DE2164892B2 - - Google Patents

Description

bow stabilizing effect. It was also found that the impact strength of the weld metal is improved by using LiF and complex metal fluorides.

Ilmenite and rutile, which are usually used as the main slag formers, have a number of disadvantages, such as poor arc-sealing properties, and are slightly reduced by the strongly degassing elements such as Al and Mg, which increases the titanium content of the weld metal extremely sharply. For this reason, they are unsuitable for the welding method according to the invention. Calcium carbonate is also unsuitable in large quantities because it makes the arc unstable and, due to the reduction of CO ₂ in the presence of Al and Mg, increases the carbon content of the weld metal, even though the gaseous CO ₂ developed by the arc has a sealing effect on the arc .

Calcium carbonate, AlF ₃ , MgF ₂ and KF are auxiliary materials that are not main components for adjusting the slag quality and for stabilizing the arc.

The deoxidizing and nitrogen-fixing effect is very important. In the case of the electrode according to the invention, the arc is kept in the absence of air _{by a fluoride, preferably CaF 2;} however, the exclusion of air is not complete, so that oxygen and nitrogen can penetrate the weld metal and pores occur and the mechanical properties, in particular the toughness, are impaired.

It is therefore necessary to stably bind the oxygen and nitrogen by adding elements such as Ca, Mg, Ti, Zr and Al and, if possible, to remove them as slag. Sufficient deoxidation and denitrification of the liquid metal is not to be expected with Ca and Mg, because these metals are instantaneously oxidized in the arc. Although Ti and Zr prevent the occurrence of pores, they are converted _{into the slag in the arc with the formation of TiO 2} and ZrO ₂ , so that its fluidity is impaired. This deteriorates the appearance of the slag and the weld seam and the peeling of the slag; in addition, the weld metal becomes brittle if these elements are alloyed in large quantities. In contrast, Al generally has little influence on the brittleness of the weld metal, although a relatively large amount is required to prevent the occurrence of pores. The impact strength is particularly good when an element such as Ni or Mn is added, which stabilizes the austenite. It has also been found that the effect is better if Al is used not by itself but in the form of a Mg-Al alloy. This is due to the fact that in the alloy the magnesium is preferentially oxidized in the arc and the aluminum is largely transferred into the weld metal in elemental form. The aluminum content of the weld metal is thereby increased, while the seal against the atmosphere is achieved by the magnesium. The oxides of magnesium and aluminum make a cheap slag.

The invention is explained in more detail below on the basis of exemplary embodiments and the drawing. In these drawings shows

F i g. 1 shows the various electrode cross-sections of the exemplary embodiments. Here, F i g. 1 A for Examples 3 and 5, FIG. 1 B for example 12, FIG. 1 C for Examples 1, 7, 8, 9 and the comparative example and F i g. 1 D for examples 2, 4, 6, 10 and 11,

F i g. Fig. 2 is a graph showing the relationship between nitrogen content and the Notched impact strength,

F i g. 3 the relationship between the aluminum content and the nitrogen content of the weld bead on a steel plate,

F i g. 4 the influence of the added amount of the Mg-Al alloy on the nitrogen content, the notched impact strength and the appearance of pores,

F i g. 5 shows the relationship between the composition of the Mg-Al alloy and the notched impact strength as well as the appearance of pores,

F i g. 6, 7 and 8 the influence of the added amount of a third metal on the notched impact strength,

F i g. 9 shows a comparison of the notched impact strengths of Examples 1 to 3 and the comparative example,

F i g. 10 shows the effect of LiF on impact strength in Examples 8 and 9 and

F i g. 11 the nitrogen content of the weld metal.

The electrode according to FIG. 1 consists of a metal jacket 1 and a flux filling. As shown in FIG. 3, the total nitrogen content increases with the aluminum content, reaches a maximum at about 0.2 % Al and then decreases. The amount of nitrogen bound as AlN increases rapidly from 0.2% Al with the aluminum content and, with an aluminum content of around 0.6% Al, almost reaches the value of the total nitrogen. On the other hand, the pores in the weld bead disappear completely when the proportion of Al is over 0.6%.

Another cause for the appearance of pores is the oxygen, which however is caused by more than 0.1% Al is stably tied.

