JP2008200751A - Wire for electroslag welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wire for electroslag welding suitable for welding of a building box column for which tenacity of a weld zone is required. <P>SOLUTION: A steel jacket or a jacket and a metal powder contain by mass% 0.002-0.1% C, 0.02-1.5% Si, 1.5-3.0% Mn, 0.01-0.10% Al, 0.05-0.28% Ti, 0.2-1.2% Mo, and 0.002-0.008% N, and B satisfying the expression, 0.006<[B]-[N]<0.01 provided [B] and [N] are contents (mass%), desirably containing 0.0090-0.016% B, and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electroslag welding wire, and more particularly to a wire suitable for welding of a box box for construction that requires toughness of a welded portion.

Box columns used in high-rise buildings are manufactured by welding skin plate corner joints, diaphragms, and skin plates. Large heat input submerged arc welding is used for corner joints, and the welds of diaphragms and skin plates are both In general, electroslag welding is used because the groove is formed in a vertical hole shape by the gold.

  Electroslag welding is a method in which a welding wire is supplied to a groove with a closed cross section formed in the vertical direction, melted by resistance heating to form a weld metal, and welded in one pass. Use as a heat source.

  In this welding, in order to secure the toughness of the welded part, a welding wire containing a large amount of alloy elements and a long nozzle are used to supply the wire to the bottom of the groove. There is a non-consumable nozzle type method in which the water-cooled nozzle is raised, and most recent electroslag welding of box columns is performed by a non-consumable nozzle type.

  On the other hand, with regard to the performance of construction steel welds, the Charpy absorbed energy of 70 J at a test temperature of 0 ° C is determined based on the results of a joint review of the MLIT / Steel Federation from the review of required toughness for steel joints triggered by the Great Hanshin Earthquake. Guidelines have been obtained.

Since the same toughness is also required for the welded portion of the box column, various welding wires for electroslag welding have been proposed for the purpose of improving the toughness of the weld metal (for example, Patent Document 1, Patent Document 2, Patent Document 3).
JP 2002-79396 A Japanese Patent Laid-Open No. 2003-340592 JP 2005-324239 A

  In electroslag welding, the groove melts due to heat transfer from the molten metal, so to ensure melting to the corner of the groove, the welding speed can be suppressed or the welding voltage can be set high to melt the groove deeply. Necessary, the welding heat input is very large, and the weld metal has a coarse grain structure.

  When controlling the weld metal structure to improve the toughness of electroslag weld metal, there are the following approaches.

  1. Addition of Ni, Mo and the like enhances the hardenability of the weld metal to form a fine bainite structure. 2. A fine ferrite structure is ensured by ensuring adequate hardenability by adding Mo and suppressing the formation of coarse grain boundary ferrite by adding B.

  In the former case, since the added amount of the welding wire alloy component is increased, the cost of the alloy component is expensive, and the strength of the weld metal is too high. In the latter B-added type welding wire, the alloy component is less than the former. Although it is economical, it has been pointed out that a wire containing a large amount of B has a remarkably low yield due to the occurrence of cracks during the production of the material, resulting in an increase in production cost.

  Therefore, an object of the present invention is to provide an economically excellent electroslag welding wire from which a weld metal having high toughness can be obtained stably.

  The present inventors have made various studies on the relationship between the chemical composition and toughness of the weld metal by electroslag welding in consideration of changes in the weld line direction, and obtained the following knowledge.

  1) The B content in the weld metal using the B-added welding wire increases on the welding start side due to the addition of B to the flux, but when the equilibrium state is reached, it is determined by the melting ratio and content of the base material and the wire.

  2) Other elements are determined by the melting ratio of the base material and the wire, and the content of the elements, excluding oxygen supplied from the flux.

  3) When generally used flux for electroslag welding is used, in order to obtain good weld metal toughness, the B content of the weld metal has an appropriate range in proportion to the N amount.

