JP3428286B2 - Manufacturing method of thick steel pipe round column - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thick-walled steel pipe round column having a low yield ratio of 60 kg, which is used for a steel structure of a building, and particularly to a thick-walled steel pipe round column designed by a limit state design method. Regarding the method.

[0002]

2. Description of the Related Art In recent years, with the trend toward higher-rise buildings and longer column intervals, steel materials used for buildings are required to have higher strength and thicker wall thickness of 40 mm or more. It is desired that the strength level is 60 kg or higher. In addition, the high-rise buildings, when hit by a huge earthquake,
A limit state design method is applied that emphasizes human safety by absorbing seismic energy by plastic deformation of column and beam members and avoiding major collapse. Therefore, the column / beam member used in the limit state design method is desired to have a yield ratio (YR) of 80% or less as a measure of high plastic deformability.

[0003] In addition, since the design of modern buildings tends to be emphasized, the demand for steel pipe round pillars having a circular cross section is larger than that of a conventional box pillar having a square cross section.
Conventionally, as a method of manufacturing a round column having a low yield ratio and high tensile strength thick-walled steel pipe, Japanese Patent Laid-Open Nos. 5-65535 and 5-117746.
No. 5, JP-A-5-117747, JP-A-6-26414.
No. 4, Japanese Patent Laid-Open No. 6-340922, there is a method by cold forming.

Of these, DQ'-T in JP-A-5-65535 and RQ-Q 'in JP-A-5-117746.
-T, in Japanese Patent Laid-Open No. 5-117747, each treatment of DQ-Q'-T is performed.
By lowering R and performing stress relief treatment (SR treatment) after forming the steel pipe, work hardening accompanying the steel pipe forming is removed, and thus YR ≦ 80% is to be satisfied. But,
In such a method, a multi-stage heat treatment is performed at the steel plate stage,
Further, a large number of heat treatments such as SR treatment after forming the steel pipe are required, which impairs productivity and economy.

Further, in both Japanese Patent Laid-Open Nos. 6-264144 and 6-340922, the YR at the steel sheet stage is made as low as possible to suppress the YR after forming to 80% or less. However, in the case of forming a thick steel plate by cold press bending, it is difficult to increase the length and thickness of the round column from the viewpoint of bending workability of a pressing device or the like.

On the other hand, in cold press-bending, the work hardening increases toward the inner and outer surfaces where the plastic strain is large, and the steel pipe has a distribution of mechanical properties in the plate thickness direction. When SR is performed, this distribution tends to be relaxed, but it does not become uniform.

[0007]

As described above, in the production of thick-walled steel pipe round columns for cold-forming, multi-stage heat treatment impairs productivity and economic efficiency, and the press equipment used during processing is reduced. It is difficult to manufacture a long steel pipe from the viewpoint of load. Further, the steel pipe has a non-uniform material in the plate thickness direction.

The present invention has been made in view of the above circumstances, and it is possible to achieve a high yield and a low yield ratio without impairing economic efficiency and productivity, and to make the material uniform. An object of the present invention is to provide a method for manufacturing a thick-walled steel pipe round column for construction, which enables

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is as follows. First, in% by weight, C: 0.06-0.
17%, Si: 0.06-0.5%, Mn: 0.5-
1.6%, P: 0.015% or less, S: 0.005% or less, Mo: 0.1-0.25%, Ti: 0.01-0.
02%, B: 0.0005 to 0.002%, Al: 0.
07% or less, N: 0.004% or less, with the balance being F
Rolling steel consisting of e and unavoidable impurities, heating the steel sheet to a temperature range of 900 to 1000 ° C., finishing bending in a temperature range of Ar ₃ or higher, and then allowing to cool or air-cool to obtain a steel pipe. Secondly, a method for manufacturing a thick-walled steel pipe round column, characterized in that, in% by weight, C: 0.06 to 0.17%, S
i: 0.06 to 0.5%, Mn: 0.5 to 1.6%,
P: 0.015% or less, S: 0.005% or less, Mo:
0.1 to 0.25%, Ti: 0.01 to 0.02%,
B: 0.0005 to 0.002%, Al: 0.07% or less, N: 0.004% or less, and Nb: 0.
005 to 0.05%, V: 0.01 to 0.1%, containing one or two selected from the group consisting of the balance Fe
And rolling steel consisting of unavoidable impurities, heating the steel plate to a temperature range of 900 to 1000 ° C., finishing bending in a temperature range of Ar ₃ or higher, and then allowing to cool or air cool to obtain a steel pipe. The present invention provides a method for manufacturing a characteristic thick-walled steel pipe round column.

