Manufacturing method of martensitic stainless steel hot rolled steel coil

Abstract

The invention belongs to the technical field of stainless steel hot working, and discloses a martensitic stainless steel hot rolled steel coil manufacturing method capable of solving the edge crack problem in the wide rolling process so as to improve the yield. Comprising the steps that firstly, a continuous casting slab is heated for the first time in a heating furnace, the temperature of a heating section is 1100-1150 DEG C, the temperature of a soaking section is 1150-1200 DEG C, the heat preservation time of the soaking section is (1.00-1.25) t min, and t is the actually measured thickness mm of the slab before the slab enters the furnace; secondly, the heated continuous casting sheet billet is rolled into an intermediate billet through a roughing rolling unit, and the outlet temperature of the roughing rolling unit is 1000-1010 DEG C; 3, returning the intermediate billet to the heating furnace for secondary heating, wherein the heat preservation time of a soaking section of the secondary heating is shorter than that of the primary heating; fourthly, the intermediate billet heated for the second time is fed into a roughing rolling unit to be rolled, and the outlet temperature of the roughing rolling unit is 1000-1010 DEG C; 5, putting into a hot coil box after rolling; sixthly, the steel plate is fed into a finishing mill group to be rolled to the target thickness, and the finish rolling temperature is 1000-1050 DEG C; and 7, after finish rolling, laminar cooling is conducted to 300-400 DEG C, and then coiling is conducted.

Description

Technical Field

[0001] This invention relates to the field of stainless steel hot working technology, and specifically to a method for manufacturing hot-rolled martensitic stainless steel coils. Background Technology

[0002] High-strength heat-resistant martensitic stainless steel (such as some high-chromium, molybdenum- and vanadium-containing martensitic stainless steels) is widely used in high-temperature pressure and transmission fields such as hot press templates and conveyor belts due to its excellent thermal strength, wear resistance and low coefficient of thermal expansion.

[0003] However, due to the high content of alloying elements (such as Cr, Mo, V, Nb, etc.), this type of steel has a narrow thermoplastic window at high temperatures and poor hot working performance. In the traditional hot rolling process, the continuously cast billet is directly subjected to rough rolling and finish rolling after being heated once in a heating furnace. This process has the following significant drawbacks: First, severe edge cracking: During the rolling process, especially when rolling wide strips with a width exceeding 1500mm, the temperature at the edge of the slab drops rapidly. Due to the poor thermoplasticity of the material itself, edge cracks are easily generated under rolling stress. Second, low yield: To eliminate severe edge cracks and ensure product dimensions and quality, the cracked parts must be cut off in subsequent processes, which leads to a large amount of metal loss and a significant reduction in yield. Third, production disruption: Severe edge cracks may further lead to production accidents such as strip breakage, affecting the stability and continuity of the rolling process and limiting the maximum rollable width of the product.

[0004] Therefore, those skilled in the art urgently need a manufacturing method that can effectively suppress edge cracking during hot rolling of wide-width, high-strength, heat-resistant martensitic stainless steel. Summary of the Invention

[0005] In view of the above-mentioned defects in the prior art, the present invention aims to provide a method for manufacturing martensitic stainless steel hot-rolled coils to solve the problem of edge cracking during wide-width rolling, eliminate the edge trimming process, and improve yield and production efficiency.

