JP3305067B2 - Method for producing 400 MPa class hot rolled steel sheet for low-rise building with extremely excellent fire 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 of manufacturing a hot-rolled steel sheet for a 400 MPa class building having extremely excellent fire resistance used for low-rise buildings in the fields of construction and civil engineering. It is intended to be omissible. A low-rise building is a building of 5 stories or less, including a warehouse and a multistory parking lot.

[0002]

2. Description of the Related Art Rolled steel sheets for general structures, steel sheets for welded structures, weather-resistant hot-rolled steel sheets for welded structures, and the like are widely used as hot-rolled steel sheets for buildings. Fire resistance is important in buildings using these materials, and various measures have been taken. As a typical example, a fire countermeasure is taken with a fireproof coating as in the technique described in JP-A-63-47451. However, this has increased construction costs and reduced the space available for buildings. Further, in some cases, harmful substances such as asbestos are used for the refractory coating, and there are many environmental issues.

[0003] Due to the above-mentioned problems, the fire-resistant design was reviewed and a new fire-resistant design method for buildings was enacted in 1987. The gist of this is that if the conventional allowable temperature of steel material in case of fire is out of the specified range (350 ° C) and the high temperature strength of the material steel sheet is 2/3 or more of the normal temperature yield point strength, the refractory coating may be uncoated. It has become possible. Therefore, as disclosed in Japanese Patent Application Laid-Open No. Hei 1-203713, a 60
The present inventors have proposed a method for producing a hot-rolled steel sheet in which the high-temperature strength at 0 ° C. is compensated.

However, in a high-rise building or the like, since there is too much combustible material in the building, the fireproof coating cannot be completely omitted, and only the fireproof coating is reduced. On the other hand, in a low-rise building of 5 stories or less, the use of a steel plate having less combustible material and higher high-temperature strength than that of a high-rise building makes it possible to completely omit the fireproof coating. In the present invention, the guaranteed temperature was 700 ° C.

[0005]

As described above, at 600 ° C.
Hot-rolled steel sheets that ensured high-temperature strength did not completely eliminate fireproof coatings in high-rise buildings. Therefore, the present invention provides a method for manufacturing a hot-rolled steel sheet in which a fireproof coating is completely omitted, limited to a low-rise building.

[0006]

The gist of the present invention is as follows: C: 0.02-0.08%, Si: 0.5% or less, Mn: 0.5-1.5 % by weight. %, P: 0.05% or less, S: 0.01% or less, Al: 0.01 to 0.1%, Mo: 0.8 to 1.5%, Nb: 0.01 to 0.05 % , V: 0.05~0.3%, N: 0.002~0.01% only contains the slab and the balance Fe and unavoidable impurities was hot rolled, coiled at a coiling temperature 400 to 600 ° C. This is a method for producing a hot-rolled steel sheet for a low-rise building of 400 MPa class, which is extremely excellent in fire resistance.

[0007]

Table 1 shows the chemical composition of the test steel. The chemical composition of the steel of the present invention is as follows.

C: 0.02 to 0.08%. If it is less than the lower limit, the strength at room temperature is insufficient and a predetermined strength of 400 MPa class cannot be achieved. If it exceeds the upper limit, the room temperature strength is too high, and the predetermined strength of 400 MPa class cannot be achieved. Si: 0.5% or less. If it exceeds the upper limit, the scale is generated on the surface, and the appearance is impaired. Mn: 0.5 to 1.5%. Mn is an indispensable element for securing strength and toughness, and if it is less than the lower limit, a predetermined strength cannot be achieved, and toughness also decreases.

P: 0.05% or less. P is an element that imparts strength and corrosion resistance, but if it exceeds the upper limit, the impact characteristics deteriorate. S: 0.01% or less. If it exceeds the upper limit, the number of inclusions increases, and the impact characteristics and workability deteriorate. Al: 0.01 to 0.1%. Al is an element generally contained in steel at the time of deoxidation and contains 0.01% or more. Exceeding the upper limit lowers the degree of cleaning of the steel. Mo: 0.8 to 1.5%. It is an important element in the present invention. By precipitating as fine carbonitride,
A predetermined high-temperature strength is obtained. If it is less than the lower limit, the effect cannot be obtained.

