JPH05106003A - Method for producing alloyed molten zinc plated steel sheet with excellent powdering resistance and press formability - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a method for producing an alloyed hot-dip galvanized steel sheet having both excellent deep drawability and powdering resistance. [Structure] C, Si, Mn, P, S, Sol. Al, N
In order to improve the powdering resistance and the deep-drawing embrittlement resistance of the coating, each component of the above is prescribed amount of Ti equal to or more than C equivalent, and a trace amount and a Ti amount compared with the Ti amount. The steel containing a limited amount of Nb is hot-rolled and cold-rolled, annealed in CGL at a temperature of 700 ° C. or higher and an Ac ₃ transformation point or lower, and then plated, and subsequently in an induction heating alloying furnace. After the alloying treatment is performed and the molten zinc layer on the surface layer disappears, it is rapidly cooled to a temperature of 300 ° C. or lower at a predetermined cooling rate. Further, if necessary, the upper layer of the galvannealed coating is subjected to Fe—Zn alloy plating with a predetermined Fe content and adhesion amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet for ultra-deep drawing having excellent powdering resistance and press formability.

[0002]

2. Description of the Related Art So-called IF steel (Interstiti), which is made by adding carbon / nitride forming elements such as Nb, Ti, Zr, and B to ultra-low carbon steel,
al Free Steel) has attracted attention as a powerful material for the continuous annealing of ultra-deep drawn cold-rolled steel sheets (EDDQ), which require deep drawability and non-aging properties. With the spread of continuous annealing processes today, Its importance has been recognized.

On the other hand, the proportion of rust-preventing steel sheets used for automobile bodies has increased rapidly in recent years, and it is fully expected that all cold-rolled steel sheets for automobiles will be replaced with rust-preventing steel sheets in the near future. Generally, rustproof steel sheets used for automobile bodies are galvanized steel sheets, but in recent years, galvanized steel sheets by the hot dip coating method that can easily increase the adhesion amount are alloyed in order to improve rustproofness and paintability. Cases used for chemical treatment are increasing.

However, the alloying treatment to form hard Fe--Zn alloy layers on both sides of the steel sheet is particularly restricted by the plastic deformation of the base steel sheet, so that the plastic anisotropy (generally evaluated by r value) is evaluated. The larger the value, the better the deep drawing formability) and the deterioration in elongation at break. Therefore, in order to impart excellent formability to the galvannealed steel sheet, it is necessary to set the material level of the base steel sheet to a high level in consideration of the material deterioration due to the formation of the plating layer. Therefore, hot-dip galvanized steel sheets made from the above IF steels are receiving attention.

Conventionally used IF steel is Ti
-Added Ti-IF steel and Nb-added Nb-IF
It is steel. In particular, Ti is a strong carbon / nitride forming element, and at the same time, S in steel is also precipitated and coarsened as sulfide, so Ti-IF steel has extremely excellent deep drawability and ductility in a wide range of components. There are characteristics that can be obtained. However, when this steel sheet is subjected to hot dip coating and further alloying treatment, the alloying reaction between Fe, which is the base material, and molten zinc is promoted by the influence of Ti in the steel, so that overalloying proceeds. It is known that the plating layer is easily peeled off during press molding, so-called powdering is likely to occur (Japanese Patent Laid-Open No. 1-222035).

On the other hand, in Nb-IF steel, by mainly fixing C in the steel and fixing solid solution C in the steel, Ti
-The same excellent deep drawability as IF steel is obtained, but if Nb is excessively added, the effect of suppressing grain growth due to NbC precipitates becomes remarkable and the material deteriorates. Therefore, Ti
-There is a problem that the range of appropriate components is narrower than that of IF steel. In addition, by adding Ti and Nb in combination, Ti
Techniques for improving the powdering resistance, which is often impaired in IF steel, have been proposed in JP-B-61-32375, JP-A-59-67319 and JP-A-59-74231.

However, according to the conventional proposal of this kind, Ti and N
The amount of b is regulated to an extremely limited amount, and even in the above three proposals, the Ti addition amount is at most equal to or less than C and N,
That is, the range is Ti ≦ (48/12) C + (48/14) N. The reason for this limitation is that when Ti is added in an amount equal to or more than C and N, both the material and the film characteristics are substantially close to those of Ti-IF steel, and the material such as deep drawability becomes good, but the powdering resistance It is said that deterioration is a problem. Since the addition amounts of Ti and Nb are defined in this way, the mean-r value is 2.0 as far as the examples are seen.
It is difficult to say that sufficient characteristics have been obtained with respect to deep drawability. On the other hand, from the viewpoint of powdering resistance, in the invention example of the above-mentioned Japanese Patent Publication No. 61-32375, although the powdering occurrence rate is reduced as compared with the comparative steel, powdering still occurs,
It cannot be said that the measures for improving the powdering resistance are completely taken.

