JPS61272389A - Steel sheet coated with al-si by hot dipping and having high corrosion resistance - Google Patents

Abstract

PURPOSE:To reduce pinholes and to improve the corrosion and heat resistances and workability by successively forming an Al-Fe-Si-Ni-Cr alloy layer having a specified composition and a coating layer of an Al-Si alloy on the surface of steel. CONSTITUTION:An Al-Fe-Si-Ni-Cr alloy layer contg. 0.2-30% Ni and 0.2-10% Cr is formed on the surface of steel to 1-7mum thickness. A coating layer of an Al-Si alloy is formed on the surface of the alloy layer to 3-40mum thickness. Thus, the corrosion and heat resistances, workability and other characteristics of a steel sheet coated with Al-Si by hot dipping are improved. More significant effects are produced by interposing an Ni-Fe diffusion layer having <50% average conc. of Ni between the surface of the steel and the Al-Fe-Se-Ni-Cr alloy layer. The thickness of the diffusion layer is <=2mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a molten AQ-Si plated steel sheet with few pinholes and excellent corrosion resistance, heat resistance and workability.

Conventional technology Aluminum-plated steel sheets have excellent heat resistance, oxidation resistance, and corrosion resistance, so they are used in many fields such as exhaust system materials, muffler materials, automobile parts, household appliances, heat-resistant parts, and industrial furnace materials. used in

As the material (original plate) for aluminized steel plate, JP-A-58
-102523 publication, Japanese Patent Application Laid-Open No. 5111-10883
Low-carbon cold-rolled steel sheets to which a small amount (0.5% or less) of alloying elements such as Cr and Ti are added, as disclosed in Publication No. 1, are mainly used. Furthermore, higher heat resistance and corrosion resistance than the above-mentioned materials were required, and JP-A-49-1
Various original plates have been developed and used, such as 1BCr stainless steel as shown in Japanese Patent Publication No. 08441, and steel containing 5 to 15% Cr as shown in Japanese Patent Publication No. 52-33579.

The problem that the invention aims to solve Corrosion resistance of various types of aluminized steel sheets.

Factors that affect performance such as heat resistance and workability include the performance characteristics of the plated original plate, the alloy layer formed as an intermediate layer between the steel material and the aluminum plating layer, and the characteristics of the aluminum plating layer. And among these.

Even if the plated base plate and the aluminum plated layer have excellent corrosion resistance, heat resistance, workability, etc. in a corrosive environment, the performance characteristics of the aluminized steel plate itself may be affected depending on the state of the alloy layer formed in the intermediate layer. It has a big impact.

In other words, if the formation of this alloy layer is incomplete and a large number of pinholes are formed, the uniformity of this upper aluminum plating layer may be
Since this impedes wettability, many defects such as pinholes in the plated layer or unplated areas that reach the surface of the plated layer are generated, resulting in deterioration of corrosion resistance and heat resistance.

In addition, in a corrosive environment where the aluminum plating layer containing N) I4 ÷ ions exhibits a sacrificial corrosion protection effect on the plated original plate,
If there are many pinholes in the alloy layer, the anodic dissolution of the aluminum plating layer becomes significant, which has the disadvantage of deteriorating the corrosion resistance life. In addition, if flaws or cracks that reach the alloy layer occur during handling or forming of aluminized steel sheets, corrosion resistance may deteriorate, and the alloy layer (usually Al2-
When the corrosion resistance of the Si--Fe alloy M) itself is poor, the corrosion resistance, heat resistance, etc. of the aluminized steel sheet are significantly deteriorated.

The heat resistance of an aluminized steel sheet is determined by the presence of A mainly composed of M and Fe, which is generated on the surface of the plated original plate due to the diffusion reaction between the aluminized layer and the base steel at the high temperatures at which it is used.
(Available by an alloyed coating layer such as L-Fe, M-Fe-Si, etc.)

