Method for producing thin 65Mn cold-rolled strip steel through cold continuous rolling

Abstract

The invention discloses a method for producing thin-specification 65Mn cold-rolled strip steel through cold continuous rolling. The method comprises the following steps of bell annealing, welding, withdrawal and straightening, acid pickling and cold continuous rolling. In the step of bell annealing, when the core temperature of a hot-rolled coil in a bell furnace reaches 650-720 DEG C, heat preservation is performed for 3-5 hours; by selecting a reasonable bell-type furnace annealing process, on the premise that the decarburization requirement is met, the hot rolling strength is reduced, the problem that the load of a rolling mill is too high is solved, cold continuous rolling of the thin-specification 65Mn is achieved, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of cold-rolled steel, and particularly relates to a method for continuously cold-rolling thin-gauge 65Mn cold-rolled strip steel. Background Art

[0002] Due to its high carbon and manganese content and the addition of other alloying elements, 65Mn steel has high elasticity, high strength, and high hardness. At the same time, it has high hardenability, good cutting performance, and wear resistance, and is widely used in various saw blades, knife blades, spring washers, spring buckles, etc.

[0003] At present, the production of cold-rolled 65Mn strip steel is restricted by three aspects: difficult welding, poor pickling quality, and high rolling load. Strip steel with a thickness of more than 2.2 mm can be produced by push-pull pickling + single-stand rolling process or pickling cold tandem rolling process, but strip steel with a thickness of less than 2.2 mm cannot be normally produced by pickling cold tandem rolling mill.

[0004] Chinese Patent CN107649512A discloses a manufacturing process for 65Mn cold-rolled wide strip steel, and discloses a method for producing 65Mn cold-rolled strip steel by using a five-stand pickling tandem rolling mill, which can realize the continuous and stable rolling of 65Mn cold-rolled wide strip steel on a five-stand acid rolling combined mill. The core of this patent lies in the slow cooling process treatment of hot-rolled steel coils, and at the same time, the welding difficulty problem and the problem of excessive rolling load of the rolling mill are solved by adding a heat treatment device through cold rolling welding process. This method requires the separate addition of a hot coil slow cooling device and a post-cold rolling welding heat treatment device, with a large investment in hardware equipment. At the same time, it is necessary to realize product production through five-stand tandem rolling, which also has high requirements for rolling mill equipment. Moreover, what it discloses is the cold tandem rolling of strip steel with a thickness of more than 2.2 mm, and it does not mention whether it can realize the cold tandem rolling of strip steel with a thickness of less than 2.2 mm. In fact, this method also cannot realize the cold tandem rolling of thin-gauge strip steel with a thickness of less than 2.2 mm.

[0005] Chinese Patent CN115870338A discloses a method and product for producing 65Mn cold-rolled strip steel by an eighteen-high single-stand rolling mill, and discloses a method for producing 65Mn cold-rolled strip steel by using an eighteen-high single-stand rolling mill after the hot-rolled pickled sheet is annealed once. It can manufacture 65Mn cold-rolled strip steel with a thickness range of 0.6 - 3.2 mm, a width of 900 - 1300 mm, a longitudinal thickness deviation in the range of -0.5% - 0.5%, and a transverse flatness difference ≤ 1%. The core of this patent lies in obtaining excellent flatness accuracy through the roll shape control of the intermediate rolls of the eighteen-high rolling mill. This patent adopts a conventional process flow, and is produced separately by an independent pickling unit, an annealing unit, and a single-stand rolling mill, which has the disadvantages of long process flow, complex material handling, low product yield, and high production cost. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for cold tandem rolling of thin-gauge 65Mn cold-rolled strip. By selecting a reasonable bell-type annealing process, on the premise of meeting the decarburization requirements, the strength of the hot coil is reduced, the problem of excessive mill load is solved, the cold tandem rolling of thin-gauge 65Mn is realized, the production efficiency is improved, and the production cost is reduced.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for cold tandem rolling of thin-gauge 65Mn cold-rolled strip, the method comprising the following steps: bell annealing - welding - tension leveling - pickling - cold tandem rolling;

[0009] In the bell annealing step, when the core temperature of the hot rolled coil in the bell furnace reaches 650 - 720 °C, it is kept warm for 3 - 5 hours. Through this bell annealing temperature and time, on the premise of ensuring the surface quality of the plate, the uniformity of the hot coil structure can be effectively improved, the strength of the hot coil is reduced, and the rollability of the strip is improved, enabling the four-stand tandem mill to have the ability to roll thin-gauge 65Mn.

