SiCrMnV spring steel and production method and application thereof

Abstract

The invention provides SiCrMnV spring steel as well as a production method and application thereof, and relates to the technical field of production and processing of special steel in the metallurgical industry. The SiCrMnV spring steel comprises C, Si, Mn, Cr, V and other elements with specific contents, and through cooperation of the elements with the specific contents, the SiCrMnV spring steel has good fatigue resistance. The invention further provides a production method of the SiCrMnV spring steel, the temperature, the air-coal ratio and the total heating time of all stages in the heating process are strictly limited, full decarburization of the SiCrMnV spring steel can be avoided, meanwhile, excessive oxidation burning loss is prevented, the prepared spring steel has the excellent decarburization performance, and the service life of the spring steel is prolonged. Soft spots caused by decarburization on the steel surface are reduced, so that fatigue sources are reduced, and the fatigue life of the steel is prolonged; the production method is simple to operate, easy to control, suitable for large-scale production and low in cost.

Description

Technical Field

[0001] This invention relates to the field of special steel production and processing technology in the metallurgical industry, and particularly to a SiCrMnV spring steel, its production method, and its application. Background Technology

[0002] Spring steel is widely used in automobiles, railways, construction machinery, and military industries. Currently, the main spring flat steel materials in China are CrV, CrMn, and SiMn series. These materials generally suffer from low strength levels, and some grades also exhibit poor toughness and hardenability. Considering the current development trend of spring steel towards high performance, lightweight, and long service life, high performance mainly refers to high strength while ensuring decarburization and hardness. Surface decarburization is one of the important indicators of spring steel, affecting its fatigue life, and complete decarburization has a fatal impact on the fatigue life of spring steel.

[0003] The SiCrMnV series spring steel is a brand-new variety independently developed by the inventor. Due to its high C and Si content, this type of spring steel is prone to decarburization during the steel rolling process, especially complete decarburization, which has a significant impact on fatigue life.

[0004] Research on avoiding complete decarburization of SiCrMnV spring steel is limited, with relevant reports mainly focusing on lower-strength SiMn steel and 55SiCr. While those skilled in the art have attempted to apply existing surface decarburization methods for SiMn and 55SiCr steels to SiCrMnV spring steel, extensive experiments have revealed that even with these decarburization control methods, SiCrMnV spring steel still exhibits varying degrees of complete decarburization, with a decarburization depth of approximately 0.03-0.05 mm, severely impacting its fatigue life. In other words, existing methods for controlling complete decarburization in lower-strength spring steel are not suitable for the production of SiCrMnV spring steel.

[0005] There are also reports of reducing the decarburized layer of SiMn spring steel by using an anti-decarburization coating, but this method is costly and complex, making it unsuitable for large-scale production, and it is also not applicable to the production of SiCrMnV spring steel.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a SiCrMnV spring steel, its production method, and its application, in order to solve at least one of the above-mentioned technical problems.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] The primary objective of this invention is to provide a SiCrMnV spring steel comprising the following chemical composition by mass fraction: C: 0.40–0.65%, Si: 1.00–1.20%, Mn: 0.40–1.20%, Cr: 0.80–1.30%, V: 0.10–0.20%, Ni: ≤0.50%, Mo: ≤0.10%, Cu: ≤0.35%, P: ≤0.020%, S: ≤0.020%, with the remainder being iron and unavoidable impurity elements.

[0010] Furthermore, based on the above-mentioned technical solution of the present invention, the thickness of the fully decarburized layer of the SiCrMnV spring steel is 0.

[0011] Furthermore, based on the above-mentioned technical solution of the present invention, the SiCrMnV spring steel includes SiCrMnV spring flat steel and / or SiCrMnV spring round steel.

[0012] The second objective of this invention is to provide a method for producing the aforementioned SiCrMnV spring steel, comprising the following steps:

[0013] The continuously cast billet made according to the chemical composition of SiCrMnV spring steel is heated, descaled, rolled and cooled in sequence to obtain SiCrMnV spring steel.

[0014] The heating process is carried out in stages, including a preheating stage, a first heating stage, a second heating stage, and a homogenization stage.

