Corrosion-resistant spring and preparation method thereof

Abstract

The invention relates to the technical field of springs, in particular to a corrosion-resistant spring and a preparation method thereof.The corrosion-resistant spring takes alloy steel as a base body and comprises, by mass, 0.45%-0.55% of C, 0.45%-0.55% of S, 0.45%-0.55% of Cr, 0.45%-0.55% of Cr, 1.5% to 2.0% of Si; 0.5% to 0.8% of Mn; 0.6%-1.0% of Cr; 0.2% to 0.3% of Cu; ni: 0.2%-0.28%; 0.05% to 0.15% of Mo; sb is less than or equal to 0.05% and cannot be 0; 0.1% to 0.15% of V; ti: 0 to 0.035%; p is less than 0.015%; s is less than 0.01%; and the balance of iron and inevitable impurities. The acid environment corrosion resistance is improved by limiting alloy steel alloy elements including Cu, Mo and Sb, and the delayed fracture resistance is improved by limiting alloy steel alloy elements including Mo, V and Ti or Mo and V.

Description

Technical Field

[0001] The present invention relates to the technical field of springs, in particular to a corrosion-resistant spring and a preparation method thereof. Background Art

[0002] A spring is a widely used elastic component. Made of elastic material, it deforms under external forces and returns to its original shape when the force is removed. Springs are generally cylindrical in shape and can be produced and processed by either cold or hot coiling. They are also called "springs." To better fit within their assembly space, springs can also be designed in non-cylindrical shapes, such as the arc springs used in automotive dual-mass flywheels. Springs come in a wide variety of shapes, primarily including coil springs, scroll springs, leaf springs, and special-shaped springs.

[0003] Springs are very common in today's applications. Various industries use springs with different strengths, stiffnesses, and service lives according to their specific uses. However, existing springs have poor delayed fracture resistance and corrosion resistance in acidic environments. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a corrosion-resistant spring and a preparation method thereof. The spring provided by the present invention improves the corrosion resistance of the spring in acidic environments by limiting the alloy elements of the alloy steel matrix to include Cu, Mo and Sb, thereby making the spring suitable for harsh atmospheric environments. By limiting the alloy elements of the alloy steel matrix to include Mo, Ti and V or Mo and V, the delayed fracture resistance of the spring is improved, thereby improving the safety of the spring.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a corrosion-resistant spring, which is based on alloy steel. The composition of the alloy steel, calculated by mass percentage, includes: C: 0.45%-0.55%; Si: 1.5%-2.0%; Mn: 0.5%-0.8%; Cr: 0.6%-1.0%; Cu: 0.2%-0.3%; Ni: 0.2%-0.28%; Mo: 0.05%-0.15%; Sb≤0.05% and cannot be 0; V: 0.1%-0.15%; Ti: 0-0.035%; P<0.015%; S<0.01%; the rest is iron and unavoidable impurities.

[0007] The spring provided by the present invention improves the corrosion resistance of the spring in acidic environments by limiting the alloy elements of the alloy steel matrix to include Cu, Mo and Sb, thereby making the spring suitable for harsh atmospheric environments. By limiting the alloy elements of the alloy steel matrix to include Mo, Ti and V or Mo and V, the delayed fracture resistance of the spring is improved, thereby improving the safety of the spring.

[0008] Furthermore, in the alloy steel, by mass percentage: Cr+Cu+Ni: 1%-1.5%;

[0009] And / or, in the alloy steel: the mass ratio of Cu to Ni is (1.0-1.2): 1;

[0010] And / or, in the alloy steel: the ratio of the mass of Cr to the sum of the mass of Cu and Ni is (2.0-3.0):1;

[0011] and / or, in the alloy steel, by mass percentage: 0.10%≤Mo+Sb≤0.20%;

[0012] And / or, in the alloy steel, by mass percentage: 0.1%≤V+Ti≤0.15%.

[0013] Furthermore, the corrosion-resistant spring is coated with a zinc-based alloy, and the coating is coated on the surface of the substrate. The composition of the zinc-based alloy includes, by mass percentage: Al: 5%-10%; Si: 0.1%-1.0%; La+Ce: 0.005%-0.05%; the rest is zinc and unavoidable impurities, and the total of other impurities is ≤0.5%.

[0014] Furthermore, the thickness of the coating is 20-100 μm.

[0015] Furthermore, the yield strength of the corrosion-resistant spring is ≥1350MPa, the tensile strength is ≥1570MPa, the elongation is ≥8%, the area reduction is ≥30%, the fatigue strength is ≥700Mpa, the hydrogen embrittlement sensitivity index is ≤18.3, and the corrosion weight loss rate is ≤0.13g / (m 2 ·h).

[0016] In a second aspect, the present invention provides a method for preparing a corrosion-resistant spring as described in the first aspect, the preparation method comprising the following steps in sequence: steelmaking, continuous casting, hot rolling of bars, surface treatment, heating-spring winding, heat treatment, and immersion plating.

[0017] Furthermore, the steelmaking step includes the following processes in sequence: blast furnace ironmaking, molten iron desulfurization treatment, converter steelmaking, and refining outside the furnace. The converter steelmaking process includes transferring the desulfurized molten iron into the converter steelmaking to obtain molten steel; the refining process outside the furnace includes LF refining and VD refining. The LF refining includes transferring the molten steel obtained by converter steelmaking into the LF refining furnace, heating it, adjusting the alloy composition, blowing in argon for stirring, and performing LF refining to obtain refined molten steel; the VD refining includes transferring the refined molten steel to a VD vacuum furnace, heating it, and evacuating it to 45Pa~55Pa for degassing to obtain cast molten steel.

