JPH0641707A - Galvannealed steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To provide a galvannealed steel sheet in which adhesion in the boundary of a plated layer and steel is remarkably improved and to provide its manufacturing method. CONSTITUTION:The galvanized steel sheet is a one in which the roughness of the boundary of the plated layer and the steel, i.e., that of the surface of the steel sheet freed from the plated layer is regulated to >=6.5mum by ten-point mean roughness Rz, and the average Fe concn. in the film is regulated to 7 to 11wt.%. This steel sheet can be manufactured by subjecting steel contg., by weight, <=0.01% C, 0.02 to 0.10% Si, <=0.8% Mn, <=0.02% S and P: less than 0.005%+0.1XSi% and furthermore contg. 0.03 to 0.20% Ti and/or 0.005 to 0.20% Nb (B may be contained as well) to annealing at >=800 deg.C in an atmosphere with -25 to -15 deg.C dew point contg. 5 to 50vol.% hydrogen, and the balance inert gas, thereafter applying it with plating in a hot dip zinc bath (Al concn.: 0.12 to 0.20wt.%) and then executing alloying treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hot-dip galvanized steel sheet for deep drawing, which has excellent adhesion between a plated layer and a base steel sheet.
The present invention relates to a coated steel sheet for home appliances, a plated steel sheet suitable as a steel sheet for automobiles, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a large amount of zinc-based plated steel sheets have been used in the industrial fields of home appliances, building materials, and automobiles. Above all, alloying excellent in rust prevention function, performance after painting, economical efficiency, etc. Hot-dip galvanized steel sheets are widely used.

Alloyed hot-dip galvanized steel sheets are usually prepared by continuously hot-dip galvanizing steel sheets in a heat treatment furnace for alloying.
Heat and hold at ambient temperature of 500 to 600 ℃ for 3 to 30 seconds, and Fe-
It is manufactured by forming a Zn alloy plating layer. The plating layer is made of an Fe-Zn intermetallic compound, and the average Fe concentration of the plating layer is generally 7 to 12% by weight. The coating weight is 25-70 g / m ^{2 on} one side, and those less than this range are difficult to manufacture by ordinary means, and those exceeding this range ensure the powdering resistance of the plating layer. It is difficult to supply, so it is not generally supplied.

The plating layer usually contains about 0.12 to 0.2% by weight of Al (aluminum). One of the reasons for this is that the alloying hot-dip galvanized steel sheet and the normal hot-dip galvanized steel sheet are often manufactured in the same production equipment, and added to the zinc bath when the normal hot-dip galvanized steel sheet is produced.
This is because Al is inevitably mixed when producing a galvannealed steel sheet. In the production of normal hot-dip galvanized steel sheet, the purpose of adding Al, because the workability of the alloy phase formed at the interface between the plating layer and the base steel sheet is poor,
This is to suppress the formation of this alloy phase and ensure the workability of the plating layer.

Another reason is that when the alloyed hot-dip galvanized steel sheet is manufactured, the powdering resistance of the plated layer of the alloyed hot-dip galvanized steel sheet is ensured and the dross is suppressed during the production. Even 0.08-0.11% by weight
This is because hot dip galvanizing is performed by adding Al to the zinc bath. Al tends to be enriched in the plating layer, and the Al concentration is 0.
If hot-dip galvanized in a zinc bath of 08-0.11% by weight,
The Al concentration in the plating layer is 0.12 to 0.2% by weight.

Conventionally, low carbon Al-killed steel has often been used as a material for alloyed hot-dip galvanized steel sheets. However, as its use has expanded in recent years, especially as it has been increasingly applied to automobile bodies, deep drawing has been performed. Because of the increased demand for high properties, the number of cases where ultra-low carbon steel called IF steel (Interstitial Free steel) is also increasing.

[0007] As described above, the alloyed hot-dip galvanized steel sheet having a wide range of uses has a drawback that the adhesion of the plating layer at the interface is low due to the fact that the plating layer is an intermetallic compound. That is, peeling easily occurs at the interface between the plating layer and the steel sheet (base material) depending on the way of deformation or the state of applying stress. In particular, peeling is likely to occur when the plating layer is subjected to a shocking deformation after being coated or a shearing force is applied to the plating layer during a process such as shearing.