  4) The welding metal dilution ratio in the electroslag welds of the box column diaphragm and skin plate needs to melt the groove to some extent in order to secure the penetration width, but the mechanical properties are lower when the welding heat input is lower. However, it is also economical and the practical range is limited.

The present invention has been made based on these findings and further studies.
That is, the present invention
1. In mass%, C: 0.002-0.1%, Si: 0.02-1.5%, Mn: 1.5-3.0%, Al: 0.01-0.10%, Ti: 0.05 to 0.28%, Mo: 0.2 to 1.2%, N: 0.002 to 0.008%, and B satisfying the following formula, the balance Fe and the amount of unavoidable impurities Wire for electroslag welding containing metal powder.
0.006 <[B]-[N] <0.01
However, [B] and [N] are contents (mass%).
2. 2. The metal powder-containing electroslag welding wire according to 1, wherein the steel outer shell is filled with metal powder and contains B: 0.0090 to less than 0.016% by mass%.
3. A solid wire for electroslag welding having the chemical component according to 3.1 or 2.

  According to the present invention, an inexpensive electroslag welding wire from which high-toughness weld metal can be obtained stably is obtained, which is extremely useful industrially.

  The reason for limiting the chemical components of the electroslag welding wire of the present invention will be described below. In addition, the content of the chemical component described below is mass% with respect to the total mass of the wire, and in the case of a wire containing metal powder (a so-called coiled cored wire produced by winding an alloy powder in a steel outer sheath). In the case of a solid wire, the mass% is based on the total mass of the solid wire and the total mass of the solid wire.

C
C is an element necessary for ensuring the strength of the weld metal, but it is difficult to ensure the strength if it is less than 0.002%, while the toughness of the weld metal tends to deteriorate if it exceeds 0.1%, 0.002 to 0.1%.

Si
Si is an element necessary for deoxidizing the weld metal, but if less than 0.02%, the effect cannot be expected. If it exceeds 1.5%, there is a tendency to deteriorate the toughness of the weld metal.

Mn
Mn is an element necessary for ensuring the strength and toughness of the weld metal, but if it is less than 1.5%, it is difficult to ensure the strength, which is not preferable from the viewpoint of ensuring toughness. On the other hand, if it exceeds 3.0%, it becomes excessive in the weld metal, and on the contrary, there is a dislike to deteriorate toughness.

Al
Al is an element effective for deoxidation of the weld metal, but if less than 0.01%, the effect cannot be expected, but if it exceeds 0.10%, there is a tendency to deteriorate the toughness of the weld metal. 0.01 to 0.10%.

Mo
Mo is an effective element for improving the strength of weld metal and improving the toughness by refining the microstructure. However, if it is less than 0.2%, the effect is poor, and if it exceeds 1.2%, the weld metal is quenched. Since there is a tendency that the toughness becomes excessive and the toughness is deteriorated, it is not preferable.

Ti
Ti is an element necessary for obtaining high toughness because deoxidation of the weld metal to ensure the effect of B and its oxynitride contributes to the refinement of the structure, but less than 0.05% The effect is insufficient. On the other hand, if it exceeds 0.28%, it is excessively contained in the weld metal, and on the contrary, the toughness is deteriorated, so 0.05 to 0.28%.

N
N is desirably originally low from the viewpoint of securing toughness in order to inhibit the effect of B, which suppresses the formation of coarse ferrite formed at the prior γ grain boundaries of the weld metal, but currently a structure that requires high toughness. The N content of steel materials applied to objects is generally in the range of 0.002 to 0.008%.

  In order to balance the N amount of the wire with the B amount necessary for obtaining high toughness, it is preferable that the N content is close to the content of the base material in order to suppress variation. Therefore, if it is less than 0.002%, it is too low with respect to the base metal, and if it exceeds 0.008%, it is too high, so the amount of N in the weld metal changes due to the change in the base metal dilution, and stable weld metal toughness is obtained. Since it is difficult, 0.002 to 0.008%.