[0018] Furthermore, the continuous casting step includes transporting the ladle containing the molten steel to a turntable, and after the turntable rotates to a pouring position, pouring the molten steel into a tundish, and then distributing the molten steel to each crystallizer through a nozzle for solidification and forming of the cast billet, and then pulling the casting out and cutting it into billets of a certain length through a straightening machine and a vibration device;

[0019] and / or, in the bar hot rolling step, the rolling temperature is controlled at 1000-1100° C.;

[0020] And / or, the surface treatment includes pickling the rolled bar to ensure that there are no cracks on the surface;

[0021] And / or, the heating-spring winding includes heating the rod to 800-900° C. to soften it and then winding it while introducing N2 to protect it from decarburization;

[0022] And / or, the heat treatment step includes a quenching + tempering process, wherein the quenching temperature is 810-850°C, the holding time is 30-60 minutes, and after the holding is completed, it is cooled to room temperature by water quenching or oil quenching; the tempering temperature is 420-520°C, the holding time is 1-2 hours, and after the holding is completed, it is air-cooled to room temperature;

[0023] And / or, the dip-plating step includes: pre-treating the spring substrate; smelting a zinc-based alloy of corresponding composition according to the coating composition, then placing the coating material in a galvanizing furnace for melting and insulation to obtain a hot-dip solution; preheating the spring substrate and immersing it in the hot-dip solution for hot-dip plating; after the hot-dip plating is completed, taking out the spring for alloying treatment, water cooling after the alloying treatment is completed, and then dehydrogenating the spring to complete the dip-plating process.

[0024] Furthermore, the pretreatment of the spring base includes the following steps in sequence: polishing the surface of the spring base with 200-400 grit sandpaper to improve the bonding strength of the coating; performing alkali washing on the spring base to remove oil, performing acid washing on the spring base to remove rust, washing the spring base with water to remove residual acid, and cleaning the spring base with anhydrous ethanol and drying it;

[0025] And / or, the temperature of the hot-dip bath is comprised between 420° C. and 460° C.;

[0026] And / or, the preheating temperature is 100-150° C. and the time is 3-5 minutes;

[0027] and / or, the spring substrate is preheated and immersed in the hot-dip bath for hot-dip plating for 5-15 seconds;

[0028] And / or, the alloying treatment includes first keeping the temperature at 490-510° C. for 20-40 seconds, then heating to 510-520° C., and keeping the temperature at 510-520° C. for 20-40 seconds.

[0029] Furthermore, the dehydrogenation treatment includes keeping the water-cooled spring in a convection atmosphere oven at 200-230° C. for 24-36 hours, and then cooling it in the oven or in air to room temperature.

[0030] Compared with the prior art, the present invention has at least one of the following advantages:

[0031] The spring provided by the present invention improves the corrosion resistance of the spring in acidic environments by limiting the alloy elements of the alloy steel matrix to include Cu, Mo and Sb, thereby making the spring suitable for harsh atmospheric environments. By limiting the alloy elements of the alloy steel matrix to include Mo, Ti and V or Mo and V, the delayed fracture resistance of the spring is improved, thereby improving the safety of the spring. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally based on conventional conditions. Unless otherwise specified, all raw materials can be purchased from the market or are commonly used materials in this industry.

[0033] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0034] In a first aspect, the present invention provides a corrosion-resistant spring, wherein the corrosion-resistant spring is based on an alloy steel, and the composition of the alloy steel, calculated by mass percentage, includes: C: 0.45%-0.55%; Si: 1.5%-2.0% (for example, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%); Mn: 0.5%-0.8% (for example, 0.5%, 0.6%, 0.7% or 0.8%). ; Cr: 0.6%-1.0% (for example, it can be 0.6%, 0.7%, 0.8%, 0.9% or 1%); Cu: 0.2%-0.3%; Ni: 0.2%-0.28%; Mo: 0.05%-0.15%; Sb≤0.05% and cannot be 0; V: 0.1%-0.15%; Ti: 0-0.035%; P≤0.015%; S≤0.01%; the rest is iron and unavoidable impurities.

[0035] The design principles of the chemical elements in the corrosion-resistant spring of the present invention are:

[0036] Carbon (C): Provides basic strength, hardness, and a high elastic limit. Too low (<0.45%): The strength, hardness, and elastic limit after quenching are insufficient, failing to meet spring performance requirements. Too high (>0.55%): The steel becomes significantly more brittle, reducing its plasticity and toughness, making it more susceptible to brittle fracture, increasing quenching cracking sensitivity, and impairing weldability. Excessive carbides may coarsen, impairing fatigue performance.

[0037] Silicon (Si): A core strengthening element that inhibits the precipitation, aggregation, and growth of carbides during the tempering process, allowing the steel to maintain high hardness and strength (enhanced relaxation resistance) after tempering at higher temperatures, significantly improving the elastic limit, yield strength ratio, strength, and tempering stability. It improves the deoxidation effect, helps form a dense surface oxide layer, and provides a certain degree of corrosion protection. Too low (<1.5%): The solid solution strengthening effect is insufficient, the elastic limit and relaxation resistance decrease, and the deoxidation effect is weakened. Too high (>2.0%): The toughness and plasticity of the steel, especially the low-temperature toughness, are seriously deteriorated; it promotes the tendency to graphitization (at high temperatures for a long time) and increases the sensitivity to surface decarburization (when heating during heat treatment). Silicon will promote surface decarburization of the steel during the heating process. The decarburized layer will seriously damage the fatigue life of the spring; it may aggravate the tendency to temper brittleness (especially in steels containing Mn and Cr); the work hardening rate is increased, and cold forming is difficult.

