JP3232118B2 - Hot-rolled steel strip for construction with excellent fire resistance and toughness and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel strip for buildings (including steel sheets; the same applies hereinafter) having excellent fire resistance and toughness suitable for applications such as construction, civil engineering and marine structures, and the production thereof. It is about the method.

[0002]

2. Description of the Related Art Rolled steel sheets for general structures (JIS G 3101) and rolled steel sheets for welded structures (JIS G 31
06), weather-resistant hot-rolled steel sheets for welded structures (JIS G 3114) and highly weather-resistant rolled steel sheets (JIS G3 125) are widely used. In buildings, fire resistance is particularly important,
Various measures have been taken from large buildings to general residential buildings.

[0003] Conventionally, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-47451, fire prevention measures are often taken with a fireproof coating. After that, the fire-resistant design was reviewed, and a new fire-resistant design law for buildings was enacted in 1987.
(50 ℃), the high temperature strength of the steel sheet and the load actually applied to the building will allow the ability of the fireproof coating to be determined. It is now possible to use steel sheets in the field. As such a steel sheet, for example, Japanese Patent Application Laid-Open No. 2-77523 proposes a steel sheet.

[0004] However, lightweight steel frames and U
In many cases, the hot-rolled steel strip is used as the material for the character-shaped columns, etc. As such a hot-rolled steel sheet, particularly, the C content level is 0.02wt.
% Or more and to which Nb is added is disclosed in JP-A-2-2824.
No. 19 has been proposed. However, it was difficult to say that the steel sheet had sufficient material, especially toughness.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned problems and to improve the Charpy characteristics and high-temperature strength over conventional low Nb-containing steel without deteriorating workability and weldability. Hot rolled steel strip for construction, together with its advantageous manufacturing method.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted numerous experiments and studies in order to achieve the above object.
It has been found that Charpy properties and high-temperature strength can be improved without deteriorating workability and weldability by adding a larger amount of Nb together with Mo than the above-mentioned conventional refractory steel sheet in combination with Mo. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. C: 0.002 wt% to 0.15 wt%, Si ≦ 2.0 wt%, Mn: 0.05 wt% to 1.5 wt%, P ≦ 0.03 wt%, S ≦ 0.01 wt%, Al: 0.01 wt% to 0.1 wt%, N ≦ 0.01% by weight, Nb: more than 0.04% by weight to 0.2% by weight, Mo: 0.1% by weight to 1.5% by weight, with the balance being Fe and inevitable impurities.
And the Charpy absorbed energy vEo at 0 ° C is 18.4 kgf
-Hot-rolled steel strip for buildings with excellent fire resistance and toughness of at least m .

[0008] 2. In (1) above, the heat for construction is excellent in fire resistance and toughness which further comprises one or two selected from Cu: 0.5 wt% to 2.0 wt% and Ni: 0.15 wt% to 1.5 wt%. Rolled steel strip.

3. The hot-rolled steel strip for building having excellent fire resistance and toughness in which the composition further contains Ti: 0.001 wt% to less than 0.02 wt% in 1 or 2 above.

[0010] 4. In the above 1, 2 or 3, Ca: 0.0005 wt% to 0.01 wt%, Rem: 0.001 wt% to 0.02
A hot-rolled steel strip for construction that has excellent fire resistance and toughness and has a composition containing one or two selected from wt%.

[0011] 5. C: 0.002 wt% to 0.15 wt%, Si ≦ 2.0 wt%, Mn: 0.05 wt% to 1.5 wt%, P ≦ 0.03 wt%, S ≦ 0.01 wt%, Al: 0.01 wt% to 0.1 wt%, N ≦ A steel slab having a composition containing 0.01 wt%, Nb: more than 0.04 wt% to 0.2 wt%, and Mo: 0.1 wt% to 1.5 wt% is directly heated at a high temperature or heated to 1000 to 1250 ° C, and then heated to 820 to 900 ° C. After completion of hot rolling at ℃, cooling rate: cooling at 15 ℃ / s or more, then
Charpy at 0 ° C by winding below 680 ° C
A hot-rolled steel strip with an absorbed energy vEo of 18.4 kgf
A method for producing a hot-rolled steel strip for building having excellent fire resistance and toughness.

