JPH0774373B2 - Method for manufacturing structural steel with excellent fire resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is intended for a steel plate used for manufacturing a structure, and has sufficient strength in a fire even if the coating of the refractory material is simplified or omitted. Involved in steel manufacturing methods.

(Prior art) For structures such as steel structures, in order to ensure sufficient strength even in the event of a fire, the steel is coated with a refractory material such as rock wool to prevent the temperature of the steel from rising above 350 ° C. It was mandatory to take measures.

In recent years, it has been permitted to simplify or omit the refractory coating depending on the strength of steel materials at high temperatures. That is,
It is said that if the steel has sufficient strength at high temperatures such as 600 ° C (2/3 or more of the normal yield strength at room temperature), the refractory coating can be omitted and bare use can be performed.

The strength of steel materials at high temperatures has been well investigated so far, and the developed material has been standardized as steel for boilers or steel for pressure vessels. Further, as in Japanese Patent Publication No. 51-15188, various improvements and developments are still being implemented.

These are steel materials having high strength when used for a long time such as tens of thousands or hundreds of thousands of hours at high temperature, that is, high creep strength.

(Problems to be solved by the invention) In a structure such as a steel frame structure, a steel material having a high temperature strength at 600 ° C., which is an important characteristic when omitting a fireproof coating, is required. To provide a method for manufacturing a steel material having strength within a few hours at the time of fire.

(Means for Solving the Problems) The inventors of the present invention have made 600 of structural steel materials used as-rolled.
As a result of various studies on the influence of chemical components and manufacturing conditions on the strength at ℃, in steels containing Mo or W added alone or in combination, the high temperature strength was remarkably improved by mild plastic working after rolling. Found.

The present invention has been made based on this finding, and (1) contains 0.05 to 0.6% of Mo in a weight% and has a carbon equivalent (Ceq = C +).
Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) is 0.35-0.50
% Steel is hot-rolled into a steel product having a predetermined size, and the steel product is subjected to plastic working of 1 to 5% at a temperature of 700 ° C. or less, and a structural steel product having excellent fire resistance strength is manufactured. Method,
(2) W-containing 0.1 to 1.2% by weight, carbon equivalent (Ce
q = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) is 0.3
Steel with 5 to 0.50% is hot-rolled into a steel material having a predetermined size, and the steel material is subjected to plastic working of 1 to 5% at a temperature of 700 ° C. or less, for structural use with excellent fire resistance Steel material manufacturing method, and (3) Mo in the range of 0.05 to 0.6% and W in the range of 0.1 to 1.2% by weight, and both (% Mo)
+ (% W / 2) is 0.05-0.6%, and carbon equivalent (Ceq = C
+ Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) is 0.35-0.
50% of steel is hot-rolled into a steel material having a predetermined size, and the steel material is subjected to plastic working of 1 to 5% at a temperature of 700 ° C. or less, which is a structural steel material having excellent fire resistance strength. It is a manufacturing method.

(Operation) Hereinafter, the present invention will be described in more detail.

0.1% C-0.15% Si-1.2% Mn-0.015% P-0.005% S-
0.55% Cr-0.3% Mo steel was hot-rolled and then re-rolled at 600 ° C to give various plastic strains. Fig. 1 shows the effect of the amount of plastic working on the ratio of fireproof strength at 600 ° C to room temperature strength (tensile strength at room temperature).

When determining the fire resistance strength at 600 ℃, considering the rising behavior of the steel material temperature at the time of fire, heat the test piece in the temperature rising pattern as shown in Fig. 3 and heat it at 600 ℃ for 15 minutes and hold it at 0.15% / The strength at a plastic strain of 0.2% was determined as the fire resistance strength by deforming at a tensile speed of min.

As shown in FIG. 1, when the plastic working amount is 1% or more, the fire resistance is improved. If the plastic working amount exceeds 5%, the effect of improving the fire resistance is saturated.

The improvement of fire resistance by plastic working is due to the compositional plasticity% Mo,% W,
It has a relation with the value of (% Mo) + (% W / 2), and as shown in Fig. 2, the value of% Mo,% W or (% Mo) + (% W / 2) is
If it is 0.05% or more, the improvement of the fireproof strength is remarkable, and if it exceeds 0.6%, the effect of improving the fireproof strength is saturated.

