JP2003221642A - Refractory steel product for construction and its manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel requiring a low production cost which satisfies a strength specified for SN400 or SN490 defined by JIS, ensures a strength at elevated temperature satisfying: (yield strength at 650°C)/(yield strength at ordinary temperature)≥0.5 and (yield strength at 700°C)/(yield strength at ordinary temperature)≥0.4, and shows an excellent weldability (Y crack stopping temperature of ≤0°C), and its manufacturing process. <P>SOLUTION: The steel contains 0.01-0.13 mass% C, 0.01-0.5 mass% Si, 0.01-0.5 mass% Mn, 0.3-1.3 mass% Mo, 0.02-0.1 mass% Nb, 0.003-0.05 mass% sol.Al and ≤0.01 mass% N, wherein the remainder comprises Fe and unavoidable impurities. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a steel material used for steel structures such as buildings and bridges which are heated to a high temperature for several hours due to fire or the like, and can withstand use at a high temperature of 650 to 700 ° C. The present invention relates to a steel material and a manufacturing method thereof.

[0002]

2. Description of the Related Art Structural steels show a decrease in strength with an increase in temperature, and a remarkable decrease in strength at 500 ° C. or higher. Therefore, in the past, steel materials have been cooled to 350
It has been proposed to apply a fireproof coating so that the temperature does not exceed ℃, and to improve the high temperature strength of the steel material itself.

For example, in Patent Documents 1 and 2, etc., Mo, V, Nb, Ti, etc. are added, and 600 ° C. or 65
Room temperature strength 400-4 with improved yield strength at 0 ° C
90 N / mm ² grade steel has been proposed.

[0004]

[Patent Document 1] Japanese Unexamined Patent Publication No. 2-170943

[0005]

[Patent Document 2] Japanese Unexamined Patent Publication No. 2-163341

[0006]

However, these steel materials mainly guarantee the safety at 600 ° C. (fire resistance: yield strength at 600 ° C. that is 2/3 or more of the normal temperature standard yield strength). Use at higher temperatures is not considered. For example, the yield strength at 700 ° C. is only about 1/3 of the normal temperature standard yield strength.

If a large amount of alloying element is added to secure high temperature strength, the room temperature strength becomes too high and SN
It exceeds the JIS standard strength of the material, and it is out of the JIS standard. Further, there is a problem that if the alloying is further increased, weldability and toughness are deteriorated.

The present invention has been made in view of the above points, and an object thereof is SN4 defined in JIS.
00 or SN490 standard strength, 65
0 ° C YS / normal temperature YS ≧ 0.5, 700 ° C YS / normal temperature YS
It is an object of the present invention to provide a steel having a low production cost that secures a high temperature strength that satisfies the relationship of ≧ 0.4 and that has excellent weldability (Y crack stop temperature of 0 ° C. or less), and a manufacturing method thereof.

[0009]

[Means for Solving the Problems] The present inventors have made detailed investigations on the composition of components that affect the high temperature strength of steel. As a result, they have found that high temperature strength can be significantly improved by precipitating fine composite carbides of Mo and Nb during high temperature fire resistance. Furthermore, the Mn content is 0.01 to 0.5.
It has been found that by making the content as low as 10%, the high temperature strength at 700 ° C. is improved and excellent weldability is obtained without impairing the low yield ratio.

That is, as a concrete guide, the present invention increases (Mo + Nb) which contributes to both room temperature strength and high temperature strength and reduces the amount of Mn which contributes only to room temperature strength.
+ Nb) / Mn ratio was made high and high temperature strength / normal temperature strength ratio was made high, and the means shown below is used.

The refractory steel material for construction according to the present invention has a mass% of
C: 0.01 to 0.13%, Si: 0.01 to 0.5
%, Mn: 0.01 to 0.5%, Mo: 0.3 to 1.3
%, Nb: 0.02 to 0.1%, sol. Al: 0.0
It is characterized by containing 03 to 0.05% and N: 0.01% or less, and the balance being Fe and inevitable impurities.

Further, the contents of Mo, Nb and Mn are
It is preferable to satisfy (Mo + Nb) / Mn ≧ 1 in mass%.

