JPH04236751A - Alloyed galvanized steel sheet with excellent formability and its manufacturing method - Google Patents

Abstract

PURPOSE:To improve the deep drawability and bulging formability of a steel sheet by subjecting a steel sheet obtd. by adding Ti whose content is specifically related to the one of C, S and N as well as Nb whose content is specifically related to the one of Ti to galvannealing with specified coating weight. CONSTITUTION:A steel constituted of, by weight, i0.0030% C, <=0.05% Si, 0.05 to 0.50% Mn, <=0.02% P, <=0.02% S, 0.03 to 0.06% SolAl, <=0.0040% N, 0.005 to 0.014% Nb, 0.04 to 0.12% Ti and the balance Fe with inevitable impurities and satisfying (Ti/C)>=7 and 7<=(Ti/Nb)<=14 is subjected to hot rolling, cold rolling and continuous annealing. One face or both faces of this steel sheet are subjected to galvannealing with >=30g/m<2> coating weight, and after that, Fe-Zn allaying treatment is executed. This plated steel sheet has the characteristic balance of mean-r value >=2.0 and n>=0.24.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloyed galvanized steel sheet for ultra-deep drawing having excellent formability and plating adhesion, and a method for producing the same.

0002

[Prior art] So-called IF steel (Inters
Titial Free Steel) is a highly deep-drawn cold-rolled steel sheet (EDDQ) that requires deep drawability and anti-aging properties.
It has attracted attention as a powerful material for manufacturing by continuous annealing, and its importance has been recognized with the spread of today's continuous annealing process. On the other hand, the proportion of rust-proof steel sheets used in automobile bodies has increased rapidly in recent years, and it is fully expected that all cold-rolled steel sheets for automobiles will be replaced by rust-proof steel sheets in the near future. Generally, the rust-preventive steel sheets used in automobile bodies are galvanized steel sheets, but in recent years, the use of galvanized steel sheets after being alloyed has been increasing in order to improve the rust-preventing effect. However, forming a hard Fe-Zn alloy layer on both sides of the steel sheet through alloying treatment restricts the plastic deformation of the base steel sheet, resulting in particularly poor plastic anisotropy (
Generally, this is a property evaluated by the r value, and the larger the r value, the better the deep drawability) and the elongation at break. Therefore, in order to impart excellent formability to alloyed galvanized steel sheets, it is necessary to set the material quality level of the base steel sheet to a high level, taking into account the material deterioration caused by the formation of the plating layer.
From this point of view, alloyed galvanized steel sheets made of the above-mentioned IF steel are attracting attention.

[0003] IF steels that have been commonly used in the past are:
Ti-IF steel with added Ti and Nb- with added Nb
It is IF steel. In particular, Ti is a strong carbon/nitride-forming element, and at the same time causes S in steel to precipitate and coarsen as sulfides, so Ti-IF steel has extremely excellent deep drawability and ductility, and is stable over a wide range of components. There are characteristics that can be obtained by doing so. However, on the other hand, it is easily oxidized and oxide-based surface defects occur during steelmaking, so strict slab care is required. Furthermore, if the C in the steel is completely fixed as TiC, problems such as a decrease in grain boundary strength and the occurrence of deep drawing embrittlement (secondary work embrittlement phenomenon) become apparent. It is also known that adding a small amount of boron (B) is effective for solving this problem, but in that case, adding 10 ppm or more of B can cause deterioration of the r value (deterioration of deep drawability). It becomes a problem.

On the other hand, Nb-IF steel mainly fixes only C in the steel, and by fixing solid solution C in the steel, Ti-I
Similar to F steel, excellent deep drawability can be obtained, but if excessive Nb is added, the grain growth suppressing effect due to NbC precipitates becomes significant and the material quality deteriorates. For this reason, there is a problem that the range of appropriate components is narrower than that of Ti-IF steel. but,
Compared to Ti, Ti-
It has been clarified that the in-plane anisotropy of the r value appears, which is different from that of IF steel.

