JPS5817252B2 - High corrosion resistance alloy plated steel products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides hot-dip Zn-A1 alloy plated steel products with high corrosion resistance that further improves the corrosion resistance of conventional hot-dip Zn-A1 alloy plating by adding Sn and Ti in combination. The present invention relates to molten Zn-Al-8n-Ti alloy plated steel products.

Generally, when applying hot-dip Zn plating to the surface of steel materials,
In the molten bath, 0.0% is usually added for the purpose of preventing oxidation of the bath surface, improving the fluidity of the bath, and further suppressing the development of a hard and brittle Zn-Fe alloy layer formed by the reaction between molten Zn and base iron.
2 to 0.3 parts of Al is added.

This prevents the development of the Zn-Fe alloy layer and improves the workability of the plated product, and the Zn on the surface acts as a sacrificial anode to protect the steel substrate even if there are pinholes in the plated layer. Although it has advantages such as industrial areas,
It is well known that corrosion resistance under various environments such as coastal areas is inferior to hot-dip Al plated products.

On the other hand, in molten Al plating, the molten Al bath is approximately 650 to 7
When heated to a high temperature of 00°C, a hard and brittle AJ? -Fe alloy layer is formed and the workability of the plated product is significantly deteriorated, so to suppress the development of such Al-Fe alloy layer, Si of about 3 to 10% or about 1% is usually added.
The following Be and the like are added.

The hot-dip Al plated products obtained in this way generally have better corrosion resistance and heat resistance than the above-mentioned hot-dip Zn plating, but if there are pinholes in the surface A1 layer, the pinholes will cause rusting of the base steel. On the contrary, the corrosion resistance tends to be worse than that of hot-dip Zn plated products, and as mentioned above, by adding Si, Be, etc. to the plating bath, Al-
What suppresses the development of the Fe alloy layer is not yet sufficient, and has the disadvantage that the plating layer is likely to peel off during processing such as bending and drawing.

Therefore, as a method to eliminate the drawbacks of hot-dip Zn plating and hot-dip Al plating and to take advantage of the advantages of both, the hot-dip Zn-A 1 alloy plating method (Japanese Patent Publication No. 46-7161) was proposed.
No., Special Publication No. 46-4045, British Patent No. 1127407
No., JP-A-50-133933, JP-A-50-133
No. 934 and Japanese Unexamined Patent Publication No. 50-133935) have been proposed.

Among the above Zn-A13 alloy plating methods, in the first two, the plating bath composition is Zn containing A125 or higher.
The bath temperature reaches a high temperature of 525°C or higher, and a hard and brittle Z n -A 1-Fe alloy layer is formed between the base iron and the plating layer, which significantly impairs the workability of the plated product, and also causes damage in the bath during plating. In order to prevent the oxidation of Al, it is necessary to make the atmosphere hydrogen-rich, which has disadvantages such as increased costs.

Furthermore, although the method disclosed in the British patent has superior corrosion resistance5 to conventional Zn plating or Al plating, it is still not sufficient.

Furthermore, the latter three are mainly intended to improve paintability, and for this purpose, trace amounts of Ca, Ti, Be, Cu, etc. are added to prevent plating blisters and improve paintability. However, it is still difficult to say that the corrosion resistance is sufficient.

In addition, a method similar to the Zn-A 1 alloy plating method in which Zn plating is applied to the surface after hot-dip Al plating has been proposed (Japanese Patent Publication No. 45-37641), but such two-step plating operation , work efficiency is very poor,
The cost will also be significantly higher.

In view of these circumstances, the present inventors have been conducting extensive research on improving the corrosion resistance of molten Zn-Al-8n alloy plating, and first developed molten Zn-Al-8n alloy plating containing a certain amount of Al and Sn. Alloy plated steel products (JP-A-51-1
No. 36533) and molten Zn-"Al-Ti alloy plated steel products containing a certain amount of Al and Ti (Japanese Patent Application Laid-open No. 1983-
13'6530), but as a result of continuing research, it was discovered that corrosion resistance could be further improved by adding a certain amount of Sn and Ti to a ZnAl bath containing a certain amount of Al. .

