JPH05311324A - Refractory steel material for structural purposes excellent in high temperature strength characteristic after reheating as well as in atmospheric corrosion resistance and production thereof - Google Patents

Abstract

PURPOSE:To improve atmospheric corrosion resistance and to reduce the thickness of the fireproofing coating of a structure by incorporating specific amounts of C, Si, Mn, Cu, Cr, Mo, and V. CONSTITUTION:The steel has a composition containing, by weight, 0.03-0.2% C, 0.05-1.5% Si, 0.3-2% Mn, 0.1-1.5% Cu, 0.05-1% Cr, 0.1-0.7% Mo, and 0.01-0.3% V. This steel is heated up to 1000-1350 deg.C and, at the time of hot rolling, the draft at a temp. not lower than (Ar3+100) deg.C and finishing temp. are regulated to >=50% and a temp. between (Ar3-100) and (Ar3+100) deg.C, respectively. Subsequently, the steel is air-cooled or is heated, after hot rolling, up to >=850 deg.C and then air-cooled. By this method, the thickness of the fireproofing coating naturally used for a structure requiring refractoriness can be reduced. Because atmospheric corrosion resistance is also improved, an external steel frame can be used without heavy coating. Further, strength after reheating can stably be secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural fire-resistant steel material having excellent weather resistance and excellent high-temperature strength properties after reheating and a method for producing the same, for example, a short time of about several hours due to a fire or the like, Steel materials used for steel structures such as buildings and bridges that are likely to become hot, especially after being once heated to a high temperature due to fire, etc. The present invention relates to an excellent steel material and a manufacturing method thereof.

[0002]

2. Description of the Related Art Structural steel materials are usually manufactured to have a sufficient predetermined strength at room temperature, but in general, the strength decreases as the temperature rises. In particular, it has already been known that the conventional structural steel materials show a marked decrease in strength in a high temperature state of about 500 ° C. or higher. For this reason, in structures that are likely to become hot due to fire, etc., especially in buildings where people live, ensure that the structures do not collapse or deform significantly even at high temperatures, ensuring safety. Therefore, a fireproof coating is applied so that the temperature of the steel material does not become extremely high.

With respect to the present fireproof measures, it is possible to reduce the thickness of the fireproof coating or to reduce other measures against fireproof by suppressing the decrease in the strength of the steel material even at high temperatures. That is, regarding a steel material to which fire resistance is imparted as a structural steel material, Japanese Patent Application Laid-Open No. 2-7752
3, JP-A-2-163341, and JP-A-3-197420.
Etc. have been announced.

[0004]

In the conventional general structural steel material as described above, when a fire occurs in the structure, the steel material once becomes a high temperature state, so that the characteristics of the steel material change. If the structure is reused after a fire, it will be necessary to replace that part. It goes without saying that replacement of members is not desirable from an economical point of view.

In the above-mentioned Japanese Patent Laid-Open No. 2-77523 and the like, although the high temperature strength characteristics of the as-manufactured steel material are excellent, the characteristics of the steel material after a fire has once been clarified. No, it cannot be reused after it has reached a high temperature. Therefore, there is no structural fire-resistant steel material that can secure sufficient strength at high temperature, can guarantee excellent high-temperature strength characteristics even after it has become hot due to a fire, etc., and can sufficiently withstand reuse. ..

Further, regarding such a structural material, with respect to the weather resistance required when considering an external steel frame (particularly important in bridges and the like, there may be an external steel frame type structure in a building as well) However, no consideration was given, that is, structural refractory steel materials that have excellent weather resistance and excellent high temperature strength properties after reheating have not been available so far, so it is possible to diversify the steel frame structure. Absent.

As a result of extensive research and speculation regarding the elimination of the above-mentioned problems in the prior art, the present invention maintains a high strength at high temperature by using a specific component composition and A structural fire-resistant steel material that maintains good high-temperature strength properties even after it has reached a high-temperature state (rather than from the viewpoint of safety) and has improved weather resistance, which was not considered in conventional steel, and its structure. It succeeded in obtaining the manufacturing method, and is as follows.

