75cr1 steel strip and method of production and use thereof

Abstract

This invention provides a method for producing 75CR1 strip steel, comprising the following steps: continuously cast billets at a temperature not lower than 500℃ are sequentially heated to 1240-1260℃ within temperature ranges of 800-1000℃, 1000-1150℃, 1100-1250℃, and 1220-1280℃ to obtain steel billets, wherein the total heating time of the steel billets is 200-400 minutes; the composition of the continuously cast billets, by mass fraction, includes 0.72 wt% < C ≤ 0.80 wt%. The steel billet is subjected to rough rolling, finish rolling, and coiling to obtain 75CR1 strip steel with a width of 2030-2080 mm. The rough rolling temperature is 1050-1150℃, the finish rolling temperature is 800-950℃, and the coiling temperature is 550-700℃. This invention achieves the production of ultra-wide 75CR1 strip steel with high microstructure consistency under stable rolling processes by optimizing the temperature settings and stress paths. (0.20Wt% < Si ≤ 0.45Wt%; 0.6Wt% ≤ Mn ≤ 0.9Wt%; 0 < P ≤ 0.03Wt%; 0 < S ≤ 0.02Wt%; 0.3 < Cr ≤ 0.6Wt%)

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a 75CR1 strip steel, its production method, and its application. Background Technology

[0002] 75CR1 steel is a high-carbon alloy tool steel that has high strength and wear resistance after heat treatment. It is often used to make the base of diamond saw blades, carbide saw blades and other circular saw blades and band saw blades, and is widely used in stone, construction and machining and other related fields.

[0003] Currently, 75Cr1 in China is mainly produced on thin slab continuous casting and rolling production lines and slab continuous casting + conventional hot rolling lines. The former organically integrates traditional independent processes such as continuous casting, heating, and hot rolling, offering advantages such as short production cycles, low energy consumption, and low investment. 75Cr1 produced by this process is generally characterized by narrow cross-sections and thin specifications. The slab continuous casting + conventional hot rolling technology typically involves first producing slabs from a continuous casting machine, then loading them into a heating furnace for heating using hot or cold charging methods, followed by production by roughing and finishing mills, resulting in thicker specifications and wider cross-sections. Regardless of the production method, temperature drops at the beginning, end, and edges are inevitable. During hot rolling, the temperature difference between the transverse and longitudinal directions generates significant differences in rolling force.

[0004] The composition of 75Cr1 steel determines its high strength and good hardenability. However, the slab is extremely sensitive to temperature changes, and its rolling stability is worse than that of ordinary steel grades such as plate. To improve the rolling stability of 75Cr1, it is necessary to control the uniformity of rolling temperature and reduce transverse and longitudinal temperature fluctuations during rolling. This involves: 1) ensuring sufficient heating temperature and time to guarantee the uniformity of the slab's overall microstructure; 2) improving the centering control of roughing and finishing rolling to reduce slab deviation; and 3) using accelerated rolling to minimize temperature drop at the tail end. Summary of the Invention

[0005] To address the technical problem of significant abnormal fluctuations in deformation resistance of 75Cr1 steel produced using the aforementioned commonly used techniques, this invention provides a method for producing 75Cr1 strip steel, comprising the following steps:

[0006] A continuously cast billet with a temperature not lower than 500℃ is sequentially heated to 1240-1260℃ within temperature ranges of 800-1000℃, 1000-1150℃, 1100-1250℃, and 1220-1280℃ to obtain a steel billet. The total heating time for the steel billet is 200-400 minutes. The composition of the continuously cast billet, by mass fraction, includes 0.72 wt% < C ≤ 0.80 wt%; 0.20 wt% < Si ≤ 0.45 wt%; 0.6 wt% ≤ Mn ≤ 0.9 wt%; 0 < P ≤ 0.03 wt%; 0 < S ≤ 0.02 wt%; 0.3 < Cr ≤ 0.6 wt%.

[0007] The steel billet is sequentially subjected to rough rolling, finish rolling and coiling to obtain 75CR1 strip steel with a width of 2030-2080mm. The finishing temperature of the rough rolling is 1050-1150℃, the finishing temperature is 800-950℃, and the coiling temperature is 550-700℃.

