JPH05132749A - Manufacture of high strength galvannealed steel sheet excellent in uniformity of fil and powdering resistance - Google Patents

Abstract

PURPOSE:To manufacture a high strength plated steel sheet improved in the uniformity of a plated film and powdering resistance by specifying grinding after hot rolling to steel having prescribed Si and P content as well as plating, alloying and cooling after cold rolling. CONSTITUTION:A steel sheet contg., by weight, 0.2 to 0.8% Si and <0.03% P is subjected to hot rolling and is pickled. Then, the surface of the steel sheet is ground so that the ground amt. W(g/m<2>) will satisfy W>=25X[%Si] denotes the wt.% of Si in the steel sheet). Next, the steel sheet is subjected to cold rolling, is thereafter passed through a continuous galvanealing line, is annealed at the temperature higher than the Ac1 transformation point and <=900 deg.C and is plated in a zinc bath having <=0.6wt.% Al content. Furthermore, the steel sheet is subjected to alloying treatment in an induction heating type alloying furnace so as to regulate the sheet temp. on the outlet side of the furnace to 450 to 550 deg.C to extinguish the hot-dip zinc layer on the surface layer and is thereafter cooled to <=300 deg.C at >=10 deg.C/sec cooling rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to high Si-added steel and high P
The present invention relates to a method for producing a high-strength galvannealed steel sheet using a high-strength steel sheet made of additive steel and high Si-P-added steel as a base steel sheet, and particularly, for automobile interior and exterior panels, high strength and uniformity of plating film. And a method for producing a galvannealed steel sheet having excellent powdering resistance.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for improvement in fuel efficiency of automobiles from the viewpoint of prevention of global warming, and there is a strong demand for high strength and thin materials in order to reduce vehicle body weight and ensure safety. On the other hand, alloyed hot-dip galvanized steel sheets have been used as a vehicle body material for a long time from the viewpoint of extending the life of the vehicle body. Therefore, in order to satisfy both of these characteristics, the development of high-strength hot-dip galvannealed steel sheet is being carried out. Generally, solid solution strengthening elements such as Si and P are added to increase the strength of steel sheets. However, when a steel plate containing Si or P is used as a plating original plate, there is a problem that uneven alloying or non-plating occurs due to nonuniformity of the steel plate surface.

Conventionally, in order to solve such a problem, a technique for preventing uneven alloying and non-plating by roughening a steel sheet surface by mechanical working to promote an alloying reaction (Japanese Patent Laid-Open No. 58-110655). No. 59-193258
(Japanese Patent Application Laid-Open No. 49-134)
531) and the like are known. However, none 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 the hot-rolled sheet is ground in a thickness range of 0.1 to 5 μm, and H ₂ : 15% or less and dew point: −5 ° C. or less in an N ₂ gas atmosphere. A technique of hot-dip plating after heating at 450 to 600 ° C. has been proposed. The purpose of this technique is to grind a hot-rolled sheet to carry out hot-dip galvanizing without unplating and to prevent deterioration of the material by low-temperature reduction annealing.

[0004]

However, according to the studies made by the present inventors, it is possible to obtain a plated steel sheet having a good surface appearance simply by grinding the surface of the hot rolled sheet based on such a technique. I knew I couldn't. That is, this is considered to be due to the following reasons. (A) A plated steel sheet having a good surface appearance may not be obtained by simply grinding the steel sheet surface. It is considered that this is 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 non-uniformity on 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, an alloying abnormality that is considered to be caused by an oxide film newly formed on the steel sheet surface occurs.

The present invention has been made in view of the conventional problems as described above, and has a good surface appearance to the extent that it can be applied to the interior and exterior panels of automobiles, and has a high strength which is excellent in the uniformity of the coating and the powdering resistance. It is an object of the present invention to provide a method capable of producing a galvannealed steel sheet.

