Production method for controlling hot rolling small convexity of high-carbon tool steel

Abstract

The invention provides a high-carbon tool steel hot rolling small convexity control production method which comprises the following steps: S1, plate blank heating: feeding a plate blank into a heating furnace in a hot charging manner at the temperature of more than or equal to 300 DEG C; after entering the furnace, sequentially passing through a preheating section, a first heating section, a second heating section and a solid solution section by adopting a heating system of segmented slow temperature rise, and discharging; s2, rough rolling: after discharging, sequentially passing through a four-roller rough rolling machine with rough descaling and width reduction of a large vertical roller, and carrying out rough rolling according to seven passes; s3, finish rolling is conducted, specifically, a four-roller seven-rack finish rolling unit is adopted for rolling, and high-speed steel rollers are adopted for finish rolling F2, F3 and F4 racks; s4, coiling is carried out; and S5, flattening is conducted, specifically, a convex roller is adopted for flattening. The heating mode of segmented slow temperature rise is adopted, it can be guaranteed that the temperature fluctuation of the head and the tail of the plate blank is small, structure austenitizing is uniform and complete, the rolling force fluctuation of rough rolling and finish rolling is small, and convexity control is more stable.

Description

Technical Field

[0001] The invention relates to the field of steel manufacturing, and in particular to a production method for controlling small crown of hot-rolled high-carbon tool steel. Background Art

[0002] High-carbon tool steel primarily refers to steel grades with a carbon content of 0.65% to 1.35%. High-carbon tool steel exhibits high hardenability and wear resistance and is widely used in the manufacture of high-precision hardware tools. After hot rolling, high-carbon tool steel typically undergoes annealing and cold rolling, with the resulting cold-rolled product requiring high thickness accuracy. Because the cold rolling process has limited ability to improve transverse thickness variation, the hot-rolled base material must possess a well-defined cross-sectional profile.

[0003] The crown of hot rolled coil generally refers to the difference between the thickness H in the middle of the width of the steel plate and the representative thickness Hx near the edge after removing the edge thinning part of the strip. It is an important indicator reflecting the cross-sectional shape and shape of the steel plate. Excessive crown can easily lead to thin edge thickness and excessive transverse thickness difference after cold rolling. Figure 1 The cross-sectional view of the strip shown in the figure shows that the convexity is calculated as Cx = H-(H x1 +H x2 ) / 2, where H is the middle thickness, H x1 is the thickness of the operating side, H x2 The thickness at the transmission side is the most common crown control measure for hot rolling, expressed as C40, which is the difference between the center thickness and the average thickness at 40mm on either side. According to feedback from downstream cold rolling mills, when the crown C40 of hot-rolled steel plates is controlled within 50μm, they are well suited for subsequent cold rolling.

[0004] Currently, crown control in hot rolling is primarily achieved through work roll shifting and bending in the front stand. However, high-carbon tool steel has high strength and is extremely sensitive to temperature changes, resulting in high rolling loads and poor rolling stability. This makes crown control difficult, and uncontrolled crowning frequently occurs, presenting significant challenges to subsequent cold rolling.

[0005] In the prior art, when hot-rolling high-carbon tool steel, the crown control has the following problems:

[0006] 1. When the rollers were used to produce high-carbon tool steel in the early stage, the amount of steel passed was small and the roller temperature was uneven, resulting in different thermal expansion of the rollers at different positions. The actual thermal crown of the rollers was too large when passing steel, and the crown of the steel coils rolled in the early stage was out of control.

[0007] 2. When the roller is used to produce high-carbon tool steel in the later stage, the middle part of the roller is severely worn. Adjustments such as roller shifting and roller bending are ineffective, and the crown of the rolled product remains high.

[0008] 3. Fluctuations in rolling force caused by temperature changes, or unreasonable control or distribution of the rolling force of the front stand when changing specifications, resulting in uncontrolled crown.

[0009] Therefore, there is an urgent need for a production method that can effectively control the small convexity of high-carbon tool steel hot rolling to meet the requirements of downstream cold rolling processing. Summary of the Invention

[0010] The purpose of the present invention is to provide a production method for controlling the small convexity of hot-rolled high-carbon tool steel. By optimizing the rolling plan arrangement, heating system, rolling process parameters, etc., the plate convexity of hot-rolled high-carbon tool steel can be effectively controlled, the thickness difference of the cross-section of the strip can be improved, and the use requirements of downstream users can be met.