[0038] Chromium (Cr): A core hardenability element, it improves the hardenability of steel, resulting in uniform and high mechanical properties, particularly fatigue strength. Cr strengthens ferrite through solid solution and forms fine, hard carbides, increasing hardness and wear resistance. Cr also improves the material's tempering stability. Excessive chromium content increases the tendency for carbides to form unevenly. Excessive Cr carbides can impair toughness and fatigue strength.

[0039] Manganese (Mn): Manganese is one of the most economical and effective elements for improving hardenability, and its effect is slightly weaker than that of chromium. It works together with silicon and chromium to ensure that the steel has good hardenability. It dissolves in ferrite and improves the strength and hardness of the steel. Manganese combines with sulfur to form manganese sulfide, which prevents sulfur from forming low-melting-point ferrous sulfide with iron and offsets the harmful effects of sulfur. Too low (<0.5%): Insufficient hardenability, the core of a large-section spring may not be fully hardened, resulting in a large gradient of strength and hardness, and poor fatigue performance; insufficient deoxidation and desulfurization, affecting the purity of the steel; Too high (>0.8%): Significantly increases the overheating sensitivity and grain growth tendency of the steel; aggravates temper brittleness (especially when coexisting with P); MnS inclusions may increase and lengthen, impairing transverse plasticity and toughness, and become a source of fatigue cracks.

[0040] Copper (Cu): Improves atmospheric corrosion resistance. Cu forms a dense oxide film on the surface of steel, significantly improving atmospheric corrosion resistance, and is especially suitable for exposed environments such as automotive suspension springs. A small amount of Cu dissolved in the matrix can slightly increase the strength, but the contribution is limited. Copper is usually precipitated in steel as very fine copper-rich phase particles (especially during the tempering process). These precipitates can also serve as efficient hydrogen traps, capturing and fixing hydrogen atoms. If the copper content is too low, the atmospheric corrosion resistance drops significantly; copper in steel has the risk of "hot brittleness". When the Cu content is >0.5%, during hot processing (such as rolling and forging), Cu will be enriched at the grain boundaries due to its low melting point (1083°C), resulting in surface cracking (hot brittleness). Methods to eliminate the hot brittleness of copper include: adding Ni (nickel), Ni and Cu form a high melting point eutectic to inhibit hot brittleness.

[0041] Nickel (Ni): Inhibits the hot brittleness of copper. Ni preferentially forms a solid solution with Cu, preventing Cu from enriching at grain boundaries. Improves toughness and low-temperature impact properties. Ni refines grains and stabilizes austenite, increasing the toughness of steel. Enhances hardenability. A small amount of Ni can help improve hardenability, but the effect is weaker than that of Cr and Mo. Improves corrosion resistance, synergistically enhancing corrosion resistance with Cr and Cu.

[0042] Molybdenum (Mo): Strongly improves hardenability. Mo significantly delays the pearlite / bainite transformation, allowing full hardening of the core of large-section springs (such as valve spring steel 55CrSiMoV). It also inhibits temper brittleness. In Cr-Mn spring steels, Mo can suppress brittleness in the tempering range of 350-550°C and prevent the segregation of impurities such as P and Sn at grain boundaries. It also improves high-temperature strength and relaxation resistance. Mo carbides (such as Mo2C) have excellent high-temperature stability and are suitable for high-temperature operating conditions (≤500°C), such as engine valve springs. It also reduces decarburization tendency and the sensitivity to surface decarburization caused by elements such as Si and Cr. Mo also forms a dense passivation film on the steel surface, improving the steel's resistance to acidic corrosion. Molybdenum forms fine carbides (such as Mo2C) in steel. These carbide particles and the molybdenum atoms themselves act as very effective "hydrogen traps," capturing diffusing hydrogen atoms and firmly binding them to trap locations (such as the carbide / matrix interface), preventing them from freely diffusing and concentrating in dangerous stress concentration areas. This significantly reduces the risk of hydrogen-induced cracking. Excessive Mo carbide content increases cost and carbide inhomogeneity, while excessive Mo carbides can impair toughness.

[0043] Antimony (Sb): Improves the corrosion resistance of steel in acidic media and sulfate ion environments; trace amounts of Sb segregate at grain boundaries, inhibiting the adhesion of iron oxide scale to the matrix, reducing hot-rolled cracks, and improving the surface quality of hot-rolled steel. A very small amount of Sb can refine the grains, but excessive amounts can lead to brittleness.

[0044] Vanadium (V) and titanium (Ti): Although added in small amounts to spring steel, they significantly enhance its performance by refining grain size, inhibiting grain boundary migration, and forming dispersion-strengthened phases. V increases yield strength, enhances the spring steel's resistance to plastic deformation, and raises its elastic limit. It also inhibits austenite grain growth, refines grain size, improves toughness, and lowers the ductile-brittle transition temperature.

[0045] Ti reacts with nitrogen in the steel to form high-temperature stable TiN (precipitated during melting), with a size of 0.1 to 1 μm, effectively inhibiting austenite grain coarsening. Ti reacts with sulfur to form TiS / Ti4C2S2, reducing MnS inclusions (long strips of MnS are a source of fatigue cracks), improving transverse toughness and fatigue life. Trace amounts of titanium form fine TiC during cooling, which synergistically strengthens the steel with VC. V and Ti carbides or nitrides act as irreversible traps for hydrogen atoms, improving the steel's delayed fracture resistance.

