JP2001314970A - Sub-merged arc press welding method for high strength reinforcing bar having excellent weld portion quality - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength of a reinforcing bar used for sub-merged arc press welding method, while keeping the characteristics of weld portion. SOLUTION: By making total content of P and S 0.03% or less, high temperature crack is prevented from developing in welded portion, and also by making the carbon equivalent, which is decided by the expression [%C]+[%Si]7+[% Mn]/5+[%V], 0.5%-0.8%, the strength of the rebar is secured, breaking from heat-affected portion is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submerged arc press welding method mainly applied to welding of steel structures and reinforced concrete structures in the fields of construction and civil engineering, and more particularly to welding for welding high-strength rebar. The present invention relates to a submerged arc press welding method for high-strength rebar having excellent quality.

[0002]

2. Description of the Related Art In recent years, in the field of construction and civil engineering, along with the enlargement of structures, the diameter and strength of reinforcing bars used for the structures have been increasing. Therefore, there is a demand for a method of welding these large-diameter, high-strength rebars at a stable quality and efficient welding at the time of building a structure.

[0003] With regard to a conventional reinforcing bar welding method, for example, a welding gap (welded portion) between a reinforcing bar and a material to be welded as disclosed in Japanese Patent Application Laid-Open No. 54-137451 is surrounded by a cylindrical backing material. In addition, there has been known an enclosed arc welding method in which manual welding or semi-automatic welding is performed with a welding material from an upper opening of a backing material.

In the enclosed arc welding method, the quality of the weld metal can be controlled by adjusting the composition of the weld metal by appropriately selecting the welding material. (Yield point 390MPa or more)
It has been applied to welding of high-strength rebar up to the rebar. However, this welding method is a method in which a steel bar is arranged horizontally, a welding gap (weld portion) with a surface of a material to be welded is surrounded by a cylindrical backing material, and welding is performed from an upper opening with a welding material. In the case where the anchor plate, the end plate, and the like, which are arranged vertically, are welded to the anchor plate, the end plate, and the like, the molten metal is likely to flow because the welding posture is horizontal, and the quality of the welded portion cannot be secured.

On the other hand, as a method for welding a vertically disposed reinforcing bar and a material to be welded, such as welding an anchor reinforcing bar and a fixing plate, a submerged arc disclosed in Japanese Patent Application Laid-Open No. 41-76859 and the like is known. Press welding is known.

[0006] The submerged arc press welding method is a welding method that can be applied to a relatively large-diameter rebar having a rebar diameter of about 32 mm. As shown in FIG. In a state in which the welding gap portion is surrounded by the powder flux 3 and the flux holder 4, the AC welding power source 7
A welding current is passed through the reinforcing bar 1 by a power cable to heat and melt the end of the reinforcing bar 1 while generating a welding arc 2 between the welding gaps. After a predetermined time has passed, the welding metal formed on the material to be welded (Molten pool) This is a method of welding by pushing a steel bar into 5.

[0007] As described above, in the submerged arc press welding method, since the steel itself such as a reinforcing bar substitutes for the welding material, the quality of the welded portion (weld metal) is greatly affected by the steel component such as the reinforcing bar. On the other hand, conventional JIS in the fields of architecture and civil engineering
Reinforcing bars stipulated in the standards were not designed with components that take into account these welding qualities.Therefore, when welding was performed using these conventional reinforcing bars, there was a problem that the mechanical properties of the welded parts were significantly reduced. Was.

This tendency becomes stronger with the recent increase in the strength of reinforcing bars. For example, when submerged arc press welding is performed using a conventional SD390 rebar (yield point of 390 MPa or more, tensile strength of 560 MPa or more), in the tensile test of the welded portion, the fracture will occur from the center of the weld metal. When welding high-strength rebar, there was a problem that the strength of the weld was reduced. For this reason, in the conventional submerged arc press welding, in order to secure the quality of the welded portion, the application to the rebar having the strength level of SD295 (yield point of 295 MPa or more, tensile strength of 490 MPa or more) has to be restricted. .

[0009]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems in the prior art, and has been developed in consideration of the above-mentioned problems.
It is an object of the present invention to provide a submerged arc press welding of a high-strength rebar that can obtain good welding quality even when a high-strength rebar having a strength of 90 MPa or more and a tensile strength of 560 MPa or more) is subjected to submerged arc press welding.

