JP2007144429A - Bond flux for downward fillet submerged arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide bonded flux for downward fillet submerged arc welding, a bonded flux that solves conventional technical problems, that enables superior bead appearance and welding workability comparable to fusible flux to be obtained, and that also enables improved mechanical performance of weld metal to be obtained, in fillet welding using bonded flux for submerged arc welding, particularly, in flat fillet submerged arc welding with deep penetration free of groove preparation. <P>SOLUTION: The bonded flux for downward fillet submerged arc welding is characterized in that it contains, by mass%, 5-15% SiO<SB>2</SB>, 12-25% MgO, 3-13% CaO, 1-7% CaF<SB>2</SB>, 8-20% Al<SB>2</SB>O<SB>3</SB>, 16-25% TiO<SB>2</SB>, 0.1-0.5% B<SB>2</SB>O<SB>3</SB>, 5-15% ZrO<SB>2</SB>, 0.5-1.0% Mn, 0.2-3.0% Si and 1.0-6.0% Fe, the balance being CO<SB>2</SB>, alkali metal oxide and unavoidable impurities. The bonded flux is also characterized in that it contains 0.01-0.04% 2Nb+V in one or two kinds of ≤0.02% Nb and ≤0.01% V. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bond flux for downward fillet submerged arc welding, and particularly, a built-in H material (three steel plates are combined so that the cross-sectional shape is H-type by combining fillet welds) frequently used for steel frames and bridges. Downward fillet submerged arc that can obtain weld metal with excellent bead shape, welding workability, penetration depth and mechanical performance when used for downward fillet of columns, beams and girders made of joined aggregates) The present invention relates to a welding bond flux.

  Fillet welded joints formed by downward fillet submerged arc welding are required to have good penetration depth, required leg length, bead shape smoothness, and good compatibility with the base metal of the weld metal. ing. Recently, there is a tendency that good mechanical performance of the weld metal is required. Conventionally, in the case of downward fillet submerged arc welding, a melting type flux that can be welded at a higher speed than a bond flux is often used. However, the melt-type flux is insufficient for obtaining a predetermined mechanical performance of the weld metal, or increasing the leg length, and increasing the welding efficiency by large heat input.

In view of these points, bond fluxes having good welding workability and mechanical performance have been studied. For example, a downward fillet submerged arc welding bond flux is disclosed in Japanese Patent Laid-Open No. 7-100689 (Patent Document 1), and a multipurpose welding bond flux including fillet welding is disclosed in Japanese Patent Laid-Open No. 11-347788 (Patent Document 2). Although disclosed in Japanese Patent Application Laid-Open No. 8-99191 (Patent Document 3) and Japanese Patent Application Laid-Open No. 11-354010 (Patent Document 4), the SiO ₂ content is large, the oxygen content of the weld metal is increased, and the toughness is increased. There is a problem of lowering.

Moreover, although the bond flux only for fillet welding is disclosed in Japanese Patent Laid-Open No. 2002-331390 (Patent Document 5), it is used for high-speed fillet welding, and speed is required for obtaining deep penetration in the welding of a built-in H material. When welding is performed with a large amount of SiO ₂ , the toughness is reduced due to a large amount of SiO ₂ , and the bead shape becomes poor due to the high viscosity of slag.

  Furthermore, a bond flux capable of obtaining good toughness is disclosed in Japanese Patent Application Laid-Open No. 2000-107885 (Patent Document 6), and a bond flux for extremely thick H-shaped steel is disclosed in Japanese Patent Application Laid-Open No. 10-29041 (Patent Document 7) and No. 9-319146 (Patent Document 8) and the like, but the bead shape is deteriorated because the amount of weld metal is excessive in the deep penetration downward fillet welding method with a large Fe content and no groove processing. However, there is a problem that the slag peelability becomes poor.

Japanese Patent Application Laid-Open No. 7-100689 Japanese Patent Laid-Open No. 11-347788 JP-A-8-99191 Japanese Patent Laid-Open No. 11-354010 JP 2002-331390 A JP 2000-107885 A Japanese Patent Laid-Open No. 10-29041 JP 9-319146 A

  The present invention solves the above-mentioned problems in fillet welding using bond flux for submerged arc welding, particularly deep penetration downward fillet submerged arc welding without groove processing, and corresponds to a melt-type flux. An object is to provide a bond flux for downward fillet submerged arc welding which can obtain a good bead appearance and welding workability and can obtain a good weld metal mechanical performance.