Further, as a steel component, in mass%, V:
0.01-0.10%, Ti: 0.005-0.10
%, Cr: 0.03 to 0.5%, Cu: 0.03 to 0.
5%, Ni: 0.03-0.5%, Ca: 0.0005
~ 0.005%, Mg: 0.0005 to 0.005%,
REM: It is preferable to further contain one or more selected from the group consisting of 0.0005 to 0.02%.

Further, it is preferable that the hardness when heated and held in the temperature range of 650 ° C. to 700 ° C. for 10 minutes to 30 minutes and then cooled to room temperature is Vickers hardness Hv10 which is 10 or more higher than that before heating.

Further, Nb-- which precipitates when heated and held in the temperature range of 650 ° C. to 700 ° C. for 10 minutes to 30 minutes
It is preferable that the amount of precipitation of Mo-based carbide is 70 ppm or more in terms of the carbon equivalent value of carbide defined by the following formula (1).

Δ [CasNbC] + Δ [CasMoC] + Δ [CasTiC] + Δ [CasVC] (1) where Δ [CasNbC] = 12/93 × {(N after high temperature holding)
b precipitation amount)-(Nb precipitation amount before holding at high temperature)} [CasMoC] = 12/96 x {(M after holding at high temperature)
o Precipitation amount)-(Mo precipitation amount before high temperature retention)} [CasTiC] = 12/48 x {(T after high temperature retention)
i precipitation amount)-(Ti precipitation amount before high temperature holding)} [CasVC] = 12/51 x {(V precipitation amount after high temperature holding)-(V precipitation amount before high temperature holding)} However, no Ti addition In the case of, Δ [CasTiC] = 0, V
In the case of no addition, Δ [CasVC] = 0.

In the method for manufacturing a refractory steel material for construction according to the present invention, after heating the steel having the above composition to 1000 ° C. or higher, hot rolling is performed so that the rolling end temperature is in the range of 800 ° C. to 1000 ° C. Characterize.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the component composition and manufacturing conditions in the present invention will be described in detail. In the following description, all units indicated by "%" are% by mass.

(Component composition) (1) C: 0.01 to 0.13% C improves the high temperature yield strength by precipitating fine composite carbide with Nb and the like at room temperature strength and 600 ° C. or higher. , 0.01% or more is added. On the other hand, if added in excess of 0.13%, the ductility and weldability as structural steel deteriorate. Therefore, the C content is set to the range of 0.01 to 0.13%.

(2) Si: 0.01 to 0.5% Si contributes to deoxidation and solid solution strengthening, so 0.01
% Or more. On the other hand, if added in excess of 0.5%, the ductility and toughness deteriorate and the room temperature strength becomes excessive. Therefore, the Si content is set to the range of 0.01 to 0.5%.

(3) Mn: 0.01 to 0.5% Mn is an important element in the present invention. High temperature strength /
In order to increase the room temperature strength ratio, the amount of Mn contributing only to room temperature strength is reduced. Mn is SN40 specified by JIS
0 or 0.01% or more in order to secure the room temperature strength as the SN490 material. On the other hand, if added in excess of 0.5%, the room temperature strength increases and the high temperature strength / room temperature strength ratio decreases, and the room temperature strength of the SN490 material may exceed the standard. In addition, the weldability also deteriorates. Therefore, the Mn content is set to the range of 0.01 to 0.5%.

(4) Mo: 0.3 to 1.3% Mo contributes to improvement of hardenability and precipitation strengthening, and improves room temperature strength. Further, 0.3% or more is added in order to form a Nb-Mo-based carbide described later by composite addition with Nb and improve high temperature strength. On the other hand, if added over 1.3%, the room temperature strength becomes too high and exceeds the standard of SN490 material specified by JIS, and the weldability and toughness deteriorate. Therefore, the Mo content is 0.3 to 1.3%
The range is.

(5) Nb: 0.02 to 0.1% Nb must be added in an amount of 0.02% or more in order to form Nb-Mo type carbides by composite addition with Mo to improve high temperature strength. is there. In order to stably secure high temperature strength, it is more preferable to add 0.04% or more. On the other hand, if added in excess of 0.1%, the weldability and toughness deteriorate. Therefore, the Nb content is set to the range of 0.02 to 0.1%.

