JP3225442B2 - Manufacturing method of hot-dip galvanized steel sheet for deep drawing with excellent perforation corrosion resistance - 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 for deep drawing having excellent perforation corrosion resistance.

[0002]

2. Description of the Related Art In the field of cold rolled steel sheets used for steel sheets for automobiles and the like, it is often required to be excellent in deep drawability. In order to further improve corrosion resistance, demand for surface-treated steel sheets subjected to various surface treatments is increasing. The surface-treated steel sheet is a hot-dip galvanized steel sheet. However, since the corrosion resistance is not sufficient, the amount of coating is increased to further improve the corrosion resistance.

[0003] Hot-dip galvanized steel sheets are conventionally known as low-carbon aluminum-killed steel sheets and ultra-low-carbon steel sheets to which Ti is added as a base, and high-strength steel sheets to which Si, Mn, P, and Cr are added to increase the strength. There are many suggestions. For example, Japanese Patent Publication No. 1-54413 discloses a galvanized steel sheet in which P is added to a low-carbon aluminum killed steel. JP-A-57-43974 discloses hot-dip galvanized steel sheets in which P and a large amount of Mn are added to ultra-low carbon Ti-added steel, but all of these have poor corrosion resistance.

[0004] In hot-dip galvanizing, hot-dip zinc and ground iron react to form an alloy layer, and this alloy layer connects the zinc layer and the ground iron. Further, in order to improve the coating adhesion, an alloying treatment is applied to the entire plating layer to form an alloy layer, but this alloy layer is hard and brittle. Since the hot-dip galvanized steel sheet is used as a member for deep drawing, it is inevitably processed. For this reason, when the thickness of the plating layer increases, the workability of the hot-dip galvanized steel sheet is determined not by the workability of the ground iron but by the workability of the plating layer. I ca n’t get it,
Further, there is a disadvantage that the peeling and damage of the plating layer become remarkable at the time of processing, and the base iron is exposed and rusted by the processing, thereby easily causing perforation corrosion.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention is not to respond to the most important corrosion resistance of a galvanized steel sheet by perforating corrosion resistance by increasing the thickness of a plating layer.
It is an object of the present invention to provide a method for producing a hot-dip galvanized steel sheet that improves the corrosion resistance of a base material and satisfies both workability and plating adhesion.

[0006]

The present inventors have conducted various studies on a method for producing a hot-dip galvanized steel sheet having both excellent workability and corrosion resistance, and found that trace amounts of Ti and Nb were added to extremely low carbon steel. By adding Cu and P to improve deep drawability and improve corrosion resistance by containing Si, Mn and Ni, Mo, Cr, etc. for higher strength and higher corrosion resistance We have obtained a hot-dip galvanized steel sheet for deep drawing with excellent corrosiveness.

[0007]

That is, in the present invention, C: 0.02 or less, Si: 1.5 or less, Mn:
0.05 to 1.8, P: 0.03 to 0.20, S: 0.
015 or less, Cu: 0.05 to 1.5, solAl:
0.005 to 0.100, N: 0.005 or less, Ti:
Comprises 0.005 to 0.15, the balance being subjected to hot rolling a slab of steel consisting of iron and unavoidable impurities 500
Winding at a temperature of 750 ° C. , pickling, cold rolling,
After that, 700-950 in continuous hot-dip galvanizing line
C. annealing or galvanizing, or iron plating in a continuous electroplating line, followed by annealing at 700 to 950 ° C. in a continuous galvanizing line and then galvanizing Provided is a method of manufacturing a hot-dip galvanized steel sheet for deep drawing having excellent corrosiveness.

