Method and apparatus for quenching hot rolled thin gauge steel strip

Abstract

The present application relates to a kind of hot-rolled thin gauge steel strip quenching method and equipment, belong to the technical field of hot-rolled steel strip continuous quenching, the quenching method includes the following steps: first to steel strip with 10 ℃ / s~30 ℃ / s cooling rate is pre-cooled to above 50 ℃±10 ℃ of bainite transformation temperature corresponding to steel CCT curve, again to steel strip with 50 ℃ / s~70 ℃ / s cooling rate is rapidly cooled to below 50 ℃±10 ℃ of Mf point corresponding to steel, then to steel strip with 10 ℃ / s~20 ℃ / s cooling rate is low-speed cooling to normal temperature.The present application carries out low cooling rate pre-cooling to steel strip, slower cooling rate plays the role of solidification surface, reduces thermal stress deformation, reduces the deformation in the quenching process of steel strip;In quenching cooling process, using fast cooling rate mode cooling, ensure the complete organization transformation of steel strip, obtain quenched martensite, both guarantee the performance of steel strip and take into account the shape of steel strip, solve the current thin gauge steel strip quenching deformation problem.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hot-rolled steel strip continuous quenching, and relates to a hot-rolled thin-gauge steel strip quenching method and equipment. BACKGROUND

[0002] In recent years, the engineering machinery, dump truck, heavy truck, money transport vehicle and other industries pay more and more attention to the structural lightweight, product upgrading, product life improvement and other aspects, and put forward higher strength, higher wear resistance, higher service life and other urgent requirements to the steel materials, especially in the thin-gauge high-strength steel field to create a huge market space.

[0003] Hot-rolled steel plate quenching usually adopts a roll press quenching machine to produce single plate, but the device has the problems of low production efficiency and poor plate shape of thin steel plate products below 3mm, which cannot meet the user's demand.

[0004] The quenching process of thin steel plate is to heat the steel plate to above the austenite transformation temperature, keep warm for a certain time, and then rapidly cool the steel plate to room temperature by water cooling or other methods to obtain martensite organization. The deformation mechanism of the steel plate is that the deformation above the martensite transformation point (Ms) depends on the thermal stress, and the deformation in the martensite transformation process (Ms to Mf) depends on the phase change stress. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a hot-rolled thin-gauge steel strip quenching method and equipment which can ensure the performance of the steel strip and take into account the plate shape of the steel strip.

[0006] To achieve the above purpose, the present application provides the following technical scheme:

[0007] A hot-rolled thin-gauge steel strip quenching method, comprising the following steps:

[0008] S1 pre-cooling: pre-cooling the steel strip at a cooling speed of 10℃ / s-30℃ / s to above 50℃±10℃ of the bainite transformation temperature corresponding to the CCT curve of the steel grade;

[0009] S2 quenching cooling: rapidly cooling the steel strip at a cooling speed of 50℃ / s-70℃ / s to below 50℃±10℃ of the Mf point corresponding to the steel grade;

[0010] S3 final cooling: low-speed cooling the steel strip at a cooling speed of 10℃ / s-20℃ / s to room temperature.

[0011] Optionally, in step S1, one-stage or multi-stage pre-cooling is adopted.

[0012] Optionally, when multi-stage pre-cooling is adopted, the cooling speed of each stage is different, and the cooling speed of the one-stage to the multi-stage gradually increases.

[0013] Optionally, when multi-stage pre-cooling is adopted, the same or different cooling medium is used in each stage.

[0014] Optionally, the pre-cooling is in a surface cooling mode, and the quenching cooling is in a line cooling mode.

[0015] Optionally, the pre-cooling is in a surface cooling mode, and the quenching cooling is in a line cooling mode.

[0016] Optionally, the pre-cooling is in a surface cooling mode, and the quenching cooling is in a line cooling mode.