The present invention solves the above-mentioned problems, and the gist of the invention is as follows.
(1) in _{mass%, SiO 2: 5~15%,} MgO: 12~25%, CaO: 3~13%, CaF 2: 1~7%, Al 2 O 3: 8~20%, TiO 2: 16-25%, B ₂ O ₃ : 0.1-0.5%, ZrO ₂ : 5-15%, Mn: 0.5-1.0%, Si: 0.2-3.0%, Fe : it contains 1.0 to 6.0%, others CO _2, alkali metal oxides and down fillet submerged arc welding bonded flux, characterized in that unavoidable impurities.
(2) Furthermore, 0.01-0.04% of Nb: 0.02% or less and V: 0.01% or less of 1 type or 2 types are contained by 2Nb + V as described in said (1) characterized by the above-mentioned It is in bond flux for downward fillet submerged arc welding.

  According to the bond flux for downward fillet submerged arc welding of the present invention, deep penetration can be obtained even in downward fillet welding without groove processing such as a built-in H material, and good welding workability, bead shape, and Excellent mechanical properties can be obtained, welding efficiency can be improved, and high quality welds can be obtained.

The present inventors first examined various conventional fluxes used for downward fillet submerged arc welding, but could not obtain a flux satisfying all of the excellent bead shape, workability, and mechanical performance. It was. For example, in the melt type flux, since the shielding effect is insufficient, the oxygen amount of the weld metal is increased, and a predetermined mechanical performance cannot be obtained. Further, in the bond flux, SiO ₂ is high, the oxygen amount of the weld metal is high, and the predetermined toughness cannot be obtained. Moreover, the viscosity of the slag was high, the bead shape became convex, and the slag peelability was insufficient.

Therefore, as a result of various investigations on the component composition of the flux, by adding Si to the bond flux and lowering the SiO ₂ , the slag peelability and bead shape are good, and the oxygen content of the weld metal is suppressed and good mechanical performance is obtained. I found out that
In general, in deep penetration down fillet submerged arc welding without groove processing, welding is performed with a large heat input in order to obtain a penetration depth, but welding with a large heat input provides good weld metal toughness. Absent. This is because coarse grain boundary ferrite (pre-deposited ferrite) precipitates at the austenite grain boundaries in the weld metal, and it is necessary to ensure high hardenability and suppress precipitation of the grain boundary ferrite. Moreover, since coarse, hard and brittle cementite is generated in the austenite grains, the weld metal toughness is lowered.

Therefore, in order to suppress coarse grain boundary ferrite, Si, Nb, and V were studied as elements that suppress austenite coarsening. In addition, the austenite grain boundary segregation effect of B was used as an element that suppresses the formation of coarse grain boundary ferrite. In addition, in order to suppress coarse cementite in austenite grains and promote the formation of acicular ferrite, hardenability is improved by adding appropriate amounts of Si, Nb, and V, and an appropriate amount of TiO _{2 serving as} a Ti source is added. Therefore, it is effective to use an oxide containing Ti that becomes a nucleus of acicular ferrite. Furthermore, in addition to the above, it has been considered that the effect of improving the welding efficiency and the concentration of the welding arc has been insufficient with a small amount of Fe so far, but in deep penetration down fillet submerged arc welding without groove processing, It was found that the penetration depth can be improved and a good bead width can be obtained by containing a small amount.

Hereinafter, the reasons for limiting the component composition of the bond flux in the present invention will be described.
SiO ₂ has a highly viscous property and affects welding workability, bead shape, and mechanical performance of the weld metal. When the content is less than 5% by mass (hereinafter referred to as “%”), the viscosity of the slag is insufficient, so that the bead shape becomes poor and the bead meanders and undercuts occur. On the other hand, if it exceeds 15%, the viscosity of the slag becomes too high, so that in the case of downward fillet welding, the bead end is overlapped, and the slag peelability is also deteriorated. Furthermore, since the oxygen content of the weld metal increases, the toughness of the weld metal deteriorates.

  MgO is an effective component for reducing the oxygen content of the weld metal, and has a high melting point and high viscosity property. When MgO is less than 12%, the oxygen content of the weld metal is increased and the toughness is lowered, and the viscosity of the slag is insufficient, so that bead meandering and undercutting occur. On the other hand, if MgO exceeds 25%, the melting point of the flux increases and the meltability of the flux decreases, so that a sufficient bead width cannot be obtained and the viscosity of the slag increases. The heel end overlaps.