(6) (Mo + Nb) / Mn ≧ 1 In order to increase the high temperature strength / normal temperature strength ratio, it is preferable to reduce the amount of Mn contributing only to the normal temperature strength so that (Mo + Nb) / Mn is 1 or more, It is more preferable to set it to 1.5 or more. However, the element symbol represents the content (mass%) of each element in the steel material. If this value is less than 1, the target YS ratio (650 ° C YS / normal temperature YS ≧ 0.5, 700 ° C
YS / normal temperature YS ≧ 0.4) cannot be obtained, or the normal temperature strength becomes high and exceeds the standard strength of SN490 material, and J
There is a risk of deviating from the IS standard.

(7) P, S: 0.03% or less P and S are unavoidable impurities and deteriorate the ductility, workability and weldability, so their contents are 0.03% respectively.
Below. The lower limit is preferably reduced within a range satisfying the production cost of structural steel, but is not particularly limited.

(8) Sol. Al: 0.003 to 0.0
Since 5% Al is deoxidized, sol. Al precipitates as AlN in the steel and is effective in refining the crystal grains, so 0.00
Add 3% or more. On the other hand, if added in excess of 0.05%, the amount of inclusions increases and the ductility decreases. Therefore, sol. The content of Al is set to the range of 0.003 to 0.05%.

(9) N: 0.01% or less N precipitates as AlN and makes the crystal grains finer, but N.
If added in excess of 01%, the toughness of the weld zone will decrease. Therefore, the N content is 0.01% or less, preferably 0.006.
% Or less.

The above is the basic component composition of the present invention. If the basic component is within the above composition range, the desired performance can be sufficiently obtained, but in order to further improve the characteristics, V, T
1 of i, Cr, Cu, Ni, Ca, Mg, REM
It is possible to add one species or two or more species.

(10) V: 0.01 to 0.10% V contributes to precipitation strengthening and increases room temperature strength and high temperature strength, so 0.01% or more is added. Especially, Mo, T
By the combined addition of i and Nb, Nb-Mo-V based composite carbide or Nb-Mo-Ti-V based composite carbide is finely precipitated, and a remarkable effect is obtained. On the other hand, if added in excess of 0.10%, it hardens and the weldability deteriorates. Therefore,
When V is added, its content is 0.01 to 0.10%
The range is.

(11) Ti: 0.005 to 0.10% Ti contributes to precipitation strengthening and increases room temperature strength and high temperature strength, so 0.005% or more is added. In particular, Mo,
By the combined addition with Nb and V, Nb-Mo-Ti based composite carbide or Nb-Mo-Ti-V based composite carbide is finely precipitated, and a remarkable effect is obtained. On the other hand, if added in excess of 0.10%, it hardens and the weldability deteriorates. Therefore, when Ti is added, its content is 0.005 to
The range is 0.10%.

(12) Cr: 0.03 to 0.5% Since Cr contributes to solid solution strengthening and increases room temperature strength and high temperature strength, 0.03% or more is added. Especially, Mo, T
By the combined addition of i and Nb, the composite carbide is finely precipitated and a remarkable effect is obtained. On the other hand, if added in excess of 0.5%, it hardens and the weldability deteriorates. Therefore, Cr
When added, the content is in the range of 0.03 to 0.5%.

(13) Cu: 0.03 to 0.5% Cu contributes to solid solution strengthening and raises room temperature strength, so 0.03% or more is added. On the other hand, if added in excess of 0.5%, it hardens and causes steel plate surface flaws. Therefore, Cu
When added, the content is in the range of 0.03 to 0.5%.

(14) Ni: 0.03 to 0.5% Ni is 0.03% in order to improve low temperature toughness and strength.
The above is added. On the other hand, if added in excess of 0.5%, it hardens and raises the production cost. Therefore, when Ni is added, its content is in the range of 0.03 to 0.5%.

(15) Ca, Mg, REM Ca, Mg, REM elements improve the toughness by controlling the morphology of inclusions and fixing impurity elements such as S. When adding, the content is Ca: 0.0005 to 0.005
%, Mg: 0.0005 to 0.005%, REM: 0.
The range is 0005 to 0.02%.

(16) Precipitates during high temperature refractory When the steel of the present invention is heated to a high temperature of 600 to 700 ° C., fine Nb-Mo type carbides are precipitated and exhibit high high temperature strength.
A large amount of these precipitates are deposited during high temperature fire resistance, resulting in a high high temperature strength / normal temperature strength ratio. Where N
When Ti is added to the b-Mo-based carbide, Nb-Mo-
Ti-based carbide, Nb-Mo-V-based carbide when V is added, and Nb-Mo-Ti-V-based carbide when Ti and V are added.

