A wire rod for an ultra-high strength spring wire

Abstract

This invention relates to the field of metal material processing technology and discloses a high-strength spring steel wire rod. The preparation method includes mechanical pretreatment of hot-rolled steel wire rod to remove iron oxide scale from its surface; subsequently, the pretreated steel wire rod is immersed in a surface treatment solution containing a phosphate film-forming agent, a complexing agent, an interface passivating agent, and a redox potential regulator. The core of this method lies in controlling the synergistic effect of each component to stabilize the redox potential of the treatment solution within a positive potential range of +200mV to +300mV, thermodynamically inhibiting the hydrogen evolution reaction, thereby generating a dense and uniform composite conversion film in situ on the steel wire surface. This invention integrates pickling and phosphating into a single step, fundamentally avoiding hydrogen embrittlement, shortening the production process, reducing energy consumption and environmental pollution, and providing an excellent lubrication base for subsequent drawing.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a wire for ultra-high strength spring steel wire. Background Technology

[0002] As a core basic component in high-end equipment, ultra-high strength spring steel wire has extremely strict requirements on its surface quality and subsequent drawing performance. Before the cold drawing process, the hot-rolled wire must be pre-treated to remove the iron oxide scale on its surface and form a bottom layer that is conducive to drawing lubrication.

[0003] Currently, the industry generally uses the traditional two-step pickling-phosphating process. This process first uses strong acids (such as hydrochloric acid and sulfuric acid) to pickle the steel wire to remove iron oxide scale. However, when strong acids react with the steel matrix, they inevitably trigger hydrogen evolution side reactions. The hydrogen atoms produced can penetrate into the steel's crystal lattice, leading to hydrogen embrittlement. This hydrogen embrittlement severely degrades the mechanical properties of the steel wire, especially the torsional performance, a key indicator for springs, thus posing a hidden danger to the quality and safety of the final product.

[0004] Furthermore, this two-step process has inherent shortcomings. Treating pickling and phosphating as two separate processes not only lengthens the production line, increases equipment investment and energy consumption, but also makes process control more complex. More importantly, the environmental impact of this process cannot be ignored. The pickling process generates a large amount of acidic wastewater, which is difficult and costly to treat; while the phosphating process generates a large amount of phosphating sludge, creating a double burden on the environment.

[0005] Therefore, developing a new steel wire surface treatment technology that can prevent hydrogen embrittlement from the source, simplify the process, and reduce environmental pollution has become an urgent need for technological development in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a wire for ultra-high strength spring steel wire, which solves the problems of hydrogen embrittlement risk, lengthy process, and environmental pollution caused by the existing steel wire pretreatment process using a two-step pickling-phosphating method.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing ultra-high strength spring steel wire includes the following steps: S1. Mechanical pretreatment is performed on hot-rolled steel wire rod to remove iron oxide scale from the surface, resulting in pretreated steel wire rod; S2. The pretreated steel wire rod is immersed in a surface treatment solution containing a phosphate film-forming agent, a complexing agent, an interface passivating agent, a redox potential regulator and a surfactant to generate a composite conversion film on the surface. S3. During the soaking process, by controlling the synergistic effect of the interface passivating agent and the redox potential regulator, the redox potential of the surface treatment solution is controlled within a certain range to suppress hydrogen evolution. S4. The steel wire rods from which the composite conversion film is generated are cleaned and dried to obtain the ultra-high strength spring steel wire.

[0008] By adopting the above technical solution, this invention integrates the traditional pickling and phosphating processes into a one-step process for generating a composite conversion film by controlling the electrochemical reaction. Its core principle lies in constructing an electrochemical buffer system composed of an interface passivator and a redox potential regulator to precisely control the redox potential of the treatment solution. This regulation brings the following key benefits: by stabilizing the redox potential in a high positive potential range, the electrode potential of the hydrogen evolution reaction is increased, thermodynamically and kinetically inhibiting hydrogen generation and penetration into the steel wire matrix, thereby fundamentally preventing hydrogen embrittlement. This electrochemical system, in conjunction with a phosphate film-forming agent, can gently dissolve the steel wire surface under hydrogen-embrittlement-free conditions and deposit in situ a dense, uniform, and finely crystalline phosphate-molybdate composite conversion film. This film not only possesses excellent corrosion resistance, but its microporous structure also provides good storage space for subsequent drawing lubricants, improving lubrication performance. This invention provides a hydrogen-embrittle-free, short-process, environmentally friendly, and highly efficient surface treatment method for ultra-high strength spring steel wire.

[0009] Preferably, the surface treatment liquid is prepared from the following raw materials in parts by weight: 59 to 176 parts of phosphoric acid, 10 to 50 parts of sodium gluconate, 1 to 5 parts of ammonium heptamolybdate tetrahydrate, 2 to 10 parts of phosphorous acid, 0.5 to 2 parts of fatty alcohol polyoxyethylene ether, and the balance being deionized water.

