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the inclusions. These inclusions then were analyzed to deter- mine of each inclusion’s amount and the dissolved cerium content. Metallographic analysis of the samples found that primary dendrite arm spacing decreased with increasing ce- rium content. Dendrite arm spacing shrank with an increase in either cerium content or the amount of Ce2


particles.10 a rise in Ce2 cles.10


the soluble cerium content. The degree of undercooling for solidification decreased with larger amounts of Ce2


The equiaxed grain area fraction increased with O3


O3 No mechanical properties were reported by Guo et al.


or CeS inclusions, but it was unaffected by O3


parti-


Lan and fellow researchers studied the effects of RE addi- tions on H13 tool steel.12


A 20 kg heat of H13 tool steel


was prepared for each experimental treatment. The melt was deoxidized with aluminum and poured at 1873K into an in- vestment casting mold preheated to 873K. Prior to pouring, misch metal was placed at the bottom of the downsprue in the mold. The solidified casting was normalized and then quenched and tempered to reduce segregation. Lan noted that microsegregation within the casting was significantly reduced for chromium, molybdenum, and vanadium. These authors also observed a reduction in the SDAS.12


Unnotched


impact testing was conducted on samples from the casting. The RE-containing samples had dramatically higher impact toughness than the reference H13 casting. This is despite similar hardnesses between the RE and non-RE samples.12 These authors attributed the improvement in impact tough- ness on the reduction in SDAS. The SDAS reduction was thought to be caused by the presence of Ce2


ing as heterogeneous nuclei.12 O3 particles act- and CeS


There has been considerable debate in the literature on the role RE oxide inclusions play in decreasing grain size. Some authors theorize the particles act as heterogeneous nuclei, while others theorize the oxides pin the austenite grain boundaries and reduce grain growth. Many of the ex- periments have been conducted in small scale laboratory experiments that may not have reflected industrial condi- tions. Of the few studies done on RE additions in an in- dustrial environment only one was done on carbon steels in a foundry environment.6


chanical properties; however, the focus was more on im- pact properties and removal of sulfur than strength.6


Only one author reported me- No


attempt was made to examine the improvements in prop- erties as a function of grain size. To address these issues, the current paper investigated the role of RE additions on the structure and properties of 1010 and 1030 steel in the as-cast condition under conditions more closely replicating foundry practice. Rare earth additions were accomplished through a ladle addition of either misch metal or rare earth silicide. Rare earth levels of 0.1 and 0.2% were evaluat- ed. Cast plates were poured from each alloy in green sand molds and sectioned for metallographic and tensile testing. An increase in tensile properties was observed for many of the RE samples. Percent elongation also dramatically improved in the 1010 material.


Experimental Procedure


A 23 kg heat of either 1010 or 1030 steel was melted in a 3 kHz induction furnace. Once the melt reached 1650ºC, car- bon, ferro-manganese, and a small amount of aluminum was


Table 1. Chemical Analysis of Rare Earth Alloy Additions


Table 2. Experimental Heat Chemical Analysis


International Journal of Metalcasting/Spring 2012


53


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