[0005] As described above, TI-IF steel and Nb-IF steel each have advantages and disadvantages in terms of their materials, but when a galvanized steel sheet is assumed, Nb-IF steel is considered to be preferable. Furthermore, a technique has been disclosed that attempts to improve properties compared to Ti-IF steel by adding Ti and Nb in combination. For example, many technologies have been disclosed for adding Nb and Ti in combination to produce cold-rolled steel sheets for ultra-deep drawing with consideration given to hot-dip galvanizing properties.
The amount of the steel is limited to an extremely limited amount, and sufficient characteristics regarding deep drawability cannot be obtained. For example, JP-A-59-
No. 67319, JP-A-59-74231, etc. are Nb+T.
It is disclosed in the range of i<0.04wt%, and its mean-r value is also less than 1.9. In addition, the special public corporation Showa 6
No. 1-32375 is a technology that can obtain a mean-r value of 2.0 or more, but if T is in the range of Ti≦(48/12)C+(48/14)N
Since the amount of i is limited, hot-rolling and high-temperature winding at 650° C. or higher is unavoidable in order to increase the mean-r value. Further, Ti: 0.010 to 0.100 wt%, Nb: 0.
A technique for adding Ti in the range of 004 to 0.04 wt% has been disclosed (Japanese Patent Application Laid-open No. 1-123058), but judging from the examples, the technique is disclosed in the range of Ti≦0.42 wt%, and In the examples, the mean-r value ≧2.2 was obtained for steel to which only Ti was added and the alloying temperature (considered to be the annealing temperature) was 880°C. However, there is a problem that the adhesion of the alloy layer deteriorates. On the other hand, from the viewpoint of materials, a technique (Japanese Patent Publication No. Sho 61-32375) has been disclosed in which Nb and Ti are added in combination in order to combine the properties of Ti and Nb. The gist of this technology is 0.003 to 0.025 wt% Nb and 0.
．． 010 to 0.037 wt% of Ti and Nb>
2.23C {(48/14)・(N-0.002)}<Ti<(4
C+3.43N) is added within a range that satisfies the conditions of
By combining the above-mentioned differences in texture between Nb and Ti, r
The content is to obtain effects such as improving the in-plane anisotropy of the value and reducing material variation within the coil.

[0006]

[Problems to be Solved by the Invention] However, even if the above-mentioned conventional techniques are examined in detail, it is still difficult to find that the zinc plating weight is 40.
[g/m2]/40 [g/m2] or more of an alloyed galvanized steel sheet, and a manufacturing technology for a steel sheet having a balance of mean-r value ≧2.0 and n value ≧0.24 is not disclosed.

In recent years, cold-rolled steel sheets used for automobile bodies have been changed from the conventional ultra-deep drawing method in response to the increasingly complex shapes of car body parts, the promotion of integral forming, and the expansion of applications for alloyed galvanized steel sheets. There is an increasing demand for steel sheets with formability superior to that of steel sheets (EDDQ). From this perspective, Ti
An example of product development based on additive IF steel, divided into a deep drawing-oriented type and a stretch forming-oriented type (Shibazaki et al.:
Materials and Processes 2 (1989)” p. 1931) has also been reported, but the n value and mean-
The balance of r value is the former (deep drawing emphasis type), n value =
0.265, mean-r value = 2.50, n value = 0.278 in the latter (stretch molding emphasis type), mean-r value = 2
．． 15, and it is clear that when this is applied to the base steel sheet of an alloyed galvanized steel sheet, the property balance that is the objective of the present invention cannot be obtained.

From a practical standpoint, the present invention discloses an alloyed galvanized steel sheet that has both deep drawability and stretch formability, and a method for manufacturing the same.
[g/m2]/40 [g/m2] or more, the mean-r value, which is an index for evaluating deep drawability, is 2.0 or more,
Work hardening index n (10%
The object of the present invention is to obtain an alloyed galvanized steel sheet having an n value (evaluated in the tensile strain range of ~20%) of 0.24 or more and having extremely excellent peeling resistance of the plated layer during press forming.