[0008] Furthermore, the steel billet is sequentially subjected to rough rolling, finish rolling, and coiling. The rough rolling is performed in seven passes to obtain an intermediate billet with a thickness of 40-56 mm. The reduction ratios of the seven rolling passes are 10%-20%, 15%-25%, 18%-28%, 20%-30%, 23%-33%, 25%-35%, and 28%-38%, respectively.

[0009] The reduction ratios of the finishing mill are distributed as follows: 30%–40%, 28%–38%, 25%–35%, 20%–30%, 15%–25%, 10%–20%, and 8%–15%.

[0010] Furthermore, the steel billet is sequentially subjected to rough rolling, finish rolling and coiling. The rough rolling process also includes descaling the steel billet in passes 1, 3 and 5, with a descaling pressure of 18-22 MPa and a descaling speed of 1.0-1.5 m / s.

[0011] Furthermore, the width of the vertical rolls in the roughing process is 2030–2100 mm, and the width of the vertical rolls in the finishing process is 2040–2110 mm. The roughing process also includes: reducing the width of the vertical rolls in the 1st, 3rd, 5th, and 7th passes. Based on the width of the vertical rolls in the roughing process, the reduction ratio for each pass is as follows: 30%–40%, 30%–40%, 20%–30%, and 0–15%.

[0012] Furthermore, during the finishing rolling process, the billet crown is 20-60 μm, and the wedge value of the billet fluctuates by no more than 30 μm.

[0013] Furthermore, when the wedge value W40 of the billet is greater than 30 μm, the roll gap on the operating side of the front frame is reduced, where the wedge value W40 is the thickness difference between the operating side edge at 40 mm and the transmission side edge at 40 mm.

[0014] Furthermore, the winding process includes a side guide opening width of 2130–2280 mm during the winding process, and a side guide opening width of 2060–2140 mm after tensioning.

[0015] Furthermore, the production of the continuously cast billet includes the following steps: molten steel corresponding to the composition of the continuously cast billet is refined and continuously cast to obtain the continuously cast billet, wherein the casting speed is not less than 0.8 m / min, the thickness of the continuously cast billet is 230-240 mm, the hot width is 2030-2080 mm, and the length is 8-10 m.

[0016] The present invention also provides a 75CR1 strip steel, which is produced by any of the production methods described above. The composition of the 75CR1 strip steel, by mass fraction, includes 0.72 wt% < C ≤ 0.80 wt%; 0.20 wt% < Si ≤ 0.45 wt%; 0.6 wt% ≤ Mn ≤ 0.9 wt%; 0 < P ≤ 0.03 wt%; 0 < S ≤ 0.02 wt%; 0.3 < Cr ≤ 0.6 wt%; the width of the 75CR1 strip steel is 2030–2080 mm, and the thickness is 4–15 mm.

[0017] The present invention also provides an application of the production method of 75CR1 strip steel as described above in the conventional hot rolling line process of 2250.

[0018] Compared with the prior art, the present invention has at least the following advantages:

[0019] This invention uses segmented heating of the continuously cast billet as a pretreatment for subsequent rolling, resulting in smaller temperature fluctuations at the beginning and end of the billet, and more uniform and complete austenitization of the microstructure. This effectively avoids the impact of the high temperature sensitivity of 75Cr1 steel on the quality of the finished steel product. It should also be noted that this invention is specifically designed for the production of 75Cr1 strip steel with a width of 2030–2080 mm. The production of extremely wide strip steel often amplifies the impact of uneven texture on product quality; this invention utilizes segmented heating to further mitigate these effects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a width curve diagram from Embodiment 1 of the present invention.

[0022] Figure 2 This is a width curve diagram from Embodiment 2 of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0025] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0026] This invention provides a method for producing 75CR1 strip steel, comprising the following steps:

[0027] S1. A continuously cast billet with a temperature not lower than 500℃ is successively heated to a temperature range of 800~1000℃, 1000~1150℃, 1100~1250℃, and 1220~1280℃ to obtain a steel billet, wherein the total heating time of the steel billet is 200~400min.

[0028] In some specific embodiments, the temperature ranges of 800–1000°C, 1000–1150°C, 1100–1250°C, and 1220–1280°C correspond to the preheating section, the first heating section, the second heating section, and the soaking section, respectively.

[0029] The temperature of the continuously cast billet is not lower than 500℃, meaning that the continuously cast billet is charged into the furnace hot, and the steel plate does not need to be cooled to room temperature and then reheated. This can save energy costs and reduce the risk of the billet cracking due to overcooling.