  CaO is an important component for adjusting the oxygen content, melting point, and slag fluidity of the weld metal. If CaO is less than 3%, the amount of oxygen in the weld metal increases, and the toughness deteriorates. In addition, the fluidity of the slag deteriorates, the bead collar ends overlap, the familiarity with the base material deteriorates, and the bead shape becomes convex. On the other hand, if it exceeds 13%, the solidification temperature of the slag becomes high, undercut is likely to occur, and the slag peelability is deteriorated.

CaF ₂ has properties of low melting point and low viscosity, and is an effective component to keep the bead smooth when welding under high current welding conditions, and part of it decomposes during generation of fluorine gas. To do. Fluorine gas has a shielding effect during welding, reduces oxygen in the weld metal, and improves toughness. When CaF ₂ is less than 1%, there is no effect in improving the bead shape and toughness, and when it exceeds 7%, the fluidity of the slag becomes excessive, undercut is likely to occur, and the slag peelability is deteriorated.

Al ₂ O ₃ is an effective component for adjusting the viscosity and solidification temperature of slag. If Al ₂ O ₃ is less than 8%, the viscosity of the slag is insufficient, and undercut is likely to occur. On the other hand, if it exceeds 20%, the viscosity of the slag becomes excessive and the bead shape becomes convex.
TiO ₂ is effective in obtaining the smoothness of the bead surface, and further reduced during melting and yielded as an oxide containing Ti in the weld metal, and is very effective in improving toughness as a core of acicular ferrite. Is an essential ingredient. When TiO ₂ is less than 16%, there is no effect in improving the smoothness and toughness of the bead, and when it exceeds 25%, the slag is seized and the slag peelability is deteriorated.

B ₂ O ₃ is a component that is reduced by welding heat, is retained in the weld metal as B, segregates at the austenite grain boundaries, suppresses the formation of coarse grain boundary ferrite, and is a very effective component for improving the toughness of the weld metal. It is. If B ₂ O ₃ is less than 0.1%, the effect of improving toughness cannot be obtained, and if it exceeds 0.5%, hot cracking tends to occur.

ZrO ₂ increases the viscosity of the slag. If ZrO ₂ is less than 5%, the viscosity of the slag is insufficient, and an undercut occurs at the end of the bead collar. On the other hand, if it exceeds 15%, the viscosity of the slag becomes too high, the bead collar ends overlap, and the bead shape becomes convex. Furthermore, the oxygen content of the weld metal increases, and the toughness of the weld metal deteriorates.

  Mn is an effective component for improving hardenability and increasing strength and toughness. If the content is less than 0.5%, the hardenability at the time of high heat input welding is insufficient, and the toughness is lowered. If it exceeds 1%, the hardenability becomes excessive, the strength of the weld metal increases, and the toughness decreases. As the Mn source, one or two of metal Mn and Fe—Mn can be used.

  Si improves hardenability and is an effective component as a deoxidizing component by combining with oxygen during welding and slag-out, and increases the strength and toughness of the weld metal. If the Si content is less than 0.2%, the deoxidizing effect cannot be obtained and the toughness is lowered. On the other hand, if it exceeds 3.0%, the hardness of the weld metal becomes excessive and the toughness deteriorates. As the Si source, one or two of metal Si and Fe—Si can be used.

  Fe is effective in improving arc concentration and welding efficiency. When Fe is less than 1.0%, the depth of penetration becomes insufficient in deep penetration downward fillet welding without groove processing due to weak arc concentration. In addition, the amount of weld metal is insufficient and a sufficient bead width cannot be obtained. On the other hand, if it exceeds 6.0%, the concentration power of the arc becomes excessive, so that the blow-up during welding becomes intense and the welding workability is deteriorated. Since the amount of weld metal becomes excessive, the bead shape becomes convex, the leg length of the bead becomes excessive, and the bead appearance deteriorates.

Further, by including 0.01 to 0.04% of Nb 0.02% or less and V 0.01% or less of 1 or 2 at 2Nb + V as a component of the present invention, the hardenability of the weld metal is increased and the toughness is improved. . When 2Nb + V is less than 0.01%, the hardenability of the weld metal is insufficient and the toughness is lowered. On the other hand, if 2Nb + V exceeds 0.04%, Nb exceeds 0.02%, or V exceeds 0.01%, the hardenability of the weld metal becomes excessive and the strength becomes excessive, so that the toughness decreases. As component composition other than the above components, alkali metal oxides such as CO ₂ of metal carbonates such as MgCO ₃ and CaCO ₃ and K ₂ O, Na ₂ O and Li ₂ O from water glass used at the time of flux production are used. Others are inevitable impurities.

