JPH0288754A - Hot-dip aluminized steel sheet excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To improve corrosion resistance, to inhibit the growth of an alloy phase, and to improve the adhesive strength of plating by applying a hot-dip aluminizing layer containing specific amounts of Si and Cr to the surface of a steel sheet. CONSTITUTION:A hot-dip aluminizing layer consisting of 1.0-12% Si, 0.01-2% Cr, and the balance Al with inevitable impurities is applied to the surface of a steel sheet. Si has a function of inhibiting the growth of the alloy layer of the plated steel sheet and providing the adhesive strength of plating, and further, corrosion resistance is improved by the addition of Cr by the amount in a specific range. Owing to the protective effect of the above plating layer, the service life of the parts used under highly corrosive conditions can be improved. This hot-dipped steel sheet is applicable to automobile mufflers, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a hot-dip aluminized steel plate with excellent corrosion resistance.

BACKGROUND OF THE INVENTION Aluminum-plated steel sheets, which are formed by applying hot-dip aluminum plating to the surface of steel sheets, have excellent corrosion resistance and heat resistance, and are therefore widely used as materials for various heating appliances and automobile exhaust systems.

Such molten aluminum plated steel sheets are generally produced by heating the plated original plate in a non-oxidizing furnace or an oxidizing furnace to oxidize and burn off surface dirt, rolling oil, etc., and then introducing it into a reducing furnace.
The oxide film on the surface is reduced in a reducing atmosphere to activate the surface, annealed at the same time to give workability, and then cooled to a temperature suitable for plating, and then immersed in a plating bath to form aluminum plating. It is then lifted into the atmosphere, the amount of plating applied is adjusted using gas wiping, etc., and after being cooled it is rolled up.

The properties of hot-dip aluminized steel sheets manufactured by such a plating method vary significantly depending on the composition of the original plated steel, and the addition of Ti to the steel (Japanese Unexamined Patent Publication No. 58-102523) is a method of increasing oxidation resistance at high temperatures. (Japanese Patent Publication No. 52-1999), or adding Cr to steel to improve corrosion resistance (Japanese Patent Publication No. 52-
33579) is known to be effective. As described above, conventionally, the performance characteristics of hot-dip aluminized steel sheets have been improved mainly by adjusting the composition of the plated original steel sheet.

Problems to be Solved by the Invention However, in recent years, there has been an increasing need to improve the corrosion resistance of hot-dip aluminized steel sheets under various environments. Therefore, as a means to improve corrosion resistance, Cr-added steel (Japanese Patent Publication No. 52-3
3579) or stainless steel (Japanese Patent Application Laid-Open No. 82-2
74060)) has been adopted. Although this method has a certain effect on improving corrosion resistance, the protective effect of the plating layer is relatively short under severe corrosion conditions such as in automobile mufflers, and after the aluminum plating layer disappears, the plating original plate The service life is determined by the corrosion resistance of the material itself. The present invention advantageously overcomes these drawbacks.

Means for Solving the Problems The present invention provides a hot-dip aluminized steel sheet in which the corrosion resistance of the aluminized layer is significantly improved.

That is, the present invention has discovered that corrosion resistance is significantly improved by incorporating Cr into the plating layer. For this purpose, by adding 0.01% or more of Cr to the aluminum plating bath, Cr is contained in the plating layer, which has a remarkable effect on improving corrosion resistance.

The plating bath composition in the present invention is 1 to 12% Si, C
r [Contains 101 to 2%, with the remainder consisting of M and unavoidable impurities.

Therefore, Si is added to suppress the growth of the alloy layer of the hot-dip aluminized steel sheet and provide plating adhesion, and the amount added is required to be 1% or more, preferably 5% or more. Furthermore, if the amount of Si in the plating bath exceeds 12%, the alloy layer suppressing effect is saturated and the alloy layer becomes saw-toothed, reducing plating adhesion, so the upper limit was set at 12%.

Next, the amount of Cr added to the plating bath is as shown in Figure 1, which shows the effect of the Cr content. As the amount of Cr added increases, the corrosion loss tends to gradually decrease, and especially when 0.01% or more is added, the corrosion resistance increases. Stability improves. However, the amount of Cr added is about 0.4
% in the coating bath at normal coating bath temperature.
Since Cr becomes supersaturated and adheres to the plating surface in the form of lidos, it is necessary to raise the plating bath temperature as the amount of Cr added increases, and in actual plating operations, 2% addition is the limit.