[0030] The staged heating process after entering the furnace minimizes temperature fluctuations at the beginning and end of the slab, resulting in uniform and complete austenitization. This staged heating process optimization is well-suited to the temperature sensitivity of 75Cr1 steel. When applied to common thin slab continuous casting and rolling, it can overcome abnormal fluctuations in deformation resistance, producing high-quality 75Cr1 steel.

[0031] In some embodiments, the production of a continuously cast billet includes the steps of: refining molten steel and continuously casting it to obtain a continuously cast billet, wherein the casting speed is not less than 0.8 m / min, the thickness of the continuously cast billet is 230-240 mm, the hot width is 2030-2080 mm, and the length is 8-10 m.

[0032] By mass fraction, the composition of the continuously cast billet includes 0.72 wt% < C ≤ 0.80 wt%; 0.20 wt% < Si ≤ 0.45 wt%; 0.6 wt% ≤ Mn ≤ 0.9 wt%; 0 < P ≤ 0.03 wt%; 0 < S ≤ 0.02 wt%; 0.3 < Cr ≤ 0.6 wt%, with the remainder being iron and unavoidable trace elements.

[0033] S2. The steel billet is sequentially subjected to rough rolling, finish rolling and coiling to obtain a strip steel with a width of 2030-2080mm, wherein the finishing temperature of the rough rolling is 1050-1150℃, the finishing temperature of the finish rolling is 800-950℃, and the coiling temperature is 550-700℃.

[0034] In many large-scale mining operations, large-sized saw blades can greatly improve the size and efficiency of cutting materials. However, large-sized saw blades require that the hot-rolled steel plate raw materials also be wide enough. However, the wider the material, the greater the rolling force, and the more difficult it is to control the plate crown and straightness. This places higher demands on rolling stability and the overall throughput of the equipment. In addition, due to the unique high strength and high hardness characteristics of 75CR1, currently commonly used thin plate hot rolling processes, including the 2250 conventional hot continuous rolling process, can only produce 75CR1 steel with a width of less than 2030mm.

[0035] Based on this, in addition to improving the heating process of the continuously cast billet, this invention also reduces the rolling force in key passes and improves rolling stability by optimizing the reduction distribution during roughing and finishing rolling, as well as controlling the related rolling cooling water flow. Furthermore, it optimizes the side pressure of vertical rolls, side guides, and other equipment, and performs rolling leveling based on centerline and wedge curves to improve rolling deviation, avoid edge impact damage, and improve overall throughput. By simultaneously optimizing rolling stability and rolling throughput, the production of extremely wide 75CR1 steel (2030–2080 mm wide) in a conventional 2250 hot rolling line process has been achieved.

[0036] Specifically, optimizing the reduction distribution during roughing and finishing rolling includes:

[0037] The roughing process is carried out in seven passes to obtain an intermediate billet with a thickness of 40-56 mm; wherein the reduction ratio of the seven passes is distributed as follows: 10%-20%, 15%-25%, 18%-28%, 20%-30%, 23%-33%, 25%-35%, and 28%-38%.

[0038] In some embodiments, after exiting the furnace, the material sequentially passes through a roughing descaling mill, a roughing mill with large vertical rolls, and a four-high roughing mill. The descaling pressure is 18–22 MPa, and the descaling speed is 1.0–1.5 m / s.

[0039] For example, the roughing process also includes descaling the billet in passes 1, 3, and 5, with a descaling pressure of 18–22 MPa and a descaling speed of 1.0–1.5 m / s.

[0040] In other embodiments, when rolling thinner gauges, the thickness of the intermediate billet is controlled at a lower limit to reduce the finishing rolling force.

[0041] The reduction ratios of the finishing mill are distributed as follows: 30%–40%, 28%–38%, 25%–35%, 20%–30%, 15%–25%, 10%–20%, and 8%–15%.

[0042] In some embodiments, finishing rolling is performed using a seven-stand finishing mill with small vertical rolls. In the F1 to F7 mills, F1: 30% to 40%, F2: 28% to 38%, F3: 25% to 35%, F4: 20% to 30%, F5: 15% to 25%, F6: 10% to 20%, and F7: 8% to 15%.

[0043] In other embodiments, speed-up rolling can be used to reduce the tail rolling force and improve rolling stability.

