Thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip and manufacturing process thereof

Abstract

According to the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip and the manufacturing process thereof, a hot-rolled coil plate with the thickness of 2.5-3.0 mm is adopted as a raw material, the reduction rate is only 27.3-60% when the hot-rolled coil plate is rolled to the target thickness through a single-stand rolling mill, the target thickness can be achieved only through one-time rolling, the yield strength is 780-820 MPa, the hardness HRC is 30-35, and a finished product is uniform in grain structure and good in obdurability; and the user requirements are better met. Compared with the prior art, the technical problems that the thin-gauge spring steel 51CrV4 cold-rolled wide steel is large in rolling difficulty, complex in production process, high in manufacturing cost, poor in thickness precision control and the like are solved, the size precision and the product quality of products are guaranteed, the production process is shortened, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of alloy production, and in particular relates to a thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip and a manufacturing process thereof. Background Art

[0002] Alloy spring steel 51CrV4 is widely used in the manufacture of various springs and spring parts, such as suspension springs, valve springs, brake springs, lifter springs, clutch diaphragm springs, etc. It has good strength and elasticity, as well as good fatigue resistance and corrosion resistance, making it an ideal material for high loads and harsh working environments.

[0003] Since alloy spring steel has high content of Cr, V and other alloys, its strength and hardness are relatively high and difficult to process. With the development of market diversification, the demand for thin-gauge, high-precision, and excellent-performance alloy spring steel is increasing. However, the thinner and wider the finished product, the more difficult it is to process, which poses a more severe challenge to equipment capabilities and manufacturing methods.

[0004] However, the current production process of alloy spring steel 51CrV4 cold-rolled wide strip with thickness > 3mm is mainly used, which has poor precision and low yield rate. And the production process of thin alloy spring steel 51CrV4 cold-rolled steel is mainly used for narrow strip (width < 600mm), which has long process path, high production cost and low production efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip and its manufacturing process, which realizes the production of thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip with a finished product thickness of 1mm to 2mm and a width of 1000 to 1300mm through the process flow of hot-rolled steel strip pickling, spheroidizing annealing, cold rolling and stripping, and has high precision, high yield rate and high production efficiency.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A manufacturing process of a thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip includes the following process flows:

[0008] Hot rolling - pickling - spheroidizing annealing - cold rolling - slitting.

[0009] The hot rolling uses a 1580 hot rolling mill. The hot rolling speed is 13 - 14 m / s, and a coiling process at a high temperature of 710 - 720 °C is adopted. The obtained hot rolled steel strip has a thickness of 2.5 mm - 3.0 mm and a width of 1000 mm - 1300 mm. The production of hot rolled steel strip with a thickness below 3.0 mm is more difficult than that with a thickness above 3.0 mm (mainly due to the rapid temperature drop and high deformation resistance). To solve this problem, new coil plate specifications are developed. By adopting a rolling speed of 13 - 14 m / s and a coiling temperature of 710 - 720 °C, hot rolled steel plates meeting the requirements are achieved.

[0010] For the pickling, the pickling speed is 70 - 100 m / min. A push-pull type pickling unit is used. The acid solution temperature is 80 - 85 °C, the acid solution concentration is 195 - 220 g / L, a pickling accelerator is added, and the concentration is controlled at 1‰ - 2‰. The coiling tension is 140 - 160 KN. Among them, the preferred pickling accelerator model is KT-GC02.

[0011] Since spring steel contains alloying elements such as Cr and V, the scale on its surface is thicker and more difficult to remove. When the acid solution temperature is 80 - 85 °C, the chemical reaction rate is faster, and adding a certain proportion of accelerator is more conducive to removing the scale. The pickling method of the present invention has good surface quality of the pickled strip steel and higher pickling efficiency.

