JPH0790529A - Method for producing hot dip galvanized steel sheet containing silicon and alloyed hot dip galvanized steel sheet - Google Patents

Abstract

(57) [Summary] (Corrected) [Constitution] The polishing meshes 2 of the roll 1 are evenly distributed in the roll axial direction, and the roll surface roughness (Raθ) in the roll circumferential direction is 0.1 to 0.6 μm. After cold rolling a steel sheet with a Si content of 0.2 wt% or more using a work roll with a diameter of 200 mm or more, the surface of the steel sheet is subjected to an oxidizing atmosphere (for example, O ₂ , H ₂ O, CO ₂ , CO 2 Etc.) in a reducing atmosphere (for example, ₂ to 10% by volume of H _2).
Hot dip galvanizing, after heating in nitrogen gas included)
Alternatively, alloying treatment is further performed. [Effect] Using a silicon-containing steel plate as a base material, there is no non-plating,
A hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet having good plating adhesion can be produced with high efficiency.
This steel sheet is suitable as a material steel sheet used in the industrial fields such as automobiles and building materials.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet, which are used in the industrial field of automobiles, building materials, etc., and whose base material is a high-strength steel sheet containing silicon (Si). Manufacturing method.

[0002]

2. Description of the Related Art As a steel sheet for automobiles, a high-strength steel sheet is often used for the purpose of reducing the weight of a vehicle body, and it is required to apply a surface treatment such as plating in order to enhance a rust prevention effect. .

As a plating method, a hot dipping method is employed, which enables easy thick plating and is excellent in productivity. This method, as described in JP-A-55-122865, heats the base steel sheet in a non-oxidizing furnace to remove oil adhering to the steel sheet surface, and then annealing in a reducing furnace. , 0.08 ~
This is a method of plating on the surface of a steel sheet by immersing it in a molten zinc bath containing 0.15% by weight of aluminum.

Si is often added in order to increase the tensile strength of the base steel sheet and at the same time ensure the ductility, but the Si content is 0.2
When a high-strength steel sheet with a weight percentage of more than 5% is used as the base material, silicon (Si), manganese (Mn), aluminum (Al), phosphorus (P), etc. in the steel are oxidized on the surface of the steel sheet during heating in a non-oxidizing furnace. It is concentrated as a substance and is not reduced even if it is annealed in a reducing furnace, which causes poor wetting during plating, poor adhesion of the plated film, and delay of alloying when alloying is performed.

In order to solve the above problems when using a silicon-containing steel plate as a base material, the air ratio in the furnace is increased during heating in a non-oxidizing furnace so that iron (Fe) oxide is added to the surface of the steel plate. It is known that good plating can be obtained by applying reduction annealing after the formation. However, in an actual plating line, since the line speed, the furnace temperature and the heating cycle are constantly changing, it is necessary to increase the air ratio to control the temperature to a predetermined level.
In addition, it is extremely difficult to control the amount of oxides generated, stable operation is not possible, and especially in steel with a high Si content, the formation of Fe oxides is suppressed as the Si content increases, so practical application is possible. Had a problem.

It has also been suggested that residual strain and residual stress on the surface of the steel sheet introduced by the polishing treatment after pickling may improve the reactivity between the molten zinc and the base steel sheet (for example, iron and Steel Vol.79 No.5 (1993) pp. 590-596),
JP-A-4-202630 discloses the average oxidation rate in the oxidation zone.
Performs rapid oxidation at 30 Å / sec or more to form Fe oxides before Si and Mn, which are easily oxidized, diffuse and oxidize on the surface of the steel sheet, then annealed in an atmosphere containing hydrogen and then melted zinc A method of performing plating has been proposed.

However, although a method of grinding the surface of the base steel sheet is considered as a concrete means for giving an effective residual stress to the surface of the steel sheet, it is not economical because the number of steps is increased. In addition, large-scale equipment is required to perform the rapid oxidation treatment, which increases the manufacturing cost.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet, which have no plating and have good plating adhesion, using a silicon-containing steel sheet as a base material with high efficiency. It was made as an issue to provide.

[0009]

Means for Solving the Problems The present inventors have found that when the residual stress on the surface of a steel sheet is high, it is easily oxidized during heating and an oxide layer having a high ratio of Fe oxide is formed. It has been found that the layer becomes a layer containing a large amount of reduced iron during subsequent annealing in a reducing atmosphere, and suppresses the concentration of Si, Mn, Al, P, etc. on the steel sheet surface during reduction annealing.