[0044] Specifically, the control of rolling cooling water flow includes:

[0045] During finishing rolling, the water flow is controlled in a manner that is lower at the beginning and higher at the end. Specifically, the water flow from the inter-stand nozzles of the front stands F1 and F2 is reduced or closed, while the inter-stand water flow of the rear stands F3-F7 is set to a delayed-on mode. The cooling water flow rate for the rolls and work rolls is set according to the system settings to reduce impact roll marks and improve rolling stability. Alternatively, the inter-stand water flow (ISC) of F1 and F2 can be closed, the rear stands can be set to a delayed-on mode, and the cooling water flow rate for the rolls and work rolls can be automatically set according to the system settings to further reduce impact roll marks.

[0046] Specifically, optimizing the side pressure of equipment such as vertical rolls and side guides, and performing rolling leveling based on curves such as centerlines and wedges include:

[0047] During the roughing process, the width of the vertical roll is 2030-2100mm. The width of the vertical roll is reduced in the 1st, 3rd, 5th and 7th passes. The distribution ratio of the width reduction in each pass is 30%-40%, 30%-40%, 20%-30% and 0-15%, respectively.

[0048] During the finishing rolling process, the finishing stands F2, F3, and F4 use high-speed steel rolls, and the finishing roll shape is CVC roll. The thickness is controlled by absolute AGC mode.

[0049] The vertical roller width is set to a target width +10 to 30 mm, where the target width is 2030 mm to 2065 mm.

[0050] The target value for strip crown is set between 20 and 60 μm, and the wedge shape is controlled within ±30 μm. A multi-function instrument is used to monitor parameters such as thickness, crown, and wedge shape. The thickness control of the finishing mill adopts the absolute value AGC mode.

[0051] To further refine this, when the wedge value W40 > 30 μm, the roller gap on the operating side of the front frame is reduced, where the wedge value W40 is the thickness difference between the operating side edge at 40 mm and the transmission side edge at 40 mm.

[0052] In some embodiments, the present invention also utilizes the pressure of side guide devices such as the operating side and drive side of the front frame to control the lateral deviation of the strip: when threading the strip, the main adjustment is the waviness; whichever side has a larger waviness, the pressure on that side is reduced. When the strip is biased towards the operating side, the operating side of the front frame is pressed down more until it is close to the center, and then a correction is considered to prevent the waviness of the rear frame from being too large; when the strip is biased towards the drive side, the drive side of the front frame is pressed down more until it is close to the center line, and then a correction is considered to prevent the waviness of the rear frame from being too large.

[0053] During the cooling process before winding, after the strip is cooled and centered by the side guide, the strip is wound into a coil by the pinch rolls. The opening width of the side guide is set according to the target width + 100 to 200 mm to ensure that the extra-wide part at the head can also pass smoothly. After the tension is established, the side guide is clamped, and the width is controlled according to the target width + 30 to 60 mm to ensure the overall coil quality.

[0054] Laminar cooling, also known as laminar flow cooling, can be achieved through sparse cooling.

[0055] In some embodiments, during the coiling process, after the strip enters the coiler and is tensioned, it is still adjusted according to the degree of deviation of the centerline curve and the wedge curve.

[0056] In summary, in the 2250 hot-rolled plate process, which includes continuous casting → heating → rough rolling → finish rolling → laminar flow cooling → coiling → inspection, packaging and warehousing, this invention optimizes the rolling stability and rolling throughput throughout the entire 2250 hot-rolled plate process.

[0057] The present invention has the following beneficial effects:

[0058] 1. It breaks through the upper limit of the width of 75Cr1 produced by the conventional 2250 hot strip rolling line, and can stably produce 75Cr1 with an actual width of more than 2030mm. The 75Cr1 produced has excellent performance, good plate shape, and stable edge quality.

[0059] 2. Compared with the 75CR1 single-rolled steel plate produced by medium and heavy plate rolling mills, the 75CR1 produced by this invention has advantages such as high production efficiency, low cost, and high dimensional accuracy, which reduces the procurement cost of downstream saw blade manufacturers and shortens the delivery cycle.

[0060] 3. This invention optimizes the existing 2250 conventional hot rolling line process without modifying the original production line and equipment, making it highly feasible and with a low technological threshold.

