A hot rolling process based on wedge-shaped thin slabs

Abstract

This invention discloses a hot rolling process based on wedge-shaped thin slabs, belonging to the field of steel manufacturing. The process includes heating → roughing rolling → finishing rolling → coiling; flat plates are produced using wedge-shaped thin slabs with a thickness of 45-90mm; the roughing rolling adopts a three-pass rolling mode. The zeroing logic of the flat roll load relay in the roughing rolling zone in the first-level control program is as follows: when the flat roll load gradually decreases to below 200 tons, before the flat roll load relay signal returns to zero, it is determined whether the vertical roll load relay has a signal and whether the vertical roll load relay signal returns to zero within 3 seconds. If either of the two conditions is met, the flat roll load relay signal is forced not to disappear. Compared with the prior art, this process has the characteristics of cost reduction and efficiency improvement.

Description

TECHNICAL FIELD

[0001] The present application is a divisional application of the invention patent "Production process of flat plate using wedge-shaped thin slab rolling on ordinary hot rolling production line" (2021114657875), and relates to a steel production method, in particular to a production process suitable for using wedge-shaped thin slab rolling on ordinary hot rolling strip production line, which is used to produce flat plate using 45-90mm thick wedge-shaped thin slab on conventional hot rolling production line, and can produce flat plate with the thinnest thickness of 3.0mm. BACKGROUND

[0002] When the domestic continuous casting and rolling production line is started or the site is abnormal, the rough rolling is accompanied by the production of thin slab, and the obtained thin slab is pushed out and offline into the warehouse by the scrap pushing mechanism after shearing. A part of the thin slab in this part exists a part of the wedge-shaped blank rolled by the rough rolling mill, the thickness of the slab is uneven along the length, the market sales are limited and the profit is relatively low, and the inventory pressure is large. If it is directly cut and returned to the furnace, not only economic losses are caused, but also the workload of the site operators is increased. Therefore, a production process of flat plate using wedge-shaped thin slab rolling on ordinary hot rolling strip production line is developed, which not only can create economic benefits for enterprises, but also can reduce inventory pressure and reduce site workload.

[0003] The conventional slab used in the ordinary hot rolling line has a thickness fluctuation of ±5mm along the length, while the wedge-shaped thin slab involved in the present application has uneven thickness along the length, and the thickness gradually thins to become wedge-shaped, with a thickness fluctuation of up to 45mm. The main difficulties in rolling control are: ① In the currently published thin slab rolling technology, the thinnest slab thickness used is 75mm, while the slab thickness involved in the present application is thinner, with a thinnest thickness of 45mm. During the heating process using the walking beam type heat storage heating furnace, it is more likely to cause slab bending and unable to be tapped; ② During the first pass rolling process of rough rolling, the rolling force of the intermediate blank tail gradually decreases to 0, which will cause tracking abnormal stop. ③ Due to the uneven thickness of the slab, abnormal buckling of the head is prone to occur during the rough rolling process, resulting in scrap steel. Therefore, the utilization of thin slab in the industry is only for thin slab with a thickness of 75-90mm, such as the process of "Process of rolling thin slab pattern plate on ordinary hot rolling strip production line" (CN202110335865.3) discloses a method of producing flat plate using 75-90mm thick thin slab on ordinary hot rolling line, but the patent cannot produce using wedge-shaped blank below 75mm specification, and cannot use wedge-shaped thin slab with uneven thickness along the length. SUMMARY

[0004] The technical task of the present application is to overcome the shortcomings of the prior art, and to provide a production process of flat plate using wedge-shaped thin slab rolling on ordinary hot rolling strip production line. The present application provides a production process of flat plate using wedge-shaped thin slab rolling on ordinary hot rolling strip production line, which realizes the production of wedge-shaped thin slab using ordinary hot rolling strip production line.

