Low-density steel based on short-process hot galvanizing and preparation method thereof

Abstract

The invention relates to low-density steel based on short-process hot galvanizing and a preparation method of the low-density steel. The steel comprises the following chemical components in percentage by mass: 0.05%-0.13% of C, 0.4%-0.9% of Si, 0.6%-1.2% of Mn, less than or equal to 0.02% of P, less than or equal to 0.03% of S, 3.0%-6.0% of Al, 0.012%-0.052% of Ti, 0.0012%-0.0042% of N and the balance of Fe and inevitable impurities. The production process has the advantages that the production process of converter or electric furnace smelting, medium and thin slab continuous casting and rolling, acid pickling, cold rolling, nickel plating and hot galvanizing is adopted, the hot-galvanized low-density steel with the yield strength of 330-500 MPa, the tensile strength of 590-700 MPa and the elongation rate of 25%-35% is produced, and the hot-galvanized low-density steel has the advantages of being low in density, high in formability, low in emission and high in surface quality.

Description

Technical Field

[0001] The invention belongs to the field of alloy steel manufacturing, and in particular relates to a 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] At present, most low-density steels are designed with high manganese and high aluminum alloy components and produced by traditional production lines, which are costly, complex in process, and difficult to produce. For example, patent publication number CN115216704 A discloses a short-process production method for low-density steel based on thin strip continuous casting, which adopts a high manganese and high aluminum component design, with a manganese content of 16% to 25% and an aluminum content of 6% to 12%. Due to the high alloy content, the production cost of low-density steel products is high and the application is limited. At the same time, the excessive manganese content causes the continuous casting billet to crack easily, making production difficult. Patent publication number CN112877606 A discloses an ultra-high-strength fully austenitic low-density steel and preparation method, which adopts a high alloy component design, with a manganese content of 25% to 30%. Due to the high alloy content, the cost of low-density steel is high, the continuous casting production is difficult, and the corrosion resistance is poor. Patent publication number CN108950392A 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 manganese content of this low-density steel is 8-10%, which is lower than the cost of the previous two patents. However, due to the complex microstructure and processing technology of the low-density steel with a medium manganese composition system, it is difficult to produce and it is difficult to ensure a high yield. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a short-process hot-dip galvanized low-density steel and a preparation method thereof, which reduces the production difficulty by cleverly matching the composition design with the process design, and produces hot-dip galvanized low-density steel with a yield strength of 330 to 500 MPa, a tensile strength of 590 to 700 MPa, and an elongation of 25% to 35%.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A short-process hot-dip galvanized low-density steel, characterized in that the chemical composition of the steel is as follows in terms of mass percentage:

[0007] C: 0.05% ~ 0.13%, Si: 0.4% ~ 0.9%, Mn: 0.6% ~ 1.2%, P ≤ 0.02%, S ≤ 0.03%, Al: 3.0% ~ 6.0%, Ti: 0.012% ~ 0.052%, N: 0.0012% ~ 0.0042%, the balance is Fe and unavoidable impurities.

[0008] The microstructure of the hot-dip galvanized low-density steel consists 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%.

[0009] The yield strength of the hot-dip galvanized low-density steel is 330-500 MPa, the tensile strength is 590-700 MPa, the elongation is 25%-35%, and the density is less than 7.45×10 3 kg / m 3 .

[0010] The main functions of the components in the short process low-density steel in the present invention are:

[0011] 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%.

[0012] 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%.

[0013] Si: Si can inhibit the precipitation of cementite and also play a role in solid solution strengthening. 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.

[0014] 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. 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.

[0015] P: The P element plays a role in strengthening steel on the one hand, and inhibits the precipitation of cementite on the other hand.

[0016] S: S is a harmful element in steel, and the lower its content, the better.

[0017] 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.

[0018] 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.

