Core flux composition for flux-cored wires

A core flux composition of a flux-cored wire for welding and surfacing high-strength steels with a gas-shielded process comprises the core flux ingredients taken in the following amounts, by weight %: ______________________________________ rutile concentrate 14.0-23.0 fluorite concentrate 7.0-12.0 sodium fluosilicate 2.0-6.0 ferromanganese 6.0-10.0 ferrosilicon 1.5-4.0 ferromolibdenum 1.0-2.5 chromium (elemental) 1.0-2.5 nickel (elemental) 4.0-9.0 iron powder 31.0-63.5 ______________________________________

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to materials for arc welding, and in 
particular to flux composition for flux-cored wires for welding and 
surfacing high-strength alloyed steels with a gas-shielded process. 
The invention may be used more efficiently in flux-cored wires designed for 
automatic and semiautomatic welding in normal, inclined and in horizontal 
position in a vertical plane. 
2. The Prior Art 
Known in the art are flux compositions for flux-cored wires which are used 
for welding and surfacing high-strength alloyed steels with CO.sub.2 
-shielded process in all welding positions and which comprise a steel 
sheath filled with powdered flux forming a core thereof. There is also 
known a flux-cored wire having a flux core containing the following 
ingredients, by weight %: 
______________________________________ 
low-carbon ferrochromium 
18.7-75.0 
ferromolybdenum 2.1-8.4 
manganese 0.8-2.9 
ferrosilicon 3.0-13.7 
iron powder 69.0-0 
(cf. U.S. Pat. No. 3,253,120) 
______________________________________ 
It is a common knowledge that during welding a great amount of hydrogen 
dissolves at molting temperature in the weld joint metal, which lowers the 
resistance thereof to cracks. As the weld seam produced by welding 
high-strength alloyed steels is liable to cracks the hydrogen content in 
the weld seam metal should be kept as low as possible. Since the 
flux-cored wire having a core formed from the above flux composition does 
not prevent hydrogen from its dissolving in the weld metal the hydrogen 
content therein is considerable. In addition, the weld seams produced with 
the use of this flux-cored wire have a bead shape which lowers their 
fatigue strength. 
The best results in welding and surfacing high-strength alloyed steels have 
been obtained with the use of a flux-cored wire having a core flux 
composed of the following ingradients, by weight %: 
______________________________________ 
calcium fluoride 5-25 
magnesium oxide 5-15 
silicon dioxide 0-25 
ferrosilicon 5-10 
ferromanganese 2-5 
ferrochromium 0-5 
ferromolybdenum 0-20 
nickel 0-20 
alluminium magnesium powder 
0-15 
(cf. U.S. Pat. No. 3,424,892) 
______________________________________ 
The weld seam produced with the use of a wire having the above core flux 
composition features high mechanical properties. Calcium fluoride 
contained in the above flux composition prevents the formation on the weld 
seam surface of the oxide film of the high melting-point oxides, and to 
some extent binds hydrogen dissolving in the weld metal, in the course of 
welding, to form volatile fluorides, thereby lowering hydrogen content in 
the weld metal. However, in the process of welding with the above 
flux-cored wires there takes place intensive spattering of the electrode 
metal, which is due to the fact that calcium fluoride contained in the 
above flux composition is known to be an active destabilizer of the arc. 
In addition, weld seams produced with the use of flux-cored wires having 
the above core flux composition are of a bead shape and have coarse 
ripples, which lowers their fatigue strength. To remedy this disadvantage 
the resulting weld seam has to be machined, which is associated with 
additional labour consumption. It should be also noted that the weld seam 
thus obtained contains from 0.040 to 0.045 weight percent oxygen, and 
hydrogen inspite of the fact that the latter is partially bound by calcium 
fluoride at a rate of 4-5 cm.sup.3 per 100 g of the weld metal. Such 
content of gases in the weld metal lowers resistance thereof to cold 
cracks and its impact strength at temperatures both below and above zero. 
