Corrosion-resistant fatigue spring steel wire, wire rod, and method for manufacturing the same

Abstract

This invention discloses corrosion-resistant fatigue spring steel wire, wire rod, and a method for manufacturing the same. The chemical composition of the wire rod and steel wire is, by mass percentage, C: 0.2-0.7%, Si: 0.8-1.6%, Mn: 0.5-1.7%, Al: 0.35-0.85%, Nb: 0.1-0.5%, Cr: 0.5-1.0%, Mo: 0.1-0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities.

Description

Technical Field

[0001] This application is filed based on the Chinese patent application with application number CN202311085007.3 and filing date August 28, 2023, claims the priority of the Chinese patent application, and incorporates the entire content of the above patent application by reference into this application.

[0002] The present invention belongs to the technical field of steel manufacturing, and relates to a corrosion-resistant fatigue spring steel wire, a wire rod for corrosion-resistant fatigue spring steel wire, and a manufacturing method for the wire rod for corrosion-resistant fatigue spring steel wire.

Background Art

[0003] As a safety-bearing component, springs are widely applied in fields such as automobiles, machinery, and railways, and often bear high-cycle alternating loads during the service process. With the progress of science and technology and the improvement of manufacturing levels, new energy vehicles are gradually emerging, and their sales volume is gradually increasing in the automotive industry. However, due to the relatively large weight of new energy vehicles, strict requirements are put forward for the spring steel wire applied to the suspension springs. Not only is a relatively high strength required to improve the load capacity of the vehicle, but also development towards lightweight is necessary to reduce energy consumption during vehicle driving and improve the cruising ability.

[0004] However, the current spring steel has relatively poor corrosion resistance performance. When applied in the humid environment in the north, since the snow accumulation is relatively thick in winter in the north, the roads are usually cleared by salting to melt the snow, resulting in a large amount of chloride ions in the roads. It is easy to generate corrosion pits on the surface of the spring steel, form stress concentration, and reduce the fatigue strength of the spring steel. In addition, the intrusion of hydrogen during the corrosion process causes hydrogen-induced delayed cracking, causing sudden fracture of the component under conditions far below the allowable cycles or loads of the component, seriously affecting the service life of the component, and bringing huge hidden dangers to the safe operation of automobiles and railways. Therefore, it is necessary to develop a spring steel wire with high strength, lightweight, and excellent corrosion resistance performance to meet the application requirements of new energy vehicles in the northern environment.

Summary of the Invention

[0005] The object of the present invention is to provide a wire material for corrosion-resistant fatigue spring steel wire and a method for manufacturing the same, and also relates to corrosion-resistant fatigue spring steel wire.

[0006] To achieve the above-mentioned objective of the invention, one embodiment of the present invention provides a method for manufacturing a wire rod for corrosion-resistant fatigue spring steel wire. The chemical composition of the wire rod is, by mass percentage, C: 0.2~0.7%, Si: 0.8~1.6%, Mn: 0.5~1.7%, Al: 0.35~0.85%, Nb: 0.1~0.5%, Cr: 0.5~1.0%, Mo: 0.1~0.4%, P≦0.02%, S≦0.02%, with the remainder being Fe and unavoidable impurities. The above manufacturing method includes a sequentially performed molten iron pre-desulfurization process, converter refining process, LF refining process, RH refining process, continuous casting process, mass separation process, flaw detection and polishing process, high-speed wire rolling process, and controlled cooling process. In the converter refining process, the refining raw materials, consisting of high-quality scrap steel, ferromolybdenum, and molten iron after pre-desulfurization, are sent into the converter for refining. Here, the weight ratio of molten iron after pre-desulfurization to high-quality scrap steel is 7:1 to 8:1, and the temperature of the molten iron when sent to the converter is 1350 to 1450°C.

[0007] In the aforementioned continuous casting process, the crystallizer liquid level (molten steel level in the mold) is protected by a protective slag specifically for high-Al steel, and the chemical composition of the protective slag specifically for high-Al steel is, by mass percentage, CaO + Al2O3 = 50-60%, and CaO / Al2O3 = 1.4-1.5, Na2O: 15-20%, MgO: 5-12%, K2O: 3-6%, Li2O: 2-5%, BaO: 1-2%, SiO2: 0.8-1.1%, and CaF2: 4-9%.

[0008] In the high-speed wire rolling process, the intermediate steel billet is heated in a heating furnace, scale is removed with high-pressure water, and then it is rolled into a wire by a high-speed continuous wire rolling process. Here, the heating process includes a first heating stage, a second heating stage, and a soaking stage. The heating temperature of the first heating stage is 780-820°C and the heating time is ≤30 min. The heating temperature of the second heating stage is 900-950°C and the heating time is ≤30 min. The heating temperature of the soaking stage is 1030-1070°C and the heating time is ≤60 min. The high-speed continuous wire rolling process includes sequentially performed rough rolling, intermediate rolling, pre-finishing rolling, finish rolling, and discharge. The rolling start temperature for rough rolling is 890-910°C, the rolling start temperature for finish rolling is 860-890°C, the rolling end temperature for finish rolling is ≤960°C, and the discharge temperature is 860-880°C.