According to the present invention, there are also provided, by weight%, C: 0.02 or less, Si: 1.5 or less, Mn:
0.05 to 1.8, P: 0.03 to 0.20, S: 0.
02 or less, Cu: 0.05-1.5, solAl: 0.
005 to 0.100, N: 0.005 or less, and T
i: 0.005 to 0.15, Nb: 0.005 to 0.1
5%, up to 1% Ni, up to 3% Mo and up to 7% C
r wherein one or two or more, the balance is subjected to hot rolling a slab of steel consisting of iron and unavoidable impurities 50
It is wound at a temperature of 0 to 750 ° C. , cold-rolled after pickling, and then 700 to 9 in a continuous galvanizing line.
Annealed at 50 ° C. and galvanized, or an iron plating at a continuous electroplating line, followed by annealing at 700 to 950 ° C. at a continuous galvanized line and then galvanized. Provided is a method for producing a hot-dip galvanized steel sheet for deep drawing having excellent perforated corrosion resistance.

[0009] The present invention also provides steel B in an amount of 0.0003 to 0.1.
003% is provided.

[0010] The present invention also provides the manufacturing method according to any one of the preceding items, wherein the galvanizing performed in the hot-dip galvanizing line includes a process of alloying the galvanized layer at a temperature of 400 to 650 ° C.

First, the reason why the action and content of each component in the method for producing a steel sheet according to the present invention are limited to the above ranges will be described. C is preferable as it is small because it deteriorates ductility, but is acceptable up to 0.02%. Therefore, C is set to 0.02% or less.

[0012] Si is a preferable element for improving the strength of steel without impairing the workability, but according to the study of the present inventors, in the Sendzimer type continuous galvanizing line, about 0.10
%, Non-plating occurs. Therefore, 0.10
% Is desirable. However, this problem can be solved by performing electroplating with iron plating having a coating weight of about 2 g / m 2 before passing through the Zenzimer-type continuous galvanizing line. However, if Si exceeds 1.5%, it becomes hard and ductility deteriorates, so the upper limit was made 1.5%.

Mn is effective in preventing hot brittleness due to S. For that purpose, Mn must be at least 0.05% or more. On the other hand, although it is a preferable element for improving the strength, it is 1.8.
%, The ductility and the deep drawability decrease, so the lower limit was set to 0.05% and the upper limit was set to 1.80%.

P and Cu are characteristic elements in the present invention, and the combined addition of these elements significantly improves the pitting corrosion resistance. P must be 0.03% or more and Cu must be 0.05% or more in order to improve pitting corrosion resistance. On the other hand, when P exceeds 0.20% and Cu exceeds 1.5%, the improvement effect is saturated and the ductility is deteriorated. Therefore, P has a lower limit of 0.03% and an upper limit of 0.20%. Cu has a lower limit of 0.05% and an upper limit of 1.5%.

S is an element which is essentially harmful to steel, and the smaller the value, the better. However, S is acceptable up to 0.02%.

Al must be present in an amount of 0.005% or more in order to play a role as a deoxidizing agent. However, inclusions such as Al.sub.2 O.sub.3 exceeding 0.10% increase to deteriorate workability and surface quality. Therefore, the lower limit is 0.005% and the upper limit is 0.
10%.

N is an element which is essentially harmful to steel, and it is desirable that the N content is as small as possible.

Ti and Nb represent C, S and N as TiC, T
It has an effect of fixing as a precipitate such as iS, TiN, NbC and the like, and is an effective element for securing excellent deep drawability. To obtain such an effect, the effect is not recognized at 0.005% or less, and the effect is saturated even if C is added in excess of 0.15% in the present invention. For this reason, the lower limit was made 0.005% and the upper limit was made 0.15%.

Further, in the present invention, in order to increase the strength of the steel sheet and to improve the pitting corrosion resistance, it is preferable to use Ni up to 1%, 3%
Of Mo and up to 7% of Cr.

Ni effectively acts on prevention of hot brittleness by Cu and improvement of pitting corrosion resistance.
The effect is saturated and the manufacturing cost is high. For this reason, the upper limit is set to 1%.

Mo effectively acts to increase the strength of the steel sheet and to improve the corrosion resistance to perforation. However, if it exceeds 3%, the effect is saturated and the production cost becomes high. Therefore, the upper limit is set to 3%. .

Although Cr effectively acts to improve the pitting corrosion resistance, if it exceeds 7%, the production cost becomes extremely high. Therefore, the upper limit is made 7%.

