JP2003251401A - Method for producing cold-rolled steel sheet and method for producing galvanized steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a cold-rolled steel sheet which is used as the original sheet for surface treatment and is excellent in plating property, chemical convertibility and the adhesion of plating and chemical film, when any surface treatment of a hot-dip coating, an electric plating and a chemical conversion is applied to the cold-rolled steel sheet. <P>SOLUTION: When the cold-rolled steel sheet is produced by applying an annealing after applying the cold-rolling in a plurality of passes to a steel plate containing ≥0.1 mass% Si, the cold-rolling except the last pass, is performed under condition of satisfying formula [Si]≤0.459×Ra<SP>-0.365</SP>×p/34 (wherein [Si] (mass%) is a Si content in the steel; Ra (μm) is an average roughness of the surface of a rolling roll; and p (cSt) is a viscosity of rolling oil). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to hot dip galvanizing,
The present invention relates to a method for producing a cold-rolled steel sheet suitable as an original plate for various surface treatments such as electroplating and chemical conversion treatment. Further, the present invention is
The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet that can be suitably used in the fields of automobiles, building materials, home appliances, and the like.

[0002]

2. Description of the Related Art In recent years, high-strength steel sheets have been increasingly used in the fields of automobiles, building materials, home appliances and the like. Particularly in the automobile industry, the use of high-strength steel sheets is rapidly increasing from the viewpoint of improving fuel efficiency by reducing the weight of vehicle bodies and improving collision safety. Examples of these high-tensile steel plates include, for example, JP-A-61-1
291924, JP-A-60-17052, JP-B-61-112
For example, those having a composition to which elements such as Si, Mn, Ti, Al and P disclosed in Japanese Patent Publication No. 94 are added.

In all of these high-strength steel sheets, when the Si content is increased, a Si oxide film is formed on the surface of the steel sheet in the annealing step, which results in chemical conversion treatment, electrogalvanizing adhesion, hot dip galvanizing, and hot dip galvanizing. It is known that adhesion and the like deteriorate. In particular, poor hot-dip galvanizing of high-strength steel sheet containing Si, that is, when hot-dip galvanizing is performed, so-called non-plating occurs without hot-dip galvanization partially adhering to the galvanized layer. If the steel sheet contains 0.1 mass% or more of Si, the continuous adhesion of RTH (all radiant tube) type heating furnace and NOF (non-oxidizing furnace) type heating furnace is a serious problem. Even in the hot-dip galvanizing line, there are problems that it is difficult to perform plating and that a plated layer cannot be stably formed.

Recently, demands for weight reduction and collision safety of vehicle bodies have been further increased.
Steel sheets with a higher content rate have also been developed,
It is more difficult to secure the plating property when such a steel sheet is hot dip galvanized.

[0005]

While the development of such high-strength steel sheet having a high Si content is being advanced, a technique for removing the Si oxide film formed on the steel sheet surface before the plating treatment, for example, In the pickling step before plating, a method of pickling while flushing the steel sheet (Japanese Patent Laid-Open No. 61-159590), the surface of the steel sheet is polished before electroplating, and a pickling treatment of 10 seconds or less is continued. Application method (Japanese Patent Laid-Open No. 5-230
No. 689, JP-A-5-320981), a steel sheet is pickled with a pickling solution of 20 wt% or more of sulfuric acid, 13 wt% or more of hydrochloric acid, and 3 wt% or more of hydrofluoric acid for a time of 3 seconds to 15 seconds. A method of performing a washing treatment (Japanese Patent Laid-Open No. 7-126888) has been proposed.

However, it is difficult to completely remove and suppress the Si oxide film by any of these methods, and it is possible to obtain a steel sheet and a hot-dip galvanized steel sheet which are excellent in stable plating adhesion. I couldn't. For this reason, for example, when press working a hot-dip galvanized steel sheet in an automobile manufacturer, a trouble due to peeling of the plating often occurs.

Also, when performing electroplating, if a Si oxide film is present on the surface of the cold-rolled steel sheet that is the material to be plated, there is a problem with the adhesion of the plating and there is unevenness in the amount of plating deposited. There was a problem of slippage, and there were also problems such as repellency and coarsening of chemical conversion crystals when performing chemical conversion treatment. In view of such problems, the present invention is a method for producing a cold rolled steel sheet that can be produced by suppressing surface enrichment of Si, a cold rolled steel sheet that is subjected to various surface treatments such as chemical conversion treatment, electroplating, and hot dip coating. The purpose is to provide
An object of the present invention is to provide a method for producing a galvanized steel sheet having excellent plating adhesion.