[0015] The temperature of the preheating section is 500–720°C;

[0016] The temperature of the heating section is 750–900℃, and the air-to-coal ratio of the heating section is 0.8–1.2.

[0017] The temperature of the second heating stage is 950–1020℃, and the air-coal ratio of the second heating stage is 0.5–1.0.

[0018] The temperature of the homogenization zone is 950–1020℃, and the air-to-coal ratio of the homogenization zone is 0.5–1.0.

[0019] The total heating time is 90 to 150 minutes.

[0020] Furthermore, based on the above-mentioned technical solution of the present invention, the heating furnace used for heating is a walking beam furnace with a walking beam rate of 90-100 seconds / step.

[0021] Furthermore, based on the above technical solution of the present invention, the specifications of the continuously cast billet are 240mm×240mm.

[0022] Furthermore, based on the above technical solution of the present invention, the phosphorus removal pressure is ≥16MPa.

[0023] Furthermore, based on the above technical solution of the present invention, the cooling method is water cooling, the cooling temperature is ≤740℃, and the cooling time is ≤2min.

[0024] Furthermore, based on the above-mentioned technical solution of the present invention, after cooling, the process also includes the steps of inspection, finishing, packaging, and warehousing.

[0025] The third objective of this invention is to provide applications of the above-mentioned SiCrMnV spring steel or SiCrMnV spring steel produced by the above-mentioned production method for the automotive, railway, engineering machinery or military industries.

[0026] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0027] (1) The present invention provides a SiCrMnV spring steel, which includes specific amounts of C, Si, Mn, Cr, V and other elements. Through the synergistic cooperation between the above-mentioned specific amounts of elements, the SiCrMnV spring steel has good fatigue resistance.

[0028] (2) This invention provides a method for producing the aforementioned SiCrMnV spring steel. By strictly limiting the temperature, air-to-coal ratio, and total heating time at each stage of the heating process, complete decarburization of the SiCrMnV spring steel can be avoided, while excessive oxidation loss is prevented. This results in spring steel with excellent decarburization performance, reducing soft spots on the steel surface caused by decarburization, thereby reducing fatigue sources and extending the fatigue life of the steel. Furthermore, this production method is simple and easy to control, suitable for large-scale production, and has low cost.

[0029] (3) The present invention also provides the application of the above-mentioned SiCrMnV spring steel. In view of the advantages of the SiCrMnV spring steel of the present invention, it can be used to make high-strength, high-stress, long-life, lightweight steel leaf springs or other elastic elements to meet the future development needs of products. It can be widely used in automobiles, railways, engineering machinery, military industry and other fields. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0031] Figure 1 This is a decarburized microstructure diagram of 51SiCrMnV spring steel provided in Embodiment 1 of the present invention;

[0032] Figure 2 This is a decarburized microstructure diagram of 51SiCrMnV spring steel provided in Embodiment 2 of the present invention;

[0033] Figure 3 This is a decarburized microstructure diagram of 51SiCrMnV spring steel provided in Example 3 of the present invention;

[0034] Figure 4 This is a decarburized microstructure diagram of 51SiCrMnV spring steel provided in Example 4 of the present invention;

[0035] Figure 5 This is a diagram of the decarburized microstructure of 51SiCrMnV spring steel provided in Comparative Example 2 of this invention;

[0036] Figure 6 This is a diagram of the decarburized microstructure of 51SiCrMnV spring steel provided in Comparative Example 4 of this invention.

[0037] Figure 7 This is a diagram of the decarburized microstructure of 51SiCrMnV spring steel provided in Comparative Example 6 of this invention.

[0038] Figure 8 This is a diagram of the decarburized microstructure of 51SiCrMnV spring steel provided in Comparative Example 8 of this invention.

[0039] Figure 9 This is a decarburized microstructure diagram of the 51SiCrMnV spring steel provided in Comparative Example 10 of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0041] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0042] According to a first aspect of the present invention, a SiCrMnV spring steel (51SiCrMnV spring steel) is provided, comprising the following chemical composition by mass fraction: C: 0.40–0.65%, Si: 1.00–1.20%, Mn: 0.40–1.20%, Cr: 0.80–1.30%, V: 0.10–0.20%, Ni: ≤0.50%, Mo: ≤0.10%, Cu: ≤0.35%, P: ≤0.020%, S: ≤0.020%, with the remainder being iron and unavoidable impurity elements.

