CEMP-E
TI 809-26
1 March 2000
2. FLUX CORED ARC WELDING (FCAW).
a. Process Principles. Flux cored arc welding (FCAW) is an arc welding process that uses a
continuous tubular electrode fed from a coil or spool into a welding "gun". The electrode core contains
alloy additions, deoxidizers and flux materials. The heat of the arc causes the base metal, tubular
electrode wire and core materials to melt. The flux materials bind impurities, rise to the top of the molten
weld, and protect the cooling weld from atmospheric nitrogen or oxygen. Shielding of the exposed arc is
provided either by the decomposition of the core in self-shielded electrodes, designated FCAW-S, or by
an externally supplied gas or gas mixture, designated FCAW-G.
(1) With FCAW-G, carbon dioxide (CO2) or a mixture of argon (Ar) of 75 to 90% and of CO2 10 to
25% is used in addition to the gas provided by the flux core. The shielding gas selection may affect the
mechanical properties (yield and tensile strength, elongation, and notch toughness) of the weld. Carbon
dioxide, as a reactive gas, may cause some of the alloys in the electrode to become oxidized, and
therefore less alloy is transferred to the weld deposit. When an inert gas such as argon is substituted for
CO2, alloy transfer typically increases. With more alloy in the weld deposit, higher yield and tensile
strengths and reduced ductility is expected. The notch toughness of the weld deposit may increase or
decrease, depending on the alloys affected.
(2) The power source is usually the constant voltage type, using either direct current electrode
positive or electrode negative polarity. A separate wire feeder sends wire into the welding gun at a preset
rate. The Welding Procedure Specification (WPS) provides the appropriate voltage, wire feed speed,
electrode extension, and travel speed. For a given wire feed speed and electrode extension, a specific
current (amperage) will be provided. As the wire feed speed is increased, the current is likewise
increased. The WPS should, preferably, state the wire feed speed to be used because electrode
extension, polarity and electrode diameter also affect current. Shorter electrical stickout results in higher
current for a given wire feed speed. If current is used in the WPS, an inaccurate electrode extension may
go undetected.
(3) FCAW is most commonly used as "semiautomatic", wire fed but with the welding gun
manipulated by the welder. It may also be used as automatic, but the intensity of arc rays from the high
current arc, and the significant volume of smoke generated, make Submerged Arc Welding (SAW) more
desirable for automatic welding.
b. Filler Metal Designation, Specification and Certification. FCAW electrodes are specified in AWS
filler metal specifications AWS A5.20 and A5.29. AWS A5.20 is applicable to carbon steel electrodes,
and AWS A5.29 is applicable to low alloy steel electrodes. The classification and identification system
used for these two specifications is summarized in Tables C-6 and C-7.
(1) All FCAW electrodes are considered low hydrogen. Self-shielded FCAW electrodes are limited
to 550 MPa (80 ksi) tensile strength of less, but higher strengths are available from gas-shielded FCAW
electrodes. AWS A5.20 electrodes EXXT-2, -3, -10, -13, -14, and -GS electrodes are not permitted by
AWS D1.1 because they are limited to single pass welds. AWS A5.20 electrodes EXXT-3, EXXT-11, and
EXXT-14 are for limited thickness applications only, and the manufacturer's recommendations should be
consulted.
(2) Tables C-8 and C-9 provide additional information regarding electrode limitations, usage and
toughness properties for electrodes permitted by AWS D1.1 for classification strengths of 550 MPa (80
ksi) and lower. For higher strength and other electrodes, the AWS A5.20 and A5.29 specifications should
be consulted.
C-8
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