[0009] In the controlled cooling process described above, a Stermore air cooling line is used to control the cooling of the wire. During the period when the temperature of the wire end is 810 to 860°C, the first to fifth fans on the Stermore cooling line are operated with their airflow controlled to 65 to 75%, the roller table speed is set to 0.50 to 0.65 m / s, and the cooling rate is set to 4.5 to 5.5°C / s. During the period when the temperature of the wire end is 690 to 810°C, the sixth to eighth fans on the Stermore cooling line are operated with their airflow controlled to 50 to 60%, the roller table speed is set to 0.2 to 0.3 m / s, and the cooling rate is set to 1.5 to 2°C / s.

[0010] As a further improvement of one embodiment of the present invention, the chemical composition of the wire is, by mass percentage, C: 0.2~0.7%, Si: 0.8~1.6%, Mn: 0.5~1.7%, Al: 0.35~0.85%, Nb: 0.1~0.5%, Cr: 0.5~1.0%, Mo: 0.1~0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities, and [Si] / [Al] = 1.5~3.5.

[0011] As a further improvement of one embodiment of the present invention, in the molten iron preliminary desulfurization process, the blast furnace molten iron is desulfurized in a KR desulfurization apparatus to achieve a slag removal rate of ≤0.002% in the molten iron, a slag removal rate of ≥97%, and a molten iron temperature after desulfurization of ≥1350°C.

[0012] As a further improvement of one embodiment of the present invention, in the converter refining process, the converter refining employs upper-bottom composite blowing, constant-pressure lance control, and double slag operation, the C ≥ 0.15% and P ≤ 0.01% in the molten steel at the end of the converter refining, the tapping temperature ≥ 1650°C, there are no floating slag lumps in the ladle (steel pack) before tapping, the cold slag steel at the bottom of the ladle < 0.5 tons, and ferromanganese, ferrosilicon, ferrochrome, lime, and 1 / 3 aluminum lumps are laid at the bottom of the ladle before tapping.

[0013] As a further improvement of one embodiment of the present invention, in the converter refining process, bottom blowing of argon gas into the ladle is started before tapping, the pressure of the bottom-blown argon gas is controlled to 0.5 to 0.6 MPa, and the diameter of the bright ring (a stirring ring formed on the surface of the molten steel) is set to 250 to 400 mm. After 3 / 4 of the tapping has progressed, the pressure of the bottom-blown argon gas in the ladle is adjusted to 0.4 to 0.5 MPa, and the diameter of the bright ring is controlled to 200 to 350 mm.

[0014] As a further improvement of one embodiment of the present invention, in the LF refining process, the flow rate of the ladle bottom-blown argon gas is 40-80 NL / min during the refining waiting period, the flow rate of the ladle bottom-blown argon gas is 200-600 NL / min when adding the refining protection slag and alloy, and the flow rate of the ladle bottom-blown argon gas during the heating period after the addition of the alloy is 200-400 NL / min.

[0015] The chemical composition of the aforementioned refining protection slag is, by mass percentage, 45-50% CaO, 30-40% Al2O3, with a CaO / Al2O3 ratio of 1.7-1.8, 4-8% MgO, and 4-7% SiO2.

[0016] As a further improvement of one embodiment of the present invention, in the RH refining process, after the molten steel circulation, the remaining 2 / 3 of the aluminum ingot is first added to perform alloying, and after the alloying is completed, vacuum treatment is started, with a vacuum degree of ≤67 Pa and a vacuum treatment time of ≥20 min, with O ≤18 ppm and H ≤1.5 ppm in the molten steel, and after the vacuum treatment is completed, soft stirring is performed with argon gas blown from the bottom of the ladle, and silicon calcium core wire is added to perform inclusion modification treatment, with a soft stirring time of ≥20 min and a silicon calcium core wire feeding speed of 120 to 150 m / min.

[0017] As a further improvement of one embodiment of the present invention, in the continuous casting process, the continuous casting uses a ladle long nozzle, an immersion nozzle, and a tundish (intermediate ladle or intermediate container) covered with pre-melted hollow particle coating and carbonized rice husks, employs an argon seal for full protective pouring, sets the depth of the immersion nozzle to 200-300 mm, sets the back pressure of the argon seal to ≥ 0.05 Bar, the carbonized rice husks cover the outer layer of the pre-melted hollow particle coating, and the weight ratio of the pre-melted hollow particle coating to the carbonized rice husks is 1:3.

[0018] To achieve the objective of the above invention, one embodiment of the present invention further provides a wire rod for corrosion-resistant fatigue spring steel wire, the chemical composition of the wire rod being, by mass percentage, C: 0.2~0.7%, Si: 0.8~1.6%, Mn: 0.5~1.7%, Al: 0.35~0.85%, Nb: 0.1~0.5%, Cr: 0.5~1.0%, Mo: 0.1~0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities.

[0019] As a further improvement of one embodiment of the present invention, the wire rod for corrosion-resistant fatigue spring steel wire is manufactured by the method for manufacturing the wire rod for corrosion-resistant fatigue spring steel wire described above.

[0020] To achieve the above-mentioned objective of the invention, one embodiment of the present invention further provides a corrosion-resistant fatigue spring steel wire, the chemical composition of which the steel wire comprises, by mass percentage, C: 0.2-0.7%, Si: 0.8-1.6%, Mn: 0.5-1.7%, Al: 0.35-0.85%, Nb: 0.1-0.5%, Cr: 0.5-1.0%, Mo: 0.1-0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities.

