium between carbon atoms in cementite and ferrite at a certain temperature. The carbon concentration at this equilibrium is closely related to the radius of curvature of the cementite. Because the radius of curvature of cementite corners is smaller, carbon atoms from these corners more easily diffuse into the adjacent ferrite. This results in a significantly higher carbon concentration in the ferrite near the corners than in the ferrite near the straight portions of the cementite. This ultimately causes carbon diffusion within the ferrite, disrupting the dynamic equilibrium. To maintain this dynamic equilibrium, the cementite corners continue to dissolve and precipitate in the straight portions. This continuous process of dissolution and deposition gradually transforms the lamellae of cementite into spherical cementite with a nearly identical radius of curvature. Pearlite is composed of two phases, α phase and cementite. Due to the different thermal expansion coefficients of these two phases, the distortion caused by pearlite transformation results in defects such as dislocations and subgrain structures. Dislocations and subgrain structures cause local depressions in the lamellar cementite. The curvature radius of the cementite on both sides of the depression is smaller than that of the lamellar cementite. Subsequently, a carbon diffusion process of dissolution and deposition occurs, which eventually causes the lamellar cementite to be segmented. After segmentation, the blocky cementite continues to undergo a carbon diffusion process of dissolution and deposition, causing the sharp corners to gradually dissolve, forming spherical cementite.

[0015] In the technical solution of the present invention, the existing special steel annealing equipment is used, and the index requirements of the wire rod for high-strength lifting round link chain are achieved through the identification of the special characteristics of the steel grade and the optimization of the annealing process system. There is no need to add additional equipment and processes. The method is simple and practical, with strong applicability, and can effectively improve the comprehensive performance of the finished product. After annealing, the metallographic structure of the wire rod is ferrite + spheroidize, the spheroidization rate is ≥95%, the depth of the wire rod decarburization layer is ≤0.05mm, the microhardness of the wire rod is ≤187HV, and the core-surface microhardness difference is ≤5HV. After annealing, the wire rod is knitted into a chain and quenched and tempered. The breaking tensile strength of the finished chain is ≥1100MPa, and the cross-sectional elongation is ≥20%, which meets the technical index requirements of the high-strength lifting round link chain. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a physical and chemical test table of the wire rod for high-strength lifting round link chain after annealing in an embodiment of the present invention; Figure 2 This is a table showing the breaking tensile properties of the finished high-strength round link chain in the embodiment of the present invention; Figure 3 This is a metallographic structure diagram of the wire rod for high-strength round-link lifting chain after annealing in an embodiment of the present invention; Figure 4 This is a decarburized metallographic structure diagram of the wire rod for high-strength round-link lifting chain in an embodiment of the present invention. DETAILED DESCRIPTION Example

[0017] To make the present invention more clear, the following further describes a high-strength wire rod for lifting round link chain and its spheroidizing annealing method in conjunction with 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.

[0018] In this embodiment, a spheroidizing annealing method for a wire rod for a high-strength lifting round link chain is provided, wherein the hood-type annealing furnace process comprises: material rack preparation → charging → furnace loading → lifting and locking the inner hood → air tightness test → N2 pre-purge → selection of annealing curve → fastening the heating hood → ignition → heating and annealing → lifting the heating hood → fastening the cooling hood → cooling → lifting the cooling hood → loosening and lifting the inner hood → unloading → unloading → transfer.

[0019] After annealing, the metallographic structure of the wire rod is ferrite + spheroidize, the spheroidization rate is ≥95%, the depth of the wire rod decarburization layer is ≤0.05mm, the wire rod microhardness is ≤187HV, the core-surface microhardness difference is ≤5HV, after annealing, the wire rod is knitted into a chain and quenched and tempered, the breaking tensile strength of the finished chain is ≥1100MPa, and the cross-sectional elongation is ≥20%, which meets the technical index requirements of high-strength lifting round link chain.

[0020] In this embodiment, the mass fraction of the main elements of the wire rod for the high-strength lifting round link chain is: 0.21%≤ω[C]≤0.26%, 0.10%≤ω[Si]≤0.30%, 1.00%≤ω[Mn]≤1.30%, 0.40%≤ω[Cr]≤0.60%, 0.60%≤ω[Ni]≤0.90%, ω[Cu]≤0.10%, 0.20%≤ω[Mo]≤0.40%, 0.025%≤ω[Al]≤0.050%, ω[O]≤0.0020%, ω[N]≤0.0070%, ω[H]≤0.0001%, ω[P]≤0.015%, ω[S]≤0.010%, and 0.001%≤ω[B]≤0.005%.

[0021] Phase transition temperature determination: The specimen was processed into a cylindrical shape with a diameter of φ6±0.06mm and a length of 25±0.1mm. Both ends were ground flat to ensure good contact. The surface finish of the specimen was 6 (roughness Ra1.60). The specimen was heated from room temperature to 1000°C at a rate of 3K / min. The temperature and expansion were simultaneously recorded, and an expansion curve or differential curve was plotted. The peak or inflection point of the differential curve corresponds to the phase transition start / end temperature. The measured phase transition points AC1 and AC3 were 726°C and 827°C, respectively. The spheroidizing annealing temperature was set below the critical temperature of AC1.

