JPS61147866A - Aluminum hot dipped steel sheet and its production - Google Patents

Abstract

PURPOSE:To obtain a plated steel sheet having the excellent resistance to high- temp. oxidation, high-temp. gaseous corrosion and salt damage corrosion by subjecting a steel sheet contg. Cr at a specified ratio to hot dipping of an Al-Si alloy with a small ratio of Ni incorporated therein. CONSTITUTION:The Cr-contg. steel plate contg. 2.4-25% Cr and >=1 kinds among Ti, Zr, Nb and V at the atomic equiv. of the content of (C+N) or above and consisting of the balance Fe and inevitable impurities is used. The one side of such steel sheet is subjected to an Ni deposition treatment at (Al hot dipping deposition X 1/300)g/m<2>. The steel sheet is then subjected to Al hot dipping consisting of 5-13% Si and the balance Al and inevitable impurities. The steel sheet is otherwise subjected to the Al hot dipping consisting of 5-13% Si, 0.1-2% Ni and the balance Al and inevitable impurities is used in this stage. The coating layer having a stable sacrificial corrosion preventive effect is formed by the above-mentioned method.

Description

[Detailed Description of the Invention] 1. The present invention provides a molten metal with excellent high-temperature oxidation resistance, high-temperature gas corrosion resistance, and salt corrosion resistance for use in chemical plant parts, automobile exhaust system parts, etc. This relates to aluminized steel sheets.

In recent years, due to the acidification of the atmospheric environment, automobile exhaust system parts and chemical plant parts used at high temperatures have not only become resistant to internal oxidation and gas corrosion.

There is also a strong demand for improved corrosion resistance on the outer surface. Especially when it comes to automobile exhaust system parts.

Salt corrosion caused by the spraying of rock salt to prevent freezing, which is used in North America and elsewhere, is also a major problem.

As a material currently used for such applications.

Although austenitic stainless steel plates are widely used, it would be very advantageous if hot-dip aluminized steel plates or chromium-containing steel plates could be used because they are inexpensive.

However, hot-dip aluminized steel sheets have SO2 at high temperatures.

Although it is superior in terms of gas corrosion caused by CO and salt corrosion, there is a problem in that severe corrosion occurs in areas where the hot-dip aluminum plating layer is cracked due to severe processing.

In general, hot-dip aluminized steel sheets contain 5 to 50% Si, which has the effect of suppressing the growth of the alloy layer, in consideration of workability after plating.
It is plated in an AI bath containing 13 wt%, and the coating layer is an Al-Fe-5i ternary alloy layer with a thickness of 2 to 3 μm and an Al-5
Consists of an i-alloy plating layer. but.

This alloy layer is very hard and brittle, so it easily cracks when subjected to severe processing, and stress concentrates on the Al-5i plating layer in the cracked area, causing the plating layer itself to break. In the case of hot-dip aluminized steel sheets, the sacrificial anti-corrosion effect of AI is almost absent in the atmospheric environment, so the steel base at the cracks is locally eroded.

On the other hand, although chromium-containing steel sheets do not suffer from deterioration in quality characteristics due to processing, they are susceptible to pitting corrosion in environments with a large amount of chlorine ions, and therefore have problems in salt corrosion resistance.

Therefore, various attempts have been made to solve these problems by coating a chromium-containing steel plate with aluminum (Japanese Patent Publication No. 52-33579, Japanese Patent Publication No. 50-36421, etc.), but none of them have yielded satisfactory results.

When a chromium-containing steel sheet with a Cr content of 2.4 wt% or more is coated with aluminum, the base material and AI
-Al-3 due to the difference in natural potential with the Si alloy plating layer
This produces a sacrificial anti-corrosion effect on the i-alloy plating layer, and can suppress pitting corrosion of the base material to some extent at locations where the plating layer is cracked due to processing. However, when this aluminum-coated chromium-containing steel sheet is heated to a temperature of 500°C or higher, Al-Fe interdiffusion occurs, and the coating layer becomes Al.

It changes into a continuous intermetallic compound layer, ie, an alloy layer, containing Fe as a main ingredient and Cr and Si. Along with this alloying reaction, the difference in natural potential between the base material and the coating layer becomes smaller and the sacrificial anticorrosion effect of the coating layer decreases. Pitting corrosion is inevitable. Normally, the operating temperature of chemical plant parts, automobile exhaust system parts, etc. rises to 500° C. or higher, so it is essential to improve the corrosion resistance of the outer surface of aluminum-coated chromium-containing steel sheets.