In addition, when the plated steel sheets are joined by an adhesive, they may be separated at the interface between the plated layer and the steel sheet (hereinafter referred to as "plating layer / steel interface").

Also in the case of electroplated steel sheets such as Ni-Zn and Fe-Zn, since the plating layer is an intermetallic compound, the adhesion of the plating layer at the interface is low, but a suitable pretreatment means (for example, It is known that this problem can be solved by performing Ni or Fe undercoating prior to alloy plating. However, in the case of alloyed hot dip Zn plated steel sheet, there is no suitable solution.

The factors that cause the peeling of the plating layer at such an interface include not only the interfacial adhesion strength, but also the geometrical shape of the interface,
Mechanical properties and physical constants (e.g., elastic modulus) of the plated layer and the base steel sheet are considered. Therefore, in order to obtain an alloyed hot-dip galvanized steel sheet with excellent adhesion at the interface, modification of the plating layer, optimization of the geometrical shape of the interface between the plating layer and the steel sheet, chemical composition of the base steel sheet It is necessary to take measures from the perspective of optimizing, etc.

The inventors of the present invention have made basic studies on the adhesive strength at the interface of the galvannealed steel sheet, and as a result, as a means for improving the adhesiveness of the plated layer, Al in the plated layer has been improved.
It was found that when the concentration was increased to 0.30 to 0.5% by weight, the adhesiveness at the interface was improved to some extent. But,
Not practically enough.

As a known technique related to the above findings, Al
An alloyed hot dip galvanized steel sheet having a concentration of 0.05 to 0.25% by weight, the balance Zn and Fe (8 to 12% by weight), and a Γ phase at the interface of 1.0 μm or less is disclosed in Japanese Patent Publication No.
Although it is disclosed in Japanese Laid-Open Patent Publication No. -55544, this is intended to improve the flaking resistance and is insufficient for ensuring the adhesion of the plating layer / steel interface under severe conditions.

[0013]

As described above, in the alloyed hot-dip Zn plated steel sheet, since the plating layer is an intermetallic compound, the adhesion of the plating layer at the interface is low, which results in severe deformation. It has the drawback that it cannot withstand shock and impact (especially after painting). On the other hand, alloyed hot-dip galvanized steel sheets are excellent in paintability, corrosion resistance, weldability, economic efficiency, etc., and therefore their demand is increasing in the industrial fields such as home appliances, automobiles and building materials, and the adhesion of plated layers is improved. Are being increasingly demanded.

It is an object of the present invention to provide an alloyed hot-dip galvanized steel sheet having a significantly improved adhesion at the plating layer / steel interface and a method for producing the same.

[0015]

Means for Solving the Problems As a result of repeated studies to achieve the above object, the present inventors have found that the plating layer / steel interface after alloying treatment has severe irregularities, and the plating layer and steel are It has been found that it is effective to have a complicated and intricately complex state, and the state of this interface changes greatly depending on the crystal orientation and chemical composition of the base steel sheet. That is, when the Γ phase is formed at the plating layer / steel interface during the alloying process, the surface of the base steel sheet is eroded in a concave shape by Zn, but the rate of this Γ phase formation reaction depends on the crystal orientation of the base metal. In contrast, since the α phase {111} plane is small and the α {100,110} plane is large, the orientation of the α {100} plane and α {111, 100}
By appropriately controlling the orientation of the plane, that is, specifically, the intensity ratio Iα (222) / Iα (200) of α (222) and α (200) by X-ray diffraction of the steel surface is set to 6 to 9 By setting the range, only a part of the surface of the base steel sheet is preferentially eroded,
The shape of the plating layer / steel interface, that is, the surface morphology of the steel sheet after the galvannealed layer is removed,
It is possible to make the surface roughness large. In addition,
The X-ray diffraction intensity of α (110) is approximately proportional to the intensity of α (200).

Further, the rate of the Γ phase formation reaction is greatly influenced by the chemical composition of the steel sheet. Especially, when the content of P and C is small and Si is contained to some extent, the Γ phase formation reaction of the crystal orientation is caused. The speed difference becomes large, and it is effective for roughening the surface morphology of the steel sheet after removing the galvannealed layer. Furthermore, it is desirable that a suitable amount of Al be present in the zinc bath. It should be noted that even if the surface of the steel sheet is roughened or roughened in advance before the hot dip galvanizing treatment, the roughness of the steel sheet surface is lost during the alloying process, so that the adhesion of the plating layer / steel interface is improved. No effect is observed.

