Method for rolling high-strength wide thin plate through heavy and medium plate mill

Abstract

The invention relates to a method for rolling a high-strength ultra-thin plate by a heavy and medium plate mill, which solves the problems that the thickness specification is 5.0 + / -0.5 mm, the width is less than or equal to 2800mm, the rolling yield reaches 950MP level, and the rolled plate shape and performance of a quenched and tempered 600Mpa steel plate are unstable through the technological means of blank selection, hot blank temperature difference limitation, finish rolling constraint rolling, straightening, twice quenching and tempering. The unevenness of the obtained thin and wide steel plate is smaller than or equal to 3 mm / m, the thickness tolerance meets the deviation requirement of the national standard GB / T709-2006, the yield strength level can reach 650-720 Mpa, and the impact at-196 DEG C is larger than or equal to 90 J. The method is suitable for batch production of high-strength wide thin plates, high in percent of pass and good in plate shape, can be realized by most medium and thick plate factories at present, and has good process applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a method for rolling medium and thick plates into high-strength ultra-thin plates. Background Art

[0002] For a long time, the shape control of thin plates has always troubled major domestic wide and thick plate companies, especially thin plates below 6mm, which are one of the most difficult to control. Even if some companies can barely produce in batches, they are basically mainly below 460MPa level. There are few reports on the mass production of high-strength wide and thin plates above 600MPa level. This is mainly because after exceeding a certain strength level, it increases the difficulty of rolling and shape control of the rolling mill. Usually, for high-strength wide and thin steel plates, plate shape problems such as steel jamming, sickle bending, and wave shape often occur during rolling. These are basically related to the heating quality of the billet, cooling uniformity and the stability of the rolling mill. For general conventional specifications of steel plates, the difference in plate shape control is not large, but for extreme specifications of steel plates such as high-strength wide and thin plates, the difference in rolling difficulty and plate shape control is still large. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for rolling high-strength wide thin plates on a medium and heavy plate rolling mill, so as to solve the problem of unstable rolled plate shape of steel plates with a thickness specification of 5.0±0.5mm and a width of ≤2800mm. The strength level of the obtained thin and wide steel plates can reach 600Mpa and the impact resistance at -196℃ is ≥90J, thereby realizing the ability of the medium and heavy plate rolling mill to mass-produce high-strength wide thin plates.

[0004] The technical solution of the present invention: A method for rolling high-strength ultra-thin plates using a medium and heavy plate rolling mill comprises the following steps: S1. Billet and heating: The continuous casting billet thickness is 100-120mm, and the billet design yield is 78%-84.5%. Heating is carried out in a walking beam heating furnace. S2. Rolling: Rolling is performed in ten passes at a speed of 2.0m / s to 2.8m / s. The upper and lower water dephosphorization is turned on in the first pass to prevent the steel plate from warping after widening. The pre-flushing water is turned off between passes. The rolling speed is 2.4 to 3.2m / s. The reduction ratio of the first three passes is 18.00 to 24.50%, the reduction ratio of the fourth to ninth passes is 25.44 to 32.16%, and the reduction ratio of the tenth pass is 14.34 to 18.80%. The starting rolling temperature is 1020 to 1110°C, and the finishing rolling temperature is 820 to 880°C. S3, straightening: three passes of hot straightening; S4. Heat treatment: The first quenching temperature is 820-830℃, the heating time is PLC+20min, the second quenching temperature is 670-680℃, the heating time is PLC+30min, the quenching machine water flow rate is 4400m³ / min, the quenching machine roller speed is 57.6m / min, the tempering temperature is 570-580℃, and the furnace time is 110min.

[0005] Preferably, in step S1, the billet heating time is 10 min / cm, the heating temperature is 1250-1270°C, the core temperature of the billet is 1040-1120°C, and the temperature difference between the upper and lower surfaces of the billet is ≤30°C.

[0006] Preferably, in step S2, a single-stand rolling mode is adopted, the roller cooling water is turned off, the roller diameter of the finishing mill is 1000-1060 mm, and the crown is 0.04-0.08 mm.

