JP2551250B2 - Method for manufacturing structural refractory steel with excellent high-temperature strength properties after reheating - 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 for manufacturing a steel material for use in a steel structure such as a building or a bridge, which is likely to be in a high temperature state for a short time such as a few hours due to fire or the like. The present invention relates to a method for producing a structural fire-resistant steel material having excellent high-temperature strength properties after reheating, which can be reused once it has been heated to a high temperature.

[0002]

PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION
Structural steel materials are manufactured to have a sufficient predetermined strength at room temperature, but generally the strength decreases as the temperature rises. In particular, it has been already known that the conventional structural steel materials show a marked decrease in strength in a high temperature state of about 500 ° C. or higher. Therefore, in structures where there is a risk that the temperature will rise to a high temperature due to a fire, etc., especially in buildings where humans live, prevent the structures from collapsing or deforming significantly even under high temperature conditions. In order to secure the temperature, a fireproof coating is applied so that the temperature of the steel material does not rise significantly.

As a countermeasure against such existing fire resistance, if the strength reduction of the steel material can be suppressed to a small level even at high temperature, the thickness of the fire resistant coating can be reduced, or
It is possible to reduce other measures for fire resistance.

Regarding steel materials that guarantee strength at high temperatures,
Research has been conducted in the field of steel for pressure vessels,
For example, in the Japanese Industrial Standard (JIS), JIS G 3
124; It has already been standardized for high-strength steel plates for medium / normal temperature pressure vessels. Further, although not specifically defined, as a steel for a pressure vessel, which is premised on having high strength at medium and high temperatures exceeding room temperature, for example, in JIS, JIS G
3118; Carbon steel plate for medium / normal temperature pressure vessel, JIS G
3119; Manganese molybdenum steel and manganese molybdenum nickel steel plates for boilers and pressure vessels, JIS G
3120; tempered manganese molybdenum steel and manganese molybdenum nickel steel sheet for pressure vessels, JIS G 4
109; chrome molybdenum steel steel plates for boilers and pressure vessels. Further, Japanese Patent Publication No. 60-35985 discloses high strength and toughness steel for pressure vessels. The steel disclosed here is not limited to the characteristics at high temperatures, but is premised to have a certain degree of high-temperature strength as a pressure vessel steel.

However, in the case of such steel,
Usually, expensive alloy elements such as Cr and Mo are added in a large amount of 0.5% or more in order to increase the high temperature strength. It is generally done. In addition, JIS G 31
24; In the high-strength steel sheet for medium / normal temperature pressure vessels, the amount of alloying elements added is relatively small, but the strength at high temperature is regulated up to 400 ° C. That is, sufficient strength cannot be obtained at a considerably high temperature exceeding 400 ° C. Moreover, these steel materials are premised on steel materials for pressure vessels,
It cannot be said that it has sufficient properties as a structural steel material. Furthermore, when a fire occurs in a structure, the steel material is once in a high temperature state, so it is expected that the characteristics of the steel material will change, and when the structure is reused after the fire,
It becomes necessary to replace that part. Replacement of components is, of course, not desirable from an economical point of view.

[0006] A structural steel material having fire resistance is disclosed in Japanese Patent Application Laid-Open No. 2-77523, but the steel disclosed here has a high Mo addition amount of 0.4 to 0.7%. However, it is a high alloy type component as a structural steel material that is normally used. Furthermore, although Japanese Patent Laid-Open No. 2-77523 stipulates high-temperature strength characteristics up to manufacturing,
There is no indication of the properties of the steel once a fire has occurred, and it is difficult to reuse this steel after it has reached a high temperature.

As described above, for a structure which can sufficiently secure the strength at high temperature, can guarantee the excellent high-temperature strength characteristics even after the temperature becomes high due to a fire or the like, and can sufficiently endure the reuse. At present, almost no refractory steel materials have been developed. In other words, to summarize the current problems,
It looks like this:

(1) A method for producing a steel material that satisfies the sufficient characteristics (high weldability, high ductility and toughness, etc.) as a structural steel material and that maintains high high-temperature strength at about 400 ° C. or higher has not been established. . (2) In order to satisfy the characteristics of (1), a large amount of expensive alloy elements are added, so that the steel material cost is very high. (3) The normal temperature and high temperature characteristics of the steel material once deteriorated to a high temperature state cannot be reused.

The present invention has been made in view of the above circumstances, and retains high strength at high temperatures without adding a large amount of expensive alloying elements, and is good even after once being in a high temperature state. Of high-strength structural fire-resistant steel that has excellent weldability and ductility, which are advantages of conventional structural steels, and excellent high-temperature strength characteristics after reheating. It is intended to provide a manufacturing method.

