JPH0360894A - Welded structure for steel frame building and welding procedure thereof - Google Patents

Abstract

PURPOSE:To stably provide a welded structure with which the strength of the weld zone is less degraded at a low cost by constituting a deposited metal of specific weight % of C, Si, Mn, P, Cr, Mo, sol.Al, O, N, and Fe and forming the same of a chemical compsn. having specific PCM. CONSTITUTION:The deposited metal part of the welded structure for steel frame buildings is formed of the deposited metal which is high in high-temp. modulus of elasticity and high-temp. tensile strength. The deposited metal is constituted, by weight ratios, of 0.04 to 0.15% C, 0.01 to 0.90% Si, 0.30 to 2.00% Mn, <=0.05% P, 0.10 to 2.00% Cr, 0.03 to 1.00% Mo, <=0.10% sol.Al, <=0.08% O, <=0.05% N, and the balance Fe and unavoidable impurities. The deposited metal is constituted of the chemical compsn. with attains <=0.30% PCM expressed by formula I. The weld zone which is less degraded in strength and modulus of elasticity and has a high toughness value even when exposed to a high temp. at the time of a fire or the like is obtd. in this way.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a welded part with high toughness, and even if the temperature of the welded part increases due to, for example, a fire, the elastic modulus and strength of the part will not decrease. This article relates to welded structures for steel frame buildings, which are rare, and their welding construction methods.

<Prior art and its challenges> In recent years, the number of steel-frame buildings used for skyscrapers has increased, but this is because steel frames with high strength and flexibility are suitable for building large structures, and .

This is because it has many advantages, such as the ability to increase the living area because the size of the beam can be reduced.

By the way, with regard to steel structures for such steel-framed buildings, fireproof construction methods were previously uniformly and strictly stipulated by the Building Standards Law, but from 1981 to 1981 the Ministry of Construction's Comprehensive Technology Project "Buildings As a result of the results of the ``Development of Disaster Prevention Design Methods,'' it has become possible to ``reduce the thickness of fireproof coating'' and even ``to make steel frames uncoated,'' provided that ``structural stability in the event of a fire'' can be confirmed through numerical simulations and experiments.'' This greatly improves the flexibility of fireproof construction methods for steel structures compared to conventional methods.

However, with the steel materials currently used, for example, 6
As the strength decreases significantly in the high temperature range exceeding 00℃, and structural stability cannot be guaranteed when exposed to high temperatures in the event of a fire, in reality we have no choice but to adopt a fireproof construction method that mainly involves spraying rock wool. The reality is that you can't get it. just,
Although this fireproof construction method of spraying Rosokuul is said to be low-cost, spraying around a curing sheet at the construction site not only prolongs the construction period as it requires additional work, but it also creates a poor environment. There was a strong recognition that there was a need for improvement.

In addition, methods to avoid this rock wool spraying work are as follows: a) A method of pasting a fireproof board instead of rock wool spraying.

b) A method of using structural steel that does not lose its strength even when exposed to high temperatures.

is possible. However, the former method requires additional work to apply some kind of partial covering to protect the exposed edges of the steel material, and the fireproof board itself is expensive, so there is a problem that there are few benefits in terms of construction. .

On the other hand, if the latter method is used, which is ``application of steel materials that do not lose their high temperature strength even when exposed to high temperatures in the event of a fire,'' the above-mentioned fireproofing method will not be adopted and the ``structural stability in the event of a fire'' will be improved.
Since it is possible to guarantee the

As steels used for applications requiring high-temperature strength, low alloy steels for pressure vessels containing Mo, such as those disclosed in Japanese Patent Publication No. 57-19731 or Japanese Patent Publication No. 59-42745, have so far been used. is being developed. but,
It is common knowledge that the strength of steel used as pressure vessel steel is guaranteed at temperatures below 500°C, and even at temperatures above 500°C, even at temperatures above 600°C.
It can be said that there has been no attempt to guarantee high-temperature strength at temperatures around 'C.

Moreover, even if a prepared material that can suppress the decrease in strength at high temperatures is developed, consideration must be given to the fact that it cannot be said to be sufficient as a structural member for steel-framed buildings.

