CN114892074B - A kind of hot-dip aluminum-silicon medium-manganese steel suitable for hot forming process and preparation method thereof - Google Patents

Abstract

The application relates to a hot-dip aluminum-silicon medium-manganese steel suitable for a hot forming process and a preparation method thereof, belonging to the technical field of iron and steel. The hot-dip aluminum-silicon medium-manganese steel suitable for the hot forming process provided by the application, by using the medium-manganese steel as the coating substrate, the addition of Mn element is controlled to be 8%-12% (wt%) to ensure that there is a sufficient amount of Mn The element diffuses into the coating. After the hot-dipped aluminum-silicon is out of the pot, the coated substrate is cooled in sections at high temperature and low temperature. In the high temperature section, a low cooling rate is used to ensure that the Mn element diffuses into the coating during the growth of the coating. In the low temperature area, a high cooling rate is used to ensure The thickness of the coating is not super thick; the holding time is increased during the subsequent thermoforming heating process, so that the Mn element in the substrate continues to diffuse into the coating, so that the content of the Mn element in the coating is between 0.8%-2% (wt%), due to the Mn The presence of elements reduces the hardness of the coating, thereby increasing the toughness of the coating to reduce the tendency of cracking in the subsequent hot forming process.

Description

A kind of hot-dip aluminum-silicon medium-manganese steel suitable for hot forming process and preparation method thereof

technical field

The application relates to the technical field of iron and steel, in particular to a hot-dip aluminum-silicon-medium manganese steel suitable for a hot forming process and a preparation method thereof.

Background technique

Hot-formed steel means that the steel plate is heated at a high temperature (generally 900°C-950°C) and then formed once, and then cooled rapidly, thereby comprehensively improving the strength of the steel plate. The steel processed in this way is called hot-formed steel.

Medium manganese steel refers to austenitic manganese steel with a manganese content between 4% and 12% (wt%). Due to the addition of more manganese, the austenitization temperature can be reduced, thereby reducing the temperature of the hot forming process. The heating temperature can reduce energy consumption, reduce scale and decarburization layer, and can increase the elongation of the formed part.

Al-Si coatings are commonly used for hot forming steels. Al-Si coatings have excellent high temperature resistance and will not melt and evaporate under high temperature heating conditions. However, the addition of about 10% silicon element in the Al-Si coating leads to a decrease in the plasticity of the coating. In addition, during the heating process, the Fe element will diffuse with the Al element to form a Fe-Al alloy brittle phase, so there are more in the coating after forming. Cracks affect the corrosion resistance and mechanical properties of the coating.

Contents of the invention

The present application provides a hot-dipped aluminum-silicon medium-manganese steel suitable for a hot forming process and a preparation method thereof to solve the technical problem in the prior art that the coating plasticity of the hot-dipped aluminum-silicon hot-formed steel is poor after hot forming.

In the first aspect, the present application provides a hot-dip aluminum-silicon-medium-manganese steel suitable for hot forming process, the hot-dip aluminum-silicon medium-manganese steel includes a coated substrate and an aluminum-silicon coating, wherein, in terms of mass fraction,

The first chemical composition of the coated substrate includes: C: 0.05%-0.2%, Mn: 8%-12%, Al: 0.5%-2%, Si: 0.1%-0.4%, Nb: 0.01%-0.05 %, Cr: 0.05%-0.2%, Cu: 0.01%-0.2%, Mo: 0.5%-1%, V: 0.01%-0.05%, P: ≤0.005%, N: ≤0.005%, S: ≤0.005 %, the rest is Fe and unavoidable inclusions;

The second chemical composition of the aluminum-silicon coating includes: Si: 10%-16%, Fe: 1%-3%, and the rest is Al and inevitable inclusions.

Optionally, in terms of volume fraction, the metallographic structure of the hot-dip aluminum-silicon-manganese steel includes: martensite: 70%-95%, ferrite: 0-15%, retained austenite: 5% -15%.

Optionally, the thickness of one side of the aluminum-silicon coating is 5-30 μm, and the thickness of the alloy layer of the aluminum-silicon coating is 1-5 μm.

