Corrosion fatigue-resistant spring steel wire, and wire rod and production method therefor

Abstract

The present invention discloses a corrosion-fatigue resistant spring steel wire, wire rod and production method thereof. The chemical composition of the wire rod and steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

Description

[0001] The present application is based on and claims priority to Chinese Patent Application Number CN202311085007.3 filed on August 28, 2023, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

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

[0003] As safety-bearing components, Springs were widely applied in the fields of automobiles, machinery, railways, etc., and often undertook high-cycle alternating loads during service. With technological progress and improved manufacturing levels, new energy vehicles gradually emerged, and their sales gradually climbed in the automotive industry. However, new energy vehicles had larger weights, which imposed strict requirements on spring steel wires applied to suspension springs, not only requiring high strength to enhance the load capacity of vehicles, but also needing to develop toward lightweight to reduce energy consumption during vehicle operation and improve cruising ability.

[0004] However, current spring steels had poor corrosion resistance. When applied in the humid environment of northern regions, since northern regions had thick snow accumulation in winter and usually adopted salt spreading for snow melting to clear roads, roads contained large amounts of chloride ions, which easily produced corrosion pits on the surface of spring steel, formed stress concentration, and reduced the fatigue strength of spring steel. Moreover, hydrogen entry during the corrosion process would cause hydrogen-induced delayed cracking, causing components to suddenly fracture under conditions far below allowable cycles or loads, seriously affecting the service life of components and creating huge safety hazards for the safe operation of automobiles and railways. Therefore, it was necessary to develop spring steel wires that simultaneously possessed high strength, lightweight, and excellent corrosion resistance to meet the application requirements of new energy vehicles in northern environments.SUMMARY

[0005] An object of the present application is to provide a wire rod for corrosion-fatigue resistant spring steel wire and a production method thereof, and also relates to a corrosion-fatigue resistant spring steel wire.

[0006] To achieve the above object, one embodiment of the present invention provides a production method of a wire rod for corrosion-fatigue resistant spring steel wire, wherein the chemical composition of the wire rod comprising in percent by mass: 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%, and the balance is Fe and unavoidable impurities; the production method comprises hot metal pre-desulfurization process, converter smelting process, Ladle Furnace refining process, RH Vacuum degassing refining process, continuous casting process, cogging process, flaw detection and grinding process, high-speed wire rod rolling process, and controlled cooling process performed sequentially; wherein, in the converter smelting process, smelting raw materials composed of high-quality scrap steel, ferromolybdenum, and hot metal after pre-desulfurization are fed into a converter for smelting, wherein the weight ratio of the hot metal after pre-desulfurization to high-quality scrap steel is 7:1~8:1, and the temperature of the hot metal when fed into the converter is 1350~1450°C; in the continuous casting process, the mold liquid level adopts protective slag specially for high-Al steel for protected casting, wherein the chemical composition of the protective slag specially for high-Al steel comprises in percent by mass: 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%; in the high-speed wire rod rolling process, intermediate billets are heated in a heating furnace and then subjected to high-pressure water descaling, after which high-speed wire rod continuous rolling is performed to roll into wire rod, the heating process comprises first heating zone, secondary heating zone and soaking zone, the heating temperature of first heating zone is 780~820°C, and the heating time is ≤30 min; the heating temperature of secondary heating zone is 900~950°C, and the heating time is ≤30 min; the heating temperature of soaking zone is 1030~1070°C, and the heating time is ≤60 min; the high-speed wire rod continuous rolling process comprises rough rolling, intermediate rolling, pre-finish rolling, finish rolling and laying head performed sequentially, the rolling start temperature of rough rolling is 890~910°C, the rolling start temperature of finish rolling is 860~890°C, the rolling finish temperature of finish rolling is ≤960°C, and the laying head temperature is 860~880°C; in the controlled cooling process, a Stelmor air cooling line is adopted to perform controlled cooling on the wire rod, when the temperature of the wire rod edge is 810~860°C, fans from No.1 to No.5 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 65~75% of the maximum air volume, the roller table speed is 0.50~0.65 m / s, and the cooling rate is 4.5~5.5°C / s; when the temperature of the wire rod edge is 690~810°C, fans from No.6 to No.8 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 50~60% of the maximum air volume, the roller table speed is 0.2~0.3 m / s, and the cooling rate is 1.5~2°C / s.

[0007] As a further improvement of one embodiment of the present invention, the chemical composition of the wire rod comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities; wherein [Si] / [Al]=1.5~3.5.

[0008] As a further improvement of one embodiment of the present invention, in the hot metal pre-desulfurization process, blast furnace hot metal is desulfurized in KR desulfurization equipment until S≤0.002% in the hot metal, the slag removal rate of desulfurization is ≥97%, and the temperature of the hot metal after desulfurization is ≥1350°C.

[0009] As a further improvement of one embodiment of the present invention, in the converter smelting process, the converter smelting adopts top-bottom combined blowing, constant pressure variable lance, and double slag operation, content of C is ≥0.15% and content of P is ≤0.01% in the molten steel at the end point of converter smelting, and the tapping temperature is ≥1650°C; there are no floating slag debris 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 of aluminum blocks are laid at the bottom of the ladle before tapping.

[0010] As a further improvement of one embodiment of the present invention, in the converter smelting process, bottom argon blowing of the ladle is turned on before converter tapping, the pressure of bottom argon blowing is controlled at 0.5~0.6 MPa, the bright ring diameter is 250~400 mm, after 3 / 4 of the molten steel is tapped, the pressure of bottom argon blowing of the ladle is adjusted to 0.4~0.5 MPa, and the bright ring diameter is controlled at 200~350 mm.

[0011] As a further improvement of one embodiment of the present invention, in the Ladle Furnace refining process, during the waiting period for smelting, the flow rate of bottom argon blowing of the ladle is 40~80 NL / min; when adding refining protective slag and alloys, the flow rate of bottom argon blowing of the ladle is 200~600 NL / min; heating is performed after adding alloys, and during heating, the flow rate of bottom argon blowing of the ladle is 200~400 NL / min; the chemical composition of the refining protective slag comprises in percent by mass: CaO: 45~50%, Al 2 O 3 : 30~40%, and CaO / Al 2 O 3 =1.7~1.8, MgO: 4~8%, SiO 2 : 4~7%.

[0012] As a further improvement of one embodiment of the present invention, in the RH Vacuum degassing refining process, after molten steel circulation, the remaining 2 / 3 of aluminum blocks are first added for alloying, vacuum treatment is started after alloying is completed, the vacuum degree of vacuum treatment is ≤67 Pa, the vacuum treatment time is ≥20 min, so that the content of O is ≤18 ppm and the content of H is ≤1.5 ppm in the molten steel; after vacuum treatment is finished, bottom argon blowing of the ladle is performed for soft stirring, and silicon-calcium cored wire is added for inclusion modification treatment, the soft stirring time is ≥20 min, and the wire feeding speed of the silicon-calcium cored wire is 120~150 m / min.

[0013] As a further improvement of one embodiment of the present invention, in the continuous casting process, continuous casting adopts ladle long nozzle, submerged entry nozzle, tundish covered with pre-melted hollow particle covering agent and carbonized rice husk, and adopts argon sealing for fully protected casting, the depth of the submerged entry nozzle is 200~300 mm, the back pressure of argon sealing is ≥0.05 Bar, the carbonized rice husk covers the outer layer of the pre-melted hollow particle covering agent, and the weight ratio of the pre-melted hollow particle covering agent to carbonized rice husk is 1:3.

[0014] To achieve the above object, one embodiment of the present invention further provides a wire rod for corrosion-fatigue resistant spring steel wire, wherein the chemical composition of the wire rod comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0015] As a further improvement of one embodiment of the present invention, the wire rod for corrosion-fatigue resistant spring steel wire is prepared by the production method of the wire rod for corrosion-fatigue resistant spring steel wire as described above.

[0016] To achieve the above object, one embodiment of the present invention further provides a corrosion-fatigue resistant spring steel wire, wherein the chemical composition of the steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0017] As a further improvement of one embodiment of the present invention, the corrosion-fatigue resistant spring steel wire is prepared from the wire rod for corrosion-fatigue resistant spring steel wire as described above as base material through acid pickling, drawing, and heat treatment processes performed sequentially.

