JP2003003238A - Zn-Al-Mg BASED HOT DIP PLATED STEEL HAVING EXCELLENT CORROSION RESISTANCE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plated steel sheet having high corrosion resistance characteristics peculiar to a Zn-Al-Mg based hot dip plating while suppressing the embitterment of a molten metal. SOLUTION: The plated steel is obtained by forming a Zn-Al-Mg based plated layer containing 4 to 22% Al and 0.05 to 10% Mg on base steel containing 0.0005 to 0.25% C, <=0.007% N, <=1.5% Si, 0.05 to 2.0% Mn, 0.005 to 0.10% Al and 0.00002 to 0.01% B, and, if required, containing one or more kinds selected from Ti, Nb, V and Zr by 0.01 to 1.20% in total, and, if required, containing one or more kinds selected from 0.05 to 2.0% Cu, 0.02 to 2.0% Ni, 0.02 to 1.0% Cr and 0.030 to 0.12% P. The plated layer can contain one or more kinds selected from 0.002 to 0.1% Ti, 0.001 to 0.045% B and <=2.0% Si as well. The plated steel can be produced by any of a continuous hot dip plating method and a dip brazing method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a building material, various structural materials, machine structural parts, piping, etc., and maintains excellent corrosion resistance and mechanical strength for a long period of time.
-Mg-based hot dip plated steel material.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets are used in a wide range of applications such as roofing materials, structural materials, pipes, parts, etc. which are exposed to a corrosive atmosphere by utilizing their excellent corrosion resistance. Among them, Zn-A
The 1-Mg hot-dip galvanized steel sheet has been attracting attention as a material replacing the conventional galvanized steel sheet because it maintains excellent corrosion resistance and mechanical strength for a long period of time in recent years when environmental degradation is serious. The plating layer formed on the surface of the Zn-Al-Mg hot-dip galvanized steel sheet is Al / Zn / Zn ₂
Primary ternary eutectic matrix of Mg with primary Al phase or primary Al
Phase and Zn single phase dispersed structure, Al and M
Corrosion resistance is improved by g. In particular, since a dense and stable corrosion product derived from Mg is uniformly formed on the surface of the plated layer, the corrosion resistance of the plated layer is significantly improved.

[0003]

As for the Zn-Al-Mg hot-dip galvanized steel sheet, the applicant of the present invention has disclosed that in Japanese Patent Laid-Open No. 10-226865.
It is a plated steel sheet introduced in Japanese Patent Laid-Open Publication No. 10-306357, etc., and its application development in various fields is being promoted by utilizing high corrosion resistance. In the process, it was found that there were some cracks which were not a problem in the conventional hot-dip galvanized steel sheet. For example, when a welded steel pipe is manufactured by welding a Zn—Al—Mg hot-dip galvanized steel sheet formed into an open pipe shape, cracks are likely to occur in the heat affected zone. Therefore, the present applicants propose to prevent welding cracks by controlling the welding conditions in Japanese Patent Application No. 2000-3080.
Proposed in No. 83.

Although welding cracks are certainly suppressed by controlling the welding conditions, this method is limited in the scope of application to welded steel pipes manufactured through the welding process. Similar cracks also occur when a Zn-Al-Mg hot-dip galvanized steel sheet assembled into a product shape is used under tension. When cracks occur, the exposed portion of the base steel through the cracks becomes a starting point of corrosion occurrence, impairing the high corrosion resistance of the Zn-Al-Mg-based plating layer, and of course reducing mechanical strength and fatigue characteristics.

[0005]

The present invention has been devised to solve such a problem, and the composition of the base steel and the hot-dip plated layer is set to a specific combination to obtain Zn
-Al-Mg-based Zn-which suppresses the cracks that tend to occur in hot-dipped steel sheets and can utilize the original high corrosion resistance for a long period of time-
It is an object to provide an Al-Mg hot-dip galvanized steel material.

