Production method of high-elongation 780MPa-grade galvanized dual-phase steel strip

Abstract

The invention discloses a production method of a high-elongation 780MPa-grade galvanized dual-phase steel strip. The high-elongation 780MPa-grade galvanized dual-phase steel strip comprises the following chemical components in percentage by mass: 0.15-0.18% of C, less than or equal to 0.45% of Si, 2.00-2.30% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.5-0.8% of Alt, 0.10-0.30% of Cr, less than or equal to 0.020% of Ti, 0.0010-0.0030% of Ca, less than or equal to 0.0070% of N and the balance of Fe and inevitable impurities. The invention further discloses main processes and parameters of the production method. The galvanized dual-phase steel strip disclosed by the invention has higher elongation rate, and can better meet the harsh requirement on high elongation rate of a material in a specific application scene, so that a product has better formability, and the requirements of light-weight and complex formed parts in the automobile industry are met.

Description

Technical Field

[0001] This invention relates to the field of metallurgical sheet technology, and in particular to a method for producing a high-elongation 780MPa grade galvanized duplex steel strip. Background Technology

[0002] In the current new energy vehicle sector, the demand for high-strength, corrosion-resistant steel is increasing, placing higher requirements on both strength and elongation. 780MPa grade galvanized duplex steel strip has attracted widespread attention due to its high strength and good formability; however, some similar products on the market still need improvement in elongation, failing to fully meet the stringent high elongation requirements of certain specific applications. Therefore, developing a 780MPa grade galvanized duplex steel strip with high elongation and its production method is of significant practical importance.

[0003] Currently, the 780MPa grade galvanized duplex steel produced by Tangshan Vocational and Technical College of Science and Technology (a method for improving the performance uniformity of 780MPa grade galvanized duplex steel, application number 202110290916.5) has a composition design of C: 0.07-0.10%, Mn: 1.70-2.10%, Nb: 0.013-0.030%, Mo: 0.15-0.25%, B: 0.0010-0.0025%, which differs from the composition design of this invention. The higher Nb, Mo, and B content increases product cost, and the homogenization temperature of 750-780℃ differs from the process of this invention. Furthermore, the 800MPa grade cold-rolled hot-dip galvanized duplex steel produced by Wuhan Iron and Steel Co., Ltd. (an 800MPa grade cold-rolled hot-dip galvanized duplex steel) The composition of the steel produced by Shougang Group (application number 201811126345.6) is different from that of the present invention. The steel has a composition of C: 0.05-0.10%, Nb: 0.010-0.050%, and Mo: 0.05-0.30%, with higher Nb and Mo content, affecting product cost. The 780MPa grade cold-rolled hot-dip galvanized duplex steel produced by Shougang Group (application number 201110439563.7) has a higher Nb content (0.03-0.04%) and Mo content (0.2-0.25%), affecting product cost. Its coiling temperature is 640-700℃, which differs from the composition and process of the present invention. Its elongation is 13%, lower than that of the present invention. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing high-elongation 780MPa grade galvanized duplex steel strip. This galvanized duplex steel strip has a higher elongation, which can better meet the stringent requirements for high elongation in specific applications, resulting in better formability and meeting the needs of the automotive industry for lightweight and complex molded parts. Mechanical properties meet: Yield strength R p0.2420~550MPa, tensile strength R m 780~900MPa, elongation A 50 ≥19%, strain hardening index n value ≥0.13.

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

[0006] This invention discloses a method for producing high-elongation 780MPa grade galvanized duplex steel strip, wherein the chemical composition by mass percentage is: C: 0.15-0.18%, Si≤0.45%, Mn: 2.00-2.30%, P≤0.020%, S≤0.008%, Alt: 0.5-0.8%, Cr: 0.10-0.30%, Ti≤0.020%, Ca: 0.0010-0.0030%, N≤0.0070%, with the remainder being Fe and unavoidable impurities; the production method includes:

[0007] (1) Smelting-continuous casting production process: hot metal pretreatment—converter—LF refining—RH refining—slab continuous casting; oxygen blowing and decarburization are carried out during the top and bottom blowing smelting of the converter. During the tapping process of the converter, aluminum ferromanganese, ferrosilicon and other materials are added for deoxidation and alloying. The P and S composition is controlled to prevent the steel liquid from over-oxidation. The tapping temperature is ≥1620℃; the LF ladle refining adopts the LF full-process argon blowing process. The vacuum degree of RH refining is ≤2.6mbar and the vacuum time is ≥10min. After calcium treatment, the soft blowing time is guaranteed to be ≥8min. The composition is adjusted to the target composition according to the steel composition; the superheat of slab continuous casting is 15~40℃ and the casting speed is controlled at 0.8~1.6m / min;

