JP3383121B2 - Stainless steel hot-dip aluminized steel sheet with excellent corrosion resistance and heat resistance and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to heat resistance mainly used for automobile exhaust system materials, building materials, home appliances, various heat appliances, etc.
The present invention relates to a stainless steel hot-dip aluminized steel sheet having excellent corrosion resistance and a method for producing the same.

[0002]

2. Description of the Related Art A hot-dip aluminized steel sheet is an aluminum-plated layer mainly composed of aluminum (hereinafter referred to as a plated layer), and a layer composed of an intermetallic compound which is a reaction product of the steel sheet to be plated and aluminum (hereinafter referred to as an alloy layer). It is known that the steel sheet having a) has excellent heat resistance and corrosion resistance. Taking advantage of these features, it is widely used in automobile exhaust system materials, home appliances such as heat appliances, and building materials such as roofs and walls. On the other hand, stainless steel sheets are similarly excellent in heat resistance and corrosion resistance and are used for the same purposes. However, in recent years, for example, the demand for high durability of automobile exhaust system materials has increased, and the needs for products having further improved heat resistance and corrosion resistance are expanding. Therefore, various inventions have been made in which corrosion resistance and heat resistance are further improved by using stainless steel as the aluminum original plate. The applicants of the present application also used Cr-Mo-added steel as a plating base plate (Japanese Patent Publication No. 6-
No. 60380). On the other hand, there are many examples in which elements are added to the aluminum plating bath to improve the corrosion resistance. For example, in Japanese Examined Patent Publication No. 63-23264, Si:
An example of a steel sheet having a plating layer containing 3% or less and Mn: 0.5 to 4% is also disclosed in Japanese Patent Publication No. 6-11906, in which Cr: 0.01 to 2% is added to a plating bath. There is a manufacturing method for steel sheets.

[0003]

However, the above-mentioned invention has the following problems. For example, by using Cr steel as the plating base plate, the corrosion resistance is certainly improved, but this is mainly due to the improvement of the corrosion resistance due to the base plate, and from the viewpoint of the corrosion resistance of the plating itself, there is a large difference from the ordinary aluminum plated steel plate. There wasn't.
On the other hand, even in the invention in which the element is added to the plating bath, the addition amount of the element to the plating bath needs to be limited to a certain amount in order not to raise the temperature of the plating bath, and the addition is sufficient to sufficiently enhance the corrosion resistance. There is a problem that it is difficult to add the amount.

[0004]

The present invention provides a hot-dip aluminized steel sheet having high corrosion resistance and high heat resistance, which overcomes the above problems. The inventors of the present invention repeated the various experiments on the properties of the steel composition, the plating layer and the alloy layer, which affect various characteristics of the hot-dip aluminized steel sheet, and obtained the following findings. That is, it was found that when Mn and Cr are added together to the aluminum plating bath, these elements are not uniformly dispersed in the plating layer, but are significantly concentrated in the alloy layer. This is a phenomenon observed remarkably when the elements are added in combination. Specifically, the concentration of these elements in the plating layer is about 1/5 to 1/10 of the addition amount, and the rest is in the alloy layer. Thicken. These elements are particularly concentrated in the upper part of the alloy layer, that is, at the interface between the plating layer and the alloy layer. Therefore, it becomes possible to create a layer with an increased concentration of additional elements that are effective in corrosion resistance and heat resistance, and a hot-dip aluminized steel sheet with a harder composition has significantly better corrosion resistance and heat resistance than conventional steel sheets. I found it to have.

Further, both Sn and Zn in the plating bath are elements which significantly impair the corrosion resistance of the aluminized steel sheet. Therefore, the sum of these impurity elements needs to be limited to a certain amount or less. As described above, the effect of improving corrosion resistance and heat resistance by adding Mn and Cr is M at the interface of the plating layer-alloy layer.
It is speculated that this is because the n, Cr concentrated layer significantly contributes to the heat resistance of the steel sheet or the corrosion resistance when corrosion progresses.