In order to achieve the object, the Zn-Al-Mg hot-dip galvanized steel material of the present invention has C: 0.0005-
0.25 mass%, N: 0.007 mass% or less, Si:
1.5 mass% or less, Mn: 0.05 to 2.0 mass% or less, Al: 0.005 to 0.10 mass%, B: 0.00
002 to 0.01% by mass, if necessary Ti, Nb, V,
One or two or more types of Zr: Al: 4 to 22 mass% and Mg: to a base steel containing 0.01 to 1.20 mass% in total.
A Zn-Al-Mg based plating layer containing 0.05 to 10 mass% is formed.

The base steel further contains Cu: 0.05 to 2.0 mass%, Ni: 0.02 to 2.0 mass%, Cr: 0.02.
.About.1.0 mass%, P: 0.030 to 0.12 mass%, or one or more kinds thereof may be contained. The Zn-Al-Mg-based plating layer further contains Ti: 0.002 to 0.1% by mass,
B: 0.001-0.045 mass%, Si: 2.0 mass% or less 1 type or 2 types or more can be included. This Z
The n-Al-Mg-based hot-dip galvanized steel material is manufactured by either a continuous hot-dip plating method in which a steel strip that is continuously conveyed is introduced into a hot-dip plating bath or a dobbing method in which a steel material formed into a predetermined shape is dipped in the hot-dip plating bath. It

[0008]

The present inventors have investigated and studied the mechanism of cracking occurring in Zn-Al-Mg hot-dip galvanized steel sheets from various viewpoints. As a result, it was clarified that the embrittlement of molten metal along the grain boundaries is the cause of cracking. The molten metal embrittlement is a phenomenon in which the molten plated metal or its components permeate into the crystal grain boundaries of the underlying steel until the molten plated metal in contact with the underlying steel is solidified, and the crystal grain boundaries are embrittled. A similar phenomenon occurs during welding when the hot dip layer remelts. To suppress the embrittlement of molten metal that causes cracking when welding hot-dip galvanized steel sheets, lowering the composition of the base steel, P
It has been reported that addition of S, S, and Zr and Ti are effective countermeasures (Kawasaki Steel Technical Report Vol. 25, No. 1, No. 20-2).
Page 6). However, these measures are not effective for the embrittlement of the molten metal that occurs in the Zn-Al-Mg hot-dip galvanized steel sheet.
In fact, the investigations and studies by the present inventors did not detect a significant difference in the occurrence of cracks due to the embrittlement of the molten metal due to the lower composition of the base steel and the addition of S. It was also found that B, which is said to have an adverse effect on cracking susceptibility, is effective in preventing cracking of Zn-Al-Mg hot-dip galvanized steel sheets.

The difference in crack prevention measures suggests that cracks generated during welding of hot-dip galvanized steel sheets and Zn-Al-Mg hot-dip steel sheets have different mechanisms.
The present inventors presume the crack generation mechanism of the Zn-Al-Mg hot-dip galvanized steel sheet as follows. When the Zn-Al-Mg alloy plating bath comes into contact with the plating base plate during continuous hot dipping or dipped plating, A with high activity is obtained.
l reacts with Fe of the plating original plate first, and Fe-
An Al alloy layer is formed. Zn via Fe-Al alloy layer
-Al-Mg-based plating layer is formed, but Al of Zn-Al-Mg-based plating layer is formed as the Fe-Al alloy layer is formed.
The concentration decreases, and the Mg concentration increases reflectively. Increasing the Mg concentration lowers the melting point of the Zn-Al-Mg-based plating layer. Incidentally, the solidification end temperature is lowered to 360 ° C. with Zn-3 mass% Mg.