[0010] The thickness of the hot rolled strip forming the hot rolled coil is less than 2.2 mm. For hot rolled coils with a thickness of more than 2.2 mm, annealing is not required, and they can directly enter the welding process for welding, and then pickling and cold rolling are carried out.

[0011] In the bell annealing step, the annealing atmosphere is an inert gas; the annealed hot rolled coil is cooled with the furnace.

[0012] Further, the annealing atmosphere is preferably hydrogen, nitrogen, or a mixture of hydrogen and nitrogen, and more preferably hydrogen.

[0013] In the welding step, the welding speed is 2.4 - 2.6 m / min, and the welding machine power is 10 - 12 kW.

[0014] Further, in the welding step, a wire filling welding method is adopted, and the wire filling speed is 3.0 - 3.4 m / min.

[0015] In the tension leveling step, the total tension is limited within 300 kN, and the weld seam adopts a quick opening method in the tension leveling machine.

[0016] In the tension leveling step, the meshing amount is 15 mm for the 1# unit, 15 mm for the 2# unit, and 10 mm for the 3# unit.

[0017] In the pickling step, four-stage overflow pickling is adopted. The free acid concentration in the first stage is 40-60 g / L, in the second stage is 80-100 g / L, in the third stage is 100-140 g / L, and in the fourth stage is 130-150 g / L. The acid solution temperature is 70-90 °C. Under such pickling conditions, the scale on the surface of the steel strip can be fully removed, ensuring good surface quality.

[0018] In the tandem cold rolling step, four-stand tandem rolling production is adopted.

[0019] In the tandem cold rolling step, the tensions at the exits of the F1 stand, F2 stand, F3 stand, F4 stand, and F4 stand are 6-8, 12-16, 13-18, 14-18, and 2-5 kg / mm respectively 2 ; the reduction ratios of the F1 stand, F2 stand, F3 stand, and F4 stand are 18-23%, 18-26%, 18-27%, and 0.2-0.8% respectively.

[0020] In the tandem cold rolling step, the roll roughness of the F1 stand and F2 stand is 0.6-0.8 μm; the roll roughness of the F3 stand is 0.35-0.55 μm; the roll roughness of the F4 stand is 3.0-4.0 μm.

[0021] By adopting the new process route of hot coil bell annealing, the present invention improves the uniformity of the hot coil structure and reduces the rolling difficulty of the cold rolling mill. After welding, tension leveling, and pickling, combined with the rolling reduction setting and process setting of the four-stand tandem rolling mill, the tandem rolling mill is capable of producing thin-gauge 65Mn.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention conducts a reasonable bell annealing process for thin-gauge 65Mn hot-rolled coils with a thickness of less than 2.2 mm. On the premise of meeting the decarburization requirements, the strength of the hot coil is reduced, and the problem of excessive mill load is solved; after the bell annealing process, the thin-gauge steel strip is more easily welded. Combined with the welding process, the weld quality is ensured, and stable production of the tandem rolling is guaranteed.

[0024] By controlling the pickling process, the present invention improves the pickling quality and efficiency.

[0025] In the tandem cold rolling process, the present invention ensures the stable production of the four-stand tandem rolling through reasonable reduction setting.

[0026] The method provided by the present invention can smoothly produce thin-gauge 65Mn with a thickness of less than 2.2 mm on the pickling tandem rolling mill, improving the cold rolling production efficiency of thin-gauge 65Mn steel and reducing the production cost. Description of the Drawings

[0027] Figure 1 Front view of the hot-rolled coil after bundling;

[0028] Figure 2 Side view of the hot-rolled coil after bundling;

[0029] Figure 3 Top view of the hot-rolled coil after bundling. Specific implementation manner

[0030] A method for cold tandem rolling to produce thin-gauge 65Mn cold-rolled strip provided by the present invention includes the following steps: bell annealing - welding - tension leveling - pickling - cold tandem rolling;

[0031] In the bell annealing step, the core temperature of the hot-rolled coil in the bell furnace is maintained at 650 - 720 °C for 3 - 5 hours; the annealing atmosphere is an inert gas.