[0010] By employing the above technical solution, a highly efficient synergistic effect is achieved among the components. Phosphoric acid serves as the main film-forming agent and acidity source; ammonium heptamolybdate tetrahydrate and phosphorous acid constitute the core electrochemical control pair; sodium gluconate acts as a complexing agent, stabilizing metal ions in the solution and refining the film grains; and fatty alcohol polyoxyethylene ether acts as a surfactant, ensuring uniform wetting of the treatment solution on the steel wire surface. Within this ratio range, a balance can be achieved between reaction rate, film quality, and process stability.

[0011] Preferably, in S2, the phosphate film-forming agent is phosphoric acid, the complexing agent is sodium gluconate, the interface passivating agent is ammonium heptamolybdate tetrahydrate, the redox potential regulator is phosphorous acid, and the surfactant is fatty alcohol polyoxyethylene ether.

[0012] By adopting the above technical solution, the specific chemical substances corresponding to each functional component are identified, and their reaction mechanism is described as follows: In the acidic environment provided by phosphoric acid, the iron metal on the surface of the steel wire substrate undergoes electrochemical dissolution, transforming into ferrous ions which enter the treatment solution. These newly generated ferrous ions then combine with phosphate ions in the solution, generating in-situ insoluble ferrous phosphate through a precipitation reaction. This substance constitutes the structural framework of the composite conversion membrane. Phosphorous acid, as a reducing agent, establishes a dynamic equilibrium with ammonium heptamolybdate tetrahydrate (providing molybdate ions), which acts as an oxidizing agent and passivating agent, in the solution. Heng stabilizes the redox potential of the entire system within a preset positive potential range. Under this potential condition, molybdate ions preferentially react and deposit at highly active sites on the steel wire surface, forming an initial passivation layer, thereby suppressing the hydrogen evolution side reaction that leads to hydrogen embrittlement. Sodium gluconate regulates the nucleation and growth rate of ferrous phosphate by forming a soluble complex with some ferrous ions, thereby refining the crystal structure of the film and preventing grain coarsening. At the same time, fatty alcohol polyoxyethylene ether reduces the surface tension of the treatment liquid, ensuring that the liquid can uniformly wet the entire steel wire surface, so that the film formation reaction can proceed uniformly.

[0013] Preferably, in S1, the mechanical pretreatment is shot blasting, in which hot-rolled steel wire rods are mechanically pretreated by passing them through a shot blaster with a running linear speed of 85 to 95 meters per minute and a rotation speed of 2700 to 3000 revolutions per minute.

[0014] By adopting the above technical solution, high-speed steel shot is used to physically impact the surface of steel wire, which can efficiently and pollution-free remove iron oxide scale and obtain a certain surface roughness, providing a good physical basis for the subsequent adhesion of conversion film. Compared with chemical pickling, it is more environmentally friendly.

[0015] Preferably, in S3, the immersion time of the wire rod in the surface treatment solution is 5 to 10 minutes.

[0016] By adopting the above technical solution, within this time range, it is possible to ensure that the conversion membrane grows sufficiently to achieve the required membrane thickness and density, while avoiding overgrowth or loosening of the membrane layer due to excessive time.

[0017] Preferably, during the immersion process, the steel wire rod is immersed in the surface treatment solution at a temperature of 65 to 68°C, a pH value of 2.2 to 2.5, and an oxidation-reduction potential of +250mV to +280mV.

[0018] By adopting the above technical solutions, the process parameters can be controlled within a more refined and preferred range, thereby achieving the best overall effect. This temperature range ensures an appropriate reaction rate; this pH range is the optimal balance point between film formation reaction and substrate micro-dissolution; and this redox potential range is the optimal window for suppressing hydrogen embrittlement and ensuring film formation efficiency.

[0019] Preferably, the fatty alcohol polyoxyethylene ether is fatty alcohol polyoxyethylene ether AEO-9.

[0020] The reason for adopting the above technical solution and selecting this specific type of surfactant is that fatty alcohol polyoxyethylene ether AEO-9 has excellent wetting and penetrating properties, and good stability under acidic heating conditions, which can ensure full contact between the treatment solution and the steel wire substrate.

[0021] Preferably, the cleaning steel wire is passed through a spray cleaning zone with room temperature deionized water and a spray pressure of 0.25 to 0.35 MPa.

[0022] By adopting the above technical solution and using deionized water spray with a certain pressure, the residual treatment liquid adhering to the surface of the conversion membrane can be removed efficiently, avoiding the influence of impurity ions on subsequent processes and ensuring the purity of the membrane layer.

[0023] Preferably, the composite conversion film on the surface of the ultra-high strength spring steel wire prepared by the method has a film weight of 3.62 to 5.41 g / m³. 2 .