However, the heat resistance of the aluminized steel sheet obtained by such an effect is limited by pinholes in the alloy layer formed as an intermediate layer between the aluminum plating layer and the original plate to be plated, unplated aluminum due to these, etc. If there are pinholes or non-plating in the plating layer, a good heat-resistant alloyed film cannot be obtained, or if the alloy layer interferes with the diffusion reaction between the base steel and the aluminium-plated layer during heating. Also, the good heat resistance of aluminized steel sheets cannot be obtained.

In recent years, in response to the demand for improved performance of aluminized steel sheets,
For example, Ti, Cr, Si, M, etc. are added to the plated original plate, but these elements are enriched on the steel plate surface and are relatively easily oxidized, resulting in poor wettability of the aluminum plating bath and the uniform formation of the alloy layer. This makes it even more difficult to solve the problem of improving the performance characteristics of aluminized steel sheets.

Means for Solving the Problems The present inventors have developed various methods for the purpose of solving the drawbacks and problems of aluminized steel sheets caused by the alloy layer formed as an intermediate layer between the plated original sheet and the aluminized layer described above. As a result of the study, we found that a uniform and dense plating layer with extremely few pinholes was formed on the steel surface of plated original plates of various steel components, and an M-Si-Fe-Ni-Cr alloy layer with excellent corrosion resistance.
Alternatively, M-3i-Fe can be
-Aluminized steel sheets with a Xi-Cr alloy layer and an aluminum plating layer such as M or M-Si alloys on top have excellent performance characteristics such as corrosion resistance, heat resistance, and workability. I found out something.

That is, the present invention.

(1) The steel surface has a thickness of 1 to 7μ and a Ni content of 0.2
~30%, M-Si-Fe with Cr content 0.2-10%
-Ni-Cr alloy layer and M-S with thickness 3~40#L
A molten M-Si plated steel plate with excellent corrosion resistance and an i-based alloy coating layer, and (2) a steel surface with a thickness of 2μ or less and an average Ni concentration of 50
% prior-Fe-based diffusion layer, and M- with a thickness of 1 to full with a Ni content of 0.2 to 30% and a Cr content of 0.2 to 10%.
Molten Al with excellent corrosion resistance, having a 3i-Fe-Ni-Cr alloy layer and a M-Si alloy coating layer with a thickness of 3 to 40 g.
-Si-based plated steel plate.

action The details of the present invention will be explained below.

Figures 1 and 2 show a plating layer made of AQ-8,5%Si alloy with a Mosquito-Si-Fe-Ni-Cr alloy layer with approximately the same thickness but varying Ni and Cr contents. The amount of pinhole formation and corrosion loss in the alloy layer of an aluminized steel sheet is shown.

From the results shown in FIG. 1, it can be seen that when the Xi content is 0.2% or more, the formation of pinholes and unplated areas is significantly reduced.

Furthermore, as shown in FIG. 2, an aluminized steel sheet having an alloy layer containing 0.2% or more of aluminum and 0.2% or more of Cr has a remarkable effect of improving corrosion resistance.

The corrosion resistance shown in Figure 2 is the value obtained by conducting a sealed test at 80°C for 30 days using test solutions containing Ig/l of ammonium sulfate, 1.5g/l of ammonium nitrate, and 0.5g/l of ammonium chloride. It is.

Table 1 also shows M-8 having an M-Si-Fe-Xi-Or alloy layer with varying amounts of Xi and Cr in one alloy layer.
, showed the effect of preventing pitting corrosion on the edges of an aluminized steel plate having a plating layer made of a 5% Si alloy.

The test method is 0.1% hydrochloric acid, 0.1% nitric acid, 1% formic acid.
A corrosive solution containing 1% acetic acid and 1% acetic acid was adjusted to pH 8 with aqueous ammonia, and a 70m×15G+sm specimen was immersed half of the specimen in the corrosive solution at 80°C for 14 days to detect corrosion at the gas-liquid interface. The evaluation was made as follows.

■------Corrosion from the edge 0~5mmQ---
-- // 8
~10m meal Δ---- tt
11~15+s Peng X --------//
15 m+s or more On the other hand, if the Ni content in this alloy layer exceeds 30% and the Cr content exceeds 10%, the effect of reducing pinholes, non-plating, etc. and improving corrosion resistance will be saturated, and the alloy layer will become hard. cracks occur more often during processing.

