Method for controlling end cracks of hot-rolled spring flat steel

Abstract

The application provides a hot-rolled spring flat steel end crack control method, and belongs to the field of steel rolling processing in the metallurgical industry. The control method comprises uniform heating of the billet before rolling, uniform cooling of the flat steel after rolling, and high-temperature baking of the flat steel end after cooling. The method is a combined special control method of "billet heating uniformity control + flat steel heat preservation and cooling control after rolling + high-temperature baking of the flat steel after cutting", and realizes the generation of no cracks at the end of the hot-rolled spring flat steel. Especially for the cooled flat steel, since the spring flat steel after cutting still has certain stress which cannot be released, high-temperature baking is carried out at the end of the flat steel respectively, so as to ensure that no cracks are generated at the end.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling and processing in the metallurgical industry, and specifically relates to a method for controlling end cracks in hot-rolled spring flat steel. Background Technology

[0002] Spring flat steel is a raw material used to manufacture leaf springs for automotive suspension systems. Commonly used steel grades include 60Si2Mn, 55CrMn, 60CrMn, 50CrV, 55SiMnVB, and 60CrMnB, with a width generally not exceeding 160mm and a thickness not exceeding 60mm. Spring flat steel is a major component of leaf springs in automotive suspension systems, and its quality directly affects vehicle ride comfort, driving stability, and safety. In steel mills, the processing steps for spring flat steel include: billet heating, hot rolling, cooling on a cooling bed, and shearing into sections. However, during this process, end cracks frequently occur at both ends of the spring flat steel, posing significant quality control risks to its production and use.

[0003] Because spring flat steel is a medium-to-high carbon steel, its inherent properties cause it to generate significant stress with temperature changes. In actual production, temperature variations are substantial, ranging from 20℃ to 1200℃ and back to 20℃. This results in thermal stress caused by uneven heating or cooling, combined with structural stress caused by the non-synchronous nature of microstructural transformation and the unevenness of internal microstructure transformation. The combined stress creates significant stress that locally exceeds the strength of the spring flat steel, leading to stress cracks. These superimposed stress cracks typically range in depth from 0.1mm to 10mm, in length from 2mm to penetrating the cross-section of the flat steel, with an opening size of 0.1mm to 1.5mm; severe cases result in direct cracking.

[0004] Traditional methods typically involve controlling end cracks by adjusting either the cooling rate or the final rolling temperature. However, these methods are not very effective and cannot address stress cracking in every single flat steel bar. Summary of the Invention

[0005] The present invention aims to provide a method for controlling end cracks in hot-rolled spring flat steel, so as to solve the problem of end cracks in hot-rolled spring flat steel and ensure the quality of hot-rolled spring flat steel.

[0006] The technical solution of this invention is as follows:

[0007] A method for controlling end cracks in hot-rolled spring flat steel, the method comprising: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0008] Furthermore, the uniform heating includes: the uniform heating temperature is 1060-1240℃.

[0009] Furthermore, the uniform heating includes: along the direction perpendicular to the horizontal of the billet, the temperature difference between the two surfaces of the billet does not exceed 8°C.

[0010] Furthermore, the uniform heating includes: along a direction parallel to the horizontal of the billet, the temperature difference between the two surfaces of the billet does not exceed 5°C.

[0011] Furthermore, the uniform cooling includes controlling multiple heat insulation covers on the cooling bed to gradually rise from the head and tail ends of the flat steel to the middle along the length direction of the flat steel.

[0012] Furthermore, the upward angle between the insulation cover and the horizontal line does not exceed 30°.

[0013] Furthermore, along the length of the flat steel, multiple insulation covers from the ends of the flat steel on the cooling bed are controlled to gradually rise, and the upward angle with the horizontal line gradually increases from 0° to the maximum, not exceeding 30°.

[0014] Furthermore, the high-temperature baking includes: baking the head and tail ends of the flat steel at high temperature using a flame.

[0015] Furthermore, the high-temperature baking time is 40–150 seconds.

[0016] Furthermore, the high-temperature baking temperature is 800-1100℃.

