Medium-thickness plate production method capable of reducing iron oxide defects on surface of ship plate steel

Abstract

The invention discloses a medium-thickness plate production method capable of reducing iron oxide defects on the surface of ship plate steel, which belongs to the technical field of steel rolling and comprises the working procedures of plate blank heating, rough descaling, rough rolling, finish rolling, steel plate hot straightening, cooling bed cooling, shearing and warehousing. Keeping the temperature for a period of time to completely convert a slab crystal phase into an austenite structure, and reducing the number of oxide scales which are difficult to treat; in the descaling process, oxide scales on the surface of a steel billet or a steel plate are removed by spraying high-pressure water, and the oxide scales are prevented from being pressed into the surface of a plate blank to generate pits in the rolling process; the rolling process adopts a single-stand rolling mill for rolling, the rolling pass of the rough rolling process is less than or equal to 8, and the rolling pass of the finish rolling process is more than or equal to 7; a one-pass straightening method is adopted in the hot straightening process, and a plate blank subjected to hot straightening is put on a cooling bed to be cooled to the room temperature, sheared and then put in storage. The method can effectively reduce the scale defect on the surface of the ship plate steel, and has good surface quality.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling, and in particular to a method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel. Background Art

[0002] Ship plate steel is the abbreviation of ship structure steel, which is mainly used to manufacture the hull, deck and other structures of ocean-going, coastal and inland shipping ships. Due to the working conditions, ship plate steel has high requirements for surface quality. The scale defect on the surface of ship plate steel is a kind of surface defect of ship plate steel. This defect is easy to cause problems such as pits and scale residue on the surface of ship plate steel after shot peening, affecting the surface quality of ship plate steel.

[0003] At present, the ship plate steel produced by the company has some pits of varying depths on the surface after shot peening (such as Figures 2~4 ), although its depth and area meet the national standard requirements for surface quality, as the competition in the ship plate steel market becomes increasingly fierce, customers have put forward more stringent requirements on the surface quality of ship plate steel, and proposed to avoid the appearance of such iron oxide scale defects on the surface of ship plate steel. Summary of the invention

[0004] Technical problem to be solved: In view of the technical problems existing in the production process of ship plate steel in the prior art, the present invention provides a method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel, which can effectively reduce iron oxide scale defects on the surface of ship plate steel and has good surface quality.

[0005] Technical solution: The present invention discloses a method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel, the method comprising the steps of heating the slab, rough descaling, rough rolling, finishing rolling, hot straightening of the steel plate, cooling on a cooling bed, shearing, and storage; The slab heating process heats the rolled steel slab to a temperature above the required temperature and keeps the temperature for a period of time so that the slab crystal phase is completely converted into an austenite structure, thereby reducing the amount of iron oxide scale that is difficult to handle; The descaling process removes the iron oxide scale on the surface of the steel billet or steel plate by spraying high-pressure water to prevent the iron oxide scale from being pressed into the surface of the slab during rolling to produce pitting; The rolling process adopts a single-stand rolling mill: the rough rolling process has ≤8 passes, and the finishing rolling process has ≥7 passes; The hot straightening process adopts a one-pass straightening method. The hot-straightened slab is cooled to room temperature on a cooling bed and then sheared and stored.

[0006] Preferably, the thickness of the medium and thick plate is 6 to 40 mm.

[0007] Preferably, the heating temperature of the slab heating process is controlled at 1100-1250° C., and the slab is kept in the furnace for >1.0 min / mm.

[0008] Preferably, in the slab heating process, the furnace pressure of the heating furnace is controlled at 5-30 MPa.

[0009] Preferably, the high-pressure water pressure in the rough descaling process is greater than 15 MPa; the rough rolling process performs 1 to 4 descaling passes; and the finishing rolling process performs ≤3 descaling passes.

[0010] Preferably, in the cooling process, when the slab thickness is 6 mm < slab thickness ≤ 15 mm, air cooling is adopted; when the slab thickness is 15 mm < slab thickness ≤ 40 mm, cooling is performed at a cooling rate of 2 to 10° C. / s.

[0011] Preferably, the rolling torque of the rough rolling process is 0~2674KNm, and the rolling speed is 2~5m / s; the rolling torque of the finish rolling process is 0~6140KNm, and the rolling speed is 2~6m / s.

