as plate thickness increases, ultra-large heat input welding
becomes unavoidable. As a result, it is difficult to
obtain stable weld metal properties. Since dilution of the
base metal is large, it is important to adjust the composition
of the welding wire and flux corresponding to conditions,
but composition adjustment of solid wires
requires time and increases costs. Given this situation,
technical development was carried out to enable quick,
low cost composition adjustment corresponding to welding
conditions by using an ESW wire as a metal cored
wire (MCW) design13). Elements that cannot be added
stably in solid wires can be added easily by this MCW
design, and stabilization of the properties of the weld
metal of ESW is possible with extra thick materials.
Ministerial approval has already been obtained for these
wires, and final tests have been carried out aiming at the
practical application stage.
Regarding technical development in the field of steel
pipes, the following introduces a multiple electrode submerged
arc welding (SAW) method that can be applied
to welding of the longitudinal seam of welded pipes, as
performed in the UOE pipe manufacturing process. In
recent years, there has been a high need for heavy wall
thickness, high strength steel pipes. As a result, the
welding process has become the rate-determining step in
the manufacturing process, and decreased toughness of
the heat affected zone (HAZ) due to excessive heat input
and other negative effects have become a concern. Hitherto,
the compositions of the base metal and the weld
metal have been designed to be suitable for large heat
input welding, and study centered on large heat input,
high speed welding by multiple electrode SAW. However,
as shown schematically in Fig. 6, it is possible to
increase penetration depth and deposition efficiency,
even with the same welding current, by using a small
diameter wire, which had not been studied in the past.
Based on this, a heat input-saving SAW technology
which enables efficient welding was developed by
increasing the degree of freedom in control of the pene