[0017] Furthermore, the control method is applicable to the end crack control of spring flat steel with grades 60Si2Mn, 55CrMn, 60CrMn, 50CrV, 55SiMnVB, 60CrMnB, and SUP9.

[0018] Furthermore, the control method is applicable to end crack control of spring flat steel with a width not exceeding 160mm and a thickness not exceeding 60mm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention is particularly significant in the cooling control of flat steel (intermediate rolled product) after rolling. It controls the cooling rate by raising the insulation cover of the cooling bed at different angles to control the airflow, which is different from the conventional cooling method of the insulation cover being directly lowered (placed parallel above the cooling bed). This invention places the insulation cover above the cooling bed at different angles of 0 to 30°, which greatly improves the cooling uniformity of the flat steel.

[0021] This invention involves high-temperature baking of the cooled flat steel ends to release stress and prevent end cracks from forming during subsequent cooling. This improves the stress generated during the cutting process and perfectly solves the stress cracking problem of hot-rolled spring flat steel.

[0022] In addition, the present invention can also bundle the cooled flat steel into bundles (each bundle of steel has about 30-120 pieces depending on different specifications), and bake the ends of the bundles at high temperature so that both ends of each piece of steel are annealed to relieve stress, so that there will be no phenomenon of missing a few problematic pieces of steel.

[0023] This invention eliminates the traditional single control method and perfectly solves the end crack problem of hot-rolled spring flat steel by combining control from billet to intermediate rolled piece and from intermediate rolled piece to bundled piece, thus achieving a stable improvement in product quality. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the state of the heat insulation cover used in this invention;

[0025] Figure 2 This is a schematic diagram of the flame baking state of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. The embodiments of this invention are implemented based on the technical solutions of this invention, and detailed implementation methods and processes are given. However, the scope of protection of this invention is not limited to the following embodiments. Those skilled in the art should understand that the embodiments are merely helpful in understanding this invention and should not be considered as specific limitations on this invention. 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.

[0027] 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.

[0028] In this invention, unless otherwise specified and / or stated, all numerical values ​​relating to component amounts are by weight throughout. Process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions. The raw materials described in the following examples are all available from publicly available commercial sources.

[0029] This invention provides a method for controlling end cracks in hot-rolled spring flat steel. The method includes: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0030] This invention employs a unique combined control method—combining billet heating uniformity control, post-rolling flat steel heat preservation and cooling control, and post-cut flat steel high-temperature baking—to achieve crack-free ends of hot-rolled spring flat steel. Particularly for cooled flat steel, since some stress remains after rolling and cutting, high-temperature baking at the ends ensures no cracks occur. Preferably, the cooled flat steel is bundled, and then both ends of each bundle are baked. This baking process is equivalent to a simplified stress-relief annealing, because the ends of the flat steel generate significant stress during shearing, while the middle section generates less stress, resulting in less stress accumulation. Therefore, baking only the ends, and baking after bundling, ensures that each piece of steel undergoes high-temperature end treatment without any omissions.

[0031] The control method of the present invention is applicable to the end crack control of spring flat steel with grades such as 60Si2Mn, 55CrMn, 60CrMn, 50CrV, 55SiMnVB, 60CrMnB, and SUP9.

[0032] The control method of this invention is applicable to the end crack control of spring flat steel with a width not exceeding 160mm and a thickness not exceeding 60mm. Specifically, the width of the spring flat steel can be, for example, 160mm, 150mm, 140mm, 130mm, 120mm, 100mm, 90mm, 88mm, 85mm, 80mm, 75mm, 70mm, 65mm, 60mm, 50mm, etc.; the thickness can be, for example, 60mm, 50mm, 40mm, 30mm, 28mm, 25mm, 20mm, 18mm, 16mm, 15mm, 12mm, 10mm, 9mm, 8mm, 7mm, 6mm, 5mm, etc.

[0033] As an optional embodiment of the present invention, the uniform heating includes: the uniform heating temperature is 1060-1240℃ (e.g., 1070℃, 1090℃, 1110℃, 1130℃, 1150℃, 1170℃, 1190℃, 1210℃, 1230℃).

