A method for controlling the proportion of ferrite in the decarburized layer of spring steel

Abstract

A method for controlling the ferrite proportion in the decarburized layer of spring steel is disclosed. The method includes billet treatment and heating steps. Billet treatment involves peeling the billet twice using a grinding wheel. Heating involves feeding the billet into a heating furnace and employing a four-stage heating method. The preheating stage temperature is 500-700℃, the valves for the first and second heating stages are closed, the third heating stage temperature is 1100±50℃, and the soaking stage temperature is 1100±50℃. The total heating time is ≤100 minutes. During heating, the air-to-gas ratio is 2.5-3.0 for the third heating stage and 2.0-2.5 for the soaking stage. The residual oxygen content in the furnace is <3.0%, and the furnace pressure is maintained at 25-30 Pa. This method effectively reduces the ferrite proportion in the decarburized layer of spring steel to ≤20%.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, specifically to a method for controlling the proportion of ferrite in the decarburized layer of spring steel. Background Technology

[0002] Spring steel is used to manufacture springs and various elastic components. Its superior properties make it widely used in various mechanical equipment in military, automotive, railway, aerospace, home appliances, and instrumentation industries, making it an important steel grade supporting the national economy. Decarburization significantly reduces the hardness, fatigue strength, and wear resistance of workpieces. Therefore, researchers both domestically and internationally have paid great attention to the decarburization problem of spring steel and have conducted extensive research. However, research has mainly focused on reducing the depth of the decarburized layer in spring steel, without systematic and in-depth research on the proportion of ferrite in the decarburized layer, and without effective control methods.

[0003] At the same time, with increasing public concern about the living environment, reducing energy consumption and environmental pollution has become an urgent problem to be solved. Spring steel plays a crucial role in automotive shock absorption systems, making the optimization of the decarburization layer control process for spring steel of great significance. This research will improve vehicle reliability and accelerate the pace of lightweighting, environmental protection, and energy conservation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the proportion of ferrite in the decarburized layer of spring steel, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for controlling the ferrite ratio in the decarburized layer of spring steel, the method comprising the steps of billet processing and heating, wherein the billet processing involves peeling the billet and performing two peeling processes using a grinding wheel; the heating involves feeding the billet into a heating furnace and heating it in a four-stage heating manner, wherein the preheating stage temperature is 500-700℃, the valves of the first and second heating stages are closed, the third heating stage temperature is 1100±50℃, the soaking stage temperature is 1100±50℃, the total heating time is ≤100 minutes, during the heating process, the air and gas ratio is: air flow rate / gas flow rate in the third heating stage is 2.5-3.0, the air flow rate / gas flow rate in the soaking stage is 2.0-2.5, the residual oxygen content in the heating furnace is <3.0%, and the pressure in the heating furnace is maintained at 25-30 Pa.

[0006] Preferably, the two-stage peeling process using a grinding wheel specifically involves using a 16-mesh grinding wheel for the first coarse peeling process, followed by using a 24-mesh grinding wheel for the second fine peeling process.

[0007] Preferably, the steel billets in the heating furnace are arranged in a one-half or one-third configuration.

[0008] Preferably, the temperature difference between the heating section and the heat spreader section should be ≤10℃.

[0009] Preferably, the high-temperature heating period lasts for ≤45 minutes.

[0010] Preferably, after the heating step is completed, high-pressure water descaling, rolling, and cooling are performed, and the final rolling temperature is 800-900℃.

[0011] Compared with the prior art, the beneficial effects of the present invention are:

[0012] (1) It effectively reduces the ferrite ratio in the decarburized layer of spring steel, with the ferrite ratio in the decarburized layer being ≤20%.

[0013] (2) Significantly improves the residual stress level and fatigue life of automotive parts after shot blasting, thereby improving the reliability of vehicle operation. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the decarburized layer of the spring flat steel product produced in Embodiment 1 of the present invention;

[0015] Figure 2 This is a schematic diagram of the decarburized layer of the spring round steel product produced in Embodiment 2 of the present invention;

[0016] Figure 3 The decarburized layer of the spring flat steel product before improvement. Detailed Implementation

[0017] The technical solutions of 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.

[0018] Example 1

[0019] Please see Figure 1 , 3 This embodiment provides a method for controlling the ferrite ratio in the decarburized layer of 30mm*100mm 51CrV4 spring flat steel used in automotive leaf springs. The specific implementation steps are as follows:

[0020] (1) Steel billet treatment: The steel billet is peeled. The first coarse peeling is performed using a 16-mesh grinding wheel, followed by a second fine peeling using a 24-mesh grinding wheel. After peeling, the surface of the steel billet is smooth, without sharp edges, and the corners are rounded.

[0021] (2) Steel placement in the heating furnace: The method of half-load is adopted, that is, load one steel billet, skip one step and load another steel billet.