In steels containing Mo or W alone or in combination, the plastic working improves the fire resistance strength.
Lattice defects such as dislocations are introduced into the steel by plastic working, and during the temperature rise when testing the fireproof strength (therefore equivalent to the temperature rise process of the steel material at the time of fire), carbides mainly composed of Mo and W are This is because nucleation precipitates in the lattice defects of and inhibits the movement of dislocations, and it is necessary to include Mo and W and to add plastic working.

However, in processing at a temperature higher than 700 ° C, plastic strain is partially or wholly released by recrystallization or transformation, so that the refractory strength improving effect is small. There is no problem if the temperature is lower than 700 ° C, and processing may be performed at room temperature.

Ceq is Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
And is an index of weldability and has a strong correlation with the strength at room temperature. Depending on the manufacturing heat treatment conditions, if Ceq is less than 0.35% as rolled, the strength as a structural steel material cannot be obtained, and if Ceq is more than 0.50%, the strength is too high and ductility, toughness and weldability deteriorate. Is a problem.

Therefore, C, Si, and M should be adjusted so that Ceq should be 0.35 to 0.50%.
Controls n, Ni, Cr, Mo, V.

Each element is preferably within the following range.

C is an element effective in increasing the room temperature strength and the fire resistance strength, and is preferably added in an amount of 0.05% or more. However, if the addition amount is too large, the weldability is impaired, so the addition amount and the upper limit are preferably 0.15%.

Since Si is deoxidized, 0.02% or more is added, but if the addition amount is large, the toughness decreases, so the upper limit is preferably 0.5%.

Mn is an element effective for fixing S and increasing the strength, but if the addition amount is large, segregation in the material becomes remarkable and the anisotropy of toughness is increased, so Mn is preferably 0.1 to 1.5%. .

Ni is an element that improves the toughness of steel, and when such effects are required, it is added in an amount of 0.05% or more. However, if it exceeds 0.5%, the addition cost is too high and it is unsuitable as a structural steel material. Therefore, it is preferable to set the upper limit to 0.5%.

Cr is an element that enhances hardenability and precipitates carbonitrides by tempering to improve fire resistance. When such effects are required, 0.05% or more is added. But 1.5%
Since the addition of super is unnecessary for structural steel materials, the upper limit is 1.
It is preferably 5%.

V forms carbonitrides to improve the strength and fire resistance of steel alone, and it is desirable to add 0.005% or more in order to further enhance the effect of improving the fire resistance of these elements by coexistence with Mo and W. If it exceeds 0.3%, the effect corresponding to the addition cannot be obtained.

P is an element that reduces toughness, and microsegregates to impair weldability, so the upper limit is preferably 0.03%.

S forms a non-metallic inclusion MnS in the steel, increases the toughness direction difference, and lowers the upper shelf energy in the Charpy test, so the upper limit is preferably made 0.02%.

Cu is an element that enhances the hardenability of steel and also improves the corrosion resistance. When such effects are required, 0.05% or more is added. However, addition of more than 0.5% impairs hot workability. Therefore, the upper limit of the amount of Cu added is preferably 0.5%.

Nb is an element that forms stable carbonitrides and has the effect of improving the fire resistance of steel. In addition, rolling induces work-induced precipitation to prevent movement of crystal grain boundaries and prevent coarsening of recrystallized grains. When such an effect is required, 0.005% or more must be added. On the other hand, if it exceeds 0.05%, the effect corresponding to the added amount cannot be obtained, so it is preferable to economically suppress the content to 0.05% or less.

Ti, like Nb, forms carbonitrides and has the effect of improving the fire resistance of steel. When such an effect is required, 0.005% or more must be added. But 0.05%
If it exceeds 1.0, the TiC increases too much, which adversely affects the toughness, so the upper limit is preferably made 0.05%.

Al is an essential element for the deoxidation of steel, and for this purpose 0.00
Add 3% or more. However, addition of more than 0.05% is unnecessary, so 0.003% to 0.05% is preferable.

N increases the refractory strength of the steel, but if the addition amount is too large, the weldability is impaired, so the addition amount is preferably 0.02% or less.

Next, the manufacturing conditions of the material will be described.

Steel having the above-mentioned chemical components is obtained by subjecting it to melting in a converter or an electric furnace, and then subjecting it to ladle refining or vacuum degassing treatment if necessary, and ingoting it in a normal mold or a unidirectionally solidified mold. Later, it is made into a slab in chunks. Further, the slab may be directly manufactured from molten steel by a continuous casting method.

