JP2576329B2 - Method for producing high-strength alloyed hot-dip galvanized steel sheet with excellent coating uniformity and powdering resistance - Google Patents

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 a high-strength alloyed hot-dip galvanized steel sheet using a high-strength steel sheet composed of a high-addition steel and a high-Si-P-added steel as a base steel sheet. And a method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance.

[0002]

2. Description of the Related Art In recent years, improvement in fuel efficiency of automobiles has been called for from the viewpoint of prevention of global warming and the like, and high strength and thin materials are strongly demanded from the viewpoint of weight reduction of a vehicle body and ensuring safety. On the other hand, alloyed hot-dip galvanized steel sheets have long been used as body materials from the viewpoint of extending the life of the vehicle body. Therefore, development of a high-strength alloyed hot-dip galvanized steel sheet has been performed in order to satisfy both of these characteristics. Generally, a solid solution strengthening element such as Si or P is added to increase the strength of a steel sheet. However, when a steel sheet containing Si or P is used as a plating base sheet, there is a problem that uneven alloying or non-plating due to non-uniformity of the surface of the steel sheet occurs.

Conventionally, in order to solve such a problem, a technique for roughening the surface of a steel sheet by mechanical working to promote an alloying reaction to prevent uneven alloying and non-plating (Japanese Patent Application Laid-Open No. 58-1106). 6 No. 5, JP-A-59-193258
) , A technique for enhancing the pickling speed (Japanese Patent Application Laid-Open No. 49-13 / 1979)
No. 4531). However, any of these methods has a problem that a plated steel sheet having a good surface appearance cannot be obtained. On the other hand, in JP-A-3-61352, the surface of a hot-rolled sheet is ground in a range of 0.1 to 5 μm in an N ₂ gas atmosphere of H ₂ : 15% or less, dew point: -5 ° C. or less. A technique of performing hot-dip plating after heating at 450 to 600 ° C. has been proposed. The purpose of this technique is to apply hot-dip plating without grinding by grinding a hot-rolled sheet, and to prevent the material from being damaged by low-temperature reduction annealing.

[0004]

However, according to the study by the present inventors, it has been found that simply grinding the surface of a hot-rolled sheet based on such a technique can provide a plated steel sheet having a good surface appearance. Turned out to be impossible. That is, it is considered that this is due to the following reasons. (A) Simply grinding the steel sheet surface may not provide a plated steel sheet having a good surface appearance. This is considered to be because the amount of grinding is not sufficient in relation to the amount of Si-based oxide or the like formed on the surface of the steel sheet, and the unevenness of the surface of the steel sheet is not sufficiently eliminated. (B) Even if the non-uniformity of the steel sheet surface is once eliminated by grinding, alloying abnormality which is considered to be caused by an oxide film newly formed on the steel sheet surface occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has high surface strength such that the surface appearance is good enough to be applicable to automotive interior and exterior panels, and the coating is excellent in uniformity and powdering resistance. An object of the present invention is to provide a method capable of producing an alloyed hot-dip galvanized steel sheet.

[0006]

Means for Solving the Problems The present inventors have further studied the above points (a) and (b) and have found the following facts. (A) The required grinding amount that can eliminate the surface non-uniformity of the steel sheet depends on the amounts of Si and P contained in the steel sheet, and depends on the amounts of Si and P in the steel sheet to eliminate the non-uniformity of the steel sheet surface. There is a lower limit of the grinding amount. (B) A new oxide is formed on the surface of the steel sheet due to frictional heat at the time of grinding, and this is considered to be one of the causes of abnormal alloying despite the grinding. When the alloying process after plating is performed by a gas heating method as in the past, alloying abnormalities caused by the oxides inevitably occur, but the alloying process is performed by an induction heating type alloying furnace. By doing so, occurrence of such alloying abnormality can be appropriately avoided. The present invention has been made based on such knowledge, and the configuration is as follows.

