JPH1096043A - Fire resistant steel for building structure excellent in galvanizing cracking resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase high temp. strength of a steel and to simplify and eliminate fireproofing coatings according to the Building Standards Act, by specifying its compsn., executing controlled cooling after hot rolling and precipitating an optimum amt. of VN into the structure. SOLUTION: The steel contains, by weight, 0.01 to 0.15%C, <=0.6% Si, 0.5 to 1.5% Mn <=0.030% P, <=0.030% S, 0.005 to 0.05$ Al, 0.2 to 0.7% Mo, 0.01 to0.15% V and 0.0050 to 0.0120% N, contg. one or >= two kinds among 0.001 to 0.15% Ti, 0.001 to 0.030% rare earth metals, 0.0005 to 0.0030% B, 0.0005 to 0.0030% Ca and 0.001 to 0.05% Zr and preferably contg. one or >= two kinds among 0.05 to 0.5% Cu, 0.05 to 0.5% Ni, 0.05 to 0.5% Cr and 0.005 to 0.3% Nb as well. This steel is subjected to hot rolling and is thereafter subjected to cooling in such a manner that the average cooling rate is regulated to <=αdefined by the formula I and the cooling stopping temp. is regulated to >=(Ar3-200 deg.C) based on Ar3 defined by the formula II.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory steel for a building structure which has sufficient strength in a fire even if the refractory coating is simplified or omitted, and more particularly to a refractory steel material for a building structure having galvanized crack resistance. It relates to the manufacturing method.

[0002]

2. Description of the Related Art Steel building structures include, for example, JI
Thick steel sheets, hot-rolled steel sheets, shaped steel or steel pipes manufactured by hot rolling in accordance with S G3136 rolled steel for building structures (SN standard) are used in large quantities as members. Generally, rolled H-section steel and steel pipe are used as hot-rolled members, but thick steel plates and hot-rolled steel plates are welded H-section steel, box columns, cold-formed columns, welded lightweight H-sections. It is used after being processed into a member such as steel.

In recent years, the Building Standards Law has been revised, and it has become possible to simplify or omit the refractory coating according to the strength of steel at high temperatures. For example, it is said that if a steel material has a high-temperature proof strength of 2/3 or more of the standard yield strength at room temperature at 600 ° C., the refractory coating is omitted and bare use becomes possible. In particular, by using a steel material with fire resistance, great effects such as elimination of the number of construction steps, reduction of construction costs, and expansion of the effective space are produced.

[0004] As a steel material having such fire resistance, for example, Japanese Patent Publication No. 8-32945 discloses that
0.2%, carbon equivalent (Ceq = C + Mn / 6 + Si / 24 + Ni /
40 + Cr / 5 + V / 14) of 0.35 to 0.50% has been proposed, which has excellent fire resistance. However, when the refractory coating is omitted, it is necessary to perform galvanizing on the steel material from the viewpoint of corrosion resistance. In the refractory steel materials already proposed, there is a problem that galvanizing cracks occur in the base metal or the weld heat-affected zone during hot-dip galvanizing, and there is a demand for refractory steels having excellent galvanizing crack resistance. Was.

[0005]

The present invention is based on JIS G3136
Not only satisfy the strength, toughness and weldability specified in, but also have excellent toughness and strain aging resistance of the welded heat-affected zone required for steel materials for building structures, as well as strength at 600 ° C and galvanizing crack resistance. An object of the present invention is to propose a refractory steel material for building structures having excellent heat resistance and a method for producing the same.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, especially the improvement of galvanizing resistance to fire-resistant steel. As a result, V and N were added in appropriate amounts and VN was reduced. By precipitating an appropriate amount, VN becomes a transformation nucleus of ferrite and pearlite, promoting the refinement of the structure, and further suppressing the formation of the pearlite band, whereby the pearlite (second phase) structure can be uniformly dispersed, and the zinc plating cracking It has been newly found that the remarkably improved properties and that the proper precipitation of VN is important to optimize the cooling rate and cooling stop temperature after hot rolling.