The effect of improving the corrosion resistance and heat resistance by the Mn, Cr concentrated layer described above is due to the plating layer itself. By using Cr-added steel as a plating base plate for a plating bath that becomes even harder, the base plate's corrosion resistance and heat resistance are also improved, and it becomes possible to obtain overall excellent corrosion resistance and heat resistance. Thus, the above-mentioned plated steel sheet has a certain amount of C, Mn, Si, Ti, Cr, Al, N, and further N.
A plating base plate containing one or two kinds of i, Mo and Cu is plated with a plating bath in which a specific amount of Mn, Cr, Fe and Si is added and the sum of impurities Sn and Zn is limited to a specific amount. It can be manufactured by

The present invention will be specifically described below. According to the present invention, as a plating original plate, C: 0.02% or less, Mn:
0.1-1.5%, Si: 0.2% or less, Ti: 0.1
.About.0.5%, Cr: 10 to 25%, N: 0.004% or less, Al: 0.01 to 0.08%, and further Ni: 0.1.
-1%, Mo: 0.1-2%, Cu: 0.1-1% 1
A steel sheet containing one or more species and the balance being substantially Fe and impurity elements, and having an average composition of Fe: 25 to 50%, Si: 3 to 18%, Mn:
0.1 to 5%, Cr: 1 to 5%, the balance is substantially Al
And having an alloy layer having a thickness of 5 μm or less,
Furthermore, Si: 2 to 12%, Fe: 1% or less, M
n: 0.005-0.3%, Cr: 0.05-0.2
%, The balance consisting essentially of Al, and Sn in the impurities
There is provided a hot dip aluminized steel sheet having a plating layer in which the total of Zn and Zn is 1% or less. Moreover, as a manufacturing method of such a hot-dip aluminized steel sheet, Si: 3 to 12%,
Fe: 0.5-2.5%, Mn: 0.05-1.0%,
Provided is a manufacturing method of plating with a plating bath in which Cr: 0.02 to 0.15%, the balance substantially consists of Al, and the sum of Zn and Sn in impurities is 1% or less.

The reasons for limitation of the present invention will be described below.
First, the composition of the original plating plate will be described. C: As the C content increases, the grain boundary precipitated carbides generally increase,
It promotes intergranular corrosion of stainless steel, and at the same time, C is also a heat resistance inhibiting element. From this point of view, it is desirable that the C content be small, and in the present invention, it is limited to 0.02% or less. Mn: Mn is an element that impairs the workability of steel sheet, and if the content thereof exceeds 1.5%, the workability is significantly deteriorated, so the upper limit is set to this amount. Further, since it is difficult to set Mn to 0.1% or less by an ordinary steelmaking method, this amount is made the lower limit.

Si: Si is Si on the surface of the steel plate during the plating process.
It is an element that forms an oxide and hinders the plating wettability.
If the plating wettability is poor, a large amount of micro-non-plating will occur, and the corrosion resistance and heat resistance will deteriorate from this point. Therefore, it is preferable that the amount of Si is small, and the upper limit is 0.2%. Ti: Ti is an element that reacts with C, N in steel, or O invading from the outside to improve the heat resistance of the aluminized steel sheet. To achieve this effect, the amount of Ti needs to be about 20 times the total amount of C and N, and it must correspond to an industrially reducible value of C and N (C + N: 0.003 to 0.004%). The lower limit of the content is 0.1%. On the other hand, the effect of Ti on heat resistance is saturated, so the upper limit is made 0.5%.

Cr: Cr is an element that contributes to the improvement of corrosion resistance and heat resistance of the steel sheet. Coexistence with Mo, Ni and Cu is particularly desirable for applications requiring high corrosion resistance. Cr
The larger the amount is, the more the corrosion resistance is improved, but it is necessary to add 10% or more in order to obtain the corrosion resistance targeted by the present invention. On the other hand, Cr is an expensive metal, and the addition thereof more than necessary is not desirable because it lowers the productivity in the steps such as hot rolling and pickling and impairs workability. For this reason, the upper limit is set to 25%. Al: Al is added in order to adjust oxygen in the steel in the refining process of molten steel, but if it is too much, it impairs aluminum plating property and causes non-plating, and it also hinders workability of steel plate. Therefore, the lower limit is 0.01% and the upper limit is 0.
It was set to 08%. N: N is an element that hinders the workability of steel and is an element that combines with Ti to increase the required amount of Ti, so its lower content is desirable. Therefore, it is limited to 0.004% or less.

