JP3322065B2 - Method of manufacturing low yield ratio thick steel tube column for building - 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 producing a thick steel pipe column having a low yield ratio of about 40 to 150 mm and used for high-rise buildings and marine structures.

[0002]

2. Description of the Related Art Thick steel pipes used for high-rise buildings and offshore structures are required to have high strength, high toughness, low yield ratio, high weldability and the like. Therefore, in the case of relatively thin steel pipes, a low-component composition is used to ensure weldability, and high-strength and high-toughness steel sheets are manufactured using technologies such as controlled rolling and controlled cooling, and then cooled. It is formed into a tube by cold working. In this case, since the material changes due to work hardening at the time of forming into a tubular shape, a heat treatment such as a stress removing process is required after the forming to achieve predetermined characteristics.

[0003] On the other hand, at present, the height of buildings is increasing, and there is a tendency that thicker steel tube columns for buildings are required. In the case of a thick steel pipe, cold forming is not possible from the viewpoint of the load of the press device during working, and warm forming or hot forming is employed.

[0004] However, when hot forming is adopted for the pipe making, the effect on the strength obtained by controlled rolling or the like is lost, so that a material having a high component composition is used. In a high-component system, toughness and weldability are reduced.

Further, regarding warm forming, Japanese Patent Application Laid-Open No. 62-5 / 1987
No. 4018 discloses that a steel sheet subjected to controlled rolling or controlled rolling and accelerated cooling is reheated to an Ac ₁ temperature of 750 to 400 ° C. or lower, and immediately or after cooling, 750 to 250 ° C.
It is disclosed that by processing in the above temperature range, excellent material properties such as toughness can be obtained.

However, when warm forming is employed, the deformation resistance tends to increase due to the temperature drop during processing,
Further, it is difficult to achieve a low yield ratio, which is one of the important characteristics of building steel pipes, because the yield ratio tends to increase with decreasing temperature.

On the other hand, as a method for obtaining a low yield ratio, a steel pipe is heated to a temperature range of Ac ₃ −250 ° C. to Ac ₃ −20 ° C. and water-cooled, or a processing strain is imparted after these heat treatments. Tempering (Japanese Unexamined Patent Publication No. 3-87318), or air cooling after heating to Ac ₃ or higher and Ar ₃ −
250 ° C. to Ar ₃ -20 ° C. or water cooling from a temperature range of, or a method (Japanese Unexamined Patent Publication No. 3-87317) to temper to impart working strain after these heat treatments, further the Ac ₃ -200 ° C. or more steel heated to a temperature, Ac ₃ -200
℃ to start the strain applied in the above, Ac ₃ -200 ℃ ~Ac ₃ -
A method has been proposed in which the strain application is terminated in a temperature range of 20 ° C., and the material is cooled with water and then tempered (Japanese Patent Laid-Open No. 4-321). However, in these methods, a complicated treatment is applied to the steel pipe, and economic efficiency and productivity are significantly impaired.

[0008]

As described above, in the production of thick-walled steel pipe columns for construction, it is difficult to produce by cold working from the viewpoint of the capacity of a forming machine. Therefore, the composition must be made into a high-strength, high-component system, which causes inconvenience such as impairment of toughness and weldability.

On the other hand, even in the case of warm forming, in the case of warm forming after heating to a temperature of Ac ₁ or less, the deformation resistance tends to increase due to the temperature drop during processing, and the yield ratio increases with the temperature drop. This tends to increase, and causes a problem that a low yield ratio is not achieved. In addition, various heat treatments have been attempted on steel pipes in order to achieve a low yield ratio, but all of these methods are complicated and impair economical efficiency.

