JP3171215B2 - Hot-dip aluminum-coated steel sheet with improved corrosion resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip aluminized steel sheet having improved corrosion resistance, which is suitable as a material for members of exhaust gas systems such as automobiles.

[0002]

2. Description of the Related Art Hot-dip aluminized steel sheets are roughly classified into those for heat resistance and those for corrosion resistance.
It contains about 0% of Si and is called type I. The inclusion of Si in the Al coating suppresses the development of an alloy layer generated during plating and suppresses the diffusion of Al into Fe, resulting in excellent workability and heat resistance. This type I is widely used for members of exhaust gas systems of automobiles, combustion equipment of home appliances, inner plates of oil stoves, oven toasters and the like.

[0003] The latter type, which is plated with pure Al (including a small amount of Si), is called type II. This type II is inferior in heat resistance to type I due to the development of the alloy layer generated during plating, but is superior in corrosion resistance.
In particular, it is widely used for building materials and ducts which require less workability.

[0004] In any case, in order to satisfy such performance, the hot-dip aluminum-plated steel sheet uses a steel sheet having oxidation resistance and high-temperature strength as a plating base sheet to improve the performance. Low-carbon aluminum-killed steel sheets, ultra-low-carbon steel sheets, steel sheets containing Ti or Nb based on these steel sheets, and steel sheets containing appropriate amounts of Si, Mn, Cu, Cr, etc., and in some cases stainless steel sheets There are many suggestions for application.

[0005] For example, an ultra-low carbon steel in which Ti and Cr are added to improve the high-temperature oxidation resistance is disclosed in Japanese Patent Publication No. 63-3929, in which the addition of Si, Mn and Nb mainly provides high-temperature strength. Improvements are disclosed in JP-B-64-5108, JP-B-2-24903, JP-B-2-2-2939 and JP-B-2-37408. Further, those in which the corrosion resistance is improved by adding Cr and Cu are disclosed in Japanese Patent Publication No. 2-50979 and Japanese Patent Publication No.
No. 33579 discloses this. These proposals improve the heat resistance and high-temperature strength of the aluminum-plated steel sheet.

[0006] By the way, the use of hot-dip aluminized steel sheet for automobile exhaust gas-related applications, which is due to recent improvements in engine performance and changes in the exhaust system, and furthermore, due to salt damage in the operating environment, etc. There has been a demand for a hot-dip aluminum-coated steel sheet having excellent properties, and under such conditions, the use of the above-mentioned steel sheet as an original sheet was insufficient. For this reason, stainless steel, which has excellent heat resistance, oxidation resistance, and corrosion resistance, is used as the original plate for aluminum-plated steel sheets.

[0007] As a technique for hot-dip aluminum plating on stainless steel, there are, for example, those described in Iron and Steel, 73 (1987), S437 and Nisshin Steel Technical Report (1988), 60, p. A steel sheet coated with hot-dip aluminum has been developed.

In general, hot-dip aluminized steel sheets are
Like the hot-dip galvanized steel sheet, it is manufactured on a continuous plating line of the Sendzimer type (in-line annealing type). However, when stainless steel is used as the base metal for the aluminum-coated steel sheet, a particular problem in manufacturing is that And Ni
Non-plating occurs due to the large amount of. For non-plating of these stainless steels,
Measures have been taken such as pre-electroplating Ni or the like on stainless steel plates before applying hot-dip aluminum plating.

[0009] However, stainless steel is expensive, the production cost increases, and the manufacturability is very poor.
In the case of i pre-plating, there is also a problem that the aluminum is partially eluted into the Al layer and the corrosion resistance is deteriorated.

[0010]

SUMMARY OF THE INVENTION In view of the circumstances described above, the present invention has been developed to improve the corrosion resistance and high-temperature strength of hot-dip aluminized steel sheet even if the hot-dip aluminized steel sheet has a steel composition close to ordinary steel. It is an object of the present invention to obtain a hot-dip aluminized steel sheet which is improved in corrosion resistance and heat resistance which can be sufficiently applied to exhaust gas system members of automobiles.