[0006]

Means for Solving the Problems As a result of further studies on the points (a) and (b), the present inventors have found the following facts. (A) The required grinding amount that can eliminate the surface nonuniformity of the steel sheet depends on the Si and P amounts contained in the steel sheet, and depends on the Si and P amounts in the steel sheet to eliminate the nonuniformity of the steel sheet surface. There is a lower limit of grinding amount. (B) It is considered that a new oxide is formed on the surface of the steel sheet due to frictional heat during grinding, which is one of the causes of abnormal alloying despite grinding. Then, when performing the alloying treatment after plating by a gas heating method as in the conventional case, an alloying abnormality due to the above-mentioned oxides inevitably occurs, but the alloying treatment is performed in an induction heating type alloying furnace. By doing so, the occurrence of such alloying abnormality can be appropriately avoided. The present invention has been made on the basis of such findings, and its constitution is as follows.

(1) Si: 0.2 to 0.8 wt%,
P: Steel containing less than 0.03 wt% is hot-rolled, pickled and cold-rolled, and then passed through a continuous hot-dip galvanizing line for plating and alloying treatment,
In the method for producing a high-strength hot-dip galvanized steel sheet, the surface of the pickled plate is W ≧ 25 × [% Si] where [% Si]: Grinding amount W (%) that satisfies the Si amount (wt%) of the steel plate. g / m ² ) and then cold-rolled, and then passed through a continuous hot-dip galvanizing line.
After annealing at a temperature above the _C1 transformation point and below 900 ° C, A in the bath
plating in a zinc bath with an amount of 0.16 wt% or less,
Successively, in the induction heating type alloying furnace, alloying treatment is performed so that the furnace outlet plate temperature is 450 to 550 ° C,
High strength alloyed molten zinc excellent in film uniformity and powdering resistance, characterized by cooling to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more after disappearance of the surface molten zinc layer Manufacturing method of plated steel sheet.

(2) Si: less than 0.2 wt%, P:
Steel containing 0.03 to 0.15 wt% is hot-rolled,
After pickling and cold rolling, by passing through a continuous hot-dip galvanizing line and performing plating and alloying treatment, in the method for producing a high-strength galvannealed steel sheet, the surface of the pickled sheet, W ≧ 75 × [% P] +2 However, [% P]: Grinding with a grinding amount W (g / m ² ) that satisfies the P amount (wt%) of the steel sheet, followed by cold rolling, and then continuous hot dip galvanizing Pass through the line, A
After annealing at a temperature above the _C1 transformation point and below 900 ° C, A in the bath
plating in a zinc bath with an amount of 0.16 wt% or less,
Successively, in the induction heating type alloying furnace, alloying treatment is performed so that the furnace outlet plate temperature is 450 to 550 ° C,
High strength alloyed molten zinc excellent in film uniformity and powdering resistance, characterized by cooling to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more after disappearance of the surface molten zinc layer Manufacturing method of plated steel sheet.

(3) Si: 0.2 to 0.8 wt%,
Steel containing P: 0.03 to 0.15 wt% is hot-rolled, pickled and cold-rolled, and then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to obtain a high In a method for producing a strength alloyed hot-dip galvanized steel sheet, a grinding amount W (g
/ M ² ), [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 × [% P] +2 However, [% Si]: Si amount of steel sheet (wt%) [% P]: P amount of steel sheet (wt%) Then, after cold rolling, it is passed through a continuous hot dip galvanizing line. , A _C1 transformation temperature or higher and 900 ° C. or lower, followed by plating in a zinc bath with an Al content in the bath of 0.16 wt% or less, and subsequently in an induction heating type alloying furnace, the furnace exit side plate temperature was 450. Uniformity of the coating characterized by cooling to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more after the alloying treatment is performed at 550 ° C. to 550 ° C. And a method for producing a high-strength galvannealed steel sheet having excellent powdering resistance.

(4) The above (1), (2) or (3)
In the method described in (1), after alloying treatment and cooling, 1 g / g of Fe—Zn alloy plating film having Fe content of 50 wt% or more is electroplated on the upper layer of the alloying plating film.
A method for producing a high-strength galvannealed steel sheet having excellent coating uniformity and powdering resistance, which is characterized in that the coating amount is m ² or more.

