1978 Volume 47 Issue 3 Pages 136-141
The concept that the toughness of low and medium strength steels is well defined by the two parameters δi (COD at fibrous crack initiation) and Ti (fibrous-cleavage transition temperature in fracture initiation) has been applied to the toughness evaluation of welded joint. Tests were made on the coarse-grained region of the heat-affected zone (HAZ) of SM50C by using 3 point bend specimens in the tem-perature range from -196°C to room temperature.
Although δi of HAZ specimen takes almost the same value as that of base metal, Ti's of HAZ specimens show high temperatures than those of the base metal by 60°-70°C, for both fatigue-precracked and 0.1R mechanical-notched specimens. The value of the stretched zone depth (SZD) measured on the fracture surface shows the value of COD at fracture initiation regardless of the material (base metal or HAZ) and fracture mode (fibrous or cleavage). Therefore, the toughness of a welded joint could be evaluated by SZD instead of COD.