590MPa-grade short-process hot-dip galvanized low-density steel and preparation method thereof

Abstract

The invention relates to the technical field of alloy steel, in particular to 590MPa-grade short-process hot-dip galvanized low-density steel and a preparation method thereof. The high-strength steel is composed of the following chemical components in percentage by weight: 0.06%-0.11% of C, 0.5%-0.8% of Si, 0.7%-1.15% of Mn, 0.01%-0.04% of P, less than or equal to 0.03% of S, 3.0%-5.8% of Al, 0.01%-0.05% of Ti, 0.001%-0.004% of N and the balance of Fe and inevitable impurities. The technological process comprises the steps of smelting, medium and thin slab continuous casting and rolling, acid pickling, cold rolling and hot galvanizing. The hot-dip galvanized low-density steel has the tensile strength of more than 590 MPa and the elongation of more than 25%, is low in cost, simple in process and low in production difficulty, and can meet the requirements of environmental protection, energy conservation and emission reduction.

Description

Technical Field

[0001] The invention relates to the technical field of alloy steels, and in particular to a 590MPa-grade short-process hot-dip galvanized low-density steel and a preparation method thereof. Background Art

[0002] At present, with the rapid development of new energy vehicles, lightweighting has become the mainstream trend of the automotive industry. The development and application of high-strength and ultra-high-strength automotive steels have greatly promoted the development of lightweighting of automobiles. Among them, low-density steel has the characteristics of high strength and low density at the same time, which has attracted widespread attention from automobile manufacturers.

[0003] Currently, most low-density steels are designed with high manganese and high aluminum alloy components and produced using traditional processes. This has high costs, complex processes, and great production difficulties, making it difficult to meet the requirements of environmental protection and energy conservation and emission reduction.

[0004] A Chinese patent document with publication number CN115216704 A discloses "a short-process production method for low-density steel based on thin strip continuous casting". Although it greatly shortens the production process and reduces environmental pollution, it adopts a high-manganese and high-aluminum composition design, with a manganese content of 16% to 25%, resulting in a high alloy cost and limited application.

[0005] The Chinese patent with announcement number CN112877606 B discloses "an ultra-high strength fully austenitic low-density steel and its preparation method", which adopts a high-alloy composition design with a manganese content of 25% to 30%. It has a high alloy content, is difficult to produce, and has poor corrosion resistance.

[0006] The Chinese patent with announcement number CN108950392 B discloses "an ultra-high ductility low-density steel and its preparation method", which adopts a medium manganese and high carbon composition design, with a manganese content of 8% to 10% and a carbon content of 0.3% to 0.5%. The processing technology is complex and the production is difficult. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a 590MPa grade short-process hot-dip galvanized low-density steel and a preparation method thereof, which has low cost, streamlined process, low production difficulty, and can meet the requirements of environmental protection and energy conservation and emission reduction.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A 590MPa grade short-process hot-dip galvanized low-density steel, composed of the following chemical components in percentage by weight:

[0010] C: 0.06% ~ 0.11%, Si: 0.5% ~ 0.8%, Mn: 0.7% ~ 1.15%, P: 0.01% ~ 0.04%, S ≤ 0.03%, Al: 3.0% ~ 5.8%, Ti: 0.01% ~ 0.05%, N: 0.001% ~ 0.004%, the balance is Fe and unavoidable impurities.

[0011] The microstructure of the above-mentioned 590MPa grade short-process hot-dip galvanized low-density steel is composed of ferrite, martensite, bainite and a small amount of austenite, the volume percentage of ferrite is 70% to 85%, the total volume percentage of martensite and bainite is 8% to 20%, and the volume percentage of austenite is 5% to 10%.

[0012] The density of the above 590MPa grade short process hot dip galvanized low density steel is less than 7.4g / cm 3 , tensile strength ≥590MPa, elongation ≥25%.

[0013] The preparation method of the above-mentioned 590MPa grade short-process hot-dip galvanized low-density steel has a process flow of smelting → medium-thin slab continuous casting and rolling → pickling → cold rolling → hot-dip galvanizing, which is specifically as follows:

[0014] 1) Use converter or electric furnace for smelting;

[0015] 2) Continuous casting and rolling of medium and thin slabs:

[0016] Medium-thin slab continuous casting is used to obtain continuous casting slabs, which are then hot-charged and hot-transported, and then hot-rolled;

[0017] The hot rolling start temperature is controlled at 1000-1150°C, the hot rolling final rolling temperature is controlled at 850-1000°C, and the hot rolled plate coiling temperature is controlled at 500-700°C;

[0018] 3) Cold rolling:

[0019] The cold rolling reduction rate is 30% to 70%;

[0020] 4) Hot dip galvanizing:

[0021] The heating and soaking temperature is controlled to be 760-850°C, the soaking time is 60-90s, the slow cooling outlet temperature is 680-700°C, the slow cooling rate is 2-10°C / s, the fast cooling outlet temperature is 450-470°C, the fast cooling rate is >10°C / s, and then the surface is galvanized.

