JPH0277523A - Production of building low yield ratio steel having excellent fire resistance and building steel material using same steel - Google Patents

Abstract

PURPOSE:To economically produce the title building low yield ratio steel having excellent fire resisting characteristic by heating a low-C and low-Mn steel contg. a trace amt. of Nb and an appropriate amt. of Mo and having a specified composition to a specified temp., and then hot-rolling the steel at a relatively high temp. CONSTITUTION:A billet contg., by weight, 0.04-0.15% C, <=0.6% Si, 0.5-1.6% Mn, 0.005-0.04% Nb, 0.4-0.7% Mo, <=0.1% Al, 0.001-0.006% N, >=1 kind among 0.005-0.10% Ti, 0.005-0.03% Zr, 0.005-0.10% V, 0.005-0.5% Ni, 0.05-1.0% Cu, 0.05-1.0% Cr, 0.0003-0.002% B, 0.0005-0.005% Ca, and 0.001-0.02% REM, as required, the balance Fe, and inevitable impurities is reheated to 1100-1300 deg.C. The heated slab is then hot-rolled at 800-1000 deg.C, and then allowed to cool in the air to room temp. As a result, the Nb, Mo, etc., are sufficiently solution- treated, and a steel having high-temp. yield strength and toughness is obtained. An excellent fire-resistant structural material is obtained from the steel with a relatively thin refractory coating.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to a method for manufacturing a low yield ratio steel material with excellent fire resistance for use in various buildings in the fields of architecture, civil engineering, marine structures, etc., and the use of the steel material. This invention relates to constructed steel materials for construction.

[Conventional technology]

As is well known, rolled steel for shell structures (
JIS G 3101), rolled steel materials for welded structures (JIS
G 3106), weather-resistant hot rolled steel for welded structures (J
IS G 3114), highly weather resistant rolled steel (JIS G
3125) and carbon steel pipes for shell structures (JIS G
3444), - square steel pipe for shell structure (JIS G 34
66) etc. are widely used.

These steel materials are usually produced by removing S and P from hot metal obtained in a blast furnace, then refining it in a converter furnace, turning it into steel billets in a continuous casting or blooming process, and then hot rolling to obtain the desired properties. It will be commercialized as equipped.

By the way, when using the above-mentioned steel materials for buildings such as buildings, offices, and residences that are closely connected to daily life, it is mandatory to apply sufficient fireproof coating to ensure safety in the event of a fire. Building laws and regulations stipulate that the temperature of steel materials should not exceed 350"C in the event of a fire.

In other words, when the above-mentioned steel materials are used in buildings, their yield strength at around 350°C is 60 to 70% of that at room temperature, which may cause the building to collapse. We must use it without losing its power. For example, - rolled steel for shell structure (
In the case of a building whose columns are made of shaped steel specified in JIS G 3101), spraying material or felt based on slag wool, rock wool, glass wool, asbestos, etc., is spread on the surface. In addition, it is necessary to carefully apply a fireproof coating, such as enveloping it with fireproof mortar, or protecting it with a thin metal plate, such as an aluminum or stainless steel plate, on top of the heat insulating layer.

Therefore, the construction cost of fireproof coating becomes high compared to the cost of steel materials, and it is impossible to avoid a significant increase in construction cost.

Therefore, a technology has been proposed in which round or square steel pipes are used as construction materials to allow cooling water to circulate, preventing temperature rises and reducing load capacity in the event of a fire. Expansion is being planned.

For example, Japanese Utility Model Publication No. 52-16021 discloses a fire-resistant building in which a water tank is placed on the top of the building and cooling water is supplied to pillars made of hollow steel pipes.

[Problem to be solved by the invention]

As mentioned above, when conventional steel is used in buildings, it is inexpensive, but due to its poor high-temperature properties, it cannot be used uncoated or with a light liquid layer, and must be coated with a relatively expensive fire-resistant coating.

Therefore, there are problems in that the construction cost increases and the usable space of the building becomes narrower, reducing economic efficiency.

On the other hand, the method of forced cooling using hollow steel materials with the aim of improving fire resistance has the problem of a complicated structure, which increases equipment costs in addition to design and construction costs, and high maintenance costs. be.

