Si-mn spring steel without full decarburized layer and manufacturing method thereof

Abstract

The application provides a SiMn spring steel without a full decarburization layer and a manufacturing method thereof, and the manufacturing method comprises the following steps: blank loading, heating treatment, dephosphorization treatment and rolling treatment; the heating treatment comprises a preheating section, a first heating section, a second heating section and a soaking section; the temperature of the preheating section is 600-800 DEG C; the temperature of the first heating section is 1000-1100 DEG C; the temperature of the second heating section is 1050-1200 DEG C; and the temperature of the soaking section is 1150-1250 DEG C. The SiMn spring steel prepared by the manufacturing method has a full decarburization layer thickness of 0, a total decarburization layer thickness meeting the requirement of GB standard, and a yield rate of greater than or equal to 95%.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a SiMn spring steel without a fully decarburized layer and its manufacturing method. Background Technology

[0002] Spring steel is widely used in automobiles, railways, construction machinery, and military industries. In recent years, due to the demand for lightweight automobiles, spring steel has also been developing towards higher strength, lighter weight, and longer service life. Surface decarburization is a crucial indicator affecting the fatigue life of spring steel, and complete decarburization has a fatal impact on its fatigue life. Because the thermal expansion coefficients of the fully decarburized layer and the semi-decarburized layer are different, microcracks are easily generated at the interface between the two layers during quenching due to residual stress. These microcracks will rapidly propagate under the alternating stress during spring use, leading to spring failure and fracture. Literature reports that the formation of a fully decarburized layer can reduce the fatigue limit of a spring by 50%.

[0003] SiMn series spring steels, such as 60Si2Mn and 60Si2MnA, have high C and Si content, making them prone to decarburization during the rolling process, especially complete decarburization, which has a significant impact on fatigue life.

[0004] There are many studies on reducing the decarburized layer thickness of SiMn spring steel, but most of the literature is experimental research, and many of them only reduce the total decarburized layer, but cannot completely eliminate the decarburized layer of SiMn spring steel.

[0005] Patent CN102560046A discloses a method for controlling surface decarburization of spring steel wire. This method controls heating temperature, heating time, furnace atmosphere, toasting temperature, and cooling rate to achieve the goal of preventing a completely decarburized layer. However, this method is applicable to the production of 55SiCr wire, not to the production of 60Si2Mn spring steel flat bars and bars. Patent CN113699335A discloses a method for manufacturing high-quality 60Si2Mn with a low decarburization layer. While this method reduces the total decarburization layer, it does not mention its impact on the completely decarburized layer. There are also reports of reducing the decarburization layer of SiMn spring steel by using anti-decarburization coatings, but this method is costly and complex, making it unsuitable for large-scale production.

[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 SiMn spring steel without a fully decarburized layer and its manufacturing method. The manufacturing method is simple and easy to control, suitable for large-scale production, and low in cost. The SiMn spring steel obtained has a fully decarburized layer thickness of 0, and the total decarburized layer thickness meets the requirements of GB standards.

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

[0009] This invention provides a method for manufacturing SiMn spring steel without a fully decarburized layer, including billet loading, heat treatment, descaling treatment and rolling treatment;

[0010] The heating process includes a preheating section, a first heating section, a second heating section, and a homogenization section; the temperature of the preheating section is 600–800°C; the temperature of the first heating section is 1000–1100°C; the temperature of the second heating section is 1050–1200°C; and the temperature of the homogenization section is 1150–1250°C.

[0011] Furthermore, when loading billets into the furnace, the total heating time of each billet is shortened by spacing adjacent billets by 1-3 billet widths; preferably, the total heating time of the heat treatment is 120-200 min.

[0012] Furthermore, the soaking time for the heating treatment is 30-90 minutes.

[0013] Further, the air-coal ratio of the first heating stage is 0.5 to 1.5; the air-coal ratio of the second heating stage is 1.0 to 2.0; and the air-coal ratio of the homogenization stage is 2.0 to 3.0.

