A method of controlling high carbon alloy steel coils

Abstract

The application discloses a method for controlling high-carbon alloy steel pancake, which comprises the following steps: S1, heating process control; S2, laminar flow cooling control; S3, cooperation setting of a coiler and a coiler roll; S4, coiler tension control setting; S5, high-temperature coiling; S6, delayed uncoiling; and S7, slow cooling in a holding pit. The application controls the coiling temperature of a billet, reduces the expansion difference between phase transformation layers of a steel coil, guarantees the coiling quality and structural stability of the steel coil, effectively alleviates the incoordination deformation caused by phase transformation expansion, solves the problem that high-carbon alloy steel is prone to pancake in a hot continuous rolling production process, improves the quality of the steel coil and the processing efficiency of downstream customers, reduces the production cost, and is convenient to popularize and use.

Description

Technical Field

[0001] This invention relates to the field of strip steel coiling technology, and in particular to a method for controlling high-carbon alloy steel flat coils. Background Technology

[0002] hot rolling production line such as Figure 1 As shown, a typical hot rolling mill includes the following steps: billet casting (I), heating (II), primary descaling (III), primary roughing (IV), secondary roughing (V), secondary descaling (VI), multi-pass finishing (VII), cooling (VIII), and coiling (IX). These steps require equipment such as heating furnaces, roughing mills, seven-stand finishing mills, laminar flow cooling systems, side guides, pinch rolls, and coilers. The coiler is responsible for coiling the strip steel from the hot rolling line into coils for storage and transportation. The strip steel coiling process is as follows... Figure 2 As shown, after cooling, the steel coil passes between the upper pinch roller 1 and the lower pinch roller 2, and is guided to finally wind onto the coiler mandrel 3, where it is wound up with the help of multiple winding rollers 4. The outer side of the coiler mandrel 3 is generally provided with... Figure 2 The cover structure consists of multiple sector plates 5, with gaps reserved between adjacent sector plates 5, and the auxiliary roller 4 is movably set in the gaps.

[0003] Flattened coils are one of the most challenging issues to handle in the uncoiling process. After receiving the steel coils, downstream customers perform a series of processing steps according to their product requirements, such as leveling, pickling, and slitting. All subsequent processing of the steel coils requires uncoiling. If a steel coil is flattened, its inner diameter decreases, making it difficult or even impossible for the uncoiler to wind it. A normal steel coil has a standard inner diameter of 762mm; if the coil is deformed or flattened, its inner diameter can drop to a minimum of 620mm. Therefore, if the downstream customer's uncoiler mandrel diameter is greater than 620mm, it will prevent normal winding.

[0004] Research has revealed the following main reasons for flattening and curling:

[0005] (1) Phase transition factors

[0006] At different coiling temperatures, hot-rolled strip steel undergoes austenite to ferrite, pearlite, bainite, and martensite transformations. The expansion relationship of each microstructure in the steel is: austenite < ferrite < pearlite < bainite < martensite. During the cooling process, the strip steel undergoes varying degrees of volume expansion due to differences in the types and contents of the generated microstructures. This expansion is further exacerbated by the significant difference in cooling rates between the inner and outer rings of the coil, as well as the uneven temperature distribution between the coil layers (e.g., ...). Figure 3 As shown in the figure, the phase transformation is not synchronized in different parts of the steel coil. The uneven volume expansion of the inner and outer rings of the steel coil and between each layer leads to interlayer misalignment, which in turn destroys the stability of the steel coil and causes it to flatten under its own weight.

[0007] (2) Mechanical factors

[0008] During the coiling process on the rolling line, if the tension is set too low or unstable, the steel coil will not be tightly coiled, resulting in gaps between layers and a loose overall structure. This "soft coil" has even worse compressive strength during subsequent stacking and is more prone to flattening. The inner ring of the steel coil is particularly important; after being tightly coiled, the inner ring can act as a rigid mandrel to support the steel coil.

[0009] (3) Operation and stacking factors

[0010] Even after hot rolling, the steel coils are still at a high temperature and relatively soft. If they are stacked at this time (especially the lower layer of coils), they are very prone to plastic deformation under the pressure of their own enormous weight.

