JP2009280859A - Hot dip galvannealed steel sheet having excellent workability, plating adhesion, corrosion resistance and appearance quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot dip galvannealed steel sheet having excellent powdering resistance and corrosion resistance, free from the generation of linear alloying unevenness elongating to the rolling direction, and having excellent characteristics suitable for an automobile outer panel at high productivity with a Ti-containing extra-low carbon steel sheet having excellent deep drawability and ductility as an original sheet. <P>SOLUTION: In the hot dip galvannealed steel sheet, at least one side of an extra-low carbon steel comprising Ti is provided with a plating layer essentially consisting of Zn, having an Fe content of 8 to 13 wt.% and further comprising Al, Ni and inevitable impurities, and the respective coating weights of Al and Ni in the plating layer satisfy 190≤Al(Mg/m<SP>2</SP>)≤550 35≤Ni(mg/m<SP>2</SP>)≤350-(1/2)Al. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an alloyed hot-dip galvanized steel sheet having a plating layer excellent in powdering resistance and corrosion resistance, using a Ti-containing ultra-low carbon steel sheet excellent in deep drawability and ductility as a base plate. Since the present invention has an excellent appearance quality for an automobile outer plate and can be manufactured at a relatively low annealing temperature, the productivity is extremely high.

  Ti-containing ultra-low carbon steel sheets have been widely applied as cold steel sheets for automobiles or electrogalvanized steel sheets for automobiles because excellent deep drawability and ductility can be stably obtained. However, in recent years, when alloyed hot-dip galvanized steel sheets have become the mainstream of steel sheets for automobiles, it has become difficult to use Ti-containing ultra-low carbon steel sheets as original sheets. This is because Ti-containing ultra-low carbon steel sheets have clean crystal grain boundaries, so an outburst phenomenon occurs during the alloying reaction and partial alloying progresses. This is to cause plating peeling due to.

  In order to suppress the outburst phenomenon during the alloying reaction, it is effective to use ultra-low carbon steel to which Nb and Ti are added in combination (Patent Documents 1 and 2). If this steel plate is used, the powdering property becomes good, but the formability is inferior to that of the Ti-containing ultra-low carbon steel plate, and the productivity is inferior because the annealing temperature is high.

  As a conventional technique for suppressing the outburst of a Ti-containing ultra-low carbon steel sheet, for example, Patent Document 3 discloses that an initial alloy layer having a high Al concentration at the base iron-plating interface is obtained by increasing the Al concentration in the hot dip galvanizing bath. A method for localizing is disclosed. Non-Patent Document 1 reports that if the Al concentration in the plating bath is increased, the amount of Fe—Al-based compound forming the initial alloy layer increases.

  As a technology for improving the powdering properties of low-carbon cold-rolled steel sheets, Patent Document 4 can suppress the formation of ζ phase even when alloyed at low temperatures by adding a small amount of Al and Ni to the hot dip galvanizing bath. A method is disclosed. As a technology for improving the corrosion resistance of processed parts of galvannealed steel sheets using hot-rolled steel sheets as the original sheet, Patent Document 5 describes that after hot pre-plating the steel sheet surface to obtain a clean and active surface, hot dip galvanization is performed. A method of alloying is disclosed.

  As a technique for obtaining an alloyed hot-dip galvanized steel sheet having an excellent appearance using an Nb, Ti composite-added ultra-low carbon steel as a base plate, Patent Document 6 discloses Fe-Ni-Al- A method is disclosed in which after a Zn alloy layer is formed, the Zn alloy layer is dispersed by heat treatment to form a Zn—Fe alloy layer in which Ni and Al are dispersed.

As a conventional technique for improving the corrosion resistance, workability, and paintability of an alloyed hot-dip galvanized steel sheet using an ultra-low carbon steel sheet as the original sheet, Patent Document 7 describes that after pre-plating Ni on an annealed steel sheet, Al is used. A method is disclosed in which a specific ratio (%) of Al and Ni is contained in the plating layer by plating with a hot-dip galvanizing bath added in a trace amount and alloying by heating.
Japanese Patent Publication No. 61-32375 JP-A-5-106003 JP-A-8-269665 JP-A-4-13855 No. 2783452 JP 2006-299341 A JP 2007-84913 A Makoto Isobe, Akira Yasuda, Koji Yamato: CAMP-SIJ, Vol. 5, p1629 (1992)

However, these conventional techniques have problems.
The technique of Patent Document 3 suppresses outburst during alloying by the barrier effect of the initial alloy layer having a high Al concentration generated at the base metal-plating interface, and has a certain effect, but has a high Al concentration. Because the phases are localized, the effect is not perfect, and powdering cannot be suppressed by this method alone. Further, there is no effect on linear alloying unevenness described later.

