JPH02163341A - Steel material for structural purposes having excellent fire resistance and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the material having improved strength at a high temp. by heating a steel having specified content of V and carbon equivalent and ending its rolling in a specified temp. range. CONSTITUTION:A steel added with, by weight, 0.005 to 0.2% V and having 0.35 to 0.50% carbon equivalent (Ccq=C+Mn/6+Bi/24+Ni/40+Cr/5+V/14) is cast. The steel is heated to 1000 to 128 deg.C and its rolling is ended at 800 to 1000 deg.C. After the rolling, the steel is allowed to cool or is subjected to accelerated cooling. Or, after the rolling, the steel is cooled and is subjected to normalizing treatment. To the above steel, 0.005 to 0.6% Mo is preferably incorporated. Since the steel plate has excellent fire resistance at a high temp., fireproofing can be simplified or obviated in the manufacture of a steel structure or the like.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention is directed to steel plates used in the manufacture of structures, which have sufficient strength in the event of a fire even if the fireproof coating is simplified or omitted. It is concerned with steel materials and their manufacturing methods.

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

In recent years, the Building Standards Act has been revised, and fireproof coatings can now be simplified or omitted depending on the strength of the steel material at high temperatures. That is, if the steel material has sufficient strength at 600°C (2/3 or more of the standard yield strength at room temperature), it is said that the fireproof coating can be omitted and the steel material can be easily used for collection purposes.

The strength of steel materials at high temperatures has been well studied, and the developed materials have been standardized as boiler steel or pressure vessel steel. Also, special public service 51-151H
As shown in the publication, various improvements and developments are still being carried out.

These steel materials have high strength when used at high temperatures or for long periods of time, such as hundreds of thousands of hours, that is, have high creep strength.

(Problem to be solved by the invention) The fire resistance strength that the present invention is concerned with is the strength that can be maintained within several hours at the most during a fire, and is completely different from the high-temperature strength that has been the subject of development for a long time. It is something.

Therefore, the object of the present invention is to provide a steel material whose strength at 600°C, which is an important property when omitting a fireproof coating, is significantly improved over conventional steels in structures such as steel structures, and a method for manufacturing the same. .

(Means for Solving the Problems) As a result of various studies on the effects of chemical components on the strength of structural steel materials at 600°C, the present inventors found that
It has been found that the combined addition of V and V is extremely effective.

The present invention was made based on this knowledge, and (1)
! ff m % l:: Te, ■ 0.005 to 0.2
96 carbon equivalent m (Ccq-C+Mn/6+si
/24+Ni/4o+Cr/5 + V/14) is 0
．． Structural steel material with excellent fire resistance strength, characterized by a resistance of 35 to 0.5096, (in terms of weight percent,
~0.2% and 0.005-0.8% Mo,
1 t of carbon (Ceq-C+Mn/ 6 +Si/ 2
4+Ni/40+Cr/ 5 +Mo/ 4 +V/
14) Structural steel material with excellent fire resistance strength characterized by having a content of 0.35% to 0.50%, by heating the steel described in (1) or (2) above at 1000 to 1280°C,
A method for manufacturing a structural steel material with excellent fire resistance strength, characterized in that rolling is completed at 0 to 1000 ° C. and cooling is carried out either by standing or accelerated cooling after rolling, 0) the steel described in (1) or (21) above,
This is a method for producing structural steel materials with excellent fire resistance, which is characterized by heating at 1000 to 1280°C, finishing rolling at 800 to 1000°C, and normalizing after rolling.

(for production) The present invention will be explained in more detail below.

■0,1%C-0,15%Si-1,2%M by addition
n-0,0+5%P -0,005%S -0,55%
Figure 1 shows the change in fire resistance of Cr steel at 600°C.

When determining the fire resistance strength at 600°C, we took into account the rise behavior of steel material temperature in the event of a fire, and heated the test piece in the temperature increase pattern shown in Figure 3.
It was deformed at a tensile rate of 15%/sin, and the plastic strain was 0.
The strength at 2% was determined as the fire resistance strength.

