JPH04311520A - Method for producing structural fire-resistant steel material with a strength of 60 kg or more with excellent high-temperature strength properties after reheating - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is suitable for use in steel structures such as buildings and bridges that are likely to be exposed to high temperatures for a short period of several hours due to fire, etc. 60 kgf/mm2 or more, and in particular, relates to a method for manufacturing structural fire-resistant steel materials that have excellent high-temperature strength characteristics after reheating and can be reused once they have reached a high temperature due to fire, etc. .

0002

BACKGROUND OF THE INVENTION Structural steel materials are normally manufactured to have sufficient strength at room temperature, but their strength generally decreases as the temperature rises. In particular, it is already known that conventional structural steel materials exhibit a significant decrease in strength at high temperatures of about 500° C. or higher. Therefore, in structures where there is a risk of high temperatures due to fire etc., especially buildings where humans live,
To prevent structures from collapsing or deforming significantly even in high-temperature conditions, and to ensure safety, fireproof coatings are applied to prevent the temperature of steel materials from rising significantly.

[0003] In the current fireproofing measures, if it is possible to suppress the decrease in the strength of steel materials even under high temperature conditions, it is possible to reduce the thickness of the fireproofing coating, or
It becomes possible to reduce the need for other measures for fire resistance.

Regarding steel materials with guaranteed strength at high temperatures,
Research has been conducted in the field of steel materials for pressure vessels.
For example, in the Japanese Industrial Standards (JIS), JIS G
3124: Already standardized for high-strength steel plates for medium- and room-temperature pressure vessels. Although not specifically stipulated, for example, JIS specifies that steel for pressure vessels should have high strength at medium and high temperatures exceeding room temperature.
G 3118; Carbon steel plate for medium/normal temperature pressure vessels, J
IS G 3119; Manganese molybdenum steel and manganese molybdenum nickel steel sheet for boilers and pressure vessels, JIS G 3120; Heat-treated manganese molybdenum steel and manganese molybdenum nickel steel sheet for pressure vessels, JIS G 4109; Chromium molybdenum for boilers and pressure vessels There are steel plates, etc. In addition, special public notice 1986-
No. 35985 discloses a high-strength steel for pressure vessels. The steel disclosed here does not need to specify any particular properties at high temperatures, and since it is a steel for pressure vessels, it already assumes a certain degree of high-temperature strength.

However, in the case of such steel,
Usually, in order to increase high-temperature strength, a large amount of 0.5% or more of expensive alloying elements such as Cr and Mo is added. It is commonly done. Also, JIS G
3124; In high-strength steel sheets for medium- and room-temperature pressure vessels, the amount of alloying elements added is relatively small, but the strength at high temperatures is specified up to 400°C at most. In other words, sufficient strength cannot be obtained at a considerably high temperature exceeding 400°C. Also,
These steel materials are intended to be used as pressure vessel steel materials, and cannot be said to have sufficient characteristics as structural steel materials. Furthermore, in the event of a fire in a structure, the properties of the steel material are expected to change as the steel material once reaches a high temperature, and if the structure is to be reused after the fire, it is necessary to replace that part. The need arises. Naturally, replacing parts is not desirable from an economical point of view.

[0006] Structural steel materials with fire resistance are disclosed in Japanese Patent Laid-Open No. 2-77523, but the steel disclosed therein has a high Mo content of 0.4 to 0.7%. Therefore, commonly used structural steel materials have high alloy components. Furthermore, although JP-A-2-77523 stipulates high-temperature strength characteristics up to manufacturing,
There is no information regarding the properties of steel once a fire has occurred, and it is difficult to reuse this steel after it reaches a high temperature.

[0007] JP-A-2-254134 also discloses contents regarding fire-resistant steel materials, but it is essential to add Cr, Ni, and Cu, and it is necessary to use high-alloy steel.
The tensile strength at room temperature is less than 60 kgf/mm2, and sufficient strength is not ensured. Further, nothing is disclosed regarding the high temperature strength properties after reheating, and the product cannot be reused after reaching a high temperature state.

[0008] In this way, 60 kgf can be stably produced at room temperature.
It has a strength of 30kgf/mm2 or more, and can secure a high-temperature yield strength of 30kgf/mm2 or more without adding large amounts of alloy components such as Mo and Cr. At present, very few structural fire-resistant steel materials have been developed that can guarantee excellent high-temperature strength properties even after use, and can sufficiently withstand reuse. In other words, the current problems can be summarized as follows.