In addition, heat-resistant steel materials such as stainless steel are very expensive, and although they have good high-temperature properties, their use as construction materials is extremely difficult due to production and construction technology as well as economic aspects. Have difficulty.

In recent years, buildings have become taller, and due to improved design technology and higher reliability, fire-resistant design has been reviewed, and in 1986, a new building fire-resistant design law was enacted. It's arrived. As a result, the ability of fireproof coating can be determined based on the high-temperature strength of the steel material and the load actually applied to the building, without being subject to the 350°C temperature limit mentioned above, and in some cases, it is possible to use steel without coating. It has also become possible.

However, there is currently no steel material that can be supplied to the market at an economical price as a structural steel material with excellent fire resistance.

An object of the present invention is to provide a method for producing a steel material with excellent high-temperature properties and excellent fire resistance that can be supplied to the market at an economical price, as well as a steel material for construction with fire resistance.

[Means to solve the problem]

The present invention overcomes the aforementioned problems and achieves the objectives.
Specific means are shown in the following sections.

70 weight ratio, C0.04~0.15%, Si0.6%
Below, Mn 0.5-1.6%, Nb 0.005-0
．． A steel piece containing 0.4% Mo, 0.4-0.7% Mo, 10.1% or less A, 0.001-0.006% N, and the balance consisting of Fe and unavoidable impurities is heated at 1100-1300°C.
A method for producing a low yield ratio steel material for construction with excellent fire resistance, which comprises reheating in a temperature range of 800 to 1000°C and then finishing hot rolling in a temperature range of 800 to 1000°C.

41 weight ratio, C0.04~0.15%, Si0.6%
Below, Mn 0.5~1.6%, Nb 0.005~
0.04%, Mo 0.4-0.7%, A10.1% or less, N0.001-0.006% plus T i 0
．． 005-0.10%, Zr 0.005-0.03%
, V 0.005~0.10%, Ni 0.05~
0.5%, Cu 0.05-1.0%, Cr 0.05
~1.0%, B0.0O03~0.002%, Ca0
．． 0005-0.005%, REM 0. OOL~
A steel piece containing one or more of 0.02% and the remainder consisting of Fe and unavoidable impurities is 1100-13
After heating in the temperature range of 00℃, hot rolling is carried out at 800~tooo
A method for producing low yield ratio steel for construction with excellent fire resistance that terminates in the temperature range of ℃.

(1) A method for producing a low yield ratio steel material for construction with excellent fire resistance, which further comprises plastic working the steel material obtained by the method described in the above item (a) or the above item (a) in a hot process.

A method for producing a low yield ratio steel material for construction with excellent fire resistance, which comprises plastically working the steel material obtained by the method described in the above-mentioned items (a) to (c) in a cold process.

E. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by spreading an inorganic fibrous fire-resistant thin layer material on the heat-receiving surface of the steel material obtained by the method described in items (A) to (2) above.

A low yield ratio steel material for construction with excellent fire resistance, which is obtained by coating a heat-receiving surface of a steel material obtained by the method described in items (a) to (ii) above with a highly heat-resistant paint.

G. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by attaching a heat shield plate to the heat-receiving surface of the steel material obtained by the method described in Items A to 2 above.

A low yield ratio steel material for construction with excellent fire resistance, which is obtained by filling concrete into a hollow steel material obtained by the method described in items (a) to (2) above.

(k) A low yield ratio steel material for construction with excellent fire resistance, which is obtained by spreading an ultra-thin metal onto the heat-receiving surface of the steel material obtained by the method described in items (a) to (2) above.

[For production]

Now, as a result of research on the strength of steel materials in the event of a fire, the present inventors have found that when uncoated use is targeted, the maximum temperature reached in the event of a fire is 1000 degrees Celsius, so the steel material has a room temperature yield strength of 70% at that temperature. It was learned that in order to provide a yield strength of more than 30%, a large amount of expensive alloying elements must be added, which would result in a loss of economic efficiency.

In other words, the unit price of the steel material becomes higher than the cost of the conventional steel material and the cost of installing a fireproof coating in addition to the cost of the conventional steel material, and such steel material cannot be practically used.

Therefore, as a result of further research, we found that the most economical steel material is a steel material whose high-temperature yield strength at 600'C is 70% (approximately 2/3) or more of that at room temperature, and the amount of expensive additive elements can be reduced. In addition to a method for producing steel that can be used without coating when the fire load is small, we have developed a steel material that has fire-resistant properties.