[0046] Low phosphorus and sulfur content minimizes the adverse effects of harmful impurities on toughness, ductility, and fatigue strength. Phosphorus segregates at grain boundaries, significantly increasing the steel's cold brittleness (dramatically decreasing low-temperature toughness) and potentially reducing ductility. Sulfur forms sulfide inclusions (primarily MnS). Long, strip-shaped MnS inclusions can severely fracture the matrix, becoming a source of fatigue cracks and significantly reducing the steel's transverse ductility, toughness, and fatigue strength. Low sulfur content is crucial for components like springs that are subject to alternating loads.

[0047] The spring provided by the present invention improves the corrosion resistance of the spring in acidic environments by limiting the alloy elements of the alloy steel matrix to include Cu, Mo and Sb, thereby making the spring suitable for harsh atmospheric environments. By limiting the alloy elements of the alloy steel matrix to include Mo, V and Ti or Mo and V, the delayed fracture resistance of the spring is improved, thereby improving the safety of the spring.

[0048] In the aforementioned corrosion-resistant spring, as an optional embodiment, the alloy steel comprises, by mass percentage, 1% to 1.5% Cr, Cu, and Ni. For example, the sum of the mass percentages of Cr, Cu, and Ni can be 0.70%, 0.90%, 0.11%, 0.13%, or 0.15%. By limiting the sum of the mass percentages of Cr, Cu, and Ni to 1% to 1.5%, the present invention can synergistically regulate strength and corrosion resistance.

[0049] In the corrosion-resistant spring described above, as an optional embodiment, the alloy steel has a Cu to Ni mass ratio of (1.0-1.2):1. If this ratio is outside this range, the surface may be susceptible to cracking during hot working (such as rolling and forging), and Ni may not be effective in suppressing the hot brittleness of Cu.

[0050] In the above-mentioned corrosion-resistant spring, as an optional embodiment, the ratio of the mass of Cr to the sum of the mass of Cu and Ni in the alloy steel is (2.0-3.0): 1. If it is not within this range, the corrosion resistance is reduced.

[0051] In the corrosion-resistant spring, as an optional embodiment, the alloy steel has the following mass percentage: 0.10%≤Mo+Sb≤0.20%. If it is outside this range, the carbides are uneven, the mechanical properties are reduced, and the brittleness is increased.

[0052] In the corrosion-resistant spring, as an optional embodiment, the alloy steel has a V+Ti content, calculated by mass percentage, of 0.1% ≤ V + 0.15%. For example, the sum of the mass percentages of V and Ti can be 0.1%, 0.11%, 0.13%, or 0.15%. Exceeding this range may reduce the delayed fracture resistance of the steel and increase production costs.

[0053] In the above-mentioned corrosion-resistant spring, as an optional embodiment, the corrosion-resistant spring is coated with a zinc-based alloy. The coating is coated on the surface of the substrate. The composition of the zinc-based alloy, by mass percentage, includes: Al: 5%-10% (for example, 5%, 6%, 7%, 8%, or 10%); Si: 0.1%-1.0% (for example, 0.1%, 0.3%, 0.5%, 0.7%, or 1%); La+Ce: 0.005%-0.05% (for example, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%); the remainder is zinc and unavoidable impurities, with the total amount of other impurities being ≤0.5%. The coating provided by the present invention can improve the corrosion resistance of the spring.

[0054] In the present invention, the Al content is limited to 5%-10%. A high Al content can improve the corrosion resistance of the coating in an acidic environment and extend the protective life of the coating. The Si content is limited to 0.1%-1.0%, so that the coating has better protective ability and improves its corrosion resistance and wear resistance. If the silicon content is too high, the cost will increase, and if it is too low, the protective ability of the coating will be affected, and the corrosion resistance and wear resistance will be reduced. The La+Ce content is limited to 0.005%-0.05%, so that the corrosion products have higher stability and the protective ability of the coating is stronger, thereby improving the overall corrosion resistance of the spring. If the content is too high, the cost will increase, and if the content is too low, the stability of the corrosion products will be reduced, the protective ability of the coating will be weakened, and the overall corrosion resistance of the spring will be affected.

[0055] In the above-mentioned corrosion-resistant spring, as an optional embodiment, the thickness of the coating is 20-100 μm, for example, 20 μm, 40 μm, 60 μm, 80 μm or 100 μm.

[0056] In the aforementioned corrosion-resistant spring, as an optional embodiment, the corrosion-resistant spring has (mechanical properties after heat treatment) yield strength ≥1350MPa, tensile strength ≥1570MPa, elongation ≥8%, and area reduction ≥30%. The extremely high yield strength and tensile strength give the spring a strong load-bearing capacity and resistance to deformation / fracture, enabling it to withstand high operating stresses. The elongation (≥8%) provides basic toughness, ensuring the material has a certain plasticity that can buffer accidental overloads and avoid complete brittle fracture. The area reduction (≥30%) is the key to toughness, greatly enhancing the spring's ability to resist fatigue crack initiation and propagation, which is the core factor determining the spring's service life (fatigue life) under repeated loads. It also provides higher resistance to brittle fracture safety. As can be seen from the aforementioned mechanical properties, the spring provided by the present invention has excellent resistance to permanent deformation, high load-bearing capacity, excellent fatigue life, and good safety and reliability under extremely high operating stresses and harsh cyclic loading conditions. This type of spring is usually used in situations where performance, life and safety are extremely demanding, such as high-performance automotive suspensions, heavy-loaded mechanical valves, and critical aerospace components.

