Method for producing 500MPa-grade high-strength checkered plate based on conventional hot rolling unit

Abstract

The invention relates to the technical field of hot-rolled plate strip production, in particular to a method for producing a 500MPa-grade high-strength checkered plate based on a conventional hot rolling unit. The checkered plate has the chemical component requirements that the carbon content is 0.06-0.12%; the content of manganese is 0.8%-1.5%; the content of niobium is 0.02%-0.07%; the content of titanium is 0.02%-0.06%; the copper content is 0.2%-0.5%; the thickness of a finished product is larger than or equal to 2.0 mm and smaller than or equal to 4.0 mm, and the thickness of a rough rolling intermediate billet is 40-44 mm The thickness of a finished product is larger than 4.0 mm, and the thickness of a rough rolling intermediate billet is 45-50 mm; the finished product thickness is larger than or equal to 2.0 mm and smaller than or equal to 3.0 mm, and the reduction rate of a finish rolling end rack is larger than or equal to The finished product thickness is larger than 3.0 mm and smaller than or equal to 6.0 mm, and the finish rolling end rack reduction rate is larger than or equal to 14%; the thickness of a finished product is larger than 6.0 mm, and the reduction rate of a finish rolling end rack is larger than 13%; on the premise that the reduction rate of the last rack is guaranteed, the reduction rates of the other racks are distributed according to equal-proportion convexity; and the last group of laminar cooling upper collecting pipe is sealed by cooling water, meanwhile, the last group of laminar cooling reverse spraying water is forcibly input, the maximum rolling speed of the finishing mill group is controlled not to exceed 12.5 m / s, and it is guaranteed that the temperature of laminar cooling outlet strip steel meets the coiling temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-rolled plate and strip production, and in particular relates to a method for producing 500MPa-grade high-strength checkered plates based on a conventional hot rolling mill. Background Art

[0002] Steel strips with patterns on their surface are called checkered plates. Hot-rolled checkered plates are widely used in transportation, construction, interior design, shipbuilding, and other fields due to their strength, anti-slip properties, and attractive appearance.

[0003] At present, the hot-rolled checkered plates supplied domestically usually use plain carbon and low-carbon steel (such as Q235B and SPHC), with a yield strength of about 250MPa, and the requirements for mechanical properties are not high. For checkered plates with a yield strength of 500MPa, in order to ensure that the pattern height of the checkered plate meets the requirements, a greater reduction load must be applied to the finishing mill, which may cause the mill to have the risk of overcurrent shutdown. At the same time, the greater load makes it more difficult to control the strip shape, and it is easy to have a wave shape or a bend, which cannot meet the requirements of the finished product. In order to ensure the pattern height, high-strength checkered plates require the final stand to apply a greater reduction rate. There is a process contradiction between the plate shape control and the coil shape control under the condition of a large reduction rate, which increases the production difficulty of high-strength checkered plates. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing 500MPa grade high-strength checkered plates based on a conventional hot rolling mill, thereby achieving stable production of high-strength checkered plates.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A method for producing 500MPa grade high-strength checkered plate based on a conventional hot rolling mill, the production process includes slab heating, rolling, cooling, and coiling, wherein:

[0007] 1) Chemical composition requirements of patterned plates: carbon content 0.06% to 0.12%; manganese content 0.8% to 1.5%; niobium content 0.02% to 0.07%; titanium content 0.02% to 0.06%; copper content 0.2% to 0.5%;

[0008] 2) Slab heating:

[0009] 2.0mm≤finished product thickness≤4.0mm, slab heating temperature is 1230~1250℃;

[0010] Finished product thickness>4.0mm, slab heating temperature is 1210~1240℃;

[0011] 3) Rolling:

[0012] ①Rough rolling: The outlet temperature is 1040 - 1070°C;

[0013] For the rough rolling intermediate slab thickness: when 2.0mm ≤ finished product thickness ≤ 4.0mm, the rough rolling intermediate slab thickness is 40 - 44mm; when the finished product thickness > 4.0mm, the rough rolling intermediate slab thickness is 45 - 50mm;