[0043] Specifically, carbon (C) can improve strength and hardenability, but excessive C content will reduce toughness. Therefore, in order to balance the strength and toughness of spring steel, this invention adopts a medium carbon design, with a carbon content of 0.40-0.65%. Typical but non-limiting mass fractions of C are 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.52%, 0.55%, 0.58%, 0.60%, 0.62%, 0.64%, or 0.65%, etc.

[0044] Si can improve strength, but excessive Si content will reduce toughness. To balance strength and toughness, the Si content is limited to 1.00-1.20%, with typical but non-limiting mass fractions of 1.00%, 1.05%, 1.10%, 1.15%, or 1.20%.

[0045] Mn can improve the strength and hardenability of spring steel and expand the austenite transformation zone, but excessive Mn content will reduce toughness. Therefore, considering all factors, the Mn content is designed to be 0.40% to 1.20%, with typical but non-limiting mass fractions of 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.00%, 1.10%, or 1.20%.

[0046] Cr can improve the strength and hardenability of spring steel, but too high a Cr content will reduce toughness. Therefore, considering all factors, the Cr content is designed to be 0.80% to 1.30%, with typical but non-limiting mass fractions of 0.8%, 0.9%, 1.00%, 1.10%, 1.20%, or 1.30%.

[0047] V can refine grains and improve the strength and toughness of steel. Therefore, taking all factors into consideration, the V content is designed to be 0.10% to 0.20%, with typical but non-limiting mass fractions of 0.10%, 0.12%, 0.14%, 0.15%, 0.18%, or 0.20%.

[0048] In addition to the elements mentioned above, the spring steel of the present invention also contains a certain amount of residual elements, such as Ni, Mo, and Cu. Typical but non-limiting mass fractions of Ni are 0.0%, 0.10%, 0.20%, 0.30%, 0.40%, or 0.50%, etc.; typical but non-limiting mass fractions of Mo are 0.0%, 0.01%, 0.02%, 0.04%, 0.40%, or 0.50%, etc.; typical but non-limiting mass fractions of Cu are 0.0%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, or 0.35%, etc.

[0049] P and S are harmful elements that will deteriorate the strength and toughness of spring steel. Therefore, their content needs to be strictly controlled. It is preferable that spring steel is completely absent in this invention. However, it is usually unavoidable that they are present. The content of P and S is limited to: P ≤ 0.020%, S ≤ 0.020%. Typical but non-limiting mass fractions of P are 0.020%, 0.018%, 0.015%, 0.012%, 0.010%, 0.008%, or 0.006%, etc.; typical but non-limiting mass fractions of S are 0.020%, 0.018%, 0.015%, 0.012%, 0.010%, 0.008%, or 0.006%, etc.

[0050] This invention provides a SiCrMnV spring steel, which, through the synergistic effect of the elements in the above-mentioned specific contents, gives the SiCrMnV spring steel better fatigue resistance.

[0051] As an optional embodiment of the present invention, SiCrMnV spring steel includes SiCrMnV spring flat steel and / or SiCrMnV spring round steel.

[0052] As an optional embodiment of the present invention, the thickness of the fully decarburized layer of SiCrMnV spring steel is 0.

[0053] According to a second aspect of the present invention, a method for producing the above-mentioned SiCrMnV spring steel is also provided, comprising the following steps:

[0054] The continuously cast billet made according to the chemical composition of SiCrMnV spring steel is heated, descaled, rolled and cooled in sequence to obtain SiCrMnV spring steel.

[0055] The heating process is carried out in stages, including a preheating stage, a first heating stage, a second heating stage, and a soaking stage.

[0056] The temperature of the preheating section is 500–720°C;

[0057] The temperature of the heating section is 750–900℃, and the air-to-coal ratio of the heating section is 0.8–1.2.