On the other hand, as a result of studying a manufacturing process in which residual stress is likely to occur on the surface of a steel sheet, a work roll having a specially polished surface, that is, polishing streaks in the roll axial direction (surface irregularities caused by polishing, , Called polishing eyes)
It was found that when the base steel sheet is cold-rolled by using the work roll in the state of being provided with, a higher residual stress is generated on the surface of the steel sheet as compared with the rolling by the normal work roll. Then, when such a steel sheet is subjected to hot dip galvanizing, the wettability of hot dip zinc is improved, non-plating is eliminated, and plating with excellent adhesion is obtained. Furthermore, the base steel sheet has a non-uniform structure. Even if there is, this is eliminated, and uniform plating can be obtained. In addition, when a galvanized steel sheet was galvanized using a plating bath with an Al concentration in the bath of approximately 0.1% by weight and subjected to an alloying treatment at approximately 500 ° C, when a silicon-containing steel sheet was used as the base steel sheet. The alloying retardation phenomenon peculiar to the alloy was not observed, and the alloying rate was significantly accelerated.

The present invention has been made on the basis of the above findings, and its gist resides in the hot-dip galvanized steel sheet and galvannealed steel sheet described below.

[0012] Grinding grains of the roll are evenly distributed in the roll axial direction, and the center line average roughness (Raθ) of the roll surface in the roll circumferential direction is 0.1 to 0.6 μm (hereinafter, the surface roughness in the circumferential direction of the roll is (Raθ), or simply referred to as surface roughness (Raθ)), using a work roll with a diameter of 200 mm or more, after cold rolling a steel sheet with a Si content of 0.2 wt% or more, oxidize the surface of the steel sheet. A method for producing a hot-dip galvanized steel sheet, which comprises heating in a reducing atmosphere, followed by heating in a reducing atmosphere, and then hot-dip galvanizing.

A method for producing an alloyed hot-dip galvanized steel sheet, which comprises hot-dip galvanizing by the method described above, and then further alloying treatment.

[0014]

The function of the present invention and the effects thereof will be described in detail below.

The base steel sheet targeted by the method of the present invention is a steel sheet having a Si content of 0.2% by weight or more.

When the Si content is less than 0.2% by weight, it is possible to deal with the problem by the conventional technique, and it is not necessary to dare to apply the method of the present invention.

The most significant feature of the method of the present invention is that a base material steel sheet is cold-rolled by using a work roll whose surface is in a specially polished state to impart a high residual stress to the surface of the steel sheet.

Generally, as a method of applying residual stress,
Bending, surface grinding, brushing and shot processing are known, but in order to carry out these methods, separate dedicated equipment is required and the number of processes increases, so productivity and manufacturing cost are improved. We cannot meet the demand for reduction. Therefore, what is most desirable is to impart a residual stress to the surface of the base steel sheet in the conventional manufacturing process, that is, in the process from cold rolling to annealing. As a result of various studies on cold rolling, the present inventors performed cold rolling on the base steel sheet using a special work roll having polishing streaks in the roll axial direction,
It has been found that a higher residual stress is generated on the surface of the steel sheet as compared with rolling using a normal work roll.

FIG. 1 is an explanatory view of the direction of the grinds of a conventional work roll (hereinafter, also simply referred to as a roll) and the work roll used in the method of the present invention. FIG. 4B is a diagram schematically showing the direction of a grain of a conventional roll, and FIG. 7C is a diagram showing a direction of a grain of a roll used in the method of the present invention. As shown in FIG. 1 (a), the polishing stitch 2 of the roll 1 has an angle of α with respect to the roll circumferential direction (direction perpendicular to the roll axis). In the conventional roll, as shown in (b), α is approximately 0 °, and the polishing grain 2 of the roll is parallel to the circumferential direction of the roll. On the other hand, in the roll used in the method of the present invention, α is almost 90% as shown in (c).
°, that is, the polishing grain 2 of the roll is made parallel to the roll axial direction on average. It should be noted that “on average” means that even if the directions of some of the polishing eyes are somewhat disturbed, it is sufficient that the polishing eyes as a whole are substantially parallel to the roll axis. As defined by α, α may be in the range of about 90 ° ± 20 °, preferably 90 ° ± 5 °.