Hereinafter, the present invention will be described specifically. First,
The experimental results on which the present invention is based will be described. C: 0.
05 wt%, Si: 0.01 wt%, Mn: 0.10 wt%, P: 0.007 wt
%, S: 0.003 wt%, Al: 0.040 wt%, N: 0.003 wt%
And Mo: based on 0.5 wt%, and Nb in an amount of 0.01 to 0.
Steel slabs containing variously varied contents in the range of 23 wt% were used.
℃, 50 ° C / s cooling rate after hot rolling until winding, winding temperature 600
A hot-rolled steel strip having a thickness of 4.50 mm was manufactured by performing hot rolling at a temperature of ° C.

FIG. 1 shows the results of investigation on the tensile properties and toughness of the obtained hot-rolled steel strip at room temperature and 600 ° C. in relation to the Nb content. The tensile test at room temperature was performed using a JIS No. 5 test piece in accordance with JIS Z 2241. The tensile test at 600 ° C. was performed according to JIS G 0567 after raising the temperature at 10 ° C./s and maintaining the temperature at 600 ° C. for 15 minutes. The toughness of these steel sheets was measured in accordance with JIS Z 2242 using a JIS Z 2202 Charpy V notch test piece.

As is clear from FIG. 1, the Nb content is 0.04
Exceeding wt%, the 0.2% proof stress at 600 ° C (YS _0.2 ) and the Charpy absorbed energy at 0 ° C ( _V E ₀ ) significantly increased.

[0015]

Next, the reason why the chemical composition of the present invention is limited to the above range will be described. C: 0.002 wt% or more, 0.15 wt% or less C is added in order to secure a desired strength at normal temperature and high temperature. However, if the added amount is less than 0.002 wt%, the effect is poor, and on the other hand, exceeds 0.15 wt%. Therefore, the content of C was set to 0.002 to 0.15 wt% because the weldability and toughness deteriorated remarkably.

Si: 2.0 wt% or less Si is an effective element as a deoxidizing agent and a solid solution strengthening element, but generates a scale pattern on the steel sheet surface during hot rolling. Therefore, considering these effects, its content is 2.0
wt% or less (preferably 0.001 wt% or more).

Mn: 0.05 wt% or more and 1.5 wt% or less Mn is an element that not only effectively contributes to solid solution strengthening but also is useful for preventing cracking during hot rolling by S. At least 0.05 wt% However, if the content exceeds 1.5 wt%, the toughness and weldability deteriorate significantly. Therefore, the content of Mn is set to 0.05 wt% or more and 1.5 wt% or less.

P: not more than 0.03 wt% P is extremely effective as a solid solution strengthening element, but a large amount of P deteriorates toughness, so that P is contained in an amount of not more than 0.03 wt% (preferably not less than 0.001 wt%). It was taken.

S: 0.01 wt% or less S not only causes cracking during hot rolling, but also deteriorates workability. Therefore, it is preferable to reduce S as much as possible. However, S is acceptable in a range of 0.01 wt% or less. .

Al: 0.01 wt% or more, 0.1 wt% or more Al needs to be added at least 0.01 wt% to clean steel. However, addition exceeding 0.1 wt% is not preferable because it causes surface defects due to alumina clusters. Therefore, Al is 0.01 wt% or more, 0.1 wt%
The content was set in the following range.

N: 0.01 wt% or less If N is contained in a large amount, the amount of Al for fixing it increases, and the ductility is deteriorated. Therefore, it is preferable to reduce N as much as possible. Acceptable in the range.

Nb: more than 0.04 wt%, not more than 0.2 wt% Nb is an element that is particularly important in the present invention. By the combination of the addition of an appropriate amount of Mo and the appropriate hot rolling conditions as described below, the structure is appropriately refined, the toughness is significantly improved, and the yield strength at high temperatures is significantly improved.
For this purpose, as shown in FIG. 1 above, it is necessary to add more than 0.04 wt%, but even if it is added in a large amount exceeding 0.2 wt%, the above-mentioned effect of improving toughness and high-temperature strength reaches saturation. Not only that, the yield ratio at room temperature exceeds 90%, so that even normal light working becomes difficult, the weldability is deteriorated, and the rolling load at the latter stage of rolling is significantly increased, resulting in a disadvantage in operation. Therefore, the content of Nb is more than 0.04 wt%, 0.2 wt%
It was as follows.

Mo: not less than 0.1 wt% and not more than 1.5 wt% Mo is formed by appropriately combining the above-described complex addition with Nb and appropriate hot rolling conditions to finely refine the structure, toughness and yield strength at high temperatures. Is significantly improved. For this purpose, at least 0.1wt% is required, but 1.5wt%
Even if a large amount is added beyond the above, not only the above-mentioned effect of improving toughness and high-temperature strength reaches saturation, but also the yield ratio at room temperature
If it exceeds 90 wt%, even normal light machining becomes difficult,
This results in significant deterioration of weldability. Therefore, the content of Mo is 0.1
wt% and 1.5 wt% or less.