[0012] For the spheroidizing annealing, a full-hydrogen bell-type annealing furnace is used, and hydrogen is used as the protective gas, which can make the crystallization more uniform. The heating process of the annealing is as follows: heat from room temperature to 420 ± 5 °C, then hold for 1 ± 0.2 hours, then heat uniformly to 685 ± 5 °C in 4 ± 0.2 hours and hold for 2 ± 0.2 hours, and then heat to 725 ± 5 °C and hold for 17 ± 1 hour; the cooling process of the annealing is as follows: cool uniformly from 725 ± 5 °C to 685 ± 5 °C in 2 ± 0.2 hours and hold for 4 ± 1 hour, then cool to 620 ± 20 °C in 2 ± 0.2 hours, then air-cool to 300 ± 5 °C, then water-cool to 80 ± 5 °C, and finally take out of the furnace. There are heat preservation sections in both the heating and cooling processes of this process, making the temperature inside and outside the strip steel uniform. After annealing, the hardness of the strip steel decreases, the globular carbide structure is uniform, which is beneficial to reducing subsequent processing cracking and improving the wear resistance of the strip steel. The annealing spheroidization rate is over 93%.

[0013] The cold-rolled and annealed steel strip is cold-rolled using a single-stand six-high reversible cold rolling mill; during cold rolling, a steel strip with a thickness of 2.5 - 3.0 mm is rolled to a target thickness of 1 - 2 mm in 3 - 4 passes. The total deformation rate is 27.3 - 60%, the deformation rate in the first pass is controlled at 16 - 21%, the deformation rates in the second and third passes are controlled at 17 - 23%, and starting from the fourth pass for finishing effect, the deformation rate should not be too large, controlled at 12 - 17%, and the total reduction is 0.75 - 1.5 mm. For the cold rolling, the total rolling force is controlled at 13000 - 17000 KN, the rolling speed is 3 - 7 m / s, and the thickness tolerance is controlled at -0.05 - 0.05 mm. This process can produce finished products in one rolling process by optimizing the rolling schedule and reduction, with a short process route, low processing cost, and simple and efficient processes.

[0014] For the slitting, the cold-rolled steel strip is sheared and slit using a 1500×4 mm longitudinal slitting unit. The slitting is a conventional process and is adjusted according to customer needs; in the present invention, a steel strip with a width of 1000 mm - 1300 mm is slit into narrow strips with a width of 100 - 600 mm. The outer diameter of the blade is 500 - 600 mm, the blade thickness is 20 mm, the blade gap is 0.15 - 0.2 mm, and the shearing speed is 80 - 120 m / min. The present invention has good edge cutting quality and high shearing efficiency.

[0015] A thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip provided by the present invention is obtained by the above method. The finished thickness of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip is 1 mm - 2 mm, and the width is 1000 - 1300 mm.

[0016] The yield strength of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip is 780 - 820 MPa, and the hardness is HRC30 - 35.

[0017] The production of thin-gauge alloy spring steel 51CrV4 is extremely difficult. Since the alloy spring steel has high alloy contents such as Cr and V, its strength and hardness are relatively high, making it difficult to process. To solve this problem, the present invention has optimized the production process. Firstly, a new hot-rolled strip steel specification has been developed. Secondly, a more efficient pickling process and spheroidizing annealing are used to improve the surface and properties of the strip steel. Finally, finished products are produced by optimizing the cold rolling process (reasonably distributing the rolling passes and reduction, and adjusting parameters such as tension according to different passes).

[0018] Compared with the prior art, the present invention uses a hot-rolled coil with a thickness of 2.5 - 3.0 mm as the raw material, and the reduction rate for rolling to the target thickness using a single-stand rolling mill is only 27.3 - 60%. It only needs one rolling to reach the target thickness, with a yield strength of 780 - 820 MPa, a hardness of HRC30 - 35, uniform grain structure of the finished product, good strength and toughness, and better meeting the user's needs.

[0019] In the prior art, the thickness of cold-rolled wide spring steel strips is above 3 mm and multiple annealing and rolling processes are required, resulting in high production costs, complex processes, poor finished product dimensional accuracy. This method fills the gap in thin-specification products of 51CrV4 cold-rolled wide alloy spring steel strips, solves technical problems such as great difficulty in rolling thin-specification 51CrV4 spring steel cold-rolled wide strips, complex production processes, high manufacturing costs, and poor thickness accuracy control, ensures the dimensional accuracy and product quality of the products, shortens the production process, and reduces the production cost. This method only requires one annealing and rolling process to obtain thin-specification products, without the need for multiple annealing and rolling processes after slitting. The production process is less, the manufacturing cost is lower, and the production efficiency is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 For the surface of the product in Example 1, the surface quality is good after pickling;