[0011] In the technical solution adopted by the present invention, the high carbon tool steel composition includes: C: 0.65-1.35%, Si: 0-0.35%, Mn: 0-1.0%, Cr: 0-1.0%, P≤0.030%, S≤0.030%, and the rest is iron and unavoidable impurities.

[0012] A production method for controlling small crown of hot-rolled high-carbon tool steel of the present invention comprises the following steps:

[0013] S1. Rolling plan arrangement: The rolling production of high-carbon tool steel must be arranged into the early and middle stages of the rolling cycle. The amount of steel passed through the roughing working rolls shall not exceed 100,000 tons, and the number of kilometers of steel passed through the finishing F7 rolls shall not exceed 80 kilometers. Steel grades with a width greater than 200mm greater than the target width of high-carbon tool steel and a thickness greater than 4.0mm shall be used as transition materials for hot rolling. The hot rolling range shall ensure that the contact position between the strip and the rolls at the roll shifting limit is covered. The amount of transition materials for the start of rolling (transition materials are generally steel coils that transition from thick gauge to thin gauge, so they are often also called thickness transition materials) shall be controlled during production scheduling. At the same time, the number of transition materials must be ≥10 coils or the number of kilometers of F7 steel passed must be greater than 8 kilometers before thin gauge rolling can be carried out to ensure uniform roll temperature and form normal roll thermal crown.

[0014] S2. Slab Heating: Continuous casting slabs are 220-240mm thick and are hot-charged into the heating furnace at an entry temperature of ≥300°C. After entering the furnace, a staged, slow-heating heating system is adopted, with the slabs passing through the preheating section, first heating section, second heating section, soaking section, and finally exiting the furnace. The preheating section temperature is 400-700°C, the first heating section temperature is 700-900°C, the second heating section temperature is 900-1100°C, the soaking section temperature is 1000-1200°C, and the soaking time is ≥50 minutes. The exit temperature is 1100-1200°C, and the total time in the furnace is 200-300 minutes.

[0015] S3, Roughing: After exiting the furnace, the steel passes through a four-high roughing mill with rough descaling and width reduction using large vertical rolls. Roughing is performed in seven passes, with descaling performed in the first, third, and fifth passes. The flat roll reduction ratios for these seven passes are: 15%-25%, 15%-25%, 18%-28%, 20%-30%, 23%-33%, 25%-35%, and 28%-38%. The intermediate bar thickness for roughing is set at 30-56mm, and the finishing temperature is 1000-1150°C. For thinner gauges, hot coil boxes are used after roughing to reduce the intermediate bar thickness and lower the rolling forces during finishing.

[0016] S4, finishing rolling: adopt four-roll seven-stand finishing rolling mill, finishing rolling F2, F3, F4 stands use high-speed steel rolls, finishing roll shape is CVC roll, finishing working roll shifting range is -150 ~ 150mm, bending roll force preset 0 ~ 2000KN. The finishing thickness is controlled in absolute value AGC mode, with the rolling crown set at 20-40 μm. A multi-function instrument is used to monitor parameters such as thickness and C40 crown. The inter-stand water (ISC) of F1 and F2 is turned off, and the rear stand is kept open. The final rolling temperature is 800-950°C. The finishing reduction ratio is: F1: 40%-55%, F2: 40%-55%, F3: 30%-45%, F4: 25%-40%, F5: 20%-30%, F6: 15%-25%, F7: 8%-20%. The roller cooling water flow rate is 900-1200 m³ / min for the front stand. 3 / h, the cooling water of the rear stand working roll should be appropriately reduced to 500~1000m 3 / h to reduce the rolling force; optimize the rolling speed. When the tail temperature drop is large, resulting in large tail rolling force and convexity, the rolling speed can be increased to reduce the tail rolling force; the guide width on the finishing entrance side is controlled at +30 to 50 mm of the rolling width to effectively prevent the strip from running off, improve rolling stability and centering, and avoid long-term wear of the rolls on the same side.

