High-strength and high-elongation lining spring wire and processing method thereof

Abstract

The invention discloses a high-strength and high-elongation lining spring wire and a processing method thereof, and the processing method comprises the following steps: carrying out one-time continuous cold rolling on an SUS304 stainless steel raw wire, annealing, and cooling to obtain the high-strength and high-elongation lining spring wire. According to the method, the SUS304 stainless steel raw wire is subjected to annealing treatment after being subjected to one-time continuous cold rolling, original rolling state delivery of the lining spring wire is overturned, the tensile strength and the ductility are improved through optimization and innovation of process design and delivery in a state after heat treatment, and the method is suitable for production and machining of large-specification high-elasticity lining springs; cost waste caused by repeated rolling and solid solution is avoided, and the machining cost is saved.

Description

Technical Field

[0001] This invention relates to the field of leaf spring wire processing technology, and in particular to a high-strength, high-elongation leaf spring wire and its processing method. Background Technology

[0002] Piston rings are divided into ordinary oil rings and composite oil rings. Among them, composite oil rings are widely used in high-speed engines. They consist of an upper oil scraper, a lower oil scraper, and a liner spring that generates radial and axial elastic force. This type of oil ring has very thin scrapers, high specific pressure on the cylinder wall, strong oil scraping effect, and the upper and lower oil scrapers are independent, which has good adaptability to the cylinder and has the effects of small weight and large oil return path.

[0003] SUS304 possesses excellent corrosion resistance, heat resistance, low-temperature strength, and mechanical properties, making it a widely used material in the manufacture of leaf springs for composite oil rings in automotive engines. However, SUS304 leaf spring wire faces challenges in practical applications, including low strength and poor elongation. Optimization and innovation in processing technology and raw materials are urgently needed, which are the primary means of manufacturing high-strength, high-elongation leaf spring wire.

[0004] The technical requirements for large-diameter SUS304 leaf spring wire are: hardness 180-250 HV and elongation ≥40%. Currently, leaf spring wire is mainly delivered in rolled form. To meet the hardness and elongation requirements, the main processing method for large-diameter leaf spring wire is one rolling → one solution treatment → two rolling → two solution treatment → three rolling. The final wire hardness is around 210 HV, and the elongation barely reaches 40%. However, while this elongation barely meets the requirements, it results in poor plasticity and makes the wire prone to breakage during leaf spring processing, especially when processing high-elasticity leaf springs. Furthermore, the multiple rolling and solution treatment processes are time-consuming and labor-intensive. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a high-strength, high-elongation liner spring wire and its processing method, avoiding the cost waste of multiple rolling and solution treatments, and developing a high-strength, high-elongation liner spring wire.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The present invention first provides a processing method for high-strength, high-elongation leaf spring wire, which includes the following steps: after continuous cold rolling of SUS304 stainless steel raw wire, annealing treatment and cooling are performed to obtain high-strength, high-elongation leaf spring wire.

[0007] As a further improvement to the above-mentioned solution of the present invention, the total reduction rate of the first cold rolling is 105%-111%.

[0008] As a further improvement to the above-mentioned solution of the present invention, the continuous cold rolling is carried out using a cold rolling mill, which includes rolling heads one, two, three, four and five arranged in sequence. The reduction rate of rolling head one is 37%-43%, the reduction rate of rolling head two is 30%-36%, the reduction rate of rolling head three is 16%-22%, the reduction rate of rolling head four is 9%-15%, and the reduction rate of rolling head five is 1%-7%.

[0009] As a further improvement to the above-mentioned solution of the present invention, the annealing temperature is 870-890℃, and the annealing time t satisfies: 60 <t≤80s。

[0010] As a further improvement to the above-mentioned solution of the present invention, the annealing temperature is 940-1000℃, and the annealing time t satisfies: 40≤t≤60s.

[0011] Currently, heat treatment of SUS304 typically involves only two methods: stabilization treatment (850-900℃) and solution treatment (1010-1150℃). This invention explores the changes from the stabilization temperature to the solution temperature range, in order to better investigate the performance of existing SUS304 materials and optimize and improve the liner springs.

