JPH10265902A - Hot-dip galvanized steel sheet with no wrinkled surface defects - Google Patents

Abstract

(57) [Problem] To provide a hot-dip galvanized steel sheet having no wrinkle-like surface defects and excellent workability. SOLUTION: C: 0 to 0.0030 wt%, Si: 0
~ 0.05wt%, Mn: 0 ~ 0.5wt%, P: 0 ~
0.02 wt%, S: 0 to 0.020 wt%, sol.
Al: 0.010 to 0.080 wt%, N: 0 to 0.0
030 wt%, B: 0.0001 wt% or more 0.000
Less than 4 wt%, Cu: 0.01 to 0.05 wt%, and C / 12 ≦ Ti / 48 + Nb / 96 + Zr / 9
1 + V / 51-N / 14-S / 32 ≦ 4 × (C / 12)
This is a hot-dip galvanized steel sheet having a sheet thickness of 1.2 mm or less, wherein a steel sheet having a component composition containing one or more of Ti, Zr, V, and Nb in an amount satisfying the following is used as a base steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner and outer panel of an automobile,
TECHNICAL FIELD The present invention relates to a hot-dip galvanized steel sheet having a favorable surface appearance suitable for electrical equipment and building materials.

[0002]

2. Description of the Related Art Since high workability is required for automobile inner and outer panels, a so-called IF steel in which Ti, Nb, etc. are added in an atomic ratio of not less than C and N to precipitate and fix these solute elements is used. Have been. This IF steel is suitable as a hot-dip galvanized steel sheet because a non-aged steel sheet can be produced without performing overaging treatment in continuous annealing, and many proposals have been made in connection with this. However, IF steel has many problems due to reduced impurity elements. For example, problems such as secondary working embrittlement due to weak grain boundaries are pointed out. Have been.

[0003]

In response to such a problem, in recent years, a B-added IF steel in which B which is easily segregated at grain boundaries is added to strengthen the grain boundaries has been used (for example, JP-A-59-140333). We consider this B
In the process of investigating and examining the properties of
The steel has a large yield point elongation at the unregulated stage compared with the B-free IF steel, and as a result, particularly in a thin material having a thickness of 1.2 mm or less, a wrinkle-like defect tends to occur in the manufacturing process. I found something. In recent years, demands from users for the steel sheet surface quality have become increasingly severe, and there has been a need to prevent or reduce the occurrence of such fine defects that were conventionally overlooked.
Accordingly, an object of the present invention is to provide a hot-dip galvanized steel sheet that does not have such a wrinkled surface defect and has excellent workability.

[0004]

The present invention for solving the above-mentioned problems is characterized by the fact that C: 0 to 0.0030 wt%, S:
i: 0 to 0.05 wt%, Mn: 0 to 0.5 wt%,
P: 0 to 0.02 wt%, S: 0 to 0.020 wt%,
sol. Al: 0.010-0.080 wt%, N: 0
-0.0030 wt%, B: 0.0001 wt% or more and less than 0.0004 wt%, Cu: 0.01-0.05 w
t%, an amount of Ti, Zr, V, N satisfying the following equation (1):
A hot-dip galvanized steel sheet having a thickness of 1.2 mm or less and having no wrinkled wrinkle-like surface defect, characterized in that a steel sheet having a component composition containing one or more kinds of b is used as a base steel sheet. C / 12 ≦ Ti / 48 + Nb / 96 + Zr / 91 + V / 51−N / 14−S / 3 2 ≦ 4 × (C / 12) (1) where Ti: Ti content (wt%), Zr: Zr content Amount (wt%), V: V content (wt%), Nb: Nb content (wt%), C: C content (wt%), N: N content (wt%), S: S content Amount (wt%)

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limitation will be described below. The present inventors have investigated and investigated the cause of the occurrence of the above-described waistline wrinkle-like defect, and as a result, it was found that waistline wrinkles occurred near the top roll of the Sendzimir continuous galvanizing line, It originated from the iron-zinc alloy inevitably generated in the hot dipping line called our dross.
The added IF steel has a yield point elongation B at a temperature range of 300 ° C or lower.
The fact that it was larger than that of the unadded IF steel was ascertained.

Based on these facts, it is considered that the occurrence of the wrinkle-like defect is caused by the following mechanism. In other words, usually, in a continuous line, 1-5 kgf / mm ²
It is thought that dross adhering to the steel plate surface in the hot-dip galvanizing pot was pushed into the steel plate by the top roll due to the application of this tension, and this part would cause waist breakage. Can be And especially,
In the case of a thin steel plate with a thickness of 1.2 mm or less, in which the dross diameter is relatively large as compared with the steel plate thickness, it is considered that the steel plate receives more remarkable stress concentration, so that obvious wrinkle breakage occurs. Can be If the steel sheet yields continuously, even if it receives such stress concentration, it does not become a surface defect, but if the steel sheet yields discontinuously, it is considered that a wrinkle-like defect occurs.