In a second aspect, the present application provides a method for preparing a hot-dip aluminum-silicon-medium manganese steel suitable for a hot forming process described in the first aspect, the method comprising:

Obtain cold-rolled medium manganese steel coated substrate;

performing continuous annealing on the coated substrate, followed by first cooling;

Hot-dip the coated substrate after the first cooling through a plating solution containing the second chemical composition, and then perform second cooling in a staged cooling manner to obtain hot-dipped aluminum-silicon-medium manganese steel;

The staged cooling includes:

Cooling in the high temperature section, the cooling in the high temperature section is cooled to 450°C-500°C at a cooling rate of 2°C/s-10°C/s;

Cooling in the low temperature section, the cooling in the low temperature section is to cool down to below 250°C at a cooling rate of 30°C/s-50°C/s.

Optionally, the obtained cold-rolled medium manganese steel coated substrate includes:

obtaining a cast slab of medium manganese steel containing the first chemical composition;

Hot rolling the medium manganese steel cast slab to obtain a medium manganese steel hot rolled coil;

The hot-rolled medium manganese steel coil is covered and cold-rolled to obtain a cold-rolled medium-manganese steel coated substrate; wherein,

The parameters of the mask annealing include: the annealing temperature is 500°C-620°C, and the annealing time is 10h-30h;

The parameters of cold rolling include: cold rolling reduction is 30%-60%.

Optionally, the first cooling includes: cooling to 660°C-730°C at a cooling rate of 10°C/s-50°C/s, and the second cooling includes: cooling to below 250°C.

Optionally, the parameters of the continuous annealing treatment include:

The annealing temperature is 720°C-850°C, the annealing time is 100s-200s, and the dew point temperature is -20°C to 5°C;

In terms of volume fraction, the gas components of the annealing atmosphere include: H ₂ : 3%-8%, and the rest is N ₂ .

In a third aspect, the present application provides a method for preparing a thermoformed part, the method comprising:

Obtain the hot-dip aluminum-silicon medium-manganese steel described in the first aspect;

The hot-dipped aluminum-silicon medium-manganese steel is skinned, stretched and coiled to obtain a hot-dipped aluminum-silicon steel coil;

The steel coil is uncoiled and blanked and then subjected to thermoforming processing to obtain parts. The thermoforming process is as follows: heating temperature is 750°C-900°C, heating time is 5min-20min, transfer time is 4s-10s and holding time is 6s -15s, cool down to below 200°C by water cooling and open the mold.

Optionally, the aluminum-silicon coating on one side of the hot-dipped aluminum-silicon steel coil after thermoforming has a thickness of 10-50 μm, wherein the thickness of the alloy layer of the aluminum-silicon coating is 2-10 μm.

Optionally, in terms of volume fraction, the metallographic structure of the hot-formed part includes: martensite: 75%-95%, ferrite: 0-15%, retained austenite: 5%-10%.

Compared with the prior art, the above-mentioned technical solution provided by the application has the following advantages:

The hot-dip aluminum-silicon medium-manganese steel suitable for the hot forming process provided by the application, by using the medium-manganese steel as the coating substrate, the addition of Mn element is controlled to be 8%-12% (wt%), so as to ensure that there is a sufficient amount of Mn The element diffuses into the coating. After the hot-dipped aluminum-silicon is out of the pot, the coated substrate is cooled in sections at high temperature and low temperature. In the high temperature section, a low cooling rate is used to ensure that the Mn element diffuses into the coating during the growth of the coating. In the low temperature area, a high cooling rate is used to ensure The thickness of the coating is not super thick; increase the holding time during the subsequent thermoforming heating process, so that the Mn element in the substrate continues to diffuse into the coating, so that the content of the Mn element in the coating is between 0.8%-2% (wt%), due to Mn The presence of elements reduces the hardness of the coating, thereby increasing the toughness of the coating to reduce the tendency of cracking in the subsequent hot forming process. In order to control the thickness of the aluminum-silicon coating and the alloy layer, the application appropriately increases the content of the Si element in the coating, which is 10%-16% (wt%), thereby increasing the Fe-Al-Si ternary element in the aluminum-silicon coating during the heating process. Phase content, in order to hinder the growth of Fe-Al binary phase.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description serve to explain the principles of the invention.

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, In other words, other drawings can also be obtained from these drawings without paying creative labor.

Fig. 1 is the cross-sectional coating morphology and EDS analysis diagram of the hot-dipped aluminum-silicon medium-manganese steel in Example 3 of the present application after hot forming.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of this application, but not all of them. Based on the embodiments in the present application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present application.