[0011]

[Means for Solving the Problems]

According to the present invention, C: 0.01% or less, Mn: 0.05-3.0% P: 0.03-0.20%, S: 0.02% by weight%
Below, Cu: 0.05 ~ 2.0%, Al: 0.005 ~ 0.100%, N:
0.008 or less, and in some cases, Ti: Ti /
(C + N) is 4 or more and 0.5% or less, Nb: 0.01 to 0.30%,
V: 0.01 to 0.30%, Si: 1.5% or less, Mo: 3.0% or less,
W: 0.01 to 0.30%, Ni: 2.0% or less, Cr: 6.0% or less,
B: Cold-rolled steel sheet containing 0.0003 to 0.005% of one or more kinds, the balance being iron and unavoidable impurities. Provide hot-dip aluminized steel sheet.

In addition, the hot-dip aluminum-coated steel sheet is passed through an in-line annealing type continuous hot-dip aluminum plating line, annealed at a temperature of 700 to 950 ° C. in this line, and then subjected to aluminum plating. It can be advantageously manufactured by performing.

[0014]

When a steel sheet in which P and Cu are added in the above range is used as the base steel sheet, the corrosion resistance of the hot-dip aluminum coated steel sheet is remarkably improved. This improvement in corrosion resistance can be performed for both type I and type II molten aluminum steel sheets. Therefore, 8.0 to 12% by weight of Si in Al,
In the case of Type I containing preferably 9.0 to 10% by weight, an aluminum-plated steel sheet having excellent corrosion resistance and good heat resistance can be obtained while having a composition close to that of ordinary steel. Thus, an aluminum-plated steel sheet having more excellent corrosion resistance can be obtained.

Further, in the steel to which P and Cu are added in a composite manner, when the above-mentioned other elements are appropriately contained in the above-mentioned range (the detailed operation thereof will be described later), the corrosion resistance is improved and the high-temperature strength and the like are further improved. Be improved.

When the cold-rolled steel sheet is passed through an in-line annealing type continuous hot-dip aluminum plating line and annealed at a temperature of 700 to 950 ° C. in this line, the workability of the hot-dip aluminized steel sheet is improved.

Some elements in steel cause non-plating when its content is large. For example, if the Si content is 0.5
%, Non-plating occurs. In such a case, it is advisable to apply iron plating in a continuous electroplating line and then pass the plate through a continuous molten aluminum plating line. Thereby, a high quality molten aluminum steel sheet can be obtained.

Hereinafter, the action of each component in the base steel sheet of the hot-dip aluminized steel sheet according to the present invention and the outline of the reason for limiting the content range will be described.

C is desirable to reduce the workability and the high-temperature oxidation resistance of the steel sheet product, but is desirably small. However, C is acceptable up to 0.01%, so it is set to 0.01% or less.

Although Si is a preferable element for improving the strength of the steel without impairing the workability, in the Sendzimer type (in-line annealing type) continuous aluminum plating line, when the content of Si in the steel exceeds about 0.5%, non-plating occurs. Easy to occur. Therefore, it is desirable that Si be 0.5% or less. However, this problem can be solved by applying an iron plating with a coating weight of about 2 g / m ^{2 by} electroplating prior to passing the Sendzimer-type continuous aluminum plating line. However, if Si exceeds 1.5%, this effect saturates and becomes hard, resulting in poor ductility. Therefore, when Si is contained, the upper limit is made 1.5%.

Mn is effective as a deoxidizing agent at the time of steelmaking and is effective in preventing hot brittleness due to S as an impurity. Therefore, at least 0.05% is required. It is also an element desirable for improving the strength of steel. However, if it exceeds 3.0%, ductility and toughness become poor. Therefore, the amount of Mn is
0.05 to 3.0%.

