JP2010184295A - Solid wire for welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid wire, even in the case welding operation conditions are relaxed, which can secure tensile strength and toughness of a weld metal. <P>SOLUTION: The solid wire for welding has a composition comprising, by mass, 0.02 to 0.12% C, 0.30 to 1.0% Si, 1.2 to 2.0% Mn and 0.05 to 0.30% Ti, respectively, and further comprising one or more selected from the group composed of 0.2 to 2.5% Cu and/or 0.5 to 3.5% Ni, ≤1.0% (excluding 0%) Cr and/or 0.5 to 1.5% Mo, 0.0005 to 0.020% Mg, ≤0.0020% (excluding 0%) Ca, ≤0.050% (not including 0%) Al and ≤0.2% (excluding 0%) Zr, and the balance iron with inevitable impurities; wherein, X value expressed by formula (1) satisfies 4.5≤X≤6.0: X=2.5×[Mn]+5×[Ti]+50×[Mg]-100×[Ca]-30×[Al]+2.5×[Zr]...(1). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid wire for welding, for example, a solid wire used for gas shielded arc welding.

Gas shield arc welding is widely used in the field of steel sheet welding in the manufacturing process of buildings, shipbuilding, automobiles, and the like. Particularly in the field of building steel frames, carbon dioxide shielded arc welding using CO ₂ as a shielding gas is often used from the viewpoint of economy. On the other hand, in recent years, the application of high-strength steel is expanding from the viewpoint of improving earthquake resistance, and the demand for joining high-strength steel by carbon dioxide shielded arc welding is increasing.

  Non-Patent Document 1 discloses an example in which a 780 MPa class high-strength steel for building structure is subjected to carbon dioxide shielded arc welding. According to Non-Patent Document 1, when welding high strength steel of 780 MPa class, it is necessary to strictly manage the heat input and interpass temperature below a certain level in order to ensure a certain level of tensile strength of the weld metal. The effect is described. However, when performing on-site welding with low heat input and inter-pass temperature (hereinafter, these may be collectively referred to as “construction conditions”), there may be an excessive number of passes, resulting in poor fusion. Inconveniences such as reduced construction efficiency occur. Therefore, it is important to ensure the tensile strength of the weld metal even when the enforcement conditions are relaxed.

  On the other hand, since the tensile strength and toughness of the weld metal are generally in a trade-off relationship, increasing the tensile strength of the weld metal decreases the toughness.

  That is, there is a demand for the development of a solid wire that can ensure the tensile strength of weld metal and further ensure toughness even when the welding conditions are relaxed.

For example, Patent Document 1 discloses a solid wire for welding high-strength steel of 900 MPa or more that ensures the strength and toughness of a weld metal, but uses Ar—CO ₂ as a shielding gas, and is a carbon dioxide shielded arc. It is not welded.

  Patent Documents 2 and 3 disclose solid wires that can ensure the strength and toughness of the weld metal even when large heat input and high interpass temperature are used in carbon dioxide shielded arc welding. The solid wire of Patent Document 2 is a solid wire for high strength steel of 590 MPa class that contains B and the balance of various components is adjusted. Such a B-added solid wire is a solid wire for high strength steel of 780 MPa class. When applied as a wire, hot cracking occurs. Further, Patent Document 3 discloses a 490 to 780 MPa class high-strength steel solid wire, but as with Patent Document 2, B is presupposed, and a problem of hot cracking occurs.

“2nd Yoshimoto Building”, Steel Construction Technology, June 2004, p. 56-65

JP 2007-260697 A JP 2004-237333 A JP 2007-260697 A

  The present invention has been made in view of such problems of the prior art, and its purpose is to ease welding conditions such as heat input and interpass temperature when carbon dioxide shielded arc welding of 780 MPa class high strength steel. Even if it is a case, it is providing the solid wire which can ensure the tensile strength and toughness of a weld metal.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, while appropriately controlling the composition of the various components of the solid wire and appropriately controlling the balance of the contents of the six elements Mn, Ti, Mg, Ca, Al and Zr that affect the formation of oxides The present inventors have found that a weld metal excellent in tensile strength and toughness can be obtained even when the welding conditions are relaxed, and the present invention has been completed.