Hereinafter, the effects of the present invention will be described in detail by way of examples.
The flanged steel plate S2 is inclined by 55 ° with respect to the horizontal plane without the groove processing of the 1000 mm length shown in FIG. 1 with the web material having a thickness of 26 mm and the flange material having a thickness of 36 mm shown in Table 1. In the groove assembled with the end face of the web steel plate S1 in contact with the center of the surface of the flange steel plate S2, the wire flux shown in Table 2 and the bond flux of various components shown in Table 3 are used. In combination with each other, a deep penetration down fillet submerged arc welding without groove processing of one pass by two electrodes was performed under the welding conditions shown in Table 4. After welding, slag peelability, bead shape, bead edge, bead width, penetration depth and weld metal toughness were investigated.

  Evaluation of welding workability investigated slag peelability, bead shape, the presence or absence of a defect of a bead edge, and penetration depth. Regarding slag peelability, it is good if the slag is easily peeled off by lightly hitting it with a hammer or chisel. The case where seizure of the slag was observed after peeling was taken as x. As for the bead appearance, a good bead shape was obtained when the bead surface was uniform and beautiful, and a slight convex shape was indicated by Δ, and an excessive convex shape was indicated by ×.

  For the defect evaluation of the bead end, it is indicated as ○ if there is no welding defect such as undercut or overlap, and △ if there is an undercut or overlap less than 0.3 mm, and undercut greater than 0.3 mm. Or when there was an overlap, it was set as x. In the case of complete penetration, the penetration depth of the weld metal M1 welded first and the weld metal M2 welded later contact when both sides are welded as shown in FIG. It was set as ○, and when the penetration part did not contact, it was set as ×.

  As for toughness, Charpy impact test pieces (JIS Z3111-4) were sampled around 7 mm below the bead surface of the weld metal part shown in FIG. 2, and toughness was evaluated by Charpy impact test at 0 ° C., each with 3 repetitions. The average was evaluated. The Charpy absorbed energy was determined to be good if it was 100 J or more. The results are summarized in Table 5.

  In Table 5, welding symbols 1 to 10 are examples of the present invention, and welding symbols 11 to 32 are comparative examples. In welding symbols 1 to 10 which are examples of the present invention, the amount of each component of the combined flux symbols A1 to A10 is an appropriate amount, and therefore, a good value with a Charpy absorbed energy of the weld metal of 100 J or more was obtained. Also, the slag peelability was good, the bead shape was smooth and smooth, the bead collar end portion with no undercut and overlap and a sufficient bead width were obtained, and good welding workability and bead appearance were obtained. Further, the penetration depth was extremely satisfactory, such as good complete penetration in which the weld metals on both sides were in contact.

In the comparative example, the weld symbol 11 has a low SiO ₂ flux symbol B1, so that the viscosity of the slag is insufficient, the undercut occurs at the end of the bead, the weld metal has poor hardenability, and the Charpy absorbed energy is low. .
In welding symbol 12, since the SiO _{2 of} flux symbol B2 is high, the viscosity of the slag becomes high, an overlap occurs at the end of the bead collar, and the bead shape becomes convex. Moreover, the oxygen content of the weld metal was high, and the Charpy absorbed energy was low.

Since the welding symbol 13 had a low MgO of the flux symbol B3, the amount of oxygen in the weld metal was high and the Charpy absorbed energy was low. In addition, the viscosity of the slag decreased and undercut occurred at the bead end.
Since the weld symbol 14 has high MgO of the flux symbol B4, the viscosity becomes high, the bead becomes convex, overlap occurs at the flange end portion, and a sufficient bead width cannot be obtained.

Since the weld symbol 15 had a low CaO of the flux symbol B5, the slag fluidity was insufficient, the bead appearance was poor, the oxygen content of the weld metal increased, and the Charpy absorbed energy of the weld metal was low.
Since the weld symbol 16 has high CaO of the flux symbol B6, the fluidity becomes excessive, undercut occurs at the end of the bead collar, and the slag peelability becomes poor.