[0008] (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet soaking time 30-65 min, furnace time 170-280 min, furnace exit temperature 1200-1280℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finish rolling adopts 7-stand rolling mill, finish rolling start temperature 1000-1040℃, finish rolling end temperature 860-910℃, hot rolled steel strip thickness 2.3-3.4 mm; cooling adopts laminar flow cooling equipment, coiling temperature 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 48-65% and a thickness of 0.8-1.6 mm.

[0010] (4) Continuous hot-dip galvanizing and finishing process: After uncoiling the cold-hardened steel strip, continuous welding is carried out. The furnace speed is 55-120 m / min, the soaking temperature is 790-830℃, the temperature is slowly cooled to 670-700℃, and then cooled to 445-470℃. The temperature of entering the zinc pot is 445-475℃, the temperature of the top of the cooling tower is 200-240℃, the finishing elongation is 0.15%-0.4%, and the tension leveling elongation is ≤0.3%.

[0011] Furthermore, its chemical composition by mass percentage is C: 0.18%, Si: 0.37%, Mn: 2.13%, P: 0.011%, S: 0.001%, Alt: 0.56%, Cr: 0.21%, Ti: 0.014%, Ca: 0.0012%, N: 0.0053%, with the remainder being Fe and unavoidable impurities.

[0012] Furthermore, its chemical composition by mass percentage is C: 0.17%, Si: 0.40%, Mn: 2.15%, P: 0.015%, S: 0.006%, Alt: 0.60%, Cr: 0.12%, Ti: 0.013%, Ca: 0.0016%, N: 0.0036%, with the remainder being Fe and unavoidable impurities.

[0013] Furthermore, its chemical composition by mass percentage is C: 0.16%, Si: 0.31%, Mn: 2.07%, P: 0.008%, S: 0.004%, Alt: 0.77%, Cr: 0.19%, Ti: 0.018%, Ca: 0.0012%, N: 0.0048%, with the remainder being Fe and unavoidable impurities.

[0014] Furthermore, the furnace exit temperature is 1218-1276℃, the finishing rolling start temperature is 1004-1037℃, the finishing rolling finish temperature is 866-905℃, and the coiling temperature is 575-602℃.

[0015] Furthermore, the furnace speed is 65–107 m / min, the soaking temperature is 793–826℃, the temperature is slowly cooled to 676–696℃, and then cooled to 448–468℃. The temperature at the zinc pot is 446–475℃, the temperature at the top of the top roller cooling tower is 205–235℃, the finishing elongation is 0.18%–0.30%, and the tensile elongation is 0.08–0.22%.

[0016] Furthermore, the mechanical properties of the produced galvanized duplex steel strip meet the following requirements: yield strength R p0.2 443~468MPa, tensile strength R m 812~841MPa, elongation A 50 : 24.5%~27.0%, n value 0.20~0.23.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] This invention provides a high-elongation 780MPa grade galvanized duplex steel strip with higher elongation, better meeting the stringent requirements for high elongation in specific applications. This results in superior formability, satisfying the automotive industry's needs for lightweight, complex molded parts. Mechanical properties meet: Yield strength R... p0.2 420~550MPa, tensile strength R m 780~900MPa, elongation A 50 ≥19%, strain hardening index n value ≥0.13. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 This is a microstructure diagram of Embodiment 1 of the present invention. Detailed Implementation

[0021] 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.

[0022] Example

[0023] According to the above steelmaking process requirements, the actual chemical composition of the slab is shown in Table 1.

[0024] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0025]

[0026]

[0027] According to the above hot rolling process requirements, the hot rolling thickness is 2.3 to 3.4 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 1.6 mm, and 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]

[0034] The mechanical properties of the steel strip in this embodiment of the invention were tested, and the test results are shown in Table 4.

[0035] Table 4 Mechanical properties of steel strip in embodiments of the present invention

[0036]

[0037] As shown in Table 4, the mechanical properties of the high elongation 780MPa grade galvanized duplex steel strip of this invention are as follows: Yield strength R p0.2 443~468MPa, tensile strength R m 812~841MPa, elongation A 50 The content of the steel strip produced by this process is 24.5%–27.0%, and the n-value is 0.20–0.23. In summary, the steel strip products obtained through this process have shown suitable performance, good formability, and good corrosion resistance in user applications, and are suitable for widespread use.