[0014] ②Finish rolling: The inlet temperature is 1020 - 1040°C, and the finishing temperature is 870 - 900°C;

[0015] When 2.0mm ≤ finished product thickness ≤ 3.0mm, the reduction rate of the last finishing stand is ≥ 16.3%;

[0016] When 3.0mm < finished product thickness ≤ 6.0mm, the reduction rate of the last finishing stand is ≥ 14%;

[0017] When the finished product thickness > 6.0mm, the reduction rate of the last finishing stand > 13%;

[0018] On the premise of ensuring the reduction rate of the last stand, the reduction rates of the other stands are distributed according to equal - proportion convexity;

[0019] ③The shifting roll step length of finish rolling is set at the maximum shifting roll step length - 10mm to the maximum shifting roll step length - 20mm. At the same time, it is required that the engraved pattern length of the work roll of the last finishing stand is more than 240mm longer than the width of the finished product;

[0020] 4) Cooling: The cooling water of the last set of upper headers in laminar cooling is closed, and at the same time, the last set of reverse spray water in laminar cooling is forced to be input. Control the maximum rolling speed of the finishing mill group not to exceed 12.5m / s to ensure that the strip temperature at the outlet of laminar cooling meets the coiling temperature.

[0021] 5) Coiling: The pressure of the coiling pinch roll is 4000 - 8000kgf. Before the tail of the strip enters the coiler, the No. 1 coiling roll is lowered in advance to control the coil shape of the high - strength patterned plate.

[0022] The thickness of the slab in step 2) is 220 - 230mm.

[0023] Compared with the existing technology, the beneficial effects of the present invention are:

[0024] In the composition design of the present invention, solid - solution strengthening of carbon, silicon, and manganese and fine - grain strengthening of niobium and titanium achieve a high strength of 500Mpa yield strength level. To meet the requirements of high - strength patterns in railway and marine environments, copper element is added. Copper can form a dense copper oxide film on the steel surface to improve the atmospheric corrosion resistance.

[0025] To meet the requirements for the pattern height, certain requirements are first imposed on the reduction ratio of the last finishing stand, i.e., the F7 stand, and at the same time, the process requirements for shape control are taken into account, and parameters such as load distribution and intermediate slab thickness are designed. To ensure the high-strength coiling shape and strength requirements, the laminar cooling mode, coiling pressure, etc. are set.

[0026] By using the method of the present invention, batch production of high-strength pattern plates of 500 MPa grade can be achieved, and the pattern height, shape, and coiling temperature all meet the requirements. After using this method on a conventional hot rolling production line and fine-tuning the process parameters according to their respective production lines, production can be put into operation. Specific Embodiments

[0027] It should be noted that unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The mention of "embodiment" in this text means that the specific features, structures, or characteristics described in connection with the embodiment can be included in at least one embodiment of this application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0028] A method for producing high-strength pattern plates of 500 MPa grade based on a conventional hot rolling mill, the production process includes slab heating, rolling, cooling, and coiling, wherein:

[0029] 1) Chemical composition requirements for the pattern plate: carbon content 0.06% - 0.12%; manganese content 0.8% - 1.5%; niobium content 0.02% - 0.07%; titanium content 0.02% - 0.06%; copper content 0.2% - 0.5%; because the tensile test of the pattern plate is affected by the pattern to a certain extent, in order to ensure high strength, mainly carbon-silicon-manganese solid solution strengthening and niobium-titanium fine grain strengthening are adopted to achieve a yield strength of 500 Mpa level. Copper can form a dense copper oxide film on the steel surface to improve the anti-atmospheric corrosion ability.