[0011]

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

(B) Scaled alloying unevenness: An abnormal alloying (unevenness) having a width of about 1 cm, which may leave traces even after coating, which is not preferable in appearance. This alloying anomaly is caused by the fact that Fe / Si-based low melting point complex oxides are partially formed on the surface of the slab during heating of the hot rolled slab, and they easily remain after hot rolling and pickling. It was found to be due to the alloying reaction taking place.

(B) Selective oxidative alloying unevenness: It is an alloying abnormality (unevenness) of about several hundreds of μm, and the amount of coating adhered locally increases (abnormal alloying), which deteriorates the powdering resistance. .. It has been found that this abnormal alloying is caused by the presence of coarse and dense Si-based oxides formed by selective oxidation on the surface of the original plate immediately before plating.

(C) Non-plating: This is a portion where the wettability with molten zinc is poor and the film is missing. The scale or selective oxidative original plate surface oxide remains particularly thick, and zinc and iron react at all. It turned out that it occurs when it does not (wet).

(D) Occurrence of local Fe-Zn reaction at the grain boundary of the underlying ferrite: It was found that this occurs when the Si-containing steel sheet is wound at high temperature during hot rolling. It is presumed that this is due to the selective oxidation of ferrite grain boundaries during hot rolling at high temperature.

(E) Non-uniform alloying of P-added steel: Generally P
In the added steel, P in the steel is likely to be concentrated in the grain boundaries, and when P is concentrated in the grain boundaries in this way, the alloying reaction rate of the grain boundaries becomes slow during the alloying treatment after plating. For this reason, fine streak unevenness occurs on the surface after the alloying treatment and the surface appearance is impaired, and the streak unevenness also adversely affects the chemical conversion treatment property and the paintability.

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
The case where a high-strength steel plate containing 5 wt% is used as a plating original plate is targeted. If the Si content is less than 0.2 wt%, the above problems relating to the plating film characteristics do not occur, while S
If i exceeds 0.8 wt%, the oxide film on the surface of the original plate that is scaleable or selectively oxidizable remains particularly thick, so that the production method of the present invention cannot prevent non-plating and various alloying abnormalities. Further, when P is less than 0.03 wt%, the stripe unevenness due to the grain boundary concentration of P is at a level without any problem. On the other hand, P
Is more than 0.15 wt%, P segregates in the slab during continuous casting of steel, and this is stretched by hot rolling and cold rolling and becomes present in the form of fine streaks.
When the amount of P added is extremely large as described above, the alloying abnormality cannot be appropriately prevented even by using the method of the present invention.

Among the factors relating to the alloying abnormality as described above, the non-plating and the alloying abnormality due to the 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 differs depending on the amount of Si in the steel sheet, and the degree of grain boundary enrichment changes depending on the amount of P in the steel sheet.
The uniformity of the steel sheet cannot be sufficiently secured unless the grinding amount is set according to the i and P amounts.

FIG. 1 shows the results of examining the effect of the amount of surface grinding of the hot rolled pickled sheet on the alloying unevenness using the Si-containing steel sheets shown in Table 1. In this test, the surface of the pickled plate was subjected to target grinding amounts of 0 g / m ² , 3 g / m ² , 5 g / m ² , 10 g / m ² .
After grinding at m ² , 15 g / m ² , and 20 g / m ² , respectively, cold rolling was performed, and then the steel was passed through a continuous hot-dip galvanizing line (hereinafter referred to as CGL), annealed at 850 ° C., and then bathed. After plating with 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 outlet plate temperature is 500 ° C., then 25 ° C.
It cooled at the cooling rate of / sec. The alloying unevenness was visually evaluated.

In FIG. 2, using the P-containing steel plate shown in Table 1,
The result of having investigated the effect of the amount of surface grinding of a hot rolled pickling board with respect to alloying unevenness is shown. In this test, the surface of the pickled plate was subjected to target grinding amounts 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 was performed, and then the steel was passed through a continuous hot-dip galvanizing line (hereinafter referred to as CGL) and annealed at 850 ° C.,
The bath is plated with a zinc bath having an Al concentration of 0.13 wt%, and then the temperature on the outlet side of the furnace is set to 50 in an induction heating alloying furnace.
After alloying treatment to 0 ℃, 25 ℃ / sec
It cooled at the cooling rate of. The alloying unevenness was visually evaluated.

