JP2512640B2 - Method for producing hot-dip galvanized cold-rolled steel sheet for folded sheet roofing material with excellent high temperature characteristics - 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 cold-rolled steel sheet for folded sheet roofing materials, which has excellent high temperature characteristics and is used in various structures.

[0002]

2. Description of the Related Art In the JIS standard (A 6514) for metal folding plate roof components, hot dip galvanized steel sheets and strips (JIS G 33
02), coated hot-dip galvanized steel sheet and steel strip (JIS
G 3312) <hereinafter referred to as a well-known steel plate> is defined, and these are generally widely used as the roof constituent material. However, when applied to a building, from the viewpoint of fire resistance, it is used after being coated with a non-combustible material as in the technique described in JP-A-63-47451. Therefore, the manufacturing cost is high and asbestos or the like is used as the non-combustible material, which may cause health problems when inhaled.

Therefore, it has been required to simplify the coating of the non-combustible material, and a method using a steel sheet excellent in high temperature characteristics has been proposed for that purpose. That is, a method of using a stainless steel plate having good high temperature characteristics is conceivable, for example,
The technique disclosed in Japanese Patent Laid-Open No. 2-185916 is one of them. This is a technique for producing a ferritic stainless steel sheet for a roof, but it is inevitable that a large amount of expensive additive elements such as Cr is used, so that an increase in production cost is inevitable.

As a technique for producing a hot-dip galvanized cold-rolled steel sheet having excellent fire resistance, Japanese Patent Application No. 1-301983.
There is a technology described in the publication. However, although there is a regulation of high temperature strength with this technology, a roof loading heating test (Ministry of Construction Notification No. 2999) required when used as a fireproof folded plate roofing material
No.) and forming tests for folded plate roofs.

Against this background, there has been a demand for a technique for inexpensively producing a hot-dip galvanized cold-rolled steel sheet for a folded sheet roof material, which has excellent high temperature characteristics and which can simplify the use of incombustibles. .

[0006]

With the above-mentioned known steel sheet, it is difficult to improve the high temperature strength due to crystal grain growth, coarsening of precipitates, dissolution of carbides and the like. The high alloy heat resistant metal plate is a stainless steel plate or the like in the iron system, but it is economically problematic as a roof material that is consumed in a large amount.
Therefore, a known steel plate is used with a fireproof coating, which causes an increase in construction cost and health problems during construction.

The present invention solves the above conventional problems and is excellent in high temperature characteristics as a roof material,
It is an object of the present invention to provide a method for producing a hot-dip galvanized cold-rolled steel sheet for a folded sheet roofing material with a steel composition close to that of ordinary steel so that the refractory coating can be simply omitted and the cost can be reduced.

[0008]

In order to achieve the above object, the gist of the present invention is as follows. (1) Mass%, C: 0.03-0.2%, Mn: 0.3-1.0% Si: 0.5% or less, Nb: 0.005-0.0
5%, Mo: 0.3 to 1.0%, Al: 0.05% or less, N: 0.01% or less, and a steel slab containing the balance iron and unavoidable impurities directly or at 1100 at high temperature. After heating to ˜1300 ° C., rolling at an Ar ₃ point or higher and winding at 600 ° C. or lower to form a hot-rolled steel strip, which is cold-rolled, then 650 in a reducing atmosphere in a continuous hot dip galvanizing line. A method for producing a hot-dip galvanized cold-rolled steel sheet for a folded sheet roof material, which is excellent in high-temperature characteristics, characterized by immersing it in a galvanizing bath and performing hot-dip galvanizing after heating to 830C. ) Mass% C: 0.02-0.2%, Mn: 0.3-1.0%, Si: 0.5% or less, Nb: 0.005-0.0
5%, Mo: 0.4 to 1.0%, Al: 0.05% or less, N: 0.01% or less, and Ti: 0.01 to 1.0%, V: 0. 1 to 1.0%, Cu: 0.5 to 1.0%, Cr: 0.05 to 1.0%
Among them, steel slabs containing 1 or 2 or more and the balance iron and unavoidable impurities are directly or 11
After heating at 00 to 1300 ° C, rolling at Ar ₃ point or more 60
A hot-rolled steel strip is wound at 0 ° C or lower, cold-rolled, and then heated at 650 to 830 ° C in a reducing atmosphere in a continuous hot-dip galvanizing line, and then immersed in a galvanizing bath. The present invention is a method for producing a hot-dip galvanized cold-rolled steel sheet for a folded sheet roof material, which is excellent in high temperature characteristics and is characterized by performing hot dip galvanizing.

