JPH10280093A - Steel sheet for galvannealing - Google Patents

Abstract

(57) Abstract: The present invention provides a steel sheet for galvannealing excellent in workability, formability, plating adhesion and the like. SOLUTION: In weight%, C: 0.0001 to 0.00.
4%, Si: 0.001 to 0.10%, Mn: 0.01
0.50%, P: 0.001 to 0.015%, S:
0.015% or less, Al: 0.005 to 0.10%, T
i: 0.002 to 0.10%, N: 0.0005 to 0.
004%, the balance being Fe and unavoidable impurities, and a high P concentration part (P content of 0.02 to 2 μm or more per side of at least 1 μm on one surface of the steel sheet)
0.10%).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloyed hot-dip galvanized steel sheet, and more particularly, to a steel sheet having excellent formability and workability including deep drawability, and excellent plating adhesion. Steel plate that can be made.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets are very frequently used in automobiles, home appliances, building materials, etc. because of their excellent paint adhesion, paint corrosion resistance, and weldability. The alloyed hot-dip galvanized steel sheet is formed by coating the surface of the steel sheet with hot-dip zinc, and then immediately heating and maintaining the temperature above the melting point of zinc to diffuse Fe from the steel sheet into zinc to form a Zn-Fe alloy. However, since the alloying speed varies greatly depending on the composition and structure of the steel sheet, the control thereof requires a fairly advanced technique. On the other hand, extremely high formability is required for steel plates used for automobile outer panels and difficult-to-form parts, and in recent years the demand for rust-prevention performance of automobiles has increased, and alloyed hot-dip galvanized Are increasing. In this case, since the steel sheet is formed with a very high working degree, the steel sheet is required to have excellent workability and high plating adhesion at the same time.

[0003] In an alloyed hot-dip galvanized steel sheet, as a result of an alloying reaction between the steel sheet and the zinc layer, the plated layer becomes a ζ phase, δ ₁
And Zn-Fe-based intermetallic compound called a Γ phase. While these alloy phases improve paintability, paint adhesion, and weldability, the hardness of the alloy layer itself is high, and especially the Γ phase is fragile. And so-called powdering phenomenon is easily caused. Powdering not only impairs the soundness of the plating, but also causes the powdered plating that has peeled off to accumulate on the press die and significantly degrade the appearance of the pressed product. In recent years, thick alloyed hot-dip galvanized steel sheets have become popular in order to enhance the rust prevention performance of automobile bodies, but the above-mentioned powdering phenomenon is more likely to occur as the amount of plating applied increases, so powdering resistance is reduced. There is a strong demand for improved performance.

On the other hand, as the shape of the automobile body becomes more complicated, the requirements for the formability of the steel sheet have become more severe, and a steel sheet having excellent formability such as deep drawability has been used more than ever before. It is also required for plated steel sheets. In order to obtain such workability, as a component of the steel sheet,
A typical example is steel in which C is reduced to an extremely low level and then Ti is added, or steel in which Ti and Nb are added in combination. However, these steels have a problem that the alloying speed in galvanizing alloying is extremely high, so that alloying proceeds too much, the Γ phase grows thickly, and the powdering performance tends to deteriorate. For such steel, lower the plating bath temperature, increase the Al concentration in the plating bath,
Operational measures such as lowering the alloying temperature and increasing the heating time have been addressed, but insufficient alloying is likely to cause flaky plating delamination called flaking, so stable plating is not always necessary. Adhesion is not obtained.
In addition, the change of these operating conditions causes a stop of the production line, thereby lowering productivity and increasing costs.

A method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance is disclosed in JP-A-2-31035.
No. 2, Japanese Patent Application Laid-Open No. 2-310353 proposes a technique for defining the soaking conditions after alloying as well as the conditions for the alloying heat treatment and the cooling conditions. The productivity is low and not economic. Further, as a method for producing an alloyed hot-dip galvanized steel sheet excellent in deep drawability and plating adhesion, JP-A-5-331612 discloses a composition of a steel sheet, hot rolling conditions and cooling conditions, and annealing conditions after cold rolling. In addition, there has been proposed a technique for limiting the relational expression between the P and Ti contents of a steel sheet and the effective Al concentration in a plating bath.
No. 142 proposes a technique for limiting the relational expression between the P and Ti contents of the steel sheet and the effective Al concentration in the plating bath, in addition to the composition of the steel sheet, hot rolling conditions, and annealing conditions after cold rolling. ing. However, in these methods, Al
Changing or adjusting the operating conditions of the plating line by controlling the concentration lowers the productivity of the plating line and increases the cost.