In the first aspect, the present application provides a hot-dip aluminum-silicon-medium-manganese steel suitable for hot forming process, the hot-dip aluminum-silicon medium-manganese steel includes a coated substrate and an aluminum-silicon coating, wherein, in terms of mass fraction,

The first chemical composition of the coated substrate includes: C: 0.05%-0.2%, Mn: 8%-12%, Al: 0.5%-2%, Si: 0.1%-0.4%, Nb: 0.01%-0.05 %, Cr: 0.05%-0.2%, Cu: 0.01%-0.2%, Mo: 0.5%-1%.V: 0.01%-0.05%, P: ≤0.005%, N: ≤0.005%, S: ≤0.005 %, the rest is Fe and unavoidable inclusions;

The second chemical composition of the aluminum-silicon coating includes: Si: 10%-16%, Fe: 1%-3%, and the rest is Al and inevitable inclusions.

In the present application, the positive effect of the first chemical composition (mass fraction, wt%) of the coated substrate:

C: 0.05%-0.2%; for medium manganese steel, the main function of C element is to increase the stability of retained austenite. With the increase of C content, the stability of retained austenite increases, but the increase of C content will cause forming Therefore, the C content is controlled in the range of 0.05-0.2.

Mn: 8%-12%; Mn element is the core element of medium manganese steel, which plays a role in expanding the austenite phase zone and stabilizing austenite. As the Mn content increases, the retained austenite content increases, and the strength of the ferrite matrix also increases. However, if the Nn content is too high, it will cause casting difficulties, increase the band structure in the substrate, and reduce the plasticity. Therefore, the Mn content should not be too high. The purpose of specifying that the Mn element content in the substrate is 8-12 is to ensure that the Mn element in the coating can reach the specified range during the heating process of thermoforming.

Si: 0.1%-0.4%; Si element is a ferrite forming element, which can promote the formation of ferrite during annealing, and can inhibit the formation of carbides to improve the stability of retained austenite. However, the increase of Si content will cause the deterioration of the surface quality of the substrate, thereby affecting the wettability of the hot-dip process.

Al: 0.5%-2%; Adding a certain amount of Al elements instead of Si elements in the substrate can improve the surface quality of the substrate, and can reduce the density of the substrate, which is more conducive to the lightweight of the car body. By adding Si and Al elements, the formed parts There is a stable retained austenite in it, which can increase the elongation of the part and improve the safety of the part in the case of deformation during subsequent use.

Nb: 0.01%-0.05%; Nb has the effect of significantly refining grains, and can hinder the formation of bainite, promote the nucleation of martensite, and increase the content of acicular ferrite and retained austenite. Considering the cost, the amount of Nb added is 0.01-0.05.

Cr: 0.05%-0.2%; Cr can improve the hardenability and tempering stability of steel, and ensure that the parts have good comprehensive mechanical properties after direct forming or forming and tempering.

Cu: 0.01%-0.2%; Cu can improve the stability of austenite and strengthen ferrite to increase the corrosion resistance of the substrate. However, excessive addition of Cu will cause copper embrittlement, and the addition of Cu should be controlled below 0.2%.

Mo: 0.5%-1%; Mo element mainly plays the role of improving hardenability and thermal stability, so that the material can maintain sufficient strength and creep resistance under high temperature conditions.

V: 0.01%-0.05%; adding a small amount of V can improve the thermal stability of the substrate, refine the grains of the substrate during austenitization, and improve the tempering stability of martensite.

In this application, the mechanical properties of hot-dip aluminum-silicon medium-manganese steel include: tensile strength: 1200-1700MPa, yield strength: 500-1000Mpa, elongation A50: 7%-15%

As an embodiment of the present application, in terms of volume fraction, the metallographic structure of the hot-dip aluminum-silicon medium-manganese steel includes: martensite: 70%-95%, ferrite: 0-15%, retained austenite Body: 5%-15%.

As an embodiment of the present application, the thickness of the aluminum-silicon coating alloy layer is 1-5 μm, the thickness of one side of the aluminum-silicon coating is 5-30 μm, and the thickness of one side of the aluminum-silicon coating is preferably 15-25 μm.

In a second aspect, the present application provides a method for preparing a hot-dip aluminum-silicon-medium manganese steel suitable for a hot forming process described in the first aspect, the method comprising:

Obtain cold-rolled medium manganese steel coated substrate;

performing continuous annealing on the coated substrate, followed by first cooling;

Hot-dip the coated substrate after the first cooling through a plating solution containing the second chemical composition, and then perform second cooling in a staged cooling manner to obtain hot-dipped aluminum-silicon-medium manganese steel;

The staged cooling includes:

Cooling in the high temperature section, the cooling in the high temperature section is cooled to 450°C-500°C at a cooling rate of 2°C/s-10°C/s;

Cooling in the low temperature section, the cooling in the low temperature section is to cool down to below 250°C at a cooling rate of 30°C/s-50°C/s.