[0022] Wire rod spheroidizing annealing: After the wire rod is loaded into the furnace, use a special lifting device to lift the inner cover to the top of the furnace, slowly lower it, and buckle it steadily on the base. If the inner cover is found to be tilted during the descent, there is friction or impact sound between the wire rod and the inner cover guide tube, or the inner cover is not stable after being buckled on the base, the inner cover must be lifted, the cause must be confirmed and dealt with, and the inner cover must be buckled again. The furnace is baked at 200℃*1h. After the air tightness test and pre-purge are completed, the heating cover is placed. The annealing curve is to slowly heat up to 700-720℃ for 6h to ensure uniform and slow heating. The insulation section is kept warm for 10h and cooled to below 500℃ for 7h. The cooling rate is controlled to be ≤30℃ / h. The cooling cover must be replaced in time, and the interval must not exceed 1h. The heating cover must not be lifted away when there is no cooling cover.

[0023] After adopting the spheroidizing annealing method of the present invention, the physical and chemical tests of the high strength lifting round link chain wire rod after annealing are as follows: Figure 1 As shown, the breaking tensile properties of the high strength round link chain finished product are as follows Figure 2 As shown in the figure, the metallographic structure and decarburization of the wire rod for high strength lifting round link chain after annealing are as follows: Figure 3 and Figure 4As shown in the chart, the metallographic structure of the wire rod after annealing is ferrite + spheroidize, the spheroidization rate is ≥95%, the depth of the wire rod decarburization layer is ≤0.05mm, the wire rod microhardness is ≤187HV, the core-surface microhardness difference is ≤5HV, and after the annealed wire rod is knitted into a chain and quenched and tempered, the breaking tensile strength of the finished chain is ≥1100MPa, and the cross-sectional elongation is ≥20%, which meets the technical requirements of high-strength lifting round link chain.

[0024] The method of the present invention does not require additional equipment and processes, is simple and practical, has strong applicability, and has good promotion and reference significance for improving product quality.

[0025] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A high-strength wire rod for a round-link lifting chain, characterized by: The main elements and mass fractions of the wire rod include: 0.21%≤ω[C]≤0.26%, 0.10%≤ω[Si]≤0.30%, 1.00%≤ω[Mn]≤1.30%, 0.40%≤ω[Cr]≤0.60%, 0.60%≤ω[Ni]≤0.90%, ω[Cu]≤0.10%, 0.20%≤ω[Mo]≤0.40%, 0.025%≤ω[Al]≤0.050%, ω[O]≤0.0020%, ω[N]≤0.0070%, ω[H]≤0.0001%, ω[P]≤0.015%, ω[S]≤0.010%, and 0.001%≤ω[B]≤0.005%.

2. A spheroidizing annealing method for a high-strength lifting round-link chain wire rod as claimed in claim 1, characterized in that: The bell-type annealing furnace adopts N2 purge protection, the furnace temperature is 200℃*1h, after the air tightness test and pre-purge are completed, the heating cover is placed, the annealing curve is 6h slowly heating to 700~720℃, keeping warm for 10h, cooling to below 500℃ for 7h, controlling the cooling rate to ≤30℃ / h, and replacing the cooling cover for cooling.

3. The spheroidizing annealing method for high-strength lifting round-link chain wire rod according to claim 2, characterized in that: The bell-type furnace annealing operation steps are: material rack preparation → loading → furnace loading → lifting and locking the inner cover → air tightness test → N2 pre-purge → selection of annealing curve → buckle the heating cover → ignition → heating and annealing → lifting the heating cover → buckle the cooling cover → cooling → lifting the cooling cover → loosening and lifting the inner cover → unloading → unloading → transfer.

4. The spheroidizing annealing method for high-strength lifting round-link chain wire rod according to claim 2, characterized in that: The spheroidizing annealing temperature is set to be lower than 726°C.

5. The spheroidizing annealing method for high-strength lifting round-link chain wire rod according to claim 4, characterized in that: When determining the spheroidizing annealing temperature, the sample is processed into a cylindrical shape with a diameter of φ6±0.06 mm and a length of 25±0.1 mm. Both ends are ground flat, and the surface roughness of the sample is Ra1.

60. The sample is heated from room temperature to 1000°C at a rate of 3K / min. The temperature and expansion amount are simultaneously recorded, and an expansion curve or a differential curve is plotted. The peak or inflection point of the differential curve corresponds to the start / end temperature of the phase transition. The measured phase transition point AC1 temperature is 726°C, and the AC3 temperature is 827°C. A temperature lower than the critical temperature of AC1 is used as the spheroidizing annealing temperature.

6. The spheroidizing annealing method for high-strength lifting round-link chain wire rod according to claim 2, characterized in that: The replacement interval of the cooling cover shall not exceed 1 hour. The heating cover shall not be lifted away when there is no cooling cover.

7. The spheroidizing annealing method for high-strength lifting round-link chain wire rod according to claim 2, characterized in that: After annealing, the metallographic structure of the wire rod is ferrite + spheroidized body, the spheroidization rate is ≥95%, the depth of the wire rod decarburization layer is ≤0.05mm, the wire rod microhardness is ≤187HV, and the core-surface microhardness difference is ≤5HV.

8. The spheroidizing annealing method for high-strength lifting round-link chain wire rod according to claim 2, characterized in that: After annealing, the wire rod is braided into a chain and then quenched and tempered. The finished chain has a breaking tensile strength of ≥1100MPa and a cross-sectional elongation of ≥20%, meeting the technical requirements of high-strength lifting round link chains.

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