(I) Vickers hardness Hv10 The object of the present invention is 650 ° C. YS / normal temperature YS ≧ 0.5,
In order to satisfy 700 ° C. YS / normal temperature YS ≧ 0.4,
It is necessary to precipitate a certain amount or more of Nb-Mo-based carbide during high temperature heating.

For this purpose, the hardness when heated to 650 ° C. to 700 ° C. for 10 to 30 minutes and then cooled to room temperature has a Vickers hardness Hv10 of 10 or more higher than that before heating. If the difference in Hv10 is less than 10, the amount of Nb-Mo-based carbides that precipitate during high temperature heating may be insufficient, and the above properties may not be obtained. here,
With Vickers hardness Hv10, the load condition of the indenter is 10k
Hardness index when measured as g. The difference in hardness is the difference in the value of room temperature hardness at the position of 1/4 t in the plate thickness direction before and after heating the same steel plate.

(Ii) Δ [CasNbC] + Δ [CasM
oC] Δ [CasNbC] + Δ [CasMoC] + Δ [Cas
TiC] + Δ [CasVC] It is desirable that the Nb-Mo-based carbide precipitated during high temperature heating has the following composition and precipitation amount.

When heated and held in the temperature range of 650 ° C. to 700 ° C. for 10 minutes to 30 minutes, the newly deposited precipitate is a (Nb-Mo) C composite carbide, and the amount of precipitation is as follows (1). 'Carbide carbon equivalent value represented by the formula, 7
It is preferably 0 ppm or more. Mo is usually Mo ₂
Although it precipitates as C, from the observation by the transmission electron microscope and the analysis result of the extraction depth, in the steel of the present invention, (Nb-Mo) C
It was found that this composite carbide contributes to the improvement of high temperature strength. The amount of precipitation is 70p in terms of carbon equivalent value of carbide
If it is less than pm, the desired high temperature strength may not be obtained. Note that the upper limit of the carbon equivalent value of the carbide is 300 ppm from the viewpoint of not deteriorating the weldability and toughness. Δ [CasNbC] + Δ [CasMoC] ... (1) ′.

When Ti or V is added, (N
b-Mo-Ti) C, (Nb-Mo-V) C or (N
A b-Mo-Ti-V) C composite carbide is formed, and the high temperature strength is further improved. In this case, the amount of precipitation is preferably 70 ppm or more in terms of the carbon equivalent value of carbide represented by the following formula (1). Δ [CasNbC] + Δ [CasMoC] + Δ [CasTiC] + Δ [CasVC] ... (1).

However, when Ti is not added, Δ [CasT
iC] = 0, when V is not added, Δ [CasVC] = 0
And

Here, the above Δ [CasNbC], Δ [C
asMoC], Δ [CasTiC], Δ [CasVC]
Are respectively calculated as follows. Δ [CasNbC] = 12/93 × {(N after holding at high temperature
b precipitation amount)-(Nb precipitation amount before holding at high temperature)} [CasMoC] = 12/96 x {(M after holding at high temperature)
o Precipitation amount)-(Mo precipitation amount before high temperature retention)} [CasTiC] = 12/48 x {(T after high temperature retention)
i precipitation amount)-(Ti precipitation amount before high temperature holding)} Δ [CasVC] = 12/51 × {(V precipitation amount after high temperature holding)-(V precipitation amount before high temperature holding)} where Δ [CasNbC ], Δ [CasMoC], Δ
[CasTiC] and Δ [CasVC] are Nb carbide, Mo carbide, Ti carbide, and
The amount of carbon consumed when V carbide newly deposits in the structure is shown. The amount of each metal element deposited is determined by ICP emission spectrometry of the residue extracted from the steel by 10% acetylacetone-methanol electrolytic extraction.

(Manufacturing method) (17) Slab heating temperature: 1000 ° C. or higher The slab heating temperature is such that Ti, Nb, and V are solid-dissolved.
In order to obtain the effect of improving the high temperature strength by the combined addition of Mo and Nb, in order to satisfy the standard strength of the SN490 material specified in JIS, the temperature is 1000 ° C or higher.