From the results shown in FIG. 1 and FIG.
For steel plates containing 0.8 wt% Wsi ≧ 25 × [Si
%] (However, [% Si]: Si amount (wt%) of the steel sheet), the grinding amount Wsi [g / m ² ] is satisfied, and P is 0.
Wp ≧ 7 for steel plates containing 03 to 0.15 wt%
5 × [P%] + 2 (however, [% P]: P amount of steel plate (wt
%)) With a grinding amount Wp [g / m ² ] satisfying the above condition, a plating film free from uneven alloying or non-plating caused by non-uniformity of the surface of the hot-rolled sheet may be obtained. found.

From the above results, Si content of 0.2-0.
For a steel sheet containing 8 wt% and 0.03 to 0.15 wt% P, W ≧ 25 × [% Si] is satisfied when [% Si] ≧ 3 × [% P] +2/25 When grinding is performed with a grinding amount W [g / m ² ] and [% Si] ≦ 3 × [% P] +2/25, a grinding amount W [g] that satisfies W ≧ 75 × [% P] +2. / M ² ]. Figure 3
Shows the relationship between the amount of Si and the proper amount of grinding that does not cause abnormal alloying of the plating film of a steel sheet containing 0.10 wt% of P.

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

Although there is no particular upper limit to the grinding amount, the grinding amount is 5 from the standpoint of obtaining the effect due to the grinding, since the effect does not change even if the grinding amount is usually more than 50 g / m ^2.
It is desirable to set it to 0 g / m ² or less. It is also possible to grind the cold-rolled sheet, but if the grinding is carried out at such a stage, surface flaws remain, so it is not suitable for applications such as automobile inner and outer sheets where the surface appearance is important.

The pickled plate thus ground is cold-rolled and then passed through CGL. The annealing heating temperature in this CGL is not lower than the Ac ₁ transformation point and not higher than 900 ° C. Recrystallization can be caused in the rolled steel sheet by setting the heating temperature to the Ac ₁ transformation point or higher. However,
The effect does not change even if heated above 900 ° C, and the upper limit is 900 ° C from the viewpoint of energy saving.

After the above-mentioned 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 for not causing non-plating and selective oxidation alloying abnormality as well as the alloying treatment by the induction heating method described later.

FIG. 4 shows the results of examining the relationship between the amount of Al in the bath and the film characteristics. 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, pass through CGL,
After annealing at 850 ° C., plating is performed with a zinc bath in which the amount of Al in the bath is variously changed, and subsequently alloying heat treatment is performed in an induction heating type alloying furnace so that the furnace outlet plate temperature is 500 ° C., Cooling rate: 25 ° C./sec. According to FIG. 4, when the Al content in the bath exceeds 0.16 wt%, non-plating and alloying unevenness are likely to occur. For the above reasons, 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 subsequently alloyed, and this alloying treatment is carried out in an induction heating (high frequency induction heating) type alloying furnace.
By performing the alloying treatment by such a heating method, the alloying abnormality can be appropriately prevented.

By grinding the hot-rolled pickled sheet under the conditions specified by the present invention, the non-plating and uneven alloying caused by the non-uniformity of the surface of the original plate caused in the hot rolling process including the slab heating process are improved. can do. However, as described above, a new oxide film is formed again on the surface of the plate after grinding due to frictional heat during grinding of the hot-rolled pickled plate, and this oxide film is alloyed abnormally or, in a significant case, unplated. Etc. will be caused. Also, during the annealing of CGL, selective oxidation occurs depending on the amount of the added element, and such an oxide also causes abnormal alloying. 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 normally used gas heating method. Regardless of the above, it is considered that the reaction between the surface iron and molten zinc is forcibly caused and the alloying abnormality is suppressed. Specific advantages of the alloying treatment by the induction heating method are as follows.