[0009]

Next, the reasons for limiting the constituents of the present invention will be described in detail. C is 0.03 to obtain strength at normal temperature or high temperature.
% Is required. If it is less than this range, the required structure or clusters or precipitates for strengthening cannot be obtained. Also,
If it exceeds 0.2%, the strength becomes too high and the formability as a roofing material deteriorates.

Mn is required to be 0.3% in order to secure the strength, but if it exceeds 1.0%, the plating adhesion is deteriorated. Si reduces the adhesion of the plating, so the content is made 0.5% or less.

Nb and Mo are extremely important elements in the present invention. That is, fine clusters or precipitates are formed at high temperature to improve high temperature strength. In order to obtain sufficient strength at high temperature, it is extremely necessary to add Nb and Mo in combination. In order to obtain the combined effect of Nb and Mo, 0.005% and 0.3% or more are required, respectively. Also, each
The effect is saturated at 0.05% and 1.0%, and excessive addition impairs economic efficiency.

Al is an element generally contained in deoxidized upper steel. However, if the amount of Al increases, the cleanliness of the steel deteriorates, the number of inclusions increases, and the formability as a roof material deteriorates. Therefore, it is set to 0.1% or less. N is generally contained in steel as an unavoidable impurity, but it also has the effect of forming and improving nitrides. However, when the amount of N exceeds 0.01%, it becomes brittle and the formability as a roof material deteriorates.

In the present invention, in addition to the above components, Ti,
The effects of the present invention can be further exerted by appropriately adding one or more of V, Cu and Cr. That is, these elements can form clusters or precipitates and improve high temperature strength. Ti, V, C
r forms a carbide or a nitride to improve the high temperature strength. If Ti is less than 0.01%, no effect is obtained, and if it exceeds 1.0%, the effect is saturated, and excessive addition deteriorates economic efficiency.
If V is less than 0.1%, there is no effect, and if it exceeds 1.0%, the effect is saturated, and excessive addition lowers economic efficiency. If Cr is less than 0.05%, no effect is obtained, and if it exceeds 1.0%, the effect is saturated, and excessive addition deteriorates economic efficiency. Also, Cu
Forms clusters or precipitates by itself and enhances high temperature strength. If it is less than 0.5%, there is no effect, and if it exceeds 1.0%, the effect is saturated, and excessive addition lowers economic efficiency.

Next, the reasons for limiting the hot rolling conditions will be described in detail. The heating temperature is 1100 to 1300 ° C. This is necessary for solution treatment of NbC that improves high temperature characteristics, and if the temperature is less than 1100 ° C, solution treatment is insufficient and high temperature characteristics deteriorate. The upper limit is set to 1300 ° C, which is possible with actual equipment. The finish rolling temperature is Ar ₃ or higher. If it is less than this, the worked ferrite structure remains, and the shape of the hot-rolled steel sheet is significantly reduced. The winding temperature is 600 ° C or lower. If it exceeds this, Nb, Mo clusters or precipitates become coarse during winding, and the high temperature characteristics deteriorate. The lower limit does not change the characteristics even at room temperature.

The plate temperature in the reducing furnace in the continuous hot dip galvanizing line is 650 to 830.degree. This temperature range is important in the present invention. The inventors of the present invention left the unrecrystallized structure with a high dislocation density in the range allowed by the formability as described above, and
The inventors have found a technique in which good high-temperature characteristics can be obtained by suppressing dislocation movements by clusters or precipitates of b and Mo.

[0016]

Example A steel having the components shown in Table 1 was used as a slab that was tapped in a converter. The symbols A, B, G, H, I have components within the scope of the invention. The symbols C, D, E and F are comparative example steels. C steel has a lower C and Mn content, D steel has a higher Si and Mn content, E steel has a higher C, Al and N content, and F steel has a lower Nb and Mo content.

These steels were hot-rolled, cold-rolled and hot-dip galvanized under the conditions shown in Table 2, and the tensile properties and plating adhesion of the obtained steel sheets were investigated. Further, using the obtained steel sheet, a roof loading heating test was performed without coating as a folded plate roof forming test and a fire resistance test. The results are also shown in Table 2.

