KR20200076071A - Heating method of aluminum plated steel sheet for hot forming - Google Patents

Abstract

The present invention relates to a heating method for performing heating for hot forming on a plated steel material, and more specifically, to a heating method of an aluminum plated steel material for hot forming, which includes: a step of preparing an aluminum plated steel material and a block for heating the aluminum plated steel material; a step of primary heating by contacting the aluminum plated steel material with the block; a step of secondary heating for non-contact heating of the primarily heated aluminum plated steel material; and a step of third heating the second heated aluminum plated steel material by contacting the same with the block.

Description

Heating method of aluminum plated steel for hot forming {HEATING METHOD OF ALUMINUM PLATED STEEL SHEET FOR HOT FORMING}

The present invention relates to a heating method in heating for hot forming a plated steel material, and more particularly, to a heating method for an aluminum plated steel material for hot forming.

In manufacturing automotive parts using automotive materials, a hot press forming (HPF) process is applied to reduce the weight of parts.

The hot press forming process includes a process of heating the material, and is usually performed in a heating furnace of a roller hearth furnace type.

On the other hand, in the case of a plating material, since the heating rate is slow during heating for hot press forming, the length of the heating furnace must be sufficiently long, which increases the installation space and cost of the heating furnace.

In order to solve the above problems, a method of rapidly heating with high-frequency heating or infrared heating, etc. may be applied instead of a heating furnace when heating a plating material, but in the case of high-frequency heating, the material is uniformly temperatured according to a blank shape. It is difficult to heat the furnace, and in the case of infrared heating, expensive equipment is required.

In addition, when the above plating material is an aluminum-plated steel material, there is a problem in that, during rapid heating, high-temperature heating is performed in a state in which the plating layer is not sufficiently alloyed and thus adheres to a roll or a mold.

In addition, as a method for securing the strength of the final parts in various ways by applying different heating temperatures for each area when heating the plating material, a method of passing through a heating furnace having a difference in ambient temperature, initially after heating at an intermediate temperature as a whole Various processes such as a method of additionally heating only a portion or a method of initially heating a portion at a high temperature and cooling only a portion have been proposed. However, the above methods have a problem in that the time period for adding the temperature difference to the plating material becomes longer, and thus the temperature transition period becomes longer.

Accordingly, there is a need for a method capable of quickly heating in an economical manner that minimizes the space for equipment for heating and improves productivity while ensuring a healthy plating layer during heating for hot press molding using a plating material.

One aspect of the present invention is to provide a method capable of rapid heating while securing a plating layer quality while heating to form an aluminum plated steel.

The subject of this invention is not limited to the above-mentioned content. Anyone having ordinary knowledge in the technical field to which the present invention pertains will have no difficulty in understanding additional problems of the present invention from the contents throughout the present specification.

One aspect of the present invention, preparing a block for heating an aluminum plated steel and the aluminum plated steel; Primary heating by contacting the aluminum plated steel with a block; A second heating step of contactlessly heating the first heated aluminum plated steel; And a third heating by contacting the second heated aluminum plated steel with a block,

The first heating step and the third heating step are performed by contacting different blocks, and the second heating step is performed so that the Fe content in the plating layer of the aluminum plated steel is 30 to 60% by weight. Provided is a method of heating an aluminum plated steel for hot forming.

Another aspect of the present invention comprises the steps of preparing a block for heating the aluminum plated steel and the aluminum plated steel and rapidly heating the aluminum plated steel in contact with the block,

The aluminum plated steel provides a method of heating an aluminum plated steel for hot forming, wherein the Fe content in the plating layer is alloyed to 30% by weight or more.

According to the present invention, in heating to form an aluminum plated steel material, it is possible to effectively shorten the heating time.

In addition, by the heating method according to the present invention, the quality of the plating layer can be satisfactorily ensured when the aluminum plated steel is heated.

1 is a graph showing a heating method of a conventional aluminum plated steel.
2 is a graph illustrating an example of a method for heating an aluminum plated steel and a method for heating a conventional aluminum plated steel in one embodiment of the present invention.
3 is in one embodiment of the present invention, it is shown by observing the surface state of the aluminum plated steel according to the primary heating temperature (the line observed in (b) and (c) of FIG. 3 is Thermocouple (T/C ) It is a wire mark).
Figure 4 shows the results of GDS analysis of the specimen heated to 695 ℃ by the conventional heating method of aluminum plated steel.
Figure 5 shows the results of GDS analysis of the specimen heated to 730 ℃ by the heating method of a conventional aluminum plated steel.
FIG. 6 is a view illustrating a cross-section of a plated layer of a plated steel material (comparative example) subjected to primary to tertiary heating in one embodiment of the present invention.
7 is a view showing a cross-section of a plated layer of a plated steel material (invention example) subjected to primary to tertiary heating in one embodiment of the present invention.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. However, the spirit of the present invention is not limited to the embodiments presented, and a person skilled in the art who understands the spirit of the present invention may add another component within the scope of the same spirit, change, delete, etc. Other embodiments included within the scope of the invention idea can be easily proposed, but this will also be included within the scope of the invention.

