Thick-gauge hot-dip galvanized steel and production method thereof

Abstract

The invention provides thick-gauge hot-dip galvanized steel and a production method thereof. The production method comprises the following steps: continuously casting molten steel to obtain a casting blank; sequentially carrying out hot rolling on the casting blank to obtain a hot-rolled coil, and controlling the convexity of the hot-rolled coil to be 10-30 microns; the hot-rolled coil is subjected to cold rolling to obtain a cold hard coil, and the convexity of the cold hard coil is 5-15 microns; the cold hard coil is sequentially subjected to high-temperature annealing treatment, hot galvanizing treatment and finishing rolling treatment, the thick-specification hot-dip galvanized steel is obtained, and the thickness of the thick-specification hot-dip galvanized steel is not smaller than 1.5 mm. According to the method, the defect of non-finishing edges of the edges is overcome, meanwhile, the problem of deterioration of actual performance of materials is avoided, gain is remarkable, and the method is worthy of popularization.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-dip galvanizing, and in particular relates to thick-gauge hot-dip galvanized steel and a production method thereof. Background Art

[0002] Hot-dip galvanized products are metal products that have been treated by hot-dip galvanizing. They have excellent corrosion resistance and decorative properties and are widely used in many fields such as construction, transportation, electricity, and communications. After galvanizing and cooling, hot-dip galvanized products must be subjected to skin-pass rolling to obtain a uniform silver-white luster on the surface. However, due to the thinning area on the edge of the strip, the edge area is not easily rolled to form non-skin-pass defects during the skin-pass rolling process.

[0003] Especially for thick galvanized steel (h ≥ 1.5 mm), as the thickness increases, its internal stress distribution and deformation characteristics become more complicated, and it is more likely to produce uneven deformation, making the convexity difficult to control.

[0004] Based on this, it is necessary to provide a thick-gauge hot-dip galvanized steel and a production method thereof to alleviate or solve the above problems. Summary of the invention

[0005] In order to solve the technical problem that thick-gauge galvanized steel is prone to non-smooth edge defects during skin-pass rolling in the above-mentioned common technology, the present invention provides a production method of thick-gauge hot-dip galvanized steel, comprising the steps of:

[0006] Molten steel is continuously cast to obtain ingots;

[0007] The ingot is hot-rolled to obtain a hot-rolled coil, and the convexity of the hot-rolled coil is controlled to be 10 to 30 microns;

[0008] The hot rolled coil is cold rolled to obtain a chilled coil, and the convexity of the chilled coil is 5 to 15 microns;

[0009] The cold hardened coil is sequentially subjected to high temperature annealing treatment, hot dip galvanizing treatment and skin pass rolling treatment to obtain thick specification hot dip galvanized steel, and the thickness of the thick specification hot dip galvanized steel is not less than 1.5 mm.

[0010] Furthermore, the thick gauge hot-dip galvanized steel is interstitial-free steel.

[0011] Furthermore, the reduction rate during the cold rolling process is controlled within a range of 50% to 60%.

[0012] Furthermore, in the high temperature annealing treatment, the annealing temperature is 790-810° C., and the annealing time is 20-30 seconds.

[0013] Furthermore, in the hot-dip galvanizing treatment, the hot-dip galvanizing temperature is 450-460°C; and the strip steel after the hot-dip galvanizing treatment is cooled to a temperature not higher than 40°C.

[0014] Furthermore, in the skin-pass rolling process, the elongation of the skin-pass mill is 1.0%-1.2%, the tension is 20-30KN, and the rolling force is more than 200 tons.

[0015] Furthermore, the skin-pass rolling process adopts negative bending rolling with a bending roll force of -4KN, and the crown of the working roll of the skin-pass mill is controlled within a range of -80 to -60um.

[0016] Furthermore, in the step of subjecting the cold hardened coil to high temperature annealing, hot dip galvanizing and skin pass rolling in sequence to obtain thick specification hot dip galvanized steel, it also includes trimming the strip after the skin pass rolling treatment, and controlling the single side cutting amount in the trimming treatment to be 7 to 10 mm.

[0017] Furthermore, the thickness of the ingot is 230 mm, the thickness of the hot-rolled coil is 3.8 to 5.0 mm, and the thickness of the chilled coil is 1.5 to 2.5 mm.