Furthermore, when forming a steel pipe into a steel pipe from a steel plate, a tensile stress acts on the outer surface of the steel pipe, a compressive stress acts on the inner surface of the steel pipe, and a phenomenon occurs in which the stress does not act on the center of the sheet thickness, which is a neutral axis of the stress. In the case of hot forming or hot forming, even at the same processing temperature, a lower yield ratio is obtained at the center of the sheet thickness compared to the inner and outer surfaces, but the strength is extremely low, and conversely, a predetermined strength is achieved in the inner and outer tables, but a lower yield ratio is obtained. Tend to not achieve.
In the case of warm forming or hot forming, the temperature at which processing is performed differs depending on each part in the steel sheet, and the part subjected to processing at a relatively high temperature has a low yield ratio, but has a low strength, and conversely, processing at a low temperature. Although a given strength can be achieved in a part to be affected, a low yield ratio tends not to be achieved. For this reason,
In pipe forming by warm forming or hot forming, the distribution of mechanical properties in the thickness direction becomes maximum in the final processed portion where the processing temperature is lowest.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to achieve excellent weldability, high strength and a low yield ratio in each part of the sheet thickness without impairing economy and productivity. It is an object of the present invention to provide a method for manufacturing a thick-walled steel pipe column for building, which is possible.

[0012]

SUMMARY OF THE INVENTION The present inventors have achieved high strength and a low yield ratio in each part of the sheet thickness without requiring equipment having a large working capacity in pipe production and without causing a decrease in weldability. As a result of examining in detail the method that can be performed, a steel sheet of a specific component composition is heated to a two-phase region, bending processing for pipe making is started from the plate end from that temperature region, and is lower than the transformation end temperature. It has been found that the above-mentioned problem can be solved by completing the processing at the central portion of the plate in the temperature range of and cooling by air. That is, it has been known that a low yield ratio can be obtained by heating to a two-phase region, but at the same time, it causes a decrease in toughness.
No processing was performed in this temperature range. However, by defining the components as described above, and further controlling the pipe production sequence during warming, the deterioration of toughness is suppressed, and excellent weldability and high strength and a low yield ratio are achieved in each part of the plate thickness. You can do it.

The present invention has been completed on the basis of these findings. First, C: 0.05 to 0.05% by weight.
0.25%, Si: 0.10 to 0.50%, Mn: 0.
5 to 2.0%, sol. Al: 0.005 to 0.10
%, Mo: 0.05 to 0.25%, with the balance being Fe and
A steel sheet consisting of
Heating to the temperature range of the two-phase region of c3 or less, starting the processing by the press bend method into a tube from the temperature range of Ar1 or more from the end of the plate, and ending the processing at the center of the plate in the temperature range of less than Ar1 The present invention also provides a method for producing a high-strength steel pipe column for a thick building having a high toughness and a low yield ratio, which is characterized by air cooling thereafter.

Second, C: 0.05 to 0.5% by weight.
25%, Si: 0.10 to 0.50%, Mn: 0.5 to
2.0%, sol. Al: 0.005 to 0.10%, M
o: 0.05-0.25%, Ca: 0.0005-0.
005%, the balance being Fe and inevitable impurities.
The steel sheet is heated to a temperature range of a two-phase region of not less than Ac1 and not more than Ac3, and pressed into a tubular shape from a temperature range of not less than Ar1.
Processing by the bend method starts from the end of the plate, finishes the processing in the center of the plate in a temperature range lower than Ar1, and then air-cools. It is intended to provide a manufacturing method.

Hereinafter, the method for producing a thick steel pipe according to the present invention will be described in detail with respect to composition and molding conditions. (Composition) In the present invention, C, Si, M
It contains n, solAl, and Mo, and Ca is added as needed to control the morphology of inclusions. The reasons for limiting these component elements will be described below. In the following description, all percentages indicate weight%.

C: 0.05% of C is necessary for ensuring the strength of this type of steel at low cost and effectively. However, if it exceeds 0.25%, low-temperature cracking, high-temperature cracking and the like occur, and the weldability and toughness are impaired. For this reason, the C content is in the range of 0.05 to 0.25%.

Si: Si is added for deoxidation, but if it is less than 0.10%, a sufficient deoxidizing effect cannot be obtained. On the other hand, if it exceeds 0.50%, toughness and weldability are not obtained. It causes deterioration. Therefore, the content of Si is set to 0.10 to 0.50%.
Range.

Mn: Mn is added as a basic element of steel which is effective for improving the strength and toughness of the steel. When the content is less than 0.5%, its effect is small, and when it exceeds 2.0%, the weldability and toughness are increased. Significantly deteriorates. Therefore, the Mn content is in the range of 0.5 to 2.0%.