2A and 2B are explanatory views of slippage (deviation) between the surface of the roll and the surface of the metal plate in cold rolling. (A) is a vertical sectional view of a roll bite part, and (b) is a roll. It is a figure which shows the transfer pattern on the surface of a metal plate of a certain point on the surface of.

In FIG. 2A, the metal plate S is attached to the work roll 1
When rolling from the thickness t ₁ to t ₂ in the X direction by
The point at which the rolling speed v of the metal plate S becomes the same as the peripheral speed V of the roll is the neutral point (N point), and is forward from the N point (roll exit side).
Is the advanced area, and the area from the N point behind (on the roll entry side) is the reverse area. Further, if the rolling speed of the metal plate S on the roll entrance side (point A) is v ₁ and the rolling speed on the roll exit side (point B) is v ₂ , then v ₁ <v ₂ .

Now, paying attention to a certain point on the surface of the roll 1, when the one point rotates in the order of A point → N point → B point,
The locus on the surface of the metal plate S at that point is A point → N point → B point as shown in (b). That is, the rolling direction X is in the same direction between the points A and N, and the rolling direction X is the reverse between the points N and B. This is the metal plate 1 in the above-mentioned advanced region and backward region.
Because there is a difference in the rolling speed, and the relationship between the peripheral speed V of the roll and the rolling speeds v ₁ and v ₂ of the metal plate S is v ₁ <V <v ₂ . As a result, the transfer of a certain point on the surface of the roll onto the surface of the metal plate (hereinafter referred to as the transfer pattern) is (b)
As indicated by the shaded area, a deviation from A to N will occur. That is, as will be described later, the convex portion on the surface of the roll is emphasized and transferred onto the surface of the metal plate.

FIG. 3 shows a metal plate having a grain of the roll of which the grain of the roll is parallel to the circumferential direction of the roll when cold rolling is performed using the conventional roll shown in FIG. 1 (b). Fig. 2 is a diagram showing the state of transfer onto the surface, (a) is a plan view showing the state of rolling, (b) is a diagram showing the transfer pattern onto the metal plate surface of the roll's abrasive grain, and (c) is the roll. It is a longitudinal cross-sectional view showing a contact state in the width direction of the metal plate and.

As shown in (a), when the metal plate S is rolled in the X direction by a conventional roll whose roll grinding marks 2 are parallel to the circumferential direction of the roll, the grinding marks 2 of the roll are described with reference to FIG. As described above, when the image is transferred onto the surface of the metal plate S, a shift (slip) occurs, so that the transfer pattern has a shift from the point A to the point N to the point B as shown in (b). The area where one polishing eye 2 slides on the surface of the metal plate S is S ₁ . (c) is a vertical cross section near the surface of the metal plate S. Since the projections 3 of the roll's polishing eyes are slipped in the metal plate side, they are displaced in the rolling direction (direction perpendicular to the paper surface). In the state where both the scratches caused by slippage and the scratches caused by the transfer of the polishing marks of the roll overlap each other, the polishing marks of the roll are emphasized and transferred to the metal plate, resulting in minute irregularities.

FIG. 4 shows that the carbon (C) content is 0.05% by weight,
High-strength steel sheet with Si content of 0.5% by weight (specified in JIS
SPFC 780Y) has a conventional roll (diameter 400 mm, α ≈ 0 °, surface roughness Ra with the polishing pattern shown in FIG. 3 (a) above.
θ: 0.07 μm, surface roughness RaL: 0.30 μm, where surface roughness RaL means the center line average roughness of the roll surface in the roll axial direction) and cold rolling in 4 passes (4th pass rolling reduction) 22%) is applied to the surface state of the steel sheet and a sectional curve of roughness in the rolling direction and the sheet width direction.
The unevenness of the cross-sectional curve in the plate width direction is severe, but this is because the polishing grain of the roll parallel to the circumferential direction of the roll is transferred to the surface of the metal plate.

FIG. 5 shows the polishing of a roll when cold rolling is performed using the roll defined by the method of the present invention shown in FIG. FIG. 3A is a plan view showing the state of rolling of a roll on the surface of the metal plate, FIG. 2B is a plan view showing the transfer pattern of the roll on the surface of the metal plate, and FIG. c) is a vertical cross-sectional view showing a contact state between the roll and the metal plate in the rolling direction.