[0012] The present invention also provides a high-strength, high-elongation leaf spring wire, which is formed by the processing method described above.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention revolutionizes the traditional rolled state delivery of leaf spring wire by subjecting SUS304 stainless steel wire to continuous cold rolling followed by annealing. Through optimized and innovative process design, the wire is delivered in a heat-treated state to improve tensile strength and elongation, making it suitable for the production and processing of large-size, high-elasticity leaf springs. This avoids the cost waste of multiple rolling and solution treatment processes, saving processing costs. Furthermore, it develops large-size, high-strength, and high-elongation leaf spring wire, preventing problems such as wire breakage and insufficient elasticity during application. Attached Figure Description

[0014] Figure 1 Hardness diagrams of sheet spring wires annealed at different temperatures and times; Figure 2 Elongation diagram of sheet spring wires annealed at different temperatures and times; Figure 3 Microscopic images of sheet spring wires obtained by annealing at 870℃ for different times; Figure 4 Microscopic images of sheet spring wires obtained by annealing at 890℃ for different times; Figure 5 Microscopic images of sheet spring wires obtained by annealing at 910℃ for different times; Figure 6 Microscopic images of sheet spring wires obtained by annealing at 940℃ for different times; Figure 7 Microscopic images of sheet spring wires obtained by annealing at 970℃ for different times; Figure 8 Microscopic images of sheet spring wires annealed at 1000℃ for different times; Figure 9 Microscopic images of sheet spring wires obtained by annealing at 1020℃ for different times; Figure 10 Microscopic images of sheet spring wires annealed at 1050℃ for different times. Detailed Implementation

[0015] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0017] Example 1 This embodiment proposes a high-strength, high-elongation leaf spring wire, the processing method of which includes the following steps: SUS304 stainless steel raw wire is cold-rolled once, then annealed and cooled to obtain the high-strength, high-elongation leaf spring wire. In this embodiment, the cold rolling is performed using a cold rolling mill, with the reduction rates of the rolling mill head one being 40%, head two 33%, head three 19%, head four 12%, and head five 4%. The annealing in this embodiment is performed at 870℃ for 70 seconds. The mass percentages of the components of the SUS304 stainless steel raw wire in this embodiment are: C 0.038%, Si 0.44%, Mn 0.98%, P 0.027%, S 0.001%, Cr 18.07%, Ni 8.02%, with the balance being Fe.

[0018] Example 2 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 870°C for 80 seconds.

[0019] Example 3 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 890°C for 70 seconds.

[0020] Example 4 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 890°C for 80 seconds.

[0021] Example 5 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 940°C for 40 seconds.

[0022] Example 6 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 940°C for 60 seconds.

[0023] Example 7 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 970°C for 40 seconds.

[0024] Example 8 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 970°C for 60 seconds.

[0025] Example 9 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 1000℃ for 40 seconds.

[0026] Example 10 The difference between this embodiment and Embodiment 1 is that the annealing in this embodiment is carried out at 1000℃ for 60 seconds.

[0027] Comparative Example 1 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 870°C for 20 seconds.

[0028] Comparative Example 2 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 870°C for 40 seconds.

[0029] Comparative Example 3 The difference between this comparative example and Example 1 is that the annealing in this example is carried out at 870°C for 60 seconds.

[0030] Comparative Example 4 The difference between this comparative example and Example 1 is that the annealing in this example is carried out at 890°C for 20 seconds.

[0031] Comparative Example 5 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 890°C for 40 seconds.

[0032] Comparative Example 6 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 890°C for 60 seconds.

[0033] Comparative Example 7 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 910°C for 20 seconds.

[0034] Comparative Example 8 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 910°C for 40 seconds.

[0035] Comparative Example 9 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 910°C for 60 seconds.

[0036] Comparative Example 10 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 940°C for 20 seconds.

[0037] Comparative Example 11 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 970°C for 20 seconds.

