ABSTRACT
The safe use of an engineering structure relies on each of its components possessing the necessary mechanical properties, the most important of these properties usually being strength and toughness. This chapter describes how these properties are measured and how they can be influenced by changes in the microstructure. The theory of the connection between microstructure and toughness has been described by Knott and co-workers. The two most common testing methods are tensile and impact toughness testing. The quantity measured by impact toughness testing is the energy absorbed during fracture. The impact toughness data are notorious for their scatter, particularly in the transition temperature range where the fracture mode changes from ductile to brittle. The microstructure of the weld metal consists of massive ferrite and the strength of a multirun all-weld metal sample is around 350 MPa. Thus, the general microstructure and the inclusions are the two basic factors determining fracture toughness.
