JPS5877563A - One-side aluminum plated steel plate having rolled and annealed structure and its manufacture - Google Patents

Abstract

PURPOSE:To provide superior corrosion resistance and workability to a one-side Al plated steel plate consisting of a steel plate contg. specified amounts of N and C and of an Al plating layer contg. a specified amount of Si by rolling and annealing the plated steel plate under specified conditions. CONSTITUTION:A one-side Al plated steel plate consisting of a steel plate contg. 0.0050-0.2000wt% N and <=0.02wt% C and of an Al plating layer contg. 1- 15wt% Si is manufactured. The plated steel plate is rolled at 20-60% draft to break an intermetallic Al-Fe-Si compound present at the interface between the steel plate and the Al plating layer. The rolled plate is then subjected to recrystallization annealing at 500-600 deg.C to recrystallize the steel plate and the Al plating layer without causing the counter diffusion of Al and Fe at the interface. Thus, a thin Al plated steel plate with high corrosion resistance and workability can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a thin, one-sided aluminum-plated steel plate having an aluminum-plated surface with excellent workability and corrosion resistance on one side and a steel plate surface with excellent paintability on the other side; It concerns its manufacturing method.

Aluminum-plated steel sheets have the excellent corrosion resistance, heat resistance, and
It is used in a wide range of fields as a composite material that has both the surface gloss and the strength of steel sheets. However, in recent years, double-sided galvanizing is not necessarily required from a functional perspective, and rather single-sided galvanized steel plates are preferred from the viewpoint of paintability on the machined surface, and the demand for such single-sided aluminium-plated steel plates has increased. There is. However, single-sided aluminum-clad steel sheets with excellent workability and corrosion resistance have extremely high manufacturing costs and cannot necessarily meet these demands.

Against this background, there is a demand for an improved single-sided aluminium-plated steel plate that is based on a single-sided molten aluminium-plated steel plate that is inexpensive to manufacture and has good corrosion resistance on the plated surface and good workability. In reality, there is also a strong desire to make this steel plate thinner. However, it has been extremely difficult to manufacture ultra-thin aluminized steel sheets with a total thickness of 0.6 mm or less, for example. In other words, ordinary single-sided hot-dip aluminized steel sheets are manufactured by line reannealing or flux methods, but as the thickness of the steel sheet becomes thinner, the shape becomes extremely poor due to thermal distortion during immersion in an aluminum plating bath. It has become impossible to manufacture thin single-sided aluminum-plated steel sheets because it is difficult to modify the shape by temper rolling or the like. Furthermore, in the line reannealing method, when the thickness of the steel plate becomes thinner, the high temperature strength of the steel plate decreases, which causes the steel plate to break when the tension required for operation in a non-oxidation furnace or heating furnace is applied.

Therefore, as a method for producing a single-sided aluminized steel plate with a thickness of 0.6 mm or less, a method can first be considered in which a thick steel plate is coated with molten aluminum in advance and then rolled to a desired size. However, in the case of a single-sided aluminized steel plate that has been rolled, the steel plate and the Al-Si coating layer on one side form a rolling structure, resulting in loss of workability of the steel plate itself, or
There is a problem in that the corrosion resistance as a plating material decreases due to the stress applied to the l-Si coating layer. Furthermore, if the rolling reduction ratio is increased, many microcracks will occur in the Al--Si coating layer, making it impossible to put it to practical use. Therefore,
After rolling in an appropriate rolling reduction range, it is necessary to recrystallize the steel sheet having the rolled structure and the Al-Si coating layer.

However, when recrystallization annealing is applied to a rolled steel plate coated with hot-dip aluminium on one side, the plated surface becomes Al3 due to interdiffusion of Al-Fe at the interface between the steel plate and the Al-Si coating layer.
Binary intermetallic compounds such as Fe and Al5Fe2 are formed. Since this intermetallic compound is very hard and brittle, when it is formed, the Al--Si coating layer easily peels off during processing.

Therefore, in the recrystallization annealing treatment, it is a necessary condition that the recrystallization start temperature of the steel sheet with the rolled structure is lower than the formation temperature of the intermetallic compound.