  As reported in Non-Patent Document 1, the amount of Fe—Al-based compound forming the initial alloy layer increases as the Al concentration in the bath increases, but there is almost no difference in the amount generated due to the type of plating plate. In order to suppress outburst and linear alloying unevenness of Ti-containing ultra-low carbon steel sheets with a high alloying speed, a large amount of Fe-Al-based compound is required. Become. However, in this bath, almost the same amount of Fe—Al-based compound is produced even in other steel types having a low alloying rate. Then, in the case of a P-added BH steel sheet that originally has a low alloying speed, the alloying speed is further slowed down to a level that cannot be industrially produced. In the case of NbTi-sulc, the alloying rate is faster than that of the P-added BH steel, so that the production is possible but the productivity is remarkably lowered. That is, even if a high Al bath is pursued, it becomes a plating bath for Ti-sul only, and other steel types must be replaced with a low Al bath, which is not economical.

  The techniques of Patent Documents 4 and 5 are not effective even if applied to ultra-low carbon steel as they are. The technique of Patent Document 6 is effective in improving the appearance of the Nb and Ti composite-added ultra-low carbon steel sheet, but cannot suppress outburst and linear alloying unevenness of the Ti-containing ultra-low carbon steel sheet. The technique of Patent Document 7 has a certain effect in suppressing outburst of a Ti-containing ultra-low carbon steel sheet, but when subjected to severe forming processing, powdering occurs, and it is impossible to suppress linear alloying unevenness. .

  Here, the linear alloying unevenness of the Ti-containing ultra-low carbon steel sheet will be described. Ti-containing ultra-low carbon steel sheets often have non-recrystallized grains partially extending linearly in the rolling direction in the base metal structure after annealing due to variations in hot rolling finishing temperature and annealing temperature. In such a case, when alloying hot-dip galvanizing is produced by a normal method, alloying is fast on unrecrystallized grains and alloying is slow on recrystallized grains, so that linear alloying that can be visually discerned is possible. Unevenness (linear pattern) occurs. As a result, the appearance quality as an automobile outer plate is lowered. In order to prevent this, it is conceivable to reduce the variation in the hot rolling finishing temperature to the limit (for example, within 20 ° C. in the full width and the total length) or to raise the annealing temperature to prevent the remaining of non-recrystallized grains. The former is not difficult or economical in view of process capability, and the latter sacrifices the low annealing temperature, which is an advantage in the manufacture of Ti-containing ultra-low carbon steel sheets, and decreases productivity.

  In other words, in the prior art, an extremely low carbon steel plate containing Ti having excellent deep drawability and ductility is used as a base plate, which has excellent powdering resistance and corrosion resistance, and linear alloying unevenness extending in the rolling direction occurs. In addition, it has not been possible to provide an alloyed hot-dip galvanized steel sheet having excellent characteristics that can be applied to automobile outer plates with high productivity.

In order to solve the above-mentioned problems of the prior art, the present inventors applied Ni pre-plating to an annealed steel sheet disclosed in Patent Document 7, and then plated with a hot dip galvanizing bath to which a small amount of Al was added. Focusing on the technology for heating alloying, we have intensively studied for improvement. Although the role of Ni pre-plating was previously thought to be suppression of non-plating by preventing oxidation of the steel sheet surface, the present inventors considered the function of Ni pre-plating on the initial alloying reaction in the hot dip galvanizing bath. did. As a result, in the Ni pre-plating method, two types of Fe—Al-based compound and Ni ₂ Al ₃ can be generated as the initial alloy layer, and the former has a barrier effect that suppresses outburst and non-linear alloying unevenness. The latter is absent, and therefore, it is necessary to generate a certain amount or more of Fe-Al based compound in the initial alloy layer as a result of the initial alloying reaction in the bath. Ni ₂ Al ₃ is an initial alloy. The present inventors have found out a guideline that it should be generated in the plating layer without being generated in the layer.