The present invention has been made on the basis of the above findings, and its gist resides in the following alloyed hot-dip galvanized steel sheet, and the following and the manufacturing method thereof.

Adhesion characterized in that the roughness of the steel sheet surface after removing the plating layer is 6.5 μm or more in 10-point average roughness Rz, and the average Fe concentration of the plating layer is 7 to 11% by weight. Alloyed hot-dip galvanized steel sheet with excellent properties.

% By weight, C: 0.01% or less, Si: 0.02
~ 0.10%, Mn: 0.8% or less, S: 0.02% or less, P: 0.0
Steel containing less than 05% + 0.1 x Si%, containing Ti: 0.03 to 0.20% and / or Nb: 0.005 to 0.20%, and the balance being substantially Fe, with dew point of -25 to -15 ° C, hydrogen : After annealing at 800 ° C or higher in an atmosphere containing 5 to 50% by volume and the balance consisting of an inert gas, plating in a hot dip zinc bath containing 0.12 to 0.20% by weight of Al, and then alloying treatment. A method for producing an alloyed hot-dip galvanized steel sheet having excellent adhesion.

In addition to the above ingredients, further B: 0.
[0020] Steel containing less than or equal to 20% by weight has a dew point of -25 to -15 ° C.
Then, after annealing at 800 ° C or higher in an atmosphere containing hydrogen: 5 to 50% by volume and the balance consisting of an inert gas, plating is performed in a molten zinc bath containing 0.12 to 0.20% by weight of Al, and then alloying treatment is performed. A method for producing an alloyed hot-dip galvanized steel sheet having excellent adhesion, which is characterized by:

[0021]

The constitutional requirements of the present invention (the above-mentioned inventions) and their effects will be described below. In addition, "%" of the chemical composition in steel and a plating layer means "weight%."

In the hot-dip galvannealed steel sheet of the present invention, as described above, the morphology of the plating layer / steel interface after the alloying treatment has an important effect. The plating layer / steel interface after alloying treatment is a steel plate surface obtained by removing the plating layer without impairing the condition of the steel plate surface forming the interface with this layer. When the 10-point average roughness Rz is less than 6.5 μm, the adhesiveness is insufficient. When the average roughness Rz is more than this value and the unevenness is more severe, excellent adhesiveness is exhibited.

By increasing the surface roughness, the plating layer and the steel become intricately intricate and the adhesion is increased. Therefore, the 10-point average roughness Rz of the steel sheet surface after removing the plating layer was 6.5 μm or more. It should be noted that removing only the plating layer from the galvannealed steel sheet without impairing the state of the steel sheet surface that forms the interface with the plating layer is performed by adding an appropriate inhibitor for hydrochloric acid to about 10% by weight hydrochloric acid. It can be easily performed by washing.

The average Fe concentration of the plating film is 7 as described above.
~ 11% This is because when the average Fe concentration of the coating is less than 7%, the degree of alloying is low, so that the η (Zn) phase is likely to remain, the weldability and the corrosion resistance after coating are reduced, and it is common for alloyed hot-dip galvanized steel sheets. This is because the performance deteriorates. However, the η phase has ductility and the propagation of cracks generated at the time of impact is mitigated, so that the adhesiveness at the interface is relatively high.
On the other hand, the upper limit of the average Fe concentration of the film is 11%, which is 11%.
If it exceeds 1.0, the plating phase / steel interface is likely to be flattened due to the progress of the alloying reaction, it is relatively difficult to secure Rz of 6.5 μm or more, and the powdering phenomenon is likely to occur.

The Al concentration in the plating layer is not particularly limited. It suffices if the Al content is 0.15% or more and less than 0.4% in a normal level.

The inventions and are methods for producing the galvannealed steel sheet of the inventions. In these manufacturing methods, as described above, a steel having a predetermined chemical composition is annealed under an appropriate annealing condition so that the texture of the steel sheet surface has an α {100} plane orientation and an α {111, 100} plane orientation. Azimuth
As described above, Iα (222) / Iα (2
00) is controlled to be 6 to 9, and then hot dip galvanization and alloying treatment are performed.

