A method for manufacturing a hot-rolled steel strip of a Cr-Mo steel

Abstract

The application provides a preparation method of a hot-rolled strip steel of Cr-Mo steel material, the Cr-Mo steel material contains Cr: 0.80-1.10wt%, Mo: 0.15-0.25wt%, the laminar cooling process adopts U-shaped cooling, after the strip steel head passes through the last rack in the multi-rack finishing rolling process, the pinch roll cooling water, the coiling roll cooling water and the mandrel cooling water are closed, after the coiling mandrel is built for a period of time, the pinch roll cooling water and the coiling roll cooling water are opened, the multi-rack finishing rolling process is ended, after the strip steel is tail thrown from the last rack for a period of time, the pinch roll cooling water and the coiling roll cooling water are closed, the mandrel cooling water is opened after the strip steel is discharged from the coiling machine, vertical transportation is adopted after the coiling is unloaded, the steel coil after rolling is placed for slow cooling in the warehouse area, so that the mechanical property uniformity of the steel coil can be obviously improved, the performance stability is improved, the thickness fluctuation of the cold rolling process is reduced, and the flatness quality of the product is improved.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology and relates to a method for preparing hot-rolled strip steel. Background Technology

[0002] In the production of hot-rolled strip steel, during the conventional hot continuous rolling process, the slab exits the heating furnace and is rolled into strip steel through a roughing mill and a seven-stand finishing mill. After laminar flow cooling, the strip steel is coiled into coils by a coiler and then transported to the finished product warehouse by an uncoiling trolley. Cr-Mo steel contains 0.80-1.10% Cr and 0.15-0.25% Mo, exhibiting strong hardenability. After laminar flow cooling, the strip steel made from Cr-Mo steel experiences performance fluctuations at both the beginning and end due to the cooling water from the pinch rolls, the auxiliary coiling rolls, and the mandrel. Simultaneously, the contact between the coil and the saddle after uncoiling causes heat transfer, resulting in significant performance fluctuations at the tail end of the coil. Furthermore, the placement of the coil in the warehouse and its mixing with coils from different coiling temperatures also contribute to performance fluctuations. The performance differences between the beginning, middle, and end of the coil can sometimes exceed 100 MPa. In summary, hot-rolled strip steel of Cr-Mo steel exhibits large thickness fluctuations, poor performance uniformity, and low performance stability after cold rolling. Summary of the Invention

[0003] To address the problems of large thickness fluctuations, poor performance uniformity, and low performance stability of hot-rolled Cr-Mo steel strips after cold rolling as described in the background art, this invention provides a method for preparing hot-rolled Cr-Mo steel strips.

[0004] The method of the present invention includes:

[0005] The process includes the following steps: hot metal pretreatment and deep desulfurization, converter top and bottom combined blowing, continuous casting, heating furnace heating, primary descaling, side press, rough rolling, secondary descaling, multi-stand finishing rolling, laminar flow cooling, coiling, uncoiling, vertical transportation, and slow cooling in the storage area.

[0006] The Cr-Mo steel contains 0.80-1.10 wt% Cr and 0.15-0.25 wt% Mo. The laminar flow cooling process adopts U-shaped cooling. During the multi-stand finishing rolling process, after the strip head passes through the last stand for a period of time, the pinch roll cooling water, coiling roll cooling water, and mandrel cooling water are turned off. After the mandrel is tensioned for a period of time, the pinch roll cooling water and coiling roll cooling water are turned on, and the multi-stand finishing rolling process ends. After the strip is thrown off the last stand for a period of time, the pinch roll cooling water and coiling roll cooling water are turned off. After the strip exits the coiler, the mandrel cooling water is turned on. After uncoiling, the strip is transported vertically and the rolled steel coil enters the warehouse for slow cooling.