[0006] The manufacturing method of martensitic stainless steel hot-rolled coil according to the present invention includes the following steps: Step 1: The continuously cast slab is loaded into a heating furnace for the first heating. The heating section temperature is 1100~1150℃, the soaking section temperature is 1150~1200℃, and the soaking section holding time is (1.00~1.25)t minutes, where t is the actual measured thickness of the slab before entering the furnace, in mm; Step 2: The heated continuously cast slab is rolled by a roughing mill to form an intermediate slab. The outlet temperature of the roughing mill is controlled at 1000~1010℃; Step 3: ... The intermediate billet is returned to the heating furnace for a second heating, and the holding time in the soaking section of the second heating is shorter than that of the first heating. Step four: The intermediate billet that has undergone a second heating is sent back to the roughing mill for rolling, and the exit temperature of the roughing mill is controlled at 1000~1010℃. Step five: The head and tail are exchanged through the hot coil box. Step six: It is sent to the finishing mill for rolling to the target thickness, and the final rolling temperature is controlled at 1000~1050℃. Step seven: After finishing rolling, laminar flow cooling is performed, and the billet is coiled at 300~400℃ to obtain a hot-rolled steel coil.

[0007] Furthermore, the chemical composition of martensitic stainless steel by weight percentage includes: C≤0.30%, Si≤2.00%, Mn≤1.00%, P≤0.040%, S≤0.020%, Cr: 11.00~17.50%, Ni≤5.00%, Mo≤2.00%, V≤1.00%, Ti≤1.00%, Cu≤5.00%, Nb≤0.45%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, between step one and step two, there is also a first descaling step: the continuous casting slab after step one is subjected to high-pressure water descaling at a pressure of 30~40MPa.

[0009] Furthermore, in step two, the roughing mill performs at least three rolling passes, resulting in an intermediate billet thickness of (0.6~0.7)t.

[0010] Furthermore, in step three, the heat soaking time for the second heating is (0.5~0.7)t minutes.

[0011] Furthermore, in step four, the roughing mill performs 3 to 5 passes of rolling to make the intermediate billet thickness 30 to 45 mm.

[0012] Furthermore, between steps three and four, a second descaling step is included: the intermediate billet after step three is descaled with high-pressure water at a pressure of 30-40 MPa.

[0013] Furthermore, in step five, a hot roll box is used to exchange the beginning and end of the roll.

[0014] Furthermore, in step six, the finishing mill performs 5 to 7 rolling passes.

[0015] Furthermore, the width of the hot-rolled steel coil shall not be less than 1500 mm.

[0016] Compared with the traditional single-heating, continuous rolling process, the manufacturing method of martensitic stainless steel hot-rolled coil of the present invention has the following advantages: 1) In the long single-heat rolling process of existing technology, the temperature of the edge and tail of the slab inevitably drops to the low plasticity range of the material. After hot rolling, the steel coil with edge cracks is trimmed. This not only fails to solve the problem at its root, but also leads to metal loss, increased energy consumption and extended process. The present invention actively and accurately compensates for heat through a second heating, so that the intermediate slab as a whole returns to the high plasticity window. It also eliminates the head and tail temperature difference before finishing rolling through the hot rolling box, creating uniform deformation conditions. This achieves a qualitative change from covering up the problem to eliminating the root cause of the problem.

[0017] 2) In existing technologies, after a single heating cycle, the slab cools naturally on the rolling line, which cannot guarantee optimal plasticity, especially for the edges of wide plates, during the critical deformation stage of finishing rolling. This is because the slab cannot reach the optimal plasticity temperature (≥1000℃). In contrast, this invention constructs a precise energy input model for the first heating and the second heating and reheating. The first heating ensures sufficient austenitization, and the second heating is not a simple repetition but rather a shorter process ((0.5-0.7)t). Targeted heating (min) is performed, which is highly efficient and has relatively controllable energy consumption. It is specifically used to repair temperature unevenness and edge temperature drop after initial rolling. At the same time, hot rolling box treatment is performed between the second roughing and finishing rolling, which solves the problem of temperature difference of tens of degrees between the beginning and end of finishing rolling in traditional processes. In addition, this application ensures that the deformation body is always within the temperature range where the material is least likely to crack from the beginning to the end of rolling by strictly controlling the roughing exit temperature (1000-1010℃) and the finishing rolling temperature (1000-1050℃). This is a precise temperature field management throughout the entire process that is highly consistent with the inherent law of high-temperature plasticity of materials.

