the transition lines in Figure 13 (as stated in the paper on p 9). The manual addition may influence to some extent the inoculation efficiency as well as slight changes in metal tem- perature during tapping or the time elapse between filling of the ladle and the pouring of the Y-block. Possibly, this could explain variations in nodularity. However, we have no facts to prove this hypothesis.
Reviewer: Nickel is mentioned to affect the results but there is no explanation as to why. Also, if nickel has an effect, what other elements have an effect that are not mentioned.
Authors: When we compare the results of samples contain- ing about 0.7 percent Ni of our previous publication (refer- ence 8) with the present results shown in Figure 18, only one data point has higher nodularity for a given oxygen activity (nodularity 35% at aO
300 ppb, 30 ppm S) than the corre-
sponding samples without nickel. It does not allow any con- clusions with respect to nickel.
In general an element X can influence oxygen activity in two ways: • The element can combine with oxygen, or • The element could change the oxygen activity due to its interaction coefficient.
Moreover, the element could influence nodularity by varying the graphite growth. An element j can change the oxygen activity by means of the (first order) interaction coefficient ei
as discussed for example in reference 29. A list of interac- tion coefficients for liquid iron is given by Sigworth and El- liot (reference below). However, these data are valid for liq- uid iron measured at much higher temperature than in case of the present conditions for cast iron. Extrapolation from liquid iron to liquid cast iron may result in large errors.
j
At present, we did limited research to study the influence of elements on oxygen activity in cast iron. In case of gray iron, an increase in carbon content decreases oxygen activ- ity. However, when Mg is present in the melt we found that oxygen activity is controlled by this element only. We did not examine the effect of cerium. In fact, in all our experiments, cerium was never added. (Reference: Sigworth, J.K., Elliot, J.F., “The Thermodynamics of Liquid Dilute Iron Alloys,” Metal Science, vol. 8, pp 298-310, 1974).
Reviewer: Figures 1 and 2 and later figures show up to 22% elongation with nodularities 60% and below and ex-
plain this with different measurement methods for nodular- ity. For the same test with 22% elongation, they have one estimate with >90% nodularity, then two others that are around 60%. The photo does not appear to be 90% but seems to be more than 60%.
Authors: In Figure 14, nodularity is defined differently in each case. For NF A04-197 it is equal to type V + VI; for ISO 16112 it is equal to type VI + 0.5 (IV + V) and the present method considers graphite particles with length to thickness ratio
Reviewer: On fig 6 the min O ppb is 300, on fig 7 it is 350, on fig 10 it is 200, on fig. 12 it is 400. If we look at individual heats, on fig. 10 it is 400 for heat 80563 and on fig 11 at least 500 for heat 80742. Thus, it can be concluded that while the properties trend well with the oxygen content, oxygen is not the only significant variable. This suggests that nodularity is not a function of O alone.
Authors: In the Figures mentioned, different properties are plotted as a function of oxygen activity (tensile strength, proof strength and elongation). The figures simply show that for a given test bar, one property may be lower than re- quired by ISO while the others properties comply. This fact has been noted regularly. In order to satisfy all ISO require- ments, the minimal oxygen activity corresponding to ten- sile strength, proof strength and elongation must be taken. Oxygen activity is certainly not the only parameter which influences nodularity. Another parameter is the inoculation efficiency. Better inoculation will increase nodularity. Since sulfur is known too for its effect on inoculation, this factor can play a role too. Finally, cooling rate has a strong influ- ence. Higher cooling rate increases nodularity.
International Journal of Metalcasting/Spring 10
43
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