(1) Si: 0.2-0.8 wt%,
P: After hot rolling, pickling and cold rolling a steel containing less than 0.03 wt%, the steel is passed through a continuous hot-dip galvanizing line to perform plating and alloying treatment.
In the method for producing a high-strength galvannealed steel sheet, the surface of the pickled sheet is subjected to the following process: W ≧ 25 × [% Si] where [% Si]: Si amount (wt%) of the steel sheet (W%) g / m ² ), then cold-rolled, passed through a continuous hot-dip galvanizing line,
After annealing at a temperature between the _C1 transformation point and 900 ° C,
plating in a zinc bath having an amount of 0.16 wt% or less,
Subsequently, in an induction heating type alloying furnace, an alloying treatment is performed so that the furnace exit side sheet temperature becomes 450 to 550 ° C.
A high-strength alloyed zinc alloy having excellent coating uniformity and powdering resistance, characterized in that after the surface molten zinc layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more. Manufacturing method of plated steel sheet.

(2) Si: less than 0.2 wt%, P:
Hot rolling a steel containing 0.03 to 0.15 wt%,
After pickling and cold rolling, by passing through a continuous hot-dip galvanizing line and performing plating and alloying treatment, in the method of manufacturing a high-strength galvannealed steel sheet, the surface of the pickled plate is W ≧ 75 × [% P] +2 [% P]: Grinding with a grinding amount W (g / m ² ) that satisfies the P amount (wt%) of the steel sheet, then cold rolling, and then continuous galvanizing Pass through the line, A
After annealing at a temperature between the _C1 transformation point and 900 ° C,
plating in a zinc bath having an amount of 0.16 wt% or less,
Subsequently, in an induction heating type alloying furnace, an alloying treatment is performed so that the furnace exit side sheet temperature becomes 450 to 550 ° C.
A high-strength alloyed zinc alloy having excellent coating uniformity and powdering resistance, characterized in that after the surface molten zinc layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more. Manufacturing method of plated steel sheet.

(3) Si: 0.2-0.8 wt%,
P: After hot rolling, pickling and cold rolling a steel containing 0.03 to 0.15 wt%, the steel is passed through a continuous hot-dip galvanizing line and subjected to plating and alloying treatment to obtain a high content. In a method for producing a high-strength galvannealed steel sheet, the surface of the pickled plate is ground W (g
/ M ² ), and when [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 × [% P] +2 where [% Si]: Si content of steel sheet (wt%) [% P]: P content of steel sheet (wt%) Then, after cold rolling, it is passed through a continuous hot-dip galvanizing line. After annealing at a temperature not lower than the A _C1 transformation point and not higher than 900 ° C., plating is carried out in a zinc bath having an Al content of 0.16 wt% or less in the bath, and subsequently, in an induction heating type alloying furnace, the temperature of the exit side plate is 450 ° C. Alloying treatment at a temperature of up to 550 ° C., and after the molten zinc layer on the surface disappears, the coating is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more. Method for producing high-strength alloyed hot-dip galvanized steel sheet with excellent powdering resistance.

(4) The above (1), (2) or (3)
In the method described in 1, after the alloying treatment and cooling, a 1 g / Fe-Zn based alloy plating film having an Fe content of 50 wt% or more is electroplated on the upper layer of the alloyed plating film.
A method for producing a high-strength alloyed hot-dip galvanized steel sheet having excellent coating uniformity and powdering resistance, characterized by being applied with an adhesion amount of at least m ² .

[0011]

The details and reasons for limitation of the present invention will be described below. The present inventors have studied the problems on the plating film on the assumption that a steel sheet containing an appropriate amount of Si or P or both of them is used as an original plate for plating. As a result, it was found that the form and factors of alloying abnormality of these steel sheets can be arranged as follows.

(A) Non-uniform scale alloying: An alloying abnormality (non-uniformity) having a width of about 1 cm, which may leave traces even after painting, which is not preferable in appearance. This alloying anomaly occurs because Fe / Si-based low melting point composite oxides are partially formed on the slab surface during heating of a hot-rolled slab, and they are likely to remain after hot rolling and pickling. It was found that this was due to the occurrence of an alloying reaction.

(B) Non-uniformity in selective oxidation alloying: abnormal alloying (unevenness) of about several hundred μm, locally increasing the amount of coating (abnormal alloying), and deteriorating powdering resistance . It has been found that this alloying abnormality is caused by the presence or absence of the Si-based oxide formed by selective oxidation on the surface of the original sheet immediately before plating.

(C) Non-plating: poor wettability with molten zinc, a part where the film is missing, a particularly large scale or selectively oxidizable surface oxide of the original plate remains, and zinc reacts completely with iron It was found to occur when not (wet).

