JPS6045996B2 - Flux-cored wire for self-shield arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flux-cored wire for self-shielded arc welding, and in particular to a flux-cored wire that is free from welding defects such as pits and poor fusion and can obtain weld metal with excellent toughness by all-position welding. It is related to.

Flux-cored wire is a metal sheath filled with granular flux, and when used, there is no need to separately supply shielding gas or flux, so it has good welding workability and excellent wind resistance. It has various advantages.

By the way, the main component of the filling flux used in flux-cored wires is Ca, which has a melting point of 1-generated slag close to that of steel and has a slag-forming effect and a shielding effect.
Alkaline earth metal fluorides such as F2, SrF2 and BaF2, 2 Shielding effect to prevent nitrogen and oxygen from the atmosphere from entering the molten metal, or strong deoxidizing effect to alleviate the negative effects even if they do enter. Generally used are Mg, which has a strong deoxidizing effect, and Al7, which has both a strong deoxidizing effect and a nitrogen fixing effect.

However, the flux-cored wire as described above has a problem in that the appropriate range of welding conditions is narrow and welding defects are likely to occur.

These welding defects can be broadly classified into two types: one is slag entrainment and poor fusion, and the other is porosity defects such as pits and flow holes, and silver balls. In the former case, the causes of these defects include Al and M in the slag.
Reaction products of high melting point oxides (Al.O., Mg
The melting point of the slag is much higher than the melting point of steel due to the large amount of O) contained, and the penetration is shallow.In the latter case, the shielding effect is insufficient, and the hydrogen in the wire The inventors of the present invention focused on the above-mentioned circumstances, first of all, further pursued and clarified the causes of the above-mentioned defects, and also devised appropriate improvement measures. We have been conducting research to eliminate this defect by doing so.

As a result, alkali metal compounds (such as NaF, LiF.
Ll2SiO3, Na2O, K2O, etc.) have high vapor pressure, so they have a good shielding effect, and have strong arc force, so they have deep penetration, but on the other hand, they have a large amount of inherent moisture and are highly hygroscopic. Therefore, it was confirmed that the water content of the filling flux was high, and this was the main cause of frequent occurrence of pore defects. However, LiBaF3, which is a composite of an alkali metal compound, has the above-mentioned characteristics of an alkali metal compound, has a low inherent moisture content, and is difficult to absorb moisture, and has excellent performance as a main component for filling flux. As a result of further research, he completed the present invention. That is, the flux-cored wire for self-shielded arc welding according to the present invention is a steel sheath containing a powdery flux containing the following components as essential components in an amount of 10 to 30% (wt%) based on the total weight of the wire. The same applies hereafter) The gist lies in the filling.

LiBaF3: 5-75% Ae: 3-12% Mg: 2-10% Mn: 0.5-10% LiBaF3 used in the present invention has excellent slag forming effect, shielding effect, and penetration improvement as a filling flux component. In addition to having a stable arc effect and an arc stabilizing effect, it also has the unique property of having little inherent moisture and being difficult to absorb moisture. ) can be prevented as much as possible, such as pore defects such as bits and blowholes, and as a result, the appropriate arc voltage range can be greatly expanded.

By the way, Figures 1 and 2 show BaF2: 40%, Al: 7%
, Mg: 8%, Mn: 3.5%, CaO: 0.5%, the balance is Fe as a basic composition, and LiF: 0 to 40% or LiBaF3: 0 to 40% is blended in the form of powder. Flux was filled into a mild steel sheath to an amount of 20% of the total weight of the wire, and this was wire-drawn to make a 2Tgnφ flux-cored wire. Effects of LiF and LiBa on performance (appropriate arc voltage range) or defect (poor fusion, slag entrainment) occurrence rate
This is an experimental graph examining the effect of F3.

However, the welding conditions and test method were as follows. [1] Bit resistance (appropriate arc voltage range) Welding current: 250A,
Welding speed: 20 (CTn/min), current type/polarity: D
C, wire (-), wire protrusion length: 25 (7T0n
), torch angle: 0 degrees, flat plate (JIS G3lO
6, SM-501257mt×5007707! ') 1 bus welding with the top facing down, X-ray transmission test (JISZ3
The appropriate voltage range was defined as the voltage range in which type 1 grade 1 was obtained with lO4).