[0017] S5. Coiling: After laminar cooling, the steel is coiled into a coil at a coiling temperature of 550-700°C.

[0018] S6. Leveling: Convex rollers are used for leveling, with a roller crown of -0.4 to +0.4mm, a rolling force of 2000KN to 10000KN, and a tension of 50 to 300KN. Using convex rollers can reduce the stress on the edges during leveling, significantly improving the double-sided waves on the strip edges, while also reducing thickness drop and making the transverse thickness of the strip more uniform.

[0019] Technical effects of the present invention:

[0020] The present invention starts with the arrangement of rolling plans, and puts forward clear requirements for the use cycle of the rolls, the requirements for hot roll materials, and the roll thermal crown formation system. It can ensure that the actual crown during hot rolling production is within a controllable range, and at the same time can improve the uneven wear and service life of the rolls and reduce roll consumption.

[0021] The present invention adopts a heating method of slow temperature increase in stages, which can ensure that the temperature fluctuation at the head and tail of the slab is small, the austenitization of the structure is uniform and complete, the rolling force fluctuation of rough rolling and finish rolling is small, and the crown control is more stable.

[0022] By reducing inter-stand water flow in the front stand of the finishing mill, optimizing rolling load distribution and rolling speed, and increasing cooling water flow to the front stand work rolls, this ensures minimal roll deformation and facilitates the formation of a good thermal crown. Combined with the CVC work roll shifting and bending functions to control crown, this enables stable, mass-produced production of high-carbon tool steel with low crown.

[0023] The present invention innovatively proposes the use of convex rollers for the production of flat high-carbon tool steel, which can better control edge waves while improving the transverse thickness difference of the strip.

[0024] Compared with other technologies, the present invention does not require equipment improvement, has good operability, can significantly improve the convexity qualification rate of high-carbon tool steel, reduce the average convexity of high-carbon tool steel hot rolling by more than 10μm, and reduce the unqualified rate from the original 15.9% to less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the cross section of the strip steel;

[0026] Figure 2 is the influence curve of rolling force change on crown;

[0027] Figure 3 is the influence curve of slab temperature change on rolling force and crown;

[0028] Figure 4 The SK4 convexity curve obtained before applying the method of the present invention;

[0029] Figure 5 The SK4 convexity curve is obtained by applying the method of the present invention. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to specific embodiments.

[0031] Example 1: Small Crown Control of 75CR1 Hot-Rolled Strip Steel

[0032] 75CR1 is an alloy tool steel with good hardenability, widely used in various sawing tools such as circular saw blades, band saw blades, and knives. Its chemical composition is: C: 0.76%, Si: 0.24%, Mn: 0.82%, Cr: 0.49%, P: 0.012%, S: 0.010%, with the remainder being iron and unavoidable impurities. When planning to produce 75CR1 in a size of 2.5 x 1200 mm, the production steps are as follows:

[0033] 1) Rolling plan: Hot rolling is performed when the roughing work rolls have a steel throughput of approximately 60,000 tons. During the finishing roll change, the F7 rolls must pass no more than 80 kilometers of steel. The initial transition material is Q355B with a cross-section of 4.5*1500mm. After rolling 10 pieces of Q355B, 75CR1 with a thickness of 3.0*1200mm is produced. The thickness is then transitioned to 2.5mm depending on the rolling conditions. To ensure uniform roll temperature and normal roll thermal crown during production scheduling, transition material must be rolled first. Rolling high-carbon steel directly in the first few rolls can cause unstable crown control, sometimes resulting in very large crowns. The number of transition material rolls must be ≥10 or the F7 rolls must pass more than 8 kilometers.

[0034] 2) Slab Heating: Continuous casting slabs are 230mm thick and are hot-charged into the furnace at an entry temperature of 580°C. A stepwise, slow-heating system is employed, with the slabs undergoing preheating, heating, second heating, soaking, and finally exiting the furnace. The preheating temperature is 660°C, the first heating stage is 850°C, the second heating stage is 950°C, the soaking stage is 1150°C, and the soaking time is 50 minutes. The exit temperature is 1190°C, for a total furnace time of 230 minutes.