As shown in FIG. 1, the fire resistance strength increases with the addition amount. Addition of V less than 0.005% has no significant effect. Further, when V addition exceeds 0.2%, the effect of improving fire resistance strength tends to be saturated.

Furthermore, as shown in FIG. 2, it is recognized that the improvement in fire resistance strength due to (1) has a synergistic effect with the addition of Mo, and the improvement in fire resistance strength S due to the combined addition with Mo is remarkable. If the amount of Mo added exceeds 0.8%, no effect commensurate with the addition is observed, so the upper limit of the amount added is set to 0.6%. Also, 0.005
Since no effect is observed when Mo is less than 0.005%, the lower limit of Mo addition is set at 0.005%.

However, the reason why the fire resistance is improved by adding V or V+Mo is that the dislocations that have started to deform and move at high temperatures,
This is because carbides mainly composed of V and V + Mo precipitate nucleates and inhibit the movement of dislocations. ■Although it is effective alone, the combined addition of V + Mo causes a large number of such precipitates to precipitate. This is convenient.

Ccq is Ccq −C+ Mn/ 6 + Si/ 2
4+Ni/ 40+Cr/ 5 + No/ 4 +V
/14, which is an index of weldability and has a strong correlation with the strength of 40-50 kg steel at room temperature.

Although it depends on the manufacturing heat treatment conditions, Ceq is 0.3 as rolled.
If Ceq is less than 5%, the strength as a structural steel material cannot be obtained, and if Ceq is greater than 0.50, the strength increases too much, causing problems of deterioration in ductility, toughness, and weldability.

For this reason, C, St, Mn, Nl, Cr, Mo, and V are regulated so that Ceq is 0.35 to 0.50%.

Further, each element is preferably within the following range.

C is an effective element for increasing room temperature strength and fire resistance strength, and is preferably added in an amount of 0.05% or more. However, if the amount added is too large, weldability will be impaired, so the upper limit of the amount added is 0.
15% is preferred.

Si is added in an amount of 0.02% or more for deoxidation, but if the amount added is too large, the toughness decreases, so the upper limit is preferably 0.5%.

Ml is an H-effect element that fixes S and increases strength, but if added in a large amount, it will cause significant segregation within the material and increase the anisotropy of toughness. It is preferable that

N1 is an element that improves the toughness of steel materials, and when such an effect is required, it is added in an amount of 0.05% or more.

However, if it exceeds 0.5%, the addition cost increases too much and it is unsuitable for use as a structural steel material, so it is preferable to set the upper limit to 0.5%.

C is an element that increases hardenability and precipitates carbonitrides during 4-tempering, improving fire resistance.When such an effect is required, 0.0596 or more is added. However, 1.5% Since addition of more than 1% is unnecessary for structural steel materials, it is preferable to set the upper limit to 1.5%.

P is an element that not only micro-segregates in steel and causes significant directional differences in toughness, but also reduces toughness, so the upper limit is set to 0.
．． It is preferable to set it to 0.03%.

S forms nonmetallic inclusions MnS in steel, increases the directional difference in toughness, and lowers the upper shelf energy in the Charpy test, so the upper limit is preferably 0.02%.

Cu is an element that increases the hardenability and corrosion resistance of steel materials. When such an effect is required, 0.05% or more is added. However, addition of more than 0.5% impairs hot workability. For this reason, the upper limit of the amount of Cu added is set at 0.5%.
It is preferable that

Nb is an element that forms stable carbonitrides and has the effect of improving the fire resistance of steel. Further, it prevents deformation-induced precipitation due to rolling, movement of grain boundaries, and coarsening of recrystallized grains. If you need such an effect, 0.00
It is necessary to add 5% or more. On the other hand, if it exceeds 0.05%, the effect commensurate with the amount added cannot be obtained, so it is economically
It is preferable to suppress it to 0.05% or less.