[0024] By adopting the above technical solution, this film weight range indicates that a conversion film of moderate thickness and complete coverage can be generated, which can provide sufficient corrosion protection and lubricant adsorption capacity, and will not cause brittle peeling during subsequent drawing process due to excessive film thickness.

[0025] Preferably, in S4, the steel wire enters the drying process where the temperature is 115 to 125°C and the air velocity is 14 to 16 m / s for hot air circulation drying.

[0026] By adopting the above technical solution and using high-temperature hot air for rapid drying, the moisture on the surface of the steel wire can be quickly removed, preventing secondary oxidation or watermarks on the surface of the conversion film and ensuring the surface quality of the finished wire.

[0027] This invention provides a wire for ultra-high strength spring steel wire. It has the following beneficial effects: 1. This invention fundamentally avoids the risk of hydrogen embrittlement of steel wire. This is due to the synergistic effect of the interface passivator and the redox potential regulator, which precisely controls the redox potential of the treatment solution in a high positive potential range. This electrochemical environment thermodynamically inhibits the occurrence of hydrogen evolution side reactions and prevents hydrogen atoms from penetrating into the steel wire matrix, thereby completely preserving the original excellent mechanical properties of ultra-high strength steel wire, especially the key torsional resistance.

[0028] 2. The preparation method of the present invention integrates the traditional two separate processes of pickling and phosphating into a one-step composite conversion membrane generation process. This change directly shortens the production process, reduces equipment footprint and energy consumption. More importantly, since there is no need to use strong acid for pickling, the present invention eliminates the generation of acidic wastewater. At the same time, the amount of sludge generated in its film formation process is far less than that of traditional phosphating, reducing environmental pressure.

[0029] 3. The composite conversion film prepared by this invention has a more compact structure, finer grains, and uniform distribution. This is the result of the synergistic effect of multiple components such as phosphate film-forming agent, complexing agent, and interface passivating agent under controlled electrochemical conditions. This high-quality film not only improves the corrosion resistance of steel wire, but its microporous structure also provides an excellent adsorption carrier for the lubricant in the subsequent drawing process, ensuring the stability and smoothness of the high-speed drawing process. Attached Figure Description

[0030] Figure 1 This is a comparison chart of the conversion membrane weights of the embodiments and comparative samples of the present invention; Figure 2 This is a comparison chart of the adhesion levels of the conversion films in the embodiments of the present invention and the comparative sample; Figure 3 This is a comparison diagram of the fracture torsion cycles of the embodiments of the present invention and the comparative sample; Figure 4 This is a comparison chart of the lubricant adsorption amounts of the embodiments and comparative samples of the present invention; Figure 5 This is a two-dimensional distribution diagram of the simulated pull-out performance of the successfully pulled-out samples in the embodiments and comparative examples of the present invention; Figure 6 This is a comparison diagram of the corrosion resistance performance of the embodiments of the present invention and the comparative sample; Figure 7 This is a two-dimensional correlation diagram of the surface roughness parameters of the embodiments and comparative samples of the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Please see the appendix Figure 1 - Appendix Figure 7 , The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0033] Phosphoric acid, CAS No.: 7664-38-2, the product used is a commercially available industrial grade product with a mass fraction of 85%; Sodium gluconate, CAS No.: 527-07-1, the product used is a commercially available industrial grade product with a purity of not less than 98%; Ammonium molybdate, specifically ammonium heptamolybdate tetrahydrate, CAS No.: 12054-85-2, is a commercially available analytical grade product. Phosphorous acid, CAS No.: 13598-36-2, the product used is a commercially available industrial grade product with a purity of not less than 98%; The nonionic surfactant, specifically fatty alcohol polyoxyethylene ether AEO-9, CAS number 68131-39-5, is a commercially available industrial-grade product. The steel wire rod is made of SWOSC-V grade ultra-high strength spring steel wire rod with a diameter of 5.5mm. It is a commercially available hot-rolled product.

[0034] In this embodiment, the units of measurement for the amount of each material and solvent are uniformly referred to as parts by weight.

[0035] Example 1: This embodiment provides a method for preparing ultra-high strength spring steel wire, including the following steps: S1. The hot-rolled steel wire rod is mechanically pretreated by a continuous shot blasting machine with a running linear speed of 90 meters / minute and G40 steel shot at a speed of 2800 rpm to remove the iron oxide scale on its surface.

[0036] S2. Add 861 parts of deionized water to the reactor equipped with a stirrer, heat to 45°C while stirring at 200 rpm, and then slowly add 118 parts of phosphoric acid, 30 parts of sodium gluconate, 3 parts of ammonium heptamolybdate tetrahydrate, 5 parts of phosphorous acid, and 1 part of fatty alcohol polyoxyethylene ether AEO-9 in sequence. Stir continuously for 10 minutes after each material is added to ensure complete dissolution. After all components have been added, heat the treatment solution to 65°C for later use.

