Production method of galvanized steel strip with yield strength of 340 MPa grade and tensile strength of 480 MPa grade for building structure

Abstract

The invention discloses a production method of a galvanized steel strip with 340MPa-grade yield strength and 480MPa-grade tensile strength for a building structure, which comprises the following steps: (1) smelting-continuous casting: defining the components of molten steel for a casting machine in percentage by mass; (2) hot rolling; (3) pickling and cold rolling; and (4) continuous hot galvanizing and finishing are conducted, specifically, the soaking temperature ranges from 700 DEG C to 730 DEG C, slow cooling is conducted to 610 DEG C to 650 DEG C, then cooling is conducted to 450 DEG C to 475 DEG C, the temperature in a zinc pot ranges from 450 DEG C to 480 DEG C, the temperature of the top of a top roll cooling tower is smaller than or equal to 250 DEG C, the finishing elongation is 0.6%-1.4%, and the withdrawal and straightening elongation is smaller than or equal to 0.5%. The product provided by the invention has high yield strength and high tensile strength, also has good ductility and corrosion resistance, and can meet the building structure production requirements of users. The mechanical properties meet the requirements that the yield strength Rt0.5 is larger than or equal to 340 MPa, the tensile strength Rm is larger than or equal to 480 MPa, and the ductility A50 is larger than or equal to 12%.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical sheet technology, and particularly relates to a method for producing galvanized steel strip with a yield strength of 340MPa and a tensile strength of 480MPa for building structures. Background Technology

[0002] In the current field of building structures, with the ever-increasing demands for building safety and durability, the demand for steel with high strength and good corrosion resistance is growing. Traditional steel strips used in construction often struggle to simultaneously meet high standards in both yield strength and tensile strength, and their corrosion resistance is insufficient, which limits their application in complex environments. Especially in coastal areas or humid environments, ordinary steel strips are prone to corrosion, leading to a decline in structural performance and affecting the overall safety and service life of buildings. Therefore, developing a galvanized steel strip that possesses both high yield strength and high tensile strength, along with good corrosion resistance, has become an urgent problem to be solved in this field.

[0003] Currently, the S350GD+Z galvanized structural steel (a process for producing S350GD+Z hot-dip galvanized products with a thickness of less than 2.0mm, application number 201911207362.7) produced by Rizhao Baohua New Materials Co., Ltd. has a composition design of C ≤ 0.045%, Mn: 0.05~0.11%, and a total elongation controlled at 7.8~8.5%, which is different from the composition design and process of this invention. The composition and process design of this product requires incomplete annealing to achieve the desired strength, which has an adverse effect on the elongation. The tensile strength of the product is ≥420MPa, which is different from the performance of this invention. The document "Trial Production of High-Strength Hot-Dip Galvanized Steel on Hot Rolling Production Line" published by Baogang Technology in December 2015, Vol. 41, No. 6, reports that the product composition design has C: 0.20~0.25%, Mn: 1.2~1.5%, which is different from the composition design of this invention. The higher C and Mn content affects the welding process and continuous production of thick-gauge products, which is not conducive to the mass production and application of the product. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures. The product of this invention possesses both high yield strength and high tensile strength, as well as good elongation and corrosion resistance, thus meeting the needs of users in building structure production. Mechanical properties meet: Yield strength R... t0.5 ≥340MPa, tensile strength R m ≥480MPa, elongation A 50 ≥12%.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures, comprising:

[0007] (1) Smelting-continuous casting production process: hot metal pretreatment—converter—LF refining—slab continuous casting; oxygen blowing for decarburization and temperature rise is carried out in the top and bottom blowing smelting of the converter, and aluminum ferromanganese and manganese ferromanganese are added during the tapping process of the converter for deoxidation and alloying, controlling the P and S composition to prevent the steel liquid from over-oxidizing, and the tapping temperature is ≥1620℃; LF ladle refining adopts the LF full-process argon blowing process, and the soft blowing time after calcium treatment is ≥8min, which is adjusted to the target composition according to the steel composition, and the quality of the steel supplied to the casting machine is... The composition by weight percentage is C: 0.16–0.19%, Si ≤ 0.05%, Mn: 0.80–1.10%, P ≤ 0.018%, S ≤ 0.010%, Alt: 0.015–0.050%, Nb: 0.015–0.030%, Ca: 0.0008–0.0020%, with the remainder being Fe and impurities; the slab is continuously cast at a superheat of 15–35℃, and the casting speed is controlled at 1.0–1.6 m / min;

[0008] (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet time in the furnace is 160-280 min, furnace exit temperature is 1170-1240℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finish rolling adopts 7-stand rolling mill, finish rolling start temperature is 970-1030℃, finish rolling end temperature is 850-890℃, hot rolled steel strip thickness is 2.5-4.8mm; cooling adopts laminar flow cooling equipment, coiling temperature is 560-620℃;

[0009] (3) Pickling and cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold rolled by a 5-stand cold rolling mill with a cold rolling reduction rate of 60-75% and a thickness of 0.8-2.1 mm.