(1) There is no established method for manufacturing a steel material that satisfies sufficient properties as a structural steel material (high weldability, high ductility, etc.) and maintains high high-temperature strength at temperatures above about 400°C. . (2) In order to satisfy the characteristics of (1), a large amount of expensive alloying elements are added, so the cost of the steel material is extremely high. (3) Once the steel material reaches a high temperature state, its room temperature and high temperature characteristics deteriorate and it cannot be reused.

The present invention was made in view of the above circumstances, and maintains high strength at high temperatures without adding large amounts of expensive alloying elements, and maintains good strength even after reaching high temperatures. In addition, it has the advantages of conventional structural steel materials such as high weldability and high ductility, and has a tensile strength of 60 kgf/mm2 or more at room temperature, which is higher than that of conventional structural steels. The purpose of the present invention is to provide a method for manufacturing a structural fire-resistant steel material having a strength at room temperature higher than that of 40 or 50 kg structural steel, and having a strength of 60 kgf/mm2 or more and excellent high-temperature strength characteristics after reheating. .

[0011]

[Means and effects for solving the problems] In order to achieve the above objects, the present invention firstly provides C:
0.05% or more, less than 0.20% Si: 0.1% or more, less than 2.0% Mn: 0.3% or more, less than 2.0% P: 0.03% or less S: 0.03% Below Mo: 0.1% or more, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01%
or more, less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0
．． 0010% or more, less than 0.020%

100% of the steel containing
When heated to 0 to 1350°C and hot rolled, 9
After setting the reduction rate to 30% or more at 00℃ or higher and setting the finishing temperature to Ar3 to Ar3 +150℃, immediately quenching or air cooling, reheating to 880℃ or higher, quenching, and then reheating to a temperature of 700℃ or lower. 60K, which is characterized by heating and air cooling, and has excellent high-temperature strength properties after reheating.
Provided is a method for manufacturing a structural fire-resistant steel material having a strength of gf/mm2 or more. Second, to the steel having the above composition, Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more, less than 2.0% Cr: 0.05% or more, 1.5% Less than B: 0.0005% or more, less than 0.005% Nb: 0.
005% or more, less than 0.05%

[0013] Steel containing one or more of the above is heated to 1000 to 1350°C and when hot rolled, the rolling reduction is 30% or more at 900°C or higher, and the finishing temperature is Ar3 to Ar3.
High-temperature strength properties after reheating characterized by heating to +150°C and immediately quenching, or air cooling, reheating to 880°C or higher, quenching, then reheating to 700°C or lower and air cooling. Provided is a method for manufacturing a structural fireproof steel material having an excellent strength of 60 kgf/mm2 or more. Thirdly, in weight percent, C: 0.05% or more, less than 0.20% Si: 0.1% or more, 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, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01%
or more, less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0
．． 0010% or more, less than 0.020%

100% of the steel containing
When heated to 0 to 1350°C and hot rolled, 9
After setting the reduction rate to 30% or more at 00°C or higher and setting the finishing temperature to Ar3 to Ar3 +150°C, immediately quenching or air cooling, reheating to 880°C or higher and quenching, and then heating to a temperature of 740 to 840°C. 6 with excellent high-temperature strength properties after reheating, characterized by being reheated and quenched, then reheated to a temperature of 700°C or less and air cooled.
Provided is a method for manufacturing a structural fireproof steel material having a strength of 0 kgf/mm2 or more. Fourth, in the steel having the above composition, Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more, less than 2.0% Cr: 0.05% or more, 1.5% Less than B: 0.0005% or more, less than 0.005% Nb: 0.
005% or more, less than 0.05%

[0015] Steel containing one or more of the following is heated to 1000 to 1350°C, and when it is hot rolled, the rolling reduction is set to 30% or more at 900°C or higher, and the finishing temperature is set to Ar3 to Ar3.
After heating to +150℃, immediately quenching or air cooling, reheating to 880℃ or higher and quenching, then 740~8℃
Quenched by reheating to a temperature of 40°C, followed by 700°C
60kgf/mm2 with excellent high-temperature strength properties after reheating, characterized by being reheated to a temperature below ℃ and then air cooled
A method for manufacturing a structural fireproof steel material having the above strength is provided.

In the present invention, the most important point is that, after considering weldability, cost, etc., the steel material should have a tensile strength of 60 kgf/mm2 or more at room temperature and a high temperature yield of 600°C in the manufactured state. Strength is 30kgf/m
It has a sufficiently high high temperature strength property of m2 or more, and also maintains sufficient room temperature and high temperature strength properties even after reaching a high temperature state.