[0037] S3. The steel wire rods pretreated by S1 are continuously passed through the treatment tank containing the treatment solution prepared by S2 at a running linear speed of 10 meters / minute, ensuring that the steel wire is immersed in the treatment solution for 8 minutes. Throughout the treatment process, the treatment temperature is strictly kept constant at 65℃, the pH value of the treatment solution is kept constant at 2.5, and the oxidation-reduction potential of the treatment solution is kept constant at +250mV through an online monitoring and feedback control system.

[0038] S4. The processed steel wire is first passed through a room temperature deionized water spray cleaning zone with a spray pressure of 0.3MPa. The steel wire passes through this zone for 30 seconds. Then it enters a hot air circulation drying channel with a hot air temperature of 120℃ and a wind speed of 15m / s. The steel wire passes through the drying channel for 1.5 minutes to ensure that its surface is completely dry. Finally, a finished wire with a uniform composite conversion film on its surface is obtained.

[0039] Example 2: This embodiment provides a method for preparing ultra-high strength spring steel wire, including the following steps: S1. The hot-rolled steel wire rod is passed through a continuous shot blasting machine with a linear speed of 85 meters / minute and G40 steel shot at a speed of 3000 rpm to perform mechanical pretreatment in order to remove the iron oxide scale on its surface.

[0040] S2. Add 936.5 parts of deionized water to a reactor equipped with a stirrer, heat to 45°C while stirring at 200 rpm, and then slowly add 59 parts of 85% phosphoric acid, 10 parts of sodium gluconate, 1 part of ammonium heptamolybdate tetrahydrate, 2 parts of phosphorous acid, and 0.5 parts of fatty alcohol polyoxyethylene ether AEO-9 in sequence. Stir continuously for 10 minutes after each material is added to ensure complete dissolution. After all components have been added, heat the treatment solution to 60°C for later use.

[0041] S3. The steel wire rods pretreated by S1 are continuously passed through the treatment tank containing the treatment solution prepared by S2 at a running linear speed of 8 meters / minute, ensuring that the steel wire is immersed in the treatment solution for 10 minutes. Throughout the treatment process, the treatment temperature is strictly kept constant at 60℃, the pH value of the treatment solution is kept constant at 3.0, and the oxidation-reduction potential of the treatment solution is kept constant at +200mV through an online monitoring and feedback control system.

[0042] S4. The processed steel wire is first passed through a room temperature deionized water spray cleaning zone with a spray pressure of 0.25MPa. The steel wire passes through this zone for 35 seconds. Then it enters a hot air circulation drying channel with a hot air temperature of 115℃ and a wind speed of 16 m / s. The steel wire passes through the drying channel for 1.6 minutes to ensure that its surface is completely dry. Finally, a finished wire with a uniform composite conversion film on its surface is obtained.

[0043] Example 3: This embodiment provides a method for preparing ultra-high strength spring steel wire, including the following steps: S1. The hot-rolled steel wire rod is passed through a continuous shot blasting machine with a linear speed of 95 meters / minute and G40 steel shot at a speed of 2700 rpm to perform mechanical pretreatment in order to remove the iron oxide scale on its surface.

[0044] S2. Add 783 parts of deionized water to a reactor equipped with a stirrer, heat to 45°C while stirring at 200 rpm, and then slowly add 176 parts of 85% phosphoric acid, 50 parts of sodium gluconate, 5 parts of ammonium heptamolybdate tetrahydrate, 10 parts of phosphorous acid, and 2 parts of fatty alcohol polyoxyethylene ether AEO-9 in sequence. Stir continuously for 10 minutes after each material is added to ensure complete dissolution. After all components have been added, heat the treatment solution to 70°C for later use.

[0045] S3. The steel wire rods pretreated by S1 are continuously passed through the treatment tank containing the treatment solution prepared by S2 at a running linear speed of 16 meters / minute, ensuring that the steel wire is immersed in the treatment solution for 5 minutes. Throughout the treatment process, the treatment temperature is strictly kept constant at 70℃, the pH value of the treatment solution is kept constant at 2.0, and the oxidation-reduction potential of the treatment solution is kept constant at +300mV through an online monitoring and feedback control system.

[0046] S4. The processed steel wire is first passed through a room temperature deionized water spray cleaning zone with a spray pressure of 0.35MPa and a time of 25 seconds. Then it enters a hot air circulation drying channel with a hot air temperature of 125℃ and a wind speed of 14 m / s. The time of 1.4 minutes in the drying channel is used to completely dry the surface, and finally a finished wire with a uniform composite conversion film on the surface is obtained.

[0047] Example 4: This embodiment provides a method for preparing ultra-high strength spring steel wire, including the following steps: S1. The hot-rolled steel wire rod is passed through a continuous shot blasting machine with a linear speed of 88 meters / minute and G40 steel shot at a speed of 2900 rpm to perform mechanical pretreatment in order to remove the iron oxide scale on its surface.