[0010]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, and the gist thereof is as follows. (1) In a state where the periphery of the welding gap between the end portion of the steel bar and the material to be welded is surrounded by the particulate flux, the end portion of the steel bar is heated and melted by an arc generated from the end portion of the steel bar to the material to be welded by energization. In a submerged arc press welding method in which a predetermined amount of a molten pool is generated on the surface of a material to be welded, and the end portion of the steel bar is pressed into the molten pool and welded, as a component of the steel bar, C: 0. 1-0.3%, Si: 0.1-0.4%, Mn: 0.5-2.0%, V: 0.05-0.3%, the balance being Fe and inevitable impurities. And the total amount of P and S is regulated to 0.03% or less, and the C equivalent of the following formula satisfies 0.5 to 0.8. Submerged arc press welding method for high-strength rebar. C equivalent (%) = [% C] + [% Si] / 7 + [% Mn] / 5 +
[2] The submerged arc press of a high-strength rebar excellent in weld quality according to claim 1, wherein the yield strength of the steel bar is 390 MPa or more and the tensile strength is 560 MPa or more. Welding method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The high-strength rebar used in the submerged arc press welding method of the present invention has a high strength not lower than the level of SD390 rebar (yield point of 390 MPa or more, tensile strength of 560 MPa or more), and its components are as follows. Contains C, Si, Mn, and V, which are general component systems, without using special component elements from the viewpoint of economic efficiency. In order to ensure the quality of Pb, their contents and carbon equivalent, and further, the contents of P and S are defined as follows. In addition,% of the component content and C equivalent shown below.
Means mass%.

FIG. 3 shows the relationship between the carbon equivalent of a reinforcing steel base material and its yield point strength. As shown in FIG. 3, the strength of the rebar base material can be adjusted by the C equivalent of the rebar base material. For example, in order to obtain the yield strength 11 of the SD345 rebar according to the JIS standard, the C equivalent must be 0.5. In order to obtain the yield strength 12 of the SD390 rebar according to JIS,
By setting it to 0.6 or more, the strength of the reinforcing steel base material can be secured.

Here, the C equivalent of the present invention is defined by the following equation. C equivalent (%) = [% C] + [% Si] / 7 + [% Mn] / 5 +
[% V]

In the present invention, the C equivalent of the steel bar used for welding must be specified to be 0.5 or more in order to obtain the yield point strength of the SD390 rebar of 390 MPa or more in JIS standard.

Further, the inventors of the present invention have developed SD390 rebar (yield point of 390 MPa or more, tensile strength of 560 MPa or more).
As a result of a detailed study of the welded portion when a high-strength rebar of a level or higher was welded by the submerged arc press welding method, as shown in FIG. 2, the rebar end face of the weld metal 5 produced by heating and melting the rebar during welding. It is found that fine hot cracks are generated in the butt solidified portion 9 of the dendrite 10 generated from each of the steel plate side and the hot cracks are caused by the total amount of the impurity components P and S contained in the reinforcing steel base material. Was.

FIG. 4 shows the relationship between the C equivalent having a good correlation with the strength of the reinforcing steel base material and the total amount of P and S in the reinforcing steel base material as shown in FIG. The result of a tensile test is shown. When the total amount of P and S in the reinforcing steel base material exceeds 0.03% as shown in FIG. 4, fine hot cracks occur in the center of the weld metal as shown in FIG. It was found that the part broke. Further, when the C equivalent is 0.1.
With high-strength rebar exceeding 8%, fracture at the weld metal due to hot cracking does not occur, but brittle fracture from the weld heat-affected zone (HAZ) of the rebar base material occurs. Was. Based on the above findings, the present invention sets the total amount of P and S to 0.03% in order to prevent fine hot cracks from being generated in the central portion of the weld metal after the welding by the Boom-Age press and to prevent fracture from the central portion of the weld metal. % Or less.

Further, in the present invention, the lower limit of the C equivalent of the reinforcing steel base material component is set to 0.5% in order to obtain a reinforcing steel strength not lower than the SD390 reinforcing bar (yield point: 390 MPa or more) level from FIG. Heat affected zone (HAZ) of reinforcing steel base metal shown in Fig.
The upper limit of the C equivalent is specified to be 0.8 so as not to cause brittle fracture from.

The basic components of the present invention, C, Si,
The reasons for limiting Mn and V are as follows. C: C is a component for improving the strength. At a low C content of less than 0.1%, the strength of the reinforcing bar is insufficient, and at a C content of more than 0.3%, the toughness of the weld metal and the weld heat affected zone deteriorates. At the same time, hot cracking is likely to occur. Therefore, in the present invention, C
The content is 0.1% or more and 0.3% or less. From the viewpoints of hardening of the weld metal and prevention of hot cracking, the C content is preferably as low as possible.

Si: Si is added as a deoxidizing agent and a strengthening element, but if its content is less than 0.1%, its effect is not sufficient.
On the other hand, a large amount of Si becomes a defect at the time of pressure welding of the rebar. Therefore, the content is set to 0.1% or more and 0.4% or less.

Mn: Mn is a useful element for improving the strength of a reinforcing bar, but if its content is less than 0.5%, it has no effect.
%, The hardening of the weld metal and the occurrence of blowholes are promoted, so the content is made 0.5% or more and 2.0% or less.

