JPS616261A - Steel sheet plated with aluminum, superior in corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an aluminum steel sheet superior in corrosion resistance by applying molten aluminum plating to a steel sheet incorporating specified ratios of C, Cr, Mn, Si, N, Al to steel. CONSTITUTION:The steel sheet consisting <=0.01% C, 3-18% Cr, 0.1-1.5% Mn, <=0.1% Si, <=0.004% N, 0.005-0.08% Al and the balance iron with inevitable impurities subjected to molten aluminum plating. It is preferable to regulate to >=about 0.3% and <= about 0.2% a P and S respectively. In this way, the aluminum plate steel sheet superior in heat resistance and useful for exhaust system material for automobile having improved corrosion resistance is obtained.

Description

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

BACKGROUND OF THE INVENTION Aluminum-plated steel sheets have excellent corrosion resistance and heat resistance, so they have been used as inexpensive corrosion-resistant and heat-resistant materials for household heating appliances, automobile exhaust system materials, and the like. Of course, stainless steel plates are used in extremely harsh operating environments, but stainless steel plates contain expensive metals such as Ni, Cr, and No, resulting in high costs.
Aluminized steel sheets are used in less demanding conditions. However, in recent years, due to changes in the usage environment of aluminized steel sheets and lower costs of the materials used,
There is also an increasing demand for the supply of steel sheets with properties intermediate between stainless steel sheets and aluminized steel sheets. In particular, materials that have both heat resistance and corrosion resistance are most preferable as exhaust system materials for automobiles, but depending on the usage conditions, there are some members for which corrosion resistance is particularly important.

For example, the temperature of an automobile muffler is 300 to 400°C, and the heat resistance of conventional aluminized steel sheets is sufficient at this temperature, but the inside of the muffler is extremely susceptible to corrosion due to condensed water, so Materials with excellent corrosion resistance are required.

Therefore, one way to improve the corrosion resistance of aluminized steel sheets is to apply chemical treatments such as chromate treatment to the plated surface after plating, but the performance of this chromate film deteriorates significantly due to heat, so it cannot be applied to parts that are subjected to heat. There is a problem.

There is also a method of extending the service life by increasing the thickness of the plating layer, but if the thickness of the plating layer increases excessively, problems such as variations in the plating thickness and peeling of the plating during processing occur.

Furthermore, there is a so-called type IT hot-dip aluminized steel plate plated with pure aluminum as a corrosion-resistant aluminized steel plate, but there is a problem that the plating layer peels off when heated at 200 to 300°C.

Furthermore, the following techniques attempt to improve the corrosion resistance of aluminized steel sheets by using high C-containing steel sheets whose compositions have been changed.

One of them is, as shown in Japanese Patent Publication No. 52-33579, the steel composition is 5% to less than 15% Cr, 2.0% Si.
% or less, C011% or less, and further contains Ti, Zr, N
The base material is a steel plate to which one or more of b) is added in an amount sufficient to react with C and N present in the steel and substantially exist as carbides and nitrides in the steel base. This method is used as However, this method produces Fe-9i oxides on the steel surface due to the high content of Si, which inhibits plating wettability and reactivity, resulting in plating defects such as unplated areas and pinholes. This has the disadvantage of locally reducing corrosion resistance.

The other one is as shown in JP-A-58-102568, which contains 0.001 to 0.02% of C and Cr in the base steel sheet.
0.01-5%, Mn 0.05-1.0%, Si
0.04-2%, A9!0, O1-0.1%, N 0.
01% or less, contains Ti 0.2-0.6%, Ti/C
There is a method of improving the heat resistance of aluminized steel sheets by adding Ti so that the +N ratio is 20 or more. However, this method has the problem that adding a large amount of Ti causes surface defects in the steel sheet and deteriorates the appearance.

Problems to be Solved by the Invention The inventors of the present invention have conducted various tests with the aim of producing aluminized steel sheets with better corrosion resistance. We discovered that it is necessary to form a healthy plating layer without any oxidation, that is, to form a uniform alloy layer, and by using a steel plate with the composition described below as a base material and plating it with hot-dip aluminum, we were able to achieve a synergistic effect between the steel components and aluminum plating. In particular, corrosion resistance has been significantly improved,
This purpose has been achieved.

Means for Solving the Problems The present invention provides C0.01% or less, Mn0.1 to 1.5%,
Si 0.1% or less, N 0.004% or less, A9θ
, 005 to 0.08%, and 3 to 18% of Cr, with the balance consisting of iron and unavoidable impurities, is used as a plating original plate, and hot-dip aluminium plating is applied to this.

Function Next, the reason why the steel components of the present invention are determined as described above will be explained in detail.

The plated original plate is melted into steel with the above components, then cast, hot rolled, pickled, cold rolled, and then processed by the Sendzimer method.
Alternatively, aluminum or aluminum alloy plating is performed by a non-oxidizing furnace method.

