JP5009035B2 - Manufacturing method of high-tensile alloyed hot-dip galvanized steel sheet with excellent appearance - Google Patents

Description

  The method of the present invention relates to a method for producing a high-tensile alloyed hot-dip galvanized steel sheet having an excellent appearance.

  Alloyed hot-dip galvanized steel sheets are excellent in corrosion resistance, paint adhesion, etc., and are widely used in building materials, home appliances, etc. mainly on steel sheets for automobiles.

  In particular, as rust-proof steel sheets for domestic automobiles, there are extremely many alloyed hot-dip galvanized steel sheets, and materials are being developed from various viewpoints for automobile applications.

  There are many required qualities and performances for automotive applications, but especially for the body constituting the outer surface of the vehicle body, good appearance and moldability are emphasized. The good appearance is the appearance quality after assembling as an automobile and painting, and if the rust-proof steel plate has slight unplating or dirt, the appearance quality after painting is greatly impaired. In addition, with the recent increase in automobile crash safety, there is a high demand for high-tensile steel sheets.

  In response to these demands, steel companies have promoted hardware measures for hot-dip plating production lines and soft measures for steel materials. There are various types of hot dip plating lines, but there are two types when roughly classified. These are the old-style non-oxidation furnace-reduction furnace system and the total reduction furnace system.

  The feature of the non-oxidation furnace-reduction furnace method is that the cold rolled steel sheet with the rolling oil adhered is burned and removed in a non-oxidizing furnace, so there is no degreasing section on the entry side before annealing, and no oxidation The rolling oil can be incinerated in the furnace and continuously hot-plated. Although it is reasonable as a method of hot dipping, it is not suitable for applications that require high appearance quality such as automobile bodies, because the plating appearance stains due to carbon on the steel sheet remaining after annealing occur.

  For this reason, in recent years, instead of a non-oxidizing furnace, there is a degreasing section on the entry side, so that the all-reduction furnace method that cleans the oil adhering to the steel plate and prevents it from being brought into the furnace has become the mainstream. Currently.

  On the other hand, from the viewpoint of formability and high strength, steel sheet formability improvement and high strength have progressed, and in order to achieve both of these, the addition of C, Mn, P, Si, etc. mainly increases the strength. In response to user needs. In order to secure strength and increase weight reduction, high-strength steel sheets added with Mn, P, and Si have been expanded from applications for internal parts of automobiles to applications requiring high appearance quality such as the aforementioned body.

  However, Mn, P, and Si added in order to achieve both formability improvement and high strength, when the steel sheet is heated to the iron transformation region, for example, around 800 ° C. in the hot rolling process, annealing process, etc. It is characterized by segregation at the boundary or precipitation as an oxide. For this reason, since the P and Si concentration distribution on the steel plate surface generated in the hot rolling and annealing furnace remains plated, this concentration variation causes the reaction between zinc and iron in the hot alloying process after hot dipping. Disperse, causing streaks and dots. This pattern also occurs in the all-reduction furnace method because the reduction atmosphere of the annealing reduction furnace only reduces iron and cannot suppress the oxidation of P and Si. Furthermore, this pattern also affects the chemical conversion treatment and coating after molding, and the same pattern is raised. Patterns of high-strength steel sheets with Mn, P, and Si added were acceptable to some extent if used for invisible automobile internal parts, but for applications that require high appearance quality per person such as the body. It was a big problem because I couldn't stand it.

  With respect to this problem, in Patent Document 1 and Patent Document 2, the variation is eliminated by removing the surface concentrate of P or Si generated by annealing by a technique such as pickling or grinding. However, in Patent Document 1, since pickling is performed after annealing, a configuration different from that of a general hot dipping line in which molten metal mainly composed of hot dip galvanizing is allowed to pass through without being brought into contact with the atmosphere is required. In addition, in Patent Document 2, all of the equipment restrictions are extremely large, such as requiring a grinding process after passing through the molten metal after completion of annealing. Patent Document 3 attempts to improve the appearance by controlling the S content in the steel, but in addition to forcing desulfurization costs, it is basically related to ultra-low carbon mild steel, and Mn, P, and Si are added. The effect is never enough in high-strength steel. In patent document 4, the dispersion | variation in alloying is suppressed by providing a Mn compound to a steel plate prior to annealing. However, the application method is application of an aqueous solution, and the problem of picking up the oxide to the hearth roll is inevitable because it is Mn oxide rather than application of metal Mn, and the risk to the outer plate is great. Moreover, in patent document 5, the plating adhesion defect and alloying defect are improved by carrying out pre electroplating of Ni etc. prior to annealing. Since electroplating is a means for forcibly electrodepositing with electricity, it is uniformly deposited regardless of the presence or absence of local P or Si surface concentrates produced by annealing. Therefore, in the electroplating method which is an advantage to uniformly adhere, the degree of the effect of the metal imparted by the portion where the surface concentration of Mn, P, Si is locally concentrated and the portion where it is not concentrated is equivalent, The variation in alloying at the portion where the surface concentration of Mn, P, or Si occurs cannot be eliminated.