[0019] A method for preparing low-density steel based on short-process hot-dip galvanizing, including converter or electric furnace smelting, medium-thin slab continuous casting and rolling, pickling, cold rolling, nickel plating, and hot-dip galvanizing processes; specifically including:

[0020] 1) Continuous casting and rolling of medium-thin slabs: Continuous casting of medium-thin slabs is adopted to obtain continuous casting slabs with a thickness of 130-190 mm; hot charging and hot delivery are carried out for hot rolling; the rolling process is as follows: the starting rolling temperature is 1000-1150°C, the final rolling temperature is 850-1000°C, the cooling method adopts laminar cooling method, and the coiling temperature is 500-700°C;

[0021] 2) After pickling to remove oxides on the surface of the hot-rolled steel sheet, cold rolling is performed, and the cold rolling reduction rate is 30% to 70%;

[0022] 3) Nickel plating: nickel plating is performed by electrochemical or chemical methods, and the thickness of the nickel layer is 10 to 30 μm;

[0023] 4) Hot-dip galvanizing: The heating and soaking temperature is 760-850℃, the soaking time is 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 controlled at 10-50℃ / s, and then the surface is galvanized, and the zinc pot temperature is 450-470℃.

[0024] Step 4) The skin-pass elongation of the galvanized strip is 0.3% to 0.6%.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The hot-dip galvanized low-density steel produced by the present invention can be used to produce automotive structural parts, safety parts, battery packs and other parts. The present invention adopts the production process of converter or electric furnace smelting, medium and thin slab continuous casting and rolling, pickling, cold rolling, nickel plating, and hot-dip galvanizing to produce hot-dip galvanized low-density steel with a yield strength of 330-500MPa, a tensile strength of 590-700MPa, and an elongation of 25%-35%, which has the advantages of low density, high formability, low emissions, and high surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a metallographic diagram based on short process hot dip galvanized low density steel. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation modes of the present invention are further described below in conjunction with examples. However, it should be noted that the implementation of the present invention is not limited to the following implementation modes.

[0029] Based on short process hot dip galvanized low density steel, see Figure 1 , the chemical composition of steel in mass percentage is:

[0030] C: 0.05% to 0.13%, Si: 0.4% to 0.9%, Mn: 0.6% to 1.2%, P ≤ 0.02%, S ≤ 0.03%, Al: 3.0% to 6.0%, Ti: 0.012% to 0.052%, N: 0.0012% to 0.0042%, the remainder is Fe and unavoidable impurities. The microstructure of hot-dip galvanized low-density steel is composed of ferrite, martensite, bainite and a small amount of austenite, with the volume percentage of ferrite being 70% to 85%, the total volume percentage of martensite and bainite being 8% to 20%, and the volume percentage of austenite being 5% to 10%.

[0031] The yield strength of hot-dip galvanized low-density steel is 330-500MPa, the tensile strength is 590-700MPa, the elongation is 25%-35%, and the density is less than 7.45×10 3 kg / m 3 .

[0032] The preparation method of short-process hot-dip galvanized low-density steel comprises the following steps:

[0033] 1) Smelting is carried out by converter or electric furnace smelting;

[0034] 2) Continuous casting and rolling of medium-thin slabs: The continuous casting process adopts continuous casting of medium-thin slabs to obtain continuous casting billets with a thickness of 130-190 mm; hot charging and hot delivery are carried out for hot rolling; the rolling process is as follows: the starting rolling temperature is 1000-1150°C, the final rolling temperature is 850-1000°C, the cooling method adopts laminar cooling method, and the coiling temperature is 500-700°C;

[0035] 3) Pickling: The conventional pickling method is used, the main purpose of which is to remove oxides on the surface of the hot-rolled steel plate.

[0036] 4) Cold rolling: The cold rolling reduction rate is 30-70%.

[0037] 5) Nickel plating: Nickel plating is performed by electrochemical or chemical methods, and the thickness of the nickel layer is 5 to 30 μm.

[0038] 6) Hot-dip galvanizing: The heating and soaking temperatures are both 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 10-50°C / s, and then the surface is galvanized. The zinc pot temperature is 450-470°C. The skin-clearing elongation of the galvanized strip is 0.3%-0.6%.

[0039] The hot-dip galvanized low-density steel with a yield strength of 330-500 MPa, a tensile strength of 590-700 MPa and an elongation of 25%-35% can be obtained by the above method.

[0040] The following are the chemical compositions and preparation methods of the embodiments:

[0041] The chemical composition of the embodiment is shown in Table 1. After obtaining the ingot, hot rolling is performed, and the hot rolling process is shown in Table 2. After hot rolling, pickling, cold rolling, nickel plating and hot-dip galvanizing are performed. The cold rolling nickel plating and hot-dip galvanizing annealing processes are shown in Table 3. The mechanical properties and surface quality results of the steel plate finally obtained are shown in Table 4.