The tensile test was carried out according to the method described in JIS Z2241 using a No. 5 test piece of JIS Z2201. The plating adhesion was evaluated by an impact test. In the method, a hemispherical punch (diameter: 12.7 mmφ) was dropped on a steel plate, a tape was attached to the formed circular recess and then peeled off, and the amount of plating attached to the tape was visually determined.
The evaluation is as noted in the table. The roof is formed as shown in Fig. 1 with a round seam roof with a mountain height of 160 mm.
Those that could be molded without cracks and the like were accepted. A roof load heating test (30 minutes fire resistance) and an impact test were conducted in accordance with Ministry of Construction Notification No. 2999. Table 3 shows the details of the test method
Shown in The roof loading heating test was performed by the amount of deflection (δ) during heating, and the impact test was performed by dropping the weight on the heating surface and determining whether the hole penetrated.

Table 2 No. 1, 2, 11, 12, and 13 are steel plates manufactured according to the manufacturing method of the present invention, and have excellent formability as a roofing material and high-temperature characteristics. Moreover, the adhesiveness of hot dip galvanizing is also good.

No. 2 in Table 2 3, 4, 5, 6, 7, 8, 9,
10 is a comparative steel example. No. In No. 3, since the heating temperature was too low, the solution treatment of NbC was insufficient and the high temperature characteristics deteriorated.
No. In No. 4, since the coiling temperature was too high, the precipitates of NB and Mo became coarse and the high temperature characteristics deteriorated. No. No. 5 was too high because the plate temperature in the reducing furnace of the continuous hot dip galvanizing line was too high.
Since the precipitates of b and Mo were coarsened and a non-recrystallized structure having a high dislocation density could not be obtained at all, the high temperature characteristics were deteriorated. No. In No. 6, the plate temperature in the reducing furnace of the continuous hot-dip galvanizing line was too low, so the unrecrystallized structure increased more than necessary, and the formability as a roof material deteriorated. No. 7 is C, M
Since n is less than the lower limit value, the strength is lowered, and accordingly, the high temperature characteristics are also lowered. No. In No. 8, since Si and Mn exceeded the upper limit values, the plating adhesion was deteriorated. No. In No. 9, C, Al, and N were more than the upper limit values, so that the steel became brittle and the moldability as a roofing material deteriorated. N
o. In No. 10, Nb and Mo are less than the lower limit, so Nb and Mo
No clusters or precipitates were obtained and the high temperature characteristics deteriorated.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

EFFECTS OF THE INVENTION Due to high-rise buildings and dense houses, fire countermeasures have become a major social issue. Under the circumstances, the present invention produces a hot-dip galvanized cold-rolled steel sheet for a folded sheet roof material with a steel composition close to ordinary steel for excellent roof formability, high temperature characteristics, and cost reduction. It is a technology that can be developed. As a result, the refractory coating can be simply omitted, the manufacturing cost can be reduced, and the amount of asbestos or other environmentally problematic material used can be reduced or omitted. As described above, the present invention greatly contributes to the solution of the social problems described above.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a roof type (circle-sealed roof).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C22C 38/28 C22C 38/28

Claims (2)

(57) [Claims] 1. Mass%, C: 0.03-0.2%, Mn: 0.3-1.0%, Si: 0.5% or less, Nb: 0.005-0.05%, A steel slab containing Mo: 0.3 to 1.0%, Al: 0.1% or less, N: 0.01% or less, and the balance iron and unavoidable impurities is directly or at 1100 to 1300 at high temperature. After heating to ℃, rolled at ₃ or more points of Ar and wound at 600 ℃ or less to form a hot-rolled steel strip, which is cold-rolled, and then 650 to 650 in a reducing atmosphere in a continuous hot dip galvanizing line. 830
A method for producing a hot-dip galvanized cold-rolled steel sheet for a folded sheet roof material, which is excellent in high-temperature characteristics, characterized in that the hot-dip galvanized bath is subjected to hot dip galvanizing after being heated to ℃. 2. Mass% C: 0.02-0.2%, Mn: 0.3-1.0%, Si: 0.5% or less, Nb: 0.005-0.05%, Mo : 0.4 to 1.0%, Al: 0.1% or less, N: 0.01% or less, and Ti: 0.01 to 1.0%, V: 0.1 to 1.0 %, Cu: 0.5 to 1.0%, Cr: 0.05 to 1.0%, one or more of them, and a steel slab containing the balance iron and unavoidable impurities directly at high temperature. Or after heating to 1100 to 1300 ° C,
After rolling at Ar ₃ points or more and winding at 600 ° C. or less to form a hot rolled steel strip, which is cold-rolled, heated to 650 to 830 ° C. in a reducing atmosphere in a continuous galvanizing line. Then, the method for producing a hot-dip galvanized cold-rolled steel sheet for a folded sheet roof material having excellent high-temperature characteristics, which comprises immersing in a galvanizing bath to carry out hot-dip galvanizing.