Now, the feature of the present invention is that after reheating a steel billet with a composition in which a trace amount of Nb and an appropriate amount of Mo are added to a low C-low Mn steel at a high temperature, rolling is finished at a relatively high temperature. The steel material obtained by the present invention has the characteristics of having appropriate room temperature yield strength and high high temperature yield strength.

In other words, the ratio of the proof stress in the temperature range of 600° C. to the room temperature proof stress is large. The reason for this is that the microstructure is a relatively large ferrite-based structure;
600 for fine-grained ferrite, hardened and tempered structures, etc.
The yield strength at room temperature is higher than the yield strength in the temperature range of "C", so it is difficult to satisfy the standard 41L at room temperature.

The steel material according to the present invention has a low yield ratio and excellent earthquake resistance, and this is also because the micro Mi collar is made of relatively large ferrite.

Next, characteristic component elements according to the present invention and their addition amounts will be explained.

Nb r Mo forms fine carbonitrides, and furthermore,
Mo increases high-temperature strength through solid solution strengthening, but M
It is difficult to obtain sufficient yield strength in the high temperature range of 600° C. by adding o alone.

As a result of research, the present inventors have found that adding Nb and MO in combination is extremely effective in increasing the yield strength in the high temperature range.

However, if Nb and Moi are too high, weldability will deteriorate and the toughness of the weld heat affected zone (HAZ) will deteriorate, so the upper limit of the Nb and Mo contents is 0.04%, respectively.
It is necessary to set the content to 0.7%, and the lower limit is 0.005% and 90.4%, respectively, as the minimum amount to obtain a composite effect.

The use of Mo to increase high-temperature strength is known in conventional heat-resistant steels, but as mentioned above, in addition to a small amount of Mo, a small amount of Nb is added in a composite manner for fire-resistant steel materials used for construction. There are no known steel materials.

However, acicular ferritic steel for line pipes is known as a steel material with a composite addition of Nb and Mo, but in order to achieve its purpose, 1.5 acicular ferritic steel is produced by controlled rolling for strength. , because the yield strength at room temperature is increased, the yield ratio at room temperature becomes high, and the low yield ratio required for construction steel cannot be met.

Additionally, the acicular ferrite steel has a higher Mn content than the steel of the present invention. This is because, unlike the steel of the present invention, it is important to improve low-temperature toughness, and there are significant differences between the two in terms of purpose and function and effect.

Next, the reason for limiting components other than Nb and Mo in the present invention will be explained in detail.

C is for ensuring the strength of the base metal and welded part, and Nb.

Necessary to exhibit the effect of adding Mo, and 0.0
If it is less than 4%, the effect will be weakened, so the lower limit is set at 0.04%. Furthermore, too much Cl not only adversely affects the low-temperature toughness of the HAZ, but also deteriorates the toughness and weldability of the base metal, so 0.15% is the upper limit.

Si is an element contained in deoxidized steel, and as Si increases, weldability and HAZ toughness deteriorate, so the upper limit is set at 0.6%.
And so. In the steel of the present invention, AI deoxidation is sufficient, and T
It may also be deoxidized. From the viewpoint of HAZ toughness, it is desirable that the Si content be approximately 0.15%.

Next, Mn is an essential element for ensuring strength and toughness, and its lower limit is 0.5%. However, if there is too much Mail, not only will hardenability increase and weldability and HAZ toughness deteriorate, but also it will not be possible to obtain base metal strength that meets the target standards. Therefore, the upper limit of Mnl was set at 1.6%.

Al is generally an element contained in deoxidized steel, but since deoxidation is also performed by St and Ti, the present invention does not limit the lower limit of A1. However, if the amount of Al increases, the cleanliness of the steel will deteriorate and the toughness of the weld will deteriorate, so the upper limit was set at 0.1%.

N is generally contained in steel as an unavoidable impurity, but it combines with Nb to form carbonitride Nb (CN), which is effective in improving high-temperature yield strength. For this reason, 0.001% is required as the minimum amount, but if the amount of N increases, the HAZ
Since it promotes the deterioration of toughness and the occurrence of surface flaws in continuously cast slabs, the upper limit was set at 0.006%.