  As a result of further studies, in order to satisfy these guidelines, the pre-Ni adhesion amount, the Al concentration in the plating bath, the Ni concentration in the plating bath, the Fe concentration in the plating bath, the plating bath temperature, and the penetration plate temperature are appropriate. As a result, it has been found that a certain amount or more of the Fe—Al-based compound can be produced alone in the initial alloy layer. Moreover, it discovered that the alloying hot-dip galvanization obtained by alloying this was what contained Al and Ni in the specific adhesion amount range, and came to complete this invention.

The present invention comprises the following (1) to (4).
(1) At least one side of an ultra-low carbon steel containing Ti has a plating layer containing Zn as a main component and having an Fe content of 8 to 13% by mass and further containing Al, Ni and inevitable impurities. And the amount of Al and Ni deposited on the plating layer is
190 ≦ Al (mg / m ² ) ≦ 550
35 ≦ Ni (mg / m ² ) ≦ 350− (1/2) Al
An alloyed hot-dip galvanized steel sheet excellent in workability, plating adhesion, corrosion resistance, and appearance quality characterized by satisfying
(2) At least one surface of an ultra-low carbon steel containing Ti has a plating layer containing Zn as a main component and having an Fe content of 8 to 13% by mass and further containing Al, Ni and inevitable impurities. And the amount of Al and Ni deposited on the plating layer is
250 ≦ Al (mg / m ² ) ≦ 500
50 ≦ Ni (mg / m ² ) ≦ 325- (1/2) Al
An alloyed hot-dip galvanized steel sheet excellent in workability, plating adhesion, corrosion resistance, and appearance quality characterized by satisfying
(3) An galvannealed steel sheet excellent in workability, plating adhesion, corrosion resistance, and appearance quality according to claim 1 or 2, wherein the plating layer has an average thickness of Γ layer of 1.5 µm or less. .
(4) Workability, plating adhesion, corrosion resistance according to any one of the above (1) to (3), wherein the adhesion amount of the plating layer is 30 g / m ² or more and 60 g / m ² or less. Alloyed hot-dip galvanized steel sheet with excellent appearance quality.

  Since the present invention product uses Ti-added ultra-low carbon steel with high grain boundary cleanliness, the outburst reaction at the time of heat alloying is suppressed after hot dipping, so excellent formability and plating adhesion At the same time. In addition, even when non-recrystallized grains are partially generated in the original sheet structure due to variations in the hot rolling finish temperature and annealing temperature of the original sheet, linear alloying irregularities (linear patterns) caused by these Will not occur. As a result, a steel plate having an appearance quality as an automobile outer plate can be stably produced at a relatively low annealing temperature, so that the yield and productivity are high and economical.

The present invention is described in detail below.
Examples of the ultra-low carbon steel containing Ti that is the subject of the present invention include those in which Ti is added to eliminate solid solution C, those in which a small amount of Nb is added, and P, Mn, Si, B, etc. Those that have been added to improve the strength, or those that contain a trace amount of a trump element such as Ni, Cu, Sn, Cr, etc. can be used. These are called Ti-sulc, TiNb-sulc, P-Ti-sulc, B-Ti-sulc, and the like. If the cleanliness of the grain boundary is expressed by ex-C, the ex-C of the target steel is about -0.002 or less (see Table 1 described later). On the other hand, so-called NbTi-sulc ("ex-C" in Table 1: -0.0011) disclosed in Patent Document 1 has good plating adhesion, corrosion resistance, and appearance quality regardless of the method of the present invention. Therefore, it is not a subject of the present invention. In the following description,% of component content means mass%.

  Specifically, as Ti-sulc, C: 0.005% or less, Si: 0.02% or less, Mn: 0.2% or less, P: 0.02% or less, S: 0.02% or less, Ti : 0.01-0.1%, Nb: What contains less than 0.001% can be used.

  Specifically, as TiNb-sulc, C: 0.005% or less, Si: 0.02% or less, Mn: 0.2% or less, P: 0.02% or less, S: 0.02% or less, Ti : 0.01-0.1%, Nb: The thing containing 0.001-0.01% can be used.