[0007] Further, the Cr-Mo steel comprises the following components: C 0.27-0.33wt%, Si 0.15-0.35wt%, Mn 0.40-0.70wt%, P≤0.010wt%, S≤0.005wt%, Al≤0.060wt%, Cr 0.80-1.10wt%, Mo 0.15-0.25wt%, with the remainder being Fe and unavoidable impurities.

[0008] Furthermore, during the heating process in the furnace, the heating temperature is 1230°C, the furnace time is >150 min, and the steel is rolled into strip through rough rolling and finish rolling.

[0009] Furthermore, in the U-shaped winding cooling process, the target winding temperature of the steel coil is 600°C.

[0010] Furthermore, in the U-shaped winding cooling process, the temperature compensation within the first 30m length of the steel coil is increased by 30°C, and the temperature compensation within the last 50m length of the steel coil is increased by 40°C.

[0011] Furthermore, during the finishing rolling process, after the strip head passes through the last stand for a period of time t1, the cooling water for the pinch rolls, the coiling rolls, and the mandrel is shut off. Here, 0 < t1 < L / v1, where L refers to the distance from the exit of the last finishing stand to the coiler, and v1 refers to the strip speed. To ensure cooling of the pinch rolls, coiling rolls, and mandrel, the t1 time should be chosen to be as large as possible, but should not exceed L / v1.

[0012] Furthermore, after the coiling mandrel has been tensioned for a period of time t2, the cooling water for the pinch roll and the cooling water for the auxiliary coiling roll are turned on. Here, t2 = L2 / v2, where L2 is the temperature compensation length of the coiling head during U-shaped coiling cooling, and v2 refers to the strip speed.

[0013] Furthermore, after the finishing rolling process ends, the strip is thrown off the last stand for a period of time t3, and then the cooling water for the pinch rolls and the cooling water for the coiling rolls are turned off. Here, t3 = (L-L3) / v3, where L refers to the distance from the exit of the last stand of the finishing rolling mill to the coiler, L3 is the temperature compensation length of the tail end during U-shaped coiling cooling, and v3 refers to the strip speed.

[0014] Furthermore, the rolled steel coils are hoisted into the warehouse and placed separately within 30 minutes after being transported vertically.

[0015] Furthermore, the steel coils are prohibited from being stored together with steel coils with a target winding temperature exceeding 100°C in the storage area, and steel coils with a target winding temperature exceeding 200°C are prohibited from being placed around the steel coils.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) Significantly improve the uniformity of mechanical properties of steel coils: By optimizing the laminar cooling process, adopting U-shaped cooling and precisely controlling the opening and closing timing of the pinch rolls, coiling aid rolls and mandrel cooling water, the problem of performance fluctuation at the head and tail of steel coils caused by local rapid cooling is effectively reduced, thereby improving the uniformity of mechanical properties of steel coils along the entire length.

[0018] (2) Improve performance stability: By implementing full-process process optimization from molten iron pretreatment and converter blowing to vertical transportation and slow cooling in the storage area, the performance fluctuations caused by various factors during production and subsequent storage, such as contact with water cooling equipment, heat transfer with saddle, and mixed storage in the storage area, are reduced, making the mechanical properties of the final product more stable and reliable.

[0019] (3) Reduce thickness fluctuations in subsequent cold rolling processes: The improved uniformity and stability of the hot-rolled strip steel prepared by this invention provides higher quality and more consistent raw materials for subsequent cold rolling processes, thereby helping to reduce the thickness fluctuations of finished products caused by large differences in the properties of incoming materials during the cold rolling process.

[0020] (4) Improve the quality of the product's shape: Through comprehensive process optimization including heating, rolling and cooling, not only is the performance improved, but the quality of the strip steel shape is also improved, making it more in line with the requirements of high standards.