[0018] The present invention provides a thick-gauge hot-dip galvanized steel produced by any one of the production methods described above.

[0019] Compared with the prior art, the present invention has at least the following advantages:

[0020] The present invention adopts a staged convexity control process for thick hot-dip galvanized steel with a thickness greater than 1.5 mm during hot rolling and cold rolling, accurately controls the convexity transition, and realizes stable control of the edge thinning area of ​​the galvanized substrate (i.e., the strip steel after high-temperature annealing and before hot-dip galvanizing), meeting the requirements of galvanized skin-pass rolling. Specifically, the hot rolling production process controls the convexity of the hot-rolled coil to 10 to 30 microns, and the convexity value of the strip steel is inherited to the cold-hardened coil after cold rolling, and the convexity value of the cold-hardened coil is controlled between 10-20um. The galvanized substrate under this convexity value can be subjected to skin-pass rolling to obtain thick galvanized steel with uniform coloring and no non-skin-passing edge defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0022] Figure 1Schematic diagram of the formation of non-finishing defects on the surface of thick and thick hot-dip galvanized steel in one embodiment of the present invention;

[0023] Figure 2 This is a real picture of the non-smooth edge defects on the surface of medium and thick hot-dip galvanized steel in comparative example 2 of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0026] When numerical ranges are given in the embodiments, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any method, device and material of the prior art similar or equivalent to the method, device and material in the embodiments of the present invention can also be used to implement the present invention.

[0027] Non-smoothness defects exist in the edge thinning area at the end of the strip cross section, and their occurrence is closely related to the convexity of the strip.

[0028] However, the applicant has found that as the thickness increases, the stress distribution and deformation characteristics inside thick gauge galvanized steel become more complex, making it more prone to uneven deformation, resulting in difficult to control convexity, such as Figure 1 As shown in the figure, thick-gauge strip steel tends to have a small end and a large middle in cross section.

[0029] like Figure 2 As shown in the figure, the strip steel with a thickness of 2.0 mm has non-smooth edge defects after skin-pass rolling.

[0030] In order to solve the technical problems faced by the above-mentioned conventional technologies, the present invention provides a method for producing thick-gauge hot-dip galvanized steel, comprising the steps of:

[0031] S1. Molten steel is continuously cast to obtain ingots.

[0032] In some embodiments, the heavy gauge hot dip galvanized steel may be interstitial free steel.

[0033] Exemplarily, the chemical composition of the molten steel may include, by mass fraction: C 0.001% to 0.005%, N ≤ 0.003. Due to the low content of C and N, in combination with a certain amount of Ti and Nb, the C and N atoms in the steel can be fixed into carbides and nitrides, so that there are no interstitial atoms in the steel, and interstitial-free steel is obtained. Interstitial-free steel has deep drawing properties such as low yield point and yield strength ratio, high elongation, high plastic strain ratio, high work hardening index, and is non-aging.

[0034] S2. The ingot is hot-rolled to obtain a hot-rolled coil, the convexity of the hot-rolled working roll is set to 40±5um, and the convexity of the hot-rolled coil is controlled to be 10 to 30 microns.

[0035] In some embodiments, the convexity may be a C40 convexity, and the C40 convexity calculation formula may be: strip center point thickness value - (strip transmission side 40mm thickness value + strip working side 40mm thickness value) / 2.

[0036] S3. The hot rolled coil is cold rolled to obtain a chilled coil, the convexity of the working rolls in the cold rolling process is 20±5um, and a string roll control method is adopted, and the convexity of the chilled coil is 5 to 15 microns.

[0037] In some embodiments, the reduction ratio during the cold rolling process may be controlled within a range of 50% to 60%.

[0038] S4. The cold hardened coil is sequentially subjected to high temperature annealing, hot dip galvanizing and skin pass rolling to obtain thick hot dip galvanized steel, wherein the thickness of the thick hot dip galvanized steel is not less than 1.5 mm.

[0039] In the high temperature annealing treatment, the annealing temperature is 790-810℃ and the annealing time is 20-30s. The purpose of annealing is to eliminate the hardening effect of cold rolling and make the steel plate have excellent plastic forming properties. At the same time, reasonable annealing temperature and annealing time can create conditions for the skin-finishing process, so the annealing temperature is controlled at 790-810℃ and the annealing time is controlled at 20-30s.