[0007] The present invention is based on the above findings, strength, toughness,
It was completed in consideration of weldability, toughness of the heat affected zone, and strain aging. That is, the present invention provides, in weight percent,
C: 0.01 to 0.15%, Si: 0.6% or less, Mn: 0.5 to 1.6
%, P: 0.030% or less, S: 0.030% or less, Al: 0.005
-0.05%, Mo: 0.2-0.7%, V: 0.01-0.15%, N:
0.0050-0.0120%, Ti: 0.001-0.030
%, REM: 0.001 ~ 0.030%, B: 0.0005 ~ 0.0030%,
Ca: 0.0005 to 0.0030%, Zr: One or more selected from 0.001 to 0.05%, excellent in galvanizing crack resistance characterized by being composed of the balance of Fe and unavoidable impurities. The present invention is a fire-resistant steel material for building structures, and the present invention provides, in weight%, C: 0.01 to 0.15%, Si: 0.6% or less,
Mn: 0.5 to 1.6%, P: 0.030% or less, S: 0.030% or less, Al: 0.005 to 0.05%, Mo: 0.2 to 0.7%, V: 0.01
~ 0.15%, N: 0.0050 ~ 0.0120% and Ti: 0.001 ~
0.030%, REM: 0.001 to 0.030%, B: 0.0005 to 0.003
0%, Ca: 0.0005 to 0.0030%, Zr: One or more selected from 0.001 to 0.05%, and Cu:
0.05-0.5%, Ni: 0.05-0.5%, Cr: 0.05-0.5%,
Nb: One or two selected from 0.005 to 0.030%
It is a refractory steel material for building structures excellent in galvanization crack resistance, characterized by containing at least one species and the balance of Fe and unavoidable impurities.

[0008] The present invention also provides a steel described above or above, which is hot-rolled after heating and then cooled at an average cooling rate (° C / sec).
Is equal to or higher than air cooling, and is equal to or less than α defined by the following equation (1): α (° C./sec)=(V/N)×3.5 (1).
(3) _{Ar 3 (℃) = 910- 273C} + 25Si-74Mn-9Mo ............ (2) Ar 3 (℃) = 910- 273C + 25Si-74Mn-9Mo-56Ni-16Cr-5Cu-1620Nb ............ ( This is a method for producing a fire-resistant steel material for building structures excellent in galvanization crack resistance, characterized by performing cooling of (Ar ₃ −200 ° C.) or more based on Ar ₃ defined in 3).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A steel material according to the present invention is a steel plate,
It means various steel materials including hot-rolled steel sheet, shaped steel, and steel pipe. First, the chemical composition of the steel material of the present invention will be described. C: 0.01 to 0.15% C is an element that increases the strength, and requires 0.01% or more to secure the strength. However, if added over 0.15%, the strain aging resistance is reduced, so 0.01 to 0.15% Limited to. The preferred range is 0.03 to 0.12%.

Si: 0.6% or less Si is an effective element for increasing the strength, but if it exceeds 0.6%, the toughness of the heat affected zone (HAZ) significantly deteriorates.
Limited to 0.6% or less. In addition, it is preferably 0.01 to 0.40% from the viewpoint of scale control. Mn: 0.5 to 1.6% Mn is an element effective for increasing the strength like Si, but in order to obtain the effect, addition of 0.5% or more is required. However, if added over 1.6%, the formation of intragranular ferrite is inhibited, the structure becomes coarse, and the toughness is greatly reduced.
Therefore, Mn is set in the range of 0.5 to 1.6%. Incidentally, the content is preferably in the range of 0.6 to 1.5%.

P: 0.030% or less P increases the toughness and weld cracking susceptibility of the base material and the weld heat-affected zone, and is an element to be reduced as much as possible. S: 0.030% or less S is an element to be reduced as much as possible because it increases the anisotropy in rolling with respect to toughness and ductility, and the upper limit is 0.030%.
%.

Al: 0.005 to 0.05% Al is added as a deoxidizing agent, but 0.005% or more is required for deoxidation. However, if the content exceeds 0.05%, the deoxidizing effect is saturated. Was set to 0.05%. Mo: 0.2 to 0.7% Mo is a useful element that lowers the cooling transformation start temperature (Ar ₃ point), improves quenching properties, and further enhances high-temperature strength and fire resistance by single precipitation of Mo carbide. To achieve this effect, 0.2% or more must be added. However, the addition of more than 0.7% lowers the weldability, so Mo was set in the range of 0.2 to 0.7%. Preferably,
More than 0.3 to 0.6%.