[0057] In the aforementioned corrosion-resistant spring, as an optional embodiment, the corrosion-resistant spring has a fatigue strength of ≥700 MPa. Fatigue strength refers to the maximum stress at which a material can withstand an infinite number of alternating loads without breaking. A value of ≥700 MPa indicates that the spring can withstand extremely high maximum cyclic stress amplitudes (far exceeding those of typical structural steel). This means that the spring is less susceptible to sudden fracture due to fatigue accumulation when subjected to high-frequency, high-stress repeated deformation (such as vehicle suspension compressions several times per second), and exhibits an exceptionally long service life (high-cycle fatigue life).

[0058] In the above-mentioned corrosion-resistant spring, as an optional embodiment, the hydrogen embrittlement sensitivity index of the corrosion-resistant spring is ≤18.3, and the corrosion weight loss rate is ≤0.13g / (m 2 ·h).

[0059] In a second aspect, the present invention provides a method for preparing a corrosion-resistant spring as described in the first aspect, the preparation method comprising the following steps in sequence: steelmaking, continuous casting, hot rolling of bars, surface treatment, heating-spring winding, heat treatment, and immersion plating.

[0060] In the above-mentioned method for preparing corrosion-resistant springs, as an optional embodiment, the steelmaking step includes the following processes in sequence: blast furnace ironmaking, molten iron desulfurization treatment, converter steelmaking, and refining outside the furnace. The converter steelmaking process includes transferring the molten iron after desulfurization treatment into the converter steelmaking to obtain molten steel; the refining process outside the furnace includes LF refining and VD refining. The LF refining includes transferring the molten steel obtained by converter steelmaking into the LF refining furnace, heating it, adjusting the alloy composition, blowing in argon for stirring, and performing LF refining to obtain refined molten steel; the VD refining includes transferring the refined molten steel to a VD vacuum furnace, heating it, and evacuating it to 45Pa~55Pa for degassing to obtain cast molten steel.

[0061] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the continuous casting step includes transporting the ladle containing the cast molten steel to a turntable, and after the turntable rotates to the pouring position, the molten steel is poured into a tundish, and the tundish then distributes the molten steel to each crystallizer through the water nozzle for solidification and forming of the cast billet, and then the casting is pulled out and cut into billets of a certain length through a straightening machine and a vibration device.

[0062] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, in the bar hot rolling step, the rolling temperature is controlled at 1000-1100°C, for example, it can be 1000°C, 1020°C, 1040°C, 1060°C, 1080°C or 1100°C.

[0063] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the surface treatment includes pickling the rolled bar to ensure that there are no cracks on the surface.

[0064] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the heating-spring winding includes heating the rod to 800-900°C (for example, 800°C, 820°C, 840°C, 860°C, 880°C or 900°C) and winding it after softening, while introducing N2 to protect against decarburization.

[0065] In the preparation method of the above-mentioned corrosion-resistant spring, as an optional embodiment, the heat treatment step includes a quenching + tempering process, the quenching temperature is 810-850℃ (for example, it can be 810℃, 820℃, 830℃, 840℃ or 850℃), the holding time is 30-60min (for example, it can be 30min, 40min, 50min or 60min), and after the holding is completed, it is cooled to room temperature by water quenching or oil quenching; the tempering temperature is 420-520℃ (for example, it can be 420℃, 440℃, 460℃, 480℃, 500℃ or 520℃), the holding time is 1-2h, and after the holding is completed, it is air-cooled to room temperature.

[0066] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the dipping step includes: pre-treating the spring substrate; smelting a zinc-based alloy of corresponding composition according to the coating composition, and then placing the coating material in a galvanizing furnace for melting and insulation to obtain a hot-dip solution; preheating the spring substrate and immersing it in the hot-dip solution for hot-dip plating; after the hot-dip plating is completed, taking out the spring for alloying treatment, water cooling after the alloying treatment is completed, and then dehydrogenating the spring to complete the dipping process.

[0067] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the pretreatment of the spring base includes the following steps in sequence: using 200-400 mesh sandpaper to polish the surface of the spring base to improve the bonding strength of the coating; alkali washing the spring base to remove oil, pickling the spring base to remove rust, washing the spring base with water to remove residual acid, and cleaning the spring base with anhydrous ethanol and blowing it dry.

[0068] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the temperature of the hot-dip plating solution is 420-460°C, for example, 420°C, 435°C, 440°C, 445°C or 460°C.

[0069] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the preheating temperature is 100-150°C (for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C or 150°C), and the time is 3-5 minutes.

[0070] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the spring substrate is preheated and then immersed in the hot-dip plating solution for hot-dip plating for 5-15 seconds, for example, 5 seconds, 7 seconds, 9 seconds, 11 seconds, 13 seconds or 15 seconds.

[0071] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the alloying treatment includes first keeping warm at 490-510°C (for example, 490°C, 495°C, 500°C or 510°C) for 20-40s (for example, 20s, 25s, 30s, 35s or 40s), then heating to 510-520°C (for example, 510°C, 515°C or 520°C), and keeping warm at 510-520°C for 20-40s (for example, 20s, 25s, 30s, 35s or 40s).

[0072] In the above-mentioned method for preparing the corrosion-resistant spring, as an optional embodiment, the dehydrogenation treatment includes keeping the water-cooled spring in a convection atmosphere oven at 200-230°C (for example, 200°C, 210°C, 220°C or 230°C) for 24-36h (for example, 24h, 26h, 28h, 30h, 32h, 34h or 36h), and then cooling it with the furnace or air cooling it to room temperature, wherein the atmosphere includes an air atmosphere.