(18) Rolling end temperature: 800 to 1000
℃ Rolling end temperature is less than 800 ℃, high temperature strength decreases,
If the temperature exceeds 1000 ° C, the crystal grains become coarse, the hardenability is improved, and the room temperature strength becomes too high. Therefore, in order to satisfy the standard strength of SN490 material specified in JIS, the temperature range of 800 to 1000 ° C is required. And

[0045]

EXAMPLES Steel sheets were produced under various production conditions using the test steels A to X. Table 1 shows the chemical components of the test steels A to X used. Steels A to N and X are invention steels having a composition within the scope of the present invention, and steels OW are comparative steels having a composition outside the scope of the present invention. However, steel T is a missing number.

Further, Table 2 shows, as manufacturing conditions, the steel type of the sample steel, the plate thickness (mm) of the steel plate, the invention manufacturing process, the manufacturing process, the heating temperature during rolling (° C), and the rolling end temperature (° C).
And cooling conditions are shown. The indication of the invention manufacturing process is indicated by ◯ when the method according to claim 6 is followed, and is indicated by x otherwise.

The steel sheet thus obtained was subjected to a room temperature tensile test and a high temperature tensile test, respectively. Yield strength YS (N / mm ² ) and tensile strength TS (N /
mm ² ) and the yield ratio YR (%) were obtained, and the yield strength YS (N / mm ² ) at the test temperatures of 600 ° C., 650 ° C. and 700 ° C. was obtained as the high temperature tensile properties. Further, the ratio of the high temperature YS and the normal temperature YS at each test temperature (high temperature YS / normal temperature YS) was determined as the YS ratio (%). The results are also shown in Table 2. The room temperature tensile test was carried out according to JIS Z 2241, and the high temperature tensile test was carried out according to JIS G 0567.

Here, the room temperature strength is JIS G 3136.
, YS: 235-355N / m
m ² (215 to 335 N for a steel plate with a thickness of 50 mm
/ Mm ² ), TS: 400 to 510 N / mm ² that satisfies SN400 material, YS: 325 to 445 N / m
m ² (295 to 415 N for a steel plate with a thickness of 50 mm
/ Mm ² ), TS: 490 to 610 N / mm ² satisfying the requirements for SN490 material, and those not satisfying the specified strength range were outside the scope of the present invention.

The high temperature strength is 60 for SN400 material.
^{0 ℃ YS ≧ 157N / mm 2} (143N / mm 2 for steel sheet having a thickness of 50 mm) (room temperature YS 2/3 standard lower limit SN400) in, YS ≧ 138N / mm ² at 650 ° C.
(126 N / mm ² for a steel plate with a plate thickness of 50 mm),
YS ≧ 118N / mm ² at 700 ° C. (for the steel sheet having a thickness of 50mm 108N / mm ²⁾ (SN400 cold Y
The standard value is 1/2 of the S standard lower limit, and for SN490 material, YS ≧ 217 N / mm ² (plate thickness 50 m at 600 ° C.
197 N / mm ² ) for steel sheet of m (2/3 of lower limit of room temperature YS standard of SN490), YS ≧ 190 at 650 ° C.
N / mm ² (173 N / for steel plates with a plate thickness of 50 mm
mm ² ), YS ≧ 163 N / mm ² at 700 ° C. (plate thickness 50
mm steel plate: 148 N / mm ² ) (SN490
The lower limit of the room temperature YS standard of 1) was used as a reference value, and those which did not meet this standard were outside the scope of the present invention.

For the steel sheets of Comparative Examples 1 to 3 whose invention manufacturing process is out of the scope of the present invention, the standard value was set as the SN490 material.

Further, the weldability and toughness were evaluated. A Y crack test was conducted to evaluate the weldability, and a Charpy absorbed energy at 0 ° C. was measured to evaluate the toughness. These results are also shown in Table 2. here,
Weldability is out of the scope of the present invention when the crack prevention preheating temperature (Y crack stop temperature) of the Y crack test specified by JIS exceeds 0 ° C, and the toughness is Charpy absorbed energy vE0.
≧ 100 J was set as the standard value, and those which did not satisfy this were regarded as outside the scope of the present invention.

