Method for producing galvanized DP590 and common cold DP780 from same component

Abstract

The invention relates to the technical field of cold-rolled high-strength steel for automobiles, and particularly discloses a method for producing galvanized DP590 and common cold DP780 from the same component, and two different-grade products of galvanized DP590 and common cold DP780 are produced by adopting billets of the same component system. The galvanized DP590 product and the common cold DP780 product are produced by adopting the same smelting, hot rolling and acid rolling technological processes when the steel billets of the same component system are used for producing the galvanized DP590 product; the galvanized DP590 product is subjected to a cold rolling galvanizing process after acid rolling; a common cold DP780 product is subjected to a cold rolling and continuous annealing process after being subjected to acid rolling; according to the invention, the same component system is adopted to produce the DP590 product in the galvanizing process and the DP780 product in the continuous annealing process through the steel-making process, the hot rolling process and the acid rolling process under the same process, the method is suitable for industrial production, the process is easy to control, and the cost is reduced for smelting production of different levels of products in limit specifications, reduction of inventory, production organization and the like of steel enterprises.

Description

Technical Field

[0001] This invention relates to the field of cold-rolled high-strength steel technology for automobiles, specifically to a method for producing galvanized DP590 and ordinary cold-rolled DP780 with the same composition. Background Technology

[0002] In recent years, climate change and energy shortages have had an increasingly serious impact on the development of modern industry and people's daily lives. Energy conservation, emission reduction, and low-carbon environmental protection have become urgent issues for industrial development in various countries. To reduce energy consumption and ensure vehicle safety, major global automakers are using advanced high-strength steel for lightweighting automobiles, with cold-rolled duplex steel accounting for the largest proportion of advanced high-strength steel used in automobiles.

[0003] However, when faced with special user requirements, production of extreme specifications, or small order quantities for cold-rolled duplex steel products, steel companies often mix different steel grades in their actual production organization to ensure order delivery, leading to unstable product composition and ultimately unstable product process control.

[0004] Existing publicly available technologies only address the production of products with different yield strength ratios and the same tensile strength level within the same process, which differs significantly from the present patent's requirement of production in two processes. For example, patent number CN 109852900 A discloses a method for producing 600MPa grade hot-dip galvanized duplex steel with different yield strength ratios, patent number CN 109182672A discloses a method for producing economical cold-rolled DP590 steel with different yield strength levels, and patent number CN 108754307A discloses a method for producing economical cold-rolled DP780 steel with different yield strength levels, etc. Or, for products that can be produced with the same raw materials in the continuous annealing and galvanizing processes, but due to the differences between the continuous annealing and galvanizing production lines, it is difficult to produce products of the same strength level with the same composition on the two production lines, which is very different from this patent. For example, patent number CN 118460924 A discloses a method for producing two types of 590MPa grade dual-phase steel with the same composition, namely continuous annealing and galvanizing; patent number CN 115537665 A discloses a production method for producing two types of 590MPa grade DH steel with the same raw materials, namely continuous annealing and galvanizing; patent number CN 114574674 A discloses a preparation method for simultaneously producing continuous annealing and galvanizing DP780 dual-phase steel; and patent number CN 116814925A discloses an integrated manufacturing method for 600MPa grade continuous annealing and hot-dip galvanizing reinforced plastic dual-phase steel plates, etc. Or it may be a patent that only produces a single product on a single production line, which is very different from this patent. For example, patent number CN 114540707 B discloses a 590MPa grade cold-rolled high-strength steel and its production method, etc., and patent number CN120738555A discloses a low-cost, high-surface-area cold-rolled duplex steel DP780 and its production method, etc.

[0005] Therefore, exploring a low-cost, flexible manufacturing method for producing galvanized DP590 and cold-rolled DP780 using the same components has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a low-cost, flexible manufacturing method for producing galvanized DP590 and cold-rolled DP780 with the same composition. This method can not only meet the needs of the automotive industry for special composition requirements, extreme specifications, and diversified performance requirements, but also reduce costs for steel companies in terms of smelting and producing extreme specifications of different grades of products, reducing inventory, and production organization.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for producing galvanized DP590 and ordinary cold-dip DP780 with the same composition, comprising the following steps: S1. Two different grades of products, galvanized DP590 and cold-rolled DP780, are produced using steel billets with the same composition system. S2. The same steel billet with the same composition system is used to produce galvanized DP590 products and cold-rolled DP780 products using the same steelmaking, hot rolling and pickling processes. S3 and galvanized DP590 products are cold-rolled galvanized after pickling. S4 and DP780 products are cold rolled and annealed after pickling.