The composition change and melting point drop accompanying the formation / growth of the Zn-Al-Mg-based plating layer are phenomena that are not observed in the normal formation / growth process of the hot-dip galvanized layer. Zn-Al- in a molten state or a semi-molten state due to the melting point lowering
The contact time of the Mg alloy with the base steel becomes longer, and the penetration of the Zn-Al-Mg alloy into the crystal grain boundaries of the base steel proceeds. Given the process of producing and growing a Zn-Al-Mg-based plating layer, the present inventors have conceived to use B as an element that strengthens the grain boundaries of the base steel. The action of B itself for strengthening the crystal grain boundary is a conventionally known technique, but the fact that B is effective for suppressing molten metal embrittlement in the process of producing and growing a Zn—Al—Mg-based plating layer is This is a novel finding found by the present inventors. In addition, since the cracks caused by the embrittlement of the molten metal are significantly suppressed by the addition of B, the effect of B on the generation and growth of the Zn-Al-Mg-based plating layer is not limited to the strengthening of the grain boundaries. It can be seen that it is affecting. As a result, in the Zn-Al-Mg based plating layer,
It is inferred that the embrittlement of the molten metal is suppressed without "B has an adverse effect" (Kawasaki Steel Technical Report, page 24, right column, bottom line 11).

B segregates at the α crystal grain boundaries to increase the grain boundary strength, and lowers the grain boundary energy of the γ crystals to improve the hardenability. In a Zn-Al-Mg hot-dip steel sheet, Zn-Al-Mg alloy penetrates into the crystal grain boundaries of the base steel, and Zn-Al-Mg is in a molten or semi-molten state.
It is considered that the alloy has a function of preventing the steel component from leaching from the grain boundaries. In order to develop such actions and effects of B, it is required to secure an effective amount of B dissolved in the matrix of the base steel. N contained in the base steel reacts with free B to form a BN compound, which significantly reduces the amount of effective B. Therefore, by reducing N as the base steel or using a steel material in which N is fixed by Ti, Nb, V, Zr, etc., the effect of N that reduces the effective B amount is suppressed, and it is caused by molten metal embrittlement. A Zn-Al-Mg hot-dip galvanized steel sheet in which cracks are suppressed is obtained.

From the above consideration, in the present invention, the composition of the base steel and the Zn-Al-Mg based plating layer was specified as follows. [Base steel] C: 0.0005 to 0.25 mass% This is an alloy component that reduces the ductility by forming a solid solution with a ferrite phase and forming a carbide. In applications requiring high workability, the C content is The lower the better. On the other hand,
Since it also has the effect of strengthening steel, it is necessary to increase the C content to increase the strength in applications such as structural materials. From such a viewpoint, in the present invention, the upper limit of the C content is 0.2.
It was set to 5% by mass. In applications where workability is particularly required, it is preferable to secure the amount of solid solution B by setting the upper limit of the C content to 0.01% by mass. On the other hand, 0.0
Reducing the C content to less than 005% by mass requires excessive decarburization refining in the manufacturing process, which causes an increase in manufacturing cost.

N: 0.007% by mass or less N is a component which reacts with B to form BN and consumes the amount of effective B dissolved in the matrix, so that the N content is preferably as low as possible. However, excessive reduction of the N content causes an increase in the manufacturing cost of steel products. Therefore, the upper limit of the N content is set to 0.007% by mass. The adverse effect of N on the solid solution B is Ti, Nb, V,
It can also be suppressed by fixing N with Zr or the like. However, when the N content exceeds 0.007 mass%, the amount of addition of Ti, Nb, V, and Zr necessary for fixing N increases, and the steel cleanliness and workability are likely to be adversely affected.

Si: 1.5% by mass or less It is a component effective as a solid solution in the ferrite phase to improve the strength of the steel material. However, in the steel material containing a large amount of Si, a Si concentrated layer is formed on the surface of the steel material and the plating property is improved. descend. Therefore, the upper limit of the Si content is set to 1.5% by mass. Since ductility decreases as the Si content increases, it is preferable to set the upper limit of the Si content to 0.30 mass% in applications where workability is required. Mn: 0.05 to 2.0% by mass or less It is a component effective in preventing embrittlement due to S during hot rolling and improving strength, and when the content is 0.05% by mass or more, the effect of adding Mn is remarkable. Become. However, a lower Mn content is desirable for applications requiring workability and weldability, and the Mn content is set to an upper limit of 2.0 mass% because it concentrates on the steel surface and adversely affects the plating property. .