[0011] To save space, multiple high-temperature steel coils are stacked one on top of the other. The lower layer of coils has to bear the enormous weight of all the coils above it, far exceeding its load-bearing limit at high temperatures, inevitably leading to coil collapse. The higher the stack, the greater the risk.

[0012] In summary, the flattening of high-carbon alloy steel coils is caused by the combined effects of internal phase transformation expansion forces, thermal stress, and external physical factors, which compromise the stability of the steel coils, ultimately leading to deformation under gravity. Therefore, it is essential to develop a method for controlling the flattening of high-carbon alloy steel coils to address these issues. Summary of the Invention

[0013] This invention addresses the problem of flattening in high-carbon alloy steel during hot continuous rolling production due to its unique composition. It provides a method for controlling flattening of high-carbon alloy steel by comprehensively controlling parameters in heating, cooling, and coiling processes. This method mitigates the uncoordinated deformation caused by phase transformation expansion, thereby effectively controlling the occurrence of flattening and overcoming the shortcomings mentioned in the background art.

[0014] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0015] A method for controlling high-carbon alloy steel flat coils includes the following steps:

[0016] S1. Heating process control: A three-stage heating method is adopted in the heating furnace process, so that the billet passes through the low temperature preheating stage, the rapid heating stage and the heat soaking stage in sequence, so that the billet reaches the temperature state suitable for rolling and subsequent processing.

[0017] S2. Laminar flow cooling control: After rolling, the strip is cooled by adopting a cooling strategy of strong cooling in the front section and weak cooling in the back section to control the temperature change of the strip and optimize the microstructure and properties of the strip.

[0018] S3. Coupling machine and auxiliary winding roller settings: Control multiple auxiliary winding rollers so that they move outward at a uniform speed as the strip is wound up, and adhere to the outer wall of the strip to be wound up and tighten under constant pressure.

[0019] S4. Coiling Tension Control Setting: The coiling tension is dynamically adjusted according to the thickness of the steel coil, so that the strip steel always adheres to the outer wall of the adjacent steel coil during the coiling process, while ensuring that the contact area between the strip steel and the outer wall of the adjacent steel coil is subjected to uniform force.

[0020] S5. High-temperature coiling: The treated strip steel is guided onto the mandrel of the coiler at an environment of not less than 500℃. During the coiling process, the phase transformation process of the steel coil is changed.

[0021] S6. Delayed unwinding: After winding, the steel coil is left to stand in the coiler for more than 60 seconds before unwinding.

[0022] S7. Slow cooling in the insulation pit: The uncoiled steel coil is placed in the insulation pit for slow cooling.

[0023] Preferably, in S1, the parameters for the three stages of the three-stage heating method are set as follows:

[0024] In the low-temperature preheating stage, the billet is heated to 600-700℃ at a rate of 10-15℃ / min, and then enters the next stage.

[0025] During the rapid heating stage, the billet continues to heat up to 1100-1200℃ at a rate of 20-30℃ / min, and then enters the next stage.

[0026] The heat soaking stage lasts for 0.5 to 1 hour to ensure that the austenite grains are fully homogenized.

[0027] Preferably, in S2, the cooling rate of the strong cooling in the front section is set to 50-60℃ / s, and the cooling rate of the weak cooling in the rear section is set to 10-15℃ / s.

[0028] Preferably, in S3, the constant pressure control parameters of the winding roller are as follows:

[0029] The threshold pressure for enabling the constant pressure setting is 30 kN.

[0030] The constant pressure roll gap setting offset is equal to the initial roll gap minus 1.5 mm.

[0031] The constant pressure control setting for the auxiliary winding roller is 150KN.

[0032] Preferably, in step S5, the winding temperature is controlled within the range of 700–740°C.

[0033] Preferably, in S6, the dwell time of the steel coil in the coiler after winding is set to 1.5 to 3 minutes.

[0034] Preferably, in S7, the steel coil is transferred to a slow cooling pit within 10 minutes after uncoiling, and the cooling rate of the steel coil is set to below 30°C / h.

[0035] Preferably, the heating rate during the low-temperature preheating stage is controlled at 12℃ / min, and the target temperature is controlled at 650℃.

