JP3464289B2 - Method for producing hot-dip Zn-Al alloy-plated steel sheet for fire-resistant structure with excellent 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 Zn-Al alloy-plated steel sheet for a refractory structure, which has excellent corrosion resistance and can be used without a fireproof coating for various structures such as buildings.

[0002]

2. Description of the Related Art Conventionally, JIS used for buildings
Among the standard steel materials, those having a steel plate form include general structural rolled steel materials (G3101) and welded structural rolled steel materials (G310).
6), weather-resistant hot-rolled steel for welded structures (G3114), etc. are widely used, and as materials for structural lightweight steel and structural steel pipes, hot-rolled soft steel sheets (G3132) and hot-dip galvanized steel sheets (G3132) are used. G3302) and the like are widely used.

On the other hand, in order to prevent the strength from becoming insufficient due to heat during a fire and to ensure safety during a fire, the steel material is
It is obligatory in buildings to coat the steel surface with a heat-resistant refractory so that the temperature does not exceed ℃. However, if the high-temperature strength of steel is secured, it is possible to use steel without coating. Therefore, various studies have been conducted on steel materials that have high yield strength even at high temperatures.

The high-temperature strength of steel materials has been investigated for a long time, and some steel sheets have been standardized as steel sheets for boilers or pressure vessel steel sheets. That is, it is a steel material having high creep strength. In the case of fire-resistant structural materials, the strength assuming a fire is within a few hours at most, so high creep strength is virtually excluded, and the above-mentioned high temperature steel sheet is too strong at room temperature. It cannot be applied to general structures because it has poor cold workability and its weldability is significantly inferior to that of structural steel plates.

Therefore, for example, Japanese Unexamined Patent Publication No. 4-136118
In JP-A-5-79744 and JP-A-5-79744, by adding Mo and V to steel, Mo carbide and V carbide are finely precipitated during the process of exposing the steel material to a high temperature during a fire, thereby improving the high temperature of the steel material. A steel material for construction has been proposed to obtain yield strength.

[0006]

In general structures such as buildings, which are used as they are without being subjected to fireproof coating as described above, in addition to maintaining strength during a fire, they also have corrosion resistance during normal times. It is an important factor, and in order to be widely used, it is necessary that the material has good moldability and is economical.

Therefore, the object of the present invention is to provide excellent high-temperature characteristics, corrosion resistance, and formability, and without using special means in the steel making process or hot rolling process.
Another object is to obtain an economically advantageous refractory steel material for buildings having a steel composition close to that of ordinary steel.

[0008]

According to the present invention, the weight percent is
C: 0.03 to 0.20%, Si: 0.1% or less, M
n: 0.3 to 2.0%, P: 0.03 to 0.15%, S:
0.02% or less, Al: 0.005-0.1%, Mo: 0.0
05-1.0%, Cu: 0.6-2.0%, Ni: 0.3-
2.0%, depending on the case, the above Cu content
Of 0.61 to 2.0%, and further Cr: 0.
05-1.0, V: 0.005-0.2, W: 0.01-
1.0, Ti: 0.005-0.2, Nb: 0.005-
0.2 or B: A steel slab containing one or more of 0.0003 to 0.003 and the balance consisting of iron and unavoidable impurities is hot-rolled, pickled, and continuously melted Zn- Passed through the Al alloy plating equipment, and at this equipment, 4
Molten Zn-Al for refractory structures with excellent corrosion resistance, which consists of hot-dip Zn-Al alloy plating by heating to 50-750 ℃
A method for manufacturing an alloy-plated steel sheet is provided.

[0009]

Operation: Molten Zn- for refractory structure obtained by the method of the present invention
The Al alloy-plated steel sheet has excellent corrosion resistance when used for general structures such as construction, and does not cause insufficient strength even in the case of fire, so it can be used without a fireproof coating. Such properties of the material of the present invention are obtained especially by subjecting a base steel sheet to which P and Cu are added in combination to hot dip Zn-Al alloy plating. More specifically, P and C
Corrosion resistance is improved by the combined addition of u and Cu in steel
Serves to enhance the high temperature strength by precipitating ε-Cu intermetallic compound at high temperature. This also has an economical advantage because the content of expensive Mo that contributes to the improvement of high temperature strength can be reduced.