JP-A-7-70723 Japanese Patent No. 2576329 JP 2005-2363 A JP-A-11-131204 Japanese Unexamined Patent Publication No. 57-188862

  In view of the above problems, the present invention improves the variation in alloying caused by the surface concentration of Mn, P, Si, etc. contained in high-strength steel sheets and the accompanying deterioration in surface quality in the reduction furnace type hot-dip plating equipment. An object of the present invention is to provide a method for producing a high-tensile alloyed hot-dip galvanized steel sheet having excellent appearance quality.

  When the present inventors investigated the pattern part by the density distribution of P, Mn, and Si on the surface of the high-strength steel sheet, alloying was delayed locally in the pattern part, and the plating thickness was partially reduced. As a result, it was found that streaks were generated. Next, when the cause of the delay in alloying was examined, it was found that a difference in alloying reaction occurred due to the concentration of Mn, P, and Si, resulting in a difference in plating thickness.

  Therefore, in order to suppress the generation of a pattern due to the difference in the speed of the alloying reaction, it is necessary to consider a means for suppressing the surface concentration or preventing the difference in the alloying speed even when the surface is concentrated. As for the former, it is not realistic to make element concentration zero on the steel sheet surface in industrial production, and the latter was further studied.

  The alloying reaction, which is delayed by surface concentration, is caused by the Fe-Al alloy layer (barrier layer) generated by Fe in the steel sheet and Al in the molten zinc generated when the steel sheet is immersed in molten zinc. This is due to the fact that the partial concentration causes the decay delay, and when the Mn, P, and Si in the steel are high, or when the surface is locally concentrated, the alloying reaction is delayed by the decay of the barrier layer. We found that delays and differences occur. Therefore, simply disintegrating the barrier layer is not a means of reducing the difference in the alloying reaction, but preferentially speeds up the disintegration of the surface-enriched barrier layer to match the disintegration rate of the other portions. is required.

  Next, when the means for preferentially accelerating the breakdown of the barrier layer in the portion where Mn, P, and Si are surface concentrated is examined, Ni and Co are preferentially applied to the surface concentrated portion by substitution plating. It has been found that Ni or Co adheres to promote the collapse of the barrier layer, and that there is a correlation between the conditions of displacement plating and the steel components.

  The present invention has been made based on the above findings, and the gist of the present invention is as follows.

(1) In mass%,
C: 0.0001 to 0.15%,
Si: 0.005 to 1.0%,
Mn: 0.001 to 2.5%,
P: 0.005-0.2%
S: 0.0001 to 0.03%,
Al: 0.001 to 4%,
N: 0.0001 to 0.02%,
And a high-tensile steel plate containing P and Si with Si + P ≦ 1.0% and containing residual Fe and inevitable impurities using an all-reduction furnace type hot-dip galvanizing equipment, In a manufacturing method of an alloyed hot-dip galvanized steel sheet, which is made to pass through a molten metal mainly composed of hot-dip galvanized plating without being exposed to the atmosphere, and then heat-alloyed, Ni or Co in advance by substitution plating before annealing. Is in a method for producing a high-tensile galvannealed steel sheet having an excellent appearance, characterized in that 0.1 g / m ² or more and 1.0 g / m ² or less are attached in terms of metal amount.