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

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

Thirdly, since induction heating can alloy the plating in a short time, the growth time of the Γ phase is short, so that the final formation amount of the Γ phase is small, which also improves the powdering resistance. It is considered that it has contributed greatly. Fourth
In addition, as an advantage of induction heating, it is possible to perform uniform heating in the width direction and length direction of the steel plate, so it is possible to strictly control the plate temperature on the outlet side of the heating furnace. Unlike the above, there is no rise in the heated atmosphere gas (draft effect), and it is considered that overalloying is unlikely to occur.

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

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

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

In the present invention, the Fe—Zn alloy plating containing 50 wt% or more of Fe is deposited by electroplating on the upper layer of the alloyed hot-dip galvanized coating after the alloying treatment.
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 coating, and the like. The above sliding properties are related to the adhesion between the surface material of the coating and the tool, and the higher the melting point of the coating surface, the more effective it is to improve the sliding properties. The Fe content of the upper plating film is defined to be 50 wt% or more because the sliding characteristics can be improved when Fe: 50 wt% or more.

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

[0038]

【Example】

[Example 1] Each steel having the chemical composition shown in Table 1 was melted in a 50t converter, the slab was hot-rolled, and after pickling, some steel sheets were surface-ground and then each steel sheet was cooled. Cold rolling at a pressure ratio of 75% to make a thin plate having a thickness of 0.8 mm, and then annealing at 850 ° C. in CGL, bath temperature: 460 ° C., Al in the bath
Amount: 0.13 wt% hot dip galvanized in a zinc bath, and then alloying treatment in an alloying furnace by induction heating method to produce an alloyed hot dip galvanized steel sheet. Table 2 to Table 4 show the results of evaluating the plating quality of the obtained products (amount of zinc plating: 60 g / m ^{2 on} each side, Fe content in the film: about 10%), together with manufacturing conditions.
Shown in.

The evaluation items relating to the plating quality shown in Tables 2 to 7 and their evaluation criteria are as follows. * 1 [1] …… No plating (visual judgment) ◎: Very good ○: Good △: Slight spot-like non-plating is observed ×: Large spot-like non-plating is observed XX: Plating repelling Allowed * 2 [2] …… Alloying unevenness (visual judgment) ◎: Very good ○: Good Δ: Fine streak unevenness is observed ×: Clear streak unevenness is observed × ×: Clear large streak unevenness * 3 [3] …… Powdering resistance (90 ° bending) ○: Pass ×: Fail * 4 [4] …… ED coating property (visual judgment) ○: Good ×: Crater generation

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

Example 2 The influence of the Al concentration in the plating bath on the quality of the plating film was investigated. Steel E shown in Table 1
After hot-rolling the slab, the surface of this pickled hot-rolled sheet is ground, and then cold-rolled at a cold pressure ratio of 75% to obtain a sheet thickness of 0.
After making a thin plate of 8 mm, it was annealed at 850 ° C. in CGL, and then the Al concentration in the bath was variously changed. Bath temperature: 4
After plating in a zinc bath at 60 ° C., alloying treatment was performed in an induction heating type alloying furnace to produce a galvannealed steel sheet. Obtained product (amount of zinc plating: 60g / each side)
m ² and Fe content in the film: about 10%), the results of evaluation of their plating qualities are shown in Table 5 together with the production conditions.
Shown in.

[0045]

[Table 5]

[Example 3] The influence of the heating method of the alloying treatment on the quality of the plating film was investigated. The steel E slabs shown in Table 1 were hot-rolled, then pickled, the surface of the pickled plate was ground, and then cold-rolled at a cold pressure ratio of 75% to obtain a plate thickness of 0.8.
After making a thin plate of mm, it is annealed at 850 ° C. in CGL, and subsequently plated with a zinc bath at a bath temperature of 460 ° C.
Alloying treatment was carried out in an induction heating type and gas heating type alloying furnace to produce a galvannealed steel sheet. Table 6 shows the results of evaluating the plating quality of the obtained products (amount of zinc plating: 60 g / m ^{2 on} each side, Fe content in the film: about 10%), together with manufacturing conditions.

