FRACTURE-TOUGHNESS OF COLD-WORKED AND SIMULATED HEAT-AFFECTED STRUCTURAL-STEEL

Deterioration of fracture toughness due to both cold working and weldi ng are studied to investigate the combined effect which is seen in the welded part of cold worked members. It is known that fracture toughne ss is degraded in cold-worked steels by strain aging and is also degra ded in the heat affected zone (HAZ). In this experimental study, CTOD tests are carried out using simulated HAZ specimens which are pre-stra ined before heat treatment. Although multi-pass welding produces a com plex distribution of microstructures in HAZ, two types of thermal cycl es ale used to simulate the HAZ. One is to simulate intercritically re heated coarse grain HAZ (IRCG HAZ), the most degraded part in the loca l brittle zone. Another is to simulate subcritical HAZ (SC HAZ:), the least degraded part in HAZ. In these two types of simulated microstruc tures, the effects of cold working are discussed based on fracture mec hanics. It can be observed that the fracture toughness in IRCG HAZ is fairly low and the variation of fracture toughness with increasing pre -strain does not exist in that particular region. The fracture toughne ss in SC HAZ is not so crucial as seen in IRCG HAZ, but is strongly af fected by pre-strain before heat treatment. (C) 1997 Elsevier Science Ltd.