JPS6280261A - Plated steel sheet - Google Patents

Abstract

PURPOSE:To obtain a corrosion and heat resistant plated steel sheet having superior workability by forming a Ti film of a prescribed thickness on the surface of a steel sheet before plating with Al and by regulating the ratio of the thickness of the Ti film to the total thickness of the Ti and Al films. CONSTITUTION:The surface of a steel sheet is cleaned and a Ti film of 0.02-5mum thickness and an Al film are successively formed on the cleaned surface. The total thickness of the Ti and Al films is regulated to 0.5-20mum and the thickness of the Ti film to <=60% of the total thickness. The Ti film is preferably formed by ion plating in high vacuum or vacuum deposition so that the film has high adhesion and denseness. The Al film is preferably formed on the Ti film by ion plating or vacuum deposition so that the film has high denseness, superior workability and high adhesion to the base.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to improvements in aluminum-plated steel sheets.

[Prior art and its problems]

Hot-dip aluminum-plated steel sheets are well known as toughened steel sheets with excellent corrosion resistance and heat resistance. However, if a pure At bath is used for hot-dip aluminum plating, a brittle Fe--At alloy layer will grow significantly between the steel sheet and the At layer, and the plating layer will peel off during intense processing.

Therefore, a small amount of St is added to ht4 and m-5t alloy plating is applied to suppress the formation of the Fe-kL alloy layer. This hot-dip At-81 alloy plated steel sheet has improved workability compared to hot-dip KL-plated steel sheet, and
It has excellent high temperature oxidation resistance at temperatures below 00°C. However, when the temperature reaches 700 to 800°C, oxidation rapidly progresses and the heat resistance deteriorates.

For this reason, attempts have been made to improve the high-temperature oxidation resistance at 700 to 800°C by using an ultra-low carbon Cr-Ti killed steel plate as the base steel plate.

However, since these plated steel sheets are all made by hot dipping, it is inevitable that an alloy layer will be formed between the plating layer and the steel sheet, resulting in poor workability. Moreover, the film thickness of the plated steel sheet is as thick as several tens of micrometers or more, which is not economical.

Therefore, At plating by vacuum deposition has been developed in place of hot-dip plating. Vacuum deposition plating is a plating method in which At is heated and evaporated in a vacuum, and the vapor is condensed on a steel plate to form a highly pure At film on the steel plate. According to this method, no Fe-A1 alloy layer is formed between the At film and the steel sheet, and the resulting At-plated steel sheet can have excellent adhesion and workability.

However, in a vacuum-deposited At-plated steel sheet, many pinholes exist in the At film, and a corrosion current flows between the At layer near the pinholes and the Fe in the underlying steel sheet, causing At to rapidly dissolve. For this reason, sufficient corrosion resistance cannot be obtained. Moreover, at high temperatures, Al (!: Fe) is significantly alloyed, and oxidation of the base steel sheet progresses from the peeled portion of the alloy layer, resulting in a problem that sufficient heat resistance cannot be obtained.

[Purpose of the invention]

This invention has been made in view of the above circumstances, and its object is to obtain a plated steel sheet that has corrosion resistance and heat resistance, and is not susceptible to workability.

[Structure of the invention]

This invention sequentially forms a titanium film with a thickness o, o2 μm to 5 μm and an aluminum film on the surface of a steel plate, and the total film thickness is 0.5 to 20 μm, and the thickness of the titanium film is the total film thickness. It is a plated steel sheet with a thickness of 60% or less.

[Detailed description of the invention]

First, a titanium film is formed on the surface of the steel plate after cleaning it. Ion blating or vacuum deposition in a high vacuum is preferable for forming a titanium film, and ion blating in a high vacuum is particularly suitable when a thin film thickness is to be obtained.

Ion blating in low to medium vacuum using introduced gas, such as DC discharge ion blating and high frequency discharge ion blating, is also possible, but in this case, high vacuum is preferable in terms of the adhesion and density of the film. It is inferior to ion blasting.

In this way, a dense film with few pinholes and good adhesion is produced. Then, the aluminum film is formed on the titanium oxide film. The preferred formation method is ion blasting or vacuum deposition. This results in an aluminum film that is dense, has excellent workability, and has good adhesion to the base.