(D) Local Fe-Zn reaction at the ferrite grain boundaries in the base: It has been found that this occurs when a Si-containing steel sheet is hot-rolled during hot rolling. This is presumed to be caused by ferrite grain boundary selective oxidation during hot rolling at high temperature.

(E) Alloying unevenness of P-added steel:
In the added steel, P in the steel is easily concentrated at the grain boundary, and when P is concentrated at the grain boundary in this manner, the alloying reaction speed of the grain boundary at the time of alloying treatment after plating is reduced. For this reason, fine stripe unevenness occurs on the surface after the alloying treatment, and the surface appearance is impaired, and the stripe unevenness has an adverse effect on chemical conversion treatment properties, paintability, and the like.

In the method of the present invention, Si: 0.2 to 0.8 wt.
% Or P: 0.03 to 0.15 wt% or S
i: 0.2 to 0.8 wt% and P: 0.03 to 0.1
It is intended for a case where a high-strength steel sheet containing 5 wt% is used as a plating base sheet. If the content of Si is less than 0.2% by weight, the above-mentioned problem concerning the plating film characteristics does not occur, while
When i exceeds 0.8 wt%, the scale surface or selectively oxidizable original plate surface oxide film remains particularly thick, so that even if the production method of the present invention is used, non-plating and various alloying abnormalities cannot be prevented. Further, when P is less than 0.03 wt%, the line unevenness due to the grain boundary concentration of P is at a level that does not cause any problem. On the other hand, P
Exceeds 0.15 wt%, P segregates in the slab at the time of continuous casting of steel, and this is elongated by undergoing hot rolling and cold rolling, so that it is present in the form of fine streaks.
When the amount of P added is extremely large as described above, alloying abnormality cannot be properly prevented even by using the method of the present invention.

Among the above-mentioned factors relating to abnormal alloying and the like, non-plating and alloying abnormalities caused by non-uniformity of the surface of the hot-rolled sheet can be avoided by grinding the surface of the hot-rolled sheet. However, in this case, it is necessary to set the grinding amount according to the amounts of Si and P in the steel sheet. That is, the degree of oxide formation varies depending on the amount of Si in the steel sheet, and the degree of grain boundary concentration varies depending on the amount of P in the steel sheet.
Unless the grinding amount is set according to the i and P amounts, the uniformity of the steel sheet cannot be sufficiently ensured.

FIG. 1 shows the results obtained by examining the effect of the surface grinding amount of a hot-rolled pickled plate on uneven alloying using the Si-containing steel plates shown in Table 1. In this test, the pickled plate surface was subjected to target grinding amounts of 0 g / m ² , 3 g / m ² , 5 g / m ² , and 10 g / m ² .
After grinding at m ² , 15 g / m ² , and 20 g / m ² , respectively, cold rolling was performed, and subsequently, the sheet was passed through a continuous hot-dip galvanizing line (hereinafter, referred to as CGL) and annealed at 850 ° C. After plating in a zinc bath having a medium Al concentration of 0.13 wt%, and then performing an alloying treatment in an induction heating type alloying furnace so that the furnace exit side plate temperature becomes 500 ° C., then 25 ° C.
/ Sec cooling rate. The alloying unevenness was visually evaluated.

In FIG. 2, the steel sheet containing P shown in Table 1 is used.
The result of having investigated the effect of the surface grinding amount of the hot-rolled pickling plate on the alloying unevenness is shown. In this test, the pickled plate surface was subjected to a target grinding amount of 0 g / m ² , 3 g / m ² , 5 g / m ² , 10 g / m ² , 1
After grinding at 5 g / m ² and 20 g / m ² , respectively, cold rolling is performed, and subsequently, the sheet is passed through a continuous hot-dip galvanizing line (hereinafter, referred to as CGL) and annealed at 850 ° C.
Plating is carried out in a zinc bath having an Al concentration of 0.13 wt% in the bath, and then, in an induction heating type alloying furnace, the exit temperature of the furnace is set to 50%.
After performing alloying treatment at 0 ° C, 25 ° C / sec
The cooling rate was as follows. The alloying unevenness was visually evaluated.

From the results of FIG. 1 and FIG.
For steel sheets containing 0.8 wt%, Wsi ≧ 25 × [Si
%] (Where [% Si] is the amount of grinding Wsi [g / m ² ] that satisfies the Si amount (wt%) of the steel sheet), and P is set at 0.
Wp ≧ 7 for steel sheet containing 03 to 0.15 wt%
5 x [P%] + 2 (However, [% P]: P amount of steel sheet (wt
%)), It is possible to obtain a plating film free from non-uniform alloying and non-plating caused by non-uniformity of the surface of the hot-rolled sheet by grinding each with a grinding amount Wp [g / m ² ]. found.