[0018] Compared with the prior art, the beneficial effects of the present invention include: (1) In the chemical composition design scheme of the present invention, by adding a certain content of Al, not only can the density of the wire rod and spring steel wire be reduced to make them lightweight, but also the corrosion resistance can be improved. Combined with the addition and content control of other elements, especially Nb, austenite grain coarsening during the heating process can be prevented, playing the role of fine grain strengthening and improving elastic decline resistance, solving the problems of grain coarsening, multiple inclusions, and difficulty in strength improvement caused by adding Al. Further combined with the control of Si, the elastic decline resistance and corrosion resistance of the spring steel wire can be improved. Cr, as an important corrosion-resistant element, can form a passivation film on the surface of the spring steel wire, effectively preventing oxidation and improving the corrosion resistance of the matrix, further can enhance pitting corrosion resistance cooperation with Mo element. Mn, as a solid solution strengthening element, can improve the hardenability of the spring steel wire, and Mn has strong binding force with S and O, not only can deoxidize, but also can form MnS compounds, reducing the probability of S combining with Fe to form FeS, thereby alleviating or eliminating the hot brittleness effect of S. Overall, through this chemical composition design scheme, the strength and toughness, corrosion resistance, and elastic decline resistance of the wire rod and spring steel wire can be improved, making the spring steel wire lightweight, and suitable for the severe cold and humid northern environment. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use. (2) Based on the chemical composition design scheme of the present invention, combined with the control of the production process flow, not only the cleanliness and surface quality of the wire rod are improved, and the structure of the wire rod is refined, but also the finally prepared wire rod has high strength and high corrosion fatigue resistance. The wire rod has a two-phase structure of pearlite and ferrite, and the volume fraction of pearlite is ≥95%, the tensile strength is 1000~1200 MPa, the reduction of area is ≥45%, and the elongation after fracture is ≥14%. This can not only effectively reduce the wire breakage rate when further drawing to prepare spring steel wire, but also lay the foundation for further drawing to prepare spring steel wire with high strength and high corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use. (3) The spring steel wire further prepared by drawing based on the aforementioned wire rod has both high strength and excellent plasticity, with tensile strength >2000 MPa and reduction of area ≥40%, which can meet the high requirements for both strength and toughness of spring steel wire in service simultaneously proposed by heavy-load automotive suspension systems. In addition, the obtained 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, and can be applied in severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance. DETAILED DESCRIPTION

[0019] The technical solution of the present application will be further introduced below in combination with specific embodiments, but the scope of protection is not limited to the description made.

[0020] The present embodiment provides a production method of a wire rod for corrosion-fatigue resistant spring steel wire, and a wire rod for corrosion-fatigue resistant spring steel wire prepared by the production method.

[0021] Specifically, the chemical composition of the wire rod for corrosion-fatigue resistant spring steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0022] One embodiment of the present invention further provides a corrosion-fatigue resistant spring steel wire, which is prepared from the above-mentioned wire rod for corrosion-fatigue resistant spring steel wire as base material and has the same chemical composition as the wire rod for corrosion-fatigue resistant spring steel wire.

[0023] 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 spring steel wire be reduced to make them lightweight, but also the corrosion resistance can be improved. Combined with the addition and content control of other elements, especially Nb, austenite grain coarsening during the heating process can be prevented, playing the role of fine grain strengthening and improving elastic decline resistance, solving the problems of grain coarsening, multiple inclusions, and difficulty in strength improvement caused by adding Al. Further combined with the control of Si, the elastic decline resistance and corrosion resistance of the spring steel wire can be improved. Cr, as an important corrosion-resistant element, can form a passivation film on the surface of the spring steel wire, effectively preventing oxidation and improving the corrosion resistance of the matrix, further can enhance pitting corrosion resistance cooperation with Mo element Mn, as a solid solution strengthening element, can improve the hardenability of the spring steel wire, and Mn has strong binding force with S and O, not only can deoxidize, but also can form MnS compounds, reducing the probability of S combining with Fe to form FeS, thereby alleviating or eliminating the hot brittleness effect of S. Overall, through this chemical composition design scheme, the strength and toughness, corrosion resistance, and elastic decline resistance of the wire rod and spring steel wire can be improved, making the spring steel wire lightweight, and suitable for severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use.

[0024] Preferably, the chemical composition of the wire rod for corrosion-fatigue resistant spring steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities; wherein [Si] / [Al]=1.5~3.5.

[0025] Wherein [Si] represents the mass percent of Si, and [Al] represents the mass percent of Al.

[0026] Through the limitation of [Si] / [Al], the finally prepared spring steel wire can have both corrosion resistance and elastic decline resistance, enabling the spring steel wire to have excellent relaxation resistance and extremely good elastic deformation recovery capability.

[0027] The specific processes in the production method of the wire rod for corrosion-fatigue resistant spring steel wire are introduced below.(1) Hot metal pre-desulfurization process

[0028] Blast furnace hot metal is desulfurized in KR desulfurization equipment until S≤0.002% in the hot metal, the slag removal rate of desulfurization is ≥97%, and the temperature of the hot metal after desulfurization is ≥1350°C.(2) Converter smelting process

[0029] Smelting raw materials composed of high-quality scrap steel, ferromolybdenum, and hot metal after pre-desulfurization are fed into a converter for smelting, wherein the weight ratio of the hot metal after pre-desulfurization to high-quality scrap steel is 7:1~8:1, and the temperature of the hot metal when fed into the converter is 1350~1450°C. By adding ferromolybdenum before the start of converter smelting, excessive addition of alloys during the middle stage of converter smelting that would cause excessive temperature drop of the molten steel can be avoided, so as not to affect the purity of the molten steel and the removal effect of inclusions.

[0030] The high-quality scrap steel here refers to waste steel with S≤0.012% and P≤0.015%. The use of high-quality scrap steel can effectively control the residual element content in the molten steel, reduce the sulfur return amount in the molten steel, effectively reduce slag-metal reactions in the refining process, reduce the generation of large-sized inclusions in the molten steel, and improve the cleanliness of the molten steel.

[0031] Preferably, the converter smelting adopts top-bottom combined blowing, constant pressure variable lance, and double slag operation, content of C is ≥0.15% and content of P is ≤0.01% in the molten steel at the end point of converter smelting, and the tapping temperature is ≥1650°C. The so-called double slag operation means slag removal twice.

[0032] Preferably, before tapping, it is ensured that there are no floating slag debris in the ladle, and the cold slag steel at the bottom of the ladle is <0.5 tons, to ensure smooth bottom blowing. Ferromanganese, ferrosilicon, ferrochrome, lime, and 1 / 3 of aluminum blocks are laid at the bottom of the ladle before tapping to facilitate deoxidation alloying during the converter tapping process. Here only 1 / 3 of the total aluminum blocks are laid, and the remaining 2 / 3 of the total aluminum blocks are added in the RH Vacuum degassing refining process.

[0033] Preferably, bottom argon blowing of the ladle is turned on before converter tapping, the pressure of bottom argon blowing is controlled at 0.5~0.6 MPa to make the molten steel surface agitated, the bright ring diameter is 250~400 mm, after 3 / 4 of the molten steel is tapped, the pressure of bottom argon blowing of the ladle is adjusted to 0.4~0.5 MPa, and the bright ring diameter is controlled at 200~350 mm.(3) Ladle Furnace refining process

[0034] The molten steel after converter smelting is sent to an ladle furnace for smelting. After the ladle arrives at the station, bottom argon blowing is connected and turned on, refining protective slag is added to the ladle, then alloys are added for chemical composition adjustment and inclusion control, and electric heating is applied to raise the temperature of the molten steel that has dropped after adding alloys. During this period, temperature measurement, sampling detection, diffusion deoxidation and heating are continuously performed until the molten steel composition, slag composition and molten steel temperature all meet the standards, then tapping is performed. The alloys include metallic manganese, ferrosilicon and ferrochrome.

[0035] Preferably, during the waiting period for smelting, the flow rate of bottom argon blowing of the ladle is 40~80 NL / min to make the slag surface fluctuate; when adding refining protective slag and alloys, the flow rate of bottom argon blowing of the ladle is 200~600 NL / min; in addition, heating is performed after adding alloys, and during heating, the flow rate of bottom argon blowing of the ladle is 200~400 NL / min. Specifically, the bottom argon blowing during the smelting process can be executed according to an automatic argon blowing model.

[0036] Preferably, aluminum granules and calcium carbide are used for slag surface deoxidation to reduce the oxygen content in the molten steel, and lime is added to adjust the slag to white in time, and the white slag time is controlled at ≥15 min.