[0014] And / or, the total residual oxygen concentration in the heating furnace is <3%.

[0015] Furthermore, the billet is charged into the furnace in the form of a cold billet; preferably, the cold billet is obtained by stacking and cooling at room temperature.

[0016] And / or, the heat treatment employs a walking beam furnace.

[0017] Furthermore, in the phosphorus removal process, the phosphorus removal pressure is ≥18MPa.

[0018] Furthermore, in the rolling process, the initial rolling temperature is 1080-1180℃, and the final rolling temperature is 850-950℃.

[0019] Furthermore, in the rolling process, the billet is rolled into flat steel or round steel;

[0020] Preferably, the flat steel has a specification of (6~40)mm×(60~150)mm; the round steel has a specification of φ16mm~φ90mm;

[0021] Preferably, the thickness of the decarburized layer of the flat steel is 0, and the total decarburized layer thickness is less than or equal to 1.5% of its thickness; the thickness of the decarburized layer of the round steel is 0, and the total decarburized layer thickness is less than or equal to 0.8% of its diameter.

[0022] Furthermore, the billet is a 60Si2Mn billet;

[0023] Preferably, the composition of the 60Si2Mn billet by weight percentage is: C: 0.56-0.64%, Si: 1.5-2.0%, Mn: 0.7-1.0%, Cr: ≤0.35%, Ni: ≤0.35%, Cu: ≤0.25%, P: ≤0.025%, S: ≤0.020%, with the balance being Fe and other essential elements;

[0024] Preferably, the billet is a 60Si2Mn continuously cast billet;

[0025] More preferably, the continuous casting billet has a size of 240mm × 240mm.

[0026] In addition, the present invention also provides a SiMn spring steel without a fully decarburized layer, which is obtained by the above-described manufacturing method.

[0027] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0028] The manufacturing method of SiMn spring steel without a fully decarburized layer provided by the present invention is simple and easy to control, suitable for large-scale production, and low in cost; the SiMn spring steel obtained by this manufacturing method has a fully decarburized layer thickness of 0, the total decarburized layer thickness meets the requirements of GB standard, and the yield is ≥95%.

[0029] Specifically, the thickness of the decarburized layer of the flat steel is 0, and the total decarburized layer thickness does not exceed 1.5% of the finished product thickness, which meets the requirement of GB / 33164.1 that it does not exceed 2.0% of the thickness of the flat steel; the thickness of the decarburized layer of the obtained SiMn spring steel round bar is 0, and the total decarburized layer thickness does not exceed 0.8% of its diameter, which meets the requirement of GB / 33164.2 that it does not exceed 1.5% of the diameter of the round bar. Attached Figure Description

[0030] The accompanying drawings, which form part of this specification, 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 The diagram shows the decarburized microstructure of the 60Si2Mn spring flat steel prepared in Example 1;

[0032] Figure 2 The image shows the decarburized microstructure of the 60Si2Mn spring flat steel prepared in Example 2. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] According to a first aspect of the present invention, a method for manufacturing SiMn spring steel without a fully decarburized layer is provided, comprising billet loading into a furnace, heat treatment, descaling treatment, and rolling treatment;

[0036] The heating process includes a preheating section, a first heating section, a second heating section, and a soaking section; the temperature of the preheating section is 600–800℃; the temperature of the first heating section is 1000–1100℃; the temperature of the second heating section is 1050–1200℃; and the temperature of the soaking section is 1150–1250℃.

[0037] Typical but non-limiting preheating temperatures are 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, and 800°C, as well as numerical ranges between any two points.

[0038] Typical but not limiting heating temperatures are 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, and any range between any two points.

[0039] Typical but non-limiting heating two-stage temperatures are 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, and any range between any two points;

[0040] Typical but non-limiting soaking temperatures are 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, and any range between any two points.