  As P-Ti-sulc, specifically, C: 0.007% or less, Si: 0.5% or less, Mn: 0.05 to 2.0%, P: 0.02 to 0.1%, S : 0.02% or less, Ti: 0.01 to 0.1%, Nb: less than 0.001%, B: 1 to 10 ppm.

  Specifically, as B-Ti-sulc, C: 0.005% or less, Si: 0.02% or less, Mn: 0.2% or less, P: 0.02% or less, S: 0.02% or less , Ti: 0.01 to 0.1%, Nb: less than 0.001%, B: 1 to 10 ppm.

  In addition, NbTi-sulc that is not the subject of the present invention is, in detail, C: 0.005% or less, Si: 0.02% or less, Mn: 0.2% or less, P: 0.02% or less, S: 0.02% or less, Ti: 0.01 to 0.1%, Nb: more than 0.01%, 0.03% or less.

The plated layer of the alloyed hot dip galvanizing of the present invention has Zn content of 8 to 13% by mass and further contains Al, Ni and unavoidable impurities. If the Fe content is less than 8% by mass, the corrosion resistance after coating becomes poor because it is not alloyed, and the slidability becomes poor because of the ζ phase, causing flaking during processing. If the Fe content exceeds 13% by mass, the Γ phase becomes thick and the powdering properties deteriorate. In order to satisfy the flaking property, the powdering property, and the corrosion resistance after coating to a higher degree, the Fe content is preferably 9 to 12% by mass. In order to keep the powdering property good, the Γ phase thickness is preferably 1.5 μm or less. More preferably, it is 1 μm or less. When used as a steel sheet for automobiles, it is preferable that the adhesion amount of the plating layer is 30 g / m ² or more and 60 g / m ² or less. If it is less than 30 g / m ² , the corrosion resistance is insufficient. If it exceeds 60 g / m ² , the continuous spotting property at the time of spot welding is lowered.

There exists a suitable range as shown in FIG. 1 for the adhesion amount of Al and Ni contained in the plating layer. The basis for this will be described in turn below.
The Ti-containing ultra-low carbon steel plate that is the subject of the present invention has a clean crystal grain boundary, and therefore an outburst phenomenon is likely to occur during the alloying reaction. In addition, non-recrystallized grains extending linearly in the rolling direction are often partially formed in the annealed steel structure, and linear alloying irregularities (linear patterns) are likely to occur. In order to suppress these, it is necessary to form an appropriate initial alloy layer by controlling the initial alloying reaction in the hot dip galvanizing bath.

The inventors of the present invention have focused on the technique of performing Ni pre-plating on an annealed steel sheet, then plating with a hot-dip galvanizing bath with a small amount of Al added thereto, and forming a heat alloy. The conversion reaction was examined. As a result, the following knowledge was obtained.
1) The initial alloy layer, two types of Fe-Al compound and _Ni 2 Al ₃ are able to form. This is because, in the plating bath, Fe eluted from the steel plate and Ni eluted from the pre-plating react competitively with Al in the plating bath.
2) Fe—Al-based compounds have a barrier effect that suppresses outburst and non-linear alloying, but Ni ₂ Al ₃ has no effect.
3) When NbTi-sulc is used as the original plate, outburst or non-linear alloying does not occur even if the above two kinds of compounds are mixed in the initial alloy layer. This is because with NbTi-sul, the Fe diffusion rate during alloying is slow.
4) When the Ti-containing ultra-low carbon steel plate is used as the original plate, outburst and uneven linear alloying are likely to occur if the above two types of compounds are mixed in the initial alloy layer. This is because a Ti-containing ultra-low carbon steel sheet has a very high Fe diffusion rate during alloying.
5) Therefore, in order to suppress outburst and linear alloying irregularity using a Ti-containing ultra-low carbon steel plate as a base plate, an Fe—Al-based compound is generated alone as a certain amount as an initial alloy layer, and Ni ₂ Al ₃ should be generated in the plating layer, not in the initial alloy layer.