[0006]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide an alloyed hot-dip galvanized steel sheet capable of simultaneously achieving excellent workability and formability and high plating adhesion. I have.

[0007]

The present inventor has studied various means for improving the plating adhesion without reducing the workability of the steel sheet and the productivity of the hot-dip galvanizing line. By precisely controlling the composition in the thickness direction, C,
A steel sheet to be plated with reduced P, N, etc., in hot-dip galvanizing, by controlling the P content in the surface layer of the steel sheet to be coated that reacts with the molten zinc, thereby achieving both workability and plating adhesion of the steel sheet. Was found. That is, the gist of the first invention of the present invention is that, by weight%, C: 0.
0001-0.004%, Si: 0.001-0.10
%, Mn: 0.01 to 0.50%, P: 0.001 to
0.015%, S: 0.015% or less, Al: 0.00
5 to 0.10%, Ti: 0.002 to 0.10%, N:
A steel sheet comprising 0.0005 to 0.004%, with the balance being Fe and unavoidable impurities, wherein the surface of the steel sheet has a high P concentration portion (P
(Content of 0.02 to 0.10%). Second embodiment of the present invention
The gist of the invention is that, in the first invention, the steel sheet is further added as an additional component in Nb: 0.002% by weight.
It is in a steel sheet for galvannealing containing 0.10%. The gist of the third invention of the present invention is that, in the first invention, the Ti content in steel is determined by the following formula (1) ([% X]
Is an alloyed hot-dip galvanizing steel sheet that satisfies the conditions given by (content of alloying element X expressed in% by weight). [% Ti] ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (1) The gist of the fourth invention is that in the second invention, Ti and The content of Nb is as follows (2) to
(3) An alloyed hot-dip galvanizing steel sheet that satisfies the condition given by the formula ([% X] is the content of the alloying element X expressed in% by weight). ([% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1. 5 [% S] (2) [% Ti] ≧ 0.009% (3) The gist of the fifth invention of the present invention is the first invention, the second invention, the third invention or the fourth invention. In the above, the steel sheet further contains B: 0.0001 to
In a steel sheet for galvannealing containing 0.003%.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the reasons for limiting the range of each component in the present invention will be described. In the present invention,% means% by weight unless otherwise specified. In the steel sheet of the present invention,
Although the composition differs between the steel sheet surface part and the rest,
The range of each component described below is the average of the entire steel sheet. C: C is an element that increases the strength of steel and is 0.0001%
It is effective to contain the above, but if it is contained excessively, the strength is too high and the workability is lowered, so the upper limit content is made 0.004%. When particularly high workability is required, the C content is preferably 0.003% or less, particularly preferably 0.002% or less. Si: Si is also an element for improving the strength of steel, and is 0.0%.
Although it is contained in an amount of not less than 01%, an excessive amount impairs workability and hot-dip galvanizing property, so the upper limit is 0.10%.
And Particularly when high workability is required, the Si content is set to 0.05% or less. Mn: Since Mn is also an element that increases the strength of steel and decreases workability, the upper limit content is set to 0.50%.
The lower the Mn content, the better the workability. However, the lower limit of the content is set to 0.01% because the refining cost becomes large in order to reduce the content to 0.01% or less. From the balance of strength, workability and cost, the Mn content is more preferably 0.05 to 0.30%. P: Since P is also an element that increases the strength of steel and decreases workability, the upper limit content is set to 0.015%. The lower the content of P, the better the workability. It is more preferable that the content be 0.010% or less. On the other hand, since the scouring cost is high in order to reduce the P content to less than 0.001%, the lower limit content is 0.001%. From the balance of strength, workability and cost, the P content is more preferably 0.003 to 0.010%. S: Since S is an element that lowers the hot workability and corrosion resistance of steel, it is preferably as small as possible, and the upper limit content is 0.015%
And more preferably 0.010% or less. However,
Since it is costly to reduce the S content of the ultra-low carbon steel as in the present invention, it is not necessary to excessively reduce S from the viewpoint of workability and plating adhesion, hot workability, S may be reduced to a necessary level from corrosion resistance and the like. Al: It is necessary that Al contains 0.005% or more as a deoxidizing element of steel, but if it is contained excessively, coarse nonmetallic inclusions are formed and workability is impaired. It is more preferably 0.10%, and from the viewpoint of good steel sheet quality, it is more preferably 0.070% or less. Ti: In order to fix C and N in steel as carbides and nitrides, it is necessary to add 0.002% or more.
It is more preferable to contain 010% or more. On the other hand, 0.1
If the addition exceeds 0%, the effect is no longer saturated, but the cost of alloy addition simply increases unnecessarily. Therefore, the upper limit content is set to 0.10%. Excess solid solution Ti may impair the workability and surface quality of the steel sheet, so it is more preferably 0.050% or less. N: Since N increases the strength of the steel and lowers the workability, the upper limit is made 0.004%. In particular, when high workability is required, the upper limit is more preferably 0.003% or less. 0.002% or less is particularly preferable. The lower the content of N, the better. However, since reducing the content to less than 0.0005% requires excessive cost, the lower limit of the content is 0.1%.
0005%.