In the present invention, one or more of the following elements can be added. Coexistence with elements such as Ni: Cr is effective in suppressing the progress of local corrosion. But 0.1% to get the effect
The above is necessary. If it exceeds 1%, the effect is saturated, so this amount is made the upper limit. Mo: Mo has a great effect on occurrence of local corrosion of steel and suppression of progress. The effect is remarkable at 0.1% or more, but 2%
It becomes saturated when it exceeds. Cu: When Cu coexists in a component system based on Cr and Mo, the corrosion resistance is improved. If it is less than 0.1%, the coexistence effect is not sufficient, and if it exceeds 1%, the corrosion resistance is saturated,
Workability deteriorates.

Next, the composition of the plating layer and the bath composition of the manufacturing method will be described. Si: As described above, a very hard and brittle alloy layer is formed on the hot dip aluminized steel sheet in addition to the aluminum plating layer, and this layer hinders the plating adhesion. In order to reduce this effect, about 10% of Si is usually added to the plating bath to suppress the thickness of the alloy layer. Also in the present invention, Si is added for the same purpose. For this purpose, the minimum amount of Si in the plating bath is 3%.
The i amount is 2% or more. On the other hand, if Si is added too much, coarse primary crystal Si is generated in the plated layer and adversely affects the corrosion resistance, so the upper limit is made 12%. Si in the plating layer at this time
The amount is about 12%.

Fe: Fe is eluted from the plating original plate or the equipment in the bath and is not particularly positively added in the present invention. Usually, the plating layer also contains about 0.3 to 0.8%. Fe is preferable because it has a bad effect on the corrosion resistance, and the upper limit is 1% in the plating layer. Originally, the smaller the amount, the better. However, as described above, it is difficult to completely remove the element that is inevitably mixed. It is an unavoidable element even in the bath, and it is almost impossible to remove it. If it is forcibly reduced, the equipment in the bath is likely to be melted, so the lower limit value in the bath is set to 0.5%. The upper limit value in the bath is set to 2.5% because appearance stains due to corrosion resistance inhibition or dross appear.

Mn: This element is of particular importance in the present invention. It is an element that has a remarkable effect on corrosion resistance, heat resistance, etc. when it is concentrated in the alloy layer, and at least 0.05% is necessary in the plating bath to exert its effect. When plating is performed in this plating bath, 0.005% is contained in the plating layer, so this concentration is the lower limit value in the plating layer. On the other hand, the solubility of Mn in the plating bath is about 0.6% at a normal plating temperature of 650 ° C. A1-Mn Binary phase diagram M
Although the solubility of n is about 1%, it seems that the solubility decreases in a bath containing about 10% Si. M
To dissolve n by 0.6% or more, it is necessary to raise the bath temperature,
Then, the alloy layer becomes thick and easy to grow, which causes a problem that the plating adhesion is deteriorated. Therefore, the upper limit of the Mn concentration in the bath is 1%. The maximum Mn concentration in the plating layer when plating is performed in this bath is about 0.3% , which is the upper limit of Mn in the plating layer.

Like Cr: Mn, it is also an important element in the present invention. Cr has a particularly large effect on the corrosion resistance and has the effect of concentrating Mn in the alloy layer. In order to exert this effect, it is necessary to add 0.02% or more to the bath. Cr, like Mn, has low solubility in the plating bath,
At 0.1% at 650 ° C, the bath temperature must still be raised for any further dissolution. Then, the alloy layer grows thickly, so 0.15% is made the upper limit of the Cr content in the bath. In the Al-Cr binary phase diagram, the solubility of Cr in Al is 0.
Although it is 4%, it seems that the solubility is lowered for the same reason as Mn. Further, the amount of Cr in the plating layer becomes equal to or higher than the concentration in the bath because diffusion from the steel occurs depending on the steel composition. When the Cr content in the steel is in the above range, the lower limit concentration is 0.05% and the upper limit concentration is 0.2%.