P and Cu are characteristic elements in the present invention, and the addition of these elements significantly improves the corrosion resistance of a molten aluminum steel sheet. For this improvement, the content of P must be 0.03% or more (preferably in an amount exceeding 0.04%) and the content of Cu must be 0.05% or more (preferably 0.15% or more). On the other hand, if P exceeds 0.2% and Cu exceeds 2.0%, the effect of improving corrosion resistance saturates and ductility deteriorates. Therefore, P has a lower limit of 0.03% (preferably 0.04%) and an upper limit of 0.2%, and Cu has a lower limit of 0.05% (preferably 0.15%).
%) The upper limit is 2.0%.

S is an element which is essentially harmful to steel, and it is desirable that the content thereof be as small as possible. However, S is allowable up to 0.02%, so it is set to 0.02% or less.

Al must be present in an amount of at least 0.005% in order to function as a deoxidizing agent.
_Since the inclusions such as ₂ O ₃ increase and deteriorate the workability and surface quality, the lower limit is set to 0.005% and the upper limit is set to 0.10%.

N is an element that is essentially harmful to the steel sheet of the present invention. The smaller the number, the better, but the allowable amount is up to 0.008%.

Further, in the present invention, in order to increase the strength of the steel sheet and improve the corrosion resistance, Ni of up to 2.0% and M of up to 3.0% are used.
o, may contain up to 6.0% Cr.

Ni effectively acts to prevent hot brittleness by Cu and to improve the corrosion resistance. However, if it exceeds 2.0%, the effect is saturated and the manufacturing cost becomes high.
The following is assumed.

Mo effectively acts to increase the high-temperature strength of the steel sheet and to improve the corrosion resistance. However, if the Mo content exceeds 3.0%, the effect is saturated and the manufacturing cost becomes high.
And

Although Cr effectively acts to increase the high-temperature strength and improve the corrosion resistance, if it exceeds 6.0%, the production cost becomes expensive, so the upper limit is made 6.0%.

B is an element that has the effect of strengthening the crystal grain boundaries and preventing secondary processing cracks. When such an effect is required, the addition of 0.0003% or more is necessary. However, if the addition exceeds 0.005%, the effect is saturated, so the lower limit is 0.0003%,
The upper limit is 0.005%.

Ti fixes C and N as TiC and TiN, and effectively acts on improving workability and non-aging. For this purpose, it is necessary that Ti be four times or more in the ratio of Ti / (C + N). Ti has the effect of improving high-temperature oxidation resistance,
To obtain such an effect, the more it is, the better, but 0.
If it exceeds 5%, it becomes hard and ductility and toughness deteriorate. For this reason, the lower limit is set to be 4 times the Ti / (C + N) ratio and the upper limit is set to 0.5%.

Nb, V, and W are elements that provide an effect of increasing high-temperature strength. In order to obtain these effects, all elements must be 0.01% or more, but if added over 0.3%, they become hard and the ductility and toughness deteriorate.
Therefore, these elements have a lower limit of 0.01% and an upper limit of 0.3%.

In the present invention, a steel containing such components is subjected to a hot rolling process and a cold rolling process to produce a cold-rolled steel sheet, which is annealed and then subjected to hot-dip aluminum plating. The hot-rolling finishing temperature is preferably not less than the Ar ₃ transformation point from the viewpoint of workability of the final product, and the winding temperature may be in the range of 500 to 750 ° C. Further, the cold rolling rate in the cold rolling step is preferably 50 to 95%.

By setting the annealing temperature in the continuous molten aluminum line at 700 ° C. or higher, the workability of the hot-dip aluminum-coated steel sheet is improved. However, if the annealing temperature exceeds 900 ° C., the effect of improving the workability is saturated and the surface flaw is easily generated in the continuous hot-dip aluminum plating line. Therefore, the annealing temperature is preferably in the range of 700 to 900 ° C.

[0035]

【Example】

 [Example 1]

Each steel having the chemical composition values shown in Table 1 was converted into a hot-rolled steel sheet having a thickness of 3.2 mm under the hot rolling conditions shown in Table 2, and after pickling,
A 1.0 mm-thick cold rolled sheet was obtained. Each cold-rolled sheet was annealed at the annealing temperature shown in Table 2 in a continuous hot-dip aluminum plating line, and subsequently, hot-dip aluminum plating was applied at a coating weight of 40 g / m ^{2 on} one side. Next, skin pass rolling with an elongation of 0.8% was performed. The hot-dip aluminum plating bath was of type I with Si content of 9.5%.
Maintained at 655 ° C.

