JPH0978261A - Dipping member for molten metal bath excellent in corrosion resistance and wear resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dipping member for a molten metal bath excellent in corrosion resistance and wear resistance by forming a protective film comprising fluorides and oxides on the surface layer of a dipping member body and controlling the proportions of fluorides and oxides so as to match the coefft. of thermal expansion of the protective film to that of the main body. SOLUTION: In the process to dip a steel sheet or the like in a molten metal bath such as zinc and aluminum for hot dipping, a protective film is formed on the surface layer having 5 to 1000μm thickness of a dipping member body. This protective film contains one kind or more fluorides of Li, Na, Mg, Ca, Sr, Ba, Pb or rare earth elements by 5 to 95wt.% and the balance of one kind or more oxides of Mg, Si, Al, Ca, Ti, Cr, Fe, Co, Ni, Zr and rare earth elements and inevitable impurities. Further, proportions of the fluorides and oxides are controlled to match the coefft. of thermal expansion of the film to that of the base body member. Thus, cracks or peeling in the protective film can be effectively prevented to improve the corrosion resistance and wear resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll or the like installed in a molten metal bath in a continuous hot-dip galvanizing line for thin steel sheets used in the production of automobiles, home appliances, office equipment, building materials and the like. The present invention relates to a dipping member for a molten metal bath, and particularly to a dipping member for a molten metal bath in which an inorganic film having excellent corrosion resistance and wear resistance is formed on the surface of a base material.

[0002]

2. Description of the Related Art Hot-dip galvanized and hot-dip aluminum-plated steel sheets are widely used as heat and corrosion resistant members for automobile steel sheets and building materials. These are mainly manufactured by continuous hot dip coating line, but in members such as sink rolls, support rolls, bearing parts, and snouts that are immersed in the molten metal bath of these facilities, they are eroded by molten metal and pass through. Wear due to the steel plate becomes a problem. As a solution to this problem,
A method of coating the surface of the immersion member with oxide ceramics such as Al ₂ O ₃ or a carbide such as WC or Cr ₃ C ₂ and Co or NiC
A method of coating a composite layer with a metal such as r has been proposed.

[0003]

In the above-mentioned prior art, although the life of each member is longer than that in the case without the coating layer, it is still insufficient. For example, in the case of oxide ceramics, local peeling occurs due to a difference in coefficient of thermal expansion with the base material, low adhesion strength, etc., and defects such as transfer of the scratch as a pattern to the steel plate surface occur. . Also in the carbide cermet, although the carbide itself has corrosion resistance,
The coexisting metals are eroded and the same phenomenon as described above occurs. An object of the present invention is to overcome the above-mentioned conventional problems and provide a dipping member for a molten metal bath which is excellent in corrosion resistance and wear resistance.

[0004]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, mixed a fluoride and an oxide as a protective film for a member immersed in a molten metal bath, Moreover, they have found that the one in which the coefficient of thermal expansion is matched with that of the base material is effective, and have completed the present invention.

That is, as a protective film for a molten metal bath dipping member, a ceramic material which is unlikely to react with molten metal is said to be suitable from the viewpoint of corrosion resistance. However, conventional alumina, mullite, when the protective coating is produced using a ceramic material such as zirconia, when the member is inserted into the molten metal bath, cracks due to the difference in the coefficient of thermal expansion between the substrate and the coating, The occurrence of peeling has always been a problem.

To solve this problem, a coating having a coefficient of thermal expansion that matches the coefficient of thermal expansion of the substrate is required. Generally, the substrate is a metal, and the coefficient of thermal expansion of the oxide used for the film formed on the surface of the substrate is smaller than that of the substrate.
Therefore, in order to match the thermal expansion coefficient of the substrate and the film,
This is possible if a material having a coefficient of thermal expansion larger than that of the base material is used together with the oxide. Therefore, the inventors of the present invention have been able to solve the problem of the present invention by focusing on fluoride as a result of searching for a substance having a large thermal expansion coefficient and capable of withstanding the use of the member.

The thermal expansion coefficients of typical fluorides, oxides and metallic materials related to the present invention are shown below. Published by Gihodo: From Fine Ceramics Dictionary

[0008] Published by Gihodo: From Fine Ceramics Dictionary

[0009] Edited by Japan Institute of Metals and Japan Iron and Steel Institute: Iron and Steel Handbook

As is clear from each table, it has been found that it is possible to obtain coatings having various thermal expansion coefficients by selectively blending and using these fluorides and oxides, and molten metal, especially It was possible to remarkably improve the corrosion resistance to the molten zinc bath, the molten zinc / aluminum bath and the molten aluminum bath. With this structure, the coefficient of thermal expansion can be freely manipulated, so that it is possible to cope with different substrates.