[0008]

In the above-mentioned prior art,
It was noted that the Si oxide film formed on the steel sheet surface during heat treatment such as recrystallization annealing was removed before the plating treatment.
It was difficult in these processes to remove the Si oxide film before plating by these methods. Therefore, the present inventors have studied the relationship between the cold rolling conditions and Si concentration on the steel sheet surface after annealing, which has not been paid attention in the past, and as a result, control the rolling conditions during cold rolling. As a result, it was found that the Si surface concentration during the subsequent annealing can be suppressed and the plating adhesion of Si-containing steel can be improved.

The present invention has been made based on this finding. That is, a steel sheet containing Si: 0.1% or more by mass% is cold-rolled by a plurality of passes, then annealed and cold-rolled. In producing a steel sheet, cold rolling other than the final pass is performed by the Si content [Si] (mass%) in the steel, the average roughness Ra (μm) of the surface of the rolling roll, and the viscosity p (cSt) of the rolling oil. Is a method for manufacturing a cold-rolled steel sheet, which is performed under the conditions that satisfy the following expression (1).

[Si] ≦ 0.459 × Ra ^−0.365 × p / 34 (1) Further, according to the present invention, a steel sheet containing Si: 0.1% or more by mass% is subjected to a multi-pass cold rolling. After that, annealing is performed, and further, in producing a hot-dip galvanized steel sheet by applying a hot-dip galvanizing treatment, cold rolling except for the final pass is
Si content [Si] (mass%) and average roughness R of the surface of the rolling roll
The method for producing a hot-dip galvanized steel sheet is characterized in that a (μm) and the viscosity p (cSt) of the rolling oil satisfy the following formula (1).

[Si] ≦ 0.459 × Ra ^−0.365 × p / 34 (1) Here, immediately after the annealing, the hot dip galvanizing treatment is performed, or after the annealing, the surface of the steel sheet. It is preferable to remove the oxides produced in step 1 by pickling, and then perform annealing in a reducing atmosphere and immediately perform the hot dip galvanizing treatment. Furthermore, after performing the hot dip galvanizing treatment,
The plating layer may be alloyed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that by suppressing the amount of strain introduced into the surface layer of a steel sheet during cold rolling to a low level, surface enrichment of Si during subsequent annealing can be suppressed. Then, as a result of repeated studies on a cold rolling method for suppressing the amount of strain during cold rolling, the surface roughness Ra of the rolling roll used during cold rolling was lowered, and the viscosity of the rolling oil was further reduced.
It was found that when p is increased, the surface concentration of Si during annealing tends to decrease. Below, in the present invention
The reasons for defining the Si content and the cold rolling conditions will be described.

The present invention is directed to a steel plate containing 0.1 mass% or more of Si in steel. Si content in steel is 0.1% by mass
If it is less than the above, the surface concentration of Si due to annealing is small, and the decrease in plating adhesion does not pose a problem. Here, as long as it is a known steel sheet containing 0.1% by mass or more of Si in the steel, the present invention can be applied, depending on the desired strength and characteristics,
It may be a steel sheet in which elements such as C, Mn, P, S, Al, Ti, Nb, Cr, Mo, B, O and N are appropriately contained. However, since the Si content is more than 2.0 mass% in the steel sheet, even if the cold rolling conditions described below are applied, the Si surface concentration is likely to occur during annealing. It is suitable to apply.

Considering the manufacturing cost and workability when used as a steel sheet for automobiles, C: 0.0005 to 0.25 mass%, M
n: 0.5 to 3.5 mass%, P: 0.001 to 0.20 mass%, S: 0.0001
A steel sheet containing 0.01 to 0.01 mass% and Al: 0.005 to 1.0 mass% is suitable. In addition to these elements, in order to further control the strength-ductility balance, Ti: 0.15 mass% or less, N
A steel sheet containing b: 0.15 mass% or less, Cr: 1 mass% or less, Mo: 1 mass% or less, and B: 0.001 to 0.005 mass% may be used. The balance is preferably Fe and inevitable impurities.

