JPH073418A - Hot-dip galvanized steel sheet for fuel exhaust pipe systems with excellent corrosion resistance - Google Patents

Abstract

(57) [Summary] [Purpose] A hot-dip aluminized steel sheet with excellent corrosion resistance that has a long life in severe corrosive environments such as combustion exhaust systems. [Structure] A layer component Cr: 8 to 13%, Si: 0.2%
Hereinafter, B layer component C: 0.02% or less, Cr: 18 to 35
%, Mo: 0.1 to 3% when casting steel A-B-A
The multi-layered steel sheet having the above structure is plated with a bath having Si: 12% or less and the balance substantially consisting of Al. [Effect] The hot-dip aluminized steel sheet has significantly higher corrosion resistance than conventional materials.

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 excellent corrosion resistance, which is unlikely to cause perforation due to corrosion even when exposed to a severe corrosive environment such as an exhaust system after combustion of fuel in an automobile or the like. It is a thing.

[0002]

2. Description of the Related Art In recent years, the demand for stainless steel sheets has been increasing for applications requiring characteristics such as corrosion resistance, high temperature oxidation resistance and high temperature strength. More recently, JP-A-61-1478
As disclosed in Japanese Patent Laid-Open No. 65-65, Japanese Patent Laid-Open No. 62-274060, and the like, steel sheets having improved corrosion resistance have also been developed by applying hot dip aluminum plating thereon. This is a method in which stainless steel is subjected to hot dip aluminum plating to diffuse Cr in the steel into the aluminum plating layer to improve the corrosion resistance of the plating layer due to the effect of Cr. For example, due to the use of gasoline to alcohol-containing fuels) and the use of catalytic converters in accordance with exhaust gas regulations, the above-mentioned materials do not always have sufficient corrosion resistance. In addition, it is desirable to improve the corrosion resistance against corrosion from the outer surface of the exhaust system due to spray salt for road freezing prevention in winter. In order to improve the corrosion resistance against these problems, there is a method of increasing the Cr addition amount in the original plate.
In this case, there is an upper limit to the Cr concentration in the steel because Cr is easily selectively oxidized in the non-oxidizing furnace and the reducing furnace to cause non-plating.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of these situations, and increases the Cr content in the steel without impairing the plating property of the stainless steel material, and also improves the Cr content in the plating layer. By diffusing, it provides a steel sheet with significantly improved corrosion resistance even in a severe corrosive environment.

[0004]

[Means for Solving the Problems] High chromium steel having a Cr concentration of 18% to 35%, which is more excellent in corrosion resistance than the above conventional knowledge, and a Cr concentration of 8%, which is capable of diffusing Cr in a plating layer and performing molten Al plating. In order to solve this problem, a steel plate with a multi-layer structure of low chromium steel of up to 13% produces a multi-layer slab by the casting method, and then hot-rolls and cold-rolls the normal stainless steel to perform hot-dip aluminum plating. The A layer is a steel component containing Cr: 8 to 13%, Si: 0.2% or less, the B layer is C: 0.02% or less, Cr: 18 to 35%,
Mo: AB consisting of steel components containing 0.1 to 3%
Corrosion resistance obtained by applying a hot dip aluminized layer of a cast structure of A and containing no inclusions in the boundary layer above the average value of the B layer to the average value of the B layer and containing Si: 12% or less with the balance being substantially Al. It is an excellent aluminum plated steel sheet for fuel exhaust pipe systems.

The structure of the present invention and the reasons for limitation will be described below. A steel plate obtained by hot-rolling or further cold-rolling the above-described slab is used as a plating original plate, hot-dip aluminum plating is performed by the Zenzimer method or the non-oxidizing furnace method, and the amount of plating adhesion is adjusted and then cooled. Generally, Al-
In order to suppress the growth of the Fe alloy layer, about 9% of Si is added, and Fe inevitably mixed from the strip or roll.
About 1% to 2%. However, the growth rate of the Al-Fe alloy layer of stainless steel is lower than that of ordinary steel,
Even if the amount of Si added is reduced, the plating adhesion is relatively ensured.