Further, from the above results, the content of Si was set to 0.2 to 0.1.
For a steel sheet containing 8 wt% and P in an amount of 0.03 to 0.15 wt%, when [% Si] ≧ 3 × [% P] +2/25, W ≧ 25 × [% Si] is satisfied. When grinding is performed with the grinding amount W [g / m ² ], and when [% Si] ≦ 3 × [% P] +2/25, the grinding amount W [g that satisfies W ≧ 75 × [% P] +2 / M ² ]. FIG.
Shows the relationship between the amount of Si of a steel sheet containing 0.10 wt% of P and the appropriate amount of grinding that does not cause abnormal alloying of the plating film.

Therefore, in the present invention, the condition that the hot-rolled pickled plate is ground with a grinding amount W (g / m ² ) satisfying the following conditions according to the content of Si and P in the steel plate is set as the condition. And Si: 0.2 to 0.8 wt%, P: steel plate with less than 0.03 wt% W ≧ 25 × [% Si] where [% Si]: Si amount (wt%) of steel plate Si: less than 0.2 wt% P: 0.03-0.15w
t% steel sheet W ≧ 75 × [% P] +2 where [% P]: P amount (wt%) of steel sheet Si: 0.2 to 0.8 wt%, P: 0.03 to 0.1
5 wt% steel sheet [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 × [% P] +2 where [% Si]: Si amount of steel sheet (wt%) [% P]: P amount of steel sheet (wt%)

Although there is no particular upper limit on the amount of grinding, the effect is not changed even if the grinding amount exceeds 50 g / m ^2, and the amount of grinding is 5 from the viewpoint of obtaining the effect by grinding.
It is desirably 0 g / m ² or less. It is also conceivable to perform grinding on a cold-rolled sheet. However, if the grinding is performed at such a stage, surface flaws remain, so that the method is not suitable for applications that emphasize surface appearance, such as inner and outer plates for automobiles.

The pickled plate ground as described above is cold-rolled and then passed through CGL. The annealing heating temperature in this CGL is set to be from the Ac ₁ transformation point to 900 ° C. By setting the heating temperature to be equal to or higher than the Ac ₁ transformation point, the rolled steel sheet can be recrystallized. However,
The effect does not change even if heating is performed at a temperature exceeding 900 ° C., and 900 ° C. is set as the upper limit from the viewpoint of energy saving.

After the above-described annealing, the steel sheet is plated in a hot-dip galvanizing bath. In the present invention, the amount of Al in this zinc bath is specified to be 0.16 wt% or less. The amount of Al in the bath is an important requirement not to cause non-plating and abnormalities in selective oxidizing alloying together with the alloying treatment by the induction heating method described later.

FIG. 4 shows the result of examining the relationship between the amount of Al in the bath and the film properties. In this test, the pickled plates of steels B, E and G in Table 1 were ground at a grinding amount of 20 g / m ² ,
Then, after pickling and cold rolling, it is passed through CGL,
After annealing at 850 ° C., plating was performed in a zinc bath in which the amount of Al in the bath was variously changed, and subsequently, in an induction heating type alloying furnace, alloying heat treatment was performed so that the furnace exit side sheet temperature was 500 ° C. Cooling rate: Cooled at 25 ° C./sec. FIG. 4 shows that when the Al content in the bath exceeds 0.16 wt%, non-plating and alloying unevenness are likely to occur. For the reasons described above, in the present invention, the amount of Al contained in the hot-dip galvanizing bath is specified to be 0.16 wt% or less.

The hot-dip galvanized steel sheet is continuously alloyed. One of the features of the present invention is that the alloying treatment is performed in an induction heating (high frequency induction heating) type alloying furnace.
By performing the alloying treatment using such a heating method, abnormal alloying can be appropriately prevented.