Next, the cold rolling conditions will be described. In the present invention, cold rolling other than the final pass is performed by measuring the Si content [Si] (mass%) in steel and the average roughness Ra (μ
m) and the viscosity p (cSt) of the rolling oil satisfy the following equation (1). [Si] ≦ 0.459 × Ra ^−0.365 × p / 34 (1) Here, the cold rolling pass performed under the condition that satisfies the formula (1) is not the final pass in the cold rolling process. Normally, cold-rolled steel sheets are manufactured by performing cold rolling in multiple passes, but in the final pass of multiple passes, the main purpose is to add a dullness to the steel sheet surface for the purpose of oil retention during press forming, etc. And a light reduction is performed. During cold rolling under such a light pressure, the amount of strain introduced to the surface of the steel sheet is small even if the rolling is not performed under the conditions that satisfy the formula (1) described later. Therefore,
The rolling conditions in the cold rolling in the final pass are not specified. In order to avoid introducing strain, it is preferable that the rolling reduction in the final pass is 2% or less.

In the present invention, it is important to carry out rolling satisfying the above formula (1) during cold rolling other than the final pass, which is a pass mainly for reducing thickness. That is, by reducing the surface roughness Ra of the rolling roll, and by increasing the viscosity p of the rolling oil, it is possible to reduce the amount of strain introduced to the steel sheet surface during rolling, and also Si in the steel. Since it is necessary to reduce the amount of strain as the content increases, it suffices to reduce the surface roughness Ra of the rolling roll and increase the viscosity p of the rolling oil. Then, as a result of investigating the influence of the Si content in the steel, the surface roughness Ra of the rolling roll, and the viscosity p of the rolling oil on the surface treatability after annealing, the above (1) is determined according to the Si content in the steel. Surface roughness Ra and viscosity p within the range that satisfies the formula
By controlling hot dip galvanizing, electroplating,
It was found that the surface treatability such as chemical conversion treatment can be improved to a level without problems. Here, even if the surface roughness of the rolling roll is very small, if the viscosity of the rolling oil is less than 10 cSt (centistokes), the effect of reducing strain introduction during rolling cannot be obtained, so the viscosity of the rolling oil is 10 cSt. The above is preferable. If the viscosity of the rolling oil exceeds 90 cSt, cold rolling becomes difficult, so it is preferable to set the viscosity to 90 cSt or less. The amount of rolling oil used is not particularly limited, but in order to obtain the effect of the present invention, it is necessary to use 1000 l / min or more per stand as a 1% emulsion.

The surface roughness Ra of the rolling roll is 0.01 to 1
The range of μm is preferred. It is difficult to manufacture a rolling roll having a surface roughness of less than 0.01 μm at a low cost.
This is because if it exceeds m, the rolling load becomes large during rolling, so that the amount of reduction per pass cannot be increased and the productivity is hindered. The surface roughness Ra of the rolling roll refers to the arithmetic average roughness Ra, and in accordance with JIS B 0601, the cutoff value is 0.25 mm in the circumferential direction of the rolling roll, and the evaluation length is 1.25 mm.
Shall be obtained at.

The number of passes for rolling is generally about 3 to 5 times, excluding the last pass, but the higher the number, the better. That is,
When the total rolling reduction is the same, the rolling reduction per pass can be reduced by increasing the number of passes, and the amount of strain introduced into the steel sheet surface can be reduced. However, increasing the number of rolling passes becomes a factor that hinders productivity, and when rolling is performed by a tandem rolling mill having a plurality of rolling stands, the number of stands becomes too large, which is disadvantageous in capital investment.

If the total rolling reduction in cold rolling is less than 20%, the mechanical properties of the steel sheet may not be imparted, and if it exceeds 90%, rolling becomes difficult. , 20 to 90% is preferable. Further, in order to reduce the amount of strain introduced into the surface of the steel sheet, it is preferable that the rolling speed is high, and at least 100 mpm or more. Although the mechanism is not clear, if the rolling speed is high, oil pit-like fine irregularities are likely to be generated, and the metal flow on the surface of the rolled material is easily suppressed due to the encapsulation effect of rolling oil, and it is introduced to the steel plate surface. It is estimated that the amount of distortion will be smaller. Generally, in cold rolling of steel strips, the tip and tail ends are connected to the previous material or the next material at the welding points, so the rolling speed must be reduced. It is preferably 100 mpm or more in the stationary part.

