JP3413341B2 - Hot-dip galvanized steel sheet having high yield strength at 800 to 850 ° C and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet used for roofs, walls, etc. of buildings that is less likely to buckle during a fire and a method for producing the same.

[0002]

2. Description of the Related Art A material used for a building is required to have sufficient strength so that the building is not easily damaged or collapsed even in case of fire. In general, the strength of steel materials decreases at high temperatures, so even if a building is exposed to fire heating (standard heating) specified by the Building Standards Act,
It has been used with a fireproof coating such as rock wool so that the temperature of the steel itself does not rise extremely. That is, a steel material having a fireproof coating has been used for a building according to standard heating of 925 ° C. for 1 hour, 1010 ° C. for 2 hours, and 1050 ° C. for 3 hours.

However, this standard heating is intended for buildings with a lot of combustible materials such as offices and houses, and even if a fire occurs in a parking lot or as sodium, the room will not flash over and the steel frame The ultimate temperature is assumed to be 600 ° C or lower. This was proposed in 1987 by the Ministry of Construction Comprehensive Technology Development Project by the "Comprehensive fire protection design method for buildings" that comprehensively evaluates disaster prevention and safety by the fire conditions and design conditions of buildings and the performance of materials used. However, as a result, as shown in Japanese Patent Publication No. 4-50362 and Japanese Patent Publication No. 7-68578, a steel material having a yield strength at 600 ° C. of ⅔ or more of the room temperature standard yield strength is “fire-resistant steel”. Has been developed and applied to the pillars and beams of such buildings.

On the other hand, JIS G3 can be used for roofs and walls of buildings.
302 hot-dip galvanized steel sheet and JIS G3
Although the coated hot-dip galvanized steel sheet specified in 312 is used with a fireproof coating, in this case, for example, for roofing materials, as described in Ministry of Construction Notification No. 2999, a weight of 65 kg / m ² is used. Put it on, surface temperature 84 in 30 minutes
When heated to 0 ℃, the maximum amount of deflection is L
_{When it is set to 1} mm, it is required that L ₁ / 80,000 mm or less. In such a case, in order to omit the refractory coating, ferritic stainless steel is used as disclosed in JP-A-2-185916, or columns or beams are used as disclosed in JP-B-6-104859. It has been proposed to use a steel material having a proof stress at 600 ° C. that is ⅔ or more of a normal temperature standard proof stress as in the case of the refractory steel.

However, ferritic stainless steel is costly for such applications, and in the case of using refractory steel whose proof stress at 600 ° C. is ⅔ or more of room temperature standard proof strength, roofs and walls are actually used. It has been pointed out that the fire resistance required is not satisfied. That is, there is not a certain correlation between the proof stress at 600 ° C in the standard and the proof stress in the temperature range reached by the steel material that is actually used, and the roof and walls of buildings without fireproof coating, etc. When using a hot-dip galvanized steel sheet, the necessary property is that it has a proof stress necessary to prevent buckling of the structure in the temperature range reached by the steel material in the load test.

[0006]

As described above, when the structure is used in the temperature range reached by the steel material in the loading test when it is used without a fireproof coating on the roof or wall of a building requiring fire resistance. It has been an object to provide a hot-dip galvanized steel sheet having a proof stress necessary for preventing the product from buckling and a manufacturing method thereof.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors conducted a tensile test at a high temperature on a hot-dip galvanized steel sheet SGCC specified in JIS G3312,
In the temperature range of 750 to 800 ° C, where the steel material used as the roof of the building after having been subjected to fireproof coating so that buckling does not occur at the time of fire, is expected to reach in the load heating test,
When the yield strength is the smallest, it becomes clear that it becomes 13 MPa, while when the refractory coating is not performed, the temperature of the steel material reaches 800 to 850 ° C.
If the yield strength at 0 ° C is 15 MPa or more, it is determined that buckling will not occur during a fire even if the roof or wall is used without a fireproof coating, and the steel sheet is processed into a roof or wall. The proof stress at room temperature is JIS so as not to cause any trouble
We worked on the development of a hot-dip galvanized steel sheet satisfying 340 MPa or less of the hot-dip galvanized steel sheet SGCC specified in G3312, and as a result of diligent studies, as a result, P was present in ferrite in a solid solution state in the ultra-low carbon steel, By utilizing the solid solution strengthening, the yield strength at room temperature is 340 MPa.
Below, and the proof stress at 800 ~ 850 ℃ 15MP
The present invention has been made by the finding that it can be a or more, and the gist thereof is as follows.