The reason why both elements are concentrated in the alloy layer when Cr and Mn are added in combination is still unclear at present, but a stable metal of Cr--Mn--Fe (--Al--Si) system is used. It is considered that Cr and Mn move to the original plate side with a high Fe concentration due to the formation of intermetallic compounds. Zn, Sn: All of these are elements that significantly impair the corrosion resistance of Al and accelerate the occurrence of white rust. Therefore, the sum of these elements is limited to 1% or less in both the plating layer and the bath.

Next, the reasons for limiting the composition of the alloy layer will be described. Si: As described above, Si: 3 to 12% is added to the plating bath for the purpose of suppressing alloy layer growth. At this time, the Si concentration in the alloy layer is 3 to 18%. Therefore S in the alloy layer
i is limited within this range. The Fe: alloy layer is formed mainly by the reaction between Al of the plating bath and Fe of the original plate. At this time, the Fe concentration in the alloy layer becomes 25 to 50%. Therefore, Fe in the alloy layer is limited to this range.

Mn: Mn added to the bath is concentrated in the alloy layer by the effect of Cr as described above. Due to this effect, various properties such as corrosion resistance, oxidation resistance, and adhesion are greatly improved.
A minimum of 0.1% Mn is required for these effects to appear. On the other hand, since the Mn concentration in the bath has an upper limit as described above, the Mn concentration in the alloy layer also has an upper limit. This is 5
%. Like Cr: Mn, Cr also concentrates in the alloy layer. However, if Cr is contained in the steel, the contribution of diffusion from the steel becomes large.
In the amount of Cr in steel within the range of the present invention, the lower limit is 1% and the upper limit is 5%.
Is.

The upper limit of the alloy layer thickness is 5 μm because if it is too thick, the plating adhesion is impaired. The alloy layer hinders plating adhesion and is preferably thin, so the lower limit is not set. Under normal operating conditions, the alloy layer thickness of the stainless steel material is about 2 μm. The aluminum-plated steel sheet according to the present invention has excellent corrosion resistance. The reason is, as described above, M concentrated in the upper part of the alloy layer (near the interface with the plating layer).
It is considered that n and Cr have a great influence. A feature of the product of the present invention is that the propagation of corrosion from the end faces and scratches is greatly suppressed, and high corrosion resistance can be expected in a molded product including a flaw during molding and a spot welded portion. The product of the present invention may be subjected to zero spangle treatment to make its appearance beautiful. Also, for the purpose of initial rust prevention, it is not detrimental to the gist of the present invention to use chromate containing chromic acid as a main component for use.

[0020]

EXAMPLES Next, the present invention will be described in more detail by way of examples. Hot-rolled and cold-rolled steel sheets having a thickness of 0.8 mm and having several types of steel components as shown in Table 1 are used as plating base plates, and hot dip aluminum plating is performed in a non-oxidizing furnace-reducing furnace type line. It was After plating, the coating weight was adjusted to about 120 g / m ² on both sides by the gas wiping method, and after cooling, it was wound. At this time, Si, Mn, and Cr were added as plating bath components to perform plating, and plating with a good appearance was possible. The aluminum plated steel sheet thus obtained was evaluated. The evaluation method is shown below. In addition, manufacturing conditions and evaluation results are summarized in Tables 2 and 3.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

(1) Method for analyzing composition of plating layer and alloy layer Plating layer: 3% NaOH + 1% AlCl ₃ .4H ₂ O
Only the plating layer was peeled off by electrolytic peeling, and each element was quantitatively analyzed as a plating layer composition analysis liquid. Alloy layer: After the above electrolytic stripping, the alloy layer was stripped with chemical conversion soda to obtain an alloy layer composition analysis liquid, and quantitative analysis of each element was performed.