[0058] The temperature of the second heating stage is 950–1020℃, and the air-coal ratio of the second heating stage is 0.5–1.0.

[0059] The temperature of the homogenization zone is 950–1020℃, and the air-to-coal ratio of the homogenization zone is 0.5–1.0.

[0060] The total heating time is 90 to 150 minutes.

[0061] Oxidation and decarburization occur in continuously cast billets (steel billets) during the heating process before rolling. In steel rolling production practice, the soaking temperature of 51SiCrMnV is generally between 950-1300℃. However, through extensive production practice, the inventors discovered that when the soaking temperature is between 1020 and 1180℃, the decarburization rate on the billet surface is greater than the oxidation rate, resulting in complete decarburization after rolling. When the soaking temperature exceeds 1180℃, the oxidation rate on the billet surface exceeds the decarburization rate, and the completely decarburized layer disappears. However, excessively high heating temperatures lead to an excessively thick oxide layer on the billet surface, resulting in reduced yield and affecting the surface quality of the steel. Furthermore, prolonged heating time increases both the total decarburized layer and oxidation loss. Therefore, to avoid complete decarburization of SiCrMnV and prevent excessive oxidation loss, this invention strictly limits the temperature, air-to-coal ratio, and total heating time at each stage of the heating process.

[0062] The heating process is divided into four stages: preheating, first heating, second heating, and soaking. The preheating stage primarily utilizes the waste heat from the furnace flue gas to preheat the steel billet. The preheating temperature cannot be too low (below 500℃), otherwise, excessive temperature differences across the billet cross-section can easily lead to internal stress cracks. Conversely, the preheating temperature cannot be too high (above 720℃), otherwise, it can easily exacerbate decarburization. Therefore, typical but non-limiting heating temperatures for the preheating stage are 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, 680℃, 700℃, or 720℃, or any range between any two points.

[0063] The primary heating stage is used to preheat the steel billet to its austenitizing temperature. The temperature of this stage cannot be too low (below 750℃), otherwise it will lead to uneven temperature distribution across the billet cross-section, causing internal stress cracks. Conversely, the temperature cannot be too high (above 900℃), otherwise it will exacerbate decarburization. Therefore, typical but not limiting heating temperatures for the primary stage are 750℃, 780℃, 800℃, 820℃, 850℃, 880℃, or 900℃, or any range between any two points.

[0064] The second heating stage is primarily used to ensure that the steel billet reaches the austenitizing temperature required for rolling. The temperature of the second heating stage cannot be too low (below 950℃), otherwise incomplete austenitization of the billet and excessive hardness will damage the rolling equipment. Conversely, the temperature cannot be too high (above 1020℃), otherwise it can easily lead to a sharp increase in decarburization. Therefore, typical but non-limiting heating temperatures for the second heating stage are 950℃, 960℃, 980℃, 1000℃, or 1020℃, or any range between any two points.

[0065] The soaking zone is primarily used to ensure that the entire cross-section of the steel billet reaches the austenitizing temperature required for rolling. The temperature in the soaking zone cannot be too low (below 950℃), otherwise incomplete austenitization of the billet and excessive hardness will damage the rolling equipment. Conversely, the temperature cannot be too high (above 1020℃), otherwise decarburization will be drastically aggravated. Therefore, typical but not limiting heating temperatures in the soaking zone are 950℃, 960℃, 980℃, 1000℃, or 1020℃, or any range between any two points.

[0066] In this invention, "air-to-gas ratio" refers to the ratio of air to coal gas during the heating process of steel billets. The air-to-gas ratio for the first heating stage is limited to 0.8 to 1.2. If the air-to-gas ratio is too low, it is easy to cause incomplete combustion or even flameout and furnace shutdown. If the air-to-gas ratio is too high, it is easy to cause accelerated oxidation and burn-off. Therefore, typical but non-limiting ratios are 0.8, 0.9, 1.0, 1.1 or 1.2, etc.

[0067] The air-coal ratio in the second heating stage is limited to 0.5 to 1.0. If the air-coal ratio is too low, it is easy to cause incomplete combustion and fail to heat the steel billet to the required temperature. If the air-coal ratio is too high, it is easy to cause accelerated oxidation and burn-off and aggravate decarburization. Therefore, typical but non-restrictive ratios are 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0, etc.