In the present invention, in addition to the above, in order to fix C and N in steel as carbides and nitrides as additional components, Nb can be added under the above-mentioned addition of Ti. In order to sufficiently exert the C and N fixing effect by adding Nb, 0.002% or more is necessary, and more preferably 0.005% or more. Even if Nb is added in excess of 0.10%, the effect is no longer saturated, but the cost only increases unnecessarily. Therefore, the upper limit content is set to 0.10%. Excessive Nb addition raises the recrystallization temperature of the steel sheet and lowers the productivity of the hot-dip galvanizing line.

In the present invention, the P content in the portion where the surface layer thickness of at least one side of at least one side of the steel sheet is at least 1 μm is 0.02 to 0.10% (high P). Based on reason. The heat alloying reaction between the hot-dip galvanized layer and Fe is, of course, an interfacial reaction that proceeds at the interface where zinc and iron are in contact. Therefore, the composition near the surface of the steel sheet to be plated (from the plating interface to the surface layer on the substrate side) Dominates all or most of the alloying reaction. Therefore, it is possible to control the alloying reaction by controlling the P content on the steel sheet surface (to increase the P content), and to obtain an alloyed hot-dip galvanized steel sheet having good characteristics. When the P content is increased in the entire steel sheet, the plating adhesion is improved, but the strength of the steel sheet itself is excessively increased and the workability and formability are reduced. On the other hand, when the total P content of the steel sheet is reduced and the P content of the surface layer alone is set to a predetermined high P concentration range, the workability of the steel sheet and the adhesion of plating can be satisfied at the same time. Here, the P content of the surface layer is required to be 0.02% or more for the purpose of suppressing generation of a brittle intermetallic compound typified by the Γ phase at the iron / plating interface and improving plating adhesion. Even if the content exceeds 0.10%, the effect is no longer saturated, but the alloying rate is excessively reduced and the productivity of the hot-dip galvanizing line is reduced. 0.10%. Particularly when the productivity of the plating line is required, the P content of the surface layer is preferably set to 0.050% or less. Further, even when extremely high workability is required, the P content of the surface layer is preferably set to 0.050% or less.

For the purpose of controlling the alloying reaction between zinc and iron to secure plating adhesion, the thickness of the surface layer in which the P content is in the above range must be at least 1 μm. Here, the thickness of the surface layer means, of course, the depth in the thickness direction from the surface of the steel plate to be plated. When the thickness of the surface layer is less than 1 μm, the effect of suppressing alloying is insufficient, and the alloying reaction tends to be uneven in the width direction and the length direction of the steel sheet surface. On the other hand, from the viewpoint of plating adhesion, there is no upper limit to the thickness of the surface layer, but if the thickness of the high P concentration portion of the surface layer is too thick, the workability of the surface layer affects the workability of the entire steel sheet.
Since the workability of the entire steel sheet is reduced, the thickness of the surface layer is preferably set to 40 μm or less, and the thinner the workability and formability, the better. In a steel plate to be plated having a thickness of less than 0.8 mm, the thickness of the high P concentration portion in the surface layer is more preferably 1/20 or less of the thickness of the steel plate to be plated.
Here, when the galvannealing is performed on both surfaces of the steel plate to be plated, it is preferable that the thickness of the surface high P concentration portion be in the above range in total on both the front and back surfaces.