V: 0.01% to 0.15% V precipitates as VN alone in austenite during rolling and cooling, becomes a ferrite transformation nucleus, refines the structure, increases the toughness, further increases the strength of the base material, and balances the strength and toughness. It is an indispensable element to improve. In addition, VN suppresses generation of a pearlite band as a nucleus of pearlite transformation, and effectively acts to improve zinc plating crack resistance of a base material.
In order to exert these effects, 0.01% or more of addition is necessary. On the other hand, even if added in excess of 0.15%, the effect is saturated with respect to the improvement of galvanization crack resistance, and the weld hardening is enhanced. V is 0.01-0.15% because welding crack resistance decreases.
Range. In addition, it is preferably 0.03 to 0.12%.

N: 0.0050% to 0.0120% N combines with V to form VN, and is an element that plays an important role in improving the galvanizing resistance of the base material. If it is less than 0.0040%, the effect is small, and if it exceeds 0.0120%, on the contrary, the toughness of the heat affected zone is significantly reduced and the strain aging property is promoted. Therefore, N is set in the range of 0.0050 to 0.0120%. From the viewpoint of preventing strain aging and embrittlement, it is desirable that N be such that V / N is 3.6 or more in relation to V.

Ti: 0.001 to 0.030%, REM: 0.001 to
0.030%, B: 0.0005-0.0030%, Ca: 0.0005-0.0030
%, Zr: one or more selected from 0.001 to 0.05% These elements are effective elements that have a remarkable effect on the improvement of the toughness of the heat affected zone and the improvement of the galvanization crack resistance.
To obtain these effects, Ti, REM, B, Ca, and Zr should be added at 0.001% or more, 0.001% or more, 0.0005% or more, respectively.
0005% or more and 0.001% or more need to be added alone or in combination. However, Ti, REM, B, Ca, and Zr were 0.030%, 0.030%, 0.0030%, 0.0030%, and 0.3%, respectively.
When added in excess of 0030%, the cleanliness of the base material is reduced,
Decreases toughness.

Therefore, Ti is 0.001 to 0.030%, and REM is
0.001 to 0.030%, B is 0.0005 to 0.0030%, Ca is 0.0005
0.000.0030%, Zr was in the range of 0.001 to 0.05%. Cu: 0.05-0.5%, Ni: 0.05-0.5%, Cr: 0.05-0.5
%, Nb: one or two or more selected from 0.005 to 0.030% In the case of requiring a thick material size or a high strength, which has a small effect of microstructure refinement by rolling and cannot expect a sufficient cooling rate Is selectively one of Cu, Ni, Cr, and Nb.
Seeds or two or more are added. Cu, Ni, Cr, and Nb have the effect of lowering the cooling transformation start temperature (Ar _three points) after hot rolling and suppressing the transformation of ferrite from austenite grain boundaries. Effectively increases the strength of the steel. To achieve this effect,
Cu, Ni, Cr, Nb are 0.05%, 0.05%, 0.05%, respectively.
It is necessary to add 0.005% or more. Since Cu impairs hot workability, it is necessary to add Ni at the same time when adding a large amount. However, if the addition exceeds 0.5%, the production cost becomes too high, so the upper limits of Cu and Ni are set to 0.5%. If Cr and Nb are added in excess of 0.50% and 0.0030%, respectively, the weldability and toughness are impaired. For this reason, Cu
0.05-0.5%, Ni 0.05-0.5%, Cr 0.05-0.5%,
Nb was set in the range of 0.005 to 0.030%.

The remainder is Fe and inevitable impurities. Next, the manufacturing conditions will be described. The steel having the above composition is heated and hot-rolled. Steel plate by hot rolling,
It is formed into hot rolled steel sheet, shaped steel, and steel pipe. Although each hot rolling is not particularly limited, all known rolling methods are suitable. The heating temperature is preferably in the range of 1100 ° C. to 1350 ° C., and the rolling end temperature is preferably higher than the _three Ar points.