As a result, if a defect occurs that reaches the steel base due to flaws caused by forming, etc., the potential of the alloy layer will be too high compared to that of the plated original plate, which is undesirable as it will easily cause perforation corrosion of the plated original plate. , M-Si-Fe-
The Ni content contained in the Ni-Cr alloy layer is 0.2%
Cr content is 0.2% to 10%, preferably 1.5 to 7%.
It is in the range of 5%.

In addition, the thickness of this alloy layer has the above-mentioned pinhole reduction effect,
In order to obtain the effect of improving corrosion resistance, it is necessary to use at least 1 l, preferably at least 3 l.

That is, even if the alloy layer is configured with the above composition.

If the thickness is less than 1μ, a uniform coating effect on the plated original plate cannot be obtained.On the other hand, if the thickness exceeds 71L, the pinhole reduction effect and corrosion resistance improvement effect are saturated, and the alloy layer, which is harder than the plating layer, is saturated. When formed thickly, cracks often occur in the alloy layer during processing, causing peeling of the plated coating layer or deterioration of corrosion resistance. Therefore, its thickness is limited to less than full, preferably less than 5 l.

Furthermore, this alloy layer containing Xi and Cr promotes a diffusion reaction with the aluminum plating layer when heated to a high temperature. As a result, in high-temperature applications, an alloy layer film mainly composed of All and Fe with excellent heat resistance and oxidation resistance is easily formed on the surface of the plating layer, improving oxidation resistance at high temperatures. That is, since cracks in the plating layer due to the difference in thermal expansion between the plating coating layer, the alloy layer, and the base steel are prevented during heating, there is no problem of the base steel being oxidized through cracks and deteriorating heat resistance. There is an advantage that a coating layer mainly composed of an M1-Fe alloy having a uniform composition is formed.

Furthermore, the present invention provides a plated original plate which may be provided with a Ni-Fe diffusion layer having a Ni concentration of 50% or less and a thickness of 2 μl or less as a base treatment layer for this M-Si-Fe-Ni-Cr alloy layer. By providing a former -Fe diffusion layer on the surface, the corrosion resistance of the plated original plate is improved and Al1-Si-Fe-Xi -Cr
Reduces pinholes in alloy layers.

In other words, the Ni-Fe alloy diffusion layer of the plated original plate is
If a defect is generated in the aluminized steel sheet that reaches the surface of the original plate, the corrosion resistance life of the plated original plate is extended.

However, when the Ni concentration of this diffusion alloy layer exceeds 50%, the corrosion resistance of this diffusion alloy layer itself is improved. If a defect occurs in this diffusion layer, this surface layer becomes a potential liability, and there is a risk that the base steel will suffer pitting corrosion. Therefore, the Ni concentration in this diffusion alloy layer is 50%.
It is preferably 30% or less.

In addition, if a Ni-Fe alloy diffusion layer exists in the plated original plate, when it is immersed in an aluminum plating bath containing Si and subjected to plating coating treatment, its melting point is lower than that of the plated original plate, so The wetting reactivity with the molten aluminum plating bath is improved, and the reaction to form an alloy layer with the molten aluminum plating bath is promoted.

As a result, a uniform Al-Si-Fe-Ni-Cr alloy layer with fewer pinholes or unplated areas is produced, which is effective in improving the corrosion resistance of aluminized steel sheets.

However, if the thickness of this alloy diffusion layer exceeds 2 μl, the Ni-Fe alloy is relatively hard, which may cause cracks to occur during processing, leading to deterioration of corrosion resistance. Preferably it is 1.5w or less.

In addition, since this Ni-Fe alloy diffusion layer exists on the surface of the original plated plate, when the aluminized steel sheet is used in a high-temperature heating atmosphere, this Ni-Fe alloy diffusion layer becomes a driving force. The aluminized steel sheet treated with the present invention has the effect of facilitating the formation of an alloy layer with excellent heat resistance and oxidation resistance, which is mainly composed of 5M and Fe, all the way to the surface of the aluminum plating layer. Excellent effects can also be obtained.