[0010]

The present invention, in order to achieve the above object, is expressed in weight%, C: 0.05% or more and less than 0.20% Si: 0.1% or more, 2.0 % Less Mn: 0.3% or more, less than 2.0% P: 0.03% or less S: 0.03% or less Mo: 0.1% or more, less than 0.4% Ti: 0.003% or more, Less than 0.1% V: 0.01% or more and less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020%

When steel containing Al and unavoidable impurities, the balance of which is heated to 1050 to 1350 ° C. and hot-rolled, the rolling ratio is set to 50% or more at a temperature of Ar ₃ + 200 ° C. or more and finish the temperature Ar ₃ ~Ar ₃ +
Provided is a method for producing a structural refractory steel material excellent in high-temperature strength characteristics after reheating, which is characterized by cooling to 200 ° C. and then air cooling. The present invention is also applied to steel having the above composition, further comprising: Cu: 0.01% or more and less than 1.5% Ni: 0.02% or more and less than 1.5% B: 0.0005% or more, 0. Less than 005% Nb: 0.005% or more, less than 0.05%

A method for producing a structural refractory steel material having excellent high-temperature strength properties after reheating, characterized in that a step similar to the above step is performed on steel containing one or more of the above To do. In this case, if necessary, 700 after air cooling
850 after heating to below ℃ and air cooling, or after hot rolling
A step of heating to ℃ or more can be added.

In the present invention, the most important point is that, in consideration of weldability, cost, etc., the steel material has sufficiently high high-temperature strength characteristics in a manufactured state, and once it is in a high-temperature state. That is, it retains sufficient room temperature / high temperature strength properties even afterwards. In consideration of such a situation, in the present invention, hot rolling is mainly performed on steel to which Mo, V, and Ti are added in combination under specific conditions. These M
By presenting a predetermined amount of o, V, and Ti, it is possible to impart sufficiently high temperature strength characteristics without lowering the weldability and increasing the cost, and at room temperature / high temperature strength after reheating. The characteristics can be made sufficiently high.

FIG. 1 is a steel within the scope of the present invention, Mo-V.
The relationship between the reheating temperature and the room temperature / high temperature strength characteristics of steel and the Mo-Nb steel which is a comparative steel is shown. The steel of the present invention Mo-
With V steel, when the reheating temperature rises, the room temperature / high temperature strength rather rises, and the effect of increasing the high temperature strength is particularly remarkable.
On the other hand, in the case of the comparative steel, Mo-Nb steel, the strength tends to monotonously decrease as the reheating temperature rises. That is, it is apparent that the room temperature / high temperature strength characteristics after reheating are improved by applying the manufacturing method according to the present invention. Next, the reasons for limiting the content of each additive element will be shown.

C: C is an effective element for stably ensuring the room temperature strength and high temperature strength of steel. But 0.0
If it is less than 5%, it is difficult to obtain a predetermined sufficient strength, and if it is 0.20% or more, the weldability deteriorates. Therefore, the content of C is specified to be 0.05% or more and less than 0.20%.

Si: Si is an element effective as a deoxidizing element, and it is necessary to add at least 0.1%. Further, Si is an element effective for solid solution strengthening, but 2.
If the addition amount is 0% or more, there are problems such as reduction in ductility and increase in inclusions. Therefore, the Si content is set to 0.
It is specified to be 1% or more and less than 2.0%.

Mn: Mn is an element effective in securing strength, and for that purpose, 0.3% or more is required to be added. If it is 2.0% or more, the weldability is deteriorated. Therefore, the Mn content is specified to be 0.3% or more and less than 2.0%.

P, S: P and S are impurity elements and cause problems such as deterioration in ductility, workability, and weldability, so it is desirable to minimize them. However, if it is significantly reduced, the cost will increase. For this reason, the content of these is specified to be 0.03% or less, which is a range in which the cost is not increased and the material is not significantly deteriorated.

Mo: Mo is an effective element that increases the strength of steel by improving hardenability, precipitation strengthening, etc.
It is effective for medium and high temperature strength. However, 0.1%
If it is less than 1, it is difficult to obtain the effect, and if it is 0.
Addition of a large amount of 4% or more not only raises the cost but also deteriorates the weldability. Therefore, the content of Mo is 0.1% or more and 0.1.
Specify less than 4%.

V: V is an element which is effective not only for increasing the high temperature strength even when added in a small amount, but also for improving the room temperature / high temperature strength characteristics after reheating. However, if it is less than 0.01%, such an effect cannot be obtained, and addition of a large amount of 0.1% or more deteriorates the weldability and increases the cost. Therefore, the V content is specified to be 0.01% or more and less than 0.1%.