With respect to the steel sheets of Examples 1, 5, 8, 9 and Comparative Example 3, the hardness before and after heating at 700 ° C. was evaluated and the morphology of the precipitate was analyzed. As an evaluation of hardness,
The test piece before heating to 700 ° C and the heating to 700 ° C,
A Vickers hardness with a load of 10 kg was measured for each test piece after heating and holding for about 30 minutes and then cooling to room temperature, and a Vickers hardness difference before and after heating (hardness after heating-hardness before heating) was determined. It was

The morphological analysis of the precipitate is 700
The Nb, Mo, Ti, and V precipitation amount (extracted metal amount) of the test piece before and after heating at ℃ were measured, and Δ [Ca
sNbC], Δ [CasMoC], Δ [CasTi
C] and Δ [CasVC] were calculated. From this result, the carbon equivalent carbon value of the precipitate was obtained. The amount of each metal element deposited was determined by extracting the residue from the steel by 10% acetylacetone-methanol electroextraction and using the extraction residue as the amount of extracted metal by ICP emission spectrometry. The results are shown in Table 3.

As shown in Table 2, the steel sheets of Examples 1 to 19 produced using the steels A to N and X of the present invention according to the present invention have room temperature strength of 600 ° C. which satisfies the SN490 standard defined by JIS. , YS at 650 ° C. and 700 ° C. all satisfied the standard values. Also, the YS ratio at 600 ° C. ≧ 6
1%, YS ratio at 650 ° C ≧ 55%, YS at 700 ° C
An excellent value of ratio ≧ 46% was obtained. Further, the Y crack preventing temperature was 0 ° C. or lower, and the Charpy absorbed energy at 0 ° C. was 100 J or more, which were excellent values.

On the other hand, the steel sheet of Comparative Example 1 in which the steel A of the present invention was used, but the slab heating temperature was less than 1000 ° C., which was outside the range of the present invention, was low, was SN490 material and had a room temperature strength of
It was lower than the S standard and the high temperature strength YS was also low. In addition, S
The N400 material satisfied the room temperature strength standard stipulated in JIS, and also satisfied the high temperature strength YS reference value.

Similarly, using the steel A of the present invention, the steel sheet of Comparative Example 2 in which the rolling end temperature was higher than 1000 ° C. was high,
The room temperature strength of the SN490 material exceeded the JIS standard.

Similarly, the steel A of the present invention was used, but the steel sheet of Comparative Example 3 in which the rolling end temperature was less than 800 ° C., which was outside the range of the present invention, was low, and the high temperature strength YS was low as SN490 material.

The steel sheets of Comparative Examples 4 to 7 in which the Mn content was higher than 0.5%, the Nb was not added, and the (Mo + Nb) / Mn was less than 1 were used for the steel sheets of Comparative Examples 4 to 7 under any conditions.
As the 0 material, the high temperature strength was low, and the Y crack preventing temperature was as high as 25 ° C.

When the amount of Mn is more than 0.5% and high, (Mo +
The steel sheets of Comparative Examples 8 to 10 using P steel, Q steel, and R steel with Nb) / Mn less than 1 have room temperature strengths higher than the SN490 standard specified by JIS, and the Y crack prevention temperature is also high. It was

The Mo content is as low as less than 0.3%, and (Mo + N
The steel sheet of Comparative Example 11 using S steel having b) / Mn of less than 1 satisfies both room temperature strength of SN400 and 490 specified by JIS, but high temperature strength of SN.
It was low even when viewed as 400 materials.

The steel sheet of Comparative Example 12 using U steel having a low Nb content of less than 0.02% had the normal temperature strength of SN400 material even though the manufacturing process of SN490 material was used. Further, the high temperature strength was lower than the standard value of SN400 material.

The steel sheet of Comparative Example 13 using V steel having a high Nb content of more than 0.1% had a room temperature strength YS exceeding JIS standard and a high temperature strength YS ratio as SN490 material.
Further, the Y crack preventing temperature was as high as 50 ° C., and the toughness was further deteriorated.

The steel sheet of Comparative Example 14 using W steel having a high C content exceeding 0.13% had a low high temperature strength YS ratio and a high Y crack prevention temperature of 50 ° C. as SN490 material.

Further, as shown in Table 3, the steel sheets of Examples 1, 5, 8 and 9 produced using the steels A, D and E of the present invention under the production conditions within the scope of the present invention were 700 The hardness after heating and holding at 0 ° C. was Vickers hardness Hv10, which was 10 or more higher than that before heating. Moreover, the amount of precipitation of the Nb-Mo-based composite carbide was 70 ppm or more in terms of the carbon equivalent value of the carbide. As a result, as shown in Table 2, the high temperature strength was excellent.