The obtained molten aluminum steel sheets were examined for tensile properties and corrosion resistance at room temperature and high temperature. The tensile test at room temperature was performed using a No. 5 test piece of JIS Z 2201. High temperature tensile test according to JIS G 0567, at 600 ° C for 15 minutes
After holding, the tensile strength was measured. For corrosion resistance, a test piece of 70 x 150 mm was cut out and subjected to JI as a corrosion test in a salt corrosion environment.
A salt spray test according to SZ 1371 was performed. In the corrosion test, the end face of the test piece was masked with paraffin to remove the influence of the ground iron on the end face. The corrosion resistance was evaluated by measuring the corrosion weight loss after 900 hours. Table 2 shows the results.
It was also described in.

[0038]

[Table 1]

[0039]

[Table 2]

As is clear from the results in Table 2, the molten aluminum steel sheets of Examples C to H according to the present invention have a higher corrosion resistance than those of Comparative Examples A and B (lower P and Cu contents of the original sheet steel). The strength at room temperature is sufficient and the strength at high temperatures is improved. In addition, the present invention examples C to H
Although the heat resistance of the steel sheet is not shown in Table 2, it shows the original characteristics of the type I molten aluminum steel sheet.

[Embodiment 2]

Each steel having the chemical composition values shown in Table 3 was
A hot-rolled steel sheet having a thickness of 3.2 mm was obtained under the hot rolling conditions shown in Table 4, and after pickling, a cold-rolled steel sheet having a thickness of 1.0 mm was obtained. Adhesion amount of each cold-rolled sheet in continuous electroplating line: Fe-0.05% of ² g / m ²
After the plating of B, the steel sheet was annealed at the annealing temperature shown in Table 4 in a continuous hot-dip aluminum plating line, and then hot-dip aluminum plating was applied with a coating weight on one side of 40 g / m ² . Next, the steel sheet was subjected to spin-rolling with an elongation of 0.8%. The hot-dip aluminum plating bath was Type I with a Si content of 9.5%, and the bath temperature was maintained at 655 ° C.

The properties of each of the obtained molten aluminum steel sheets were evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0044]

[Table 3]

[0045]

[Table 4]

As can be seen in Table 4, examples J to J according to the invention
Each of N has remarkably excellent corrosion resistance, a sufficient room temperature strength, and an improved high temperature strength as compared with Comparative Example I (one in which the content of P and Cu in the original sheet steel is low). Although the heat resistance of Examples J to N of the present invention is not shown in Table 4, it shows the original characteristics of the type I molten aluminum steel sheet.

[0047]

As described above, according to the present invention, a base steel sheet having a steel composition close to that of ordinary steel is used, and an appropriate amount of P and Cu are added to the base steel in a complex manner to obtain a hot-dip aluminized steel sheet. Can be significantly improved in corrosion resistance. Further, the high-temperature properties of the hot-dip aluminum-coated steel sheet can be improved and the corrosion resistance can be further improved without impairing the effect of improving corrosion resistance by P and Cu.

This improvement in corrosion resistance can be realized for any type I or type II hot-dip aluminum-plated steel sheet, and particularly for use in automobile exhaust gas system members, such as corrosion resistance, high-temperature characteristics, and formability. Thus, it is possible to provide an economical material which is not found in conventional materials because of both excellent heat resistance.