[0073] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0074] Example 1

[0075] A method for preparing a corrosion-resistant spring comprises the following steps:

[0076] 1) Steelmaking: The process includes the following steps in sequence: blast furnace ironmaking, molten iron desulfurization, converter steelmaking, and off-furnace refining. The converter steelmaking step includes transferring the desulfurized molten iron into a converter steelmaking step to obtain molten steel. The off-furnace refining step includes LF refining and VD refining. The LF refining step includes transferring the molten steel obtained from converter steelmaking into an LF refining furnace, heating it, adjusting the alloy composition, blowing in argon gas for stirring, and performing LF refining to obtain refined molten steel. The VD refining step includes transferring the refined molten steel into a VD vacuum furnace, heating it, and vacuuming it to 50 Pa for degassing to obtain cast steel. The cast steel comprises, by mass percentage, the following components: C : 0.5%, Si: 1.5%, Mn: 0.7%, Cr: 0.8%, Ni: 0.2%, V: 0.1%, Cu: 0.2%, Sb: 0.05%, Mo: 0.05%, P: 0.011%, S: 0.005%, O: 0.0025%, N: 0.003%, the rest are iron and unavoidable impurities (satisfying 1%≤Cr+Cu+Ni≤1.5%, Cu:Ni=1.0:1, 2.0:1≤Cr:(Cu+Ni)≤3.0:1), 0.10%≤Mo+Sb≤0.20%, 0.1%≤V+Ti≤0.15%);

[0077] 2) Continuous Casting: The ladle filled with refined molten steel is transported to the turntable. After the turntable rotates to the pouring position, the molten steel is poured into the tundish. The tundish then distributes the molten steel to each crystallizer through the nozzle for solidification and forming of the cast billet. The casting is then pulled out and cut into billets of a certain length by a straightening machine and a vibration device.

[0078] 3) Hot rolling of bars: the ingot is heated to 1100℃ and then subjected to multiple rolling deformation;

[0079] 4) Surface treatment: The surface of the rolled bar is pickled to ensure that there are no defects such as cracks on the surface of the bar;

[0080] 5) Heating - Spring Winding - Heat Treatment: The rod is heated to 850°C to soften it and then wound, while nitrogen is introduced to prevent decarburization. The wound spring substrate is then placed in an alloy furnace for heat treatment, kept at 830°C for 30 minutes, water quenched, cooled to room temperature, and tempered at 450°C for 60 minutes. After tempering, it is air-cooled to room temperature.

[0081] 6) Immersion plating:

[0082] a) Surface treatment: The spring substrate surface was pre-polished with 200-grit sandpaper to improve the adhesion of the coating. The substrate was then cleaned sequentially with NaOH solution (pH = 12), HCl solution (5 wt %), deionized water, and anhydrous ethanol, and then dried.

[0083] b) Coating composition (wt%): Al: 6.5%, Si: 0.2%, La + Ce: 0.02% (La: 0.01%, Ce: 0.01%), with the balance being Zn and unavoidable impurities (impurity content ≤ 0.5%). A zinc-based alloy having a corresponding composition according to the coating composition is smelted, and the coating material is then placed in a galvanizing furnace for melting and heat preservation to obtain a hot-dip bath, the hot-dip bath temperature being 440° C.

[0084] c) Hot dip coating: preheat the surface treated spring substrate at 120°C for 3 minutes and then immerse it in the hot dip coating solution for 5 seconds.

[0085] d) Alloying treatment: After hot-dip plating, take out the spring, keep it at 490℃ for 30s, then raise the temperature to 510℃ and keep it at 510℃ for 30s;

[0086] e) Cooling to room temperature with water, the coating thickness is 50 μm;

[0087] f) Dehydrogenation: The water-cooled spring was kept in a convection air oven at 210°C for 24 hours and then cooled to room temperature.

[0088] Example 2

[0089] The preparation method of the corrosion-resistant spring of Example 2 is basically the same as that of Example 1, except that, in step 1), Mo: 0.15%, Sb: 0.05%, 0.1%<Mo+Sb=0.2%.

[0090] Example 3

[0091] The preparation method of the corrosion-resistant spring of Example 3 is basically the same as that of Example 1, except that, in step 1), V: 0.1%, Ti: 0.03%, 0.1% < V + Ti = 0.13% < 0.15%.

[0092] Example 4

[0093] The preparation method of the corrosion-resistant spring of Example 4 is basically the same as that of Example 1, except that, in step 1), Cr: 1%, Cu: 0.25%, Ni: 0.25%, 1%<Cr+Cu+Ni=1.5%, Cu:Ni=1:1, 2.0:1≤Cr:(Cu+Ni)≤3.0:1).

[0094] Example 5

[0095] The preparation method of the corrosion-resistant spring of Example 5 is basically the same as that of Example 1, except that, in step 5), water quenching is performed after keeping at 850°C for 30 minutes, cooling to room temperature, and then tempering at 440°C for 60 minutes, and air cooling to room temperature after tempering.

[0096] Example 6

[0097] The preparation method of the corrosion-resistant spring of Example 6 is basically the same as that of Example 1, except that, in step 6), La: 0.02%, Ce: 0.02%, 0.005%<La+Ce=0.04%<0.05%.

[0098] Comparative Example 1

[0099] The preparation method of the corrosion-resistant spring of Comparative Example 1 is substantially the same as that of Example 1, except that, in step 1), Sb: 0.05% and the composition of the cast steel liquid does not include Mo.