[0021] As a further improvement of one embodiment of the present invention, the corrosion-resistant fatigue spring steel wire is manufactured by sequentially performing pickling, drawing, and heat treatment processes using the above-described corrosion-resistant fatigue spring steel wire as the base material. [Effects of the Invention]

[0022] Compared to conventional technology, the beneficial effects of the present invention include the following: (1) In the chemical composition design of the present invention, by adding a certain amount of Al, it is possible not only to reduce the density of wire rods and spring steel wires, but also to achieve weight reduction and improve corrosion resistance. By combining the addition and content control of other elements, particularly Nb, austenite grain coarsening during the heating process is prevented, and the effects of fine grain strengthening and improved elasticity reduction performance are achieved, solving the problems of grain coarsening, increased inclusions, and difficulty in improving strength caused by Al addition. Furthermore, by combining it with the control of Si, the elasticity reduction performance and corrosion resistance performance of spring steel wires can be improved, and Cr, as an important corrosion-resistant element, can form a passivation film on the surface of spring steel wires, effectively prevent oxidation, and improve the corrosion resistance of the base material, and furthermore, by cooperating with the element Mo, the pitting corrosion resistance can be improved. As a solid solution strengthening element, Mn can improve the hardenability of spring steel wire. Furthermore, because of the relatively strong bonding force between Mn, S, and O, it not only deoxidizes but also forms MnS compounds, reducing the probability of S and Fe bonding to form FeS, thereby mitigating or eliminating the effects of thermal brittleness caused by S. Overall, this chemical composition design improves the toughness, corrosion resistance, and elastic fatigue resistance (resistance to sagging) of wire rods and spring steel wires, allows for lighter spring steel wires, and is applicable to harsh, humid northern environments. It also possesses excellent corrosion resistance and fatigue performance even under road conditions with salt-spreading for snow melting in winter, extending the service life of spring steel wires and improving their safety during use.

[0023] (2) Based on the chemical composition design of the present invention, by combining with the control of the manufacturing process flow, not only the cleanliness and surface quality of the wire rod are improved, but also the structure of the wire rod is refined, and finally the manufactured wire rod can have high strength and high corrosion fatigue resistance performance. Among them, the wire rod is a two-phase structure of pearlite and ferrite, and the volume ratio of pearlite ≥ 95%, the tensile strength is 1000 - 1200 MPa, the cross-sectional shrinkage rate ≥ 45%, and the elongation after fracture ≥ 14%. Moreover, when further drawing to produce spring steel wire, not only can the wire breakage rate be effectively reduced, but it also lays a foundation for further drawing and manufacturing spring steel wire with high strength and high corrosion fatigue resistance performance, which is beneficial to extending the service life of the spring steel wire and improving its use safety.

[0024] (3) The spring steel wire further drawn and manufactured with the aforementioned wire rod as the base material has both high strength and excellent plasticity, the tensile strength > 2000 MPa, and the cross-sectional shrinkage rate ≥ 40%, and can meet the high requirements simultaneously put forward by the strength and toughness of the supply spring steel wire for the large-load automobile suspension system. Furthermore, the bending fatigue life of the obtained spring steel wire exceeds 260,000 cycles, and the corrosion fatigue life during the salt spray experiment exceeds 18,000 cycles, which can be applied to the harsh, humid northern environment and also has excellent corrosion fatigue resistance performance under the road environment of salt spreading for snow melting in winter.

Embodiments for Carrying out the Invention

[0025] Hereinafter, the technical solution of the present invention will be further introduced in combination with specific embodiments, but the scope of the claimed protection is not limited to the described explanation.

[0026] This embodiment provides a manufacturing method for a wire rod for corrosion fatigue resistant spring steel wire and a wire rod for corrosion fatigue resistant spring steel wire manufactured by the aforementioned manufacturing method.

[0027] Specifically, the chemical composition of the wire rod for corrosion-resistant fatigue spring steel wire, in mass percentage, includes C: 0.2 - 0.7%, Si: 0.8 - 1.6%, Mn: 0.5 - 1.7%, Al: 0.35 - 0.85%, Nb: 0.1 - 0.5%, Cr: 0.5 - 1.0%, Mo: 0.1 - 0.4%, P ≤ 0.02%, S ≤ 0.02%, with the balance being Fe and unavoidable impurities.

[0028] One embodiment of the present invention further provides a corrosion-resistant fatigue spring steel wire, which is manufactured using the above wire rod for corrosion-resistant fatigue spring steel wire as the base material and has the same chemical composition as the wire rod for corrosion-resistant fatigue spring steel wire.

[0029] In the chemical composition design of the present invention, by adding a certain content of Al, not only can the density of the wire rod and the spring steel wire be reduced, weight reduction be achieved, but the corrosion resistance performance can also be improved. By combining with the addition and content control of other elements, especially Nb, the coarsening of austenite grain size during the heating process can be prevented, the effects of fine grain strengthening and improvement of anti-elastic relaxation performance can be exerted, and the problems of grain coarsening, increase in inclusions, and difficulty in improving strength caused by the addition of Al can be solved. By combining with the control of Si, the anti-elastic relaxation performance and corrosion resistance performance of the spring steel wire can be improved. As an important corrosion-resistant element, Cr can form a passive film on the surface of the spring steel wire, effectively prevent oxidation, and improve the corrosion resistance ability of the base material. By cooperating with the Mo element, the pitting corrosion resistance ability can be improved. As a solid solution strengthening element, Mn can improve the hardenability of the spring steel wire. Moreover, since the binding force between Mn and S, O is relatively strong, not only can deoxidation be achieved, but MnS compounds can be formed, reducing the probability of S and Fe combining to form FeS, thereby reducing or eliminating the influence of hot brittleness caused by S. Generally speaking, this chemical composition design can improve the toughness, corrosion resistance performance, and anti-elastic relaxation performance of the wire rod and the spring steel wire, reduce the weight of the spring steel wire, and is applicable to the harsh, humid northern environment. It also has excellent corrosion-resistant fatigue performance even under the road environment of salt spreading for snow melting in winter, which is advantageous for extending the service life of the spring steel wire and improving its use safety.