[0048] S2. Add 879.2 parts of deionized water to a reactor equipped with a stirrer, heat to 45°C while stirring at 200 rpm, and then slowly add 94 parts of 85% phosphoric acid, 20 parts of sodium gluconate, 2 parts of ammonium heptamolybdate tetrahydrate, 4 parts of phosphorous acid, and 0.8 parts of fatty alcohol polyoxyethylene ether AEO-9 in sequence. Stir continuously for 10 minutes after each material is added to ensure complete dissolution. After all components have been added, heat the treatment solution to 68°C for later use.

[0049] S3. The pretreated steel wire rods from S1 are continuously passed through a treatment tank containing the treatment solution prepared in S2 at a linear speed of 13.3 m / min, ensuring that the steel wire is immersed in the treatment solution for 6 minutes. Throughout the entire treatment process, the treatment temperature is strictly kept constant at 68℃, the pH value of the treatment solution is kept constant at 2.2, and the oxidation-reduction potential of the treatment solution is kept constant at +280mV through an online monitoring and feedback control system.

[0050] S4. The processed steel wire is first passed through a room temperature deionized water spray cleaning zone with a spray pressure of 0.28 MPa. The steel wire passes through this zone for 32 seconds. Then it enters a hot air circulation drying channel with a hot air temperature of 118℃ and a wind speed of 15.5 m / s. The steel wire passes through the drying channel for 1.55 minutes to ensure that its surface is completely dry. Finally, a finished wire with a uniform composite conversion film on its surface is obtained.

[0051] Comparative Example 1: This comparative example uses a traditional strong acid pickling-phosphating multi-step process to treat the surface of the steel wire. The specific steps are as follows: First, the steel wire, which has undergone the same pretreatment as in Example 1, is pickled in a 15% (mass fraction) hydrochloric acid solution containing hexamethylenetetramine corrosion inhibitor at 50°C for 8 minutes; then it is washed with water at room temperature; then it is surface-adjusted; subsequently, it is phosphating in a zinc-based phosphating solution at 60°C for 8 minutes; finally, it is washed with water and dried.

[0052] Comparative Example 2: Compared with Example 1, the difference is that 30 parts of sodium gluconate are not added in the preparation of S2 treatment solution. In order to keep the total number of parts unchanged, the amount of deionized water is increased to 891 parts accordingly. The other group proportions, process steps and parameters are exactly the same as those in Example 1.

[0053] Comparative Example 3: Compared with Example 1, the difference is that: in the preparation of the S2 treatment solution, 3 parts of ammonium heptamolybdate tetrahydrate are not added, and in order to keep the total number of parts unchanged, the amount of deionized water is increased to 864 parts accordingly; since there is no key oxidizing passivation component in the system, the redox potential of the treatment solution is not controlled in S3, and the other group proportions, process steps and parameters are exactly the same as in Example 1.

[0054] Comparative Example 4: Compared with Example 1, the difference is that: in the preparation of the S2 treatment solution, 5 parts of phosphorous acid are not added, and in order to keep the total number of parts unchanged, the amount of deionized water is increased to 866 parts accordingly; since there is no key redox potential regulator in the system, the redox potential of the treatment solution is not controlled in S3, and only its natural potential change during the treatment process is monitored. The other group proportions, process steps and parameters are exactly the same as those in Example 1.

[0055] Comparative Example 5: Compared with Example 1, the difference is that in the S3 one-step composite treatment, by changing the replenishment rate of phosphorous acid and ammonium molybdate, the oxidation-reduction potential (ORP) of the treatment solution was stably controlled at +150mV (lower than the range required by the present invention) and +350mV (higher than the range required by the present invention) for two independent experiments. The other group proportions, process steps and parameters are exactly the same as those in Example 1.

[0056] Test Example 1: Samples with a length of 100 mm were cut from the steel wires obtained after processing in Examples 1-4 and Comparative Examples 1-5, and three parallel samples were prepared for each numbered sample.

[0057] The sample was degreased and cleaned with acetone in an ultrasonic cleaner for 5 minutes, then rinsed with deionized water, dehydrated with anhydrous ethanol, and dried in an oven at 105°C for 30 minutes.

[0058] After the sample has cooled to room temperature, its initial mass is weighed using an analytical balance with an accuracy of 0.1 mg and recorded as m1.

[0059] The weighed sample was completely immersed in the stripping solution (the stripping solution consisted of 20 g / L chromic acid trioxide, 50 g / L phosphoric acid, and the remainder being deionized water) and soaked in a constant temperature water bath at 75°C for 15 minutes to completely dissolve the conversion film on the sample surface.

[0060] Remove the sample, rinse it thoroughly with deionized water, dehydrate it with anhydrous ethanol, and dry and cool it as described in step 2.

[0061] The mass of the sample after film removal was measured using the same analytical balance and recorded as m2.

[0062] Calculate the membrane weight (W) of the conversion membrane using the formula: , where S is the surface area of ​​the sample, and the final result is the average of three parallel samples.