[0040] In the hot-dip galvanizing process, the hot-dip galvanizing temperature is 450-460°C. After the hot-dip galvanizing is completed, the temperature of the strip is reduced to below 230°C, and further cooled. When the strip temperature drops below 40°C, the strip is subjected to skin-pass rolling.

[0041] In the skin-pass rolling process, the elongation of the skin-pass mill can be 1.0%-1.2%, the tension can be 20-30KN, and the rolling force can be more than 200 tons. There is no yield platform in interstitial-free atomic steel. The purpose of the skin-pass rolling process is to flatten the slag particles or other uneven points on the surface, so that the surface becomes smooth and flat, and finally obtain a surface with more uniform gloss. The greater the skin-pass elongation, the greater the strength of the product and the worse the product performance. However, the lower the skin-pass elongation, the lower the rolling force, which affects the skin-pass effect and color of the product surface. At the same time, the increase in elongation may also lead to the redistribution of internal stress of the strip and the decrease in surface quality. Therefore, the present invention controls the skin-pass elongation at 1.0%-1.2%. In coordination with the tension control of 20-30KN and the rolling force control of more than 200 tons, a substantial improvement in the uniformity of the strip surface is finally achieved.

[0042] The present invention controls the tension during skin-pass rolling to 20-30KN. The tension and speed during skin-pass rolling also have an important influence on the surface quality of the strip. Excessive tension may cause the strip to be stretched or broken during rolling; while too fast a speed may cause rolling instability and reduced surface quality. For thick-gauge hot-dip galvanized products, due to the thicker material and higher hardness, more precise control of tension and speed is required to avoid the generation of non-skin-pass edges.

[0043] An exemplary rolling force may be 200-350 tons.

[0044] It should also be noted that the present invention controls the rolling force to more than 200 tons. Due to the high thickness specifications, the ideal elongation cannot be achieved if the rolling force is insufficient, and excessive rolling force may cause excessive deformation or cracks on the edge of the strip, thereby forming a non-smooth edge.

[0045] In some embodiments, the skin-pass rolling process may adopt negative bending rolling, with a bending roll force of -4KN, and the crown of the working roll of the skin-pass mill is controlled to be -80 to -60um. Since the thickness reduction area at the edge of the strip cannot be eliminated, there is a difference between the edge rolling effect and the middle rolling effect of the strip under normal skin-passing.

[0046] The use of negative bending rolling can reduce the color difference between the edge and the middle. At the same time, in order to avoid the uneven rolling of the strip edge during the negative bending roll rolling process, negative convexity control is adopted for the skin-pass working roll, and the convexity of the skin-pass working roll is controlled at -80 to -60um, and the bending roll force is -4KN.

[0047] In some embodiments, the strip steel after the skin-pass rolling process may be subjected to edge trimming, and the single-side cutting amount in the edge trimming process is controlled to be 7 to 10 mm, and the edges with different colors are cut off.

[0048] During the skin-pass rolling process, negative bending rolling and high rolling force technology are used to roll the thinner edge areas, reducing the color difference between the edge and the middle. At the same time, the poorly rolled edge areas are cut off in the subsequent process to ensure the consistency of the color of the edge and the middle of the strip.

[0049] In some embodiments, the thickness of the ingot is 230 mm, the thickness of the hot rolled coil is 3.8 to 5.0 mm, and the thickness of the chilled coil is 1.5 to 2.5 mm. The precise linkage between the convexity control process and the thickness control ensures the stability of the rolling process and avoids the problem of deteriorating the actual performance of the material.

[0050] In some embodiments, the thickness of the thick gauge hot dip galvanized steel may be 1.5 mm to 2.5 mm.

[0051] For example, the produced thick gauge hot dip galvanized steel may be oiled and coiled.

[0052] In summary, the present invention provides a thick specification (h≥1.5mm) IF steel plate, which adopts a reasonable convexity control process in hot rolling and cold rolling processes, realizes stable control of the thinning area at the edge of the galvanized substrate, and meets the requirements of galvanized skin-pass rolling;

[0053] The present invention provides a thick specification (h≥1.5mm) IF steel plate, which realizes stable control of the edge finishing quality of the galvanized plate by uniquely controlling the production process of the skin-pass machine;

[0054] The invention provides an IF steel plate with a thick specification (h≥1.5mm), and after the edge of the strip steel is cut off after skin-pass rolling treatment, the edge quality of the strip steel is optimized.