[0021] Figure 2 For the surface of the product in Comparative Example 2, the surface of the strip is poor, with obvious strip-shaped scale residues. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] To make the objectives, technical solutions, and advantages of the embodiments 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. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Example 1

[0024] A manufacturing process for thin-specification 51CrV4 cold-rolled alloy spring steel strips, using 51CrV4 hot-rolled alloy spring steel strips. Its main chemical components are: C: 0.51%, Si: 0.25%, Mn: 0.98%, P: 0.012%, S: 0.004%, Cr: 1.03%, V: 0.14%, Ni: 0.01%, Als: 0.015%, and the balance is Fe and inevitable impurities. The specifications of the hot-rolled strips are 2.5×1250 mm, and the specifications of the cold-rolled finished products are 1.0×1250 mm. After slitting, the specifications of the finished products are 299.0×1.0 mm + 298.0×1.0 mm + 304.0×1.0 mm + 348.0×1.0 mm, a total of 4 small coils. The main manufacturing process steps are as follows:

[0025] 1) Hot rolling: Use a 1580 hot rolling mill for hot rolling, with a rolling speed of 14 m / s and a coiling temperature of 720°C.

[0026] 2) Pickling: The hot-rolled steel strip is pickled using a push-pull pickling line. The pickling threading speed is 30 m / min, the normal operating speed is 75 m / min, the circulating acid temperature is 82 °C, the hydrochloric acid concentration is 198 g / L, 40 kg of pickling accelerator KT-GC02 is added, the concentration is controlled at 1.3‰, and the coiling tension is 150 KN. The surface of the strip is in good condition and there is no residual scale.

[0027] 3) Annealing: A fully hydrogen bell-type annealing furnace is used with hydrogen as the protective gas to make the crystallization more uniform. The heating process of annealing is to rapidly heat from room temperature to 420 °C, then hold for 1 hour, then uniformly heat to 685 °C in 4 hours and hold for 2 hours, and then heat to 725 °C and hold for 17 hours. The cooling process of annealing is to uniformly cool from 725 °C to 685 °C in 2 hours and hold for 4 hours, then cool to 620 °C in 2 hours, then air-cool to 300 °C, then water-cool to 80 °C, and finally take out of the furnace. The spherical carbide structure is uniform and the annealing spheroidization rate is 93%.

[0028] 4) Cold rolling: Rolling is carried out using a 1450 single-stand rolling mill. The thickness of the hot coil of 2.5 mm is rolled to 1.0 mm according to the 4-pass rolling schedule, and the thickness tolerance is controlled within -0.05 to 0.05 mm. The surface of the strip is smooth, the yield strength is 815 MPa, and the hardness is HRC33. The specific rolling parameters are shown in Table 1.

[0029] 5) Slitting: Slitting is carried out using a 1500×4 mm longitudinal slitting line. The knife gap is 0.15 mm, the shearing speed is 100 m / min, the edge quality is good, and there is no burr.

[0030] Table 1 Rolling parameters of Example 1

[0031]

[0032] Example 2

[0033] A manufacturing process for cold-rolled steel strip of thin-specification alloy spring steel 51CrV4 selects hot-rolled steel strip of alloy spring steel 51CrV4. Its main chemical components are: C: 0.52%, Si: 0.24%, Mn: 0.99%, P: 0.013%, S: 0.006%, Cr: 1.02%, V: 0.13%, Ni: 0.02%, Als: 0.017%, and the balance is Fe and unavoidable impurities. The hot-rolled steel strip specification is 2.75×1200 mm, the cold-rolled finished product specification is 1.3×1200 mm, and the finished product specification after slitting is 330.0×1.3 mm + 365.0×1.3 mm + 395.0×1.3 mm + 110.0×1.3 mm, a total of 4 small coils. The main manufacturing process steps are as follows:

[0034] 1) Hot rolling: The hot rolling is carried out using a 1580 hot rolling mill, with a rolling speed of 13 m / s and a coiling temperature of 718 °C.

[0035] 2) Pickling: The hot rolled steel strip is pickled using a push-pull pickling line. The pickling threading speed is 40 m / min, the normal operating speed is 70 m / min, the circulating acid temperature is 83 °C, the hydrochloric acid concentration is 202 g / L, 30 kg of pickling accelerator KT-GC02 is added, and the concentration is controlled at 1.0‰. The coiling tension is 160 KN. The surface of the strip is in good condition and there is no residual scale.