[0007] Preferably, in step S2, the rolling force of the first four passes is 19000-35000 kN, and the rolling force of the fifth to tenth passes is 37000-42000 kN; the torque of the first five passes is 1900-2900 kNm, and the torque of the sixth to tenth passes is 900-2000 kNm.

[0008] Preferably, in step S3, the straightening force of the first and second passes is 200-300 tons, and the straightening force of the third pass is 150-200 tons.

[0009] Preferably, in step S4, the first quenching temperature is 820°C, the second quenching temperature is 670°C, and the tempering temperature is 570°C.

[0010] Preferably, the process further includes step S5, finishing and warehousing: trimming the edges by double-sided shearing and fixed-length shearing as required, and then conducting performance inspection, number spraying, and warehousing.

[0011] Preferably, in step S5, the width of the finished product is ≤2800 mm, the length of the finished product is 500 mm < ≤26000 mm, and the thickness is 5.0±0.5 mm.

[0012] Preferably, in step S2, a medium plate rolling mill is used for rolling medium thickness steel plates, and the thickness of the produced steel plates is usually above 6 mm.

[0013] Principle of the Invention: The present invention can achieve stable production of high-strength, thin and wide steel plates in medium and thick plate rolling mills by means of uniform billet temperature, rapid rolling of a single stand, closed-water temperature control during the process, reasonable reduction in each pass, and quenching and tempering and other process guarantee measures. The main principle is that the temperature drops quickly during the rolling of wide and thin plates, which easily leads to uneven temperature, thereby increasing the difficulty of rolling and control. Therefore, it is necessary to strictly control each process stage of such extreme specification steel plates. The first is to ensure that the billet temperature is uniform, and the temperature deviation between the surface and the core does not exceed 30°C. After leaving the furnace, it should be quickly transferred to the front of the rolling mill for closed-water rolling to avoid too rapid temperature drop of the billet. However, in order to ensure the surface quality of the steel plate, except for the first pass where the upper and lower water are opened for descaling, the other passes are all closed-water rolling, and rapid warm straightening is performed. The final plate shape quality of the steel plate is further improved by reasonably controlling the magnitude of the straightening force in different passes.

[0014] Beneficial effects of the present invention: The present invention provides a method for rolling high-strength ultra-thin plates on a medium and thick plate mill. By selecting billets, limiting the temperature difference of hot billets, finishing rolling with constraints, straightening, double quenching and tempering processes, the method solves the problem of unstable plate shape and performance of steel plates with a thickness specification of 5.0±0.5mm, a width ≤2800mm, a yield strength of 950MP in the rolled state, and a 600Mpa after quenching and tempering. The resulting thin and wide steel plates have an unevenness of ≤3mm / m, a thickness tolerance that meets the deviation requirements of the national standard GB / T709-2006, a yield strength level of 650-720Mpa, and an impact strength of ≥90J at -196°C. The method of the present invention is suitable for mass production of high-strength wide and thin plates, has a high pass rate, and good plate shape. It can be implemented by most current medium and thick plate mills and has good process applicability. DETAILED DESCRIPTION

[0015] The present invention will be further described below with examples.

[0016] The embodiment of the present invention is carried out in a 3500 mm wide and thick plate mill, using a four-roll reversible medium and thick plate rolling mill. Example 1

[0017] The steel grade is 9Ni; the target thickness of the rolled steel plate is 5mm, the actual average thickness is 5.3mm; the finished steel plate width is 2000mm; the length of the rolled mother plate is 23000mm; the process steps include: S1. The continuous casting billet thickness is 110mm, and the designed billet yield rate is 83%. A walking beam heating furnace is used, with a heating temperature of 1258-1267°C, a core temperature of 1040-1090°C, and an 18°C ​​temperature difference between the upper and lower surfaces of the billet.