[0030] Preferably, the chemical composition of the wire rod for corrosion-resistant fatigue spring steel wire is, by mass percentage, C: 0.2-0.7%, Si: 0.8-1.6%, Mn: 0.5-1.7%, Al: 0.35-0.85%, Nb: 0.1-0.5%, Cr: 0.5-1.0%, Mo: 0.1-0.4%, P ≤ 0.01%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities, and [Si] / [Al] = 1.5-3.5.

[0031] [Si] represents the mass percentage of Si, and [Al] represents the mass percentage of Al.

[0032] The [Si] / [Al] restriction allows the final manufactured spring wire to possess both corrosion resistance and elastic erosion resistance, resulting in a spring wire with excellent anti-relaxation properties and extremely good elastic deformation recovery capability.

[0033] The following describes in detail each step in the manufacturing method of the corrosion-resistant fatigue spring steel wire.

[0034] (1) Preliminary desulfurization process of molten iron The blast furnace molten iron was desulfurized using a KR desulfurization unit to achieve a slag content of ≤0.002% in the molten iron, with a slag removal rate of ≥97% and a molten iron temperature of ≥1350°C after desulfurization.

[0035] (2) Converter refining process The refining process involves sending a raw material composed of high-quality scrap steel, ferromolybdenum, and molten iron after pre-desulfurization into a converter. The weight ratio of pre-desulfurized molten iron to high-quality scrap steel is 7:1 to 8:1, and the temperature of the molten iron when it is sent to the converter is 1350 to 1450°C. By adding ferromolybdenum before starting converter refining, it is possible to avoid excessive alloy addition during the middle of the converter refining process, which would cause an excessive drop in the temperature of the molten steel, thus preventing an impact on the purity of the molten steel and the effectiveness of inclusion removal.

[0036] In this context, high-quality scrap steel refers to scrap steel with S ≤ 0.012% and P ≤ 0.015%. By using high-quality scrap steel, the residual element content in the molten steel can be effectively controlled, the amount of sulfur re-contaminating the molten steel can be reduced, the slag-steel reaction in the refining process can be effectively suppressed, the formation of large inclusions in the molten steel can be reduced, and the cleanliness of the molten steel can be improved.

[0037] Preferably, converter refining employs top-bottom composite blowing, constant-pressure lance control, and double slag operation, with C ≥ 0.15% and P ≤ 0.01% in the molten steel at the end of converter refining, and the tapping temperature ≥ 1650°C. The so-called double slag operation is the process of removing slag in two separate stages.

[0038] Preferably, ensure that there are no floating slag lumps in the ladle before tapping, and keep the cold slag steel at the bottom of the ladle <0.5 tons to ensure smooth bottom blowing. Before tapping, ferromanganese, ferrosilicon, ferrochrome, lime, and 1 / 3 aluminum ingots are laid at the bottom of the ladle to promote deoxidation alloying during the converter tapping process. Here, only 1 / 3 of the total aluminum ingots are laid, and the remaining 2 / 3 of the aluminum ingots are added in the RH refining process.

[0039] Preferably, bottom blowing of argon gas into the ladle is started before tapping in the converter, and the pressure of the bottom-blown argon gas is controlled to 0.5 to 0.6 MPa to stir the molten steel surface, resulting in a clear ring diameter of 250 to 400 mm. After 3 / 4 of the tapping has progressed, the pressure of the bottom-blown argon gas in the ladle is adjusted to 0.4 to 0.5 MPa, and the clear ring diameter is controlled to 200 to 350 mm.

[0040] (3) LF refining process After converter refining, the molten steel is sent to an LF furnace for further refining. Upon arrival in the ladle, it is connected to a bottom-blowing argon system to begin bottom-blowing of argon gas. Refining protection slag is added to the ladle, followed by the addition of the alloy to adjust the chemical composition and inclusions. The molten steel temperature, which has dropped after the addition of the alloy, is restored by electric heating. Temperature monitoring, sampling inspections, diffusion deoxidation, and heating are continuously performed throughout the process. The steel is tapped only after the molten steel composition, furnace slag composition, and molten steel temperature have all reached the required standards. The alloy contains metallic manganese, ferrosilicon, and ferrochrome.

[0041] Preferably, during the smelting waiting period, the flow rate of the ladle bottom-blown argon gas is set to 40-80 NL / min to agitate the slag surface, and during the addition of smelting protection slag and alloy, the flow rate of the ladle bottom-blown argon gas is set to 200-600 NL / min. Furthermore, during heating after alloy addition, the flow rate of the ladle bottom-blown argon gas during the heating period is set to 200-400 NL / min. Specifically, the bottom-blown argon gas during the smelting process can be controlled according to an automatic injection model.