By grinding the hot-rolled pickled plate under the conditions specified by the present invention, the non-plating and alloying unevenness caused by the non-uniformity of the original plate surface generated in the hot rolling process including the slab heating process are improved. can do. However, as described above, frictional heat during grinding of the hot-rolled pickling plate causes a new oxide film to be formed again on the surface of the plate after grinding, and this oxide film is abnormal in alloying or, in the case of extreme, unplated. And so on. Also, during CGL annealing, selective oxidation occurs depending on the amount of the added element, and such an oxide also causes an alloying abnormality. In addition, when an induction heating type alloying furnace is used for the alloying treatment, the surface layer of the steel sheet is preferentially heated, unlike the gas heating method which is usually used, so that such heating causes unevenness of the surface of the steel sheet. Regardless of this, it is considered that the reaction between the iron on the surface layer and the molten zinc occurs forcibly, and abnormal alloying is suppressed. The advantages of the alloying process using the induction heating method are specifically described below.

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 process, the steel sheet and the plating film are compared with each other in the atmosphere heating method such as gas heating. Fe-Zn at the interface
The reaction takes place in a short period of time and occurs uniformly irrespective of the position on the steel sheet, so that there is no partial overalloy or alloy phase remaining due to oxides on the steel sheet surface, and uniform powdering resistance can be obtained. It is estimated to be.

Secondly, it is presumed that the induction heating directly heats the surface layer of the steel sheet as described above, and that a uniform alloying reaction occurs microscopically. That is, in the conventional alloying treatment by gas heating, heating is likely to be uneven because heat is applied from the outside of the film,
For this reason, the alloying reaction is likely to be microscopically non-uniform. In particular, since the crystal grain boundaries are highly reactive, a so-called outburst reaction is likely to occur. When such an outburst structure is generated, a Γ phase starts to grow from this portion, and the formation of the Γ phase lowers the powdering resistance. to degrade. In contrast, induction heating directly heats the surface layer of the steel sheet, so that there are few local variations in the alloying as described above, and there is also an oxide on the steel sheet surface and an alloying inhibitor (Fe ₂ Al) generated in the bath. _{Since 5} ) is also easily diffused, it is thought that a uniform alloyed film can be obtained even in microscopic terms.

Third, induction heating can shorten the growth time of the 短時間 phase because the plating can be alloyed in a short time, and thus the final amount of Γ phase formed is small, which also improves the powdering resistance. It is considered to have contributed greatly. 4th
In addition, as an advantage of induction heating, uniform heating in the width and length directions of the steel sheet is possible, so that strict sheet temperature control on the exit side of the heating furnace is possible, and the atmosphere heating method such as gas furnace Unlike this, it is considered that there is no rise in the heated atmosphere gas (draft effect), so that overalloy hardly occurs.

Further, as for press formability, as described above, alloying is uniformly performed macro and micro, and as a result,
Stable and uniform press-formability is obtained, and when the heating after hot-dip plating is performed by induction heating, the plating surface is not oxidized, so that the upper plating can be appropriately adhered on the alloyed plating layer. Therefore, it is considered that stable press-formability can be obtained by plating the upper layer with a smaller amount of adhesion as compared with the case where the alloying treatment is performed by gas heating.

In the alloying treatment, after the molten zinc layer on the surface of the plating film has disappeared, cooling is performed at a cooling rate of 10 ° C./sec or more until 300 ° C. or less at which the Fe—Zn alloying reaction does not proceed so much. This is because after a predetermined plating film structure (crystal structure) is obtained by the alloying heat treatment, it is formed at the interface between the plating film and the base steel sheet, and deteriorates powdering resistance.
This is to prevent the phase from growing as much as possible. By adopting such cooling conditions, the powdering resistance can be further improved.

Further, by controlling the temperature of the steel sheet on the exit side of the steel sheet in the induction heating alloying furnace in the range of 450 to 550 ° C.,
A film having more excellent powdering resistance can be formed. When the furnace exit side plate temperature is lower than 450 ° C., it takes a long time for alloying, which is not preferable due to restrictions of the alloying equipment.
If it exceeds 550 ° C., the alloying ratio of the film tends to be excessive,
Powdering resistance deteriorates. In the present invention, the reason why the sheet temperature on the exit side of the induction heating furnace is controlled is that the temperature becomes the highest sheet temperature in the alloying heat cycle. In addition, since the growth rate of the alloy phase is maximized in this vicinity, it is possible to cause an alloying reaction at that temperature by controlling the outlet sheet temperature.