[0035] 3) Roughing: After exiting the furnace, the steel passes through a four-high roughing mill with rough descaling and width reduction using large vertical rolls. Roughing is performed in seven passes, with descaling performed in the first, third, and fifth passes. The flat roll reduction ratios for the seven passes are: 18%, 20%, 22%, 22%, 23%, 26%, and 31%. The intermediate bar thickness for roughing is 34mm, and the finishing temperature for roughing is 1100°C.

[0036] 4) Finishing rolling: The four-roll seven-stand finishing mill is used for rolling. The finishing rolling F2, F3, and F4 stands use high-speed steel rolls. The finishing roll shape is CVC rolls. The working roll shifting positions of F1 to F7 are: -45mm, -34mm, -6mm, -2mm, 76mm, 55mm, and 34mm respectively. The bending roll forces of F1 to F7 are set to 897.6KN, 803.6KN, 1068.2KN, 919.9KN, 1227.5KN, 1079.8KN, 722.7KN; the finishing thickness is controlled in absolute value AGC mode, the rolling crown is set at 20μm, and a multi-function instrument is used to monitor parameters such as average thickness and C40 crown; the inter-stand water (ISC) of F1 and F2 is turned off, and the rear stand is normally open; the final rolling temperature is 920℃; the finishing rolling reduction ratio is: F1: 46%, F2: 44%, F3: 35%, F4: 31%, F5: 26%, F6: 16%, F7: 10%; the roller cooling water flow rate is: the working water flow rate of the front stand is 993m 3 / h, cooling water for rear stand working rolls 630m 3 / h; adopt the rolling speed increase to reduce the tail rolling force and crown; set the guide width on the finishing rolling entrance side to 1250mm to prevent the strip from running off, improve the rolling stability and centering, and avoid wearing the rolls on the same side for a long time.

[0037] 5) Coiling: After laminar cooling, the steel is coiled into a coil at a coiling temperature of 650°C.

[0038] 6) Leveling: Using convex rollers for leveling, the leveling rolling force is 6810KN and the tension is 180KN.

[0039] The plate convexity of the produced 75CR1 strip steel is within 45μm, and the convexity difference between the head, middle and tail of the strip steel is within 18μm, which meets the subsequent user requirements.

[0040] In addition, after statistics on the production line, the failure rate was reduced from the original 15.9% to 4.25%.

[0041] Example 2 SK4 hot-rolled strip small crown control process

[0042] SK4 is a carbon tool steel with high toughness and hardness. It is widely used in hardware, cutting tools, and other tools, such as turning tools, planers, drill bits, paper cutters, and measuring tools. Its chemical composition is: C: 0.98%, Si: 0.25%, Mn: 0.36%, Cr: 0.19%, P: 0.015%, S: 0.009%, and the remainder is iron and unavoidable impurities. When planning to produce SK4 with a size of 2.0*1250mm, the production steps are as follows:

[0043] 1) Rolling schedule: Hot rolling is performed when the roughing work rolls have a steel throughput of approximately 60,000 tons. During the finishing roll change, the F7 rolls must be operated for a maximum of 80 kilometers of steel. Initially, a 4.5x1500mm cross-section Q235B transition material is rolled for hot rolling. After rolling 6-10 rolls, 3.0x1250mm SK4 is produced. After producing two rolls of 3.0mm thick and two rolls of 2.5mm thick transition material, a thin 2.0mm SK4 is produced. To ensure uniform roll temperature and proper roll thermal crown, the amount of transition material must be controlled during production scheduling. Directly rolling high-carbon steel in the first few rolls can lead to unstable crown control, sometimes resulting in excessive crown. Therefore, hot rolling of transition material is necessary. The number of transition material rolls must be ≥10, or the F7 rolls must be operated for hot rolling. The number of transition material rolls must be ≥10, or the F7 rolls must be operated for a maximum of 8 kilometers.