[0036] The present invention has the following beneficial effects:

[0037] 1. By controlling the coiling temperature of the steel billet, and based on measures to delay the start time of phase transformation and extend the time required for phase transformation, combined with furnace temperature control, laminar flow cooling control, coiler auxiliary roll control, coiler tension control, uncoiling control, and steel coil cooling control, the difference in expansion between phase transformation layers of the steel coil is reduced, ensuring the coiling quality and structural stability of the steel coil, effectively alleviating the uncoordinated deformation caused by phase transformation expansion, and solving the problem of flattened coils that easily occur in the hot continuous rolling process of high carbon alloy steel.

[0038] 2. Through this process, based on existing equipment, by comprehensively controlling the control parameters of heating, cooling, and coiling, the flattening phenomenon caused by phase transformation, mechanics, and operational stacking factors can be reduced, thereby improving the quality of steel coils and the processing efficiency of downstream customers, reducing production costs, and facilitating widespread application. Attached Figure Description

[0039] Figure 1 This is a general process flow diagram of a hot continuous rolling production line in the existing technology.

[0040] Figure 2 This is a demonstration diagram illustrating the effect of the finishing rolling process to the coiling process provided by the present invention.

[0041] Figure 3 This is a diagram showing the interlayer temperature distribution of a steel coil under the difference in cooling rates between the inner and outer rings.

[0042] Figure 4 The isothermal transformation curve of supercooled austenite in low alloy steel Q355B provided in the embodiments of the present invention is shown.

[0043] Figure 5 The isothermal transformation curve of supercooled austenite in high-carbon alloy steel 75Cr1 provided in the embodiments of the present invention is shown.

[0044] Figure 6 The process flow diagram of the method for controlling high-carbon alloy steel flat coils provided by the present invention.

[0045] In the picture:

[0046] Upper pinch roller-1; lower pinch roller-2; winding mandrel-3; winding aid roller-4; fan-shaped plate-5. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

[0048] In the description of this invention, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of the components, and therefore should not be construed as a limitation of this invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of this invention.

[0049] In studying the influencing factors of flat coils, it was found that different alloy steels have different phase transformation points. For example, the hot-rolled microstructure of high-carbon alloy steel and low-alloy steel is generally required to be ferrite and pearlite. Low-alloy steel has a higher phase transformation point, and most of the phase transformation is completed before coiling. After coiling, the phase transformation volume expansion is relatively slow, and flat coiling generally does not occur. In the embodiments given in this application, low-alloy steel Q355B was selected for experiments and data were recorded, as shown below. Figure 4 The isothermal transformation curve of supercooled austenite in low alloy steel Q355B is shown.

[0050] In the embodiments provided in this application, high-carbon alloy steels such as 75Cr1 and 80CrV2 were selected for experiments and data were recorded. Because high-carbon alloy steels have high carbon content and a large number of alloying elements, their phase transformation temperature is low. Phase transformation generally occurs during and after the winding process, resulting in significant volume expansion during and after winding, making flattening more likely. Specifically, as... Figure 5 As shown, it records the isothermal transformation curve of supercooled austenite in high-carbon alloy steel 75Cr1.

[0051] Table 1 is obtained based on the experimental data given in the above embodiments.

[0052] Table 1. Phase transformation start and end times for Q355B and 75Cr1

[0053]

[0054] The "-" in Table 1 indicates that there is no corresponding data, that is, no relevant transition time information was recorded.

[0055] pass Figure 4 and Figure 5 The curve display information and the data in Table 1 show that Q355B begins phase transformation at 820℃, while 75Cr1 only begins phase transformation at 720℃.

[0056] like Figure 6 As shown, in response to the above findings, the present invention provides a method for controlling the flat coil of high-carbon alloy steel, comprising the following steps:

[0057] S1. Heating process control: A three-stage heating method is adopted in the heating furnace process, so that the billet passes through the low temperature preheating stage, the rapid heating stage and the heat soaking stage in sequence, so that the billet reaches the temperature state suitable for rolling and subsequent processing.

[0058] The parameters for the three stages of the three-stage heating method are as follows:

[0059] In the low-temperature preheating stage, the billet is heated to 600-700℃ at a rate of 10-15℃ / min before entering the next stage; this avoids thermal stress cracks caused by rapid heating of the billet.