[0022] (3) Heating in a walking beam furnace: A four-stage heating method is adopted, wherein the preheating stage is 680℃, the valves of the first and second heating stages are closed, the third heating stage is 1130℃, and the temperature of the soaking stage is 1080℃. The temperature difference between the heating stage and the soaking stage should be ≤10℃. The total heating time is 95 minutes, and the heating time of the high-temperature stage is 40 minutes. The air and gas ratio is: the air flow rate / gas flow rate of the third heating stage is 2.8, and the air flow rate / gas flow rate of the soaking stage is 2.3. The furnace atmosphere is: the residual oxygen content is 1.5%, and the furnace pressure is maintained at 25-30Pa.

[0023] (4) After the steel billet is taken out of the furnace, it is descaled by high pressure water.

[0024] (5) Then rolling is carried out, using 4 roughing mills → 6 intermediate mills → 5 intermediate mills → 3 finishing mills in sequence, with a final rolling temperature of 850℃.

[0025] (6) Cooling bed cooling.

[0026] (7) Cold shearing.

[0027] (8) Quality inspection → Packaging, weighing, tagging → Warehousing.

[0028] Test results: The ferrite content in the decarburized layer on the surface of 51CrV4 spring flat steel is ≤10%. Figure 1 As shown in the attached figure. Compared with the decarburized layer of the product before improvement, the proportion of ferrite has been significantly reduced. Figure 3 As shown.

[0029] Example 2

[0030] Please see Figure 2 , 3 This embodiment provides a method for controlling the proportion of ferrite in the decarburized layer on the surface of φ28mm 55Cr3 round spring steel used in automotive stabilizer bars. The specific implementation steps are as follows:

[0031] (1) Steel billet treatment: The steel billet is peeled. The first coarse peeling is performed using a 16-mesh grinding wheel, followed by a second fine peeling using a 24-mesh grinding wheel. After peeling, the surface of the steel billet is smooth, without sharp edges, and the corners are rounded.

[0032] (2) Steel placement in the heating furnace: One-third method is used, which means loading one steel billet, skipping two steps, and then loading another steel billet.

[0033] (3) Heating in a walking beam furnace: A four-stage heating method is adopted, wherein the preheating stage is 650°C, the valves of the first and second heating stages are closed, the third heating stage is 1150°C, and the temperature of the soaking stage is 1100°C. The temperature difference between the heating stage and the soaking stage should be ≤10°C. The total heating time is 88 minutes, and the heating time of the high-temperature stage is 35 minutes. The air and gas ratio is: the air flow rate / gas flow rate of the third heating stage is 2.9, and the air flow rate / gas flow rate of the soaking stage is 2.4. The furnace atmosphere is: the residual oxygen content is 1.0%, and the furnace pressure is maintained at 25-30Pa.

[0034] (4) After the steel billet is taken out of the furnace, it is descaled by high pressure water.

[0035] (5) Then rolling is carried out in sequence, using 5 roughing mills → 6 intermediate mills → 6 intermediate mills → 3 pre-finishing mills → 5 PSM finishing mills, with a final rolling temperature of 880℃.

[0036] (6) Cooling bed cooling.

[0037] (7) Cold shearing.

[0038] (8) Quality inspection → Packaging, weighing, tagging → Warehousing.

[0039] Test results: The ferrite content in the decarburized layer on the surface of 55Cr3 spring round steel is ≤15%. Figure 2 As shown in the attached figure. Compared with the decarburized layer of the product before improvement, the proportion of ferrite has been significantly reduced. Figure 3 As shown.

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for controlling the ferrite ratio in the decarburized layer of spring steel, characterized in that: The method includes billet processing and heating steps. Billet processing involves peeling the billet twice using a grinding wheel. Heating involves feeding the billet into a heating furnace and using a four-stage heating method. The preheating stage temperature is 500-700℃, the valves for the first and second heating stages are closed, the third heating stage temperature is 1100±50℃, and the soaking stage temperature is 1100±50℃. The total heating time is ≤100 minutes. During heating, the air-to-gas ratio is: air flow rate / gas flow rate in the third heating stage is 2.5-3.0, and in the soaking stage it is 2.0-2.

5. The residual oxygen content in the furnace is <3.0%, the furnace pressure is maintained at 25-30 Pa, the temperature difference between the heating and soaking stages is ≤10℃, and the high-temperature heating time is ≤45 minutes.

2. The method for controlling the ferrite ratio in the decarburized layer of spring steel according to claim 1, characterized in that: The two-stage peeling process using a grinding wheel specifically involves using a 16-mesh grinding wheel for the first coarse peeling process, followed by a 24-mesh grinding wheel for the second fine peeling process.

3. The method for controlling the ferrite ratio in the decarburized layer of spring steel according to claim 1, characterized in that: The steel billets in the heating furnace are arranged in a one-half or one-third manner.

4. The method for controlling the ferrite ratio in the decarburized layer of spring steel according to claim 1, characterized in that: After the heating step is completed, high-pressure water descaling, rolling, and cooling are performed, with the final rolling temperature being 800-900℃.

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