However, in conventional single-sided aluminized steel sheets made of low-carbon rimmed steel as a base material, the recrystallization start temperature overlaps with the formation temperature range of intermetallic compounds, so it has been impossible to prevent the formation of intermetallic compounds.

For this reason, even if a thin single-sided aluminized steel plate is obtained by rolling a thick single-sided molten aluminized steel plate, the plated surface becomes alloyed during recrystallization annealing, resulting in loss of corrosion resistance and workability. Furthermore, since it is virtually impossible to manufacture a single-sided aluminized steel plate so thin that this rolling process can be omitted, the emergence of a rolled-annealed single-sided aluminized steel plate that has both corrosion resistance and workability is considered impossible. was.

The purpose of the present invention is to overcome this problem, and as a result of extensive research from a comprehensive perspective, the present inventors have developed a new material with excellent corrosion resistance and workability that has a new organizational state and structure. We have successfully developed a type of rolling annealed single-sided aluminized steel plate. The rolled annealed single-sided aluminized steel sheet according to the present invention has an Al-Si coating layer with a rolled recrystallized structure on one surface of the steel plate with a rolled recrystallized structure, and has a fractured state at the interface between the steel plate and the Al-Si coating layer. Al-Fe-Si
It is characterized by the presence of intermetallic compounds, and among the components in the steel in the steel plate layer, the N content is 0.0050 to 0.
By setting the C content to 0.0200 wt% or less, problems caused by the formation of intermetallic compounds as described above are solved and workability is improved, and at the same time, the steel has a rolled recrystallized structure on one side. The Al--Si coating layer has excellent corrosion resistance, and the opposite side has a cold-rolled steel sheet surface with a rolled recrystallized structure and good paintability. This new single-sided aluminized steel plate with excellent workability and corrosion resistance is produced by a rolling process in which a single-sided molten aluminized steel plate previously manufactured on a plating line is rolled to a predetermined thickness, and a steel plate and Al-Si coating are used. Al− at the layer interface
Rolled steel sheet and Al without causing Fe interdiffusion
- It has been found that it can be advantageously manufactured by a recrystallization annealing step in which the Si coating layer is recrystallized.

At that time, the rolling process is carried out at a reduction rate of 20 to 60%, and the recrystallization annealing process is carried out at a reduction rate of 500 to 60%.
It is preferable to carry out the test in a temperature range of 00°C. Further, the Si content in the aluminum plating layer is preferably 1 to 15% by weight.

The details of the present invention will be specifically explained below based on test results. , conventional low carbon rimmed steel (as a typical example, C; 0.07,
Mn; 0.21, Si; tr, P; 0.009, S; 0
．． 013, N; 0.0024 balance Fe, both wt%
When a molten aluminized steel plate is rolled at a rolling reduction of 50% and then recrystallized annealed at a temperature of approximately 480°C, the steel plate forms an Al-Fe binary intermetallic compound without recrystallizing. It forms and grows, and the surface changes color to grayish black in a few hours. In order to recrystallize this plated original sheet having a rolled structure, it was necessary to annealing it at a temperature of 500° C. or higher.

On the other hand, C in steel is 0.02wt%, N is 0.0074w
After molten aluminum plating on the plated original plate of t%, the rolling reduction rate was 5.
Even if an aluminized steel sheet rolled at 0% is annealed for 10 hours at a temperature of 530°C, which is within the recrystallization temperature range of the original sheet, the formation and growth of Al-Fe binary intermetallic compounds will not occur. Softening of the material was observed.

Table 1 shows that rimmed steel strips (thickness: 0.8 mm) with various C and N wt% steel components were immersed in a molten aluminum bath containing 10 wt% Si and plated with molten aluminum. 1
The presence or absence of the formation of Al-Fe binary intermetallic compounds and the recrystallization of plated original sheets when stepped rolled at various rolling reductions in the range of 0 to 80% and recrystallized annealed at the indicated temperatures for 10 hours. This is the result of a survey to see if there is any.

However, the display symbols in Table 1 are as follows.

〇...The plating base material recrystallizes without the formation of intermetallic compounds.

×...No intermetallic compound is generated, but the plating base material is not recrystallized.

Δ: The plating base material recrystallizes, but intermetallic compounds are generated and the surface becomes grayish-black.

