A flexible and efficient production method for controlling the tiger skin on the surface of hot-rolled strip steel

Abstract

The present application belongs to the technical field of hot-rolled strip production, and discloses a production method for flexibly and efficiently controlling the tiger skin on the surface of hot-rolled strip. The process comprises smelting a casting blank, heating the blank, rough rolling, descaling, finish rolling, cooling and coiling. The descaling process uses two groups of headers to descale the intermediate blank. The descaling parameters of the two groups of headers are regulated according to the high-temperature oxide scale peelability coefficient D, so that the occurrence rate of the tiger skin on the surface of the hot-rolled strip is less than or equal to 0.10%. The present application first proposes the high-temperature oxide scale peelability coefficient. The coefficient is used as a key threshold for finish rolling descaling, and corresponding descaling parameters are designed. The surface quality of the hot-rolled strip is ensured, and the descaling cost is greatly reduced, so that the surface quality of the product and the production cost are balanced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hot-rolled strip steel production, and particularly relates to a production method for flexibly and efficiently controlling tiger stripes on the surface of hot-rolled strip steel. BACKGROUND

[0002] With the gradual trend of high strength and thinning of products such as automobile plates and engineering machinery steels, alloy elements such as Si, Cr and Ni are generally added in the composition of the slab of such high-strength steel products, so as to facilitate the improvement of the strength, plasticity and toughness of the products, and meanwhile reduce the manufacturing cost. However, with the addition of such alloy elements, the surface of the strip steel will appear typical tiger stripe surface defects in the hot-rolling production process. The tiger stripe defects have become the key quality defects that users strongly complain about in recent years. The existence of the tiger stripe defects seriously affects the surface quality of the steel plate. After shot blasting, pickling, electrophoresis and painting, the surface still has marks, color difference is formed, and more and more users complain about the tiger stripes on the surface of the steel plate, and even raise quality disputes.

[0003] It is considered that the tiger stripe defects are essentially the residual scale that is not removed clean on the surface of the strip steel before the finishing rolling in the hot-rolling process, and the uneven thickness of the residual scale is pressed into defects in the rolling process. For this reason, the prior art proposes to upgrade the descaling system by using super-high pressure descaling, which can improve the tiger stripe defects to a certain extent. However, the super-high pressure descaling also has certain problems in the use process. On the one hand, the super-high pressure will cause the descaling manifold to vibrate greatly, the nozzle to wear fast, the replacement cycle to be short, and the power consumption of the descaling to increase significantly than the normal descaling, which seriously increases the maintenance and use cost of the equipment. On the other hand, the water consumption of the descaling is increased, which causes the slab temperature to drop greatly, and the slab heating temperature needs to be increased or the main motor power of the rolling mill needs to be increased, which further increases the production cost. Therefore, without considering the composition and rolling process, merely increasing the descaling pressure cannot completely remove the scale on the surface of the strip steel, is not economical and energy-saving, and cannot achieve good results. SUMMARY

[0004] The present application solves the technical problems existing in the prior art, and provides a production method for flexibly and efficiently controlling the tiger stripes on the surface of hot-rolled strip steel. The descaling parameters are flexibly controlled, the surface quality of the hot-rolled strip steel is ensured, the descaling cost is greatly reduced, and the balance between the surface quality of the product and the production cost is achieved.

[0005] To solve the technical problems of the present application, the present application provides a production method for flexibly and efficiently controlling the tiger stripes on the surface of hot-rolled strip steel. The process includes smelting a slab, heating the slab, rough rolling, descaling, finishing rolling and cooling and coiling.

[0006] In the scheme, the descaling process adopts two groups of headers to descale the intermediate blank, each group of headers includes an upper header above the upper surface of the intermediate blank and a lower header below the lower surface of the intermediate blank, and the two groups of headers are opened at the same time to spray water on the upper and lower surfaces of the intermediate blank for descaling.

[0007] Further, the two groups of headers are arranged in parallel along the length direction of the intermediate blank, the upper header and the lower header of each group of headers are horizontally arranged and symmetrically distributed along the intermediate blank, and the water spraying area of each header covers the entire upper surface or lower surface of the intermediate blank.

[0008] In the scheme, the descaling temperature of the intermediate blank is 1050-1100℃.

[0009] In the scheme, the descaling parameters of the two groups of headers are adjusted according to the high-temperature oxide scale peelability coefficient D, and the calculation formula of the high-temperature oxide scale peelability coefficient D is:

[0010] D = Si / 0.15 + Cr / 0.2 + Ni / 0.1 - Cu / 0.25 - P / 0.030 - T / 1070

[0011] In the formula, Si, Cr, Ni, Cu and P are the mass percentages of Si, Cr, Ni, Cu and P in the steel, respectively, and the unit is %; T is the descaling temperature, and the unit is ℃.