Therefore, in the present invention, the limited range of Si is 1
2% or less. As described above, since the growth of the alloy layer is suppressed even in a bath to which Si is not added, no particular lower limit is set, but Si is used in an amount of 3% to 12% in applications requiring severe processing.
%, Particularly for applications requiring corrosion resistance, it is desirable to perform plating in a bath containing 1% or less of Si. The reason for this is that when workability is required, it is advantageous that the alloy layer thickness is thin, and when corrosion resistance is particularly required,
This is because the reduction of Si is advantageous in obtaining a thick plated product due to the growth of the alloy layer, and is effective in obtaining the protective effect of the aluminum plated layer for a long period of time. The reason for limiting the upper limit is that further addition causes precipitation of coarse Si crystals, which impairs corrosion resistance and workability of the plating layer.

Next, the reasons for limiting the composition of the original plating plate will be described. First of all, the B layer has a Cr content of 1 in order to obtain sufficient corrosion resistance even in a harsh environment such as an exhaust system.
8% or more is necessary, and the upper limit is 35% from the viewpoint of workability, particularly hot workability. Mo is an element that improves the pitting corrosion resistance of a material such as stainless steel that easily takes the form of pitting corrosion, and its effect is exhibited by adding 0.1% or more. On the other hand, since the effect is saturated and the element Mo is relatively expensive and costly, the upper limit is 3%. In stainless steel, C precipitates as Cr ₂₃ C _{6 in the} grain boundary of the welded portion, deteriorates corrosion resistance, and is also an unfavorable element for workability. Therefore, a lower value is desirable, and a low value of 0.02% or less is obtained. limit. Further, elements such as Ni, Cu and Ti may be added for the purpose of further improving the corrosion resistance.

Next, for the layer A, Cr is required to be 8% or more in order to diffuse the Cr into the plated layer after the hot dip aluminum plating to improve the corrosion resistance as described above. Further, if the steel contains a non-reducing element such as Cr or Si, an oxide film such as Cr ₂ O ₃ or SiO ₂ is formed on the surface to cause non-plating and reduce the plating adhesion.
The upper limits of Si are 13% and 0.2%, respectively, preferably 0.1.
It is 1% or less. Also in this layer, the composite addition of elements such as Ni, Cu and Ti does not impair the gist of the present invention. Next, the multi-layer steel sheet is manufactured from the A and B layers, and since different layers are superposed, it is determined whether the original performance is exhibited by the interface.

That is, in the present invention, since the A and B layers are both Cr-containing steels, Cr-based oxides are easily generated on the surface,
Oxide inclusions are likely to occur at the B layer interface. It is necessary to reduce such inclusions as much as possible in order to make fractures easily occur at the interface, and in the present invention, it is necessary that the inclusions not contain more than the average value of the mother layer at the interface. In the present invention, the plate thickness ratio of the A layer and the B layer is not particularly limited, but the ratio of the B layer to the total thickness is preferably 70% or more and 95% or less from the viewpoint of component cost and the viewpoint of ensuring corrosion resistance and workability. Further, the aluminum-plated steel sheet thus obtained can be used as it is or after being subjected to chemical conversion treatment and painting. As described above, according to the present invention, a product having extremely excellent corrosion resistance can be provided as a material for a combustion exhaust pipe system of an automobile or a two-wheeled vehicle due to the synergistic effect of each steel component of the multiple layers and the coating layer.

[0010]

【Example】

Example 1 A slab was manufactured by adjusting the composition of each of the A layer and the B layer by a casting method using an electromagnetic brake, and thereafter, a cold rolled coil was obtained through a normal hot rolling and cold rolling process of stainless steel. .
This cold rolled coil was plated in an aluminum plating bath in which Si was adjusted to about 9% in a continuous hot dip galvanizing line without oxidation furnace, and the basis weight was adjusted to 120 g / m ² on both sides and then wound up for evaluation. . Tables 1 and 2 show the chemical composition of the A layer and the B layer of the present invention steel and the comparative steel. A multi-layer steel sheet was also manufactured by the rolling press-bonding method, and its composition is also shown. Table 3 shows the characteristics of each steel type shown in Table 1 and Table 2.