The principal object of the invention is to provide a flux composition of 
flux-cored wires for welding and surfacing high-strength alloyed steels, 
which would improve welding properties of flux-cored wires. 
Another object of the invention is to impart high mechanical properties to 
the weld seam metal. 
Still another object of the invention is to lower oxygen and hydrogen 
content in the weld seam metal. 
Yet another object of the invention is to improve notch impact strength of 
the weld seam metal at temperatures both above and below zero. 
A further object of the invention is to enhance resistance of the weld seam 
metal both to cold and hot cracks. 
Other objects and advantages of the present invention will be apparent from 
the specification given below. 
SUMMARY OF THE INVENTION 
These and other object of the invention are accomplished by that a flux 
composition of flux-cored wire for welding and surfacing steels with a 
gas-shielded process, containing calcium fluoride, ferrosilicon, 
ferromanganese, elemental chromium, ferromolybdenum and elemental nickel, 
according to the invention further includes rutile concentrate, sodium 
fluosilicate, and iron powder with all the above ingredients being taken 
in the following amounts, by weight percent: 
______________________________________ 
rutile concentrate 
14.0-23.0 
fluoride concentrate 
7.0-12.0 
sodium fluosilicate 
2.0-6.0 
ferromanganese 6.0-10.0 
ferrosilicon 1.5-4.0 
ferromolybdenum 1.0-2.5 
(elemental) 
chromium 1.0-2.5 
(elemental) 
nickel 4.0-9.0 
iron powder 31.0-68.5 
______________________________________ 
The flux-cored wires having the proposed core flux composition permits 
forming weld seams in normal, inclined and horizontal positions in a 
vertical plane, with the amount of spattering electrode metal constituting 
from 4 to 6% by weight. The resultant weld seams have a smooth surface and 
even transition to the basic metal, i.e. metal being welded. The resultant 
weld metal is well deoxidized and contains 0.020-0.080 weight percent 
oxygen, and small amount of hydrogen from 0.8 to 1.5 cm.sup.3 per 100 g of 
weld deposit. It should be also noted that the weld seam metal features 
high resistance to cold and hot cracks and a high notch impact strength at 
low temperatures. 
The presence in the proposed core flux composition of rutile concentrate in 
said amounts provides for stable arcing and proper formation of the weld 
seam. The resultant seam has a smooth surface and a gradient transition to 
the basic metal. 
Decreasing the rutile concentrate content below the said lower limit 
increases the convexity of the seam and results in more intensive 
spattering of the electrode metal. At the same time increasing the rutile 
concentrate content in the proposed flux composition above the said upper 
limit results in poor welding properties of the slag: its gas permeability 
becomes lower, and the range of its crystallization gets smaller, which 
affects the formation of the weld seam. 
Introduction into the proposed flux composition of sodium fluosilicate in 
the said amounts makes it possible to bring down the hydrogen content in 
the weld seam metal to 0.8-1.5 cm.sup.3 per 100 g of the weld deposit. 
Decreasing its content below the said lower limit results in the increased 
hydrogen content in the weld metal, whereas the hydrogen content exceeding 
the said upper limits leads to intensive spattering of the electrode 
metal. 
The presence in the proposed composition of alloying elements, such as 
ferromolybdenum, nickel and chromium improves mechanical properties of the 
weld seam metal with respect to the yielding, tensile strength and notch 
impact strength thereof at temperatures above and below zero. The 
resistance of the weld metal to cold cracks is also improved as a result. 
Introducing the above alloying elements in amounts below the said lower 
limit impairs mechanical properties of the resultant weld seam, such as 
yielding and tensile strength. 
Decreasing the ferromolybdenum and nickel content in the proposed core flux 
composition below the said lower limit results in a lower notch impact 
strength of the weld seam metal produced with the use of the flux-cored 
wire having the proposed core flux composition, at temperatures below 
zero. The ferromolybdenum and nickel content in the proposed flux 
composition exceeding the said upper limit affect the plasticity (specific 
elongation and impact strength) of the weld seam metal produced with the 
use of the flux-cored wire having a core formed from the proposed core 
flux composition. Increasing the content of chromium in the proposed core 
flux composition results in lower resistance of the weld seam metal to 
cold cracks.