In order to mold using aluminum plated steel, when the aluminum plated steel is heated in a general heating furnace, it has a temperature rising curve as shown in FIG. 1. Specifically, as shown in FIG. 1, it can be seen that the temperature is rapidly increased at the initial stage of heating, but the temperature rise rate is greatly reduced while passing around 600 to 700°C. For this reason, it takes a lot of time for heating in the later stage of heating, and there is a problem in that productivity is lowered as additional equipment is required for sufficient heating.

The present inventors have confirmed the above-mentioned problems and studied in depth how to heat the second half of the heating, which is generally heated at a slow heating rate.

As a result, in heating the aluminum plated steel, it is possible to provide a heating method capable of securing the quality of the plating layer while reducing the total heating time to the target temperature by applying different heating means for each heating section, that is, the temperature section. It confirmed and came to complete this invention.

Hereinafter, the present invention will be described in detail.

A method of heating an aluminum plated steel for hot forming according to an aspect of the present invention includes preparing an aluminum plated steel and a block, and then first heating the aluminum plated steel by contacting the block with the block; A second heating step of contactlessly heating the first heated aluminum plated steel; And it may include the step of the third heating by contacting the secondary heated aluminum plated steel with a block.

It is shown in Figure 2 as an embodiment of a method for heating the aluminum plated steel for hot forming.

First, the aluminum-plated steel material is a steel material that can be molded as mentioned above, and any one produced by methods such as ordinary hot-dip plating, alloyed hot-dip plating, and electroplating may be used, and is not particularly limited.

However, in the case of the aluminum-plated steel, in addition to having a plating layer made of aluminum (Al) on at least one surface of the steel sheet, plating with a plating layer containing a small amount or a small amount of silicon (Si), iron (Fe), etc. in addition to aluminum It can be steel. At this time, the Si and Fe may be included in 6% to 12% and 1% to 4% by weight, respectively.

A means for heating the aluminum plated steel together with the above-mentioned aluminum plated steel, specifically, a block is prepared.

The block is a material capable of heating to a temperature intended in the present invention, and may be, for example, a mold heated to a desired temperature.

In general, in order to hot-form a plated steel material, first, the plated steel material is heated to a temperature (final heating temperature) for hot forming. After molding, molding is performed (see FIG. 1).

The present invention has technical significance in suggesting a new heating method, as it is confirmed that there are various problems when heating the aluminum plated steel in the same manner as described above.

Specifically, according to the present invention, in heating the aluminum plated steel to a final heating temperature, primary heating may be performed to an intermediate temperature, and then a subsequent heating process may be performed.

When the aluminum plated steel is rapidly heated to the final heating temperature, melting occurs in the aluminum plated layer, and there is a problem of sintering with a block or the like contacted during heating or molding.

Therefore, in the present invention, the aluminum plated steel material may be heated to a temperature in the range of a temperature intermediate to the final heating temperature, preferably lower than the melting point of the plated layer of the aluminum plated steel material, and more preferably 500 to 650°C. .

More specifically, after heating the block to the above-described temperature range, the aluminum plated steel can be first heated to the intended temperature range by contacting the block with the aluminum plated steel.

That is, in the present invention, by using a pre-heated block as a means for heating the aluminum plated steel material, there is an effect of shortening the heating time compared to a conventional heating method while minimizing equipment required for heating.

As described above, the aluminum-plated steel can be rapidly heated to the above-mentioned temperature range by first heating the aluminum-plated steel in contact with the heated block in a temperature range of 500 to 650°C.

Figure 3 shows the observation of the surface state of the aluminum plated steel according to the primary heating temperature.

Of these, FIG. 3(a) shows a specimen of aluminum plated steel before contacting the block heated to the primary heating temperature, and FIGS. 3(b) and 3(c) are heated to 600°C and 660°C, respectively. Each of the specimens after heating the aluminum plated steel using the block is shown.

As shown in FIG. 3, the specimen (b) subjected to primary heating by contact with a block heated to 600° C. can be confirmed that the surface (appearance) state appears at a level similar to that of the specimen (a) before the initial heating. Melting of the plating layer hardly occurred. On the other hand, the specimen (c) subjected to primary heating by contacting with a block heated to 660° C. shows traces of the plating layer melting on the surface.