[0030] 2) Slab heating:

[0031] When 2.0 mm ≤ finished product thickness ≤ 4.0 mm, the slab heating temperature is 1230 - 1250 °C; when the finished product thickness > 4.0 mm, the slab heating temperature is 1210 - 1240 °C; during rough rolling and finish rolling of high-strength steel, the load is relatively large. Coupled with the requirement of embossing patterns, the load is even greater than that of low-carbon pattern plates and high-strength steel. The tapping temperature should be set appropriately. If the temperature is too high, the austenite grains will be coarse, and the grains of the final finished product will be large, affecting the strength of the finished product. If the temperature is low, the rolling load will be large, and there is a risk of overcurrent in rough rolling and finish rolling.

[0032] 3) Rolling:

[0033] ① Rough rolling: The outlet temperature is 1040 - 1070 °C. For 2.0 mm ≤ finished product thickness ≤ 4.0 mm, the thickness of the rough rolling intermediate billet is 40 - 44 mm; for the finished product thickness > 4.0 mm, the thickness of the rough rolling intermediate billet is 45 - 50 mm. The design of the intermediate billet thickness should take into account the load distribution between rough rolling and finish rolling. If the intermediate billet thickness is designed to be large, the bearing pressure ratio of the F1 - F7 stands for high-strength steel is greater, especially the load of the last stand F7, and there is a very high risk of motor overcurrent tripping in production. If the intermediate billet thickness is designed to be small, the cooling rate of the strip in the finish rolling area is faster, and the load may not decrease but increase instead.

[0034] ② Finish rolling: The inlet temperature is 1020 - 1040 °C, and the final rolling temperature is 870 - 900 °C; because embossing patterns on the last stand F7 increases the single-pass load, if the temperature is too low, a large load is likely to induce the risk of overcurrent.

[0035] When 2.0 mm ≤ finished product thickness ≤ 3.0 mm, the reduction ratio of the last finish rolling stand ≥ 16.3%; when 3.0 mm < finished product thickness ≤ 6.0 mm, the reduction ratio of the last finish rolling stand ≥ 14%; when the finished product thickness > 6.0 mm, the reduction ratio of the last finish rolling stand > 13%; according to the ideal theoretical calculation formula for controlling the pattern height in rolling, H - h ≥ 20%h (where H represents the inlet thickness of the last stand F7 and h represents the outlet thickness of the last stand F7), the single-pass reduction ratio needs to reach the requirement of 17%. Under the condition of the same reduction ratio, the load of high-strength pattern plates is greater and the springback is relatively large. Therefore, adjust the single-pass reduction ratio of the last stand to meet the dual needs of pattern height and rolling mill load. On the premise of ensuring the reduction ratio of the last stand, the reduction ratios of the other stands are distributed according to equal proportion convexity to ensure the shape of the finished strip steel.

[0036] ③ The shifting roll step length of finish rolling is set at the maximum shifting roll step length - 10 mm to the maximum shifting roll step length - 20 mm. The shifting roll step length is close to the maximum step length to make the rolls wear evenly. To reduce the influence of continuous rolling wear, pattern plates are produced in the early stage of the service life of work rolls and backup rolls. At the same time, it is required that the embossed pattern length of the work roll of the last finish rolling stand is more than 240 mm longer than the finished product width to ensure the pattern quality of the finished product.

[0037] 4) Cooling:

[0038] The cooling water of the last upper header of the laminar cooling is closed, and at the same time, the reverse spray water of the last group of the laminar cooling is forced to be input. To prevent water from accumulating on the upper surface of the pattern plate, and at the same time, control the maximum rolling speed of the finishing mill not to exceed 12.5 m / s to ensure that the strip temperature at the outlet of the laminar cooling meets the coiling temperature.

[0039] 5) Coiling:

[0040] The pressure of the coiling pinch roll is 4000 - 8000 kgf. Before the tail of the strip enters the coiler, the No. 1 coiling helper roll is lowered in advance to control the coiling shape of the high-strength pattern plate and prevent poor coiling.