[0055] In order to facilitate those skilled in the art to further understand the present invention, examples are given below:

[0056] Example 1

[0057] The ingot with a thickness of 230 mm is hot rolled to obtain a hot rolled coil, the thickness of the hot rolled coil is 3.6 mm, and the convexity value is 25 um.

[0058] The hot rolled coil is deformed into a chilled coil by a cold rolling reduction rate of 58.3%. The thickness of the chilled coil is 1.5 mm and the convexity value is 9 um.

[0059] The cold hard coil is annealed at an annealing temperature of about 806℃ for 20s, then cooled to 450-460℃ for hot-dip galvanizing. After galvanizing, it is cooled to 223℃, and then continued to cool to 38℃ to enter the skin-pass rolling process. At this time, the crown of the working roll of the skin-pass mill is -60umm, the bending roll force is -4KN, the skin-pass elongation is 1.07%, the tension is 23KN, and the skin-pass rolling force is 218 tons. Under this skin-pass process, the surface of the strip is fully rolled, and finally 7mm is cut off on one side in the trimming process to obtain a 1.5mm thick IF steel plate with excellent edge quality.

[0060] Example 2

[0061] The ingot with a thickness of 230 mm is hot rolled to obtain a hot rolled coil, the thickness of the hot rolled coil is 4 mm, and the convexity value is 20 um.

[0062] The hot rolled coil is deformed by a cold rolling reduction rate of 55% to become a chilled coil. The thickness of the chilled coil is 1.8 mm and the convexity of the chilled coil is 10 um.

[0063] The cold hard coil is annealed at an annealing temperature of about 803℃ for 23s, and then cooled to 450-460℃ for galvanizing. After galvanizing, it is cooled to 215℃, and then continued to cool to 35℃ to enter the skin-pass rolling process. At this time, the crown of the working roll of the skin-pass mill is -60umm, the bending roll force is -4KN, the skin-pass elongation is 1.15%, the tension is 25KN, and the skin-pass rolling force is 216 tons. Under this skin-pass process, the surface of the strip is fully rolled, and finally 8mm is cut off on one side in the trimming process to obtain a 1.8mm thick IF steel plate with excellent edge quality.

[0064] Example 3

[0065] The ingot with a thickness of 230 mm is hot rolled to obtain a hot rolled coil, the hot rolled coil has a thickness of 4.5 mm and a convexity value of 22 um.

[0066] The hot rolled coil is deformed into a chilled coil by a cold rolling reduction rate of 55.6%. The thickness of the chilled coil is 2.0 mm and the convexity of the chilled coil is 12 um.

[0067] The cold hard coil is annealed at an annealing temperature of about 796℃ for 25s, and then cooled to 450-460℃ for hot-dip galvanizing. After hot-dip galvanizing, it is cooled to 225℃, and then continued to cool to 37℃ to enter the skin-pass rolling process. At this time, the crown of the working roll of the skin-pass mill is -60umm, the bending roll force is -4KN, the skin-pass elongation is 1.13%, the tension is 24KN, and the skin-pass rolling force is 224 tons. Under this skin-pass process, the surface of the strip is fully rolled, and finally 7mm is cut off on one side in the trimming process to obtain a 2.0mm thick IF steel plate with excellent edge quality.

[0068] Example 4

[0069] The ingot with a thickness of 230 mm is hot rolled to obtain a hot rolled coil, the thickness of the hot rolled coil is 4.9 mm, and the convexity value is 19 um.

[0070] The hot rolled coil is deformed into a chilled coil by a cold rolling reduction rate of 53.1%. The thickness of the chilled coil is 2.3 mm and the convexity of the chilled coil is 12 um.

[0071] The cold hard coil is annealed at an annealing temperature of about 798℃ for 26s, and then cooled to 450-460℃ for galvanizing. After galvanizing, it is cooled to 232℃, and then continued to cool to 35℃ to enter the skin-pass rolling process. At this time, the crown of the working roll of the skin-pass mill is -80umm, the bending roll force is -4KN, the skin-pass elongation is 1.15%, the tension is 26KN, and the skin-pass rolling force is 219 tons. Under this skin-pass process, the surface of the strip is fully rolled, and finally 9mm is cut off on one side in the trimming process to obtain a 2.3mm thick IF steel plate with excellent edge quality.

