JP2948231B2 - Fire-resistant steel for building structures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a steel material used for a building structure, and in particular, strength, toughness and weldability at room temperature are equivalent to JIS standard structural steel (SM50, etc.). In addition to maintaining the above characteristic values, the proof stress at high temperatures is further improved.

(Conventional technology) Conventionally, steel materials specified in JISG3106 “Rolled steel materials for welded structures” have been used as steel materials for building structures, but these steel materials have a proof stress when exposed to high temperatures of 350 ° C or more. Therefore, even if a fire occurs in a building, it is required to apply a fire-resistant coating so that the temperature of the steel material does not exceed 350 ° C.

Implementation of such a fireproof coating not only raises construction costs, but also increases the area occupied by columns and the like, and hinders effective use of living space.

Accordingly, various studies have been made on the use of steel materials having high proof stress even at high temperatures in order to enable the reduction or reduction of such refractory coating treatment.

However, conventional high-temperature steels, such as 1 / 2Mo steel and 1Cr-1 / 2Mo steel, have too high a normal temperature strength to have difficulties in workability, and their weldability is significantly higher than that of structural steels such as SM50 steel. Therefore, it cannot be used for building structures.

In addition, JP-B-56-31867, JP-A-57-140855 and JP-A-57-174435 disclose the above 1 / 2Mo.
Steels and high-temperature steels with improved weldability by reducing the amount of alloying elements such as 1Cr-1 / 2Mo steel have been proposed, but these steels also do not have sufficient high-temperature strength as fire-resistant steel for building structures. It is difficult to obtain, and has the drawbacks of high strength at room temperature and poor weldability.

(Problems to be Solved by the Invention) An object of the present invention is to improve the weldability as compared with conventional low-alloy steels for high temperature, and to have higher temperature strength (particularly yield strength or proof stress) than conventional welded structural steel. High and room temperature strength,
An object of the present invention is to propose a refractory steel material for a building structure having similar characteristics such as toughness.

(Means for Solving the Problems) The inventors of the present invention have conducted intensive studies on the composition of steel materials in order to achieve the above object. As a result, i) addition of an appropriate amount of Mo and then limiting the amount of Mn can suppress a decrease in proof stress at high temperatures, and ii) improve the oxidation resistance by adding Cr, Ni, Cu, etc., iii) Further, by adding a small amount of V or Nb and suppressing the increase in carbon equivalent to secure the room temperature strength, the room temperature strength, toughness and weldability are equal to or higher than those of the conventional welded structural steel, It has been found that the proof stress at high temperatures is remarkably improved (for example, the proof stress at 600 ° C. is 60% or more of the proof stress at room temperature).

In addition, they have found that the addition of Al, Ti, REM, etc., in addition to the above-mentioned components also improves the large heat input welded joint characteristics.

 The present invention is based on the above findings.

That is, the present invention provides: C: 0.03 to 0.15 wt% (hereinafter simply indicated as%), Si: 0.01 to 1.0%, Mn: 0.10 to 0.90%, Cr: 0.05 to 0.40%, Ni: 0.05 to 0.30%, Mo: 0.10 to 0.40%, Cu: 0.05 to 0.30% and one or two selected from V and Nb: 0.005 to 0.
Containing at least one selected from the group consisting of Al: 0.005 to 0.10%, Ti: 0.005 to 0.020%, and REM: 0.001 to 0.020%, with the balance being Fe and unavoidable impurities. The strength, toughness and weldability at room temperature are characterized in that the carbon equivalent (Ceq) shown in
This is a fire-resistant steel material for building structures that is equivalent to JIS standard structural steel and has excellent strength at high temperatures.

Hereinafter, the present invention will be described specifically.

First, the reason for limiting the component composition to the above range in the present invention will be described.

C: 0.03 to 0.15% C is added to secure a predetermined strength.
If it is less than 0.1%, the effect of the addition is poor. On the other hand, if it exceeds 0.15%, the weldability and toughness are deteriorated. Therefore, the content is limited to the range of 0.03 to 0.15%.

Si: 0.01 to 1.0% Si is added as a deoxidizing agent and a strength improving element at the time of steel making, but if less than 0.01%, its effect is poor, while 1.0%
If the ratio exceeds 1, the toughness is significantly deteriorated.

Mn: 0.10 to 0.90% Mn requires at least 0.10% to ensure the deoxidation of steel and the strength at room temperature, but the addition of a large amount of Mn in the presence of Mo not only significantly reduces the proof stress at high temperatures, ,
Since the weldability also deteriorates, it is added in the range of 0.10 to 0.90%.

FIG. 1 shows the relationship between the yield point or proof stress at 600 ° C., the yield point or proof stress ratio at normal temperature, and the amount of Mn.

As is clear from the figure, when Mn exceeds 0.90%, the yield point and proof stress at high temperatures are sharply reduced as compared with the room temperature strength.

Cr: 0.05 to 0.40% Cr requires at least 0.05% to improve room-temperature strength, high-temperature strength, and oxidation resistance, but if it exceeds 0.40%, the weldability deteriorates. Limited.

Ni: 0.05 to 0.30% Ni is added to improve strength and toughness.
If it is less than 05%, the effect is poor. On the other hand, if it exceeds 0.30%, the hardenability becomes too high, and it becomes economically expensive.

Mo: 0.10 to 0.40% Mo is an extremely effective element for improving high-temperature strength, and requires at least 0.10% to exert its effect. However, if it exceeds 0.40%, it adversely affects weldability and toughness. 0.10 ~ 0.40
%.