[0005] The technical scheme for solving the technical problems of the present application is: a hot rolling process based on wedge-shaped thin slab, using 45-90mm thick wedge-shaped thin slab to produce flat plates on a conventional hot rolling production line, the process including heating, rough rolling, finishing rolling and coiling; characterized in that: the rough rolling process adopts a three-pass mode, the rough rolling pass reduction is given as 30±2mm for the first pass, 20±2mm for the second pass and 8±2mm for the third pass, the rough rolling pass speed is given as 1.8-2.3m / s for the first pass, 2.0-3.0m / s for the second pass and 2.2-4m / s for the third pass, and the intermediate slab thickness is 32mm; the zero judgment logic of the flat roll load relay in the rough rolling first-stage control program is: when the flat roll load gradually decreases to below 200 tons, before the flat roll load relay signal is zeroed, it is judged whether the vertical roll load relay has a signal and whether the vertical roll load relay signal is zeroed≤3s, and if one of the two conditions is met, the flat roll load relay signal is forced to not disappear.

[0006] Further, the slab used in the heating process is a wedge-shaped thin slab, the thick end of which faces the rolling line direction, the slab is centrally loaded into the furnace, and the length of the slab loaded into the furnace is determined according to the heating step beam spacing; the furnace temperature of the first loading section is controlled at 700-800℃, the furnace temperature of the second loading section is controlled at 850-1000℃, the furnace temperature of the third loading section is controlled at 1050-1160℃, the soaking furnace section is controlled at 1180-1220℃, and the in-furnace time is controlled at 70-110min.

[0007] Further, in the rough rolling process, the descaling temperature after the furnace is controlled at 1000-1050℃, and the rough rolling area temperature drop is controlled≤30℃.

[0008] Further, the descaling mode in the rough rolling process is one group after the furnace, and no descaling is used before and after the rough rolling mill, and one group of descaling is used for finishing rolling.

[0009] Compared with the prior art, the present application has the following outstanding beneficial effects:

[0010] 1. The present application provides a production process for using wedge-shaped thin slab to roll flat plates on a conventional hot rolling strip production line, which realizes the production of flat plates using 45-90mm thick wedge-shaped thin slab on a conventional hot rolling production line, not only creating economic benefits for enterprises, but also reducing inventory pressure and reducing on-site workload;

[0011] 2. Compared with direct delivery slab, the use of wedge-shaped slab to roll hot-rolled steel coils can increase the profit per ton of steel by 300 yuan / ton, with an annual benefit increase of tens of millions of yuan. DETAILED DESCRIPTION

[0012] The present application will be further described below in conjunction with specific embodiments.

[0013] The application discloses a production process for rolling flat plates by using wedge-shaped thin slabs in a common hot-rolled strip steel production line.

[0014] S1, slab heating:

[0015] The thickness of the selected wedge-shaped thin slab is controlled to be 90±5 mm at one end and greater than or equal to 45 mm at the other end, and the thickness fluctuation along the length is controlled to be less than or equal to 45 mm. The width reduction of the slab is controlled to be 10-30 mm. Compared with a normal slab with a thickness of 210 / 230 mm, the wedge-shaped thin slab has a smaller reduction in the rough rolling area, and the width extension is insufficient, so that equal-width or width-expanding rolling is prone to cause the finished product to have a narrow width. When the width reduction is too large, the slab is too thin, and the intermediate slab tail has no actual reduction in the first pass in the rough rolling, so that the intermediate slab is prone to have edge turning, arching or skin buckling defects.

[0016] The 90 mm end of the slab faces the rolling line direction, so as to ensure the stability of the first pass in the rough rolling. The slab is centrally loaded into the furnace, the length of the slab loaded into the furnace is determined according to the interval of the heating walking beams, and the cantilever length of the two ends of the slab is controlled to be less than or equal to 600 mm. If the cantilever length is too large, the slab is prone to be bent and deformed during the heating process, and the head and tail are prone to be buckled.

