JPH02170943A - Fireproof steel for construction - Google Patents

Abstract

PURPOSE:To improve the high temp. strength of the steel material for structural purposes having high weldability and high ductility and toughness by specifying the contents of Nb, V and Ti of a steel having specific compsn. and the total amounts of these elements by a specific inequality. CONSTITUTION:The steel material for structural purposes contains, by weight, 0.05<=C<0.20, 0.10<=Si<2.0, 0.30<=Mn<2.0, 0.03<=S, 0.10<=Mo<0.50, 0.002<=Sol Al<0.20, 0.0010<=N<0.020 and the balance Fe and furthermore contg. 0.005<=Nb<0.20, 0.01<=V<0.1 and 0.003<=Ti<0.03 in the range of inequality I. In the steel, high temperature yield strength shown by inequality II to IV is satisfied. In the inequality II to IV, YS (RT), YS (450), YS (550) and YS (650) denote the yield strength (kgf/mm<2>) each in normal temp., >400 to 500 deg.C, >500 to 600 deg.C and >600 to 650 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to 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, for example. It is related to steel materials.

[Prior Art] Structural steel materials are normally manufactured to have sufficient strength at room temperature, but their strength generally decreases as the temperature increases. In particular, it is already known that conventional structural steel exhibits 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 inhabited by humans, safety must be ensured to ensure that the structures do not collapse or deform significantly even in high g conditions. To ensure that the temperature of the steel does not rise significantly, a fireproof coating is applied.

In such current fireproofing measures, by keeping the decrease in the strength of steel materials small even in high-temperature conditions, it becomes possible to reduce the thickness of the fireproofing coating or to reduce the need for other fireproofing measures.

Steel materials with guaranteed strength at high temperatures have been researched in the field of steel materials for pressure vessels, and some have already been standardized as JIS G 3124 high strength MM plates for medium and room temperature pressure vessels. Although not specifically stipulated, for example, JIS G 3118; Medium/Normal; , JIS G3
119; Manganese molybdenum steel and manganese molybdenum nickel steel sheet for boilers and pressure vessels, JIS G3
120, tempered manganese molybdenum steel and manganese molybdenum nickel steel plate for pressure vessels, JIS G 4
109: Chrome-molybdenum steel sheets for boilers and pressure vessels, etc. In addition, although the Japanese Patent Publication No. 60-35985 stipulates the contents regarding high-strength and tough steel for pressure vessels, there is no need to specifically specify properties at high temperatures, and since the steel is for pressure vessels, it is assumed that high-temperature strength is already present to some extent. It is said that Furthermore, in such cases, it is common to add large amounts of alloying elements such as Cr and Mo.

However, it has sufficient strength at high temperatures, and
At present, there are almost no structural steel materials that can guarantee this. Steel materials for pressure vessels and structural steel materials have completely different purposes and uses, and therefore have completely different required properties. For example, regarding the usage amount and application situation, pressure vessel steel materials are used in pressure vessels manufactured for special purposes, and these are also limited, whereas structural steel materials are used in a very wide range of applications. It is used in structures, and the amount used is overwhelmingly larger than that of steel for pressure vessels. Furthermore, since structural steel materials can be used by a wide variety of users, it is necessary that the methods of use, such as welding construction management, be easy.

Furthermore, in order to ensure strength at high temperatures exceeding 400°C as stipulated in the present invention, pressure vessel steel must be
．． It is customary to add about 5% or more of Cr%MO, which is inappropriate as a structural steel from the viewpoint of cost and weldability.

In this way, it fully satisfies the characteristics as a structural steel material,
Furthermore, it can be said that until now there have been almost no steel materials that maintain high medium- and high-temperature strength.

[Problems to be Solved] As mentioned above, it can be said that there are almost no structural steel materials that have conventionally maintained or specified high-temperature strength. In addition, in steel materials for pressure vessels, Cr is generally 0.15% or more in order to increase high-temperature strength.

A large amount of expensive alloying elements such as Mo are added.

Furthermore, JIS G 3124: High-strength tW4M plates for medium- and room-temperature pressure vessels contain relatively few alloying elements, but the strength at high temperatures is specified at 400°C at most. In other words, sufficient strength cannot be obtained at a considerably high temperature exceeding 400°C. Furthermore, these steel materials are intended for use as pressure vessel steel materials, and cannot be said to have sufficient characteristics as structural steel materials.

In other words, it can be said that there has been no steel material that satisfies sufficient properties (high weldability, high elongation toughness, etc.) as a structural steel material and maintains high high temperature strength at about 400° C. or higher. Furthermore, in order to increase the high-temperature strength, a large amount of expensive alloying elements are added, making the cost of the steel material very high.