Further, Ti: 0.010 to 0.100 wt
%, Nb: a technique of adding in the range of 0.004 to 0.04 wt% (JP-A-1-123058) is disclosed, but it is disclosed in the range of Ti ≦ 0.042% as judged from Examples. And the mean-r value ≧ 2.
No. 2 is steel containing only Ti and Nb
No example is shown in which a mean-r value of more than 2.0 is obtained by the combined addition of Ti and Ti.

[0009]

DISCLOSURE OF THE INVENTION Even when the prior art is examined in detail as described above, the manufacturing technique of the alloyed hot-dip galvanized steel sheet having the excellent material and the powdering resistance of the plating film is disclosed. There is no. The present invention has been made in view of such a situation as described above, and it is possible to obtain excellent deep drawability and powdering resistance by not only the composition of the material but also the plating conditions, in particular, the alloying conditions. The present invention provides a method for producing an alloyed hot-dip galvanized steel sheet having both of the above.

[0010]

That is, the present invention has the following configuration. (1) C ≦ 0.0030 wt%, Si ≦ 0.30 wt
%, 0.05 wt% ≤ Mn ≤ 1.0 wt%, P ≤ 0.0
6 wt%, S ≦ 0.02 wt%, 0.03 wt% ≦ So
l. Al ≦ 0.06 wt%, N ≦ 0.0040 wt%,
0.040 wt% ≦ Ti ≦ 0.080 wt%, 0.00
3 wt% ≤ Nb ≤ 0.025 wt% and Ti * / [C] ≥ 7 where Ti * / [C] =% Ti * / (4x% C)% Ti * =% Ti-{( 48/14) x% N + (48 /
32) ×% S)}% C: C content (wt%)% Ti: Ti content (wt%)% N: N content (wt%)% S: S content (wt%) 2 ≦ ( % Ti /% Nb) ≦ 14 However, steel having a composition of% Ti: Ti content (wt%)% Nb: Nb content (wt%) and having the balance Fe and unavoidable impurities is hot-rolled and After cold rolling, in a continuous hot dip galvanizing line, a steel sheet is annealed at a temperature of 700 ° C. or higher and Ac ₃ transformation point or lower, and then plated, and after adjusting the coating weight, alloying is performed in an induction heating alloying furnace. After the molten zinc layer on the surface disappears, the temperature is up to 300 ° C and below 20 ° C
A method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance and press formability, which comprises cooling at a cooling rate of not less than 1 sec / sec.

(2) After the above alloying treatment, F containing 50 wt% or more of Fe is added to the upper layer of the galvannealed coating film.
A method for producing an alloyed hot-dip galvanized steel sheet excellent in powdering resistance and press formability, which comprises performing e-Zn alloy plating at 1 g / m ² or more.

(3) In the manufacturing method of the above (1) or (2), plating is performed in a zinc bath containing 0.08 to 0.14 wt% of Al, and a furnace exit side plate temperature is set in an induction heating type alloying furnace. The method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance and press formability is characterized in that the alloying treatment is performed so as to be 450 to 550 ° C.

[0013]

The details of the present invention and the reasons for limitation thereof will be described below. The plating original plate used in the present invention has a wide allowable range in component design, the material is stable against manufacturing conditions,
From the viewpoint of superior grain growth compared to Nb-added steel,
Based on Ti-IF steel, further, in order to improve the powdering resistance and the deep drawing embrittlement resistance of the film, a small amount of Nb is added as compared with the Ti amount and a limited amount of Nb is added in relation to the Ti amount. That is the basic feature.

