The fracture behavior for welded joint of new generation fine grained steel SS400 wasinvestigated and assessed on the basis of fitness for purpose philosophy. The actualcritical defect sizes for the SS400 base metal and its weld HAZ (heat affected zone)defined by the gross yielding criterium have been determined directly by means ofwide plate tests. It has been shown that although the HAZ grain growth occurs dueto the welding heat, the resistance to fracture is not deteriorated. The deformationbehavior of wide plate specimen was also studied by finite element (FE) analysis. Thedeformation of weld HAZ is protected by the high strength weld metal, so it is easierto get the general yielding for the welded joint specimen.