[0017] A hot-rolled thin-gauge steel strip quenching device comprises a pre-cooling system, a quenching system, a final cooling system and a drying system arranged in sequence along the running direction of the steel strip, and the cooling devices of the systems are arranged symmetrically above and below the steel strip.

[0018] Optionally, the pre-cooling system is a one-stage or multi-stage cooling system.

[0019] Optionally, the pre-cooling system is a one-stage or multi-stage cooling system.

[0020] Optionally, the pre-cooling system is a one-stage or multi-stage cooling system.

[0021] Optionally, the pre-cooling system is a one-stage or multi-stage cooling system.

[0022] The beneficial effects of the present application are as follows: before quenching cooling, the steel strip surface is cooled to 50℃±10℃ above the bainite transformation temperature corresponding to the CCT curve of the steel grade by using one-stage or multi-stage pre-cooling with different cooling speeds, the slower cooling speed plays a role of solidifying the surface and reducing thermal stress deformation, and the deformation in the quenching process of the steel strip is reduced; during the quenching cooling process, the steel strip is cooled by using a rapid cooling speed mode, the complete transformation of the steel strip is ensured, and quenched martensite is obtained, which not only ensures the performance of the steel strip but also takes into account the shape of the steel strip, and solves the problem of quenching deformation of the current thin-gauge steel strip.

[0023] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following specification, and will be learned from the practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the drawings, in which: In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the drawings, in which:

[0025] Figure 1 Figure 1 is a schematic diagram of a hot-rolled thin-gauge steel strip quenching device according to the present application.

[0026] Figure 1 is a schematic diagram of a hot-rolled thin-gauge steel strip quenching device according to the present application. DETAILED DESCRIPTION

[0027] The present application is described in greater detail by the specific embodiments below, and other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure herein. The present application can also be implemented or applied in other different embodiments, and various modifications or changes can be made to the details herein based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following embodiments only schematically illustrate the basic concepts of the present application, and the features in the following embodiments and examples can be combined with each other without conflict.

[0028] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical drawing, and should not be understood as a limitation on the present application. In order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual product size. It is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0029] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that the orientations or positional relationships indicated by terms such as "upper", "lower", "left", "right", "front", "back", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present application. For those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0030] Please refer to Figure 1 A hot-rolled thin-gauge steel strip quenching method, the specific steps are as follows:

[0031] 1. First-stage pre-cooling: cool the steel strip surface to 800°C. The cooling method can use a seam or a nozzle, and the cooling medium can use but is not limited to air, nitrogen, steam, gas mist, etc., and the cooling speed is slow, controlled at 10°C / s to 20°C / s;

[0032] 2. Secondary pre-cooling: the surface of the steel strip is cooled to 50℃±10℃ above the bainite transformation temperature corresponding to the CCT curve of the steel grade, and the cooling method can adopt but is not limited to a surface cooling method such as a conical nozzle, an atomizing nozzle, etc., the cooling medium is water, the cooling speed is relatively fast, and is controlled at 20℃ / s~30℃ / s;

[0033] 3. Quenching cooling: the steel strip is cooled to 50℃±10℃ below the Mf point, and the cooling method can adopt but is not limited to a line cooling method such as a water gap nozzle (water knife), a fan-shaped nozzle, etc., the cooling medium is water, the cooling speed is fast, and is controlled at 50℃ / s~70℃ / s;

[0034] 4. Final cooling: the steel strip is cooled to normal temperature, and the cooling speed is slow, and is generally controlled at about 15℃ / s;

[0035] 5. Blow drying: the surface of the steel strip is blown dry.

[0036] In order to reduce quenching deformation, the present application adopts slow cooling from the start of the quenching point to 50℃±10℃ above the bainite transformation temperature of the CCT curve to reduce thermal stress caused by rapid cooling; in order to avoid bainite or pearlite transformation of the supercooled austenite, the present application adopts fast cooling near the bainite transformation temperature of the CCT curve. The present application first adopts different media and methods to pre-cool the surface of the steel strip in multiple stages, solidifies the surface, reduces thermal stress deformation, and then completes the martensite transformation through strong water quenching to obtain the required strength, and then cools the steel strip to normal temperature through low-speed cooling to complete quenching, thereby solving the problem of quenching deformation of the current thin-gauge steel strip.