In the present invention, an Fe—Zn alloy plating containing 50 wt% or more of Fe is deposited on the upper layer of the alloyed hot-dip galvanized film after the alloying treatment by electroplating with an adhesion amount of 1%.
By applying g / m ² or more, it is possible to improve the sliding characteristics between the plating film and the press tool during press working, the cratering resistance during painting, and the like. The above-mentioned sliding characteristics are related to the adhesion between the surface material of the film and the tool, and the higher the melting point of the surface of the film, the more effective in improving the sliding characteristics. The reason why the Fe content of the upper plating film is specified to be 50 wt% or more is that the sliding characteristics can be improved with Fe: 50 wt% or more.

[0037] Regarding the amount of adhesion, if it is less than 1 g / m ² , it is impossible to coat a sufficiently uniform upper plating film over the entire plating surface, so it is specified as 1 g / m ² or more. Although there is no particular upper limit on the amount of plating, the amount is preferably 5 g / m ² or less from the viewpoint of cost. When the alloying treatment after the hot-dip plating is performed by induction heating as in the present invention, the plating surface is not oxidized, so that the upper plating can be appropriately adhered on the alloyed plating layer, and thus, the gas heating can be performed. As compared with the case where the alloying treatment is performed, the adhesion amount of the upper layer plating can be reduced.

[0038]

【Example】

[Example 1] Steels having the chemical components shown in Table 1 were melted in a 50-ton converter, the slab was hot-rolled, and after pickling, some steel sheets were subjected to surface grinding, and then each steel sheet was cooled. Cold-rolled at a pressure ratio of 75% to form a thin plate having a thickness of 0.8 mm, and then annealed at 850 ° C. in CGL, bath temperature: 460 ° C., Al in the bath
The hot dip galvanizing was performed in a zinc bath having an amount of 0.13 wt%, and subsequently the alloying treatment was performed in an alloying furnace using an induction heating method to produce a galvannealed steel sheet. With respect to the obtained products (amount of galvanized coating: 60 g / m ^{2 on} each side, Fe content in the film: about 10%), the results of evaluating the plating quality are shown in Tables 2 to 4 together with the manufacturing conditions.
Shown in

The evaluation items relating to plating quality and the evaluation criteria described in Tables 2 to 7 are as follows. * 1 [1]… non-plating (visual judgment) ：: very good ：: good 点: spot-like non-plating slightly observed ×: spot-shaped non-plating with large diameter 認 め ×: plating repellency Recognized * 2 [2]: Alloying unevenness (visual judgment) ：: Very good 良好: Good ：: Fine streak unevenness observed X: Clear streak unevenness observed ×: Clear large streak unevenness * 3 [3]: Powdering resistance (90 ° bending) ○: Acceptable ×: Fail * 4 [4]: ED paintability (visual judgment) ○: Good ×: Crater generation

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

Example 2 The effect of the Al concentration in the plating bath on the quality of the plating film was examined. Steel E shown in Table 1
Is hot-rolled and then pickled, the surface of the hot-rolled pickled sheet is ground, and then cold-rolled at a cold pressure ratio of 75% to obtain a sheet thickness of 0.
After forming a thin plate of 8 mm, in CGL, annealing was performed at 850 ° C., and then the Al temperature in the bath was variously changed.
After galvanizing in a zinc bath at 60 ° C., it was alloyed in an induction heating type alloying furnace to produce a galvannealed steel sheet. Obtained product (galvanized adhesion amount: each side 60g /
(m ² , Fe content in the coating: about 10%), the results of evaluating the plating quality thereof are shown in Table 5 together with the manufacturing conditions.
Shown in

[0045]

[Table 5]

Example 3 The effect of the heating method of the alloying treatment on the quality of the plating film was examined. After hot rolling a slab of steel E shown in Table 1, it was pickled, the surface of this pickled plate was ground, and then cold rolled at a cold pressure ratio of 75% to a plate thickness of 0.8.
mm, and then annealed at 850 ° C. in CGL, and subsequently plated in a zinc bath at a bath temperature of 460 ° C.
Alloying treatment was performed in an induction heating type and gas heating type alloying furnace to produce an alloyed hot-dip galvanized steel sheet. Table 6 shows the results of evaluating the plating quality of the obtained products (galvanized coating amount: 60 g / m ^{2 on} each side, Fe content in the film: about 10%), together with the manufacturing conditions.