Fe, which is an inevitable impurity in the plating bath, is eluted from the plating original plate, and its content generally varies depending on the amount of Si in the plating bath and the plating bath temperature, but is approximately 1 to 3%.
This does not pose any problem for the purpose of the present invention.

The reason why the corrosion resistance is improved by including Cr in the plating layer is that the aluminized steel sheet forms a dense passive film under the corrosive environment due to the effect of Cr in the plating layer. .

The effect of improving the corrosion resistance of the aluminized layer by adding Cr to the plating bath and containing it in the plating layer can be applied to not only general low carbon steel, but also steel types and steel compositions such as Cr-added steel and stainless steel. This is what you get. Also, Cr-added steel,
In aluminum plating of stainless steel plates, etc., pre-plating with 0.01 to 5 gem' of Ni, Fe, Co, or an alloy of these per side may be used as a means for improving hot-dip plating properties.

Example Examples of the present invention will be described below.

As detailed in Table 1, low carbon steel is used as the plating base plate.
Ultra-low carbon Ti-added steel, ultra-low carbon Cr-added steel (Cr content in steel, 2.5z, 5.1χ, 7.3%), YUS409
D, 5US430.22%Cr steel etc. with plate thickness 0,8
It was cold-rolled to a diameter of 1.5 mm, and was used to perform aluminization using a non-oxidation furnace method.

The target Si addition amount for the coating bath composition is 1. Oz, 2.5z
, 3.5z, 5.0! , 8.0χ, 10%, and further C in the bath
Comparative example without addition), 0.01%, 0.
Aluminum plating is performed in a bath containing 0.05%, 0.1%, 1%, and 2%, and after plating, the amount of plating adhesion is reduced to 1 by gas wiping method.
After adjusting to 00 g/rn', it was cooled and rolled up.

The plating bath temperature during plating is M-3 for the amount of Si added.
i The temperature is 50 to 70°C higher than the liquidus line of the equilibrium phase diagram,
Also, with respect to the amount of Cr added, if the amount of Cr added is 0.1% or less, Si
The plating bath temperature is set according to the amount of addition.
%), aluminum plating was performed at 750°C and good plating was obtained.

Table 1 shows the results of examining the corrosion resistance of the obtained aluminized steel sheet under various environments, including an outdoor exposure test, a salt spray test, and a simulated exhaust gas condensate immersion test assuming a corrosive environment inside an automobile muffler. In all the corrosion resistance tests, the corrosion loss was significantly reduced compared to the comparative example, indicating that the corrosion resistance was improved by adding Or to the plating bath.

The corrosion resistance test method was performed as follows.

(1) Outdoor exposure test A specimen measuring 50 x 200 mm was subjected to an outdoor exposure test for 3 years in a heavy industrial area with an inclination of 30 degrees southward, and the corrosion loss was measured.

(2) Salt water spray test specimen size: 70 x 150 Ilm, JIS Z 2
A salt spray test was conducted for 30 days in accordance with 371, and the corrosion weight loss was measured.

(3) Simulated exhaust gas condensate immersion test Specimen dimensions were 70 x 650 am, and the specimen was immersed half-submerged in the test liquid in a beaker, and kept at 80°C in a semi-closed state.
After testing for 30 days, the corrosion weight loss was measured.

Test liquid composition So, 2- 0.1% NO3- 0,015% Ci- 0,03% N mountain C00H CH3COOH H8 0.4% 0.3% 0.1% 0.1% (hereinafter blank) of the invention As explained in detail, according to the present invention, Si1.0-1 is added to the M bath.
By adding 2% and 01 to 2% of CrO, it is possible to obtain an aluminized steel sheet that has excellent corrosion resistance, suppresses the growth of the alloy layer, and has good plating adhesion.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Cr in the hot-dip aluminizing bath and the corrosion resistance of an alumino-tinted steel sheet (30 days of salt spray test).

Claims (1)

[Claims] On the surface of the steel plate, Si1.0-12%, Cr0.01-2
A hot-dip aluminized steel sheet having excellent corrosion resistance, characterized in that it is coated with a hot-dip aluminized layer containing % of Al and the remainder consisting of Al and unavoidable impurities.