[0042] Preferably, aluminum granules and carbide are used to deoxidize the slag surface, reducing the oxygen content in the molten steel, and lime is added to adjust the slag in a timely manner to whiten the furnace slag, controlling the white slag time to ≥ 15 min.

[0043] The chemical composition of the refining protection slag is, by mass percentage, 45-50% CaO, 30-40% Al2O3, with a CaO / Al2O3 ratio of 1.7-1.8, MgO 4-8%, and SiO2 4-7%. The refining protection slag has good fluidity and adsorption capacity for non-metallic inclusions, effectively controlling the type and content of inclusions, improving the purity of the molten steel, and ultimately improving the fatigue resistance of the wire rods and spring steel wires produced.

[0044] (4) RH refining process The molten steel is sent into an RH vacuum furnace for vacuum refining to further remove inclusions. Specifically, after the molten steel is circulated, the remaining 2 / 3 of the aluminum ingot is first added to perform alloying. After alloying is complete, vacuum treatment is started, with a vacuum level of ≤67 Pa and a vacuum treatment time of ≥20 min to further reduce the oxygen content in the molten steel, to O ≤18 ppm and H ≤1.5 ppm. After the vacuum treatment is completed, soft stirring is performed using argon gas blown from the bottom of the ladle, and silicon calcium core wire is added to perform inclusion modification treatment. The soft stirring time is ≥20 min, and the silicon calcium core wire feeding speed is 120-150 m / min to promote the floating of nonmetallic inclusions and improve the purity of the molten steel.

[0045] The chemical composition of the silicon calcium core wire is as follows, by mass percentage: SiO2: 48-55%, CaO: 40-50%, Al2O3: 3-5%, and MgO: 1-2%. The cutting temperature is 1575-1585°C.

[0046] (5) Continuous casting process A continuous casting machine is used to cast the molten steel extracted in the RH refining process into continuous casting slabs. The crystallizer liquid surface is protected by using a protective slag specifically for high-Al steel, and the chemical composition of the said protective slag specifically for high-Al steel is, by mass percentage, CaO + Al2O3 = 50-60%, and CaO / Al2O3 = 1.4-1.5, Na2O: 15-20%, MgO: 5-12%, K2O: 3-6%, Li2O: 2-5%, BaO: 1-2%, SiO2: 0.8-1.1%, and CaF2: 4-9%.

[0047] Preferably, continuous casting uses a ladle long nozzle, an immersion nozzle, and a tundish coated with pre-molten hollow particle coating agent and carbonized rice husks, employing an argon seal for full protective pouring, with the immersion nozzle depth set to 200-300 mm and the argon seal back pressure ≥ 0.05 Bar. Specifically, the tundish is coated with granular pre-molten hollow particle coating agent, and then the outer layer of the pre-molten hollow particle coating agent is coated with the carbonized rice husks. The weight ratio of the pre-molten hollow particle coating agent to the carbonized rice husks is 1:3.

[0048] Preferably, the chemical composition of the pre-melted hollow particle coating agent includes, by mass percentage, CaO: 30-35%, Al2O3: 10-15%, SiO2: 40-45%, Fe2O3: 2-4%, and MgO: 1-10%.

[0049] Preferably, the tundish is heated to 38-45°C, the nitrogen increase during the continuous casting process is ≤0.0002%, the liquid level fluctuation in the crystallizer is <2mm, the surface temperature of the continuously cast slab in the straightening stage is ≥920°C, and after the completion of continuous casting, the continuously cast slab is sent to a heat-insulating pit to cool slowly to below 200°C before being removed from the pit, with a slow cooling time of ≥36h.

[0050] Preferably, the cross-sectional dimensions of the continuously cast slab are 300 mm × 390 mm.

[0051] (6) Blooming process The continuously cast slabs are heated in a bloc-splitting furnace and then rolled into intermediate steel billets with a cross-section of 150 mm x 150 mm. The heating temperature is 1160-1190°C, the furnace time is 170-190 min, and the rolling start temperature for the bloc is 1040-1070°C. After bloc-splitting, all billets undergo manual polishing and fluorescent testing to guarantee and inspect the surface quality of the intermediate steel billets, ensuring that there are no quality problems on the slab surface.

[0052] (7) Flaw detection polishing process All intermediate steel billets obtained in the bloc splitting process are subjected to surface polishing, and the surface quality of the intermediate steel billets is inspected by fluorescence inspection. Polishing is performed based on the inspection results until there are no surface defects or decarburized layers on the surface of the intermediate steel billets, which is advantageous for controlling the surface quality during the subsequent rolling process.

[0053] (8) High-speed wire rolling process The intermediate steel billet is heated in a heating furnace, then scale is removed using high-pressure water, and subsequently the intermediate steel billet is rolled into wire rods with a diameter of 5 to 17 mm by high-speed continuous wire rolling.

[0054] The heating process includes a first heating stage, a second heating stage, and a soaking stage. The heating temperature for the first heating stage is 780-820°C with a heating time of ≤30 min, the heating temperature for the second heating stage is 900-950°C with a heating time of ≤30 min, and the heating temperature for the soaking stage is 1030-1070°C with a heating time of ≤60 min. By controlling the heating temperature and heating time in stages, the formation of oxide scale that is difficult to remove from the wire surface is avoided, the difficulty of scale removal is reduced, the scale removal efficiency is improved, the scale removal effect is enhanced, and the impact on the fatigue life of the final manufactured spring steel wire is avoided.