On the other hand, in the steel sheet of Comparative Example 3 in which the steel A of the present invention was used but the rolling end temperature was low, the hardness difference was as low as less than 10 in Vickers hardness Hv10 and the amount of precipitate was 70 ppm.
It was less than less. As a result, the high temperature strength was poor as shown in Table 2.

As described above, the steel sheet having the composition within the scope of the present invention and manufactured according to the present invention is excellent in high temperature strength.

[0067]

[Table 1]

[0068]

[Table 2-1]

[0069]

[Table 2-2]

[Table 3]

[0070]

As described above in detail, according to the present invention, J
Satisfies the standard strength of SN400 or SN490 specified by IS, and further 650 ° C YS / room temperature YS ≧ 0.5,
To provide a steel with a low production cost that secures high-temperature strength that satisfies the relationship of 700 ° C YS / normal temperature YS ≧ 0.4 and that has excellent weldability (Y crack stop temperature 0 ° C or less), and a manufacturing method thereof. And is extremely useful industrially.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiro Nakamichi             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Takashi Abe             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Kazuhide Takahashi             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Kaoru Sato             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Saburo Tani             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Masatoshi Toyonaga             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4K032 AA01 AA04 AA05 AA08 AA11                       AA14 AA16 AA19 AA20 AA21                       AA22 AA23 AA31 AA35 AA36                       AA40 CA02 CA03 CC03 CC04

Claims (6)

[Claims] 1. C: 0.01 to 0.13% by mass%,
Si: 0.01 to 0.5%, Mn: 0.01 to 0.5
%, Mo: 0.3 to 1.3%, Nb: 0.02 to 0.1
%, Sol. Al: 0.003-0.05%, N: 0.
A refractory steel material for construction which is excellent in high-temperature fire resistance characteristics and weldability, and is characterized by containing 0.1% or less, and the balance being Fe and inevitable impurities. 2. The refractory steel material for construction according to claim 1, wherein the contents of Mo, Nb and Mn satisfy (Mo + Nb) / Mn ≧ 1 in mass%. 3. As a steel component, in mass%, V: 0.01
~ 0.10%, Ti: 0.005 to 0.10%, Cr:
0.03-0.5%, Cu: 0.03-0.5%, N
i: 0.03-0.5%, Ca: 0.0005-0.0
05%, Mg: 0.0005 to 0.005%, REM:
1 selected from the group consisting of 0.0005 to 0.02%
The fire-resistant steel material for construction according to any one of claims 1 and 2, further containing one or more kinds. 4. The temperature range from 650 ° C. to 700 ° C. is 10
After heating and holding for 30 minutes to 30 minutes, the hardness when cooled to room temperature is Vickers hardness Hv10, which is 10% higher than that before heating.
The fire resistant steel material for construction according to any one of claims 1 to 3, which is higher than the above. 5. A temperature range from 650 ° C. to 700 ° C. of 10
5. The precipitation amount of Nb-Mo-based carbide that precipitates when heated for 30 minutes to 30 minutes is 70 ppm or more in terms of the carbon equivalent value of the carbide defined by the following formula (1). The fireproof steel material for construction according to any one of 1. Δ [CasNbC] + Δ [CasMoC] + Δ [CasTiC] + Δ [CasVC] (1) where Δ [CasNbC] = 12/93 × {(N after high temperature holding)
b precipitation amount)-(Nb precipitation amount before holding at high temperature)} [CasMoC] = 12/96 x {(M after holding at high temperature)
o Precipitation amount)-(Mo precipitation amount before high temperature retention)} [CasTiC] = 12/48 x {(T after high temperature retention)
i precipitation amount)-(Ti precipitation amount before high temperature holding)} [CasVC] = 12/51 x {(V precipitation amount after high temperature holding)-(V precipitation amount before high temperature holding)} However, no Ti addition In the case of, Δ [CasTiC] = 0, and in the case of no V addition, Δ [CasVC] = 0 6. A hot rolling process in which the steel having the composition according to any one of claims 1 to 3 is heated to 1000 ° C. or higher, and then the rolling end temperature is set in the range of 800 ° C. to 1000 ° C. A method for producing a 490 N / mm ² class refractory steel material for construction, which is excellent in high temperature fire resistance characteristics and weldability.