[0012] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The method for producing medium and thick ship plate steel of the present invention optimizes and improves the slab heating, rough rolling, finish rolling, cooling process and descaling process, and controls the furnace temperature, furnace pressure and holding time of the slab heating process, thereby reducing the generation of iron oxide scale which is difficult to handle; controls the process parameters of rough rolling and finish rolling and the descaling process in the process, thereby improving the removal quality of iron oxide scale and reducing the formation of pits during the rolling process of iron oxide scale; adopts different cooling systems according to the thickness of ship plate steel to compensate for the strength loss caused by high temperature final rolling; 2. The process parameters of the present invention are set, and the surface of the medium and thick ship plate steel produced has no visible spots and pits, and the generated iron oxide scale is evenly distributed, dense and thin, and can be cleaned by shot blasting process without defects such as pits and wrinkles. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a production flow chart of medium and thick ship steel plates according to an embodiment of the present invention; Figure 2 This is a picture of a pit caused by iron oxide scale on the surface of ship plate steel before the implementation of the present invention; Figure 3 This is a picture of a pit caused by iron oxide scale on the surface of ship plate steel before the implementation of the present invention; Figure 4 This is a picture of a pit caused by iron oxide scale on the surface of ship plate steel before the implementation of the present invention; Figure 5 This is a surface picture of a medium and thick plate according to an embodiment of the present invention; Figure 6 This is a surface picture of a medium and thick plate according to an embodiment of the present invention; Figure 7This is a surface picture of a medium and thick plate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0014] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the following will be combined with the attached Figures 1 to 7 The technical solutions of the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the described embodiments of the present invention belong to the scope of protection of the present invention.

[0015] A specific implementation mode of the present invention is described by taking a 3500mm production line as an example.

[0016] Example 1: Figure 1 As shown, the method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to the embodiment of the present invention has an initial slab thickness of 220 mm and a final rolling thickness of medium and thick plates of ship plate steel of 15 mm. The production method includes slab heating, rough descaling, rough rolling, finishing rolling, hot straightening of steel plates, cooling on a cooling bed, shearing, and warehousing. The specific processes of each process are as follows: (1) Slab heating process: The rolled steel slab is heated to 1190°C, the furnace pressure of the heating furnace is controlled at 22 MPa, and the slab is kept in the furnace for 262 min, so that the slab crystal phase is completely transformed into an austenite structure, reducing the amount of iron oxide scale that is difficult to handle.

[0017] (2) Descaling process: The iron oxide scale on the surface of the steel billet or steel plate is removed by spraying high-pressure water to prevent the iron oxide scale from being pressed into the surface of the slab during rolling to produce pitting. The high-pressure water pressure of the rough descaling process is 19.5 MPa. Two descaling operations are performed in the rough rolling process and two descaling operations are performed in the finishing rolling process. By accurately controlling the descaling operation during the slab rolling process, the removal effect of the iron oxide scale on the slab surface is improved, thereby providing a guarantee for the surface quality of the slab rolling.

[0018] (3) Rolling process: A single-stand rolling mill is used for rolling. The rolling torque of the rough rolling process is 2300 KNm, the rolling speed is 3 m / s, and the rough rolling process is rolled 6 times; the rolling torque of the finish rolling process is 4500 KNm, the rolling speed is 4 m / s, and the finish rolling process is rolled 8 times.

[0019] (4) The hot straightening process adopts a one-pass straightening method.

[0020] (5) The hot-corrected slab is cooled to room temperature on a cooling bed using air cooling.

[0021] (6) After cooling, the slab is sheared and put into storage.

[0022] Example 2: Figure 1As shown, the method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to the embodiment of the present invention has an initial slab thickness of 320 mm and a final rolling thickness of medium and thick plates of ship plate steel of 40 mm. The production method includes slab heating, rough descaling, rough rolling, finishing rolling, hot straightening of steel plates, cooling on a cooling bed, shearing, and warehousing. The specific processes of each process are as follows: (1) Slab heating process: The rolled steel slab is heated to 1230°C, the furnace pressure of the heating furnace is controlled at 15 MPa, and the slab is kept in the furnace for 329 min, so that the slab crystal phase is completely transformed into an austenite structure, reducing the amount of iron oxide scale that is difficult to handle.

[0023] (2) Descaling process: The iron oxide scale on the surface of the steel billet or steel plate is removed by spraying high-pressure water to prevent the iron oxide scale from being pressed into the surface of the slab during rolling to produce pitting. The high-pressure water pressure of the rough descaling process is 18.9 MPa. Three descaling operations are performed in the rough rolling process, and two descaling operations are performed in the finishing rolling process. By accurately controlling the descaling operation during the slab rolling process, the removal effect of the iron oxide scale on the slab surface is improved, providing a guarantee for the surface quality of the slab rolling.

[0024] (3) Rolling process: A single-stand rolling mill is used for rolling. The rolling torque of the rough rolling process is 2200 KNm, the rolling speed is 3 m / s, and the rough rolling process is rolled 8 times; the rolling torque of the finish rolling process is 3000 KNm, the rolling speed is 3 m / s, and the finish rolling process is rolled 10 times.