[0017] The furnace temperature of the first furnace section is controlled to be 700-800 DEG C, the furnace temperature of the second furnace section is controlled to be 850-1000 DEG C, the furnace temperature of the third furnace section is controlled to be 1050-1160 DEG C, the furnace temperature of the soaking furnace section is controlled to be 1180-1220 DEG C, and the time in the furnace is controlled to be 70-110 min. Low-temperature steel burning is adopted in the first furnace section, the second furnace section and the third furnace section, the temperature of the soaking furnace section is appropriately increased, and the time in the furnace is shortened. If the time in the furnace is too long, the bending deformation of the slab gradually increases during the running process in the furnace, and the steel is affected.

[0018] S2, rough rolling

[0019] The rough rolling is performed in a three-pass mode, the thickness of the intermediate slab is 32 mm, the descaling temperature after the furnace is controlled to be 1000-1050 DEG C, and the temperature drop in the rough rolling area is controlled to be less than or equal to 30 DEG C.

[0020] The reduction of each pass in rough rolling: the first pass is given 30±2mm, the second pass is 20±2mm, and the third pass is 8±2mm. Since the thin slab is a wedge-shaped blank with a thickness of 45-90mm, if the first pass of rough rolling directly reduces the intermediate blank thickness to below 45mm, there is a risk of slipping or abnormal buckling of the head. If the first pass reduction is ≤45mm, there will be no rolling force when the tail of the slab is rolled, resulting in abnormal tracking. By reducing the thickness of the intermediate blank and increasing the total reduction of rough rolling and the first pass reduction, the distance without rolling force during the first pass rolling process can be reduced, and abnormal buckling during rolling can be prevented.

[0021] The speed of each pass in rough rolling is given: the rolling speed of the first pass is 1.8-2.3m / s, the rolling speed of the second pass is 2.0-3.0m / s, and the rolling speed of the third pass is 2.2-4m / s. The minimum value of the speed interval is taken as the bite speed of each pass. Since the wedge-shaped blank is prone to buckling during rolling, compared with the existing thin slab rolling process, the bite speed and rolling speed of the wedge-shaped blank during rolling are reduced, ensuring the stability of rolling.

[0022] The first-level control program of rough rolling is modified, and the zero (disappearance) judgment logic of the flat roller load relay is added as a judgment condition: ① the vertical roller load relay has a signal; ② the zero of the vertical roller load relay signal is ≤3s; if one of the two conditions is met, the flat roller load relay signal will be forced to be long. The time setting (3s) after the vertical roller ejection in the second judgment condition needs to be calculated and optimized based on the actual distance between the vertical roller and the flat roller and the first pass rolling speed. The actual rolling situation is combined to make the following explanations about this technical scheme:

[0023] In the conventional mode, the zero (disappearance) judgment logic of the flat roller load relay in the rough rolling area only has one condition, which is that the flat roller rolling force is ≤200 tons. That is, when the flat roller rolling force is ≤200 tons, the flat roller load relay will be zero (the signal will disappear). After the flat roller load relay signal is zero, the system defaults no strip, and the model will automatically issue the second pass data (roll gap depression, front and rear mill roll reversal). The thickness fluctuation of the normal slab (thickness 210 / 230mm) is generally between ±5mm, and since the reduction of each pass in rough rolling is much greater than 10mm, under normal circumstances, the flat roller rolling force will be ≤200 tons and the flat roller load relay will be zero only after the flat roller ejection, so there will be no scrap.

[0024] However, during the first pass rolling process of the wedge-shaped blank, the flat roller rolling force will gradually decrease to 0 as the reduction decreases. If the conventional control logic is used in the rough rolling area, when the flat roller load is ≤200 tons, the relay signal will be zero (i.e. the signal disappears, the system defaults no strip), and at this time the flat roller has not been ejected, resulting in abnormal tracking, such as roll gap depression, front and rear mill roll reversal, and thus causing scrap.