(2) Corrosion resistance test: The following three tests were carried out. JIS Z 23 for salt spray test size 70 × 150 mm sample
The salt spray test according to No. 71 was performed for 30 days, and the corrosion weight loss was measured. Automobile exhaust system simulated condensed water immersion test A sample having a size of 70 × 150 mm was immersed in the solution of Table 4 for 30 minutes and dried at 70 ° C. for 30 minutes. 1000 this cycle
The cycle was repeated, and the corrosion weight loss after the test was measured.

[0026]

[Table 4]

(3) Plating adhesion: The following two tests were conducted. Reverse Bend Test A test piece was subjected to impact bending in a shape as shown in FIG. 1 and the state of plating peeling at the bent portion was observed to give a rating. The criteria for rating are shown below. Rating Criteria 1 No abnormality 2 Cracks in plating layer 3 Spot plating peeling 4 Foil plating peeling 5 Full surface plating peeling Cup drawing test Blank diameter: 50 mm Drawing depth: 10 mm Die shoulder radius: 2 mm Punch diameter: 33 mm Drawing was performed under the above conditions, and the state of plating peeling on the side surface was observed. The scoring criteria are the same as in the reverse bend test.

(4) Heat resistance test A sample having a size of 100 × 100 mm was held at 800 ° C. for 48 hours and then cooled. One cycle was repeated, and this cycle was repeated 5 times to measure the increase in oxidation after the test. (5) Press-moldability Moldability was evaluated by forming a crack with a diameter of 80 mm and a depth of 40 mm. ◯: No cracking ×: Cracking occurred

[0029]

The aluminized steel sheet obtained according to the present invention has excellent corrosion resistance and heat resistance. Although it has excellent corrosion resistance even in a salt spray environment, it is a remarkable feature that the plate thickness phenomenon due to corrosion is small, especially in a severe environment such as an automobile exhaust system immersion environment. Moreover, since it has excellent heat resistance, it is considered to be an extremely promising material for automobile exhaust systems.

[Brief description of drawings]

FIG. 1 is an explanatory view of a forming shape and a procedure of a reverse bend method which is a plating adhesion evaluation method.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI C23C 28/02 C23C 28/02 (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C23C 2/12 C23C 28/02

Claims (2)

(57) [Claims] 1. C .: 0.02% or less Mn: 0.1 to 1.5% Si: 0.2% or less Ti: 0.1 to 0.5% Cr: 10 25% N: 0.004% or less Al: 0.01 to 0.08% is contained, and further Ni: 0.1 to 1% Mo: 0.1 to 2% Cu: 0.1 to 1% On the surface of a steel sheet containing one kind or two or more kinds, and the balance being substantially Fe and unavoidable impurity elements, the average composition is wt%, Fe: 25 to 50% Si: 3 to 18% Mn: 0.1 to 5% Cr: 1 to 5% The balance has an intermetallic compound coating layer that is substantially composed of Al and has a thickness of 5 μm or less, and further has a weight on the surface of the intermetallic compound coating layer. %, Si: 2 to 12% Fe: 1% or less Mn: 0.005 to 0.3% Cr: 0.05 to 0.2% Is the balance substantially Al? Will, and Zn in the impurities, S
A hot-dip aluminized steel sheet having excellent heat resistance and corrosion resistance, which has a coating layer having a total n content of 1% or less. 2. C: 0.02% or less Mn: 0.1 to 1.5% Si: 0.2% or less Ti: 0.1 to 0.5% Cr: 10 25% N: 0.004% or less Al: 0.01 to 0.08% is contained, and further Ni: 0.1 to 1% Mo: 0.1 to 2% Cu: 0.1 to 1% A steel sheet containing one or more kinds and the balance being substantially Fe and inevitable impurity elements, Si: 3 to 12% Fe: 0.5 to 2.5% Mn: 0.05 to 1. 0% Cr: 0.02 to 0.15% The balance consists essentially of Al and Zn, S in impurities
A method for producing a hot-dip aluminized steel sheet having excellent heat resistance and corrosion resistance, which comprises hot-dip aluminum plating in a plating bath having a total n content of 1% or less.