Although the basic components have been described above, in the present invention, one or two selected from Cu and Ni can be further added as a high-temperature strength improving component. Cu: 0.5 wt% or more, 2.0 wt% or less, Ni: 0.15 wt% or more,
1.5 wt% or less Both Cu and Ni effectively contribute to the improvement of high-temperature strength. However, if the content is less than the lower limit, the effect of addition is poor, while if the content exceeds the upper limit, adverse effect on the surface quality of the steel sheet. Is increased, so that it is contained in the above-mentioned range in either case of single addition or composite addition. Note that Cu also contributes to improvement of corrosion resistance in the above range.

Further, in the present invention, Ti can be appropriately added as a component for improving toughness and high-temperature strength. Ti: 0.001 wt% or more, less than 0.02 wt% Ti, like Nb, effectively contributes to the improvement of toughness and high-temperature strength, but if it is less than 0.001 wt%, the effect of its addition is poor, while 0.02 wt% or more. In this case, material anisotropy due to unrecrystallized austenite zone rolling in the latter stage of hot rolling is likely to occur, so the content is set in the range of 0.001 wt% or more and less than 0.02 wt%.

Further, in the present invention, Ca or Rem can be appropriately added as a component for improving workability and toughness. Ca: 0.0005 wt% or more, 0.01 wt% or less, Rem: 0.001 wt%
As described above, 0.02 wt% or less Both Ca and Rem control the morphology of MnS and improve the workability and toughness. However, large amounts of these themselves become large inclusions and deteriorate ductility. Therefore, in either case of the single addition or the composite addition, a range where the above-mentioned fear does not occur, that is, Ca is 0.0005 wt% or more,
Within 1.5 wt% or less, and 0.001 wt% for Rem
As described above, the content is set to 0.02 wt% or less.

Next, the reasons for limiting the hot rolling conditions of the steel of the present invention will be described. Hot rolling is performed immediately after continuous casting of the slab (so-called CC-DR) or 1000 to 1250 ° C.
Perform after heating. When performing CC-DR, heat retention or slight heating of the end may be performed.
When heating, if the heating temperature exceeds 1250 ℃,
Austenite coarsens, the grain structure of the finally obtained structure becomes insufficient, and not only the desired toughness and high-temperature strength are not obtained, but also particularly Cu scabs, while if less than 1000 ° C, After the hot rolling, it is difficult to secure the target finish rolling temperature. Therefore, when heating, it is necessary to set the temperature to 1000 to 1250 ° C.

The hot rolling finishing temperature is 820 to 900 ° C. Because when hot rolling is over 900 ° C,
This is because grain refinement of the finally obtained structure is insufficient, and it is difficult to obtain desired toughness and high-temperature strength. On the other hand, if it is less than 820 ° C., ductility and toughness after hot rolling are remarkably deteriorated.
The finishing temperature is more preferably 870 ° C or lower.

After hot rolling, the cooling rate before winding is 15
C / s or more. This is because if the cooling rate is less than 15 ° C./s, the grain structure of the finally obtained structure will be insufficient, and not only the desired toughness and high-temperature strength will not be obtained, but also
In particular, in the case of Cu-added steel, ε-Cu precipitates during cooling and deteriorates ductility. It should be noted that, if the quenching is more than necessary, the final structure may be baked and the room temperature strength may become too high, which may cause deterioration in workability.

The winding temperature is 680 ° C. or less. This is because if the film is wound at a temperature exceeding 680 ° C., the grain structure of the finally obtained structure is insufficient, and the desired toughness and high-temperature strength cannot be obtained. Especially in the case of Cu-added steel,
After winding, ε-Cu precipitates and deteriorates ductility.
The temperature is preferably set to 50 ° C. or lower. However, unnecessarily low-temperature winding causes burning in the final structure, and not only deteriorates workability due to excessively high strength at room temperature, but also causes poor shape.

The hot rolled coil obtained as described above is
It may be used as it is as a coil or as a cutting plate,
Further, passing through a skin pass or a leveler is advantageous in adjusting the yield point strength at normal temperature. Further, secondary processing may be performed using the product as a material to obtain a product.