The lower limit voltage was set to the voltage at which the wire detected out. [■] Defect occurrence rate Welding current: 250CA), Welding voltage: 20-23 (V)
, Welding speed: 15-25 (Cm/min), Type of current, Polarity: DCl wire (1), Wire protrusion length: 25 (in order), Temperature between passes/preheating: 150-200℃, Back side hanging A test plate (2577 m
t x 50he) in a downward position, 4 layers 6 baths on the front side, 3 layers on the back side
After welding with layer 4 bus, ultrasonic flaw detection test) (JISZ3
The total length of slag entrainment and poor fusion defects was measured by the total weld length (500Tm!n
) is the defect occurrence rate (%).

As is clear from FIG. 1, when 5% or more of LiBaF3 is added, the appropriate arc voltage range is greatly expanded compared to that using LiF.

As shown in Figure 4 below, this is true for LiBaF3
This is thought to be due to the large difference in water content between LiF and LiF. Also, according to FIG. 2, LiBaF3 or LiF
As long as the blending ratio is 5% or more, the defect occurrence rate is the same and both are extremely excellent.

Figure 4 also shows LIF and Li2S, which are said to have relatively low inherent moisture and hygroscopicity among alkali metal compounds.
3 shows the change in moisture absorption amount of iO3 and LlBaF3 of the present invention over time.

Inherent moisture refers to the amount of moisture immediately after production (crystal water, adsorbed water, etc.), and the moisture increase rate when left (30℃, 80% RH) is calculated from the increase in released moisture when heated at 1000℃. Ta. As is clear from Figure 4, LiBaF3 is Li
It has significantly lower inherent moisture and hygroscopicity than F, Li2SiO3, etc. Therefore, when LiBaF3 is used as a component of the filling flux, the moisture content of the entire flux is reduced and the amount of hydrogen in the arc atmosphere is suppressed to a low level, thereby preventing the occurrence of pore defects such as bits and blowholes caused by hydrogen. This can be prevented as much as possible, and the arc voltage range for obtaining a proper weld can be expanded. As mentioned above, LjBaF3 is suitable as a filling flux (specifically, a main slag forming agent or an auxiliary slag forming agent) for flux-cored wires, but in order to effectively utilize these features of LiBaF3, It must be blended so that the content in the total flux is in the range of 5 to 75%.

However, if it is less than 5%, as shown in FIG. 1, the effect of expanding the appropriate arc voltage range will not be significantly exhibited, and the shielding effect and the effect of suppressing slag entrainment and fusion failure will also be insufficient. On the other hand, if it exceeds 75%, the fluidity of the generated slag becomes excessive, and the molten metal and slag tend to drip in the vertical or upward position, resulting in poor workability and poor bead shape. The slag forming agent to be used in combination with LIBaF3 includes various known fluorides and oxides, but the most preferred are alkaline earth metal fluorides such as CaF2, SrF2 and BaF2, or those with the general formula MxNyOz(M
: alkaline earth metal, N: FelMn. ．． Si. ．． Ni
．． ．． Ti. ．． Al, etc., 0: oxygen, X) y) z: positive number) complex oxide (specifically Ca2MnO, S
r2FeO4, Sr7FelOO22, BaFe2O4
, SrMnO3, Ba(MnO4)2, etc.).

In addition, LiF. K2
ZrF6, K2SiF6, NaF. ．． Na3AeF6,
K2O, Na2OlLl2SlO3, IiMnO3, L
Alkali metal compounds such as iFeO2; FeO. ．． MnO
、． SlO2, ZrO2, TiO2, MgO. ．． Ae2
Oxides such as O3, Bl2O3, B2O3; Li2CO3
, carbonates such as NacO3, BacO3, SrcO3, CacO3, etc. can also be used in combination. The content of these slag forming agents in the total filling flux is LiBa
It is preferable to set it in the range of 35 to 85% including F3.