Another problem is that when an aluminum-coated chromium-containing steel plate is heated to 600° C. or higher, the coating layer formed into a single alloy peels off. When an aluminum-coated chromium-containing steel sheet is used in a high-temperature environment of 700°C or higher, N in the steel diffuses to the surface layer and forms lumps of A at the interface between the 2-alloyed coating layer and the base metal.
IN is precipitated, and peeling occurs during the cooling process after heating due to the difference in shrinkage rate from the base material. And the subsequent oxidation resistance,
Gas corrosion resistance is extremely reduced. Therefore, it can be said that suppression of this thermal peeling is an essential improvement point for the practical use of aluminum-coated chromium-containing steel sheets.

The inventors of the present invention, who are experts in fortune-telling, have diligently studied these problems and have found that
By containing 0.1 wt% or more of Ni in the Al-5i alloy plating layer, the coating layer as plated and after heat alloying has a stable sacrificial corrosion protection effect on the chromium-containing steel base material; as well as Ti, Zr, V,
It has been found that the heating peeling phenomenon of the coating layer can be suppressed by adding one or more types of Nb to the base material. Furthermore, it has been found that Ni precipitates on a chromium-containing steel sheet as a method for making the Al--Si alloy plating layer contain 0.1 wt% or more of Ni during hot-dip aluminum plating on a Sendzimir type continuous plating line. On the contrary,
When hot-dip aluminizing chromium-containing steel sheets using the flux method.

Since there is no need to worry about plating wettability, there is no problem in adding Ni to the aluminum plating bath.

According to the present invention, Cr: 2.4 to 25 wt%, and further Ti.

One or more of Zr, Nb, and V (C+N)
The base material is a chromium-containing steel plate containing more than the atomic equivalent of the chromium content, the remainder consisting of Fe and unavoidable impurities, and the coating layer is Si: 5 to 13 wt%, Ni 0.1 to 2 wt%.
, high temperature oxidation resistance, the remainder consisting of Al and unavoidable impurities;
A hot-dip aluminized steel sheet with excellent high-temperature gas corrosion resistance and salt corrosion resistance is provided.

Also according to the invention. Contains 2.4 to 25 wt% Cr, and one or more of Ti, Zr, V, and Nb in an atomic equivalent of the (C+N) content, and the remainder is F.
(Hot-dip aluminum coating amount x 1/300) g/
After Ni precipitation treatment of rd or more, Si is 5 to 13%1
1%, the balance being A1 and unavoidable impurities.
A method for producing a hot-dip aluminized steel sheet with excellent high-temperature gas corrosion resistance and salt corrosion resistance is provided.

Also according to the invention. A chromium-containing steel plate containing 2.4 to 25 wt% of Cr, as well as Ti, Zr, V, and Nb (711 types or two or more types) in an amount equal to or more than the atomic equivalent of the (C+N) content, with the balance consisting of Fe and unavoidable impurities is fluxed. Hot-dip aluminization is carried out by the method, and at that time, Si: 5
-13wt%, Ni 0.1-2wt%, and the balance is Al and inevitable impurities.High-temperature oxidation resistance, high-temperature gas corrosion resistance, and salt corrosion resistance. Provided is a method for producing a hot-dip aluminized steel sheet with excellent properties.

In the hot-dip aluminized steel sheet of the present invention, if it is less than the base material, sacrificial corrosion protection of the base material after alloying by heating cannot be expected.

Ti, Zr, Nb, and V are fixed elements of C, .

The base steel contains Mn as an impurity 1. Owt% or less, s
o, oswt% or less, P 0.01wt% or less, N
It may contain 0.02 wt% or less, Si 0.1% It% or less.

The A1 coating layer contains 5 to 13 wt% of Si. Considering the workability of aluminized steel sheets, it is necessary to contain 5 wt% or more of Si in order to suppress the growth of the alloy layer after aluminizing, but if it exceeds 13 wt%, plate-like Si may be present in the plating layer. Coarse crystallization occurs, and the workability of the plating layer itself is significantly reduced. The Al coating layer needs to contain at least 0.1 wt% of Ni in order to produce the above effect. There is no commensurate benefit even if the content exceeds 2%.