[0072] Example 5

[0073] The thickness of the hot rolled coil is 5.0 mm and the convexity value is 21 um.

[0074] The hot rolled coil is deformed into a chilled coil by a cold rolling reduction rate of 51.9%. The thickness of the chilled coil is 2.5 mm and the convexity of the chilled coil is 13 um.

[0075] The cold hard coil is annealed at an annealing temperature of about 795℃ for 28s, then cooled to 450-460℃ for galvanizing, cooled to 235℃ after galvanizing, and then continued to cool to 39℃ to enter the skin-pass rolling process. At this time, the crown of the working roll of the skin-pass mill is -80umm, the bending roll force is -4KN, the skin-pass elongation is 1.14%, the tension is 26KN, and the skin-pass rolling force is 225 tons. Under this skin-pass process, the surface of the strip is fully rolled, and finally 8mm is cut off on one side in the trimming process to obtain a 2.5mm thick IF steel plate with excellent edge quality.

[0076] Analysis example 1

[0077] Comparison of proportional parameters and non-smooth edge effects

[0078]

[0079] Among them, the actual picture of non-smooth edge defects on the surface of medium and thick hot-dip galvanized steel in comparative example 2 is as follows Figure 2 shown.

[0080] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for producing thick-gauge hot-dip galvanized steel, characterized in that: Includes steps: Molten steel is continuously cast to obtain ingots; The ingot is hot-rolled to obtain a hot-rolled coil, and the convexity of the hot-rolled coil is controlled to be 10 to 30 microns; The hot rolled coil is cold rolled to obtain a chilled coil, and the convexity of the chilled coil is 5 to 15 microns; The cold hardened coil is sequentially subjected to high temperature annealing treatment, hot dip galvanizing treatment and skin pass rolling treatment to obtain thick specification hot dip galvanized steel, and the thickness of the thick specification hot dip galvanized steel is not less than 1.5 mm.

2. The method for producing thick-gauge hot-dip galvanized steel according to claim 1, characterized in that: The thick gauge hot dip galvanized steel is interstitial free steel.

3. The method for producing thick-gauge hot-dip galvanized steel according to claim 1, characterized in that: The reduction rate during the cold rolling process is controlled at 50% to 60%.

4. The method for producing thick-gauge hot-dip galvanized steel according to claim 1, characterized in that: In the high temperature annealing treatment, the annealing temperature is 790-810° C. and the annealing time is 20-30 seconds.

5. The method for producing thick-gauge hot-dip galvanized steel according to claim 4, characterized in that: In the hot-dip galvanizing treatment, the hot-dip galvanizing temperature is 450-460°C; the strip steel after the hot-dip galvanizing treatment is cooled to a temperature not higher than 40°C.

6. The method for producing thick gauge hot dip galvanized steel according to claim 5, characterized in that: In the skin-pass rolling process, the elongation of the skin-pass mill is 1.0%-1.2%, the tension is 20-30KN, and the rolling force is more than 200 tons.

7. The method for producing thick-gauge hot-dip galvanized steel according to claim 6, characterized in that: The skin-pass rolling process adopts negative bending rolling with a bending roll force of -4KN, and the crown of the working roll of the skin-pass mill is controlled within -80 to -60um.

8. The method for producing thick-gauge hot-dip galvanized steel according to claim 6, characterized in that: The step of subjecting the cold hardened coil to high temperature annealing, hot dip galvanizing and skin pass rolling in sequence to obtain thick specification hot dip galvanized steel also includes trimming the strip after the skin pass rolling, and controlling the single side cutting amount in the trimming process to be 7 to 10 mm.

9. The method for producing thick gauge hot dip galvanized steel according to claim 1, characterized in that: The thickness of the ingot is 230 mm, the thickness of the hot-rolled coil is 3.8 to 5.0 mm, and the thickness of the chilled coil is 1.5 to 2.5 mm.

10. A thick gauge hot dip galvanized steel, characterized in that: The product is produced by the production method according to any one of claims 1 to 9.

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