Welding Inspection & Metallurgy API ICP Self Study Notes

Both solidification cracking and hot cracking refer to the formation of
shrinkage cracks during the solidification of weld metal, although hot cracking
can also refer to liquation cracking. Solidification cracks can appear in several
locations, and orientations, but most commonly are longitudinal centreline
cracks (coincident with the intersection of grains growing from opposite sides
of the weld), or 'flare' cracks, again longitudinal, but at an angle to the
through-thickness direction ( Fig.1). Where there is a central segregate band
in the plate, cracking may extend from this position at the fusion boundary
( Fig.2). The cracks in all locations can be buried ( Fig.3) or surface-breaking.
http://www.twi-global.com/technical-knowledge/faqs/material-faqs/faq-what-is-hotcracking-solidification-cracking/