The present invention solves the above-mentioned problems and creates a structure that maintains high strength at high temperatures, has the advantages of conventional structural steel materials such as high weldability and high ductility, and is low in cost. The objective of this project is to provide fire-resistant steel materials for industrial use.

[Means for Solving the Problems] The structural fireproof steel material of the present invention has C=0.05 in weight%.
% or more and less than 0.20%, 5i = 0.10% or more and 2.0%
less than, Mn=0.30% or more and less than 2.0%, P=0.0
3% or less, S-〇, 03 or less, Mo=0.10% or more 0
．． Less than 50%, sol, AI=0.002 or more 0.20
%, N=0.0010% or more and less than 0.020%, the remainder consists of unavoidable impurities and Fe, and further Nb=
0.005% or more and less than 0.20%, V-O 801% or more”
2 less than 0.1% and Ti=0.003% or more 0.03%
A structural fire-resistant m-shrine with excellent weldability and elongation toughness that satisfies the high temperature yield strength shown by the following formula, and further contains less than 0.005%≦Nb+2V+1.5Ti≦0.30%. It is.

YS (RT) - Yield strength at room temperature (kgf/Il
YS (450) - Yield strength at temperatures above 400°C and below 500°C (kgf/nJ) YS (560) - Yield strength at temperatures above 500°C and below 600°C (kgf/mJ) YS (650) - Temperature 600 Yield strength (kgf/mJ) at temperatures above 650°C
1% or more and less than 1.5%, Ni = 0.02% or more and 1.5%
less than, Cr=0.05% or more and less than 1.0%, B=0.0
0.005% or more and less than 0.005%.

[Function] The most important point in the present invention is to keep the respective components of Nb, V, and Ti within the above range, and to
It is to contain 2V+1.5Ti in a range of 0.005% or more and 30% or less.

From the inventors' detailed experimental results, as shown in Figure 1,
It has become clear that the high temperature strength (YS) can be accurately organized using the formula Nb+2V+1.5Ti, which is expressed by the added amounts of Nb5V and Ti.

That is, if it is less than 0,005%, which is outside the range of this formula, sufficient strength at high temperatures cannot be obtained. On the other hand, if it exceeds 0.30%, the amount of added elements increases, the cost increases, and weldability deteriorates.

Therefore, Nb+2V+1,5Ti is limited to the above range.

Generally, structures are designed based on yield strength, and since yield strength is a more important factor in design than tensile strength, the ratio of yield strength at high temperature to yield strength at 7H is It is shown by .

Next, the reason for limiting the amount of each additive element added will be explained.

C; Less than 0.05%" 20. Less than 20% C is an effective element for stably ensuring the room temperature strength and high temperature strength of steel. If it is less than 0.05%, it will not provide sufficient strength for the specified purpose. Moreover, since weldability deteriorates when the content is 0.02% or more, the content of ClTh is set to 0.05% or more and less than 0.20%.

3i; 0.1% or more and less than 2.0% Si is an effective element as a deoxidizing element, and at least 0
It is necessary to add 1% or more. In addition, although Si is an effective element for solid solution strengthening, if it is added in an amount of 2.0% or more, there are problems such as a decrease in ductility and an increase in inclusions. The content was set to be less than 2.0%.

Mn: 0.3% or more and less than 2.0% Mn is an effective element for ensuring strength, and it is necessary to add 0.3% or more. In addition, if the content is 2.0% or more, weldability deteriorates, so it is set to 0.3% or more - less than 2.0%.

P: 0.03% or less, S: 0.03% or less PSS is an impurity element that causes problems such as decreased ductility, workability, and weldability, and should be reduced as much as possible. desirable. However, since a significant reduction would lead to an increase in cost, the upper limit of the amount that would not cause significant material deterioration was set at 0.039 ci or less.

Mo: 0.1% or more and less than 0.5% 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. On the other hand, adding a large amount will increase the cost.
Since it also deteriorates weldability, it is set at 0.1% or more and less than 0.5%.

so 1. Al; 0.002% or more and less than 0.2% so
1. AI precipitates in steel as AIN, is effective in refining crystal grains, and needs to be added in an amount of 0.002% or more.

Moreover, if it is added in an amount of 0.2% or more, inclusions will increase and ductility will deteriorate, so it is set to be less than 0.2%.

N, 0.0010% or more” 20, Less than 020% N is AIN
Although it is effective in refining the crystal grains that precipitate, adding a large amount deteriorates the toughness of the weld zone, so it is set at 0.0010% or more and less than 0.020%.