[0041] In their steel rolling production practice, the inventors discovered that the soaking temperature of SiMn spring steel is generally between 1050-1300℃. When the soaking temperature is between 1050℃ and less than 1150℃, the decarburization rate on the billet surface is greater than the oxidation rate, resulting in a fully decarburized layer after rolling. When the soaking temperature is ≥1150℃, the oxidation rate on the billet surface is greater than the decarburization rate, and the fully decarburized layer disappears as the temperature rises. However, excessively high heating temperatures can lead to an excessively thick oxide layer on the billet surface, resulting in a loss of yield and affecting the surface quality of the steel. Therefore, it is necessary to control the soaking temperature within a suitable range. This invention removes the fully decarburized layer without causing an excessively thick oxide layer on the billet surface by controlling the soaking temperature within the range of 1150-1250℃.

[0042] On the other hand, the longer the billet heating time, the greater the total decarburization layer and oxidation loss of the steel. To shorten the billet heating time, this invention adopts a method of spacing 1-3 steps between adjacent billets when loading them into the furnace. That is, by spacing adjacent billets 1-3 billet widths apart when loading them into the furnace, the total heating time of each billet is shortened. If there is a 1-step gap, it is equivalent to a 1-bill width gap between adjacent billets. By controlling the gaps between billets, the heating time of the billets is shortened without affecting the hourly output. The number of gaps can be varied with specifications or determined according to product needs.

[0043] In a preferred embodiment of the present invention, the total heating time for the heat treatment is 120 to 200 min. Typical but non-limiting total heating times are 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, and any range between any two points.

[0044] More preferably, the soaking time for the heat treatment is 30-90 min. Typical but non-limiting soaking times are 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, and any range between any two points.

[0045] In a preferred embodiment of the present invention, the air-coal ratio of the first heating stage is 0.5 to 1.5; the air-coal ratio of the second heating stage is 1.0 to 2.0; and the air-coal ratio of the homogenization stage is 2.0 to 3.0.

[0046] Typical, but not limited, air-to-coal ratios for the heating stage are 0.5, 1.0, and 1.5, and the range between any two points.

[0047] Typical, but not restrictive, air-to-coal ratios for the second heating stage are 1.0, 1.5, and 2.0, and the numerical range between any two points.

[0048] Typical, but not restrictive, air-to-coal ratios for the homogenization zone are 2.0, 2.5, and 3.0, and the range between any two points.

[0049] The control of the air-coal ratio directly affects the oxidation loss rate of the billet. The reason why the air-coal ratio of the homogenization section in this invention is higher than the conventional setting is to take advantage of the fact that the oxidation reaction trend is greater than the decarburization reaction trend at this temperature to avoid the full decarburization layer and reduce the total decarburization layer. At the same time, since the total heating time of this invention is shortened, even if the air-coal ratio is set higher, it will not cause a high oxidation loss rate.

[0050] In a preferred embodiment of the present invention, the total residual oxygen concentration in the heating furnace is <3%.

[0051] In a preferred embodiment of the present invention, the billet is loaded into the furnace as a cold billet. The cold billet loading of the present invention adopts the conventional cooling method of stacking and cooling to below 200°C, and no longer requires slow cooling in a slow cooling pit, which saves process, improves efficiency, and does not affect the treatment effect of avoiding the complete decarburization layer.

[0052] In a preferred embodiment of the present invention, a walking beam furnace is used in the heat treatment.

[0053] In a preferred embodiment of the present invention, the dephosphorization pressure is ≥18MPa during the dephosphorization process; a high-pressure dephosphorizer is used to remove the generated oxide scale.

[0054] In a preferred embodiment of the present invention, the initial rolling temperature is 1080-1180℃ and the final rolling temperature is 850-950℃.

[0055] Typical but non-limiting rolling temperatures are 1080°C, 1090°C, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, and 1180°C, as well as numerical ranges between any two points.

[0056] Typical but non-limiting final rolling temperatures are 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, and 950°C, as well as numerical ranges between any two points.

[0057] In a preferred embodiment of the present invention, during the rolling process, the billet is rolled into flat steel or round steel;

[0058] Preferably, the flat steel has a specification of (6-40) mm × (60-150) mm; the round steel has a specification of...