As can be seen from Table I, the aluminum content of the weld metal increases to at most 0.5%, even if metallic aluminum or ferroaluminum alone or together with magnesium is added up to a mixing ratio of 30% of the flux. To such a high proportion To alloy aluminum into the weld metal, a Mg-Al alloy is used. After the attempts 11,12,13,14 and 15 in Table I it is possible to increase the aluminum content in the weld metal to more than 0.6% and to prevent the occurrence of pores.

In the tests, a weld bead was placed on a steel plate under the following conditions:

Base material SS 41;
Amperage: 400A;
Voltage 26 to 35V;
Welding speed: 20 cm / min;
Rod length 30 mm.

An X-ray examination served to determine the number of pores at Hner weld bead length of 230 mm.

The Mg-Al alloy used contained 40% Mg, the ferroaluminum 75% Al.

Table I.

attempt Mg-Al-
alloy Mg Metallic
Al Ferrous
aluminum CaF ₂ AlF, MgF ₂ Ferrous
silicon
(45% Si) Ferrous
manganese
(75 <Mn) (° / o) (° / o) (V.) C / o) C / o) C / o) C / o) C / o) C /.) 1 30th 63 3 4th 2 20th 73 3 4th 3 30th 66 4th 4th 20th 73 3 4th 5 8th 12th 73 3 4th 6th 12th 12th 72 4th 7th 12th 12th 40 29 3 4th 8th 16 12th 65 3 4th 9 16 50 15th 3 4th 10 12th 24 57 3 4th 11 17th 76 3 4th 12th 20th 76 4th 13th 20th 60 16 4th 14th 25th 68 3 4th 15th 30th 63 3 4th

Table II

Flow- Pores C. Si Mn Al N _gra attempt middle-
relationship (V.) (Vo) (Vo) (Vo) (V.) (Vl) numerous 0.1 0.1 0.5 0.3 0.052 1 20th numerous 0.1 0.1 0.4 0.1 0.061 2 20th numerous 0.1 traces 0.6 0.5 0.053 3 20th numerous 0.1 0.1 0.5 0.3 0.058 4th 20th numerous 0.1 0.1 0.5 0.5 0.058 5 20th numerous 0.1 traces 0.5 0.5 0.050 6th 20th numerous 0.1 0.1 0.6 0.5 0.045 7th 20th numerous 0.1 0.1 0.5 0.5 0.044 8th 20th numerous 0.1 0.1 0.5 0.5 0.041 9 20th numerous 0.1 0.1 0.5 0.5 0.048 10 20th no 0.1 0.2 0.7 0.6 0.037 11 20th no 0.1 0.1 0.7 0.9 0.036 12th 20th no 0.1 traces 0.7 1.0 0.032 13th 20th no 0.1 0.2 0.8 1.2 0.035 14th 20th no 0.1 0.2 0.9 1.5 0.034 15th 20th

However, if the weld metal has a high content of aluminum, the mechanical properties are not always satisfactory, in particular the elongation, ductility and impact strength are impaired. It is therefore necessary to add other elements. The influence on the addition of the further alloying element on the notched impact strength is shown in FIG. 7 shown. Thereafter, by adding Ni and Mn, the impact strength is effectively improved, while Co, Cr and Mo have no effect. As far as the proportion of CaF ₂ , which is an example of fluoride, is concerned, according to FIG. 2 40 to 80% CaF ₂ suitable. If the proportion is below 40%, the arc termination worsens and the amount of slag decreases, so that pores are formed and the quality of the weld bead is impaired. If the proportion of CaF _{8 is} over 80%, the proportions of the other core components become too low and the arc becomes unstable. As on the other hand from FIG. 4 shows, the optimum for the addition of the magnesium-aluminum alloy is 10 to 20%. Below 10% the nitrogen binding is insufficient, and pores arise, above 30% the aluminum content in the weld metal increases in an undesirable way and the mechanical properties, in particular the notched impact strength, are impaired.
As shown in FIG. 5, a Mg-Al alloy with 30 to 70% Al is suitable for the electrode according to the invention. Since the content of Mg becomes insufficient if the alloy contains over 70% Al, the aluminum content of the weld metal is reduced and is

Insufficient deoxidation and nitrogen fixation. This also applies to aluminum contents below 30%.