That is, the welding solid wire according to the present invention that has solved the above-mentioned object is C: 0.02 to 0.12% (meaning mass%, the same applies hereinafter), Si: 0.30 to 1. 0%, Mn: 1.2 to 2.0%, Ti: 0.05 to 0.30%, respectively, and Cu: 0.2 to 2.5% and / or Ni: 0.5 to 3.5%, Cr: 1.0% or less (excluding 0%) and / or Mo: 0.5-1.5%, Mg: 0.0005-0.020%, Ca: 0.0020% 1 (one or more) selected from the group consisting of the following (not including 0%), Al: not exceeding 0.050% (not including 0%), and Zr: not exceeding 0.2% (not including 0%) The balance is iron and inevitable impurities, and the X value represented by the following formula (1) satisfies 4.5 ≦ X ≦ 6.0. It is what.
X = 2.5 × [Mn] + 5 × [Ti] + 50 × [Mg] −100 × [Ca] −30 × [Al] + 2.5 × [Zr] (1)
(However, [Mn], [Ti], [Mg], [Ca], [Al], and [Zr] represent the contents (mass%) of Mn, Ti, Mg, Ca, Al, and Zr, respectively. )

  The solid wire according to the present invention may further contain Nb: 0.012% or less (not including 0%) and / or V: 0.010% or less (not including 0%).

  According to the solid wire for welding according to the present invention, various component compositions are appropriately controlled, and the balance of the contents of Mn, Ti, Mg, Ca, Al, and Zr affecting the formation of oxides is within an appropriate range. Because it is controlled, the strength and toughness of the weld metal is ensured even when the welding conditions such as heat input and interpass temperature are relaxed (that is, the heat input is increased and the interpass temperature is increased). be able to.

FIG. 1A is a schematic diagram showing the groove shape of the steel sheet, and FIG. 1B is a schematic diagram showing the number of weld layers and the number of passes. FIG. 2A is a schematic diagram showing the sampling position of the weld metal tensile test piece, and FIG. 2B is a schematic diagram showing the sampling position of the Charpy impact test piece of weld metal.

  The solid wire according to the present invention is characterized in that various component compositions are appropriately controlled and the balance of the contents of Mn, Ti, Mg, Ca, Al, and Zr is controlled within a certain range. Hereinafter, it demonstrates in order.

  First, the chemical components of the solid wire of the present invention will be described.

[C: 0.02 to 0.12%]
C is an element effective for ensuring the strength of the weld metal. Therefore, the C amount is set to 0.02% or more. The amount of C is preferably 0.03% or more, and more preferably 0.05% or more. On the other hand, when the amount of C is excessive, hard structures such as martensite are increased in the weld metal, and the toughness is deteriorated. Therefore, the C amount is set to 0.12% or less. The amount of C is preferably 0.1% or less, and more preferably 0.09% or less.

[Si: 0.30 to 1.0%]
Si is a deoxidizing element and has a function of cleaning the weld metal. Further, when the yield is in the weld metal, the weld metal is strengthened by solid solution strengthening. Therefore, the amount of Si is set to 0.30% or more. The amount of Si is preferably 0.5% or more, and more preferably 0.6% or more. On the other hand, when the amount of Si is excessive, the strength of the weld metal is excessively increased or a hard structure such as martensite is generated, resulting in deterioration of toughness. Therefore, the Si amount is determined to be 1.0% or less. The amount of Si is preferably 0.8% or less, and more preferably 0.7% or less.

[Mn: 1.2 to 2.0%]
Mn is a deoxidizing element and has a function of cleaning the weld metal. Further, when Mn yields in the weld metal, the strength and toughness of the weld metal can be ensured by refining the structure of the weld metal. Therefore, the amount of Mn is set to 1.2% or more. The amount of Mn is preferably 1.5% or more, more preferably 1.6% or more. On the other hand, if the amount of Mn is excessive, the hardenability is improved and the strength is excessively increased, or the toughness is deteriorated due to segregation of Mn to form a hard structure such as martensite. Therefore, the amount of Mn is set to 2.0% or less. The amount of Mn is preferably 1.9% or less, more preferably 1.8% or less.

[Ti: 0.05-0.30%]
Ti is a deoxidizing element, cleans the weld metal, and also functions as a microstructure nuclei called acicular ferrite, and thus contributes to refinement of the structure. Therefore, the Ti amount is set to 0.05% or more. The amount of Ti is preferably 0.07% or more, and more preferably 0.1% or more. On the other hand, when the amount of Ti becomes excessive, toughness deteriorates due to precipitation strengthening of TiC. Therefore, the amount of Ti is set to 0.30% or less. The amount of Ti is preferably 0.28% or less, and more preferably 0.25% or less.