  Therefore, the manufacturing conditions in the pre-Ni plating method for satisfying the above 5) were studied earnestly. As a result, it is necessary to optimize the pre-Ni plating amount, the Al concentration in the plating bath, the Ni concentration in the plating bath, the Fe concentration in the plating bath, the penetration plate temperature, and the plating bath temperature according to the Fe diffusion rate for each steel type. I found out. An appropriate range satisfying the above 5) and the reason thereof will be described below while comparing with the respective preferable ranges disclosed in Patent Document 7.

a) Pre-Ni plating amount: 0.05 to 0.25 g / m ² is appropriate By reducing the pre-Ni plating amount from 1) above, the Fe and plating eluted from the steel plate in the vicinity of the surface of the ground iron in the plating bath Reaction in the bath with Al in the bath can be preferentially caused. As a result, the Fe—Al-based compound can be generated alone as the initial alloy layer.
b) Al concentration in plating bath: 0.185 to 0.195 mass% is appropriate Ti-containing ultra-low carbon steel sheet has a high Fe elution rate in the plating bath. Therefore, more Fe—Al-based compounds can be generated by increasing the Al concentration in the bath.
c) Ni concentration in the plating bath: 0.05 to 0.06% by mass is appropriate When the steel plate after pre-Ni plating is immersed in hot dipping, the elution of Ni occurs abruptly. Be inhibited. In order to prevent this, the Ni concentration in the plating bath is set high.
d) Fe concentration in the plating bath: 0.01 to 0.02% by mass is appropriate In order to promote elution of Fe when the steel plate after pre-Ni plating is immersed in hot dipping, contrary to c) above. In addition, the Fe concentration in the plating bath is set low.
e) Invasion plate temperature: 405 to 415 ° C is appropriate For the same reason as c) above, the invasion plate temperature is set lower. When the penetration plate temperature is high, Ni elution occurs abruptly. On the other hand, the elution of Fe can be promoted by setting the penetration plate temperature slightly lower than the plating bath temperature.
f) Plating bath temperature: 430 to 440 ° C. is appropriate For the same reason as c) above, the plating bath temperature is also set lower. When the bath temperature is high, Ni elution occurs abruptly.

  FIG. 2 schematically shows the alloying reaction in the plating bath and the alloying reaction after heating in the inventive example and the comparative example. The initial alloying reaction in the plating bath is completed in the state after wiping. When this is heat-alloyed, alloying occurs uniformly in the example of the present invention and the thickness of the Γ layer becomes uniform, whereas in the comparative example, alloying occurs nonuniformly, resulting in uneven outburst and linear alloying. Occurs and the Γ layer becomes thick and non-uniform.

Here, there is no increase or decrease in the adhesion amount (mg / m ² ) of Al and Ni in the plating layer from the state after completion of wiping to the completion of heating alloying. Therefore, the adhesion amounts of Al and Ni after the completion of alloying and the relationship between the two values can only take values reflecting the state after completion of wiping, that is, the state at the time of completion of initial alloying. Therefore, the inventors conducted plating experiments under various production conditions while paying attention to the above a) to f). At this time, by analyzing the composition and structure of both the sample after completion of wiping (GI stopper) and the sample after completion of alloying (GA material), and evaluating the performance of the GA material, the above 5) It was confirmed that the suitable ranges of the Al and Ni adhesion amounts of the GI stopper material satisfying the above and the GA material satisfying the target performance coincided. The preferred range will be described below.

Plating layer Al coating weight of GA material, the amount of the initial alloy layer Fe-Al compound of GI stopper member and ^{corresponds, 190mg / m 2 ~550mg / m} 2 are preferred. If it is less than 190 mg / m ² , the amount of Fe—Al-based compound produced is insufficient, and outburst and linear alloying unevenness cannot be suppressed. Even when the hot rolling conditions and annealing conditions vary greatly, it is more preferable that the Al adhesion amount is 250 mg / m ² or more so as not to cause linear alloying unevenness. On the other hand, if it exceeds 550 mg / m ² , the alloying speed is remarkably slow due to the barrier effect of the Fe—Al-based compound, and the alloying temperature must be increased to a high temperature, for example, 600 ° C. or higher, or the sheet feeding speed must be slowed. It is not economical. More preferably, it is 500 mg / m ² or less.