It was found through experiments that the particle size of the Mg-Al alloy was remarkable Influence on the appearance of pores and on the mechanical properties, in particular the notched impact strength, owns. In Fig. 6 is the dependence of the voltage range of the arc and the notched impact strength of the weld deposit at 0 ° using an alloy with 60% Mg and 40% Al and varying Mixing ratio and a grain size below 0.074 mm are shown. From Fig. 6 it can be seen that by increasing the amount of Mg-Al alloy added with a particle size below 0.074 mm Impact strength is improved, but the arc voltage range is reduced. if if the proportion exceeds 70%, pores appear to a large extent. On the other hand, although the range of the arc voltage increases when the proportion is less than 10%, but the impact strength becomes extraordinary reduced. For this reason, the proportion of fine powder is below a particle size 0.074 mm 10 to 70%.

When adding the alloying elements, note the following: The ductility and toughness of the weld metal is improved when the flux contains manganese in an amount of 2 to 20%, but the effect is different if manganese alone is added. In order to achieve stable behavior, 5 to 15% nickel can also be added. When adding nickel, however, the proportion of manganese should be be limited to 2 to 10%. The nickel can also be added as a Ni-Mg alloy.

The reason why the proportions of Mn and Ni are fixed in the above manner is the fact that no effect can be achieved if the proportion is less than the lower limit and that that Weld metal is hardened and its tensile strength is abnormally increased when the proportion exceeds the upper limit exceeds.

According to the investigations on which the invention is based, the weld metal becomes very brittle if it contains too much Si and Ti. It is therefore necessary to completely oxidize these elements or to use them in a limited amount. The relationship between the silicon content and the notched impact strength at 0 ^° C. of the weld metal is shown in FIG. 8 shown. After that, the notched impact strength suddenly drops sharply above 0.18% silicon if a large proportion of Al remains in the weld metal. The proportion of silicon should therefore be limited to such a small amount that the weld metal contains a maximum of 0.18% silicon. The impact strength deterioration caused by titanium is greater than that of silicon. However, the addition of a small amount of this element causes grain refinement. However, the titanium content should be below 0.05%.

The notched impact strength of the weld metal is greatly improved if the core filling contains a complex metal fluoride such as K ₂ ZrF ₆ and K ₂ TiF _{6 in addition to CaF 2} LiF.

F i g. 9 shows the effect of LiF and complex metal fluorides as a function of the total content (P + S) on the impact strength. From the course of the curve it can be seen that in comparison with the conventional electrode (curve 1) gives very good impact strength even if the total at (P + S) in the weld metal is relatively high.

However, if the total content of (P + S) in curves 2 and 3 has a value of 0.040% and in Curve 4 exceeds a value of 0.050%, the notched impact strength suddenly drops. This is also possible the effect of the complex metal fluoride lost, so that the total content of the electrode of phosphorus and sulfur should be below 0.04%.

It can be assumed that the complex metal fluorides, such as K ₂ ZrF ₆ , Na ₂ ZrF ₆ , K ₂ TiF ₆ and Na ₂ TiF ₆ , im

ίο Easily dissociate the arc and form fluorides with very high vapor pressure, such as ZrF ₄ , TiF ₄ , KF and NaF, which complete the arc, and that the toughness of the weld metal is also reduced by Zr or Ti, which are made up of the complex metal fluorides in small quantities reach the weld metal and reduce the grain size, is noticeably improved.

The added amounts of the complex metal fluorides are 0.5 to 10%. Below 0.5% there was no effect can be determined, and if the amount is large, the amount of Zr or Ti in the weld metal becomes too high.

In order to improve the welding result, the addition of 1 to 20% CaCO _{3 is} useful, even if the mechanical properties are somewhat impaired. Less than 1% CaCO ₃ has no effect, and more than 20% of this compound causes explosions by dissociating CaCO ₃ into CO ₂ and CaO, thereby increasing the spray loss and deteriorating the physical properties of the slag.