[0059] Preferably, the thickness of the decarburized layer of the flat steel is 0, and the total decarburized layer thickness is less than or equal to 1.5% of its thickness; the thickness of the decarburized layer of the round steel is 0, and the total decarburized layer thickness is less than or equal to 0.8% of its diameter.

[0060] In a preferred embodiment of the present invention, the billet is a 60Si2Mn billet;

[0061] Preferably, the composition of the 60Si2Mn billet by weight percentage is: C: 0.56-0.64%, Si: 1.5-2.0%, Mn: 0.7-1.0%, Cr: ≤0.35%, Ni: ≤0.35%, Cu: ≤0.25%, P: ≤0.025%, S: ≤0.020%, with the balance being Fe and other essential elements;

[0062] Preferably, the billet is a 60Si2Mn continuously cast billet;

[0063] More preferably, the continuous casting billet has a size of 240mm × 240mm.

[0064] According to a second aspect of the invention, a SiMn spring steel without a fully decarburized layer is also provided, which is obtained by the above-described manufacturing method.

[0065] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0066] Example 1

[0067] In this embodiment, 60Si2Mn spring steel continuously cast billet was selected, with a specification of 240mm×240mm×6m (width×thickness×length). The mass percentage of the composition is as follows: C: 0.60%; Si: 1.73%; Mn: 0.87%; Cr: 0.20%; Ni: 0.05%; Cu: 0.02%; P: 0.016%; S: 0.003%; the remainder is Fe and other unavoidable elements, with a total mass fraction of 100%.

[0068] Step 1: The billets are transported to the walking beam furnace by cold billet loading, with one step space between adjacent billets.

[0069] Step 2: Control the temperature of the preheating section to 700℃; the temperature of the first heating section to 1080℃, and the air-to-coal ratio of the first heating section to 0.8; the temperature of the second heating section to 1150℃, and the air-to-coal ratio of the second heating section to 1.6; the temperature of the homogenization section to 1160℃, and the air-to-coal ratio of the homogenization section to 2.5.

[0070] Step 3: Control the tapping rhythm and the total furnace storage time to 190 minutes.

[0071] Step 4: Use a high-pressure dephosphorizer to remove phosphorus, with the dephosphorization pressure controlled at 20MPa.

[0072] Step 5: After descaling, the steel is rolled through a rolling mill at an initial rolling temperature of 1160℃ and a final rolling temperature of 900℃, ultimately producing flat steel with a thickness of 16mm and a width of 90mm.

[0073] Step 6: Through segmentation, cooling on a cooling bed, and shearing, the final product is off the production line.

[0074] The 60Si2Mn flat steel produced in this embodiment has a total decarburized layer thickness of 0.12 mm and a decarburization percentage of 0.75%. Its decarburized microstructure is shown in the attached diagram. Figure 1 As shown, the above data on the total decarburized layer thickness, total decarburized layer thickness, and decarburization percentage are averages obtained from the corresponding data of three rolled flat steel bars. Using this process, approximately 20 tons of steel can be produced with a final yield rate of 95.8%.

[0075] Example 2

[0076] In this embodiment, 60Si2Mn spring steel continuously cast billet with dimensions of 240mm×240mm×6m was selected. The mass percentage of the composition was as follows: C: 0.59%; Si: 1.72%; Mn: 0.90%; Cr: 0.19%; Ni: 0.03%; Cu: 0.05%; P: 0.013%; S: 0.004%; with the remainder being Fe and other unavoidable elements, totaling 100% by mass.

[0077] Step 1: The billets are transported to the walking beam furnace by cold billet loading, with one step space between adjacent billets.

[0078] Step 2: Control the preheating section temperature to 710℃; the first heating section temperature to 1070℃, with an air-to-coal ratio of 1.5; the second heating section temperature to 1160℃, with an air-to-coal ratio of 1.7; and the homogenization section temperature to 1170℃, with an air-to-coal ratio of 2.6.