[0032] In the welding step, the welding speed is 2.4 - 2.6 m / min, and the welding machine power is 10 - 12 kW. The wire filling welding method is adopted, and the wire filling speed is 3.0 - 3.4 m / min.

[0033] In the tension leveling step, the meshing amount of the 1# unit is 15 mm, the 2# unit is 15 mm, the 3# unit is 10 mm, the total tension is limited within 300 kN, and the weld seam adopts a quick-opening method on the tension leveling machine.

[0034] In the pickling step, four-stage overflow pickling is adopted. The free acid concentration in the first stage is 40 - 60 g / L, the second stage is 80 - 100 g / L, the third stage is 100 - 140 g / L, the fourth stage is 130 - 150 g / L, and the acid solution temperature is 70 - 90 °C.

[0035] In the cold tandem rolling step, four-stand tandem rolling production is adopted; the tensions at the outlets of the F1 stand, F2 stand, F3 stand, F4 stand, and F4 stand are 6 - 8, 12 - 16, 13 - 18, 14 - 18, 2 - 5 kg / mm 2 ; the reduction ratios of the F1 stand, F2 stand, F3 stand, and F4 stand are 18 - 23%, 18 - 26%, 18 - 27%, 0.2 - 0.8% respectively; the roll roughnesses of the F1 stand and F2 stand are both 0.6 - 0.8 μm; the roll roughness of the F3 stand is 0.35 - 0.55 μm; the roll roughness of the F4 stand is 3.0 - 4.0 μm.

[0036] The present invention will be described in detail below with reference to the embodiments.

[0037] Embodiment 1

[0038] The hot-rolled steel coil in this embodiment has a steel grade of 65Mn, with a raw material specification of 1.9mm * 1250mm. After cold rolling, the finished product specification is 1.0mm * 1250mm.

[0039] The method for producing 65Mn cold-rolled strip on an acid pickling tandem cold rolling mill is as follows:

[0040] (1) The appearance quality of the hot coil raw material is inspected in the hot rolling storage area. The raw material steel coil with a thickness of 1.9mm is released normally within the tower-shaped overflow range of 10mm. Steel coils exceeding the above standard range are sent to cold rolling after being repaired by hot rolling leveling and recoiling.

[0041] (2) After being stored in the hot rolling area, it continues to be air-cooled to room temperature. For the raw material steel coil with a thickness of 1.9mm, two additional axial bundling and three radial bundling are carried out. The axial bundling lock is left on the outer ring of the steel coil ( Figure 1 ). This bundling method is to prepare for lifting into the bell-type furnace, which can ensure good coil shape when the steel coil is lifted into the bell-type furnace, and avoid coil loosening and collapse.

[0042] (3) After bundling, the hot coil is lifted into the bell-type annealing furnace. The bell-type annealing furnace has a full-hydrogen atmosphere. When the core temperature of the hot coil reaches 680°C, it is held for 4 hours, and then cooled in the furnace to an outlet temperature < 85°C before being taken out of the furnace.

[0043] (4) After the 65Mn hot coil is uncoiled, straightened, and the head and tail are cut off, it enters the laser welding machine. Filler wire welding is used, with a filler wire speed of 2.8m / min, a welding speed of 3.2m / min, a welding machine power of 11kW, a pre-heating power of 10kW, and a post-heating power of 18kW. After passing the bending test on the sample, it is released.

[0044] (5) The tension control mode is adopted in the tension leveling process. The meshing amount of the 1# unit is 15mm, the 2# unit is 15mm, and the 3# unit is 10mm. The total tension is limited within 300kN. The weld seam adopts a quick-opening method in the tension leveling machine.

[0045] (6) The four-stage overflow pickling process is adopted for pickling. The free acid concentration in the first stage is 45g / L, the second stage is 85g / L, the third stage is 110g / L, and the fourth stage is 140g / L. The acid solution temperature is 83°C, and the pickling speed is controlled within 180mpm.