(1) C: 0.03 to 0.20% by weight, Si:
0.05 to 1.5%, Mn: 0.3 to 2.0%, Cu: 0.1 to 1.5%,
Cr: 0.05 to 1.0%, Mo: 0.1 to 0.7%, V: 0.01 to 0.3
%, The balance being Fe and unavoidable impurities, the structural refractory steel material having excellent weather resistance and excellent high-temperature strength properties after reheating.

(2) Ti: 0.003 to 0.1%, Nb: 0.005 to
0.20%, Zr: 0.003 to 0.3% Any one kind or two or more kinds are also contained, and the weather resistance described in the above item (1) is excellent and the high temperature strength property after reheating is excellent. Structural fire-resistant steel material.

(3) Ni: 0.02 to 1.5%, B: 0.0005 to 0.
For structural purposes, which has excellent weather resistance as described in the above item (1) or (2), and which also has excellent high-temperature strength properties after reheating, characterized in that it also contains any one or two of 005%. Fire resistant steel.

(4) Ti: 0.003 to 0.1%, Nb: 0.005 to
0.20%, Zr: 0.003 to 0.3%, and also contains one or more of them, Ni: 0.02 to 1.5%, B: 0.0005
To 0.005% of any one kind or two kinds, which is excellent in weather resistance as described in the above item (1) or (2) and excellent in high temperature strength property after reheating. Fire resistant steel material.

(5) The steel described in the above items (1) to (4) is heated to 1000 to 1350 ° C. and the rolling reduction at Ar ₃ + 100 ° C. or more is 50% or more at the time of hot rolling, and the finishing temperature. or air-cooling after the _{Ar 3 -100 ℃ ~Ar 3 + 100} ℃, or heated to 850 ° C. or higher after hot rolling excellent in weather resistance, characterized by air cooling, and high-temperature strength characteristics after reheating An excellent method for manufacturing structural refractory steel.

(6) The steel described in the above items (1) to (4) is heated to 1000 to 1350 ° C. and hot rolled to produce Ar ₃
After setting the rolling reduction at + 100 ° C or higher to 50% or higher and the finishing temperature to Ar ₃ -100 ° C to Ar ₃ + 100 ° C, it is forcibly cooled at a cooling rate of 2 to 20 ° C / sec to 400 to 600 ° C.
A method for producing a structural refractory steel material, which is excellent in weather resistance and is excellent in high-temperature strength property after reheating, which is characterized by stopping cooling at 0 ° C and air-cooling.

[0014]

The operation relationship of the present invention as described above will be explained. First, the reasons for limiting the component composition are as follows. C: 0.03 to 0.20%. C is an effective element for stably securing the room temperature strength and high temperature strength of steel, and if it is less than 0.03%, it is difficult to obtain a predetermined sufficient strength, and if it exceeds 0.20%. However, since the weldability deteriorates, the C content was set to 0.03 to 0.20%.

Si: 0.05 to 1.5%. Si is an element effective as a deoxidizing element, and at least 0.
It is necessary to add more than 05%. Si is also an effective element for solid solution strengthening, but if added in an amount of more than 1.5%, there are problems such as reduced ductility and increased inclusions. The above is set to 1.5%.

Mn: 0.3 to 2.0%. Mn is an element effective in securing strength, and addition of 0.3% or more is necessary. On the other hand, if it exceeds 2.0%, the weldability deteriorates, so the content was made 0.3% to 2.0%.

Cu: 0.1 to 1.5%. Cu is an element that improves weather resistance, is an element that is also effective in increasing the strength at room temperature, and is an element that can be expected to strengthen the precipitation when it is about 1% or more. However, addition of more than 1.5% causes a problem of surface scratches of steel in addition to cost increase, so the content was made 0.1 to 1.5%.