[0018] 3) Existing technologies often limit product width due to their inability to address the severe edge cracking caused by wide widths. This invention, through proactive temperature management, enables the stable production of wide, high-strength, heat-resistant martensitic stainless steel hot-rolled coils with a width ≥1500mm. This meets the urgent demand for wide materials in high-end markets such as hot-pressing templates, opening up new market opportunities. Uniform temperature control throughout the entire process means more uniform deformation and microstructure evolution, resulting in better consistency in the final product's microstructure, performance, and shape, and more stable and reliable quality. Furthermore, since this invention completely eliminates edge cracking, the edge trimming process after hot rolling can be eliminated. For wide steel coils, the weight loss from edge trimming is significant. This invention directly converts this portion of metal into finished products, increasing the yield by 3%-5% or even higher, resulting in substantial economic benefits.

[0019] 4) In existing technologies, severe edge cracks can easily expand during rolling, leading to serious production accidents such as strip breakage, causing production line shutdowns and huge losses. This invention greatly reduces the risk of strip breakage by eliminating edge cracks, ensuring the continuity and stability of production, and improving the operating rate. On the surface, adding a reheating step may extend the cycle, but because the edge trimming process is eliminated and production interruptions caused by edge cracks and strip breakage are avoided, the overall production efficiency is actually improved. This is an advanced concept that improves overall efficiency by optimizing the inherent quality of the process.

[0020] 5) The material science problem of poor thermoplasticity caused by high alloying, which is addressed by this invention, is universal and has important reference value and promotion potential for other steel grades (such as certain special steels and high-temperature alloys) that face similar hot rolling difficulties due to high alloying. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A schematic flowchart of a method for manufacturing martensitic stainless steel hot-rolled coils according to an embodiment of the present invention is shown. Detailed Implementation

[0022] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0023] Figure 1 A flowchart illustrating a method for manufacturing hot-rolled martensitic stainless steel coils according to an embodiment of the present invention is shown. Figure 1As shown, the manufacturing method of hot-rolled martensitic stainless steel coil according to the present invention includes the following steps: Step 1 S1: The continuously cast slab (preferably 160-230 mm thick) is loaded into a heating furnace for the first heating. The heating section temperature is 1100~1150℃, the soaking section temperature is 1150~1200℃, and the soaking section holding time is (1.00~1.25)t minutes, where t is the actual measured thickness of the slab before entering the furnace (mm), ensuring that continuously cast slabs of different thicknesses can be fully heated; Step 2 S2: The heated continuously cast slab is rolled by a roughing mill to form an intermediate slab. The outlet temperature of the roughing mill is controlled at 1000~1010℃, which is one of the optimal plasticity ranges for high-alloy martensitic stainless steel. The initial deformation is completed at this temperature, which can minimize cracking; Step 3 S3: The intermediate slab is returned to the heating furnace for a second heating. The soaking section of the second heating is held for (1.00~1.25)t minutes. The holding time for the second heating is shorter than that for the first heating. The purpose of this heating is not complete reheating, but rather warming and homogenizing. Therefore, the holding time for the homogenization section in the second heating can be significantly shorter than that for the first heating. Step 4 (S4): The intermediate billet undergoing the second heating is fed back into the roughing mill for rolling. The exit temperature of the roughing mill is controlled at 1000~1010℃ to prepare billets with uniform temperature and suitable thickness for finishing rolling. Step 5 (S5): After rolling, the billet is treated in a hot coil box to prevent the temperature from dropping too quickly, especially at the beginning and end, before entering the finishing mill. Step 6 (S6): The billet is fed into the finishing mill for rolling to the target thickness. The final rolling temperature is controlled at 1000~1050℃ to ensure that the deformation process is always completed within the high plasticity range of the material. Step 7 (S7): After finishing rolling, laminar cooling is performed to control the phase transformation. The billet is cooled to 300~400℃ and then coiled to obtain a hot-rolled steel coil with martensitic structure and good coil shape.