The adhesion amount of Ni in the plating layer of the GA material corresponds to the amount of Ni ₂ Al ₃ generated after the completion of the initial alloying reaction of the GI stopper. At the same time, it corresponds to the amount of pre-Ni plating before bath penetration, and the value obtained by subtracting the amount of Ni dissolved and diffused offshore in the bath from the amount of pre-Ni plating is the amount of Ni deposited in the plating layer of the GA material. . When the pre-Ni plating amount is set to 0.05 g / m ² or more, the Ni adhesion amount in the plating layer of the GA material is 35 mg / m ² or more. If it is less than 35 mg / m < ² >, the amount of pre-Ni plating is less than 0.05 g / m < ² >, and non-plating will occur when subsequently performing hot dip galvanization. On the other hand, when the adhesion amount of Ni in the plating layer of the GA material exceeds 350- (1/2) Al (mg / m ² ), Ni ₂ Al ₃ is generated in the initial alloy layer of the GI stopper. Therefore, the Fe-Al compound is not alone. When such a GI stopper is heated and alloyed, outburst and linear alloying are likely to occur. More preferably, 50 mg / ^{m 2} or more and less 350- (1/2) Al (mg / m 2).

The adhesion amount of Al and the adhesion amount of Ni in the plating layer of the GA material also affect the corrosion resistance of the GA. The reason is not clear, but when Al and Ni are uniformly dispersed in the plating layer by a certain amount or more during the alloying process, there is an effect of improving the corrosion resistance of the plating layer. However, when the Ni adhesion amount is 300 mg / m ² or more, or when the Ni adhesion amount is 190 mg / m ² or more and the Ni / Al ratio is 1.45 or more, that is, Ni is more than the Ni / Al ratio of Ni ₂ Al _3. In this case, Ni is likely to concentrate on the plating surface layer during the alloying process, and an adverse effect on the corrosion resistance is observed.
Further, when both the Al adhesion amount and the Ni adhesion amount are less than 190 mg / m ² , the effect of improving the corrosion resistance by Al and Ni is insufficient.

  Of the operating conditions shown in the above a) to f), a) and e) can be changed in a chance-free manner depending on the steel type of the plating base plate. Therefore, NbTi-sulc and P-added BH steel plate were used as the plating base plate, and a) and e) were changed while the conditions of b) to d) and f) were fixed within the above ranges. It was confirmed that GA has a range in which GA can be produced under industrially producible alloying conditions. That is, by using a single plating bath satisfying b) to d) and f) and optimizing the conditions of a) and e) according to the steel type, the Ti-added ultra-low carbon steel sheet, NbTi-sulc And GA of P-added BH steel sheet can be made separately.

Next, the present invention will be described in detail by way of examples.
(1) Test steel material Table 1 shows the components of the annealed ultra-low carbon steel plate. NbTi-sulc was used as a comparative material. Each plate thickness is 0.6 mm.

(2) Plating conditions The test material was degreased by immersing it in an alkaline aqueous solution of NaOH 50 g / l and 65 ° C., and then immersed in an aqueous solution of H ₂ SO ₄ 100 g / l and 30 ° C. for 5 s and pickled. .
Then, Ni pre-plating was performed at a current density of 30 A / dm ² using a Ni plating bath having a composition shown in Table 2 (bath temperature 60 ° C., pH 2.7). This was heated to the intrusion plate temperature at a rate of temperature increase of 50 ° C./s in a 4% H ₂ —N ₂ atmosphere, and immediately immersed in a hot dip galvanizing bath having the composition and bath temperature shown in Table 3 to be described later. The immersion time was 2.5 to 3.5 s. After getting out of the bath, the basis weight was controlled by wiping and immediately alloyed. The heating rate was 50 ° C./s, the alloying temperature was the value shown in Table 3, without soaking time, and after 15-20 s slow cooling at 5 ° C./s, it was cooled at 25 ° C./s for 5-7 s. Then, 0.3% temper rolling was performed. A sample (GI stopper) that was not heated and alloyed after being removed from the bath was also prepared and used for analysis of the initial alloy layer.
The plating conditions of the comparative example were as follows. Comparative Examples 35 to 40 in Table 3 are based on the pre-Ni plating method described in Patent Document 7. An annealed ultra-low carbon steel sheet was subjected to hot dip galvanization and heating / alloying after alkali degreasing, pickling and Ni pre-plating. On the other hand, the comparative examples 41-43 manufacture the ultra-low carbon steel plate before annealing with a normal method in the hot dip galvanized steel plate manufacturing line with an annealing furnace, without performing pre Ni plating. The annealing conditions are 740 ° C. and 60 s in a 5% H ₂ —N ₂ atmosphere. Immediately after annealing, hot dip galvanizing and heating alloying were performed.

