mine their effects on late inoculation of MgFeSi (no REE) treated ductile irons.
Base iron (wt-%: 3.96C, 0.96Si, 0.45Mn, 0.027P, 0.016S) was produced as synthetic iron (steel scrap, low-sulphur re- carburizer and ferroalloys) by acidic refractory lined core- less induction melting (100kg, 2400Hz).
Experimental heats were superheated to 1,520-1,550˚C/2,768- 2,822˚F and maintained 10 minutes at this level. Before tap- ping, the iron melt was superheated a short time (3 minutes) up to 1,570-1,580˚C/2,858-2,876˚F, and then tapped into the nodulizing ladle.
ements were achieved at low level (wt-%): 0.03Cu, 0.01Ni, 0.03Cr, 0.001V, 0.002Ti, 0.003Sn, 0.003Sb, 0.001Pb, 0.002Nb, 0.004Co, 0.01W, 0.01As. A relatively high purity iron in terms of anti-nodularising trace elements was ob- tained (K = 0.37), at a medium level of pearlite promoting factor (Px
The same Tundish-Cover Mg-treatment technique was used and a 2.5wt-% FeSiMg6 [wt-%: 6.1 Mg, 1.0 Ca, 1.0 Al, 46 Si, Fe bal] master alloy was used. Un-inoculated and differ- ent inoculated irons were tested. Typical chemistry of the Mg-treated iron was (wt-%): 3.8C, 2.0Si, 0.44Mn, 0.014S, 0.027P, 0.05Mgres
with a 4.4 carbon equivalent. Residual el- = 2.88).
– ASTM – A367, 25.4 x 44.4 x 127mm (1.0 x 1.75 x 5.0in), cooling modulus CM= 4.5mm/0.177in] and a cylindrical bar (φ20 x 150 mm/0.79 x 5.9in). In-mould addition rates for Ca bearing FeSi75 [assay: 0.5-1.0% Ca, 1.2-1.5% Al, 74-78% Si, Fe-bal] ranged from 0.1 wt-% to 0.3 wt-%; the complex OS-IE alloy [assay: 35-39% Si, 34- 36.5% oxy-sulphide forming elements, Fe-balance],40
The test castings were made using the same test mould shown in Figure 1, but for an in-mould inoculation pattern including three work positions and two sample types: wedge sample [W3 1/2
was
added in much smaller amounts, 0.01 wt-% to 0.03 wt-%. In-mould inoculation was used simultaneously at three inoc- ulant levels in multi-cavity test moulds to evaluate chill ten- dency, microstructure and Brinell hardness characteristics.
The graphs shown in Figure 8 summarize the test data of chill depth and chilling tendency (Fig. 8a), the carbides amount (Fig. 8b) and pearlite amount (Fig. 8c) at different distances from the apex of wedge samples, of un-inocu- lated and in-mould inoculated irons versus inoculant ad- dition level. Even at the significantly reduced silicon addi- tion rate of 0.03 wt-% the proprietary OS-IE inoculant was comparable with or slightly more effective than 0.30 wt-% FeSi75 inoculated iron (Fig. 8a). At these addition lev- els, the proprietary OS-IE inoculated chill wedge showed 8.0mm/0.31in of clear chill, compared with 9.0mm/0.35in of clear chill in the Ca-bearing FeSi75 inoculated wedge, at the same level of the total chill. It took almost 10 times the weight of calcium-bearing FeSi75 to equal the perfor- mance of the OS-IE inoculant.
74
The effects of inoculation were further examined by com- paring the microstructures of irons treated with different amounts of FeSi75 and OS-IE inoculant, as graphite char- acteristics. Chill wedge test samples were again utilized for the measurements. The graphite phase feature is illus- trated by Figure 9, which compares the microstructures of 0.2 wt-% FeSi75 and 0.01 wt-% OS-IE alloy in-mould inoculation, at the same distances from apex of wedge sample. Despite the ten times lower inoculant addition rate, average graphite shape factor (see Equation 4) is practically the same, as 0.72 - 0.77 main range, for 25 - 40 µm as average size range.
The effect of inoculation with the various alloys on Brinell hardness was studied utilizing the 20 mm/0.79 in. diameter bars. These results are shown in Figure 10. Brinell hard- ness values decreased with increasing inoculant additions, regardless of inoculant type. The OS-IE inoculant reduced hardness values more rapidly than did the conventional FeSi75 inoculant.
International Journal of Metalcasting/Volume 8, Issue 2, 2014
Chill wedge test samples were also utilized for the struc- tural analysis. Structure characteristics were determined along the geometrical centerline of the chill wedge and at different distance from the wedge apex (10, 25 and 40mm/0.39, 0.98 and 1.57 in). At distances farthest from the chill wedge, the cooling rates are very shallow. Fig- ure 8b illustrates that an inverse relationship exists and between the amount of free carbide levels and distance from the chill wedge apex. As the amount of each inocu- lant increased, the percentage of free carbides diminished; the amount of free carbides also decreased with increasing inoculant additions and with increasing distance from the apex. The first measurements of free carbides were taken 10 mm/0.39 in from the wedge apex and in a clear chill or mottled zone. It was found that despite the white iron ap- pearance, the samples contained different amounts of free carbides and a small amount of graphite, depending on the type of inoculant and its addition rate. It was also found that the OS-IE inoculant was more efficient in eliminating free carbides than Ca bearing FeSi75.
The base metal matrix (Ferrite + Pearlite = 100%) is also af- fected by the cooling rate (distance from the apex of wedge sample) and inoculation parameters (inoculant type and addition rate) (Fig. 8c). According to the chemical analy- sis of the treated irons, mainly expressed by the relatively high pearlite promoting factor Px matrix characterized the W31/2
= 2.88, prevalent pearlitic test samples (80–100% Pearl-
ite / 0–20% Ferrite). As expected, lower cooling rates and higher inoculant additions yielded higher ferrite levels in all of experimental irons, but with the complex alloy as perfor- mance. Generally, 0.03 wt-% of the OS-IE inoculant alloy performed the same as metal matrix characteristics, as 0.30 wt-% FeSi75 alloy addition. Thus, it was found that OS- IE, used as a solo addition was 10 times as effective as Ca- bearing 75% FeSi.
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