Tensile Deformation of Cast Iron During Pearlite :Austenite Transformation

Abstract

Remarkable elongations have been obtained on cast iron samples subjected to alternate thermal cycles around the A₁ critical point, under a tensile stress lower than the yield stresses of the stable phases. This procedure makes use of the “phase transformation plasticity”, characterised by an apparent softening of the material during its structural evolution. The influence of the applied stress, as well as the heating and cooling rates,on the elongation per cycle has been studied. A quantitative comparison between this “soft” technique and the more classical high-temperature metal forming techniques (deformation in stable α or γ domains, or in α + γ domain, high temperature creep) showed that, for an equal strain, the internal cavitation resulting from the thermomechanical cycling deformation of spheroīdal graphite cast iron is much smaller than for other techniques. This soft technique leads to higher mechanical characteristics at room temperature.