[0032]

EXAMPLES Steel having various component compositions shown in Tables 1 and 2 was used.
After the converter refining, the slab was formed by continuous casting, and then immediately or after heating, hot-rolled under the conditions shown in Tables 3, 4 and 5. The hot rolled material thus obtained was examined for tensile properties at room temperature and 600 ° C and toughness at 0 ° C. The obtained results are also shown in Tables 3, 4, and 5. In addition,
The tensile test at normal temperature and 600 ° C. and the toughness at 0 ° C. were conducted by the methods described above. However, 10 mm thick
In the toughness investigation for the following steel sheets, a test piece having a sub-size closest to the original thickness was used.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

As is clear from Tables 3, 4 and 5, the ratio of YS _0.2 at 600 ° C. to YS _0.2 at room temperature was 0.65 or more, and most of the hot-rolled steel strips obtained according to the present invention were 0.75 or more. It has excellent high-temperature strength as described above, high Charpy absorbed energy at 0 ° C., and excellent toughness.

Further, in FIG. 2, Charpy absorbed energy _V E ₀ at YS _0.2 and 0 ℃ in YS _0.2 and 600 ° C. at room temperature
The steel strips shown in Tables 3, 4 and 5 are compared with the steel sheet described in JP-A-2-282419. Each of the target materials has a plate thickness of 4.50 mm. As is apparent from the figure, the steel strip according to the present invention is much superior in high-temperature strength and 0 ° C. toughness as compared with the conventional steel sheet.

[0040]

Thus, according to the present invention, it is possible to obtain a hot-rolled steel sheet having excellent toughness as well as room-temperature strength and high-temperature strength, and is required to have toughness as well as fire resistance. It has a great effect when used for such purposes.

[Brief description of the drawings]

[1] 0.2% yield strength (YS _0.2) at room temperature tensile, tensile strength (TS), 0.2% proof stress at 600 ℃ (YS _0.2), and Charpy absorbed energy _(V E ₀₎ at 0 ℃ and Nb containing It is the graph which showed the relationship with quantity.

FIG. 2 shows the temperature of a steel strip according to the present invention and a conventional steel sheet at room temperature.
0.2% yield strength (YS _0.2) and 0.2% proof stress at 600 ℃ (YS _0.2) and Charpy absorbed energy at ₀ ℃ _(V E 0) and is a graph comparatively showing.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-34116 (JP, A) JP-A-3-64441 (JP, A) JP-A-2-282419 (JP, A) JP-A-2- 77523 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00 301 C21D 8/02 C21D 9/46 C22C 38/12

Claims (5)

(57) [Claims] 1. C: 0.002 wt% to 0.15 wt%, Si ≦ 2.0 wt%, Mn: 0.05 wt% to 1.5 wt%, P ≦ 0.03 wt%, S ≦ 0.01 wt%, Al: 0.01 wt% to 0.1 wt%, N ≦ 0.01 wt%, Nb: more than 0.04 wt% to 0.2 wt%, Mo: 0.1 wt% to 1.5 wt%, with the balance being Fe and unavoidable impurities.
And the Charpy absorbed energy vEo at 0 ° C is 18.4 kgf
-Hot-rolled steel strip for buildings with excellent fire resistance and toughness of at least m . 2. The fire resistance according to claim 1, further comprising a composition containing one or two selected from Cu: 0.5 wt% to 2.0 wt% and Ni: 0.15 wt% to 1.5 wt%. Hot rolled steel strip for construction with excellent toughness. 3. The hot-rolled steel strip for building according to claim 1 or 2, further comprising Ti: 0.001 wt% to less than 0.02 wt%, and having excellent fire resistance and toughness. 4. The method of claim 1, 2 or 3, further comprising: Ca: 0.0005% by weight to 0.01% by weight, Rem: 0.001% by weight to 0.02% by weight.
%. A hot-rolled steel strip for building which has excellent fire resistance and toughness, and has a composition containing one or two selected from the above. 5. C: 0.002 wt% to 0.15 wt%, Si ≦ 2.0 wt%, Mn: 0.05 wt% to 1.5 wt%, P ≦ 0.03 wt%, S ≦ 0.01 wt%, Al: 0.01 wt% to 0.1 wt% A steel slab having a composition containing wt%, N ≦ 0.01 wt%, Nb: more than 0.04 wt% to 0.2 wt%, and Mo: 0.1 wt% to 1.5 wt% is directly heated at a high temperature or heated to 1000 to 1250 ° C. Thereafter, after the hot rolling is completed at 820 to 900 ° C., the cooling rate is cooled at 15 ° C./s or more.
Charpy at 0 ° C by winding below 680 ° C
A hot-rolled steel strip with an absorbed energy vE o of 18.4 kgf
A method for producing a hot-rolled steel strip for building having excellent fire resistance and toughness.