(2) The displacement plating of (1) further satisfies the following formula (A), and is a method for producing a high-tensile alloyed hot-dip galvanized steel sheet having an excellent appearance. {[t] · (Si / 28 + P / 31 + C / 12)} / {[C] · [T]} ≦ 1 × 10 ^−4.
Here, [C]: Solution concentration mol / l of metal used for displacement plating, [T]: Temperature during displacement plating (K), [t]: displacement plating time (seconds)

(3) In the steel plate according to (1) or (2), further in mass%,
Nb: 0.001 to 1%,
Ti: 0.001 to 1%,
V: 0.001 to 1%,
Zr: 0.001 to 1%,
Hf: 0.001 to 1%,
Ta: 0.001 to 1%,
Ce: 0.001 to 1%,
Mo: 0.001 to 1%,
Cr: 0.001 to 1%,
Ni: 0.001 to 1%,
Cu: 0.001 to 0.5%,
Co: 0.001-1%,
W: 0.001 to 1%,
Mg: 0.001 to 0.1%,
B: 0.0001 to 0.01%
Y: 0.001 to 1%,
REM: 0.0001 to 0.01%,
Ca: 0.0001 to 0.01%,
In the manufacturing method of the high-tensile-alloyed hot-dip galvanized steel sheet excellent in appearance characterized by containing one or more of the above.

  As described above, the present invention provides means for eliminating the patterns that are likely to occur in high-tensile alloyed hot-dip galvanized steel sheets and stabilizing the appearance quality strictly required for automobile outer panels. The contribution of is extremely large.

  Hereinafter, the present invention will be described in detail.

  First, the hot dip galvanizing equipment in the present invention is premised on being a total reduction furnace.

  Here, the total reduction system refers to a hot dipping facility in which a reducing atmosphere for Fe, for example, an atmosphere such as a hydrogen-nitrogen atmosphere constitutes the entire annealing furnace.

  The reason why Ni and Co imparted to the steel plate prior to annealing is preferentially replaced by plating on the concentrated portion of Mn, P, Si, etc. on the steel plate surface is not clear, but is presumed as follows. Displacement plating is a reaction in which metal precipitates due to a potential difference between the iron that is the base metal component of the steel sheet and the metal that is more precious than the iron to be replaced. Cheap. When Mn, P, Si, or the like is added to the steel, a local battery is formed in the steel plate, and iron is likely to elute locally, so that Ni or Co is preferentially substituted at the concentrated position.

  Displacement plating is an electrochemical reaction in which a metal precipitates due to a potential difference between iron and a metal ion having a potential nobler than iron and the iron dissolves, and an electric current is forcibly applied to exchange electrons with iron. It is a plating different from the electroplating that does not need to be performed. In displacement plating, the reaction proceeds by bringing a steel sheet into contact with an aqueous solution containing metal ions having a potential more noble than iron, and it is not necessary to apply any current. When energized from the outside, even if the current is weak, it is distinguished as electroplating and the effect on the present invention does not appear. In addition, electroless plating that does not cause electron exchange between the base material and metal ions in the solution by adding a reduction auxiliary agent is distinguished from displacement plating because electron exchange with the base material is not performed. The effect of the invention does not appear.

  The reason why the Ni or Co imparted causes the barrier layer to collapse is not clear, but it is assumed that the iron constituting the barrier layer is partly replaced and is easily collapsed.

The amount of Ni or Co deposited by displacement plating is preferably 0.1 g / m ² or more, and if it is less than 0.1 g / m ² , the effect of canceling the pattern is poor. Moreover, since an effect will be saturated even if it gives 1.0g / m < ² > or more, considering cost, it shall be 1.0 g / m < ² > or less. Considering that the time for performing substitution plating in the line is about several seconds, 0.1 g / m ² or more and 0.5 g / m ² or less are easy to operate, and more preferable.

  Next, the steel components of the galvannealed steel of the present invention will be described.

C: 0.0001 to 0.15%
C is a strengthening element of steel, but if the amount of C exceeds 0.15%, it tends to become brittle, so the upper limit is made 0.15%. In addition, the occurrence of patterns such as linear marks is particularly large in C: 0.0051% or more, and the present invention is more effective for a steel sheet containing a C amount of 0.0051% or more. In addition, since there is also a kind of ultra-low carbon steel in the high-tensile steel plate, a lower limit is not particularly defined, but unavoidably 0.0001% or more is included.

