KR102180802B1 - Manufacturing method of aluminum plated member - Google Patents

Abstract

In the present invention, in manufacturing a member having an intended shape by forming an aluminum-plated steel material, a member having high strength while solving problems such as that the plated layer is maintained soundly during cold forming and the plated layer is volatilized during heat treatment after forming It is intended to provide a method that can be manufactured.

Description

Manufacturing method of aluminum plating member {MANUFACTURING METHOD OF ALUMINUM PLATED MEMBER}

The present invention relates to a method of manufacturing an aluminum plated member.

In recent years, the application of high-strength steel is increasing due to the demand for weight reduction of automobile parts.

However, when cold forming is applied to make high-strength steel into automobile parts, the number of rolls increases during roll forming due to an increase in the radius of curvature of the part or an increase in the forming step due to the limitation of securing formability due to the low formability of the high-strength steel. There is.

In addition, in order to eliminate the increased springback phenomenon of the high-strength steel, the forming step increases, and accordingly, the number of rolls increases during mold or roll forming. In addition, there are problems such as an increase in the price of a mold or roll and an increase in wear for securing structural safety and increase in load during molding and roll forming due to the high strength of the material.

As an alternative to solve the above problems, a technique of performing post heat treatment after cold forming high strength steel has been proposed. Specifically, while having low strength in the cold forming step, since it has high strength through post heat treatment, it is possible to partially solve various problems that occur during cold forming of high-strength steel.

However, in the case of performing post-heat treatment after cold forming high-strength steel, when the high-strength steel is a plated material, the plating layer is damaged in the cold forming step, or in the post heat treatment process, most rapidly heat up to shorten the processing time. As a result, the plating layer may be volatilized or alloying may not be sufficient.

However, in the case of the heat treatment process after roll forming performed as a continuous process, rapid heating is essential in order to match the process time.

Therefore, in the case of rapid heating for post-heat treatment after molding of the plated material, development of a technology capable of achieving high strength while securing the quality of the plated layer is required.

Korean Patent Application Publication No. 10-2010-0132371

In one aspect of the present invention, in manufacturing a member having an intended shape by forming an aluminum-plated steel material, a method for manufacturing a member having high strength while solving problems such as volatilization of the plating layer during heat treatment after forming I want to provide.

The subject of the present invention is not limited to the above description. Anyone of ordinary skill in the art to which the present invention pertains will not have difficulty in understanding the additional subject of the present invention from the contents throughout the present specification.

One aspect of the present invention, the step of preparing an aluminum-plated steel; Alloying the aluminum-plated steel material; Cold forming the alloyed aluminum-plated steel material; And heat-treating the cold-formed aluminum plated steel,

The alloyed aluminum plated steel material provides a method of manufacturing an aluminum plated member having an Fe content of 60 to 70% by weight in the plated layer.

Advantageous Effects of Invention According to the present invention, it is possible to provide a method capable of obtaining a member having a significantly improved strength while ensuring a good plating layer even when forming and rapid heating are performed on an aluminum-plated steel material.

1 shows a series of process diagrams for manufacturing a component (member) using a conventional steel material.
Figure 2 shows a cross-sectional photograph of the plating layer of the aluminum-plated steel.
3 shows a cross-sectional shape (A) of a molded article after forming an aluminum-plated steel material by a conventional method and a cross-sectional photograph (B) of the plated layer inside the curved portion (arrow).
Figure 4 shows a cross-sectional photograph of the plating layer after heating the aluminum-plated steel in a conventional method.
5 shows a cross-sectional photograph of a plating layer of an aluminum-plated steel material subjected to an alloying heat treatment according to an aspect of the present invention.
6 shows a cross-sectional photograph of a plated layer after cold forming an alloyed heat-treated aluminum plated steel according to an aspect 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 presented embodiments, and those skilled in the art who understand the spirit of the present invention can add, change, or delete other elements within the scope of the same idea. Other embodiments included within the scope of the inventive concept may be easily proposed, but it will be said that this is also included within the scope of the inventive concept.

In general, the process of heat treatment after cold forming a steel material undergoes a series of processes as shown in FIG. 1, and a member manufactured therefrom may have high strength.

On the other hand, when the steel material is a plated material, when cold forming is performed on such a plated material, an aluminum plated steel material having a plated layer as shown in FIG. 2 may be used. Aluminum-plated steel has a problem in that the aluminum-based plating layer is damaged due to friction and bending with a mold during cold forming. For example, in the case of the inside of the curved portion as shown in FIG. 3B, there is a problem in that the plating layer is pushed by the pull of the mold to become thinner or crack.

In addition, in the case of rapid heating to increase the strength of the aluminum-plated steel material subjected to cold forming according to the above, there is a problem that the aluminum-based plating layer is melted.