[0037] The chemical composition of the refining protective slag comprises in percent by mass: CaO: 45~50%, Al 2 O 3 : 30~40%, and CaO / Al 2 O 3 =1.7~1.8, MgO: 4~8%, SiO 2 : 4~7%. The refining protective slag has good fluidity and the ability to adsorb non-metallic inclusions, can effectively control the types and contents of inclusions, and improve the purity of the molten steel, thereby improving the fatigue resistance of the finally prepared wire rod and spring steel wire.(4) RH Vacuum degassing refining process

[0038] The molten steel is sent to an RH vacuum furnace for vacuum refining to further remove inclusions in the molten steel. Specifically, after molten steel circulation, the remaining 2 / 3 of aluminum blocks are first added for alloying, vacuum treatment is started after alloying is completed, the vacuum degree of vacuum treatment is ≤67 Pa, the vacuum treatment time is ≥20 min to further reduce the oxygen content in the molten steel, so that the content of O is ≤18 ppm and the content of H is ≤1.5 ppm in the molten steel. After vacuum treatment is finished, bottom argon blowing of the ladle is performed for soft stirring, and silicon-calcium cored wire is added for inclusion modification treatment, the soft stirring time is ≥20 min, and the wire feeding speed of the silicon-calcium cored wire is 120~150 m / min to promote the floating of non-metallic inclusions and improve the purity of the molten steel.

[0039] The chemical composition of the silicon-calcium cored wire comprises in percent by mass: SiO 2 : 48~55%, CaO: 40~50%, Al 2 O 3 : 3~5%, MgO: 1~2%. The tapping temperature is 1575~1585°C.(5) Continuous casting process

[0040] A continuous casting machine is used to cast the molten steel from the RH Vacuum degassing refining process into continuous casting billets. The mold liquid level adopts protective slag specially for high-Al steel for protected casting. The chemical composition of the protective slag specially for high-Al steel comprises in percent by mass: 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%.

[0041] Preferably, continuous casting adopts ladle long nozzle, submerged entry nozzle, tundish covered with pre-melted hollow particle covering agent and carbonized rice husk, and adopts argon sealing for fully protected casting, the depth of the submerged entry nozzle is 200~300 mm, the back pressure of argon sealing is ≥0.05 Bar. Specifically, the granular pre-melted hollow particle covering agent is covered on the tundish, then the carbonized rice husk is covered on the outer layer of the pre-melted hollow particle covering agent, and the weight ratio of the pre-melted hollow particle covering agent to carbonized rice husk is 1:3.

[0042] Preferably, the chemical composition of the pre-melted hollow particle covering agent comprises in percent by mass: CaO: 30~35%, Al 2 O 3 : 10~15%, SiO 2 : 40~45%, Fe 2 O 3 : 2~4%, MgO: 1~10%.

[0043] Preferably, the superheat of the tundish is controlled at 38~45°C, the nitrogen increase during the continuous casting process is ≤0.0002%, the liquid level fluctuation of the mold is <2 mm, the surface temperature of the continuous casting billet in the straightening section is ≥920°C. After continuous casting is completed, the continuous casting billets are sent to an insulation pit for slow cooling to below 200°C before being removed from the pit, and the slow cooling time is ≥36 h.

[0044] Preferably, the cross-sectional dimension of the continuous casting billet is 300 mm×390 mm.(6) Cogging process

[0045] The continuous casting billets are heated in a bloom reheating furnace and then rolled and cogged into intermediate billets with a cross-section of 150 mm×150 mm. The heating temperature is 1160~1190°C, the time in the furnace is 170~190 min, and the rolling start temperature for cogging is 1040~1070°C. After cogging, full billet grinding + fluorescence detection is adopted to ensure and inspect the surface quality of the intermediate billets, ensuring that there are no billet surface quality problems.(7) Flaw detection and grinding process

[0046] The surface of the intermediate billets obtained from the cogging process is subjected to full billet grinding, and fluorescence detection is used to detect the surface quality of the intermediate billets. Grinding is performed according to the detection results until there are no surface defects and decarburized layers on the surface of the intermediate billets, which is beneficial to the implementation of surface quality control in subsequent rolling processes.(8) High-speed wire rod rolling process

[0047] The intermediate billets are heated in a heating furnace and then subjected to high-pressure water descaling, after which high-speed wire rod continuous rolling is performed to roll the intermediate billets into wire rods with a diameter of 5~17 mm.

[0048] The heating process comprises first heating zone, secondary heating zone and soaking zone. The heating temperature of first heating zone is 780~820°C, and the heating time is ≤30 min; the heating temperature of secondary heating zone is 900~950°C, and the heating time is ≤30 min; the heating temperature of the soaking zone is 1030~1070°C, and the heating time is ≤60 min. By controlling the heating temperature and heating time in zones, the formation of oxide scale that is difficult to remove on the wire rod surface is avoided, thereby reducing the descaling difficulty, improving descaling efficiency, and improving descaling effect, so as not to affect the fatigue life of the finally prepared spring steel wire.

[0049] The high-speed wire rod continuous rolling process comprises rough rolling, intermediate rolling, pre-finish rolling, finish rolling and laying head performed sequentially. The rolling start temperature of rough rolling is 890~910°C, the rolling start temperature of finish rolling is 860~890°C, the rolling finish temperature of finish rolling is ≤960°C, and the laying head temperature is 860~880°C.

[0050] Preferably, the air-fuel ratio of the heating furnace is ≤0.55, and the descaling water pressure is ≥15 MPa.(9) Controlled cooling process

[0051] A Stelmor air cooling line is adopted to perform controlled cooling on the wire rod. When the temperature of the wire rod edge is 810~860°C, fans from No.1 to No.5 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 65~75% of the maximum air volume the roller table speed is 0.50~0.65 m / s, and the cooling rate is 4.5~5.5°C / s; when the temperature of the wire rod edge is 690~810°C, fans from No.6 to No.8 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 50~60% of the maximum air volume, the roller table speed is 0.2~0.3 m / s, and the cooling rate is 1.5~2°C / s. That is to say, the controlled cooling process controls the number of fans turned on, their positions, roller table speed and cooling rate according to different temperatures of the wire rod edge.

[0052] In summary, based on the chemical composition design of the present invention, combined with the control of the aforementioned production process flow, not only the cleanliness and surface quality of the wire rod are improved, and the structure of the wire rod is refined, but also the finally prepared wire rod has high strength and high corrosion fatigue resistance. The wire rod has a two-phase structure of pearlite and ferrite, and the volume fraction of pearlite is ≥95%, the tensile strength is 1000~1200 MPa, the reduction of area is ≥45%, and the elongation after fracture is ≥14%. This can not only effectively reduce the wire breakage rate when further drawing to prepare spring steel wire, but also lay the foundation for further drawing to prepare spring steel wire with high strength and high corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use.

[0053] Specifically, the wire rod is further drawn into spring steel wire through acid pickling, drawing, and heat treatment processes performed sequentially.(10) Acid pickling process

[0054] An aqueous solution with 20% hydrochloric acid is used to pickle the wire rod at 20~30°C for 15~25 min, then washing with clean water, then placing the wire rod in a phosphating solution for phosphating treatment. The coating mass per unit area of the phosphating film is 10 g / m 2< , after phosphating treatment, the wire rod is washed with water, and saponified with soapy water before natural air drying.(11) Drawing process

[0055] The wire rod after acid pickling is cold-drawn using dies of different diameters into spring steel wire with a diameter of 3.5~15 mm, and the area reduction rate per pass during drawing is >10%.(12) Heat treatment process

[0056] On a production line equipped with online induction heating, the spring steel wire obtained from the drawing process is subjected to quenching and tempering sequentially. The quenching temperature is Ar3+20°C~Ar3+50°C, where Ar3 is the austenitization temperature of the wire rod. In this embodiment, the quenching temperature is 915~945°C, and the tempering temperature is 390~400°C.

[0057] Based on the aforementioned wire rod, the heat treatment process can make the spring steel wire form fine grains, thereby having both high strength and excellent plasticity. The tensile strength is >2000 MPa, and the reduction of area is ≥40%, which can meet the high requirements for both strength and toughness of spring steel wire in service simultaneously proposed by heavy-load automotive suspension systems. In addition, the obtained 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, and can be applied in severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance.

[0058] The specific embodiments of the present invention are further introduced through the following 13 examples. Of course, these 13 examples are only part of the numerous variant embodiments included in this embodiment, not all of them. Other embodiments made based on the aforementioned embodiments do not depart from the technical spirit of the present invention.