Hereinafter, Ti, which is the most important element of the present invention,
Regarding Nb and Nb, the limitations and the test results that are the main grounds for the limitations will be described. First, in the present invention, Ti * / [C] (atomic weight% ratio) defined by the following formula is specified. Ti * / [C] =% Ti * / (4 ×% C)% Ti * =% Ti-{(48/14) ×% N + (48 /
32) ×% S)}% C: C content (wt%)% Ti: Ti content (wt%)% N: N content (wt%)% S: S content (wt%)

In the present invention, when fixing C in steel, C
By adding more than the equivalent amount of Ti, the aim is to fix carbon / nitride. FIG. 1 shows Ti: 0.01 to 0.20.
wt%, Nb: 0 wt% and 0.002-0.03w
With respect to steel in the range of t%, the influence of the above Ti * / [C] on the mean-r value and the Δr value defined below was investigated and arranged. [Mean-r] _{= ([r 0] +2 [} r 45] + [r 90]) / 4 Δr = ([r 0] + [r 90] -2 [r 45]) / 2 where, [r ₀ ]: R value in the rolling direction of the steel sheet [r ₄₅ ]: r value in the 45 ° direction relative to the rolling direction of the steel plate [r ₉₀ ]: r value in the 90 ° direction relative to the rolling direction of the steel plate When Nb is added, solid solution Nb
It can be seen that the level of mean-r value rises due to the grain refinement of the hot-rolled sheet structure caused by.

Next, in the present invention, from the relationship between the mean-r value after forming the alloyed hot-dip galvanized layer and the powdering resistance,
The addition amounts of Ti and Nb are limited. Fig. 2 shows the cold-rolled steel sheet with a thickness of 0.8 mm with various additions of Ti and Nb.
After annealing at 50 ° C, zinc bath temperature: 460 ° C, Al content in the bath:
The powdering resistance of the galvannealed steel sheet obtained by galvanizing under the condition of 0.12 wt% and then subjecting to the alloying furnace exit side plate temperature of about 500 ° C. for alloying treatment is examined. In order to do a draw test,
It shows the relationship between the plating film peeling amount (hereinafter referred to as DB peeling amount) obtained as a result, the mean-r value, and the weight% ratio of Ti and Nb. Note that the DB peeling amount of the plating film is influenced by the basis weight and has a relationship as shown in FIG. That is, when the plate thickness is kept constant at 0.8 mm, the basis weight is 60
The level of good powdering resistance of the g / m ² material is that the DB peeling amount is 4 g / m ² or less.

According to FIG. 2, T of C ≦ 0.003 wt%
In i-IF steel, the mean-r value increases as the Ti content increases. On the other hand, when the amount of Nb is increased with respect to the amount of Ti, the DB peeling amount decreases, but the mean-r value deteriorates due to the presence of excess Nb. On the other hand, if the amount of Nb is decreased with respect to the amount of Ti, the amount of DB peeling increases. From the above results, mean-r value ≧ 2.0, DB peeling amount ≦ 4.0 g /
The component system capable of obtaining the characteristics of m ² (unit weight: 60 g / m ² material) is Ti: 0.040 to 0.080 wt%, Nb: 0.
It can be seen that the range is 003 to 0.025 wt% and 2 ≦ (% Ti /% Nb) ≦ 14, where% Ti: Ti content (wt%) and% Nb: Nb content (wt%).

Next, based on the above test results and the like, Ti and Nb
The reasons for limitation are described below. Ti is a strong carbon / nitride-forming element as described above, and Ti * / [C] ≧ 1 is sufficient to fix C in the steel in an equilibrium state. It has been found that it is preferable to set Ti * / [C] ≧ 7 in which the addition amount is slightly higher than the C equivalent Ti in order to increase the size to a certain extent and to have an excellent grain growth property. Therefore, in the present invention, it is defined that Ti * / [C] ≧ 7.

Further, in the present invention, in addition to the above definition, Ti
As an addition amount, 0.040 wt% ≦ Ti ≦ 0.080w
Defined as t%. When Ti is less than 0.040 wt%, C in steel can be fixed, but coarsening of TiC hardly occurs, and it is necessary to take measures such as winding at high temperature during hot rolling in the process. On the other hand, when it is added in an amount of more than 0.080 wt%, the outburst generation region is remarkably increased during hot dipping, and the powdering resistance of the plating film becomes a problem.

Nb is an essential addition element in the present invention, but its addition amount is limited to a minute range of 0.003 to 0.025 wt%. In particular, as shown in FIG. 2 described above, limiting% Ti /% Nb to the range of 2 to 14 is effective not only for ensuring the mean-r value but also for ensuring the powdering resistance of the plating film. is necessary.