Therefore, the present inventors minimize damage to the plating layer during rapid heating in order to improve strength after cold forming the aluminum-plated steel in using aluminum-plated steel as a raw material for manufacturing automobile parts (members), etc. Thus, while securing good plating quality, a deep study was conducted to provide a method for obtaining a member having high strength of a target level, and accordingly, the present invention was provided.

Hereinafter, the present invention will be described in detail.

A method of manufacturing an aluminum plated member according to an aspect of the present invention includes the steps of preparing an aluminum plated steel and then alloying it; It may include cold forming and heat treatment.

First, the aluminum-plated steel material is a steel material capable of performing cold forming as mentioned above, and any bar may be used as long as it is produced by a method such as hot-dip plating, alloying hot-dip plating, and electroplating, and it is not particularly limited.

However, in the case of the aluminum-plated steel, not only has a plating layer made of aluminum (Al) on at least one surface of the holding steel sheet, but also has a plating layer including a small amount or a small amount of silicon (Si), iron (Fe), etc. in addition to aluminum. It can be steel. In this case, the Si and Fe may be included in 6 to 12% and 1 to 4% by weight, respectively.

In the present invention, prior to cold forming the above-described aluminum plated steel, the aluminum plated steel may be subjected to an alloying treatment.

That is, as the present invention confirms that there are various problems when forming and rapidly heating an aluminum-plated steel material through a series of processes as shown in FIG. 1, a new method is proposed in manufacturing the final member using the aluminum-plated steel material. There is a technical significance to it.

Specifically, the present invention can alloy the plated layer of the aluminum plated steel by alloying the aluminum plated steel, the alloying treatment is the Fe content in the plated layer is 60% by weight or more, more advantageously 60 to 70% by weight It is preferable to perform so as to be.

The alloying treatment is not particularly limited, as long as any means capable of sufficiently diffusing Fe in the holding steel sheet of the aluminum-plated steel material into the plating layer can be applied.

As an embodiment, it may be carried out by a method of alloying by maintaining at a temperature of 750°C or less, preferably 500 to 750°C for a certain period of time. When the temperature exceeds 750°C during the alloying treatment, excessive oxides are generated on the surface layer, whereas when the temperature is less than 500°C, the alloying cannot be sufficiently performed.

Here, the holding time is not particularly limited, as it can be performed for a time when the Fe content in the plating layer becomes 60% or more.

As already mentioned, it was confirmed that the general aluminum plated steel has a problem in that the plating layer is damaged due to friction and bending with the mold during cold forming (see FIG. 3). This can be described in detail with the description of FIG. 4 below.

4 shows the state of the plated layer after heating an aluminum plated steel material containing a certain amount of Si in the plated layer by a conventional method, and the Fe content in the plated layer has a level of 50% as a whole, and at this level of alloying, the plated layer is brittle. There is a problem with having.

Here, heating by a conventional method means a process of heating to a high temperature, and may be, for example, heating above the Ac3 temperature.

However, in the case of the present invention, the plating layer is alloyed through an alloying process prior to forming and heat treatment of the aluminum-plated steel to secure the Fe content of 60% by weight or more in the plating layer, so that the plating layer is soft (soft). ) Has a property (see FIG. 5).

Such an aluminum-plated steel material can obtain a member having the intended strength while securing a plated layer of good foam quality even through subsequent cold forming and heat treatment processes, and has excellent cold formability.

The aluminum-plated steel material subjected to the alloying treatment according to the above may be cold formed.

The cold forming is not particularly limited because any can be applied as long as it is a means capable of cold forming the aluminum-plated steel material. However, as the cold forming process, a cold stamping process or a roll forming process may be used.

Through the above-described cold forming process, it is possible to manufacture a member of the aluminum-plated steel material having a specific shape. Here, the specific shape may be a shape that can be suitably applied to automobile parts, and the like, but is not limited thereto.

In accordance with the above, the cold-formed aluminum plated steel may be heat treated.

The heat treatment after the cold forming is a process for increasing the strength of the formed aluminum-plated steel, and may include a process of heating and then cooling the formed aluminum-plated steel.

Specifically, the heat treatment process generates austenite transformation in the holding steel sheet through heating of the formed aluminum-plated steel, and sufficiently secures a martensite structure in the subsequent cooling process, thereby having a tensile strength of 1000 to 2000 MPa after such heat treatment. It is desirable.

More preferably, the process of heating the molded aluminum-plated steel is performed at A3 or higher to achieve sufficient austenite transformation, and at this time, it may be maintained at a heated temperature for a certain period of time. The strength and uniformity of the aluminum-plated steel material finally heat-treated from the heating and holding process can be secured, and the holding time at this time is not particularly limited, and the above-described effects can be sufficiently obtained.

After going through the heating process or the heating and holding process according to the above, cooling may be performed at a rate equal to or higher than the critical cooling rate of the aluminum plated steel. If the cooling is performed at a rate slower than the critical cooling rate of the plated steel, there is a concern that the transformation into a structure capable of obtaining a tensile strength of 1000 MPa or more in the cooling process may not be sufficiently achieved.

