A high-efficiency and environmentally friendly method for treating the surface of hot-rolled steel plates

Abstract

The present invention discloses a method for surface treatment of hot-rolled steel plates, comprising: (1) forming slabs from molten steel obtained by converter smelting; (2) coiling the slabs into steel coils after heating, rough rolling and finish rolling; (3) flattening the steel coils after uncoiling to obtain steel plates; (4) the steel plates enter a surface treatment device for treatment to remove surface oxides; (5) purging, baking and oiling the treated steel plates. The method of the present invention can effectively remove oxides on the surface of hot-rolled steel plates, has high production efficiency and is environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of surface treatment control in hot rolling production in the metallurgical field, and in particular to a method for efficiently and environmentally friendly treatment of the surface of a hot-rolled steel plate. Background Art

[0002] With the rapid development of social economy and the continuous improvement of material life, people pay more and more attention to the protection of the surrounding environment and sustainable development. They are paying more and more attention to whether the production of materials is economical, whether the energy consumption is low-carbon, whether the emission is pollution-free, whether the workshop is clean, whether the noise is harmful to industrial workers, etc. In recent years, the national environmental protection department has restricted the environmental protection requirements of the steel product production process in the form of legislation, and has also placed great importance on whether the subsequent processing of materials is environmentally friendly. Therefore, whether the whole process of steel material processing and application, which is widely used in production and life, is green and environmentally friendly is also taken seriously, so as to achieve the green requirements of the whole life cycle of materials such as production, application, recycling and reuse.

[0003] There are two traditional methods for removing iron oxide from the surface of hot-rolled steel plates. The first is pickling. The disadvantage of this method is that the acid has strict requirements on safety and medium during use and storage. At the same time, the acid will volatilize during use. The recovery and discharge of waste acid and waste residue after use will cause serious harm and pollution to personnel and the environment. Therefore, this production method is gradually eliminated. The second method is shot blasting. The disadvantage of this method is that the surface roughness of the steel plate is large due to the coarseness of the shot particles used, which cannot meet the surface requirements of high-end products. The drum-type, turntable-type, hanging-type and other shot blasting methods rely on the weight (force) of the shot particles themselves to hit the surface of the steel plate, and the iron oxide scale cannot be completely removed. In addition, shot blasting also has noise and dust pollution, which causes serious physical and mental harm to practitioners.

[0004] In addition, the common disadvantage of the above two methods is that there is no linkage with upstream production (hot rolling process) before treatment. If the elements that are easy to generate strong adhesion, such as Si, Cr, Ni, B, etc. in steel are not controlled during material production, or the rolling temperature and speed are not effectively controlled during hot rolling, thin oxides with strong adhesion will be produced, which is not conducive to the processing efficiency of pickling and shot blasting. In addition, some quality problems such as silicon streaks, oxide residues and pits will be formed because they cannot be completely removed. Summary of the invention

[0005] In view of the above problems, the present invention is proposed to provide a method for efficiently and environmentally friendly surface treatment of hot-rolled steel plates that overcomes the above problems or at least partially solves the above problems.

[0006] Specifically, the present invention is achieved through the following technical solutions:

[0007] A method for surface treatment of a hot-rolled steel plate, comprising:

[0008] (1) Forming slabs from molten steel obtained from converter smelting;

[0009] (2) The slab is heated, rough rolled and finish rolled before being coiled into a steel coil;

[0010] (3) After uncoiling, the steel coil is flattened to obtain a steel plate;

[0011] (4) The steel plate enters the surface processor for treatment to remove surface oxides;

[0012] (5) The treated steel plate is purged, baked and oiled.

[0013] Optionally, in step (1), the molten steel contains Cr≤0.06%, Ni≤0.05%, Mo≤0.010%, B≤0.0003%, and Si≤0.10%.

[0014] Optionally, in step (1), the molten steel contains Cr≤0.06%, Ni≤0.05%, Mo≤0.003%, B≤0.0003%, and Si≤0.08%.