Like Nb, TI forms carbonitrides and has the effect of improving the fire resistance of steel. If such an effect is required, it is necessary to add 0.005% or more. but,
If it exceeds 0.05%, TiC will increase too much and will actually harm the toughness, so the upper limit is preferably 0.05%.

Ap is an essential element for deoxidizing steel, and for this purpose 0
．． Add 0.003% or more. However, since addition of more than 0.05% is unnecessary, o,ooa to 0.05% is preferred.

Although N increases the fire resistance strength of steel, too much addition impairs weldability, so the addition amount is preferably 0.02% or less.

Next, the rolling conditions will be described.

Steel with the above chemical composition is obtained by melting in a converter or electric furnace, then subjecting it to ladle smelting or vacuum degassing treatment as necessary, and is usually formed into an ingot using a mold or one-way solidification mold. Afterwards, it is made into slabs by blooming.

Alternatively, the slab may be manufactured directly from molten steel by continuous casting.

Any soaking/pressing method may be used in the blooming process. That is, the slab may be soaked after being cooled, or the slab may be charged into a soaking furnace with hot pieces as it is.

After soaking at 1000 to 1300°C, a slab is formed by rolling or forging. Slab thickness is 1.3 to 2.5 of product board thickness
About double that is preferable.

The heating temperature before final rolling is 10°C due to the solid solution of the added elements.
00℃ or higher. However, when it exceeds 1280'C,
The temperature is preferably 1280° C. or lower because the austenite grains become too coarse and it becomes difficult to refine them by rolling.

The rolling end temperature is 800 to 1000°C. That is,
Below 800'C, the fire resistance strength decreases to 1o0
If it exceeds 0'c, the austenite grains will not be sufficiently refined by rolling, and the structure will become coarse, making it difficult to ensure toughness, which is not preferable.

Next, as the cooling condition after rolling, natural cooling or accelerated cooling is adopted. After the rolling is completed, it is sufficient to allow natural cooling, and the result will be approximately 5 to 5 b, depending on the thickness of the plate. Accelerated cooling is a method of cooling by water spray after rolling when the plate thickness is thick or when it is desired to lower the Ceq of the steel material, and even for plate thicknesses exceeding 100 mm, the cooling rate is approximately 120°C/m1n or more. Speed can be ensured.

The steel plate manufactured in this way can be used as a structural material after processing such as cutting and welding. Furthermore, it can also be used after being normalized after the various secondary processes described above. In this case, V, V+M added to improve fire resistance strength
In order to fully bring out the effect of o, a normalizing temperature of 800° C. or higher is required.

Furthermore, if the heating temperature for normalizing is too high, the toughness will be impaired, so it needs to be 1000° C. or lower. The cooling method for normalizing is basically air cooling (air cooling), but accelerated cooling such as water cooling may also be used. When performing normalizing, it is difficult to improve the fire resistance strength with the same composition compared to when using as-rolled steel sheets, but it is possible to obtain stable steel sheets with excellent toughness and less variation in properties in the plate thickness. can be supplied.

(Implementation) Steel having the chemical components shown in Table 1 was heated at 1150° C., rolled to a thickness of 25 mm, and allowed to cool. The rolling end temperature is 890-910℃, and the cooling rate is approximately 25℃
/ Ilin was.

Table 2 shows the tensile properties of the steel materials at room temperature, the Charpy impact absorption energy at 0°C, and the fire resistance strength at 600°C.

Steel plate containing 0-005% or more of V, which is the steel of the present invention (
A, B, C), #, and 0.005% or more v and 0
．． Steel plate containing MO of 0.003% or more (D.

E, F, G, H, I) are conventional steels (J, N, L, M) with Mo and V contents of less than 0.003%.

Tensile properties (tensile strength, 0.2) at room temperature equivalent to N, O)
% yield strength, elongation at break, and area of area at break), and the fire resistance strength at 600° C. is good at 20 kg f /- or more.

(Example 2) Steel plates were manufactured using steels A and F shown in Table 1 under the conditions shown in Table 3, and their properties were investigated.