Cu: 0.05-0.30% Cu is a useful element that not only enhances room-temperature strength and high-temperature strength without impairing weldability, but also improves weather resistance. On the other hand, if it exceeds 0.30%, the hot workability deteriorates. Therefore, the content is limited to the range of 0.05 to 0.30%.

V and / or Nb: 0.005 to 0.03% Both V and Nb are effective elements for improving room-temperature strength, high-temperature strength and toughness due to the effect of grain refinement, and require at least 0.005%, but 0.03% On the other hand, if it exceeds 0.005%, then not only the toughness but also the weldability will be degraded.

In addition, room temperature strength and weldability are JIS standard welded structure SM5
To achieve the same level as 0, SM53, etc., the carbon equivalent (Ceq)
Adjustment is important, and it is important to limit such Ceq to 0.43 or less.

The above are the basic components of the present invention.
Further, by adding Al, Ti, REM, etc. in the following range, the toughness of the large heat input welded joint can be improved.

Al: 0.005 to 0.10% Al has no effect when its content is less than 0.005%.
If it exceeds 0%, hot workability and toughness are deteriorated.
Limited to the range of 0.10%.

Ti: 0.005 to 0.020% Ti has no effect when its content is less than 0.005%.
If it exceeds 20%, not only the toughness of the base material but also the toughness of the joint will be reduced, so the amount of addition is made 0.005 to 0.020%.

REM: 0.001 to 0.020% REM has no effect when its content is less than 0.001%.
If the content exceeds 020%, the cleanliness of the steel is significantly reduced.
The range was 01 to 0.020%.

(Operation) In producing the steel of the present invention, the steel is melted in a converter or an electric furnace, and then slab is formed by continuous casting or ingot-bulking method. The method of making steel is particularly advantageously suitable, but is not limited to such a production method.

(Example) A 200 mm thick slab was prepared from molten steel having various component compositions (symbols A to L) shown in Table 1, heated to 1200 ° C, and then rolled into a 60 mm thick steel sheet. .

Thickness thus obtained: room temperature of rolled material of 60 mm and 600
Table 1 also shows the results of a study on the tensile properties at 0 ° C and the toughness of the base material and the weld bond at 0 ° C.

In the same table, F, G, H, J, K and L steels are applicable examples, while A,
B, C, D, E and I steels are comparative examples.

Steel A is a normal rolled steel material for welded structure SM50, but its proof stress at high temperatures is significantly reduced. B steel is Cr on SM50 steel
Is 0.3%, but the high-temperature proof stress has not been improved. C steel has a low C content and is added with 0.05% of V, but has insufficient strength at normal temperature and high temperature. D steel is SM50
This is a steel obtained by adding 0.3% of Mo to steel. Although the high-temperature strength is improved, the toughness is significantly reduced and the weldability is also deteriorated.

E steel is determined from the proper component composition range of the present invention by the amount of Mn and Ceq.
Exceeds the upper limit, and although the strength is sufficient, the toughness and weldability are inferior.

Steel I has Mn content, V content and Ceq exceeding the upper limits of the present invention. Similarly, although the strength is sufficient, the toughness and weldability are significantly reduced.

In contrast, the F, G, H, J, K, and L steels according to the present invention all show good characteristic values at room temperature strength, high temperature strength, weldability, toughness, and bond toughness, and the It turns out that it is an excellent steel as a refractory steel material for goods.

(Effects of the Invention) As described above, the steel of the present invention is a steel material used for building structures that has the same room temperature strength, toughness, and weldability as conventional rolled steel materials for welded structures, and also has a proof stress at high temperatures. In conventional steel, the allowable stress up to 350 ° C can be increased to 600 ° C or more, and extremely high effects can be obtained in building construction such as omitting the fireproof coating process.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between proof stress ratio and Mn amount at 600 ° C. and ordinary temperature.

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Claims (2)

(57) [Claims] [Claim 1] C: 0.03 to 0.15 wt%, Si: 0.01 to 1.0 wt%, Mn: 0.10 to 0.90 wt%, Cr: 0.05 to 0.40 wt%, Ni: 0.05 to 0.30 wt%, Mo: 0.10 to 0.40 wt% wt%, Cu: 0.05-0.30 wt%, and one or two selected from V and Nb: 0.005-0.
JIS standard structure with strength, toughness and weldability at room temperature, characterized by containing 0.3wt%, the balance being Fe and unavoidable impurities, and having the following carbon equivalent (Ceq) of 0.43wt% or less. Refractory steel for building structures that is equivalent to structural steel and has excellent strength at high temperatures. 2. C: 0.03 to 0.15 wt%, Si: 0.01 to 1.0 wt%, Mn: 0.10 to 0.90 wt%, Cr: 0.05 to 0.40 wt%, Ni: 0.05 to 0.30 wt%, Mo: 0.10 to 0.40 wt% wt%, Cu: 0.05-0.30 wt%, and one or two selected from V and Nb: 0.005-0.
Containing at least one selected from the group consisting of Al: 0.005 to 0.10 wt%, Ti: 0.005 to 0.020 wt%, and REM: 0.001 to 0.020 wt%, with the balance being Fe and inevitable impurities, In addition, the carbon equivalent (Ceq) shown below is 0.43 wt% or less, and the strength, toughness and weldability at room temperature are equivalent to those of JIS standard structural steel, and the building structure has excellent strength at high temperatures. Refractory steel for goods.