[0015] Optionally, in step (2), the heating temperature is 1180-1270° C., and the heating time is 160-200 minutes.

[0016] Optionally, in step (2), the descaling water pressure of the rough rolling is 16-22 MPa, and the descaling temperature is 1180-1200°C.

[0017] Optionally, in step (2), the start rolling temperature of the finishing rolling is 1040-1090°C, the finishing rolling speed is 5-12 m / s, and the final rolling temperature is 850-900°C.

[0018] Optionally, in step (2), the coiling temperature is 540-620°C.

[0019] Optionally, in step (4), a mixture of stainless steel grit and water in a weight ratio of 1:(10-50) is used to spray the surface of the steel plate to remove surface oxides.

[0020] Optionally, the particle size of the stainless steel grit is 30-100 meshes, and the spraying angle is 20°-160°.

[0021] Optionally, in step (4), the rotation speed of the turbine of the surface processor is 1600 to 3000 rpm, and the running speed of the steel plate is 3 to 20 m / min.

[0022] Compared with the prior art, the surface treatment method of the hot-rolled steel plate of the present invention has at least the following beneficial effects:

[0023] The method of the invention can completely remove the oxides produced by high-temperature iron oxide scale and low-temperature rust on the surface of hot-rolled steel coils or steel plates.

[0024] Compared with the traditional production method, the method of the present invention has high efficiency, environmental protection, high surface quality, lower production cost, and has strong promotion value. DETAILED DESCRIPTION

[0025] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the technical terms involved in the present invention have the meanings commonly understood by those skilled in the art.

[0026] In view of the problem that the current method of removing iron oxide on the surface of steel plates is inefficient and cannot be completely and effectively removed, the inventor of the present invention proposes the following design concept:

[0027] The first step is to remove the pre-linkage preparation and limit the elements in the steel that affect the removal of oxides during production. During smelting, the raw materials added, such as molten iron, scrap steel, alloys and furnace charges that must be added due to performance requirements, are restricted due to the unavoidable introduction of elements, such as Si, Cr, Ni, Mo, B, etc., or removed through corresponding technologies and processes, such as Si removal treatment; in addition, under the premise of not affecting the performance during hot rolling, the hot rolling temperature and speed are intervened to reduce the oxide eutectoid reaction and avoid the production of thin and dense oxides.

[0028] The second step is to remove oxides. Based on the first step, the steel coil (or plate) is rolled up, the steel coil needs to be cut, enter the straightening machine for plate straightening, and then enter the surface processor, so that a mixture of fine stainless steel sand (sand grains 30-100 mesh) and water is sprayed on the surface of the steel plate at a certain angle after turbocharging, so that the oxide on the surface of the steel plate is broken and fallen off, and then rinsed with clean water, and finally the surface moisture is dried, oiled, and re-rolled and packaged.

[0029] Based on the above design concept, the inventors of the present invention have creatively proposed a method for surface treatment of hot-rolled steel plates, by which hot-rolled steel plates with effectively removed surface oxides can be produced. The method comprises: (1) forming slabs from molten steel obtained from converter smelting; (2) coiling the slabs into steel coils after heating, rough rolling and finish rolling; (3) flattening the steel coils after uncoiling to obtain steel plates; (4) the steel plates enter a surface treatment device for treatment to remove surface oxides; and (5) purging, baking and oiling the treated steel plates.

[0030] The method of the present invention uses "smelting + hot rolling + cooling + uncoiling (or flat plate) + head cutting + straightening + surface treatment + drying + oiling + cross-cutting or recoiling + packaging" as the production process flow, and is suitable for hot-rolled steel strips (plates) such as carbon structural steel, low-alloy high-strength steel and medium-high alloy steel that are suitable for production in hot rolling lines and need to be processed after removing surface oxides.

[0031] As a preferred embodiment, the surface treatment method of a hot rolled steel plate of the present invention comprises:

[0032] (1) The molten steel obtained by converter smelting is made into slabs.