[0036] 3) Annealing: A full-hydrogen bell-type annealing furnace is used, with hydrogen as the protective gas, which can make the crystallization more uniform. The heating process of annealing is to rapidly heat from room temperature to 415 °C, then hold for 1 hour, then heat uniformly to 680 °C in 4 hours and hold for 2 hours, and then heat to 725 °C and hold for 18 hours. The cooling process of annealing is to cool uniformly from 725 °C to 680 °C in 2 hours and hold for 5 hours, then cool to 600 °C in 2 hours, then air-cool to 300 °C, and then water-cool to 80 °C, and finally take out of the furnace. The spherical carbide structure is uniform and the annealing spheroidization rate is 94%.

[0037] 4) Cold rolling: The rolling is carried out using a 1450 single-stand rolling mill. The thickness of the hot coil is rolled from 2.75 mm to 1.3 mm according to the 4-pass rolling schedule. The surface of the strip is smooth, the yield strength is 818 MPa, and the hardness is HRC32. The specific rolling parameters are shown in Table 2.

[0038] 5) Slitting: The slitting is carried out using a 1500×4 mm longitudinal slitting line. The knife gap is 0.16 mm, the shearing speed is 90 m / min, the edge quality is good, and there is no burr.

[0039] Table 2 Rolling parameters of Example 2

[0040]

[0041]

[0042] Comparative Example 1

[0043] A manufacturing process for cold-rolled steel strip of thin-gauge alloy spring steel 51CrV4, using alloy spring steel 51CrV4 hot-rolled steel strip, whose main chemical components are: C: 0.51%, Si: 0.23%, Mn: 0.98%, P: 0.014%, S: 0.005%, Cr: 1.02%, V: 0.14%, Ni: 0.02%, Als: 0.018%, and the balance is Fe and unavoidable impurities. The hot-rolled steel strip specification is 2.5×1250 mm, and the cold-rolled finished product specification is 1.0×1250 mm. The main manufacturing process steps are as follows:

[0044] Hot rolling: The 1580 hot rolling mill is used for hot rolling, and the rolling speed 4 m / s coiling temperature 620℃ . During the rolling process, the rolling force is too large, exceeding the load capacity of the mill, and it is impossible to roll to the target thickness of 2.5 mm.

[0045] It can be seen that in Comparative Example 1, the rolling speed and coiling temperature were not controlled according to the present invention, and the deformation resistance of the steel strip was too large during the rolling process, making it impossible to roll to the target thickness.

[0046] Comparative Example 2

[0047] A manufacturing process for thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip. Alloy spring steel 51CrV4 hot-rolled steel strip is selected, and its main chemical components are: C: 0.51%, Si: 0.22%, Mn: 0.99%, P: 0.013%, S: 0.006%, Cr: 1.01%, V: 0.14%, Ni: 0.03%, Als: 0.015%, and the balance is Fe and unavoidable impurities. The specifications of the hot-rolled steel strip are 2.5×1250 mm, and the specifications of the cold-rolled finished product are 1.0×1250 mm. The main manufacturing process steps are as follows:

[0048] 1) Hot rolling: The 1580 hot rolling mill is used for hot rolling, the rolling speed is 14 m / s, and the coiling temperature is 720°C. During the rolling process, the rolling force fluctuates little and the thickness control is normal.

[0049] 2) Pickling: The push-pull pickling line is used to pickle the hot-rolled steel strip. The pickling threading speed is 40 m / min, the normal operating speed is 75 m / min, and the temperature of the circulating pickling solution 72℃， hydrochloric acid concentration 187 g / L . The surface of the strip is poor. As Figure 2 shown, there are obvious strip-shaped scale residues, which do not meet the product requirements.

[0050] Comparative Example 2: In the pickling process, the temperature of the circulating pickling solution used in the comparative example is 72°C, and the hydrochloric acid concentration is 187 g / L. After pickling, the surface of the strip is poor, with obvious strip-shaped scale residues, and it cannot meet the product requirements. According to the pickling process of the present invention, the surface quality after pickling is good. For the effect comparison, see Figure 1 、 Figure 2 .