□... Intermetallic compounds are generated and the plating base material does not recrystallize.

As is clear from Table 1, the N content in the steel is 0.00
It can be seen that when the content is 50 wt% or more, the plated original plate can be recrystallized without forming Al-Fe binary intermetallic compounds.

Note that the higher the N content in the steel, the higher the effect of suppressing the formation of Al-Fe intermetallic compounds, but if it is too high, the steel plate itself will harden, so the N content in the steel is 0.0200W.
It is preferably t% or less. The reason why N in steel suppresses the formation of Al-Fe intermetallic compounds is not clear at all, but the interstitial presence of N in steel increases the activity of Al diffusing into Fe. This is thought to be because it increases the chemical energy and inhibits the formation of intermetallic compounds.

Regarding C in steel, as is clear from Table 1, the lower the C content, the higher the temperature at which intermetallic compounds are formed. Particularly, when the content is less than 0.02 wt%, the formation temperature of intermetallic compounds is significantly higher than when the content is more than 0.02 wt%. The reason for this is thought to be as follows. C; 0.02
The wt% approximately coincides with the maximum C solubility of α-iron. Therefore, C larger than this exists as Fe3C. This Fe3
C has the solubility of N, and its presence has the effect of reducing the solid N content in Fe, which increases the temperature at which intermetallic compounds are formed. On the other hand, when C is less than 0.02 wt%, Fe3C is in an extremely small amount and the effective N amount does not decrease. From the above results, it is preferable that the amount of C in the steel be 0.02wt% or less, but even if the amount of C is 0.02wt% or more, if the amount of N in the steel is large, the temperature at which intermetallic compounds will form can be made higher. In this way, since C and N in steel influence each other, it is advantageous to select their respective contents so that the recrystallization temperature range of the steel sheet is wide.

Furthermore, as is clear from Table 1, the recrystallization temperature was set to 500
If the annealing temperature is above 600°C, recrystallization of the rolled steel sheet can occur, but if the annealing temperature is above 600°C, it will exceed the melting point of the Al-Si coating layer on the plated surface, so the annealing temperature range It is necessary to set the temperature at 500 to 600°C.

Next, regarding the rolling conditions, as shown in Table 1,
When a single-sided molten aluminized steel plate is rolled at a rolling reduction of less than 20%, the recrystallization start temperature increases. For this reason,
Since the annealing temperature range in which recrystallization can be achieved without forming an Al-Fe binary intermetallic compound is narrowed, care must be taken in manufacturing. In addition, when the rolling reduction ratio is less than 20%, 2 to 4 μ
It becomes impossible to completely divide the alloy layer (Al-Fe-Si intermetallic compound layer) of about m. One of the features of the product of the present invention is that the alloy layer is rolled and divided and is intermittently present at the Fe-Al interface, thereby improving the workability and peeling resistance of the Al-Si coating layer. However, the rolling reduction rate is 20%
If it is less than this, the processability and peeling resistance of the Al-Si coating layer will be slightly reduced due to the above-mentioned phenomenon. On the other hand, when the rolling reduction exceeds 60%, the Al-S on the plating surface
A large number of microcracks occur in the coating layer, making it impossible to use it as a product. Therefore, the rolling reduction ratio is 20 to 60%.
It is desirable to set it within the range of .

On the other hand, the Si concentration in the Al--Si coating layer on the plated surface has a very large influence on the rolling process of a single-sided molten aluminum plated steel sheet.

Table 2 shows C: 0.015wt%, N: 0.0115w
After immersing a steel strip (1.2 mm thick) in a molten aluminum bath with varying Si content to plate it with molten aluminum on one side, it was stepped at various rolling reductions in the range of 10 to 80%. These are the results of observing the morphology of the Al-Si coating layer and alloy layer during rolling using a cross-sectional microscope.

As is clear from Table 2, the Si concentration in the bath is 1 wt% or less, that is, the Si concentration in the Al-Si coating layer is 1 wt%.
The alloy layer on the plated surface of the single-sided molten aluminum plated steel sheet below is about 15 to 20 μm, and even when rolled at a low reduction rate, large cracks occur in the alloy layer and the Al-Si coating layer easily peels off. I will come to you.