As a method of measuring the P concentration and the thickness of the high P concentration portion of the surface layer, for example, the P concentration of the high P concentration portion is measured by sputtering from the surface of the steel sheet using glow discharge emission spectroscopy (GDS). Concentration and thickness can be measured simultaneously. Alternatively, in the cross section of the steel sheet, X
By performing line analysis in the plate thickness direction using a line microanalyzer (EPMA), the P concentration and the thickness of the high P concentration portion may be measured simultaneously.

In the present invention, in order to further improve the formability and workability of the steel sheet, the content of Ti is set to a range satisfying the following expression (1). [% Ti] ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (1) When the Ti content is in the above range, C is an element that inhibits workability. This is because N and N can be effectively fixed by Ti and the workability of the steel sheet can be improved. Alternatively, the contents of Ti and Nb are set to satisfy the following expressions (2) and (3). ([% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1. 5 [% S] (2) [% Ti] ≧ 0.009% (3) When the contents of Ti and Nb are within the above range, C and N, which are elements that impair workability, are removed. Ti and N
This is because the workability of the steel sheet can be increased by effectively fixing the composite effect of b, but the effect of improving the workability is not sufficient by adding Nb alone, and the Ti content is 0.009.
% Or more, the effect of the composite addition of Ti and Nb becomes remarkable. In this case, if the contents of Ti and Nb satisfy the expression (2), it is possible to effectively fix C and N with Ti and Nb. it can.

In the present invention, the steel sheet may further contain B as an additional component in an amount of 0.0002 to 0.003%, which aims at improving the secondary workability. If the content of B is less than 0.0002%, the effect of improving the secondary workability is not sufficient, and even if added over 0.003%, the effect is no longer saturated, and the moldability decreases. Therefore, when B is added, the range is 0.1.
0002 to 0.003%. When a particularly high deep drawability is required, the amount of B added is more preferably 0.0015% or less.

A method for controlling the P content of the surface layer to a predetermined range,
That is, the desired thickness and desired P
The method of forming the high P concentration portion with the concentration is not particularly limited, and any method can be applied as long as the above conditions are satisfied. For example, a steel containing P in a mold during continuous casting is applicable. A method of adding with a wire, a method of adding iron powder containing P to casting powder, a method of spraying steel containing P on the slab surface before hot rolling, and the like can be appropriately selected.

The steel sheet of the present invention may be manufactured by applying a normal hot-rolled steel sheet (hot strip) or cold-rolled steel sheet (cold strip) manufacturing step. The P content of the surface layer is set to a predetermined range near the surface of the steel plate to be plated. Therefore, in consideration of the fact that the surface layer thickness is oxidized or dissolved and reduced during oxidation before heating, oxidation during hot rolling and oxidation during and after cooling, pickling after hot rolling, and the like. Therefore, it is important to manufacture a steel sheet. When the P content of the surface layer is in the above range,
Even if an interstitial element such as C, N, or B or another substitutional alloy element is simultaneously contained as an impurity or an alloy element other than P for other purposes, the effect of the present invention is not changed. , Does not depart from the scope of the present invention. However, care must be taken because interstitial elements diffuse rapidly in the steel, and may diffuse from the surface layer into the steel sheet to reduce the formability of the steel sheet in each heating step of steel sheet production.

In the present invention, O in the steel sheet is not particularly limited. However, since O generates oxide-based inclusions and impairs the workability and corrosion resistance of the steel, it is preferably 0.004% or less. preferable.

[0018] In addition to the above components, the steel sheet of the present invention has the following objectives to further improve the corrosion resistance and hot workability of the steel sheet itself.
Alternatively, other alloying elements can be contained as inevitable impurities from the auxiliary material such as scrap, and the inclusion of other alloying elements does not depart from the scope of the present invention. As such alloy elements, Cu, Ni, C
r, Mo, W, Co, Ca, rare earth elements (including Y),
V, Zr, Ta, Hf, Pb, Sn, As, Sb, Bi
Is mentioned. Since the steel sheet of the present invention can be applied to a normal hot-dip galvanized steel sheet manufacturing line to obtain an alloyed hot-dip galvanized steel sheet having excellent workability, formability and plating adhesion, there is no particular restriction on the manufacturing process. . A process may be appropriately selected in consideration of cost and productivity.