It is preferable that the roll diameter of the rolling roll is large so that the amount of strain introduced to the surface of the steel sheet can be made small, but 1000 is preferable.
If it exceeds mmφ, the cost of rolling equipment increases. Also, 200m
If it is less than mφ, rolling control such as shape control becomes difficult.
Therefore, it is preferable to use a rolling roll having a roll diameter within the range of 200 to 1000 mmφ. By performing cold rolling under the rolling conditions described above, Si during annealing
Although the mechanism of suppressing the surface enrichment of steel has not been clearly clarified, cold rolling under the above rolling conditions tended to facilitate the formation of oil pit-like fine irregularities on the surface of the steel sheet. As a result, rolling oil is easily filled in the irregularities, which suppresses metal flow in the surface layer of the base metal and suppresses the destruction of the grain boundary oxide layer that is generated during hot rolling, which is effective in suppressing surface concentration. It is thought that this is due to

In the present invention, after the cold rolling, the annealing treatment mainly for recrystallization is performed. The annealing conditions are not particularly specified, and the desired mechanical properties may be obtained while taking into consideration the recrystallization temperature depending on the steel type, but it is preferable to perform annealing at 700 ° C. or higher for 10 seconds or more. Since the cold-rolled steel sheet produced in this manner suppresses the surface enrichment of Si after annealing, if it is used as an original plate for various surface treatments such as hot dip plating, electroplating, and chemical conversion treatment, it can be plated or chemically treated. The effect that a surface-treated steel sheet having a good adhesion of the treated film can be stably produced is obtained.

The hot-dip galvanizing may be hot-dip galvanizing, or alloying hot-dip galvanizing obtained by alloying it.
In addition, all zinc-based alloy plating in which alloy elements are added can be applied. Examples of the zinc-based alloy plating include zinc-5% aluminum alloy plating, zinc-55% aluminum alloy plating, zinc-aluminum-magnesium alloy plating, zinc-aluminum-magnesium-silicon alloy plating, and Al. In addition to the additive elements such as Mg, Si, and Pb, elements such as Pb, Bi, Sb, Ni, Cr, and Fe may be added according to desired characteristics.

As the electroplating, electrozinc-based plating containing zinc as a main component is particularly suitable, and all known zinc-based plating can be applied. Examples include pure zinc electroplating, electrozinc alloy plating containing elements such as Fe, Ni, Co, and Mo, and those in which an inorganic compound or an organic compound is dispersed or co-deposited in these electrozinc plating. To be done.

Examples of other plating include vapor deposition zinc plating and electroless zinc plating. Further, the chemical conversion treatment includes a zinc phosphate-based chemical conversion treatment, and the cold-rolled steel sheet of the present invention can be applied as a general original plate for chemical conversion treatment.
The cold-rolled steel sheet of the present invention can remarkably improve the plating adhesion, adhesion unevenness, repellency, chemical conversion treatment crystal coarsening, etc., against various surface treatments.

When hot-dip galvanizing is performed as the surface treatment, hot-dip galvanizing may be performed under general conditions. Usually, 0.08 to 0.25 mass% of Al is added, and the temperature is adjusted.
In a molten zinc bath adjusted to about 450-500 ° C, the plate temperature is 450-5
It is performed by immersing the steel plate that has reached 00 ° C. If the Al concentration in the molten zinc bath is lower than 0.08% by mass, the adhesion of the plating cannot be secured, and conversely, if the Al concentration is higher than 0.25% by mass, the weldability will decrease or the plating layer after plating will be applied. When the alloying treatment of (1) is applied, there is a problem that the alloying is delayed. The amount of plating applied is 30 to 120 g / m ² per side
Is generally used, but it may be appropriately adjusted depending on the required characteristics such as corrosion resistance and the application. When alloying the plating layer after plating, perform it at 450 to 600 ° C and
It is preferable to control the concentration to be 8 to 13% by mass. If the alloying temperature or Fe concentration is lower than the above range, alloying becomes insufficient and appearance defects such as burning unevenness occur, and a soft ζ phase is excessively generated to form a plating layer called a flaking phenomenon during steel plate processing. Peeling is likely to occur. Further, if the alloying temperature or the Fe concentration is higher than the above range, a hard and brittle alloy phase called Γ phase grows, and when the plated steel sheet is processed, peeling of the plating layer at the time of steel plate processing called powdering phenomenon is processed. Is likely to occur, which is not preferable.

When hot-dip galvanizing is performed, hot-dip galvanizing may be performed immediately after annealing, or after performing annealing, pickling is performed and annealing is performed in a reducing atmosphere. Hot dip galvanizing may be applied. When performing hot dip galvanizing immediately after annealing, annealing is performed in a continuous hot dip galvanizing line.
It is preferable to continuously perform hot dip galvanizing. When adopting the steps of annealing-pickling-reduction annealing-hot dip galvanizing, annealing is performed mainly for recrystallization by a continuous annealing line, and pickling, reduction annealing, hot dip galvanizing is performed in the hot dip galvanizing line. It is preferable to perform plating.