[Cu: 0.2 to 2.5% and / or Ni: 0.5 to 3.5%]
Cu and Ni are effective elements for ensuring the strength and toughness of the weld metal. Therefore, the Cu amount is set to 0.2% or more, and the Ni amount is set to 0.5% or more. The amount of Ni is preferably 1.0% or more, and more preferably 1.5% or more. On the other hand, when the amount of Cu or Ni is excessive, the hardenability is improved and the strength is excessively increased, so that the toughness is deteriorated. Therefore, the Cu amount is set to 2.5% or less, and the Ni amount is set to 3.5% or less. The amount of Cu is preferably 2.3% or less, more preferably 2% or less. The amount of Ni is preferably 2.5% or less, more preferably 2.2% or less.

[Cr: 1.0% or less (not including 0%) and / or Mo: 0.5 to 1.5%]
Cr and Mo are effective elements for ensuring the strength of the weld metal. In order to effectively exhibit such an effect, the Cr content is preferably 0.1% or more (more preferably 0.15% or more). Further, the Mo amount was determined to be 0.5% or more. The amount of Mo is preferably 0.6% or more, and more preferably 0.7% or more. On the other hand, when the amount of Cr or Mo is excessive, the hardenability is improved and the strength is excessively increased, so that the toughness is deteriorated. Therefore, the Cr content is set to 1.0% or less and the Mo content is set to 1.5% or less. The amount of Cr is preferably 0.8% or less, and more preferably 0.6% or less. The amount of Mo is preferably 1.0% or less, and more preferably 0.8% or less.

[Mg: 0.0005 to 0.020%, Ca: 0.0020% or less (not including 0%), Al: 0.050% or less (not including 0%), and Zr: 0.2% or less ( 1 or more selected from the group consisting of:
Mg, Ca, Al, and Zr are all strong deoxidizing elements and have the effect of cleaning the deposited metal by deoxidation. In order to effectively exhibit such an effect, the Mg content is set to 0.0005% or more. The Ca content is preferably 0.0005% or more (more preferably 0.0008% or more), the Al content is preferably 0.003% or more, and the Zr content is 0.03% or more. preferable. On the other hand, when the amount of Ca is excessive, spatter increases and workability is remarkably deteriorated. The Ca content is preferably 0.0018% or less, more preferably 0.0017% or less. Moreover, although Mg has the effect of refining the oxide as will be described later, when the amount of Mg is excessive, the fine oxide aggregates to form a coarse oxide. Therefore, the Mg content is set to 0.020% or less. The amount of Mg is preferably 0.018% or less, more preferably 0.015% or less. Since Al is an element that easily forms a coarse oxide as will be described later, the Al content is determined to be 0.050% or less. The amount of Al is preferably 0.045% or less, and more preferably 0.043% or less. If the amount of Zr is excessive, coarse carbides are formed and the toughness is lowered.

  The basic components of the solid wire according to the present invention are as described above, and the balance is substantially iron. However, it is naturally allowed that unavoidable impurities (for example, P, S, N) brought in depending on the situation of raw materials, materials, manufacturing equipment, etc. are included in the wire. Furthermore, the solid wire according to the present invention may contain the following optional elements as necessary.

[Nb: 0.012% or less (not including 0%) and / or V: 0.010% or less (not including 0%)]
Nb and V have the effect of improving the strength of the weld metal by refining the structure, but when Nb and V carbides precipitate, the ductility deteriorates and the toughness is prevented from being improved. It is also preferable to limit as much as possible. Therefore, the Nb amount is preferably 0.012% or less (more preferably 0.005% or less), and the V amount is preferably 0.010% or less (more preferably 0.005% or less). In particular, from the viewpoint of improving toughness, it is preferable not to contain Nb and V.

  Since the solid wire of the present invention has a controlled chemical composition as described above, it is possible to ensure a sufficient tensile strength of the weld metal even when the welding conditions are relaxed.

  On the other hand, the toughness of the weld metal is generally influenced by the microstructure of the weld metal, but particularly for high-tensile steels of 780 MPa class or higher, in addition to the influence of the microstructure, it is largely controlled by the oxide form. It becomes like this. This is because the oxide acts as a starting point for voids. In order to improve the toughness of the weld metal, it is effective to finely disperse the oxide in the weld metal, but the present inventors have included six elements of Mn, Ti, Mg, Ca, Al, and Zr. Has been found to greatly affect the fine dispersion of oxides.