The chemical composition that the steel should contain is defined as above for the following reasons.

C suppresses the crystal orientation dependence of the Γ phase growth,
It has the function of flattening the surface of the steel sheet after the alloying treatment. Therefore, the C content needs to be as low as possible, and the upper limit is set to 0.01%.

Si promotes the dependence of the Γ phase growth on the crystal orientation to some extent, and promotes the penetration of Zn into the α phase grain boundary to make Zn less likely to enter the α phase, so-called anchoring effect is increased, and interface adhesion is increased. Improve sex. However, if less than 0.02%, this effect is not sufficient, while if over 0.1%, non-plating is likely to occur, so the Si content was made 0.02 to 0.10%.

Mn must be added to prevent embrittlement due to S. However, the crystal orientation dependence of Γ-phase growth is slightly suppressed, so the upper limit was made 0.8%.

Since S forms TiS and the like and reduces the effectiveness of Ti, it is desirable that the content thereof be low, and the upper limit is 0.02.
%. It is preferably 0.01%.

Since P remarkably suppresses the crystal orientation dependence of the Γ phase growth, it is desirable that the content thereof be as low as possible. However, Si mitigates the adverse effect of P, and 0.005% + 0.1
Since there is no problem even if P of less than × Si% is present, the P content is set to less than 0.005% + 0.1 × Si%.

Both Ti and Nb have a function of fixing C, and suppress the above-mentioned adverse effect of C. But Ti
For at least 0.03% and Nb for at least 0.005%, the adverse effect of C remains.
The i and Nb contents were 0.03% or more and 0.005% or more, respectively. The effect of fixing C is saturated up to 0.20%, and it is uneconomical to add more than this. Only one of these components may be added.

Al is not particularly limited, but as sol.Al is 0.
If it is 07% or less, there is no problem even if it is included. However,
If it exceeds 0.1%, there is a problem that non-plating is likely to occur.

In addition to the above components, it is the above-mentioned invention that the steel having the balance substantially Fe is subjected to the annealing treatment under the following conditions to carry out the hot dip galvanizing and alloying treatment.

The invention of (3) is the case of using the steel of (1), in which, in addition to the above-mentioned respective components, B is contained in an amount of 0.0020% or less. B has the effect of increasing the r value, that is, the effect of improving the formability of the steel sheet, but if it exceeds 0.0020%, its anisotropy increases, so the upper limit was made 0.0020%.

It should be noted that Cr, Cu and Ni are the total of them.
Even if the content is 0.2% or less, there is no substantial effect.

The annealing treatment is carried out by cold rolling the steel having the above chemical composition, and then, in a reducing furnace of a continuous galvanizing apparatus (CGL), with a dew point of -25 ° C to -15 ° C and hydrogen of 5 to 5 ° C. 800 ℃ in an atmosphere containing 50% by volume and the balance of inert gas
The above is performed by heating. If the heating temperature is 800 ° C or lower, or the dew point is lower than -25 ° C, α {111}
If the surface is hard to develop and the dew point exceeds -15 ° C, α {100,
The growth of the 110} plane is suppressed excessively, and both are α {100}
Since the orientation of the plane and the orientation of the α {111, 100} plane are not in a proper balance, it is not possible to make the shape of the plating layer / steel interface rough and rough.

The annealed steel sheet is plated with a hot dip galvanizing bath containing 0.12 to 0.20% by weight of Al. The Al concentration is the effective Al concentration obtained by subtracting the total Fe concentration from the total Al concentration in the plating bath. This is because if the Al concentration is less than 0.12% by weight, the crystal orientation dependence of the Γ phase growth is suppressed, and if it exceeds 0.2% by weight, the alloying reaction is greatly suppressed, and smooth alloying processing becomes difficult.

By the above means, the roughness of the plated layer / steel interface after alloying, that is, the surface of the steel sheet after removing the plated layer is made into a rough state of 6.5 μm or more in 10-point average roughness Rz, It is possible to produce an alloyed hot-dip galvanized steel sheet having excellent adhesion.