B is effective for improving the embrittlement of secondary working,
For that purpose, it is necessary to add 0.0003% or more. On the other hand, even if it exceeds 0.003%, the effect is saturated. Therefore, B is 0.0003-0.003%
And

In the present invention, steel having such a composition is subjected to hot-dip galvanizing through a hot rolling step and a cold rolling step. In this case, the finishing temperature in the hot rolling step is equal to or higher than the Ar3 transformation point. Is preferable, and the winding temperature is 500 to
The temperature must be in the range of 750 ° C. Winding temperature is 500
If the temperature is lower than 0 ° C, TiC or the like is finely precipitated, and after cold rolling annealing.
There is a possibility that sufficient deep drawability cannot be obtained. on the other hand,
If the winding temperature exceeds 750 ° C, the effect of improving
The pickling deterioration due to the increase in the scale thickness
You will be invited.

In the cold rolling step, a cold rolling rate of 50 to 95% is required in order to secure the deep drawability. Cold rolling rate is 50%
If it is less than 0.5%, the deep drawability is inferior, and if the cold rolling ratio exceeds 95%, the load on the cold rolling mill increases, and the productivity is poor.

The reason why the lower limit of the annealing temperature in the continuous hot-dip galvanizing line is set to 700 ° C. or higher is to improve the workability above the recrystallization temperature and to set the upper limit to 950 ° C. or lower. This is because the improvement of the properties is saturated and the surface flaw is easily generated in the continuous galvanizing line.

Next, regarding the alloying treatment of the hot-dip galvanized steel sheet, the alloying treatment does not particularly impair the material of the steel of the present invention, and improves the coating adhesion and the lap resistance weldability of the galvanized steel sheet. Therefore, it can be said that this is a preferable treatment in terms of application of the material of the present invention. Usually, the alloying is performed in a continuous hot-dip galvanizing line, and in that case, at a temperature range of 400 to 650 ° C., the achievement of the alloying is necessary and sufficient. That is, if the temperature is lower than this temperature range, the alloying is insufficient, and if the temperature is higher, the alloying is excessive and the adhesion of the plating layer is impaired.

[0028]

DETAILED DISCLOSURE OF THE INVENTION

Example 1 Using a steel having the composition shown in Table 1, a hot-rolled sheet having a thickness of 3.2 mm was formed by hot rolling under the conditions shown in Table 2 and further cold-rolled to obtain a sheet having a thickness of 0.8 mm. Cold rolled steel sheet. The obtained cold-rolled steel sheet was subjected to annealing and galvanization with a coating weight of 30 g / m 2 in a continuous hot-dip galvanizing line, and then the elongation percentage was:
0.8% skin pass rolling was performed, and the properties of the obtained steel sheet were investigated.

Table 2 shows the results. In addition, the mechanical characteristics used the No. 5 test piece of JISZ2201. In the corrosion resistance test, a 70 × 150 mm test piece was cut out and subjected to a composite corrosion test. The combined corrosion test is based on the salt water spray test of JIS Z2371. The salt water spray test with a salt water concentration of 5% is 2 hours → the hot air drying at 60 ° C is 4 hours → the wet test of JIS C1234 is 2 hours, and a total of 8 hours is one cycle. The maximum erosion depth due to corrosion was measured.

As can be seen from the results in Table 2, P and Cu are lower than specified in the present invention (outside the scope of the present invention)
In hot-dip galvanized steel sheet manufactured using comparative steel,
No. In Comparative Steel No. 1, the elongation (El) and the plastic strain ratio (r) were low and the corrosion resistance was inferior despite the low tensile strength (TS). No. C is low. In the comparative steel No. 2, the elongation (El)
And the plastic strain ratio (r) are good, but the corrosion resistance is poor.

On the other hand, No. 1 having a component composition within the range specified in the present invention. 3-No. The hot-dip galvanized steel sheet manufactured using the No. 10 steel has a high plastic strain ratio (r), a good ductility (El), and excellent corrosion resistance despite high tensile strength (TS).