[0009]

[Means for Solving the Problems] Therefore, the present invention has the following configuration. (1) C≦0.0030wt%, Si≦0.05w
t%, 0.05wt%≦Mn≦0.50wt%, P≦0
．． 02wt%, S≦0.02wt%, 0.03wt%≦
Sol. Al≦0.06wt%, N≦0.0040wt
%, 0.005wt%≦Nb≦0.014wt%, 0.
04wt%≦Ti≦0.12wt%, and
(Ti*/[C])≧7 However, Ti*/[C]=[wt%Ti
*]/4 [wt%C] [
wt%Ti*]=[wt%Ti]-{(48/14)・
[wt
%N〕+(48/32)・[
wt%S]} [wt%C
] :C content (wt%)
[wt%Ti]: Ti content (wt%)
[wt%N]: N content (wt
%) [wt%S]:
S content (wt%) 7≦([wt%Ti]/[wt%N
b])≦14 However, [wt%Ti]: Ti content (
wt%) [wt%Nb]: A steel plate that satisfies the Nb content (wt%) and has a composition consisting of the balance Fe and unavoidable impurities is used as the base steel plate, and one or both sides of the steel plate is coated with a galvanized area weight. An alloyed galvanized steel sheet with excellent formability and having an alloyed galvanized layer of 30 g/m2 or more per side. (2) C≦0.0030wt%, Si≦0.05w
t%, 0.05wt%≦Mn≦0.50wt%, P≦0
．． 02wt%, S≦0.02wt%, 0.03wt%≦
Sol. Al≦0.06wt%, N≦0.0040wt
%, 0.005wt%≦Nb≦0.014wt%, 0.
04wt%≦Ti≦0.12wt%, and
(Ti*/[C])≧7 However, Ti*/[C]=[wt%Ti
*]/4 [wt%C] [
wt%Ti*]=[wt%Ti]-{(48/14)・
[wt
%N〕+(48/32)・[
wt%S]} [wt%C
] :C content (wt%)
[wt%Ti]: Ti content (wt%)
[wt%N]: N content (wt
%) [wt%S]:
S content (wt%) 7≦([wt%Ti]/[wt%N
b])≦14 However, [wt%Ti]: Ti content (
wt%) [wt%Nb]: A steel that satisfies the Nb content (wt%) and has a composition consisting of the balance Fe and unavoidable impurities is hot rolled, cold rolled and continuously annealed in a conventional manner, Continue applying 30g/m2 to one or both sides of the steel plate.
A method for producing an alloyed galvanized steel sheet with excellent formability, which comprises performing the above zinc plating and then performing an Fe-Zn alloying treatment. (3) In (2) above, slab heating temperature ≦12
After hot rolling at 00°C, hot rolling winding temperature: 580 to 640°C, cold rolling at a rolling ratio of 76 to 84%, then 80°C.
An alloy with excellent formability characterized by continuous annealing at 0°C to 880°C, subsequent zinc plating with a basis weight of 30 g/m2 or more on one or both sides of the steel plate, and then Fe-Zn alloying treatment. A method for producing galvanized steel sheets.

The details of the present invention will be explained below. The present invention is based on Ti-added IF steel because of the following points: ■ wide tolerance range in composition design, ■ stable material under manufacturing conditions, and ■ superior grain growth compared to Nb-added steel. Furthermore, with the aim of improving surface properties, controlling texture, and improving resistance to deep drawing embrittlement, the basic idea is to add Nb in a small amount compared to the amount of Ti and in a limited amount in relation to the amount of Ti. It has the following characteristics.

First, the fundamental difference between the present invention and the prior art described above is that Ti*/[
C] (atomic weight % ratio) is limited to 7 or more. Ti*/[C]=[wt%Ti*]/4[
wt%C] [wt%Ti*] = [wt%T
i]-{(48/14)・[wt%N]+
(48/32)
・[wt%S]} However,
[wt%C]: C content (wt%)
[wt%Ti]: Ti content (wt%)
[wt%N] :N content (wt%)
[wt%S]: S content (wt%)

The present invention aims at completely fixing carbon and nitrides and coarsening their precipitates by adding a sufficient amount of Ti when fixing C in steel. Figure 1 shows Ti: 0.01 to 0.20 wt%, Nb:
For steels in the range of 0 wt% and 0.002 to 0.03 wt%, the above Ti*/[C] is defined as me
The effects on the an-r value and the Δr value were investigated and organized. [mean-r]=([r0]+2[r45]
+[r90])/4
Δr=([r0]+[r90]-2[r45])/2
However, [r0]: r value in the steel plate rolling direction [r
45]: r value at 45° to the steel plate rolling direction
[r90]: r value at 90° to the steel plate rolling direction According to the same figure, a trace amount of N
It can be seen that when b is added, the level of the mean-r value increases due to grain refinement of the hot rolled sheet structure as solid solution Nb.

