JPH0313330A - Highly corrosion-resistant steel plate - Google Patents

Abstract

PURPOSE:To enhance corrosion resistance regardless of the defect of surface treatment by constituting the original plate of a matrix containing S and Cu as chemical components and a clad material and employing material quality having a characteristic hard to rust as the matrix and employing material quality having a characteristic easy to rust as the clad material. CONSTITUTION:A matrix A contains S<=0.020%, 0.030%>=Cu>=0.010% and S/Cu <=2.0 as chemical components and other quality is, for example, set to a cold rolled steel plate prescribed by JIS G3141 or other quality added to the above mentioned chemical components is set, for example, to a hot rolled steel plate prescribed by JIS G3131. The clad materials B, B combined with both surfaces of the matrix A contains S<=0.045% and S/Cu>=2.1 as chemical components and other quality is set, for example, to the cold rolled steel plate or hot rolled steel plate same as mentioned above and the original plate P is constituted of these materials. Surface treatment layers C, C are barrier type ones protecting the original plate P.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to the improvement of highly corrosion-resistant steel sheets used as materials for forming the bodies of automobiles, for example.

(Prior art) For example, as a material forming the body of an automobile, conventionally,
A surface-treated steel plate as shown in FIG. 2 is used. That is, a is, for example, a cold rolled steel plate specified in JIS G 3141 or, for example, JIS G31
This is an original plate made of a hot-rolled steel sheet defined by No. 31, and both sides of the original plate a made of cold- and hot-rolled steel sheets are surface-treated.

It is covered with b. The above-mentioned surface treatment layers are roughly classified into so-called barrier type and sacrificial corrosion type. The surface treatment for the above barrier type is P
Examples include b-Sn alloy plating, Sn-based plating, Ni-based plating, and organic coating films. That is, the feature of this type of surface treatment is that it can prevent the occurrence of rust as much as possible, keep rust away for a long period of time, and protect the original plate a from corrosion. As for the sacrificial corrosion type surface treatment mentioned above, Zn
Examples include plating based on Zn-Ni alloy, Zn-Fe alloy plating, AI plating, and Zn-Al alloy plating. That is, a characteristic of this type of surface treatment is that it is easy to rust, and corrosion and elution occur over a long period of time. The original plate a is protected from corrosion until the corrosion is completely eluted. In other words, the surface treatment layer b undergoes self-sacrificial corrosion to retard the corrosion of the original plate a.

(Problems to be Solved by the Invention) As described above, any surface treatment has the desired effect, but if the surface treatment itself has a defect, for example, a problem remains. In other words, if the surface treatment layer is incompletely treated, or if the surface treatment layer is completely treated but due to careless handling by the user, defects such as pinholes, cracks, and scratches may occur in the surface treatment layer. arise. Such defects may reach the original plate a from the surface of the surface-treated layer through the thick inside. The cold- and hot-rolled steel sheet itself, which is the original sheet a, has low corrosion resistance, so the portion of the original sheet a that faces the defective part corrodes and rust occurs, and over long-term use, corrosion will occur around and inside the sheet. progress and expand. That is, although the surface of the original plate a is covered with a surface treatment layer and hardly changes, the corrosion inside this plate progresses quickly and may suddenly lead to pitting. It is extremely difficult to completely and reliably prevent the occurrence of defects in the above-mentioned surface treatment layer, and it takes time and effort to discover the locations where defects occur.
Even if it is discovered, post-processing is troublesome. therefore,
Recently, it has been recognized that the occurrence of defects in the surface treatment layer is unavoidable even if it is prevented as much as possible, and efforts have been made to improve the corrosion resistance of the original plate a itself. .

The present invention has been made in view of the above-mentioned circumstances, and includes a base material made of a base material and a cladding material, the base material being made of a material that does not easily rust, and the cladding material being made of a material that is easily rusted. It is an object of the present invention to provide a highly corrosion-resistant steel sheet that can improve corrosion resistance regardless of defects in surface treatment.

[Structure of the invention]

(Means to solve problems) In the present invention, the chemical component is S≦0.020%.

0.030%≧Cu≧0.010%, S/Cu≦2.0
A cold rolled steel plate or a hot rolled steel plate is used as the base material, and the chemical composition of this base material is S≦0.045%, S/Cu.
≧2.1 cold rolled steel plate or hot rolled steel plate as the cladding material.