Al: 0.005 to 0.10% by mass This is a component added as a deoxidizing agent during steel making, and N in the steel.
Is fixed as AlN to prevent deterioration of workability due to age hardening of N, and is also effective in securing an effective B amount that is easily consumed as BN. Such an effect becomes remarkable when the Al content is 0.005 mass% or more.
Assuming that N is fixed by Al, N ≦ Al × 0.5
It is preferable to set the Al content so that 2 is satisfied. However, if an excessive amount of Al is contained in excess of 0.10% by mass, oxide-based inclusions increase, which adversely affects workability and plateability.

B: 0.00002 to 0.010% by mass An alloying component effective in suppressing the embrittlement of molten metal, and 0.00
When it is 002 mass% or more, the effect of adding B becomes remarkable,
The addition effect is saturated at 10% by mass. The addition of an excessive amount of B exceeding 0.010 mass% promotes the formation of borides, the inhibition of crystal grain growth, and the like, which also causes the workability of the steel sheet to deteriorate. The segregation of B to the crystal grain boundary depends on the generation and movement of the crystal grain boundary and the diffusion rate of B, and effective grain boundary segregation of B may not be expected at the α grain boundary as transformed. In such a case, manufacturing conditions that allow B to sufficiently diffuse into the grain boundaries are adopted in the cold rolling / annealing process.

One or more of Ti, Nb, V, and Zr: 0.01 to 1.20% by mass in total is an alloy component added as needed, and N is fixed as a nitride. In addition, it exerts an effect of securing the amount of solid solution B effective for suppressing the embrittlement of molten metal, and the effect of addition becomes remarkable when the content is 0.01 mass% or more.
It is also effective for fixing C. However, addition of more than 1.20 mass% causes increase in manufacturing cost, as a matter of course.
Deteriorates the workability of steel materials. T contained in base steel
i, Nb, V, Zr, etc. are eluted into the hot dip coating bath at the same time when Fe is eluted from the steel sheet immersed in the hot dip bath. The hot dip coating bath near the steel sheet forms a hot dip coating layer after the steel sheet is pulled out of the hot dip coating bath, and most of Ti, Nb, V, Zr and B dissolved in the hot dip coating bath are incorporated in the hot dip coating layer. Be done. As a result, the structure of the hot-dip layer is refined, and a hot-dip layer having a uniform and beautiful appearance is formed.

The base steel used in the present invention further comprises Cu, N
One, two or more of i, Cr and P may be contained.
Of these optional components, Cu is complex with P to improve the corrosion resistance and is also effective for improving the strength. The effect of addition becomes remarkable at 0.05% by mass or more, but excessive addition exceeding 2.0% by mass. Then, ductility is lowered. Ni is also a component effective for improving the strength, and the addition effect becomes remarkable at 0.02 mass% or more, but excessive addition exceeding 2.0 mass% causes a decrease in ductility. Cr is a component effective for improving the strength and improving the corrosion resistance of the base material, and the addition effect becomes remarkable when the content is 0.05% by mass or more, but excessive addition exceeding 1.0% by mass leads to deterioration of workability. When P is added as an alloy component, 0.030-
The P content is selected within the range of 0.12% by mass.

P, S, etc. are mixed as impurities into the base steel from the viewpoint of steelmaking. Since P as an impurity adversely affects the ductility, it is preferable that the P content be as low as possible in applications where high workability is required. However, in applications where high strength is required because it also works to improve strength, P may be contained in the range of up to 0.12 mass% which does not adversely affect workability and plating property. S is a cause of hot embrittlement and is a harmful component that deteriorates workability and corrosion resistance.
Except for applications requiring special properties such as free-cutting property, it is preferable to regulate the content as low as possible (specifically, 0.03 mass% or less).

[Zn-Al-Mg-based plating layer] Al: 4 to 22% by mass Al hardly elutes from the plating layer, and forms a Zn-Al-based corrosion product in the portion which was the original plating layer. To do. The Zn-Al-based corrosion product has extremely strong adhesiveness, and even if the Mg-containing Zn-based corrosion product in the upper layer disappears in the corrosion process, it serves as a barrier having an environmental barrier function and suppresses corrosion of the underlying plating layer. To do. Part of the Zn-Al-based corrosion product takes in SOx in the environment and also acts as a stronger protective film. In order to form a Zn—Al-based corrosion product that has strong adhesion and acts as a barrier to the substrate,
An Al content of 4% by weight is required. It is also effective in reducing N which is harmful to the solid solution B by reacting with N in the steel to form AlN when the hot-dip coating layer is formed. But 2
When an excess amount of Al exceeding 2 mass% is contained, Zn-A
Not only is the effect of the 1-based corrosion product saturated, but the workability of the plating layer is also reduced.