Any soaking and rolling in the slab may be used. That is, the slab may be cooled and then subjected to soaking, or the slab may be charged into the soaking furnace as a slab with hot pieces. After soaking at 1000 to 1320 ℃, slab is made by rolling or forging. The slab thickness is preferably about 1.3 to 2.5 times the product plate thickness.

The heating temperature before final rolling shall be 1000 ℃ or higher, but 12
If the temperature exceeds 80 ° C, the austenite grains will become too coarse and it will be difficult to reduce the grain size by rolling.
The following is preferable.

The rolling end temperature is preferably Ar ₃ or more and 1000 ° C. or less. If the temperature is below the Ar ₃ temperature, it will be a two-phase region rolling and the strength will rather decrease. 1000
If the temperature exceeds ℃, the structure is rough and the toughness is low.

Cooling after rolling may be natural cooling, and when the plate thickness is thick or when it is desired to reduce the carbon equivalent of the steel material, forced cooling may be performed by water cooling or the like after rolling.

As the means for imparting plastic working, light reduction by a rolling roll or leveler working can be used.

Here, the steel material dimension (thickness) at the end of hot rolling needs to be finished in consideration of the thickness that decreases with the plastic working amount at 700 ° C or less with respect to the final product thickness.

The steel sheet manufactured in this manner can be used as a structural material for construction or the like after processing such as cutting and welding.

(Examples) Steels having the chemical composition shown in Table 1 were used, rolled and cooled under the conditions shown in Table 2, and subjected to plastic working by rolling rolls.

The steels of the present invention B1, C1, D1, E1, F1, G1 and H1 have a high fire resistance temperature of 20 kgf / mm ² or more, and a ratio of the fire resistance strength to room temperature strength (PS ₆₀₀ / TS _RT ) of 0.5 or more. Are better. Further, the toughness (vEo) is as good as 10 kgf-m or more.

On the other hand, conventional steel A1 is 1% at 324 ° C below 600 ° C.
Despite the above plastic strain, it does not contain Mo and W, so its fire resistance is low and PS ₆₀₀ / TS _RT is poor at 0.30. Steel plate C2 has a high plasticizing temperature of over 600 ° C and low fire resistance. Steel plates E2 and H2 also have poor fire resistance because they have not undergone plastic working.

(Effect of the invention) The steel sheet produced by the present method not only satisfies the yield strength, the tensile strength and the toughness of the welded structural steel (JIS G3106) at room temperature, but also has a high fire resistance at high temperature which is important as a fire resistant steel. It is excellent, and the refractory coating can be simplified or omitted in the production of buildings such as steel structures, which has great industrial value.

[Brief description of drawings]

Figure 1 is a chart showing the effect of plastic working amount at 700 ℃ or less on the ratio of fireproof strength to room temperature strength (tensile strength at room temperature).
Fig. 2 is a table showing the effect of (% Mo) + (% W / 2) on the ratio of fireproof strength to room temperature strength in steel materials with plasticity of 2-3%. Fig. 3 shows fireproof strength. It is a chart showing the temperature rising pattern of the test piece when obtaining.

Claims (3)

[Claims] 1. A carbon equivalent (Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 1) containing 0.05 to 0.6% Mo in weight%.
4) 0.35 to 0.50% steel is hot-rolled into a steel material having a predetermined size, and the steel material is subjected to plastic working of 1 to 5% at a temperature of 700 ° C or less, which is excellent in fire resistance. Of manufacturing structural steel. 2. A carbon equivalent (Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 1) containing 0.1 to 1.2% W in weight%.
4) 0.35 to 0.50% steel is hot-rolled into a steel material having a predetermined size, and the steel material is subjected to plastic working of 1 to 5% at a temperature of 700 ° C or less, which is excellent in fire resistance. Of manufacturing structural steel. 3. Mo to 0.05-0.6% and W in% by weight
Both are included in the range of 0.1 to 1.2%, and (% Mo) + (% W /
2) is 0.05-0.6%, and carbon equivalent (Ceq = C + Mn / 6 + S
i / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) 0.35 to 0.50% steel is hot-rolled into a steel material of a predetermined size,
A method for producing a structural steel material having excellent fire resistance strength, which comprises subjecting plastic working of 1 to 5% at a temperature of 0 ° C or lower.