Therefore, the M-3i-Fe-Ni-Cr alloy layer of the present invention and the M alloy plating layer containing Si or the old-Fe
Alloy diffusion layer, M-Si-Fe-Ni-Cr alloy layer, S
The method for obtaining the M alloy no-2-ki coating layer containing i is not particularly limited, and examples include the following methods.

That is, on the surface of the plated original plate (As Co1d material) manufactured through the normal steel plate manufacturing process and surface cleaning treatment process,
Electrolytic Nt-Cr-Fe alloy is produced by cathodic electrolysis using an electroplating bath containing Ni, Fe, and Cr ions (e.g., nickel sulfate-nickel chloride-iron sulfate-chromium sulfate-boric acid alloy plating bath). layers are provided.

Next, the Al1-Si-Fe is annealed in an atmosphere containing hydrogen gas, subjected to a reduction process, immersed in an M-based molten aluminum plating bath containing Si, and subjected to plating amount control treatment.
-A Ni-Cr alloy layer and an aluminum plating layer containing Si are produced.

In addition, as another example, a steel plate containing Cr is used as a plating original plate, and a Ni-Fe electroalloy plating layer is applied to the surface by (nickel sulfate-nickel chloride-iron sulfate-boric acid system).Next, hydrogen gas is applied. After an annealing and reduction process in an atmosphere containing N1 by diffusion on the surface of the plated original plate.
After the -Cr-Fs diffusion alloy layer is generated, it is immersed in an aluminum-based hot-dip aluminum plating bath containing Si and subjected to a plating amount control treatment, and the Al1-Si-Fe-Ni-C
An r-based alloy layer and an aluminum plating layer containing Si are produced.

Next, these AQ -Si -Fe -Ni -Cr
An Xl-Fs alloy diffusion coating layer is provided below the Xl-Fs alloy layer, and a three-layer structure consisting of the diffusion alloy layer, the AQ-Si-Fe-Ni-Cr alloy layer, and the Si-containing aluminum alloy plating coating layer is formed. The method for obtaining an aluminized steel sheet with a film structure is to apply Fe to the surface of the plated original plate (As Co1d material) as described above.
-Electroplating the interest layer or using Ni4+ ions,
It is applied by applying an aqueous solution containing Fe static ions to a pIK cloth and annealing it in a non-oxidizing or reducing atmosphere.

After that, for example, a Fe-old-Cr alloy plating layer is provided on the surface, and then Xl-Fe alloy is diffused onto the plated original plate surface by immersing it in an M-based aluminum plating bath containing Si and controlling the plating amount. Layer 1M-Si-Fe-Ni
-A Cr-based alloy layer and an aluminum plated coating layer containing Si are produced.

Therefore, in order to obtain the aluminized steel sheet of the present invention, the above-mentioned (
Fe-Ni or Fe-Xl-Cr electroalloy plating,
M-Si-Fe- containing the amount of Ni specified in the present invention is carried out using an aqueous solution coating method containing coexisting Fa, Ni, and Cr ions, with the Ni content determined in advance.
This is advantageous for obtaining a Xi-Cr alloy layer and a Ni-Fe alloy diffusion layer.

That is, by Ni plating method, application of Ni4+ ion-containing aqueous solution, etc., in the heating process before aluminum plating, a Fe-metal diffusion layer is created by diffusion with the plated original plate, and in the hot-dip aluminum plating process, it is formed with an AQ-5r plating bath. A ML-Si-Fe-Xi-Cr alloy layer is obtained by the reaction.

However, when using Xi gold metal alone, in order to ensure the coating composition of the present invention, strict control of heating temperature and heating time, or strict control of plating temperature and plating immersion time with plating bath, etc. Since management and coordination are required,
It is more advantageous to employ an alloy plating pretreatment in which the i concentration or the old Cr concentration is set.