[0021] In summary, this invention employs conventional hot continuous rolling technology. By optimizing the smelting, heating, rolling, cooling, and post-rolling slow cooling processes, it can significantly improve the uniformity of the mechanical properties of steel coils, enhance performance stability, reduce thickness fluctuations in the cold rolling process, and improve the sheet quality of the product. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the strip steel performance along its length obtained in an embodiment of the present invention. Rel: yield strength, Rml: tensile strength. Detailed Implementation

[0023] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0024] A method for preparing hot-rolled strip steel of Cr-Mo steel includes the following process flow: hot metal pretreatment and deep desulfurization, converter top and bottom combined blowing, continuous casting, heating furnace heating, primary descaling, side press, rough rolling, secondary descaling, multi-stand finishing rolling, laminar flow cooling, coiling, uncoiling, vertical transportation, and slow cooling in the storage area.

[0025] Cr-Mo steel contains 0.80-1.10 wt% Cr and 0.15-0.25 wt% Mo. Specifically, Cr-Mo steel comprises the following components: 0.27-0.33 wt% C, 0.15-0.35 wt% Si, 0.40-0.70 wt% Mn, ≤0.010 wt% P, ≤0.005 wt% S, ≤0.060 wt% Al, 0.80-1.10 wt% Cr, 0.15-0.25 wt% Mo, with the remainder being Fe and unavoidable impurities.

[0026] The laminar flow cooling process adopts U-shaped coiling cooling. During the multi-stand finishing rolling process, after the strip head passes through the last stand for a period of time, the pinch roll cooling water, the auxiliary coiling roll cooling water, and the mandrel cooling water are turned off. After the mandrel is tensioned for a period of time, the pinch roll cooling water and the auxiliary coiling roll cooling water are turned on. The multi-stand finishing rolling process ends. After the strip is thrown off the last stand for a period of time, the pinch roll cooling water and the auxiliary coiling roll cooling water are turned off. After the strip exits the coiler, the mandrel cooling water is turned on. After uncoiling, the strip is transported vertically and the rolled steel coil enters the warehouse for slow cooling.

[0027] Among them, the coiling mandrel tensioning refers to the tension being established when the strip head is wound around the mandrel and tension is generated between the mandrel and the pinch rolls. The strip tail exiting from the last stand means that the finishing rolling is completed and the strip tail exits from the last stand, indicating that the entire strip has completed the finishing rolling process.

[0028] Specifically, in this invention, during heating in the furnace, the heating temperature is 1230℃, the furnace time is >150min, and the strip is rolled into steel through rough rolling and finish rolling. During U-shaped coiling and cooling, the target coiling temperature is 600℃; the temperature compensation within the first 30m of the coil is increased by 30℃, and the temperature compensation within the last 50m of the coil is increased by 40℃.

[0029] More specifically, during the finishing rolling process, after the strip head passes through the last stand for a period of time t1, the pinch roll cooling water, the coiling roll cooling water, and the mandrel cooling water are shut off. Here, 0 < t1 < L / v1, where L refers to the distance from the exit of the last finishing stand to the coiler, and v1 refers to the strip speed.

[0030] More specifically, after the coiling mandrel has been tensioned for a period of time t2, the cooling water for the pinch roll and the cooling water for the auxiliary coiling roll are turned on. Here, t2 = L2 / v2, where L2 is the temperature compensation length of the coiling head during U-shaped coiling cooling, and v2 refers to the strip speed.

[0031] More specifically, after the finishing rolling process ends and the strip is thrown off the last stand for a period of time t3, the cooling water for the pinch rolls and the cooling water for the coiling rolls are turned off. Here, t3 = (L-L3) / v3, where L refers to the distance from the exit of the last stand of the finishing rolling mill to the coiler, L3 is the temperature compensation length of the tail end during U-shaped coiling cooling, and v3 refers to the strip speed.

[0032] More specifically, after being transported vertically, the rolled steel coils should be hoisted into the warehouse and placed separately within 30 minutes. Steel coils must not be stored together with steel coils whose target winding temperature exceeds 100°C in the warehouse, and steel coils with a target winding temperature exceeding 200°C must not be placed around the rolled steel coils. Example

[0033] Hot-rolled strip steel of Cr-Mo steel is prepared using the method of the present invention.