In consideration of the above, the inventors of the present application have made extensive studies to solve the above problems, and have found that hot rolling under specific conditions is mainly applied to steel with composite additions of Mo, V, and Ti. It has been found that by applying this, sufficiently high strength properties at room temperature and high temperature can be imparted, and the strength properties at room temperature and high temperature after reheating can be made sufficiently high. The present invention as described above has been made based on the knowledge of the inventors of the present application. Next, the reason 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. However, 0.
If it is less than 0.05%, it is difficult to obtain a sufficient predetermined strength, and if it is more than 0.20%, weldability deteriorates. Therefore, the content of C is specified to be 0.05% or more and less than 0.20%.

Si: Si is an effective deoxidizing element and must be added in an amount of at least 0.1%. In addition, although Si is an effective element for solid solution strengthening, 2
．． If the amount added is 0% or more, there are problems such as a decrease in ductility and an increase in inclusions. For this reason, the Si content is reduced to 0.
．． Specified at 1% or more and less than 2.0%.

Mn: Mn is an effective element for ensuring strength, and for this purpose it is necessary to add 0.3% or more. Moreover, if it exceeds 2.0%, weldability deteriorates. 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,
Since it causes problems such as a decrease in ductility, workability, and weldability, it is desirable to minimize it as much as possible. However, a significant reduction will lead to an increase in cost. Therefore, the content of these elements is set to 0.03% or less, which is a range that does not cause an increase in cost and does not cause significant material deterioration.

Mo: Mo is an effective element for increasing the strength of steel by improving hardenability, precipitation strengthening, etc., and is particularly effective for medium and high temperature strength. However, 0.1
If it is less than 0%, it is difficult to obtain the effect;
．． Adding a large amount of 4% or more not only increases cost but also deteriorates weldability. For this reason, the content of Mo should be reduced to 0.1% or more.
．． Specified at less than 4%.

V: V is an element that is effective not only in increasing high-temperature strength even when added in a small amount, but also in improving the strength characteristics at room temperature and high temperature after reheating. However, if it is less than 0.01%, such an effect cannot be obtained, and if it is added in a large amount of 0.1% or more, weldability deteriorates and costs increase. For this reason, the V content should be 0.01% or more and 0.1%
stipulated below.

Ti: Ti has the effect of forming TiN and refining austenite grains, and is effective in improving toughness. Solid solution Ti forms TiC at high temperatures, increasing high-temperature strength, and furthermore, It also improves strength and toughness at room temperature and high temperature after heating. However, if it is less than 0.003%, these effects cannot be obtained, and if it is added in a large amount of 0.1% or more, weldability deteriorates. For this reason, the Ti content was reduced to 0.00
Specified at 3% or more and less than 0.1%.

[0025] sol. Al: sol. Al is AlN
It is an element that precipitates in steel and is effective in refining crystal grains. However, if it is less than 0.002%, this effect cannot be obtained, and if it is added in an amount of 0.2% or more, oxide-based inclusions increase and the ductility deteriorates. For this reason, sol. The Al content is defined as 0.002% or more and less than 0.2%.

N: N is an element that precipitates AlN or TiN, and is effective in refining crystal grains. However, if it is less than 0.0010%, the effect cannot be obtained, and
If added in a large amount of 0.020% or more, the toughness of the weld will deteriorate. For this reason, the N content should be 0.0010% or more and 0.0% or more.
Specified at less than 20%.

Nb: Nb is an element that is effective not only for improving the strength at room temperature but also for increasing the strength at high temperatures. However, 0
．． If it is less than 0.005%, the effect cannot be obtained;
If added in excess of 5%, the toughness of the weld will deteriorate. For this reason, the content of Nb is specified to be 0.005% or more and less than 0.05%.

Cu: Cu is an element that is effective for solid solution strengthening, and is also an element that can be expected to cause precipitation strengthening when the content is about 1% or more. It is also effective for corrosion resistance. However, the effect cannot be obtained at less than 0.01%, and 1.5%
% or more increases the cost and causes surface scratches on the steel plate. For this reason, the Cu content should be increased to 0.01% or more.
Specified at less than 5%.

Ni: Ni is an element effective in improving low temperature toughness. However, if it is less than 0.02%, the effect is small, and since Ni is expensive, if it is more than 2.0%, the cost will increase significantly. For this reason, the Ni content was reduced to 0.02%.
It shall be specified as above or less than 2.0%.

Cr: Cr is effective as a solid solution strengthening element, and is also effective in increasing high temperature strength and corrosion resistance. However, if it is less than 0.05%, the effect will not be obtained, and if it is more than 1.5%, the cost will increase and
Deteriorates weldability. For this reason, the Cr content was reduced to 0.0
Specified at 5% or more and less than 1.5%.