As shown in (a), when the metal plate S is rolled in the X direction by the rolls defined by the method of the present invention, a deviation from A point → N point → B point occurs as shown in (b). It becomes a transfer pattern. The area in which one polishing grain 2 of the roll slides on the surface of the metal plate S is S ₂ , which is considerably larger than the sliding area S ₁ in the case of rolling by the conventional roll shown in FIG. 3 (b). Since this slip acts as a shearing force on the surface layer of the metal plate, it remains as residual stress, and the difference between S ₂ and S ₁ appears as the difference in residual stress on the surface. (c) is a vertical cross section near the surface of the metal plate S. Since the convex portions 3 of the roll-grinding glide in the rolling direction shown in the figure, a part of the metal plate is pressed by the convex portions 3 and roll-polished. A minute convex portion 4 (a minute convex flaw) that is raised along the concave portion of the eye and continues in the plate width direction (direction perpendicular to the paper surface) is formed.

FIG. 6 shows a roll (diameter 400 mm, α) defined by the method of the present invention having the same polishing plate as shown in FIG. 5A for the same steel plate as that used in FIG. ≈ 90
° ± 5 °, surface roughness Raθ: 0.32μm, RaL: 0.07μm)
FIG. 3 is a diagram showing a surface state of a steel sheet after cold rolling for four passes in FIG. 4 and a sectional curve of roughness in a rolling direction and a sheet width direction. The black streak seen in the plate width direction in the figure is a bulge (a minute convex portion 4 in FIG. 5) generated by being pressed by the convex portion of the polishing mesh of the roll.

In the method of the present invention, the grain of the roll is parallel to the axial direction of the roll, the surface roughness (Raθ) of the roll in the roll circumferential direction is 0.1 to 0.6 μm Ra, and the diameter is 2
The reason for using a work roll of 00 mm or more is as follows.

If the direction of the grinds of the roll is slightly inclined from the circumferential direction of the roll in the axial direction, residual stress due to the slip of the grinds of the roll occurs on the surface of the steel sheet after rolling, but if the tilt is small. The residual stress generated is small. Also,
Sufficient residual stress occurs when the inclination is 30 ° or more,
The residual stress has a large component in the plate width direction, which meanders during rolling and causes twisting of the steel plate, which impairs the stripability in the next step, which is not preferable. Therefore, the direction of the polishing eye of the roll is
The roll axis direction is set so that the residual stress in the plate width direction is small.

The surface roughness (Raθ) in the circumferential direction of the roll is 0.1.
If it is less than μm, the roughness of the roll is too small compared to the oil film thickness and the roughness of the steel plate surface, so the convex parts of the roll's polishing edges (the tops of the irregularities on the surface) do not reach the surface of the steel plate sufficiently and the residual stress Does not occur. On the other hand, the surface roughness (Ra
When θ) exceeds 0.6 μm, the convex portions of the roll-polished mesh penetrate deeply into the surface of the steel sheet during rolling, the friction coefficient during rolling increases, and rolling becomes unstable. Furthermore, abrasion powder is often generated, and new defects such as local seizure flaws and indentation flaws due to the abrasion powder of the steel sheet occur. Therefore, the surface roughness (Raθ) in the roll circumferential direction is 0.1 to 0.6 μm.

The work roll having a diameter of 200 mm or more is used for rolling in order to increase the residual stress on the surface of the steel sheet.

The slip of the convex portion of the roll-polished mesh as shown in FIG. 5 on the surface of the metal plate and the residual stress caused by this slip are determined by the length of the arc of contact between the roll and the metal plate during rolling. That is, the longer the length from the point A to the point B, the larger the length. This length becomes larger as the rolling reduction becomes larger and the diameter of the work roll becomes larger. However, in rolling 1
There is a limit to the rolling reduction that can be rolled in a pass, and it is usually 35% or less. Therefore, if the rolling reduction is constant, the larger the diameter of the work roll, the longer the contact length between the roll and the metal plate.
A small roll with a work roll diameter of less than 200 mm does not provide a sufficient contact length and does not give the required residual stress. Therefore, the work roll diameter should be 200 mm or more.
It is preferably 400 mm or more.

It is not necessary to use the work rolls defined by the method of the present invention for all the rolls of each stand of the rolling mill, but at least for the rolls in the final pass.
If the rolling reduction in that case is too small, the length of the contact arc becomes short when the work roll has a small diameter, and when the work roll has a large diameter, the oil film thickness drawn between the roll and the steel plate during rolling is small. Since the projections of the rolls become thicker and the projections of the rolls cannot reach the surface of the steel sheet, the rolling reduction is preferably 5% or more, and more preferably 10% or more.