Continuation of the front page (51) Int.Cl. ⁷ identification symbol FI C23C 2/40 C23C 2/40 (56) References JP-A-5-255806 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (9)

(57) [Claims] C .: 0.01% or less, Mn: 0.05% by weight
~ 3.0%, P: 0.03 ~ 0.20%, S: 0.02% or less, Cu: 0.
Corrosion resistance of a cold-rolled steel sheet consisting of steel containing 0.05 to 2.0%, Al: 0.005 to 0.100%, and N: 0.008% or less, with the balance being iron and unavoidable impurities, and subjected to hot-dip aluminum plating A hot-dip aluminized steel sheet with improved properties. 2. In% by weight, C: 0.01% or less, Mn: 0.05
~ 3.0% P: 0.03 ~ 0.20%, S: 0.02% or less, Cu: 0.0
5 to 2.0%, Al: 0.005 to 0.100%, N: 0.008 or less, T
i: The corrosion resistance is improved by using a cold-rolled steel sheet of Ti / (C + N) of 4 or more and 0.5% or less, with the balance being iron and unavoidable impurities, and subjecting it to hot-dip aluminum plating. Hot-dip aluminized steel sheet. 3. C: 0.01% or less, Mn: 0.05% by weight
~ 3.0% P: 0.03 ~ 0.20%, S: 0.02% or less, Cu: 0.0
5 to 2.0%, Al: 0.005 to 0.100%, N: 0.008 or less, T
i: Ti / (C + N) is 4 or more and contains 0.5% or less, Nb: 0.01 to 0.30%, V: 0.01 to 0.30%, Si: 1.5% or less, Mo: 3.0% or less, W: 0.01 to 0.30 %, Ni: 2.0% or less, Cr: 6.0% or less, B: One or two or more of 0.0003 to 0.005%, the balance being steel and a cold-rolled steel sheet consisting of iron and unavoidable impurities. Hot-dip aluminized steel sheet with improved corrosion resistance by applying hot-dip aluminum plating to this. 4. The hot-dip aluminized steel sheet according to claim 1, wherein the P content in the steel exceeds 0.04%. 5. The hot-dip aluminized steel sheet according to claim 1, wherein the Cu content in the steel is 0.15% to 2.0%. 6. The hot-dip aluminum plating is made of Si in Al.
6. The hot-dip aluminized steel sheet according to claim 1, which is a type I steel containing 8.0 to 12% by weight of the steel. 7. In% by weight, C: 0.01% or less, Mn: 0.05
~ 3.0%, P: 0.03 ~ 0.20%, S: 0.02% or less, Cu: 0.
A steel slab containing 05 to 2.0%, Al: 0.005 to 0.100%, and N: 0.008% or less, with the balance being iron and unavoidable impurities, hot-rolled, pickled, and cold-rolled to the target thickness A cold-rolled steel sheet is manufactured, and the cold-rolled steel sheet is passed through an in-line annealing type continuous hot-dip aluminum plating line. For producing a galvanized steel sheet with improved corrosion resistance. 8. In% by weight, C: 0.01% or less, Mn: 0.05
~ 3.0%, P: 0.03 ~ 0.20%, S: 0.02% or less, Cu: 0.
05 to 2.0%, Al: 0.005 to 0.100%, N: 0.008% or less, Ti: Ti / (C + N) is 4 or more and 0.5% or less, Nb: 0.01 to 0.30%, V: 0.01 to 0.30 %, Si: 1.5
%, Mo: 3.0% or less, W: 0.01 to 0.30%, Ni: 2.0
% Or less, Cr: 6.0% or less, B: 0.0003 to 0.005%, one or more of which contains steel and the remainder consisting of iron and unavoidable impurities, hot-rolled, pickled, and pickled. A cold-rolled steel sheet is manufactured by cold rolling to a thickness, and the cold-rolled steel sheet is passed through an in-line annealing type continuous hot-dip aluminum plating line, annealed at a temperature of 700 to 950 ° C. in this line, and then subjected to aluminum plating. A method for producing a hot-dip aluminum-coated steel sheet having improved corrosion resistance. 9. The method according to claim 7, wherein the cold-rolled steel sheet is passed through a continuous electroplating line, subjected to iron plating, and then passed through an in-line annealing type continuous molten aluminum plating line. A method for producing a galvanized steel sheet with improved corrosion resistance.