In the present invention, in the steel sheet after cold rolling, the amount of strain introduced into the surface layer of the steel sheet is small, so that surface concentration of easily oxidizable elements such as Si can be suppressed to a small level even after annealing. However, it is difficult to eliminate the surface concentration of easily oxidizable elements after annealing. Therefore, it is preferable to perform plating after removing the surface-enriched easily oxidizable element by pickling. The acid used for pickling is usually hydrochloric acid or the like,
The acid used for pickling the steel sheet may be used, and in addition to this, sulfuric acid, nitric acid, phosphoric acid, etc. may be mentioned.

Further, when performing pickling, after pickling,
It is preferable to heat in a reducing atmosphere before plating. This is performed for the purpose of reducing the thin oxide film formed by pickling, and in order to obtain this effect, it is preferable to heat to a temperature of 650 ° C. or higher. However, 8
If the temperature exceeds 50 ° C, the surface of Si will be concentrated again, which is not preferable.
The reducing atmosphere may be 1 to 100 vol% H ₂ —N ₂ atmosphere.

This double annealing method has a Si content of 0.25% by mass.
As described above, particularly for steel plates with a large Si content,
It is preferable to carry out the single annealing method when it is difficult to improve the plating property.

[0030]

[Example] C: 0.07 to 0.14 mass%, Mn: 1.0 to 2.6 mass%, P: 0.005 to 0.08 mass%, S: 0.004 to 0.009 mass%,
After slabs (300 mm thick) of high-strength steel containing Al: 0.03 to 0.2 mass% and having the Si content shown in Table 1 are heated at 1250 ° C. and hot rolled into hot rolled steel sheets with a thickness of 2.8 mm. It was wound at 580 ° C. Then, after removing the black skin by pickling, cold rolling was performed under the condition that the total rolling reduction was 40 to 80% and the rolling speed of the final stand was 400 mpm.

The cold rolling was carried out by a tandem rolling mill having five stands, and the final stand was a rolling for the purpose of making a dull, and a light reduction with a reduction rate of 1 to 2%. As the rolling rolls for the first to fourth stands, those having surface roughness Ra (μm) shown in Table 1 were adopted. A rolling roll having a roll diameter of 550 to 600 mmφ was used. Also,
In the 1st to 4th stands, rolling was performed using rolling oil having a viscosity p (cSt) shown in Table 1. The amount of rolling oil used is 6000 l / min per stand as a 1% emulsion.

The cold-rolled steel sheet obtained in the above steps was subjected to various surface treatments shown in Table 2. Regarding hot dip galvanizing treatment, after electrolytic degreasing of the cold rolled steel sheet described above, when recrystallization annealing is performed at 800 ° C in a continuous hot dip galvanizing line to perform continuous plating (single annealing method), the electrolytic degreasing is performed. The cold-rolled steel sheet after that was recrystallized and annealed at 850 ° C. in a heating furnace, and after being pickled at 60 ° C. and 5% hydrochloric acid, it was cooled to 5% H ₂ -N _{2 in} a continuous hot dip galvanizing line. Either one of the cases of reheating at 780 ° C. in a reducing atmosphere (secondary heat treatment step) and continuous plating (two-time annealing method) was adopted. Also, for some hot dip galvanized steel sheets, 520 ° C after plating
The alloying treatment was applied to the plated layer so that the Fe content in the plated layer was within the range of 9 to 12%. The plating bath was a zinc bath having an Al concentration of 0.20 mass% when the alloying treatment was not performed, and a zinc bath having an Al concentration of 0.12 mass% when the alloying treatment was performed. The bath temperature of the plating bath was 450 ° C., and when the temperature of the steel plate reached 450 ° C., the steel plate was immersed in the plating bath for plating. The amount of plating adhered is adjusted by wiping when the steel plate is pulled up from the plating bath. If not alloyed, it is 90 g / m ² per side, if alloyed, it is per side
It was adjusted to 50 g / m ² .

Regarding electroplating and chemical conversion treatment,
After annealing the above cold-rolled steel sheet at 800 ° C., the types of treatments shown in Table 2 were performed by a known method. The maximum adhesion amount is as shown in Table 1. For the hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, electroplated steel sheet, and chemical conversion treated steel sheet obtained by the above method, the plating property by the appearance observation, or the evaluation of the chemical conversion treatment property, and the plating or the surface treatment film The adhesion was evaluated. Table 2 shows the evaluation results.