Note that the steel material of the present invention contains P and S as inevitable impurities. Since P and S have a small effect on high-temperature strength, their amounts are not particularly limited, but generally the properties of steel materials, such as toughness and strength in the thickness direction, improve as the amounts of P and S decrease. Desirable amounts of P and S are each 0.02
%, 0.005% or less.

The basic components of the steel material of the present invention are as described above, and the purpose can be fully achieved, but the following elements, namely Ti,
When Zr, V, Ni, Cu, Cr, B, Ca, and REM are selectively added, more favorable results can be obtained in terms of improvement in strength and toughness.

Next, the additive elements and their amounts will be explained.

Ti is an element that has almost the same effect as the aforementioned Nb, and
, T if AIIJ is small at oos ~ 0.02%
It forms oxides and carbonitrides of i and improves HAZ toughness, but if it is less than 0.005%, it has no effect (if it exceeds 0.1%, it has an adverse effect on weldability, etc., and is not preferable.

■ is also an element that has almost the same effect as Nb and Ti, and its effect on high-temperature yield strength is smaller than that of Nb and Ti, but 0.
．． HAZ toughness is improved in the range of 0.005 to 0.10%. However, below 0.005%, there is no effect <0.1
If it exceeds 0%, it will have an unfavorable effect on HAZ toughness.

Next, Ni improves the strength and toughness of the base metal without adversely affecting weldability and HAZ toughness, but 0.05
If it is less than 0.5%, the effect is weak, and if it is added more than 0.5%, it becomes extremely expensive as a building steel material and loses economic efficiency, so the upper limit was set at 0.5%.

In addition to having almost the same effects as Ni, Cu precipitates increase high-temperature strength and improve corrosion resistance. It is also effective in improving weather resistance. However, if the Cu content exceeds 1.0%, Cu cracking occurs during hot rolling, making manufacturing difficult.
If it is less than 0.05%, there is no effect, so the amount of Cu should be 0.05 to 1.0%.
Limited to 0%.

Cr is an element that increases the strength of the base metal and welded parts, and is effective in improving weather resistance, but if it exceeds 1.0%, it deteriorates weldability and HAZ toughness, and if it is less than 0.05%, it is not effective. is thin. Therefore, Cri is set to 0.05 to 1.0%.

According to the knowledge of the present inventors, Cr is an element that increases high temperature yield strength like Mo, but unlike MO, the effect of increasing high temperature yield strength at 600° C. is relatively small compared to the increase in room temperature yield strength.

B is an element that increases the hardenability of steel and increases its strength, and BN combined with N acts as a ferrite generation nucleus,
Refine the HAZ structure. In order to obtain this kind of effect, a minimum of ff1o and 0003% Bl is required; less than this is ineffective, and too much B results in coarse B-constituent precipitating at the prior austenite grain boundaries in the HAZ. and deteriorate low-temperature toughness. Therefore, the upper limit of the amount of B is limited to 0.002%.

Ca and REM control the morphology of sulfide (MnS), increase Charpy absorbed energy, improve low-temperature toughness, and are also effective in improving hydrogen-induced cracking resistance. However, if the amount of Ca is less than 0.0005%, it has no practical effect, and if it exceeds 0.005%, a large amount of CaO and CaS will be generated and become large inclusions, which will impair not only the toughness but also the cleanliness of the steel. , which also has a negative effect on weldability, so 1. C
The range of the amount of a added is 0.0005 to 0.005%.

In addition, REM has the same effect as Ca, and increasing the amount added causes the same problems as Ca, and is also less economical, so the lower limit of REM amount is set to o, ooi%, and the upper limit is set to 0.02%. %.

Next, a method for manufacturing steel materials according to the present invention will be explained.

At room temperature, rolled steel for welded structures (JIS G 31
In order to satisfy the performance specified in 06) and maintain high yield strength at a high temperature of 600°C, the conditions for heating and rolling the steel are important as well as the steel composition. Nb and M are characteristic of the steel components of the present invention.