[0042] Table 1 Chemical composition of the examples, wt%

[0043] Steel Grade C Si Mn P S Al Ti N A1 0.051 0.43 1.16 0.016 0.007 3.4 0.014 0.0024 A2 0.055 0.48 1.10 0.013 0.023 3.9 0.016 0.0036 A3 0.063 0.52 1.06 0.007 0.009 4.5 0.027 0.0016 A4 0.069 0.64 0.95 0.009 0.015 4.2 0.029 0.0019 A5 0.072 0.73 0.87 0.012 0.013 4.0 0.035 0.0029 A6 0.086 0.85 0.76 0.008 0.011 4.8 0.033 0.0034 A7 0.097 0.56 0.64 0.007 0.013 5.2 0.028 0.0039 A8 0.106 0.42 0.72 0.006 0.009 5.4 0.037 0.0029 A9 0.115 0.83 0.85 0.012 0.006 5.7 0.045 0.0019 A10 0.126 0.87 0.68 0.014 0.015 4.8 0.049 0.0029

[0044] Table 2 Hot rolling process of the embodiment

[0045]

[0046]

[0047] Table 3 Cold rolling and continuous annealing process of the embodiment

[0048]

[0049] Table 4 Mechanical test and surface quality test results of the examples

[0050]

[0051]

[0052] The present invention adopts the production process of converter or electric furnace smelting, medium and thin slab continuous casting and rolling, pickling, cold rolling, nickel plating and hot-dip galvanizing to produce hot-dip galvanized low-density steel with a yield strength of 330-500MPa, a tensile strength of 590-700MPa and an elongation of 25%-35%. The steel has the advantages of low density, high formability, low emission and high surface quality.

Claims

1. A short-process hot-dip galvanized low-density steel, characterized in that: The chemical composition of steel in mass percentage is: C: 0.05% ~ 0.13%, Si: 0.4% ~ 0.9%, Mn: 0.6% ~ 1.2%, P ≤ 0.02%, S ≤ 0.03%, Al: 3.0% ~ 6.0%, Ti: 0.012% ~ 0.052%, N: 0.0012% ~ 0.0042%, the balance is Fe and unavoidable impurities.

2. The short-process hot-dip galvanized low-density steel according to claim 1, characterized in that: The microstructure of the hot-dip galvanized low-density steel consists 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%.

3. The short-process hot-dip galvanized low-density steel according to claim 1, characterized in that: The yield strength of the hot-dip galvanized low-density steel is 330-500 MPa, the tensile strength is 590-700 MPa, the elongation is 25%-35%, and the density is less than 7.45×10 3 kg / m 3 .

4. A method for preparing low-density steel based on short-process hot-dip galvanizing according to any one of claims 1 to 3, characterized in that: It includes converter or electric furnace smelting, medium and thin slab continuous casting and rolling, pickling, cold rolling, nickel plating, and hot-dip galvanizing processes; specifically, it includes: 1) Continuous casting and rolling of medium-thin slabs: Continuous casting of medium-thin slabs is adopted to obtain continuous casting slabs with a thickness of 130-190 mm; hot charging and hot delivery are carried out for hot rolling; the rolling process is as follows: the starting rolling temperature is 1000-1150°C, the final rolling temperature is 850-1000°C, the cooling method adopts laminar cooling method, and the coiling temperature is 500-700°C; 2) After pickling to remove oxides on the surface of the hot-rolled steel sheet, cold rolling is performed, and the cold rolling reduction rate is 30% to 70%; 3) Nickel plating: nickel plating is performed by electrochemical or chemical methods, and the thickness of the nickel layer is 5 to 30 μm; 4) Hot-dip galvanizing: The heating and soaking temperature is 760-850℃, the soaking time is 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 controlled at 10-50℃ / s, and then the surface is galvanized, and the zinc pot temperature is 450-470℃.

5. The method for preparing low-density steel based on short-process hot-dip galvanizing according to claim 4, characterized in that: Step 4) The skin-pass elongation of the galvanized strip is 0.3% to 0.6%.

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