[0060] Optimal, the heating rate during the low-temperature preheating stage is controlled at 12℃ / min, and the target temperature is controlled at 650℃.

[0061] During the rapid heating stage, the billet continues to heat up to 1100-1200℃ at a rate of 20-30℃ / min, entering the next stage; this ensures uniform internal temperature of the billet.

[0062] The soaking stage lasts for 0.5 to 1 hour to ensure that the austenite grains are fully homogenized. This process ensures that the overall temperature of the billet is uniform and that the temperature deviation of each part of the billet is controlled within ±20℃.

[0063] S2, Laminar flow cooling control: In this embodiment, as shown... Figure 2 As shown, a finishing mill is used to roll the billet in multiple passes, and the finishing mill has seven rolls numbered from F1 to F7. After rolling, the strip is cooled by using a cooling strategy of strong cooling in the front section and weak cooling in the back section to control the temperature change of the strip and optimize the microstructure and properties of the strip. The temperature uniformity of the head and tail of the strip is ensured, and the temperature difference between the head and tail of the strip is ≤20℃ to avoid stress concentration caused by uneven local phase transformation.

[0064] The cooling rate of the front-end strong cooling is set to 50-60℃ / s, and the cooling rate of the rear-end weak cooling is set to 10-15℃ / s.

[0065] S3, Coordination settings for coiler and auxiliary coiling rollers 4: Control multiple auxiliary coiling rollers 4 so that they move outward at a uniform speed as the strip is coiled, adhering to the outer wall of the strip to be coiled and tightening it with constant pressure; to ensure that the inner ring of the steel coil is formed in accordance with the requirements.

[0066] The constant pressure control parameters for the winding roller 4 are as follows:

[0067] The threshold pressure for enabling the constant pressure setting (i.e., the constant pressure setting of the auxiliary roll 4 for the outer wall of the strip) is 30KN.

[0068] The constant pressure roll gap setting offset is equal to the initial roll gap minus 1.5 mm.

[0069] The constant pressure control setting for the auxiliary winding roller 4 is 150KN.

[0070] In the embodiments provided in this application, the pre-expansion diameter of the mandrel is 745 mm, the number of mandrel expansion coil turns is 2.5, the number of lifting turns of the auxiliary winding roller 4 is 7, and the inner diameter of the steel coil is 761 mm to 763 mm. These measures ensure that the inner coil is tightly wound.

[0071] S4. Coiling Tension Control Setting: The coiling tension is dynamically adjusted according to the thickness of the steel coil, so that the strip steel always adheres to the outer wall of the adjacent steel coil during the coiling process, while ensuring that the contact area between the strip steel and the outer wall of the adjacent steel coil is subjected to uniform force; constant and sufficient tension can prevent the steel coil layers from loosening, ensuring the stability and quality of the steel coil during the coiling process.

[0072] In the embodiments provided in this application, the cooled steel coil enters the coiler, and the coiling tension is dynamically adjusted according to the thickness of the steel coil. The parameters are recorded as shown in Table 2.

[0073] Table 2. Tension Setting Data

[0074]

[0075] S5. High-Temperature Coiling: The treated strip steel is guided onto the coiling mandrel 3 of the coiler at an environment of not less than 500℃. Under high-temperature conditions, the phase transformation initiation time and the time required for phase transformation of high-carbon alloy steel are both relatively long. During the coiling process, the phase transformation process of the steel coil is altered.

[0076] The coiling temperature is controlled within the range of 700–740℃. By controlling the coiling temperature of the material, the onset time of the phase transformation can be delayed, allowing the phase transformation to occur after coiling. After complete coiling, the temperature uniformity of the steel coil is improved, resulting in smaller differences in interlayer expansion after the subsequent phase transformation. Simultaneously, the time required for phase transformation (the time required for phase transformation is the difference between the end time and the start time of phase transformation) is extended, allowing the phase transformation to complete within a longer period and slowing down the rate of volume expansion caused by the phase transformation. This application provides examples of the phase transformation temperature and time for 75Cr1, as shown in Table 3.