The improvement in the sacrificial anticorrosion effect of the Al-Si alloy plated layer due to the addition of Ni is due to the fact that the AI-Ni intermetallic compound finely dispersed and precipitated in the plated layer has a cathodic effect on Al. This is thought to be due to the fact that it functions as a site. Therefore, it is possible to add Ni to low-carbon aluminum-killed steel sheets, which are generally used as the plating base material for hot-dip aluminized steel sheets.
0. Even if an aluminum coating containing lwt% or more is applied,
Similar effects can be expected to some extent. However, when a low carbon aluminium-killed steel plate is used as the base material for plating, the base material itself has a low natural potential, so it does not necessarily exhibit a stable sacrificial prevention effect.
When a steel plate containing chromium containing 1 % or more is used as a plating base material, since the base material itself has a high natural potential, its sacrificial anticorrosion effect is further stabilized, which has a great practical effect.

As a method of adding Ni to the plating layer, a method of directly adding it to the aluminum plating bath can also be considered.

When hot-dip aluminizing chromium-containing steel sheets on a Sendzimir-type continuous plating line, the annealing process in the line concentrates Cr on the surface of the steel sheets and inhibits plating wettability, so the chromium-containing steel sheets are pre-plated with Ni. After that, it is desirable to adopt a process of hot-dip aluminum plating. Improvement in hot-dip plating properties by this Ni pre-plating method is described in Japanese Patent Publication No. 55-49152, an application relating to hot-dip PB-5N alloy plating.

However, in Japanese Patent Publication No. 55-49152, the pre-plated Ni layer reacts with Sn in the plating bath, and Ni
-In contrast to forming a Sn alloy layer, in the case of hot-dip aluminization, the pre-plated Ni layer is eluted into the plating bath, and some of the eluted Ni is incorporated into the Al-Si alloy plating layer. There are characteristics. That is, the pre-plated Ni layer is eluted into the aluminum bath.

The matrix directly reacts with the molten Al-Si bath to form an alloy layer. On the other hand, the Ni eluted into the plating bath remains near the passage of the steel strip through the bath, as shown in FIG.

Approximately 20 to 30% of the pre-plated Ni is dispersed and precipitated in the Al--Si alloy plating layer after being pulled out of the bath. Therefore, when manufacturing a hot-dip aluminized chromium-containing steel sheet with a coating weight of 80 g/rrr on one side, if a Ni pre-plating layer of 0.27 g/r or more is precipitated in advance, it is possible to avoid adding it to the Ni plating bath. A product of the present invention having a sacrificial anticorrosion effect can be obtained.

In other words, 1/3 of the target amount of hot-dip aluminum plating
If the amount of Ni precipitated is 0.00 or more, the product of the present invention having a sacrificial anticorrosion effect can be obtained.

In addition, when obtaining the product of the present invention by hot-dip aluminizing a chromium-containing steel plate using the flux method, Ni is directly added to the plating bath because the drop in wettability of the plating due to the concentration of Cr on the surface does not occur. You may.

Another problem, which is the peeling of the alloy layer during heating, can be solved by adding one or more of Ti, Zr, Nb, and V to the steel. Since Ti, Zr, Nb, and V added to the chromium-containing steel base metal combine with N in the steel to form nitrides, precipitation of lumpy AIN at the alloy layer-base metal interface during heating is suppressed.

However, since Ti, Zr, Nb, and V in steel are elements that easily form carbides, in order to completely precipitate N in steel as nitrides, it is necessary to It is necessary to add one or more of Ti, Zr, Nb, and V; for example, in the case of Ti.

It is desirable to add it to the steel in an amount of at least four times the amount (C1N) in terms of weight percent.

Example 1 (1) Plating base material chemical components: C: 0.062wt%, Si
: 0.089wt%, Mn: 0.34wt%,
P: 0.021wt%s S: 0-007w
t%.

Cr: 18.1wt%, Ti: 0.29wt
%, N: 0.0062wt%.

Plate thickness 0.8+w consisting of balance Fe and unavoidable dull materials
A chromium-containing steel plate that had been annealed and pickled was used as the plating base material.