[0008] Specifically, the chemical composition of the steel billet in step S1, by weight percentage, includes: C: 0.08%-0.12%, Si: 0.15%-0.25%, Mn: 1.9%-2.1%, P≤0.015%, S≤0.007%, Als: 0.02%-0.07%, Cr: 0.2%-0.4%, Nb+Ti: 0.005%-0.02%, with the balance being Fe and unavoidable inclusions.

[0009] Specifically, the hot rolling process in step S2 is as follows: slab heating temperature 1200-1270℃, furnace time 210-280min; seven-stand continuous rolling, roughing rolling start temperature 1050-1090℃, finishing rolling start temperature 1000-1060℃, finishing rolling finish temperature 870-920℃; laminar flow cooling mode is adopted after rolling; U-shaped coiling is used, coiling temperature within 40 meters of the head and tail is 540-600℃, and the temperature in the middle is 510-570℃; slow cooling for 72 hours after coiling.

[0010] Specifically, the pickling and rolling process in step S2 is as follows: pickling to remove hot-rolled iron oxide scale, and continuous rolling with a total reduction rate of 40-75% according to the target thickness of cold rolling.

[0011] Specifically, the parameters for the cold-rolled galvanizing process of the galvanized DP590 product in step S3 after pickling are as follows: soaking temperature 760-800℃; slow cooling temperature 660-700℃; rapid cooling temperature 440-470℃; zinc pot temperature 440-470℃; flattening elongation 0.3-0.8%; cooling rate ≥20℃ / s; and belt speed selected according to thickness as 70-200m / min.

[0012] Specifically, the volume fraction of martensite in the microstructure of the galvanized DP590 product in step S3 is 15-25%.

[0013] Specifically, the parameters for the cold rolling continuous annealing process of the DP780 product in step S4 after pickling are as follows: soaking temperature 810-850℃; slow cooling temperature 660-700℃; rapid cooling temperature 250-290℃; over-aging temperature 250-285℃; flattening elongation 0.3-0.8%; cooling rate ≥20℃ / s; belt speed selected according to thickness as 70-200m / min.

[0014] Specifically, the martensite volume fraction in the microstructure of the DP780 product in step 4 is 20-35%.

[0015] The present invention has the following beneficial effects: The present invention provides a method for producing galvanized DP590 and cold-rolled DP780 using the same composition. This method achieves the production of DP590 products in the galvanizing process and DP780 products in the continuous annealing process using the same composition system and the same steelmaking, hot rolling, and pickling processes. The method provided by the present invention is applicable to industrial production, and the process is easy to control. It reduces costs for steel companies in terms of smelting and producing different grades of products to extreme specifications, reducing inventory, and production organization. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the microstructure of the galvanized DP590 product prepared in Example 1 of the present invention using SEM.

[0017] Figure 2 This is a schematic diagram of the microstructure of the DP780 product prepared in Example 2 of the present invention using SEM. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Example 1: As Figure 1 As shown, the present invention produces galvanized DP590 products, comprising the following steps: The chemical composition of the DP590 zinc-plated product in Example 1 of this invention, by weight percentage, includes: C: 0.08%-0.12%, Si: 0.15%-0.25%, Mn: 1.9%-2.1%, P≤0.015%, S≤0.007%, Als: 0.02%-0.07%, Cr: 0.2%-0.4%, Nb+Ti: 0.005%-0.02%, with the balance being Fe and unavoidable inclusions. The specific chemical composition of Example 1 is shown in Table 1.