[0038] Comparative Example 12 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1000°C for 20 seconds.

[0039] Comparative Example 13 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1020°C for 20 seconds.

[0040] Comparative Example 14 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1020°C for 40 seconds.

[0041] Comparative Example 15 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1020°C for 60 seconds.

[0042] Comparative Example 16 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1050°C for 20 seconds.

[0043] Comparative Example 17 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1050°C for 40 seconds.

[0044] Comparative Example 18 The difference between this comparative example and Example 1 is that the annealing in this comparative example is carried out at 1050°C for 60 seconds.

[0045] Comparative Example 19 This comparative example presents a leaf spring wire, the processing method of which includes the following steps: One-time rolling: The SUS304 stainless steel wire is rolled in one pass using a cold rolling mill: the reduction rate of the first rolling mill is 30%, the reduction rate of the second rolling mill is 30%, the reduction rate of the third rolling mill is 6%, and the reduction rate of the fourth rolling mill is 5%. One solution treatment: 1050℃, 60s; Secondary rolling: The SUS304 stainless steel wire rod is rolled twice using a cold rolling mill: the reduction rate of the first rolling mill is 30%, the reduction rate of the second rolling mill is 18%, the reduction rate of the third rolling mill is 6%, and the reduction rate of the fourth rolling mill is 4%. Secondary solution treatment: 1050℃, 50s; Three rolling processes: The SUS304 stainless steel wire rod is rolled twice using a cold rolling mill: the reduction rate of the first rolling mill is 4%, the reduction rate of the second rolling mill is 3%, the reduction rate of the third rolling mill is 3%, and the reduction rate of the fourth rolling mill is 3%.

[0046] Test case The leaf spring wires prepared in the above embodiments and comparative examples were subjected to performance tests. The test results are shown in Table 1 and... Figure 1-2 As shown. Among them, tensile strength and elongation tests were conducted in accordance with GB / T 228.1-2021; Vickers hardness tests were conducted in accordance with GB / T 4340.1-2024.

[0047] Table 1 Performance Test Results

[0048] Based on the test results: Overall, the experimental data shows that the tensile strength and matrix hardness of the spring wire gradually decrease with increasing annealing temperature / annealing time. Under the same annealing time, the elongation first gradually decreases and then gradually increases with increasing annealing temperature. Under the same annealing temperature, within 20-60s, the elongation gradually increases with increasing annealing time, but if the annealing time is ≤20s, the material elongation does not meet the requirements. After the annealing time reaches 60s, the elongation tends to stabilize and shows a downward trend. Based on the results of Examples 1-4 and Comparative Examples 1-6, annealing within the stabilization temperature range (850-900℃): at the same annealing time of 40-60s, when the elongation reaches a maximum of 55%, the hardness (255HV) exceeds the technical requirement of 250HV, failing to meet the requirements; when the annealing time exceeds 60s, both the elongation and matrix hardness meet the requirements; Based on the results of Examples 5-10 and Comparative Examples 7-12, within the annealing temperature range of 940-1000℃ in this invention: under the same annealing time, as the temperature increases, the tensile strength and matrix hardness of the material gradually decrease, while the elongation gradually increases; when the annealing temperature is 1000℃, the hardness at annealing times of 60s and 40s are 210HV and 223HV respectively, which are in the middle of the technical requirement of 180~250HV, and the elongation is at a peak of 55%, which is close to the elongation level under the solution treatment process of this material. Moreover, as the annealing time increases, the hardness still decreases slightly, but the elongation does not change much; in addition, as the annealing time increases, from 20s to 60s, the tensile strength and elongation of the material gradually decrease, and the relationship is basically linear, which can basically be judged that the tensile strength and hardness of the material decrease to the solution treatment level; Based on the results of Comparative Examples 13-18, annealing within the solution treatment temperature range (1010-1150℃) shows that, under the same annealing time, as the temperature increases, the tensile strength and matrix hardness of the material gradually decrease, while the elongation gradually increases. When the annealing temperature reaches a certain level (e.g., 1050℃), the tensile strength, hardness, and elongation tend to stabilize with increasing time and temperature.