Nb: 0.01 to 0.05%. In the present invention, it is an important element together with Mo. That is, by adding it in combination with Mo, it precipitates as fine carbonitrides and increases the high-temperature strength. If it is less than the lower limit, the effect cannot be obtained, and if it exceeds the upper limit, the room temperature strength increases.
V: 0.05 to 0.3%. It is an important element in the present invention. That is, high-temperature strength can be improved by finely depositing mainly as nitride.
Below the lower limit, there is no effect, and above the upper limit, the effect is saturated. N: 0.002 to 0.01 %. It is an important element in the present invention. That is, nitrides are finely precipitated as nitrides together with V, Nb and the like, and the high-temperature strength can be improved. If the amount is less than the lower limit, the effect is not obtained. If the amount exceeds the upper limit, the room temperature strength increases and the material becomes hard.

[0011]

[Table 1]

[0012]

EXAMPLES Table 2 shows the hot rolling conditions of the steel of the present invention. HT is a slab heating temperature of 1100 to 1300 ° C. Since the present invention secures high-temperature strength by strengthening the precipitation of Mo, Nb, and V carbonitrides as described above, it is necessary to completely dissolve these elements in the slab heating step. If it is less than the lower limit, this effect cannot be obtained. The upper limit is set to a value that can be obtained with the existing equipment. FT is the finishing temperature of hot rolling at 800 to 95
0 ° C. If it is less than the lower limit value, the processed structure increases, and the workability of pipe making and the like deteriorates. The upper limit is a value that can be obtained with the current equipment in relation to the heating temperature.

[0013] CT is a temperature at which a steel strip is wound during hot rolling at 400 to 600 ° C. If it is less than the lower limit, low-temperature products such as bainite and martensite increase,
The room temperature strength increases, and a predetermined strength of 400 MPa class cannot be obtained. If it exceeds the upper limit, carbonitrides of Mo, Nb, and V precipitate due to overaging, and the strength at normal temperature or the strength at high temperature decreases.

[0014]

[Table 2]

FIG. 1 is a diagram showing the relationship between the winding temperature of the steel of the present invention and the tensile strength at room temperature. The range of the winding temperature suitable for a 400 MPa class hot rolled steel sheet is 400 to 600 ° C.
At 300 ° C winding temperature, tensile strength is 500-610MPa
It is about. This is considered to be due to the formation of low-temperature products such as bainite, and the strength increased. On the other hand, at a winding temperature of 700 ° C., the tensile strength decreases at about 390 MPa. This is presumed to be due to the over-aged state of carbonitrides such as Mo and Nb.

FIG. 2 is a diagram showing the relationship between the winding temperature of the steel of the present invention and the yield point strength at room temperature. For the same reason as in FIG.
The winding temperature range suitable for 0 MPa class hot rolled steel sheet is 40
0-600 ° C. FIG. 3 shows a comparison between the comparative steel of Table 1 and the high temperature properties of the yield point strength using a material having a winding temperature of 500 ° C. in the optimum winding temperature range obtained in FIGS. . The value of ／ of the room temperature yield point strength of a general 400 MPa class hot rolled steel sheet is 157 MPa. If the yield point strength exceeds the specified value at a given temperature, the building will not collapse.
The steel of the present invention satisfies the specified value in the range of 700 to 750 ° C, but the comparative steel is less than the specified value.

[0017]

According to the manufacturing method of the present invention, a hot-rolled steel sheet of 400 MPa class having extremely excellent fire resistance can be stably manufactured, and thereby, a low-rise building (including a parking lot, a warehouse, etc.) can be manufactured.
Can completely omit the refractory coating. Accordingly, it is possible to reduce the number of personnel required for construction work and to omit spray coating of refractory, which is an environmental problem, and to greatly reduce construction costs.

[Brief description of the drawings]

FIG. 1 is a table showing a relationship between a winding temperature and a tensile strength according to the present invention.

FIG. 2 is a table showing a relationship between a winding temperature and a yield point strength according to the present invention.

FIG. 3 is a table showing the relationship between yield point strength and test temperature.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Makoto Temori 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Works (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 8/00 -8/10 C21D 9/46-9/48 C22C 38/00-38/60

Claims (1)

(57) [Claims] 1. A weight ratio of C: 0.02 to 0.08%, Si: 0.5% or less, Mn: 0.5 to 1.5%, P: 0.05% or less, S: 0 0.01 % or less, Al: 0.01 to 0.1%, Mo: 0.8 to 1.5%, Nb: 0.01 to 0.05%, V: 0.05 to 0.3%, N : the 0.002 to 0.01 percent seen including, slabs and the balance Fe and unavoidable impurities was hot-rolled, extremely excellent fire resistance, wherein the winding at a coiling temperature 400 to 600 ° C. 400 MPa For manufacturing hot rolled steel sheets for low-grade buildings.