Ti: Ti has the effect of forming TiN and refining the austenite grains, and is effective in improving toughness, while solid solution Ti forms TiC in a high temperature state and also increases high temperature strength. Improves room temperature / high temperature strength and toughness after heating. However, if less than 0.003%, these effects cannot be obtained, and addition of a large amount of 0.1% or more deteriorates weldability. Therefore, the Ti content is 0.003
% Or more and less than 0.1%.

Sol. Al: sol. Al is an element that precipitates in the steel as AlN and is effective in refining the crystal grains. However, if it is less than 0.002%, the effect cannot be obtained, and if it is added in an amount of 0.2% or more, oxide-based inclusions increase, and ductility deteriorates. Therefore, sol. Al
Content of 0.002% or more and less than 0.2%.

N: N is an element for precipitating AlN or TiN, and is effective for refining crystal grains. But,
If less than 0.0010%, the effect cannot be obtained, and
If a large amount of 0.020% or more is added, the toughness of the welded portion deteriorates. Therefore, the content of N is 0.0010% or more and 0.0
Specify less than 20%.

Nb: Nb is an element effective not only in strength at room temperature but also in strength at high temperature. However, 0.
If it is less than 005%, the effect cannot be obtained.
%, The toughness of the weld will deteriorate. Therefore, the Nb content is specified to be 0.005% or more and less than 0.05%.

Cu: Cu is an element effective for solid solution strengthening, and if it is about 1% or more, precipitation strengthening can be expected. It is also effective for corrosion resistance. But,
If it is less than 0.01%, the effect cannot be obtained, and it is 1.5%.
In addition to the cost increase, the above additions have a problem of surface scratches on the steel sheet. Therefore, the Cu content is 0.01% or more and 1.5
Specify less than%.

Ni: Ni is an element effective in improving low temperature toughness. However, if it is less than 0.02%, its effect is small, and since Ni is expensive, if it is 1.5% or more, the cost rises significantly. Therefore, the Ni content is specified to be 0.02% or more and less than 1.5%.

[0027]

B: B is an effective element that enhances the hardenability of steel when added in a trace amount, and if it is 0.0005% or more, the effect is sufficiently exhibited. Further, if it is 0.005% or more, the effect of improving the hardenability becomes small and the weldability deteriorates. Therefore, the content of B is 0.0005% or more and 0.0
Specify less than 05%. Next, the manufacturing process will be described.

First, 1050 to 1 of the steel having the above-described composition is prepared.
Heat to 350 ° C. This is because if the heating temperature is less than 1050 ° C, it is impossible to secure a predetermined rolling end temperature, and if it exceeds 1350 ° C, the heating cost remarkably increases.

Then, hot rolling is performed. In this case, in order to obtain the desired characteristics, it is necessary to refine the austenite crystal grains, but for that reason, it is necessary to sufficiently process in the austenite recrystallization region, and at least 50%.
The above processing is required. From this point of view, the hot rolling condition is such that the rolling reduction is 50% or more in the temperature range of Ar ₃ + 200 ° C. or more, which is the austenite recrystallization region.

If the rolling finishing temperature is lower than the Ar ₃ temperature, the rolling will be a two-phase region rolling, the room temperature strength will be remarkably increased, and the anisotropy of the characteristics of the steel material will be remarkable. From such a viewpoint, the finishing temperature is specified to be Ar ₃ or higher. Also, A
The upper limit of the finishing temperature was set to Ar ₃ + 200 ° C. from the viewpoint that the rolling reduction is 50% or more at r ₃ + 200 ° C. or higher.

If necessary, a step of heating to a temperature of 700 ° C. or lower and then air cooling can be added. As a result, it is possible to remove the strain and the like generated after hot rolling and prevent the strain generated after cutting. This temperature is 70
If the temperature exceeds 0 ° C, the two-phase region may be partially heated. Therefore, the upper limit of the heating temperature at this time is set to 700 ° C.

In the present invention, the predetermined properties can be achieved by heating as-rolled or by heating at 700 ° C. or lower and air cooling as described above, but by adding a step of heating to 850 ° C. or higher after hot rolling. It is also possible to improve the low temperature toughness by hot working or refining the structure of the manufactured steel material. In this case, if the temperature is less than 850 ° C., the refinement of the structure cannot be achieved, and the low temperature toughness improving effect is small. Therefore, the heating temperature at this time is 8
Set to 50 ° C or higher.

[0034]

Embodiments of the present invention will be described below.

Table 1 shows the chemical composition and Ar ₃ temperature of the test steel. Steels A to D are components and compositions within the scope of the present invention, and reference symbols E and F are comparative steels that deviate from the components and compositions of the present invention. Comparative Steel E does not include V, which is an essential element in the present invention, but does include Cr. Similarly, Comparative Steel F is a comparison of Invention Steel A, and Comparative Steel F
Again, V was not added, which is outside the scope of the present invention.