The inventors of the present invention are concerned with a method for producing a thick-walled steel pipe round column which is capable of achieving high strength and a low yield ratio without requiring a facility having a large working capacity when producing a pipe, and which has a uniform material. I examined it in detail.

The steel pipe targeted by the present invention is a thick product having a wall thickness of 40 mm or more, and if it is press-formed in the γ region, the deformation resistance is small, and the steel pipe can be made thick and long. Further, the processing strain introduced in the γ region disappears due to the transformation during the subsequent cooling, resulting in a uniform material. However, in this case, the cooling rate after hot press forming becomes slow, and it is difficult to obtain high strength. Although the addition of alloying elements is effective in increasing strength,
Since an increase in the amount of alloying elements causes deterioration of weldability, it is necessary to avoid adding more than necessary.

Therefore, the relationship between the quench hardening index (D _I ) and the weldability was investigated by using a steel type capable of obtaining a tensile strength (TS) of 60 kg by heating at 900 ° C. and cooling. The result is shown in FIG. From this figure, without impairing the weldability,
In order to improve the hardenability, it is considered that Ti-B type steel is effective.

Further, from the viewpoint of securing strength of 60 kg class, addition of Mo as a third element is effective, and 0.10C-0.
23Si-1.45Mn-0.014Ti-0.001
Using 1B as a basic component system, the balance between the amount of Mo and the strength and toughness of the steel pipe was investigated. The result is shown in FIG. As is clear from this figure, the Mo content is 0.1 to 0.25.
%, High strength and good toughness can be obtained.

Based on the above results, the present inventors
A steel in which 0.1 to 0.25% of Mo is added to the i-B system is hot-rolled, and the steel plate is 900-
The above problem can be solved by heating to a temperature range of 1000 ° C., starting the bending process for pipe manufacturing from that temperature range, and finishing the process in the temperature range above the transformation start temperature and air cooling. I found it possible. The present invention has been completed based on such findings.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The composition of the steel used in the thick-walled steel pipe round column obtained in the present invention is, by weight%, C: 0.06 to 0.17%,
Si: 0.06-0.5%, Mn: 0.5-1.6%,
P: 0.015% or less, S: 0.005% or less, Mo:
0.1 to 0.25%, Ti: 0.01 to 0.02%,
B: 0.0005 to 0.002%, Al: 0.07% or less, N: 0.004% or less. Further, as a selective component, Nb: 0.005 to 0.0
5%, V: 0.01 to 0.1%, and 1 or 2 kinds selected from the group consisting of further is contained.

The reasons for limiting the contents of these component elements will be described below. In the following, all percentages are by weight. C: 0.06 to 0.17% C is contained in an amount of 0.06% or more in order to secure the strength of the steel, but if it is contained in a large amount, the toughness and weldability are deteriorated, so the upper limit thereof is such an influence. Without limit 0.17
%.

Si: 0.06 to 0.5% Si is an element necessarily contained in steel for deoxidation.
The content is set to 0.06% or more from the viewpoint of ensuring a low yield ratio, but if Si is too much, it has an unfavorable effect from the viewpoint of HAZ toughness and weldability, so that the upper limit does not show such an effect. The limit is 0.5%.

Mn: 0.5 to 1.6% Mn is required to be 0.5% or more in order to improve the strength and toughness of the steel sheet and suppress the formation of FeS. As a result, a hardened layer appears at the time of welding to increase the crack susceptibility, and the upper limit is set to 1.6% of the limit that does not have such an adverse effect.