It was found that LiF not only has a better sealing _{effect than CaF 2} with respect to the free atmosphere and produces a better slag, but also easily dissociates and forms elemental lithium with a strongly degassing and refining effect, which also corresponds to the diagram in FIG. 10 improves the toughness of the weld metal. From Fig. 10 also shows the effect of reducing the nitrogen content in the weld metal as a result of the final effect of the LiF. While the addition of less than 0.5% has no effect, the upper limit according to FIG. 10 do not determine. However, since LiF is expensive and adding too large an amount deteriorates the viscosity of the slag, the maximum content is 10%. Even with the addition of LiF, the toughness suddenly decreases if the total (P + S) content of the weld metal exceeds 0.040%.

It has also been found that when complex metal fluoride and LiF are added at the same time, the Arc termination by the complex metal fluoride and the effect of Zr and Ti on the grain size superimpose the action of LiF, so that the notched impact strength is greatly improved. The effect of LiF and the complex metal fluoride on the nitrogen content of the weld metal is shown in FIG. 11th

The great advantage of LiF and complex metal fluoride according to Examples 8 and 9 is that that they enable a reduction in the aluminum content of the weld metal. Aluminum is true Very effective as a deoxidizer and denitrant, but reduces the toughness of the weld metal suddenly when its content exceeds about 1.0%. Then defects such as pores appear. It is therefore of great advantage that the aluminum content due to the addition of complex metal fluoride and LiF can be decreased. Like curve 4 of FIG. 9 shows, the toughness drops even when used at the same time of complex metal fluoride and LiF suddenly

509514/217

21

borrowed when the total content of (P -f S) in the weld metal exceeds 0.050%.

The core filling can contain up to 30% metal oxide (for example MgO, Al ₂ O ₃ , TiO ₂ ) in order to improve the physical properties of the slag. Contents above 30% are at the expense of the fluoride and other components.

B ei sρ ie 1 1 ίο

Composition of the core filling

CaF .. 7iy

Mg-Ai alloy '(4Ö'% 'Äi) '.'.'...'.'.'.'.'. 20%

Mn 2%

Iron powder 7%

Proportion of flux (based on

Total amount of welding material) 22% electrode sheath:

Mild steel 3.2 mm ao

Electrode cross section F i g. 1 C

Base material:

Mild steel (P + S) 0.038%

Weld metal analysis

C 0.06%

Si 0.21%

Mn 0.73%

P 0.012%

S 0.007%

Al 0.98%

35

40

45

Stretch limit
(cb) Tensile strength
speed
(cb) strain
(7o) Notch impact
toughness
0 ⁰ C
(J) 43.5 47.1 37.1 42

Example 2 Composition of the core filling

CaF ₈ 78%

Mg-Al alloy (60% Al) 12%

Flux content 20%

Electrode sheath:

Mild steel 2.4 mm

Electrode cross section F i g. 1 D

Base material:

Mild steel (P + S) 0.035%

Weld metal analyzes

C 0.05%

Si 0.16%

Mn 1.60%

P 0.010%

S 0.007%

Al 1.26%

Stretch limit
(cb) Tensile strength
speed
(cb) strain
(V.) Notch impact
toughness
O ⁰ C
(J) 40.3 45.6 32.4 92

892

10

Example 3 Composition of the core filling

CaF ₂ 72%

Mg-Al alloy (60% Al) 12%

Ferromanganese (45% Mn) 6%

Nickel 3%

Ni-Mg alloy (50% Ni) 4.5%

Iron powder 5.5%

Flux content 18%

Electrode sheath:

Mild steel 3.2 mm

Electrode cross section F i g. 1 A

Base material:

Mild steel (P + S) 0.031%

Weld metal analysis

C 0.04%

Si 0.10%

Mn 0.96%

P 0.011%

S 0.005%

Ni 1.34%

Al 1.09%

Stretch limit
(cb) Tensile strength
speed
(cb) strain
(%) Notch impact
toughness
0 ⁰ C
(J) 46.7 51.2 31.2 105

55

6o

Example 4

Composition of the core filling

CaF ₂ 57%

Mg-Al alloy (40% Al) 28%

Mn 3%

Ni 12%

Flux content 24%

Electrode sheath:

Soft jet 2.4 mm

Electrode cross section F i g. 1 D

Base material:

Mild steel (P + S) 0.030%

Weld metal analysis

C 0.05%

Si 0.11%

Mn 1.31%

P 0.010%

S 0.005%

Ni 3.1%

Al 1.2%

Stretch limit
65
(cb) Tensile strength
speed
(cb) strain
(° / o) Notch impact
toughness
O ⁰ C
(J) 48.9 534 30.6 112