V: V is a useful element for improving the strength of reinforcing steel, but if its content is less than 0.05%, its effect is not sufficient.
Since the addition of more than 0.3% promotes the hardening of the weld metal, its content is made 0.05% or more and 0.3% or less.

[0022]

EXAMPLES The effects of the present invention will be described below based on examples. The rebar was heated from a 150 mm square slab melted in a converter to 1150 ° C. and then hot rolled to a diameter of 32 mm (D
32). Table 1 shows the components of the rebar used in the examples. No. Nos. 1 and no. 2 is an example of the present invention, and corresponds to SD345 and SD390, respectively, and all components are within the scope of the present invention. In addition, no. 3-No. 5
Is a comparative example. 3 corresponds to SD390, and S
Examples in which the total amount of i, V, P and S is out of the range of the present invention;
No. No. 4 is an example in which the C content and C equivalent are lower than the range of the present invention. 5 is an example in which the C content and the C equivalent are higher than the range of the present invention.

[0023]

[Table 1]

A steel plate having a thickness of 22 mm and S
Submerged arc press welding to M490 material was performed.
The welding current was 1000 A and the welding time was 20 seconds. In addition, the powder flux surrounding the welded portion was the component shown in Table 2. Table 3 shows the results of the tensile tests of the welds of the present invention and comparative examples.

[0025]

[Table 2]

[0026]

[Table 3]

No. Although the reinforcing bar of No. 3 was able to secure the strength, in particular, since the total amount of P and S was high, a hot crack was generated at the center of the weld metal, and it was broken from the weld metal. No.
The reinforcing steel of No. 4 did not break from the weld metal part, but had insufficient strength due to a low C equivalent. No. 5 rebars
Since the C equivalent was high, it was broken from the weld heat affected zone of the reinforcing steel base material.

On the other hand, the reinforcing steel of the present invention has a standard strength of SD345 (yield point of 345 MPa, tensile strength of 490 MPa) or more and a standard strength of SD390 (yield point of 390 MPa).
a, tensile strength of 560 MPa) or more was satisfied, and the occurrence of hot cracking of the weld metal was prevented, and the fracture occurred from the reinforcing steel base material.

As described above, according to the present invention, in the submerged arc press welding, while maintaining the strength equal to or higher than the standard strength of SD345 (yield point: 345 MPa, tensile strength: 490 MPa), there is no occurrence of high-temperature cracking of the welded metal part and good Quality welds can be obtained.

[0030]

According to the present invention, in submerged arc press welding, the standard strength of SD345 (yield point 345) is used.
MPa, tensile strength of 490 MPa) or more, and it is possible to obtain a welded part of good quality without the occurrence of hot cracks in the welded metal part. It can sufficiently meet the needs for improving the reliability of reinforcing bars and welds.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of submerged arc press welding

FIG. 2 is a view showing a cross section of a submerged arc press welded part.

FIG. 3 is a diagram showing the relationship between the C equivalent of a reinforcing steel base material and the yield point strength.

FIG. 4 is a diagram showing a fracture state of a welded portion in reinforcing bars having different C equivalents and P and S amounts.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rebar 2 Welding arc 3 Powder flux 4 Flux holder 5 Molten metal generated by melting of rebar 6 Steel plate 7 Welding power source 8 Power cable 9 Butt solidification part 10 Growth direction of dendrite 11 Standard yield point of SD345 material 12 SD390 Standard yield point of material

Continued on the front page (72) Inventor Masakuni Wakabayashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Shigeki Terasaki 2-6-3 Otemachi, Chiyoda-ku, Tokyo New Japan Inside (72) Inventor Takashige Nagato 12 Nakamachi, Muroran-shi, Hokkaido F-term in Muroran Works, Nippon Steel Corporation (Reference) 4E001 AA03 BB05 BB12 CC04 EA10

Claims (2)

[Claims] An arc generated from the end of a steel bar to a material to be welded by energization while the periphery of a welding gap between the end of the steel bar and the material to be welded is surrounded by a particulate flux, and the end of the steel bar is heated and melted. After a predetermined amount of molten pool is formed on the surface of the material to be welded, the bar steel end is pushed into the molten pool and welded by a submerged arc press welding method. 0.1-0.3%, Si: 0.1-0.4%, Mn: 0.5-2.0%, V: 0.05-0.3%, the balance being Fe and inevitable Excellent in weld quality characterized by being composed of impurities and controlling the total amount of P and S to 0.03% or less, and satisfying the following equation, C equivalent of 0.5 to 0.8. Arc press welding method for high strength rebar. C equivalent (%) = [% C] + [% Si] / 7 + [% Mn] / 5 +
[% V] 2. The method according to claim 1, wherein the bar has a yield point strength of 390 MPa or more and a tensile strength of 560 MPa or more. .