[0033] During smelting, the raw materials added, such as molten iron, scrap steel, alloys and furnace charges that must be added due to performance requirements, and the elements that cannot be avoided, such as Si, Cr, Ni, Mo, B, etc., are restricted. If the smelting process conditions permit, they can also be removed by corresponding technologies, such as Si removal treatment.

[0034] The inventors have found through research that by controlling the content of Cr, Ni, Mo, B, and Si in molten steel, the adhesion between high-temperature oxides and the substrate can be changed, thereby making it easier to remove oxides when processing steel plates in a surface processor.

[0035] Preferably, the molten steel contains Cr≤0.06%, Ni≤0.05%, Mo≤0.010%, B≤0.0003%, and Si≤0.10%. More preferably, the molten steel contains Cr≤0.06%, Ni≤0.05%, Mo≤0.003%, B≤0.0003%, and Si≤0.08%.

[0036] The inventors have found through research that if the contents of Cr, Ni, Mo, B and Si exceed the content range specified in the present invention, the oxides or mixtures of two or more oxides produced by these five elements at high temperature have strong adhesion, which is not conducive to subsequent descaling treatment and may even cause surface defects due to incomplete removal.

[0037] The method for controlling the content of Cr, Ni, Mo, B and Si in molten steel can be reasonably selected by those skilled in the art in combination with actual production conditions. As an example, the scrap steel or alloy added during smelting can be classified and managed to avoid the introduction of scrap steel or alloy with excessive content, thereby controlling the content of Cr, Ni, Mo, B and Si in molten steel.

[0038] (2) The slab is rolled and then coiled into a steel coil.

[0039] The slab is sent to a heating furnace for heating, the heating temperature is 1180-1270°C (for example, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, 1260°C or 1270°C, etc.), and the heating time is 160-200 minutes (for example, 160 minutes, 170 minutes, 180 minutes, 190 minutes or 200 minutes, etc.). With the heating temperature and heating time of the present invention, it is possible to ensure that the slab is burned through and the alloy elements are fully dissolved, but to prevent overburning, overheating, and excessively thick oxide scale produced by the furnace.

[0040] After heating, the slab is rough rolled, the rough rolling descaling water pressure is 16-22Mpa (for example, 16Mpa, 18Mpa, 20Mpa or 22Mpa, etc.), and the descaling temperature is 1180-1200°C (for example, 1180°C, 1190°C or 1200°C, etc.).

[0041] Before finishing rolling, descaling water is normally added to ensure sufficient water pressure, the finishing rolling start temperature is controlled at 1040-1090°C (for example, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C or 1090°C, etc.), and the finishing rolling speed is controlled at 5-12m / s (for example, 5m / s, 6m / s, 8m / s, 10m / s or 12m / s, etc.). The final rolling temperature is controlled at 850-900°C (for example, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C, etc.).

[0042] The inventors have found through research that, under the premise of not affecting the material properties, hot rolling can ensure the residence time of the steel plate in the high temperature zone by reducing the rolling speed and / or increasing the rolling temperature, thereby ensuring a certain thickness of the oxide film, and making the produced oxide thick and loose. In addition, by controlling the hot rolling process temperature and rolling speed, the proportion of Fe3O4, FeO, and elemental Fe phases in the oxide and their respective distribution and morphology can be controlled, thereby reducing the oxide adhesion and preparing for the next step of cleaning.

[0043] In the present invention, the hot rolling process takes two aspects into consideration, namely, ensuring that the parameters such as temperature and speed in hot rolling allow the strengthening elements in the steel to play their due strengthening role, and also ensuring the type, thickness, adhesion, degree of eutectic transformation, etc. of the oxide film produced on the surface of the steel plate to facilitate subsequent removal.

[0044] The rolled steel plate is coiled into a coil, and the coiling temperature is controlled at 540-620°C (for example, 540°C, 560°C, 580°C, 600°C or 620°C, etc.). The coiling temperature avoids the eutectoid transformation temperature of the oxide, which can avoid the phase change of FeO, ensure that the oxide is still loose and easy to remove, and does not affect the performance of the steel plate.

