a novel method to obtain an excellent
quality underwater wet welding joint.
Experimental Procedure
Q460 steel (equivalent to Gr. 65 steel
of AST-USA or E460DD steel of 630-
ISO) delivered as rolled sections with
the dimensions of 300 × 90 × 8 mm was
used as the base metal. The single-V
weld groove had a 60-deg included angle
with a 2-mm root face and 1.5-mm root
opening. The chemical composition of
the sheets is shown in Table 1. Prior to
welding, the oxide layers on the surfaces
of the plates were removed by stainless
steel wire brushing and the weld zone
was degreased using acetone. The asreceived
plates were welded together
with the gas tungsten arc (GTA) and
flux cored arc (FCA) welding processes.
GTAW was used for the root pass to fix
the plates with 100-A DC and 20 V in
air. Underwater wet FCAW was used for
the fill passes and optimized welding
parameters are listed in Table 2. TiO2
-
CaF2 type flux-cored wire with a diameter
of 1.2 mm produced by Paton Welding
Institute was chosen.
A schematic of the assembled device
is shown in Fig. 1. The device
could be divided into two sections: underwater
welding system and induction
heating system. The water in the
tank was stationary and the water
depth was 300 mm. A circular, 60-mmdiameter
induction coil was installed
behind the welding gun in the welding
direction and below the plates in the
vertical direction. The welding gun
and induction coil were fixed together
and moved at the same speed. The parameter
L — defined as the distance
between the center of the coil and the
welding gun — was constant. The induction
heating source had an output
voltage of 70–550 V. Changing the induction
heating voltage meant changing
the output power due to the constant
system impedance. Type-K thermocouples
with shielding were placed
at different locations from the edge of
the weld groove to measure the temperature
profile. Four-channel data
loggers were used to record the temperature
measurements with a sampling
frequency of 25 Hz. The measurement
method of the HAZ temperature
field was as follows: weld HAZ
without installed thermocouples was
first identified to be about 2.0 mm
from the weld interface, then the thermocouples
located at or near 2.0 mm
from the weld interface were identified
as that representing the HAZ
thermal cycle (Ref. 23).
A CCD camera with a frame rate of
2000 frames/s was used to record images
of the arc behavior in order to investigate
the effect of the induction
magnetic field. The metallographic
specimens of a typical cross section
were prepared vertical to the weld joint
and all specimens were polished with
SiC papers up to grit 1000, and ultrasonically
cleaned with acetone to remove
oil and other contaminants from
the specimen surfaces. Etching with 5%
nitric acid and alcohol solution for 3–4 s
was used to reveal the weld beam. The
macro- and microstructure fracture
morphology were observed by optical
microscopy (OM) and scanning electron
microscopy (SEM), respectively. Mechanical
property tests such as tensile
testing, impact testing, and bend testing
were investigated to build an empirical
relationship between induction heating
voltages and mechanical properties.
Results and Discussion
Welding Process Stability
A welding arc is an electric discharge
between two electrodes and a
heated and ionized gas, called plasma
(Ref. 24). Therefore, the arc stability
could be adversely affected as a result
of the magnetic field of induction
heating and eddy current. Figure 2
shows the captured images of arc