[0034] In the above technical solution, the homogenization temperature is controlled between 1060℃ and 1240℃ according to different steel grades and performance requirements. This avoids damage to the rolling mill or cracking of the steel due to low homogenization temperatures, and also avoids overheating or burning of the steel billet due to high homogenization temperatures, which would affect the steel's performance or render it unusable. This invention provides uniform heating. In addition to controlling the actual operating temperature (i.e., the homogenization temperature of the homogenization section), preheating heating (i.e., preheating section heating control) and heating rise heating (i.e., heating section heating control) can also be performed. The heating section can be a single section or multiple sections. Preheating heating control and heating rise heating control can use existing conventional technologies, such as a preheating temperature ≤ 850℃, and the heating section temperature (from the preheating temperature to the homogenization temperature) being 850~1240℃.

[0035] As an optional embodiment of the present invention, the uniform heating includes: along the direction perpendicular to the horizontal of the billet, the temperature difference between the two surfaces of the billet does not exceed 8°C (e.g., 8°C, 7°C, 6°C, 5°C, 4°C, 3°C, 2°C, 1°C, 0°C).

[0036] As an optional embodiment of the present invention, the uniform heating includes: along the direction parallel to the horizontal of the steel billet, the temperature difference between the two surfaces of the steel billet does not exceed 5°C (e.g., 5°C, 4°C, 3°C, 2°C, 1°C, 0°C).

[0037] As an optional embodiment of the present invention, the uniform heating includes: along the direction perpendicular to the horizontal of the billet, the temperature difference between the two surfaces of the billet does not exceed 8°C; along the direction parallel to the horizontal of the billet, the temperature difference between the two surfaces of the billet does not exceed 5°C.

[0038] In the above technical solution, the uniformity of temperature across the entire cross-section of the billet is controlled to avoid excessive temperature differences across the billet cross-section, which could generate significant stress and lead to cracking at the ends of the flat steel or failure to meet standard performance requirements. Specifically, the uniformity of surface and internal temperature of the billet is controlled by a combination of soaking time (e.g., 40–60 min) and soaking temperature (e.g., 1200–1220 °C). For example, when the soaking temperature is higher, such as 1220 °C, the soaking time is controlled to be shorter, such as 40 min; or when the soaking temperature is lower, such as 1200 °C, the soaking time is controlled to be longer, such as 60 min, in order to control the temperature uniformity of the billet after heating.

[0039] In this invention, along the direction perpendicular to the horizontal, that is, the direction of the height or thickness of the billet, the two opposite surfaces of the billet are the upper and lower surfaces of the billet; along the direction parallel to the horizontal, that is, the length direction of the billet, the two opposite surfaces of the billet are the left and right surfaces of the billet, that is, the ends of the billet, i.e., the head and tail.

[0040] As an optional embodiment of the present invention, the uniform cooling includes: controlling multiple heat insulation covers from the beginning and end of the flat steel to the middle on the cooling bed to gradually rise along the length direction of the flat steel. Further, controlling the upward angle between the heat insulation covers and the horizontal line to not exceed 30° (e.g., 30°, 27°, 25°, 20°, 18°, 15°, 12°, 8°, 6°, 3°, 0°).

[0041] In the above technical solution, the cooling rate is controlled by gradually raising the insulation cover of the cooling bed at different angles to control the airflow. This differs from conventional cooling where the insulation cover falls directly (placed parallel above the cooling bed), and can improve the cooling uniformity of the flat steel. This setting ensures uniform cooling of the head, middle, and tail of the flat steel, avoiding the head and tail cooling being too fast in actual production.

[0042] In this invention, the length direction of the flat steel is consistent with the length direction of the billet. The head (end) of the flat steel refers to the head (end) of the billet; the tail (end) of the flat steel refers to the tail (end) of the billet. "Billet" and "flat steel" are different names for spring flat steel before and after rolling.