[0012] Further, when D≤2.5, the pressure of the first group of headers is 250-280bar, and the pressure of the second group of headers is 160-180bar; when 2.5

[0013] Further, when D≤2.5, the total flow of the upper and lower headers of the first group of headers is 210-220m 3 / h, and the total flow of the upper and lower headers of the second group of headers is 260-310m 3 / h; when 2.5 3 / h, and the total flow of the upper and lower headers of the second group of headers is 290-300m 3 / h; when D>5, the total flow of the upper and lower headers of the first group of headers is 230-250m 3 / h, and the total flow of the upper and lower headers of the second group of headers is 270-300m 3 / h.

[0014] Further, when D≤2.5, the surface temperature drop of the intermediate blank after descaling is 10-20℃; when 2.5

[0015] In the above scheme, the chemical composition of the hot-rolled strip steel is as follows in terms of mass percentage: C: 0.03-0.30%, Si: 0.05-1.2%, Mn: 0.5-1.80%, P: 0.01-0.045%, S: 0.001-0.005%, Cr: 0.05-0.50%, Ni: 0.01-0.1%, Cu: 0.02-0.30%, N: 0.0035-0.0045%, and the rest is iron and inevitable inclusions.

[0016] In the above scheme, the discharge temperature of the heated billet is 1200-1310℃.

[0017] In the above scheme, the final rolling temperature of the rough rolling is 1070-1120℃.

[0018] In the above scheme, the occurrence rate of the tiger skin pattern on the surface of the hot-rolled strip steel is ≤0.10%.

[0019] The technical concept of the present application is:

[0020] The factors affecting the tiger skin pattern defect on the surface of the hot-rolled strip steel include the steel composition, the rolling process and the descaling process parameters. The three factors influence and restrict each other.

[0021] Si element produces Fe2SiO4 under high temperature conditions, which is in liquid state above 1173℃. When the temperature is lower than 1173℃, the liquid Fe2SiO4 solidifies on the grain boundary of the oxide scale, pinning the scale, making the scale difficult to be completely removed, and forming the tiger skin pattern defect. When Si>0.15%, the occurrence probability of the tiger skin pattern defect increases.

[0022] Cr element forms Fe2CrO4 under high temperature, which is complete and dense, making the scale on the surface of the strip thin and difficult to be completely removed. When Cr>0.2%, the occurrence probability of the tiger skin pattern defect increases.

[0023] Ni element forms internal oxidation on the matrix side, making the interface between the scale and the matrix form a mountain shape, deteriorating the interface between the scale and the matrix, and making the scale difficult to be completely removed. When Ni>0.1%, the occurrence probability of the tiger skin pattern defect increases.

[0024] Cu element is easy to be enriched at the interface between the scale and the matrix, and has a low melting point (1083℃). When the temperature is higher than 1083℃, Cu presents a liquid phase, which is helpful for the removal of the surface oxide scale. When Cu>0.25%, the occurrence probability of the tiger skin pattern defect decreases.

[0025] P element forms low melting point eutectic product at high temperature, which presents liquid state at high temperature, and is beneficial to the removal of iron scale, and when P>0.03%, the probability of tiger skin defect is reduced.

[0026] The descaling temperature T of the strip surface is crucial to the removal of the surface iron scale, and when the temperature is higher than 1070 DEG C, the occurrence rate of the surface tiger skin defect is reduced.

[0027] Therefore, in combination with the key process parameters affecting the surface tiger skin, the high-temperature iron scale peelability coefficient D is first proposed, and when D≤2.5, it indicates that the high-temperature iron scale on the surface of the steel can be peeled off well, and is easy to remove, and is not prone to form the tiger skin defect; when 2.5

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] 1) The present application is directed to the problem that the hot-rolled strip surface is prone to have tiger skin, and in combination with the design features of the steel and the rolling process parameters, the high-temperature iron scale peelability coefficient is first proposed, the calculation method of the coefficient is provided, and the coefficient is taken as the key threshold of the finishing descaling, and the corresponding descaling parameters are designed to realize that the surface iron scale of the strip can be completely removed, the occurrence rate of the tiger skin defect is reduced, the service life of the descaling equipment is prolonged, the production cost of the descaling process is effectively reduced, flexible and efficient stable control production is realized, and the balance between the product surface quality and the production cost is achieved.

[0030] 2) The present application has strong universality, and can be basically applied to all steel grades in hot rolling production, and is flexible and efficient, low in cost, and can be widely applied in hot rolling production line. According to the design of the present application, the proportion of steel grades requiring super-high pressure descaling is only about 10%, which avoids the overuse of super-high pressure, and reduces the wear and tear of the descaling equipment and the energy consumption. DETAILED DESCRIPTION

[0031] In order to better understand the present application, the content of the present application is further illustrated below in combination with examples, but the content of the present application is not limited to the following examples.

[0032] Examples 1-10

[0033] The chemical composition and the weight percentage content of the hot-rolled strip in examples 1-10 are shown in table 1.