[0061] In summary: This invention employs a segmented, slow heating method, which ensures minimal temperature fluctuations at the beginning and end of the slab, resulting in uniform and complete austenitization. Furthermore, by optimizing processes such as water distribution between stands and rolling load allocation before finishing rolling, the rolling force fluctuations during roughing and finishing rolling are minimized, leading to a stable rolling process.

[0062] This method improves rolling centering by limiting the width of the vertical rolls and side guides. By adjusting the crown and wedge shape of the CVC work rolls through the functions of roll shifting and bending, as well as the horizontal value of the roll gap on both sides, the strip deviation during rolling is controlled, effectively avoiding damage to the strip edge from impact. It can stably and in batches produce the extreme specifications with a width of 2030 to 2080 mm.

[0063] This invention provides a 75CR1 strip steel, produced by the production method described above. The 75CR1 strip steel, by mass fraction, comprises: 0.72 wt% < C ≤ 0.80 wt%; 0.20 < Si ≤ 0.45 wt%; 0.6 wt% ≤ Mn ≤ 0.9 wt%; 0 < P ≤ 0.03 wt%; 0 < S ≤ 0.02 wt%; 0.3 < Cr ≤ 0.6 wt%. The 75CR1 strip steel has a width of 2030–2080 mm and a thickness of 4–15 mm.

[0064] The present invention also provides an application of the production method of 75CR1 strip steel as described above in the conventional hot rolling line process of 2250.

[0065] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0066] Example 1

[0067] A method for producing 75Cr1 hot-rolled steel coils with a width of 2065mm

[0068] 1. A method for producing 75Cr1 hot-rolled steel coils with an ultra-wide specification, the target specification being 7.5*2065mm, the technical solution being as follows:

[0069] (1) Slab continuous casting: The composition of the ladle in the continuous casting is C: 0.75%, Si: 0.22%, Mn: 0.81%, Cr: 0.51%, P: 0.019%, S: 0.014%; the remainder is iron and unavoidable trace elements. The continuous casting speed is 1.0 m / min, the slab thickness is 235 mm, the hot slab width is 2102 mm, and the slab length is 8.9 m.

[0070] (2) Heating Furnace: The continuously cast billet is charged into the heating furnace hot, with an initial temperature of 537℃. After entering the furnace, a segmented and slow heating regime is adopted, passing through the preheating section → first heating section → second heating section → soaking section → exiting the furnace. The preheating section temperature is 983℃, the first heating section temperature is 1130℃, the second heating section temperature is 1248℃, the soaking section temperature is 1239℃, the soaking time is 39 minutes, the exit temperature is 1243℃, and the total time in the furnace is 256 minutes.

[0071] (3) Rough rolling: After exiting the furnace, the slab passes through a rough descaling mill, a rough rolling mill with large vertical rolls, and a four-high roughing mill in sequence. The descaling pressure is 18 MPa and the descaling speed is 1.5 m / s. The rough rolling is carried out in 7 passes. The slab is descaled only in passes 1, 3, and 5. The vertical rolls are widened in passes 1, 3, 5, and 7. The width reduction ratios for each pass are 35%, 35%, 20%, and 10%, respectively. The flat roll reduction ratios for the 7 passes are 14%, 21%, 20%, 28%, 29%, 32%, and 34%, respectively. The thickness of the intermediate slab in the rough rolling is set to 50 mm, and the final rolling temperature is 1072 °C.

[0072] (4) Finishing: A seven-stand finishing mill with small vertical rolls is used. The target width of the vertical rolls is set to 2080 mm. High-speed steel rolls are used in finishing stands F2, F3, and F4. All finishing rolls are CVC rolls. The thickness is controlled in absolute AGC mode. The target value of strip crown is set to 35 μm, and the wedge shape is controlled within ±30 μm. A multi-function instrument is used to monitor parameters such as thickness, crown, and wedge shape. The finishing thickness control adopts absolute value AGC mode. The interstand water supply (ISC) between F1 and F2 is closed, and the subsequent stands are set to open with a delay. The rolling mill's working roll cooling water flow rate is automatically set by the system to avoid impact roll marks; the final rolling temperature is 850℃; the finishing rolling reduction rates are: F1: 35%, F2: 35%, F3: 29%, F4: 24%, F5: 16%, F6: 12%, F7: 9%; an accelerated rolling process is adopted, with the rolling speed of the F1 stand increasing from 0.78m / s at the head to 1.05m / s, and the rolling force at the tail is approximately 34000N, ensuring a stable rolling process; the rolling process adjusts for deviation through centerline curves, wedges, etc.