The present invention was completed based on this knowledge.

That is, in the present invention, Al is about 2 to 20 inches, Sn is about 0.0
1 to 3.5 parts, Ti about 0.001 to 0.1 part, remainder Zn
The present invention provides steel products hot-dip plated by a molten Z n-Al-8n-Ti alloy plating bath consisting of
The corrosion resistance was dramatically improved by adding the same.

The composition of the molten alloy plating bath of the present invention will be explained below.

Al mainly reinforces the corrosion resistance of Zn, and
It has the function of suppressing the formation of an n-alloy layer, and if it is less than about 2%, it is not sufficient to exhibit this function.

However, when the temperature exceeds about 20, the plating bath temperature must be raised, and therefore, even with the addition of Si, which will be described later, it is no longer possible to suppress the development of the hard and brittle Zn-Al-Fe alloy layer. The workability of the plating layer decreases rapidly.

Therefore, Al is added in a range of about 2 to 20 parts.

Sn and Ti are additive elements that are extremely effective in improving corrosion resistance, and as described below, by simultaneously adding about 0.01% or more of Sn and about 0.001% or more of Ti, a remarkable improvement effect is brought about.

Although there is virtually no upper limit for the amount of addition of both elements,
Even if the content of Sn exceeds about 3.5% and the content of Ti exceeds about 0.1%, the corrosion resistance improving effect reaches disaturation, which is disadvantageous because it only increases the cost.

Therefore, Sn is about 0.01-3.5% and Ti is about 0.0%.
It is added in a range of 0.01 to 0.1%.

The above-mentioned combined addition of Sn and Ti is a feature of the present invention, and in the presence of conventional Zn-AIJ alloy plating baths, the quality characteristics of plating may be affected, such as deterioration of adhesion of the plating layer and plating blistering after painting. Since Sn is considered to cause deterioration, Sn is treated as an impurity and its amount is regulated, and Ti is added as a means to overcome the negative effects of Sn.

However, in the present invention, Sn is actively blended, and S
The combined addition of n and Ti contributes to a dramatic improvement in corrosion resistance.

FIG. 1 shows Z samples obtained by adding various amounts of Sn and Ti to a plating bath with Zn:Al=85:15 (weight ratio).
It is a graph showing the results of measuring the corrosion resistance of steel products plated using the n-A l-8n -T i alloy plating bath (plating layer thickness: 25 μm) using a “salt spray test.”

The numbers in the figure indicate the spraying time (Hr) until the occurrence of red rust 1st factor (area ratio).

As is clear from the figure, Sn is approximately 0.01% or more, Ti is
The spraying time is 60 minutes due to the combined addition of approximately o, oo1% or more.
It is recognized that it exhibits excellent corrosion resistance of up to 00 hours.

The plating layer obtained using the alloy plating bath having the composition described above not only has excellent corrosion resistance, but also has excellent corrosion resistance without cracking or peeling in the 180° close bending test, as shown in the examples below. Provides workability.

This processing method can be further improved by adding a small amount of Si.

This is because the addition of Si has the effect of suppressing the formation of an alloy layer between the base iron and the plating layer.

The amount added is approximately 0.001 to 0.5%.

There are no particular restrictions on the plating operation in the present invention, and it may be carried out in accordance with a conventional method.
The material to be treated is kept at 50°C, fed into the bath for an appropriate immersion time, then taken out from the bath and wiped to form a plated layer with a thickness of about 5 to 35 μm. Corrosion resistance, workability, etc. You can obtain excellent steel products.