The hot-dip Zn-Al alloy plating layer applied to the base steel sheet secures its corrosion resistance and makes the surface beautiful when the material of the present invention is used for a general structure, thus significantly increasing the product value.

The inventors of the present invention have conducted various tests and studies in order to know the influence of the chemical composition in the steel and the manufacturing conditions on the strength and corrosion resistance of the plated steel sheet at 600 ° C. For this purpose, M in a composition system close to ordinary steel
Strictly adding o, Cu and P within the above range,
Furthermore, based on the addition of Mo, Cu and P, C
We have found that strictly adding r, V, W, Ti, Nb or B in the above range is extremely effective.

From this, it has been found that a hot-dip Zn-Al alloy-plated steel sheet for fireproof structure, which has a yield strength at 600 ° C. of 0.6 or more than a yield strength at room temperature and is excellent in corrosion resistance and workability, can be advantageously produced. .

The action of each component of the base steel sheet according to the present invention and the reason for limiting the content range are as follows.

C is an element necessary for ensuring a predetermined strength of the steel sheet, but if it is less than 0.03%, its effect is poor, and if it exceeds 0.20%, workability, weldability and toughness are deteriorated. It will be lost, so it was limited to 0.03 to 0.20%.

Si is effective as a strength improving element. However, Si has a comparatively small effect of improving the high temperature strength and corrosion resistance that the material of the present invention must have, so the content of Si is limited to 0.10% or less.

Mn effectively acts to increase the strength, but
If the content is less than 30%, the effect is small, and if the content exceeds 2.0%, the workability is deteriorated.
Limit to 0% range.

In the material of the present invention, P effectively acts to improve the strength and, particularly, interacts with Cu to improve the corrosion resistance. Therefore, although it is an element exhibiting a characteristic action in the present invention, if it is less than 0.03%, its effect is small, and
If the content exceeds 15%, embrittlement is promoted, so 0.03 to 0.1
Limited to 5%. The preferred amount of P is 0.038-
0.10%, more preferably more than 0.04% to 0.08
%.

S is an element which is essentially harmful to the base steel sheet and is preferably as small as possible, but in the case of the material of the present invention, it is 0.0
Since up to 2% is acceptable, it was set to 0.02% or less.

Al not only plays a role as a deoxidizing material at the time of manufacturing steel, but also serves to fix N in the steel as AlN. For this purpose, 0.005% or more is required, but if it exceeds 0.10%, inclusions increase and workability and surface quality deteriorate, so 0.005% as acid-soluble Al. The range is 0.10%.

Mo acts as a solid solution in the steel or precipitates carbide to improve the high temperature strength of the steel sheet. To obtain such effects, it is necessary to add more than 0.05%, but even if added over 1.0%, the effects commensurate with the addition cannot be obtained, so 0.05-1.0% The range is. In addition, as shown in Examples described later, even if Mo is reduced by adding Cu and P in combination, good high temperature strength and corrosion resistance can be maintained. Therefore, the content is preferably 0.005% or more and less than 0.60%.

Cu is a characteristic element in the steel sheet of the present invention, and has a function of forming a solid solution in the steel or finely precipitating as ε-Cu to improve the high temperature strength. Further, by interacting with P, a fine corrosion product is formed to improve the corrosion resistance. These effects are remarkable when Cu is added in an amount of 0.6% or more, but when added in an amount of more than 2.0%, the effect is saturated and embrittlement occurs during hot rolling, resulting in significant hot cracking. Therefore, the Cu content is set to the range of 0.6 to 2.0%. One of Cr, V, W, Ti, Nb, B
Or, in the steel sheet containing two or more kinds, the Cu content is
The range is 0.61 to 2.0%.

Ni is an element that improves the corrosion resistance. It is also an element effective in preventing hot brittleness of steel. In order to obtain such an effect, it is necessary to add 1/2 or more of Cu. Therefore, in the present invention, the range is 0.30 to 2.0%.

Cr improves the corrosion resistance of the base steel sheet, but 0.05% or more is required to obtain this effect. However, since the addition of more than 1.0% is unnecessary for the structural material of the present invention, the range is set to 0.05 to 1.0%.