Sol. Al: sol. Al is added as a deoxidizing agent, but if it is less than 0.005%, a sufficient deoxidizing effect cannot be obtained, and if about 0.10% is added, the effect is saturated. Therefore, sol. Al content 0.005
The range is 0 to 0.10%.

Mo: Mo has the effect of increasing the strength in each part of the plate thickness by solid solution strengthening, and has the effect of suppressing the degradation of toughness due to the structural change due to the increase in hardenability when added in a small amount. However, when its content is 0.1.
If the content is less than 0.05%, these effects are not sufficient, and high strength and suppression of toughness deterioration are insufficient. In addition, 0.25%
If a large amount is added beyond that, weldability and toughness are impaired, and economics are impaired. Therefore, the Mo content is in the range of 0.05 to 0.25%.

Ca: Ca has the effect of spheroidizing the form of inclusions, thereby preventing hydrogen-induced cracking and lamellar tearing. However, if it is less than 0.0005%, the effect cannot be obtained, and about 0.005% The effect is saturated by the addition of, and the addition of a larger amount is not preferable from an economical point of view. Therefore, the Ca content is set to 0.0005 to 0.005.
% Range.

(Forming Conditions) In the present invention, the steel sheet is heated to a temperature range of a two-phase region of not less than Ac1 and not more than Ac3, and the steel sheet is processed from a temperature range of Ar1 or more to a tubular shape by a press bend method from an end of the plate. Start and finish the processing at the center of the plate in the temperature range less than Ar1,
Then air-cool.

[0023] Here, the steel sheet is heated to a temperature range of Ac ₁ or more and Ac ₃ following the two-phase region, to start processing into tubular from Ar ₁ above temperature range, the processing at a temperature below Ar ₁ The reason for the termination is to reduce the deformation resistance and to form the tube into a tube without requiring a large facility capacity, and to achieve a low yield ratio by processing at a high temperature. In addition, air cooling after that has an effect of suppressing that the micro segregated portion formed by the transformation accompanying the reheating is transformed in the cooling process and leads to deterioration in toughness.

Further, starting the processing from the end of the plate and ending the processing at the center of the plate can be achieved by forming the end of the plate having a high temperature drop during the processing at the beginning and forming the center of the plate at a relatively low temperature drop. Forming the part later has the effect of reducing the temperature difference during processing in each part of the plate.

For forming into a tubular shape, an ordinary method of processing into a cylindrical shape such as press bend can be used.
It is not limited to this. Although Ar ₃ varies depending on the amount of C, Mn, or the like, it is approximately 750 ° C.

[0026]

The use of the present invention can achieve a high strength and a low yield ratio in each part of the sheet thickness without impairing toughness and weldability due to the following effects.

C, Si, Mn, sol. Al and M
By controlling the content of o or Ca to a specific content, and further controlling the conditions and order of pipe making in a warm state, high strength is achieved in each part of the plate thickness without impairing weldability. In other words, in the production of steel pipe columns, the material changes due to the strain distribution at the time of forming into a tubular shape, the strength is reduced at the center of the plate thickness, and the high yield ratio is generated in the inside and outside tables. Of the components, the effect of large solid solution strengthening by the addition of Mo, and the reduction in the distribution of the processing temperature in the steel sheet by controlling the order of pipe making during warming, cause a small change in the material in the thickness direction.

Further, the steel sheet is heated to a temperature range of Ac ₁ or more and Ac ₃ following the two-phase region, to start processing into tubular from Ar ₁ above temperature range, the processing at a temperature below Ar ₁ Finishing has the effect of reducing deformation resistance, forming into a tube without requiring large equipment capacity, and achieving a low yield ratio by processing at high temperatures. In addition, air cooling after that has an effect of suppressing that the micro segregated portion formed by the transformation accompanying the reheating is transformed in the cooling process and leads to deterioration in toughness.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. (Example 1) A sheet thickness of 70 m having the components and compositions shown in Table 1
Immediately after heating the steel sheet of m to 800 ° C., forming into a tubular shape by press bending was started from the end of the sheet, finished at 550 ° C. in the center of the sheet, and then air-cooled. At this time, the ratio D / t of the outer diameter D of the steel pipe to the plate thickness t was set to 10. Table 1 also shows the mechanical properties of the thus formed steel pipe in the final processed portion where the processing temperature is the lowest and the distribution of the mechanical properties in the thickness direction is large.

