JP2009028765A - Weld metal and titania-based flux cored wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titania-based flux cored wire capable of forming weld metal having high temperature cracking resistance equivalent or higher than that of solid wire, and obtaining this weld metal at high welding workability (all position welding). <P>SOLUTION: The weld metal formed by the titania-based flux cored wire comprises, by mass, ≥0.029% C, and B, C, Mn, N, P, S, Si and Ti in such an amount, based on the total mass% of the weld metal that when they are respectively represented by [B], [C], [Mn], [N], [P], [S], [Si] and [Ti], the solidus temperature Ts defined by the following expression becomes ≥1,355°C, Ts=1,538-8,903×[B]-982×[C]-6.64×[Mn]-511×[N]-368×[P]-3,603×[S]-47.0×[Si]-205×[Ti]-17. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a weld metal welded with a TiO ₂ (titania) flux-cored wire (hereinafter referred to as FCW: Flux Cored Wire) and the titania flux-cored wire. It is related with the technology which improves to the same level or more.

  In the field of manufacturing large-scale welded structures such as shipbuilding and bridges, in order to improve the efficiency of welding, when welding butt joints composed of medium-thick steel plates, the joints are narrowed while 1 In order to increase the amount of welding per pass and complete welding with as few passes as possible, such as 1 to 3 passes, a high-efficiency welding method is adopted, where construction is performed with a small heat input by gas shield arc welding. Yes. In such a high-efficiency welding method, FCW, which has a higher welding speed than a solid wire, is frequently used as a welding wire.

  This titania-based FCW for all positions can be welded in all positions with one wire, and also has features such as good welding workability, high efficiency, and good weld metal performance (Patent Document 1). ).

  However, as one of the disadvantages of the titania FCW, the titania FCW is inferior to the solid wire in hot crack resistance, particularly hot crack resistance when welding the groove first layer portion and the narrow portion. A point is mentioned. Under such circumstances, research has been conducted on improving the hot cracking performance of weld metal (for example, Non-Patent Document 1). In the publication of Non-Patent Document 1, it is described that elements such as P, S, and B significantly deteriorate hot cracking resistance, and that addition of Mn is effective for preventing this hot cracking. Has been. These elements such as P, S, and B aggregate in the final solidified portion when the weld metal solidifies to form a low-melting eutectic. This eutectic portion remains in a molten state, and is presumed to undergo solidification shrinkage from the surroundings and generate cracks after completion of solidification.

  On the other hand, in Patent Document 2, compositional supercooling due to Nb addition to the weld metal and equiaxed crystallization of columnar crystals at the center of the weld metal due to the combined effect of the nucleation catalytic effect due to the addition of Al and Ti. The crack is suppressed.

JP 2002-137090 A JP 2004-358552 A Journal of the Japan Welding Society, Vol. 49 (1980), No. 1, pages 19 to 23 and Vol. 44 (1975), No. 7, pages 20 to 25, etc. Metal materials, vol. 17, NO. 7, pages 18-24

  However, as described above, the titania-based FCW disclosed in Non-Patent Document 1 does not satisfy the recent requirements for the high temperature crack resistance of the titania-based flux-cored wire. Recently, as hot cracking resistance, specifically, hot cracking resistance equivalent to that of solid wire is required.

  Further, in Patent Document 2, Al is excessively added, and such excessive Al addition is not desirable because it causes a decrease in the ductility of the weld metal.

  As described above, there is no conventional titania FCW having good workability and high-temperature crack resistance at a solid wire level.

  The present invention has been made in view of such problems, and is capable of obtaining a weld metal having a high temperature crack resistance equivalent to or higher than that of a solid wire, and obtaining this weld metal with high welding workability (all-position welding). An object of the present invention is to provide a titania-based flux-cored wire.

  The weld metal according to the present invention is a weld metal welded with a titania-based flux-cored wire, and the content of C is 0.029 mass% or more, and is mass% with respect to the total mass of the weld metal. B, C, Mn, N , P, S, Si, Ti content is [B], [C], [Mn], [N], [P], [S], [Si], [Ti] The solid phase temperature Ts defined by 1 is 1355 ° C. or higher, and each component is contained.