W has the function of improving the high temperature strength of the steel by forming a solid solution or precipitating carbide in the steel. To obtain the effect of this, it is necessary to add more than 0.01%, but even if added over 1.0%, the effect commensurate with the addition cannot be obtained, so 0.01 to 1.0% It is limited to the range of.

V, Ti, and Nb are all elements having the same action in improving the room temperature strength and the high temperature strength, but if less than 0.005%, no effect is recognized and 0.00
Even if it exceeds 2%, the effect corresponding to the added amount cannot be obtained, so the range is 0.005 to 0.2% in all cases.

B has the functions of improving the hardenability of steel and strengthening the grain boundaries. When such effects are required, it is necessary to add 0.0003% or more. But 0.00
Even if added over 3%, the effect will be saturated,
The range is 0.0003 to 0.003%.

In the present invention, a steel having the above-described composition is made into a slab by a normal process and then hot-rolled to obtain a steel plate having a predetermined thickness. In this hot-rolling, the slab heating temperature is set. It is desirable to perform hot rolling under the conditions of 1050 to 1250 ° C, hot rolling finishing temperature of 800 to 950 ° C, and winding temperature of 500 to 700 ° C.

Then, after pickling the hot-rolled sheet, it is passed through a continuous hot dip galvanizing equipment, and 450 to 75
Heated to 0 ° C. to perform hot dip Zn-Al alloy plating. If the heating temperature in the continuous hot dip coating equipment is less than 450 ° C, the plating adhesion will be poor. On the other hand, if it exceeds 750 ° C., surface defects are likely to occur and it becomes difficult to obtain a good product. The heating at 450 to 750 ° C. in the equipment is performed in a reducing atmosphere.

The hot-dip Zn-Al alloy plating applied in the present invention means a normal hot-dip Zn-Al alloy plating in which the amount of Al is 3 to 60% by weight and the balance is substantially Zn. The target is Zn-Al alloy plating containing 5 wt% or Zn-Al alloy plating containing about 50 wt% Al.

The effects of the present invention will be specifically described below with reference to examples.

[0031]

[Examples] Steels having the chemical composition values shown in Table 1 were melted and made into slabs by an ordinary method, and the slabs were hot-rolled under the conditions shown in Table 2 to obtain hot-rolled steel sheets with a plate thickness of 3.2 mm. . The hot-rolled steel sheet obtained was pickled and then heated to the heating reduction temperature shown in Table 2 in a continuous hot dip galvanizing facility, and then aluminum 4.
8 wt% hot-dip Zn-Al alloy plating applied 45 g / m ²
I gave it in.

Test pieces were taken from each of the obtained plated steel sheets and subjected to a room temperature tensile test, a high temperature tensile test and a corrosion resistance test. The results are shown in Table 2.

The tensile test at room temperature is JISZ22.
No. 5 test piece No. 01 was used. High temperature tensile test is JI
According to SG0567, the tensile strength and the yield strength were measured after keeping at 600 ° C. for 15 minutes. As a high temperature strength index, the ratio of the yield strength at 600 ° C. and the yield strength at room temperature (yield strength ratio) was determined.

For the corrosion resistance test, a 70 mm × 150 mm test piece cut out from each plated steel sheet was subjected to a combined cycle corrosion test under the conditions shown in FIG. As shown in the figure, this is 5% NaCl under a temperature of 35 ° C and a relative humidity of 98%.
Sprayed with salt water for 2 hours, 60 ℃, relative humidity 20 ～ 30 ℃
A total of 8 hours of complex corrosion cycle of drying for 4 hours in a furnace kept at 4 hours and keeping in a humid atmosphere at a temperature of 50 ° C and a relative humidity of 95% or more for 2 hours is set as one cycle, and this cycle is continuously performed for 240 cycles. Conduct (3 per day
Cycle), the corrosion products were removed from the test pieces after the final cycle, and the maximum erosion depth was measured, and this maximum erosion depth was used as an index of the corrosion resistance of the plated steel sheet.

[0035]

[Table 1]

[0036]

[Table 2]

As shown in the results of Table 2, Mo, Cu
And Comparative Example M containing no P and P in the range specified in the present invention
The hot-dip Zn-Al alloy-plated steel sheet of No. 1 has a required strength ductility at room temperature, but the yield strength at 600 ° C. is greatly reduced, and the high-temperature characteristics are inferior because the yield strength ratio of 0.6 or more is not satisfied. In addition, the maximum erosion depth is as deep as 0.93 mm and the corrosion resistance is poor.