As an embodiment of the present application, the obtained cold-rolled medium manganese steel coated substrate includes:

obtaining a cast slab of medium manganese steel containing the first chemical composition;

Hot rolling the medium manganese steel cast slab to obtain a medium manganese steel hot rolled coil;

The hot-rolled medium manganese steel coil is covered and cold-rolled to obtain a cold-rolled medium-manganese steel coated substrate; wherein,

The parameters of the mask annealing include: the annealing temperature is 500°C-620°C, and the annealing time is 10h-30h;

The parameters of cold rolling include: cold rolling reduction is 30%-60%.

As an embodiment of the present application, the first cooling includes: cooling to 660°C-730°C at a cooling rate of 10°C/s-50°C/s, and the second cooling includes: cooling to below 250°C.

As an embodiment of the present application, the parameters of the continuous annealing treatment include:

The annealing temperature is 720°C-850°C, the annealing time is 100s-200s, and the dew point temperature is -20°C to 5°C;

In terms of volume fraction, the gas components of the annealing atmosphere include: H ₂ : 3%-8%, and the rest is N ₂ .

In a third aspect, the present application provides a method for preparing a thermoformed part, the method comprising:

Obtain the hot-dip aluminum-silicon medium-manganese steel described in the first aspect;

The hot-dipped aluminum-silicon medium-manganese steel is skinned, stretched and coiled to obtain a hot-dipped aluminum-silicon steel coil;

The steel coil is uncoiled and blanked and then subjected to thermoforming processing to obtain parts. The thermoforming process is as follows: heating temperature is 750°C-900°C, heating time is 5min-20min, transfer time is 4s-10s and holding time is 6s -15s, cool down to below 200°C by water cooling and open the mold. Wherein, the heating time is preferably 7min-15min.

As an embodiment of the present application, the single-side thickness of the aluminum-silicon coating of the hot-dipped aluminum-silicon steel coil after hot-forming is 10-50 μm, and the thickness of the alloy layer is 2-10 μm, wherein the single-side thickness of the aluminum-silicon coating is preferably 25 μm. -40 μm.

As an embodiment of the present application, in terms of volume fraction, the metallographic structure of the hot-formed part includes: martensite: 75%-95%, ferrite: 0-15%, retained austenite: 5% -10%.

In this application, the mechanical properties of the thermoformed parts include: tensile strength: 1400-1900MPa, yield strength: 900-1400MPa, elongation A50: 9%-15%.

The hot-dipped aluminum-silicon-medium-manganese steel suitable for the hot-forming process of the present application, its preparation method, and the preparation method of hot-formed parts will be described in detail below in conjunction with specific examples.

Substrate alloy composition (wt%) in different embodiment/comparative example in table 1

/ C mn al Si Nb Cr Cu Mo V Example 1 0.05 8 0.5 0.1 0.01 0.05 0.05 0.5 0.01 Example 2 0.1 9 1 0.2 0.02 0.1 0.1 0.7 0.02 Example 3 0.15 10 1.5 0.3 0.04 0.15 0.15 0.8 0.04 Example 4 0.2 12 2 0.4 0.05 0.2 0.2 1 0.05 Comparative example 1 0.15 5 1 0.5 0.05 0.01 0.04 0.4 0.04 Comparative example 2 0.15 10 1.5 0.3 0.04 0.15 0.15 0.8 0.04 Comparative example 3 0.15 10 1.5 0.3 0.04 0.15 0.15 0.8 0.04

Plating solution composition (wt%) in the different embodiment/comparative examples of table 2

/ al Si Fe Example 1 89 10 1 Example 2 86 12 2 Example 3 83 14 3 Example 4 81 16 3 Comparative example 1 83 14 3 Comparative example 2 90 7 3 Comparative example 3 83 14 3

Physical and chemical properties of materials after hot-dip in different embodiments/comparative examples of table 3

Thermoforming process in different embodiments/comparative examples of table 4

/ Heating temperature/℃ Heating time/min transfer time/s Holding time/s Example 1 900 5 10 15 Example 2 850 10 8 12 Example 3 800 15 6 10 Example 4 750 20 4 6 Comparative example 1 800 15 6 10 Comparative example 2 800 15 6 10 Comparative example 3 900 4 10 15