(3) Analysis After dissolving only the plating layer of the GI stopper using fuming nitric acid and confirming that there was no over-dissolution by SEM, the remaining initial alloy layer was analyzed by X-ray diffraction, and Fe-Al compound The presence or absence of (Fe ₂ Al ₅ Zn _x ) and Ni ₂ Al ₃ was determined. For the determination of the Fe—Al compound (Fe ₂ Al ₅ Zn _x ), the diffraction line of d = 2.85 is used for the determination of d = 3.80 and Ni ₂ Al ₃ , and other diffraction lines are also referred to. While judging. The GA material was dissolved in 5% hydrochloric acid containing an inhibitor, and the adhesion amount of Zn, Fe, Al, and Ni was determined by ICP. The total of these was taken as the amount of adhesion of the plating layer.
(4) Performance evaluation The thickness of the Γ layer was determined by etching the plated cross section with an etching agent such as nital (alcohol + nitric acid) and observing the vicinity of the ground iron interface with an optical microscope. The samples were set to N = 3, and for each sample, 10 points of average visual fields that were sufficiently separated were observed to measure the thickness, and the average of the whole was taken as the Γ layer thickness.
Evaluation of plating adhesion was performed as follows. The specimen was cut into 50 mm × 200 mm, and after applying press oil, a draw bead test was performed with a load of 400 kgf (about 3922.66 N). The bead passing portion was peeled off and the degree of blackening of the tape was measured. The larger the degree of blackening, the more intense the powdering and the poorer the plating adhesion.
4: Blackening degree 2 or less 3: Blackening degree 2 or more, less than 4 2: Blackening degree 4 or more, less than 6 1: Blackening degree 6 or more Evaluation of the linear pattern is performed per 100 mm in the width direction of the test material. The number of patterns that can be visually confirmed is evaluated as follows.
4: No linear pattern 3: 1 to 5 2: 6 to 10: more than 1: 10 Corrosion resistance was evaluated as follows. The test material was cut into 70 mm × 150 mm, and alkaline degreasing (Nihon Parkerizing, FC-E2001), chemical conversion treatment (Nihon Parkerizing, PB-SX35), cationic electrodeposition coating (Nihon Paint, PN120M, film thickness 20 μm) After going, a cut was made in the center to reach the railway. This was subjected to a corrosion acceleration test for 4 weeks by the JASO M609-91 method, and the film swelling width from the cut was measured.
4: coating film swelling width less than 1 mm 3: coating film swelling width of 1 mm or more and less than 2 mm 2: coating film swelling width of 2 mm or more and less than 4 mm 1: coating film swelling width of 4 mm or more Grade) was determined as follows according to the annealing temperature necessary to secure a material suitable for the grade. The lower the annealing temperature, the better the productivity.
4: Annealing temperature less than 750 ° C 3: Annealing temperature 750 ° C or more and less than 760 ° C 2: Annealing temperature 760 ° C or more and less than 770 ° C 1: Annealing temperature 770 ° C or more

Table 3 shows the performance evaluation results.

In all of the products according to the present invention, the initial alloy layer of the GI stopper is formed of only an Fe—Al-based compound, and the adhesion amount (mg / m ² ) of Al and Ni in the GA plating layer is surrounded by a one-dot chain line in FIG. Or within the range surrounded by a broken line. As a result, while using a Ti-containing ultra-low carbon steel plate excellent in deep drawability and ductility as an original plate, it can be manufactured with high plating adhesion, appearance quality, and corrosion resistance, and high productivity.

On the other hand, in Comparative Examples 35 to 37 and 40, the adhesion amount (mg / m ² ) of Al and Ni is not within the range surrounded by the one-dot chain line in FIG. Fe—Al-based compound and Ni ₂ Al ₃ are mixed, and as a result, the plating adhesion and the appearance quality are inferior to those of the examples of the present invention. Comparative Examples 38 and 39 are comparative examples using NbTi-sulc. Regardless of whether the adhesion amount of Al and Ni (mg / m ² ) is within the range surrounded by the one-dot chain line in FIG. 1, excellent plating adhesion and appearance quality can be obtained, but the annealing temperature is high and the productivity is high. Inferior to Moreover, it is inferior to Ti containing ultra-low carbon steel sheet in deep drawability and ductility.