[0034]

[Table 1]

[0035]

[Table 2]

For the appearance observation and the adhesion evaluation, the following various evaluations were carried out. "Appearance Observation" The galvannealed steel sheet after hot dip galvanizing or after the galvannealing of the galvanized layer was visually evaluated for non-plating according to the following criteria.

◯: No non-plating Δ: A little non-plating occurs but there is almost no problem X: Significant non-plating occurs For steel plates that have been electroplated or chemically treated,
Whether or not there is unevenness in the adhered amount was visually determined by visual observation and evaluated according to the following criteria.

◯: No uneven coating amount Δ: Small uneven coating amount occurred ×: Significant uneven coating amount occurred “Evaluation of plating adhesion” Alloyed hot-dip galvanized steel sheet was coated with cellophane tape and taped. Face 90
° After bending and bending back, peel off the tape, measure the amount of plating peeled per unit length by fluorescent X-ray for the Zn count number, and in accordance with the criteria in Table 3, ranks 1 and 2 are good (○, (Triangle | delta) The thing of 3 or more was evaluated as a defect (x).

[0039]

[Table 3]

The hot-dip galvanized steel sheet which was not alloyed was subjected to a ball impact test, and after the cellophane tape was applied to the processed portion, the steel sheet was peeled off, and the presence or absence of peeling of the plated layer was evaluated according to the following criteria. ◯: No peeling of the plating layer Δ: Peeling of a small amount of plating layer ×: Significant peeling of the plating layer After folding, the cellophane tape was attached to the bent portion of the evaluation surface, peeled off, and the amount of the plating layer attached to the cellophane tape was visually observed to evaluate the plating adhesion according to the following criteria.

◯: No peeling of the plating layer Δ: Peeling of a small amount of the plating layer ×: Significant peeling of the plating layer As apparent from Tables 1 and 2, the cold-rolled steel sheet of the present invention has Si
It can be seen that, despite the large content, a plating or chemical conversion treatment film having excellent appearance after plating or chemical conversion treatment and excellent adhesion was obtained.

[0042]

According to the method for producing a cold rolled steel sheet of the present invention,
Despite the high Si content in the steel, the surface concentration of Si is suppressed after annealing, so a cold-rolled steel sheet with excellent surface treatment properties such as hot dip galvanizing, hot dip galvanizing, and chemical conversion treatment is obtained. To be Further, according to the method for producing a hot-dip galvanized steel sheet or the method for producing an alloyed hot-dip galvanized steel sheet of the present invention, even though the Si content in the steel is high, the surface concentration of Si is suppressed after annealing. In each case, there is an effect that a plating layer having excellent adhesion can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 2/40 C23C 2/40 // C22C 38/00 301 C22C 38/00 301T 38/38 38/38 F Term (reference) 4E002 AA07 AD05 BC08 BC10 CB10 4K027 AA02 AA23 AB07 AB28 AB42 AC02 AC18 AC73 AD15 AE11

Claims (5)

[Claims] 1. A steel sheet containing Si: 0.1% or more by mass% is cold-rolled by a plurality of passes and then annealed to produce a cold-rolled steel sheet. Si content in steel [Si] (mas
s%), the average roughness Ra (μm) of the surface of the rolling roll and the viscosity p (cSt) of the rolling oil satisfy the following formula (1). [Si] ≦ 0.459 × Ra ^−0.365 × p / 34 ・ ・ ・ (1) 2. A hot-dip galvanized steel sheet is manufactured by subjecting a steel sheet containing Si: 0.1% or more by mass% to multiple passes of cold rolling, annealing, and hot dip galvanizing treatment. , Cold rolling other than the final pass, the Si content in the steel [Si] (mass
s%), the average roughness Ra (μm) of the surface of the rolling roll, and the viscosity p (cSt) of the rolling oil are performed under the condition that the following formula (1) is satisfied. . [Si] ≦ 0.459 × Ra ^−0.365 × p / 34 ・ ・ ・ (1) 3. The method for producing a hot-dip galvanized steel sheet according to claim 2, wherein the hot-dip galvanizing treatment is performed immediately after the annealing. 4. The hot-dip galvanizing treatment is carried out by pickling and removing oxides formed on the surface of the steel sheet after the annealing, and then annealing again in a reducing atmosphere. 2. The method for producing a hot-dip galvanized steel sheet according to 2. 5. The method for producing a hot-dip galvanized steel sheet according to claim 2, wherein an alloying treatment of a plating layer is performed after the hot-dip galvanizing treatment.