JP3266008B2 - Manufacturing method of hot-dip galvanized steel sheet without galvanizing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip galvanized steel sheet having no blister.

[0002]

2. Description of the Related Art Conventionally, in the field of civil engineering and construction, a hot-dip galvanized steel sheet obtained by galvanizing a hot-rolled steel sheet having a thickness of 1.5 mm or more has been widely used. Many of these hot-dip galvanized steel sheets are plated by a continuous hot-dip galvanizing facility without hot rolling and pickling, and without going through a cold rolling step.

[0003] However, in the reduction process, hydrogen enters from the atmospheric gas into the hot-dip coated steel sheet manufactured in this manner, and this hydrogen is gradually released to the outside of the steel sheet over time after plating. . Since the galvanized film has a lower diffusion coefficient of hydrogen than the steel sheet, the hydrogen stays at the interface between the film and the steel sheet and generates blister-like defects in the film ("Zinc iron plate" V01.40 No. 6p.28). .

[0004] As a method for solving this problem, there is a method in which components such as B and N are added to steel to increase the hydrogen storage capacity of the steel and suppress the generation of defects (Japanese Patent Laid-Open No. Sho 5).
6-163250). However, the addition of these components causes an increase in production cost.

On the other hand, after the reduction, 45
A method of performing dehydrogenation while maintaining the temperature at 0 to 550 ° C. to release hydrogen in the steel sheet before plating is disclosed in
Although disclosed in Japanese Patent No. 30443, this method requires a dehydrogenation step between the annealing / reduction step and the plating step, which is disadvantageous in terms of equipment and productivity.

[0006] As still another method, an annealing temperature of 600
Japanese Patent Laid-Open Publication No. 52-95543 discloses a method in which the temperature is reduced to about 720 ° C. to suppress the intrusion of hydrogen in the annealing / reduction step. However, depending on the type of steel sheet, by limiting the annealing temperature, There is a problem that the control of the material, the shape and the plating property is restricted.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a hot-dip galvanizing method that can prevent plating swelling while securing the flexibility of the annealing temperature in the annealing step. An object of the present invention is to provide a method for manufacturing a plated steel sheet.

[0008]

In order to solve the above-mentioned problems, the present invention provides a hot-rolled steel sheet having a thickness of 1.5 mm or more, after pickling, annealing in a continuous hot-dip galvanizing line,
Do not perform alloying after plating in a hot dip zinc bath.
A method of manufacturing a have galvanized steel sheet, annealing furnace Kiri
When the hydrogen concentration (%) of the atmosphere is H and the annealing temperature (° C.) is RT, these are controlled so as to satisfy the following equations (1) and (2). To provide a hot-dip galvanized steel sheet manufacturing method. 650 ≦ RT ≦ 950 (1) 1 ≦ H ≦ −0.05 × RT + 57.5 (2)

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in order to prevent plating swelling, it is effective to reduce the amount of hydrogen absorbed in the annealing / reduction step. For this reason, the annealing temperature is lowered. However, there are various problems as described above.

The present inventor has proposed a hot-rolled steel sheet having a thickness of 1.5 mm or more.
As a result of intensive studies on a method for preventing plating swelling of the sheet, it was found that the occurrence of plating swelling depends not only on the annealing temperature but also on the hydrogen concentration of the atmosphere gas during annealing. That is, even at high annealing temperature be lower the hydrogen concentration blistering plating does not occur, material, shape, while ensuring the annealing temperature required in view of coatability, plating skin
It is possible to prevent blistering of the membrane .

The reasons for limiting the annealing temperature and the hydrogen concentration in the atmosphere in the annealing furnace will be described below. First, regarding the annealing temperature, if the annealing temperature is lower than 650 ° C., a shape defect occurs depending on the type of the steel sheet. On the other hand, when the temperature exceeds 950 ° C., the crystal grains of the steel sheet become coarse, and the ductility deteriorates. Therefore, the annealing temperature is set to 6 as shown in the above equation (1).
The range is 50 to 950 ° C.

Next, regarding the hydrogen concentration in the atmosphere in the annealing furnace, if the hydrogen concentration exceeds −0.05 × RT + 57.5 (RT is the annealing temperature) , blistering of the plating film occurs. On the other hand, if the hydrogen concentration is less than 1%, even if the annealing temperature is increased, the reduction reaction does not sufficiently proceed, causing defects such as non-plating and poor adhesion. Therefore, in the annealing furnace
The hydrogen concentration in the atmosphere is defined in the range of the above equation (2) in relation to the annealing temperature. As described above, in the present invention, the hydrogen concentration and the annealing temperature in the atmosphere in the annealing furnace are defined, and the ranges are as shown by the hatched portions in FIG.

[0013]

EXAMPLES In order to confirm the effects of the present invention, a hot-dip galvanized steel sheet of the present invention was manufactured in a continuous hot-dip galvanizing line. Table 1 shows the components of the steel sheet used for the plating base material.

[0014]

[Table 1]

This steel sheet was hot-rolled at a finishing temperature of 750 to 800 ° C. and wound at a winding temperature of 650 ° C. After that, it was pickled, and was not subjected to cold rolling, but was annealed in a continuous hot-dip galvanizing line under predetermined conditions, and then galvanized. The composition of the plating bath was such that the Al concentration was 0.14% and the balance was Zn. Further, the plating bath temperature was 465 ° C., the penetration plate temperature was 475 ° C., and the coating weight was 270 g / m ₂ or more on both sides. Other manufacturing conditions were standard when passing equivalent materials through a continuous hot-dip plating line.

In Table 2, No. Examples 1, 6, and 18 are comparative examples deviating from the present invention, and other examples are examples satisfying the scope of the present invention. The presence or absence of blisters on these test materials
Evaluation was made by visual observation and observation of the surface appearance by a 10-fold rule. Further, a 0T bending test was performed, and a tape peeling test was performed on the outside of the bent portion to evaluate plating adhesion. No plating was observed in any of the test materials. Table 2 shows the results.

[0017]

[Table 2] As is clear from this table, those in the range of the present invention exhibited good plating swelling and adhesion.

[0018]

As described above, according to the present invention ,
The hydrogen concentration in the furnace atmosphere gas during annealing as well as the annealing temperature
Since the temperature is controlled to a low level, the annealing temperature
Even if it does, blistering of the plating film does not occur. others
Required from the viewpoint of material, shape and plating properties
Effectively prevents blistering of plating film while maintaining temperature
Can be

[Brief description of the drawings]

FIG. 1 is a view showing a range of annealing conditions in the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keishi Yamashita 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Soichi Shimada 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan (56) References JP-A-6-184716 (JP, A) JP-A-6-184715 (JP, A) JP-A-5-311370 (JP, A) JP-A-5-306444 (JP) JP-A-5-287482 (JP, A) JP-A-3-191047 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] [Claim 1] After pickling the thickness 1.5mm or more hot-rolled steel sheet, annealing in a continuous galvanizing line, then dissolved
A method of manufacturing a <br/> galvanized steel sheet is not performed alloying treatment after the plating at fusion zinc bath, annealing furnace Uchikiri囲
When the hydrogen concentration (%) of gas is H and the annealing temperature (° C.) is RT, these are controlled so as to satisfy the following equations (1) and (2). No galvanized steel sheet manufacturing method. 650 ≦ RT ≦ 950 (1) 1 ≦ H ≦ −0.05 × RT + 57.5 (2)