(1) C: 0.0005 to 0.
0050%, Si: 0.5% or less, Mn: 0.03 to
1.0%, P: 0.04 to 0.20%, S: 0.015
% Or less, Al: 0.005 to 0.1%, Ti: 0.01
.About.0.08%, N: 0.0040% or less, balance Fe and unavoidable impurities, and% C,%
% When P and% Ti are C, P and Ti contents, respectively.
A hot-dip galvanized steel sheet that satisfies P ≧ 53 ×% C × √ (% Ti), has a proof stress at room temperature of 340 MPa or less, and a proof stress at 800 to 850 ° C. of 15 MPa or more. (2) B: 0.0002 to 0.0020% by weight,
Nb: A hot-dip galvanized steel sheet containing at least one of 0.01 to 0.05, having a yield strength at room temperature of 340 MPa or less and a yield strength at 800 to 850 ° C. of 15 MPa or more as described in (1) above.

(3) C: 0.0005 to 0.
0050%, Si: 0.5% or less, Mn: 0.03 to
1.0%, P: 0.04 to 0.20%, S: 0.015
% Or less, Al: 0.005 to 0.1%, Ti: 0.01
.About.0.08%, N: 0.0040% or less, balance Fe and unavoidable impurities, and% C,%
% When P and% Ti are C, P and Ti contents, respectively.
When a slab having a composition satisfying P ≧ 53 ×% C × √ (% Ti) is subjected to finish rolling at a temperature of Ar ₃ points or higher and% P is defined as P content, (700−150 × √% P) ° C. It is wound up into a hot-rolled steel strip below, and if necessary, cold-rolled at 90% or less, then annealed and melted for 180 seconds or less in a temperature range of 650 ° C to 850 ° C in a continuous hot dip galvanizing facility. A method for producing a hot-dip galvanized steel sheet having a proof stress at room temperature of 340 MPa or less and a proof stress at 800 to 850 ° C of 15 MPa or more, characterized by performing a galvanizing treatment. (4) B: 0.0002 to 0.0020% by weight,
Nb: hot-dip galvanized steel sheet containing at least one of 0.01 to 0.05%, having a proof stress at room temperature of 340 MPa or less and a proof stress at 800 to 850 ° C. of 15 MPa or more as described in (3) above. Is a manufacturing method.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
First, C, Si, Mn, P, S, Al, Ti, N, N
The reasons for limiting the numerical values of b and B will be described. C is an extremely important element that determines the yield strength of the steel sheet at room temperature, and
If it exceeds 0050%, it becomes difficult to set the proof stress at room temperature to 340 MPa or less after annealing in the continuous hot dip galvanizing equipment of the in-line annealing method as defined in the present invention. On the other hand, if C is less than 0.0005%, the time required for vacuum degassing becomes extremely long, and the manufacturing cost increases significantly.

Si forms a SiO ₂ film on the surface of the steel sheet, impairs the plating adhesion, and adversely affects the chemical conversion treatment property. Therefore, the addition amount of Si is preferably not more than 0.5%. Since Mn suppresses hot embrittlement, 0.0
It is necessary to add 3% or more. However, if the addition amount exceeds 1.0%, the metal structure becomes a band shape and the workability is impaired.

P is the most important element in the present invention, and when it exists in a solid solution state in ferrite, it is 800 to 8
The yield strength at 50 ° C is increased by solid solution strengthening. 80
To make the yield strength at 0 to 850 ° C 15 MPa or more, 0.04% or more is required to be added, but if the amount exceeds 0.20%, the yield strength at room temperature increases remarkably,
It exceeds 340 MPa, and cold rolling property deterioration and secondary work embrittlement occur. When the contents of C and Ti are respectively C and% Ti, the amount of P added is 53 ×% C × √ (% Ti)
When the amount is less than the above, a compound presumed to be FeTiP is likely to precipitate even after performing a series of heat treatments as defined in the present invention, and a sufficient amount of P for solid solution strengthening at high temperature is dissolved in ferrite. It does not exist in a state, and it is difficult to set the proof stress at 800 to 850 ° C to 15 MPa or more.