The reason for this is that if it is less than 35%, the amount of slag produced will be insufficient and the encapsulation will deteriorate, and if it exceeds 85%, the amount of slag will be excessive and workability will deteriorate. Ae is an essential element as a strong deoxidizing agent and denitrifying agent and as a nitrogen fixing agent, and traps oxygen and nitrogen that enter from the atmosphere to prevent the formation of pores. In order to exhibit this effect of Af, it must be contained in the flux at least 3%, but if it is too high, an excessive amount of Ae will remain in the weld metal, causing the crystal grains to become coarse and brittle, so it must be contained at 12% or less. should be kept to a minimum. In addition to metal Ae, sources of A' include Fe-Af, . Af
)-Mg. ．． It is also possible to use an Al alloy such as A'i. In addition to having a strong deoxidizing function, Mg easily turns into metal vapor due to arc heat and exhibits an excellent shielding effect.

If the amount of Mg is less than 2%, these effects will be sufficiently exhibited, but the yield of Ae used in combination will decrease, and the Ae denitrification effect and nitrogen fixation effect will not be sufficiently exhibited. However, if it is too large, the amount of fume generated will increase significantly, making it difficult to observe the molten pool, contaminating the working environment, and causing deterioration of encapsulation due to increased spatter and increased slag viscosity, so it should be kept below 10%. Should. It is also possible to use metallic Mg as the Mg source, but since this tends to undergo explosive vaporization due to arc heat and cause frequent spatter, Ae-Mg. ．． Mg-Si,. Mg-S
i-Ca. ．． Ni-Mg,. It is preferable to include it as an Mg alloy such as Li-Mg. Mn has the effect of increasing the strength of the weld metal, lowering the surface tension of the molten metal and adjusting the bead shape, and must be contained in an amount of at least 0.5%.

However, if it exceeds 10%, the strength of the weld metal becomes excessively high, resulting in poor ductility and cracking resistance. Metal Mn is used as a Mn source.
Mn alloys such as , Fe-■, Fe-Sl-Mn, etc. are used, but in addition to these, oxides such as MnO and MnO2, and even Ll.
Complex oxides such as MnO3, SrMnO3, Ba (MnO4) can also be used as the Mn source. The reason for this is that Nakagawa Ko, the flux used in the present invention, contains a large amount of elements (Al and Mg) that have a greater affinity for oxygen than Mn, so Mn oxide undergoes deoxidation and converts to metallic Mn. This is because it will be done. The essential components of the flux used in the present invention are as described above, but especially when applied to fields such as offshore structures where iodothermic toughness (generally -10 to -60°C) is required, Ni: 0.5-20%, Zr: 0
．． 1-4%, Ti: 0.01-0.5%, B: 0.01
It is also effective to blend ~0.2% and also blend rare earth elements such as Ce9.

A brief explanation of these subcomponent components will be added below. Ni is an austenite-forming element, and a large amount of A
It has the effect of suppressing the coarsening of ferrite crystal grains due to the yield of e and improving the notch toughness of the weld metal.

These effects are effectively exhibited when the content is 0.5% or more, but when the content exceeds 20%, the strength becomes excessive and the cracking resistance becomes poor. As a Ni source, in addition to metal Ni, Fe-Ni-
Cr. ．． Ni alloy such as Ni-Mg, or NiO. ．．
Examples include oxides and composite oxides such as Ba2NiO4.
Zr has the effect of refining the crystal grains of the weld metal and fixing the intruded nitrogen to improve notch toughness, and these effects are effectively exhibited when added at 0.1% or more. If it exceeds 4%, slag seizure becomes significant and releasability deteriorates, and notch toughness also deteriorates.

As a Zr source, alloys such as Fe-ZrlZr-Si and K
2ZrF6, Na! Common monsters such as RF6, Alliha Zr
O2, ZrSiO4 (zircon sand), Li2ZrO
Examples include oxides such as No. 3 oxides and composite oxides. T1 has the effect of increasing notch toughness in a very small amount, and its effect is 0.0
Effective at 1% or more. In this case, the effect becomes even more remarkable when used in combination with Zr in the range mentioned above and B in an amount of 0.01 to 0.2%. However, if the Ti amount exceeds 0.5%, slag seizure becomes significant, and the bead appearance and welding efficiency deteriorate. The Tj source is metal Ti. In addition to alloys such as Fe-Ti, oxides such as TlO2 and Tl2O3, or composite oxides such as Li2TiO3, CaTl2O4, and CaTlO2 may also be used. B alone shows almost no effect on improving notch toughness, but as mentioned above, an appropriate amount of Ti
When used in combination with Ti, it works to enhance the effect of Ti.