[0025] (4) The hot straightening process adopts a one-pass straightening method.

[0026] (5) The hot-corrected slab is cooled to room temperature on a cooling bed at a cooling rate of 2 to 10°C / s (the cooling rate is a process parameter and any value in the range can be used).

[0027] (6) After cooling, the slab is sheared and put into storage.

[0028] Example 3: Figure 1 As shown, the method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to the embodiment of the present invention has an initial slab thickness of 220 mm and a final rolling thickness of medium and thick plates of ship plate steel of 8 mm. The production method includes slab heating, rough descaling, rough rolling, finishing rolling, hot straightening of steel plates, cooling on a cooling bed, shearing, and storage. The specific processes of each process are as follows: (1) Slab heating process: The rolled steel slab is heated to 1200°C, the furnace pressure of the heating furnace is controlled at 25 MPa, and the slab is kept in the furnace for 450 min to completely transform the slab crystal phase into an austenite structure and reduce the amount of iron oxide scale that is difficult to handle.

[0029] (2) Descaling process: The iron oxide scale on the surface of the steel billet or steel plate is removed by spraying high-pressure water to prevent the iron oxide scale from being pressed into the surface of the slab during rolling to produce pitting. The high-pressure water pressure in the rough descaling process is greater than 15 MPa. Four descaling passes are performed in the rough rolling process, and two descaling passes are performed in the finishing rolling process. By accurately controlling the descaling operation during the slab rolling process, the effect of removing the iron oxide scale on the slab surface is improved, thereby providing a guarantee for the surface quality of the slab rolling.

[0030] (3) Rolling process: A single-stand rolling mill is used for rolling. The rolling torque of the rough rolling process is 2674 KNm, the rolling speed is 2 m / s, and the rolling passes of the rough rolling process are ≤ 8 passes; the rolling torque of the finishing rolling process is 5140 KNm, the rolling speed is 3 m / s, and the rolling passes of the finishing rolling process are ≥ 7 passes.

[0031] (4) The hot straightening process adopts a one-pass straightening method.

[0032] (5) The hot-corrected slab is cooled to room temperature on a cooling bed using air cooling.

[0033] (6) After cooling, the slab is sheared and put into storage.

[0034] Before the production method of the present invention is implemented, the existing ship plate steel oxide scale causes pit defects on its surface (such as Figures 2~4 As shown in the figure, the ship plate steel medium and thick plates produced in Examples 1 to 3 of the present invention have a smooth rolling process, and the surface quality of the rolled steel plates after shot blasting is good (as shown in the figure Figures 5 to 7 No iron oxide scale defect.

[0035] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel, characterized in that: The production method of medium and thick plates includes the steps of slab heating, rough descaling, rough rolling, finish rolling, hot straightening of steel plates, cooling on a cooling bed, shearing, and warehousing; The slab heating process heats the rolled steel slab to a temperature above the required temperature and keeps the temperature for a period of time so that the slab crystal phase is completely converted into an austenite structure, thereby reducing the amount of iron oxide scale that is difficult to handle; The descaling process removes the iron oxide scale on the surface of the steel billet or steel plate by spraying high-pressure water to prevent the iron oxide scale from being pressed into the surface of the slab during rolling to produce pitting; The rolling process adopts a single-stand rolling mill: the rough rolling process has ≤8 passes, and the finishing rolling process has ≥7 passes; The hot straightening process adopts a one-pass straightening method. The hot-straightened slab is cooled to room temperature on a cooling bed and then sheared and stored.

2. The method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to claim 1, characterized in that: The thickness of the medium and thick plate is 6 to 40 mm.

3. The method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to claim 1, characterized in that: The heating temperature of the slab heating process is controlled at 1100-1250° C., and the slab time in the furnace is greater than 1.0 min / mm.

4. The method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to claim 3, characterized in that: In the slab heating process, the heating furnace pressure is controlled at 5-30 MPa.

5. The method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to claim 1, characterized in that: The high-pressure water pressure in the rough descaling process is greater than 15 MPa; the rough rolling process performs 1 to 4 descaling passes; and the finishing rolling process performs ≤3 descaling passes.

6. The method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to claim 1, characterized in that: In the cooling process, when the slab thickness is 6 mm < slab thickness ≤ 15 mm, air cooling is adopted; when the slab thickness is 15 mm < slab thickness ≤ 40 mm, cooling is performed at a cooling rate of 2 to 10° C. / s.

7. The method for producing medium and thick plates for reducing iron oxide defects on the surface of ship plate steel according to claim 1, characterized in that: The rolling torque of the rough rolling process is 0~2674KNm, and the rolling speed is 2~5m / s; the rolling torque of the finish rolling process is 0~6140KNm, and the rolling speed is 2~6m / s.

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