Next, in the present invention, the amounts of Ti and Nb added are limited based on the relationship between the mean-r value and the amount of drawbead peeling after forming the alloyed galvanized layer. Figure 2 shows a plate thickness of 0.8m.
After annealing a cold-rolled steel plate of m at 850°C, zinc bath temperature: 460°C
, Al content in the bath: 55 g/m2 on both sides under each condition of 0.12%
Ti and Nb addition amounts and the weight % ratio of Ti and Nb [wt%Ti]/[wt
%Nb], the amount of drawbead (hereinafter referred to as DB) peeling, and the mean-r value. According to this, an increase in Ti amount results in an increase in Ti*/[C] in steel with C≦0.003%, and the mean-
Although the r value increases, the amount of DB peeling increases when Ti is added alone. On the other hand, when the amount of Nb increases relative to the amount of Ti, the amount of DB peeling decreases, but due to the presence of excess Nb, the amount of DB peeling decreases.
The an-r value deteriorates. From the above results, mean-r
The component system that provides the properties of value ≧ 2.0 and DB peeling amount < 4 g/m2 is Ti: 0.04 to 0.12%, Nb: 0.0
05% to 0.014%, and 7≦[wt%Ti]/
[wt%Nb] is in the range of 14, and furthermore, the mean
-The component system that provides the characteristics of r value ≧ 2.2 and DB peeling amount < 4 g/m2 is Ti: 0.06 to 0.12%, Nb: 0
．． 005% to 0.012%, and 7≦[wt%Ti
]/[wt%Nb]≦14.

[0014] Therefore, the reasons for limiting Ti and Nb, which are the most important additive elements in the present invention, will be described. As already mentioned, Ti is a strong carbon/nitride forming element, and is an element that provides the above-mentioned merits (1) to (2). In particular, in order to fix C in steel in an equilibrium state, Ti*/
[C] ≧1 is sufficient, but if the precipitate size is sufficiently coarsened and excellent grain growth is achieved, <111>//ND
In order to increase the accumulation of oriented recrystallized grains, Ti*/[C
] It is also suggested from FIG. 1 that it is preferable to set ≧7. Therefore, in the present invention, Ti*/[C]≧7 is defined.

Furthermore, in the present invention, in addition to the above provisions, Ti
The amount added is defined as 0.04wt%≦Ti≦0.12wt%. When Ti is less than 0.04 wt%, it is possible to fix C in the steel, but coarsening of TiC becomes difficult to occur, and countermeasures such as winding at a high temperature during hot rolling are required in the process. On the other hand, even if it is added in excess of 0.12 wt%, not only is no significant addition effect observed, but surface defects also appear.
Increased alloy costs are a problem.

Nb is an essential additive element in the present invention, but its addition amount is limited to a very small range of 0.005 to 0.014 wt%. In particular, as shown in Figure 2 above, limiting [wt%Ti]/[wt%Nb] to a range of 7 to 14 ensures not only the mean-r value but also the adhesion of zinc plating. It is also necessary from above. Also, N
It has become clear that adding a small amount of b is also effective in improving deep drawing embrittlement resistance. In order to obtain such an effect, the lower limit of Nb addition is specified to be 0.005 wt%. Further, the upper limit of the amount added is limited to 0.014 wt% from the viewpoints of large variations in material quality depending on manufacturing conditions, adverse hardening of the material, and increase in alloy cost.

Furthermore, as a secondary effect of the present invention, when a small amount of Nb is added to steel to which Ti is added in the range of Ti*/[C]≧7, the surface of the continuous casting slab changes as shown in FIG. It was found that the quality was significantly improved. Although the mechanism by which such an effect is obtained is not necessarily clear, it is thought that the presence of a small amount of Nb suppresses the oxidation reaction of Ti on the slab surface. From this point of view as well, it has become clear that the component system of the present invention has excellent properties as a base material for alloyed galvanized steel sheets.