Here, the thickness of the entire plating film must be 0.5 to 20 μm, and preferably in the range of 2 to 8 μm. The reason for this is that if it is less than 0.5 μm, sufficient corrosion resistance and heat resistance cannot be obtained, and if it exceeds 20 μm, the temperature of the underlying steel sheet increases during film formation, which may impair the mechanical properties of the steel sheet, and it is also economical. It's not the right thing to do.

The thickness of the titanium film must be O,oλ to 5 μm, particularly preferably in the range of 0.5 to 3 μm. The reason for this is that if the thickness is less than 0.1) 2 μm, the effect of the titanium film cannot be obtained, and if it exceeds 5 μm, the workability will deteriorate.

Furthermore, the thickness of the titanium film relative to the total film thickness must be 60 inches or less. The reason for this is 60el.

This is because if it exceeds this, corrosion resistance and heat resistance cannot be obtained.

According to this structure, even if a pinhole exists in the aluminum film, it does not directly reach the underlying steel plate, and corrosion resistance is significantly improved due to the interaction between the titanium film and the aluminum film.

Furthermore, during high-temperature heating, the titanium film prevents Fe in the underlying steel sheet from diffusing into the aluminum film, and at the same time captures oxygen diffusing from the surface layer as an oxide, preventing it from diffusing into the underlying steel sheet.

As a result, high temperature oxidation resistance is significantly improved.

Example First, an At-killed steel plate having a thickness of 0.8 mm was pretreated by Ar ion densification. That is, 1.0X10-5 Torr
A high-frequency discharge is generated in the Ar gas atmosphere of It's a method.

Next, the steel plate is heated to 200°C and plated with titanium.

This process involves placing the titanium plated material in a water-cooled copper crucible at an atmospheric pressure of 1.0 x 10 Torr or less, and applying a 10kV
It is made by heating and evaporating the titanium particles with an electron beam of 1300 to 1000 nIA, ionizing the evaporated titanium particles with a molybdenum electrode to which a positive voltage of 20 V is applied, and plating on a steel plate to which a negative voltage of -500 V is applied.

Thereafter, aluminum is plated at the same atmospheric pressure.

This treatment was carried out by placing aluminum in a ceramic crucible and heating and evaporating it with an electron beam of 10kv 1300-1000 to plate the steel plate.

Plated steel sheets having a titanium film and an aluminum film were produced by the above-mentioned plating process, with the thickness of each film being varied. For comparison, a titanium film having a thickness outside the range of the present invention was manufactured.

These steel plates have adhesion, adhesion after processing, corrosion resistance,
Corrosion resistance and heat resistance after processing were investigated. The results are shown in Table 1.

Adhesion was evaluated by a folded tape peel test.

In this test, a tape peeling test is performed every time a 180° OT bend is performed, and this is repeated until the base material breaks, and the presence or absence of peeling of the plating film is examined.
evaluated.

Adhesion after processing is Erichsen processing (7 crn extrusion)
Thereafter, a tape peel test was conducted to evaluate whether or not the plating layer peeled off.

Corrosion resistance was evaluated by a 5% salt spray test.

Corrosion resistance after processing was evaluated by a 5% salt spray test after Erichsen processing (7 m extrusion).

Heat resistance was evaluated by oxidation weight gain when a heating cycle of heating at 800° C. for 48 hours in the air and air cooling to room temperature was repeated twice.

From the table above, it can be seen that both the Examples and Comparative Examples have excellent adhesion and post-processing adhesion. However, while the steel sheets of the present invention have excellent corrosion resistance, those with aluminum and titanium single films (AI, A7, A8, Ya 10, Black 11, A14)
It can be seen that when the ratio of the titanium film thickness to the total film thickness exceeds 60% (A5, A6, Al 3 ), the corrosion resistance deteriorates. Furthermore, regarding post-processing corrosion resistance, the one of the present invention is excellent, whereas the one with a single aluminum film, the one with a ratio of titanium film thickness to the total film thickness of more than 60 inches, and the one with a titanium film thickness of 5 μm or more. If it exceeds (413, 41
It can be seen that the corrosion resistance of sample 6) deteriorated after processing. Furthermore, it can be seen that the non-inventive steel sheet has superior heat resistance compared to the comparative example.

Claims (1)

[Claims] A titanium film and an aluminum film with a thickness of 0.02 μm to 5 μm are sequentially formed on the steel plate surface, and the total film thickness is 0.5 μm.
~20 μm, the thickness of the titanium film is 60 μm of the total film thickness.
% or less plated steel sheet.