®COPYRIGHT
2000 THE ESAB GROUP, INC. LESSON
VI CARBON
AND LOW
ALLOY STEEL
FILLER METALS
FOR THE
GMAW, GTAW
AND SAW
WELDING
PROCESSES 6.1 INTRODUCTION
6.1.0.1
During the early part of the 20th century,
some welding was done using bare steel wires
or rods. The weld quality was poor because of the oxides and nitrides found
in the weld metal.
Even after the advent of the extruded coated electrode in 1927, automated
welding using
bare wires (or lightly coated wires) continued to be used, despite the poor qualities
of the welds,
because this method allowed more rapid deposition of the weld metal. Critical
welds, however, were made with coated
electrodes. 6.1.0.2
The advantages of using an inert gas
to shield the arc were known during the 20’s and
30’s, but the inert gases, such as helium and argon, were too expensive to
produce. 6.1.0.3
In 1935, submerged arc welding (then
known as submerged melt welding) was introduced
and provided a method of producing quality welds at greater welding speeds than
were obtainable with coated electrodes.
6.1.0.4 During
World War II, the aircraft industry needed a reliable process for welding
magnesium engine parts and as a result,
gas tungsten arc welding (GTAW), using a bare filler wire
and a helium gas shield, was developed. 6.1.0.5
Economical methods of producing the
inert gases were ultimately developed, leading
to the use of solid wire with a helium or argon gas shield in the 1940’s.
This process became
known as metal inert gas (MIG) welding. 6.1.0.6
In the early 1950’s, it was realized
that a more economical shielding gas, such as carbon
dioxide, could be used if the wire chemistry was adjusted to neutralize the oxidizing
effect of this gas. Since carbon
dioxide (CO2) is not an inert gas, the name
MIG welding actually
did not apply to this process since CO2
is a reactive gas. As a result, the American
Welding Society has standardized on
the term GMAW (Gas Metal Arc Welding) to include the inert
gases, active gases, and gas mixtures as covered in Lesson II. In Europe,
the term MIG (Metal
Inert Gas) welding still applies to the process if an inert gas or mixtures of
inert and active
gases are used, and the term MAG (Metal Active Gas) is used if straight CO2
is em- ployed
as the shielding gas.