[0046] (7) The pickled strip is rolled on a four-stand six-high tandem cold rolling mill. The total cold rolling reduction reaches 47.4%, which is significantly higher than the conventional reduction of 30% - 40%. The main rolling parameters of each stand are shown in Table 1. The emulsion concentration is controlled at 2.5%, the rolling speed reaches 260mpm, the rolled finished product thickness is 1.0mm, the thickness accuracy is within -0.02 - 0.02mm, and the rolling is stable without strip breakage.

[0047] Table 1 Rolling process parameters of 65Mn cold-rolled coil with a thickness of 1.0 mm in Example 1

[0048] frame F1 F2 F3 F4 F4 outlet Unit Tension (kg / mm2) 7.8 14 15 16 2.8 Outlet Thickness (mm) 1.539 1.255 1.005 1.000 / Reduction Ratio (%) 19 18.5 19.9 0.5 / Rolling Force (t) 1516 1338 1274 532 /

[0049] Example 2

[0050] The hot-rolled steel coil in this example has a steel grade of 65Mn, a raw material specification of 1.9 mm * 1250 mm, and a finished product specification of 0.8 mm * 1250 mm after cold rolling.

[0051] The method for producing 65Mn cold-rolled strip on an acid pickling tandem cold rolling mill is as follows:

[0052] (1) The appearance quality of the hot coil raw material is inspected in the hot rolling storage area. The raw material steel coil with a thickness of 1.9 mm is released normally within the tower-shaped overflow range of 10 mm. Steel coils exceeding the above standard range are sent to cold rolling after being repaired by hot rolling skin pass rewind.

[0053] (2) After hot rolling and entering the warehouse, it is continuously air-cooled to room temperature. The raw material steel coil with a thickness of 1.9 mm is additionally banded axially 2 times and radially 3 times. The axial banding lock is left on the outer ring of the steel coil ( Figure 1 ).

[0054] (3) After banding, the hot coil is lifted into a batch annealing furnace. The batch annealing furnace is in a full-hydrogen atmosphere. When the core temperature of the hot coil reaches 680 °C, it is held for 4 hours, and then cooled in the furnace until the furnace outlet temperature < 85 °C before discharging.

[0055] (4) The 65Mn hot coil enters the laser welding machine after uncoiling, straightening, and trimming the head and tail. Filler wire welding is used, with a filler wire feeding speed of 2.8 m / min, a welding speed of 3.2 m / min, a welding machine power of 11 kW, a preheating power of 10 kW, and a post-heating power of 18 kW. After passing the bend test on the sample, it is released.

[0056] (5) The tension leveling process adopts a tension control mode. The engagement amount of the 1# unit is 15 mm, the 2# unit is 15 mm, and the 3# unit is 10 mm. The total tension is limited within 300 KN. The weld seam adopts a quick-opening method on the tension leveling machine.

[0057] (6) The pickling process adopts a four-stage overflow pickling. The free acid concentration in the first stage is 45 g / L, the second stage is 83 g / L, the third stage is 114 g / L, the fourth stage is 141 g / L, the acid solution temperature is 83 °C, and the pickling speed is controlled within 180 mpm.

[0058] (7) The pickled strip steel is rolled by a four-stand six-high cold tandem rolling mill. The total cold rolling reduction reaches 57.9%, which is significantly higher than the conventional reduction of 30% - 40%. The main rolling parameters of each stand are shown in Table 2. The emulsion concentration is controlled at 3.0%, the rolling speed reaches 280 mpm, the thickness of the rolled finished product is 0.8 mm, the thickness accuracy is within -0.018 - 0.018 mm, the rolling is stable, and there is no strip breakage.

[0059] Table 2 Rolling process parameters for producing 65Mn cold-rolled coil with a thickness of 0.8 mm in Example 2

[0060] frame F1 F2 F3 F4 F4 outlet Unit Tension (kg / mm2) 7.8 14 16 17 3.5 Outlet Thickness (mm) 1.464 1.092 0.804 0.800 / Reduction Ratio (%) 22.9 25.4 26.4 0.5 / Rolling Force (t) 1576 1544 1363 557 /

[0061] Example 3

[0062] The hot-rolled steel coil in this example has a steel grade of 65Mn, a raw material specification of 1.9 mm * 1250 mm, and a finished product specification of 0.8 mm * 1250 mm after cold rolling.