P: 0.015% or less, S: 0.005%
Hereinafter, P and S inevitably exist as impurities mixed in the steel, but reduction of P is effective in preventing intergranular fracture, and reduction of S is effective in preventing hydrogen cracking in the weld heat affected zone. , 0.015% or less at which such effects are exhibited,
It was set to 0.005% or less.

Mo: 0.1-0.25% Mo has the effect of achieving high strength by solid solution strengthening and improving hardenability. However, if the content is less than 0.1%, the hardening is not sufficiently exhibited, and if the content exceeds 0.25%, the toughness and weldability are deteriorated, so the content of Mo is 0.1 to 0.25%. The range is.

B: 0.0005 to 0.002% B is an element which, when present as a solid solution B, remarkably improves the hardenability and increases the strength of the base metal, but when the amount is less than 0.0005%. Such an effect is not sufficiently exhibited, and on the other hand, even if it exceeds 0.002%, no further hardenability improving effect is observed. Therefore, the content of B is 0.000
The range is 5 to 0.002%.

Ti: 0.01 to 0.02% In order to secure the above solid solution B, it is necessary to fix the solid solution N, but Ti is an element that easily forms a nitride,
Ti is added as TiN to fix the solid solution N. However, if the content is less than 0.01%, such an effect is not sufficiently exhibited, while if it exceeds 0.02%, the toughness of the base material and the weld heat affected zone is significantly deteriorated due to the formation of TiC. Therefore, the content of Ti is 0.01 to
The range is 0.02%.

Al: 0.07% or less Al is an element contained in steel for deoxidation, but if it is contained in a large amount, the cleanliness of the steel is deteriorated and the toughness of the welded portion is deteriorated. Is set to 0.07%, which is the limit without such an influence.

N: 0.004% N is an unavoidable impurity contained in steel and forms BN and TiN together with B and Ti described above. Then, first, TiN is formed, and when the N content increases, TiN increases.
In addition, since BN is formed and the solid solution B is reduced, its upper limit is set to 0.004%, which is the limit without such influence.

Nb: 0.005 to 0.05% Nb is an element that effectively acts to increase strength and toughness due to the precipitation effect of fine carbonitrides, but its content is 0.0
If it is less than 05%, the effect is not exhibited, and if it is added in an amount of 0.05% or more, the precipitation ratio is hindered by excessive precipitation hardening. Therefore, when Nb is added, the amount is 0.005 to 0.
The range is 05%.

V: 0.01 to 0.1% V is an element that improves the hardenability by adding a small amount, but if the content is less than 0.01%, its effect is not sufficiently exhibited, and V is 0. If added in an amount of more than 0.1%, the weldability is deteriorated.
The range is 0.1%.

Next, the manufacturing conditions in the present invention will be described. First, a steel having the above composition is formed into a steel slab by ordinary ingot casting or continuous casting, and the steel slab is hot-rolled to form a steel plate. Then, the steel sheet is heated to a temperature range of 900 to 1000 ° C., and bending is completed in a temperature range of Ar ₃ or higher.

The process up to the production of the steel sheet is not particularly limited and may be carried out under the conditions usually adopted. The obtained steel sheet is heated to a temperature range of 900 to 1000 ° C., and the bending work is finished in the temperature range of Ar ₃ or higher. This is because the strain can disappear by the transformation during the subsequent cooling. The subsequent cooling may be cooling by air or air, and this can also sufficiently obtain a strength of 60 kg.

[0029]

EXAMPLES Specific examples of the present invention will be described below. The test material having the chemical composition shown in Table 1 was press-molded under the manufacturing conditions shown in Table 2 to obtain a tube length of about 12 m.
Manufactured steel pipe. Tensile test pieces, V-notch Charpy impact test pieces, full-thickness hardness samples and y-type weld crack test pieces were sampled from the steel pipes thus manufactured, and the mechanical properties in the pipe axis direction were measured. The results are also shown in Table 2.