[0010] (4) Continuous hot-dip galvanizing and finishing process: After uncoiling the cold-hardened steel strip, it is welded for continuous production. The furnace speed is 65-130 m / min, the soaking temperature is 700-730℃, the temperature is slowly cooled to 610-650℃, and then cooled to 450-475℃. The temperature of entering the zinc pot is 450-480℃, the temperature of the top roller cooling tower is ≤250℃, the finishing elongation is 0.6%-1.4%, and the tension leveling elongation is ≤0.5%.

[0011] Furthermore, its chemical composition by mass percentage is C: 0.18%, Si: 0.04%, Mn: 1.06%, P: 0.008%, S: 0.002%, Alt: 0.038%, Nb: 0.022%, Ca: 0.0011%.

[0012] Furthermore, its chemical composition by mass percentage is C: 0.19%, Si: 0.04%, Mn: 1.09%, P: 0.016%, S: 0.001%, Alt: 0.022%, Nb: 0.028%, Ca: 0.0013%.

[0013] Furthermore, its chemical composition by mass percentage is C: 0.17%, Si: 0.04%, Mn: 0.86%, P: 0.015%, S: 0.002%, Alt: 0.026%, Nb: 0.017%, Ca: 0.0013%.

[0014] Furthermore, its chemical composition by mass percentage is C: 0.17%, Si: 0.03%, Mn: 0.88%, P: 0.011%, S: 0.005%, Alt: 0.033%, Nb: 0.021%, Ca: 0.0017%.

[0015] Furthermore, the billet is in the furnace for 166–258 min, the furnace exit temperature is 1180–1237℃, the initial finishing rolling temperature is 975–1024℃, the final finishing rolling temperature is 855–887℃, the hot-rolled steel strip thickness is 2.5–4.8 mm, and the coiling temperature is 566–600℃.

[0016] Furthermore, the furnace speed is 67–105 m / min, the soaking temperature is 705–720℃, the temperature is slowly cooled to 618–644℃, and then cooled to 450–465℃. The temperature at the zinc pot is 455–475℃, the temperature at the top of the top roller cooling tower is 211–246℃, the finishing elongation is 0.7%–1.39%, and the tensile elongation is 0.05–0.22%.

[0017] Furthermore, its mechanical properties: yield strength R t0.5 377~431MPa, tensile strength R m 511~532MPa, elongation A 50 : 27.5%~32.0%.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] This invention provides a galvanized steel strip with a yield strength of 340 MPa and a tensile strength of 480 MPa. This strip possesses both high yield strength and high tensile strength, along with good elongation and corrosion resistance, meeting the production requirements of users' building structures. Mechanical properties meet: Yield strength R... t0.5 ≥340MPa, tensile strength R m ≥480MPa, elongation A 50 ≥12%. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 This is a microscopic tissue diagram of Example 1. Detailed Implementation

[0022] The present invention will be described in detail below through specific embodiments. These embodiments are only intended to help understand the present invention and do not limit the scope of the present invention.

[0023] Example

[0024] According to the above steelmaking process requirements, the actual chemical composition of the slab is shown in Table 1.

[0025] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0026]

[0027] According to the above hot rolling process requirements, the hot rolling thickness is 2.5 to 4.8 mm, and the actual process is shown in Table 2.

[0028] Table 2 Hot rolling process of embodiments of the present invention

[0029]

[0030] According to the above requirements for cold rolling, hot-dip galvanizing, and finishing processes, the cold rolling thickness is 0.8 to 2.1 mm. The actual hot-dip galvanizing and finishing processes are shown in Table 3.

[0031] Table 3 Hot-dip galvanizing and finishing processes of embodiments of the present invention

[0032]

[0033] The mechanical properties of the steel strip in this embodiment of the invention were tested, and the test results are shown in Table 4.