Si: 0.005 to 1.0%
Si is an element having the effects of solid solution strengthening and deoxidation of steel. However, if over 1.0% is added, uneven plating or non-plating occurs during hot dip galvanizing, and the pattern cannot be completely eliminated even by means of the present invention, so the upper limit is made 1.0%. Although the lower limit is not particularly defined, it is one of the few elements that can be strengthened without deteriorating the material such as the Rankford value, and is a strengthening element advantageous in terms of cost. 0.005% for high strength of steel It is preferable to add more.

Mn: 0.001 to 2.5%
Mn is also an element having the effect of increasing the strength of steel and deoxidizing. However, if added over 2.5%, it becomes brittle and material such as elongation falls. Further, not only the wettability of the plating is hindered during hot dip galvanization, but also the plating adhesion is deteriorated, and the plating pattern cannot be lost even if displacement plating is used, so the upper limit is set to 2.5%. If less than 0.001%, the strength cannot be secured, so the lower limit is made 0.001%.

P: 0.005-0.2%
P is one of the elements essential for increasing the strength of steel. In particular, it is a few elements that can increase the strength without deteriorating the material such as the Rankford value, and 0.005% or more is preferable from the viewpoint of increasing the strength of the steel. However, if added over 0.2%, embrittlement is likely to occur, plating unevenness or non-plating occurs during hot dip galvanizing, and the pattern cannot be completely eliminated even by the means of the present invention, so the upper limit is set to 0. 2%. In consideration of the fact that 340 MPa to 980 MPa is frequently used as a high-strength steel sheet for automobiles, 0.01 to 0.1% is more preferable in consideration of increasing strength and brittle balance.

S: 0.0001 to 0.03% or less S is an impurity, and it is desirable to reduce the amount because it deteriorates workability and hot brittleness. However, since the extremely low is economically disadvantageous, the lower limit is set to 0.0001%. . Further, if added over 0.03%, the weldability and the manufacturability during casting and hot rolling are adversely affected, so the content is made 0.03% or less.

Al: 0.001 to 4%
Al is added in an amount of 0.001% or more in order to improve the deoxidized strength ductility balance or to promote the alloying behavior of the plating. However, if it exceeds 4%, the weldability, plating wettability and manufacturability are adversely affected, so the upper limit was made 4%.

N: 0.0001 to 0.02%
N is an impurity, and it is desirable to reduce the N content because it degrades workability and hot brittleness. However, since the extremely low is economically disadvantageous, the lower limit is set to 0.0001%. Moreover, even when adding for the purpose of improving bake hardenability and strength, if it exceeds 0.02%, the material deterioration is larger, and the upper limit is made 0.02%.

  In addition, the high-tensile steel plate which this invention makes object is Si + P <= 1.0%. FIG. 1 shows the Si concentration in steel, the P concentration in steel, and the region where non-plating or material deterioration occurs. ○ in the figure indicates that no abnormalities such as unplating or pattern were observed, × indicates that there was no significant plating or patterning, ▲ indicates that there was a problem with the material, and ▼ indicates that there was a problem with the material This is a plot of an example where there was a problem and the occurrence of non-plating or pattern was remarkable. When Si + P exceeds 1.0%, uneven plating or non-plating occurs during hot dip galvanizing, and the pattern cannot be completely eliminated even by the means of the present invention. Further, if P exceeds 0.2%, there is a problem in the material, so it is set below this. The range of the white region in FIG. 1 corresponds to the range of the present invention.

Further, in the present invention, the metal ion concentration C (mol / l) in the aqueous solution of the metal to be displacement plated, the temperature T (K) for displacement plating, the time t (second) for displacement plating, and the steel component C concentration (%) ), P concentration (%), and Si concentration (%), it is more preferable to satisfy the following formula (A). FIG. 2 shows the Si + P concentration in steel, the value on the left side of formula (A), the range of the present invention, and a more preferable range together with data plots. ◎ in the figure indicates a uniform appearance with no plating or unevenness, ○ indicates that there is almost no unevenness or pattern in the appearance and is a level that can be used for automotive interior parts, and × indicates that there is no plating or pattern This is a plot of the example that occurred. The mechanism of action is not clear, but the appearance and plating adhesion can be further improved by maintaining within the shaded area in FIG.
{[T] · (Si / 28 + P / 31 + C / 12)} / {[C] · [T]} ≦ 1 × 10 ^−4.
Here, [C]: solution concentration mol / l of metal used for displacement plating, [T]: temperature during displacement plating (K), [t]: displacement plating time (seconds), Si, P, C: each It is the mass% of an ingredient.