  The weld metal according to the present invention has B: 0.005 mass% or less (excluding 0), N: 0.0045 to 0.02 mass%, Ti: 0.025 to 0.1 mass%, Mn: 1 0.0 to 1.7% by mass, Si: 0.2 to 0.7% by mass, C: 0.05 to 0.09% by mass, and O: 0.05 to 0.09% by mass, It contains at least one element selected from the group consisting of Cu, Ni, Cr, Mo, Al, Nb, and V in an amount of 0.5% by mass or less (excluding 0), with the balance being Fe and inevitable impurities. It is preferable to have a composition.

A titania-based flux-cored wire according to the present invention is obtained by filling a steel outer shell with a flux, and using ordinary steel as a welding target, a titania-based wire for obtaining a weld metal according to any one of claims 1 to 3. a flux-cored wire, the wire total mass, N: 0.001 to 0.022 wt%, _TiO 2: 5 to 7 wt%, Mn: 2.30 to 3.75 wt%, and C: 0. The content of B, C, Mn, N, P, S, Si, Ti, and TiO ₂ is contained in the content (mass%) with respect to the total mass of the wire. ], [C], [Mn], [N], [P], [S], [Si], [Ti], [TiO ₂ ], the solidus temperature Ts defined by Equation 2 below. Each component is contained so that the temperature becomes 1355 ° C. or higher. .

  In this titania-based flux-cored wire, B: 0.0155 mass% or less (0 is not included), Si: 0.85 mass% or less (0 is not included), or Ti: 0.60 mass% or less ( 0 is not included).

  In the present invention, the hot cracking resistance of the weld metal can be improved by setting the solidus temperature calculated by Equation 1 based on the content of the weld metal component to 1355 ° C. or higher.

  According to the present invention, it is possible to obtain a weld metal having excellent hot cracking resistance, and as a titania-based flux cored wire for obtaining this weld metal, a flux cored wire having improved welding workability in all-position welding. Obtainable.

  Hereinafter, the present invention will be specifically described with reference to the accompanying drawings. First, the reasons for adding components and limiting the composition of the weld metal of the present invention will be described.

“B: 0.005% by mass or less (excluding 0)”
B is added as an element for improving the toughness of the weld metal part. However, if the content of B exceeds 0.005% by mass, the hot cracking resistance is inferior, so that it is 0.005% by mass or less. Is desirable.

“N: 0.0045 to 0.02 mass%”
N is an element that ensures the strength of the weld metal part. N has the effect of improving the hot cracking resistance by fixing B as BN. However, these effects are not sufficient when N is less than 0.0045% by mass. On the other hand, when N content exceeds 0.02 mass%, the toughness of a weld metal part will fall remarkably. For this reason, N is preferably 0.0045 to 0.02 mass%.

“Ti: 0.025 to 0.1% by mass”
Ti is added as a deoxidizer and for improving workability. However, when Ti is less than 0.025% by mass, the effect is not sufficient, and conversely, when Ti is contained in excess of 0.1% by mass, The toughness of the weld metal decreases. For this reason, Ti is preferably 0.025 to 0.1% by mass.

“Mn: 1.0 to 1.7% by mass”
Mn is added to adjust the mechanical properties of the deoxidizer and the weld metal, but if Mn is less than 1.0% by mass, the toughness (impact value) of the weld metal is low. Moreover, when Mn exceeds 1.7 mass%, the intensity | strength of a weld metal will become high too much. Therefore, the amount of Mn is preferably 1.0 to 1.7% by mass.

“Si: 0.2 to 0.7 mass%”
Si is added to adjust the fluidity of the deoxidizer and the weld metal to improve the fit of the weld bead. However, if Si is less than 0.2% by mass, the beads are likely to be convex beads, and blow holes (pores) due to insufficient deoxidation frequently occur. On the other hand, when Si exceeds 0.7 mass%, the strength of the weld metal becomes too high, and the toughness of the weld metal is remarkably lowered, and the hot crack resistance is deteriorated. Therefore, the Si amount is preferably 0.2 to 0.7% by mass.