[0020] The hot rolling process of Embodiment 1 of this invention is as follows: slab heating temperature 1200-1270℃, furnace time 210-280 min; seven-stand continuous rolling, roughing rolling start temperature 1050-1090℃, finishing rolling start temperature 1000-1060℃, finishing rolling finish temperature 870-920℃; laminar flow cooling mode is adopted after rolling; U-shaped coiling is used, with coiling temperature of 540-600℃ within the first and last 40 meters, and 510-570℃ in the middle; slow cooling for 72 hours after coiling. Specific implementation process is shown in Table 2.

[0021] The pickling and rolling process in Embodiment 1 of this invention is as follows: pickling removes hot-rolled iron oxide scale, and continuous rolling is performed with a total reduction rate of 40-75% according to the target thickness of cold rolling.

[0022] The galvanizing process in Embodiment 1 of this invention is as follows: homogenization temperature 760-800℃; slow cooling temperature 660-700℃; rapid cooling temperature 440-470℃; zinc pot entry temperature 440-470℃; flattening elongation rate 0.3-0.8%; cooling rate ≥20℃ / s; belt speed selected according to thickness, 70-200m / min. Specific implementation details are shown in Table 2.

[0023] Example 2: Figure 2 As shown, the present invention produces the continuous annealing DP780 product, comprising the following steps: The chemical composition of the DP780 product of Example 2 of this invention, by weight percentage, includes: C: 0.08%-0.12%, Si: 0.15%-0.25%, Mn: 1.9%-2.1%, P≤0.015%, S≤0.007%, Als: 0.02%-0.07%, Cr: 0.2%-0.4%, Nb+Ti: 0.005%-0.02%, with the balance being Fe and unavoidable inclusions. The chemical composition of Example 1 is shown in Table 1.

[0024] The hot rolling process in Embodiment 2 of this invention is as follows: slab heating temperature 1200-1270℃, furnace time 210-280 min; seven-stand continuous rolling, roughing rolling start temperature 1050-1090℃, finishing rolling start temperature 1000-1060℃, finishing rolling finish temperature 870-920℃; laminar flow cooling mode is adopted after rolling; U-shaped coiling is used, with coiling temperature of 540-600℃ within the first and last 40 meters, and 510-570℃ in the middle; slow cooling for 72 hours after coiling. Specific implementation details are shown in Table 2.

[0025] The pickling and rolling process in Embodiment 2 of the present invention is as follows: pickling to remove hot-rolled iron oxide scale, and continuous rolling with a total reduction rate of 40-75% according to the target thickness of cold rolling.

[0026] The continuous annealing process in Embodiment 2 of the present invention is as follows: heating temperature 810-850℃; slow cooling temperature 660-700℃; rapid cooling temperature 250-290℃; over-aging temperature 250-285℃; flattening elongation rate 0.3-0.8%; cooling rate ≥20℃ / s; belt speed selected according to thickness as 70-200m / min.

[0027] Table 1. Actual smelting composition (mass percentage, %) of the embodiments Example Brand C Si Mn P S T-Al Cr Nb 1 590DPD+Z 0.08 0.19 2.01 0.009 0.002 0.038 0.31 0.013 2 590DPD+Z 0.087 0.25 2.05 0.008 0.005 0.039 0.33 0.005 3 780DP 0.08 0.23 2.02 0.012 0.001 0.04 0.29 0.015 4 780DP 0.087 0.25 2.05 0.008 0.005 0.039 0.33 0.005 Table 2 Main process control parameters of the embodiments

[0028] Microstructure analysis and mechanical property testing were performed on the galvanized DP590 and cold-annealed DP780 products obtained in Examples 1 and 2. The test and analysis results are shown in Table 3.

[0029] Microstructure analysis and volume fraction calculation of each phase show that the galvanized DP590 and cold-annealed DP780 products obtained in Examples 1-2 of this invention are mainly composed of ferrite (F) and martensite (M), with the volume fraction of martensite in the microstructure of galvanized DP590 being 21% and the volume fraction of martensite in the microstructure of continuously annealed DP780 being 25.6%.