[0051] Comparative Example 3

[0052] Manufacturing process of a thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip. Select alloy spring steel 51CrV4 hot-rolled steel strip, whose main chemical components are: C: 0.51%, Si: 0.24%, Mn: 0.98%, P: 0.013%, S: 0.006%, Cr: 1.03%, V: 0.13%, Ni: 0.01%, Als: 0.016%, and the balance is Fe and unavoidable impurities. The hot-rolled steel strip specification is 2.5×1250mm, and the cold-rolled finished product specification is 1.0×1250mm. The main manufacturing process steps are as follows:

[0053] 1). Hot rolling: Use a 1580 hot rolling mill for hot rolling, with a rolling speed of 14m / s and a coiling temperature of 718°C.

[0054] 2). Pickling: Use a push-pull pickling unit to pickle the hot-rolled steel strip. The pickling threading speed is 30m / min, the normal operating speed is 75m / min, the circulating acid solution temperature is 83°C, the hydrochloric acid concentration is 196g / L, add 40kg of KT-GC02 pickling accelerator, and the concentration is controlled at 1.3‰. The coiling tension is 150KN. The surface of the strip is good, without residual scale.

[0055] 3). Annealing: Use a full-hydrogen bell-type annealing furnace, with hydrogen as the protective gas, which can make the crystallization more uniform. The heating process of annealing is to quickly heat from room temperature to 425°C, then hold for 1 hour, then heat uniformly to 685°C in 4 hours and hold for 2 hours, and then heat to 725°C and hold for 17 hours. The cooling process of annealing is to cool from 725°C to 620°C in 4 hours , then air-cool to 300°C, then water-cool to 80°C, and finally take out of the furnace, The annealing spheroidization rate is 85%.

[0056] 4). Cold rolling: Use a 1450 single-stand rolling mill for rolling, and roll the 2.5mm hot coil thickness to 1.0mm according to the 4-pass rolling schedule. During the first pass of rolling, the rolling force gradually increases, and the steel strip breaks when the rolling reaches about 200 meters from the strip tail.

[0057] In Comparative Example 3, the cooling process is to cool from 725°C to 620°C in 4 hours, then air-cool to 300°C, then water-cool to 80°C, and finally take out of the furnace. During the cooling process, no holding section is set, resulting in uneven temperature inside and outside the strip, uneven hardness and spherical carbide structure in the inner circle part of the strip, and causing the strip to break during the first pass of cold rolling.

[0058] Comparative Example 4

[0059] Manufacturing process of a thin - gauge alloy spring steel 51CrV4 cold - rolled steel strip. Select alloy spring steel 51CrV4 hot - rolled steel strip, and its main chemical components are: C: 0.52%, Si: 0.23%, Mn: 0.97%, P: 0.014%, S: 0.007%, Cr: 1.02%, V: 0.13%, Ni: 0.01%, Als: 0.017%, and the balance is Fe and unavoidable impurities. The specification of the hot - rolled steel strip is 2.75×1200mm, and the specification of the cold - rolled finished product is 1.3×1200mm. The main manufacturing process steps are as follows:

[0060] 1), Hot rolling: Use a 1580 hot - rolling mill for hot rolling, with a rolling speed of 14m / s and a coiling temperature of 719°C.

[0061] 2), Pickling: Use a push - pull pickling unit to pickle the hot - rolled steel strip. The pickling threading speed is 40m / min, the normal running speed is 70m / min, the circulating acid temperature is 84°C, the hydrochloric acid concentration is 212g / L, add 41kg of KT - GC02 pickling accelerator, the concentration is controlled at 1.3‰, and the coiling tension is 150KN. The surface of the strip is good, without residual scale.

[0062] 3), Annealing: Use a full - hydrogen bell - type annealing furnace, with hydrogen as the protective gas, which can make the crystallization more uniform. The heating process of annealing is to quickly heat from room temperature to 415°C, then hold for 1 hour, then heat uniformly to 680°C in 4 hours and hold for 2 hours, and then heat to 725°C and hold for 18 hours. The cooling process of annealing is to cool uniformly from 725°C to 680°C in 2 hours and hold for 5 hours, then cool to 600°C in 2 hours, then air - cool to 300°C, and then water - cool to 80°C, and finally take out of the furnace. The globular carbide structure is uniform, and the annealing spheroidization rate is 93%.