21

Example 5 Composition of the core filling

CaF, 46%

Mg-Al alloy (40% Al) 20%

CaCO, 3%

Ferromanganese (45% Mn) 4%

Ni 12%

Iron powder 15%

Flux content 19%

Electrode sheath:

Mild steel 3.2 mm

Electrode cross section F i g. 1 A

Base material:

Mild steel (P + S) 0.037%

Weld metal analysis

C 0.10%

Si 0.13%

Mn 1.12%

F 0.014%

S 0.005%

Ni 2.8%

Al 0.8%

64 892

Comparative example Composition of the core filling

CaF ₂ 67%

CaCO ₃ 3%

Ferromanganese (75% Mn) 5%

Al-Mg alloy (55% Mg) 17%

Ni 8%

Flux content 22%

ίο electrode jacket:

Mild steel 2.4 mm

Electrode cross section F i g. 1 C

Base material:

Mild steel (P + S) 0.022%

Weld metal analysis

C 0.07%

Si 0.11%

ao Mn 0.75%

P 0.010%

S 0.004%

Ni 1.46%

Al 1.34%

Stretch limit
(cb) Tensile strength
speed
(cb) strain
(° / o) Notch impact
toughness
0 ° C
(J) 47.4 51.1 28.3 98

Example 6 Composition of the core filling

CaF, 50%

Mg-Al alloy (40% Al) 24%

CaCO ₃ 15%

Ferromanganese (75% Mn) 3%

Ni 8%

Flux content 20%

Electrode sheath:

Mild steel 3.2 mm

Electrode cross section F i g. 1 D

Base material:

Mild steel (P + S) 0.034%

Weld metal analysis

C 0.17%

Si 0.11%

Mn 1.00%

P 0.012%

S 0.004%

Ni 1.7%

Al 0.9%

Stretch
border
(cb) Tensile strength
speed
(cb) strain
(7.) Notched impact strength
0 ⁰ C
(J) 45.4 56.1 30.2 71 80 76

Stretch limit
(cb) Tensile strength
speed
(cb) strain
(%) Notch impact
toughness
O ⁰ C
(J) 45.2 50.6 29.1 78

Example 7 Composition of the core filling

CaF ₂ 63%

K ₂ ZrF ₈ 4%

CaCO ₃ 2%

Ferromanganese (75% Mn) 5%

Al-Mg alloy (55% Mg) 15%

Ni 8%

MgO 3%

Flux content 31%

Electrode cladding metal:

Mild steel 2.4 mm

Electrode cross section F i g. 1 C

Base material:

Mild steel (P + S) 0.026%

Weld metal analysis

C 0.06%

Si 0.10%

Mn 0.78%

P 0.009%

S 0.005%

Ni 1.38%

Al 0.95%

Zr 0.06%

Stretch
border
(cb) Zvg'estig-
speed
(cb) strain
(%) Notched impact strength
0 ⁰ C
(J) 46.7 '"1.6 31.2 156 163 151

Example 8 Composition of the core filling

CaF ₈ 66%

LiF 7%

CaCO 3 ° /

Ferromanganese (75% Mn) '..'. '..' .. '.. 5%

Al-Mg alloy (55% Mg) 15%

Ni 4%

Flux content 21%

Electrode cladding metal:

Mild steel 2.4 mm

Electrode cross section F i g. 1 C

Base material:

Mild steel (P + S) 0.020%

Weld metal analysis

C 0.07%

Si 0.11%

Mn 0.75%

P 0.008%

S 0.003%

Ni 0.80%

Al 0.97%

Example 10

Composition of the core filling

CaF ₂ 53%

NaF 3%

LiF 3%

K ₂ TiF ₆ 2%

MgCO ₃ 2%

ίο Ferromanganese (75% Mn) 6%

Al-Mg alloy (67% Mg) 20%

Ni 3%

Iron powder 5%

MgO 3%

Flux content 25%

Electrode cladding metal:

Mild steel 2.4 mm

Electrode cross section F i g. 1 D

Base material:

high strength steel, tensile strength .. 60 cb

(P + S) in the weld material 0.023%

Result of the tensile strength test

Stretch limit (cb)