[0045] The coiling process of the present invention (especially the selection of the coiling temperature) ensures the precipitation of strengthening elements, tissue recovery, etc., and also ensures that the surface oxide film does not undergo eutectoid transformation, making the produced oxide film easier to remove.

[0046] (3) Uncoiling and flattening

[0047] The steel coil is unrolled and cut off by the coiler (flat plate does not need to be cut off), and then the plate shape is straightened by the straightening machine. Straightening is to facilitate the threading (over-steel) during surface treatment and prevent defects such as scratches, while meeting the requirements for the unevenness of the steel plate in subsequent processing.

[0048] (4) Removal of oxides from the steel plate surface

[0049] The leveled steel plate enters the surface processor, which is filled with a mixture of stainless steel grit and water. The mixture is turbocharged and sprayed onto the surface of the steel plate at a certain angle. The oxide on the surface of the steel plate is completely removed through repeated spraying and then repeatedly rinsed with clean water.

[0050] The particle size of the stainless steel grit is 30 to 100 meshes (Taylor standard sieve), preferably 50 to 80 meshes, and more preferably 60 to 70 meshes. The smaller the particle size of the steel grit, the smaller and more uniform the surface roughness of the steel plate after shot blasting. The stainless steel grit can be purchased commercially.

[0051] The weight ratio of stainless steel grit to water is 1:(10-50), preferably 1:(10-30), and more preferably 1:(12-15). Controlling the weight ratio of stainless steel grit to water within the scope of the present invention can make the mixture more fluid in the delivery pipeline and nozzle, and also reduce the processing efficiency and the loss of steel grit due to mutual collision and breakage.

[0052] The rotation speed of the turbine is 1600-3000 rpm, preferably 2500-2800 rpm, the mixture of stainless steel grit and water is pressurized to 1.2-1.6 MPa, and then sprayed on the surface of the steel plate at an angle of 20°-160° between the spray line and the moving direction of the steel plate, and the speed of the steel plate moving forward is 3-20 m / min. Controlling the pressure and spray angle of the mixture within the scope of the present invention can effectively improve the efficiency of removing oxides on the surface of the steel plate and reduce the ineffective collision and loss between the steel grits during the treatment process.

[0053] After the stainless steel grit, oxides and water in the processor are filtered, the grit and water can be reused. Some damaged stainless steel grit that does not meet the particle size requirements are filtered out and then replenished by adding new sand. The water loss due to evaporation is also replenished by adding new water. The oxide can be used as an oxidant and raw material for steelmaking after filtration, precipitation and recovery.

[0054] After the steel plate is processed, it is first observed with the naked eye to see if it shows the metallic luster of the original color of the metal. At the same time, it is wiped with a white soft cotton cloth or a white paper towel with strong adsorption. Whether there is any black-gray or yellow-brown residue on the surface of the cloth and paper and how much residue remains can be used to judge whether the oxide on the steel plate is completely removed. If necessary, samples can also be taken to display the electronic energy spectrum of the steel plate surface for judgment and analysis.

[0055] (5) Purge, bake and oil the treated steel plate

[0056] The steel plates processed by the processor are purged and baked with high-temperature and high-pressure gas to dry out moisture and ensure that the steel plates are dry.

[0057] The dried steel plate passes through an oiler, and anti-rust oil is evenly applied to the upper and lower surfaces of the steel plate by an electrostatic oiler.

[0058] Then cross-cut or rewind for packaging.

[0059] Example

[0060] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0061] Embodiment 1

[0062] Remove surface oxides from 510L hot-rolled steel coils for automobile beams with specifications of 8.0×1840×C mm to achieve high surface requirements

[0063] (1) Smelting

[0064] After smelting in a top and bottom double-blown converter, the chemical composition (weight percentage, wt%) of the converter steel liquid is: C: 0.07%; Si: 0.10%; Mn: 1.35%; P: 0.012%; S: 0.006%; Nb: 0.020%; Al: 0.026%; Cr: 0.02%; Ni: 0.008%; Mo: 0.001%; ​​B: 0.0001%, and the remainder is iron and unavoidable impurities.