[0022] Furthermore, in step 2), the thickness of the hot rolled coil is 2.0 to 5.0 mm.

[0023] Furthermore, in step 2), laminar cooling is adopted.

[0024] Furthermore, in step 4), in-furnace humidification is adopted during the strip heating process.

[0025] Further, in step 4), the dew point temperature is controlled to be -20°C to 0°C under the condition of 5% H2+95% N2.

[0026] Furthermore, in step 4), the temperature of the zinc pot is controlled to be 450-470° C., and the skin-pass elongation of the galvanized strip is 0.3%-0.6%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention adopts a low-carbon, low-silicon, low-manganese, aluminum-containing alloy composition design, replacing the high-manganese, high-aluminum alloy composition design of traditional low-density steel, which reduces the alloy cost. At the same time, the present invention makes full use of the aluminum element to reduce the density of steel and improve the expansion of the ferrite phase, and utilizes the good forming performance of ferrite, so that the low-density steel of the present invention has good forming performance while having a high strength of 590MPa.

[0029] 2. The present invention adopts a low-carbon, low-silicon, low-manganese, aluminum-containing alloy composition design, utilizes the aluminum element to expand the role of the ferrite phase, avoids peritectic reaction within the composition system range, improves the high-temperature thermal strength and thermoplasticity of low-density steel, and improves continuous casting performance. However, due to the high-manganese and high-aluminum composition system design of traditional low-density steel, peritectic reaction is very likely to occur during the continuous casting production process, resulting in poor high-temperature performance of the continuous casting billet, resulting in production accidents such as billet breakage.

[0030] 3. The present invention has been applied to the medium-thin slab continuous casting and rolling production line of Anshan Iron and Steel Group. Compared with the traditional production line, it has the advantages of low process cost and greatly reduced energy consumption and carbon emissions.

[0031] In summary, the present invention is a hot-dip galvanized low-density steel with a tensile strength greater than 590 MPa and an elongation greater than 25%, which has low cost, simple process, low production difficulty, and can meet the requirements of environmental protection and energy saving and emission reduction. It has the advantages of low density, high formability, low emissions, and high surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the optical microscope metallographic diagram of the present invention.

[0033] Figure 2 It is a scanning electron microscope organization diagram of the present invention. DETAILED DESCRIPTION

[0034] The present invention discloses a 590MPa grade short-process hot-dip galvanized low-density steel and a preparation method thereof. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all deemed to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0035] A 590MPa grade short-process hot-dip galvanized low-density steel, composed of the following chemical components in percentage by weight:

[0036] C: 0.06% ~ 0.11%, Si: 0.5% ~ 0.8%, Mn: 0.7% ~ 1.15%, P: 0.01% ~ 0.04%, S ≤ 0.03%, Al: 3.0% ~ 5.8%, Ti: 0.01% ~ 0.05%, N: 0.001% ~ 0.004%, the balance is Fe and unavoidable impurities.

[0037] The alloy design of the present invention, i.e. the reasons for selecting the addition amounts (weight percentages) of the above-mentioned elements and their effects are described as follows:

[0038] C: C element plays a major role in solid solution strengthening in steel, improving the strength of steel plates. It is also an austenite stabilizing element, stabilizing austenite. If the C element content is too low, the strength of the steel will be reduced; if the C element content is too high, cementite will easily precipitate at the grain boundary, reducing the plasticity of the steel. Therefore, the C element content ranges from 0.05% to 0.13%.

[0039] Mn: Mn plays a role in solid solution strengthening and stabilizing austenite in steel. If the Mn content is too low, the strength of the steel plate will be reduced; if the Mn content is too high, the strength of the steel plate will be too high and the elongation will decrease. Therefore, the Mn content ranges from 0.6% to 1.2%.

[0040] Si: Si can inhibit the precipitation of cementite, and also play a role in solid solution strengthening and reducing the density of steel plates. If the Si content is too low, it will not inhibit the precipitation of cementite; if the Si content is too high, the surface quality of the steel plate will be reduced.

[0041] Al: Al in steel plays a role in reducing the density of steel plates, increasing the strength of ferrite and inhibiting the precipitation of cementite. At the same time, it forms AlN precipitates with N elements to inhibit grain growth. If the Al content is too low, the density reduction effect will not be obvious; if the Al content is too high, it will cause production difficulties.