(2) Manufacture of hot-dip aluminized steel sheets After degreasing the plating base material according to a conventional method.

In a nickel chloride bath, the current density was kept constant at 5 A/drrr, and the amount of Ni deposited on one side was 0.16 to 5 g by varying the current application time.
The 6Ni plated base material that was subjected to the Ni plating treatment in /A was heated at 700°C in a 50:50 H2N2 atmosphere.
After preheating for 30 seconds, heat at 670℃ under the same atmosphere.
Q-6. Hot-dip aluminization was performed by immersion in a 6.5% Si bath for 2 seconds to produce a hot-dip aluminized steel plate with a coating weight of 80 g/m on one side. Note that steel sheets without Ni pre-plating have significant unplatedness, so they were produced using the molten salt flux method. The aluminum plating bath used at this time was also 6.
The plating weight was adjusted to 80 g/m2 on one side using AQ-6, 5% Si composition at 70°C.

(3) Accelerated corrosion test The hot-dip aluminized steel sheet obtained in this way is
After bending 2 based on 2224g, JIS
An accelerated corrosion test was conducted in which one cycle consisted of a salt spray test based on 22371 for 3 hours, followed by 1 hour of hot air drying at 50"C. In addition, after bending 2, heating at 700°C for 100 hours was conducted. The sample was also used in this test.

The degree of each corrosion is determined by accelerated corrosion test 1, corrosion products and residual waves after 000 cycles ylJf! Dissolve I.

The maximum erosion depth of the base metal when removed was measured and evaluated.

Table 1 summarizes the corrosion state of each sample after 1,000 cycles of the accelerated corrosion test and the maximum corrosion depth of the base material. Steel sheets that are not hot-dip aluminized or contain ROM (
In No. 8), pitting corrosion occurred through the steel plate, whereas the depth of corrosion in the base material of the aluminum-coated chromium-containing steel plate was relatively small.

For hot-dip aluminized steel sheets (No. 1, No. 2) with Ni content in the plating layer of 0.05v, t%,
When heated at 700°C for 100 hours, corrosion of the base material becomes significant. This tendency is particularly noticeable in the bending part.

On the other hand, the hot-dip aluminized steel sheet of the present invention containing 0.1 wt% or more of Ni in the coating layer exhibits an excellent sacrificial corrosion protection effect even after the coating layer is alloyed by heat treatment, and the base metal is not eroded. Almost unrecognizable.

In this way, 0.00% of Ni is added to the plating layer. It can be seen that by adding lwt% or more, the salt corrosion resistance of the aluminum-coated chromium-containing steel sheet is significantly improved.

Example 2 (1) Chemical components of the plating base material: C: 0.052wt%, Si
: 0.089wt%, Mn: 0.33wt%,
P: 0.015wt%, S: 0.009w
t%.

Cr: 5.8wt%, Nb: 0.58wt%
, N: 0.0042wt%, balance Fe and unavoidable impurities, an annealed and pickled chromium-containing steel plate with a thickness of 0.6 mm was used as the plating base material.

(2) Production of hot-dip aluminized steel sheets As an aluminizing bath, AQ -10.5% at 650℃
Same as Example 1 except that a Si bath was used.

(3) Accelerated corrosion test Same as Example 1.

Table 2 shows the corrosion state of each sample after 1,000 cycles of the accelerated corrosion test.

As is clear from the table, the maximum corrosion depth of the base material is slightly larger than the result of Example 1 using a plated base material with a Cr content of 18 wt% in the steel, but the Ni content in the plating layer is 0.
When the content exceeds 1 wt%, the sacrificial anticorrosion effect of the coating layer tends to significantly improve the corrosion resistance, which is similar to the result of Example 1.

Example 3 (1) Plating base material chemical components: C: 0.040wt%, Si
: 0.75wt%.

Mn: 0.26wt%, P: 0.017wt
%+S: 0.012wt%, Cr:12.1wt
%, Ti: 0.13wt%, Nb: 0.4
A plated base material was an annealed and pickled chromium-containing steel plate with a thickness of 0.6 cm, consisting of 3wt% N, 0.0056wt% N, and the remainder Fe and unavoidable impurities.