“C: 0.029 mass% or more, preferably C: 0.05 to 0.09 mass%”
C is an element that increases the strength of the weld metal. For this reason, it is necessary to add 0.029% by mass or more. If C is less than 0.05% by mass, the desired strength cannot be obtained. On the other hand, if C exceeds 0.09% by mass, the toughness of the weld metal decreases, which is not desirable. For this reason, the amount of C is preferably 0.05 to 0.09 mass%.

“O: 0.05 to 0.09 mass%”
In general, oxygen in a steel material tends to lower toughness and malleability characteristics, and it is desirable that O be 0.09% by mass or less. On the other hand, by containing 0.05 mass% or more of oxygen in the weld metal, finely dispersed inclusions are formed and good toughness is obtained. From the above, the oxygen content is preferably 0.05 to 0.09 mass%.

“Ts ≦ 1355 ° C.”
In research on hot cracking performance of weld metal (for example, Non-Patent Document 2), the generation mechanism of hot cracking of weld metal is disclosed as follows. When the weld metal begins to solidify, there is a solidification brittle temperature region (BTR) with very low ductility during solidification, and in this temperature region (BTR) where the solid phase and the liquid phase coexist, the low melting point element is in the liquid phase. Segregation occurs, and cracks occur when the liquid phase region of the low melting point element that exists immediately before the completion of solidification cannot resist the shrinkage strain. Therefore, it is considered effective to reduce the solidification brittle temperature region (BTR) as a method for suppressing hot cracking.

  However, as a result of experimental research by the present inventors, in the method of estimating the melting point of the liquid phase from the composition of the weld metal part, the melting point of the liquid phase in the solidified part where hot cracking actually occurs is accurately determined from the influence of segregation and the like. It was found that it cannot be evaluated. As a result, an accurate hot cracking suppression index has not been obtained, and a welding wire with improved hot cracking resistance has not been developed. Therefore, the present inventor conducted various experiments to improve the hot crack resistance of the first layer bead in gas shielded arc welding with a large heat input with a small pass like a butt joint, and also cooled the weld metal part. As a result of calculating the segregation degree of the weld metal component in consideration of the speed and diffusion of the weld metal component, the distribution of the component between the solid phase and the liquid phase, and the solidification form of the columnar crystal of the weld metal, the equation 1 is defined. It was found that the parameter Ts (solidus temperature) is a parameter that affects the hot cracking resistance of the first layer bead. As a result of various experiments based on this parameter Ts, it was found that controlling Ts to a range of 1355 ° C. or higher is extremely effective in improving the hot crack resistance of the first layer bead. It was.

“Cu, Ni, Cr, Mo, Al, Nb, V: 0.5% by mass or less (excluding 0)”
In the present invention, in order to adjust the strength and toughness of the weld metal, at least one of Cu, Ni, Cr, Mo, Al, Nb, and V should be within a range of 0.5% by mass or less. For example, it may be contained because it does not affect the solidus temperature Ts.

“P: 0.015 mass% or less”
P is an impurity element, but if the P content exceeds 0.015% by mass, the hot cracking resistance is remarkably inferior, so P is preferably 0.015% by mass or less.

“S: 0.015 mass% or less”
S is an impurity element, but when the S content exceeds 0.015% by mass, the hot cracking resistance is remarkably inferior, so S is preferably 0.015% by mass or less.

Next, the titania-based flux cored wire according to the present invention will be described. This titania-based flux-cored wire has B: 0.0155 mass% or less (excluding 0), P: 0.025 mass% or less, S: 0.021 mass% or less, N: 0.002 to 0.022 mass%, Ti: 0 to 0.60 wt%, _TiO 2: 5 to 7 wt%, Mn: 2.30 to 3.75 wt%, Si: 0.85 wt% or less (0 is not included), C : It has a composition of 0.030 to 0.055 mass%. These wire compositions are determined in order to make the composition of the weld metal predetermined in consideration of the yield to the weld metal.