[0042] P: The P element plays a role in strengthening steel on the one hand, and inhibits the precipitation of cementite on the other hand.

[0043] S: S is a harmful element in steel, and the lower its content, the better.

[0044] Ti: Ti element plays a role in precipitation strengthening in steel. On the other hand, Ti element combines with C and N elements at high temperature to form precipitates such as TiN, TiC, and Ti(CN), which inhibit the growth of ferrite and austenite grains during high-temperature rolling and play a role in grain refinement. Too high Ti element content will lead to increased costs and poor plasticity of steel plates; too low Ti element content will result in insufficient content of TiN, TiC, Ti(CN) and other precipitates, which cannot play a role in grain refinement.

[0045] N: The main function of N in steel is to combine with Ti and Al to form nitrides, which refines the grains, especially the high-temperature δ-ferrite.

[0046] The density of the above 590MPa grade short process hot dip galvanized low density steel is less than 7.4g / cm 3 , tensile strength ≥590MPa, elongation ≥25%.

[0047] The method for preparing the above-mentioned 590MPa grade short-process hot-dip galvanized low-density steel comprises the following process steps: smelting → continuous casting and rolling of medium and thin slabs → pickling → cold rolling → hot-dip galvanizing.

[0048] The specific steps of the preparation process are as follows:

[0049] The smelting is carried out by a converter or electric furnace smelting method, and the chemical composition of the molten steel is as follows by mass percentage: C: 0.06%-0.11%, Si: 0.5%-0.8%, Mn: 0.7%-1.15%, P: 0.01%-0.04%, S≤0.03%, Al: 3.0%-5.8%, Ti: 0.01%-0.05%, N: 0.001%-0.004%, and the balance is Fe and unavoidable impurities.

[0050] Continuous casting and rolling of medium and thin slabs: Continuous casting of medium and thin slabs is used to obtain continuous casting billets, which are hot charged and hot transported, and then hot rolled; the hot rolling start temperature is controlled at 1000-1150°C, the hot rolling final rolling temperature is controlled at 850-1000°C, the hot rolled plate coiling temperature is controlled at 500-700°C, and the thickness of the hot rolled coil is 2.0-5.0mm.

[0051] The pickling process is: using conventional pickling methods, the main purpose of which is to remove oxides on the surface of the hot-rolled steel plate.

[0052] The cold rolling process is as follows: the cold rolling reduction rate is 30 to 70%.

[0053] Hot-dip galvanizing process: During the heating process of the strip, the furnace is humidified, and the dew point temperature is controlled at -20℃ to 0℃ under the condition of 5% H2+95% N2; the heating and soaking temperature is controlled at 760-850℃, the soaking time is controlled at 60-90s, the slow cooling outlet temperature is 680-700℃, the slow cooling rate is 2-10℃ / s, the fast cooling outlet temperature is 450-470℃, the fast cooling rate is >10℃ / s, and then the surface is galvanized, the zinc pot temperature is 450-470℃, and the skin-clearing elongation of the strip after galvanizing is 0.3%-0.6%.

[0054] [Example]

[0055] The present invention is described in more detail below with reference to examples. These examples are merely descriptions of the best mode for carrying out the present invention and do not impose any limitation on the scope of the present invention.

[0056] The chemical composition of the embodiment is listed in Table 1. After the ingot is obtained, hot rolling is performed. The hot rolling process is shown in Table 2. The mechanical properties of the hot-rolled plate are shown in Table 3. After hot rolling, pickling, cold rolling, nickel plating and hot-dip galvanizing are performed. The cold rolling and hot-dip galvanizing annealing processes are shown in Table 4. The mechanical properties and surface quality results of the steel plate finally obtained are shown in Table 5.

[0057] Table 1 Chemical composition of the examples, wt%

[0058] Steel Grade C Si Mn P S Al Ti N A1 0.062 0.52 1.14 0.015 0.006 3.5 0.011 0.0021 A2 0.067 0.59 1.12 0.011 0.025 3.8 0.017 0.0032 A3 0.064 0.53 1.09 0.019 0.010 4.4 0.022 0.0012 A4 0.068 0.65 0.96 0.017 0.012 4.1 0.026 0.0016 A5 0.074 0.74 0.85 0.011 0.014 4.8 0.031 0.0027 A6 0.085 0.76 0.74 0.026 0.010 4.2 0.038 0.0038 A7 0.096 0.57 0.72 0.029 0.012 5.1 0.025 0.0035 A8 0.107 0.43 0.78 0.038 0.007 5.3 0.035 0.0024 A9 0.109 0.64 0.87 0.033 0.009 5.6 0.042 0.0015 A10 0.084 0.78 0.83 0.032 0.013 4.2 0.048 0.0018