Next, reasons for limiting other elements will be explained. In order to improve the C:n value, it is necessary to limit not only the size of TiC but also its total amount.
In order to obtain this value, the upper limit of C is defined as 0.0030 wt%. Si: Even if it is at the level of ordinary steel, it does not have a particularly negative effect on the effects of the present invention, but in order to maintain a high level of ductility and improve the adhesion of zinc plating, Si should be set at 0.05 wt% or less. do. Mn: Since Ti contributes to the fixation of S, there is no problem even if Mn is lower than the level of general steel, but if it is less than 0.05 wt%, the cost of hot metal pretreatment increases, so the lower limit is set to 0.05 wt%. stipulate. On the other hand, when it exceeds 0.50 wt%, YP increases due to solid solution strengthening by Mn, and the n value decreases. Therefore, the upper limit is defined as 0.50 wt%. P: P is a grain boundary embrittling element, and its upper limit must be strictly controlled, especially in IF steel where grain boundaries tend to become brittle. Therefore, in the present invention, the upper limit is set to 0.02 wt%. In particular, in order to make the remarkable improvement effect of the deep drawing embrittlement resistance by adding a small amount of Nb more stable, P should be 0.01w.
It is preferable to set it to t% or less. S: S decreases the effective Ti amount (Ti*) by precipitating as TiS. Therefore, in the present invention, the upper limit is set to 0.02wt%.
It is stipulated that

Sol. In the case of Al:Ti added steel, N is T
Since it is fixed as iN, if the purpose is only to fix N, the amount of Al added can be reduced within the range that allows continuous casting. However, in the present invention, Al is added to the same amount as in ordinary Al-killed steel. This is because, in addition to improving the flowability during casting of ultra-low carbon steel, deoxidizing with Al suppresses oxidation of Ti and reduces the occurrence of surface defects. From the above viewpoint, Sol. 0.03 as Al
It is defined in the range of wt% to 0.06wt%. N: N is
From the viewpoint of the material quality of IF steel, the lower the value, the better, and in particular, the mean-r value is improved as nitrides are reduced. However, in the present invention, since Ti*/[C] is set at a sufficiently high level, a variation in the amount of N at a normal level does not cause an extreme change in the material quality. Therefore, in the present invention, the n value, m
The upper limit of the allowable level for the ean-r value is defined as 0.0040 wt%.

[0020] The alloyed galvanized steel sheet disclosed in the present invention can be used as a product by a conventional method to obtain properties exceeding the level of conventional alloyed galvanized steel sheets, but the most A manufacturing method for imparting good properties will be disclosed below. For the component system of the present invention, slab heating temperature ≦1200°C, hot rolling winding temperature: 58
Most preferably, the temperature is 0 to 640°C, cold rolling rate: 76 to 84%, and continuous annealing temperature: 800 to 880°C.

The most important of these are the hot rolling winding temperature and the cold rolling rate. In order to obtain an extremely high mean-r value as a base steel sheet for a galvanized steel sheet, it is preferable that the carbon/nitrides in the hot rolled sheet be coarse and that the ferrite grain size be small. Regarding the former, by setting Ti*/[C]≧7, the winding temperature can be lowered, and this can be achieved. Moreover, since Nb contributes to grain refinement as solid solution Nb, the latter state can be achieved. As an example showing this effect, Fig. 4 shows steel number 1 in Tables 1 and 2.
3 (Ti-Nb system) and Steel No. 12 (Ti system)
Effect of winding temperature on value - n value balance (winding temperature LCT: 620°C, winding temperature HCT:
680°C). As is clear from the figure, Ti-Nb
The mean-r value of the system is higher than the mean-r value of the Ti system, and furthermore, by winding at 620°C,
It can be seen that the mean-r value increases compared to winding at 0°C. Based on the above results, the upper limit of the winding temperature is preferably 640°C from the viewpoint of the mean-r value. However, if the winding temperature is lower than 580°C, TiC will precipitate finely, resulting in a decrease in the mean-r value of the product. Therefore, the lower limit of the winding temperature is preferably 580°C.

Next, the cold rolling reduction was determined from the viewpoints of mean-r value and deep drawing embrittlement resistance. Figure 5 shows the slab heating temperature H: 1250°C, L: 1 for the steel used in Figure 4.
150℃, winding temperature LCT: 620℃, HCT: 68
This figure shows the balance between the deep drawing embrittlement transition temperature Tth and the mean-r value of steel sheets manufactured under the conditions of 0° C. and cold rolling reductions of 75%, 79%, and 82%. As is clear from the figure, the deep drawing embrittlement critical temperature (Tth) of Ti-IF steel is improved by adding a small amount of Nb. In particular, slab heating temperature: 1
When manufactured under the conditions of 150°C and a winding temperature of 620°C, Tth is improved to about -90°C. Also, Tth
As with the mean-r value, dependence on the cold compression ratio is recognized. However, while the mean-r value is improved by increasing the cold compression ratio, Tth conversely increases. This is considered to be a phenomenon related to changes in grain boundary characteristics due to changes in texture. From the viewpoint of the mean-r value, the lower limit of cold reduction is preferably 76% (preferably 80%), while the upper limit is determined by measures against deep drawing embrittlement and the mean-r value in the 0° rolling direction. Considering the decrease in
It is preferably 4%.