In the flux-cored wire, examples of the B source include Fe—B, Fe—Si—B, and B ₂ O ₃ . P and S are contained in the wire from impurities of the steel outer shell and the flux raw material. The N source is contained in the wire from the steel outer sheath, chromium nitride, titanium nitride, impurities of the flux raw material, and the like. Examples of the Ti source include metal Ti and Fe—Ti. Examples of TiO ₂ sources include rutile, calcium titanate, potassium titanate glass, and lucoxin. Incidentally, TiO ₂ is becomes lower than a lower limit value (5 wt%), degraded workability TatsuMuko, exceeds the upper limit value (7 wt%), there is a tendency that the oxygen content in the weld metal increases. Examples of the Mn source include Mn in the steel outer shell, metal Mn, Fe—Mn, and Fe—Si—Mn in the flux. Examples of the Si source include Si in the steel outer shell, Fe-Si, Fe-Si-Mb, Fe-Si-B, Fe-Si-Mg, and REM-Ca-Si in the flux. Examples of the C source include C in the steel outer shell, C simple substance in the flux, iron powder, and metal powder C.

Fe in the wire of the present invention is contained in an amount of 80% by mass or more, and the Fe source includes steel outer skin, iron powder, Fe in Fe alloy, and the like. The rest is composed of components other than the corresponding components of the raw materials used as the B, P, S, N, Ti, TiO ₂ , Mn, Si, and C sources, and metals Cu, Ni, Cr, Mo, Al, Nb, Inevitable impurities such as Mg, V, Ca, Zn and a slag forming agent are included. As the slag-forming _{agent, SiO 2, CaO, Na 2} O, ZrO 2, K 2 O, Al 2 O 3, Li 2 O, Bi 2 O 3, K 2 SiF 6, CaF 2, BaF 2, NaF , V ₂ O ₅ , FeO, Nb ₂ O ₅ , Cr ₂ O ₃ , Fe ₂ O ₃ , SnO ₂ , SrF ₂ , AlF ₃ , MgF ₂ , LiF, CaCO ₃ , MgCO ₃ , BaCO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , Sr ₂ CO _{3 and the} like. Moreover, the flux filling rate of the flux-cored wire is 10 to 20% by mass of the total mass of the wire.

  The base material to be welded is, for example, plain steel such as a rolled steel plate for welded structure (SM400B, SM490A) or a steel plate for shipbuilding (AH32, DH36). An example of the composition of these steel types is shown in Table 1 below.

  Next, the effects of the present invention will be described by comparing the characteristics of the examples of the present invention with comparative examples that depart from the scope of the present invention.

The welding conditions are as follows.
・ Welding posture: Downward ・ Shielding gas: 100 volume% CO ₂
・ Welding current: 240A
・ Welding voltage: 30V
-Welding speed: 375 mm / min-Wire diameter: 1.2 mm
・ Test steel plate: SM400B
・ Groove shape: 35 ° V groove ・ Gap gap = 4mm

  The welding speed of 375 mm / min is a target value, and in the actual welding test, a slight speed difference occurred. The welding speed in each example and comparative example is shown in Table 2-2. However, the variation in the welding speed as shown in Table 2-2 has a small effect on the test result. The steel type to be tested is SM400B steel (see Table 1 for composition).

  The compositions (mass%) of the weld metal obtained in this welding test are shown in Tables 2-1 and 2-2 below. Moreover, the composition of the used titania-based flux-cored wire is shown in Tables 3-1 and 3-2 below.

  FIG. 1 is a cross-sectional view showing a groove shape of a weld base material used for a hot crack resistance test. As shown in FIG. 1, the weld base material 1 has a V-shaped groove, and a refractory 2 as a backing material is disposed on the back surface of the V-shaped groove portion. The aluminum tape 3 is attached to the back surface of the base material 1. The groove angle of this V shape was set to 35 °, and the route interval of the portion where the backing material was arranged was set to 4 mm. Then, the welding current 240A, the rod method was straight, the number of repetitions was two, single-sided welding was performed, and the initial layer welding was checked for internal cracks in an X-ray transmission test (JISZ3104), and the total length was measured. The crack ratio is calculated by the crack ratio W = (total crack length) / (weld length) × 100.