That is, since steel materials for building structures are intended to be used for columns and beams, the absence of "buckling" is also an extremely important required characteristic. Therefore, in addition to suppressing a decrease in strength when heated to high temperatures such as during a fire, it is also an extremely important requirement that the decrease in elastic modulus be small in a high temperature range. Therefore, it is difficult to develop steel materials for such applications based solely on the knowledge of pressure vessel steels as mentioned above, and research and development based on numerous experiments and studies from different viewpoints are absolutely necessary. Met.

Furthermore, steel buildings generally have a welded structure, so when considering the safety of the entire structure, it is important to minimize the decline in strength and elastic modulus even when exposed to high temperatures such as during a fire. The most important point is to realize a "welded part" that can be used. Despite this, the actual situation is that no particular study has been made of the materials in order to maintain the above-mentioned required performance in the welded part.

However, regarding the steel material (base material) itself, in addition to adjusting the chemical composition, it is also necessary to devise rolling conditions or perform heat treatment to ensure fine precipitates that contribute to property improvement and achieve the desired performance. However, in the case of welded parts, there is usually no processing such as rolling performed after welding, so the structure remains solidified, so it is generally difficult to achieve high performance. In addition, post-weld heat treatment not only increases costs, but it is practically not carried out because the welded parts of welded steel structures usually have very complex shapes. That was impossible.

For these reasons, it is urgent that welded steel structures for steel buildings have welded parts that have high toughness and less decrease in strength and elastic modulus even when exposed to high temperatures such as during a fire. there were.

Therefore, the present inventors conducted various experiments to examine the required characteristics of welded parts, which are particularly difficult to ensure performance in welded steel structures, and determined that the mechanical properties at room temperature meet JIS G31.
0 I-specified 5S41 or JISC; 3106
In a welded part of steel that satisfies the performance of 3M50 specified in
-If the above is true and it has sufficient toughness,
It was confirmed that it is possible to realize a welded steel structure with excellent structural stability that can withstand temperature rise during a fire even when the fireproof coating is reduced or omitted.

Therefore, the object of the present invention is to provide mechanical properties at room temperature of J
It satisfies the performance of 5S41 or 5M50 specified by IS, has mechanical properties (tensile strength) at 600°C that are 60% of the target value at room temperature, and has an elastic modulus of 15,000 kgf/- or more. The aim was to find a means of realizing welded structures for steel construction with welded parts.

Means for Solving the Problems The present inventors have obtained the following knowledge from the results of numerous experiments and studies conducted to achieve the above object.

<8+ It is effective to add Cr+ Mo, V, Nb, etc. to the weld metal in order to increase the strength 2 elastic modulus of the welded part at high temperatures. However, addition of large amounts is not only uneconomical, but also significantly increases the strength at room temperature, leading to an imbalance with the steel material (base material), and also leading to deterioration of the toughness of the weld metal. It needs to be carried out under careful control.

(b) In order to satisfy the required mechanical properties at room temperature and obtain the desired properties at high temperatures, it is necessary to suppress the formation of ferrite in the weld metal and to improve the structure of the weld metal.
It is important to create a bainite structure that suppresses the introduction of martensite, which leads to an increase in strength at room temperature.

(C) Additionally, since the welded metal parts of welded steel structures for steel construction tend to have a solidified structure, it is necessary to introduce means to improve the chemical composition in order to improve the properties. is the most practical method, but in order to prevent the strength 2 modulus of elasticity from decreasing in the temperature range when a steel frame building is exposed to a fire, this temperature increase can be used to prevent the fine precipitation of Cr and Mo. It is extremely effective to adjust the ingredients so that this occurs.

The present invention was made based on the above-mentioned findings, etc., and provides a welded structure for steel-framed buildings.

St: 0.01-0.90%, Mn: 0.
30-0.90%.

Si: 0.05% or less, Cr: 0.10-0
．． 90%.

Mo: 0.03-1.00%, sol, Ai
': 0.10% or less.

0: 0.08% or less, N? 0.05% or less,
Alternatively, Nb: 0.08% or less, V: 0.10% or less.

Cu: 0.50% or less, Ni: 0.10
%below.