Nb: 0.005% or more and less than 0.05% V: 0.01%
0.003% or more and less than 0.03% Ti; 0.003% or more and less than 0.03% Nb, V, T
i is an essential element in the present invention, and is an element that is effective not only for improving the strength at room temperature but also for increasing the strength at medium and high temperatures. For individual elements, Nb, less than 0.005%;
V: less than 0.01%, Ti: less than 0.003%,
Almost no effect on increasing strength at room temperature, medium or high temperature (Also, Nb: 0.05% or more, V: 0.1% or more, Ti: 0
．． If it exceeds 0.03%, weldability deteriorates, so the above predetermined range was set.

Further, Cu: 0.01% or more and less than 1.5% Cu is an effective element for solid solution strengthening, and is also an element that can be expected to cause precipitation strengthening when it is about 1% or more. It is also effective for corrosion resistance. However, addition of 1.5% or more increases costs and causes surface flaws on the steel sheet, so it is set at 0.01% or more and less than 1.5%.

Ni: 0.02% or more - L1, less than 5% Ni is an effective element for improving low temperature toughness, and 0.02% or more.
If it is less than 1.5%, the effect will be small, and if it is more than 1.5%, the cost will increase to an acceptable level because Ni is expensive.

Cr: 0.05% or more J: less than 1.0% Cr is effective as a solid solution strengthening element, and is also effective in increasing high temperature strength and corrosion resistance, and its effects are 0.
It is necessary to add 0.05% or more, but if it exceeds 1.0%, the cost will increase and weldability will deteriorate.
% or more and less than 1.0%.

ago, 0.005% or more but not 0.005% B is an effective element that increases the hardenability of steel when added in small amounts, and is 0.0
Addition of 0.005% or more sufficiently exhibits the effect. Also, 0
．． If it is more than 0.005%, the effect of improving hardenability will be small and the weldability will be deteriorated.

[Example] Table 1 shows the chemical composition of the test steel.

There are six types of steels of the present invention, labeled A to F, and two types, labeled G and H, were used as comparative steels.

MA −F i;i, Mo defined in the present invention; 0.10
% or more and less than 0.50% and CFNb+2V+1°5Ti satisfies the conditions of 0.005% or more and 20.30% or less, but Steels G and H are outside this range.

The composition of the test steel was determined in order to vary the strength level. In addition to the additive elements of Nb and V%Ti, Cu%Ni
, , Or, B, AI, N, etc. are added.

Table 2 shows the mechanical properties of steel sheets manufactured by various processes using the steels shown in Table 1.

Manufacturing processes include as-rolled, controlled rolling, controlled cooling, direct quenching-tempering, reheating quenching-tempering, etc. By selecting these processes, it is possible to change the strength and toughness at room temperature, and even the same chemical composition can exhibit different mechanical properties. In addition, the strength at high temperatures also changes.

YS at high temperature is over 400°C and 500°C as shown in the claim range.
Below ℃, over 500℃ 600℃ Below ℃, over 600℃ 65
A tensile test was conducted by selecting a test temperature from each range below 0° C., and the ratio with normal 1HYS was also displayed. In the steel of the present invention, a sufficiently high yield strength is obtained at each temperature, and the ratio of the yield strength to the room temperature YS is also a sufficiently high value. Furthermore, the toughness level is also sufficiently high.

Comparative steels G-1 and G-2 have component systems outside the scope of the present invention, and have a low YS at high temperatures, with a strength equal to or lower than the strength water q defined in the present invention. Comparative n4H1 has a sufficiently high high-temperature YS, but has low toughness and is inappropriate as a structural steel, and even compared to Invention M (e.g. B-2) with the same strength level. , it is clear that the toughness is quite low.

Note that although hot rolling is not particularly specified in the present invention, sufficient characteristics can be obtained by performing predetermined hot rolling or equivalent hot rolling. However, in general, as shown in the above example, the slab heating temperature is set to 1300°C or lower from the viewpoint of heating cost, etc., and the rolling temperature range and rolling reduction rate are adjusted according to the target toughness and strength level of m44. , implement controlled rolling to control the rolling end temperature. Also, regarding the cooling method after rolling, air cooling or forced cooling is performed depending on the toughness and strength level of the target steel material. Furthermore, similarly, reheating treatment may be performed at a temperature below ACl, or quenching and tempering treatment may be performed.