[0018] S2. Rolling: Single-stand rolling mode is adopted, roller cooling water is closed, crown is 0.05mm; seven passes are rolled, steel biting speed is 2.0-2.7m / s, upper and lower water descaling is opened in the first pass, pre-flushing water is closed between passes, rolling speed is 2.7-3.0m / s; the first pass reduction rate is 20.38%, the second pass reduction rate is 21.79%, the third pass reduction rate is 22.56%, the fourth to ninth passes reduction rate is 25.44~29.86%, and the tenth pass reduction rate is 16.08%; the starting rolling temperature is 1020℃, and the finishing rolling temperature is 850℃. The rolling force of the first four passes is 32,000 to 35,000 kN, and the rolling force of the fifth to tenth passes is 41,000 to 42,000 kN; the torque of the first five passes is 2,500 to 2,900 kNm, and the torque of the sixth to tenth passes is 1,900 to 2,000 kNm.

[0019] S3, straightening: 3 passes of hot straightening, the straightening force of the first and second passes is 290 / 300 tons, and the straightening force of the third pass is 190 tons.

[0020] S4. Heat treatment: first quenching temperature 825℃, heating time PLC+20min, second quenching temperature 675℃, heating time PLC+30min, quenching machine water flow 4400m³ / min, quenching machine roller speed 57.6m / min, tempering temperature 575℃, furnace time 110min.

[0021] S5. Finishing and warehousing: According to the contract requirements, double-sided shearing and cut-to-length shearing are performed for edge trimming, followed by performance inspection, number spraying, and warehousing.

[0022] Table 1: Version and performance of Example 1

[0023] Example 2 The steel grade is 9Ni; the target thickness of the rolled steel plate is 5mm, the actual average thickness is 5.0mm; the finished steel plate width is 2500mm; the length of the rolled mother plate is 26000mm; the process steps include: S1. The continuous casting billet thickness is 120mm, and the designed billet yield rate is 84.5%. A walking beam heating furnace is used, with a heating temperature of 1250-1260℃, a core temperature of 1090-1120℃, and a temperature difference of 30℃ between the upper and lower surfaces of the billet.

[0024] S2. Rolling: Single-stand rolling mode is adopted, roller cooling water is turned off, finishing mill roller diameter is 1000-1060mm, crown is 0.04-0.08mm; 10 passes are rolled, steel bite speed is 2.5m / s-2.8m / s, upper and lower water dephosphorization is turned on in the first pass to avoid warping of steel plate after widening, pre-flushing water is turned off between passes, rolling speed is 2.4-3.1m / s; first pass reduction rate is 19.16%, second pass reduction rate is 20.02%, third pass reduction rate is 23.40%, fourth to ninth pass reduction rate is 28.91-32.16%, tenth pass reduction rate is 18.80%; starting rolling temperature is 1070℃, finishing rolling temperature is 820℃. The rolling force of the first four passes is 19,000 to 22,000 kN, and the rolling force of the fifth to tenth passes is 37,000 to 39,000 kN; the torque of the first five passes is 1,900 to 2,100 kNm, and the torque of the sixth to tenth passes is 900 to 12,000 kNm.

[0025] S3, straightening: 3 passes of hot straightening, the first and second pass straightening force is 260 / 270 tons, the third pass straightening force is 200 tons.

[0026] S4. Heat treatment: first quenching temperature 830℃, heating time PLC+20min, second quenching temperature 680℃, heating time PLC+30min, quenching machine water flow 4400m³ / min, quenching machine roller speed 57.6m / min, tempering temperature 570℃, furnace time 110min.

[0027] S5. Finishing and warehousing: According to the contract requirements, double-sided shearing and cut-to-length shearing are performed for edge trimming, followed by performance inspection, number spraying, and warehousing.

[0028] Table 2: Version and performance of Example 2

[0029] Example 3 The steel grade is 9Ni; the target thickness of the rolled steel plate is 5.5mm, the actual average thickness is 6.0mm; the finished steel plate width is 2800mm; the length of the rolled mother plate is 25000mm; the process steps include: S1. The continuous casting billet thickness is 100mm, and the designed billet yield rate is 82.40%. A walking beam heating furnace is used, with a heating temperature of 1260-1270℃, a core temperature of 1080-1100℃, and a temperature difference of 20℃ between the upper and lower surfaces of the billet.