Table 2 shows the manufacturing conditions and the room temperature tensile test and high temperature tensile test results of the steel plates (plate thickness 35 mm) manufactured using the test steels A to F. The high temperature tensile test was performed not only on the as-manufactured material but also on the steel material reheated to 600 ° C. In Table 2, the alphabets shown at the beginning of the reference numerals correspond to A to H in Table 1, and for example, when written as A-1, it indicates that the steel A shown in Table 1 was used.

Reference symbols A-1 to 3, B, C , D-1 and D-2
Are examples satisfying the components and compositions within the scope of the present invention, and the manufacturing conditions, and are denoted by reference symbols A-4, E-1, 2 and F-1.
3 is a comparative example out of these ranges.

As is clear from Table 2, in the case of Examples, the high-temperature yield strength (YS) after reheating is 2% higher than the as-manufactured high-temperature yield strength even after rolling or after heat treatment.
~ 3kgf / mm ² It has risen more than about a degree. From this result, it was confirmed that, within the range of the present invention, the high temperature strength characteristics after the reheating treatment assuming a fire were excellent.

On the other hand, the components and compositions of the comparative example A-4 are within the range of the present invention, but the heat treatment temperature is outside the range of the present invention, and therefore, compared with the example A-3. Normal temperature strength,
The high temperature strength is extremely low.

As shown in Table 1, the components and compositions of Comparative Examples E- 1 to F-3 are outside the scope of the present invention, so that the manufacturing conditions are within the scope of the present invention. The high-temperature strength after reheating is lower than the high-temperature strength of the as-manufactured material, and good high-temperature strength characteristics after reheating, which is the object of the present invention, are not obtained.

As described above, the steel having the components / compositions and manufacturing conditions within the scope of the present invention is excellent in the high temperature strength property at about 600 ° C. and, even when the reuse after the fire is considered, the steel after the reheating is considered. It was confirmed that the high temperature strength was rather increased and that it had excellent properties as a structural refractory steel material.

[0042]

According to the present invention, high strength can be maintained at high temperature without adding a large amount of expensive alloying elements, and good high temperature strength characteristics can be maintained even after once becoming high temperature. Further, there is provided a method for producing a structural refractory steel having excellent weldability and high ductility, which are advantages of conventional structural steels, and excellent in high temperature strength characteristics after reheating. For this reason, it is expected that the thickness of the fireproof coating, which was naturally used in the structure that has conventionally been required to have fireproof properties, can be reduced or the design and construction method can be simplified, and that measures for other fireproof can be reduced. effective.

[0043]

[Table 1]

[0044]

[Table 2]

[Brief description of drawings]

FIG. 1 is a graph showing the results of normal temperature and high temperature tensile tests after reheating the steels of the present invention and comparative steels.

 ─────────────────────────────────────────────────── ───Continued from the front page (72) Inventor Hiroshi Ishikawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Makoto Muraki 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Within the corporation (56) References JP-A-3-39418 (JP, A)

Claims (6)

(57) [Claims] 1. In% by weight, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more, less than 2.0% P : 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more, 0.1 Less than% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020%, with the balance being Fe and inevitable impurities 1
When it is heated to 050 to 1350 ° C. and hot-rolled, the rolling reduction is 50 at a temperature of Ar ₃ + 200 ° C. or higher.
% Or more and, after the finishing temperature was Ar ₃ ~Ar ₃ + 200 ℃, method for producing superior structural refractory steel high-temperature strength characteristics after reheating, characterized in that the air-cooled. 2. The method for producing a structural refractory steel material having excellent high-temperature strength properties after reheating according to claim 1, further comprising the step of heating to 700 ° C. or lower and air cooling after the air cooling. . 3. The method for producing a structural refractory steel material having excellent high-temperature strength properties after reheating according to claim 1, further comprising the step of heating to 850 ° C. or higher after hot rolling. 4. In% by weight, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more but less than 2.0% P : 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more, 0.1 Less than% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020% included Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more , Less than 1.5% B: 0.0005% or more, less than 0.005% Nb: 0.005% or more, less than 0.05% Contains one or more of the following, with the balance being Fe and inevitable impurities. When the steel is heated to 1050 to 1350 ° C. and hot-rolled, the rolling reduction is 50% or more and the finishing temperature is A at a temperature of Ar ₃ + 200 ° C. or more.
A method for producing a structural refractory steel material having excellent high-temperature strength properties after reheating, which comprises cooling to r _{3 to} Ar ₃ + 200 ° C. and then air cooling. 5. The method for producing a structural refractory steel material having excellent high-temperature strength characteristics after reheating according to claim 4, further comprising the step of heating to 700 ° C. or lower and air cooling after the air cooling. . 6. The method for producing a structural refractory steel material having excellent high-temperature strength properties after reheating according to claim 4, further comprising the step of heating to 850 ° C. or higher after hot rolling.