In order to increase the high-temperature yield strength through the combined addition of these elements, it is necessary to sufficiently dissolve these elements during heating. Therefore, the lower limit of the heating temperature of the steel slab made of the components of the present invention is set to 11.
Let it be 00'C. In addition, if the heating temperature is too high, the crystal grains will become large and the low temperature toughness will deteriorate, so the upper limit is 13
It must be brought to 00℃.

Next, the heated steel slab is hot rolled, and the rolling end temperature is set to a high temperature of 800° C. or higher. The reason for this is to prevent carbonitrides of Nb and Mo from precipitating during rolling. If these elements precipitate in the T range, the precipitate size increases and the high temperature yield strength decreases significantly.

Conventional low-temperature rolling (controlled rolling) is used for low-temperature rolling such as line pipes.
This is an essential requirement for steel materials that require iA properties, but when there is no high demand for low-temperature toughness, such as the steel of the present invention, and rather the balance between room-temperature yield strength and high-temperature yield strength at 600'C is important, rolling is not required. Must be finished at high temperature. This is also important as a condition for reducing the yield ratio. Further, in the present invention, the upper limit of the rolling end temperature is set to 1000''C, and the reason for this is to ensure toughness as a construction steel.

After hot rolling, the product is allowed to cool to room temperature.

In addition, after producing the steel material of the present invention, for the purpose of dehydrogenation etc., Ac,
Even if the steel material is reheated to a temperature below its transformation point, the characteristics of the steel material of the present invention are not impaired in any way.

Furthermore, in the present invention, the steel billet is heated and then hot-rolled to produce a product as described above, and after that, in order to further manufacture a desired steel material, the product is further subjected to hot or cold plastic processing. You may.

For example, in addition to forming a steel billet into a bloom or a billet and then hot-working it into a section steel, the product may be used as a raw material and cold-worked to produce a desired steel material such as a section steel or a steel pipe. At that time, heat treatment is appropriately performed as necessary.

Next, the mechanical properties of the steel material of the present invention will be explained in detail in comparison with known steel materials.

Table 1 shows a compositional comparison between the steel material of the present invention and JIS G 3106 rolled steel material for welded structures (5M50A).

In addition, the steel material of the present invention contains 120 pieces of steel having the components shown in the table above.
heated to 0°C and hot rolled at a rolling end temperature of 950'C;
After rolling, the product was left to cool to room temperature.

In Figure 1, the vertical axis shows stress (kgf/M") and the horizontal axis shows temperature (°C). The solid line 1 indicates the steel of the present invention, and the broken line 2 indicates the comparative steel (3M50A). ), where TS represents tensile strength and YP represents yield point.

As is clear from Figure 1, the difference disappears at temperatures exceeding 800°C, but the steel of the present invention maintains twice the yield strength of 5M50A at 600°C to 700°C, and has excellent properties as a building steel. It can be seen that it is equipped with

In Figure 2, the vertical axis shows the elastic modulus (kgf/mm") and the horizontal axis shows the temperature (°C). The solid line 1 represents the change in the steel according to the invention, and the broken line 2 represents the change in the 5M50A. Figure 3 also shows creep strain (%) on the vertical axis and time (%) on the horizontal axis.
), and the stress at 600°C applied to the test piece (
kg f / +rrra'') is used as a parameter, and the change in the steel of the present invention is shown by a broken line, and FIG. 4 similarly shows the change in 5M50A by a broken line.

As is clear from Fig. 2, the elastic modulus of the steel of the present invention rapidly decreases at temperatures exceeding 700°C, whereas
The elastic modulus of M50A drops dramatically at around 600°C. Furthermore, as is clear from FIGS. 3 and 4, the steel of the present invention has a stress level of 15 kgf/mm" that acts on structural members such as pillars and beams of ordinary buildings at a temperature of 600°C, and Even at the maximum duration of 3 hours, the progress of creep strain is extremely small, but in 5M50A,
When a stress level of 10 kgf/mm is applied at a temperature of 600'C, the progress of creep strain is extremely large.The fact that the elastic modulus does not decrease at high temperatures and that the progress of creep strain is small reduces the deformation of the building in the event of a fire. Therefore, it can be seen that the steel material of the present invention has superior properties as a steel material for construction compared to 5M50A.

The present inventors obtained similar results in comparison with comparative steel material SS41.

From this, it is clear that the steel of the present invention requires a thinner fireproof coating when the fire load is the same compared to 5M50A and SS41, and it is also possible to get away with no coating when the fire load is not large. it is obvious.