42.7

tensile strenght (cb)

strain

(Vo)

2 mm F-notch

Charpy value of the Impact strength at

0 ⁰ C

(J)

200 223

54.5 28.0

Example 9 Composition of the core filling

CaF ₂ 61%

LiF 4%

K ₂ ZrF ₆ 2%

CaCO ₃ 3%

Ferromanganese (75% Mn) 5%

Al-Mg alloy (55% Mg) 15%

Ni 5%

MgO 5%

Flux content 21%

Electrode sheath:

Mild steel 2.4 mm

Electrode cross section F i g. 1 C

Base material:

high strength steel tensile strength ... 50 cb 50 kg high tension steel

(P + S) 0.021%

Weld metal analysis

C 0.06%

Si 0.11%

Mn 0.70%

P 0.009%

S 0.003%

Ni 0.81%

Al 0.92%

Zr 0.04%

Stretch
border Tensile strength
speed
(cb) strain
(Vo) Charpy value
Notched impact strength
0 ⁰ C
(J) 43.2 56.3 28.1 250 265 252

Weld metal analysis

C 0.08%

Si 0.10%

Mn 1.35%

P 0.011%

S 0.003%

Ni 0.50%

Al 0.83%

Ti 0.03%

Stretch
border
(cb) Tensile strength
speed
(cb) strain
(Vo) Notched impact strength
0 ⁰ C
(J) 55.5 65.5 25.5 190 185 193

Example 11
Composition of the core filling

CaF ₂ 49%

LiF 5%

K ₂ TiF ₆ 2%

MgCO ₃ 3%

Ferromanganese (75% Mn) 6%

Al-Mg alloy (67% Mg) 16%

Cr 4%

Ni 9%

Cu 3%

MgO 3%

Flux content 23%

Electrode cladding metal:

Mild steel 2.4 mm

Electrode cross section F i g. 1 D

Base material:

high strength steel, tensile strength .. 80 cb 80 kg / mm ² high tension steel

(P + S) 0.20%

Weld metal analysis

C ..

Si ..

Mn

0.11%

0.09%

1.31%

0.008%

S 0.003%

1.62%

0.65%

0.43%

0.98%

0.03%

Stretch
border
(cb) Tensile strength
speed
(cb) strain
(Vo) Notched impact strength
0 ⁰ C
(J) 73.5 84.3 23.0 124 118 136

Example 12 Composition of the core filling

CaF ₂ 57%

NaF 2%

LiF 8%

MgCO ₃ 2%

Ferromanganese (75% Mn) 6%

Cr 5%

Al-Mg alloy (67% Mg) 15%

Iron powder 5%

Flux content 25%

Electrode cladding metal:

SUS-28 (stainless steel) 3.2mm

Electrode cross section F i g. 1 B

Base material:
stainless steel (P + S) in that

Welding material 0.031

Weld metal analysis

C 0.03%

Si 0.06%

Mn 2.10%

P 0.017%

S 0.003%

Cr 19.30%

Ni 9.65%

Al 0.73%

In addition 6 sheets of drawings

509514/217

Claims (12)