[0034] The preparation of hot-rolled strip steel of Cr-Mo steel includes the following process flow: hot metal pretreatment and deep desulfurization, converter top and bottom composite blowing, continuous casting, heating furnace heating, primary descaling, side press, rough rolling, secondary descaling, multi-stand finishing rolling, laminar flow cooling, coiling, uncoiling, vertical transportation, and slow cooling in the storage area.

[0035] Cr-Mo steel comprises the following components: C 0.27-0.33wt%, Si 0.15-0.35wt%, Mn 0.40-0.70wt%, P≤0.010wt%, S≤0.005wt%, Al≤0.060wt%, Cr 0.80-1.10wt%, Mo 0.15-0.25wt%, with the remainder being Fe and unavoidable impurities.

[0036] The laminar flow cooling process employs U-shaped coiling cooling. In the multi-stand finishing rolling process, there are seven stands: F1, F2, ..., F7. During finishing rolling, the strip passes through each stand sequentially. After the strip head passes through stand F7, t1 seconds later, the pinch roll cooling water, coiling roll cooling water, and mandrel cooling water are shut off. After t2 seconds of mandrel tensioning, the pinch roll cooling water and coiling roll cooling water are turned on, ending the multi-stand finishing rolling process. The strip is then discarded from stand F7. Three seconds later, the cooling water for the pinch rolls and the cooling water for the coiling rollers are turned off, and the cooling water for the mandrel after the strip exits the coiler is turned on. After unloading, vertical transportation is adopted to reduce the performance fluctuations at the tail end caused by heat transfer from the strip to the saddle. After the rolled steel coil is vertically transported, it is hoisted into the insulated warehouse and placed separately within 30 minutes. After the rolled steel coil enters the warehouse, it is placed to slow down cooling. Steel coils are not allowed to be mixed with steel coils with a target coiling temperature exceeding 100°C in the insulated warehouse, and steel coils with a target coiling temperature exceeding 200°C are not allowed to be placed around the steel coil.

[0037] In the process flow, the heating furnace is heated to 1230℃, and the furnace time is >150min. The strip steel is then rolled into steel through rough rolling and finish rolling. The target coiling temperature is 600℃. During the U-shaped coiling cooling process, the temperature is compensated by increasing the temperature by 30℃ within the first 30m length of the coil and by increasing the temperature by 40℃ within the last 50m length of the coil.

[0038] t1, t2, and t3 will vary depending on the strip rolling speed. Specifically, 0 < t1 < L / v1, where L is the distance from the F7 exit of the finishing mill to the coiler, and v1 is the strip speed. To ensure cooling of the pinch rolls, auxiliary coiling rolls, and mandrel, t1 should be chosen as long as possible, but should not exceed L / v1. t2 = L2 / v2, where L2 is the compensation length at the U-shaped coiling head, and v2 is the strip speed. t3 = (L - L3) / v3, where L is the distance from the F7 exit of the finishing mill to the coiler, L3 is the compensation length at the U-shaped coiling tail, and v3 is the strip speed.

[0039] The performance fluctuations in the length direction of the steel coils obtained in this implementation are shown in Table 1 below, and the performance diagram of the strip in the length direction is shown in Figure 1 below. Figure 1 As shown, Rel: yield strength, Rml: tensile strength.

[0040] Table 1. Properties of steel coils along their length

[0041] Location / m 0 6 12 18 24 30 37 44 51 58 65 72 300 350 Rel / MPa 430 428 425 420 418 423 420 419 422 433 425 420 420 417 Rml / MPa 527 525 520 520 519 519 518 520 520 521 518 521 515 516 Location 400 450 628 635 642 649 656 663 670 676 682 688 694 700 Rel / MPa 418 425 423 422 420 418 420 420 424 426 425 425 430 435 Rml / MPa 515 518 514 511 522 516 522 522 522 513 520 517 525 533

[0042] From Table 1 and Figure 1 It can be seen that the performance fluctuations of yield strength and tensile strength in the length direction of the steel coil are within 40 MPa, the performance uniformity is significantly improved, and the performance stability is greatly enhanced.