Example 2 A steel having the composition shown in Table 3 was hot-rolled and then cold-rolled under the conditions shown in Table 4 to obtain a cold-rolled steel sheet having a thickness of 0.8 mm. The obtained cold-rolled steel sheet was subjected to iron plating (Fe-0.1% B) with a coating amount of 2 g / m 2 in a continuous plating line, and then annealed and coated in a continuous hot-dip galvanizing line: 3
0 g / m 2 of zinc plating was applied. After that, the elongation rate: 0.
8% skin pass rolling was performed, and the characteristics of the obtained steel sheet were investigated.

The evaluation of the characteristics was performed in the same manner as in Example 1. As can be seen from the results in Table 4, the No. values outside the range specified in the present invention. Comparative steel No. 11 has good tensile properties and plastic strain ratio (r), but has low P and Cu,
Since r, Mo, and the like are not added, the corrosion resistance is poor.

On the other hand, No. 1 having a component composition within the range specified in the present invention. 12-No. The hot-dip galvanized steel sheet manufactured using the No. 15 steel has good tensile strength (TS), high elongation (El), and high plastic strain ratio (r).
Furthermore, it has excellent corrosion resistance.

[0035]

As described above, according to the present invention, the amount of coating on a hot-dip galvanized steel sheet excellent in deep drawability can be reduced, the press workability is deteriorated due to the increase in the amount of coating, and the plating layer is peeled off. Such problems can be avoided, and the corrosion resistance of the hot-dip galvanized steel sheet is improved, and the industrial effect is extremely remarkable.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C25D 5/26 C25D 5/26 C (72) Inventor Mikio Soshita 11-1, Showa-cho, Kure-shi, Hiroshima Nisshin Steel Co., Ltd. Steel and Steel Research Laboratory, Process and Steel Research Department (72) Inventor Toshiro Yamada 11-1 Showa-cho, Kure-shi, Hiroshima Nisshin Steel Corporation Steel Research Laboratory, Process and Steel Research Department (56) References Special JP-A-3-111519 (JP, A) JP-A-62-243738 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 301 C22C 38/54 C23C 2/02 C23C 2/06 C25D 3/20 C25D 5/26

Claims (4)

(57) [Claims] (1) C: 0.02 or less by weight%, Si: 1.
5, Mn: 0.05 to 1.8, P: 0.03 to 0.
20, S: 0.015 or less, Cu: 0.05 to 1.5,
solAl: 0.005 to 0.100, N: 0.005
Hereinafter, Ti: comprises 0.005 to 0.15, balance facilities hot rolling a slab of steel consisting of iron and unavoidable impurities
And then rolled at a temperature of 500 to 750 ° C. , pickled, and then cold-rolled.
After performing an annealing at 00 to 950 ° C. and performing galvanization, or after performing iron plating in a continuous electroplating line,
A method for producing a hot-dip galvanized steel sheet for deep drawing, which is excellent in pitting corrosion resistance, comprising annealing at 700 to 950 ° C. in a continuous hot-dip galvanizing line and then galvanizing. 2. C: 0.02 or less in weight%;
5, Mn: 0.05 to 1.8, P: 0.03 to 0.
20, S: 0.015 or less, Cu: 0.05 to 1.5,
solAl: 0.005 to 0.100, N: 0.005
Hereinafter, Ti: 0.005 to 0.15, and Nb:
Containing one or more of 0.005 to 0.15%, up to 1% Ni, up to 3% Mo and up to 7% Cr,
The remainder is subjected to hot rolling on a steel slab consisting of iron and unavoidable impurities , winding at a temperature of 500 to 750 ° C. , pickling, cold rolling, and then 700 to 1000 in a continuous galvanizing line. Galvanizing by annealing at 950 ° C. or iron plating in a continuous electroplating line, and then 700 to 95 in a continuous galvanizing line.
A method for producing a hot-dip galvanized steel sheet for deep drawing, which is excellent in perforation-corrosion resistance and comprises galvanizing after annealing at 0 ° C. 3. The method according to claim 1, wherein the steel contains 0.0003 to 0.003% of B. 4. The method according to claim 1, wherein the galvanizing performed in the hot-dip galvanizing line includes a process of alloying the galvanized layer at a temperature of 400 to 650 ° C.