[0063] The method for producing 65Mn cold-rolled strip steel on an acid pickling cold tandem rolling mill is as follows:

[0064] (1) The appearance quality of the hot coil raw material is inspected in the hot rolling storage area. For the raw material steel coil with a thickness of 1.9 mm, if it is within the tower-shaped overflow range of 10 mm, it is released normally; if it exceeds the above standard range, the steel coil is sent to cold rolling after being repaired by hot rolling skin pass and recoiling.

[0065] (2) After hot rolling and entering the warehouse, it is continuously air-cooled to room temperature. For the raw material steel coil with a thickness of 1.9 mm, 2 additional axial bundling straps and 3 radial bundling straps are added. The axial bundling locks are left on the outer ring of the steel coil ( Figure 1 ).

[0066] (3) After bundling, the hot coil is lifted into the bell-type annealing furnace. The bell-type annealing furnace is in a full-hydrogen atmosphere. When the core temperature of the hot coil reaches 650 °C, it is held for 4 hours, and then cooled in the furnace until the furnace outlet temperature < 85 °C and then taken out of the furnace.

[0067] (4) The 65Mn hot coil enters the laser welding machine after uncoiling, straightening, and cutting the head and tail. Filler wire welding is used, with a filler wire feeding speed of 2.8 m / min, a welding speed of 3.2 m / min, a welding machine power of 11 KW, a preheating power of 10 KW, and a post-heating power of 18 KW. After passing the bend test on the sample, it is released.

[0068] (5) The tension control mode is adopted for the tension leveling process. The meshing amount of the 1# unit is 15 mm, the 2# unit is 15 mm, and the 3# unit is 10 mm. The total tension is limited within 300 KN. The weld seam adopts a quick-opening method in the tension leveling machine.

[0069] (6) The pickling process adopts a four-stage overflow pickling. The free acid concentration in the first stage is 45 g / L, in the second stage is 83 g / L, in the third stage is 114 g / L, and in the fourth stage is 141 g / L. The acid solution temperature is 83 °C, and the pickling speed is controlled within 180 mpm.

[0070] (7) The pickled strip steel is rolled by a four-stand six-high cold tandem mill. The total cold rolling reduction reaches 57.9%, which is significantly higher than the conventional reduction of 30% - 40%. The main rolling parameters of each stand are shown in Table 2. The emulsion concentration is controlled at 3.5%. The rolling speed reaches 280 mpm. The thickness of the rolled finished product is 0.8 mm, and the thickness accuracy is within -0.018 - 0.018 mm. The rolling is stable and there is no strip breakage.

[0071] Table 3 Rolling process parameters for producing 65Mn cold-rolled coil with a thickness of 0.8 mm in Example 3

[0072]

[0073]

[0074] Example 4

[0075] The hot-rolled steel coil in this example has a steel grade of 65Mn, a raw material specification of 1.9 mm * 1250 mm, and a finished product specification of 0.8 mm * 1250 mm after cold rolling.

[0076] The method for producing 65Mn cold-rolled strip steel on a pickling cold tandem mill is as follows:

[0077] (1) The hot coil raw material is inspected for the appearance quality of the steel coil in the hot-rolled storage area. The raw material steel coil with a thickness of 1.9 mm is released normally within the tower-shaped overflow range of 10 mm. The steel coil exceeding the above standard range is sent to cold rolling after being repaired by hot-rolled leveling and recoiling.

[0078] (2) After hot-rolled storage, it continues to be air-cooled to room temperature. The raw material steel coil with a thickness of 1.9 mm is additionally strapped axially 2 times and radially 3 times. The axial strapping lock is left on the outer ring of the steel coil ( Figure 1 ).

[0079] (3) After strapping, the hot coil is lifted into the bell-type annealing furnace. The bell-type annealing furnace has a full-hydrogen atmosphere. When the core temperature of the hot coil reaches 720 °C, it is held for 4 hours, and then cooled in the furnace to an out-of-furnace temperature < 85 °C before being taken out of the furnace.

[0080] (4) The 65Mn hot coil enters the laser welding machine after uncoiling, straightening, and trimming the head and tail. Filler wire welding is used. The filler wire feeding speed is 2.8 m / min, the welding speed is 3.2 m / min, the welding machine power is 11 KW, the pre-heating power is 10 KW, and the post-heating power is 18 KW. After passing the bend test on the sample, it is released.