[0047]

[Table 6]

Example 4 The effect of the upper layer plating on the quality of the plating film was investigated. The steel E slabs shown in Table 1 were hot-rolled, then pickled, the surface of the 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, it was annealed at 850 ° C. in CGL, and subsequently plated with a zinc bath with a bath temperature of 460 ° C., and then alloyed in an induction heating alloying furnace to form an alloyed hot dip galvanized steel sheet : 60 g / m ^{2 on} each side, F in the film
e content: about 10%) was obtained. Some of the alloyed hot-dip galvanized steel sheets were subjected to Fe-Zn alloy plating with an Fe content of 75% by electroplating as the upper layer plating of the alloyed plating film. Table 7 shows the evaluation results of the plating quality of the obtained products together with the manufacturing conditions.

[0049]

[Table 7]

[Brief description of drawings]

FIG. 1 When grinding the surface of a pickled plate of Si-containing steel,
A graph showing the effect of the grinding amount on the occurrence of alloying anomalies in the plating film in relation to the Si amount in the steel sheet.

FIG. 2 is a graph showing the effect of the amount of grinding on the occurrence of alloying anomalies in the plating film when grinding the surface of a P-containing steel pickled 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 the proper amount of grinding that does not cause alloying abnormalities in the plating film of a steel sheet containing 0.10 wt% P.

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

Claims (6)