This is a highly corrosion-resistant steel plate characterized by the combination of

(Function) The chemical component used as the base material is S≦0.020%,
0.030%≧Cu≧0.010%, S/Cu≦2.0
Cold-rolled steel sheets or hot-rolled steel sheets have rust-resistant characteristics, whereas cold-rolled steel sheets with chemical compositions of S≦0.045% and S/Cu≧2.1, which are the cladding materials that are compatible with these, have the property of being resistant to rust. Since rolled steel plates or hot rolled steel plates are susceptible to rust, the cladding material corrodes first, delaying corrosion penetration into the base material over a long period of time.

(Example) Hereinafter, an example of the present invention will be described based on FIG. A in the figure indicates that the chemical composition is S≦0.020%, 0.03
0%≧Cu≧0.010%, S/Cu≦2.0, and other qualities are, for example, JIS G 3141.
For example, the base material is a cold rolled steel sheet defined by JIS G 3131 or a hot rolled steel sheet defined by JIS G 3131. B and B are clad materials that are applied to both sides of this base material A, and have chemical components of S≦0.045%, S/Cu≧2.1, and other qualities such as cold-formed materials similar to those described above. Consists of rolled steel plate or hot rolled steel plate. These base material A and cladding materials B, B
This constitutes the original plate P.

C1C is a surface treatment layer covered on the surfaces of the cladding materials B and B, and is made of, for example, Pb-Sn alloy plating, Sn-based plating, Ni-based plating, or organic coating film, and prevents the occurrence of rust. This is a so-called barrier type surface treatment that prevents rust as much as possible and protects the original plate P for a long period of time.

In the highly corrosion-resistant steel sheet constructed in this manner, for example, if there is a defect in the surface treatment layer C8C, the conditions for corrosion to occur are aligned in the portion of the original plate P that faces the defective portion. Since the cladding materials B and B, which are directly exposed to these conditions, have the characteristic of being easily rusted, corrosion naturally occurs. This corrosion spreads in the surface direction from the location where it occurs, and further deepens in the thickness direction with time. Base material A is the above clad material B
, B are protected for a long period of time by corrosion, and the time when corrosion actually occurs is delayed for an extremely long time.

Moreover, since it itself has the property of being resistant to rust, the rate of corrosion progresses slowly.

In the above embodiment, as the surface treatment layer C1C,
Pb-Sn alloy plating, Sn-based plating.

Although a so-called barrier type material consisting of Ni-based plating or an organic coating film was used, the present invention is not limited to this, for example, Zn-based plating.

Zn-Ni alloy plating, Zn-Fe alloy plating, A
It may be a so-called sacrificial corrosion type surface treatment layer such as I-based plating or Zn-Al alloy-based plating. In other words, this type of surface treatment layer is easily corroded and eluted, resulting in cladding material B.
, B to delay the onset of corrosion. Also, clad material B,
B itself exhibits the above-mentioned effects.

Alternatively, in the above embodiment, both sides of the base material A were covered with the surface treatment layer C1C via the cladding materials B, but the present invention is not limited to this, and depending on the application, the base material A It is also possible to cover only one side of the surface with the surface treatment layer C via the cladding material B.

Further, the surface treatment layer C is not necessarily required, and may be composed of the base material A and the cladding material B.

〔Effect of the invention〕

As explained above, according to the present invention, the cladding material is combined with the base material. It is possible to extremely retard the progress of corrosion of the base material, and has the effect of improving corrosion resistance.

[Brief explanation of drawings]

FIG. 1 is a partial longitudinal cross-sectional view of a highly corrosion-resistant steel plate showing an embodiment of the present invention, and FIG. 2 is a partial vertical cross-sectional view of a surface-treated steel plate showing a conventional example of the present invention. A: Base material, B: Clad material, P: Original plate, C
...Surface treatment layer.

Claims (1)

[Claims] Chemical components S≦0.020%, 0.030%≧Cu≧0
．． 010%, S/Cu≦2.0, a cold rolled steel plate or a hot rolled steel plate is used as the base material, and the chemical component is S/Cu.
A highly corrosion-resistant steel plate comprising a cold-rolled steel plate or a hot-rolled steel plate with S/Cu≧2.1 and S/Cu≦0.045% as a cladding material.