In addition, the Si concentration in the bath is 15 wt% or more, that is, Al-
The plated surface of surface-fusing aluminized steel with a Si concentration in the Si coating layer of 15 wt% or more has hard and brittle plate-like Si scattered in the Al-Si coating layer, and cannot be rolled at a low reduction rate. However, large cracks occur in the Al--Si coating layer. For this reason, the Si concentration in the plating layer is set to 1.0 to 1.5 wt%.
It is necessary to

In the present invention, the rolled steel sheet and the Al-Si coating layer are simultaneously recrystallized, but depending on the purpose, the Al-Si coating layer may be recrystallized.
It is also possible to form only the i-coating layer into a recrystallized structure. The Al--Si coating layer on the plated surface of a single-sided molten aluminum plated steel sheet has a cast structure in the as-plated state, and the processing properties of the plated layer are poor and there are many pinholes. However, by rolling the Al-Si coating layer to crush the pinholes and then recrystallizing it, it is possible to form a strain-free, very sound coating layer with good corrosion resistance. Therefore, for applications where the workability of the plated original plate is not a concern, after rolling, 3
By heating at a temperature of 00 to 450℃, Al-S
The processability of the plating layer can also be improved by recrystallizing only the i-coating layer.

In addition, when manufacturing the product of the present invention, the amount of molten aluminum plating and the thickness of the plated surface are not necessarily limited. This is because the amount of plating on the molten aluminum plated surface is determined by the amount of aluminum plating after rolling treatment and recrystallization annealing treatment.

Alternatively, no matter how many times the rolling process→recrystallization annealing process is repeated until a predetermined plate thickness is obtained, the characteristics of the product of the present invention do not change at all.

As described above, the single-sided aluminized steel sheet according to the present invention has a cross-sectional structure as shown in FIG. 1, however, in FIG. 1, 1 is the base material for recrystallization after rolling, and C≦
0.12wt%, N; 0.005-0.0200wt%
It is preferable to contain. Reference numeral 2 is an Al-Si coating layer on the fastening surface that is recrystallized after rolling, and the Si content in the coating layer is preferably 1.0 to 15 wt%.

3 Al-F generated during molten aluminum plating on the plating surface
The e-Si alloy layer is separated during rolling.

As described above, the plated surface of the product of the present invention consists of the steel sheet layer 1 with a rolled recrystallized structure, the Al-Si coating layer 2 with a rolled recrystallized structure, and the Al-Fe-Si alloy layer 3 in a divided state at the interface between both of them. It has a three-layer structure.

Next, the excellent characteristics of the aluminized steel sheet according to the present invention will be clarified through examples.

Example 1 (1) C; 0.063 wt%, Si; t melted in a steel sheet converter
r, Mn; 0.30wt%, P; 0.018wt%, S
;0.011wt%, N;0.0018wt%, remainder F
An appropriate amount of MnN is added into the mold during ingot making of low carbon steel having the component e, and steel ingots having various N contents are manufactured. Next, this steel ingot is subjected to blooming, defect removal, hot rolling, pickling, and cold rolling in a conventional manner to produce a plated original sheet. Further, these cold rolled steel sheets were decarburized and annealed in a wet hydrogen atmosphere to produce plated original sheets having various C and N contents as shown in Table 3.

(2) Manufacture of steel plate with rolling annealing structure on one side aluminized ), heat-treated in a reducing heating atmosphere after drying, and immersed in an Al-9.5Si bath at 670°C for 5 seconds to perform single-sided molten aluminum plating, with a coating weight of 80 g/
m2, and after plating the masking surface, the masking agent was mechanically removed to obtain a single-sided aluminum-plated steel plate.

After rolling this molten aluminized steel plate at a reduction rate of 50%,
Recrystallization annealing was performed by heating in a reducing atmosphere at 530°C for 10 hours, the adhesion on the plated surface was 40g/m2, and the total plate thickness was 0.4m.
A steel plate with a single-sided aluminium-plated rolling annealing structure of m.