[0038] 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 a high-elongation 780MPa grade galvanized duplex steel strip, characterized in that: Its chemical composition by mass percentage is as follows: C: 0.15–0.18%, Si ≤ 0.45%, Mn: 2.00–2.30%, P ≤ 0.020%, S ≤ 0.008%, Alt: 0.5–0.8%, Cr: 0.10–0.30%, Ti ≤ 0.020%, Ca: 0.0010–0.0030%, N ≤ 0.0070%, with the remainder being Fe and unavoidable impurities; Its production methods include: (1) Smelting-continuous casting production process: hot metal pretreatment—converter—LF refining—RH refining—slab continuous casting; In the converter top and bottom combined blowing smelting, oxygen blowing is used for decarburization and heating. During the converter tapping process, ferroaluminum, ferromanganese, and ferrosilicon 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. The RH refining vacuum degree is ≤2.6mbar and the vacuum time is ≥10min. After calcium treatment, the soft blowing time is guaranteed to be ≥8min. The composition is adjusted to the target composition according to the steel composition. The slab continuous casting superheat is 15~40℃ and the casting speed is controlled at 0.8~1.6m / min. (2) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet soaking time 30-65 min, furnace time 170-280 min, furnace exit temperature 1200-1280℃, rough rolling adopts 3+3 mode 2-stand rolling mill, finish rolling adopts 7-stand rolling mill, finish rolling start temperature 1000-1040℃, finish rolling end temperature 860-910℃, hot rolled steel strip thickness 2.3-3.4 mm; cooling adopts laminar flow cooling equipment, coiling temperature 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 48-65% and a thickness of 0.8-1.6 mm. (4) Continuous hot-dip galvanizing and finishing process: After uncoiling the cold-hardened steel strip, continuous welding is carried out. The furnace speed is 55-120 m / min, the soaking temperature is 790-830℃, the temperature is slowly cooled to 670-700℃, and then cooled to 445-470℃. The temperature of entering the zinc pot is 445-475℃, the temperature of the top of the cooling tower is 200-240℃, the finishing elongation is 0.15%-0.4%, and the tension leveling elongation is ≤0.3%.

2. The method for producing high elongation 780MPa grade galvanized duplex steel strip according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.18%, Si: 0.37%, Mn: 2.13%, P: 0.011%, S: 0.001%, Alt: 0.56%, Cr: 0.21%, Ti: 0.014%, Ca: 0.0012%, N: 0.0053%, with the remainder being Fe and unavoidable impurities.

3. The method for producing high elongation 780MPa grade galvanized duplex steel strip according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.17%, Si: 0.40%, Mn: 2.15%, P: 0.015%, S: 0.006%, Alt: 0.60%, Cr: 0.12%, Ti: 0.013%, Ca: 0.0016%, N: 0.0036%, with the remainder being Fe and unavoidable impurities.

4. The method for producing high elongation 780MPa grade galvanized duplex steel strip according to claim 1, characterized in that: Its chemical composition by mass percentage is C: 0.16%, Si: 0.31%, Mn: 2.07%, P: 0.008%, S: 0.004%, Alt: 0.77%, Cr: 0.19%, Ti: 0.018%, Ca: 0.0012%, N: 0.0048%, with the remainder being Fe and unavoidable impurities.

5. The method for producing high elongation 780MPa grade galvanized duplex steel strip according to claim 1, characterized in that: The furnace exit temperature is 1218-1276℃, the finishing rolling start temperature is 1004-1037℃, the finishing rolling finish temperature is 866-905℃, and the coiling temperature is 575-602℃.

6. The method for producing high elongation 780MPa grade galvanized duplex steel strip according to claim 1, characterized in that: The furnace speed is 65–107 m / min, the soaking temperature is 793–826℃, the slow cooling temperature is 676–696℃, and then the cooling temperature is 448–468℃. The temperature at the zinc pot is 446–475℃, the temperature at the top of the top roller cooling tower is 205–235℃, the finishing elongation is 0.18%–0.30%, and the tensile elongation is 0.08–0.22%.

7. The method for producing high elongation 780MPa grade galvanized duplex steel strip according to claim 1, characterized in that: The mechanical properties of the produced galvanized duplex steel strip meet the following requirements: yield strength R p0.2 443~468MPa, tensile strength R m 812~841MPa, elongation A 50 : 24.5%~27.0%, n value 0.20~0.23.

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