[0049] Based on the results of Examples 1-10 and Comparative Example 19, the tensile strength and elongation of the wires in Examples 1-10 of the present invention are higher than those in Comparative Example 19, indicating that the process of the present invention can improve the tensile strength and elongation of the wires.

[0050] Figures 3-10 To obtain microstructure diagrams of spring wires obtained at different annealing temperatures and times, from... Figures 3-10 It can be seen that: As the annealing temperature and annealing time increase, the microstructure begins to recrystallize to varying degrees, and the elongation continues to increase. When recrystallization is complete, an equiaxed austenitic microstructure is obtained, at which point the elongation reaches its maximum. As the annealing temperature increases, the fibrous structure of the induced martensite structure along the rolling direction is gradually broken and destroyed, the fiber boundaries are fused and disappear, the strength and hardness decrease slightly, and the elongation increases, similar to recovery. As the annealing time increases, the fibrous structure of the induced martensite structure along the rolling direction is gradually broken and destroyed. The fiber boundaries are fused and disappear. Then, new equiaxed grains without distortion are gradually formed. The strength and hardness decrease significantly, the plasticity is significantly improved, and recovery and recrystallization occur. Observation of the internal microstructure revealed that after annealing for 20 seconds, there was no significant change from the rolled state microstructure, only a slight recovery process. After annealing for 40 seconds, the internal microstructure underwent significant changes, with a small number of equiaxed grains gradually appearing. This was especially evident in the 40-second annealing treatment at 1000℃, where the newly formed equiaxed microstructure was more pronounced. After annealing for 60 seconds, the induced martensite fibrous microstructure along the rolling direction basically disappeared, and a large amount of new equiaxed austenite microstructure was formed inside.

[0051] In summary, to meet the requirements of Vickers hardness of 180~250HV and elongation of ≥40% for the sheet spring wire, while achieving high elasticity and avoiding application breakage, an annealing temperature of 1000℃ and an annealing time of 40s are preferred for annealing treatment.

[0052] In summary, this invention revolutionizes the traditional delivery of sheet spring wire in its rolled state. While ensuring mechanical properties, it develops an annealing process for SUS304, delivering the wire in its annealed state. It optimizes the rolling forming process, avoiding the cost waste of multiple rolling + solution treatment + rolling processes, thus saving processing costs. It also develops large-size, high-strength, and high-elongation sheet spring wire, avoiding the problems of breakage and insufficient elasticity in customer applications.

[0053] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for processing high-strength, high-elongation leaf spring wire, characterized in that, It includes the following steps: After continuous cold rolling, SUS304 stainless steel wire is annealed and cooled to obtain high-strength, high-elongation leaf spring wire.

2. The processing method of the high-strength, high-elongation leaf spring wire according to claim 1, characterized in that, The total reduction rate of the single cold rolling is 105%-111%.

3. The processing method for high-strength, high-elongation leaf spring wire according to claim 2, characterized in that, The continuous cold rolling is carried out using a cold rolling mill, which includes rolling heads 1, 2, 3, 4, and 5 arranged in sequence. The reduction rate of rolling head 1 is 37%-43%, the reduction rate of rolling head 2 is 30%-36%, the reduction rate of rolling head 3 is 16%-22%, the reduction rate of rolling head 4 is 9%-15%, and the reduction rate of rolling head 5 is 1%-7%.

4. The processing method of the high-strength, high-elongation leaf spring wire according to claim 1, characterized in that, The annealing temperature is 870-890℃, and the annealing time t satisfies: 60... <t≤80s。 5. The processing method of the high-strength, high-elongation leaf spring wire according to claim 1, characterized in that, The annealing temperature is 940-1000℃, and the annealing time t satisfies: 40≤t≤60s.

6. A high-strength, high-elongation leaf spring wire, characterized in that, It is formed by the processing method described in any one of claims 1-5.

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