(3) Workability test The obtained rolled annealed structure single-sided aluminized steel sheet was
A close bending test was conducted based on 2248, and the surface appearance and cross-sectional structure of the bent portion of the plated surface were judged according to the criteria in Table 4 below.The results are shown in Table 5 below.

(4) Corrosion resistance test Rolled annealed single-sided aluminized steel sheets were subjected to a salt spray test based on JIS2371, and the time until white rust and red rust appeared were measured, and the results are shown in Table 5 below.

In addition, in this workability test and corrosion resistance test, as a comparison material, the plating surface adhesion amount was 40 g/m2, the plate thickness was 0.8
single-sided molten aluminized steel plate with a normal casting structure of mm (base material components: C: 0.045 wt%, Si: tr, M
n: 0.30wt%, P: 0.018wt%, S: 0.
011wt%, N; 0.0023wt%, balance Fe,)
Nara hinimetsuki surface adhesion amount 80g/m2, board thickness 0.8mm
50% of single-sided molten aluminized steel plate with normal casting structure
The as-rolled material was used.

The materials of the present invention (sample numbers 2, 3, 5, 7, and 8) do not cause cracks in the Al-Si coating layer on the plated surface even when subjected to close bending, and the number of days for white rust and red rust to occur is normal. This value is significantly higher than that of hot-dip aluminized steel sheets with the same coating weight.

On the other hand, test materials (sample numbers 1, 4, and 6) obtained by applying molten aluminum on one side to a conventional low-carbon rimmed steel sheet, rolling it, and then annealing it by heating at a temperature of 530°C for 10 hours were hard and brittle.
It is observed that the l-Fe intermetallic compound grows to the surface and the workability and corrosion resistance are significantly reduced.

Further, in the test material (sample number 10), which is a normal single-sided hot-dip aluminized steel plate rolled at a rolling reduction of 50%, improvement in corrosion resistance is observed, but the plated base material breaks during close bending. Table 5 does not list the results of the paintability test on the steel plate surface, but the results of testing the prepaintability with a phosphate treatment agent that is commonly used for JISS PCC materials showed that the steel plate surface was good. Yes, there was no significant difference in the plating surface.

Example 2 (1) Steel plate C manufactured by the same method as Example 1: 0.015w
A steel plate (thickness: 0.7 mm) having a chemical composition of t%, N: 0.0083 wt% was used.

(2) Manufacture of rolling-annealed steel sheet with single-sided aluminium-plated steel sheet (
After degreasing and pickling a plate (thickness: 0.7 mm) according to the usual method, one side aluminum plating was performed in the same manner as in Example 1 to obtain a single side molten aluminum plated steel plate with a plating weight of 80 g/m2. did.

This single-sided molten aluminum-plated steel plate was rolled at a rolling reduction of 50%, then heated at a temperature of 550°C for 6 hours to perform recrystallization annealing, resulting in a plated surface coating amount of 40 g/m2 and a total plate thickness of 0.35 mm.
The rolled annealed structure was a single-sided aluminized steel sheet.

(3) Workability test Same as Example 1 (4) Corrosion resistance test Same as Example
g/m2, 80 g/m2, conventional single-sided fused aluminized steel plate with a plate thickness of 0.9 mm (as a base material component, C; 0.054
wt%, Si; tr, Mn; 0.30%, P; 0.01
3wt%, S; 0. O10wt%, N; 0.0021w
t%, balance Fe).

Table 6 shows the results of this processing test and corrosion resistance test.

As is clear from the results in Table 6, it is recognized that the material of the present invention (sample number 1) exhibits superior workability compared to ordinary single-sided hot-dip alkyl plated steel sheets.

In addition, regarding the corrosion resistance, it is recognized that the material of the present invention has 1.5 to 2 times better corrosion resistance than a normal single-sided fused aluminized steel plate.

Table 6 does not list the results of the coating test on the steel plate surface, but when treated with the pre-painting conditions (phosphate treatment) normally applied to JIS SPCC materials, the steel plate surface was found to be the same as the SPCC material. It was confirmed that it was at the same level and in good condition.

Therefore, there was no noticeable difference as noticeable.

Example 3 (1) Steel plate C:0.0 manufactured by the same method as in Example 1.
A steel plate having a chemical composition of 0.018 wt%, N; 0.064 wt% was used.