[0030] Table 3 Mechanical properties and martensite content of the embodiments Example Brand Yield strength / MPa Tensile strength / MPa Elongation A80 / % Hole expansion rate / % Martensite / % 1 590DPD+Z 369 616 24.5 55 21.4 2 590DPD+Z 384 623 25 52 22.3 3 780DP 466 790 19 41 25.6 4 780DP 481 799 18.5 30 28.3 As can be seen from the mechanical properties, Examples 1 and 2 of the present invention achieve the production of DP590 products in the galvanizing process and DP780 products in the continuous annealing process using the same composition system and the same steelmaking, hot rolling, and pickling processes. The method provided by the present invention is applicable to industrial production, the process is easy to control, and it can reduce costs for steel companies in terms of smelting and producing extreme specifications of different grades of products, reducing inventory, and production organization.

[0031] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0032] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method of producing galvanized DP590 and plain cold DP780 of the same composition, characterized in that, The method comprises the following steps: S1, producing two different grade products of galvanized DP590 and common cold DP780 by using the same component system billet; S2, producing the galvanized DP590 product and the common cold DP780 product by using the same steelmaking, hot rolling and pickling process of the same component system billet; S3, adopting the cold rolling and galvanizing process for the galvanized DP590 product after pickling; S4, adopting the cold rolling and continuous annealing process for the common cold DP780 product after pickling.

2. The method of producing galvanized DP590 and cold rolled DP780 of the same composition according to claim 1, characterized in that, The chemical components of the same component system billet in the step S1 include, in percentage by weight, C: 0.08%-0.12%, Si: 0.15%-0.25%, Mn: 1.9%-2.1%, P≤0.015%, S≤0.007%, Als: 0.02%-0.07%, Cr: 0.2%-0.4%, Nb+Ti: 0.005%-0.02%, and the balance of Fe and inevitable inclusions.

3. The method of producing galvanized DP590 and cold rolled DP780 with the same ingredients according to claim 1, characterized in that, The hot rolling process in the step S2 is as follows: the slab heating temperature is 1200-1270℃, the furnace time is 210-280min; seven-stand continuous rolling, the rough rolling opening temperature is 1050-1090℃, the finish rolling opening temperature is 1000-1060℃, and the finish rolling final rolling temperature is 870-920℃; after rolling, the laminar flow cooling mode is adopted; U-shaped coiling is used, the coiling temperature of the head and tail part within 40 meters is 540-600℃, and the middle part temperature is 510-570℃; after coiling, slow cooling is performed for 72 hours.

4. The method of producing galvanized DP590 and cold rolled DP780 with the same ingredients according to claim 1, characterized in that, The pickling process in the step S2 is as follows: the hot rolling iron oxide scale is removed by pickling, and the total reduction is 40-75% for continuous rolling according to the cold rolling target thickness.

5. The method of producing galvanized DP590 and cold rolled DP780 with the same ingredients according to claim 1, characterized in that, The parameters of the cold rolling and galvanizing process for the galvanized DP590 product in the step S3 after pickling are as follows: the soaking temperature is 760-800℃, the slow cooling temperature is 660-700℃, the fast cooling temperature is 440-470℃, the zinc pot temperature is 440-470℃, the flattening elongation is 0.3-0.8%, the cooling speed is ≥20℃ / s, and the strip speed is selected as 70-200m / min according to the thickness.

6. The method of producing galvanized DP590 and cold rolled DP780 with the same composition according to claim 1, characterized in that, The martensite volume fraction in the microstructure of the galvanized DP590 product in the step S3 is 15-25%.

7. The method of producing galvanized DP590 and cold rolled DP780 with the same ingredients according to claim 1, characterized in that, The parameters of the cold rolling and continuous annealing process for the common cold DP780 product in the step S4 after pickling are as follows: the soaking temperature is 810-850℃, the slow cooling temperature is 660-700℃, the fast cooling temperature is 250-290℃, the overaging temperature is 250-285℃, the flattening elongation is 0.3-0.8%, the cooling speed is ≥20℃ / s, and the strip speed is selected as 70-200m / min according to the thickness.

8. The method of producing galvanized DP590 and cold rolled DP780 with the same ingredients according to claim 1, characterized in that, The martensite volume fraction in the microstructure of the common cold DP780 product in the step S4 is 20-35%.

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