  In Comparative Example 41, Ni was added to the plating bath by the method of Patent Document 4 instead of the pre-Ni plating method. The initial alloy layer is composed only of an Fe—Al-based compound, but its production amount is insufficient, and it is not possible to suppress outburst and linear alloying unevenness due to heating alloying. Further, Ni added in the bath concentrates on the plating surface layer in the process of alloying, and adversely affects the corrosion resistance.

  In Comparative Examples 42 and 43, the Al concentration in the plating bath was changed not by the pre-Ni method but by the usual Sendzimir method. Comparative Example 42 is a bath composition and plating conditions adopted in many steel types including NbTi-sulc, but when applied to Ti-sulc, the amount of Fe-Al-based compound produced in the initial alloy layer is other than that. It can be obtained only to the same extent as the steel type, and it is impossible to suppress outburst and linear alloying unevenness due to heat alloying. In Comparative Example 43, the Al concentration in the plating bath is increased. Although the amount of Fe-Al compound generation has increased, it is still insufficient. Even if a higher Al addition bath is pursued, it becomes a plating bath for Ti-sul only, and other steel types must be replaced with a low Al bath, which is not economical.

  In order to clarify the inventive step of the present invention, the same examples of steel types and comparative examples will be compared side by side. The conventional technique based on the Sendzimir method is Comparative Example 42, the conventional technique based on the pre-Ni method of the same steel type is Comparative Example 36, and the example of the present invention is Example 18. The thickness of the Γ layer is 2.5 μm, 1.7 μm, and 0.7 μm in order, and accordingly, the plating adhesion and the linear pattern are greatly improved. In addition, the corrosion resistance is greatly improved as compared with the prior art.

  Since excellent deep drawability and ductility can be stably obtained by the present invention, Ti-containing ultra-low carbon steel sheet, which has been widely applied as a cold-rolled steel sheet for automobiles, can also be used as an original sheet for galvannealed steel sheets. It can be used. This means that not only the quality and performance of automobile steel sheets can be improved, but also in the steel industry, cold rolled steel sheets and galvannealed steel sheets can be integrated. Therefore, its industrial utility value is extremely large.

It is a graph which shows the relationship of the adhesion amount of Ni and Al in the plating layer which concerns on the Example of this invention. However, within the one-dot chain line in the graph, the range of the respective adhesion amounts of Ni and Al of the invention according to claim 1 of the claims is shown, and within the broken line is the respective adhesion amount of Ni and Al of the invention according to claim 2 Each range is shown. It is a schematic diagram of the initial alloying reaction and the alloying reaction after a heating in the plating bath of the example of this invention and a comparative example.

Claims (4)

At least one side of the ultra-low carbon steel containing Ti has a plating layer containing Zn as a main component and having an Fe content of 8 to 13% by mass and further containing Al, Ni and inevitable impurities, Each adhesion amount of Al and Ni in the plating layer is
190 ≦ Al (mg / m ² ) ≦ 550
35 ≦ Ni (mg / m ² ) ≦ 350− (1/2) Al
An alloyed hot-dip galvanized steel sheet excellent in workability, plating adhesion, corrosion resistance, and appearance quality characterized by satisfying At least one side of the ultra-low carbon steel containing Ti has a plating layer containing Zn as a main component and having an Fe content of 8 to 13% by mass and further containing Al, Ni and inevitable impurities, Each adhesion amount of Al and Ni in the plating layer is
250 ≦ Al (mg / m ² ) ≦ 500
50 ≦ Ni (mg / m ² ) ≦ 325- (1/2) Al
An alloyed hot-dip galvanized steel sheet excellent in workability, plating adhesion, corrosion resistance, and appearance quality characterized by satisfying   3. The galvannealed steel sheet excellent in workability, plating adhesion, corrosion resistance, and appearance quality according to claim 1 or 2, wherein the plating layer has an average thickness of Γ layer of 1.5 μm or less. The adhesion amount of the plating layer is 30 g / m ² or more and 60 g / m ² or less, which is excellent in workability, plating adhesion, corrosion resistance, and appearance quality according to any one of claims 1 to 3. Alloyed hot-dip galvanized steel sheet.

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