The present invention made based on the above findings,
The surface layer of the dipping member body having a thickness of 5 to 1000 μm contains 5 to 95% by weight of one or more of Li, Na, Mg, Ca, Sr, Ba, Pb and rare earth fluorides.
Contains, balance Mg, Si, Al, Ca, Ti, Cr, F
e, Co, Ni, Zr, and rare earth elements, one or more kinds of oxides and unavoidable impurities, characterized by matching the coefficient of thermal expansion with the base member body by the content ratio of fluoride and oxide. The gist is a dipping member for a molten metal bath that has excellent corrosion resistance and wear resistance.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of the present invention will be described.
The reasons for limiting the constituent components and the quantitative range of the surface coating of the immersion member for a molten metal bath of the present invention will be described. L as a fluoride
Fluorides of i, Na, Mg, Ca, Sr, Ba, Pb and rare earth elements are selected because they have a relatively large coefficient of thermal expansion compared to metals and can form a film and can be economically used. This is because. Further, as oxides, Mg, Si,
The oxides of Al, Ca, Ti, Cr, Fe, Co, Ni, Zr, and rare earth elements have a relatively small coefficient of thermal expansion compared to metals, can form a film, and are economically used. Because it is possible. Further, these fluorides and oxides hardly react with molten metal and are particularly suitable for molten zinc, molten aluminum and their alloy baths.

Next, the reasons for limiting the component composition range will be described. If the amount of fluoride is too small, the coefficient of thermal expansion is not so different from that of oxide alone, and matching of the coefficient of thermal expansion with the substrate becomes difficult. On the other hand, if the amount of fluoride is too large, there is not much difference from the case of only fluoride. Since the present invention is intended to be compatible with various substrates, the range requires 5 to 95% by weight of fluoride, and the balance is oxides and unavoidable impurities.

The means for forming the surface layer coating of the present invention is not particularly limited, but means for spraying the compounded raw material of the surface layer coating composition of the present invention, or means for coating the raw material in the form of slurry on a substrate and baking it or a green sheet of the raw material. It is possible to employ a method of producing the above, sticking it to the surface of the base material, and firing it.

[0015]

EXAMPLES The present invention will be described specifically with reference to Examples.
This does not limit the invention. Example A test piece having a surface coating having the composition and thickness shown in Table 4 was prepared.

[0016]

No. 1 to 9 are examples of the present invention, and N
o. 10 to 12 are comparative examples. Table 5 shows the test results obtained by suspending these test pieces in a molten zinc bath.

[0018] Note * 1: Immersion test with a sprayed sample suspended in a molten zinc bath with Mo wire * 2: Describe the situation after 1 week

When the examples of the present invention are compared with the comparative examples, in the molten zinc corrosion test, the surface layer coating of the present invention does not react with the coating itself, and neither cracks nor peeling occur. Does not happen. On the other hand, in the comparative material, there is a reaction of the surface layer coating itself, and cracks and peeling of the coating occur due to a large difference in the coefficient of thermal expansion between the coating and the base material. Adhesion of molten zinc is seen.

[0020]

EFFECTS OF THE INVENTION Since the present invention is constructed as described above, it has excellent corrosion resistance and wear resistance as a molten metal bath dipping member and is extremely useful industrially.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hideyasu Nagayoshi Inventor Hideyasu Nagayoshi 1-3-8 Yaesu, Chuo-ku, Tokyo Within Nittetsu Hard Co., Ltd. (72) Inventor Kiyomi Ashida 1719 Omama, Omama-cho, Yamada-gun, Gunma Prefecture Within Paulex Co., Ltd.

Claims (1)

[Claims] 1. The surface layer of the dipping member body having a thickness of 5 to 1000 μm comprises Li, Na, Mg, Ca, Sr, and B by weight.
a, Pb, and rare earth element fluorides containing one or more kinds in an amount of 5 to 95% with the balance being Mg, Si, Al, C
a, Ti, Cr, Fe, Co, Ni, Zr, and rare earth elements, which are composed of one or more kinds of oxides and inevitable impurities, and have a base member body and a thermal expansion coefficient depending on the content ratio of fluoride and oxide. Immersion member for molten metal bath with excellent corrosion resistance and wear resistance, characterized by matching