[0037] Further, the first-stage pre-cooling and the secondary pre-cooling can be used simultaneously or not simultaneously for different specifications and different steel grades.

[0038] Further, the water as the cooling medium can be added with quenching liquid or not.

[0039] A hot-rolled thin-gauge steel strip quenching device, comprising a pre-cooling system, a quenching system, a final cooling system and a blow drying system arranged in sequence along the running direction of the steel strip, the cooling devices of each system are arranged symmetrically above and below the steel strip, and the steel strip is conveyed through a roller way.

[0040] Further, the pre-cooling system comprises a first-stage pre-cooling system and a secondary pre-cooling system.

[0041] Further, it further comprises a straightening device, the straightening device comprises pressure rollers arranged at intervals on the upper side of the steel strip, the pressure rollers are at a certain distance from the steel strip to limit the deformation amount of the steel strip; the pressure rollers are located directly above the conveying rollers of the roller way. The straightening device can effectively limit the deformation of the steel strip during the quenching process, and the pressure rollers can be passive rollers, and the number thereof is set according to actual needs.

[0042] Further, it also comprises a water receiving tank and a drainage system, the drainage system is composed of a drainage pipeline and a water pump, the water receiving tank is located at the lowest part of the quenching device, the drainage pipeline is connected with the lowest point of the water receiving tank, and the quenching wastewater is discharged into the water circulation system through the water pump.

[0043] Further, it also comprises a waste gas drainage system composed of a waste gas drainage pipeline 13, a waste gas fan 14, a waste gas chimney 15, etc., which discharges the waste gas for quenching and the steam generated in the quenching process to the outside of the plant through the waste gas drainage pipeline 13, the waste gas fan 14 and the waste gas chimney 15 connected with the furnace shell.

[0044] Example 1

[0045] A Q960D high-strength engineering machinery steel with a production specification of 2mmx1500mm is produced. After the steel coil is unwound, the steel strip is heated to 930℃ through a heating furnace and kept for 10 minutes, and then enters the quenching machine. After passing through a first-stage pre-cooling system 1, the steel strip is cooled to 850℃ at a cooling speed of 15℃ / s; after passing through a second-stage pre-cooling system 2, the steel strip is cooled to 700℃ at a cooling speed of 25℃ / s; after passing through a quenching system 3, the steel strip is cooled to 150℃ at a cooling speed of 50℃ / s; after passing through a final cooling system 4, the steel strip is cooled to room temperature; after passing through a blow-drying system 5, the water on the surface of the steel strip is blown dry and then enters a tempering treatment process. During the process, the steel strip is constrained by a 1# compression roller 6, a 2# compression roller 7, a 3# compression roller 8, a 4# compression roller 9, a 5# compression roller 10 and a 6# compression roller 11, so as to reduce deformation and ensure that the cooling medium is uniformly sprayed onto the upper and lower surfaces of the steel strip by each cooling system. All the cooling processes are completed in a sealed cover 12, and the medium for cooling and the generated steam will not escape into the plant, the quenching water is discharged into a circulating water pool through a drainage system 16, and the waste gas is finally discharged to the outside of the plant through a waste gas drainage pipeline 13, a waste gas fan 14 and a waste gas chimney 15.