(2) Manufacture of rolling-annealed steel sheet with single-sided aluminium-plated steel sheet (
After degreasing and pickling a plate (thickness 0.7 mm) according to the usual method, a masking agent was applied in the same manner as in Example 1, dried, and after reduction heating under the same conditions, Al-6.7wt was heated at 650°C. %
The plated surface was 80 g/m2 by immersion in a Si bath for 5 seconds, and after the masking surface was plated, the masking agent was mechanically removed to obtain a single-sided aluminum plated steel plate.

This single-sided molten aluminized steel plate was rolled at various reduction ratios in the range of 10 to 30%, and then recrystallized by heating at a temperature of 530°C for 10 hours to obtain various rolled annealed single-sided aluminized steel plates. Ta.

(3) Processing test Same as Example 1.

(4) Corrosion resistance test Same as Example 1.

The results of both tests are shown in Table 7.

As shown in Table 7, when the rolling reduction ratio is 10%, the alloy layer is not completely separated, so slight cracks occur in the close contact bending test.

In addition, when the rolling reduction ratio was 70%, fine cracks occurred in the Al-Si breakdown layer, and in the salt spray test,
A wrinkled red rust appears in a short period of time.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of the material of the present invention. 1 is the base material that has been recrystallized after rolling, 2 is the Al-Si coating layer on the tight surface that has been recrystallized after rolling, and 3 is Al-F in a divided state.
e-Si alloy layer applicant Kenji Aida, agent of Nisshin Steel Co., Ltd.

Claims (10)

[Claims] (1) In a single-sided aluminized steel sheet in which one side is an aluminum-plated surface and the opposite side is a steel sheet surface, the steel sheet has a rolled recrystallized structure, and the aluminum plated layer has an Al-plated layer that has a rolled recrystallized structure. A steel plate having an aluminum plated surface with excellent workability and corrosion resistance and excellent paintability, which is a Si coating layer and has a divided Al-Fe-Si intermetallic compound present at the interface between the steel plate and the aluminum plated layer. A single-sided aluminized steel plate with a rolling annealing structure. , (2) The N content in the steel components of the steel plate is 0.0050
The single-sided aluminum-plated steel sheet with a rolling annealing structure according to claim 1, wherein the content is 0.0200% by weight. (3) A single-sided aluminized steel sheet with a rolling annealing structure according to claim 1 or 2, wherein the C content in the steel components of the steel sheet is 0.02% by weight or less. (4) Si content in the aluminum plating layer is 1 to 15% by weight
An aluminized steel sheet with a rolled annealed structure according to claim 1, 2, or 3. (5) A steel plate with an aluminum plated surface on one side is reduced to the required thickness at a rolling reduction rate necessary to break up the Al-Fe-Si intermetallic compound present at the interface between the steel plate and the aluminum plated layer. a recrystallization annealing step in which both the steel sheet in the rolled structure and the aluminum plating layer are annealed under conditions that do not cause Al-Fe interdiffusion at the interface and that recrystallize both the steel sheet in the rolled structure and the aluminum plating layer. A method for manufacturing a single-sided aluminized steel plate with a rolling annealing structure, comprising: (6) N content in the steel components of the steel plate is 0.0050
The method for producing a single-sided aluminized steel sheet with a rolling annealing structure according to claim 5, wherein the content is 0.0200% by weight. (7) The C content in the steel components of the steel plate is O. A method for producing a single-sided aluminized steel sheet with a rolling annealing structure according to claim 5 or 6, wherein the content is 0.02% by weight or less. (8) Si content in the aluminum plating layer is 1 to 15 weight
%, the method for manufacturing a single-sided aluminized steel sheet with a rolling annealing structure according to claim 5, 6, or 7. (9) A method for producing a single-sided aluminized steel plate with rolling annealing structure described in Patent Information Scope Item 5, Item 6, Item 7, or Item 8, in which the rolling reduction rate in the rolling process is 20 to 60%. . (10) The annealing temperature in the recrystallization annealing process is 500 to 600
Claims 5, 6, 7, and 8 which are
A method for manufacturing a single-sided aluminized steel plate with a rolling annealing structure according to item 1 or 9.