[0063] Table 1: Conversion membrane resorption test results of each embodiment and comparative sample

[0064] Based on the data in Table 1 and Figure 1 It can be seen that the membrane weight of Examples 1-4 of the present invention is all between 3.62 and 5.41 g / m³. 2 The preset target range proves that the process of the present invention can stably form a sufficient amount of composite conversion film. The traditional phosphating film of Comparative Example 1 is too thick, while the film weight of Comparative Examples 2-5 is too low, indicating that an effective film layer has not been formed. The results of Comparative Examples 2-5 confirm that chelation descaling represented by sodium gluconate, interface passivation represented by ammonium molybdate, and precise control of redox potential achieved by phosphorous acid are necessary conditions for achieving stable film formation. The absence of any one of these steps will lead to the failure of the film formation reaction.

[0065] Test Example 2: Samples with a length of approximately 200 mm were cut from the steel wires obtained after processing in Examples 1-4 and Comparative Examples 1-5, and three parallel samples were prepared for each sample.

[0066] Take a sample and tightly wrap it around a 5.5mm diameter mandrel (1d, which is the same as the diameter of the steel wire itself) in the middle position, and continue to wrap it for 8 turns to ensure that the coils are in close contact.

[0067] Remove the wound sample from the mandrel and carefully observe the surface condition of the conversion film in the bent and deformed area using a 10x magnifying glass.

[0068] The adhesion of the film was rated according to the severity of cracking, peeling, or flaking, based on a pre-defined 0-4 grade standard. The rating standards were as follows: Grade 0: The film is intact with no visible cracks or peeling; Grade 1: The film has micro-cracks but no peeling or flaking; Grade 2: The film has obvious cracks with localized slight peeling; Grade 3: The film has severe cracking with obvious flaky peeling or flaking; Grade 4: The film has peeled off over a large area, exposing the substrate significantly. The rating result for each sample was recorded, and the final result was the average grade of three parallel samples.

[0069] Table 2: Evaluation results of conversion film adhesion level for each embodiment and comparative sample

[0070] Based on the data in Table 2 and Figure 2 The results show that the composite conversion films prepared in Examples 1-4 of this invention achieved an adhesion level of 0-1 after 1 day of bending deformation, indicating that the film layer is firmly bonded to the substrate and has excellent toughness. The traditional phosphating film in Comparative Example 1 exhibited brittle fracture (level 3) due to coarse crystals. Comparative Examples 2, 4, and 5 failed to form an effective film layer and therefore had no actual adhesion (level 4). The results of Comparative Example 3 further illustrate that the lack of a molybdate-induced interfacial passivation layer will lead to insufficient bonding strength between the film layer and the substrate. In summary, the multi-component synergy and electrochemical control of this invention are the key to obtaining a high-adhesion film layer.

[0071] Test Example 3: Samples with a length of 550 mm (100 times the wire diameter) were cut from the steel wire obtained after processing in Examples 1-4 and Comparative Examples 1-5, as well as from a piece of original wire rod that underwent the same pretreatment as in Example 1 but without any chemical treatment (as a baseline control). Three parallel samples were prepared for each sample.

[0072] The sample is clamped on the computer-controlled torsion testing machine, ensuring that the sample is firmly and straight, and the gauge length is set to 550 mm.

[0073] An axial preload equivalent to 2% of the sample’s nominal tensile strength is applied to keep it straight during torsion.

[0074] Start the testing machine and twist one end of the sample in one direction at a constant angular velocity of 30 rpm until it breaks completely.

[0075] The total number of torsion cycles from the start of torsion to the point of fracture is recorded by the automatic counting system of the testing machine.

[0076] Repeat the above steps for three parallel samples of each number, calculate and record their average fracture torsion cycles.

[0077] Table 3: Torsional performance test results of each embodiment and comparative sample

[0078] Based on the data in Table 3 and Figure 3 It can be concluded that the torsion cycles of Examples 1-4 of the present invention are not significantly different from the baseline control group, indicating that the process of the present invention does not cause hydrogen embrittlement damage to the steel wire matrix. The torsion performance of Comparative Example 1 (traditional pickling) and Comparative Example 3 (lacking ammonium molybdate) is severely deteriorated, confirming that the lack of passivation layer formed by molybdate ions leads to severe hydrogen evolution reaction. The performance decline of Comparative Examples 4 and 5 indicates that the inaccurately controlled redox potential cannot suppress the hydrogen evolution side reaction. The results confirm that the present invention preferentially promotes interface passivation through electrochemical regulation, thereby kinetically inhibiting hydrogen penetration and protecting the toughness of the matrix.

[0079] Test Example 4: Samples with a length of 100 mm were cut from the steel wires obtained after processing in Examples 1-4 and Comparative Examples 1-5, and three parallel samples were prepared for each number.