Physical and chemical properties after thermoforming in different embodiments/comparative examples of table 5

The preparation method of the thermoformed part of the application embodiment 1-4 and comparative example 1-3 comprises the following steps:

1) According to the composition of the substrate described in Table 1, the rest is Fe and unavoidable inclusions. After molten iron pretreatment, converter smelting, alloy fine-tuning, LF furnace refining, continuous casting, hot rolling and cold rolling, the medium manganese steel for hot-dip aluminum-silicon is obtained substrate. Among them, during the hot rolling process, the casting billet temperature ranges from 1200°C to 1300°C, and the final rolling temperature ranges from 800°C to 950°C. After hot-rolling, the hot-rolled coil needs to be annealed. The annealing temperature is 500°C-620°C, and the annealing time is 10h-30h. The hot-rolled coils are cold-rolled after pickling, and the cold-rolling reduction is 30%-60%.

2) The above-mentioned cold-rolled substrate is subjected to continuous annealing treatment, the continuous annealing temperature is controlled between 720°C-850°C, the annealing time is controlled between 100s-200s, the dew point temperature in the furnace is controlled at -20°C-5°C, the annealing furnace The inner atmosphere is (by volume fraction): 3%-8% H ₂ , and the rest is N2. Then cool to 660°C-730°C at a cooling rate of 10°C/s-50°C/s, the temperature of the aluminum-silicon pot is 650°C-700°C, the composition of the plating solution is shown in Table 2, and the hot-dip time is 2s- 10s. After plating, cool at 2°C/s-10°C/s to 450°C-500°C, and then cool at 30°C/s-50°C/s to below 250°C. 3.

3) After smoothing, stretching and straightening to adjust the shape of the plate, after being oiled, it is coiled into a steel coil, and then cut and blanked to obtain blanks for the production of parts, and the forming process is carried out according to the thermoforming process shown in Table 4 , the physical and chemical properties of the material after forming are shown in Table 5.

In different embodiments, the toughness of the coating is characterized by measuring the hardness of the coating. The greater the hardness of the coating, the poorer the toughness of the coating. The hardness at 20 μm (with the surface as the zero point) of the coating after forming is measured. There is no Mn element in the coating When the coating hardness is about 1000HV. From Comparative Example 1, it can be seen that when the content of Mn element in the substrate is reduced, the performance of the substrate will be seriously affected, the tensile strength and yield strength are greatly reduced, and the mechanical properties after forming are also correspondingly reduced. Due to the low content of Mn element in the substrate, even if the hot forming method in the patent is used, the content of Mn element in the coating is still low, and the hardness of the coating is high and the toughness is not good.

From Comparative Example 2, it can be seen that when the content of Si element in the plating solution decreases, the thickness of the coating layer and the thickness of the alloy layer will both increase, and the increase of the thickness of the alloy layer will hinder the diffusion of Mn element. In addition, as the thickness of the coating increases, the Mn element is likely to cause uneven distribution in the coating, and stress concentration will occur during the deformation process, thereby affecting the toughness of the coating. From Table 3 and Table 5, the increase of coating thickness slightly reduces the tensile strength and yield strength of the forming, mainly affects the elongation of the material, the elongation before forming decreases by 20%, and the elongation after forming decreases by 33%. From Comparative Example 3, it can be seen that when the holding time in the thermoforming process is reduced, the content of Mn element in the coating decreases, resulting in an increase in the hardness of the coating, thereby reducing the elongation of the material. The invention has excellent economic benefits and low production difficulty, and can obviously improve the toughness of the aluminum-silicon (Al-Si) coating.

Compared with the prior art, the above-mentioned technical solution provided by the application has the following advantages:

(1) In order to improve the toughness of the coating, in the prior art, rare earth elements such as cerium are often added to the plating solution, which will increase the cost and increase the difficulty of production. However, no additional elements are added in this patent, and only Al is present in the plating solution. , Si, Fe three elements, control the coating thickness by adjusting the content of Si element.

(2) Using medium manganese steel instead of traditional manganese boron steel as the substrate can reduce the heating temperature in the hot forming process, save energy and reduce emissions, and the formed parts have better tensile strength and elongation.

(3) By adjusting the cooling method after the material leaves the plating solution pot, two methods are used for cooling and prolonging the heat preservation time in the hot forming process, so that the Mn element in the substrate can diffuse into the coating, and the Mn element content in the coating can be reduced. (wt%) is controlled between 0.8-2, plays the role of reducing the hardness of the coating and improving the toughness of the coating.