[0043] As an optional embodiment of the present invention, the uniform cooling includes: along the length direction of the flat steel, controlling multiple heat insulation covers from the head and tail ends of the flat steel to the middle on the cooling bed to gradually rise, and the angle between the cover and the horizontal line gradually increases from 0° to the maximum, not exceeding 30°.

[0044] In the above technical solution, control is achieved by gradually changing the angle of multiple insulation covers (see...). Figure 1 Multiple insulation covers are raised at different angles to control the airflow and cooling intensity of various parts of the flat steel. This controlled airflow ensures uniform cooling and microstructural transformation of the flat steel, thereby reducing stress. Specifically, the angle between the insulation covers at both ends of the flat steel and the horizontal line is set to 0°, while the angle between the insulation cover in the middle and the horizontal line is set to the maximum. The angle gradually increases from the ends to the middle of the flat steel, either in a gradient (e.g., 0°, 5°, 10°, 15°, 20°, 25°, 30°) or a non-gradient increase (e.g., 0°, 8°, 15°, 24°, 30°). In this invention, the upper surface of the insulation cover is a metal plate, and the lower surface is asbestos, which is attached to the metal plate. Asbestos has good thermal insulation properties, preventing rapid heat loss and thus avoiding excessive stress on the flat steel due to rapid cooling. The insulation cover being raised means it forms a certain angle with the cooling bed, which is parallel to the ground.

[0045] As an optional embodiment of the present invention, the high-temperature baking includes: baking both ends of the flat steel at high temperature using a flame. Further, the high-temperature baking temperature is 800-1100℃ (e.g., 850℃, 900℃, 958℃, 989℃, 1000℃, 1050℃, 1092℃, 1100℃), and the baking time is 40-150s (e.g., 50s, 76s, 90s, 113s, 130s, 140s).

[0046] In the above technical solution, since the spring flat steel still retains some stress after rolling and cutting, a flame heating technique is used to control it. Preferably, at the spring flat steel collection point, a flame heater is designed at each end of the bundled flat steel (see...). Figure 2 Each of the steels is baked at a high temperature of 800-1100℃, and the baking time is controlled at 40-150 seconds depending on the steel grade and shearing temperature.

[0047] The spring flat steel production process of this invention includes: billet heating -- exiting the heating furnace -- rolling into the required specifications -- cooling on a cooling bed -- cutting into the required length -- stacking and bundling -- end baking -- hoisting and stacking. The billet before heating can be obtained using existing technology.

[0048] The present invention will now be described in further detail with reference to specific embodiments.

[0049] Example 1

[0050] A method for controlling end cracks in hot-rolled spring flat steel, the method comprising: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0051] The uniform heating includes: a uniform heating temperature of 1200-1220℃, and a maximum temperature difference of 6℃ between the upper and lower surfaces of the billet along the direction perpendicular to the horizontal; and a maximum temperature difference of 5℃ between the head and tail ends of the billet along the direction parallel to the horizontal.

[0052] Uniform cooling includes controlling the upward angle between the insulation cover of the cooling bed and the horizontal line to be 0° at both ends, increasing in increments of 7.5° towards the middle, up to a maximum of 30° in the middle.

[0053] High-temperature baking includes: using a flame to bake both ends of the flat steel at a high temperature of 1050℃ for 100 seconds.

[0054] The spring flat steel grade is 60Si2Mn, with a thickness of 12mm and a width of 75mm. 120 tons of spring flat steel were tested and found to have no surface cracks at both ends, with a pass rate of 100%.

[0055] In this invention, the method for testing end cracks of all flat steel bars is as follows: professional inspectors first conduct visual inspection, and products that are suspected of being unqualified (such as suspected cracks) after visual inspection will undergo ultrasonic testing.

[0056] Example 2

[0057] A method for controlling end cracks in hot-rolled spring flat steel, the method comprising: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0058] The uniform heating includes: a uniform heating temperature of 1100-1130℃, and a maximum temperature difference of 7℃ between the upper and lower surfaces of the billet along the direction perpendicular to the horizontal; and a maximum temperature difference of 5℃ between the head and tail ends of the billet along the direction parallel to the horizontal.