[0059] Specifically, all 13 examples provide a wire rod for corrosion-fatigue resistant spring steel wire and spring steel wire, with chemical compositions shown in Table 1, and the balance is Fe and unavoidable impurities. Table 1ExampleChemical composition in percent by mass(wt,%)CSiMnAlNbCrMoPS10.70.81.70.450.30.60.10.0140.01520.71.31.50.800.20.50.20.0150.01530.21.20.70.700.50.80.40.0110.02040.31.30.50.700.10.80.30.0180.01350.40.91.60.550.20.50.20.0150.01860.41.61.20.850.21.00.10.0120.01970.51.41.10.750.30.60.30.0130.01180.51.61.50.850.50.70.30.0150.00990.41.01.00.400.10.40.30.0170.009100.60.91.50.350.40.70.20.0180.010110.51.20.90.450.30.60.10.0190.014120.61.51.20.600.30.90.10.0140.016130.61.41.60.400.40.70.30.0110.012

[0060] For the production methods of the wire rods in each example, they all adopt the processes comprising hot metal pre-desulfurization process, converter smelting process, Ladle Furnace refining process, RH Vacuum degassing refining process, continuous casting process, cogging process, flaw detection and grinding process, high-speed wire rod rolling process, and controlled cooling process performed sequentially. The specific operations of each process are as described above and will not be repeated here.

[0061] For the wire rods of Examples 1~13, sampling and microstructure detection and mechanical property testing were performed according to the same test methods. The specific test methods and test results are as follows: (1) In terms of microstructure, 10 samples were taken from the head, middle, and tail of the wire rod respectively, totaling 30 samples, which were made into metallographic samples. After mechanical grinding and polishing and nitric acid alcohol etching, they were placed under a metallographic microscope for microstructure observation, and the lamellar spacing of pearlite of individual samples was measured at 10,000× magnification. The average value of the lamellar spacing of pearlite of the 30 samples was calculated as the lamellar spacing of pearlite of the wire rod of each example. It was measured that the microstructures of the wire rods of Examples 1~13 were all two-phase structures of pearlite and ferrite, and the percentage of pearlite and the lamellar spacing of pearlite are shown in Table 2 respectively; (2) In terms of mechanical properties, referring to ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products, a tensile testing machine was used to test the mechanical properties of the wire rods. The tensile strength, reduction of area, and elongation after fracture of the wire rods of Examples 1~13 are shown in Table 2 respectively. Table 2 ExampleDiameter / mmPercentage of pearlite / %Lamellar spacing of pearlite / nmTensile strength / MPaReduction of area / %Elongation after fracture / %1179517111544814.42179517211524615.13169516610085216.4415951651048541651595164112755176139516610935616.57119616510755416.68119616410565316.9999616111035217.21099616011255516.81189715911195416.5126.59715811315517136.59715811285017

[0062] The wire rods of Examples 1~13 were further drawn into spring steel wires through the acid pickling, drawing, and heat treatment processes performed sequentially as described above. The specific operations of each process are as described above and will not be repeated here.

[0063] Mechanical property testing, bending fatigue life and corrosion fatigue life testing were performed on the obtained spring steel wires respectively. The specific test methods and test results are as follows: (1) In terms of mechanical properties, referring to ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products, a tensile testing machine was used to test the mechanical properties of the spring steel wires. The tensile strength and reduction of area of the spring steel wires of Examples 1~13 are shown in Table 3 respectively; (2) In terms of bending fatigue life and corrosion fatigue life, referring to KS B ISO 1143, rotating bending fatigue tests were performed on spring steel wire specimens with a diameter of 4 mm to measure the bending fatigue life of the spring steel wires of Examples 1~13 as shown in Table 3; referring to KS D 9502 ISO 3768 / 7263, salt spray tests were used to measure the corrosion fatigue life of the spring steel wires of Examples 1~13 in salt spray environment as shown in Table 3. Table 3 ExampleTensile strength / MPaReduction of area / %Bending fatigue life / cyclesCorrosion fatigue life / cycles1210045324000230002206953377000270003206851284000310004205952315000180005209353293000190006208155331000180007208551325000210008207349328000250009207951327000190001020645126900028000112088523340002600012209252346000250001320744834500024000

[0064] In summary, it can be seen that the wire rods of Examples 1~13 produced according to the present embodiment have a two-phase structure of pearlite and ferrite, and the volume fraction of pearlite is ≥95%, the tensile strength is 1000~1200 MPa, the reduction of area is ≥45%, and the elongation after fracture is ≥14%; the spring steel wires of Examples 1~13 produced according to the present embodiment have tensile strength >2000 MPa and reduction of area ≥40%, with excellent toughness, which can meet the high requirements for both strength and toughness of spring steel wire in service simultaneously proposed by heavy-load automotive suspension systems. In addition, the obtained 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, and can be applied in severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance.

[0065] The above descriptions are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art, within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, equivalent substitutions or changes should be covered within the protection scope of the present invention.

Examples

Embodiment Construction

[0019]The technical solution of the present application will be further introduced below in combination with specific embodiments, but the scope of protection is not limited to the description made.

[0020]The present embodiment provides a production method of a wire rod for corrosion-fatigue resistant spring steel wire, and a wire rod for corrosion-fatigue resistant spring steel wire prepared by the production method.

[0021]Specifically, the chemical composition of the wire rod for corrosion-fatigue resistant spring steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0022]One embodiment of the present invention further provides a corrosion-fatigue resistant spring steel wire, which is prepared from the above-mentioned wire rod for corrosion-fatigue resistant spring steel wire as base material and has the same chemical composition a...

[0001] The present application is based on and claims priority to Chinese Patent Application Number CN202311085007.3 filed on August 28, 2023, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

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

[0003] As safety-bearing components, Springs were widely applied in the fields of automobiles, machinery, railways, etc., and often undertook high-cycle alternating loads during service. With technological progress and improved manufacturing levels, new energy vehicles gradually emerged, and their sales gradually climbed in the automotive industry. However, new energy vehicles had larger weights, which imposed strict requirements on spring steel wires applied to suspension springs, not only requiring high strength to enhance the load capacity of vehicles, but also needing to develop toward lightweight to reduce energy consumption during vehicle operation and improve cruising ability.

[0004] However, current spring steels had poor corrosion resistance. When applied in the humid environment of northern regions, since northern regions had thick snow accumulation in winter and usually adopted salt spreading for snow melting to clear roads, roads contained large amounts of chloride ions, which easily produced corrosion pits on the surface of spring steel, formed stress concentration, and reduced the fatigue strength of spring steel. Moreover, hydrogen entry during the corrosion process would cause hydrogen-induced delayed cracking, causing components to suddenly fracture under conditions far below allowable cycles or loads, seriously affecting the service life of components and creating huge safety hazards for the safe operation of automobiles and railways. Therefore, it was necessary to develop spring steel wires that simultaneously possessed high strength, lightweight, and excellent corrosion resistance to meet the application requirements of new energy vehicles in northern environments.SUMMARY

[0005] An object of the present application is to provide a wire rod for corrosion-fatigue resistant spring steel wire and a production method thereof, and also relates to a corrosion-fatigue resistant spring steel wire.

[0006] To achieve the above object, one embodiment of the present invention provides a production method of a wire rod for corrosion-fatigue resistant spring steel wire, wherein the chemical composition of the wire rod comprising in percent by mass: 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%, and the balance is Fe and unavoidable impurities; the production method comprises hot metal pre-desulfurization process, converter smelting process, Ladle Furnace refining process, RH Vacuum degassing refining process, continuous casting process, cogging process, flaw detection and grinding process, high-speed wire rod rolling process, and controlled cooling process performed sequentially; wherein, in the converter smelting process, smelting raw materials composed of high-quality scrap steel, ferromolybdenum, and hot metal after pre-desulfurization are fed into a converter for smelting, wherein the weight ratio of the hot metal after pre-desulfurization to high-quality scrap steel is 7:1~8:1, and the temperature of the hot metal when fed into the converter is 1350~1450°C; in the continuous casting process, the mold liquid level adopts protective slag specially for high-Al steel for protected casting, wherein the chemical composition of the protective slag specially for high-Al steel comprises in percent by mass: 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%; in the high-speed wire rod rolling process, intermediate billets are heated in a heating furnace and then subjected to high-pressure water descaling, after which high-speed wire rod continuous rolling is performed to roll into wire rod, the heating process comprises first heating zone, secondary heating zone and soaking zone, the heating temperature of first heating zone is 780~820°C, and the heating time is ≤30 min; the heating temperature of secondary heating zone is 900~950°C, and the heating time is ≤30 min; the heating temperature of soaking zone is 1030~1070°C, and the heating time is ≤60 min; the high-speed wire rod continuous rolling process comprises rough rolling, intermediate rolling, pre-finish rolling, finish rolling and laying head performed sequentially, the rolling start temperature of rough rolling is 890~910°C, the rolling start temperature of finish rolling is 860~890°C, the rolling finish temperature of finish rolling is ≤960°C, and the laying head temperature is 860~880°C; in the controlled cooling process, a Stelmor air cooling line is adopted to perform controlled cooling on the wire rod, when the temperature of the wire rod edge is 810~860°C, fans from No.1 to No.5 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 65~75% of the maximum air volume, the roller table speed is 0.50~0.65 m / s, and the cooling rate is 4.5~5.5°C / s; when the temperature of the wire rod edge is 690~810°C, fans from No.6 to No.8 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 50~60% of the maximum air volume, the roller table speed is 0.2~0.3 m / s, and the cooling rate is 1.5~2°C / s.