FIG. 4 shows that, when the galvannealed steel sheet used in FIG. 2 is manufactured, the output of the alloying furnace is turned off to obtain a galvanized steel sheet, and then Zn in the surface layer of the coating is dissolved with dilute hydrochloric acid. Then, the outburst tissue portion was observed under a microscope and the area ratio was measured. further,
FIG. 5 shows the effect of the area ratio of the outburst structure on the amount of DB peeling based on the results of FIGS. 2 and 4. According to this, in the sample in which the amount of DB peeling exceeds 4 g / m ² , the area ratio of the outburst structure generated during immersion in the zinc bath is as high as 20% or more, and the powdering resistance deteriorates due to the increase in the outburst generation area. It is thought that it was done. This can be easily understood by considering the cause of the outburst tissue. According to the academic literatures to date, the outburst structure has a Zn content in a zinc bath, especially when an extremely low carbon steel plate containing Ti, Nb, etc. is used as a material.
-Fe is likely to be produced in the alloying process or the alloying process in the alloying furnace that follows, and the mechanism is as follows.
Zn that penetrates into a very clean ferrite grain boundary part because there is almost no solid solution C causes volume expansion and cracks at grain boundaries, resulting in direct reaction between Zn and Fe. It is said that. The portion where the outburst reaction has occurred can be easily judged from the microscopic structure (the arrow indicates the outburst structure) as shown in the photograph of FIG. 7. If a large number of the outburst structures are nonuniformly produced, the nonuniformity of the plating film structure is further emphasized after the alloying treatment. That is,
In the outburst reaction part, a thick Γ phase that deteriorates the powdering resistance of the plating film is likely to be generated.

From the above points, the weight% ratio of Ti and Nb is an important parameter when defining the amount of Nb. T
Regarding the relationship between the i amount and the Nb amount, from the result of FIG.
Although addition of a large amount of Nb with respect to the amount suppresses the outburst reaction, but the mean-r value deteriorates.
The lower limit of% Ti /% Nb is limited to 2. On the other hand, when Nb is decreased with respect to the Ti amount, the outburst generation area increases and the DB peeling amount increases as shown in FIG. 4, so the upper limit of the Nb amount is% Ti / 14, that is,% Ti.
The upper limit of /% Nb is 14. Thus, 2 ≦ (% T
Within the range of i /% Nb) ≦ 14, a local alloying reaction that occurs in the plating bath, that is, a so-called outburst reaction is suppressed, and good powdering resistance can be obtained. This is because when the amount of Nb is increased with respect to the amount of Ti, some of the carbides re-dissolve during annealing in the continuous hot dip coating line,
It is considered that the segregation at the grain boundaries makes it difficult to cause the above grain boundary reaction.

The addition of a small amount of Nb is also effective in improving the secondary workability, and in order to obtain such an effect, the lower limit of Nb addition is specified to be 0.003 wt%. .. In addition, the upper limit of the addition amount is 0.025 wt from the viewpoint of hardening due to excessive addition and easy deterioration of the material.
Limited to%.

Next, the reasons for limiting the components other than Ti and Nb will be described. C: Ti for improving deep drawability
It is necessary to limit not only the size of C but also the total amount thereof, and in the present invention, the upper limit of C is defined as 0.0030 wt% in order to ensure good deep drawability. Si: Si may be added to adjust the strength level, but since it tends to reduce the adhesion of the coating film of the hot-dip galvanized steel sheet, it is specified to be 0.30 wt% or less.

Since Mn: Ti contributes to the fixation of S, M
There is no problem if n is lower than the general steel level, but 0.0
If it is less than 5 wt%, the hot metal pretreatment cost increases, so
The lower limit is specified as 0.05 wt%. Further, Mn can also be used for increasing the strength, but its upper limit is defined as 1.0 wt% because of the problem that it has the effect of deteriorating the r value and the cost increase. P: P is also Si or Mn
Similarly, it is effective for increasing the strength of the steel sheet, but when the content exceeds 0.06 wt%, the elongation and deep drawability of the steel sheet are significantly deteriorated, so 0.06 wt% is the upper limit.

S: S reduces the effective Ti amount (Ti *) by precipitating as TiS. Therefore, in the present invention, the upper limit is specified as 0.02 wt%. Sol.
In the case of Al: Ti-added steel, N is fixed as TiN. Therefore, for the purpose of only fixing N, the amount of Al added can be reduced within the range where continuous casting is possible. However, in the present invention, Al is added as is the case with ordinary Al-killed steel. This is because in addition to improving the flowability of the ultra-low carbon steel during casting, it suppresses the oxidation of Ti by deoxidizing with Al,
This is to reduce the occurrence of surface defects. From the above viewpoint,
Sol. The Al content is specified in the range of 0.03 wt% to 0.06 wt%.