[0079] Step 3: Control the total furnace storage time to 180 minutes by controlling the stepping rhythm.

[0080] Step 4: Use a high-pressure dephosphorizer to remove phosphorus, with the dephosphorization pressure controlled at 20MPa.

[0081] Step 5: Roll the steel into round bars with a diameter of 25mm using a rolling mill.

[0082] Step 6: Through segmentation, cooling on a cooling bed, and shearing, the final product is off the production line.

[0083] The 60Si2Mn round steel produced in this embodiment has a total decarburized layer thickness of 0 mm, a total decarburized layer thickness of 0.16 mm, and a decarburization percentage of 0.64%. Its decarburized microstructure is shown in the diagram below. Figure 2 As shown, this process can produce approximately 20 tons of steel with a final yield rate of up to 96%.

[0084] Example 3

[0085] In this embodiment, except that the temperature of the heat spreader is 1250°C, the other steps and processes are the same as in Example 1.

[0086] The 60Si2Mn flat steel produced in this embodiment has a total decarburized layer thickness of 0, a total decarburized layer thickness of 0.15mm, and a decarburization percentage of 0.94%. By using this process to produce about 20 tons of steel, the final yield can reach 95%.

[0087] Example 4

[0088] In this embodiment, except for steps 2 and 3 which differ from those in Embodiment 1, the other steps are the same as in Embodiment 1. Steps 2 and 3 of this embodiment are as follows:

[0089] Step 2: Control the preheating section temperature to 620℃; the first heating section temperature to 1030℃, with an air-to-coal ratio of 1.2; the second heating section temperature to 1060℃, with an air-to-coal ratio of 1.6; and the homogenization section temperature to 1190℃, with an air-to-coal ratio of 2.6.

[0090] Step 3: Control the total furnace storage time to 190 minutes by controlling the stepping rhythm.

[0091] The 60Si2Mn flat steel produced in this embodiment has a total decarburized layer thickness of 0, a total decarburized layer thickness of 0.13mm, and a decarburization percentage of 0.81%. By using this process to produce about 20 tons of steel, the final yield can reach 95.5%.

[0092] Comparative Example 1

[0093] Except for steps 1-3, which differ from those in Example 1, the other steps in this comparative example are the same as those in Example 1. Steps 1-3 of this comparative example are as follows:

[0094] Step 1: The billets are transported to the walking beam furnace by cold billet loading, with one step space between adjacent billets.

[0095] Step 2: Control the preheating section temperature to 620℃; the first heating section temperature to 850℃, with an air-to-coal ratio of 1.2; the second heating section temperature to 1060℃, with an air-to-coal ratio of 1.8; and the homogenization section temperature to 1120℃, with an air-to-coal ratio of 2.1.

[0096] Step 3: Control the total furnace storage time to 190 minutes by controlling the stepping rhythm.

[0097] The 60Si2Mn flat steel produced in this comparative example has a fully decarburized layer thickness of 0.05 mm, a total decarburized layer thickness of 0.25 mm, and a decarburization percentage of 1.56%. By using this process to produce about 20 tons of steel, the final yield can reach 95%.

[0098] Comparative Example 2

[0099] Except for the temperature of the soaking zone being 1270°C, the process steps in this comparative example are the same as those in Example 1.

[0100] The 60Si2Mn flat steel produced in this comparative example has a total decarburized layer thickness of 0 and a decarburized layer thickness of 0.24 mm, with a decarburization percentage of 1.5%. By using this process to produce about 20 tons of steel, the final yield can reach 94%.

[0101] Comparative Example 3

[0102] Except for the heating stage temperature of 1260℃ and the soaking stage temperature of 1280℃, the other process steps in this comparative example are the same as those in Example 1.

[0103] The 60Si2Mn flat steel produced in this comparative example has a total decarburized layer thickness of 0 mm and a decarburization percentage of 1.7%. By using this process to produce about 20 tons of steel, the final yield can reach 93%.