After the hot rolling, the steel is cooled. Average cooling rate after rolling (° C / sec): not less than air cooling and not more than α defined by the following equation (1) α (° C / sec) = (V / N) × 3.5 (1) After hot rolling When the average cooling rate exceeds α defined by the equation (1), precipitation of VN in the austenite region is suppressed,
Since nucleation of ferrite and pearlite transformation is suppressed, a band-like structure is formed, which inhibits galvanizing crack resistance. From this, the average cooling rate after rolling was set to α or less. The lower limit of the cooling rate is the cooling rate of air cooling.

Cooling stop temperature: Ar ₃ −200 ° C. or higher Ar ₃ (° C.) = 910−273C + 25Si−74Mn−9Mo based on Ar ₃ defined by the following equation (2) or (3): _{(2) Ar 3 (℃)} = 910- 273C + 25Si-74Mn-9Mo-56Ni-16Cr-5Cu-1620Nb ............ (3) When cooled in air or more cooling rate until a temperature lower than the Ar ₃ -200 ° C., Due to the problem of shear distortion due to the increase in residual stress and the improvement of strain aging, the cooling stop temperature is Ar ₃ -200 ° C.
It was above. Preferably, the range of the cooling stop temperature is A
r ₃ −150 ° C. or higher and Ar ₃ or lower.

After the cooling is stopped, the steel plate, the rolled H-section steel and the steel pipe are allowed to cool, and the hot-rolled steel plate is wound around a coil and allowed to cool. The calculation of Ar ₃ is performed by using equation (2) or (3) depending on the chemical composition of the steel material.
Formula (2) is used when Cu, Ni, Cr, and Nb are not added, and Formula (3) is used when Cu, Ni, Cr, and Nb are added.

[0021]

EXAMPLE A steel having a chemical composition shown in Table 1 was heated and hot-rolled, and then cooled as shown in Table 2 to obtain a steel plate.
A hot-rolled steel sheet, an H-section steel and a steel pipe were used. The manufactured steel materials were examined for tensile properties (yield point (YP), tensile strength (TS), yield ratio (YR), elongation (El)) and toughness (Charpy absorbed energy at 0 ° C. (vE ₀ )).

Further, a welded joint was produced from the above steel material by heat input shown in Table 2, and the toughness of the HAZ portion (1 mm from the bond portion) (Charpy absorbed energy at 0 ° C. (vE ₀ HAZ)
)investigated. In addition, a tensile test was performed on the above steel material and the weld heat affected zone in a zinc bath at 450 ° C. to determine the aperture value, and the galvanization cracking property was evaluated. After subjecting the above steel materials to hot dip galvanizing (plating conditions: immersion in a 450 ° C bath for 10 minutes), tensile properties at 600 ° C (600 ° C
YS).

Table 2 shows the results.

[0024]

[Table 1]

[0025]

[Table 2]

From Table 2, it can be seen that the examples of the present invention show the strength toughness of the base material,
In addition to excellent toughness of the heat affected zone, fire resistance,
Excellent galvanizing crack resistance. On the other hand, the comparative examples in which the cooling conditions after rolling are out of the range of the present invention have low base metal toughness, high YR, and low zinc plating crack resistance of the base metal. Mo
No. 12 having a low N is low in fire resistance, and Nos. 13, 14, and 16 having N and V amounts out of the range of the present invention have low zinc plating cracking resistance of the base material. No. 15, in which none of Ti, REM, B, Ca, and Zr was added, had low HAZ toughness and low HAZ galvanizing cracking resistance.

As described above, by adjusting the steel composition and the cooling conditions after rolling within the scope of the present invention, not only the strength and toughness of the base metal but also the toughness and fire resistance of the weld heat affected zone and the galvanization resistance are improved. Excellent steel materials can be easily manufactured.