Therefore, in performing the primary heating according to the above, when the temperature exceeds 650°C, there is a fear that the plating layer is fused to the block contacted for heating due to melting of the plating layer. On the other hand, if the temperature is lowered to less than 500°C, the time for subsequent secondary heating is excessively long, which is not preferable.

According to the above, it is possible to perform secondary heating of the aluminum plated steel material whose primary heating is completed, and in this case, in order to uniformly heat the plated steel material, non-contact heating may be performed under a heating furnace atmosphere.

Specifically, by controlling the ambient temperature in the heating furnace, the aluminum plated steel may be heated to a temperature range of 700°C or higher, preferably 700°C to Ac1.

4 is a GDS analysis result of the plated layer of a specimen cooled by heating the aluminum plated steel specimen from a heating furnace without a holding time after heating to 695°C in a general heating furnace. As shown in FIG. 4, it can be seen that alloying does not proceed to the surface layer portion because Fe is hardly detected in the surface layer portion (for example, about 10 μm in depth).

5 is a GDS analysis result of the plated layer of the specimen cooled by rapidly heating the same aluminum-plated steel specimen from the heating furnace to 730° C. and without the holding time. As shown in Fig. 5, it is observed that Fe is present in the surface layer portion (for example, about 10 µm deep). As described above, when the plated layer of the aluminum plated steel is alloyed, the melting point becomes high, and even if rapid heating is performed, the phenomenon that the plated layer melts can be suppressed.

Specifically, by performing secondary heating to the aluminum plated steel at a temperature of 700° C. or higher, iron (Fe) in the steel plate of the aluminum plated steel can diffuse into the plated layer, from which the plated layer of the aluminum plated steel Can induce alloying.

Through the alloying of the plating layer of the aluminum plating steel as described above, rapid heating is possible in a subsequent third heating process, and for this purpose, the secondary heating is performed so that the Fe content in the plating layer of the aluminum plating steel is 30 to 60% by weight. Can.

At the time of the secondary heating, the atmosphere of the heating furnace is not particularly limited, and any atmosphere can be used as long as it is set to an intended temperature.

According to the above, the third heating may be performed in order to heat the aluminum plated steel material, which has undergone secondary heating, to the final heating temperature, and at this time, the aluminum plated steel material may be heated to the desired temperature by contacting the block heated to the final heating temperature. You can.

Specifically, the block heated to a final heating temperature, preferably Ac3 or higher, and more preferably Ac3 to 950°C, may be contacted with the secondary heated aluminum plated steel.

The block used for the third heating is different from the block used for the first heating mentioned above, and specifically, a block heated to a different temperature is used at each heating time.

In the present invention, in the third heating to the final heating temperature in the above-described temperature range, the entire surface of the block contacting the aluminum plated steel may be heated to the final heating temperature. In addition, the contact surface is divided into two or more regions, and the two or more regions may be heated to different temperatures, wherein at least one region of the two or more regions may be heated to a final heating temperature. .

In the present invention, two or more regions of the block are not particularly limited, but can be divided into a high strength region and a low strength region. The high strength region may be a temperature region in which a hard phase may be formed in the final molded product (part), for example, Ac3 to 950°C. Meanwhile, a region other than the high-strength region may be set as a low-strength region, and the low-strength region may be a temperature region in which a soft phase may be formed in a portion in contact with the low-strength region in a plated steel material. It may be 700 °C or more to Ac1 or less.

As described above, by heating to the final heating temperature using the block, the heating time can be shortened compared to the case where the heating is performed to the final heating temperature using a conventional heating furnace (see FIG. 2).

In addition, as the heating temperature is set differently for each position of the block, the length of the temperature transition section of the aluminum plated steel can be minimized, and the temperature section can be set in various ways to increase the degree of freedom of adding a temperature difference. have.

In addition, during the first heating of the aluminum plated steel, the heating is shortened while maintaining the quality of the plated layer by performing primary heating using the block to the temperature for alloying the plated layer and then performing secondary heating in a non-contact heating process. The effect can be obtained.

On the other hand, according to another aspect of the present invention, in heating an aluminum plated steel, the aluminum plated steel may use an alloyed Fe content in the plating layer of 30% or more, and contact the alloyed aluminum plated steel with a block To the final heating temperature.

That is, the heating process (primary and secondary heating processes) for alloying the aluminum plated steel material as described above can be omitted by using an aluminum plated steel material in which the plating layer is already alloyed through alloying heat treatment or the like.

Here, the term "alloying heat treatment" means a condition for alloying heat treatment of a conventional aluminum plated steel material, and the conditions are not particularly limited.