[0007] As a further improvement of one embodiment of the present invention, the chemical composition of the wire rod comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities; wherein [Si] / [Al]=1.5~3.5.

[0008] As a further improvement of one embodiment of the present invention, in the hot metal pre-desulfurization process, blast furnace hot metal is desulfurized in KR desulfurization equipment until S≤0.002% in the hot metal, the slag removal rate of desulfurization is ≥97%, and the temperature of the hot metal after desulfurization is ≥1350°C.

[0009] As a further improvement of one embodiment of the present invention, in the converter smelting process, the converter smelting adopts top-bottom combined blowing, constant pressure variable lance, and double slag operation, content of C is ≥0.15% and content of P is ≤0.01% in the molten steel at the end point of converter smelting, and the tapping temperature is ≥1650°C; there are no floating slag debris 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 of aluminum blocks are laid at the bottom of the ladle before tapping.

[0010] As a further improvement of one embodiment of the present invention, in the converter smelting process, bottom argon blowing of the ladle is turned on before converter tapping, the pressure of bottom argon blowing is controlled at 0.5~0.6 MPa, the bright ring diameter is 250~400 mm, after 3 / 4 of the molten steel is tapped, the pressure of bottom argon blowing of the ladle is adjusted to 0.4~0.5 MPa, and the bright ring diameter is controlled at 200~350 mm.

[0011] As a further improvement of one embodiment of the present invention, in the Ladle Furnace refining process, during the waiting period for smelting, the flow rate of bottom argon blowing of the ladle is 40~80 NL / min; when adding refining protective slag and alloys, the flow rate of bottom argon blowing of the ladle is 200~600 NL / min; heating is performed after adding alloys, and during heating, the flow rate of bottom argon blowing of the ladle is 200~400 NL / min; the chemical composition of the refining protective slag comprises in percent by mass: CaO: 45~50%, Al 2 O 3 : 30~40%, and CaO / Al 2 O 3 =1.7~1.8, MgO: 4~8%, SiO 2 : 4~7%.

[0012] As a further improvement of one embodiment of the present invention, in the RH Vacuum degassing refining process, after molten steel circulation, the remaining 2 / 3 of aluminum blocks are first added for alloying, vacuum treatment is started after alloying is completed, the vacuum degree of vacuum treatment is ≤67 Pa, the vacuum treatment time is ≥20 min, so that the content of O is ≤18 ppm and the content of H is ≤1.5 ppm in the molten steel; after vacuum treatment is finished, bottom argon blowing of the ladle is performed for soft stirring, and silicon-calcium cored wire is added for inclusion modification treatment, the soft stirring time is ≥20 min, and the wire feeding speed of the silicon-calcium cored wire is 120~150 m / min.

[0013] As a further improvement of one embodiment of the present invention, in the continuous casting process, continuous casting adopts ladle long nozzle, submerged entry nozzle, tundish covered with pre-melted hollow particle covering agent and carbonized rice husk, and adopts argon sealing for fully protected casting, the depth of the submerged entry nozzle is 200~300 mm, the back pressure of argon sealing is ≥0.05 Bar, the carbonized rice husk covers the outer layer of the pre-melted hollow particle covering agent, and the weight ratio of the pre-melted hollow particle covering agent to carbonized rice husk is 1:3.

[0014] To achieve the above object, one embodiment of the present invention further provides a wire rod for corrosion-fatigue resistant spring steel wire, wherein the chemical composition of the wire rod comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0015] As a further improvement of one embodiment of the present invention, the wire rod for corrosion-fatigue resistant spring steel wire is prepared by the production method of the wire rod for corrosion-fatigue resistant spring steel wire as described above.

[0016] To achieve the above object, one embodiment of the present invention further provides a corrosion-fatigue resistant spring steel wire, wherein the chemical composition of the steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0017] As a further improvement of one embodiment of the present invention, the corrosion-fatigue resistant spring steel wire is prepared from the wire rod for corrosion-fatigue resistant spring steel wire as described above as base material through acid pickling, drawing, and heat treatment processes performed sequentially.

[0018] Compared with the prior art, the beneficial effects of the present invention include: (1) In the chemical composition design scheme of the present invention, by adding a certain content of Al, not only can the density of the wire rod and spring steel wire be reduced to make them lightweight, but also the corrosion resistance can be improved. Combined with the addition and content control of other elements, especially Nb, austenite grain coarsening during the heating process can be prevented, playing the role of fine grain strengthening and improving elastic decline resistance, solving the problems of grain coarsening, multiple inclusions, and difficulty in strength improvement caused by adding Al. Further combined with the control of Si, the elastic decline resistance and corrosion resistance of the spring steel wire can be improved. Cr, as an important corrosion-resistant element, can form a passivation film on the surface of the spring steel wire, effectively preventing oxidation and improving the corrosion resistance of the matrix, further can enhance pitting corrosion resistance cooperation with Mo element. Mn, as a solid solution strengthening element, can improve the hardenability of the spring steel wire, and Mn has strong binding force with S and O, not only can deoxidize, but also can form MnS compounds, reducing the probability of S combining with Fe to form FeS, thereby alleviating or eliminating the hot brittleness effect of S. Overall, through this chemical composition design scheme, the strength and toughness, corrosion resistance, and elastic decline resistance of the wire rod and spring steel wire can be improved, making the spring steel wire lightweight, and suitable for the severe cold and humid northern environment. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use. (2) Based on the chemical composition design scheme of the present invention, combined with the control of the production process flow, not only the cleanliness and surface quality of the wire rod are improved, and the structure of the wire rod is refined, but also the finally prepared wire rod has high strength and high corrosion fatigue resistance. The wire rod has a two-phase structure of pearlite and ferrite, and the volume fraction of pearlite is ≥95%, the tensile strength is 1000~1200 MPa, the reduction of area is ≥45%, and the elongation after fracture is ≥14%. This can not only effectively reduce the wire breakage rate when further drawing to prepare spring steel wire, but also lay the foundation for further drawing to prepare spring steel wire with high strength and high corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use. (3) The spring steel wire further prepared by drawing based on the aforementioned wire rod has both high strength and excellent plasticity, with tensile strength >2000 MPa and reduction of area ≥40%, which can meet the high requirements for both strength and toughness of spring steel wire in service simultaneously proposed by heavy-load automotive suspension systems. In addition, the obtained 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, and can be applied in severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance. DETAILED DESCRIPTION

[0019] The technical solution of the present application will be further introduced below in combination with specific embodiments, but the scope of protection is not limited to the description made.

[0020] The present embodiment provides a production method of a wire rod for corrosion-fatigue resistant spring steel wire, and a wire rod for corrosion-fatigue resistant spring steel wire prepared by the production method.

[0021] Specifically, the chemical composition of the wire rod for corrosion-fatigue resistant spring steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0022] One embodiment of the present invention further provides a corrosion-fatigue resistant spring steel wire, which is prepared from the above-mentioned wire rod for corrosion-fatigue resistant spring steel wire as base material and has the same chemical composition as the wire rod for corrosion-fatigue resistant spring steel wire.