[0068] The air-coal ratio in the soaking zone is limited to 0.5 to 1.0. If the air-coal ratio is too low, it is easy to cause incomplete combustion and fail to heat the steel billet to the required temperature. If the air-coal ratio is too high, it is easy to cause accelerated oxidation and burn-off and aggravate decarburization. Therefore, typical but non-restrictive ratios are 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0, etc.

[0069] The total heating time refers to the sum of the heating times in the preheating section, the first heating section, the second heating section, and the soaking section. If the total heating time is too short (less than 90 min), it is easy to cause uneven temperature distribution in the billet section, resulting in internal stress cracks or bending during rolling. If the total heating time is too long (more than 150 min), it is easy to cause excessive oxidation loss and exacerbate decarburization. Therefore, typical but non-limiting total heating times are 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, or 150 min, etc.

[0070] The production method of SiCrMnV spring steel provided by this invention, through strict control of temperature, air-fuel ratio, and total heating time at each stage of the heating process, can avoid complete decarburization of SiCrMnV spring steel and prevent excessive oxidation loss. This results in spring steel with excellent decarburization performance, reducing soft spots on the steel surface caused by decarburization, thereby reducing fatigue sources and extending the fatigue life of the steel. Furthermore, this production method is simple and easy to control, suitable for large-scale production, and has low cost.

[0071] In one optional embodiment of the present invention, the heating furnace used is a walking beam furnace, which enables continuous production of continuously cast billets. Preferably, the walking beam rate is 90-100 seconds per step.

[0072] By controlling the storage time of continuously cast billets in the furnace, the aim is to reduce oxidation loss and the decarburized layer.

[0073] As an optional embodiment of the present invention, the continuous casting billet is charged into the furnace by cold billet charging.

[0074] As an optional embodiment of the present invention, the specifications of the continuously cast billet are 240mm × 240mm. Other specifications of billets are also possible. The present invention mainly uses a continuously cast billet with specifications of 240mm × 240mm × 6mm as an example for illustration.

[0075] After the heating process is completed, a dephosphorization treatment is performed. In an optional embodiment of this invention, the dephosphorization pressure is ≥16 MPa.

[0076] By limiting the descaling pressure, the oxide scale generated during heating is completely removed, preventing the oxide scale from being pressed into the steel surface during subsequent rolling processes, thus avoiding surface defects such as blemishes / pits.

[0077] After the dephosphorization process is completed, rolling can begin.

[0078] After the rolling process is completed, the rolled steel is cooled. As an optional embodiment of the present invention, the cooling method is water cooling, the cooling temperature is ≤740℃, and the cooling time is ≤2min.

[0079] As an optional embodiment of the present invention, after the steel is cooled, the steps of inspection, finishing, packaging and warehousing are also included.

[0080] It should be noted that the production method of SiCrMnV spring steel provided by the present invention is applicable not only to SiCrMnV spring flat steel, but also to 51SiCrMnV spring round steel.

[0081] As an optional embodiment of the present invention, the specifications of the spring flat steel range from (8 to 40) mm to (60 to 150) mm.

[0082] As an optional embodiment of the present invention, the specification range of the spring round steel is φ16mm~φ75mm.

[0083] According to a third aspect of the present invention, applications of the above-described SiCrMnV spring steel or SiCrMnV spring steel produced by the above-described method for producing SiCrMnV spring steel in the fields of automobiles, railways, engineering machinery, or military industries are also provided.

[0084] Given the advantages of the SiCrMnV spring steel provided by this invention, it can be used to manufacture high-strength, high-stress, long-life, lightweight steel leaf springs or other elastic components, meeting the future development needs of products and can be widely used in automobiles, railways, engineering machinery, military and other fields.