From the viewpoint of the material of IF steel, N: N is basically preferable as low as possible, and in particular, the mean-r value is improved with the decrease of nitrides. However, in the present invention, since Ti * / [C] is set to a sufficiently high level, there is no extreme change in the material due to the fluctuation of the N content at the normal level. Therefore,
In the present invention, the upper limit is defined as 0.0040 wt% as the level allowed for the mean-r value.

Next, regarding the annealing temperature in the continuous hot-dip galvanizing line, 700 ° C. is set in order to achieve grain growth after recrystallization.
The above temperature is required, and therefore 700 ° C. is set as the lower limit. Further, in order to improve the grain growth property, it is necessary to raise the annealing temperature, but if heating is performed above the Ac ₃ transformation point, the texture is randomized and the r value is deteriorated. Therefore, the upper limit of the annealing temperature to _3-point Ac.

In the method for producing the galvannealed steel sheet according to the present invention, induction heating (high frequency induction heating) is used as the alloying method.
It is essential to use the method, and this is a major feature. That is, when forming the alloyed hot-dip galvanized film in the continuous hot-dip galvanizing line, the advantages of the present invention can be fully exhibited by performing the alloying treatment in the induction heating type alloying furnace. This is because the induction heating method can directly heat the surface layer of the steel sheet, which is a ferromagnetic material, so that the above-described local alloying reaction is less likely to occur, and the uniform heating (alloying treatment) is also performed in the sheet thickness direction. ) Is possible. Specific advantages of the alloying treatment by the induction heating method are as follows.

First, since the surface layer of the steel sheet in contact with the plating film is directly heated by using the induction heating method in the alloying treatment, the steel sheet and the plating film are not easily separated from each other as compared with the atmosphere heating method such as gas heating. Fe-Zn at the interface
It is estimated that the reaction takes place in a short time and evenly regardless of the position on the steel sheet, so that there is no partial overalloy or residual alloy phase on the steel sheet, and uniform powdering resistance can be obtained. To be done.

Secondly, since induction heating directly heats the surface of the steel sheet as described above, it is presumed that a uniform alloying reaction occurs microscopically. That is, in the conventional alloying treatment by gas heating generally performed, since heat is applied from the outside of the coating, the heating is likely to be non-uniform,
Therefore, the alloying reaction is likely to occur microscopically inhomogeneously. In particular, since the crystal grain boundaries are highly reactive, so-called outburst reaction is likely to occur. When such an outburst structure is generated, the Γ phase begins to grow from this part, and the formation of this Γ phase makes it possible to improve the powdering resistance. to degrade. On the other hand, in induction heating, since the surface layer of the steel sheet is directly heated, the above-mentioned local variation in alloying is small, and the oxide on the steel sheet surface or the alloying-suppressing substance (Fe ₂ Al) generated in the bath is used. _{Since 5} ) also diffuses easily, it is thought that a microscopically uniform alloyed film can be obtained.

Thirdly, since induction heating can alloy the plating in a short time, the growth time of the Γ phase is short, so that the final formation amount of the Γ phase is small, which also improves the powdering resistance. It is considered that it has contributed greatly.

Fourthly, as an advantage of induction heating, since uniform heating can be performed in the width direction and the length direction of the steel plate, strict plate temperature control on the outlet side of the heating furnace is possible, and gas furnace is also possible. It is considered that overalloying is unlikely to occur because the heated atmospheric gas does not rise (draft effect) unlike the atmospheric heating method such as the above.

Regarding press formability, as a result of alloying being made macroscopically and microscopically as described above,
Stable and uniform press formability is obtained, and when the heating after hot dip coating is performed by induction heating, the plating surface is not oxidized, so that the upper layer plating can be appropriately attached on the alloyed plating layer. Therefore, it is considered that stable press formability can be obtained by depositing a smaller amount of the upper layer plating than in the case of alloying treatment by gas heating.

Furthermore, after the molten zinc layer on the surface of the plating film disappears, the Fe--Zn alloying reaction does not proceed much 30
It is cooled to 0 ° C or lower at a cooling rate of 20 ° C / sec or higher. This is to prevent as much as possible the growth of the Γ phase, which is generated at the interface between the plating film and the base steel sheet and deteriorates the powdering resistance after the predetermined plating film structure (crystal structure) is obtained by the alloying heat treatment. This is because. By adopting such cooling conditions, it is possible to further improve the powdering resistance. According to the above-mentioned steel composition regulations, adoption of induction heating method, and cooling rate regulations,
It is possible to improve the powdering resistance, which has been impaired in the conventional Ti-added steel, and this is a major feature of the present invention.