[0080] After degreasing and drying the sample, its initial mass was weighed using an analytical balance with an accuracy of 0.1 mg and recorded as m1.

[0081] All samples were completely immersed in a sodium stearate saponified lubricant solution at 80°C and a concentration of 100 g / L, and kept at this temperature for 5 minutes.

[0082] Remove the sample and hang it vertically for 10 minutes to allow excess lubricant solution to drip off naturally.

[0083] The suspended sample was placed in a constant temperature oven at 65°C for 60 minutes to completely remove moisture and allow the lubricant to solidify on the sample surface.

[0084] After the sample has cooled to room temperature, its final mass is weighed using the same analytical balance and recorded as m2.

[0085] Calculate the lubricant adsorption amount (A) according to the formula: , where S is the surface area of ​​the sample, and the final result is the average of three parallel samples.

[0086] Table 4: Test results of lubricant adsorption amount in each example and comparative sample

[0087] Based on the data in Table 4 and Figure 4 It can be seen that the lubricant adsorption capacity of Examples 1-4 of the present invention is all between 8.13 and 9.52 g / m³.2 The high-level range meets the requirements for high-performance drawing; the adsorption amount of Comparative Example 1 is acceptable but lower than that of the Example; the adsorption amount of Comparative Examples 2-5 is low and completely fails to meet the standard. This result is highly correlated with the film weight data of Test Example 1, proving that the effective adsorption of lubricant must be based on a conversion film with a suitable film weight and microporous structure; the data further confirms that only by controlling the key components and electrochemical environment as defined in this invention can a qualified lubricating carrier layer be prepared.

[0088] Test Example 5: Sufficient samples of each length were cut from the steel wires obtained after processing in Examples 1-4 and Comparative Examples 1-5 for drawing tests.

[0089] All samples were lubricated in the same sodium stearate saponified lubricant as described in Test Example 4.

[0090] A single-pass drawing test was conducted using a small laboratory horizontal wire drawing machine. The drawing die was a cemented carbide die with a die angle of 12°.

[0091] Process parameters are set as follows: drawing speed is 10m / min, and single-pass surface reduction rate is 18%.

[0092] A high-precision drawing force sensor is installed behind the wire drawing machine die to collect and record the drawing force data in real time during the drawing process.

[0093] For each successfully drawn sample, extract the force-time curve data when it enters the steady-state drawing stage, calculate the average drawing force and its fluctuation value (expressed as standard deviation), and if the sample breaks during the drawing process, record it as a broken wire during drawing. Each numbered sample is tested three times, and all results are recorded.

[0094] Table 5: Simulated Pull-out Performance Test Results of Each Example and Comparative Sample

[0095] Based on the data in Table 5 and Figure 5 It can be seen that: Examples 1-4 of the present invention all achieve smooth drawing with low drawing force and low fluctuation. Although Comparative Example 1 was successfully drawn, the drawing force and fluctuation were higher than those of the examples. Comparative Examples 2-5 all experienced wire breakage during drawing. This result is a comprehensive verification of the previous tests: Comparative Examples 2, 4, and 5 broke due to lubrication failure caused by the failure to form an effective lubricating carrier film; Comparative Example 3 broke under the dual factors of hydrogen embrittlement of the matrix and lubrication failure. This test example proves the comprehensive advantages of the process of the present invention in ensuring matrix performance and providing excellent lubrication performance from the perspective of final application.

[0096] Test Example 6: Samples with a length of 100 mm were cut from the steel wires obtained after processing in Examples 1-4 and Comparative Examples 1-5, and three parallel samples were prepared for each number.

[0097] All samples were carefully sealed at both ends using neutral paraffin to eliminate interference from end-face effects.

[0098] The samples were suspended in the salt spray test chamber at a 20° angle to the vertical direction, in accordance with the requirements of GB / T10125 standard, ensuring that the samples did not come into contact with each other.

[0099] Initiate the salt spray test with the following conditions: sodium chloride solution concentration of 45-55 g / L, pH value of 6.5-7.2, test chamber temperature of 33-37℃, and sedimentation rate of 1-2 mL / (80 cm³). 2 ·h).

[0100] The sample surface was visually inspected every hour, and the time when the first red rust spots appeared on the surface of each sample was accurately recorded.

[0101] The test lasted for 24 hours. After the test, the final corrosion state of each sample surface was recorded and evaluated. The time when the first rust spots appeared was used as the main basis for evaluating corrosion resistance.

[0102] Table 6: Neutral Salt Spray Test Results of Each Example and Comparative Sample

[0103] Based on the data in Table 6 and Figure 6 It can be seen that the samples of the embodiments of the present invention exhibit excellent corrosion resistance. Most samples did not show rust after 24 hours of salt spray test. All comparative sample samples corroded rapidly within a few hours. The rapid rusting of comparative sample 1 indicates that the corrosion resistance of the traditional phosphating film used therein is far lower than that of the composite conversion film prepared by the process of the present invention. The failure of comparative samples 2, 4 and 5 is related to the poor quality and discontinuity of their film layers. The results of comparative sample 3 show that the introduction of molybdate is crucial to improving the chemical stability of the film layer and repairing structural defects. This test case confirms that the composite film layer prepared by the present invention has a dense structure and can provide corrosion protection for the substrate.