[0030] S2. Rolling: Single-stand rolling mode is adopted, roller cooling water is turned off, finishing mill roller diameter is 1000-1060mm, crown is 0.04mm; ten passes are rolled, steel biting speed is 2.6-2.8m / s, upper and lower water descaling is turned on in the first pass, pre-flushing water is turned off between passes, rolling speed is 2.8-3.2m / s; first pass reduction rate is 18.00%, second pass reduction rate is 21.32%, third pass reduction rate is 24.50%, fourth to ninth pass reduction rate is 27.71-31.46%, tenth pass reduction rate is 14.34%; starting rolling temperature is 1110℃, finishing rolling temperature is 880℃. The rolling force of the first four passes is 30,000 to 32,000 kN, and the rolling force of the fifth to tenth passes is 39,000 to 40,000 kN; the torque of the first five passes is 2,500 to 2,700 kNm, and the torque of the sixth to tenth passes is 1,500 to 1,600 kNm.

[0031] S3, straightening: three passes of hot straightening, the straightening force of the first and second passes is 250 / 280 tons, and the straightening force of the third pass is 150 tons; S4. Heat treatment: first quenching temperature 820℃, heating time PLC+20min, second quenching temperature 670℃, heating time PLC+30min, quenching machine water flow 4400m³ / min, quenching machine roller speed 57.6m / min, tempering temperature 580℃, furnace time 110min.

[0032] S5. Finishing and warehousing: According to the contract requirements, double-sided shearing and cut-to-length shearing are performed for edge trimming, followed by performance inspection, number spraying, and warehousing.

[0033] Table 3: Version and performance of Example 3

[0034] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for rolling high-strength ultra-thin plates by a medium and thick plate rolling mill, characterized in that: The steps include: S1. Billet and heating: The thickness of the continuous casting billet is 100-120 mm, and the designed yield of the billet is 78%-84.5%. The walking beam heating furnace is used for heating; S2, rolling: rolling ten times, the steel biting speed is 2.0m / s~2.8m / s, the upper and lower water dephosphorization is turned on in the first pass to avoid the head warping after the steel plate is widened, the pre-flushing water is turned off between passes, and the rolling speed is 2.4~3.2m / s; the reduction rate of the first three passes is 18.00~24.50%, the reduction rate of the fourth to ninth passes is 25.44~32.16%, and the reduction rate of the tenth pass is 14.34~18.80%; the starting rolling temperature is 1020~1110℃, and the final rolling temperature is 820~880℃; S3, straightening: three passes of hot straightening; S4. Heat treatment: The first quenching temperature is 820-830℃, the heating time is PLC+20min, the second quenching temperature is 670-680℃, the heating time is PLC+30min, the quenching machine water flow rate is 4400m³ / min, the quenching machine roller speed is 57.6m / min, the tempering temperature is 570-580℃, and the furnace time is 110min.

2. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S1, the billet heating time is 10 min / cm, the heating temperature is 1250-1270°C, the furnace core temperature is 1040-1120°C, and the temperature difference between the upper and lower surfaces of the furnace billet is ≤30°C.

3. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S2, a single-stand rolling mode is adopted, the roller cooling water is turned off, the roller diameter of the finishing mill is 1000-1060 mm, and the crown is 0.04-0.08 mm.

4. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S2, the rolling force of the first four passes is 19000-35000 kN, and the rolling force of the fifth to tenth passes is 37000-42000 kN; the torque of the first five passes is 1900-2900 kNm, and the torque of the sixth to tenth passes is 900-2000 kNm.

5. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S3, the straightening force of the first and second passes is 200-300 tons, and the straightening force of the third pass is 150-200 tons.

6. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S4, the first quenching temperature is 820°C, the second quenching temperature is 670°C, and the tempering temperature is 570°C.

7. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: The step S5 is also included, namely, finishing and warehousing: trimming is performed by double-sided shearing and cut-to-length shearing as required, followed by performance inspection, number spraying, and warehousing.

8. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S5, the finished product width is ≤2800mm, the finished product length is 500mm<finished product length ≤26000mm, and the thickness is 5.0±0.5mm.

9. The method for rolling high-strength wide thin plates by a medium and thick plate rolling mill according to claim 1, characterized in that: In step S2, medium and thick plate rolling mill is used for rolling.

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