[0043] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings and specific examples. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing hot-rolled strip steel of Cr-Mo steel, characterized in that: The process includes the following steps: hot metal pretreatment and deep desulfurization, converter top and bottom combined blowing, continuous casting, heating furnace heating, primary descaling, side press, rough rolling, secondary descaling, multi-stand finishing rolling, laminar flow cooling, coiling, uncoiling, vertical transportation, and slow cooling in the storage area. The Cr-Mo steel contains 0.80-1.10 wt% Cr and 0.15-0.25 wt% Mo. The laminar flow cooling process adopts U-shaped coiling cooling. During the multi-stand finishing rolling process, after the strip head passes through the last stand for a period of time, the pinch roll cooling water, the coiling roller cooling water, and the mandrel cooling water are turned off. After the coiling mandrel is tensioned for a period of time, the pinch roll cooling water and the coiling roller cooling water are turned on. The multi-stand finishing rolling process ends. After the strip is thrown off the last stand for a period of time, the pinch roll cooling water and the coiling roller cooling water are turned off. After the strip exits the coiler, the mandrel cooling water is turned on. After uncoiling, the strip is transported vertically and the rolled steel coil enters the warehouse for slow cooling. During the U-shaped winding cooling process, the target winding temperature of the steel coil is 600℃; the temperature compensation within the first 30m of the steel coil is increased by 30℃, and the temperature compensation within the last 50m of the steel coil is increased by 40℃. During the finishing rolling process, after the strip head passes through the last stand for a period of time t1, the pinch roll cooling water, the coiling roll cooling water, and the mandrel cooling water are shut off. Here, 0 < t1 < L / v1, where L refers to the distance from the exit of the last stand of the finishing mill to the coiler, and v1 refers to the strip speed. After the coiling mandrel has been tensioned for a period of time t2, the cooling water for the pinch roll and the cooling water for the coiling aid roll are turned on. Here, t2 = L2 / v2, where L2 is the temperature compensation length of the coiling head during U-shaped coiling cooling, and v2 refers to the strip speed. After the finishing rolling process is completed, the strip is thrown off the last stand for a period of time t3. Then the cooling water for the pinch rolls and the cooling water for the coiling rolls are turned off. Here, t3 = (L-L3) / v3, where L refers to the distance from the exit of the last stand of the finishing rolling mill to the coiler, L3 is the temperature compensation length of the tail end in the U-shaped coiling cooling, and v3 refers to the strip speed.

2. The method for preparing hot-rolled strip steel of Cr-Mo steel according to claim 1, characterized in that: The Cr-Mo steel comprises the following components: C 0.27-0.33wt%, Si 0.15-0.35wt%, Mn 0.40-0.70wt%, P≤0.010wt%, S≤0.005wt%, Al≤0.060wt%, Cr 0.80-1.10wt%, Mo 0.15-0.25wt%, with the remainder being Fe and unavoidable impurities.

3. The method for preparing hot-rolled strip steel of Cr-Mo steel according to claim 1, characterized in that: During the heating process in the furnace, the heating temperature is 1230℃ and the furnace time is >150min. The steel strip is produced by rough rolling and finish rolling.

4. The method for preparing hot-rolled strip steel of Cr-Mo steel according to claim 1, characterized in that: The rolled steel coils are hoisted into the warehouse and placed separately within 30 minutes after being transported vertically.

5. The method for preparing hot-rolled strip steel of Cr-Mo steel according to claim 1, characterized in that: The steel coils are prohibited from being stored together with steel coils with a target winding temperature exceeding 100°C in the storage area, and steel coils with a target winding temperature exceeding 200°C are prohibited from being placed around the steel coils.

Images