Since S easily causes hot brittleness, the upper limit is made 0.015%. If Al is less than 0.005%, deoxidation may be insufficient, whereas if it exceeds 0.1%, not only the cost increases but also the surface properties deteriorate.
Although N is generally contained in steel as an unavoidable impurity,
If it exceeds 040%, it tends to be brittle, so this is the upper limit.

Ti and Nb are added for the purpose of suppressing a rise in yield strength at room temperature due to aging deterioration by fixing a part of N, C and S. When the addition amount of Ti is less than 0.01% or when the addition amount of Nb is less than 0.01%, the effect of the addition is not observed, and the press-formability is significantly deteriorated by aging. On the other hand, adding Ti in an amount of more than 0.08% or Nb in an amount of more than 0.05% not only increases the cost, but also increases the recrystallization temperature, which may increase the yield strength at room temperature to 340 MPa or more. .

B is not an essential element in the present invention, but 0.0002 to 0.002 to improve the secondary working embrittlement.
You may add 0.0020%. The amount added is 0.00
If it is less than 02%, there is no effect in improving the secondary work embrittlement, while if it exceeds 0.0020%, the yield strength at room temperature increases remarkably, exceeds 340 MPa, and the cold rolling property deteriorates.
Cu, Sn, Zn, Mo,
Even if W, Cr, and Ni are contained in a total amount of 1% or less, the effect of the present invention is not impaired, and depending on the amount, it may be preferable that the corrosion resistance is improved.

Next, the reasons for limiting the manufacturing conditions will be described. The slab used for hot rolling is not particularly limited. That is, it may be manufactured by a continuously cast slab or a thin slab caster. It is also suitable for processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting. The finishing temperature of hot rolling is to make the metal structure uniform and to distribute P evenly in the ferrite.
Ar ₃ in order to make the yield strength at 00 to 850 ° C. uniform.
It is more than a point. The winding temperature is important in the present invention,
In order to prevent P from being precipitated as FeTiP and the proof stress at 800 to 850 ° C. being less than 15 MPa, when% P is the P content (700-150 × √).
% P) ° C. or less. The winding temperature is (70
In the case of exceeding 0-150 × √% P) ° C., P precipitates as FeTiP, and as a result, the amount of P existing in a solid solution state in ferrite is insufficient, and the proof stress at 800 to 850 ° C. is less than 15 MPa. Becomes

After that, cold rolling is performed if necessary, but setting the rolling rate to 90% or more is not realistic because a large cold rolling load is required. When annealed in a continuous hot-dip galvanizing facility using an in-line annealing method, the annealing temperature is 650 ° C. or higher and 850 ° C. or lower, and the annealing time is 180 seconds or less. If the annealing temperature is less than 650 ° C, recrystallization is insufficient when cold rolling is performed, and the yield strength at room temperature is 340.
Exceeds MPa. On the other hand, P increases to F as the annealing temperature increases.
In order to precipitate as eTiP and reduce the yield strength at 800 to 850 ° C, the annealing temperature is set to 850 ° C as the upper limit and the annealing time is set to 180 seconds or less. After that, if shape correction is required, temper rolling of 0.3 to 1.5% is performed, or even if organic film treatment or the like is performed for further improvement of rust prevention, Yield strength at 340M
Pa is exceeded, or the proof stress at 800-850 ° C is 15
It does not impair the characteristics of the present invention, such as the pressure being less than MPa.

[0018]

EXAMPLES Next, examples of the present invention will be described with reference to examples. A slab having the composition shown in Table 1 was heated to 1150 ° C. to obtain a hot-rolled steel strip having a finishing temperature of 920 ° C. and a thickness of 4.0 mm.
It was wound up at the temperature shown in. After pickling, cold rolling with a reduction rate of 75% was applied to form a cold rolled steel strip with a thickness of 1.0 mm, and then as shown in Table 2 using an in-line annealing continuous hot dip galvanizing equipment. When heat treatment and shape correction under the conditions are required, temper rolling of 0.3 to 1.5% was performed to manufacture a hot dip galvanized steel sheet. A JIS No. 5 test piece is cut out from this steel strip and subjected to a tensile test at room temperature to obtain proof stress (yield strength, YP), and a high temperature tensile test according to JIS, 8
The yield strength at 00 ° C or 850 ° C was measured. The above results are shown in Table 2.