B: B is an effective element that increases the hardenability of steel when added in a small amount, and its effect is sufficiently exhibited when it is added in a small amount of 0.0005% or more. Moreover, at 0.005% or more,
The effect of improving hardenability is also reduced, and weldability is deteriorated. For this reason, the content of B is 0.0005% or more.
Defined as less than 0.005%. Next, the manufacturing process will be explained.

First, steel having the above-mentioned composition is heated to 1000 to 1
Heat to 350°C. This is because if the heating temperature is less than 1000°C, it is impossible to secure a predetermined rolling end temperature, and if it exceeds 1350°C, the heating cost increases significantly.

[0033] Next, hot rolling is performed. In this case, in order to obtain the desired properties, it is necessary to refine the austenite crystal grains, but for this purpose, it is necessary to sufficiently process the austenite recrystallization region, and to obtain at least 30%
The above processing is required. From this point of view, the hot rolling conditions were set such that the rolling reduction was 30% or more in the temperature range of 900° C. or higher, which is the austenite recrystallization region.

[0034] When the rolling finishing temperature is less than Ar3 temperature,
When rolling in the two-phase region and quenching immediately after rolling,
The hardenability is markedly reduced and it is difficult to secure a predetermined strength, and when the temperature exceeds Ar3 +150°C, the crystal grains become extremely coarse. Therefore, the finishing temperature is set to Ar3
~Ar3+150°C.

Quenching may be performed immediately from this temperature, but
It is also possible to perform quenching after air cooling and reheating to 880° C. or higher. This is because if the reheating temperature is less than 880° C., there is a possibility that the steel will be partially heated to a two-phase region, and the uniformity of the steel properties will deteriorate.

After quenching, it is reheated to a temperature of 700° C. or less and air cooled. This is because if this temperature exceeds 700° C., there is a possibility that parts of the material will be heated to a two-phase region, and the uniformity of the material will change significantly.

When steel materials for building structures are required to have a low yield ratio, the above-mentioned quenching treatment and 700%
It is necessary to add a step of reheating and quenching to a temperature range of 740 to 840°C between reheating to a temperature of 740 to 840°C. At this time, when the reheating temperature is 700°C or higher, the yield ratio decreases, but in the two-phase region below 740°C, the structure becomes non-uniform. On the other hand, if the temperature exceeds 840°C, no decrease in yield ratio can be expected. For this reason, we ensure a uniform structure and material,
The reheating temperature range was set at 740 to 840°C as the temperature range in which the yield ratio could be reduced.

[0038]

[Embodiments] Examples of the present invention will be described below.

Table 1 shows the chemical composition and Ar3 temperature of the test steel. Steels with symbols A to F have components and compositions within the scope of the present invention, and steels with symbols G to I are comparative steels that deviate from the components and compositions of the present invention. Comparative steels G, H, and I are the invention steel A
, F, and E, respectively, but comparative steels G and H do not contain V, which is an essential element in the present invention. Further, in comparative steel I, V and Mo are outside the scope of the present invention.

Table 2 shows the manufacturing conditions and the results of the room temperature tensile test and the high temperature tensile test of the steel plates produced using the test steels A to I. The high-temperature tensile test was conducted on the as-manufactured steel material as well as on the steel material reheated to 600°C. In Table 2, the alphabet shown at the beginning of the code corresponds to A to H in Table 1, and for example, when it is written as A-1, it indicates that steel A shown in Table 1 was used.

[0041] Codes A-1 to F-2 are examples that satisfy the components/compositions and manufacturing conditions within the scope of the present invention, and codes G, H, and I indicate manufacturing conditions that are within the scope of the present invention. is a comparative example whose ingredients and composition are outside the scope of the present invention.

As is clear from Table 2, the tensile strength (TS) at room temperature is 60 kgf/mm in all of the examples.
2 or more, and the yield strength in the as-manufactured high-temperature tensile test is also 30 kgf/mm as required by the present invention.
2 or more are satisfied. In addition, the high temperature yield strength (YS) after reheating to 600℃ is 30 kgf / mm2 or more, which is higher than the high temperature yield strength as manufactured, indicating that the high temperature strength properties after reheating are excellent. was confirmed.

On the other hand, for Comparative Examples G, H, and I, the manufacturing conditions were within the scope of the present invention, but the components and compositions were outside the scope of the present invention, and the tensile strength at room temperature was 60 kgf/m.
m2 Although the above is satisfied, corresponding Example A-1,
High temperature strength is lower than F-2 and E. Comparative examples H and I have a high temperature yield strength of 30 kgf/mm2.
This is less than the value required by the present invention. Furthermore, the high-temperature yield strength after reheating is lower than that as produced, and the high-temperature strength properties after reheating are insufficient. Comparative Example G has a high temperature yield strength of 30 kgf as manufactured.
/mm2 or more, but the high temperature yield strength after reheating is 3
It is less than 0 kgf/mm2 and does not meet the value required by the present invention. Regarding the high-temperature yield strength after reheating, H and I of the comparative examples were also less than 30 kgf /mm2, and it was confirmed that the high-temperature yield strength after reheating was insufficient in both comparative examples.

