On Phase Distribution and Phase Transformations in Phosphoric Irons Studied by Metallography

The microstructures of novel phosphoric irons have been studied by metallography in order to understand the phase distribution and phase transformations in the iron-rich end of the Fe-P phase diagram. Both Nital etchant and Oberhoffer’s reagent were effective in revealing dual-phase microstructures of phosphoric irons that were heat treated in the (α + γ) region. The phase distribution in dual-phase microstructures was analyzed by quantitative metallography and related to the phase diagram. The morphology of austenite depended on phosphorus content and heat-treatment temperature. The microsegregation of phosphorus and phosphorus diffusivity was studied as a function of the temperature and soaking time of the specimens. The beneficial effect of the heat treatment of phosphoric irons in the dual-phase region of the Fe-P phase diagram on mechanical behavior has been confirmed by tensile testing.