Cr: 0.05 to 1.0%. Cr is an element that improves weather resistance, is an element that is also effective in increasing the strength at room temperature, and is also effective in increasing strength at high temperatures. These effects require the addition of 0.05% or more, but if it is 1.0% or more, the cost rises and the weldability deteriorates, so the content was made 0.05 to 1.0%.

Mo: 0.1 to 0.7%. Mo is an effective element that increases the strength of steel by improving hardenability and precipitation strengthening, and is particularly effective for medium and high temperature strength. Furthermore, to improve the strength characteristics after reheating, V
A large effect is exhibited by the combined addition with. On the other hand, addition of a large amount increases the cost and also deteriorates the weldability, so the content was made 0.1 to 0.7%.

V: 0.01 to 0.3%. V is an element that is effective not only in increasing the high temperature strength even when added in a small amount, but is also effective in improving the room temperature / high temperature strength characteristics after reheating, and it is necessary to add 0.01% or more. However, if a large amount is added, the weldability is deteriorated and the cost is increased, so the content was made 0.01 to 0.3%.

In the present invention, in addition to the above-mentioned elements, the following elements can be added to further improve the characteristics. Ti: 0.003 to 0.1%. Ti is an element effective for weather resistance, and TiN
Has the effect of forming austenite grains and refining the austenite grains, and is effective in improving toughness. Further, solid solution Ti forms TiC in a high temperature state to increase high temperature strength, and further improves room temperature / high temperature strength characteristics after reheating. In order to exert these effects, it is necessary to add 0.003% or more, and since addition of a large amount deteriorates weldability, the upper limit addition amount is set to 0.003%.
It was set to 1%.

Nb: 0.005 to 0.20%. Nb is also an element effective for weathering resistance and at room temperature strength, and is also an element effective for increasing high temperature strength, but addition of a large amount deteriorates the toughness of welds. Therefore, the range is 0.005 to 0.20%.

Zr: 0.003 to 0.3%. Zr is also an element effective for weathering resistance, forms carbonitrides, and is effective for grain refinement,
It is also effective for increasing high temperature strength, and if it is less than 0.003%,
These effects cannot be exhibited, while at 0.3% or more, the effects saturate and costs increase, so 0.0
The range is from 03% to 0.3%.

Ni: 0.02 to 1.5%. Ni is an element effective not only in increasing the strength at room temperature but also in improving low temperature toughness, and is also effective in weather resistance.
If it is less than 0.02%, the effects are insufficient, and since Ni is expensive, if it exceeds 1.5%, the cost is significantly increased. Therefore, 0.02% or more and 1.5% are set. ..

B: 0.0005 to 0.005%. B is an element effective in increasing the normal temperature strength when added in a trace amount.
Addition of 0005% or more shows the effect sufficiently. Also,
If it exceeds 0.005%, the effect of improving the hardenability becomes small and the weldability deteriorates.
It was set to 0.005%.

The reasons for limiting the manufacturing conditions in the present invention are as follows. Heating temperature: 1000 to 1350 ° C. If the heating temperature is less than 1000 ° C, it is impossible to secure a predetermined rolling end temperature, while if it exceeds 1350 ° C, the heating cost remarkably increases.
It was 1350 ° C.

A reduction rate of 50% or more at Ar ₃ + 100 ° C. or more. To refine the austenite crystal grains, it is necessary to sufficiently process in the austenite recrystallization region, and at least 50%
The above processing is required. From this viewpoint, the processing rate in the temperature range of Ar ₃ + 100 ° C. or higher, which is the austenite recrystallization region, is set to 50% or higher.

