JPS6280260A - Surface treatment of steel sheet - Google Patents

Abstract

PURPOSE:To obtain desired surface characteristics by coating a steel sheet with a metal having a relatively low m.p. by hot dipping and by forming a film of a material different from the metal on the coated surface by vapor deposition or ion plating. CONSTITUTION:A cold rolled steel sheet is passed through a gas reducing furnace, where reduction with gas as well as annealing is carried out to clean the surface. The steel sheet is introduced into a hot dipping tank and coated with a metal such as Al or Zn by hot dipping. A material different from the metal is then vapor-deposited or ion-plated on the steel sheet. Since a film of the desired metal or alloy is formed on the coated surface by vacuum plating or ion plating, the corrosion and heat resistances, paintability and appearance can be improved according to the metal or alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in a method of hot-dip coating a steel plate with Zn, At, or the like.

(Prior art and its problems) Hot-dip plating, which is used as an anti-corrosion coating for steel plates, has lower production costs and higher productivity than other plating methods, so it is used for anti-corrosion steel plates for automobiles and thin steel plates for home appliance construction materials. Widely used in the field. However, metals that can be plated by hot-dip plating include Zn, At, and Pb, which can be melted at relatively low temperatures.
, Sn, and other metals, and therefore there are limits to the properties of the plating film.

On the other hand, regarding the quality of plated steel sheets, a wide variety of properties are required, including not only rust prevention, but also heat resistance, paintability, decorative properties, and wear resistance, and improvements in these properties have been desired.

As an improvement method, improvement of the heat resistance of At-plated steel sheets using titanium-added killed steel (Japan Institute of Metals Bulletin, Vol. 23)
．． 44.1984), aluminized steel sheet by separately added At bath (JIS-G 33141 type), Sn-added PB
Turn sheet with excellent gasoline resistance due to bathing, kl-Z
High corrosion resistance (iron and steel, A7.1980) using an n-alloy bath has already been put into practical use. However, these methods have a limited selection of component systems, making it difficult to arbitrarily obtain desired properties.

(Objective of the Invention) The object of the present invention is to obtain a method for surface treatment of a steel plate that can obtain desired surface characteristics.

(Structure of the Invention) In other words, the present invention hot-dip-plates a steel plate, and then vapor-deposit or ion-brate the steel plate with a material different from the hot-dip-plated material in vacuum to form a film on the hot-dip plated surface. This is a method of forming.

(Detailed Description of the Invention) First, a cold-rolled copper plate is passed through a gas reduction furnace to be annealed and at the same time gas-reduced to clean the surface, and then led to a hot-dip plating tank, where it is subjected to various types of hot-dip plating such as Al and Zn. The bath composition and plating conditions may be the usual ones, and then a material different from the hot-dip plating material is deposited or ion-bladed on the steel plate. For example, as shown in the figure, this processing apparatus includes vacuum chambers 3, 3 each having an inlet seal part 1 and an outlet seal part 2, and vacuum pumps 4, 4, respectively, to maintain the degree of vacuum at 10-3 to 10-5 Torr. Further, the crucibles 5, 5 disposed in the chambers s, s are filled with the vapor deposition material.

The hot-dipped steel plate is then introduced into a cooling tower to solidify the coating layer, and then introduced into the vacuum chamber 3.3. Here, the deposited substance in the crucibles 5, 5 is evaporated by electron gun heating, high frequency heating, resistance heating, etc., and is deposited on the surface of the plating layer. Note that ion brating can be applied depending on the deposition material. After that, it passes through the exit side sealing part 2 and continues to the post-processing process.

Further, after hot-dip plating, while the surface of the plating layer is in a molten state, similar processing may be performed within the vacuum chambers 3, 3. This promotes the reaction between the hot-dip plated surface and the vacuum plated layer during the subsequent cooling process.

Note that whether the plating layer surface is solidified and then vapor-deposited or ion-bladed, or whether it is performed in a molten state depends on the combination of plating materials and the purpose.

According to this method, a desired metal or alloy is vacuum plated or ion-bladed on the hot-dip plated surface to form a film, so corrosion resistance, heat resistance, paintability, appearance, etc. are improved depending on the metal or alloy. can do.

An example is shown in Table 1.

Table 1 (Example) Example 1 A cold-rolled steel sheet with a thickness of 0.8 ttm was subjected to gas reduction and then galvanized at a bath temperature of 450°C. After that, the plating film thickness was adjusted to 6 to 15 μm by gas wiping, and then cooled to 250°C.
led to a vacuum chamber. Vacuum chamber is 4 x 1
Under an Ar atmosphere of 0 Torr, 99.999% pure At was placed in a ceramic crucible and evaporated with a 15 kW electron gun. The deposition rate was 0.8 μm/min, and the At film thickness was controlled to 0.1 to 3 μm. No final chemical treatment was performed.

The corrosion resistance and heat resistance of the obtained steel plate were evaluated by SST. The results are shown in Table 2.

Table 2 After heating in the atmosphere at 650° C. for 24 hours From the results, it can be seen that the corrosion resistance of all of the products of the present invention is significantly improved by the At vapor deposited layer. Also A
As the film thickness of t increased, the heat resistance was also significantly improved.

Example 2 A cold-rolled steel sheet was plated with 10 μm of Zn using the same flat head as in Example 1, then cooled to 350° C., and subjected to F@ ion plating in a vacuum chamber.

At this time, the temperature of the steel plate increases due to ion blating, and it is expected that Fa is plated with the Zn layer in a molten state. Under these conditions, the deposited Fa becomes Z
It was partially alloyed with n, and strong adhesion was obtained.

This steel plate was evaluated for corrosion resistance and weldability after painting.

The results are shown in Table 3 along with comparative examples.

Table 3 *1 Phosphate treatment → 2oμ cationic electrodeposition coating → seal coat 40μ → overcoat 35μ → immersion in 40°C warm water for 240 hours, then adhesion test with 5th tape at 2m intervals.

◎; Peeling area 10 inches or less ○; Peeling area 11-79% ×; Peeling area 80 inches or more *2 Welding conditions Electrode D type electrode area 6 states φ Pressure 200mm Welding time 12 cycles 150Hz Welding speed 3 seconds/spot O ; Electrode life: 3,000 spots x ; l 3,000 spots or less *3Zn-
Double layer structure of 60% FeO, 5 μm and Zn-25% Fe 4 μm

[Brief explanation of drawings]

The drawing is an explanatory diagram showing an example of a vapor deposition processing apparatus used in the present invention. 1...Inlet side seal part, 2...Outlet side seal part, 3...
- Vacuum chamber, -4... Vacuum pump, 5... Crucible.

Claims (1)

[Claims] A method for surface treatment of a steel plate, in which a steel plate is hot-dipped, and then a material different from the hot-dip plated material is vapor-deposited or ion-plated on the steel plate in vacuum to form a film on the hot-dip plated surface.