[0100] Comparative Example 2

[0101] The preparation method of the corrosion-resistant spring of Comparative Example 2 is substantially the same as that of Example 1, except that, in step 1), Mo: 0.05% and the composition of the cast steel liquid does not include Sb.

[0102] Comparative Example 3

[0103] The preparation method of the corrosion-resistant spring of Comparative Example 3 is substantially the same as that of Example 1, except that, in step 1), the composition of the cast steel liquid does not include Cu.

[0104] Comparative Example 4

[0105] The preparation method of the corrosion-resistant spring of Comparative Example 4 is basically the same as that of Example 1, except that in step 6), the alloying treatment is not performed in stages, the alloying temperature is 500° C., and the holding time is 1 min.

[0106] Comparative Example 5

[0107] The preparation method of the corrosion-resistant spring of Comparative Example 5 is basically the same as that of Example 1, except that in step 1), the composition of the casting molten steel does not include V.

[0108] Comparative Example 6

[0109] The preparation method of the corrosion-resistant spring of Comparative Example 6 is basically the same as that of Example 1, except that in step 6), the coating composition does not include La and Ce.

[0110] Comparative Example 7

[0111] The preparation method of the corrosion-resistant spring of Comparative Example 7 is substantially the same as that of Example 1, except that, in step 1), the V content in the steel is 0.04%.

[0112] Comparative Example 8

[0113] The preparation method of the corrosion-resistant spring of Comparative Example 8 is basically the same as that of Example 1, except that in step 6), the plating solution contains 3% Al.

[0114] Performance testing:

[0115] The finished springs prepared in the examples and comparative examples were tested for mechanical properties, delayed fracture resistance, and corrosion resistance. The results are shown in Tables 1 and 2.

[0116] The tensile strength and yield strength test standards are based on GB / T 228.1-2021, "Metallic Materials Tensile Tests Part 1: Room Temperature Test Methods." Tensile tests are conducted using a mechanical properties testing machine, using standard tensile specimens. Stretching is performed until fracture, followed by splicing. Yield strength and tensile strength can be directly calculated using a computer. The elongation and area reduction are calculated by measuring the fracture length and minimum cross-sectional diameter. The specific calculation formula is as follows:

[0117] Elongation (%): (Where L0 is the original gauge length, L1 is the gauge length after breaking)

[0118] Shrinkage rate (%): (Where S0 is the original cross-sectional area of ​​the parallel segment, and S1 is the cross-sectional area of ​​the thinnest part of the parallel segment after breaking).

[0119] The fatigue strength is determined by performing a rotary bending test in accordance with the national standard GB / T 39039-2020 "Rotary Bending Method for Fatigue Test of Metallic Materials".

[0120] The hydrogen-induced delayed fracture test was conducted in accordance with the national standard GB / T 39039-2020, "Evaluation Method for Hydrogen-Induced Delayed Fracture of High-Strength Steel." Electrochemical hydrogen charging and slow strain tensile tests were used to evaluate the delayed fracture resistance of hydrogen-charged and non-hydrogen-charged specimens by comparing their tensile mechanical properties. The indicators are as follows:

[0121] Hydrogen embrittlement sensitivity index: (Where A0 is the elongation of the sample not charged with hydrogen, and A1 is the elongation of the sample charged with hydrogen).

[0122] The corrosion resistance was evaluated by conducting periodic infiltration experiments and measuring the corrosion weight loss rate. The experimental reagent was 0.01 mol / L NaHSO3 solution, and the experimental period was 72 h.

[0123] Table 1

[0124]

[0125]

[0126] Table 2

[0127]

[0128] From Tables 1 and 2, we can see at least the following points:

[0129] (1) Comparing Example 1 with Comparative Example 1, it can be seen that when Mo is not included in the spring matrix, the delayed fracture resistance is reduced, the fatigue strength is reduced, and the acid environment corrosion resistance is reduced;

[0130] (2) Comparison of Example 1 with Comparative Example 2 shows that when Sb is not included in the spring matrix, fatigue strength decreases and corrosion resistance in acidic environments decreases;

[0131] (3) Comparison of Example 1 with Comparative Example 3 shows that when Cu is not included in the spring matrix, the mechanical properties, delayed fracture resistance, fatigue strength, and acid environment corrosion resistance are reduced;

[0132] (4) Comparison of Example 1 with Comparative Example 4 shows that when the alloying process is cancelled in stages, the corrosion resistance in acidic environments decreases. The applicant speculates that the reason may be that the single-stage process may lead to a slightly lower density of the coating and a weakened resistance to acidic substance penetration; compared with the staged process, the interface segregation of rare earth elements (La / Ce) is suppressed, and the hydrogen trap efficiency is slightly reduced.

[0133] (5) Comparison of Example 1 with Comparative Example 5 or Comparative Example 7 shows that when the spring matrix does not contain V or the V content is low, the mechanical properties, delayed fracture resistance, fatigue strength, and acid environment corrosion resistance are reduced;

[0134] (6) Comparing Example 1 with Comparative Example 6, it can be seen that when La and Ce are not included in the coating, the corrosion resistance in an acidic environment decreases.

[0135] (7) Comparing Example 1 with Comparative Example 8, it can be seen that when the Al content in the coating decreases, the corrosion resistance in an acidic environment decreases.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A corrosion-resistant spring, wherein the corrosion-resistant spring is based on alloy steel and is characterized in that: The composition of the alloy steel includes, by mass percentage: C: 0.45%-0.55%; Si: 1.5%-2.0%; Mn: 0.5%-0.8%; Cr: 0.6%-1.0%; Cu: 0.2%-0.3%; Ni: 0.2%-0.28%; Mo: 0.05%-0.15%; Sb≤0.05% and cannot be 0; V: 0.1%-0.15%; Ti: 0-0.035%; P<0.015%; S<0.01%; the rest is iron and unavoidable impurities.