Regarding the slab heating temperature and continuous annealing temperature, the upper limit of the former has been set to 1 due to the problem of deep drawing embrittlement shown in FIG.
200°C, and for the latter, the lower limit is limited to 800°C to ensure sufficient grain growth after recrystallization, and Ti*/[C]≧
When the grain growth property is improved as No. 7, annealing just below the Ac3 point may cause abnormal coarsening due to secondary recrystallization, so the upper limit is limited to 880°C. Note that the steel plate of the present invention can also be manufactured by batch annealing, and although the material of the obtained steel plate is slightly inferior to that of high-temperature continuous annealing material, it can provide superior properties compared to conventional steel plates. In particular, when batch annealing is performed using Ti-IF steel as a material, there is a problem that excessive grain growth causes surface roughness, but with the material of the present invention, batch annealing can be performed without such problems. can.

The above are the basic manufacturing conditions for making the properties of the base steel sheet to an extremely good level, and the steel sheet thus obtained is galvanized (hot-dip galvanizing or electrogalvanizing) and alloyed. By forming a galvanized coating, an alloyed galvanized steel sheet having extremely superior formability compared to conventional plated steel sheets can be obtained.

As mentioned above, in the present invention, the basis weight is 30g/
In steel sheets with alloyed zinc plating of m2 or more, m
T with the aim of ean-r value ≧2.0 and n value ≧0.24.
This limits i*/[C] and [wt%Ti]/[wt%Nb]. By the way, with low Ti content, Ti*
In order to make /[C] 7 or more, it is essential to reduce C, N, and S. However, in this case, the structure of the hot rolled sheet tends to become coarse grained, and the in-plane anisotropy of the r value after cold rolling and annealing tends to increase. Regarding the above points, Figure 6 shows the amount of Ti and the amount of Ti.
*/ Regarding materials with changed balance of [C] mean-
This shows the results of examining the r value and Δr value (in addition,
The diagonal line in the figure is C: 0.001wt%, N: 0.00
1 wt% and S: 0.001 wt%, the value of Ti*/[C] with respect to the Ti amount is shown). According to this, Ti
*/[C] In the range of 7, the mean-r value ≧2.0 is obtained, but in the range of 0.04wt%≦Ti<0.06wt%, Δr≧0.4, while Ti≧ 0.06wt
% range, Δr<0.4. Therefore, in view of today's level of steelmaking technology and production costs,
Considering that there is a limit to reducing C, N, and S to the maximum, it is preferable to keep Ti in the range of 0.06 wt%.
This can be said to be more advantageous in practical terms.

[0026]

[Example] [Example 1] Regarding the steels shown in Tables 1 and 2, slab heating temperature: 1150°C, hot rolling finishing temperature: 9
00℃, coiling temperature: 620℃, cold rolling ratio: 82%, and then cold-rolled steel sheet at 820℃ in a continuous hot-dip galvanizing line.
The steel sheet was annealed at 50°C, and then galvanized and alloyed at a zinc bath temperature of 460°C and an alloying temperature of 490°C to produce an alloyed galvanized steel sheet. Obtained product (galvanized area weight: 40 [g/m2]/40 [
Tables 3 and 4 show the results of evaluating the material properties and the amount of drawbead peeling of the plating layer with respect to the alloying ratio: 10%).

[Example 2] Regarding steel numbers 8 and 13 (all steels of the present invention) shown in Tables 1 and 2, the manufacturing conditions before continuous hot-dip galvanizing were varied as shown in Tables 5 and 6. The material properties of the obtained alloyed galvanized steel sheet and the amount of drawbead peeling of the plating layer were evaluated. The results are shown in Tables 7 and 8.