FIG. 7 shows that after applying various residual stresses by changing the rolling conditions on the surface of a high-strength steel sheet having a carbon (C) content of less than 0.01% by weight and a Si content of 0.25 to 1.5% by weight, oxygen is applied. Steel sheet when heated to 550 ° C in a weakly oxidizing nitrogen (N ₂ ) atmosphere with a concentration of 500 ppm and then annealed at 850 ° C for 60 seconds in a reducing nitrogen atmosphere containing 10% by volume of hydrogen FIG. 3 is a diagram showing the content rate of Fe (solid line in the figure) and the total content rate of Si, Mn, Al and P (broken line) with respect to the residual stress on the surface of FIG. Since the level of residual stress (σ) that can be applied differs depending on the yield stress (YP) of the steel sheet, the residual stress (σ) is shown as a ratio to the yield stress in the state where the steel sheet is cold rolled. Further, the amount of elements on the surface of the steel sheet was measured by ESCA after etching the surface of the steel sheet for 5 seconds with argon (Ar).

FIG. 8 shows that the annealed steel sheet was plated in a molten zinc bath (Al content: 0.1% by weight) having a bath temperature of 460 ° C. and then alloyed at 500 ° C. for 20 seconds. FIG. 8 is a diagram showing the results of an examination of the adhesiveness of molten zinc when performing the above with respect to residual stress (displayed as a ratio to yield stress as in the case of FIG. 7). The adhesion of molten zinc was evaluated by a ball impact method in which a 500-g weight was dropped from a height of 500 mm on the test surface to check for the occurrence of cracks or peeling. The case of peeling is shown as a score 2, the case of cracking is shown as a score 3, and the case where neither crack nor peeling is observed is shown as a score 4.

As shown in FIGS. 7 and 8, the Fe content in the surface of the annealed steel sheet gradually increases as the residual stress increases, and the increase rate rapidly increases at around 50% of the yield stress. . Then, as the content of Fe increases, the adhesion of molten zinc improves. In the method of the present invention, the residual stress on the surface of the steel sheet is not particularly specified, but when a roll defined by the method of the present invention is used and rolling is performed at the suitable reduction ratio, the residual stress on the surface of the steel sheet is cold-rolled to the steel sheet. 50% or more with respect to the yield stress in the state of applying.

In the method of the present invention, after cold rolling as described above to give a residual stress to the surface of the steel sheet, it is heated in an oxidizing atmosphere to oxidize the surface, and subsequently heated in a reducing atmosphere to anneal. After that, hot dip galvanizing is performed or further alloying treatment is performed. The conditions in each step of heating (oxidation), annealing (reduction), hot dip galvanizing and alloying treatment are not particularly specified, but the following conditions are preferable.

<Oxidation conditions> Oxidation conditions include oxygen (O ₂ ), water (H ₂ O), carbon dioxide (CO ₂ ), carbon monoxide (C
(O) etc. in an oxidizing atmosphere at a temperature of about 300 to 700 ° C, or the burner air-fuel ratio is 1.0 to 1.
It is preferable to adjust the temperature to about 3 and apply the oxidizing flame to the steel sheet to heat it. It is preferable that the lower limit of the heating temperature is a temperature at which an oxidation rate sufficient to form iron oxide is obtained, and the upper limit is a temperature at which the oxidation rate becomes too fast and the iron oxide layer does not become too thick. If the iron oxide layer becomes too thick, the iron oxide will not be reduced during the reduction, and the portion will remain unplated. A preferable amount of iron oxide is about 0.5 to 5.0 g / mm ² in terms of Fe,
It can be easily controlled within the range of the above-mentioned oxidation conditions.

The lower limit of the amount of iron oxide is the amount required to improve the adhesion of molten zinc.

<Annealing Conditions> Annealing in a reducing atmosphere may be carried out in an atmosphere used in an ordinary hot dip galvanizing line. As an atmosphere gas, for example, hydrogen (H ₂ ) concentration is 2 to 10% by volume. A mixed gas of nitrogen and hydrogen having a dew point of -20 ° C to -60 ° C may be used. The annealing temperature is preferably 800 to 900 ° C for ultra-low carbon steel sheets, and it is possible to reduce iron oxides for low-carbon steel sheets with low recrystallization temperature.
℃ or above. A processing time of 30 to 180 seconds is sufficient.