[0063] 4), Cold rolling: Use a 1450 single - stand rolling mill for rolling, and roll the 2.75mm hot - rolled coil thickness to 1.3mm according to the 3 - pass rolling schedule. The specific rolling parameters are shown in Table 3. The rolling forces in the first, second, and third passes all exceed 19000 KN, and the thickness control is unstable, the thickness tolerance exceeds ±0.05 mm, and it does not meet the product requirements.

[0064] Table 3 Rolling parameters of Comparative Example 4

[0065]

[0066] It can be seen that in Comparative Example 4, the rolling schedule is rolled in 3 passes, the reduction rate distribution of the three passes is unreasonable, the rolling force exceeds 19000KN, the thickness control is unstable, the thickness tolerance exceeds ±0.05, and it does not meet the product requirements.

[0067] The underlined above are the data that do not meet the requirements of the present invention.

[0068] The description of the above embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention according to the disclosure of the present invention.

Claims

1. A manufacturing process for a cold-rolled steel strip of thin-specification alloy spring steel 51CrV4, characterized in that, The manufacturing process includes the following technological processes: Hot rolling - pickling - spheroidizing annealing - cold rolling - slitting. For the hot rolling, the hot rolling speed is 13 - 14 m / s, and coiling is carried out at 710 - 720 °C.

2. The manufacturing process of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip according to claim 1, characterized in that, The thickness of the hot - rolled steel strip obtained by hot rolling is 2.5 mm to 3.0 mm, and the width is 1000 mm to 1300 mm.

3. The manufacturing process of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip according to claim 1, characterized in that, For the pickling, the pickling speed is 70 - 100 m / min, the acid solution temperature is 80 - 85 °C, the acid solution concentration is 195 - 220 g / L, a pickling accelerator is added, and the concentration is controlled at 1‰ - 2‰, and the coiling tension is 140 - 160 KN.

4. The manufacturing process of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip according to claim 1, characterized in that, For the spheroidizing annealing, the heating process of annealing is: rapidly heated from room temperature to 420 ± 5 °C, then held for 1 ± 0.2 hours, then uniformly heated to 685 ± 5 °C at a speed of 4 ± 0.2 hours and held for 2 ± 0.2 hours, and then heated to 725 ± 5 °C and held for 17 ± 1 hour; the cooling process of annealing is: uniformly cooled from 725 ± 5 °C to 685 ± 5 °C at a speed of 2 ± 0.2 hours and held for 4 ± 1 hour, then cooled to 620 ± 20 °C in 2 ± 0.2 hours, then air - cooled to 300 ± 5 °C, and then water - cooled to 80 ± 5 °C, and finally taken out of the furnace.

5. The manufacturing process of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip according to claim 1 or 4, characterized in that, The spheroidizing rate after annealing is more than 93%.

6. The manufacturing process of the thin-specification alloy spring steel 51CrV4 cold-rolled steel strip according to claim 1, characterized in that, For the cold rolling, the steel strip with a thickness of 2.5 - 3.0 mm is rolled to the target thickness of 1 - 2 mm in 3 - 4 passes.

7. The manufacturing process of the thin-gauge alloy spring steel 51CrV4 cold-rolled steel strip according to claim 1 or 6, characterized in that, For the cold rolling, the total rolling force is controlled at 13000 - 17000 KN, the rolling speed is 3 - 7 m / s, and the thickness tolerance is controlled at - 0.05 - 0.05 mm.

8. A cold - rolled steel strip of thin - gauge alloy spring steel 51CrV4 manufactured by the manufacturing process according to any one of claims 1 - 7.

9. The cold-rolled steel strip of thin-specification alloy spring steel 51CrV4 according to claim 9, characterized in that, The finished thickness of the cold - rolled steel strip of thin - gauge alloy spring steel 51CrV4 is 1 mm to 2 mm, and the width is 1000 - 1300 mm.

10. The cold-rolled steel strip of thin specification alloy spring steel 51CrV4 according to claim 8 or 9, characterized in that The yield strength of the cold - rolled steel strip of thin - gauge alloy spring steel 51CrV4 is 780 - 820 MPa, and the hardness is HRC30 - 35.

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