[0081] (5) The tension leveling process adopts a tension control mode. The meshing amount of unit 1 is 15 mm, unit 2 is 15 mm, and unit 3 is 10 mm. The total tension is limited within 300 KN. The weld seam adopts a quick-opening method in the tension leveling machine.

[0082] (6) The pickling process adopts a four-stage overflow pickling method. The free acid concentration in the first stage is 45 g / L, the second stage is 83 g / L, the third stage is 114 g / L, and the fourth stage is 1 / 41 g / L. The acid solution temperature is / 83 °C, and the pickling speed is controlled within 180 mpm.

[0083] (7) The pickled strip steel is rolled by a four-stand six-high cold tandem mill. The total cold rolling reduction reaches 57.9%, which is significantly higher than the conventional reduction of 30% - 40%. The main rolling parameters of each stand are shown in Table 2. The emulsion concentration is controlled at 2.5%. The rolling speed reaches 280 mpm. The thickness of the rolled finished product is 0.8 mm, and the thickness accuracy is within -0.018 - 0.018 mm. The rolling is stable and there is no strip breakage.

[0084] Table 4 Rolling process parameters for producing 65Mn cold-rolled coil with a thickness of 0.8 mm in Example 4

[0085] frame F1 F2 F3 F4 F4 outlet Unit Tension (kg / mm2) 7.8 14 16 17 3.5 Outlet Thickness (mm) 1.464 1.092 0.804 0.800 / Reduction Ratio (%) 22.9 25.4 26.4 0.5 / Rolling Force (t) 1576 1544 1363 557 /

[0086] Comparative Example 1

[0087] Others are the same as in Example 1, except that in the bell annealing process, when the core temperature of the hot coil reaches 750 °C, it is kept warm for 4 hours.

[0088] The surface quality of the 65Mn steel plate produced in this comparative example is poor. After pickling and rolling, the surface of the plate is mottled, which is a pressure oxygen defect and cannot meet the surface quality requirements of the cold coil.

[0089] Comparative Example 2

[0090] Others are the same as in Example 1, except that in the bell annealing process, when the core temperature of the hot coil reaches 600 °C, it is kept warm for 4 hours.

[0091] The 65Mn steel produced in this comparative example has a high strength, the rolling mill load is too high, and the thickness fluctuation at the outlet of the rolling mill is extremely large, so it is impossible to ensure the stability of the finished product thickness.

[0092] Comparative Example 3

[0093] The hot-rolled steel coil in this example has a steel grade of 65Mn, the raw material specification is 1.9 mm * 1250 mm, and the finished product specification after cold rolling is 1.0 mm * 1250 mm. The process steps adopted are as follows:

[0094] (1) The hot-rolled coil raw materials are inspected for the appearance quality of the steel coils in the hot-rolling storage area. For the raw material steel coils with a thickness of 1.9 mm, if they are within the tower-shaped overflow range of 10 mm, they are released normally; if they exceed the above standard range, the steel coils are sent to cold rolling after being repaired by hot-rolling skin pass and recoiling.

[0095] (2) The 65Mn hot-rolled coils enter the laser welding machine after uncoiling, straightening, and trimming the head and tail. Filler wire welding is used, with a filler wire feeding speed of 2.8 m / min, a welding speed of 3.2 m / min, a welding machine power of 11 KW, a preheating power of 10 KW, and a post-heating power of 18 KW.

[0096] (3) The weld area is annealed at an annealing temperature of 650 °C for 50 s; then tension leveling is carried out.

[0097] (4) The tension control mode is adopted for the tension leveling process. The meshing amount of the 1# unit is 15 mm, the 2# unit is 15 mm, and the 3# unit is 10 mm. The total tension is limited within 300 KN. The weld is fed into the tension leveling machine in a quick-opening manner.

[0098] (5) The pickling process adopts a four-stage overflow pickling. The free acid concentration in the first stage is 45 g / L, in the second stage is 85 g / L, in the third stage is 110 g / L, and in the fourth stage is 140 g / L. The acid solution temperature is 83 °C, and the pickling speed is controlled within 180 mpm.