(2) Manufacture of hot-dip aluminized steel sheet After degreasing the plated base material according to a conventional method, the bath temperature is 400.
°C bath molten salt flux bath (ZnC1z +5nC12+
Flux treatment was performed by immersing it in KCI) for 20 seconds.

After flux treatment, the base material was immersed for 2 seconds in an Al-5.0% Si bath (bath temperature: 680°C) with various amounts of Ni added to perform hot-dip aluminization, resulting in a coating weight of 120 g.
A hot-dip aluminized steel plate of /rrr was produced.

(3) Accelerated Corrosion Test Similar to Example 1, Table 3 shows the corrosion state of each sample after 1,000 cycles of the Accelerated Corrosion Test.

As is clear from Table 3, when hot-dip aluminum plating is carried out using the flux method, the plating wettability does not deteriorate due to surface layer concentration of Cr in the steel.

Even if Ni is directly added to the plating bath, the hot-dip aluminized steel sheet of the present invention can be obtained. If the amount of Ni added in the plating bath is 0.1 wt% or more, a sacrificial anticorrosion effect will be exhibited,
Erosion of the base metal is significantly suppressed. Substantially the same amount of Ni is present in the plating layer as is present in the plating.

Haruka 1-NF),. . . , .

Example 4 (1) Plating base material An unannealed chromium-containing steel plate (thickness: 0.6 mm) in which the Cr content was varied in the range of 0 to 20 wt% was used as the plating base material.

The chemical components in the steel other than Cr are C: 0.048~
0.057wt%, Si: 0.065-0.082
wt%, Mn: 0.31-0.38wt%, P
: 0.015-0.023wt%, S: 0.007-
0.013wt%, Ti: 0.30~0.45w
t%, N: ranged from 0.0050 to 0.0082 wt%.

(2) Manufacture of hot-dip aluminized steel sheet After degreasing and pickling the plated base material according to a conventional method,
The amount of Ni precipitated in a nickel chloride bath was 0.6 g/bo on one side.
i precipitation treatment was performed. The plated base material plated with Ni was annealed at 800°C for 5 minutes in a 75% 112-N2 atmosphere, and then immersed in an Al-9.0% Si bath at 660°C in the same atmosphere for 2 seconds to perform hot-dip aluminum plating. A hot-dip aluminized steel plate with a coating weight of 100 g/rd on one side was produced.

(3) Accelerated Corrosion Test Similar to Example 1, Table 4 summarizes the corrosion state after 000 cycles of Accelerated Corrosion Test 1.

Hot-dip aluminized steel sheets (Nα1 to Na5) with a Cr content of up to 0.5 wt% were heated at 700°C for 100 hours, whereas the erosion of the base metal at the bending part was relatively unreliable. In the hot-dip plated steel sheet according to the present invention having a Cr content of 2.4 wt% or more, no corrosion of the bent portion after alloying is observed.

Thus, when the Cr content in the steel is 2.4 wt% or more.

Moreover, it can be said that the material of the present invention containing 0.1 wt% or more of Ni in the plating layer has a very stable sacrificial corrosion prevention effect.

j! 1m NF2 QF w. ,
, .

Example 5 Chemical components: C: 0.043wt%, Si:
0.095wt%, Mn: 0.35wt%, P:
'0.016wt%, S: 0.004wt%, C
Ti: steel type based on r: 12.3 wt%, N: 0.0065 wt%.

A chromium-containing steel containing various amounts of Nb, Zr, and V was prepared, rolled, annealed, and pickled to obtain a plated base material with a thickness of 0.8 mm.

(2) Production of hot-dip aluminized steel sheet The plated base material was degreased according to a conventional method, and then subjected to Ni precipitation treatment in a nickel chloride bath so that the amount of Ni deposited was 0.5 g/d on one side. Ni-plated plating base material is 50%H
2 = After preheating at 700°C in a N2 atmosphere for 30 seconds, immersion in an Al-9.0% SL bath at 660°C in the same atmosphere for 2 seconds to perform hot-dip aluminum plating, with a coating weight of 8 on one side.
A 0 g/m2 hot-dip aluminized steel plate was produced.

(3) Heating peeling test The obtained hot-dip aluminized steel plate was heated in the atmosphere at 700°C for 100 hours, and then the presence or absence of peeling of the alloy layer was determined using a Gardner impact tester specified in ASTM-D2794. .