[0073] (5) Cooling: The layer cooling adopts a front-end sparse cooling method. After exiting the layer cooling, the coil is centered by the side guide, and then wound into a roll after being tensioned by the pinch rollers. The winding temperature is 650℃. After leaving the line, the coil enters the heat preservation pit for slow cooling. The side guide opening width is preset to 2165mm to ensure that the extra-wide head portion can also pass smoothly. When the coil is tensioned, the side guide is clamped, and the width is controlled at 2115mm to ensure the overall roll shape quality.

[0074] The actual average width of the produced 75Cr1 is 2077.3 mm, and the width curve is as follows: Figure 1 As shown, it meets the relevant technical standards.

[0075] Example 2

[0076] 1. A method for producing 75Cr1 hot-rolled steel coils with an ultra-wide specification, the target specification being 4.0*2030mm, the technical solution being as follows:

[0077] (1) Slab continuous casting: The composition of the ladle in the continuous casting is C: 0.76%, Si: 0.23%, Mn: 0.85%, Cr: 0.47%, P: 0.013%, S: 0.009%; the remainder is iron and unavoidable trace elements. The continuous casting speed is 1.0 m / min, the slab thickness is 236 mm, the hot slab width is 2083 mm, and the slab length is 8.9 m.

[0078] (2) Heating Furnace: The continuously cast billet is charged into the heating furnace hot, with an initial temperature of 537℃. After entering the furnace, a segmented and slow heating regime is adopted, passing through the preheating section → first heating section → second heating section → soaking section → exiting the furnace. The temperature of the preheating section is 986℃, the temperature of the first heating section is 1149℃, the temperature of the second heating section is 1243℃, the temperature of the soaking section is 1245℃, the soaking time is 39 minutes, the exit temperature is 1248℃, and the total time in the furnace is 209 minutes.

[0079] (3) Rough rolling: After exiting the furnace, the slab passes through a rough descaling mill, a rough rolling mill with large vertical rolls, and a four-high roughing mill in sequence. The descaling pressure is 18 MPa and the descaling speed is 1.5 m / s. The rough rolling is carried out in 7 passes. The slab is descaled only in passes 1, 3, and 5. The vertical rolls are widened in passes 1, 3, 5, and 7. The width reduction ratios for each pass are 35%, 35%, 20%, and 10%, respectively. The flat roll reduction ratios for the 7 passes are 17%, 19%, 21%, 22%, 25%, 26%, and 30%, respectively. The thickness of the intermediate slab in the rough rolling is set to 39 mm, and the final rolling temperature is 1089 °C.

[0080] (4) Finishing: A seven-stand finishing mill with small vertical rolls is used. The target width of the vertical rolls is set to 2043. High-speed steel rolls are used in finishing stands F2, F3, and F4. All finishing rolls are CVC rolls. The thickness is controlled in absolute AGC mode. The target value of strip crown is set to 30μm, and the wedge shape is controlled within ±30μm. A multi-function instrument is used to monitor parameters such as thickness, crown, and wedge shape. The finishing thickness control adopts absolute value AGC mode. The interstand water supply (ISC) between F1 and F2 is closed, and the subsequent stands are set to delayed opening mode. The cooling water flow rate of the work rolls is automatically set by the system to avoid the generation of impact roll marks; the final rolling temperature is 880℃; the finishing rolling reduction rate is: F1: 44%, F2: 38%, F3: 35%, F4: 28%, F5: 19%, F6: 13%, F7: 10%; speed-increasing rolling is adopted, with the rolling speed of the F1 stand increasing from 0.82m / s at the head to 1.15m / s, and the rolling force at the tail is about 42000N, resulting in a stable rolling process; the strip deviation is adjusted during the rolling process using centerline, wedge, and other curves.

[0081] (5) Cooling: The layer cooling adopts a front-end sparse cooling method. After exiting the layer cooling, the coil is centered by the side guide, and then wound into a roll after being tensioned by the pinch rollers. The winding temperature is 650℃. After leaving the line, the coil enters the heat preservation pit for slow cooling. The side guide opening width is preset to 2130mm to ensure that the extra-wide head portion can also pass smoothly. When the coil is tensioned, the side guide is clamped, and the width is controlled at 2080mm to ensure the overall roll shape quality.