2. The corrosion-resistant spring according to claim 1, characterized in that In terms of mass percentage, the alloy steel comprises: Cr+Cu+Ni: 1%-1.5%; And / or, in the alloy steel: the mass ratio of Cu to Ni is (1.0-1.2): 1; And / or, in the alloy steel: the ratio of the mass of Cr to the sum of the mass of Cu and Ni is (2.0-3.0):1; and / or, in the alloy steel, by mass percentage: 0.10%≤Mo+Sb≤0.20%; And / or, in the alloy steel, by mass percentage: 0.1%≤V+Ti≤0.15%.

3. The corrosion-resistant spring according to claim 1, characterized in that The corrosion-resistant spring is coated with a zinc-based alloy, which is coated on the surface of the substrate. The composition of the zinc-based alloy includes, by mass percentage, Al: 5%-10%; Si: 0.1%-1.0%; La+Ce: 0.005%-0.05%; the rest is zinc and unavoidable impurities, and the total amount of other impurities is ≤0.5%.

4. The corrosion-resistant spring according to claim 3, characterized in that The thickness of the coating is 20-100 μm.

5. The corrosion-resistant spring according to any one of claims 1 to 4, characterized in that: The corrosion-resistant spring has a yield strength of ≥1350 MPa, a tensile strength of ≥1570 MPa, an elongation of ≥8%, an area reduction of ≥30%, a fatigue strength of ≥700 MPa, a hydrogen embrittlement sensitivity index of ≤18.3, and a corrosion weight loss rate of ≤0.13 g / (m 2 ·h).

6. A method for preparing a corrosion-resistant spring according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps in sequence: steelmaking, continuous casting, bar hot rolling, surface treatment, heating-spring winding, heat treatment, and immersion plating.

7. The method for preparing a corrosion-resistant spring according to claim 6, characterized in that: The steelmaking steps include the following processes in sequence: blast furnace ironmaking, molten iron desulfurization treatment, converter steelmaking, and refining outside the furnace. The converter steelmaking process includes transferring the desulfurized molten iron into the converter steelmaking to obtain molten steel; the refining outside the furnace includes LF refining and VD refining. The LF refining includes transferring the molten steel obtained by converter steelmaking into the LF refining furnace, heating it, adjusting the alloy composition, blowing in argon gas for stirring, and performing LF refining to obtain refined molten steel; the VD refining includes transferring the refined molten steel to a VD vacuum furnace, heating it, and evacuating it to 45Pa~55Pa for degassing to obtain cast molten steel.

8. The method for preparing a corrosion-resistant spring according to claim 6, wherein: The continuous casting step includes transporting the ladle containing the molten steel to a turntable, rotating the turntable to a pouring position, pouring the molten steel into a tundish, and then distributing the molten steel to each crystallizer through a nozzle for solidification and forming of the cast billet, and then pulling the casting out and cutting it into billets of a certain length through a straightening machine and a vibration device; and / or, in the bar hot rolling step, the rolling temperature is controlled at 1000-1100° C.; And / or, the surface treatment includes pickling the rolled bar to ensure that there are no cracks on the surface; And / or, the heating-spring winding includes heating the rod to 800-900° C. to soften it and then winding it while introducing N2 to protect it from decarburization; And / or, the heat treatment step includes a quenching + tempering process, wherein the quenching temperature is 810-850°C, the holding time is 30-60 minutes, and after the holding is completed, it is cooled to room temperature by water quenching or oil quenching; the tempering temperature is 420-520°C, the holding time is 1-2 hours, and after the holding is completed, it is air-cooled to room temperature; And / or, the dip-plating step includes: pre-treating the spring substrate; smelting a zinc-based alloy of corresponding composition according to the coating composition, then placing the coating material in a galvanizing furnace for melting and insulation to obtain a hot-dip solution; preheating the spring substrate and immersing it in the hot-dip solution for hot-dip plating; after the hot-dip plating is completed, taking out the spring for alloying treatment, water cooling after the alloying treatment is completed, and then dehydrogenating the spring to complete the dip-plating process.

9. The method for preparing a corrosion-resistant spring according to claim 8, characterized in that: The pretreatment of the spring base includes the following steps in sequence: polishing the surface of the spring base with 200-400 mesh sandpaper to improve the bonding strength of the coating; performing alkali washing on the spring base to remove oil, performing acid washing on the spring base to remove rust, washing the spring base with water to remove residual acid, and cleaning the spring base with anhydrous ethanol and drying it; And / or, the temperature of the hot-dip bath is comprised between 420° C. and 460° C.; And / or, the preheating temperature is 100-150° C. and the time is 3-5 minutes; and / or, the spring substrate is preheated and immersed in the hot-dip bath for hot-dip plating for 5-15 seconds; And / or, the alloying treatment includes first keeping the temperature at 490-510° C. for 20-40 seconds, then heating to 510-520° C., and keeping the temperature at 510-520° C. for 20-40 seconds.

10. The method for preparing a corrosion-resistant spring according to claim 8, characterized in that: The dehydrogenation treatment includes keeping the water-cooled spring in a convection oven at 200-230° C. for 24-36 hours, and then cooling it to room temperature in the oven or in air.

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