[0024] The manufacturing method of hot-rolled martensitic stainless steel coils in this invention first involves a first heating and extended holding period of a continuously cast slab to achieve full and uniform austenitization. Subsequently, an intermediate slab is formed through rough rolling, with the exit temperature strictly controlled within the high plasticity range. The core step involves returning this intermediate slab to the heating furnace for a shorter second heating period to quickly and efficiently restore and homogenize the unbalanced slab temperature caused by temperature drop and deformation. The intermediate slab after the second heating undergoes rough rolling again and is immediately held at the surface to lock in the temperature and eliminate the temperature difference between the beginning and end of the roll. Finally, the homogenized roll undergoes final deformation at a high plasticity temperature in the finishing mill and is coiled into a finished product through controlled cooling. The entire process constitutes a closed-loop thermomechanical treatment process with precise temperature control and homogenization at its core, enabling stable production of wide-width, high-strength, heat-resistant martensitic stainless steel hot-rolled coils with a width ≥1500mm.

[0025] The manufacturing method of hot-rolled martensitic stainless steel coils in this invention addresses the extreme temperature sensitivity of high-alloy martensitic stainless steel to thermoplasticity. Through intermittent secondary heating, the intermediate billet, which has experienced temperature drop and unevenness after preliminary rolling, is precisely replenished and homogenized. This ensures that the entire billet (especially the heat-dissipating edges and tails) returns to and stabilizes within the optimal plastic deformation window (≥1000℃) before entering the final finishing roll. Simultaneously, the coil's head and tail are exchanged immediately after the second rough rolling, eliminating the significant temperature difference, particularly at the head and tail, caused by radiative heat dissipation from the conveyor rollers before finishing rolls. These two measures complement each other, ensuring that the finishing roll deformation is carried out under conditions of highest material plasticity, lowest resistance, and highly uniform temperature throughout the coil. This completely suppresses edge cracking caused by a sudden drop in plasticity due to excessively low local temperatures. Finally, by controlling the laminar cooling rate, a martensitic microstructure is obtained, ensuring a good coil shape. The manufacturing method of hot-rolled martensitic stainless steel coils in this invention creatively solves the core contradiction of insufficient heat and uneven temperature during hot rolling of high-alloy martensitic stainless steel. It eliminates the unavoidable low-temperature embrittlement zone at the edges in the traditional single heating process through secondary heating and heat preservation, thereby achieving a fundamental breakthrough from uncontrollable edge cracking to stable production of wide-width products without edge cracking. At the same time, it brings derivative benefits such as a leap in yield, simplified process, and improved production stability.

[0026] According to the present invention, the chemical composition of martensitic stainless steel, by weight percentage, may include: C≤0.30%, Si≤2.00%, Mn≤1.00%, P≤0.040%, S≤0.020%, Cr: 11.00~17.50%, Ni≤5.00%, Mo≤2.00%, V≤1.00%, Ti≤1.00%, Cu≤5.00%, Nb≤0.45%, with the balance being Fe and unavoidable impurities. This chemical composition provides a specific high-alloy martensitic stainless steel composition system matched by this method, which is the root cause of poor thermoplasticity and easy edge cracking problems.

[0027] In a preferred embodiment, a first descaling step may be included between step S1 and step S2: the continuously cast slab after step S1 is subjected to high-pressure water descaling at a pressure of 30-40 MPa. A second descaling step is also included between step S3 and step S4: the intermediate slab after step S3 is subjected to high-pressure water descaling at a pressure of 30-40 MPa. By performing two high-pressure water descaling processes, the iron oxide scale on the slab surface is removed after each heating cycle, ensuring the smoothness of the rolled surface and preventing oxide scale from being pressed into the strip surface and causing quality defects. This is a necessary guarantee for obtaining high-quality surface products.