Mg: 0.05 to 10% by mass Mg contained in the plating layer forms a Zn-based corrosion product containing Mg in the outermost layer of the plating layer, and the corrosion rate of the plating layer in a general corrosive environment such as outdoors. Has the effect of suppressing. Such an action is observed at a Mg content of 0.05 mass% or more,
Mg: saturated at 10% by mass. Excessive Mg content exceeding 10% by mass deteriorates the stability of the hot dip plating bath due to the generation of a large amount of dross. Preferably 1.0 to 10
The Mg content is selected in the range of mass%.

Ti: 0.002 to 0.1% by mass, B:
0.001 to 0.045% by mass is an alloy component added as an optional component, which suppresses the formation of Zn ₁₁ Mg ₂ phase that adversely affects the surface appearance and crystallizes in the plating layer. The intermetallic compound has the effect of essentially only Zn ₂ Mg. In particular,
When 0.002 mass% or more of Ti is included, Zn ₁₁ Mg
Generation of _two phases is effectively suppressed. However, when an excessive amount of Ti exceeding 0.1 mass% is contained, T is contained in the plating layer.
The i-Al-based precipitate grows to form irregularities on the plating layer, and the appearance is likely to deteriorate. The formation of Zn ₁₁ Mg ₂ phase is 0.00
It is also suppressed by including 1 mass% or more of B. Even if B is contained, Ti-B-based and Al-B-based deposits are deposited in the plating layer in an excess amount of more than 0.045% by mass, and similarly, a plating layer having unevenness that causes deterioration in appearance is generated. It will be easier. Further, since the steel material containing Ti and B is used as the base steel, the same effect can be obtained by Ti and B eluted from the base steel into the hot dip bath.

Si: 0.005 to 2.0 mass% This is an alloy component added as necessary, and suppresses thick growth of the Fe-Al intermetallic compound at the interface of the base steel / plating layer, and Zn- It has the function of improving the workability of the Al-Mg hot-dip steel sheet. It is also an effective component for preventing blackening of the hot-dip plated layer and maintaining the glossiness of the surface.
The effect of Si on the suppression of the formation of the Fe-Al intermetallic compound can be seen even at a content of 0.005 mass% or more, but 2.
When the excess amount of Si exceeding 0 mass% is contained, the amount of dross generated in the hot-dip metal contained in the pot increases.

The Zn-Al-Mg alloy plating layer has, as other components, one or more of Ca, Sr, Na, Y, and misch metal, which have the function of preventing the oxidation of Mg on the surface of the plating layer, and the resistance thereof. Ni, Co, effective for blackening
One or more types of Sn, Cu effective for corrosion resistance after coating,
One or more of Cr, Mn, Zr, Mo and W may be added.

[0025]

Example 1 A cold-rolled steel strip having a composition of Table 1 and a thickness of 0.8 mm was subjected to reduction annealing at 750 to 850 ° C. for 30 seconds, and then Zn-
6.4 mass% Al-3.1 mass% Mg alloy plating bath (bath temperature: 400 ° C.) was fed at a line speed of 125 m / min, and was soaked for 2 seconds from the Zn-Al-Mg alloy plating bath. The coating weight was adjusted to 90 g / m ² .

[0026]

A test piece was cut out from each of the obtained Zn—Al—Mg hot-dip galvanized steel sheets and subjected to a welding test in which cracks due to molten metal embrittlement were most likely to appear. In the welding test,
A test piece with a width of 50 mm was welded to each other at a welding length of 40 mm under the conditions of a current of 25 A, a voltage of 12 V and a welding speed of 250 mm / min.
G welding was performed, and both ends of the welded test piece were gripped and tension was applied. Then, the welding strength was obtained by measuring the tension when the welded test piece was broken.