[0055] The high-speed wire rod continuous rolling process includes sequentially performed rough rolling, intermediate rolling, pre-finish rolling, finish rolling, and discharge. The rolling start temperature for rough rolling is 890-910°C, the rolling start temperature for finish rolling is 860-890°C, the rolling end temperature for finish rolling is ≤960°C, and the discharge temperature is 860-880°C.

[0056] Preferably, the air-fuel ratio of the heating furnace is ≤0.55 and the scale removal water pressure is ≥15 MPa.

[0057] (9) Controlled cooling process A Stermore air cooling line is used for controlled cooling of the wire. During periods when the wire end temperature is between 810 and 860°C, the first to fifth fans on the Stermore cooling line are operated with their airflow controlled to 65-75%, the roller table speed is set to 0.50-0.65 m / s, and the cooling rate is set to 4.5-5.5°C / s. During periods when the wire end temperature is between 690 and 810°C, the sixth to eighth fans on the Stermore cooling line are operated with their airflow controlled to 50-60%, the roller table speed is set to 0.2-0.3 m / s, and the cooling rate is set to 1.5-2°C / s. In other words, the controlled cooling process controls the number of fans to start, their position, the roller table speed, and the cooling rate according to the difference in wire end temperature.

[0058] In general, by combining the chemical composition design of the present invention with the control of the aforementioned manufacturing process flow, it is possible not only to improve the cleanliness and surface quality of the wire but also to refine the structure of the wire, ultimately enabling the manufactured wire to have high strength and high corrosion-resistant fatigue performance. The wire has a two-phase structure of pearlite and ferrite, with a volume fraction of pearlite of ≥95%, a tensile strength of 1000-1200 MPa, a cross-sectional shrinkage rate of ≥45%, and an elongation rate after break of ≥14%. Furthermore, it is advantageous not only in that it can effectively reduce the rate of wire breakage when drawing to manufacture spring steel wire, but also in that it lays the foundation for further drawing and manufacturing spring steel wire with high strength and high corrosion-resistant fatigue performance, extending the service life of the spring steel wire and improving its safety in use.

[0059] Specifically, the wire material is further manufactured into spring steel wire by sequentially performing pickling, wire drawing, and heat treatment processes.

[0060] (10) Pickling process The wire is pickled in a 20% hydrochloric acid solution at 20-30°C for 15-25 minutes, then rinsed with clean water and immersed in a phosphorylation solution for phosphorylation treatment. The unit area film layer mass of the phosphorylation film is 10 g / m². 2 The wire is then washed with water after phosphorylation treatment, saponified using soapy water, and then allowed to air dry naturally.

[0061] (11) Wire drawing process After pickling, the wire is cold-drawn using molds of different diameters to produce spring steel wire with a diameter of 3.5 to 15 mm. The pass reduction ratio during drawing is >10%.

[0062] (12) Heat treatment process In a production line equipped with online induction heating, the spring steel wire obtained in the wire drawing process is sequentially quenched and tempered. The quenching temperature is Ar3 + 20°C to Ar3 + 50°C, where Ar3 is the austenitization temperature of the wire. In this embodiment, the quenching temperature is 915 to 945°C and the tempering temperature is 390 to 400°C.

[0063] Using the aforementioned wire material as a base, a heat treatment process can be used to form fine crystalline grains in the spring steel wire, resulting in a combination of high strength and excellent plasticity. The resulting spring steel wire has a tensile strength >2000 MPa and a cross-sectional shrinkage rate ≥40%, satisfying the high demands on strength and toughness that heavy-load automotive suspension systems simultaneously place on the spring steel wire used. Furthermore, the resulting spring steel wire has a bending fatigue life exceeding 260,000 cycles and a corrosion fatigue life exceeding 18,000 cycles in salt spray tests, making it applicable to extremely cold and humid northern environments and demonstrating excellent corrosion fatigue resistance even in winter road conditions with salt-spreading snowmelt.

[0064] The following 13 examples further illustrate specific embodiments of the present invention. Of course, these 13 examples represent only a portion, not all, of the numerous variations included in this embodiment. Other embodiments built upon the aforementioned embodiments do not depart from the technical spirit of the present invention.

[0065] Specifically, all 13 examples provide wire rods and spring wires for corrosion-resistant fatigue spring steel wire, their chemical composition as shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0066] [Table 1]

[0067] The wire rod manufacturing method for each embodiment employs a method that includes sequentially performed processes such as molten iron pre-desulfurization, converter refining, LF refining, RH refining, continuous casting, splitting, flaw detection and polishing, high-speed wire rod rolling, and controlled cooling. For specific operations of each process, please refer to the preceding text, as there is no repetition here.

[0068] For the wires of Examples 1 to 13, sampling was performed using the same test method, followed by microstructural and mechanical performance testing. The specific test methods and results are as follows: (1) In terms of microstructure, 10 samples were taken from the tip, middle, and trailing end of the wire, for a total of 30 samples. Metallographic samples were prepared, and after mechanical polishing and nitrate alcohol etching, the microstructure was observed under a metallographic microscope. The interlayer distance of the pearlite in a single sample was measured under 10,000x magnification, and the average value of the interlayer distance of the pearlite in the 30 samples was calculated as the interlayer distance of the pearlite in the wire of each example. The microstructure of the wires in Examples 1 to 13 was measured to be a two-phase structure of pearlite and ferrite, and the percentage of pearlite and the interlayer distance of the pearlite are shown in Table 2.