[0104] In summary, as can be seen from the embodiments and comparative examples of the present invention, the thickness of the fully decarburized layer of the 60Si2Mn flat steel produced in Examples 1-4 is 0, and the total decarburized layer thickness does not exceed 0.16 mm, which meets the requirement of GB / 33164.1 that the thickness of the flat steel does not exceed 2.0%, and the final yield can reach more than 95%. Comparative Example 1 shows that if the temperatures of the first heating stage and the soaking stage are not within the control range of the present invention, the obtained 60Si2Mn flat steel will have a fully decarburized layer, the total decarburized layer will be significantly thickened, and the decarburization percentage will also increase. Comparative Example 2 shows that if the temperature of the soaking stage exceeds the control range of the present invention, the total decarburized layer will be significantly thickened, the decarburization percentage will also be significantly increased, and the final yield will be lower than that of Examples 1-4. Comparative Example 3 shows that if the temperatures of the second heating stage and the soaking stage exceed the control range of the present invention, the total decarburized layer will be significantly thickened, the decarburization percentage will also be significantly increased, and the final yield will be lower than that of Examples 1-4.

[0105] 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 method for manufacturing SiMn spring steel without a fully decarburized layer, characterized in that, This includes billet loading, heat treatment, descaling, and rolling. The heating process includes a preheating section, a first heating section, a second heating section, and a homogenization section; the temperature of the preheating section is 600–800°C; the temperature of the first heating section is 1000–1090°C; the temperature of the second heating section is 1050–1200°C; and the temperature of the homogenization section is 1150–1250°C. When loading billets into the furnace, the total heating time of each billet is shortened by spacing adjacent billets by 1-3 billet widths. The total heating time for the heat treatment is 120 to 200 minutes; The air-coal ratio of the first heating stage is 0.5 to 1.5; the air-coal ratio of the second heating stage is 1.0 to 2.0; and the air-coal ratio of the homogenization stage is 2.0 to 3.

0. The billet is a 60Si2Mn billet; The composition of the 60Si2Mn billet by weight percentage is as follows: C: 0.56-0.64%, Si: 1.5-2.0%, Mn: 0.7-1.0%, Cr: ≤0.35%, Ni: ≤0.35%, Cu: ≤0.25%, P: ≤0.025%, S: ≤0.020%, with the balance being Fe and other essential elements.

2. The manufacturing method according to claim 1, characterized in that, The soaking time for the heating treatment is 30-90 minutes.

3. The manufacturing method according to claim 1, characterized in that, The total residual oxygen concentration inside the heating furnace is <3%.

4. The manufacturing method according to claim 1, characterized in that, The billet loading method is cold billet loading; And / or, the heat treatment employs a walking beam furnace.

5. The manufacturing method according to claim 4, characterized in that, The cold billet is obtained by cold packing at room temperature.

6. The manufacturing method according to claim 1, characterized in that, In the phosphorus removal process, the phosphorus removal pressure is ≥18MPa.

7. The manufacturing method according to claim 1, characterized in that, In the rolling process, the initial rolling temperature is 1080-1180℃, and the final rolling temperature is 850-950℃.

8. The manufacturing method according to claim 1, characterized in that, In the rolling process, the billet is rolled into flat steel or round steel.

9. The manufacturing method according to claim 8, characterized in that, The flat steel has a specification of (6~40)mm×(60~150)mm; the round steel has a specification of φ16mm~φ90mm.

10. The manufacturing method according to claim 8, characterized in that, The flat steel has a total decarburized layer thickness of 0 and a total decarburized layer thickness of less than or equal to 1.5% of its thickness; the round steel has a total decarburized layer thickness of 0 and a total decarburized layer thickness of less than or equal to 0.8% of its diameter.

11. The manufacturing method according to claim 1, characterized in that, The billet is a 60Si2Mn continuously cast billet.

12. The manufacturing method according to claim 11, characterized in that, The dimensions of the continuously cast billet are 240mm × 240mm.

13. A SiMn spring steel without a fully decarburized layer, characterized in that, It is produced by the manufacturing method according to any one of claims 1-12.

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