[0044] 2) Slab Heating: Continuous casting slabs are 230mm thick and are hot-charged into the furnace at 650°C. A staged, slow-heating heating system is employed, with the slabs undergoing preheating, heating stage 1, heating stage 2, solutionizing, and finally exiting the furnace. The preheating stage is 660°C, heating stage 1 is 800°C, heating stage 2 is 900°C, soaking stage is 1100°C, soaking time is 60 minutes, and exit temperature is 1200°C. The total furnace time is 250 minutes.

[0045] 3) Roughing: After exiting the furnace, the steel passes through a four-high roughing mill with rough descaling and width reduction using large vertical rolls. Roughing is performed in seven passes, with descaling performed in the first, third, and fifth passes. The flat roll reduction ratios for these seven passes are 16%, 20%, 23%, 25%, 26%, 28%, and 31%. The intermediate bar thickness for roughing is 32mm, and the finishing temperature is 1080°C. Hot coil boxes are used to reduce the intermediate bar thickness and lower the rolling forces in finishing.

[0046] 4) Finishing rolling: The four-roll seven-stand finishing mill is used for rolling. The finishing rolling F2, F3, and F4 stands use high-speed steel rolls. The finishing roll shape is CVC rolls. The working roll shifting positions of F1 to F7 are: 107mm, 130mm, 147mm, 73mm, 55mm, 53mm, and 15mm respectively. The bending roll forces are 898.9KN, 921.5KN, 810.4KN, 812.2KN, 882.9KN, 800.6KN, and 789.6 KN; the finishing thickness control adopts the absolute value AGC mode, the rolling crown target is set at 20μm, and the multi-function instrument is used to monitor parameters such as average thickness and C40 crown; the inter-stand water (ISC) of F1 and F2 is turned off, and the rear stand is normally open; the final rolling temperature is 920℃; the finishing rolling reduction ratio is: F1: 49%, F2: 45%, F3: 36%, F4: 34%, F5: 28%, F6: 16%, F7: 11%; the roller cooling water flow rate is: the working water flow rate of the front stand is 980m 3 / h, cooling water for rear stand working roll 660m 3 / h; adopting the rolling speed increase to reduce the rolling force and crown at the tail end; setting the guide width on the finishing rolling entrance side to 1300mm to prevent the strip from running off, improve rolling stability and centering, and avoid wearing the rolls on the same side for a long time;

[0047] 5) Coiling: After laminar cooling, the steel is coiled into a coil at a coiling temperature of 620°C.

[0048] 6) Leveling: Using convex rollers for leveling, the leveling rolling force is 4650KN and the tension is 120KN.

[0049] The average convexity of the SK4 strip produced was reduced from the original 47.7μm to 20μm, and the convexity difference between the head, middle and tail of the strip was within 15μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0050] In addition, after statistics on the production line, the failure rate was reduced to 4.20%.

[0051] Example 3

[0052] The difference between this embodiment and embodiment 1 is that, in the slab heating step, the preheating section temperature is 400°C, the heating section temperature is 700°C, the heating section temperature is 900°C, the soaking section temperature is 1000°C, the soaking time is 70 minutes, the furnace discharge temperature is 1000°C, and the total furnace time is 300 minutes.

[0053] The plate convexity of the produced 75CR1 strip steel is reduced to 45.3μm, and the convexity difference between the head, middle and tail of the strip steel is within 16μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0054] Example 4

[0055] The difference between this embodiment and embodiment 1 is that, in the slab heating step, the preheating section temperature is 700°C, the heating section temperature is 900°C, the heating section temperature is 1100°C, the soaking section temperature is 1200°C, the soaking time is 50 minutes, the furnace discharge temperature is 1200°C, and the total furnace time is 200 minutes.

[0056] The plate convexity of the produced 75CR1 strip steel is reduced to 20.8μm, and the convexity difference between the head, middle and tail of the strip steel is within 11μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0057] Example 5

[0058] The difference between this embodiment and embodiment 1 is that in the rough rolling step, the reduction ratio distribution ratios of the flat rolls in the 7 passes are: 15%, 15%, 18%, 20%, 30%, 35%, and 38%.

[0059] The plate convexity of the produced 75CR1 strip steel is reduced to 42.7μm, and the convexity difference between the head, middle and tail of the strip steel is within 17μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0060] Example 6

[0061] The difference between this embodiment and embodiment 1 is that, in the rough rolling step, the reduction ratio distribution ratio of the flat rolls in the 7 passes is: 25%, 25%, 28%, 30%, 33%, 25%, and 28%.