[0034] Table 4 Mechanical properties of steel strip in embodiments of the present invention

[0035]

[0036] As shown in Table 4, the mechanical properties of the galvanized steel strip with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to the present invention are as follows: Yield Strength R t0.5 377~431MPa, tensile strength R m 511~532MPa, elongation A 50 The yield is 27.5%–32.0%. In summary, the steel strip obtained through this process has suitable properties, and the product has received no adverse feedback from users, making it suitable for widespread application.

[0037] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures, characterized in that: include: (1) Smelting-continuous casting production process: hot metal pretreatment—converter—LF refining—slab continuous casting; In the converter top and bottom combined blowing smelting, oxygen blowing is used for decarburization and temperature rise. During the converter tapping process, ferroaluminum and ferromanganese are added for deoxidation and alloying. The P and S content is controlled to prevent over-oxidation of the molten steel. The tapping temperature is ≥1620℃. The LF ladle refining adopts the LF full-process argon blowing process. After calcium treatment, the soft blowing time is ≥8min. The composition is adjusted to the target composition according to the steel composition. The composition of the molten steel supplied to the casting machine by mass percentage is C: 0.16~0.19%, Si≤0.05%, Mn: 0.80~1.10%, P≤0.018%, S≤0.010%, Alt: 0.015~0.050%, Nb: 0.015~0.030%, Ca: 0.0008~0.0020%, with the remainder being Fe and impurities. The superheating temperature of the slab continuous casting is 15~35℃, and the casting speed is controlled at 1.0~1.6m / min. (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet time in the furnace is 160-280 min, furnace exit temperature is 1170-1240℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finish rolling adopts 7-stand rolling mill, finish rolling start temperature is 970-1030℃, finish rolling end temperature is 850-890℃, hot rolled steel strip thickness is 2.5-4.8mm; cooling adopts laminar flow cooling equipment, coiling temperature is 560-620℃; (3) Pickling and cold rolling process: After the hot-rolled steel strip is pickled to remove the surface iron oxide scale, it is cold rolled by a 5-stand cold rolling mill with a cold rolling reduction rate of 60-75% and a thickness of 0.8-2.1 mm. (4) Continuous hot-dip galvanizing and finishing process: After uncoiling the cold-hardened steel strip, it is welded for continuous production. The furnace speed is 65-130 m / min, the soaking temperature is 700-730℃, the temperature is slowly cooled to 610-650℃, and then cooled to 450-475℃. The temperature of entering the zinc pot is 450-480℃, the temperature of the top roller cooling tower is ≤250℃, the finishing elongation is 0.6%-1.4%, and the tension leveling elongation is ≤0.5%.

2. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.18%, Si: 0.04%, Mn: 1.06%, P: 0.008%, S: 0.002%, Alt: 0.038%, Nb: 0.022%, Ca: 0.0011%.

3. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.19%, Si: 0.04%, Mn: 1.09%, P: 0.016%, S: 0.001%, Alt: 0.022%, Nb: 0.028%, Ca: 0.0013%.

4. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.17%, Si: 0.04%, Mn: 0.86%, P: 0.015%, S: 0.002%, Alt: 0.026%, Nb: 0.017%, Ca: 0.0013%.

5. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.17%, Si: 0.03%, Mn: 0.88%, P: 0.011%, S: 0.005%, Alt: 0.033%, Nb: 0.021%, Ca: 0.0017%.

6. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 3 or 4, characterized in that: The billet is in the furnace for 166–258 minutes, the furnace exit temperature is 1180–1237℃, the initial finishing rolling temperature is 975–1024℃, the final finishing rolling temperature is 855–887℃, the hot-rolled steel strip thickness is 2.5–4.8 mm, and the coiling temperature is 566–600℃.

7. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 5, characterized in that: The furnace speed is 67–105 m / min, the soaking temperature is 705–720℃, the slow cooling temperature is 618–644℃, and then the cooling temperature is 450–465℃. The temperature at the zinc pot is 455–475℃, the temperature at the top of the top roller cooling tower is 211–246℃, the finishing elongation is 0.7%–1.39%, and the tensile elongation is 0.05–0.22%.

8. The method for producing galvanized steel strips with a yield strength of 340 MPa and a tensile strength of 480 MPa for building structures according to claim 6, characterized in that: Its mechanical properties: yield strength R t0.5 377~431MPa, tensile strength R m 511~532MPa, elongation A 50 : 27.5%~32.0%.

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