Next, an example in which an inorganic fibrous refractory thin layer material is spread on the steel material of the present invention will be described.

Table 2 is an example regarding fireproof coating thickness, JISA 1
In the experiment specified in 304, the steel temperature was 350℃.
Indicates the required coating thickness of refractory material to ensure that the thickness is not exceeded.

By the way, in the case of the steel material of the present invention, the temperature of the steel material may rise to over 600° C., so as mentioned above, the thickness of the fireproof coating may be as thin as shown in Table 3.

As is clear from the comparison of Tables 2 and 3, when the steel of the present invention is used, the material cost and construction cost of fireproof coating can be significantly reduced.

Table 2 Table 3 Next, Figure 5 shows H-beam steel 1 (300x
300 x 10 x 15) Spraying in Table 3 is a schematic elevational view and an AA sectional view of a column on which rock wool (wet type) 2 was spread.

Figure 6 shows the test results of heating the H-shaped steel column specified in JIS A 1304, applying a load normally supported by building columns, and determining the time to failure.The vertical axis shows the temperature. ('C), time (minutes) is plotted on the horizontal axis, where the solid line 1 shows the steel temperature of the column, and the broken line 2 shows the change in heating temperature. In addition, Fig. 7 shows the transformation on the vertical axis (cs+
+), temperature (°C) and time (minutes) are plotted on the horizontal axis, and the solid broken line indicates the deformation of the column. Figures 6 and 7
As is clear from the figure, by spraying 10 mm thick with rock wool (wet method), the pillars made of the steel of the present invention do not break until the temperature exceeds 600'C, and have a fire resistance of more than 1 hour. It is clear that it is demonstrating.

Similarly, FIG. 8 shows the H-shaped steel beam 3 (4
00X 200X 8

Figure 9 shows the test results of heating the H-shaped steel beam specified in JIS A 1304, applying a load normally supported by a building beam, and determining the time to failure.The vertical axis shows the temperature. (''C), with time (minutes) plotted on the horizontal axis, where the solid line 1 represents the temperature of the beam upper flange 5, the broken line 2 represents the temperature of the beam lower flange 6, and the broken line 3 represents the temperature of the web 7. The broken line 4 shown shows the change in heating temperature.
The vertical axis shows deformation (vertical deflection) (cmL) The horizontal axis shows temperature (°C) and time (minutes), and the solid broken line shows the deformation at each point of the beam. From Figures 8 and 9 As is clear, the 10mm thick spraying is done using rock wool (wet method).
It can be seen that the beams manufactured using the steel of the present invention do not break down until the temperature exceeds 600°C, and exhibit fire resistance performance of 1 hour or more. Furthermore, it can be seen that the amount of deformation at 600° C. is also less than the allowable deformation value.

The present inventors also conducted tests on other refractory materials and obtained similar results.

Next, the steel materials of the present invention were coated with a highly heat-resistant paint and tested, and the results are shown in Table 4.

Table 4 Paint 1 and Paint 2 are foaming highly heat-resistant paints (manufactured by West German Desipak, trade name Pyrotect, types S30 and F2O).
The steel material of the present invention having a thickness of 16 mm and a square size of 220 mm was used as the test steel material.

Conventional steel materials were designed to have a steel material temperature of 350°C or lower, so even with the conventional paints 1 and 2 shown in Table 4, a fire resistance time of only 30 or 60 minutes could be secured, but as shown in the table above. Since the steel material of the present invention can ensure yield strength up to 600°C, fire resistance times of 60 minutes and 120 minutes can be ensured even by painting with Paint 1 and Paint 2. In other words, if the conventional fire resistance time is to be maintained, there is an advantage that painting can be simplified.

That is, the steel material of the present invention coated with a highly heat-resistant paint is highly economical and can reduce construction costs.

Next, FIG. 11 shows the H-shaped steel 8 according to the present invention as a thin steel plate (
This is a schematic cross-sectional view of a beam 10 surrounded by a beam (SS41 or stainless steel) 9.
supports a concrete floor 12.