[0047]

[Table 6]

Example 4 The effect of the upper plating on the quality of the plating film was examined. After hot rolling a slab of steel E shown in Table 1, it was pickled, the surface of this pickled plate was ground, and then cold rolled at a cold pressure ratio of 75% to obtain a thin plate having a thickness of 0.8 mm. After that, in CGL, it is annealed at 850 ° C., then is plated in a zinc bath at a bath temperature of 460 ° C., and then alloyed in an induction heating type alloying furnace to obtain an alloyed hot-dip galvanized steel sheet (amount of galvanized coating). : 60 g / m ^{2 on} each side, F in film
e content: about 10%). Some of the alloyed hot-dip galvanized steel sheets were electroplated with an Fe-Zn alloy having an Fe content of 75% as an upper layer plating of the alloyed plating film. Table 7 shows the results of evaluating the plating quality of the obtained products together with the manufacturing conditions.

[0049]

[Table 7]

[Brief description of the drawings]

FIG. 1 shows the case where the surface of a pickling plate of a Si-containing steel plate is ground.
Graph showing the effect of the amount of grinding on the occurrence of abnormal alloying of the plating film in relation to the amount of Si in the steel sheet

FIG. 2 is a graph showing the effect of the amount of grinding on the occurrence of alloying abnormality in a plating film in the case of grinding the surface of a pickling plate of a P-containing steel plate in relation to the amount of P in the steel plate.

FIG. 3 is a graph showing the relationship between the amount of Si and an appropriate amount of grinding of a steel sheet containing 0.10 wt% of P in which alloying abnormality of a plating film does not occur.

FIG. 4 is a graph showing the effect of the Al concentration in a plating bath on the occurrence of abnormal alloying of a plating film in relation to the amount of Si in a steel sheet.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-52431 (JP, A) JP-A-4-168229 (JP, A) JP-A-4-173946 (JP, A) JP-A-4-173946 285126 (JP, A) JP-A-4-304346 (JP, A) JP-A-4-346644 (JP, A) JP-A-5-106008 (JP, A)

Claims (6)