[0069] (2) In terms of mechanical performance, the mechanical performance tests of the wire rods were performed using a tensile testing machine, referring to the standard test methods and definitions for mechanical performance testing of ASTM A370 steel products. The tensile strength, sectional shrinkage rate, and elongation after fracture of the wire rods of Examples 1 to 13 were measured as shown in Table 2.

[0070] [Table 2]

[0071] Furthermore, the wires from Examples 1 to 13 were further drawn and manufactured into spring steel wires using the aforementioned sequential pickling, wire drawing, and heat treatment processes. For specific details of each process, please refer to the preceding text, as there is no repetition here.

[0072] Mechanical performance tests, fatigue life tests, and corrosion resistance fatigue life tests were performed on the obtained spring steel wires, and the specific test methods and test results are as follows. (1) In terms of mechanical performance, the mechanical performance tests of spring steel wires were performed using a tensile testing machine, referring to the standard test methods and definitions for mechanical performance testing of ASTM A370 steel products. The tensile strength and sectional shrinkage rate of the spring steel wires of Examples 1 to 13 were measured as shown in Table 3.

[0073] (2) In terms of fatigue life and corrosion resistance fatigue life, rotational bending fatigue tests were performed on 4 mm diameter spring steel wire samples with reference to KS B ISO 1143, and the fatigue lives of the spring steel wires of Examples 1 to 13 were measured as shown in Table 3. With reference to KS D 9502 ISO 3768 / 7263, a salt spray test was adopted, and the corrosion resistance fatigue life of the spring steel wires of Examples 1 to 13 under a salt spray environment was measured as shown in Table 3.

[0074] [Table 3]

[0075] From the above, it can be seen that the wires of Examples 1 to 13 manufactured according to this embodiment have a two-phase structure of pearlite and ferrite, with a volume fraction of pearlite ≥ 95%, a tensile strength of 1000 to 1200 MPa, a sectional shrinkage rate ≥ 45%, and an elongation rate after fracture ≥ 14%. The spring steel wires of Examples 1 to 13 manufactured according to this embodiment have a tensile strength > 2000 MPa and a sectional shrinkage rate ≥ 40%, possessing excellent toughness and being able to satisfy the high requirements for strength and toughness simultaneously imposed by heavy-load automobile suspension systems on spring steel wires used in service. Furthermore, the bending fatigue life of the obtained spring steel wires exceeds 260,000 cycles, and the corrosion fatigue life in salt spray tests exceeds 18,000 cycles, making them applicable to extremely cold and humid northern environments and possessing excellent corrosion fatigue resistance even in road environments with salt-spreading for snow melting in winter.

[0076] The above descriptions represent only relatively preferred specific embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by an expert skilled in the art within the disclosed technical scope of the present invention, based on the technical solutions and inventive concepts of the present invention, should all be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing wire, The chemical composition of the aforementioned wire is, by mass percentage, C: 0.2-0.7%, Si: 0.8-1.6%, Mn: 0.5-1.7%, Al: 0.35-0.85%, Nb: 0.1-0.5%, Cr: 0.5-1.0%, Mo: 0.1-0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities. The above manufacturing method includes a sequentially performed molten iron pre-desulfurization process, converter refining process, LF refining process, RH refining process, continuous casting process, mass separation process, flaw detection and polishing process, high-speed wire rolling process, and controlled cooling process. In the converter refining process, the refining raw materials, consisting of high-quality waste steel, ferromolybdenum, and molten iron after pre-desulfurization, are sent into the converter for refining. Here, the weight ratio of molten iron after pre-desulfurization to high-quality waste steel is 7:1 to 8:1, and the temperature of the molten iron when sent to the converter is 1350 to 1450°C. In the continuous casting process, the molten metal surface in the mold is protected by pouring with a special protective slag for high-Al steel. The chemical composition of the special protective slag for high-Al steel is, by mass percentage, CaO + Al ２ O ３ = 50 - 60%, and CaO / Al ２ O ３ = 1.4 - 1.5, Na ２ O: 15 - 20%, MgO: 5 - 12%, K ２ O: 3 - 6%, Li ２ O: 2 - 5%, BaO: 1 - 2%, SiO ２ : 0.8 - 1.1%, CaF ２ : 4 - 9% included, In the high-speed wire rolling process, the intermediate steel billet is heated in a heating furnace, scale is removed using high-pressure water, and then it is rolled into a wire by a high-speed continuous wire rolling process, where the heating process includes a first heating stage, a second heating stage, and a soaking stage, the heating temperature of the first heating stage is 780 to 820°C and the heating time is ≤ 30 min, the heating temperature of the second heating stage is 900 to 950°C and the heating time is ≤ 30 min, the heating temperature of the soaking stage is 1030 to 1070°C and the heating time is ≤ 60 min, and the high-speed continuous wire rolling process includes sequentially performed rough rolling, intermediate rolling, pre-finishing rolling, finish rolling, and discharge, the rolling start temperature for rough rolling is 890 to 910°C, the rolling start temperature for finish rolling is 860 to 890°C, the rolling end temperature for finish rolling is ≤ 960°C, and the discharge temperature is 860 to 880°C. In the controlled cooling process, a Stermore air cooling line is used to control the cooling of the wire. During the period when the temperature of the wire end is 810 to 860°C, the first to fifth fans on the Stermore cooling line are operated with their airflow controlled to 65 to 75%, the roller table speed is set to 0.50 to 0.65 m / s, and the cooling rate is set to 4.5 to 5.5°C / s. During the period when the temperature of the wire end is 690 to 810°C, the sixth to eighth fans on the Stermore cooling line are operated with their airflow controlled to 50 to 60%, the roller table speed is set to 0.2 to 0.3 m / s, and the cooling rate is set to 1.5 to 2°C / s. A method for manufacturing wire.