The direct cause of the yield elongation of the B-added IF steel is that carbides such as TiC, ZrC, NbC, and VC are re-dissolved in the annealing step, but B segregates at grain boundaries.
Seems to be promoting this through some mechanism. Since the addition of B is indispensable for the improvement of the product performance, the study was carried out to solve the above-mentioned problems on the premise of the addition of B. As a result, by adjusting the amount of B added, it was possible to obtain a processing free from wrinkle-like wrinkle-like defects. It was concluded that hot-dip galvanized steel sheet could be manufactured. Furthermore, it has been found that the effective use of Cu can more effectively prevent the generation of wrinkle-like defects. This is thought to be due to the fact that the sulfide is precipitated by adding Cu and the sulfide effectively functions as a precipitation nucleus of carbide, so that the solid solution C in the steel sheet is reduced, and as a result, the wrinkle break is improved. Can be

Hereinafter, the reasons for limiting the composition of the hot-dip galvanized steel sheet according to the present invention will be described. C: C is desirably reduced because it deteriorates the workability of the steel sheet, and is also an element that causes elongation at the yield point. Therefore, it is desirable to reduce C from the viewpoint of preventing the occurrence of creasing. Therefore, C is 0 to 0.0030 wt% as long as the effect of the present invention is not practically impaired.
(However, the case without addition is included). Si: Si not only deteriorates the workability of the steel sheet but also significantly deteriorates the adhesion between the plating film and the base steel sheet, so that it is desirable to reduce it. Therefore, as a range that does not impair the effects of the present invention, the content of Si is set to 0 to 0.05 wt% (including the case of no addition).

Mn: Mn is desirably reduced because it hardens the steel sheet and deteriorates workability.
０．５0.5 wt% (including the case of no addition). P: P is also desirably reduced because it hardens the steel sheet and deteriorates the workability.
(However, the case without addition is included). S: S is desirably reduced because S deteriorates the ductility of steel, and therefore, S is set to 0 to 0.020 wt% (including the case where no additive is added). sol. Al is added to steel as a deoxidizing agent. so
l. If the Al content is less than 0.010 wt%, the effect is not sufficient. On the other hand, if the Al content exceeds 0.080 wt%, the effect saturates, and on the contrary, there arises a problem of inducing surface defects. Therefore, sol. Al is 0.010-0.
080 wt%.

N: N is desirably reduced from the viewpoint of improving the workability of the steel sheet, and is set to 0 to 0.0030 wt% (including the case where it is not added) as a range that does not impair the effect of the present invention practically. . B: B is an essential element for steel sheets used for working applications because B is an element effective for improving the brittleness resistance in secondary working and improving the r-value and effective for reducing the grain size of the hot-rolled sheet. However, if the content of B is less than 0.0001 wt%, the effect cannot be sufficiently obtained. On the other hand, if the content of B is 0.0004 wt% or more, a wrinkle-like defect occurs, so that the content of B is 0.0001 wt% or more.
0004 wt% or less.

FIG. 1 shows a steel having the composition of steel No. 1 shown in Table 1 in which the amount of B added was changed.
For a hot-dip galvanized steel sheet manufactured under the conditions of 200 ° C., finishing temperature 890 ° C., winding temperature 640 ° C., cold rolling rate 75%, and annealing temperature 850 ° C., the amount of B added is such that generation of wrinkle-like defects and brittle transition temperature occur. It shows the effect on According to this, if B is added in an amount of 0.0004 wt% or more, a wrinkle-like wrinkle-like defect is generated. Therefore, in order to prevent the generation of the wrinkle-like wrinkle-like defect and to obtain good secondary working brittleness resistance, B is required. It turns out that the addition amount needs to be in the range of 0.0001 wt% or more and less than 0.0004 wt%.

Cu: Cu is effective not only for generating CuS and detoxifying S, but also for contributing to improvement of wrinkles by the generated CuS effectively functioning as a precipitation nucleus of carbide. If Cu is less than 0.01 wt%, the effect of the addition cannot be sufficiently obtained, while if it exceeds 0.05 wt%, surface defects called Cu flaws are easily induced. Therefore, Cu is set to 0.01 to 0.05 wt%.

[0013] Ti, Zr, Nb, V: These elements precipitate and fix solid solution elements such as C and N and improve the workability of the steel sheet. However, excessive addition not only increases the cost, but also degrades the surface quality of the steel sheet. Therefore, it is necessary to add one or more of these elements under the condition satisfying the following formula (1). If the addition amount of these elements is below the lower limit of the following formula (1), the effect of the addition cannot be sufficiently obtained. C / 12 ≦ Ti / 48 + Nb / 96 + Zr / 91 + V / 51−N / 14−S / 3 2 ≦ 4 × (C / 12) (1) where Ti: Ti content (wt%), Zr: Zr content Amount (wt%), V: V content (wt%), Nb: Nb content (wt%), C: C content (wt%), N: N content (wt%), S: S content Amount (wt%)

Among these elements, Ti and Zr form carbosulfides which are coarser than carbides and are less likely to form a solid solution again, and thus have the advantage that the precipitates can be easily coarsened in the hot rolling stage. . Therefore, in order to more reliably obtain the effects of the present invention, it is desirable to add Ti and / or Zr and to make the addition amount at least the N + S amount in atomic ratio. The balance is substantially composed of Fe, and does not prevent the inclusion of other elements as long as the effects of the present invention are not impaired. For example, Cr up to 0.1 wt% as an impurity element, 0.1 wt%
Up to 0.01 wt%, Sn and the like. The occurrence of the wrinkle-like defect is a problem peculiar to a plated steel sheet having a thickness of 1.2 mm or less. Therefore, the hot-dip galvanized steel sheet of the present invention is limited to a sheet thickness of 1.2 mm or less.