[Example 3] For steel numbers 10, 11, 13, and 21 shown in Tables 1 and 2, the plating conditions and plating film properties were variously changed, and the material properties of the obtained steel sheets and the drop of the plating layer were - The amount of bead peeling was evaluated. The results are shown in Tables 9 and 10 together with the plating conditions.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

[0034]

[Table 6]

[0035]

[Table 7]

[0036]

[Table 8]

[0037]

[Table 9]

[0038]

[Table 10]

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the influence of Ti*/[C] on the mean-r value and Δr value of Ti-added IF steel and Ti-Nb-added IF steel.

[Figure 2] Effects of Ti and Nb addition amounts on mean-r value and drawbead peeling amount and [wt%Ti]/[wt%Nb
] is a drawing showing the influence of

FIG. 3 is a drawing showing the influence of adding a small amount of Nb on the number of pinholes (after 2 mm scarf) on the slab surface of Ti-added IF steel.

FIG. 4 is a drawing showing the influence of trace amount of Nb addition and hot-rolling temperature on the balance between mean-r value and n value.

[Figure 5] Mean-r value and deep drawing embrittlement transition temperature (Tth
) is a drawing showing the influence of slab heating temperature, coiling temperature, and cold reduction rate on the balance.

[Figure 6] Effect of Ti amount and Ti on mean-r value and Δr value
It is a drawing showing the influence of the balance of */[C].

Claims (3)

[Claims] Claim 1: C≦0.0030wt%, Si≦0.
05wt%, 0.05wt%≦Mn≦0.50wt%,
P≦0.02wt%, S≦0.02wt%, 0.03w
t%≦Sol. Al≦0.06wt%, N≦0.004
0wt%, 0.005wt%≦Nb≦0.014wt%
, 0.04wt%≦Ti≦0.12wt%, and (Ti*/[C])≧7 provided that Ti*/[C]=[wt%Ti
*]/4 [wt%C] [
wt%Ti*]=[wt%Ti]-{(48/14)・
[wt
%N〕+(48/32)・[
wt%S]} [wt%C
] :C content (wt%)
[wt%Ti]: Ti content (wt%)
[wt%N]: N content (wt
%) [wt%S]:
S content (wt%) 7≦([wt%Ti]/[wt%N
b])≦14 However, [wt%Ti]: Ti content (
wt%) [wt%Nb]: A steel plate that satisfies the Nb content (wt%) and has a composition consisting of the balance Fe and unavoidable impurities is used as the base steel plate, and one or both sides of the steel plate is coated with a galvanized area weight. An alloyed galvanized steel sheet with excellent formability and having an alloyed galvanized layer of 30 g/m2 or more per side. Claim 2: C≦0.0030wt%, Si≦0.
05wt%, 0.05wt%≦Mn≦0.50wt%,
P≦0.02wt%, S≦0.02wt%, 0.03w
t%≦Sol. Al≦0.06wt%, N≦0.004
0wt%, 0.005wt%≦Nb≦0.014wt%
, 0.04wt%≦Ti≦0.12wt%, and (Ti*/[C])≧7 provided that Ti*/[C]=[wt%Ti
*]/4 [wt%C] [
wt%Ti*]=[wt%Ti]-{(48/14)・
[wt
%N〕+(48/32)・[
wt%S]} [wt%C
] :C content (wt%)
[wt%Ti]: Ti content (wt%)
[wt%N] :N content (wt
%) [wt%S]:
S content (wt%) 7≦([wt%Ti]/[wt%N
b])≦14 However, [wt%Ti]: Ti content (
wt%) [wt%Nb]: A steel that satisfies the Nb content (wt%) and has a composition consisting of the balance Fe and unavoidable impurities is hot rolled, cold rolled and continuously annealed in a conventional manner, Continue applying 30g/m2 to one or both sides of the steel plate.
A method for producing an alloyed galvanized steel sheet with excellent formability, which comprises performing the above zinc plating and then performing an Fe-Zn alloying treatment. Claim 3: After hot rolling at a slab heating temperature ≦1200°C, hot rolling coiling temperature: 580-640°C, rolling rate:
Cold rolling at 76~84% then 800℃~880℃
The production of an alloyed galvanized steel sheet with excellent formability according to claim 2, characterized in that the steel sheet is continuously annealed, then galvanized on one or both sides of the steel sheet, and then subjected to Fe-Zn alloying treatment. Method.