0.006 <[B]-[N] <0.01
This parameter formula is used to contain B, which is an effective element for improving the toughness by refining the microstructure of the weld metal, without excess or deficiency in the amount of oxygen and nitrogen in the weld metal. Is obtained in consideration of dilution of a relatively low N steel sheet (skin plate, web) used for an electroslag welded portion and a relatively high N steel sheet used for a backing metal.

  In order to optimally adjust the balance with N contained in the steel sheet by the amount of B added from the wire, the amount of ([B]-[N]) contained in the wire is not good if it is 0.006% or less. It is sufficient and good toughness cannot be obtained.

  On the other hand, if it exceeds 0.01%, B is excessive and the toughness is deteriorated. The amount of B in the wire must be 0.006% or more excess with respect to the amount of N. Therefore, in the case of the wire having the amount of B in the wire of less than 0.009%, the amount of N is less than 0.003%. Production becomes difficult.

  On the other hand, if the amount of B in the wire is 0.016%, the amount of B in the weld metal decreases and there is a concern about the occurrence of cracks. For this reason, the amount of B in the wire is preferably 0.009 to less than 0.016%.

  A specimen having a groove portion shown in FIG. 1 simulating a joint between a box column skin plate and a diaphragm is welded by non-consumable nozzle type electroslag welding using wires containing metal powder of various chemical components. The strength and toughness of the metal were investigated. The total length of the test body was 500 mm.

  In FIG. 1, 1 is a skin plate (PL1), 2 is an award (BP), 3 is a diaphragm (PL2), and Table 1 shows the thickness and chemical composition of the steel plates used for each.

  The welding conditions for electroslag welding were welding current: 380 A, welding voltage: 50 V, wire feed speed: 8.5 m / min, welding speed: 2.4 cm / min.

  FIG. 2 is a diagram for schematically explaining the sampling position and the notch position of the Charpy test piece from the obtained joint, where 4 is the weld metal (WM), 5 is the Charpy test piece, and 6 is the notch position of the Charpy test piece. The Charpy test piece 5 was sampled in a direction perpendicular to the skin plate 1 from about 1/2 of the weld length: 500 mm, and the notch position 6 was the center of the weld metal (WM4) on the upper surface side of the test body. . The tensile strength of WM5 (welded metal) was obtained from an A1 test piece (JISZ3111) collected from the upper side of the Charpy test collection position.

  Table 2 summarizes the chemical components and results of metal powder-containing wires. When the wires (symbols 1 to 4) according to the present invention are used, a weld metal with a good toughness having a Charpy absorbed energy (test temperature 0 ° C.) of 70 J or more is obtained, and the amount of B in the wire is particularly in a suitable range. In some (symbols 1 to 3), particularly excellent toughness was obtained. The tensile strength was 500 to 600 MPa class, and it was confirmed that a joint having sufficient strength as a building member was obtained.

  On the other hand, in the comparative examples (wire symbols 5 to 8), the wire composition is out of the proper range, so that the weld metal has poor toughness and is insufficient for use in a welded joint that requires high toughness.

The schematic diagram explaining the groove part for electroslag welding used for the Example. The figure explaining the collection position of the Charpy test piece from a joint part.

Explanation of symbols

1 Skin plate (PL1)
2 Money (BP)
3 Diaphragm (PL2)
4 Weld metal (WM)
5 Charpy specimen 6 Notch position of Charpy specimen

Claims (3)

In mass%, C: 0.002-0.1%, Si: 0.02-1.5%, Mn: 1.5-3.0%, Al: 0.01-0.10%, Ti: 0.05 to 0.28%, Mo: 0.2 to 1.2%, N: 0.002 to 0.008%, and B satisfying the following formula, the balance Fe and the amount of unavoidable impurities Wire for electroslag welding containing metal powder.
0.006 <[B]-[N] <0.01
However, [B] and [N] are contents (mass%).   The wire for electroslag welding containing metal powder according to claim 1, which is formed by filling a steel outer shell containing metal powder containing B: less than 0.0090 to 0.016% by mass%.   A solid wire for electroslag welding having the chemical component according to claim 1.

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