A full decarburization control process for automobile spring steel 55SiCr rod

Abstract

The application provides a full decarburization control process for automobile spring steel 55SiCr rod, and belongs to the technical field of metallurgy.The application comprises the following steps: peeling treatment is performed on alloy spring steel billets, and the corners are rounded;the steel billets are preheated in a heating furnace, the steel billets are preheated in the heating furnace, the preheating time is set, and the preheating section temperature is 880-930 DEG C;the alloy spring steel billets are heated, the heating section temperature is 950-1000 DEG C;the alloy spring steel billets are evenly heated, the even heating section temperature is 1020-1080 DEG C;after the steel billets are discharged, the temperature is reduced to 930-960 DEG C for rolling.The process provided by the application can remove the full decarburization layer on the surface of the spring steel 55SiCr rod, and improve the fatigue life of the spring steel 55SiCr.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a complete decarburization control process for 55SiCr automotive spring steel wire rod. Background Technology

[0002] The complete decarburization of the surface of 55SiCr spring steel wire rod used in automotive suspension springs has a significant impact on their fatigue service life. The stress on the spring cross section gradually increases radially from the center to the surface, with the surface bearing the greatest load and requiring the highest strength. The appearance of a complete decarburization layer on the spring surface reduces surface strength, making it prone to cracking and failure. At the same time, the different expansion coefficients of different surface structures during quenching generate structural stress, causing microcracks to form in the transition zone between the decarburized layer and the matrix on the spring surface. This accelerates spring failure and seriously threatens the safety of vehicle operation. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a complete decarburization control process for 55SiCr automotive spring steel wire rod, which can eliminate the complete decarburization layer on the surface of 55SiCr and improve the fatigue life of the spring.

[0004] The technical solution of the present invention is as follows:

[0005] A complete decarburization control process for 55SiCr automotive spring steel wire rod includes the following steps:

[0006] S1: Peel the alloy spring steel billet and round the corners;

[0007] S2: Preheat the steel billet in the heating furnace, set the preheating time, and the preheating temperature is 880~930℃;

[0008] S3: After the preheating time is over, the alloy spring steel billet is heated, and the heating temperature is set to 950~1000℃;

[0009] S4: After the alloy spring steel billet is heated, it is subjected to heat treatment, and the heat treatment temperature is set to 1020~1080℃.

[0010] S5: After the billet exits the furnace, the temperature is reduced to 930~960℃ for rolling.

[0011] Furthermore, the air-fuel ratio of the fuel gas inside the heating furnace is ≤0.50.

[0012] Furthermore, step S2 is the preheating section, step S3 is the heating section, and step S4 is the homogenization section. The total process time for the preheating section, heating section, and homogenization section is 60-80 minutes.

[0013] Furthermore, the heating time for the preheating section, heating section, and soaking section is 20-27 minutes each.

[0014] Furthermore, the residual oxygen content in the heating furnace is controlled to be below 2.5%.

[0015] Furthermore, the billet temperature is uniform from head to tail in the heating furnace, with the temperature difference between the head, middle, and tail of the billet during initial rolling being less than 30°C, and the tail rolling temperature being lower than the head rolling temperature.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] Under this controlled process, the surface of the 55SiCr spring steel wire rod used for automotive suspension springs has no completely decarburized layer, and the depth of some decarburized layers is controlled within 50 micrometers. After eliminating the complete decarburization of the wire rod, the fatigue life of the spring is increased by about 50%, and the fatigue life can reach 400,000 cycles. Attached Figure Description

[0018] Figure 1 This is a metallographic image of the fully decarburized surface of 55SiCr spring steel wire rod under the original process.

[0019] Figure 2 This is a metallographic image of the decarburized surface of spring steel 55SiCr wire rod under the process of this invention; Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] This invention provides a complete decarburization control process for 55SiCr spring steel wire rod used in automobiles, comprising the following steps:

[0022] S1: Peel the alloy spring steel billet, round the corners, remove the surface decarburization formed in the previous pass, and ensure that there is no decarburization residue on the surface of the billet before it enters the furnace.

[0023] S2: Preheat the steel billet in the heating furnace, set the preheating time, and the preheating temperature is 880~930℃; raising the steel billet to 880~930℃ can make the steel billet quickly austenitize, and the residence time in the two-phase region is short, which causes the ferrite to not have enough time to grow after it is formed.

[0024] S3: After the preheating time is over, the alloy spring steel billet is heated, and the heating temperature is set to 950~1000℃;

[0025] S4: After the alloy spring steel billet is heated, it is subjected to heat treatment, and the heat treatment temperature is set to 1020~1080℃.

[0026] S5: After the billet exits the furnace, the temperature is reduced to 930~960℃ for rolling.

[0027] Step S2 is the preheating section, step S3 is the heating section, and step S4 is the homogenization section. After the billet is heated to 880~930℃ for austenitization, it is heated evenly in two sections. The heating section and the homogenization section are each heated by about 70℃ to avoid the billet surface temperature gradient being too large due to the rapid heating rate. This would prevent the carbon on the subsurface from diffusing in time, thus increasing the surface decarburization diffusion rate and increasing the probability of the formation of a fully decarburized ferrite layer.

[0028] To reduce the oxidizing atmosphere in the heating furnace and shorten the surface diffusion time, the air-fuel ratio in the heating furnace should be controlled below 0.50. The total heating time for the preheating section, heating section, and soaking section should be 60-80 minutes, with each of the preheating section, heating section, and soaking section taking 20-27 minutes. The residual oxygen content in the heating furnace should be controlled below 2.5%.

[0029] Meanwhile, the billet temperature is uniform from head to tail in the heating furnace, and the temperature difference between the head, middle and tail of the billet during the initial rolling is less than 30℃, with the tail rolling temperature being lower than the head rolling temperature.

[0030] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A complete decarburization control process for 55SiCr automotive spring steel wire rod, characterized in that: Includes the following steps: S1: Peel the alloy spring steel billet and round the corners; S2: Preheat the steel billet in the heating furnace, set the preheating time, and the preheating temperature is 880~930℃; S3: After the preheating time is over, the alloy spring steel billet is heated, and the heating temperature is set to 950~1000℃; S4: After the alloy spring steel billet is heated, it is subjected to heat treatment, and the heat treatment temperature is set to 1020~1080℃. S5: After the billet exits the furnace, the temperature is reduced to 930~960℃ for rolling; The billet temperature is uniform from head to tail in the heating furnace. The temperature difference between the head, middle and tail of the billet during the initial rolling is less than 30℃, and the initial rolling temperature at the tail is lower than that at the head. Step S2 is the preheating section, step S3 is the heating section, and step S4 is the soaking section. The total process time for the preheating section, heating section, and soaking section is 60-80 minutes; the heating time for the preheating section, heating section, and soaking section is 20-27 minutes each.

2. The complete decarburization control process for 55SiCr automotive spring steel wire rod according to claim 1, characterized in that: The air-fuel ratio of the fuel gas in the heating furnace is ≤0.

50.

3. The complete decarburization control process for 55SiCr automotive spring steel wire rod according to claim 1, characterized in that: The residual oxygen content in the heating furnace is controlled to be below 2.5%.

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