[0028] In a preferred embodiment, in step S2, the roughing mill performs at least three rolling passes, resulting in an intermediate billet thickness of (0.6~0.7)t. This setup ensures that the initial rolling effectively breaks down the as-cast structure and provides a suitable intermediate billet thickness for subsequent second heating and rolling, which is crucial for smooth process transitions.

[0029] Furthermore, in step S3, the heat preservation time of the homogenization zone during the second heating can be (0.5~0.7)t minutes. This setting achieves precise and efficient control of the second heating (reheating) process, saving energy and time while ensuring uniform temperature.

[0030] Furthermore, in step S4, the roughing mill can perform 3 to 5 passes to achieve a rolling thickness of 30 to 45 mm for the intermediate billet. This setup ensures that the intermediate billet enters the subsequent finishing mill at a suitable thickness and temperature, preparing it for stable finishing rolling and achieving a good strip shape.

[0031] In a preferred embodiment, in step S5, the beginning and end of the steel coil are exchanged using an insulated box to reduce the temperature difference between the beginning and end.

[0032] Furthermore, in step six (S6), the finishing mill can perform 5 to 7 rolling passes. This setup ensures that the total deformation from the intermediate billet to the finished product thickness can be distributed reasonably and evenly, thereby obtaining a final product with uniform microstructure and good sheet shape.

[0033] The following are specific embodiments of the manufacturing method for hot-rolled martensitic stainless steel coils according to the present invention: Example 1 Step S1: A high-strength, heat-resistant stainless steel continuously cast slab with dimensions of 200×1580×8500mm is loaded into a continuous heating furnace. The temperature of the heating section of the furnace is 1120℃, and the temperature of the soaking section is 1160℃. The holding time in the soaking section is 218 minutes. The composition of this martensitic heat-resistant stainless steel is: C: 0.2%, Si: 0.51%, Mn: 0.82%, P: 0.025%, S: 0.001%, Cr: 12.37%, Ni: 0.4%, Mo: 1.08%, W: 0.98%, V: 0.25%.

[0034] Step 2 S2: After the billet exits the heating furnace, it is descaled with high-pressure water at a pressure of 32 MPa. Then, the continuously cast billet is sent to the roughing mill and rolled in 3 passes to form an intermediate billet. The exit temperature of the roughing mill is controlled at 1005℃ and the rolling thickness is 135 mm.

[0035] Step 3 S3: Remove this intermediate billet from the production line and reload it into the heating furnace for heating. The holding time in the homogenization zone is 105 minutes.

[0036] Step 4 S4: After the intermediate billet exits the heating furnace, it is descaled with high-pressure water at a pressure of 31 MPa; then the intermediate billet is sent back to the roughing mill and rolled in 5 passes at an exit temperature of 1006℃ and a rolling thickness of 35 mm.

[0037] Step 5 S5: After rough rolling, the coil is placed into the hot coil box.

[0038] Step S6: Feed the steel coil into the finishing mill and roll it through 7 passes. The final rolling temperature is 1035℃ and the rolling thickness is 5mm.

[0039] Step 7 S7: After rolling, the coil is subjected to laminar flow cooling to rapidly reduce the temperature of the steel coil to 385°C before coiling.

[0040] The edge quality of the steel coil is good after rolling.

[0041] Example 2 Step S1: A high-strength, heat-resistant stainless steel continuously cast slab with dimensions of 160×1500×8000mm is loaded into a continuous heating furnace. The temperature of the heating section of the furnace is 1145℃, and the temperature of the soaking section is 1176℃. The holding time in the soaking section is 176 minutes. The composition of this martensitic heat-resistant stainless steel is: C: 0.03%, Si: 0.33%, Mn: 0.51%, P: 0.022%, S: 0.001%, Cr: 15.46%, Ni: 4.8%, Cu: 3.5%, Nb: 0.25%.