[0077] Table 3. Phase transformation temperature and phase transformation time of 75Cr1

[0078]

[0079] S6. Delayed Unwinding: After winding, the steel coil is left to stand in the coiler for at least 60 seconds, typically set to 1.5–3 minutes. Unwinding is then performed. By extending the coil's dwell time in the coiler, the degree of phase transformation after unwinding is reduced, mitigating the uncoordinated deformation caused by phase transformation expansion.

[0080] S7. Slow Cooling in Insulation Pit: After uncoiling, the steel coil is placed in an insulation pit for slow cooling. Specifically, the steel coil is transferred to the slow cooling pit within 10 minutes of uncoiling, and the cooling rate is set to below 30℃ / h. This allows the phase transformation to proceed slowly, reducing the risk of sudden volume changes.

[0081] Controlling the coiling temperature of the billet, based on measures such as delaying the start time of phase transformation and extending the time required for phase transformation, combined with heating furnace temperature control, laminar flow cooling control, coiler auxiliary roll control, coiler tension control, uncoiling control, and steel coil cooling control, can effectively alleviate the uncoordinated deformation caused by phase transformation expansion.

[0082] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for controlling the flat coil of high-carbon alloy steel, characterized in that: Includes the following steps: S1. Heating process control: A three-stage heating method is adopted in the heating furnace process, so that the billet passes through the low temperature preheating stage, the rapid heating stage and the heat soaking stage in sequence, so that the billet reaches the temperature state suitable for rolling and subsequent processing. The parameters for the three stages of the three-stage heating method are as follows: In the low-temperature preheating stage, the billet is heated to 600-700℃ at a rate of 10-15℃ / min before entering the next stage; During the rapid heating stage, the billet continues to heat up to 1100-1200℃ at a rate of 20-30℃ / min, and then enters the next stage; The heat soaking stage lasts for 0.5 to 1 hour to ensure that the austenite grains are fully homogenized. S2. Laminar flow cooling control: After rolling, the strip is cooled by adopting a cooling strategy of strong cooling in the front section and weak cooling in the back section to control the temperature change of the strip and optimize the microstructure and properties of the strip. S3, Coordination setting of coiler and auxiliary coiling roller (4): Control multiple auxiliary coiling rollers (4) so ​​that multiple auxiliary coiling rollers (4) move outward at a uniform speed as the strip is coiled, and attach to the outer wall of the strip to be coiled and tighten with constant pressure. S4. Coiling tension control setting: The coiling tension is dynamically adjusted according to the thickness of the steel coil to ensure that the strip steel always adheres to the outer wall of the adjacent steel coil during the coiling process, while ensuring that the contact area between the strip steel and the outer wall of the adjacent steel coil is subjected to uniform force. S5. High-temperature coiling: The treated strip steel is guided to the coiling mandrel (3) of the coiler at an environment of not less than 500℃. During the coiling process, the phase transformation process of the steel coil is changed. The winding temperature is controlled within the range of 700–740℃; S6. Delayed unwinding: After winding, the steel coil is left to stand in the coiler for more than 60 seconds before unwinding. S7. Slow cooling in the insulation pit: Place the uncoiled steel coil into the insulation pit for slow cooling; The steel coils should be transferred to a slow cooling pit within 10 minutes of being uncoiled, and the cooling rate of the steel coils should be set to below 30℃ / h.

2. The method for controlling high-carbon alloy steel flat coils according to claim 1, characterized in that: In S2, the cooling rate of the front-end strong cooling is set to 50-60℃ / s, and the cooling rate of the rear-end weak cooling is set to 10-15℃ / s.

3. The method for controlling high-carbon alloy steel flat coils according to claim 1, characterized in that: In S3, the constant pressure control parameters of the auxiliary winding roller (4) are as follows: The threshold pressure for enabling the constant pressure setting is 30 kN. The constant pressure roll gap setting offset is equal to the initial roll gap minus 1.5 mm. The constant pressure control setting of the auxiliary winding roller (4) is 150KN.

4. The method for controlling high-carbon alloy steel flat coils according to claim 1, characterized in that: In S6, the dwell time of the steel coil in the coiler after winding is set to 1.5 to 3 minutes.

5. The method for controlling high-carbon alloy steel flat coils according to claim 1, characterized in that: The heating rate during the low-temperature preheating stage is controlled at 12℃ / min, and the target temperature is controlled at 650℃.

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