[0059] Table 2 Hot rolling process of the embodiment

[0060] Process No. Rolling temperature, ℃ Finishing rolling temperature, ℃ Coiling temperature, °C B1 1142 937 660 B2 1132 912 650 B3 1125 926 640 B4 1098 928 610 B5 1086 913 630 B6 1065 922 580 B7 1076 875 570 B8 1048 865 590 B9 1059 854 550 B10 1033 868 520

[0061] Table 3 Mechanical properties of hot rolled plates in the examples

[0062] Sample No. Process No. Rel, MPa Rm, MPa A，％ 1 B1 438 611 22.4 2 B2 432 614 27.9 3 B3 452 608 21.1 4 B4 448 602 18.8 5 B5 448 596 18.2 6 B6 442 595 17.2 7 B7 446 604 19.0 8 B8 448 605 17.3 9 B9 464 609 20.1 10 B10 463 607 19.9

[0063] Table 4 Cold rolling and hot dip galvanizing annealing process of the embodiment

[0064]

[0065] Table 5 Mechanical test and phosphating performance test results of the examples

[0066]

[0067] As shown in Table 5, the hot-dip galvanized low-density steel of the present invention has good zinc layer adhesion, a yield strength of more than 3600 MPa, a tensile strength of more than 590 MPa, and an elongation of more than 25%, and has the advantages of low density, high formability, low emissions, and high surface quality.

[0068] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A 590MPa grade short process hot-dip galvanized low-density steel, characterized in that: It is composed of the following chemical components in percentage by weight: C: 0.06% ~ 0.11%, Si: 0.5% ~ 0.8%, Mn: 0.7% ~ 1.15%, P: 0.01% ~ 0.04%, S ≤ 0.03%, Al: 3.0% ~ 5.8%, Ti: 0.01% ~ 0.05%, N: 0.001% ~ 0.004%, the balance is Fe and unavoidable impurities.

2. The 590MPa grade short-process hot-dip galvanized low-density steel according to claim 1, characterized in that: The microstructure of the 590MPa grade hot-dip galvanized low-density steel consists of ferrite, martensite, bainite and austenite, wherein the volume percentage of ferrite is 70% to 85%, the total volume percentage of martensite and bainite is 8% to 20%, and the volume percentage of austenite is 5% to 10%.

3. The 590MPa grade short-process hot-dip galvanized low-density steel according to claim 1, characterized in that: The density of the 590MPa grade hot-dip galvanized low-density steel is lower than 7.4g / cm 3 , tensile strength ≥590MPa, elongation ≥25%.

4. A method for preparing 590MPa grade short-process hot-dip galvanized low-density steel as claimed in claim 1, 2 or 3, characterized in that: The process flow is smelting → continuous casting and rolling of medium and thin slabs → pickling → cold rolling → hot-dip galvanizing, as follows: 1) Use converter or electric furnace for smelting; 2) Continuous casting and rolling of medium and thin slabs: Medium-thin slab continuous casting is used to obtain continuous casting slabs, which are then hot-charged and hot-transported, and then hot-rolled; The hot rolling start temperature is controlled at 1000-1150°C, the hot rolling final rolling temperature is controlled at 850-1000°C, and the hot rolled plate coiling temperature is controlled at 500-700°C; 3) Cold rolling: The cold rolling reduction rate is 30% to 70%; 4) Hot dip galvanizing: The heating and soaking temperature is controlled to be 760-850°C, the soaking time is 60-90s, the slow cooling outlet temperature is 680-700°C, the slow cooling rate is 2-10°C / s, the fast cooling outlet temperature is 450-470°C, the fast cooling rate is >10°C / s, and then the surface is galvanized.

5. The method for preparing a 590MPa grade short-process hot-dip galvanized low-density steel according to claim 4, characterized in that: In step 2), the thickness of the hot rolled coil is 2.0 to 5.0 mm.

6. The method for preparing a 590MPa grade short-process hot-dip galvanized low-density steel according to claim 4, characterized in that: In step 2), laminar cooling is adopted.

7. The method for preparing 590MPa grade short-process hot-dip galvanized low-density steel according to claim 4, characterized in that: In step 4), humidification is performed in the furnace during the strip heating process.

8. The method for preparing 590MPa grade short-process hot-dip galvanized low-density steel according to claim 4, characterized in that: In step 4), the dew point temperature is controlled to be -20°C to 0°C under the condition of 5% H2+95% N2.

9. The method for preparing 590MPa grade short-process hot-dip galvanized low-density steel according to claim 4, characterized in that: In step 4), the temperature of the zinc pot is controlled to be 450-470° C., and the skin-pass elongation of the galvanized strip is 0.3%-0.6%.

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