Microstructure defines the behaviour of the material in use. Despite the fact it is extremely important, this is not always normalised and is not part of the name of the material. To compare two metals, it is mandatory to compare their composition but also their microstructure. Microstructure is due to the elaboration route and post treatments. Powder metallurgy produces fine grained materials with an isotropic annealed type structure. Complex machining can be performed due to the lack of internal residual stresses. Heat treatments are possible exactly as with conventional metallurgy and they are homogeneous due to the isotropy of the microstructure. Fatigue properties are always very good due to the fine grained structure, the lack of defects, the good surface definition and no skin effect.