Welding of high yield strength structural steels
The following provides a short summary of important points that should be taken into consideration when welding high strength steels.
• Always investigate if the specification or
component design will permit use of an
under-matching weld metal. Many structures
can be fabricated so that the welded joints are
positioned where stress levels are relatively
low, permitting undermatching welds.
The term “high strength” refers to steels with a
minimum yield strength of around 460 MPa
This group of structural steels generally obtains its
strength level by rapid cooling and is delivered in the
quenched and tempered condition, according to EN
10025-6. This manufacturing process enables high
strength to be achieved with a relatively low alloy
content and thereby low Carbon Equivalent (CE),
which in turn gives good weldability. This thermal
history also produces a microstructure that gives a
combination of high strength and good toughness.
• Only use low hydrogen welding consumables.
• Ensure that safe routines are in place for storage and handling of welding consumables in
order to minimize risk of exposure to moisture.
Coated electrodes packed in a cardboard box
with shrink plastic wrapping must always be
re-dried before use.
• Tack welds and root passes require special
attention, and the needs for preheating should
be carefully observed.
In order to produce weld metal with matching mechanical properties, however, a significantly higher
alloying level than that of the steel is required,
since control of microstructure via the quenching
and tempering operation is not available to the weld
deposit. This results in the weld also having a higher
CE, with consequential increased risk for hydrogen
As a result, the weld metal is often the controlling
factor when calculating the CE, together with the
critical minimum cooling time t8-5. The cooling
time is determined by the preheat, heat input, joint
design and plate thickness.
• Quenched and tempered steels normally have
an increased CE with increased plate thickness
and welding parameters may have to be adjusted accordingly if different joint thicknesses
arise in the same structure.
• Base welding parameter calculations on the
actual chemical composition of plate and do
not rely on nominal values.
• Cooling rates can differ significantly depending on whether two-dimensional or threedimensional cooling is involved, which in
turn is determined by joint design and plate
thickness. For this reason calculate welding
parameter settings according to EN 1011-2.
• Plate manufacturers often offer software to
facilitate the above calculations.