Mo is within the range specified in the present invention, but Cu
In the hot-dip Zn-Al alloy-plated steel sheets of Comparative Examples M2 and M3 that do not contain P and P within the range specified in the present invention, no decrease in ductility at room temperature was observed, and the decrease in yield strength at 600 ° C was small, and the yield strength was low. It has a ratio of 0.6 or more and is excellent in high temperature strength. However, the maximum erosion depth is 0.
77mm, 0.74mm deep and poor in corrosion resistance.

On the other hand, in the hot-dip Zn-Al alloy-plated steel sheets of the invention steels S1 to S13, no significant decrease in ductility at room temperature was observed and the yield strength at 600 ° C. was excellent. In addition, the maximum erosion depth is shallower than that of the steel sheet of the comparative example, and it has excellent corrosion resistance.

Of these, in particular, the hot dip Zn-Al alloy plated steel sheet of the present invention steel S8 in which Cr, V and W are added in combination and the present invention steel S13 in which Nb and B are added in combination have a yield strength ratio of 0. It is as high as 72, 0.73 mm and at the maximum erosion depth as low as 0.41 mm and 0.36 mm, both high temperature characteristics and corrosion resistance are very good.

[0041]

As described above, according to the present invention,
Molten Z for refractory structures that has good corrosion resistance for various structures such as buildings and has high-temperature strength that can be used without a fireproof coating
An n-Al alloy plated steel sheet is obtained. Further, this plated steel sheet has good workability as seen in the room temperature tensile test values of the examples, and the base steel sheet has a steel composition close to that of ordinary steel and has good manufacturability, so that it is inexpensive. Therefore, it is possible to provide, at low cost, a material that is extremely useful as a building structure material in the event of a fire.

[Brief description of drawings]

FIG. 1 is a diagram showing conditions of a combined cycle corrosion test for evaluating corrosion resistance in Examples of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C23C 2/06 C23C 2/06 (56) Reference JP-A-5-306411 (JP, A) JP-A-5-331596 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 2/00-2/40 C21D 8/02 C22C 38/00 301 C22C 38/16 C22C 38/54

Claims (3)

(57) [Claims] 1. C: 0.03 to 0.20% by weight, S
i: 0.1% or less, Mn: 0.3 to 2.0%, P: 0.03
~ 0.15%, S: 0.02% or less, Al: 0.005
0.1%, Mo: 0.05-1.0%, Cu: 0.6-2.
A steel slab of 0%, Ni: 0.3 to 2.0%, the balance being iron and inevitable impurities is hot-rolled, pickled, and then passed through a continuous hot-dip Zn-Al alloy plating facility. Molten Zn-for refractory structures with excellent corrosion resistance, which consists of performing hot-dip Zn-Al alloy plating by heating to 450-750 ° C in equipment
Manufacturing method of Al alloy plated steel sheet. 2. By weight%, C: 0.03 to 0.20%, Si: 0.1% or less, Mn: 0.3 to 2.0%, P: 0.03 to 0.15%, S: 0.02% or less, Al: 0.005 to 0.1%, Mo: 0.05 to 1.0%, Cu: 0.61 to 2.0%, Ni: 0.3 to 2.0. %, Cr: 0.05 to 1.0, V: 0.005
~ 0.2, W: 0.01-1.0, Ti: 0.005-0.
2, Nb: 0.005-0.2 or B: 0.0003-
A steel slab containing 0.003 or more of 0.003 and the balance of iron and unavoidable impurities is hot-rolled, pickled, and then passed through a continuous hot-dip Zn-Al alloy plating facility. A method for manufacturing a hot-dip Zn-Al alloy-plated steel sheet for a refractory structure, which is excellent in corrosion resistance, which comprises heating at a temperature of 450 to 750 ° C. to perform hot-dip Zn-Al alloy plating. 3. The molten Zn-for refractory structure excellent in corrosion resistance according to claim 1 or 2, wherein the heating at 450 to 750 ° C. in the continuous molten Zn-Al alloy plating equipment is performed in a reducing atmosphere.
Manufacturing method of Al alloy plated steel sheet.