<Plating and alloying treatment conditions> The plating condition is that the bath temperature is 460 ° C., and when the alloying treatment is performed after plating, a plating bath with an Al content of about 0.07 to 0.11% by weight is used.
When no alloying treatment is performed, a plating bath having an Al content of 0.12 to 0.2% by weight is used.

The alloying treatment may be performed by heating at a temperature of about 500 ° C. for 20 to 30 seconds.

The method of cold rolling with a roll specified by the method of the present invention has not only the effect of imparting residual stress to the surface of the steel sheet, but also the effect of physically improving the adhesion of molten zinc. There is.

FIG. 9 is a diagram showing the relationship between the direction of the flaws (polishing flaws) on the surface of the steel sheet caused by the transfer of the polishing stitches of the roll and the plating property (the state of occurrence of non-plating). %, Si content of 0.8% by weight on high-strength steel, Fig. 1 (a)
The cold-rolled rolls having different angles α from 0 ° to 90 ° with respect to the roll circumferential direction (rolling direction) of the roll of the roll shown in FIG. After scratching, heat to 600 ° C in an oxidizing nitrogen atmosphere with an oxygen concentration of 500 ppm and then add hydrogen to 10 ° C.
It is the result of investigating the plating property of the steel sheet annealed at 850 ° C. for 60 seconds in a reducing nitrogen atmosphere containing vol%. The plating property was evaluated by visual observation, and the case where molten zinc hardly adhered to the surface of the steel plate was rated as 1,
The case where the unplating was severe was rated as 2, the case where there was slight unplating was rated as 3, and the case where there was no unplating was rated 4.

As shown in this figure, when the direction of the polishing flaws is 90 ° with respect to the rolling direction, that is, when the minute projections are present in parallel with the strip width direction, The plating property is better than that in the case where minute unevenness flaws are present in the longitudinal direction.

As described above, in the method of the present invention, the silicon-containing steel plate is cold-rolled by using the work roll having the polishing grain of the roll parallel to the roll axis and having the predetermined surface roughness and diameter, and then the normal rolling. Since heating, annealing, hot dip galvanizing, or further alloying treatment may be performed according to the method of
Does not require large-scale equipment and does not increase the number of processes,
It is possible to manufacture galvanized steel sheets and galvannealed steel sheets with high efficiency. The method of the present invention can be applied not only to hot-dip galvanizing but also to hot-dip Al-Zn alloy plating such as galfan using a 4% Al-Zn bath or galvalume using a 55% Al-Zn bath. it can.

[0048]

EXAMPLES High tensile strength steel sheets A to E shown in Table 1 (thickness: 3.2
mm, plate width: 300 mm) was used as a test material, and these steel plates were rolled for 4Hi equipped with rolling rolls having diameters, directions of polishing and surface roughness shown in Table 2 and symbols 1 to 10. It rolled using the machine under the rolling conditions shown in Table 3. For rolling up to 4 passes, the roll indicated by symbol 9 in Table 2 was used, and only for the final 5th pass, the roll shown in Table 2 was used. Table 4 shows the test materials and the rolls used in the fifth pass by symbols.

After the cold rolling, the shape of the steel sheet was investigated and the residual stress was measured. The results are also shown in Table 4. The shape of the steel sheet was evaluated based on the degree of twist. When there was no twist, the grade was ◯, when there was a slight twist, the grade was Δ, and when the twist was considerably large, x. Residual stress is indicated by ○ when the yield stress is 50% or more of the steel sheet after cold rolling in the fifth pass, Δ when it is 30% or more and less than 50%, and × when it is less than 30%. did. The yield stress of the steel sheet after cold rolling in the fifth pass is shown in Table 1.

From the results of Table 4, in the present invention examples (Nos. 1 to 12), good results were obtained in terms of both shape and residual stress, but comparative examples (No. 13
In ~ 17), at least one of shape and residual stress was evaluated as Δ or ×.

Then, after cold rolling the test material,
The surface of the steel sheet is oxidized by heating under the conditions a to d shown in
Further, after annealing under the conditions shown in Table 6, hot dip galvanizing and alloying treatment were performed under the conditions shown in Table 7. The conditions of cold rolling, oxidation, annealing, plating, and alloying treatment are shown by symbols in Table 8.