[0099] (6) The pickled strip steel is rolled by a four-stand six-high cold tandem mill. The total cold rolling reduction is 47.4%. The main rolling parameters of each stand are shown in Table 1. The emulsion concentration is controlled at 2.5% - 3.5%, and the rolling speed reaches 200 mpm. Due to the excessive mill load, the mill cannot reach the target thickness of 1.0 mm. The actual thickness of the rolled finished product is 1.2 mm, and the thickness accuracy is within 0.200 - 0.500 mm. The rolling process is unstable, and there are multiple strip breaks.

[0100] It can be seen from the above content that annealing the hot-rolled coils can reduce the rolling load of 65Mn steel and significantly improve the stability of cold rolling reduction in production.

[0101] In Comparative Examples 1 and 2, due to inappropriate control of the annealing parameters, the surface quality of the rolled strip steel does not meet the requirements, and the rolling load is high and the thickness is unstable.

[0102] In Comparative Example 3, since the hot-rolled coils are not annealed throughout the coil, the rolling load is large, the target thickness cannot be reached, the thickness accuracy of the rolled product is poor, and there are also many strip breaks during the rolling process.

[0103] The above detailed description of a method for producing thin-gauge 65Mn cold-rolled strip by tandem cold rolling with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be enumerated according to the defined scope. Therefore, changes and modifications within the general concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for producing thin-gauge 65Mn cold-rolled strip in cold tandem rolling, characterized in that, The method includes the following steps: bell annealing - welding - tension leveling - pickling - cold tandem rolling; In the bell annealing step, when the core temperature of the hot rolled coil in the bell furnace reaches 650 - 720 °C, it is held for 3 - 5 hours.

2. The method for cold continuous rolling of thin-gauge 65Mn cold-rolled strip according to claim 1, characterized in that The thickness of the hot rolled strip is less than 2.2 mm.

3. The method for cold continuous rolling to produce thin - gauge 65Mn cold - rolled strip steel according to claim 1, characterized in that, In the bell annealing step, the annealing atmosphere is an inert gas; the annealed hot rolled coil is cooled in the furnace.

4. The method for cold continuous rolling of thin gauge 65Mn cold rolled strip according to claim 1 or 3, characterized in that, In the bell annealing step, the annealing atmosphere is hydrogen, nitrogen, or a mixture of hydrogen and nitrogen.

5. The method for cold continuous rolling to produce thin gauge 65Mn cold rolled strip according to claim 1, characterized in that, In the welding step, the welding speed is 2.4 - 2.6 m / min, and the welding machine power is 10 - 12 kW.

6. The method for cold continuous rolling to produce thin gauge 65Mn cold rolled strip according to claim 1, characterized in that, In the tension leveling step, the total tension is limited within 300 kN.

7. The method for cold continuous rolling to produce thin - gauge 65Mn cold - rolled strip according to claim 1, characterized in that, In the pickling step, four-stage overflow pickling is adopted. The free acid concentration in the first stage is 40 - 60 g / L, in the second stage is 80 - 100 g / L, in the third stage is 100 - 140 g / L, in the fourth stage is 130 - 150 g / L, and the acid solution temperature is 70 - 90 °C.

8. The method for cold continuous rolling to produce thin-gauge 65Mn cold-rolled strip steel according to claim 1, characterized in that In the cold tandem rolling step, four-stand tandem rolling production is adopted.

9. The method for cold continuous rolling to produce thin gauge 65Mn cold rolled strip according to claim 8, characterized in that, In the cold tandem rolling step, the tensions at the F1 stand, F2 stand, F3 stand, F4 stand, and the outlet of the F4 stand are 6 - 8, 12 - 16, 13 - 18, 14 - 18, and 2 - 5 kg / mm respectively. 2 ; The reduction ratios of the F1 stand, F2 stand, F3 stand, and F4 stand are 18 - 23%, 18 - 26%, 18 - 27%, and 0.2 - 0.8% respectively.

10. The method for cold continuous rolling to produce thin gauge 65Mn cold rolled strip according to claim 1 or 8 or 9, characterized in that, In the cold tandem rolling step, the roll roughness of the F1 stand and the F2 stand is 0.6 - 0.8 μm; the roll roughness of the F3 stand is 0.35 - 0.55 μm; the roll roughness of the F4 stand is 3.0 - 4.0 μm.

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