  The results of the hot crack resistance in this welding test are shown in Tables 2-1 and 2-2. In the column of hot cracking resistance in Tables 2-1 and 2-2, the crack rate W is less than 5.0%, and the crack rate W is smaller than the conventional wire having the highest quality, the crack rate W An evaluation result was expressed by adding x to 5.0 mass% or more and the same level as that of a conventional general-purpose wire.

  As shown in Tables 2-1 and 2-2, all of Comparative Examples 1 to 5 in which the solidus temperature Ts is less than 1355 ° C. have a cracking ratio exceeding 5%, and have high-temperature cracking resistance. It was inferior. In addition, Comparative Examples 4 and 5 are conventional general-purpose wires, and their crack rates are 8.0% and 9.0%, respectively. Although not listed as a comparative example, even when a wire having the highest quality among the conventional general-purpose wires is used, the crack rate is limited to 5.0%.

  Further, in FIG. 2, the horizontal axis indicates the solidus temperature Ts, and the vertical axis indicates the cracking rate, and relationships shown in Tables 2-1 and 2-2 and Tables 3-1 and 3-2 (Examples 6 to 3). 23 and all data of Comparative Examples 1 to 5) are graphed. As shown in FIG. 2, when the solidus temperature Ts is 1355 ° C. or higher, the cracking rate is extremely small as compared with the other cases.

It is sectional drawing which shows the groove shape of the weld base material used for a hot cracking resistance test. It is a graph which shows the relationship between the solidus temperature of Comparative Examples 1-5 and Examples 6-23, and a crack rate.

Explanation of symbols

1; Base material 2; Refractory material 3; Aluminum tape

Claims (5)

In a weld metal welded with a titania-based flux-cored wire, the C content is 0.029% by mass or more, and B, C, Mn, N, P, S, Si, Ti in mass% with respect to the total mass of the weld metal. When the contents of [B], [C], [Mn], [N], [P], [S], [Si], and [Ti] are respectively defined, the solidus temperature defined by the following formula A weld metal comprising the above components so that Ts is 1355 ° C. or higher.
Ts = 1538-8903 × [B] −982 × [C] −6.64 × [Mn] −511 × [N] −368 × [P] −3603 × [S] −47.0 × [Si] − 205 × [Ti] -17 N: 0.0045 to 0.02 mass%, Ti: 0.025 to 0.1 mass%, Mn: 1.0 to 1.7 mass%, Si: 0.2 to 0.7 mass%, C: 0.05 to 0.09 mass%, and O: 0.05 to 0.09 mass%, and at least one selected from the group consisting of Cu, Ni, Cr, Mo, Al, Nb, and V 2. The weld metal according to claim 1, wherein the element contains 0.5% by mass or less of a seed element (0 is not included), and the balance is Fe and inevitable impurities. B: 0.005 mass% or less (0 is not included) is contained, The weld metal of Claim 2 characterized by the above-mentioned. A titania-based flux-cored wire for obtaining a weld metal according to any one of claims 1 to 3, wherein a steel outer shell is filled with a flux, and ordinary steel is used as a welding object. , N: 0.001 to 0.022 wt%, _TiO 2: 5 to 7 wt%, Mn: 2.30 to 3.75 wt%, and C: contains 0.030 to 0.055 wt%, Further, the content of B, C, Mn, N, P, S, Si, Ti, and TiO _{2 in} the content (% by mass) with respect to the total mass of the wire is [B], [C], [Mn], [ N], [P], [S], [Si], [Ti], [TiO ₂ ], each of the above-mentioned components so that the solidus temperature Ts defined by the following formula is 1355 ° C. or higher. A titania-based flux-cored wire comprising:
Ts = 1538−2938 × [B] −1640 × [C] −3.05 × [Mn] −327 × [N] −261 × [P] −2594 × [S] −26.3 × [Si] − 17.5 × [Ti] −1.95 × [TiO ₂ ] −25.5 Furthermore, B: 0.0155 mass% or less (0 is not included), Si: 0.85 mass% or less (0 is not included), or Ti: 0.60 mass% or less (0 is not included). The titania-based flux-cored wire according to claim 4.

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