[0028]

According to the present invention, according to the present invention, a steel material having high fire resistance, sufficient strength, HAZ toughness and seismic resistance, and excellent galvanization crack resistance can be secured for steel materials used for welded structural steel. Can be provided, which has an extremely beneficial effect on industry.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Fumimaru Kawabata 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. 1-chome (without address) Mizushima Works, Kawasaki Steel Corporation (72) Inventor Toru Hayashi 1-chome, Mizushima-Kawasaki-dori, Kurashiki City, Okayama Prefecture (without address) Mizushima Works, Kawasaki Steel Corporation

Claims (4)

[Claims] C .: 0.01 to 0.15% by weight, Si: 0.6% by weight
% Or less, Mn: 0.5 to 1.6%, P: 0.030% or less, S:
0.030% or less, Al: 0.005 to 0.05%, Mo: 0.2 to 0.7
%, V: 0.01 to 0.15%, N: 0.0050 to 0.0120%,
Further Ti: 0.001 to 0.030%, REM: 0.001 to 0.030
%, B: 0.0005-0.0030%, Ca: 0.0005-0.0030%, Z
r: A fire-resistant steel material for building structures excellent in galvanization crack resistance, containing one or two or more selected from 0.001 to 0.05%, the balance being Fe and unavoidable impurities. 2. In% by weight, C: 0.01 to 0.15%, Si: 0.6
% Or less, Mn: 0.5 to 1.6%, P: 0.030% or less, S:
0.030% or less, Al: 0.005 to 0.05%, Mo: 0.2 to 0.7
%, V: 0.01 to 0.15%, N: 0.0050 to 0.0120% and T
i: 0.001 to 0.030%, REM: 0.001 to 0.030%, B:
0.0005-0.0030%, Ca: 0.0005-0.0030%, Zr: 0.001
One or two or more selected from the group consisting of 0.05 to 0.5%, Cu: 0.05 to 0.5%, Ni: 0.05 to 0.5%, and Cr:
Architectural structure with excellent galvanization resistance, characterized by containing one or more selected from 0.05 to 0.5% and Nb: 0.005 to 0.030%, with the balance being Fe and unavoidable impurities. For refractory steel. 3. C .: 0.01 to 0.15% by weight, Si: 0.6% by weight
% Or less, Mn: 0.5 to 1.6%, P: 0.030% or less, S:
0.030% or less, Al: 0.005 to 0.05%, Mo: 0.2 to 0.7
%, V: 0.01 to 0.15%, N: 0.0050 to 0.0120%,
Further Ti: 0.001 to 0.030%, REM: 0.001 to 0.030
%, B: 0.0005-0.0030%, Ca: 0.0005-0.0030%, Z
r: A steel containing one or more selected from 0.001 to 0.05%, the balance consisting of Fe and unavoidable impurities is heated, then hot-rolled, and the average cooling rate (° C / sec) is air-cooled Above α defined by the following equation (1), the cooling stop temperature is based on Ar ₃ defined by the following equation (2) (Ar ₃ −2
(00 ° C.) or more. Note α (° C / sec) = (V / N) × 3.5 (1) Ar ₃ (° C) = 910-273C + 25Si-74Mn-9Mo ... (2) 4. C: 0.01 to 0.15% by weight, Si: 0.6% by weight
% Or less, Mn: 0.5 to 1.6%, P: 0.030% or less, S:
0.030% or less, Al: 0.005 to 0.05%, Mo: 0.2 to 0.7
%, V: 0.01 to 0.15%, N: 0.0050 to 0.0120% and T
i: 0.001 to 0.030%, REM: 0.001 to 0.030%, B:
0.0005-0.0030%, Ca: 0.0005-0.0030%, Zr: 0.001
One or two or more selected from the group consisting of 0.05 to 0.5%, Cu: 0.05 to 0.5%, Ni: 0.05 to 0.5%, and Cr:
After hot-rolling a steel containing at least one selected from 0.05 to 0.5% and Nb: 0.005 to 0.030%, the balance being Fe and inevitable impurities, the average cooling rate (° C.) / sec) is equal to or greater than air cooling.
A refractory steel material for building structure excellent in galvanizing crack resistance, characterized in that cooling is performed so that the cooling stop temperature becomes (Ar ₃ −200 ° C.) or more based on Ar ₃ represented by the following formula (3). Manufacturing method. Note α (° C / sec) = (V / N) × 3.5 (1) Ar ₃ (° C) = 910-273C + 25Si-74Mn-9Mo-56Ni-16Cr-5Cu-1620Nb (3)