[0065] (2) Rolling

[0066] The continuous casting machine slab is heated in a walking beam heating furnace at a temperature of 1242°C for 185 minutes to ensure that the slab is burned through and the alloy elements are fully dissolved, but to prevent overburning, overheating, and excessively thick oxide scale produced by the furnace.

[0067] The water pressure for rough rolling descaling is 18Mpa and the descaling temperature is 1190℃.

[0068] Before finishing rolling, descaling water is normally added to ensure 19Mpa. The starting temperature of finishing rolling is controlled at 1055℃. The purpose is to appropriately adjust the rolling speed (speed reduction). The finishing rolling speed is controlled at 5.5m / s to ensure the residence time of the steel plate in the high temperature zone and to ensure a certain thickness of the oxide film.

[0069] The final rolling temperature is controlled at 880°C to ensure that the FeO phase ratio in the oxide film reaches more than 50%.

[0070] The coiling temperature is controlled at 585°C to avoid phase change of FeO, while also considering the effect of coiling temperature on the properties of the steel plate.

[0071] (3) Unwinding and straightening

[0072] The process packaging tape of 510L hot-rolled steel coil for automobile beam is removed, the coil is uncoiled by the coiler, the coil head (tongue part) is cut off, and the plate shape is straightened by a 17-roll straightening machine.

[0073] (4) Removal of oxides from steel plate surface

[0074] Processor operation steps:

[0075] The steel coil enters the surface processor, where the stainless steel grit and water are mixed at a ratio of 1:12, and the stainless steel grit is 60 mesh. The mixture is turbocharged and sprayed on the steel plate surface at a 45° angle to remove the oxides on the steel plate surface, and then rinsed with clean water. The turbine rotation speed is set to 2500 rpm, the steel belt speed is 15m / min, and the steel plate surface roughness Ra is 1.1.

[0076] After the steel plate comes out of the processor, it shows metallic luster when observed with the naked eye. It is wiped with a white paper towel with strong absorbency and no residue is left.

[0077] (5) Drying and oiling

[0078] Drying and oiling operation steps:

[0079] The steel plate is fully dried to remove moisture from the upper and lower surfaces of the steel plate under high temperature and high pressure gas.

[0080] The electrostatic oiler is set to the light oiling gear to spray anti-rust oil, and the oiling is required to be uniform.

[0081] (6) Cross-cut or re-roll packaging

[0082] Rewinding packaging steps:

[0083] The tail of the steel coil is cut off before entering the straightening machine, and the steel plate is re-coiled by the coiler after the processing is completed.

[0084] The steel coils are packed according to waterproof requirements.

[0085] Embodiment 2

[0086] Remove surface oxides from 700L hot-rolled steel coils for automobile beams with specifications of 5.5×1560×C mm to achieve high surface requirements

[0087] (1) Smelting

[0088] After smelting in a top and bottom combined blowing converter, the chemical composition (weight percentage, wt%) of the converter steel liquid is: C: 0.06%; Si: 0.08%; Mn: 1.73%; P: 0.011%; S: 0.004%; Nb: 0.065%; Ti: 0.11%; Al: 0.032%; Cr: 0.01%; Ni: 0.006%; Mo: 0.002%; B: 0.0001%, and the remainder is iron and unavoidable impurities.

[0089] (2) Rolling

[0090] The continuous casting machine slab is heated in a walking beam heating furnace at a temperature of 1265°C for 191 minutes to ensure that the slab is burned through and the alloy elements are fully dissolved, but to prevent overburning, overheating, and excessive thickness of furnace oxide scale.

[0091] The water pressure for rough rolling descaling is 18Mpa and the descaling temperature is 1190℃.