Although the lower limit of the left side of the above equation is not defined, reducing the left side increases the metal ion concentration in the aqueous solution to be replaced, increases the temperature for replacement plating, or lengthens the time for replacement plating. Since it is in the direction of cost increase and productivity reduction such as necessity, conditions up to about 1 × 10 ⁻⁸ are preferable.

  In the present invention, it is also preferable to add one or more of the following elements as necessary.

Nb: 0.001 to 1%
Nb can strengthen the steel sheet by forming fine carbides, nitrides or carbonitrides for the purpose of further improving the strength. In order to exhibit the effect, 0.001% or more of addition is required, but if added over 1%, the ductility deteriorates, so the upper limit was made 1%.

Ti: 0.001 to 1%
Similarly, Ti can reinforce the steel sheet by forming fine carbides, nitrides or carbonitrides for the purpose of further improving the strength. In order to exhibit the effect, 0.001% or more of addition is required, but if added over 1%, the ductility deteriorates, so the upper limit was made 1%.

V: 0.001 to 1%
V can similarly strengthen the steel sheet by forming fine carbides, nitrides or carbonitrides for the purpose of further improving the strength. In order to exhibit the effect, 0.001% or more of addition is required, but if added over 1%, the ductility deteriorates, so the upper limit was made 1%.

Zr: 0.001 to 1%
Similarly, Zr can strengthen steel sheets by forming fine carbides, nitrides or carbonitrides for the purpose of further improving the strength. In order to exhibit the effect, 0.001% or more of addition is required, but if added over 1%, the ductility deteriorates, so the upper limit was made 1%.

Hf: 0.001 to 1%
Similarly, Hf can reinforce the steel sheet by forming fine carbide, nitride or carbonitride for the purpose of further improving the strength. In order to exhibit the effect, 0.001% or more of addition is required, but if added over 1%, the ductility deteriorates, so the upper limit was made 1%.

Ta: 0.001 to 1%
Similarly, Ta can reinforce the steel sheet by forming fine carbides, nitrides or carbonitrides for the purpose of further improving the strength. In order to exhibit the effect, 0.001% or more of addition is required, but if added over 1%, the ductility deteriorates, so the upper limit was made 1%.

Ce: 0.001 to 1%
Ce is added in an amount of 0.001% or more in order to improve plating wettability and workability. However, if over 1% is added, the manufacturability at the time of casting or hot rolling is affected or the ductility is lowered, so the upper limit was made 1%.

Mo: 0.001 to 1%
The effect of Mo is added by adding 0.001% or more, which is added for the purpose of improving corrosion resistance and hardness, but if it exceeds 1%, the ferrite is hardened and the ductility is lowered, so the upper limit was made 1%.

Cr: 0.001 to 1%
Addition of 0.001% or more improves strength. However, if over 1% is added, the workability is adversely affected, so the upper limit was made 1%.

Ni: 0.001 to 1%
Addition of 0.001% or more avoids a decrease in manufacturability during hot rolling when the strength is improved or Cu is added. However, if over 1% is added, the workability is adversely affected, so the upper limit was made 1%.

Cu: 0.001 to 0.5%
Addition of 0.001% or more improves strength and corrosion resistance. However, if added over 0.5%, the workability in hot rolling is greatly adversely affected, so the upper limit was made 0.5%.

Co: 0.001 to 1%
Addition of 0.001% or more improves strength. However, if over 1% is added, the workability is adversely affected, so the upper limit was made 1%.

W: 0.001 to 1%
Addition of 0.001% or more improves strength. However, if over 1% is added, the workability is adversely affected, so the upper limit was made 1%.

Mg: 0.001 to 0.1%
Mg is added in an amount of 0.001% or more in order to improve the plating wettability and the structure. However, if the content exceeds 0.1%, the added alloy costs are increased, and the manufacturability at the time of casting or hot rolling is affected or the ductility is lowered, so the upper limit was made 0.1%.