[0085] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0086] Example 1

[0087] This embodiment provides a method for producing SiCrMnV spring steel, including the following steps:

[0088] Step 1: Select 51SiCrMnV spring steel continuous casting billet with dimensions of 240mm×240mm×6m. The designed composition by mass percentage is: C: 0.51%, Si: 1.13%, Mn: 0.93%, Cr: 1.04%, V: 0.14%, Ni: 0.02%, Cu: 0.02%, P: 0.016%, S: 0.003%, with the remainder being Fe and other unavoidable impurity elements, totaling 100% by mass.

[0089] The continuously cast billets are cold-loaded and transported to the walking beam furnace, with one step between each billet.

[0090] Step 2: Control the preheating section temperature to 550℃; the first heating section temperature to 800℃, with an air-to-coal ratio of 1.0; the second heating section temperature to 980℃, with an air-to-coal ratio of 0.8; and the homogenization section temperature to 980℃, with an air-to-coal ratio of 0.8.

[0091] Step 3: Control the stepping rhythm, with a stepping rate of 90-100 seconds / step, and control the total furnace storage time to 120 minutes.

[0092] Step 4: Control the phosphorus removal pressure to 20 MPa.

[0093] Step 5: Roll the steel into 40mm×90mm flat steel using a rolling mill.

[0094] Step 6: After segmentation and cooling, the final product is produced and spring steel is obtained.

[0095] In this embodiment, the thickness of the fully decarburized layer of the 51SiCrMnV flat steel is 0, and the decarburized microstructure is shown in the figure below. Figure 1 As shown.

[0096] Example 2

[0097] This embodiment provides a method for producing SiCrMnV spring steel, including the following steps:

[0098] Step 1: Select 51SiCrMnV spring steel continuous casting billet with dimensions of 240mm×240mm×6m. The designed composition by mass percentage is: C: 0.51%, Si: 1.13%, Mn: 0.93%, Cr: 1.04%, V: 0.14%, Ni: 0.02%, Cu: 0.02%, P: 0.016%, S: 0.003%, with the remainder being Fe and other unavoidable impurity elements, totaling 100% by mass.

[0099] The continuously cast billets are cold-loaded and transported to the walking beam furnace, with one step between each billet.

[0100] Step 2: Control the preheating section temperature to 720℃; the first heating section temperature to 900℃, with an air-to-coal ratio of 1.2; the second heating section temperature to 1020℃, with an air-to-coal ratio of 1.0; and the homogenization section temperature to 1020℃, with an air-to-coal ratio of 1.0.

[0101] Step 3: Control the stepping rhythm, with a stepping rate of 90-100 seconds / step, and control the total furnace storage time to 150 minutes.

[0102] Step 4: Control the phosphorus removal pressure to 20 MPa.

[0103] Step 5: Roll the steel into round bars with a diameter of 25mm using a rolling mill.

[0104] Step 6: After segmentation and cooling, the final product is produced and spring round steel is obtained.

[0105] In this embodiment, the 51SiCrMnV spring round steel produced has a total decarburized layer thickness of 0, and the decarburized microstructure is shown in the figure below. Figure 2 As shown.

[0106] Example 3

[0107] This embodiment provides a method for producing SiCrMnV spring steel, including the following steps:

[0108] Step 1: Select 51SiCrMnV spring steel continuous casting billet with dimensions of 240mm×240mm×6m. The mass percentage of the composition is as follows: C: 0.40%, Si: 1.02%, Mn: 0.42%, Cr: 0.81%, V: 0.10%, Ni: 0.02%, Cu: 0.02%, P: 0.009%, S: 0.003%, with the remainder being Fe and other unavoidable impurity elements, totaling 100% by mass.

[0109] The continuously cast billets are cold-loaded and transported to the walking beam furnace, with one step between each billet.

[0110] Step 2: Control the preheating section temperature to 720℃; the first heating section temperature to 900℃, with an air-to-coal ratio of 1.2; the second heating section temperature to 1020℃, with an air-to-coal ratio of 1.0; and the homogenization section temperature to 1020℃, with an air-to-coal ratio of 1.0.

[0111] Step 3: Control the stepping rhythm, with a stepping rate of 90-100 seconds / step, and control the total furnace storage time to 150 minutes.

[0112] Step 4: Control the phosphorus removal pressure to 20 MPa.