[0104] Test Example 7: Short samples of approximately 20 mm in length were cut from the steel wires obtained after treatment in Examples 1-4, as well as the representative Comparative Examples 1 and 3. These samples were chosen because they all successfully formed macroscopically visible films, making them suitable for morphology analysis.

[0105] The sample was ultrasonically cleaned to remove surface dust, and then dried with compressed air.

[0106] The surface of each sample was observed using a Bruker ContourGT-K 3D optical profilometer.

[0107] Three non-overlapping regions were randomly selected on the cylindrical surface of each sample, and the scanning area was set to 500μm×500μm.

[0108] The instrument's built-in analysis software processes the acquired three-dimensional topography data and extracts key roughness parameters, mainly including the three-dimensional arithmetic mean height (Sa) and maximum height (Sz). The average Sa and Sz values ​​of the three measurement areas for each sample are calculated as the final characterization data of the sample.

[0109] Table 7: Surface roughness parameters of conversion films for major samples

[0110] Based on the data in Table 7 and Figure 7 It can be seen that the surface roughness parameters (Sa and Sz) of Examples 1-4 of the present invention all fall within the ideal range, indicating that they form a fine, uniform surface morphology with suitable micropores. This is the physical basis for achieving efficient lubricant adsorption. The surface of Comparative Example 1 is too rough, which will lead to wear and stress concentration during drawing. The surface of Comparative Example 3 is too smooth, reflecting insufficient film formation and inability to carry lubricant. This test reveals the fundamental reason why the process of the present invention can accurately construct the ideal lubricant carrier morphology from the microstructure level.

[0111] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a wire rod for an ultra-high strength spring wire, characterized in that, Includes the following steps: S1. Mechanical pretreatment is performed on hot-rolled steel wire rod to remove iron oxide scale from the surface, resulting in pretreated steel wire rod; S2. The pretreated steel wire rod is immersed in a surface treatment solution containing a phosphate film-forming agent, a complexing agent, an interface passivating agent, a redox potential regulator and a surfactant to generate a composite conversion film on the surface. S3. During the soaking process, by controlling the synergistic effect of the interface passivating agent and the redox potential regulator, the redox potential of the surface treatment solution is controlled within a certain range to suppress hydrogen evolution. S4. The steel wire rods from which the composite conversion film is generated are cleaned and dried to obtain the ultra-high strength spring steel wire.

2. The production method according to claim 1, characterized by, The surface treatment solution is prepared from the following raw materials in parts by weight: 59 to 176 parts of phosphoric acid, 10 to 50 parts of sodium gluconate, 1 to 5 parts of ammonium heptamolybdate tetrahydrate, 2 to 10 parts of phosphorous acid, 0.5 to 2 parts of fatty alcohol polyoxyethylene ether, and the balance being deionized water.

3. The preparation method according to claim 2, characterized in that, In S2, the phosphate film-forming agent is phosphoric acid, the complexing agent is sodium gluconate, the interface passivating agent is ammonium heptamolybdate tetrahydrate, the redox potential regulator is phosphorous acid, and the surfactant is fatty alcohol polyoxyethylene ether.

4. The preparation method according to claim 1, characterized in that, In S1, the mechanical pretreatment is shot blasting, in which hot-rolled steel wire rods are mechanically pretreated by passing them through a shot blaster with a running linear speed of 85 to 95 meters per minute and a rotation speed of 2700 to 3000 revolutions per minute.

5. The preparation method according to claim 1, characterized in that, In S3, the steel wire rod is immersed in the surface treatment liquid for 5 to 10 minutes.

6. The preparation method according to claim 1, characterized in that, During the immersion process, the steel wire rod is immersed in the surface treatment solution at a temperature of 65 to 68°C, a pH value of 2.2 to 2.5, and an oxidation-reduction potential of +250mV to +280mV.

7. The preparation method according to claim 3, characterized in that, The fatty alcohol polyoxyethylene ether is fatty alcohol polyoxyethylene ether AEO-9.

8. The preparation method according to claim 1, characterized in that, The cleaning steel wire is passed through a spray cleaning zone with room temperature deionized water and a spray pressure of 0.25 to 0.35 MPa.

9. The preparation method according to claim 1, characterized in that, The method produces a wire rod surface of an ultra-high strength spring steel wire with a composite conversion film having a film weight of 3.62 to 5.41 g / m 2 .

10. The preparation method according to claim 1, characterized in that, In S4, the steel wire enters the drying process where the temperature is 115 to 125°C and the air velocity is 14 to 16 m / s for hot air circulation drying.

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