It is important that thick section structural steels achieve adequate levels of HAZ fracture toughness, particularly in highly stressed regions. In the early 1980s, it was found that very low levels of fracture toughness could occur in localized regions within HAZs, known as local brittle zones (LBZs). However, it was not clear which aspects of steel chemistry, or welding procedure were causing the problem.In order to examine this problem, a program was undertaken to compare the HAZ toughness of a wide range of BS4360 Grade 50E steels welded at a range of heat inputs. The steels covered ingot-cast, concast, normalized, controlled-rolled, accelerated-cooled and Ti-treated. Toughness tests were conducted on as-welded and postweld heat treated (PWHT) specimens, with notches in the various potentially embrittled HAZ regions. The findings of the initial part of this program, which examined 12 steels welded by the SAW process at a heat input of 3 kJ/mm, have been published elsewhere. Further studies involving CTOD transition behavior of specific HAZ regions in 8 of the steels has also been published.This paper describes studies conducted on steels welded by the Flux-Cored Arc Welding (FCAW) process at a heat input of 1 kJ/mm and the Submerged-Arc Welding (SAW) process at a heat input of 5 kJ/mm. This involved Charpy tests and CTOD tests in the grain coarsened HAZ (GCHAZ) and subcritical/intercritical HAZ (SI/ICHAZ) regions of the multipass welds in both the as-welded and PWHT conditions. Particular emphasis was placed on fractographic and metallographic examination of CTOD specimens to establish which particular microstructural regions exhibited low fracture toughness.