, the results of the examination are shown in Table 4.

In steel plate (c), the heating temperature is lower than the range of the present invention, and the fire resistance is low. In steel plate (d), the heating temperature is high, which is outside the scope of the present invention, and the toughness is low. Steel plate (e) has a low rolling finish temperature, so it has good toughness but low fire resistance. m tentative (
In 1'), the rolling end temperature is too high, so the fire resistance is good but the toughness is poor.

On the other hand, steel plates (a) and (b) manufactured by the method of the present invention
) shows excellent values for both fire resistance strength and toughness.

(Example 3) Steel having the chemical components shown in Table 1 was heated at 1150°C, rolled to a thickness of 25 mm, and allowed to cool.

The material was cooled in the rolling path, heated at 910° C., and then normalized by air cooling. The cooling rate was approximately 25°C/min.

Table 5 shows the tensile properties of the steel materials at room temperature, the Charpy impact absorption energy at 0°C, and the fire resistance strength at 600°C.

Steel plate containing 0,005% or more of V, which is the steel of the present invention (
A, B, C), and v of 0.00596 or more and 0.
A steel plate containing 0.003% or more of Mo (D.

E, F, G, H, I) have 0 gold platinum content in MO and V.
．． Conventional steels (J, L, M.

Tensile properties at room temperature equivalent to N, 0) (tensile strength, 0.2
% yield strength, elongation at break, and area of area at break), and has a good fire resistance strength of 20 kg f/mIi or more at 600°C.

(Example 4) Using steels A and F shown in Table 1, steel plates were manufactured under the conditions shown in Table 6, and their properties were investigated.

The survey results are shown in Table 7.

In m k (c), the heating temperature is lower than the range of the present invention, and the fire resistance is low. In steel plate (d), the heating temperature is high, which is outside the scope of the present invention, and the toughness is low. In steel plate (C), rolling path J' i
Since the n degree is low, the toughness is good, but the fire resistance is low. Steel plates (") have a high rolling finish temperature, so they have good fire resistance but poor toughness.

On the other hand, steel plates (a) and (b) manufactured by the method of the present invention
) shows excellent values for both fire resistance strength and toughness.

(Effect of the invention) The steel plate produced by the method of the present invention is a welded structural steel material (JIS031
06), it not only increases the yield strength, tensile strength and toughness at room temperature, but also has a high tensile strength, which is important for fireproof steel. ji
It has excellent fire resistance strength at L, and it is of great industrial value because it allows fireproof coating to be simplified or omitted in the production of steel frame (one-frame buildings, etc.).

[Brief explanation of the drawing]

Figure 1 is a chart showing the change in fire resistance strength depending on the amount of V added.
FIG. 2 is a chart showing the effect of V addition on fire resistance strength when Mo is contained at 0.15%, and FIG. 3 is a chart showing the temperature increase pattern of a test piece when determining fire resistance strength.

Claims (1)

[Claims] 1. Contains 0.005 to 0.2% V by weight, and carbon equivalent (Ceq=C+Mn/6+Si/24+Ni/4
0+Cr/5+V/14) is 0.35 to 0.50%, and is a structural steel material with excellent fire resistance. 2. 0.005 to 0.2% V and Mo in weight%
Contains 0.005 to 0.6% of carbon equivalent (Ceq=C
+Mn/6+Si/24+Ni/40+Cr/5+Mo
/4+V/14) is 0.35 to 0.50%, a structural steel material with excellent fire resistance strength. 3. The steel according to claim 1 or 2, 1
A method for manufacturing structural steel materials with excellent fire resistance, characterized by heating at 000 to 1,280°C, finishing rolling at 800 to 1,000°C, and allowing cooling or accelerated cooling after rolling. 4. The steel according to claim 1 or 2, 1
A method for manufacturing structural steel materials with excellent fire resistance, characterized by heating at 000 to 1,280°C, finishing rolling at 800 to 1,000°C, and normalizing after cooling.