[0113] Step 5: Roll the steel into round bars with a diameter of 25mm using a rolling mill.

[0114] Step 6: After segmentation and cooling, the final product is produced and spring round steel is obtained.

[0115] In this embodiment, the 51SiCrMnV spring round steel produced has a total decarburized layer thickness of 0, and the decarburized microstructure is shown in the figure below. Figure 3 As shown.

[0116] Example 4

[0117] This embodiment provides a method for producing SiCrMnV spring steel, including the following steps:

[0118] Step 1: Select SiCrMnV spring steel continuous casting billet with specifications of 240mm×240mm×6m. The mass percentage of the composition is as follows: C: 0.64%, Si: 1.18%, Mn: 1.17%, Cr: 1.28%, V: 0.20%, Ni: 0.02%, Cu: 0.02%, P: 0.016%, S: 0.003%, with the remainder being Fe and other unavoidable impurity elements, totaling 100% by mass.

[0119] The continuously cast billets are cold-loaded and transported to the walking beam furnace, with one step between each billet.

[0120] Step 2: Control the preheating section temperature to 720℃; the first heating section temperature to 900℃, with an air-to-coal ratio of 1.2; the second heating section temperature to 1020℃, with an air-to-coal ratio of 1.0; and the homogenization section temperature to 1020℃, with an air-to-coal ratio of 1.0.

[0121] Step 3: Control the stepping rhythm, with a stepping rate of 90-100 seconds / step, and control the total furnace storage time to 150 minutes.

[0122] Step 4: Control the phosphorus removal pressure to 20 MPa.

[0123] Step 5: Roll the steel into round bars with a diameter of 25mm using a rolling mill.

[0124] Step 6: After segmentation and cooling, the final product is produced and spring round steel is obtained.

[0125] In this embodiment, the 51SiCrMnV spring round steel produced has a total decarburized layer thickness of 0, and the decarburized microstructure is shown in the figure below. Figure 4 As shown.

[0126] Comparative Example 1

[0127] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the temperature of the second heating stage is adjusted from 980°C to 900°C, the other steps are the same as in Example 1.

[0128] The 51SiCrMnV flat steel produced in this comparative example could not be rolled by the equipment because the temperature was too low, resulting in incomplete austenitization of the billet and excessive hardness.

[0129] Comparative Example 2

[0130] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the temperature of the second heating stage is adjusted from 980°C to 1050°C, the other steps are the same as in Example 1.

[0131] The 51SiCrMnV flat steel produced in this comparative example has a fully decarburized layer thickness of 0.04 mm, and the decarburized microstructure is shown in the figure below. Figure 5 As shown.

[0132] Comparative Example 3

[0133] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the air-coal ratio in the heating stage is adjusted from 0.8 to 0.4, the other steps are the same as in Example 1.

[0134] The 51SiCrMnV flat steel produced in this comparative example could not be rolled because the billet was not fully burned due to incomplete combustion.

[0135] Comparative Example 4

[0136] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the air-coal ratio in the heating stage is adjusted from 0.8 to 1.2, the other steps are the same as in Example 1.

[0137] The 51SiCrMnV flat steel produced in this comparative example has a fully decarburized layer thickness of 0.02 mm, and the decarburized microstructure is shown in the figure below. Figure 6 As shown.

[0138] Comparative Example 5

[0139] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the temperature of the soaking zone is adjusted from 980°C to 900°C, the other steps are the same as in Example 1.

[0140] The 51SiCrMnV flat steel produced in this comparative example could not be rolled by the equipment because the temperature was too low, resulting in incomplete austenitization of the billet and excessive hardness.

[0141] Comparative Example 6

[0142] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the temperature of the soaking zone is adjusted from 980°C to 1050°C, the other steps are the same as in Example 1.

[0143] The 51SiCrMnV flat steel produced in this comparative example has a fully decarburized layer thickness of 0.05 mm, and the decarburized microstructure is shown in the figure below. Figure 7 As shown.

[0144] Comparative Example 7

[0145] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the air-coal ratio in the soaking section is adjusted from 0.8 to 0.4, the other steps are the same as in Example 1.

