made with the same inoculant content of 0.3%. A total of 12 different inoculants or blends of inoculants were used (FeSi basis with different fractions of Ca, Cer, Sr, Bi etc.). Figure 6 shows an example of examinations of graphite forms in samples taken from different areas of the radial specimen. The results are for one Bi-containing inoculant of the test series. Plotted in the graph are the sums of graph- ite shapes V and VI relative to the wall thickness and the Si content. (The graphite shapes were determined through im- age analysis according to DIN EN ISO 945-1.) It is evident that with a certain type of inoculant, the percentage of the sum of graphite shapes V and VI decreases with increasing wall thickness. An important finding is that with increasing Si content the graphite shape deteriorates. This trend was even more pronounced with other inoculants. In the 0.2- in. plate, the sum of the graphite shapes V and VI scatters between 80% and 100% with all inoculants used. Only the alloy without inoculants features 70% of graphite nodules of types V and VI. In the 6.3-in. wall, the scatter band is much wider, ranging from 35% to 90%. The broader scatter band can be explained by the dependence of the graphite shape on the Si content and the chemical composition of the inoculant.
In Si-alloyed GJS materials, the graphite may deviate from the shapes V and VI depending on the solidification rate (wall thickness) and the inoculation condition. These de- viations may have a negative influence on the mechanical properties of the casting. They look in appearance macro- scopically similar to chunky graphite. Figure 7 shows such degenerated graphite assembly which has been isolated through deep etching. An appropriate inoculation technique and the use of inoculant Bi help avoid such deviating graph- ite shapes.
Investigation of the Machinability
Thanks to the uniform hardness of the metallic matrix, tool wear is much lower with ferritic ductile cast iron than with the ferritic/pearlitic alloy EN-GJS-500-7. According to Ref- erence 4, machinability is better by 10%.
To evaluate the machinability within the framework of this project, four of the investigated alloys were cast into cyl- inders of 4.73 in. diameter and 11.82 in. length. The tool life was used as a measure for the machinability of the four investigated cast iron materials. According to standard DIN 6583, the tool service life is the period elapsing until a cer- tain wear criterion is reached under identical machining con- ditions. In the tests described here, tool service life was de- termined to be the time elapsing until a flank wear of 0.008 in. was reached.
The results show that the Si-alloyed, solution strengthened materials with a ferritic matrix can be better machined than the ferritic/pearlitic materials. The ferritic materials prolong the tool lives by approximately 50% to 60% (Figure 8).
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Figure 8. Tool life at cutting speed of 9,450 in./min with the machining of the grades EN-GJS-500-7, EN-GJS-500-14, EN-GJS-600-3 and EN-GJS-600-10.
International Journal of Metalcasting/Volume 8, Issue 2, 2014
Figure 7. Graphite shape deviation comparable to chunky graphite.
Cast Techonological Properties of the High Silicon Ductile Iron
The high Si content of solution strengthened ductile cast irons is expected from previous experiences reported in the
Figure 6. This graph illustrates that inoculant, Si content and wall thickness all affect the microstructure.
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