[0023] 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 spring steel wire be reduced to make them lightweight, but also the corrosion resistance can be improved. Combined with the addition and content control of other elements, especially Nb, austenite grain coarsening during the heating process can be prevented, playing the role of fine grain strengthening and improving elastic decline resistance, solving the problems of grain coarsening, multiple inclusions, and difficulty in strength improvement caused by adding Al. Further combined with the control of Si, the elastic decline resistance and corrosion resistance of the spring steel wire can be improved. Cr, as an important corrosion-resistant element, can form a passivation film on the surface of the spring steel wire, effectively preventing oxidation and improving the corrosion resistance of the matrix, further can enhance pitting corrosion resistance cooperation with Mo element Mn, as a solid solution strengthening element, can improve the hardenability of the spring steel wire, and Mn has strong binding force with S and O, not only can deoxidize, but also can form MnS compounds, reducing the probability of S combining with Fe to form FeS, thereby alleviating or eliminating the hot brittleness effect of S. Overall, through this chemical composition design scheme, the strength and toughness, corrosion resistance, and elastic decline resistance of the wire rod and spring steel wire can be improved, making the spring steel wire lightweight, and suitable for severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use.

[0024] Preferably, the chemical composition of the wire rod for corrosion-fatigue resistant spring steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities; wherein [Si] / [Al]=1.5~3.5.

[0025] Wherein [Si] represents the mass percent of Si, and [Al] represents the mass percent of Al.

[0026] Through the limitation of [Si] / [Al], the finally prepared spring steel wire can have both corrosion resistance and elastic decline resistance, enabling the spring steel wire to have excellent relaxation resistance and extremely good elastic deformation recovery capability.

[0027] The specific processes in the production method of the wire rod for corrosion-fatigue resistant spring steel wire are introduced below.(1) Hot metal pre-desulfurization process

[0028] Blast furnace hot metal is desulfurized in KR desulfurization equipment until S≤0.002% in the hot metal, the slag removal rate of desulfurization is ≥97%, and the temperature of the hot metal after desulfurization is ≥1350°C.(2) Converter smelting process

[0029] Smelting raw materials composed of high-quality scrap steel, ferromolybdenum, and hot metal after pre-desulfurization are fed into a converter for smelting, wherein the weight ratio of the hot metal after pre-desulfurization to high-quality scrap steel is 7:1~8:1, and the temperature of the hot metal when fed into the converter is 1350~1450°C. By adding ferromolybdenum before the start of converter smelting, excessive addition of alloys during the middle stage of converter smelting that would cause excessive temperature drop of the molten steel can be avoided, so as not to affect the purity of the molten steel and the removal effect of inclusions.

[0030] The high-quality scrap steel here refers to waste steel with S≤0.012% and P≤0.015%. The use of high-quality scrap steel can effectively control the residual element content in the molten steel, reduce the sulfur return amount in the molten steel, effectively reduce slag-metal reactions in the refining process, reduce the generation of large-sized inclusions in the molten steel, and improve the cleanliness of the molten steel.

[0031] Preferably, the converter smelting adopts top-bottom combined blowing, constant pressure variable lance, and double slag operation, content of C is ≥0.15% and content of P is ≤0.01% in the molten steel at the end point of converter smelting, and the tapping temperature is ≥1650°C. The so-called double slag operation means slag removal twice.

[0032] Preferably, before tapping, it is ensured that there are no floating slag debris in the ladle, and the cold slag steel at the bottom of the ladle is <0.5 tons, to ensure smooth bottom blowing. Ferromanganese, ferrosilicon, ferrochrome, lime, and 1 / 3 of aluminum blocks are laid at the bottom of the ladle before tapping to facilitate deoxidation alloying during the converter tapping process. Here only 1 / 3 of the total aluminum blocks are laid, and the remaining 2 / 3 of the total aluminum blocks are added in the RH Vacuum degassing refining process.

[0033] Preferably, bottom argon blowing of the ladle is turned on before converter tapping, the pressure of bottom argon blowing is controlled at 0.5~0.6 MPa to make the molten steel surface agitated, the bright ring diameter is 250~400 mm, after 3 / 4 of the molten steel is tapped, the pressure of bottom argon blowing of the ladle is adjusted to 0.4~0.5 MPa, and the bright ring diameter is controlled at 200~350 mm.(3) Ladle Furnace refining process

[0034] The molten steel after converter smelting is sent to an ladle furnace for smelting. After the ladle arrives at the station, bottom argon blowing is connected and turned on, refining protective slag is added to the ladle, then alloys are added for chemical composition adjustment and inclusion control, and electric heating is applied to raise the temperature of the molten steel that has dropped after adding alloys. During this period, temperature measurement, sampling detection, diffusion deoxidation and heating are continuously performed until the molten steel composition, slag composition and molten steel temperature all meet the standards, then tapping is performed. The alloys include metallic manganese, ferrosilicon and ferrochrome.

[0035] Preferably, during the waiting period for smelting, the flow rate of bottom argon blowing of the ladle is 40~80 NL / min to make the slag surface fluctuate; when adding refining protective slag and alloys, the flow rate of bottom argon blowing of the ladle is 200~600 NL / min; in addition, heating is performed after adding alloys, and during heating, the flow rate of bottom argon blowing of the ladle is 200~400 NL / min. Specifically, the bottom argon blowing during the smelting process can be executed according to an automatic argon blowing model.

[0036] Preferably, aluminum granules and calcium carbide are used for slag surface deoxidation to reduce the oxygen content in the molten steel, and lime is added to adjust the slag to white in time, and the white slag time is controlled at ≥15 min.

[0037] The chemical composition of the refining protective slag comprises in percent by mass: CaO: 45~50%, Al 2 O 3 : 30~40%, and CaO / Al 2 O 3 =1.7~1.8, MgO: 4~8%, SiO 2 : 4~7%. The refining protective slag has good fluidity and the ability to adsorb non-metallic inclusions, can effectively control the types and contents of inclusions, and improve the purity of the molten steel, thereby improving the fatigue resistance of the finally prepared wire rod and spring steel wire.(4) RH Vacuum degassing refining process

[0038] The molten steel is sent to an RH vacuum furnace for vacuum refining to further remove inclusions in the molten steel. Specifically, after molten steel circulation, the remaining 2 / 3 of aluminum blocks are first added for alloying, vacuum treatment is started after alloying is completed, the vacuum degree of vacuum treatment is ≤67 Pa, the vacuum treatment time is ≥20 min to further reduce the oxygen content in the molten steel, so that the content of O is ≤18 ppm and the content of H is ≤1.5 ppm in the molten steel. After vacuum treatment is finished, bottom argon blowing of the ladle is performed for soft stirring, and silicon-calcium cored wire is added for inclusion modification treatment, the soft stirring time is ≥20 min, and the wire feeding speed of the silicon-calcium cored wire is 120~150 m / min to promote the floating of non-metallic inclusions and improve the purity of the molten steel.

[0039] The chemical composition of the silicon-calcium cored wire comprises in percent by mass: SiO 2 : 48~55%, CaO: 40~50%, Al 2 O 3 : 3~5%, MgO: 1~2%. The tapping temperature is 1575~1585°C.(5) Continuous casting process

[0040] A continuous casting machine is used to cast the molten steel from the RH Vacuum degassing refining process into continuous casting billets. The mold liquid level adopts protective slag specially for high-Al steel for protected casting. The chemical composition of the protective slag specially for high-Al steel comprises in percent by mass: 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%.

[0041] Preferably, continuous casting adopts ladle long nozzle, submerged entry nozzle, tundish covered with pre-melted hollow particle covering agent and carbonized rice husk, and adopts argon sealing for fully protected casting, the depth of the submerged entry nozzle is 200~300 mm, the back pressure of argon sealing is ≥0.05 Bar. Specifically, the granular pre-melted hollow particle covering agent is covered on the tundish, then the carbonized rice husk is covered on the outer layer of the pre-melted hollow particle covering agent, and the weight ratio of the pre-melted hollow particle covering agent to carbonized rice husk is 1:3.

[0042] Preferably, the chemical composition of the pre-melted hollow particle covering agent comprises in percent by mass: CaO: 30~35%, Al 2 O 3 : 10~15%, SiO 2 : 40~45%, Fe 2 O 3 : 2~4%, MgO: 1~10%.

[0043] Preferably, the superheat of the tundish is controlled at 38~45°C, the nitrogen increase during the continuous casting process is ≤0.0002%, the liquid level fluctuation of the mold is <2 mm, the surface temperature of the continuous casting billet in the straightening section is ≥920°C. After continuous casting is completed, the continuous casting billets are sent to an insulation pit for slow cooling to below 200°C before being removed from the pit, and the slow cooling time is ≥36 h.

