Ductile cast iron (DCI) has been established in many major markets due to good wear resistance, ductility and low cost. To meet the components design requirements for efficiency and safety under the conditions of high speed and heavy load, the cyclic deformation behavior of DCIs is an important issue that has received limited attention. A nanostructured multiphase is obtained in an unalloyed commercial DCI designed by a novel multi-step low-temperature austempering treatment, which consists of lenticular prior martensite (PM), needle bainitic ferrite (BF), film/block retained austenite (RA) and a nano-scaled structure composed of fine lath BF and film carbon enriched RA ((BF+RA)nano). It is shown from a low-circle tension-tension fatigue test (a stress ration R=σmin/σmax=0, a constant amplitude is 600MPa) that the developed DCI achieves a longer fatigue life than the conventional DCI or austempered DCI. This is attributed to a certain amount of RA which can suppress the crack initiation and propagation due to plastic relaxation and formation of martensite resulting from the transformation induced plasticity (TRIP) effect. The (BF+RA)nano microstructure nucleated at PM interface shows more pronounced resistance to cyclic deformation and leads to the fatigue crack closure. Also, the multiphase synergistic strengthening mechanism which occurs under cyclic deformation is evaluated.
5:00 PM–7:00 PM Apr 23, 2019
PCC North, 300 Level, Exhibit Hall C-E