The rate above the critical cooling rate of the aluminum-plated steel material is a cooling rate at which transformation occurs into a martensite phase without causing a phase transformation such as ferrite or bainite during cooling, and for example, it may be performed at a cooling rate of 30 to 50°C/s. .

In the present invention, in performing heat treatment, that is, heating and cooling the molded aluminum-plated steel, various methods other than the above-described method may be applied.

For example, when the formed aluminum-plated steel is heated, the plated steel is divided into two or more regions, and at least one of the regions is heated to a temperature of A3 or higher and the remaining region A1 or lower, and then cooling. It can be carried out at a speed equal to or higher than the critical cooling rate for the entire area.

As another example, when the formed aluminum-plated steel is heated, the plated steel is divided into two or more regions, the entire region is heated to A3 or higher, and then at least one of the regions is subjected to critical cooling. The speed above the speed and the rest of the region can be performed at a speed below the critical cooling speed.

In the present invention, two or more regions of the plated steel are not particularly limited, but may be divided into a high strength region and a low strength region. The high-strength region may be a region having a tensile strength of 1000 to 2000 MPa by forming a hard phase (for example, a martensite phase) in the final member, whereas the low-strength region may be a soft phase in the final member. Ferrite phase, etc.) may be formed to have a tensile strength of 500 to 800 MPa.

As described above, in the case of manufacturing a member having an intended shape by forming and heat treating an aluminum-plated steel material by forming and heat treating a series of processes proposed by the present invention, in the case of alloying the aluminum-plated steel material prior to the forming, forming And even through the heat treatment process, it is possible to have a plating layer of good quality.

This means that by using an aluminum plated steel material in which the plated layer is sufficiently alloyed by the alloying treatment of the present invention, not only has the target strength after forming and heat treatment, but also no problems such as melting of the plated layer have occurred. do.

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

( Example )

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

Thereafter, cold forming (roll forming step) was performed on one aluminum-plated steel material, and the plating layer (inside the curved portion (arrow)) was observed (comparative example).

For the other aluminum-plated steel, after alloying treatment at 500 to 750°C so that the Fe content in the plating layer was 70% by weight, cold forming (roll forming process) was performed, and then the plating layer (inside the curved part) was observed (Invention Example) ).

In order to observe each of the plated layers, after cutting in the thickness direction, the plated layers were observed with an optical microscope.

3 shows a plating layer of a comparative example, and it can be seen that the plating layer is severely damaged during cold forming.

On the other hand, FIG. 6 shows the plating layer of the inventive example, and it can be seen that there are no defects such as cracks in the surface or inside the plating layer, and a uniform layer is shown even after the molding process.

Claims (9)

Preparing an aluminum-plated steel material;
Alloying the aluminum-plated steel material;
Cold forming the alloyed aluminum-plated steel material; And
Including the step of heat-treating the cold-formed aluminum plated steel,
The alloyed aluminum plated steel is a method of manufacturing an aluminum plated member having an Fe content of 60 to 70% by weight in the plated layer.
The method of claim 1,
The alloying treatment is a method of manufacturing an aluminum plating member that is heated and maintained at a temperature of 500 to 750°C.
The method of claim 1,
The heat treatment step includes heating and cooling steps,
The heating is performed at A3 or higher, and the cooling is performed at a speed equal to or higher than a critical cooling rate of the plated steel.
The method of claim 1,
After the heat treatment, a method of manufacturing an aluminum plated member having a tensile strength of 1000 to 2000 MPa.
The method of claim 3,
In the heating, the plated steel is divided into two or more regions, and at least one region is heated to a temperature of A3 or higher, and the remaining region is Al or lower,
The method of manufacturing an aluminum plated member, wherein the cooling is performed at a rate equal to or higher than a critical cooling rate for the entire area.
The method of claim 3,
The heating divides the plated steel into two or more areas and heats the entire area to A3 or more,
The method of manufacturing an aluminum plating member wherein the cooling is performed at a rate of at least one or more regions equal to or higher than the critical cooling rate and the remaining regions at a rate lower than the critical cooling rate.
The method of claim 5 or 6,
At least one of the two or more regions is a high-strength region and has a tensile strength of 1000 to 2000 MPa, and the remaining region is a low-strength region and has a tensile strength of 500 to 800 MPa.
The method of claim 1,
The cold forming step is a method of manufacturing an aluminum plating member to be performed by a cold stamping or roll forming process.
The method of claim 1,
The aluminum-plated steel material includes a base steel sheet and an aluminum plating layer on at least one surface of the base steel sheet,
The aluminum plating layer is a method of manufacturing an aluminum plating member containing 6 to 12% silicon (Si), 1 to 4% iron (Fe), remaining aluminum (Al) and other unavoidable impurities in weight percent.

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