The bath temperature during the plating operation has a considerable effect on the properties of the plated layer obtained, but since the plating bath composition in the present invention has an Al content of 20% or less, stable work can be performed at a relatively low temperature. This has the effect of suppressing the development of a harmful alloy layer generated between the plating layer and the base iron, and imparting a high degree of workability.

Next, the corrosion resistance of the alloy-plated steel product of the present invention and the workability of the plating layer will be specifically explained with reference to Examples.

Example A low carbon cold-rolled steel sheet with a thickness Q of 4 mm was used as the base steel sheet, a ZnAl-8n-Ti alloy plated steel sheet was coated with the plating bath of the present invention, and a conventional hot-dip Zn plating bath and molten A were used as comparison materials.
Each plated steel sheet was manufactured using a Zn-Al plating bath and a hot-dip Zn-A1 alloy plating bath, and the properties of the plating layer, corrosion resistance, and workability were measured for each plated steel sheet.

Table 1 shows the plating bath composition used and the results obtained.

In addition, in the same table, "corrosion resistance" is evaluated by the spray time (Hr) until the first stage of red rust occurs in the "salt spray test", and "workability" is evaluated by the spray time (Hr) until the occurrence of the first stage of red rust in the "salt spray test", and "workability" is evaluated by the spray time (Hr) until the occurrence of the first stage of red rust in the "salt spray test".
The occurrence of cracking and peeling of the plating layer was divided into ratings of 5 to 1 as shown below.

Rating 5: No cracking or peeling at all, 4: Cracking or peeling observed under a 30x magnifying glass, 3: Slight cracking or peeling observed with the naked eye, 2: Cracking or peeling clearly observed with the naked eye, 1 : Severe cracking and peeling.

. As is clear from the above results, the molten Zn according to the present invention
It is recognized that the Al-8n-Ti alloy plated steel sheet (Al, 2°3) has excellent quality characteristics.

In other words, regarding corrosion resistance, which is the most important feature of the present invention, the spraying time until the first stage of red rust occurred in the salt spray test was 6000 hours, whereas the combined addition of Sn and Ti was only effective in the amount. 5,000 hours for those that do not meet the specified amount of invention (464), and 4,500 to 50 hours for those that added Sn or Ti alone (Imaginary 5 and 6).
00 hours, and conventional Z n-A1 alloy plating (A7)
The test time was as short as 4,000 hours, and the time required for Al plating (A8) and Zn plating (49) was significantly less than 1,000 hours, indicating that neither of them could reach the corrosion resistance of the present invention.

Furthermore, the material of the present invention (A 1 y 2 y 3) has a very thin alloy layer with the base iron of 0.2 μm or less.

This is a conventional hot-dip Z n -A 1 alloy plating bath (47
), etc., the A7 concentration in the bath is lower and work can be done at lower temperatures.

As described above, since the alloy layer of the present invention material is thin, the workability of the plated layer was rated 5 in all cases in the 180° close bending test, and hot-dip Zn plating (/V;

9), and has the same workability as the conventional 'l n-A1
It is recognized that this is significantly superior to the score of 3 obtained by alloy plating (6) and AA plating (7).

Also, among the materials of the present invention, those with a trace amount of Si added (/
163), the alloy layer becomes even thinner, which is recognized to be effective in improving workability.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amounts of Sn and Ti added in the Zn-Al bath and the corrosion resistance of the plating layer.

Claims (1)

[Scope of Claims] 1 Molten Zn-Al-8n- containing A12-20, SnO, 01-3.5% and TiO, 001-0.1%, the balance being Zn and inevitable impurities. Ti
Highly corrosion-resistant alloy-plated steel products characterized by alloy plating. 2 12-20%, Sn 0.01-3.5%, Ti
The melt Z contains o, ooi ~ 0.1 modulus and SiO, OO 1 to 0.5 modulus, with the balance consisting of Zn and inevitable impurities.
A highly corrosion-resistant alloy-plated steel product characterized by being plated with an n-Al-8n-Ti-8i alloy.