Next, with respect to the plating conditions, in general, Fe-Z is used for the plating bath in the continuous hot-dip galvanizing line.
Al for suppressing the n-alloying reaction and smoothing the plated surface
Is added in an amount of about 0.1 wt%, and in the present invention as well, Al having an alloying suppressing effect is added in an amount of 0.08 wt%.
It is preferable to add the above to prevent the Fe—Zn alloy layer after immersion in the hot dip galvanizing bath from being non-uniformly formed in large numbers in an outburst form. In this step, it is important not to generate the Fe-Zn alloy layer nonuniformly.
If the Zn alloy layer becomes non-uniform, this cannot be eliminated in a later step. On the other hand, the added amount of Al is 0.14 wt
If it exceeds 0.1%, the alloying suppression effect becomes excessive, and it takes time for the subsequent alloying treatment, which causes a problem such as an increase in furnace length. Therefore, the amount of Al in the bath is preferably 0.08 to 0.14 wt%.

Further, by controlling the furnace-exit side plate temperature of the steel plate in the induction heating alloying furnace within the range of 450 to 550 ° C.,
It is possible to form a film having more excellent powdering resistance. If the furnace exit side plate temperature is less than 450 ° C., it takes a long time for alloying, which is not preferable due to the limitation of alloying equipment.
If the temperature exceeds 550 ° C, the alloying rate of the coating tends to become excessive,
The powdering resistance deteriorates. The reason for controlling the plate temperature on the outlet side of the induction heating furnace in the present invention is that that part becomes the maximum plate temperature in the alloying heat cycle. Further, since the growth rate of the alloy phase becomes maximum in this vicinity, it becomes possible to cause the alloying reaction at that temperature by controlling the outlet plate temperature.

In the present invention, the upper layer of the alloyed hot-dip galvanized coating after the alloying treatment is coated with an Fe—Zn alloy plating containing 50 wt% or more of Fe by an adhesion amount of 1 g / m ² or more, thereby performing press working. It is possible to improve the sliding property between the plating film and the pressing tool at the time, the cratering resistance at the time of coating, and the like. The above sliding properties are related to the adhesion between the surface material of the coating and the tool, and the higher the melting point of the coating surface, the more effective it is to improve the sliding properties. The Fe content of the upper plating film is defined as 50 wt% or more,
This is because sliding characteristics can be improved when Fe: 50 wt% or more.

[0039] With respect to the amount deposited is less than 1 g / m ² can not be covered sufficiently uniform layer plating film over the entire plating surface, defined as 1 g / m ² or more. Although there is no particular upper limit to the coating weight, it is preferably 5 g / m ² or less in terms of cost. When the alloying treatment after hot dip plating is performed by induction heating as in the present invention, the plating surface is not oxidized, so that the upper layer plating can be appropriately attached on the alloyed plating layer, and therefore, the gas heating can be performed. It is possible to reduce the adhesion amount of the upper layer plating as compared with the case of alloying.

[0040]

【Example】

[Example 1] For the steels shown in Table 1, the slab heating temperature:
1150 ° C, hot rolling finishing temperature: 900 ° C, winding temperature: 62
After hot rolling at 0 ° C., cold rolling was performed at a cold pressure ratio of 82% to obtain a plate thickness of 0.
8 mm thin plate, then annealed at 850 ° C. in continuous hot dip galvanizing line, and then zinc bath temperature: 46
After 0 ° C., Al content in the bath: 0.12 wt%, alloying treatment furnace exit side plate temperature: 490 ° C., galvanization and alloying treatment by induction heating method are performed, and after the molten zinc layer on the surface of the plating film disappears, Immediately cool down to a temperature below 300 ℃ 25
It cooled at ° C / sec and manufactured the alloying hot-dip galvanized steel sheet. Obtained product (amount of zinc plating: 60g on each side)
/ M ² , and Fe content in the coating: about 10%), the results of evaluation of the material characteristics and the amount of DB peeling of the plating coating are shown in Table 2.

[0041]

[Table 1]

[0042]

[Table 2]

Example 2 The steels shown in Table 3 were hot-rolled at a slab heating temperature of 1150 ° C., a hot rolling finishing temperature of 900 ° C. and a coiling temperature of 620 ° C., and then cooled at a cold rolling ratio of 82%. Rolled into a thin plate with a thickness of 0.8 mm, then annealed at 850 ° C. in a continuous hot-dip galvanizing line, and subsequently zinc bath temperature: 460 ° C., Al content in bath: 0.12 wt%, alloying treatment furnace discharge Side plate temperature: Zinc plating and alloying treatment (heating by induction heating method or gas heating method) under the condition of 490 ° C, and immediately after the molten zinc layer on the surface of the plating film disappears, the cooling rate is 25 ° C up to a temperature of 300 ° C or less. The alloyed hot-dip galvanized steel sheet was manufactured by cooling at 1 / sec. Table 4 and Table 5 show the results of evaluating the material properties of the obtained products (zinc plating coating amount: 60 g / m ^{2 on} each side, Fe content in the coating: about 10%) and the draw bead peeling amount of the plating coating. Shown in.