[0146] The 51SiCrMnV flat steel produced in this comparative example could not be rolled because the billet could not be fully heated.

[0147] Comparative Example 8

[0148] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the air-coal ratio in the soaking section is adjusted from 0.8 to 1.2, the other steps are the same as in Example 1.

[0149] The 51SiCrMnV flat steel produced in this comparative example has a fully decarburized layer thickness of 0.04 mm, and the decarburized microstructure is shown in the figure below. Figure 8 As shown.

[0150] Comparative Example 9

[0151] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the total heating time is adjusted from 120 min to 80 min, the other steps are the same as in Example 1.

[0152] The 51SiCrMnV flat steel produced in this comparative example could not be rolled because the billet was not fully heated.

[0153] Comparative Example 10

[0154] This comparative example provides a method for producing SiCrMnV spring steel. Except for step 2 of Example 1, where the total heating time is adjusted from 120 min to 180 min, the other steps are the same as in Example 1.

[0155] The 51SiCrMnV flat steel produced in this comparative example has a fully decarburized layer thickness of 0.05 mm, and the decarburized microstructure is shown in the figure below. Figure 9 As shown.

[0156] As can be seen from the above examples and comparative examples, in the production of SiCrMnV spring steel, controlling the process parameters such as temperature, air-to-coal ratio and total heating time at each stage of the heating process within a specific range is necessary to avoid complete decarburization of SiCrMnV spring steel and prevent excessive oxidation loss, so that the produced spring steel has excellent decarburization performance.

[0157] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A SiCrMnV spring steel, characterized in that, The chemical composition includes the following mass fractions: C: 0.40–0.65%, Si: 1.00–1.20%, Mn: 0.40–1.20%, Cr: 0.80–1.30%, V: 0.10–0.20%, Ni: ≤0.50%, Mo: ≤0.10%, Cu: ≤0.35%, P: ≤0.020%, S: ≤0.020%, with the remainder being iron and unavoidable impurity elements.

2. The SiCrMnV spring steel according to claim 1, characterized in that, The thickness of the fully decarburized layer of the SiCrMnV spring steel is 0.

3. The SiCrMnV spring steel according to claim 1 or 2, characterized in that, The SiCrMnV spring steel includes SiCrMnV spring flat steel and / or SiCrMnV spring round steel.

4. The method for producing SiCrMnV spring steel according to any one of claims 1-3, characterized in that, Includes the following steps: The continuously cast billet made according to the chemical composition of SiCrMnV spring steel is heated, descaled, rolled and cooled in sequence to obtain SiCrMnV spring steel. The heating process is carried out in stages, including a preheating stage, a first heating stage, a second heating stage, and a homogenization stage. The temperature of the preheating section is 500–720°C; The temperature of the heating section is 750–900℃, and the air-to-coal ratio of the heating section is 0.8–1.

2. The temperature of the second heating stage is 950–1020℃, and the air-coal ratio of the second heating stage is 0.5–1.

0. The temperature of the homogenization zone is 950–1020℃, and the amount of empty coal in the homogenization zone is 0.5–1.

0. The total heating time is 90 to 150 minutes.

5. The method for producing SiCrMnV spring steel according to claim 4, characterized in that, The dimensions of the continuously cast billet are 240mm × 240mm.

6. The method for producing SiCrMnV spring steel according to claim 4, characterized in that, The heating process uses a walking beam furnace with a stepping speed of 90-100 seconds per step.

7. The method for producing SiCrMnV spring steel according to claim 4, characterized in that, The phosphorus removal pressure is ≥16MPa.

8. The method for producing SiCrMnV spring steel according to claim 4, characterized in that, The cooling method is water cooling, with a cooling temperature of ≤740℃ and a cooling time of ≤2min.

9. The method for producing SiCrMnV spring steel according to claim 4, characterized in that, After cooling, the process also includes inspection, finishing, packaging, and warehousing.

10. The application of SiCrMnV spring steel according to any one of claims 1-3 or SiCrMnV spring steel produced by the production method of SiCrMnV spring steel according to any one of claims 4-9 in the fields of automobiles, railways, engineering machinery or military industry.

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