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

[Table 3]

Next, the test method used for the characteristic evaluation is described.
I will describe. Evaluation for the inner surface of the exhaust system Targeting the corrosion of the inner surface of the exhaust pipe, the product of the present invention has a diameter of 2
Bending into a 5.4 mm pipe shape and the following evaluations
Conducted a test and measured the occurrence of red rust and the reduction of the rust plate thickness.
The corrosion resistance was relatively evaluated from the determined results. (A) Test liquid composition is 1.5 g / l NH_Four(SO_Four)₂ −
1.5g / l NH_FourNO ₃-1.5 g / l NH_FourCl and
Then, immerse the sample in the liquid heated to 90 ° C for 24 hours.
r, left at room temperature for 24 hours as one cycle and tested 200
The cycle was repeated. The gas phase part and the liquid phase part were evaluated. (B) After heating the sample at 500 ° C. for 24 hours in the atmosphere
The test of (A) was conducted.

Evaluation for the outer surface of the exhaust system A sample subjected to the same processing as that for corrosion of the outer surface of the exhaust pipe was heated to 500 ° C. for 24 hours and then subjected to JIS-Z.
A salt spray test based on 2371 was performed for 1000 hours, and the corrosion resistance was relatively evaluated from the measurement results such as the occurrence of red rust and the reduction in plate thickness of the rust portion. Workability After the product according to the present invention was formed into a steel pipe by a high frequency induction electric welding method, its elongation, pipe expansion ratio and flatness were measured, and these were relatively judged to evaluate the workability.

Plating Adhesion The following two types of processing tests were performed to observe the state of plating peeling in the processed portion, and relative evaluation of plating adhesion was performed. (A) Reverse bend adhesion V
The V-shape is subjected to impact bending, the V-shape is extended, and then the same portion is subjected to the impact V-shape and the V-shape is further extended. (B) Cup squeezing A blank die 50 mm, a die die diameter 2 mm, a squeezing depth 10 mm, and a punch diameter 33 mm are used for squeezing. Appearance of plating Appearance after plating (non-plating, pattern, etc.) was visually judged and evaluated.

Example 2 A slab was manufactured by adjusting the composition of the A layer and the B layer by a casting method using an electromagnetic brake, and thereafter, a cold rolled coil was manufactured through a normal hot rolling and cold rolling process of stainless steel. Obtained. The cold-rolled coil was plated in an aluminum plating bath containing 0.3% to 14% of Si in a non-oxidizing furnace continuous hot dip coating line, and the basis weight was adjusted to 120 g / m ² on both sides and then wound up for evaluation. I went to Table 4 and Table 5 show the components of the original plate and the components of the plating bath of the present invention and the comparative example. Table 6 shows the characteristics of the steel types shown in Tables 4 and 5. The test method used for the characteristic evaluation is the same as in Example 1.

[0018]

[Table 4]

[0019]

[Table 5]

[0020]

[Table 6]

[0021]

EFFECTS OF THE INVENTION The present invention provides a hot-dip aluminized steel sheet having a long life in an automobile exhaust system environment and excellent in corrosion resistance.

Claims (1)

[Claims] 1. The A layer comprises Cr: 8 to 13% and Si: 0.2.
% Steel content, B layer C: 0.02% or less,
Cr: 18 to 35%, Mo: 0.1 to 3% AA-B-A cast structure consisting of steel components and B in the boundary layer
The multi-layer steel sheet that does not contain inclusions above the average value of the layers, S
i: A hot-dip aluminum-plated steel sheet for a fuel exhaust pipe system having excellent corrosion resistance, characterized in that a hot-dip aluminum-plated layer containing 12% or less and the balance being substantially Al is applied.