[0059] Uniform cooling includes controlling the upward angle between the insulation cover of the cooling bed and the horizontal line to be 0° at both ends, increasing in increments of 7.5° towards the middle, up to a maximum of 30° in the middle.

[0060] High-temperature baking includes: using a flame to bake both ends of the flat steel at a high temperature of 850℃ for 130 seconds.

[0061] The spring flat steel grade is 55CrMn, with a thickness of 22mm and a width of 90mm. 100 tons of steel were tested, and there were no surface cracks at both ends, with a pass rate of 100%.

[0062] Example 3

[0063] A method for controlling end cracks in hot-rolled spring flat steel, the method comprising: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0064] The uniform heating includes: a uniform heating temperature of 1090-1110℃, and a maximum temperature difference of 5℃ between the upper and lower surfaces of the billet along the direction perpendicular to the horizontal; and a maximum temperature difference of 4℃ between the head and tail ends of the billet along the direction parallel to the horizontal.

[0065] Uniform cooling includes controlling the upward angle between the insulation cover of the cooling bed and the horizontal line to 0° at both ends, increasing in increments of 5° towards the middle, up to a maximum of 25° in the middle.

[0066] High-temperature baking includes: using a flame to bake both ends of the flat steel at a high temperature of 860℃ for 120 seconds.

[0067] The spring flat steel grade is SUP9, with a thickness of 9mm and a width of 60mm. 60 tons of steel were tested and found to have no surface cracks at both ends, with a pass rate of 100%.

[0068] Example 4

[0069] A method for controlling end cracks in hot-rolled spring flat steel, the method comprising: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0070] The uniform heating includes: a uniform heating temperature of 1100-1130℃, and a maximum temperature difference of 5℃ between the upper and lower surfaces of the billet along the direction perpendicular to the horizontal; and a maximum temperature difference of 5℃ between the head and tail ends of the billet along the direction parallel to the horizontal.

[0071] Uniform cooling includes controlling the upward angle between the insulation cover of the cooling bed and the horizontal line to be 0° at both ends, increasing in increments of 6° towards the middle, up to a maximum of 30° in the middle.

[0072] High-temperature baking includes: using a flame to bake both ends of the flat steel at a high temperature of 840℃ for 150 seconds.

[0073] The spring flat steel is grade 50CrV, with a thickness of 20mm and a width of 120mm. 120 tons of spring flat steel were tested and found to have no surface cracks at both ends, with a pass rate of 100%.

[0074] Example 5

[0075] A method for controlling end cracks in hot-rolled spring flat steel, the method comprising: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel.

[0076] The uniform heating includes: a uniform heating temperature of 1120-1150℃, and a maximum temperature difference of 5℃ between the upper and lower surfaces of the billet along the direction perpendicular to the horizontal; and a maximum temperature difference of 4℃ between the head and tail ends of the billet along the direction parallel to the horizontal.

[0077] Uniform cooling includes controlling the upward angle between the insulation cover of the cooling bed and the horizontal line to be 0° at both ends, increasing in increments of 5° towards the middle, up to a maximum of 30° in the middle.

[0078] High-temperature baking includes: using a flame to bake both ends of the flat steel at a high temperature of 800℃ for 150 seconds.

[0079] The spring flat steel grade is 60CrMnB, with a thickness of 40mm and a width of 100mm. 100 tons of spring flat steel were tested, and there were no surface cracks at both ends, with a pass rate of 100%.

[0080] Example 6

[0081] A method for controlling end cracks in hot-rolled spring flat steel differs from Example 1 in that, during uniform heating: along the direction perpendicular to the horizontal of the billet, the maximum temperature difference between the upper and lower surfaces of the billet is 7°C; along the direction parallel to the horizontal of the billet, the maximum temperature difference between the head and tail ends of the billet is 5°C. All other settings are the same as in Example 1.

[0082] The spring flat steel grade is 60Si2Mn, with a thickness of 10mm and a width of 60mm. After testing with 100 tons of spring flat steel, the spring flat steel had no surface cracks at both ends, with a pass rate of 100%.