[0046] Example 2

[0047] NM450 wear-resistant steel with a production specification of 1.5mmx1700mm is produced. After the steel coil is uncoiled, the steel strip is heated to 930 DEG C through a heating furnace and is kept for 10 minutes, and then enters a quenching machine, after passing through a first precooling system 1, the steel strip is cooled to 880 DEG C at a cooling speed of 10 DEG C / s; after passing through a second precooling system 2, the steel strip is cooled to 780 DEG C at a cooling speed of 20 DEG C / s; after passing through a quenching system 3, the steel strip is cooled to 100 DEG C at a cooling speed of 70 DEG C / s; after passing through a final cooling system 4, the steel strip is cooled to normal temperature; after passing through a blow-drying system 5, the water on the surface of the steel strip is blown dry and then enters a tempering treatment process. During the process, the steel strip is constrained by a 1# compression roller 6, a 2# compression roller 7, a 3# compression roller 8, a 4# compression roller 9, a 5# compression roller 10 and a 6# compression roller 11, so as to reduce deformation and ensure that the cooling medium is uniformly sprayed onto the upper and lower surfaces of the steel strip by each cooling system. All the cooling processes are completed in a sealed cover 12, and the medium used for cooling and the generated steam cannot escape into the plant, the quenching water is discharged through a drainage system 16 and is discharged into a circulating water pool, and the waste gas is finally discharged outside the plant through a waste gas discharge pipeline 13, a waste gas discharge fan 14 and a waste gas discharge chimney 15.

[0048] The present application solves the deformation and efficiency problems of the current thin-gauge steel strip quenching by performing slow-speed precooling on the fully heated steel strip and then performing fast-speed quenching to complete the quenching process of the steel strip.

[0049] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and are not limiting, and although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, and all should be covered in the scope of the claims of the present application.

Claims

1. A method of quenching hot rolled thin gauge steel strip characterised in that: The method comprises the following steps: S1 precooling: precooling the steel strip at a cooling speed of 10-30 ℃ / s to 50 ℃±10 ℃ above the bainite transformation temperature corresponding to the CCT curve of the steel grade; S2 quenching cooling: rapidly cooling the steel strip at a cooling speed of 50-70 ℃ / s to 50 ℃±10 ℃ below the Mf point corresponding to the steel grade; S3 final cooling: slowly cooling the steel strip at a cooling speed of 10-20 ℃ / s to room temperature; In step S1, the precooling is two-stage precooling, and the cooling mode of the first-stage precooling is a nozzle, and the cooling mode of the second-stage precooling is a conical nozzle. In step S2, the cooling mode of the quenching cooling is a water slit nozzle.

2. A method of quenching a hot rolled thin gauge steel strip as claimed in claim 1 wherein: The cooling speed is different in each stage of the two-stage precooling, and the cooling speed gradually increases from the first stage to the second stage, and the same or different cooling medium is used in each stage.

3. A method of quenching a hot rolled thin gauge steel strip as claimed in claim 1 wherein: A press roller is arranged on the upper side of the steel strip to limit the deformation amount of the steel strip and straighten the steel strip.

4. A method of quenching a hot rolled thin gauge steel strip as claimed in claim 1 wherein: The method further comprises Step S4: drying the surface of the steel strip.

5. A method of quenching a hot rolled thin gauge steel strip as claimed in claim 1, wherein: The equipment for the hot-rolled thin-gauge steel strip quenching method comprises, in sequence along the running direction of the steel strip, a precooling system, a quenching system, a final cooling system and a drying system, and the cooling devices of the systems are arranged symmetrically above and below the steel strip.

6. A method of quenching a hot rolled thin gauge steel strip as claimed in claim 5 wherein: The equipment further comprises a straightening device, which comprises press rollers arranged at intervals on the upper side of the steel strip, and the press rollers are at a distance from the steel strip to limit the deformation amount of the steel strip.

7. A method of quenching a hot rolled thin gauge steel strip as claimed in claim 5 wherein: The equipment further comprises a sealing cover, and the precooling system, the quenching system, the final cooling system and the drying system are located in the sealing cover, the bottom of the sealing cover is provided with a drainage system, and the upper part of the sealing cover is provided with a waste gas exhaust system.

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