Furthermore, the amount of impurities from the old sources used in the present invention, such as Go gold metal, incorporated into the coating composition of the present invention does not significantly adversely affect the objectives of the present invention. .

Similarly, in the Ni-Fe alloy diffusion coating layer or M-
Even if the Si--Fe--Ni--Cr alloy layer contains constituent elements 5, such as Ti, Si, etc., constituting the original plating plate used, this does not impede the object of the present invention.

Next, in the present invention, the composition of the aluminum plating layer is limited to an aluminum plating layer obtained from an aluminum-based aluminum alloy plating bath containing Si.

In an aluminum plating bath that does not contain Si, it is difficult to limit the thickness of the alloy layer, which is the main focus of the coating composition of the present invention, to a range of 1 to 71 L, especially the upper limit is less than full. Since it is currently industrially difficult to obtain plated steel sheets, we limited ourselves to aluminum-based plating baths containing Si.

In the present invention, an AQ-'Si alloy bath containing 3% to 15% of Si, particularly 5% to 11% of Si, or M, -S containing Mg, Mn, etc.
It is preferable to use i-Mg, M-Si-Mn alloy plating, etc.

In addition, some Ni or C is added to this aluminum plating layer from the Fe-Ni alloy diffusion layer or the Fe-Ni-Cr pretreatment layer.
Even if the r metal is dissolved or mixed into the AQ-Si alloy plating layer during hot-dip aluminizing, it does not particularly impede the performance of the aluminized steel sheet.

Therefore, the plated base plate used in the present invention is not particularly specified, and may be a general aluminized ordinary steel plate used for manufacturing a normal hot-dip aluminized steel plate,
Also, steel plates to which various special elements are added are used.

In particular, Ti and Wb are used to improve processability.

Steel plate to which Zr, V, B, etc. are added, strength-improving elements Si, P, or corrosion resistance-improving elements Cr, Ni,
Steel sheets that are enriched with elements that inhibit wetting reactivity with aluminum plating baths, such as steel sheets with additions of AN, etc., steel sheets that are less likely to form M-Si-Fe alloy layers with fewer pinholes, unplated surfaces, etc. The coating layer effect of the present invention is remarkable.

Therefore, in the present invention, even if an Fe-Ni diffusion layer with excellent corrosion resistance and an M-Si-Fe-Xi-Cr alloy layer with less pinholes and non-plating are generated on the plated original plate, the treatment Unless the aluminum plating coating layer formed on the surface of the layer is sufficiently formed, it is difficult to ensure long-term corrosion resistance in a corrosive environment, high-temperature oxidation resistance in a high-temperature heating atmosphere, or processing performance during processing. In the present invention, the thickness of the aluminum alloy plating coating layer containing Si is defined to be 3 to 40 microns.

That is, if the thickness is less than 3p, the plating original plate with the aluminum plating coating layer and the Al1-Si-Fe-Ni-C
If the uniform coverage of the r-based alloy layer is not sufficient and the desired effect of improving corrosion resistance and heat resistance of the present invention is not obtained, and if the thickness exceeds 401L, the effect of improving corrosion resistance and heat resistance will not be achieved. This is not preferable because it becomes saturated and becomes uneconomical, and also causes deterioration in workability such as peeling of the aluminized layer and cracking of the aluminized steel sheet during processing. Therefore,
In order to obtain the performance improvement effect aimed at by the present invention, the H thickness of the coating layer is 3 to 40 microns, preferably 5 to 25 microns.

Example Hereinafter, the present invention will be explained by giving examples.

Cold rolled material (As Co1d material) with steel composition shown in Table 2
Fe-Ni by electroplating method after degreasing and pickling.
A preliminary pretreatment layer of a predetermined composition and a predetermined thickness is provided by a multilayer of a -Cr-based alloy layer, Fe-Ni-based alloy layer, or Fe-old thread alloy diffusion layer and an electroplated layer of these alloys, and then an aluminum-based A hot-dip aluminized steel plate was obtained using a Si-containing alloy plating bath.