[0025] The modified judgment logic is equivalent to adding two judgment conditions after the original judgment logic: ① the vertical roll load relay has a signal; and ② the vertical roll load relay signal is zeroed for less than or equal to 3 seconds; if one of the two conditions is met, the horizontal roll load relay signal is forced to be long. After modifying the program logic, during the first rolling process of the wedge blank, when the horizontal roll load gradually decreases to less than or equal to 200 tons, before the horizontal roll load relay signal is zeroed, it is determined whether the vertical roll load relay has a signal and whether the vertical roll load relay signal is zeroed for less than or equal to 3 seconds; if one of the two conditions is met, the horizontal roll load relay signal is forced not to disappear. By setting the first judgment condition “the vertical roll load relay has a signal”, when the vertical roll has a load, the horizontal roll load relay signal will not be lost due to no rolling force of the horizontal roll in the middle and tail parts. After setting the second judgment condition “the vertical roll load relay signal is zeroed for less than or equal to 3 seconds”, the horizontal roll load relay signal will not be zeroed within 3 seconds after the vertical roll is thrown (within 3 seconds after the load relay is zeroed). The time setting (3 seconds) in the second judgment condition after the vertical roll is thrown needs to be calculated and optimized according to the actual distance between the vertical roll and the horizontal roll and the first pass rolling speed.

[0026] The descaling mode in the rough rolling process is one group after the furnace, and no descaling is used before and after the rough rolling mill, and one group of descaling is used in the finishing rolling. Due to the low heating temperature, reducing the descaling pass can reduce the temperature drop during rolling and improve the rolling stability.

[0027] The present application does not make specific restrictions on specific steel grades and components, and the final rolling and coiling temperature and layer cooling mode parameters in the finishing rolling and coiling area can be selected by the person skilled in the art according to the specific steel grade for rolling, and will not be repeated again.

[0028] In order to better compare the present application and the prior art, a comparative test was conducted, and the finished steel grade was designed as Q215B. In order to maintain consistency, the chemical composition was uniformly adopted in the scheme in the “Production process of a thin slab rolling limit thin gauge pattern plate” (application number 2021112784715) of the company, C: 0.03-0.09%, Si: 0.02%-0.08%, Mn: 0.08-0.15%, P≤0.03%, S≤0.010%, and the balance was Fe and impurities. 45-90mm wedge-shaped thin slabs (one end thickness controlled at 90mm, and the other end thickness controlled at 45mm) were used.

[0029] Preparation process scheme: examples 1-3 adopt the process technical features in the present application; comparative example 1 adopts the process technical scheme in the “Production process of a thin slab rolling limit thin gauge pattern plate” (application number 2021112784715) of the company; comparative example 2 adopts the process technical features in the present application in the heating part, and adopts the scheme in comparative example 1 in the rough rolling process; the final rolling and coiling temperature in each group of finishing rolling and coiling process is given according to the characteristics of Q215B steel grade.

[0030] Each group of 45-90 mm thick continuous casting wedge thin slab steel composition similar billet after heating to hot continuous rolling mill for rolling, by 3 pass roughing and finishing rolling mill control rolling, after laminar cooling for coiling, output flat plate.

[0031] Process flow route of examples 1-3 and comparative examples 1-2 is: slab heating→ rough rolling→ finishing rolling→ laminar cooling→ coiling.

[0032] Main process control parameters of slab heating are shown in the following table.

[0033]

[0034] The running state of the slab in the heating furnace in examples 1-3 and comparative example 2 is good as a whole, and there is slight S-bending, which does not affect the slab discharge and running on the roller way.

[0035] In comparative example 1, the slab bending is serious due to too high heating temperature and too long furnace time, which leads to no steel discharge and abnormal furnace shutdown.

[0036] Main process control parameters of rough rolling process are shown in the following table, and the intermediate billet thickness is 32 mm. The intermediate roller way heat preservation cover is used after rough rolling to alleviate the intermediate billet temperature drop. The rough rolling first stage control program after improvement is used in examples, and the traditional rough rolling first stage control program is used in comparative example 2.