In the present invention, C in the steel components tends to reduce the plating properties of the steel sheet, and also tends to deteriorate the corrosion resistance and workability. Therefore, in the present invention, C is considered a harmful component with 0.
It is necessary to suppress it to 0.1% or less.

Mn improves the wettability of a steel plate in an aluminum plating bath, improves uniform reactivity, prevents the occurrence of microscopic unplating, and improves corrosion resistance and heat resistance. However, if it exceeds 1.5%, as shown in Figure 2, it will impede plating adhesion and cause plating to peel off during processing, so it is necessary to keep it below 1.5%.

Further, the lower limit of the Mn content is 0.1%, but reducing it to less than 0.1% using normal steel manufacturing methods would result in high economic costs, so 0.1% was set as the lower limit.

Cr is added to improve the corrosion resistance of the aluminized steel sheet.

Figure 1 shows steel medium C for steel plates and aluminized steel plates.
These are the results of an investigation into the relationship between the amount of Cr content and the corrosion weight loss from a corrosion resistance test.The results show that compared to the corrosion resistance of the steel sheet itself, hot-dip aluminum plating significantly improves corrosion resistance, and that the effect is greater than that of the Cr content. However, as the Cr content increases, the corrosion resistance of the steel sheet improves, especially when the Cr content is 105 or more, and when the Cr content in the steel exceeds 18%, aluminum plating The corrosion resistance ratio 1 is always small, and unmetallic defects are likely to occur, and pitting corrosion from such unmetallic defects and pinholes is likely to occur, which is unfavorable in terms of corrosion resistance life.

Therefore, the amount of Cr in the steel is in the range of 3 to 18%, but the amount of Or in the range of 3 to 10% is preferable from the viewpoint of improving aluminizing properties and corrosion resistance.

If Si is contained in steel in an amount exceeding 0.1%, the wettability of the plating and This inhibits the reactivity and increases the number of microscopic unmetallic parts, resulting in a decrease in corrosion resistance or heat resistance, as shown in FIG. Therefore, in the present invention, it is necessary to suppress Si to 0.1% or less.

Since N forms chromium nitride, which reduces effective Cr and hardens the material, reducing workability, the content is preferably 0.004% or less, and the smaller the content, the better.

A9 is used as a deoxidizing agent during steel production, but if the amount of soluble M in the steel is less than 0.005%, surface defects are likely to occur on the steel plate, and if the amount of soluble M is less than 0.005%, excessive M content exceeds 0.08%. Acid-soluble 9 deteriorates aluminizing property and causes unplating. Therefore, the acid-soluble A9 acid is 0.005 to 0.0
It is necessary that 8% remain in the steel.

In addition, the content of P and S deteriorates processability and corrosion resistance, so it is preferable that the amount of P and S is as small as possible, and P is 0.03% or more.
As long as S is 0.02% or less, there is no problem in the present invention].

The test method shown in duplicate in FIGS. 1 to 3 is as follows.

(1) Corrosion test method (NH4) 2SO41g/9-1NH4N0.1,5
g/9. , 80 in an aqueous solution of NH4C10,5g/9-
It was immersed for 30 days at ℃ and the corrosion loss (g/m') was examined.

(2) Plating adhesion test By reverse bend test method.

(3) The aluminum plating weight was 80 g/rn'.

EXAMPLE A steel slab having the steel composition shown in Table 1 was obtained by the continuous casting method, and then passed through the usual hot rolling, pickling, and cold rolling processes to a plate thickness of 0.
．． It was made of a steel plate with a diameter of 8. After degreasing this board, continuous hot-dip aluminum plating was performed without using a non-oxidizing furnace, and the basis weight was 80g.
/m'' and then subjected to a corrosion test. As a result, the material of the present invention exhibited extremely superior corrosion resistance compared to the comparative material.

Heavy acid loss in vehicle edibility was measured by the corrosion test method described above.

The appearance is ■ Good, 0 Partly corroded, Δ Slightly severe corrosion, × Overall corrosion Measured using the basis of

Effects of the Invention The aluminized steel sheet obtained by the present invention has not only excellent heat resistance but also improved corrosion resistance, and is useful as an exhaust system material for automobiles.

[Brief explanation of drawings]

FIG. 1 is a graph illustrating changes in corrosion weight loss by changing the amount of Cr in the steel, FIG. 2 by changing the amount of Mn in the steel, and FIG. 3 by changing the amount of Sil in the steel.

Claims (1)

[Claims] C0.01% or less, Cr3-18%, Mn0.1-1.
5%, Si0.1% or less, N0.004% or less, Al0
．． 1. An aluminized steel sheet with excellent corrosion resistance characterized by hot-dip aluminizing a steel sheet containing 0.005 to 0.08% and the remainder consisting of iron and unavoidable impurities.