[0082] The actual average width of the produced 75Cr1 is 2048.2 mm, and the width curve is as follows: Figure 2 As shown, it meets the relevant technical standards.

[0083] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for producing 75CR1 strip steel, characterized in that, Including the following steps: A continuously cast billet with a temperature not lower than 500℃ is sequentially heated to 1240-1260℃ within temperature ranges of 800-1000℃, 1000-1150℃, 1100-1250℃, and 1220-1280℃ to obtain a steel billet. The total heating time for the steel billet is 200-400 minutes. The composition of the continuously cast billet, by mass fraction, includes 0.72 wt% < C ≤ 0.80 wt%; 0.20 wt% < Si ≤ 0.45 wt%; 0.6 wt% ≤ Mn ≤ 0.9 wt%; 0 < P ≤ 0.03 wt%; 0 < S ≤ 0.02 wt%; 0.3 < Cr ≤ 0.6 wt%. The steel billet is sequentially subjected to rough rolling, finish rolling and coiling to obtain 75CR1 strip steel with a width of 2030~2080mm. The finishing temperature of the rough rolling is 1050~1150℃, the finishing temperature is 800~950℃, and the coiling temperature is 550~700℃. The roughing process is carried out in seven passes to obtain an intermediate billet with a thickness of 40-56 mm; wherein the reduction ratio of the seven passes is distributed as follows: 10%-20%, 15%-25%, 18%-28%, 20%-30%, 23%-33%, 25%-35%, 28%-38%; and the reduction ratio of the finishing process is distributed as follows: 30%-40%, 28%-38%, 25%-35%, 20%-30%, 15%-25%, 10%-20%, 8%-15%. The width of the vertical rolls in the roughing process is 2030-2100 mm, and the width of the vertical rolls in the finishing process is 2040-2110 mm. The roughing process also includes: reducing the width of the vertical rolls in the 1st, 3rd, 5th, and 7th passes. Based on the width of the vertical rolls in the roughing process, the reduction ratio for each pass is as follows: 30%-40%, 30%-40%, 20%-30%, and 0-15%. The billet crown during the finishing rolling process is 20-60 μm, and the wedge value of the billet during the finishing rolling process fluctuates by no more than 30 μm. Rolling cooling water flow control includes: During finishing rolling, the water flow is controlled in a manner that is less at the front and more at the back. The water flow of the nozzles between the stands of the front stands F1 and F2 is reduced or turned off, while the water flow between the stands of the rear stands F3-F7 is controlled in a delayed water-start mode.

2. The production method according to claim 1, characterized in that, The roughing process also includes descaling the billet in passes 1, 3, and 5, with a descaling pressure of 18–22 MPa and a descaling speed of 1.0–1.5 m / s.

3. The production method according to claim 1, characterized in that, When the wedge value W40 of the billet is greater than 30 μm, the roll gap on the operating side of the front frame is reduced, where the wedge value W40 is the difference between the thickness at 40 mm on the operating side and the thickness at 40 mm on the transmission side.

4. The production method according to claim 1, characterized in that, The winding process includes a side guide opening width of 2130~2280mm during the winding process, and a side guide opening width of 2060~2140mm after tensioning.

5. The production method according to claim 1, characterized in that, The production of the continuously cast billet includes the following steps: molten steel corresponding to the composition of the continuously cast billet is refined and continuously cast to obtain the continuously cast billet. The casting speed is not less than 0.8 m / min. The thickness of the continuously cast billet is 230-240 mm, the hot width is 2030-2080 mm, and the length is 8-10 m.

6. A 75CR1 strip steel, characterized in that, Produced using the production method described in any one of claims 1-5, the 75CR1 strip steel comprises, by mass fraction, 0.72 wt% < C ≤ 0.80 wt% 0.20Wt%<Si≤0.45Wt%; 0.6Wt%≤Mn≤0.9Wt% 0 < P ≤ 0.03 Wt% 0 < S ≤ 0.02Wt% 0.3<Cr≤0.6Wt; the width of the 75CR1 strip is 2030~2080mm, and the thickness is 4~15mm.

7. The application of a method for producing 75CR1 strip steel as described in any one of claims 1 to 5 in a conventional hot rolling line process at 2250.

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