[0042] Step 2 S2: After the billet exits the heating furnace, it is descaled with high-pressure water at a pressure of 36 MPa. Then, the continuously cast billet is sent to the roughing mill and rolled in 3 passes to form an intermediate billet. The exit temperature of the roughing mill is controlled at 1008℃ and the rolling thickness is 108 mm.

[0043] Step 3 S3: Remove this intermediate billet from the production line and reload it into the heating furnace for heating. The holding time in the homogenization zone is 96 minutes.

[0044] Step 4 S4: After the intermediate billet exits the heating furnace, it is descaled with high-pressure water at a pressure of 33 MPa; then the intermediate billet is sent back to the roughing mill for 5 passes of rolling. The exit temperature of the roughing mill is 1006℃ and the rolling thickness is 30 mm.

[0045] Step 5 S5: After rough rolling, the coil is placed into the hot coil box.

[0046] Step S6: Feed the steel coil into the finishing mill and roll it through 7 passes. The final rolling temperature is 1045℃ and the rolling thickness is 5.5mm.

[0047] Step 7 S7: After rolling, the coil is subjected to laminar flow cooling to rapidly reduce the temperature of the steel coil to 395°C before coiling.

[0048] The edge quality of the steel coil is good after rolling.

[0049] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0050] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for manufacturing hot-rolled martensitic stainless steel coils, characterized in that, Includes the following steps: Step 1: Load the continuously cast slab into the heating furnace for the first heating. The temperature of the heating section is 1100~1150℃, the temperature of the soaking section is 1150~1200℃, and the holding time of the soaking section is (1.00~1.25)t minutes, where t is the actual thickness of the slab before entering the furnace, in mm. Step 2: The heated continuous casting slab is rolled by a roughing mill to form an intermediate slab. The outlet temperature of the roughing mill is controlled at 1000~1010℃. Step 3: Return the intermediate billet to the heating furnace for a second heating, wherein the holding time of the soaking section in the second heating is less than the holding time of the first heating; Step 4: The intermediate billet, which has undergone a second heating, is fed back into the roughing mill for rolling. The outlet temperature of the roughing mill is controlled at 1000~1010℃. Step 5: After rolling, the coil is placed into the hot coil box; Step 6: Feed the product into the finishing mill and roll it to the target thickness. The final rolling temperature is controlled at 1000~1050℃. Step 7: After finishing rolling, laminar flow cooling is performed until the temperature reaches 300~400℃, then the coil is formed to obtain a hot-rolled steel coil.

2. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1, characterized in that, The chemical composition of the martensitic stainless steel, by weight percentage, includes: C≤0.30%, Si≤2.00%, Mn≤1.00%, P≤0.040%, S≤0.020%, Cr: 11.00~17.50%, Ni≤5.00%, Mo≤2.00%, V≤1.00%, Ti≤1.00%, Cu≤5.00%, Nb≤0.45%, with the balance being Fe and unavoidable impurities.

3. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, Between step one and step two, a first descaling step is also included: the continuous casting slab after step one is descaled by high-pressure water at a pressure of 30~40MPa.

4. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, In step two, the roughing mill performs at least three rolling passes, such that the intermediate billet has a rolling thickness of (0.6~0.7)t.

5. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, In step three, the heat soaking time of the second heating is (0.5~0.7)t minutes.

6. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, In step four, the roughing mill performs 3 to 5 passes of rolling to make the intermediate billet thickness 30 to 45 mm.

7. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, Between step three and step four, a second descaling step is also included: the intermediate billet after step three is descaled by high-pressure water at a pressure of 30-40 MPa.

8. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, In step five, the rolled coil is then placed into a hot coil box.

9. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, In step six, the finishing mill performs 5 to 7 rolling passes.

10. The method for manufacturing martensitic stainless steel hot-rolled coils according to claim 1 or 2, characterized in that, The width of the hot-rolled steel coil is not less than 1500mm.

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