It also contains one or more of Ti: 0.5% or less, Ni: 1.5% or less, the balance is free from Fe and unavoidable impurities, and has a chemical composition in which Po expressed by the formula is 0.30% or less. By having a structure with a high-toughness welded metal part, the welded metal part has an elastic modulus of 15,000 kgf/- or more when heated to 600°C, and a tensile strength that is 60% or more of the room temperature strength. It is characterized by ``structural stability in the event of a fire,'' and furthermore, ``steel construction steel materials are welded at a heat input of 8 to 50 kJ/cm to achieve a specified chemical composition and PC, 4. The present invention is also characterized by the fact that the welded structure for steel frame buildings having the above-mentioned good "structural stability in the event of fire" can be stably realized by producing a welded metal of .

Hereinafter, in the present invention, the reason why the composition of the welded metal part of the welded structure for steel frame construction and the amount of heat input during welding are numerically limited as described above will be explained in detail together with the effect thereof.

A) Weld metal composition C has the effect of ensuring the desired strength, but if its content is less than 0.04%, the desired effect cannot be obtained by the above effect; If the C content exceeds 0.04, there is a concern that cracking may occur.
It was limited to ~0.15%.

Si Si is a useful component as a deoxidizing agent, but if its content is less than 0.01%, sufficient deoxidation cannot be performed;
The Si content was set at 0.01 to 0.90% because Si content exceeding 0% would cause a significant deterioration of toughness, but in order to ensure better toughness, it should be kept below 0.50%. is preferred.

Mn Mn has the effect of improving strength and toughness, but if its content is less than 0.30%, the desired effect due to the above effect cannot be obtained, while on the other hand, if it is contained more than 0.90%, the The Mn content was set at 0.30 to 0.90% because not only the effect was saturated, but also the toughness showed a tendency to deteriorate.

P is an element that accompanies weld metal as an unavoidable impurity, but if its content exceeds 0.05%, cracking susceptibility increases significantly, so the upper limit of the P content is set at 0.05%.
It was determined that

Cr Cr has the effect of promoting bainiticization of the solidified and cooled Mi weave and improving the required properties (strength 1 elastic modulus) at room temperature and at high temperature heating, but if its content is less than 0.10%, the above-mentioned The desired effect was not obtained by the action, - 0.90%
Cr content was limited to 0.10 to 0.90% since the effect would be saturated even if the content exceeded Cr content.

Like Cr, Mo also has the effect of promoting bainite formation of the solidified and cooled m weave and improving the required properties (strength 9 elastic modulus) at room temperature and when heated at high temperatures. 03
If the content is less than 1.00%, the desired effect cannot be obtained, while if the content exceeds 1.00%, the strength will increase more than necessary and it will be uneconomical. It was set at 0.03 to 1.00%.

sol, Al 5o1. All is also an essential component as a deoxidizing agent,
Since containing more than 0.10% causes deterioration of toughness, the sol and AI contents were determined to be 0.10% or less.

Both O and N are impurity elements that are mixed in large amounts into the deposited metal formed by welding, causing a decrease in hardenability and toughness. Furthermore, by suppressing N to 0.05% or less, the above-mentioned disadvantages can be alleviated to an acceptable extent, so the 0 content was limited to 0.08% or less, and the N content was limited to 0.05% or less.

ヱ■ Pe (welding cracking (cold cracking) susceptibility index) is a generally useful index that also indicates hardness, strength, toughness, etc., but if its value exceeds 0.30%, welding will occur. The PCM content was determined to be 0.30% or less because the hardness 9 strength of the metal increases significantly, causing a lack of balance with the base metal, and also leads to deterioration of toughness, making it unsuitable for use as architectural structures.

Nb, V, Cu, Ni, Ti, and B Generally, one or more of these components are included in order to improve the toughness and strength of steel materials, but the architectural welded structure according to the present invention Since the same effect can be obtained in the welded metal parts of objects, Nb, V,
One or more of Cu, Ni+Ti and B may be contained. Note that these components may be intentionally added during welding, but they may also be included through dilution of the base material. However, if these components are contained in excess, there is a concern that they may cause problems such as increasing the cracking susceptibility of the welded metal, deteriorating toughness, and significantly increasing strength, so the upper limit of each content has been set. Nb is 0.08%, ■ is 0.1
0%, Cu 0.50%, Ni 0.10%, T
j is 050%.

B was set at 0.003%.

In addition, in order to realize the chemical precepts of the weld metal mentioned above, additional component elements may be added as necessary when welding steel materials for steel structures, or base metal dilution may be used. Needless to say, it's a good thing.