Specific description of the accompanying drawings:

Among Fig. 1, the main chemical composition ((mass fraction, %)) of aluminum-silicon coating in spectrogram 1-4 is as follows:

It can be seen from FIG. 1 that after the hot-dip aluminum-silicon medium-manganese steel of the present application is hot-formed, there are no microcracks in the aluminum-silicon coating.

It should be noted that in this article, relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply these No such actual relationship or order exists between entities or operations. Furthermore, the term "includes", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes the elements not expressly listed. Other elements mentioned above, or also include elements inherent in such process, method, article or equipment. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

The above descriptions are only specific embodiments of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Accordingly, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims (6)

1. A method for preparing hot-dip aluminum-silicon-medium-manganese steel suitable for hot forming process is characterized by comprising the following steps:

obtaining a cold-rolled medium manganese steel coating substrate;

carrying out continuous annealing treatment on the coated substrate, and then carrying out first cooling;

carrying out hot plating on the first cooled plating base plate by using plating solution containing second chemical components, and then carrying out second cooling in a sectional cooling manner to obtain hot-plated aluminum-silicon-medium-manganese steel;

the staged cooling includes:

cooling at a high temperature section, wherein the cooling at the high temperature section is carried out at a cooling speed of 2-10 ℃/s to 450-500 ℃;

cooling the low-temperature section to below 250 ℃ at a cooling speed of 30-50 ℃/s;

the hot-dip aluminum-silicon medium manganese steel comprises a coating substrate and an aluminum-silicon coating, wherein the coating substrate comprises, by mass fraction,

the first chemical composition of the coating substrate comprises: c:0.05% -0.2%, mn:8% -12%, al:0.5% -2%, si:0.1% -0.4%, nb:0.01% -0.05%, cr:0.05% -0.2%, cu:0.01% -0.2%, mo:0.5% -1%, V:0.01% -0.05%, P: less than or equal to 0.005 percent, N: less than or equal to 0.005 percent, S: less than or equal to 0.005 percent, and the balance of Fe and inevitable impurities;

the second chemical composition of the aluminum-silicon coating comprises: si:10% -16%, fe: 1-3 percent of Al and inevitable impurities in balance;

according to volume fraction, the metallographic structure of the hot-dip aluminum-silicon medium manganese steel comprises: martensite: 70% -95%, ferrite: 0-15%, retained austenite: 5% -15%;

the thickness of one side of the aluminum-silicon coating is 5-30 mu m, wherein the thickness of the alloy layer of the aluminum-silicon coating is 1-5 mu m.

2. The method of claim 1, wherein the obtaining of the cold rolled medium manganese steel coated substrate comprises:

obtaining a medium manganese steel casting blank containing the first chemical component;

carrying out hot rolling on the medium manganese steel casting blank to obtain a medium manganese steel hot rolled coil;

performing cover annealing and cold rolling on the medium manganese steel hot-rolled coil to obtain a cold-rolled medium manganese steel coated substrate; wherein,

the parameters of the cover retreat comprise: the annealing temperature is 500-620 ℃, and the annealing time is 10-30 h;

the parameters of the cold rolling comprise: the cold rolling reduction is 30-60%.

3. The method of manufacturing according to claim 1, wherein the first cooling includes: cooling to 660-730 ℃ at a cooling speed of 10-50 ℃/s.

4. The method of claim 1, wherein the parameters of the continuous annealing process include:

the annealing temperature is 720-850 ℃, the annealing time is 100-200 s, and the dew point temperature is-20 ℃ to 5 ℃;

the gas composition of the annealing atmosphere comprises, in volume fraction: h ₂ :3% -8% of N ₂ 。

5. A method of making a thermoformed part, said method comprising:

obtaining the hot-dipped aluminum-silicon-medium-manganese steel according to any one of claims 1 to 4;

performing finishing, straightening and coiling on the hot-dip aluminum-silicon medium manganese steel to obtain a hot-formed hot-dip aluminum-silicon steel coil;

the steel coil is uncoiled and blanked and then subjected to hot forming processing to obtain a part, and the hot forming process comprises the following steps: heating at 750-900 deg.C for 5-20 min, transferring for 4-10 s, maintaining pressure for 6-15 s, cooling to below 200 deg.C by water cooling, and opening the mold.

6. The method of claim 5, wherein the metallographic structure of the hot-formed part comprises, in volume fraction: martensite: 75% -95%, ferrite: 0-15%, retained austenite: 5 to 10 percent.

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