Evaluation of mechanical properties of structural steel a36 on to ferrite formation

Abstract

In the present investigation it was determined that the hardness and strength are increased markedly to treatment at 850°C due to the formation of martensitic microstructure of low carbon. Treatment at 725°C, these features moderate values achieved by the presence of a mixture of ferrite and martensite (dual-phases). Perlite is replaced by the martensite phase. The toughness turns out to be higher for martensitic microstructures for dual phase microstructures (martensite-ferrite). The fractography analysis shows that for the first case, the type corresponds to intergranular fracture-ductile and for the second case, presents a quasi-type cleavage fracture caused by the discontinuous arrangement of martensite grain boundaries resulting in poor ability to absorb energy.

The tests at 725°C showed the formation of micro structural combinations of martensite and ferrite, showing a good combination of strength and elongation. Maximum increases were obtained in the tensile strength of the order of 51 and 54% for mixtures microstructural 21% martensite and 79% ferrite; 21.24% martensite and 78.76% ferrite. These quantities of martensitic and ferritic phases coincide with those considered by others to define dual phase steels.