DETAILED DESCRIPTION OF THE INVENTION 
The invention will now be explained with reference to embodiments thereof. 
EXAMPLE 1 
Welding high-strength steel test pieces was done with the use of 2.2 mm 
flux-cored wires (designated as A, B and C) having a core formed from the 
flux composition of the invention. A steel sheath of each wire constituted 
70% by weight of the electrode wire used and contained the following 
ingredients; in wgt %, carbon--0.05, manganese--0.20, silicon--0.12, 
sulphur--0.020, phosphorus--0.020. 
Welding was carried out in a normal position with a semi-automatic process 
using 350 amp welding direct current of reversed polarity, and welding arc 
voltage of 27 V. 
Carbon dioxide was used as a shielding gas. 
The steel in the test pieces 20 mm thick contained 0.12% of carbon, 1.1% of 
manganese, 0.25% of silicon, 1.5% of chromium, 0.2% of nickel, 0.50% of 
molibdenum, 0.004% of boron. 
The core flux composition used contained the following ingredients, in 
weight %: 
TABLE 1 
______________________________________ 
Flux-cored wire 
Core flux ingredients 
A B C 
1 2 3 4 
______________________________________ 
Rutile concentrate 
14.0 20.0 23.0 
Fluorite concentrate 
7.0 10.3 12.0 
Sodium fluosilicate 
2.0 4.0 6.0 
Ferromanganese 6.0 9.0 10.0 
Ferrosilicon 1.5 2.8 4.0 
Ferromolybdenum 1.0 1.8 2.5 
Chromium 1.0 1.8 2.5 
Nickel 4.0 7.0 9.0 
Iron powder 63.5 43.3 31.0 
______________________________________ 
Metal of the weld seams formed with the use of the flux-cored wires having 
a core made from the above core flux compositions was tested for notch 
impact strength, specific elongation, tensile strength, and was subjected 
to physicochemical analysis to determine the content of oxygen, nitrogen, 
and hydrogen in the weld metal. 
Mechanical tests were conducted by applying conventional methods. 
Oxygen, nitrogen and residual hydrogen content was determined by 
conventional vacuum melting method, whereas the diffusive hydrogen content 
was found by the international standard ISO 3690. 
The comparative results of mechanical tests and chemical analysis given in 
tables 2 and 3 illustrate advantages of the flux-cored wires having a core 
formed from the proposed flux composition over the prior art flux-cored 
wire (U.S. Pat. No. 3,424,892). 
TABLE 2 
______________________________________ 
Spe- Notch impact strength, 
Flux- Yield Tensile cific kgpm/cm.sup.2 (Mesnager 
cored point, strength, 
elong. 
notch test) 
wire kg/mm.sup. 2 
kg/mm.sup.2 
% +20 -40.degree. C. 
-50.degree. C. 
1 2 3 4 5 6 7 
______________________________________ 
A 65.1 77.0 18.1 10.8 8.3 6.0 
B 68.4 81.0 20.0 13.7 12.2 9.0 
C 84.5 73.4 19.0 12.7 11.0 7.6 
Prior 
art 
(U.S. 
Pat. 
No. 
3,424, 
892) 91.2 94.5 16.0 8.2 4.0 3.5 
______________________________________ 
TABLE 3 
______________________________________ 
Gas content, wgt % Hydrogen content, 
cm.sup.3 /100 g 
total (dif- 
Flux-cored fusive and 
wire Oxygen Nitrogen diffusive 
residual) 
1 2 3 4 5 
______________________________________ 
A 0.030 0.015 0.8 1.5 
B 0.025 0.010 0.6 0.8 
C 0.029 0.012 0.9 1.3 
Prior art, 
(U.S. Pat. 