[0062] The plate convexity of the produced 75CR1 strip steel is reduced to 40.2μm, and the convexity difference between the head, middle and tail of the strip steel is within 18μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0063] Example 7

[0064] The difference between this embodiment and embodiment 1 is that, in the finishing rolling step, the finishing rolling reduction rates are: F1: 40%, F2: 40%, F3: 45%, F4: 25%, F5: 30%, F6: 25%, and F7: 8%.

[0065] The plate convexity of the produced 75CR1 strip steel is reduced to 49.1μm, and the convexity difference between the head, middle and tail of the strip steel is within 15μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0066] Example 8

[0067] The difference between this embodiment and embodiment 1 is that, in the finishing rolling step, the finishing rolling reduction rates are: F1: 55%, F2: 55%, F3: 30%, F4: 40%, F5: 20%, F6: 15%, and F7: 20%.

[0068] The plate convexity of the produced 75CR1 strip steel is reduced to 47.2μm, and the convexity difference between the head, middle and tail of the strip steel is within 16μm, meeting the small convexity requirements of subsequent cold rolling processing.

[0069] Analysis of factors affecting the production of small crown strip steel:

[0070] like Figure 2 As shown in the figure, the relationship between the rolling force change trend and the crown change trend during the production of the same coil of steel is investigated. Figure 2 It can be seen from the curve shown that the changing trend of the crown is basically consistent with the changing trend of the rolling force. Therefore, to produce strip with small crown, it is necessary to minimize the rolling force to obtain strip with smaller crown.

[0071] like Figure 3 As shown in the figure, the relationship between the trend of crown change and the trend of rolling temperature change during the production of the same coil of steel is investigated. Figure 3It can be seen from the curve shown that the trend of change in convexity is opposite to the trend of change in temperature. Therefore, in order to produce strip with small convexity, it is useful to appropriately increase the temperature.

[0072] like Figure 4 and Figure 5 As shown, the convexity curves of the strip before and after adopting the production method of the present invention are respectively shown. The results show that before adopting the production method of the present invention, the overall convexity of the strip is relatively large, above 40μm. Taking Example 2 as an example, after adopting this method, the overall convexity of the strip is reduced to about 20μm.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that the preheating section temperature is 450°C, the heating section temperature is 600°C, the heating section temperature is 800°C, the soaking section temperature is 1100°C, the soaking time is 60 minutes, the furnace discharge temperature is 1200°C, and the total furnace time is 250 minutes.

[0075] The convexity of the 75CR1 strip steel finally prepared exceeded 60 μm, which could not meet the subsequent cold rolling requirements.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that the rough rolling adopts a 5-pass reduction process, and the 5-pass reduction rates are 23%, 27%, 26%, 28%, and 30% respectively. The 5-pass rough rolling results in a thicker intermediate billet and a larger finishing rolling force.

[0078] The convexity of the 75CR1 steel strip finally prepared is greater than 60 μm, which is difficult to meet the convexity requirements of subsequent cold rolling.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 1 is that the finishing rolling reduction rates F1-F7 are F1: 38%, F2: 35%, F3: 25%, F4: 42%, F5: 32%, F6: 14%, and F7: 13%, respectively.

[0081] The final 75CR1 steel strip has a plate convexity greater than 60 μm, which is difficult to meet the convexity requirements of subsequent cold rolling.

[0082] Comparative Example 4

[0083] The difference between this comparative example and Example 1 is that, when producing high-carbon tool steel, the rolling plan is scheduled to the end of the rolling mill, and the finishing rolling F7 working roll has a steel passing amount exceeding 80KM and is still in production. The final 75CR1 strip steel has a plate convexity greater than 60μm, which is difficult to meet the convexity requirements of subsequent cold rolling.

[0084] It can be seen from the above comparative examples that in the production method of the present invention, by controlling the parameters of factors such as rolling plan arrangement, slab heating, rough rolling pass, rough rolling and reduction rate, and finishing rolling reduction rate, the hot rolling convexity can be perfectly controlled to be below 50μm.

