Issue 13

F. Iacoviello et alii, Frattura ed Integrità Strutturale, 13 (2010) 3-16; DOI: 10.3221/IGF-ESIS.13.01 5 I NVESTIGATED DCI S AND EXPERIMENTAL PROCEDURES nvestigated DCIs were characterized by five different matrix microstructures and by a good graphite elements nodulization. The first three ferritic-pearlitic DCIs were obtained by means of chemical composition control: as a results, matrix microstructures ranged from a completely ferritic DCI up to a completely pearlitic one. Chemical compositions and phases volume fractions are in Tab. 1-3. C Si Mn S P Cu Cr Mg Sn 3.66 2.72 0.18 0.013 0.021 0.022 0.028 0.043 0.010 Table 1 : DCI EN GJS350-22 chemical composition (100% ferrite), Fig. 3. C Si Mn S P Cu Cr Mg Sn 3.65 2.72 0.18 0.010 0.03 - 0.05 0.055 0.035 Table 2 : DCI EN GJS500-7 chemical composition (50% ferrite – 50% pearlite), Fig. 4. C Si Mn S P Cu Mo Ni Cr Mg Sn 3.59 2.65 0.19 0.012 0.028 0.04 0.004 0.029 0.061 0.060 0.098 Table 3 : DCI EN GJS700-2 chemical composition (100% pearlite), Fig. 5. Ferritic-pearlitic DCI obtained by means of a chemical composition control (Tab.2) is characterized by the presence of ferritic shields around graphite nodules embedded in a pearlitic matrix (Fig.4). Figure 3 : DCI EN GJS350-22 microstructure (100% ferrite). Figure 4 : DCI EN GJS500-7 microstructure (50% ferrite – 50% pearlite). Figure 5 : DCI EN GJS700-2 microstructure (100% pearlite). The annealing of a pearlitic DCI EN GJS700-2 (Tab. 3) allowed to obtain a fourth ferritic-pearlitic DCI, with ferrite and pearlite volume fraction equal to about 50%. This ferritic pearlitic DCI obtained by means of heat treatment control is characterized by a microstructure that does not show ferritic shields around graphite nodules (Fig. 6), as in EN GJS500-7. However, graphite elements nodularity is always high. The fifth investigate DCI is an austempered one (ADI, GGG 70BA; chemical composition in Tab. 4) . In order to obtain an ADI, the following heat treatment was performed:  910°C (70 min.);  Salt bath cooling (2 hours at 370°C and, after, 60 sec. at 320°C);  Air cooling up to room temperature. After this heat treatment, a reduced graphite nodules degeneration was observed and a bainitic microstructure was obtained, with a really low residual ferrite volume fraction. C Si Mn Mo Ni Sn S 3.61 2.23 0.32 0.42 0.52 0.045 0.015 Table 4 : Austempered DCI chemical composition GGG 70BA, Fig. 7. I