Since the welding symbol 17 had a low CaF _{2 of the} flux symbol B7, the fluidity of the slag was insufficient, and an overlap occurred at the end of the bead collar. Further, since 2Nb + V is low, the hardenability is insufficient and there is no effect of improving the Charpy absorbed energy.
Since the weld symbol 18 is high in CaF _{2 of the} flux symbol B8, the fluidity of the slag becomes excessive, undercut occurs, and the slag peelability deteriorates.

Since the welding symbol 19 was low in Al ₂ O ₃ of the flux symbol B9, the viscosity of the slag was insufficient and undercut occurred.
Since the welding symbol 20 is high in Al ₂ O ₃ of the flux symbol B10, the viscosity of the slag becomes excessive and an overlap occurs.

The welding symbol 21 has a low TiO ₂ content of the flux symbol B11, so that the oxide containing Ti in the weld metal is insufficient, the acicular ferrite of the weld metal is reduced, coarse grain boundary ferrite is increased, and the Charpy absorbed energy is increased. It was low.
Since the welding symbol 22 is high in TiO _{2 of the} flux symbol B12, the fluidity of the slag becomes excessive, undercut occurs, and the slag peelability deteriorates. Moreover, since Nb and V were high, hardenability became excessive and Charpy absorbed energy was low.

Since the weld symbol 23 has a low B ₂ O ₃ of the flux symbol B13, the yield of B in the weld metal is lowered, segregation action on the austenite grain boundary is not obtained, coarse grain boundary ferrite is generated, and Charpy absorption occurs. Energy was low.
Since the welding symbol 24 is high in B ₂ O ₃ of the flux symbol B14, the amount of B in the weld metal is high, and hot cracking occurs. Moreover, since Nb was high, hardenability became excessive and Charpy absorbed energy was low.

In the welding symbol 25, undercutting occurred because ZrO _{2 of the} flux symbol B15 was low.
The weld symbol 26 had a low Charpy absorbed energy because the ZrO _{2 of the} flux symbol B16 was high. Moreover, the viscosity of the slag was excessive and overlapped, the bead shape became convex, and the bead width became poor.

Since the weld symbol 27 had a low Mn of the flux symbol B17, the hardenability of the weld metal was insufficient, and the Charpy absorbed energy was low.
Since the weld symbol 28 had a high Mn flux symbol B18, the strength of the weld metal was excessive and the Charpy absorbed energy was low.

The welding symbol 29 had a low Si value of the flux symbol B19, so that the hardenability was insufficient and the Charpy absorbed energy was low.
Since the welding symbol 30 has a high flux symbol B20Si, the strength of the weld metal was excessive, and the Charpy absorbed energy was low.

As for the welding symbol 31, the amount of welding was insufficient because the Fe of the flux symbol B21 was low, and the bead width was insufficient. In addition, the concentration of the welding arc was weakened and sufficient penetration could not be obtained. Moreover, since V was high, hardenability became excessive and the Charpy absorbed energy was low.
In welding symbol 32, Fe of flux symbol B22 was high and the amount of welding became excessive, the bead became convex, and the slag peelability deteriorated. Moreover, the concentration of the welding arc was strong during welding, and the welding workability was deteriorated due to a lot of blowing. Furthermore, since 2Nb + V was high, the hardenability was excessive and the Charpy absorbed energy was low.

It is sectional drawing which shows the groove shape of the downward fillet test board without groove processing used for the Example of this invention. It is sectional drawing which shows the penetration state of the weld metal of downward fillet welding.

Explanation of symbols

S1 Web steel plate S2 Flange steel plate M1 Weld metal welded first M2 Weld metal welded later a Charpy impact test piece


Patent Applicant Nippon Steel & Sumikin Welding Industry Co., Ltd.
Attorney Attorney Shiina and others 1

Claims (2)

By _{mass%, SiO 2: 5~15%,} MgO: 12~25%, CaO: 3~13%, CaF 2: 1~7%, Al 2 O 3: 8~20%, TiO 2: 16~25 _{%, B 2 O 3: 0.1~0.5} %, ZrO 2: 5~15%, Mn: 0.5~1.0%, Si: 0.2~3.0%, Fe: 1. contains 0 to 6.0%, others CO _2, alkali metal oxides and down fillet submerged arc welding bonded flux, characterized in that unavoidable impurities. The downward fillet submerged according to claim 1, further comprising 0.01 to 0.04% of Nb: 0.02% or less and V: 0.01% or less of 2 or 1 Nb at 2Nb + V. Bond flux for arc welding.

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