Figure 12 shows the JIS A 13 test specimen shown in Figure 11.
04, the vertical axis shows temperature (CL), and the horizontal axis shows time (minutes). Broken line 1 shows the heating temperature, broken line 2 is the steel temperature of the H-section steel without the thin steel plate (SS41) installed,
The broken line 3 shows the temperature of the H-shaped steel surrounded by a thin steel plate (SS41), the broken line 4 shows the temperature of the H-shaped steel when a light fireproof coating is applied on the inside of the thin steel plate (SS41), and the broken line 5 shows the temperature of the H-shaped steel surrounded by a thin steel plate (SS41). This figure shows the temperature of H-beam steel when a light fireproof coating is applied to the inside of a thin steel plate (stainless steel).

As is clear from Fig. 12, the temperature of the H-beam surrounded by the thin steel plates (SS41) is higher than that of the H-beam without the thin steel plates (SS41) for up to 30 minutes. Since the temperature rise is small and the steel of the present invention retains its strength even up to a temperature rise of over 600°C, it is possible to protect against fires with a small fire load and a short fire resistance time by surrounding the uncoated steel with a thin steel plate (SS41). is possible. Furthermore, even when the fire load is large and the fire resistance time is long, the H-shaped steel can be left uncoated by applying a light fireproof coating to the inside of the thin steel plate (SS41). Note that metal plates having a heat-insulating effect, such as stainless thin steel plates, titanium thin plates, and aluminum plates, including the above-mentioned thin steel plate 9, are collectively referred to as heat shield plates.

The steel material according to the present invention equipped with the heat shield plate does not require difficult work such as spraying fireproofing at a construction site, and can be easily installed, so it can be used economically.

Next, the graph in FIG. 13 shows that the square steel pipe according to the present invention is filled with concrete, and a fibrous refractory material based on rock wool is applied to the surface by wet spraying.
1 hour fire resistance test (JIS 1304Y)
This figure shows the temperature change of a square steel pipe obtained by conducting the above-mentioned heat treatment. Even with such a thin refractory layer, the steel material of the present invention can sufficiently achieve its purpose.

Furthermore, the graph in Figure 14 shows that the steel plate of the present invention is processed into a deck plate, and the back side is sprayed with a fibrous refractory material based on rock wool at 7.5 ma+r by a wet method. This shows the results obtained through a test (based on JIS^1304), and since the temperature of the deck plate itself does not exceed 600°C, it was confirmed that the steel material of the present invention can be used as an effective fire-resistant steel material.

Next, the 15th and FIG. 16 are graphs showing temperature rise curves when the emissivity is 0.7 and 0.4 in the fire test of uncoated steel frames, where T is the plate thickness.

As is clear from Figures 15 and 16, the plate thickness is 100 mm.
+na+, the steel material of the present invention has no problem in fire resistance for 1 hour without coating.

Furthermore, the inventors' research has shown that even if the emissivity is 0.7, if the plate thickness is 701nI11 or more, there is no problem with fire resistance for one hour, and if the steel of the present invention is coated with ultra-thin metal such as aluminum foil, It has been found that fences up to a thickness of 40 can be used without being coated with heat insulating and fireproof material.

〔Example〕

Steel materials with various steel components were manufactured using well-known converter, continuous casting, and rolling processes, and their room temperature yield strength (yield strength), high temperature yield strength (yield strength), etc. were investigated.

Tables 5, 6, and 7 show composition comparisons between the steel materials of the present invention and comparative steel materials, and Tables 8 to 12 show heating, rolling,
Mechanical properties are shown according to cooling conditions.

As is clear from Tables 8 to 12, the examples of the present invention all have good yield strength at room temperature and high temperature, whereas the comparative examples all have too high yield strength at room temperature or lack high temperature yield strength. Moreover, the ratio of the yield strength at 600''C to the yield strength at room temperature is low, making it unsuitable as a fire-resistant building material.

〔Effect of the invention〕

The steel and steel materials according to the present invention have excellent high-temperature properties and can achieve fireproofing purposes with no coating or with a coating thickness of 20 to 50% of conventional fireproof coatings, making it possible to significantly reduce the cost of fireproof construction. It is. In addition, mass production is possible, the price is low, welding is easy, the construction period can be shortened, and overall construction costs are low.

Furthermore, the manufacturing method is economically advantageous as it does not require particularly difficult operations.