Patent claims: 1. Core electrode for automatic or semi-automatic arc welding of steel in air with a steel jacket and a core filling based on an aluminum-magnesium alloy, manganese and metal fluorides, consisting of 10 to 30% of the magnesium-aluminum alloy, 40 to 80% metal fluoride, 2 to 20% manganese, as well as potassium and sodium chloride in the context of impurities. 2. core electrode according to claim 1, characterized in that the core filling 5 to 25% Metal powder except the magnesium-aluminum alloy, 1 to 20% metal carbonate, 0.5 to 10% contains complex fluoride and 0.0 to 30% metal oxide. 3. core electrode according to claim 1 or 2, characterized in that the magnesium-aluminum alloy Contains 30 to 70% aluminum. 4. core electrode according to one or more of claims 1 to 3, characterized in that it contains as metal fluoride CaF ₂ , AlF ₃ , MgF ₂ , KF, LiF or rare earth metal fluorides individually or next to one another. 5. core electrode according to one or more of claims 2 to 4, characterized in that that they contain nickel, cobalt, chromium, titanium, zirconium, rare earth metals, calcium, Magnesium, aluminum, boron, tungsten, vanadium, iron and carbon, individually or side by side, contains. 6. core electrode according to one or more of claims 2 to 5, characterized in that it contains K ₂ ZrF ₆ , Na ₂ ZrF ₆ , K ₂ TiF ₆ or Na ₂ TiF ₆ as complex fluoride. 7. core electrode according to one or more of claims 2 to 6, characterized in that it is the metal oxide MgO, Al ₂ O ₃ . TiO ₂ , ZrO ₂ , MnO, MnO ₂ , K ₂ O, Na ₂ O, CaO, SiO ₂ , FeO, Fe ₂ O ₃ and Fe ₃ O ₄ individually or next to one another. 8. core electrode according to one or more of claims 2 to 7, characterized in that it contains as metal carbonate, magnesium, lithium and barium carbonate individually or side by side. 9. core electrode according to one or more of claims 1 to 7, characterized in that it contains an aluminum-magnesium alloy powder, the particles of which have a diameter of 20 to 70% below 0.074 mm. 10. core electrode according to one or more of claims 1 to 9, characterized in that that it results in a silicon content of at most 0.18% in the weld metal. 11. core electrode according to one or more of claims 1 to 9, characterized in that the core filling is 10 to 40% of the electrode weight. 12. core electrode according to one or more of claims 1 to 10, characterized in that that the total content of phosphorus and sulfur is not more than 0.040%. The invention relates to a core electrode for automatic or semi-automatic arc welding of steel in air with a steel jacket and a core filling based on an aluminum-magnesium alloy, Manganese and metal fluorides. When arc welding in air with a bare wire, oxygen and nitrogen get into the Weld metal and lead to pore formation and brittleness. To counter this come soul electrodes with a flux core for use. The task of the flux core is the arc to shield against the atmosphere, to form a welding slag, oxygen and nitrogen to set stable, to stabilize the arc and to guarantee a high weld metal quality overall. From the French laid-open specification 20 03 107 a core electrode is already known whose core filling, Based on the total weight, 10 to 40% and from 6 to 14% calcium fluoride, 0.1 to 1.5% manganese, 0.8 to 2% nickel, 2 to 5% of an aluminum-magnesium alloy with 35 to 65% aluminum and 0.006 to 0.06% sodium and potassium chloride. Furthermore, from the British Pa- a5 tentschrift 11 90 994 a similar electrode is known, their core, however, consists of 10 to 60% alkali metal fluoride, alkaline earth metal fluoride, rare earth metal fluoride, individually or next to each other, 5 to 25% alkali metal and / or alkaline earth metal carbonate and 10 to 50% one of the nitride formers magnesium, aluminum and zirconium with a total content of metal fluoride and carbonate as well as nitride formers of at least 30%. Finally, from British patent specification 11 45 560 there is also a core electrode with a core filling of 0.4 to 2.5% aluminum, 0 to 1.3% manganese, 0.2 to 0.7% alkali and / or alkaline earth fluoride and 0 , 1 to 0.4% potassium is known.
The invention is now based on the object of creating a core electrode of the type mentioned at the outset which results in a weld metal with high toughness without the addition of chloride. The solution to this problem consists in a core electrode whose core filling contains 10 to 30% of a magnesium-aluminum alloy, 40 to 80% metal fluoride, 2 to 20% manganese and potassium and sodium chloride as part of impurities. In addition, the flux core can also contain 5 to 25% of another metal powder, 1 to 20% of metal carbonate, 0.5 to 10% of a complex fluoride or up to 30% of metal oxide individually or next to one another. The core filling preferably makes up 10 to 40%, based on the total weight. In the case of the electrode according to the invention, the arc-sealing effect and the formation of slag are ensured by using a metal fluoride which predominantly consists of fluorspar. The fluoride is easily volatilized in the heat of the arc through the formation of a gas that closes the arc and partially converts into a metal oxide that forms the slag with the Mg-Al alloy. Since the slag is basic, it improves the mechanical properties of the weld metal. Experiments have shown that fluorides other than CaF ₂ , such as NaF, KF, AlF ₃ and MgF ₂ , also have a final effect, but do not show any noticeable effect as a slag-forming agent. On the other hand, however, the addition of a small amount of an alkali metal fluoride such as NaF and KF shows a light-