[Claims] 1. Si: 0.2 to 0.8 wt%, P: 0.
Steel containing less than 03 wt% is hot-rolled, pickled and cold-rolled, and then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to obtain a high-strength hot-dip galvanized steel sheet. In the method for producing, the surface of the pickled plate is ground by W ≧ 25 × [% Si] where [% Si] is a grinding amount W (g / m ² ) that satisfies the Si amount (wt%) of the steel sheet. , Then cold-rolled, then passed through a continuous hot-dip galvanizing line, A
After annealing at a temperature above the _C1 transformation point and below 900 ° C, A in the bath
plating in a zinc bath with an amount of 0.16 wt% or less,
Successively, in the induction heating type alloying furnace, alloying treatment is performed so that the furnace outlet plate temperature is 450 to 550 ° C,
High strength alloyed molten zinc excellent in film uniformity and powdering resistance, characterized by cooling to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more after disappearance of the surface molten zinc layer Manufacturing method of plated steel sheet. 2. Si: less than 0.2 wt%, P: 0.03
Steel containing 0.15 wt% is hot-rolled, pickled and cold-rolled, then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to obtain high-strength alloy hot-dip zinc. In the method for producing a plated steel sheet, the surface of the pickled plate is W ≧ 75 × [% P] +2 where [% P] is a grinding amount W (g / m ² ) that satisfies the P amount (wt%) of the steel plate. And then cold-rolled, and then passed through a continuous hot-dip galvanizing line.
After annealing at a temperature above the _C1 transformation point and below 900 ° C, A in the bath
plating in a zinc bath with an amount of 0.16 wt% or less,
Successively, in the induction heating type alloying furnace, alloying treatment is performed so that the furnace outlet plate temperature is 450 to 550 ° C,
High strength alloyed molten zinc excellent in film uniformity and powdering resistance, characterized by cooling to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more after disappearance of the surface molten zinc layer Manufacturing method of plated steel sheet. 3. Si: 0.2-0.8 wt%, P: 0.
Steel containing 03 to 0.15 wt% is hot-rolled, pickled and cold-rolled, and then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to achieve high-strength alloying and melting. In the method for producing a galvanized steel sheet, the grinding amount W (g /
m ² ), [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 X [% P] +2 However, [% Si]: Si amount of steel plate (wt%) [% P]: P amount of steel plate (wt%) Then, after cold rolling, it is passed through a continuous hot dip galvanizing line, after annealing at a _C1 transformation point or higher 900 ° C. temperature below the bath Al content plated at 0.16 wt% or less of zinc bath, furnace delivery side temperature is continued in an alloying furnace for induction heating type 450 The alloy is subjected to an alloying treatment at 550 ° C., and after the molten zinc layer on the surface layer disappears, it is cooled to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more, and the uniformity of the film and A method for producing a high strength galvannealed steel sheet having excellent powdering resistance. 4. Si: 0.2-0.8 wt%, P: 0.
Steel containing less than 03 wt% is hot-rolled, pickled and cold-rolled, and then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to obtain a high-strength hot-dip galvanized steel sheet. In the method for producing, the surface of the pickled plate is ground by W ≧ 25 × [% Si] where [% Si] is a grinding amount W (g / m ² ) that satisfies the Si amount (wt%) of the steel sheet. , Then cold-rolled, then passed through a continuous hot-dip galvanizing line, A
After annealing at a temperature above the _C1 transformation point and below 900 ° C, A in the bath
plating in a zinc bath with an amount of 0.16 wt% or less,
Successively, in the induction heating type alloying furnace, alloying treatment is performed so that the furnace outlet plate temperature is 450 to 550 ° C,
After the molten zinc layer on the surface layer disappears, the temperature is cooled to 300 ° C. or lower at a cooling rate of 10 ° C./sec or more, and then the upper layer of the alloyed plating film has an Fe content of 5 by electroplating.
Fe-Zn alloy plating film of 0 wt% or more 1 g / m
^A method for producing a high-strength galvannealed steel sheet having excellent coating uniformity and powdering resistance, characterized by being applied in an amount of ² or more. 5. Si: less than 0.2 wt%, P: 0.03
Steel containing 0.15 wt% is hot-rolled, pickled and cold-rolled, then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to obtain high-strength alloy hot-dip zinc. In the method for producing a plated steel sheet, the surface of the pickled plate is W ≧ 75 × [% P] +2 where [% P] is a grinding amount W (g / m ² ) that satisfies the P amount (wt%) of the steel plate. And then cold-rolled, and then passed through a continuous hot-dip galvanizing line.
After annealing at a temperature above the _C1 transformation point and below 900 ° C, A in the bath
plating in a zinc bath with an amount of 0.16 wt% or less,
Then, in an induction heating type alloying furnace, alloying treatment is performed so that the furnace outlet plate temperature is 450 to 550 ° C.,
After the molten zinc layer on the surface layer disappears, the temperature is cooled to a temperature of 300 ° C. or lower at a cooling rate of 10 ° C./sec or more, and then the Fe content of 50 wt% is electrically applied to the upper layer of the alloyed plating film.
% Or more of the Fe—Zn alloy plating film is applied at an adhesion amount of 1 g / m ² or more, and a method for producing a high-strength hot-dip galvanized steel sheet having excellent film uniformity and powdering resistance. 6. Si: 0.2-0.8 wt%, P: 0.
Steel containing 03 to 0.15 wt% is hot-rolled, pickled and cold-rolled, and then passed through a continuous hot-dip galvanizing line for plating and alloying treatment to achieve high-strength alloying and melting. In the method for producing a galvanized steel sheet, the grinding amount W (g /
m ² ), [% Si] ≧ 3 × [% P] +2/25 W ≧ 25 × [% Si] [% Si] ≦ 3 × [% P] +2/25 W ≧ 75 X [% P] +2 However, [% Si]: Si amount of steel plate (wt%) [% P]: P amount of steel plate (wt%) Then, after cold rolling, it is passed through a continuous hot dip galvanizing line, after annealing at a _C1 transformation point or higher 900 ° C. temperature below the bath Al content plated at 0.16 wt% or less of zinc bath, furnace delivery side temperature is continued in an alloying furnace for induction heating type 450 After the alloying treatment is performed at 550 ° C. and the surface molten zinc layer disappears, the temperature is cooled to 300 ° C. or lower at a cooling rate of 10 ° C./sec or more, and then the upper layer of the alloyed plating film is Fe by electroplating
A high-strength galvannealed steel sheet excellent in film uniformity and powdering resistance, characterized in that a Fe-Zn electroplated film having a content of 50 wt% or more is applied with an adhesion amount of 1 g / m ² or more. Manufacturing method.