2. The chemical composition of the aforementioned wire is, by mass percentage, C: 0.2–0.7%, Si: 0.8–1.6%, Mn: 0.5–1.7%, Al: 0.35–0.85%, Nb: 0.1–0.5%, Cr: 0.5–1.0%, Mo: 0.1–0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities, and the ratio of [Si] / [Al] = 1.5–3.

5. The method for manufacturing a wire according to claim 1.

3. In the aforementioned molten iron preliminary desulfurization process, the blast furnace molten iron is desulfurized in a KR desulfurization unit to achieve a slag content of ≤0.002% in the molten iron, the slag removal rate during desulfurization is ≥97%, and the molten iron temperature after desulfurization is ≥1350°C. The method for manufacturing a wire according to claim 1.

4. In the converter refining process, the converter refining employs upper-bottom composite blowing, constant-pressure lance control, and double slag operation. At the end of the converter refining process, the molten steel contains C ≥ 0.15% and P ≤ 0.01%, the tapping temperature is ≥ 1650°C, there are no floating slag lumps in the ladle before tapping, the cold slag steel at the bottom of the ladle is < 0.5 tons, and ferromanganese, ferrosilicon, ferrochrome, lime, and 1 / 3 aluminum lumps are laid at the bottom of the ladle before tapping. The method for manufacturing a wire according to claim 1.

5. In the converter refining process, bottom blowing of argon gas into the ladle is started before tapping, the pressure of the bottom-blown argon gas is controlled to 0.5 to 0.6 MPa, and the diameter of the molten ring is set to 250 to 400 mm. After 3 / 4 of the tapping has progressed, the pressure of the bottom-blown argon gas in the ladle is adjusted to 0.4 to 0.5 MPa, and the diameter of the molten ring is controlled to 200 to 350 mm. The method for manufacturing a wire according to claim 1.

6. In the LF refining process, during the refining waiting period, the flow rate of the ladle-bottom-blown argon gas is 40 to 80 NL / min; during the addition of refining protection slag and alloy, the flow rate of the ladle-bottom-blown argon gas is 200 to 600 NL / min; and during heating after alloy addition, the flow rate of the ladle-bottom-blown argon gas during the heating period is 200 to 400 NL / min. The chemical composition of the aforementioned smelting protective slag is, by mass percentage, CaO: 45-50%, Al ２ O ３ : Contains 30-40% and CaO / Al ２ O ３ =1.7-1.8, MgO: 4-8%, SiO ２ : 4-7% The method for manufacturing a wire according to claim 1.

7. In the RH refining process, after molten steel circulation, the remaining 2 / 3 of the aluminum ingot is first added to perform alloying, and after alloying is complete, vacuum treatment is started, with a vacuum level of ≤67 Pa and a vacuum treatment time of ≥20 min, and the O ≤18 ppm and H ≤1.5 ppm in the molten steel, and after the vacuum treatment is completed, soft stirring is performed with argon gas blown from the bottom of the ladle, and silicon calcium core wire is added to perform inclusion modification treatment, with a soft stirring time of ≥20 min and a silicon calcium core wire feeding speed of 120 to 150 m / min. The method for manufacturing a wire according to claim 4.

8. In the continuous casting process described above, the continuous casting uses a ladle long nozzle, an immersion nozzle, and a tundish coated with pre-molten hollow particle coating and carbonized rice husks. Full protective pouring is performed using an argon seal, the depth of the immersion nozzle is set to 200-300 mm, the back pressure of the argon seal is set to ≥ 0.05 Bar, the carbonized rice husks are coated on the outer layer of the pre-molten hollow particle coating, and the weight ratio of the pre-molten hollow particle coating to the carbonized rice husks is 1:

3. The method for manufacturing a wire according to claim 1.

9. It is a wire, The chemical composition of the aforementioned wire is, by mass percentage, C: 0.2–0.7%, Si: 0.8–1.6%, Mn: 0.5–1.7%, Al: 0.35–0.85%, Nb: 0.1–0.5%, Cr: 0.5–1.0%, Mo: 0.1–0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities. wire rod.

10. It is a steel wire, The chemical composition of the steel wire is, by mass percentage, C: 0.2–0.7%, Si: 0.8–1.6%, Mn: 0.5–1.7%, Al: 0.35–0.85%, Nb: 0.1–0.5%, Cr: 0.5–1.0%, Mo: 0.1–0.4%, P ≤ 0.02%, S ≤ 0.02%, with the remainder being Fe and unavoidable impurities. Steel wire.

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