[Brief explanation of the drawing]

Figure 1 is a comparison graph of the yield strength of the invention steel and comparative steel.
Figure 2 is a comparison graph of elastic modulus, Figure 3 is a creep characteristic graph of the steel of the present invention, Figure 4 is a creep characteristic graph of comparative steel, and Figure 5 is a graph of the sprayed H-beam steel of the present invention. Figure 6 is a schematic elevational view (a) and A-A sectional view (b) of a column on which rock wool (wet type) is spread. Figure 6 is a graph showing the temperature rise curve of the column. Graph showing deformation, Figure 8 is a schematic elevational view (a) and A-A sectional view (b) of a beam in which sprayed rock wool (wet type) is spread on the H-beam steel according to the present invention, Figure 9 Figure 10 is a graph showing the temperature rise curve of the beam, Figure 10 is a graph showing the deformation of the beam, Figure 11 is a schematic cross-sectional view of the steel material equipped with a heat shield plate, and Figure 1 is a graph showing the temperature rise curve of the beam.
Figure 2 is a graph showing the temperature rise curve of the steel material, Figures 13 and 14 are graphs showing the temperature rise curve of concrete-filled steel pipes and deck plates, and Figures 15 and 16 are graphs showing temperature rise curves of the steel material, respectively. 2 is a graph showing a temperature rise curve of an uncoated steel frame. 1... H-beam steel, 2... Fireproof material, 3...
・H-beam steel, 4... Fireproof material, 5... Beam upper flange, 6... Beam lower flange, 7... Web, 8... H-beam steel, 9... Thin steel plate,
10... Beam, 11... Mounting bracket,
12... Concrete floor. 30th time (minutes) 4th country steel material temperature (coating thickness: 10mm) Deformation amount (coating thickness: 10mm) Fig. 7 (a) (b) Fig. 8 Steel material temperature (coating thickness = 10mm) ]○ Fig. 11 Figure 13 Figure 14

Claims (1)

[Claims] 1. C0.04-0.15% by weight, Si 0.6% or less, Mn 0.5-1.6%, Nb 0.005-0.04%, Mo 0.4-0. 7%, Al 0.1% or less, N 0.001 to 0.006%, the balance being Fe and unavoidable impurities.
After heating in a temperature range of ~1300℃, hot rolling is performed at a temperature of 800~1
A method for producing a low yield ratio steel material for construction with excellent fire resistance that terminates in a temperature range of 1,000°C. 2. By weight: C0.04-0.15%, Si0.6% or less, Mn0.5-1.6%, Nb0.005-0.04%, Mo0.4-0.7%, Al0. 1% or less, N0.001-0.006% plus Ti0.005-0.10%, Zr0.005-0.03%, V0.005-0.10%, Ni0.05-0.5% , Cu0.05-1.0%, Cr0.05-1.0%, B0.0003-0.002%, Ca0.0005-0.005%, REM0.001-0.02% or A low yield ratio steel material for construction with excellent fire resistance, in which two or more types of steel pieces, the balance of which is Fe and unavoidable impurities, are heated in a temperature range of 1100 to 1300°C, and then hot rolling is completed in a temperature range of 800 to 1000°C. manufacturing method. 3. A method for producing a low yield ratio steel material for construction with excellent fire resistance, which further comprises plastic working the steel material obtained by the method according to claim 1 or 2 in a hot process. 4. A method for producing a low yield ratio steel material for construction with excellent fire resistance, which comprises plastic working the steel material obtained by the method according to claim 1, 2 or 3 in a cold process. 5. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by spreading an inorganic fibrous fire-resistant thin layer material on the heat-receiving surface of the steel material obtained by the method according to claim 1, 2, 3 or 4. 6. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by coating a heat-receiving surface of a steel material obtained by the method according to claim 1, 2, 3 or 4 with a highly heat-resistant paint. 7. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by attaching a heat shield plate to the heat-receiving surface of the steel material obtained by the method according to claim 1, 2, 3 or 4. 8. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by filling a hollow steel material obtained by the method according to claim 1, 2, 3 or 4 with concrete. 9. A low yield ratio steel material for construction with excellent fire resistance, which is obtained by spreading an extremely thin metal onto the surface of the steel material obtained by the method according to claim 1, 2, 3 or 4.