[0044] Preferably, the cross-sectional dimension of the continuous casting billet is 300 mm×390 mm.(6) Cogging process

[0045] The continuous casting billets are heated in a bloom reheating furnace and then rolled and cogged into intermediate billets with a cross-section of 150 mm×150 mm. The heating temperature is 1160~1190°C, the time in the furnace is 170~190 min, and the rolling start temperature for cogging is 1040~1070°C. After cogging, full billet grinding + fluorescence detection is adopted to ensure and inspect the surface quality of the intermediate billets, ensuring that there are no billet surface quality problems.(7) Flaw detection and grinding process

[0046] The surface of the intermediate billets obtained from the cogging process is subjected to full billet grinding, and fluorescence detection is used to detect the surface quality of the intermediate billets. Grinding is performed according to the detection results until there are no surface defects and decarburized layers on the surface of the intermediate billets, which is beneficial to the implementation of surface quality control in subsequent rolling processes.(8) High-speed wire rod rolling process

[0047] The intermediate billets are heated in a heating furnace and then subjected to high-pressure water descaling, after which high-speed wire rod continuous rolling is performed to roll the intermediate billets into wire rods with a diameter of 5~17 mm.

[0048] The heating process comprises first heating zone, secondary heating zone and soaking zone. The heating temperature of first heating zone is 780~820°C, and the heating time is ≤30 min; the heating temperature of secondary heating zone is 900~950°C, and the heating time is ≤30 min; the heating temperature of the soaking zone is 1030~1070°C, and the heating time is ≤60 min. By controlling the heating temperature and heating time in zones, the formation of oxide scale that is difficult to remove on the wire rod surface is avoided, thereby reducing the descaling difficulty, improving descaling efficiency, and improving descaling effect, so as not to affect the fatigue life of the finally prepared spring steel wire.

[0049] The high-speed wire rod continuous rolling process comprises rough rolling, intermediate rolling, pre-finish rolling, finish rolling and laying head performed sequentially. The rolling start temperature of rough rolling is 890~910°C, the rolling start temperature of finish rolling is 860~890°C, the rolling finish temperature of finish rolling is ≤960°C, and the laying head temperature is 860~880°C.

[0050] Preferably, the air-fuel ratio of the heating furnace is ≤0.55, and the descaling water pressure is ≥15 MPa.(9) Controlled cooling process

[0051] A Stelmor air cooling line is adopted to perform controlled cooling on the wire rod. When the temperature of the wire rod edge is 810~860°C, fans from No.1 to No.5 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 65~75% of the maximum air volume the roller table speed is 0.50~0.65 m / s, and the cooling rate is 4.5~5.5°C / s; when the temperature of the wire rod edge is 690~810°C, fans from No.6 to No.8 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 50~60% of the maximum air volume, the roller table speed is 0.2~0.3 m / s, and the cooling rate is 1.5~2°C / s. That is to say, the controlled cooling process controls the number of fans turned on, their positions, roller table speed and cooling rate according to different temperatures of the wire rod edge.

[0052] In summary, based on the chemical composition design of the present invention, combined with the control of the aforementioned production process flow, not only the cleanliness and surface quality of the wire rod are improved, and the structure of the wire rod is refined, but also the finally prepared wire rod has high strength and high corrosion fatigue resistance. The wire rod has a two-phase structure of pearlite and ferrite, and the volume fraction of pearlite is ≥95%, the tensile strength is 1000~1200 MPa, the reduction of area is ≥45%, and the elongation after fracture is ≥14%. This can not only effectively reduce the wire breakage rate when further drawing to prepare spring steel wire, but also lay the foundation for further drawing to prepare spring steel wire with high strength and high corrosion fatigue resistance, which is beneficial to extending the service life of the spring steel wire and improving its safety in use.

[0053] Specifically, the wire rod is further drawn into spring steel wire through acid pickling, drawing, and heat treatment processes performed sequentially.(10) Acid pickling process

[0054] An aqueous solution with 20% hydrochloric acid is used to pickle the wire rod at 20~30°C for 15~25 min, then washing with clean water, then placing the wire rod in a phosphating solution for phosphating treatment. The coating mass per unit area of the phosphating film is 10 g / m 2< , after phosphating treatment, the wire rod is washed with water, and saponified with soapy water before natural air drying.(11) Drawing process

[0055] The wire rod after acid pickling is cold-drawn using dies of different diameters into spring steel wire with a diameter of 3.5~15 mm, and the area reduction rate per pass during drawing is >10%.(12) Heat treatment process

[0056] On a production line equipped with online induction heating, the spring steel wire obtained from the drawing process is subjected to quenching and tempering sequentially. The quenching temperature is Ar3+20°C~Ar3+50°C, where Ar3 is the austenitization temperature of the wire rod. In this embodiment, the quenching temperature is 915~945°C, and the tempering temperature is 390~400°C.

[0057] Based on the aforementioned wire rod, the heat treatment process can make the spring steel wire form fine grains, thereby having both high strength and excellent plasticity. The tensile strength is >2000 MPa, and the reduction of area is ≥40%, which can meet the high requirements for both strength and toughness of spring steel wire in service simultaneously proposed by heavy-load automotive suspension systems. In addition, the obtained 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, and can be applied in severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance.

[0058] The specific embodiments of the present invention are further introduced through the following 13 examples. Of course, these 13 examples are only part of the numerous variant embodiments included in this embodiment, not all of them. Other embodiments made based on the aforementioned embodiments do not depart from the technical spirit of the present invention.

[0059] Specifically, all 13 examples provide a wire rod for corrosion-fatigue resistant spring steel wire and spring steel wire, with chemical compositions shown in Table 1, and the balance is Fe and unavoidable impurities. Table 1ExampleChemical composition in percent by mass(wt,%)CSiMnAlNbCrMoPS10.70.81.70.450.30.60.10.0140.01520.71.31.50.800.20.50.20.0150.01530.21.20.70.700.50.80.40.0110.02040.31.30.50.700.10.80.30.0180.01350.40.91.60.550.20.50.20.0150.01860.41.61.20.850.21.00.10.0120.01970.51.41.10.750.30.60.30.0130.01180.51.61.50.850.50.70.30.0150.00990.41.01.00.400.10.40.30.0170.009100.60.91.50.350.40.70.20.0180.010110.51.20.90.450.30.60.10.0190.014120.61.51.20.600.30.90.10.0140.016130.61.41.60.400.40.70.30.0110.012

[0060] For the production methods of the wire rods in each example, they all adopt the processes comprising hot metal pre-desulfurization process, converter smelting process, Ladle Furnace refining process, RH Vacuum degassing refining process, continuous casting process, cogging process, flaw detection and grinding process, high-speed wire rod rolling process, and controlled cooling process performed sequentially. The specific operations of each process are as described above and will not be repeated here.

[0061] For the wire rods of Examples 1~13, sampling and microstructure detection and mechanical property testing were performed according to the same test methods. The specific test methods and test results are as follows: (1) In terms of microstructure, 10 samples were taken from the head, middle, and tail of the wire rod respectively, totaling 30 samples, which were made into metallographic samples. After mechanical grinding and polishing and nitric acid alcohol etching, they were placed under a metallographic microscope for microstructure observation, and the lamellar spacing of pearlite of individual samples was measured at 10,000× magnification. The average value of the lamellar spacing of pearlite of the 30 samples was calculated as the lamellar spacing of pearlite of the wire rod of each example. It was measured that the microstructures of the wire rods of Examples 1~13 were all two-phase structures of pearlite and ferrite, and the percentage of pearlite and the lamellar spacing of pearlite are shown in Table 2 respectively; (2) In terms of mechanical properties, referring to ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products, a tensile testing machine was used to test the mechanical properties of the wire rods. The tensile strength, reduction of area, and elongation after fracture of the wire rods of Examples 1~13 are shown in Table 2 respectively. Table 2 ExampleDiameter / mmPercentage of pearlite / %Lamellar spacing of pearlite / nmTensile strength / MPaReduction of area / %Elongation after fracture / %1179517111544814.42179517211524615.13169516610085216.4415951651048541651595164112755176139516610935616.57119616510755416.68119616410565316.9999616111035217.21099616011255516.81189715911195416.5126.59715811315517136.59715811285017

[0062] The wire rods of Examples 1~13 were further drawn into spring steel wires through the acid pickling, drawing, and heat treatment processes performed sequentially as described above. The specific operations of each process are as described above and will not be repeated here.