B: 0.0001 to 0.01%
When B is added in an amount of 0.0001% or more, strength and secondary workability are improved. However, if added over 0.01%, the workability deteriorates, so the upper limit was made 0.01%.

Y: 0.001 to 1%
Y is added in an amount of 0.001% or more in order to improve plating wettability and workability. However, if over 1% is added, the manufacturability at the time of casting or hot rolling is affected or the ductility is lowered, so the upper limit was made 1%.

REM: 0.0001 to 0.01%
REM is added in an amount of 0.0001% or more in order to improve workability such as plating wettability and local ductility. However, if over 0.01% is added, the manufacturability at the time of casting or hot rolling is affected or the ductility is lowered, so the upper limit was made 0.01%.

Ca: 0.0001 to 0.01%
Ca is added in an amount of 0.0001% or more in order to improve workability such as plating wettability and local ductility. However, if over 0.01% is added, the manufacturability at the time of casting or hot rolling will be affected or the ductility will be lowered, so the upper limit was made 1%.

  Although conditions for displacement plating of Ni or Co are not defined, for example, a sulfuric acid bath, a halide bath, or the like is used, and means such as dipping, spraying, or coating can be used at a bath temperature of 50 to 90 ° C. After displacement plating, it is preferable to rinse away the displacement plating bath by rinsing in order to prevent contamination by residual liquid.

  The heating alloying means is preferably internal heating rather than external heating such as a direct flame burner so that appearance quality is not impaired, and an induction heating method is suitable.

  The alloying temperature is the temperature measured on the plate temperature just above the heating furnace with various thermometers, and the temperature is not particularly limited, depending on the steel type, production rate, Al concentration in the bath, annealing conditions, and other conditions. It does not matter at a predetermined temperature or temperature range. For example, 450 ° C. to 650 ° C. can be employed.

  Here, the various thermometers may be any of non-contact thermometers such as contact thermometers and radiation thermometers.

The temperature of the hot dip galvanizing bath may be a conventionally applied condition. For example, a condition of 440 ° C. to 480 ° C. can be applied. Further, the molten metal may inevitably contain Pb, Cd, Ni, Fe, Al, Ti, Nb, Mg, Mn, etc. as long as it is mainly composed of zinc, and in order to improve the quality of the plating layer, etc. In addition, a predetermined amount of Mg, Ti, Mn, Fe, Ni, Co, and Al may be added. Thus, it can apply to various uses by performing hot-dip galvanization 30-200 g / m < ² >.

  Various electroplating, chromate treatment, and lubrication are performed as necessary for the purpose of improving the paintability, weldability, lubricity, corrosion resistance, etc. on the surface of the galvanized steel sheet and galvannealed steel sheet thus obtained. A property improving process, a phosphate process, a resin coating process, a weldability improving process, etc. can be performed.

  Next, the Example of this invention is given with a comparative example.

The test material used was a cold-rolled steel sheet having a thickness of 1.2 mm and the components shown in Table 1. As shown in Table 2-1 and Table 2-2, displacement plating employs various displacement plating baths and processing conditions to deposit various metals. Moreover, when the displacement plating method was used, the value of the left side of (A) type | formula was computed and it showed to Table 2-1 and Table 2-2. The annealing conditions were a steel plate temperature of 800 ° C., heating by a radiant tube all-reduction furnace method, and the furnace atmosphere conditions were 5% hydrogen-remaining nitrogen reducing gas, oxygen concentration 10 ppm, dew point -40 ° C. The composition of the hot dip galvanizing bath was 0.13% Al and 0.03% Fe remaining zinc. The bath temperature was 460 ° C. In hot dip plating, in both the examples and comparative examples, the plate passing time in the bath was 3 seconds, and the amount of zinc deposited was adjusted to 50 g / m ² with an N ₂ gas wiper. In addition, using an induction heating type or gas heating type heating facility, plating was performed at an alloying temperature of 500 ° C., and then cooled to room temperature by air-water cooling. Evaluation of the prepared sample was examined for appearance and plating adhesion. As for the appearance of evaluation, both the visual appearance and the appearance after processing were evaluated. The visual appearance is a visual evaluation of the as-plated sample, and it has a uniform appearance with no unplating or unevenness, etc., which can be used for automotive outer plates, such as fenders and roofs that can be seen from the outside, Almost no appearance irregularities and patterns, ○ for inner plates for automobiles, such as those that can be used for parts inside the body, although there is no non-plating, irregularities and patterns are noticeably observed on the outer appearance and are not suitable as materials for inner and outer plates of automobiles The case was evaluated as “な”, and the case where non-plating occurred and impractical was evaluated as “×”. In addition, the post-process appearance is evaluated by ◯ when the alloyed hot-dip galvanized steel sheet is ground with a whetstone and the appearance is uniform with no streaks or irregularities appearing. did.