In the case of a plated steel sheet using a group A steel material having a high N content as a base steel, the welding strength is at most 90 MPa.
Stayed at. In addition, the occurrence of cracks was detected when the tension exceeded 85 MPa. The cracks are concentrated in the heat-affected zone of the weld, and it is presumed that the cause is the embrittlement of the molten metal. In the plated steel sheet using the group B steel material with a reduced N content as the base steel, the welding strength up to fracture was slightly improved to 100 MPa, but also in this case, the occurrence of cracks was detected when the tension exceeded 85 MPa. It was

In the case of the plated steel sheet using the steel of Group C containing N added to B and having B added as the base steel, the welding strength up to fracture was further improved to 110 MPa. In addition, when observing the base steel of the plated steel sheet with a microscope, B precipitated as a compound such as BN was observed, and although it can be seen that the amount of effective B dissolved in the matrix is reduced, cracks Occurrence was suppressed.

When the N content is lowered, Ti, Nb,
The plated steel sheet using the steel material of group D in which N was fixed with V and Zr and B was added as the base steel did not break even in the state where a tension of 147 MPa was applied. In addition, the generation of cracks was not detected during the application of tension. When the welded portion was observed after the tensile test, no trace of the penetration of the plated metal into the crystal grain boundaries was detected, and the same interface structure as that of the base steel / plated layer interface before welding was maintained. As is clear from the above comparison,
Steel containing B added with a lower N content, or Ti, N
It can be seen that when a steel material in which N is fixed by b, V, and Zr is used as the original plating plate, cracking due to molten metal embrittlement can be prevented.

[0031]

[Example 2] Steel D-1 of group D, which had good results in Example 1, was used as a plating base plate, and a Zn-Al-Mg based plating layer having the composition shown in Table 2 was formed on a continuous hot dip galvanizing line. The amount of adhesion was 90 g / m ² .

[0032]

Test pieces were cut out from each Zn--Al--Mg hot-dip galvanized steel sheet and welded under the same conditions as in Example 1.
The welded specimens were corrosion tested. In the corrosion test, salt spray (JIS Z2371) was continued for 100 hours, and the corrosion rate was calculated from the corrosion weight loss of the plating layer. In addition, the test piece before welding was subjected to 180 degree contact bending and then bent back to evaluate the adhesion of the plating layer. as a result,
In the plated steel sheet provided with the plated layer (No. 9) having an Al concentration of 25.3% by mass, the plated layer was significantly peeled off, but in the plated steel sheet provided with other plated layers, no significant peeling of the plated layer was observed. The remarkable peeling of the plating layer having a high Al concentration was caused by the increase in the Al concentration of the hot dip bath and the increase in the bath temperature, and the Al-Fe alloy layer formed at the interface of the base steel / plating layer was thick. It is thought that there is a cause for growing up.

As can be seen from the test results in Table 3, the plated steel sheets provided with the plating layers Nos. 1 to 8 satisfying the composition conditions specified in the present invention were excellent in both corrosion resistance and workability. Further, in the plated steel sheet provided with the plating layers Nos. 5 to 7 containing Ti and B, a beautiful appearance without unevenness was maintained even after welding.

On the other hand, in the plated steel sheet provided with the plating layer No. 9 containing excess Al, the Fe-Al alloy layer grew excessively, and the interfacial peeling of the base steel / plating layer was partially detected after working. . On the contrary, the plated steel sheet provided with the plating layer No. 10 having a shortage of Al had insufficient corrosion resistance. Further, in the plated steel sheet provided with the plating layer No. 11 having an excessive Mg content, a structure in which the components of the plating layer penetrated into the weld heat affected zone was observed. M
In the plated steel sheet provided with the plating layer No. 12 in which g was insufficient, the plating layer components permeating the influence of welding heat were not detected, but the high corrosion resistance inherent to the Zn-Al-Mg hot-dip coating was not expressed.