[0019] The steel sheet of the present invention can be used in a hot-dip galvanizing bath.
1, Pb, Sb, Si, Fe, Sn, Mg, Mn, N
Even a plating bath containing or mixing one or more of i, Cr, Co, Ca, Li, Ti, and rare earth elements does not cause any trouble. In the present invention, the thickness of the steel sheet does not impose any restrictions on the present invention, and the present invention can be applied as long as the thickness is a commonly used thickness. Furthermore, the effect of the steel sheet of the present invention is sufficiently exhibited regardless of whether it is a cold-rolled steel sheet or a hot-rolled steel sheet manufactured by a normal process, and the effect does not greatly change depending on the history of the steel sheet. . Also,
Hot rolling conditions, cold rolling conditions, annealing conditions, etc. may be selected according to the dimensions of the steel sheet, the required strength, depending on the required strength. The present invention depends on the hot rolling conditions, cold rolling conditions, annealing conditions, etc. The effect of the steel sheet is not impaired.

As a matter of course, on the alloyed hot-dip galvanized steel sheet obtained by using the steel sheet of the present invention, various kinds of upper plating, especially electroplating, are applied for the purpose of improving the coating property and the weldability. Of course, this is also possible and does not depart from the present invention. Further, it is of course possible to add various treatments to the alloyed hot-dip galvanized steel sheet obtained by the method of the present invention, for example, chromate treatment, phosphate treatment, phosphate treatment properties. Even if a process for improving, a lubricity improving process, a weldability improving process, a resin coating process, etc. are performed, the present invention does not depart from the scope of the present invention. Can be performed.

Further, in an alloyed hot-dip galvanized steel sheet having an alloyed hot-dip galvanized layer on one surface, at least the surface of the steel sheet to be coated with the galvanized layer has a predetermined thickness and a predetermined concentration according to the present invention. The present invention does not depart from the present invention if the high P concentration portion exists. Further, regarding the P concentration and the thickness of the high P concentration portion of the surface layer of the steel sheet to be plated,
Both surfaces may be the same, or may differ between the front and back surfaces within the scope of the present invention, depending on the application and purpose. For example, when an alloyed hot-dip galvanized steel sheet is processed and used for automobiles, home appliances, building materials, etc., the high P concentration in the surface layer of the coated steel sheet corresponding to the surface (outer surface) that is directly susceptible to external impacts. Is higher than the high P concentration of the steel plate to be plated corresponding to the back surface (inner surface) side to increase the plating adhesion on the front surface (outer surface) side, without departing from the present invention. Alternatively, in the case of a so-called difference-thickness galvanized steel sheet having different amounts of coating on the front and back surfaces of the galvannealed steel sheet, the surface with the smaller amount of coating (thinner surface) has the larger amount of coating (the thicker surface). ), The alloying tends to proceed faster than in the case described above, so that the plating adhesion may be inferior. In such a case, the high P concentration of the surface layer of the steel sheet to be plated corresponding to the thinned surface is increased by the surface corresponding to the thickened surface. Making the concentration higher than the high P concentration to increase the plating adhesion on the thinned surface side does not depart from the present invention. In addition, depending on the processing of the alloyed hot-dip galvanized steel sheet, since the stress level generated on the thick-faced surface is high, there is a case where plating adhesion of the thick-faced surface is required to obtain, but in such a case, It is also outside the invention of the present application that the high P concentration of the surface layer of the steel plate to be plated corresponding to the thick surface is made higher than the high P concentration of the surface corresponding to the light surface to increase the plating adhesion on the thick surface. Not something.

The steel sheet of the present invention has a tensile strength of 3
From ordinary steel of less than 00 N / mm ² or steel sheet for ultra deep drawing, high strength steel of 300 N / mm ² or more (300, 34
0, 400, 440 N / mm ² ).

Next, the steel sheet of the present invention will be described with reference to the drawings. In FIG. 1, an alloyed hot-dip galvanizing steel sheet 3 having a high P-concentration portion 1 and a low P-concentration portion 2 on the surface layer, and having an alloyed hot-dip galvanized layer 4 as shown in FIG.
Is generated.

[0024]

Next, examples of the present invention will be described together with comparative examples. Cold rolled steel sheets (Nos. 1 to 12, N
o. 16 to 21) and hot-rolled steel sheets (No. 13 to 15,
No. 22) was used as a test material. Here, the thickness of the cold-rolled steel sheet was set to 0.8 mm, and the thickness of the hot-rolled steel sheet was set to 2.0 mm.
In Table 1, no. Nos. 1 to 15 are examples of the present invention. 16
22 are comparative examples. When continuously casting molten steel, after adding P to only the surface layer of the slab by adding Fe-P alloy powder to the powder in a tundish, each steel sheet is subjected to normal hot rolling, pickling, and cold rolling. Depending on the process, a cold-rolled steel sheet or a hot-rolled steel sheet was obtained, and the P content and the surface layer thickness of the surface layer shown in Table 1 were determined. In addition, the P content and the thickness of the high P concentration part of the surface layer are determined by EPMA for the cross section of each steel sheet.
Was used to measure the P concentration by linear analysis in the plate thickness direction.