These effects are effectively exhibited when the content is 0.01% or more, but when the content exceeds 0.2%, the cracking resistance decreases due to quench hardening and the notch toughness also becomes poor. Fe as a B source
-Alloys such as B, oxides such as B2O3, or Li2B
Examples include complex oxides such as 4O7 and Na2B4O7.
In addition, Cr.5 is added to the filling flux used in the present invention to improve the mechanical properties such as high temperature strength and corrosion resistance of the weld metal. ．． M.O. ．． Cu. ．． Nb. V. ．． C.O. ．． Elements such as P can also be blended.

The composition of the flux to be filled into the steel sheath has been explained above, but in order to effectively exhibit the effects of each component, the filling rate of the flux is also extremely important, and the amount of filling relative to the total weight of the wire is 10 to 10%. The filling rate must be set within the range of 30%.

That is, if the filling rate is less than 10%, a satisfactory effect cannot be obtained because the content of each of the flux constituents specified above is insufficient, while if it exceeds 30%, the Ae in the weld metal
There are problems such as an excessive amount of alloys such as, making it impossible to obtain the target level of mechanical properties, or an excessive amount of slag produced, resulting in significant slag entrainment and reduced welding workability. talented) Mild steel is the most common material for copper sheaths, but low alloy steel or high alloy steel can also be used depending on the purpose, and the cross-sectional structure is not particularly limited, but fine steel with a diameter of 2Tr0nφ or less may be used. In terms of diameter, a relatively simple cylindrical one is 2.4 to 4Tn! In the case of a wire with a large diameter of about nφ, it is common to have a structure in which the sheath material is folded inside in a complicated manner. The present invention is generally constructed as described above, and by specifically specifying the composition of the flux to be filled into the steel sheath, it is possible to eliminate welding defects such as bits and poor fusion, and to prevent mechanical properties (especially It has now become possible to provide a flux-cored wire for self-shielded arc welding that allows weld metal with excellent toughness to be obtained in any welding position.

Next, experimental examples will be given to clarify the effects of the present invention.

Experimental Example Powder-like flux having the chemical composition shown in Table 2 was filled into a steel sheath having the chemical composition shown in Table 1 (filling rate 20%) and wire drawing was performed to produce a 2TI011φ flux-cored wire.

Welding experiments were conducted using each of the obtained wires under the following conditions.

The results are shown in Table 3. [Welding conditions] Test plate: JISG3lOeKSM-50A1 plate thickness 45
藺×Length 500TI0nGave shape: / minute)
Wire protrusion length: 20 to 25 (w$L) Layer method: 8 layers and 14 baths on both front and back sides Welding position: Downward back side, near air gouging, then grinder
[Test method] Tensile test: JIS Z3llll As is clear from Tables 2 and 3, welding workability is There are no defects such as blowholes, slag entrainment, or poor fusion, and the mechanical properties of the welded metal are also good.

Among them, wire containing an appropriate amount of Zr in flux (N
O. 6) and Tj. Wire containing l5Zr (NO.
The low-temperature (-30'C) toughness of the weld metal obtained using 2, 3) is extremely excellent. On the other hand, when comparison wires (No. 8 to 12) lacking the requirements of the present invention were used, either the welding workability, ultrasonic flaw detection performance, or mechanical properties were poor, and the purpose of the present invention was not achieved. Can not do it.

[Brief explanation of drawings]

Figures 1 and 2 show LiF or LjBaF in the filling flux.
A graph showing the relationship between the content of No. 3 and the appropriate arc voltage range and defect occurrence rate, Figures 3 and 5 are graphs showing the groove shape adopted in the experiment, and Figure 4 is a graph showing the amount of moisture increase over time. It is.

Claims (1)

[Scope of Claims] 1. Self-shielded arc welding characterized in that a copper sheath is filled with powdery flux containing the following components as essential components in an amount of 10 to 3% by weight based on the total weight of the wire. flux-cored wire. LiBaF_3: 5-75% by weight Al: 3-12〃 Mg: 2-10〃 Mn: 0.5-10〃