[0034] Table 1 Chemical composition of hot-rolled strip steel of each embodiment of the present application

[0035]

[0036] The production method for flexibly and efficiently controlling the tiger stripes on the surface of the hot-rolled strip steel in Examples 1-10 is as follows:

[0037] 1) Smelting and casting a billet, after smelting the molten steel, the billet is cast;

[0038] 2) Heating the billet, the billet enters the heating furnace, and after heating, it is discharged from the furnace at a temperature of 1200-1310℃;

[0039] 3) Rough rolling, the heated billet is rough-rolled at a final rolling temperature of 1070-1120℃ to form an intermediate billet;

[0040] 4) Descaling, two groups of headers are arranged in parallel along the length of the intermediate billet, each group of headers includes an upper header above the upper surface of the intermediate billet and a lower header below the lower surface of the intermediate billet, the upper and lower headers are horizontally arranged and symmetrically distributed along the intermediate billet, the water spraying area of each header covers the entire upper or lower surface of the intermediate billet, both groups of headers are opened at the same time to spray water on the upper and lower surfaces of the intermediate billet for descaling, and the descaling parameters are adjusted according to the high-temperature iron oxide scale peeling coefficient D;

[0041] 5) Finish rolling, the descaled intermediate billet is finish-rolled to obtain a strip steel pre-product;

[0042] 6) Cooling, the strip steel pre-product is cooled and coiled to obtain a hot-rolled strip steel.

[0043] Table 2 Key parameters of each embodiment of the present application

[0044]

[0045] As can be seen from the above embodiments, by using the production method of the present application, the descaling parameters are flexibly adjusted by calculating the high-temperature iron oxide scale peeling coefficient D, while ensuring the surface quality of the hot-rolled strip steel, the overuse of ultra-high pressure descaling is avoided, the wear and tear of the descaling equipment and the energy consumption are reduced, and the balance between the surface quality of the product and the production cost is achieved.

[0046] The above embodiments are merely examples for clear illustration, and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art, and here, all the embodiments do not need to be exhausted, and therefore the obvious changes or variations still fall within the protection scope of the present application.

Claims

1. A production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel, the process comprising smelting a billet → heating the billet → rough rolling → descaling → finish rolling → cooling and coiling, characterized in that, The chemical composition of the hot-rolled strip steel, by mass percentage, is as follows: C: 0.03~0.30%, Si: 0.05~1.2%, Mn: 0.5~1.80%, P: 0.01~0.045%, S: 0.001~0.005%, Cr: 0.05~0.50%, Ni: 0.01~0.1%, Cu: 0.02~0.30%, N: 0.0035~0.0045%, with the remainder being iron and unavoidable inclusions; The descaling process uses two sets of manifolds to descale the intermediate billet. Each set of manifolds includes an upper manifold located above the upper surface of the intermediate billet and a lower manifold located below the lower surface. Both sets of manifolds are opened simultaneously to spray water onto the upper and lower surfaces of the intermediate billet to descale it. The descaling pressure is adjusted according to the high-temperature iron oxide scale peelability coefficient D. The formula for calculating D is: D=Si / 0.15+Cr / 0.2+Ni / 0.1-Cu / 0.25-P / 0.030-T / 1070 In the formula, Si, Cr, Ni, Cu, and P are the mass percentages of Si, Cr, Ni, Cu, and P in the steel, respectively, in percentages (%). T is the descaling temperature, in °C. When D≤2.5, the pressure of the first set of manifolds is 250~280 bar; when 2.5<D≤5, the pressure of the first set of manifolds is 280~350 bar; when D>5, the pressure of the first set of manifolds is 350~380 bar; the pressure of the second set of manifolds is controlled at 160~180 bar.

2. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, When D≤2.5, the total flow rate of the first group of manifolds is 210~220 m³ / h. 3 / h, the total flow rate of the second group of manifolds is 260~310 m³ / h. 3 / h; When 2.5 < D ≤ 5, the total flow rate of the first group of manifolds is 220~230 m³ / h. 3 / h, the total flow rate of the second group of manifolds is 290~300 m³ / h. 3 / h; When D>5, the total flow rate of the first group of manifolds is 230~250 m³ / h. 3 / h, the total flow rate of the second group of manifolds is 270~300 m³ / h. 3 / h.

3. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, The descaling temperature of the intermediate billet is 1050~1100 ℃.

4. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, When D≤2.5, the surface temperature drop of the intermediate billet after descaling is 10~20 ℃; when 2.5<D≤5, the surface temperature drop of the intermediate billet after descaling is 15~25 ℃; when D>5, the surface temperature drop of the intermediate strip billet after descaling is 20~30 ℃.

5. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, The two sets of manifolds are arranged in parallel front and back along the length of the intermediate blank. The upper and lower manifolds of each set are arranged horizontally and symmetrically distributed along the intermediate blank. The water spray area of ​​each manifold covers the entire upper or lower surface of the intermediate blank.

6. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, The furnace exit temperature of the heated steel billet is 1200~1310 ℃.

7. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, The final rolling temperature of the roughing mill is 1070~1120 ℃.

8. The production method for controlling the tiger-skin pattern on the surface of hot-rolled strip steel according to claim 1, characterized in that, The occurrence rate of tiger-skin pattern on the surface of the hot-rolled strip is ≤0.10%.

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