[0041]

[Examples] Various steel plates shown in Table 1 (all have a plate thickness of 0.8 m
m) is cut into 250 mm x 100 mm as test materials, and these test materials are degreased and washed in a NaOH solution at 75 ° C, and then the vertical hot dipping equipment is used to measure the dew point at -50 to -10 ° C. , N ₂ + H
30 to 120 at 780 to 860 ℃ in an atmosphere of ₂ (26% by volume)
After annealing for 2 seconds and cooling to 460 ℃, Al concentration is 0.
The plating was performed in a 13 wt% hot dip galvanizing bath (460 ° C.). The plating time was 1 second, and the amount of zinc deposited was adjusted to about 55 g / m ² (per surface) with a gas wiper. The plated test piece was alloyed by heating in a salt bath at 500 ° C for 15 seconds.

The test piece subjected to the alloying treatment is 150 mm × 70
After being cut into mm and subjected to chemical conversion treatment with a commercially available zinc phosphate treatment agent (using Bt3020 manufactured by Nippon Parkerizing Co., Ltd.), the thickness
Apply 30 μm electrodeposition coating (PT-U80 manufactured by Nippon Paint Co., Ltd.),
Furthermore, the intermediate coating and the top coating (Lugabake manufactured by Kansai Paint Co., Ltd.) were combined to a thickness of 70 μm, and subjected to a low temperature chipping test (stone impact test).

The low temperature chipping test is a test for evaluating the adhesion of the plating layer to a stone impact under low temperature conditions.
After crushing No. 7 crushed stone 100g to the test piece at a pressure of ² kg / cm ² under the condition of −20 ° C., a peeling test using an adhesive tape was performed.
Five pieces were selected in order from the largest peeling diameter, and the average value of the peeling diameters was expressed as the peeling diameter.

The test results are shown in Table 2. The table shows annealing conditions, dew point of atmospheric gas, Fe concentration of plating layer, and 10
The point average roughness Rz is also shown. The 10-point average roughness Rz was measured using an inhibitor (IBIT-700B manufactured by Asahi Kagaku) on the plating layer.
After dipping and dissolving in 10 wt% hydrochloric acid (25 ° C.) containing 0.5 vol% for 8 minutes to expose the steel plate surface, it was measured by a surface roughness meter. The tip diameter of the stylus at the time of measurement is 1 μm, and the cut-off is
The distance was 0.8 mm and the traverse distance was 8 mm.

From the results shown in Table 2, it is understood that in the present invention example having a large 10-point average roughness Rz, the peeling diameter is smaller than in the comparative example, and the adhesion at the plating layer / steel interface is improved.

[0046]

[Table 1]

[0047]

[Table 2 (1)]

[0048]

[Table 2 (2)]

[0049]

EFFECTS OF THE INVENTION The steel sheet produced by the method of the present invention has severe irregularities in the plating layer / steel interface after alloying treatment, and the plating layer and the steel are intricately intricate. Excellent adhesion to material steel plate. This steel sheet is suitable as a coated steel sheet for home appliances and a steel sheet for automobiles.

[0050]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C22C 38/14 C23C 2/06 2/28 2/40

Claims (3)

[Claims] 1. The surface roughness of the steel sheet after the plating layer is removed
An alloyed hot-dip galvanized steel sheet having excellent adhesion, which has a 10-point average roughness Rz of 6.5 μm or more and an average Fe concentration of the plating layer of 7 to 11% by weight. 2. By weight%, C: 0.01% or less, Si: 0.02-0.
10%, Mn: 0.8% or less, S: 0.02% or less, P: 0.005%
Less than +0.1 x Si%, Ti: 0.03 to 0.20% and / or
Nb: Steel containing 0.005 to 0.20%, the balance being substantially Fe, 800 in an atmosphere having a dew point of -25 to -15 ° C, hydrogen: 5 to 50% by volume, and the balance being an inert gas. A method for producing an alloyed hot dip galvanized steel sheet having excellent adhesion, which comprises performing annealing at a temperature of ℃ or more, followed by plating in a hot dip zinc bath containing 0.12 to 0.20 wt% Al, and then alloying treatment. 3. In addition to the components of claim 2, B: 0.00
Steel containing 20 wt% or less, the dew point is -25 ~ -15 ℃,
Hydrogen: 0.12 to 0.20% by weight after annealing at 800 ° C or higher in an atmosphere containing 5 to 50% by volume and the balance consisting of inert gas
A method for producing an alloyed hot-dip galvanized steel sheet having excellent adhesion, which comprises plating in a hot-dip zinc bath containing Al and then alloying it.