[Effects of the Invention] The structural fire-resistant steel material of the present invention is as described above, and satisfies sufficient properties as a structural steel material while maintaining high strength at high temperature. It can be expected to reduce the thickness of the fire-resistant coating used in the required structure, simplify design and construction methods, and reduce the need for other fire-resistant measures.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the relationship between the amount of (Nb+2V+1.5Ti), the ratio of high temperature YS to normal 7RYS, and toughness. Applicant's representative Patent attorney Takehiko Suzue Nb+ 2V + 1.5Ti Figure 1 1, Case description Patent Application No. 63-324918 2, Name of invention Structural fire-resistant steel material 31. Relationship with the case of the person making the amendment Patent applicant (412) Nippon Koukan Co., Ltd. 4, Agent 3-7-2 Kasumigaseki, Chiyoda-ku, Tokyo 100 Telephone 03 (502) 3181 (Main representative) 7. Contents of the amendment 1) Amend the scope of claims as shown in the attached sheet. 2) “As attached,” stated on page 6, line 20 of the specification,
'' should be amended to ``to attach.'' 3) "rO, 03 or less" stated in page 7, line 12 of the same as above is corrected to "rO, 03% or less". 4) "rO, 002 or more" stated in page 7, line 13 of the same as above is corrected to "ro, 002% or more." 5) "YS (560)" written at the beginning of page 8, line 10 of the same as above.
Correct J to rYS (550)J. 6) "Both, weldability" stated in page 9, line 14 of the same as above.
is corrected as "both toughness and weldability". 7) Table 2 on page 17 of the same page is corrected as shown in the attached sheet. 2. Claims 10% by weight, C = 0.05% or more and less than 0.20%, S
i=0.10% or more and less than 2.0%, Mn=0.30% or more and less than 2.0%, P=0.03% or less, S=0.03%
Hereinafter, Mo=0.10% or more 1: less than 0.50%, sol
, Al=0.002% or more and less than 0.20%, N=0.0
0.010% or more'' 20. Contains less than 0.020%, the remainder consists of unavoidable impurities and Fe, furthermore, Nb = 0.005% or more and less than 0.20%, V = 0
．． 01% or more and less than 0.1% and Ti=0.003% or more and less than 0.03%, and 0.005%≦Nb+2V+1
．． A structural fire-resistant steel material containing 5Ti≦0.30% and having excellent weldability and ductility that satisfies the high temperature yield strength expressed by the following formula. YS (RT) - Yield strength at room temperature (kgf/mJ
) YS (450) - Yield strength at temperatures above 400°C and below 500°C (kgf/m4) YS (550) - Yield strength at temperatures above 500°C and below 600°C (kgf/mJ) YS (650) - Temperatures above 600°C Yield strength at 650°C or less (kgf/mJ) 2. In weight%, Cu = 0.01% or more and less than 1.5%, N
i=0.02% or more and less than 1.5%, Cr=0.05% or more and less than 1.0%, B-0,0005% or more and less than 0.005%
The structural fire-resistant steel material according to claim 1, containing one or more of the following. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] 1. In weight%, C = 0.05% or more and less than 0.20%, S
i=0.10% or more and less than 2.0%, Mn=0.30% or more and less than 2.0%, P=0.03% or less, S=0.03 or less, Mo=0.10% or more and 0. less than 50%, sol. A
l = 0.002 or more and less than 0.20%, N = 0.0010
% or more and less than 0.020%, the remainder consists of unavoidable impurities and Fe, furthermore, Nb = 0.005% or more and less than 0.20%, V = 0
．． 01% or more and less than 0.1% and Ti=0.003% or more and less than 0.03%, and contains in the range of 0.005%≦Nb+2V+1.5Ti≦0.30%, and furthermore, a high temperature expressed by the following formula Structural fire-resistant steel material with excellent weldability and ductility that satisfies yield strength. [YS(450)]/[YS(RT)]×100>70
%[YS(550)]/[YS(RT)]×100>6
0% [YS(650)]/[YS(RT)]×100>
40%YS (RT) = yield strength at room temperature (kgf/
mm^2) YS (450) = Yield strength at temperatures above 400°C and below 500°C (kgf/mm^2) YS (560) = Yield strength at temperatures above 500°C and below 600°C (kgf/mm^2) YS ( 650) = Yield strength at temperature above 600°C and below 650°C (kgf/mm^2) 2. In weight%, Cu = 0.01% or more and less than 1.5%, N
Claims containing one or more of i=0.02% or more and less than 1.5%, Cr=0.05% or more and less than 1.0%, and B=0.0005% or more and less than 0.005%. Structural fire-resistant steel material according to item 1.