(57) [Claims] 1. Si: 0.2-0.8 wt%, P: 0.
After hot rolling, pickling and cold rolling a steel containing less than 03 wt%, the steel sheet is passed through a continuous galvanizing line and subjected to plating and alloying treatment to obtain a high-strength galvannealed steel sheet. The surface of the pickled plate is ground with a grinding amount W (g / m ² ) that satisfies W ≧ 25 × [% Si] where [% Si]: Si amount (wt%) of the steel plate. Then, after cold rolling, it is passed through a continuous hot-dip galvanizing line,
After annealing at a temperature between the _C1 transformation point and 900 ° C,
plating in a zinc bath having an amount of 0.16 wt% or less,
Subsequently, in an induction heating type alloying furnace, an alloying treatment is performed so that the furnace exit side sheet temperature becomes 450 to 550 ° C.
A high-strength alloyed zinc alloy having excellent coating uniformity and powdering resistance, characterized in that after the surface molten zinc layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more. Manufacturing method of plated steel sheet. 2. Si: less than 0.2 wt%, P: 0.03
After hot-rolling, pickling and cold-rolling a steel containing 0.15% by weight, the steel is passed through a continuous hot-dip galvanizing line and subjected to plating and alloying treatment to obtain high-strength alloyed hot-dip zinc. In the method for producing a plated steel sheet, the surface of the pickled plate is subjected to the following process: W ≧ 75 × [% P] +2, where [% P]: the amount of grinding W (g / m ² ) that satisfies the P content (wt%) of the steel sheet. And then cold-rolled, passed through a continuous hot-dip galvanizing line,
After annealing at a temperature between the _C1 transformation point and 900 ° C,
plating in a zinc bath having an amount of 0.16 wt% or less,
Subsequently, in an induction heating type alloying furnace, an alloying treatment is performed so that the furnace exit side sheet temperature becomes 450 to 550 ° C.
A high-strength alloyed zinc alloy having excellent coating uniformity and powdering resistance, characterized in that after the surface molten zinc layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more. Manufacturing method of plated steel sheet. 3. Si: 0.2-0.8 wt%, P: 0.
After hot-rolling, pickling, and cold-rolling a steel containing 03 to 0.15 wt%, the steel is passed through a continuous hot-dip galvanizing line to perform plating and alloying treatment, thereby obtaining a high-strength alloyed molten steel. In the method for producing a galvanized steel sheet, the surface of the pickled plate is ground W (g / g) satisfying the following formula.
m ² ), when [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 × [% P] +2 [% Si]: Si content of steel sheet (wt%) [% P]: P content of steel sheet (wt%) After cold rolling, the steel sheet was passed through a continuous hot-dip galvanizing line. After annealing at a temperature not lower than A _C1 transformation point and not higher than 900 ° C., plating is performed in a zinc bath in which the Al content in the bath is 0.16 wt% or lower, and subsequently, in an induction heating type alloying furnace, the furnace exit side sheet temperature is 450 to Alloying treatment is performed at 550 ° C., and after the surface molten zinc layer disappears, the coating is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more. A method for producing a high-strength galvannealed steel sheet with excellent powdering resistance. 4. Si: 0.2-0.8 wt%, P: 0.
After hot rolling, pickling and cold rolling a steel containing less than 03 wt%, the steel sheet is passed through a continuous galvanizing line and subjected to plating and alloying treatment to obtain a high-strength galvannealed steel sheet. The surface of the pickled plate is ground with a grinding amount W (g / m ² ) that satisfies W ≧ 25 × [% Si] where [% Si]: Si amount (wt%) of the steel plate. Then, after cold rolling, it is passed through a continuous hot-dip galvanizing line,
After annealing at a temperature between the _C1 transformation point and 900 ° C,
plating in a zinc bath having an amount of 0.16 wt% or less,
Subsequently, in an induction heating type alloying furnace, an alloying treatment is performed so that the furnace exit side sheet temperature becomes 450 to 550 ° C.
After the surface molten zinc layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more.
1 g / m of Fe-Zn based alloy plating film of 0 wt% or more
^A method for producing a high-strength galvannealed steel sheet having excellent coating uniformity and powdering resistance, characterized by being applied with an adhesion amount of ² or more. 5. Si: less than 0.2 wt%, P: 0.03
After hot-rolling, pickling and cold-rolling a steel containing 0.15% by weight, the steel is passed through a continuous hot-dip galvanizing line and subjected to plating and alloying treatment to obtain high-strength alloyed hot-dip zinc. In the method for producing a plated steel sheet, the surface of the pickled plate is subjected to the following process: W ≧ 75 × [% P] +2, where [% P]: the amount of grinding W (g / m ² ) that satisfies the P content (wt%) of the steel sheet. And then cold-rolled, passed through a continuous hot-dip galvanizing line,
After annealing at a temperature between the _C1 transformation point and 900 ° C,
plating in a zinc bath having an amount of 0.16 wt% or less,
Subsequently, in an induction heating type alloying furnace, an alloying treatment is performed so that the furnace exit side sheet temperature becomes 450 to 550 ° C.
After the molten zinc layer on the surface layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more, and then, an Fe content of 50 wt.
%. A method for producing a high-strength alloyed hot-dip galvanized steel sheet having excellent coating uniformity and powdering resistance, characterized by applying an Fe—Zn-based alloy plating film of not less than 1 g / m ² or more. 6. Si: 0.2-0.8 wt%, P: 0.
After hot-rolling, pickling, and cold-rolling a steel containing 03 to 0.15 wt%, the steel is passed through a continuous hot-dip galvanizing line to perform plating and alloying treatment, thereby obtaining a high-strength alloyed molten steel. In the method for producing a galvanized steel sheet, the surface of the pickled plate is ground W (g / g) satisfying the following formula.
m ² ), when [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 × [% P] +2 [% Si]: Si content of steel sheet (wt%) [% P]: P content of steel sheet (wt%) After cold rolling, the steel sheet was passed through a continuous hot-dip galvanizing line. After annealing at a temperature not lower than A _C1 transformation point and not higher than 900 ° C., plating is performed in a zinc bath in which the Al content in the bath is 0.16 wt% or lower, and subsequently, in an induction heating type alloying furnace, the furnace exit side sheet temperature is 450 to The alloying treatment is performed at 550 ° C., and after the surface molten zinc layer disappears, it is cooled to a temperature of 300 ° C. or less at a cooling rate of 10 ° C./sec or more, and then on the upper layer of the alloyed plating film, Fe by electroplating
High strength galvannealed steel sheet content with excellent uniformity and powdering resistance of the film, characterized in that applying 50 wt% or more Fe-Zn-based electroplated coating at 1 g / m ² or more deposition amount Manufacturing method.