Finishing temperature: Ar ₃ -100 ° C. to Ar ₃ +10
0 ° C. When the finishing temperature is less than Ar ₃ -100 ° C, the normal temperature strength is remarkably increased, and the anisotropy, which is a characteristic of the steel material, becomes remarkable, so the finishing temperature is set to Ar ₃ -100 ° C or higher. Further, from the viewpoint of setting the rolling reduction at Ar ₃ + 100 ° C. or higher to 50% or higher, the upper limit of the finishing temperature is Ar ₃ + 100 ° C. or lower, and the finishing temperature range is Ar ₃ −100 ° C. to Ar ₃ +1.
It was set to 00 ° C.

Heating to 850 ° C. or higher and air cooling. It is also possible to improve the low temperature toughness of the manufactured steel material by hot working or by refining the structure. In this case,
It is necessary to heat to 850 ° C or higher. If the temperature is lower than 850 ° C, the structure cannot be made finer and the effect of improving the low temperature toughness is small, so the heating temperature is set to 850 ° C or higher and air cooling is performed.

Forced cooling is performed at a cooling rate of 2 to 20 ° C./s, cooling is stopped at 400 to 600 ° C., and air cooling is performed. The purpose of accelerated cooling is to achieve high strength even with the same composition steel. That is, if the cooling rate is less than 2 ° C./s, the predetermined purpose cannot be achieved, and if the cooling rate exceeds 20 ° C./s, cooling distortion becomes remarkable, so the cooling rate range is set as described above. The cooling stop temperature is 400 to 600.
When the temperature is out of the range of ° C, the effect of accelerated cooling cannot be obtained, and the stability and distortion of the characteristics also increase, so the above range is set.

[0031]

EXAMPLES The present invention as described above will be explained in more detail. The most important points in the present invention are weldability,
Considering cost etc., it has excellent weather resistance, and has sufficiently high high-temperature strength characteristics in the state in which the steel material is manufactured. That is, it retains high-temperature strength characteristics. As a result of diligent studies on the room temperature / high temperature strength properties after reheating, it was revealed that it is extremely effective to add Mo and V in combination. In particular, conventional weather resistant steel (JIS
An addition amount exceeding the Mo amount (0.15%) specified in G3114) is effective for weather resistance, and the high temperature strength property after reheating can be remarkably improved.

The high-temperature strength characteristics of the refractory steel specified in the present invention are about 2/3 or more of the normal-temperature specified yield strength.
This is a guarantee even at 00 ° C. Specifically, 4
For 0 kg steel, the yield strength at room temperature is generally 24 kgf /
Because it is mm ^2, the high-temperature strength required for the refractory steel 16kg
A guideline is f / mm ² or more. In addition, the high temperature guaranteed strength of 50 kg steel is about 20 kgf / mm ² or more. In practical use, it is necessary to achieve the required guaranteed high temperature strength according to the design method, building application, etc.
As an example of a general case, the guideline of the high temperature guaranteed strength level of 40 kg steel and 50 kg steel grade refractory steel is shown, but by applying the present invention, it is possible to individually achieve the desired high temperature strength. is there.

As specific examples, some examples of sample steels adopted by the present inventors are shown in Table 1 below. A to O
The steel is the steel of the present invention, and the P to S steels are comparative steels. The composition of the comparative steel is outside the specified range of the present invention.

[0034]

[Table 1]

The manufacturing conditions for each of the above steels and the characteristic values of the steel materials obtained thereby are as shown in Table 2 below, but the sample steel was hot rolled to a plate thickness of 20 mm. The manufacturing method is a method such as hot rolling, accelerated cooling, or heat treatment.

[0036]

[Table 2]

That is, the steel materials No. 1 to 20 of the present invention are
It has sufficiently high strength even at high temperatures. further,
Regarding the high temperature strength property after reheating, which is an important property in the present invention, it is about 2 kgf / mm more than the as-manufactured high temperature strength.
A rise of about ² is shown, and it is clear that it retains excellent high temperature strength properties. Regarding the weather resistance, the ratio is based on Steel No. 10 (Steel G), but it shows good weather resistance.