[0041] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0042] Embodiment:

[0043] The hot rolling 1580 production line is equipped with two roughing mills, seven finishing mills, 15 groups of laminar cooling, and three coilers. It produces high-strength weather-resistant pattern plates of 500 MPa grade. The chemical composition of the pattern plate is shown in Table 1;

[0044] Table 1: Chemical composition %

[0045] C Mn Ni Ti Cu P Example 1 0.08 1.0 0.04 0.03 0.35 0.01 Example 2 0.06 1.2 0.07 0.05 0.25 0.012 Example 3 0.09 1.5 0.03 0.06 0.50 0.015 Example 4 0.10 0.9 0.05 0.04 0.42 0.01 Example 5 0.12 0.8 0.02 0.02 0.28 0.008

[0046] The production process is shown in Table 2;

[0047] Table 2:

[0048]

[0049]

[0050] In Embodiments 1 - 5, the shifting step length of the finishing mill is 100 mm (the maximum step length is 120 mm), the cooling water of all the upper headers of the 15th group of the laminar cooling is closed, the reverse spray water after the 15th group of the laminar cooling is forced to be input, and the maximum rolling speed of F7 is 12.3 m / s. Before the tail of the strip enters the coiler, the No. 1 coiling helper roll is lowered in advance to control the coiling shape of the high-strength pattern plate.

[0051] The performance of the finished pattern plate is shown in Table 3:

[0052] Table 3:

[0053]

[0054]

[0055] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for producing 500MPa grade high-strength patterned steel plates based on a conventional hot rolling mill, characterized in that, The production process includes slab heating, rolling, cooling, and coiling, where: 1) Chemical composition requirements for the pattern plate: carbon content 0.06% - 0.12%; manganese content 0.8% - 1.5%; niobium content 0.02% - 0.07%; titanium content 0.02% - 0.06%; copper content 0.2% - 0.5%; 2) Slab heating: When 2.0mm ≤ finished product thickness ≤ 4.0mm, the slab heating temperature is 1230 - 1250°C; When the finished product thickness > 4.0mm, the slab heating temperature is 1210 - 1240°C; 3) Rolling: ① Rough rolling: outlet temperature 1040 - 1070°C; Thickness of the rough rolling intermediate slab: when 2.0mm ≤ finished product thickness ≤ 4.0mm, the thickness of the rough rolling intermediate slab is 40 - 44mm; when the finished product thickness > 4.0mm, the thickness of the rough rolling intermediate slab is 45 - 50mm; ② Finish rolling: inlet temperature 1020 - 1040°C, final rolling temperature 870 - 900°C; When 2.0mm ≤ finished product thickness ≤ 3.0mm, the reduction rate of the last finishing stand is ≥ 16.3%; When 3.0mm < finished product thickness ≤ 6.0mm, the reduction rate of the last finishing stand is ≥ 14%; When the finished product thickness > 6.0mm, the reduction rate of the last finishing stand > 13%; On the premise of ensuring the reduction rate of the last stand, the reduction rates of the other stands are distributed according to equal - proportion convexity; ③ The shifting roll step length of finish rolling is set at the shifting roll maximum step length - 10mm to the shifting roll maximum step length - 20mm. At the same time, it is required that the engraved pattern length of the work roll of the last finishing stand is more than 240mm longer than the finished product width; 4) Cooling: The cooling water of the last set of upper headers in laminar cooling is closed, and at the same time, the last set of reverse spray water in laminar cooling is forced to be put in. Control the maximum rolling speed of the finishing mill group not to exceed 12.5m / s to ensure that the strip temperature at the outlet of laminar cooling meets the coiling temperature. 5) Coiling: The pressure of the coiling pinch roll is 4000 - 8000kgf. Before the strip tail enters the coiler, the No. 1 coiling helper roll is lowered in advance to control the coil shape of the high - strength pattern plate.

2. A method for producing 500 MPa grade high-strength patterned plates based on a conventional hot rolling mill set according to claim 1, characterized in that, The thickness of the slab described in step 2) is 220 - 230mm.

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