Using each steel sheet as a test material, an alloyed hot-dip galvanized steel sheet was manufactured through the steps of electrolytic degreasing, annealing, cooling, hot-dip galvanizing, and hot-alloying in a normal continuous hot-dip galvanizing line. . When plating, the annealing atmosphere is 5
% Hydrogen + 95% nitrogen mixed gas, annealing temperature 800
° C and the annealing time were 90 seconds. The molten zinc bath contains Al in an amount of 0.1.
The molten zinc contained 12%, and the basis weight of zinc was adjusted to 60 g / m ² with a gas wiper. The heating for the alloying was performed by using an induction heating type heating equipment so that the Fe content in the galvannealed alloying was 10 to 11%. However, in the case of a hot-rolled steel sheet, preheating to 500 ° C. (90
Seconds).

A sample was taken from each steel sheet and the plating adhesion was evaluated by the V-bending method. That is, a test piece on which a contact tape (cellophane tape) was previously adhered to the compression side was bent in a V-shape so that the bending angle was 60 °, and after bending back, the contact tape was peeled off, and the degree of peeling of the plating was measured. Was visually observed, and the plating adhesion was evaluated according to the following classification. ◎: The plating layer did not peel at all. ○: The plating peeled slightly. △: The plating peeled to a considerable extent ×: The plating almost peeled.

Further, as an index of workability, a tensile test was performed on each steel sheet for galvannealing, and the elongation and Rankford value (r value; average r value of 0 °, 45 °, 90 °; (Cold rolled steel sheet only) was measured.

The results are shown in Table 1. As is evident from Table 1, No. 1 of the present invention example. Comparative Examples Nos. 1 to 15 have excellent plating adhesion and excellent workability of the steel sheet. In Nos. 16 to 22, the plating adhesion was inferior or the workability of the steel sheet was insufficient.

[0029]

[Table 1]

[0030]

As described above, the present invention has made it possible to provide a steel sheet to be plated capable of producing an alloyed hot-dip galvanized steel sheet having excellent workability, formability and plating adhesion. There is a great deal that contributes to the development of industry.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a steel sheet for galvannealing according to the present invention.

FIG. 2 is a cross-sectional view showing an example of an alloyed hot-dip galvanized steel sheet manufactured using the steel sheet for galvannealed steel of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High P concentration part 2 Low P concentration part 3 Steel plate for alloyed hot-dip galvanizing 4 Alloyed hot-dip galvanized layer

Claims (5)

[Claims] C. 0.001 to 0.004%, Si: 0.001 to 0.10%, Mn: 0.01 to 0.50%, P: 0.001 to 0. 015%, S: 0.015% or less, Al: 0.005 to 0.10%, Ti: 0.002 to 0.10%, N: 0.0005 to 0.004%, and the balance Fe And a steel sheet comprising unavoidable impurities, and having a thickness of at least 1 μm per surface on the surface layer of the steel sheet.
m or higher high P concentration part (P content is 0.02-0.10
%), A steel sheet for galvannealing. 2. The steel sheet further comprises, as an additional component,
The steel sheet for galvannealed steel according to claim 1, wherein the steel sheet contains Nb: 0.002 to 0.10%. 3. The steel according to claim 1 wherein the content of Ti is expressed by the following formula (1) ([%
X] satisfies the condition given by (the content of the alloying element X expressed in% by weight). [% Ti] ≧ 4 [% C] +3.4 [% N] +
1.5 [% S] (1) 4. The content of Ti and Nb in steel satisfies the condition given by the following formulas (2) to (3) (where [% X] is the content of alloying element X expressed in% by weight). The steel sheet for galvannealed steel according to claim 2, wherein: ## EQU2 ## ([% Ti] +0.52 [% Nb]) ≧ 4 [%
C] +3.4 [% N] +1.5 [% S] (2) [% Ti] ≧ 0.009% (3) 5. The steel sheet, as an additional component, further comprising:
5. The steel sheet for galvannealed steel according to claim 1, wherein the steel sheet contains B: 0.0002 to 0.003%. 6.