The performance evaluation results of this aluminized steel sheet are shown in Table 3, and the product of the present invention showed extremely superior performance in terms of corrosion resistance, heat resistance, etc., compared to comparative materials.

For performance evaluation, the plate thickness is 1. Using the evaluation material of 8+u+, evaluation was performed according to the performance evaluation test and evaluation criteria shown below.

1) Evaluation of pinholes in alloy layer The aluminum plating layer of an aluminized steel sheet was immersed in 20% NaOH at 80°C for 5 minutes, and after peeling off, the surface of the alloy layer was observed to evaluate the state of pinhole formation. .

In addition, the evaluation criteria were based on the following method.

O-111 Number of bottle holes generated 10 pieces/d Less than 112 0 ---- tt 10 (11
/cts 2 to 30 pieces/dl less than 12 Δ----tt 3 Q pieces/d112 to 10
0 pieces/d layer less than 2 x----// too pieces/d112 or more 2)
Evaluation of Corrosion Resistance ■Corrosion Resistance by Salt Spray Test The occurrence of red rust after 1000 hours of the salt spray test was investigated and evaluated using the following evaluation criteria.

■---Red rust occurrence rate less than 3% Q----tt 3% or more to less than 10% Δ----
- tt IQ% or more - less than 30% X---
-/7 Corrosion resistance evaluation by method immersion test of 30% or more 1g/immune (N) 14)2SO4-1,58/l (N
H*) Corrosion test using NO3-0, 5g/l NHA CQ based ice water solution at 80℃ for 45 days in a sealed container where half of the test piece is immersed in the solution and half is in contact with the evaporated gas of the solution. was conducted and evaluated using the following evaluation criteria.

■---Corrosion loss 15 g/rrf or less 0---
-tt 1e~30 g/m'Δ----
tt 31-50 g/reX -----//
51 g/m' or more 3) Evaluation of heat resistance performance Heating test at 0650°C Continuous heating test at 850°C for 1000 hours in the atmosphere 077
Heating test at 5°C 5 cycles of heating tests were conducted, each cycle consisting of heating at 775°C for 48 hours in the air followed by air cooling, and evaluations were made using the following evaluation criteria.

■---Good condition with no surface scale 0---Very slight occurrence of dotted scale Δ---Extreme occurrence of dotted scale Cup drawing test (1) Drawing processing conditions Blank size 150φ Punch diameter 75φ Wrinkle holding force I Ton Lubricating oil Machine oil #620 (2) Evaluation ■ Good O Minute cracks Δ in the plating layer 1 to 2 point peeling of the plating layer × Large peeling of plating layer ■ Steel pipe workability test (1) Test method Steel pipe dimensions, outer diameter 42.7 + u + φ, wall thickness 1.8 + 5 m8
0°flattening test Processing degree Adhesion observation (2) Evaluation ■ Good Fine cracks occur in the O plating layer Δ Large cracks in the plating layer Effects of the invention Compared to comparative materials, the product according to the invention has fewer pinholes, corrosion resistance, and heat resistance. It showed extremely excellent performance in terms of properties such as hardness and processability.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the Ni content in the alloy layer of a hot-dip aluminized steel sheet and the amount of pinholes generated, and FIG. 2 is a diagram showing the relationship between the amount of Ni in the alloy layer and corrosion resistance.

Claims (2)

[Claims] (1) On the steel surface, with a thickness of 1 to 7μ and a Ni content of 0.2
~30%, Al-Fe-S with Cr content 0.2-10%
i-Ni-Cr alloy layer and M-Si with a thickness of 3 to 40μ
Corrosion-resistant molten Al characterized by being coated with a based alloy coating layer
-Si-based plated steel plate. (2) Steel surface with a thickness of 2μ or less and an average Ni concentration of 50%
Ni-Fe-based diffusion layer of less than
A corrosion-resistant hot-dip Al-Si plated steel sheet characterized by being coated with a Fe-Si-Ni-Cr alloy layer and an Al-Si alloy coating layer with a thickness of 3 to 40 μm.