One example of experimental results as a function of time is shown in Figure 9. Results for all experiments as a function of oxygen activity are shown in Figure 10 for tensile strength, Figure 11 for proof strength and Figure 12 for elongation. The minimal elongation of 0.5 percent is too low to make a clear separation between compacted and lamellar graphite struc- tures (Figure 12), as in case of the ferritic ones (Figure 8). For industrial applications, Figure 11 is the most important one because the mechanical components will be dimensioned based on the proof strength. For the present experimental con- ditions, all tensile bars with a pearlitic matrix and without la- mellar graphite, present a proof strength higher than required by the ISO Standard (Table 3). However, in Figures 10 and 11, the well defined transition between compacted and lamel- lar graphite occurring for the ferritic matrix (Figure 6) is at first sight absent for the pearlitic matrix. It is due to the de- liberate variation in sulfur content for the experiments with the pearlitic matrix. For ease of examination, data points in Figure 10 are colored according to the sulfur content. Again sulfur content corresponds to the sulfur content in the melt during the transition from compacted to lamellar cast iron. It
illustrates that higher sulfur content moves the transition to lower oxygen activity. Consequently, for each series of exper- iments, the oxygen activity for which ISO minimal mechani- cal properties are not met anymore, have been determined as a function of the corresponding sulfur content. This is not al- ways possible for each experiment, since sufficient Y-blocks poured in the vicinity of the transition are not always avail- able. Figure 13 summarizes the results. A similar analysis has been carried out for the transition from compacted to lamellar graphite. The two separation lines V1-V2 from Figure 6, re- appear but now as a function of the sulfur content. Figure 13 reconfirms the existence of 3 zones, one left of the red line where ISO properties are met, a zone with compacted graphite between the red and blue line where this is not the case any- more and finally a zone right of the blue line where lamellar graphite occurs. As already mentioned, the proof strength in compacted graphite iron with a pearlitic matrix is most im- portant for industrial practice. As all data in Figure 11 meet the ISO standard, the transition from compacted graphite to lamellar graphite in Figure 13 may be used to fix the maximal allowable oxygen activity.
Table 1B . Chemical Analysis for All Heats with a Predominant Pearlitic Matrix
All heats: P 0.014; Cr 0.05; Ni 0.07; Ti 0.02; V 0.03; Mo
Note: during holding the melt in the furnace, elements like Mg and S vary. The sulfur content listed here is the one when the graphite structure changes from vermicular to lamellar. When the experiment or series was finished earlier, it is the sulfur content at the end of the experiment. Magnesium content corresponds to the initial maximal value. 080405 has 40-60% ferrite in the matrix. These results have only been used for nodularity (Fig. 18).
Table 3. Minimal Mechanical Properties for Compacted Graphite Iron with a Pearlitic Matrix
International Journal of Metalcasting/Spring 10
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