  In addition, as another quality, plating adhesion was evaluated, an alloyed hot-dip galvanized steel sheet having an Fe content of 10 mass% was bent at 60 ° V, and the plating peeling width of the bent portion was measured. In the evaluation, the peeling width within 3 mm was marked with ◎, the peeling width over 3 mm, within 6 mm with ◯, and the peeling width over 6 mm with x. The results are shown in Table 2.

  Inventive Examples 1 to 44 in Table 2-1 were all excellent in appearance and plating adhesion. Furthermore, in the examples satisfying the formula (A), the appearance was particularly excellent. On the other hand, in Comparative Examples 45 to 48, 53 to 65, and 67 to 72 in which the adhesion amount shown in Table 2-2 was small or not adhered, the visual appearance and the appearance after processing were inferior. Further, in Comparative Examples 49 to 52, 61 to 64, 66, 67, and 71 using electrodeposition (electroplating method) as the treatment method, the appearance was not improved either as plated or after processing. Further, in Comparative Examples 73 to 80 using steel types in which the Mn concentration was too high or the P + Si concentration was too high, the improvement by substitution plating could not be achieved.

It is the figure which showed the area | region where Si density | concentration in steel, P density | concentration in steel, and non-plating and material deterioration generate | occur | produce. It is the figure which showed the Si + P density | concentration in steel, the value of the left side of (A) type | formula, the range of this invention, and the more preferable range with the plot of data.

Claims (3)

% By mass
C: 0.0001 to 0.15%,
Si: 0.005 to 1.0%,
Mn: 0.001 to 2.5%,
P: 0.005-0.2%
S: 0.0001 to 0.03%,
Al: 0.001 to 4%,
N: 0.0001 to 0.02%,
And P and Si are Si + P ≦ 1.0%
After annealing a high-tensile steel plate containing residual Fe and unavoidable impurities using a hot-dip galvanizing facility of the all-reduction furnace method, the hot-dip galvanizing is mainly performed without bringing the steel plate into contact with the atmosphere. In a method for producing an alloyed hot-dip galvanized steel sheet, which is made to pass through a metal and then heat-alloyed, Ni or Co is added in a metal amount of 0.1 g / m ² or more and 1.0 g in advance by displacement plating before annealing. / M ² or less, A method for producing a high-tensile galvannealed steel sheet having an excellent appearance, characterized by being adhered. The method for producing a high-tensile alloyed hot-dip galvanized steel sheet excellent in appearance, wherein the displacement plating of claim 1 further satisfies the following formula (A).
{[T] · (Si / 28 + P / 31 + C / 12)} / {[C] · [T]} ≦ 1 × 10 ⁻⁴ (A)
[C]: Solution concentration mol / l of metal used for displacement plating
[T]: Temperature during displacement plating (K)
[T]: displacement plating time (seconds) In the steel plate according to claim 1 or 2, further in mass%,
Nb: 0.001 to 1%,
Ti: 0.001 to 1%,
V: 0.001 to 1%,
Zr: 0.001 to 1%,
Hf: 0.001 to 1%,
Ta: 0.001 to 1%,
Ce: 0.001 to 1%,
Mo: 0.001 to 1%,
Cr: 0.001 to 1%,
Ni: 0.001 to 1%,
Cu: 0.001 to 0.5%,
Co: 0.001-1%,
W: 0.001 to 1%,
Mg: 0.001 to 0.1%,
B: 0.0001 to 0.01%
Y: 0.001 to 1%,
REM: 0.0001 to 0.01%,
Ca: 0.0001 to 0.01%,
A method for producing a high-tensile alloyed hot-dip galvanized steel sheet excellent in appearance, characterized by containing one or more of the above.

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