Initiation of Cleavage Fracture in a Weld Simulated Low Carbon Low Alloy Arctic Steel

The risk of brittle fracture is an important aspect when oil and gas exploration move to Arctic regions. Therefore, the present work addresses examination of fracture surfaces in scanning electron microscope to identify brittle fracture mechanisms. The study is based on Charpy and CTOD bend testing at -60 °C of weld thermal simulated specimens corresponding to both coarse grained HAZ (CGHAZ) and intercritically reheated coarse grained HAZ (ICCGHAZ). Brittle fracture was obtained by both test methods, and SEM investigation of the fracture surfaces revealed that slag particles like sulphides and oxides had initiated cleavage in the CGHAZ specimens, and that martensite-austenite (MA) particles probably were responsible for cleavage in the ICCGHAZ specimens. In both types of weld simulated structures, the crack initiation points were located close to the pre-crack tip.