[0019]

[Table 1]

[0020]

[Table 2]

As is clear from this table, the sample No. which is the sample of the present invention. Since 2, 5, 6, 8, and 9 have a proof stress at room temperature of 340 MPa or less, they can be easily processed into a roof, a wall, etc., and a proof stress at 800 to 850 ° C of 15 MPa or more, a fireproof coating. Even if it is used for roofs, walls, etc. without performing the above, buckling as a structure does not occur according to the load test. On the other hand, even with the component steel of the present invention, if the heat treatment conditions are outside the scope of the claims of the present application, sample No. Proof strength at room temperature is 340 like 3, 4, and 10
Since it is less than or equal to MPa, it can be easily processed into a roof or wall, but the yield strength at 800 to 850 ° C is 15M.
Since it is less than Pa, it buckles as a structure in the load test, or the sample No. Since the proof stress at room temperature exceeds 340 MPa as in No. 7, it is difficult to process it into a roof or a wall.

For steels other than the components of the present invention, Sample No.
Even if the heat treatment as defined in the present invention as described in Nos. 1 to 11 to 13 is performed, it is difficult to process it into a roof or a wall because the yield strength at room temperature exceeds 340 MPa.
The yield strength at room temperature is 340 MPa or less, and even if it can be easily processed into a roof, a wall, etc., since the yield strength at 800 to 850 ° C. is less than 15 MPa, the structure buckles in the loading test, and the problems of the present invention are solved. Can not.

[0023]

As described above in detail, the present invention is 800-
A hot-dip galvanized steel sheet having a proof stress of 15 MPa or more at 850 ° C., which is hard to buckle in a fire even when used for a roof, a wall, etc. of a building without applying a fireproof coating, and a manufacturing method thereof. Since the construction cost of the product can be reduced, it has an extremely great effect on the industry.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22C 38/14 C22C 38/14 C23C 2/06 C23C 2/06 (72) Inventor Kenichi Asai 2-6 Otemachi, Chiyoda-ku, Tokyo -3 Inside Nippon Steel Corporation (56) Reference JP-A-11-302793 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 9/46

Claims (4)

(57) [Claims] 1. C: 0.0005-0.00, by weight.
50%, Si: 0.5% or less, Mn: 0.03 to 1.0
%, P: 0.04 to 0.20%, S: 0.015% or less, Al: 0.005 to 0.1%, Ti: 0.01 to
0.08%, N: 0.0040% or less, balance F
e and unavoidable impurities, and further contains% C,% P,
When% Ti is the content of C, P, and Ti, respectively,% P ≧
Meets 53 x% C x √ (% Ti) and has a proof stress of 3 at room temperature
A hot dip galvanized steel sheet having a yield strength of 15 MPa or more at 40 MPa or less and 800 to 850 ° C. 2. B: 0.0002 to 0.00 in weight%.
20%, Nb: One or more of 0.01 to 0.05 is contained, and the proof stress at room temperature according to claim 1 is 340 MPa.
Below, and the proof stress at 800-850 ° C is 15MP
Hot-dip galvanized steel sheet of a or more. 3. C: 0.0005-0.00, in% by weight.
50%, Si: 0.5% or less, Mn: 0.03 to 1.0
%, P: 0.04 to 0.20%, S: 0.015% or less, Al: 0.005 to 0.1%, Ti: 0.01 to
0.08%, N: 0.0040% or less, balance Fe
And unavoidable impurities, and further% C,% P,%
% P ≧ 5 when Ti is the content of C, P and Ti, respectively
Ar ₃ with a slab having a composition satisfying 3 ×% C × √ (% Ti)
Finish rolling at a temperature above the point, and when% P is the P content, it is wound at (700-150 x √% P) ° C or less to form a hot rolled steel strip, and if necessary, 90% or less of cold rolling After hot rolling, 650 ℃ or more 850 in continuous hot dip galvanizing equipment
A proof stress of 340M at room temperature, characterized by annealing for 180 seconds or less and hot dip galvanizing in a temperature range of ℃ or less.
If it is Pa or less and the proof stress at 800 to 850 ° C is 15
A method for manufacturing a galvanized steel sheet having a pressure of MPa or more. 4. B: 0.0002 to 0.00 by weight.
20%, Nb: 0.01-0.05% of 1 or more types are contained, The yield strength at room temperature of Claim 3 is 340MP.
a or less and a proof stress at 800 to 850 ° C of 15M
A method for producing a hot-dip galvanized steel sheet of Pa or more.