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[Example 3] With respect to steel No. 4 (inventive steel) shown in Table 1, various alloying treatments and cooling conditions after plating in the hot dip galvanizing line were changed to obtain hot dip galvanized alloys. Steel plate (Zinc coating amount: 6 on each side)
The amount of DB peeling of the plating film of 0 g / m ² ) was evaluated. The results are shown in Table 6 together with alloying treatment conditions and cooling conditions.
Shown in. Other manufacturing conditions in this example are as follows. Hot rolling conditions Slab heating temperature: 1150 ° C, hot rolling finishing temperature: 900
℃, coiling temperature: 620 ℃ cold rolling conditions cold rolling rate: 82%, plate thickness: 0.8 mm CGL treatment conditions annealing temperature: 850 ℃, zinc bath temperature: 460 ℃, Al in the bath
Amount: 0.12wt%

[0048]

[Table 6]

Example 4 With respect to steel No. 4 (inventive steel) shown in Table 1, an induction heating system was used as an alloying furnace in the hot dip galvanizing line, and the alloying furnace exit side plate temperature was set to 50.
Al in the hot dip galvanizing bath under the condition of around 0 ° C
The amount of various changes was evaluated, and the free zinc part (fused zinc layer on the surface layer) and the amount of DB peeling of the coating found on the resulting alloyed hot-dip galvanized steel sheet (amount of zinc coating: 60 g / m ^{2 on} each side) were evaluated. did. The results are shown in Table 7 together with the plating conditions.
Shown in. Other manufacturing conditions in this example are as follows. Hot rolling conditions Slab heating temperature: 1150 ° C, hot rolling finishing temperature: 900
℃ Winding temperature: 620 ℃ Cold rolling condition Cold rolling rate: 82%, Plate thickness: 0.8 mm CGL treatment condition Annealing temperature: 850 ° C., Zinc bath temperature: 460 ° C., Cooling rate:
25 ° C / sec

[0050]

[Table 7]

Example 5 Steel Nos. 4, 6 and 6 shown in Table 1
For No. 7, the plating film properties were variously changed by changing the plating conditions in the hot dip galvanizing line, and the plating film characteristics of the obtained alloyed hot dip galvanized steel sheet were evaluated. The results are shown in Table 8 together with the plating conditions.
In this example, some of the steel sheets were electroplated with an Fe—Zn alloy alloy having an Fe content of 80 wt% on the upper layer of the galvannealed coating. Other manufacturing conditions in this example are as follows. Hot rolling conditions Slab heating temperature: 1150 ° C, hot rolling finishing temperature: 900
C coiling temperature: 620 ° C. cold rolling condition cold rolling rate: 82-84% CGL treatment condition annealing temperature: 850 ° C., zinc bath temperature: 458-462 ° C., Al content in the bath: 0.12-0.13 wt%, Cooling rate: 2
5 ° C / sec

[0052]

[Table 8]

Example 6 With respect to steel No. 4 (inventive steel) shown in Table 1, in a hot dip galvanizing line, after hot dip galvanizing, an alloying treatment using an induction heating method (alloying furnace exit side plate temperature : 500 ° C.), and then alloying plating film (zinc coating weight: 60 g / m ^{2 on} each side)
Fe-Zn alloy plating having an Fe content of 80 wt% was applied to the upper layer by electroplating, and the friction coefficient of the obtained plated steel sheet was measured. The results are shown in Table 9 together with the adhesion amount of the upper plating film. The other manufacturing conditions in this example are as follows. Hot rolling conditions Slab heating temperature: 1150 ° C, hot rolling finishing temperature: 900
℃ Winding temperature: 620 ℃ Cold rolling condition Cold rolling rate: 82%, Plate thickness: 0.8 mm CGL treatment condition Annealing temperature: 850 ℃, Zinc bath temperature: 460 ℃, Al in the bath
Amount: 0.12 wt%, cooling rate: 25 ° C / sec

[0054]

[Table 9]

[Brief description of drawings]

FIG. 1 shows a Ti-added IF steel and a Ti—Nb-added IF steel.
Graph showing the effect of Ti * / [C] on mean-r and Δr values

FIG. 2 is a graph showing effects of Ti and Nb addition amounts and% Ti /% Nb on mean-r value and DB peeling amount.