Table 5 summarizes the results of examining the presence or absence of thermal peeling.

As shown in Table 5, the material of the present invention containing one or more of Ti, Nb, Zr, and V in an amount equal to or more than the atomic equivalent of the (C+N) content in the steel has a It can be seen that the coating layer does not peel off.

On the other hand, the addition of Ti, Nb, Zr, and V in amounts less than the atomic equivalent of the (C+N) content in the steel all cause peeling of the coating layer, although there are differences in degree, and the subsequent corrosion resistance and Heat resistance is extremely reduced.

In this way, when using a chromium-containing steel plate coated with aluminum, it is essential to add Ti, Nb, Zr, and V to the base material.

Two people I Ti = 0.12 Total peeling
Comparative Example 2 Nb=0.18 3 Zr=0.32 Mild peeling
〃4 V=0.07 Whole surface peeling 5 Ti=0. Q4 Nb=0.19 6 Nb=0.18 Mild peeling Z
r=0.10 7 Ti=0.24 No peeling Invention 8 Nb=0.47
n9 Zr=0.49 10 V=0.34 11 Ti=0.21 Nb=0.12 II
#12 Zr=0.31 V=0.19 The effects of the hot-dip aluminized steel sheet according to the present invention, which have been described for more than 1 month and υ1 month, are summarized as follows.

1) By using a chromium-containing steel sheet with a Cr content of 2.4% or more as the plating base material, and by containing 0.1wt% or more of Ni in the Al-Si alloy plating layer, the plated material is stable both as plated and after heating. A coating layer having a sacrificial anticorrosion effect is formed, and local corrosion of the base material can be suppressed.

2) As a method for incorporating Ni into the Al-Si alloy plating layer, a method of precipitating Ni on the plating base material can be applied, so hot-dip aluminum plating without any unplated areas can be performed. Furthermore, when hot-dip aluminizing is carried out by the flux method, Ni may be directly added to the plating bath since the plating wettability does not deteriorate due to surface layer concentration of Cr in the steel.

3) Peeling of the coating layer during high temperature heating can be suppressed by adding one or more of Zr, Nb, and V to the plating base material in an amount equal to or more than the atomic equivalent of the (C1N) content.

4) Hot-dip aluminizing a chromium-containing steel sheet containing 2.4% or more of Cr improves its oxidation resistance, but adding Si to the plating base material improves the chromium-plated chromium. The high-temperature oxidation resistance of the containing steel sheet is further improved.

Procedural amendment January 25, 1985

Claims (1)

[Claims] 1. 2.4 to 25 wt% Cr, furthermore Ti, Zr, Nb
The base material is a chromium-containing steel plate containing one or more types of V in an amount equal to or more than the atomic equivalent of the (C+N) content, and the remainder is Fe and unavoidable impurities, and the coating layer is Si: 5 to 13.
A hot-dip aluminized steel sheet with excellent high-temperature oxidation resistance, high-temperature gas corrosion resistance, and salt damage corrosion resistance, consisting of 0.1 to 2 wt% of Ni and the balance being Al and inevitable impurities. 2. 2.4 to 25 wt% Cr, furthermore Ti, Zr, V,
A chromium-containing steel sheet containing one or more types of Nb in an amount equal to or more than the atomic equivalent of the (C+N) content, with the remainder consisting of Fe and unavoidable impurities, was coated on one side with (hot-dip aluminum coating amount x 1/300) g/ After performing a Ni precipitation treatment of m^2 or more, high-temperature oxidation resistance, high-temperature gas corrosion resistance, and A method for producing hot-dip aluminized steel sheets with excellent salt corrosion resistance. 3. 2.4 to 25 wt% Cr, further Ti, Zr, V,
A chromium-containing steel sheet containing one or more types of Nb in an amount equal to or more than the atomic equivalent of the (C+N) content, with the remainder consisting of Fe and unavoidable impurities, is hot-dipped aluminized by a flux method, and at that time, Si:5 to 13wt%, Ni0.1~2w
Production of a hot-dip aluminized steel sheet with excellent high-temperature oxidation resistance, high-temperature gas corrosion resistance, and salt corrosion resistance, characterized by using a hot-dip plating bath containing t% and the remainder consisting of Al and inevitable impurities. Law.