[0083] Example 7

[0084] A method for controlling end cracks in hot-rolled spring flat steel differs from Example 2 in that, during uniform cooling, the upward angle between the insulation cover of the cooling bed and the horizontal line is controlled: 0° at both ends, increasing in increments of 5° towards the middle, reaching a maximum of 25° in the middle. All other settings are the same as in Example 2.

[0085] The spring flat steel grade is 55CrMn, with a thickness of 16mm and a width of 90mm. 120 tons of steel were tested and no surface cracks were found at either end, with a pass rate of 100%.

[0086] Example 8

[0087] A method for controlling end cracks in hot-rolled spring flat steel differs from Example 3 in that the baking time during high-temperature baking is 110 seconds. All other settings are the same as in Example 3.

[0088] The spring flat steel is grade SUP9, with a thickness of 8mm and a width of 60mm. 120 tons of steel were tested and no surface cracks were found at either end, with a pass rate of 100%.

[0089] Comparative Example 1

[0090] A method for controlling end cracks in hot-rolled spring flat steel is disclosed, differing from Example 1 only in that the ends of the flat steel are not subjected to high-temperature baking after cooling. All other settings are the same as in Example 1.

[0091] Of the 100 tons of steel tested, some spring flat steel bars had no surface cracks at both ends, with a pass rate of 50%.

[0092] Comparative Example 2

[0093] A method for controlling end cracks in hot-rolled spring flat steel differs from Example 2 only in that the cooling of the flat steel employs conventional cooling where all insulation covers are directly lowered (i.e., placed parallel above the cooling bed). All other settings are the same as in Example 2.

[0094] After testing, 90 tons of steel showed that some spring flat steel had no surface cracks at both ends, with a pass rate of 40%.

[0095] Comparative Example 3

[0096] A method for controlling end cracks in hot-rolled spring flat steel differs from Example 3 only in that, during the heating of the spring flat steel billet, the homogenization temperature is 1050–1070°C, and the maximum temperature difference between the upper and lower surfaces of the billet is 10°C along the direction perpendicular to the horizontal; the maximum temperature difference between the head and tail ends of the billet is 6°C along the direction parallel to the horizontal. All other settings are the same as in Example 3.

[0097] Of the 120 tons of steel tested, some spring flat steel bars had no surface cracks at both ends, with a pass rate of 45%.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for controlling end cracks in hot-rolled spring flat steel, characterized in that, The control method includes: uniformly heating the billet of the spring flat steel and then rolling it to obtain flat steel; uniformly cooling the flat steel and then baking its ends at high temperature to obtain the spring flat steel. The uniform cooling includes controlling multiple heat insulation covers on the cooling bed to gradually rise from the head and tail ends of the flat steel to the middle along the length of the flat steel, and the angle between the cover and the horizontal line gradually increases from 0° to the maximum, not exceeding 30°.

2. The control method as described in claim 1, characterized in that, The uniform heating includes a heating temperature of 1060~1240℃.

3. The control method as described in claim 1, characterized in that, The uniform heating includes: along the direction perpendicular to the horizontal of the billet, the temperature difference between the two surfaces of the billet does not exceed 8°C.

4. The control method as described in claim 1, characterized in that, The uniform heating includes: along the horizontal direction of the billet, the temperature difference between the two surfaces of the billet does not exceed 5°C.

5. The control method as described in claim 1, characterized in that, The high-temperature baking includes: using a flame to bake the head and tail ends of the flat steel at high temperature.

6. The control method as described in claim 1, characterized in that, The high-temperature baking time is 40~150s.

7. The control method as described in claim 1, characterized in that, The high-temperature baking temperature is 800-1100℃.

8. The control method as described in claim 1, characterized in that, The control method is applicable to the end crack control of spring flat steel with grades 60Si2Mn, 55CrMn, 60CrMn, 50CrV, 55SiMnVB, 60CrMnB, and SUP9. And / or, the control method is applicable to end crack control of spring flat steel with a width not greater than 160 mm and a thickness not greater than 60 mm.

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