[0037]

[0038] The rolling process of examples 1-3 is stable as a whole, and there is no scrap steel caused by tracking abnormality in the first pass rolling process, and the head control of each pass is normal.

[0039] In comparative example 2, the rough rolling flat roll load relay signal is lost when about 1 / 3 of the first pass rolling is completed, the tracking is abnormal, the rolling mill speed is reduced to zero, the billet is pushed back to the furnace due to abnormal stop rolling, and the first pass head is seriously bent, which has the risk of scrap steel with flower frame.

[0040] Main process control parameters of finishing rolling and coiling area are shown in the following table.

[0041] Item Finish rolling finishing temperature (°C) Coiling temperature (°C) Example 1 813 486 Example 2 834 503 Example 3 842 512

[0042] The product conditions of each example are shown in the following table.

[0043] Group Thickness / mm Yield strength / Mpa Tensile strength / Mpa Elongation / % Surface quality Example 1 2.97～3.03 317 390 40.0 Good Example 2 3.96～4.05 321 382 42.5 Good Example 3 5.94～6.05 363 426 41.5 Good

[0044] From the data of the above table, it can be seen that the flat plates produced in Examples 1-3 have good size and other advantages, and by proper design of the final rolling temperature, the strength and elongation and other performance indicators meet the requirements of the users, and the rolling surface quality and the flatness are stable, there is no scrap steel due to poor rolling stability, and batch stable production can be achieved. In Comparative Example 1, abnormal shutdown is caused by too high heating temperature, and in Comparative Example 2, abnormal tracking in rough rolling and serious buckling of the head occur, and thus batch stable production cannot be achieved.

[0045] It can be seen from the above that by using the technical scheme of the present application, the purpose of stable rolling of flat plates using 45-90 mm thin slab can be achieved on the basis of using the existing production line, and unplanned shutdown caused by burning and collapsing of the end of the thin slab is reduced. The quality of the flat plates produced is not different from that of the flat plates produced by the conventional slab production method.

[0046] It should be noted that the specific embodiments of the present application have been described in detail, and various obvious modifications made by those skilled in the art without departing from the spirit and scope of the present application are within the protection scope of the present application.

Claims

1. A hot rolling process based on wedge thin slab, using wedge thin slab with thickness of 45-90 mm to produce flat plate, the process comprises heating → rough rolling → finish rolling → coiling; characterized in that: The rough rolling process adopts three-pass mode rolling, the rough rolling pass reduction is: the first pass is given 30±2mm, the second pass is 20±2mm, the third pass is 8±2mm, the rough rolling speed is given: the first pass rolling speed is 1.8-2.3m / s, the second pass rolling speed is 2.0-3.0m / s, the third pass rolling speed is 2.2-4m / s, the intermediate blank thickness is 32mm; the rough rolling first stage control program rough rolling area flat roll load relay zero determination logic is: when the flat roll load gradually decreases to 200 tons or less, before the flat roll load relay signal is zero, it is judged whether the vertical roll load relay has a signal and whether the vertical roll load relay signal is zero ≤3s, if one of the two conditions is met, the flat roll load relay signal will not disappear; the heating process uses wedge-shaped thin slab, the thick end of the specification is towards the rolling direction, the slab is centrally loaded, the slab length is determined according to the heating step beam spacing; the first furnace section temperature is controlled at 700-800℃, the second furnace section temperature is controlled at 850-1000℃, the third furnace section temperature is controlled at 1050-1160℃, the soaking furnace section temperature is controlled at 1180-1220℃, the furnace time is controlled at 70-110min.

2. The wedge thin slab based hot rolling process according to claim 1, characterized in that: In the rough rolling process, the descaling temperature after the furnace is controlled at 1000-1050℃, the rough rolling area temperature drop is controlled ≤30℃.

3. The wedge thin slab based hot rolling process according to claim 2, characterized in that: The descaling mode of the rough rolling process is one group after the furnace, the descaling is not used before and after the rough rolling mill, and one group of descaling is used for the finishing rolling.

Images