More specifically, by controlling the contents of Mn, Ti, Mg, Ca, Al and Zr so that the X value represented by the following formula (1) is 4.5 ≦ X ≦ 6.0. The toughness of the weld metal can be improved.
X = 2.5 × [Mn] + 5 × [Ti] + 50 × [Mg] −100 × [Ca] −30 × [Al] + 2.5 × [Zr] (1)
(However, [Mn], [Ti], [Mg], [Ca], [Al], and [Zr] represent the contents (mass%) of Mn, Ti, Mg, Ca, Al, and Zr, respectively. )

  The size of the oxide in the weld metal is (i) the temperature at which the oxide begins to form, (ii) the deoxidizing power of the element that forms the oxide, and (iii) the wettability of the formed oxide and molten steel, Determined by etc. The coefficients multiplied by Mn, Ti, Mg, Ca, Al and Zr in the above formula (1) are calculated from a number of basic experiments, and each element including all the factors (i) to (iii) It reflects the effect on oxide size.

  The oxide in the present invention means that it may contain a small amount of Si oxide in addition to a single oxide of Mn, Ti, Mg, Ca, Al, or Zr, and also includes an oxide in which these oxides are combined. It is.

  When the X value given by the above equation (1) is less than 4.5, the number of oxides is small, but the size becomes coarse. When it exceeds 6.0, the number of oxides becomes small. It shows a tendency to increase. In the above equation (1), Mn, Ti, Mg and Zr are multiplied by positive coefficients, and Ca and Al are multiplied by negative coefficients. That is, Mn, Ti, Mg, and Zr have the effect of reducing the size of the oxide, but if the content is excessive, the number of oxides increases. On the other hand, Ca and Al have the effect of coarsening the oxide.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  Wires having the chemical composition shown in Tables 1 and 2 were prepared (wire diameter: 1.2 mm) and shown in FIG. 1 (FIG. 1 (a) represents before welding, and FIG. 1 (b) represents after welding). The groove-shaped steel plate was welded under the following welding conditions. In Tables 1 and 2, only the amount of N in the inevitable impurities is shown.

[Welding conditions]
Current: 280A
Voltage: 35V
Welding speed: 25 cm / min
Heat input: 24 kJ / cm
Preheating temperature and interpass temperature: 250 ° C
Number of layers / number of passes: 5 layers / 10 passes Shield gas: 100% CO ₂
Base material steel plate: HT780

[Tensile test of weld metal]
From the position shown in FIG. 2A, a No. 1A test piece defined in JIS Z2201 was sampled, and a tensile test of the weld metal was performed according to JIS Z2241. The tensile strength of the weld metal was 780 MPa or more.

[Charpy impact test of weld metal]
A test piece having a size of 10 mm × 10 mm × 55 mm defined in JIS Z2242 was taken from the position shown in FIG. 2B, and Charpy absorbed energy (vE ₀ ) at 0 ° C. was determined according to JIS Z2242. A sample having a vE ₀ of 70 J or more was accepted.

  The results are shown in Tables 3 and 4.

  Steel types 1 to 17 satisfy the ranges specified in the present invention for the chemical composition and X value of the wire, and ensure the tensile strength and toughness of the weld metal even under the construction conditions of heat input: 24 kJ / cm and interpass temperature: 250 ° C. It was possible.

  On the other hand, since the steel types 18 to 30 are out of the range defined in the present invention by either the chemical component or the X value, the toughness of the weld metal is lowered.

  Steel type 31 is an example in which cracking occurred because B was added although tensile strength and toughness were good. Furthermore, steel type 32 is an example in which although the tensile strength was good, the amount of Zr was excessive and the toughness was lowered.

Claims (2)

C: 0.02 to 0.12% (meaning mass%, hereinafter the same),
Si: 0.30 to 1.0%,
Mn: 1.2 to 2.0%,
Ti: each containing 0.05 to 0.30%,
Cu: 0.2-2.5% and / or Ni: 0.5-3.5%,
Cr: 1.0% or less (excluding 0%) and / or Mo: 0.5-1.5%
Mg: 0.0005 to 0.020%, Ca: 0.0020% or less (not including 0%), Al: 0.050% or less (not including 0%), and Zr: 0.2% or less (0 Containing at least one selected from the group consisting of: and the balance being iron and inevitable impurities,
An X value represented by the following formula (1) satisfies 4.5 ≦ X ≦ 6.0.
X = 2.5 × [Mn] + 5 × [Ti] + 50 × [Mg] −100 × [Ca] −30 × [Al] + 2.5 × [Zr] (1)
(However, [Mn], [Ti], [Mg], [Ca], [Al], and [Zr] represent the contents (mass%) of Mn, Ti, Mg, Ca, Al, and Zr, respectively. ) Furthermore,
2. The solid wire for welding according to claim 1, containing Nb: 0.012% or less (excluding 0%) and / or V: 0.010% or less (excluding 0%).

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