No. 3,424,892 
0.045 0.015 2.0 4.0 
______________________________________ 
As can be seen from the above tabulated test results the weld seams 
produced with the use of the flux-cored wires having a core made from the 
core flux composition of the invention feature higher impact strength, 
especially at temperatures below zero, and lower gas content, and in 
particular a low hydrogen content. 
In addition, the flux-cored wires having the core flux composition of the 
invention provide for a proper formation of the weld seams: concave shape 
with a gradient transition to the basic metal, easy-to-remove slag film, 
high resistance to hot cracks, and low intensity of the electrode metal 
spattering. 
EXAMPLE 2 
(negative) 
Welding steel test pieces was done, in general, in the same manner as in 
Example 1, for except that the ingredients of the core flux composition 
were taken in amounts which were below the lower limit indicated in the 
appended claims. 
The above core flux composition contained the following ingredients, by 
weight %: 
______________________________________ 
Rutile concentrate 
12.8 
Fluorite concentrate 
6.8 
Sodium fluosilicate 
1.8 
Ferromanganese 5.8 
Ferrosilicon 1.4 
Ferromolybdenum 0.8 
chromium 0.8 
Nickel 3.8 
Iron powder 66.0 
______________________________________ 
Below are given results of the mechanical tests and phisicochemical 
analysis of the weld seam metal: 
______________________________________ 
Yield point, kg/mm.sup.2 
60.0 
Tensile strength, kg/mm.sup.2 
72.0 
Specific elongation, % 14.0 
Notch impact strength (Mesnager notch 
test), kgmp/cm.sup.2 : 
+20 C. -- 
-40.degree. C. 1.5 
-50.degree. C. -- 
Oxygen content, wgt. % 0.05 
Nitrogen content, wgt. % 
0.018 
Residul hydrogen, cm.sup.3 /100 g 
2.5 
Total diffusive and residual hydrogen, 
cm.sup.3 /100 g 4.5 
______________________________________ 
The weld seam produced by using the flux-cored wire having the above core 
flux composition features lower mechanical properties and higher content 
of gases, increased liability to pores and cracks, and more intensive 
spattering of the electrode metal. 
EXAMPLE 3 
(negative) 
Welding steel test pieces was done, in general, in the same manner as in 
Example 1, for except that the ingredients of the core flux composition 
were taken in amounts which were above the upper limit indicated in the 
appended claims. 
The above core flux composition contained the following ingredients, weight 
%: 
______________________________________ 
Rutile concentrate 
23.5 
Fluorite concentrate 
12.2 
Sodium fluosilicate 
6.2 
Ferromanganese 10.2 
Ferrosilicon 4.2 
Ferromolybdenum 2.7 
chromium 2.6 
Nickel 9.2 
Iron powder 29.2 
______________________________________ 
Given below are results of mechanical tests and physicochemical analysis of 
the weld metal: 
______________________________________ 
Yield point, kg/mm.sup. 2 
68.0 
Tensile strength, kg/mm.sup.2 
80.0 
Specific elongation 13.0 
Notch impact strength (Mesnager notch 
test), kgpm/cm.sup.2 : 
+20.degree. C. 7.5 
-40.degree. C. 2.0 
-50.degree. C. -- 
Oxygen content, wgt. % 0.050 
Nitrogen content, wgt. % 
0.016 
Residual hydrogen content, cm.sup.3 /100 g 
2.5 
Total residual and diffusive hydrogen, 
cm.sup.3 /100 g 4.5 
______________________________________ 
The above mechanical tests and physicochemical analysis show that the weld 
seam produced with the use of the flux-cored wire having a core made from 
the above core flux composition has lower plasticity (specific elongation 
and impact strength) and a higher content of gases. Further, in the course 
of welding there were observed more intensive spattering of the electrode 
metal, and the weld seams had coarse ripples and bead form. 
While particular embodiments of the invention have been shown and 
described, various modifications thereof will be apparent to those skilled 
in the art and therefore it is not intended that the invention be limited 
to the disclosed embodiments and the departures may be made therefrom 
within the spirit and scope of the invention as defined in the claims.