After plating, the plating property in the width direction of the plate (the state of occurrence of non-plating) and the adhesion of the plating film were evaluated. The plating property was evaluated by visual observation. When the surface of the steel sheet after plating was not adhered to the molten zinc, x was given, when there was adhesion but unevenness was evaluated as Δ, and when there was no unevenness, it was evaluated as o. The adhesion of the plating film was evaluated by the ball impact method. When there was neither cracking nor peeling of the plating film, it was rated as O, when there was cracking or partial peeling, it was rated as Δ, and when there was much peeling, it was rated as X. In addition, as a comprehensive evaluation of the steel sheet after plating, when the plating property and the adhesion of the plating film were both ◯, ◯, when Δ and ◯ were Δ, and when at least one of them was ×, it was ×. The results are also shown in Table 8.

After the alloying treatment, the adhesion and color tone of the plating film were evaluated. The adhesion was evaluated by the ball impact method. Regarding the color tone, the case where alloying was completed and the metallic luster disappeared was marked with ◯, the case where alloying was not completed was marked with Δ, and the case where there was unevenness was marked with x. The results are also shown in Table 8.

As is clear from the results of Table 8, in the examples of the present invention, both the properties after plating and the properties after the alloying treatment were good, but in the comparative examples deviating from the conditions defined by the method of the present invention, Defects were found in both the properties after plating and the properties after alloying.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

[0059]

[Table 5]

[0060]

[Table 6]

[0061]

[Table 7]

[0062]

[Table 8]

[0063]

EFFECTS OF THE INVENTION According to the method of the present invention, a galvanized steel sheet and an alloyed hot-dip galvanized steel sheet which have no plating and have good plating adhesion can be produced with high efficiency using a silicon-containing steel sheet as a base material. it can. This steel sheet is suitable as a material steel sheet used in the industrial fields such as automobiles and building materials.

[Brief description of drawings]

FIG. 1 is an explanatory view of a direction of a polishing grain of a conventional roll and a roll used in a method of the present invention.

FIG. 2 is an explanatory diagram of slippage (deviation) between the surface of a roll and the surface of a metal plate in cold rolling.

FIG. 3 is a diagram showing a state of transfer of polishing marks on a metal plate surface of a roll when cold rolling is performed using a conventional roll whose polishing marks are parallel to the circumferential direction of the roll.

FIG. 4 is a diagram showing a surface state of a metal plate after cold rolling with a conventional roll and a sectional curve of roughness in a rolling direction and a plate width direction.

FIG. 5 shows the state of transfer of the polishing marks of the roll onto the surface of the metal plate when cold rolling is performed using the roll defined by the method of the present invention, the polishing marks of the roll being parallel to the axial direction of the roll. It is a figure.

FIG. 6 is a view showing a surface state of a metal plate after cold rolling with a roll defined by the method of the present invention and a sectional curve of roughness in a rolling direction and a plate width direction.

FIG. 7 is a diagram showing the relationship between the content of Fe, Si, Mn, Al and P on the surface of a steel sheet and the residual stress.

FIG. 8 is a diagram showing the relationship between the adhesiveness of molten zinc and the residual stress on the surface of a steel sheet.

FIG. 9 is a diagram showing the relationship between the direction of a flaw (polishing flaw) on the surface of a steel sheet caused by transfer of a polishing eye of a roll (polishing flaw) and plating property.

[Explanation of symbols]

1: Roll, 2: Roll-polished mesh, 3: Roll-polished convex part, 4: Micro convex part, S: Metal plate, X: Rolling direction.

Claims (2)

[Claims] 1. A work roll having an average distribution of polishing grains in the roll axial direction, a center line average roughness (Raθ) of the roll surface in the roll circumferential direction of 0.1 to 0.6 μm, and a diameter of 200 mm or more. Steel sheet with a Si content of 0.2 wt% or more is cold-rolled, the surface of the steel sheet is heated in an oxidizing atmosphere, then in a reducing atmosphere, and then hot-dip galvanized. And a method for manufacturing a hot-dip galvanized steel sheet. 2. A work roll having an average distribution of polishing grains in the roll axial direction, a center line average roughness (Raθ) of the roll surface in the roll circumferential direction of 0.1 to 0.6 μm, and a diameter of 200 mm or more. After cold rolling a steel sheet with a Si content of 0.2% by weight or more, the surface of the steel sheet is heated in an oxidizing atmosphere, then in a reducing atmosphere, then hot dip galvanized, and then alloyed. A method for producing an alloyed hot-dip galvanized steel sheet, which comprises performing an alloying treatment.