Comparative steel material No. 21 (P) is the steel material N of the present invention.
Although it is a comparison of o.1, the composition of comparative steel material No. 21 is Cu,
Since the Cr content is out of the range of the present invention, the high temperature strength property is relatively good, but the weather resistance is significantly inferior to the steel material of the present invention. Similarly, the comparative steel material No. 23 (R) is a comparison with the steel material No. 12 (I) of the present invention, and since the components such as Cu, Cr and V are out of the scope of the present invention, weather resistance and after reheating All high temperature strength properties are inferior. Comparative steel materials No. 22, 2
No. 4 is a comparison of the steel materials No. 7 and No. 14 of the present invention, respectively, and although the comparative steel materials have good weather resistance, the high temperature strength properties after reheating are poor.

That is, it was confirmed that by applying the present invention, a structural refractory steel material having excellent weather resistance and excellent high temperature characteristics after reheating can be appropriately produced.

[0040]

As described above, according to the present invention, the thickness of the refractory coating, which is naturally used in the structure which has conventionally been required to have the fireproof property, is reduced, or the design and the enforcement method are simplified. In addition to having the effect of being able to anticipate that it can also reduce other measures against fire resistance, and because it has excellent weather resistance, it can be applied to bridges or external steel frames without heavy coating, In addition, it is possible to stably secure strength properties after reheating, which cannot be achieved with conventional refractory steel, and it is possible to further enhance the safety of the structure, so that the industrial effect It is a great invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Ishikawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Kotaro Hatakeyama 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (6)

[Claims] 1. By weight%, C: 0.03 to 0.20%, Si: 0.05 to 1.5%, Mn: 0.3 to 2.0.
%, Cu: 0.1 to 1.5%, Cr: 0.05 to 1.0%, Mo: 0.1 to 0.7
%, V: 0.01 to 0.3%, which is a structural fire-resistant steel material having excellent weather resistance and excellent high-temperature strength properties after reheating. 2. Ti: 0.003 to 0.1%, Nb: 0.005 to 0.20
%, Zr: 0.003 to 0.3% of any one kind or two or more kinds are contained, and the structure has excellent weather resistance according to claim 1 and excellent high-temperature strength characteristics after reheating. Fire resistant steel. 3. Ni: 0.02-1.5%, B: 0.0005-0.005
%, The structural fire-resistant steel material having excellent weather resistance according to claim 1 or 2, and excellent high-temperature strength properties after reheating. 4. Ti: 0.003 to 0.1%, Nb: 0.005 to 0.20
%, Zr: 0.003 to 0.3%, any one kind or two or more kinds, and Ni: 0.02 to 1.5%, B: 0.0005 to 0.005%, any one kind or two kinds. A structural refractory steel material having excellent weather resistance according to claim 1 and excellent high-temperature strength properties after reheating. 5. The steel according to claim 1 to 1000
Heated to 1350 ℃, Ar ₃ + 100 ℃ in hot rolling
The rolling reduction is 50% or more and the finishing temperature is Ar ₃ −.
A structure excellent in weather resistance and excellent in high-temperature strength property after reheating, which is characterized in that after cooling to 100 ° C to Ar ₃ + 100 ° C, it is air-cooled or is hot-rolled and then heated to 850 ° C or higher and air-cooled. For manufacturing refractory steel for automobiles. 6. The steel according to claim 1 to 1000 to 1
It is heated to 350 ° C., the rolling reduction at the time of Ar ₃ + 100 ° C. or more is 50% or more, and the finishing temperature is Ar ₃ −1 during hot rolling.
After setting the temperature to 00 ° C to Ar ₃ + 100 ° C, the cooling rate is 2 to 20 ° C
A method for producing a structural fire-resistant steel material having excellent weather resistance and excellent high-temperature strength properties after reheating, which comprises forcibly cooling at a heating speed of 1 / sec, stopping cooling at 400 to 600 ° C. and air cooling.