According to the present invention, a hot-dip galvanized steel sheet having good surface properties free of wavy crease-like surface defects can be obtained irrespective of the manufacturing conditions. From the viewpoint of workability and surface properties, a more preferable manufacturing method is as follows. From the viewpoint of coarsening the precipitate, the heating temperature is preferably 1200 ° C. or lower, the hot rolling finish temperature is preferably the Ar ₃ transformation point or higher, and the hot rolling winding temperature is preferably 550 ° C. or higher. From the viewpoint of preventing the solid solution of precipitates again and securing the grain size of the annealed plate, the annealing temperature is set to the recrystallization temperature + 20 ° C. to 8%.
Preferably, the temperature is 30 ° C.

Normally, a hot-dip galvanized steel sheet for processing applications is subjected to alloying treatment and temper rolling after plating to obtain a product.
In the present invention, the iron making method (blast furnace method, electric furnace method, smelting reduction method, etc.), slab casting method (continuous casting method, slab casting method, thin slab casting method, etc.), and hot rolling method (direct rolling, slab casting) There is no special restriction on processes such as reheating rolling, and any of these processes does not affect the effects of the present invention.

[0017]

EXAMPLE A steel slab having the composition shown in Table 1 was prepared at 1200 ° C.
To finish hot rolling at 890 ° C. and then wound up at 640 ° C. After pickling, the hot-rolled steel sheet was cold-rolled at a reduction of 75% to obtain a cold-rolled steel sheet. The cold-rolled steel sheet was annealed at 850 ° C. in a Sendzimir-type continuous hot-dip galvanizing line, and subsequently subjected to hot-dip galvanizing treatment, alloying treatment and temper rolling in order to obtain a sheet thickness of 0.7.
mm alloyed hot-dip galvanized steel sheet was manufactured. About the obtained alloyed hot-dip galvanized steel sheet, the presence or absence of a wrinkle-like wrinkle-like defect on the surface of the steel sheet, the presence or absence of plating unevenness, the ductility-brittle transition temperature as an index of secondary work brittleness resistance, and the total elongation were evaluated. Table 2 shows the results.

In the evaluation of the wrinkle-like defect, a wrinkle-free defect was evaluated as “◎” when no wrinkle was generated, and a wrinkle was generated at 10 cm ^2.
One of the following things per "○", as well 10cm ² per 2
More than books were evaluated as "x". The brittle transition temperature was determined by punching a steel sheet into a blank having a diameter of 105 mm, and then reducing the drawing ratio to 2.50 mm.
The cup was molded at a temperature of 1 and was specified at the lowest temperature at which no brittle fracture occurred when pressed in a refrigerant cooled to a predetermined temperature. According to Table 2, the hot-dip galvanized steel sheet of the present invention not only has excellent surface properties with no occurrence of creasing, but also has a sufficiently low brittle transition temperature of -90 ° C or less,
The total elongation is excellent at 47% or more, which indicates that the plated steel sheet is suitable for press forming.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As described above, according to the present invention, it is possible to obtain a hot-dip galvanized steel sheet having no surface defects such as wrinkle-like surface defects and excellent workability.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the amount of B added on the occurrence of wrinkle-like defects and brittle transition temperature.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Nakamura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Shunsaku Node 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (1)

[Claims] C: 0 to 0.0030 wt%, Si: 0
~ 0.05wt%, Mn: 0 ~ 0.5wt%, P: 0 ~
0.02 wt%, S: 0 to 0.020 wt%, sol.
Al: 0.010 to 0.080 wt%, N: 0 to 0.0
030 wt%, B: 0.0001 wt% or more 0.000
A steel sheet having a composition of less than 4 wt%, Cu: 0.01 to 0.05 wt%, and a component composition containing one or more of Ti, Zr, V, and Nb in an amount satisfying the following formula (1) is referred to as a base steel sheet. A hot-dip galvanized steel sheet having a thickness of 1.2 mm or less and having no wrinkle-like surface defects. C / 12 ≦ Ti / 48 + Nb / 96 + Zr / 91 + V / 51−N / 14−S / 3 2 ≦ 4 × (C / 12) (1) where Ti: Ti content (wt%), Zr: Zr content Amount (wt%), V: V content (wt%), Nb: Nb content (wt%), C: C content (wt%), N: N content (wt%), S: S content Amount (wt%)