[0030]

[Table 1]

As shown in Table 1, with a composition within the range of the present invention, a high strength such as a yield strength (YS) of 350 MPa or more and a tensile strength (TS) of 490 MPa or more can be obtained at each thickness. A low yield ratio of 80% or less was obtained. In addition, the Charpy absorbed energy vE at 0 ° C. was 100 J or more, which was a sufficient value for a building steel pipe column.

On the other hand, those having a component composition outside the range of the present invention have a thickness of 300 M
It exhibited low strength of YS of less than Pa and low toughness of vE of less than 100J.

In the compositions shown in Table 1, the relationship between the Mo content and YS, TS is shown in FIG. 1, and the relationship between the Mo content and vE at 0 ° C. is shown in FIG. From these figures, it is clear that high strength and low yield ratio can be obtained and the toughness is also a sufficient value when the Mo content is in the range of 0.05 to 0.25%.

(Example 2) As shown in Table 2, a steel sheet having a composition indicated by A03 in Table 1 was heated to 900 to 700 ° C, and then formed into a tubular shape by press bend at 850 to 5 ° C.
It started from the edge of the plate at 00 ° C., ended at the center of the plate at 550 to 200 ° C., and then air-cooled. At this time, the ratio D / t of the outer diameter D of the steel pipe to the plate thickness t was set to 10. Table 2 also shows the mechanical properties of the thus formed steel pipe in the final processed portion.

[0035]

[Table 2]

As shown in Table 2, under the manufacturing conditions within the range of the present invention, high strength such as YS of 350 MPa or more and TS of 490 MPa or more can be obtained at each thickness, and a low yield ratio of 80% or less is obtained. Indicated. Also, 0 ° C
In Table 1, the Charpy absorbed energy vE was 100 J or more, which was a sufficient value for steel pipe columns for construction.

On the other hand, under the manufacturing conditions out of the range of the present invention, the thickness of 300M
The strength was as low as YS less than Pa, and the yield ratio was greater than 80%. The values such as the outer diameter D, the plate thickness t, and the ratio D / t of the steel pipe are not limited to those in the above embodiment.

[0038]

As described above, according to the present invention,
Producing high-strength and low-yield-ratio thick-walled steel pipe columns with a thickness of more than 40 mm at each part of the thickness without sacrificing toughness and weldability by a highly economical process that does not require large equipment capacity. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between Mo content and YS, TS.

FIG. 2 is a graph showing the relationship between the Mo content and vE at 0 ° C.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor: Attack Hirano 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Hiroshi Nagana 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (58) Investigated field (Int.Cl. ⁷ , DB name) C21D 8/00-8/10 C22C 38/00-38/60

Claims (2)

(57) [Claims] (1) C: 0.05 to 0.25% by weight,
Si: 0.10 to 0.50%, Mn: 0.5 to 2.0
%, Sol. Al: 0.005 to 0.10%, Mo:
Contains 0.05 to 0.25%, with the balance being Fe and inevitable
A steel plate made of impurities is heated to a temperature range of a two-phase region of not less than Ac1 and not more than Ac3, and processing by a press bend method into a tubular shape from a temperature range of not less than Ar1 is started from a plate end,
A method for producing a high-strength and low-yield-ratio thick-wall steel tube column for a building, wherein the processing is completed at the center of the plate in a temperature range lower than Ar1 and then air-cooled. 2. C: 0.05 to 0.25% by weight,
Si: 0.10 to 0.50%, Mn: 0.5 to 2.0
%, Sol. Al: 0.005 to 0.10%, Mo:
0.05-0.25%, Ca: 0.0005-0.00
A steel plate containing 5% and consisting of the balance of Fe and unavoidable impurities is heated to a temperature range of a two-phase region of not less than Ac1 and not more than Ac3, and is press-formed into a tubular form from a temperature range of not less than Ar1 and a tube.
Of the high-toughness and low-yield-ratio thick-walled steel pipe columns, starting from the end of the plate, finishing at the center of the plate in a temperature range lower than Ar1, and then air cooling. Production method.