3
U B V N M
Alloy
B V N M
29.4 N Load 3.36 2.52 3.08 2.8
Results and Conclusions
According to Padan,
the results from the experiments confi rmed
that microalloying ADI with 0.1% vanadium or 0.043% niobium with
1.4% nickel improved ultimate ten- sile strength signifi cantly, superior to that of conventional ADI alloyed with 0.3% molybdenum and 1.4% nickel (Fig. 5). T e wear resistance of the microalloyed ADI improved signifi cantly, as well.
Table 3. Mechanical Properties of Austempered Ductile Irons (Austenitized at 1,652F for 1 Hour and Austempered at 635F for 1.5 Hours)
Alloy Tensile Strenth (MPa)
928 930
1088 980 960
Yield Strenth (MPa)
780 780 978 864 812
Elongation (%)
7
12.5 9.6 9
6.2
Hardness (BHN)
266 266 295 263 285
Table 4. Average Linear Wear Rates of ADIs Investigated Under Different Wear Loads
ALWR x 10-3 in µm/m
39.2 N Load 4.48 3.36 3.64 3.92
49.0 N Load 6.44 4.2
4.76 5.04
The data from the tests on
the as-cast ductile iron samples showed the percentages of nodularity were between 85% and 90%. The percentages of ferrite in the matrices of the ductile iron samples alloyed with vana- dium, niobium, molybdenum and nickel (Alloys V, N and M) were less than what was present in the unalloyed ductile iron or the iron alloyed with nickel only. There- fore, alloys V, N and M exhibited higher hardness values. The tensile strengths of Alloys V and N were 19% to 22% more than that of Alloy B. Padan attributed the increase in
the pearlitic content and the cor- responding increase in the hard- ness values and tensile strengths of the as-cast ductile iron Alloys V and N to the formation of the complex eutectic carbides or simple alloy carbides of vanadium and niobium during solidification. Through austempering study,
which involved austenitizing the samples for one hour and then austempering them for various times, Padan saw that the microal- loyed ADI samples, standard ADI sample and base ADI followed the same pattern of hardness variation. Microalloyed ADI samples
Alloy V and Alloy N showed 17% and 5% improvements in tensile strength over the nonalloyed ADI and 13% and 2% improve- ments over the standard ADI alloy (Table 3). Padan attributed the improvements in mechanical properties to grain refinement and precipitation hardening due to the presence of fine and uniformly distributed vanadium and niobium carbide precipitates (Fig. 6).
@
Fig. 5. This graph shows the comparison of the tensile properties of the ADI Alloys V, N and M with the six ADI grades specifi ed in standard ASTM A897/A897M-06.
44 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2012
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