B) Heat input during welding work As mentioned above, the deposited metal part of welded steel structures for steel buildings usually has a solidified structure, so it is difficult to ensure performance by adjusting the composition alone. is not stable, and the formation of martensite or ferrite may be promoted depending on the construction conditions.

However, when welding steel materials for building construction, if the chemical composition of the weld metal is adjusted as described above and the welding heat input is adjusted to 8 to 50 kJ/cm, bainite formation occurs smoothly, which is necessary for welded structures for construction. Performance becomes stable and achieved.

Note that if the welding heat input is less than 8 kJ/cm, the cooling rate will be fast and martensite will be produced, resulting in too high hardness. On the other hand, if the welding heat is more than 50 kJ/am, the production of ferrite will be promoted and high-temperature performance will be impaired. You won't get it.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> First, a steel plate equivalent to 5M50 (plate thickness: 20 mm) specified in JIS G3106 was prepared, and this was finished into the groove shown in FIG.

Next, the core wire is 5WY1 specified in JIS G3523.
Using a welding rod equivalent to No. 1 (4.0φ) with various coating compositions, the steel plates were welded at the heat input shown in Table 1 to obtain the target weld metal composition as shown in Table 1. A welded structural material having the following properties was obtained.

The weld metal of the welded structural material thus obtained was investigated for its "strength and elastic modulus at room temperature and 600°C,""side bending properties at room temperature," and "toughness at 0°C." The results are shown in Table 2.

Here, the "elastic modulus" was measured using a hot resonance type elastic modulus measuring device, which is a method of vibrating a test piece to determine the natural frequency and measuring the elastic modulus from the following equation.

11r100f = - - It is clear that a welded structural material having the following characteristics can be realized.

Although this example shows only an example in which coated arc welding was applied as a method for obtaining the deposited metal according to the present invention, other methods include CO2 welding and MIG welding.

Needless to say, the type of welding method is not particularly limited as long as it is a welding method that uses lye, such as submerged arc welding or TIG welding.

(Summary of Effects) As described above, the present invention enables welded structures for steel frame buildings to be produced at low cost, with very little reduction in the elastic modulus or strength of the welded parts even if the temperature of the structure rises in the event of a fire. This will bring about extremely useful effects industrially, such as making it possible to provide stable supplies.

4,

[Brief explanation of drawings]

Figure 1 shows Showing the groove shape applied in the example It is a schematic diagram.

Claims (3)

[Claims] (1) C: 0.04-0.15%, Si: 0.01-0.90 in weight percentage
%, Mn: 0.30-2.00%, P: 0.05% or less, Cr: 0.10-2.00%, Mo: 0.03-1.
00%, sol. Al: 0.10% or less, O: 0.08
% or less, N: 0.05% or less, Fe and unavoidable impurities: the remainder, and P_C_M represented by the following formula
1. A welded structure for steel frame construction, comprising a high-toughness welded metal part with high high-temperature elastic modulus and high-temperature tensile strength, having a chemical composition of 0.30% or less. P_C_M=▲There are mathematical formulas, chemical formulas, tables, etc.▼ (2) C: 0.04-0.15%, Si: 0.01-0.90 in weight percentage
%, Mn: 0.30-2.00%, P: 0.05% or less, Cr: 0.10-2.00%, Mo: 0.03-1.
00%, sol. Al: 0.10% or less, O: 0.08
% or less, N: 0.05% or less, further Nb: 0.08% or less, V: 0.10% or less, Cu: 0
．． 50% or less, Ni: 1.5% or less, Ti: 0.09%
Hereinafter, a chemical composition containing one or more types of B: 0.003% or less, the balance being composed of Fe and unavoidable impurities, and having a P_C_M represented by the following formula of 0.30% or less, A welded structure for steel construction, comprising a high-toughness welded metal part with high high-temperature elastic modulus and high-temperature tensile strength. P_C_M=▲There are mathematical formulas, chemical formulas, tables, etc.▼ (3) For steel frame construction according to claim 1 or 2, wherein the welding of steel materials for steel frame construction is performed at a heat input of 8 to 50 kJ/cm to produce a deposited metal having a predetermined chemical composition and P_C_M. Welding construction method for obtaining welded structures.