The alloyed aluminum plated steel material may be one obtained by alloying a plated layer through an alloying heat treatment of an aluminum plated steel material having a plated layer having the aforementioned alloy composition.

The step of rapidly heating the alloyed aluminum plated steel may use a block as described above, and may be performed by contacting the aluminum plated steel with a block heated to a specific temperature.

Specifically, after heating the block to a temperature for forming the aluminum plated steel, that is, a final heating temperature, the heated block may be brought into contact with the aluminum plated steel.

In addition, the surface of the block contacting the aluminum plated steel may be divided into two or more regions, and the two or more regions may be heated to different temperatures, where at least one region of the two or more regions is final. It may be heated to a heating temperature.

The two or more regions of the block may be divided into a high-strength region and a low-strength region as described above, and detailed descriptions thereof will be omitted.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the items described in the claims and the items reasonably inferred therefrom.

( Example )

An aluminum plated steel material having a plating layer containing 9% Si, 2.5% Fe, balance Al and unavoidable impurities by weight% was prepared.

Thereafter, one aluminum plated steel was first heated to 500° C. by contacting with a heated block, and then heated to 600° C. under a heating furnace atmosphere, and then heated to 900° C. for 3 seconds to maintain for 15 seconds. At this time, the third heating was performed by contacting the block. Subsequently, after cooling the aluminum plated steel having completed the third heating, the plating layer was observed with a scanning electron microscope, and the results are shown in FIG. 6.

On the other hand, the other aluminum plated steel was first heated to 500° C. by contacting with a heated block, and then heated to 710° C. under a heating furnace atmosphere for 3 seconds and then heated to 900° C. for 3 seconds. At this time, the third heating was performed by contacting the block. Subsequently, after cooling the aluminum plated steel having completed the third heating, the plating layer was observed with a scanning electron microscope, and the results are shown in FIG. 7.

As shown in Fig. 6, a dark portion of Al rich in low melting point is observed on the surface of the plated layer, which is due to the fact that the plated layer of the aluminum plated steel is not sufficiently alloyed.

On the other hand, as shown in FIG. 7, as the alloying of the plating layer was sufficiently performed in the primary and secondary heating processes, it was possible to secure a healthy plating layer even after tertiary heating by block contact. This is to prevent the phenomenon that the plating layer adheres to the block in the process of heating the aluminum plated steel.

Claims (8)

Preparing an aluminum plated steel and a block for heating the aluminum plated steel;
Primary heating by contacting the aluminum plated steel with a block;
A second heating step of contactlessly heating the first heated aluminum plated steel; And
And a third heating by contacting the second heated aluminum plated steel with a block,
The first heating step and the third heating step are performed by contacting different blocks, and the second heating step is performed so that the Fe content in the plating layer of the aluminum plated steel is 30 to 60% by weight. Method of heating aluminum plated steel for hot forming.
According to claim 1,
The first heating step is performed by contacting the aluminum plated steel material with a block heated in a temperature range of 500 to 650°C to heat the aluminum plated steel material for hot forming.
According to claim 1,
The second heating step,
A method of heating an aluminum plated steel for hot forming, wherein the primary heated aluminum plated steel is contactlessly heated to a temperature of 700° C. or higher under an atmosphere of a heating furnace.
According to claim 1,
The step of heating the secondary heated aluminum plated steel third,
The entire surface of the block contacting the aluminum plated steel is heated to Ac3~950°C, or
The surface of the block is divided into two or more regions, and one or more regions of the two or more regions are heated to Ac3~950°C, and the remaining regions are heated to 700°C or more to Ac1 or less. Method of heating steel.
According to claim 1,
A method of heating an aluminum plated steel for hot forming, further comprising forming and cooling the third heated aluminum plated steel.
Preparing a block for heating the aluminum plated steel and the aluminum plated steel and rapidly heating the aluminum plated steel in contact with the block,
The aluminum plated steel is a method of heating the aluminum plated steel for hot forming, wherein the Fe content in the plating layer is alloyed to 30% by weight or more.
The method of claim 6,
The step of rapidly heating the aluminum plating steel alloyed with the plating layer is
The entire surface of the block contacting the aluminum plated steel is heated to Ac3~950°C, or
The surface of the block is divided into two or more regions, and one or more regions of the two or more regions are heated to Ac3~950°C, and the remaining regions are heated to 700°C or more to Ac1 or less. Method of heating steel.
The method of claim 1 or 6,
The aluminum plated steel material includes a plated steel plate and an aluminum plated layer on at least one surface of the plated steel plate,
The aluminum plating layer is 6% to 12% by weight of silicon (Si), 1 to 4% of iron (Fe), residual aluminum (Al) and other inevitable impurities heating method of aluminum plating steel for hot forming .

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