Ar ₃ in Table 1 indicates the transformation start temperature during cooling during reheating. Further, the tensile test piece and the V-notch Charpy test piece were sampled in the C direction centering on a portion 5 mm inside from the outer surface of the steel pipe, and the tensile test piece was 6 mmφ.
A 30 mm GL round bar was used, and the V-notch Charpy test piece was a full size. The hardness of the plate thickness is 5 mm below the surface layer, 1
The hardness distribution in the plate thickness direction was grasped by performing the test at three places of / 2t (plate thickness center) and 5 mm below the back layer. JIS type y-type crack test piece
The one defined in Z 3158 was used.

[0031]

[Table 1]

[0032]

[Table 2]

The steel pipes with symbols A to M in Table 2 were manufactured under the conditions within the scope of the present invention. Further, the steel pipes of numbers N to Y are manufactured under the conditions outside the scope of the present invention. Steel pipes with symbols A to M, which are within the scope of the present invention, have a yield ratio after steel pipe forming of 80% or less, good toughness, a small distribution of mechanical properties in the plate thickness direction, and good weldability. It is confirmed that there is.

On the other hand, the steel pipes N to Y, which are comparative examples, were inferior in any of these. That is, Cr-M
The weldability of N, which is o type steel, and O, which is VN type steel type, was not good. Further, in the case of cold-formed P, the tube length was limited to about 4 m from the viewpoint of press load, and the uniformity of the material was low. Q with a low Mo content and S with a low Ti content had insufficient strength. R with high Mo content and T with high Ti had low toughness. U with a low B content had insufficient strength, and conversely, V with a high B content had low toughness. W having a low heating temperature at the time of molding had low toughness and low uniformity of material. The toughness was low for both X, which has a low molding end temperature, and Y, which has a high molding end temperature.

[0035]

As described above, according to the present invention,
By a process that does not require large equipment capacity and is excellent in economic efficiency and productivity, it is possible to manufacture a thick-walled steel pipe round column having a high strength, a low yield ratio, and a uniform material and having a plate thickness of more than 40 mm. The thick-walled steel pipe round column manufactured according to the present invention is suitable as a steel pipe round column designed for construction by the limit state design method.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a y-type weld crack prevention preheating temperature and a quench hardening index (D _I ) in each steel type.

FIG. 2 is a diagram showing the relationship between the strength and toughness of a steel pipe that has been air-cooled after hot forming and the amount of Mo added.

Claims (2)

(57) [Claims] 1. C: 0.06 to 0.17% by weight,
Si: 0.06-0.5%, Mn: 0.5-1.6%,
P: 0.015% or less, S: 0.005% or less, Mo:
0.1 to 0.25%, Ti: 0.01 to 0.02%,
B: 0.0005 to 0.002%, Al: 0.07% or less, N: 0.004% or less, the balance being Fe and unavoidable impurities rolled into a steel sheet. 900
A method for manufacturing a thick-walled steel pipe round column, which comprises heating to a temperature range of up to 1000 ° C., finishing bending in a temperature range of Ar ₃ or higher, and then allowing to cool or air-cool to obtain a steel pipe. 2. C: 0.06 to 0.17% by weight,
Si: 0.06-0.5%, Mn: 0.5-1.6%,
P: 0.015% or less, S: 0.005% or less, Mo:
0.1 to 0.25%, Ti: 0.01 to 0.02%,
B: 0.0005 to 0.002%, Al: 0.07% or less, N: 0.004% or less, and Nb: 0.
005 to 0.05%, V: 0.01 to 0.1%, containing one or two selected from the group consisting of the balance Fe
And rolling steel consisting of unavoidable impurities, heating the steel plate to a temperature range of 900 to 1000 ° C., finishing bending in a temperature range of Ar ₃ or higher, and then allowing it to cool or air-cool to obtain a steel pipe. A method of manufacturing a round column having a characteristic thick-walled steel pipe.