[0063] Mechanical property testing, bending fatigue life and corrosion fatigue life testing were performed on the obtained spring steel wires respectively. The specific test methods and test results are as follows: (1) In terms of mechanical properties, referring to ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products, a tensile testing machine was used to test the mechanical properties of the spring steel wires. The tensile strength and reduction of area of the spring steel wires of Examples 1~13 are shown in Table 3 respectively; (2) In terms of bending fatigue life and corrosion fatigue life, referring to KS B ISO 1143, rotating bending fatigue tests were performed on spring steel wire specimens with a diameter of 4 mm to measure the bending fatigue life of the spring steel wires of Examples 1~13 as shown in Table 3; referring to KS D 9502 ISO 3768 / 7263, salt spray tests were used to measure the corrosion fatigue life of the spring steel wires of Examples 1~13 in salt spray environment as shown in Table 3. Table 3 ExampleTensile strength / MPaReduction of area / %Bending fatigue life / cyclesCorrosion fatigue life / cycles1210045324000230002206953377000270003206851284000310004205952315000180005209353293000190006208155331000180007208551325000210008207349328000250009207951327000190001020645126900028000112088523340002600012209252346000250001320744834500024000

[0064] In summary, it can be seen that the wire rods of Examples 1~13 produced according to the present embodiment have a two-phase structure of pearlite and ferrite, and the volume fraction of pearlite is ≥95%, the tensile strength is 1000~1200 MPa, the reduction of area is ≥45%, and the elongation after fracture is ≥14%; the spring steel wires of Examples 1~13 produced according to the present embodiment have tensile strength >2000 MPa and reduction of area ≥40%, with excellent toughness, which can meet the high requirements for both strength and toughness of spring steel wire in service simultaneously proposed by heavy-load automotive suspension systems. In addition, the obtained 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, and can be applied in severe cold and humid northern environments. Even under road environments with salt spreading for snow melting in winter, it has excellent corrosion fatigue resistance.

[0065] The above descriptions are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art, within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, equivalent substitutions or changes should be covered within the protection scope of the present invention.

Examples

Embodiment Construction

[0019]The technical solution of the present application will be further introduced below in combination with specific embodiments, but the scope of protection is not limited to the description made.

[0020]The present embodiment provides a production method of a wire rod for corrosion-fatigue resistant spring steel wire, and a wire rod for corrosion-fatigue resistant spring steel wire prepared by the production method.

[0021]Specifically, the chemical composition of the wire rod for corrosion-fatigue resistant spring steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

[0022]One embodiment of the present invention further provides a corrosion-fatigue resistant spring steel wire, which is prepared from the above-mentioned wire rod for corrosion-fatigue resistant spring steel wire as base material and has the same chemical composition a...

Claims

1. A production method of a wire rod, wherein the chemical composition of the wire rod comprising in percent by mass: 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%, and the balance is Fe and unavoidable impurities; the production method comprises hot metal pre-desulfurization process, converter smelting process, Ladle Furnace refining process, RH Vacuum degassing refining process, continuous casting process, cogging process, flaw detection and grinding process, high-speed wire rod rolling process, and controlled cooling process performed sequentially; wherein, in the converter smelting process, smelting raw materials composed of high-quality scrap steel, ferromolybdenum, and hot metal after pre-desulfurization are fed into a converter for smelting, wherein the weight ratio of the hot metal after pre-desulfurization to high-quality scrap steel is 7:1~8:1, and the temperature of the hot metal when fed into the converter is 1350~1450°C; in the continuous casting process, the mold liquid level adopts protective slag specially for high-Al steel for protected casting, wherein the chemical composition of the protective slag specially for high-Al steel comprises in percent by mass: 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%, CaF2: 4~9%; in the high-speed wire rod rolling process, intermediate billets are heated in a heating furnace and then subjected to high-pressure water descaling, after which high-speed wire rod continuous rolling is performed to roll into wire rod, the heating process comprises first heating zone, secondary heating zone and soaking zone, the heating temperature of first heating zone is 780~820°C, and the heating time is ≤30 min; the heating temperature of secondary heating zone is 900~950°C, and the heating time is ≤30 min; the heating temperature of soaking zone is 1030~1070°C, and the heating time is ≤60 min; the high-speed wire rod continuous rolling process comprises rough rolling, intermediate rolling, pre-finish rolling, finish rolling and laying head performed sequentially, the rolling start temperature of rough rolling is 890~910°C, the rolling start temperature of finish rolling is 860~890°C, the rolling finish temperature of finish rolling is ≤960°C, and the laying head temperature is 860~880°C; in the controlled cooling process, a Stelmor air cooling line is adopted to perform controlled cooling on the wire rod, when the temperature of the wire rod edge is 810~860°C, fans from No.1 to No.5 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 65~75% of the maximum air volume, the roller table speed is 0.50~0.65 m / s, and the cooling rate is 4.5~5.5°C / s; when the temperature of the wire rod edge is 690~810°C, fans from No.6 to No.8 on the Stelmor cooling line are turned on, and the air volume of the fans is controlled at 50~60% of the maximum air volume, the roller table speed is 0.2~0.3 m / s, and the cooling rate is 1.5~2°C / s.

2. The production method of a wire rod according to claim 1, wherein the chemical composition of the wire rod comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities; wherein [Si] / [Al]=1.5~3.5.

3. The production method of a wire rod according to claim 1, wherein in the hot metal pre-desulfurization process, blast furnace hot metal is desulfurized in KR desulfurization equipment until S≤0.002% in the hot metal, the slag removal rate of desulfurization is ≥97%, and the temperature of the hot metal after desulfurization is ≥1350°C.

4. The production method of a wire rod according to claim 1, wherein in the converter smelting process, the converter smelting adopts top-bottom combined blowing, constant pressure variable lance, and double slag operation, content of C is ≥0.15% and content of P is ≤0.01% in the molten steel at the end point of converter smelting, and the tapping temperature is ≥1650°C; there are no floating slag debris 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 of aluminum blocks are laid at the bottom of the ladle before tapping.

5. The production method of a wire rod according to claim 1, wherein in the converter smelting process, bottom argon blowing of the ladle is turned on before converter tapping, the pressure of bottom argon blowing is controlled at 0.5~0.6 MPa, the bright ring diameter is 250~400 mm, after 3 / 4 of the molten steel is tapped, the pressure of bottom argon blowing of the ladle is adjusted to 0.4~0.5 MPa, and the bright ring diameter is controlled at 200~350 mm.

6. The production method of a wire rod according to claim 1, wherein in the Ladle Furnace refining process, during the waiting period for smelting, the flow rate of bottom argon blowing of the ladle is 40~80 NL / min; when adding refining protective slag and alloys, the flow rate of bottom argon blowing of the ladle is 200~600 NL / min; heating is performed after adding alloys, and during heating, the flow rate of bottom argon blowing of the ladle is 200~400 NL / min; the chemical composition of the refining protective slag comprises in percent by mass: CaO: 45~50%, Al2O3: 30~40%, and CaO / Al2O3=1.7~1.8, MgO: 4~8%, SiO2: 4~7%.

7. The production method of a wire rod according to claim 4, wherein in the RH Vacuum degassing refining process, after molten steel circulation, the remaining 2 / 3 of aluminum blocks are first added for alloying, vacuum treatment is started after alloying is completed, the vacuum degree of vacuum treatment is ≤67 Pa, the vacuum treatment time is ≥20 min, so that the content of O is ≤18 ppm and the content of H is ≤1.5 ppm in the molten steel; after vacuum treatment is finished, bottom argon blowing of the ladle is performed for soft stirring, and silicon-calcium cored wire is added for inclusion modification treatment, the soft stirring time is ≥20 min, and the wire feeding speed of the silicon-calcium cored wire is 120~150 m / min.

8. The production method of a wire rod according to claim 1, wherein in the continuous casting process, continuous casting adopts ladle long nozzle, submerged entry nozzle, tundish covered with pre-melted hollow particle covering agent and carbonized rice husk, and adopts argon sealing for fully protected casting, the depth of the submerged entry nozzle is 200~300 mm, the back pressure of argon sealing is ≥0.05 Bar, the carbonized rice husk covers the outer layer of the pre-melted hollow particle covering agent, and the weight ratio of the pre-melted hollow particle covering agent to carbonized rice husk is 1:3.

9. A wire rod, wherein the chemical composition of the wire rod comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

10. A steel wire, wherein the chemical composition of the steel wire comprises in percent by mass: 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%, and the balance is Fe and unavoidable impurities.

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