[0092] Before finishing rolling, descaling water is normally added to ensure 20Mpa. The starting temperature of finishing rolling is controlled at 1060℃ to create conditions for adjusting the speed. The finishing rolling speed is controlled at 5.1m / s to ensure the steel plate stays in the high temperature zone and ensure a certain thickness of the oxide film.

[0093] The final rolling temperature is controlled at 860°C to ensure that the FeO phase ratio in the oxide film reaches more than 50%.

[0094] The coiling temperature is controlled at 586°C to avoid phase change of FeO, while also considering the effect of coiling temperature on the properties of the steel plate.

[0095] (3) Unwinding and straightening

[0096] The hot-rolled steel plate is removed from the process packaging tape, loaded, and straightened on a 17-roll straightening machine.

[0097] (4) Removal of oxides from steel plate surface

[0098] Processor operation steps:

[0099] The steel coil enters the surface processor, where the stainless steel grit and water are mixed at a ratio of 1:15, and the stainless steel grit is 70 mesh. The mixture is turbocharged and sprayed on the steel plate surface at a 40° angle to remove the oxides on the steel plate surface, and then rinsed with clean water. The turbine rotation speed is set to 2800 rpm, the steel belt speed is 10m / min, and the steel plate surface roughness Ra is 1.0.

[0100] After the steel plate comes out of the processor, it shows metallic luster when observed with the naked eye. It is wiped with a white paper towel with strong absorbency and no residue is left.

[0101] (5) Drying and oiling

[0102] Drying and oiling operation steps:

[0103] The steel plate is fully dried to remove moisture from the upper and lower surfaces of the steel plate under high temperature and high pressure gas.

[0104] The electrostatic oiler is set to the heavy oiling gear to spray anti-rust oil, and the oiling is required to be uniform.

[0105] (6) Cross-cut or re-roll packaging

[0106] Cross-cut packaging operation steps:

[0107] The steel coils are cut to the specified length and stacked by the cross-cutting and leveling unit.

[0108] The steel coils are packed according to waterproof requirements.

[0109] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other substitutions, modifications, combinations, changes, simplifications, etc. made without departing from the spirit and principles of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A method for surface treatment of hot rolled steel sheet, characterized in that: include: (1) The molten steel obtained by converter smelting is made into slabs; Wherein, the molten steel contains Cr≤0.06%, Ni≤0.05%, Mo≤0.010%, B≤0.0003%, and Si≤0.10%; (2) After heating, rough rolling and finish rolling, the slab is coiled into a steel coil; Among them, the heating temperature is 1180~1270℃, the heating time is 160~200 minutes; the starting temperature of the finishing rolling is 1040~1090℃, the finishing rolling speed is 5~12m / s, the final rolling temperature is 850~900℃; the coiling temperature is 540~620℃; (3) After uncoiling, the steel coil is flattened to obtain a steel plate; (4) The steel plate enters the surface processor for treatment to remove surface oxides; (5) Blow, bake and oil the treated steel plates.

2. The hot rolled steel sheet surface treatment method according to claim 1, characterized in that: In step (1), the molten steel contains Cr≤0.06%, Ni≤0.05%, Mo≤0.003%, B≤0.0003%, and Si≤0.08%.

3. The hot rolled steel sheet surface treatment method according to claim 1, characterized in that: In step (2), the descaling water pressure of the rough rolling is 16~22Mpa, and the descaling temperature is 1180~1200℃.

4. The method for surface treatment of hot rolled steel sheet according to claim 1, characterized in that: In step (4), a mixture of stainless steel grit and water in a weight ratio of 1:(10-50) is sprayed on the surface of the steel plate to remove surface oxides.

5. The method for surface treatment of hot rolled steel sheet according to claim 4, characterized in that: The particle size of the stainless steel grit is 30-100 meshes, and the spraying angle is 20°-160°.

6. The method for surface treatment of hot rolled steel sheet according to claim 1, characterized in that: In step (4), the rotation speed of the turbine of the surface processor is 1600-3000 rpm, and the running speed of the steel plate is 3-20 m / min.