From the above results, by properly combining the composition of the base steel and the composition of the plating layer, cracks due to embrittlement of the molten metal can be suppressed, and tensile strength, fatigue characteristics, and high corrosion resistance even after welding. Is expressed.

[0037]

[0038]

[Third Embodiment] Thickness 0.8 mm, width 300 mm, length 2
A steel material D-1 having a thickness of 000 mm was bent along the center line in the longitudinal direction to produce an L-shaped material. After fluxing the L-shaped material, Al: 6.4 mass%, Mg: 3.1 mass%, T
i: 0.03 mass%, Si: 0.029 mass%, balance Z
n Zn-Al-Mg alloy plating bath (bath temperature: 400 ° C)
It was soaked for 30 seconds. Cold air was blown to the L-shaped material pulled up from the Zn-Al-Mg alloy plating bath to cool and solidify the hot-dip plated metal adhering to the surface and adjust the adhering amount.

Microscopic observation of the cross-section of the hot-dipped L-shaped material revealed an Al / Zn / Zn ₂ Mg ternary eutectic structure in which the primary Al phase was dispersed on the base steel via the Fe—Al alloy layer. The plated layer was formed, and the plated layer component that had penetrated into the grain boundaries was not detected. For comparison, in the case where the steel material A-1 was similarly dipped and plated as the base steel, the permeation of the plating layer components along the crystal grain boundaries of the base steel was detected.

[0040]

As described above, according to the present invention, the Zn-
In the Al-Mg hot-dip galvanized steel material, by appropriately controlling the composition of the base steel and the composition of the plating layer, the molten metal embrittlement caused by the penetration of the plating layer components along the grain boundaries is suppressed, and Zn -Al-Mg-based hot-dip galvanizing original high corrosion resistance is utilized, and it becomes a plated steel sheet excellent in mechanical strength, fatigue characteristics, and workability. In addition, even in the dubbing plating in which the base steel is in contact with the molten plated metal for a relatively long time, it is possible to prevent the plating layer component that causes the molten metal embrittlement from penetrating into the grain boundaries. Therefore, plated steel materials used in a wide range of fields such as building materials, various structural materials, machine structural parts, and piping are provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 2/40 C23C 2/40 (72) Inventor Nobuhiko Yamaki 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Company Technology Research Institute (72) Inventor Yuichi Higo 11-1 Showa-machi, Kure City, Hiroshima Prefecture Nisshin Steel Co., Ltd. Corporate Research Laboratory (72) Inventor Hiroshi Asada 1 Tsurumachi, Amagasaki City, Hyogo Nisshin Steel Co., Ltd. Laboratory F-term (reference) 4K027 AA02 AA05 AA23 AB05 AB07 AB44 AC12 AE03

Claims (4)

[Claims] 1. The base steel is C: 0.0005 to 0.25% by mass, N: 0.007% by mass or less, and Si: 1.5% by mass.
Hereinafter, Mn: 0.05 to 2.0 mass% or less, Al: 0.
005 to 0.10 mass%, B: 0.00002 to 0.0
1% by mass, the balance being substantially Fe composition, Al: 4
Zn-Al-Mg-based hot-dip steel material having excellent corrosion resistance, characterized in that a hot-dip galvanized layer of ˜22 mass%, Mg: 0.05-10 mass%, and the balance substantially Zn is formed. 2. The base steel further comprises 1 of Ti, Nb, V and Zr.
One or two or more: The Zn-Al-Mg hot-dip steel material according to claim 1, containing 0.01 to 1.20 mass% in total. 3. The base steel further comprises Cu: 0.05 to 2.0 mass%, Ni: 0.02 to 2.0 mass%, Cr: 0.02.
To 1.0 mass% and P: 0.030 to 0.12 mass% of one or more kinds of Zn-Al- according to claim 1 or 2.
Mg-based hot-dip galvanized steel material. 4. The hot dip plated layer further comprises Ti: 0.002-
0.1% by mass, B: 0.001-0.045% by mass, S
i: The Zn-Al-Mg hot-dip galvanized steel material according to any one of claims 1 to 3, containing one or more of 2.0% by mass or less.