FIG. 3 is a graph showing the effect of the amount of plating film deposition on the amount of DB peeling.

FIG. 4 is a drawing showing influences of Ti and Nb addition amounts and% Ti /% Nb on mean-r value and area ratio of outburst structure.

FIG. 5 is a graph showing the effect of the area ratio of outburst tissue on the amount of DB peeling.

FIG. 6 is a graph showing the effect of tensile strength on the mean-r value.

FIG. 7 is a microscopic enlarged photograph of the metal structure of the outburst portion formed in the plating film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication C22C 38/14 (72) Inventor Yoshihiro Hosoya 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor, Koji Matsubayashi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. C ≦ 0.0030 wt%, Si ≦ 0.3
0 wt%, 0.05 wt% ≤ Mn ≤ 1.0 wt%, P ≤
0.06wt%, S ≦ 0.02wt%, 0.03wt%
≤ Sol. Al ≦ 0.06 wt%, N ≦ 0.0040w
t%, 0.040 wt% ≤ Ti ≤ 0.080 wt%,
Containing 0.003 wt% ≤ Nb ≤ 0.025 wt%,
And Ti * / [C] ≧ 7 where Ti * / [C] =% Ti * / (4 ×% C)% Ti * =% Ti-{(48/14) ×% N + (48 /
32) ×% S)}% C: C content (wt%)% Ti: Ti content (wt%)% N: N content (wt%)% S: S content (wt%) 2 ≦ ( % Ti /% Nb) ≦ 14 However, steel having a composition of% Ti: Ti content (wt%)% Nb: Nb content (wt%) and having a balance of Fe and inevitable impurities is hot-rolled and After cold rolling, in a continuous hot-dip galvanizing line, the steel sheet is annealed at a temperature of 700 ° C or higher and _AC3 transformation point or lower, plated, adjusted to the coating weight, and then alloyed in an induction heating alloying furnace. , After the molten zinc layer on the surface disappears, up to a temperature of 300 ° C or lower up to 20 ° C
A method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance and press formability, which comprises cooling at a cooling rate of not less than 1 sec. 2. Plating is performed in a zinc bath containing 0.08 to 0.14 wt% of Al, and alloying treatment is performed in an induction heating type alloying furnace so that the furnace outlet plate temperature is 450 to 550 ° C. The method for producing a galvannealed steel sheet having excellent powdering resistance and press formability according to claim 1. 3. C ≦ 0.0030 wt%, Si ≦ 0.3
0 wt%, 0.05 wt% ≤ Mn ≤ 1.0 wt%, P ≤
0.06wt%, S ≦ 0.02wt%, 0.03wt%
≤ Sol. Al ≦ 0.06 wt%, N ≦ 0.0040w
t%, 0.040 wt% ≤ Ti ≤ 0.080 wt%,
Containing 0.003 wt% ≤ Nb ≤ 0.025 wt%,
And Ti * / [C] ≧ 7 where Ti * / [C] =% Ti * / (4 ×% C)% Ti * =% Ti-{(48/14) ×% N + (48 /
32) ×% S)}% C: C content (wt%)% Ti: Ti content (wt%)% N: N content (wt%)% S: S content (wt%) 2 ≦ ( % Ti /% Nb) ≦ 14 However, steel having a composition of% Ti: Ti content (wt%)% Nb: Nb content (wt%) and having a balance of Fe and inevitable impurities is hot-rolled and After cold rolling, in a continuous hot dip galvanizing line, the steel sheet is annealed at a temperature of 700 ° C or higher and A _C3 transformation point or less, then plated, and after the coating amount is adjusted, it is alloyed in an induction heating type alloying furnace. , After the molten zinc layer on the surface disappears, up to a temperature of 300 ° C or lower up to 20 ° C
1 / g ² or more of Fe-Zn alloy plating having an Fe content of 50 wt% or more is applied to the upper layer of the galvannealed coating film after cooling at a cooling rate of at least 1 / sec. A method for producing a galvannealed steel sheet having excellent ringability and press formability. 4. A plating is carried out in a zinc bath containing 0.08 to 0.14 wt% of Al, and an alloying treatment is carried out in an induction heating type alloying furnace so that a furnace outlet plate temperature is 450 to 550 ° C. The method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance and press formability according to claim 3.