[0044]

[Effects of the Invention] According to this invention, 30 kgf/mm2 can be achieved at high temperatures without adding large amounts of expensive alloying elements.
It maintains a high yield strength of 60 kgf/mm2 or more at room temperature, and maintains or improves good high temperature strength properties even after reaching a high temperature. A method for manufacturing a structural fire-resistant steel material having high weldability and high ductility, which are advantages of conventional structural steel materials, is provided. For this reason, it is expected that the thickness of the fire-resistant coating, which has conventionally been used in structures that required fire-resistant properties, will be reduced or that the design and construction methods will be simplified, and the need for other fire-resistant measures will also be reduced. Furthermore, since the strength at room temperature is 60 kgf/mm2 or more, which is higher than conventional structural steel materials, it is possible to reduce the thickness, weight, etc. of the steel materials used for the members.

[0045]

[Table 1]

[0046]

[Table 2]

Claims (4)

[Claims] Claim 1: In weight percent, C: 0.05% or more, less than 0.20% Si: 0.1% or more, 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, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01%
or more, less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0
．． 0010% or more and less than 0.020%, and the remainder is F
steel consisting of e and unavoidable impurities from 1000 to 1350
℃, and when hot rolling it, the rolling reduction is 30% or more at 900℃ or higher, and the finishing temperature is Ar3.
~Ar3 After heating to +150℃, immediately quench or
Or air cooled, reheated to 880℃ or higher, then quenched, then 7
A method for producing a structural fire-resistant steel material having a strength of 60 kg or more and having excellent high-temperature strength properties after reheating, the method comprising reheating the material to a temperature of 00° C. or less and cooling it in air. 2. In terms of weight percentage, C: 0.05% or more, less than 0.20% Si: 0.1% or more, 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, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01%
or more, less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0
．． 0010% or more, less than 0.020%, further Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more, less than 2.0% Cr: 0.05% or more, 1.5 % B: 0.0005% or more, less than 0.005% Nb: 0.
0.005% or more and less than 0.05%, with the balance consisting of Fe and unavoidable impurities. After setting the rolling reduction rate to 30% or more and setting the finishing temperature to Ar3 to Ar3 +150℃, it is immediately quenched, or it is air cooled and reheated to 880℃ or higher, then quenched, and then reheated to a temperature of 700℃ or lower. A method for manufacturing a structural fire-resistant steel material having a strength of 60 kg or more and having excellent high-temperature strength characteristics after reheating, characterized by air cooling. 3. In weight percent, C: 0.05% or more, less than 0.20% Si: 0.1% or more, 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, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01%
or more, less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0
．． 0010% or more and less than 0.020%, and the remainder is F
steel consisting of e and unavoidable impurities from 1000 to 1350
℃, and when hot rolling it, the rolling reduction is 30% or more at 900℃ or higher, and the finishing temperature is Ar3.
~Ar3 After heating to +150℃, immediately quench or
Or air cooled, reheated to 880℃ or higher, then quenched, then 7
It is characterized by being reheated to a temperature of 40 to 840 degrees Celsius and quenched, then reheated to a temperature of 700 degrees Celsius or less, and then air cooled.It has a strength of 60 kg or more with excellent high-temperature strength characteristics after reheating. A method for producing structural fire-resistant steel. 4. In weight percent, C: 0.05% or more, less than 0.20% Si: 0.1% or more, 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, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01%
or more, less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0
．． 0010% or more, less than 0.020%, further Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more, less than 2.0% Cr: 0.05% or more, 1.5 % B: 0.0005% or more, less than 0.005% Nb: 0.
0.005% or more and less than 0.05%, with the balance consisting of Fe and unavoidable impurities. After setting the rolling reduction ratio to 30% or more and setting the finishing temperature to Ar3 to Ar3 +150°C, it is immediately quenched, or it is air cooled and reheated to 880°C or higher, then quenched, and then reheated to a temperature of 740 to 840°C. A method for producing a structural fire-resistant steel material having a strength of 60 kg or more and having excellent high-temperature strength characteristics after reheating, the method comprising quenching the steel material, followed by reheating to a temperature of 700° C. or lower and air cooling.