[0085] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A production method for controlling small crown of hot-rolled high-carbon tool steel, characterized in that: The steps include: S1. Slab heating: The continuous casting slab has a thickness of 220-240mm and is hot-charged into the heating furnace with an entry temperature of ≥300°C. After entering the furnace, a staged slow heating system is adopted, which sequentially passes through the preheating section, the first heating section, the second heating section, the soaking section, and then out of the furnace; S2, rough rolling: after leaving the furnace, it passes through the four-roll rough rolling mill with rough descaling and width reduction of large vertical rolls, and the rough rolling is carried out in 7 passes; the thickness of the rough rolling intermediate billet is set to 30-56mm, and the rough rolling finishing temperature is 1000-1150℃; S3, finishing rolling: Rolling is carried out using a four-high, seven-stand finishing mill. The finishing rolling stands F2, F3, and F4 use high-speed steel rolls. The finishing roll profile is CVC rolls. The finishing work roll shifting range is -150 to 150 mm, and the bending roll force is preset to 0 to 2000 kN. The finishing thickness is controlled using the absolute value AGC mode, and the rolling crown is set at 20 to 40 μm. A multi-function instrument is used to monitor the thickness and C40 crown parameters. The water between the stands F1 and F2 is turned off, and the rear stand is kept open normally. The final rolling temperature is 800 to 950°C. S4, coiling: after laminar cooling, coiling into coils, the coiling temperature is 550 ~ 700 ℃; S5. Leveling: Use convex rollers for leveling to reduce the stress on the edges during leveling, improve the double-sided waves on the strip edges, and reduce the thickness drop at the edges, making the transverse thickness of the strip more uniform.

2. The production method according to claim 1, characterized in that High carbon tool steel includes the following elements in percentage by weight: carbon: 0.65-1.35%, silicon: 0-0.35%, manganese: 0-1.0%, chromium: 0-1.0%, phosphorus ≤0.030%, sulfur ≤0.030%, and the rest are iron and unavoidable impurities.

3. The production method according to claim 1, characterized in that During the slab heating operation, the temperature of the preheating section is 400-700℃, the temperature of the first heating section is 700-900℃, the temperature of the second heating section is 900-1100℃, the temperature of the soaking section is 1000-1200℃, the soaking time is ≥50Min, the furnace discharge temperature is 1100-1200℃, and the total furnace time is 200-300Min.

4. The production method according to claim 1, characterized in that During the rough rolling operation, rough rolling and descaling are carried out in the 1st / 3rd / 5th passes, and the flat roll reduction rate distribution ratio of the 7 passes is: 15%~25%, 15%~25%, 18%~28%, 20%~30%, 23%~33%, 25%~35%, and 28%~38%.

5. The production method according to claim 1, characterized in that During rough rolling operations, when rolling thinner slabs, the slabs are coiled in a hot coil box after rough rolling to reduce the thickness of the intermediate slab and the finishing rolling force.

6. The production method according to claim 1, characterized in that In the finishing rolling operation, the finishing rolling reduction ratio is: F1: 40% to 55%, F2: 40% to 55%, F3: 30% to 45%, F4: 25% to 40%, F5: 20% to 30%, F6: 15% to 25%, F7: 8% to 20%; Roller cooling water flow: front rack working water flow 900~1200m 3 / h, the cooling water of the rear stand working roll is reduced to 500~1000m 3 / h.

7. The production method according to claim 1, characterized in that During the finishing rolling operation, the guide width at the finishing rolling entrance is controlled at +30 to 50 mm of the rolling width.

8. The production method according to claim 1, characterized in that During the leveling operation, the roller crown is -0.4~+0.4mm, the leveling rolling force is 2000KN~10000KN, and the tension is 50~300KN.

9. The production method according to claim 1, characterized in that Before production, the rolling plan is also arranged, including: The rolling production of high carbon tool steel is scheduled to the early and middle stages of the rolling cycle, the steel passing capacity of the rough rolling work roll is within 100,000 tons, and the steel passing kilometers of the finishing rolling F7 roll is within 80KM.

10. A high carbon tool steel product produced by the production method according to claim 1.

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