specimen with a deep pocket. The temperature field in the specially designed specimen and in the shell during the casting process was simulated with MAGMASOFT. Three different prime laboratory produced coats (silica, zircon and alumina) were investigated in line with the industrial shells pre- pared around the same specimen. After foam pat- tern removal and firing, the shells were preheated to 800C and poured using HY130 steel. Shell sam- ples in contact with the steel were taken from the pocket region of the castings, polished and SEM/ EDS analyzed. Multiple interaction products, in- cluding complex Mn-Si-O, Al-Si-Mn-O and Fe-Si- Mn-Al-O oxides, were identified. The formation of interaction products was also forecast using ther- modynamic phase equilibrium in the system: liquid steel-ceramic-slag-gas. The results can be used for shell material selection.
Steel Compositions and Liquid Processing Development U.S. Army Benet Laboratory Funding
Steel compositions and mechanical properties were pre- viously studied in this project. Currently, different liquid metal processing routs are being explored for increasing steel cleanliness. Calcium wire ladle treatment to improve cleanliness of large diameter tube centrifugally cast steel was experimentally tested. Centrifugal casting provides the unique opportunity of combining improved melt refining techniques with large centrifugal forces and directional so- lidification during casting to reduce the non-metallic inclu- sions in the final product. The effects of calcium wire in- jection on the number, size, composition and morphology of non-metallic inclusions in centrifugally cast products were evaluated. Calcium-bearing wire was fed into the liq- uid steel in the ladle prior to centrifugal casting. Samples were collected throughout the steelmaking and casting
processes, starting at argon-oxygen decarburization and continuing through the centrifugally cast product. Samples were analyzed on the Aspex PICA 1020 for quantitative inclusion analysis. The effects of the calcium treatment combined with the centrifugal casting process on inclu- sions morphology and population density was evaluated. The thermodynamic mechanism of formation and kinetic of inclusions flotation were discussed using CFD modeling of solidified casting with an elongated mushy zone. The mechanical properties of industrial centrifugally cast steel were compared to steel cleanliness.
Lightweight Steel Development U.S. Army Benet Laboratory, Leonard Wood Institute and Battelle Memorial Institute Funding
Lightweight steel alloys containing aluminum and silicon contents up to 10 weight-percent are being investigated as possible replacement to 4130 and 4335 type armor steels. Work has mainly focused on a composition of Fe-30Mn- 9Al-1Si-0.9C-0.5Mo, with all compositions in weight-per- cent. The combination of a low density (6.7 g/cm3
) and peak
aged tensile strength of 1,000 MPa (145 ksi) gives these lightweight steels between 13 and 15% improvement in specific strength over current cast steel armor used in P900. Ballistic tests on the lightweight steel met MIL-PRF-32269 requirements, and high strain rate compression tests show work hardening behavior to ultimate strengths of 1,650 MPa (240 ksi). These lightweight steels have good fluidity and have demonstrated fill lengths that are 70% greater than 4130 steel. Challenges in casting lightweight steel are the control of phosphorus, eliminating dross entrapment during casting and re-oxidation of the melt. Phosphorus and steel cleanli- ness adversely affect notch toughness, but when controlled adequately, the lightweight steel will attain impact energies of 39 J at -40C in the age hardened condition. To date, the best lightweight steel P900 ballistic performance has been attained with plates cast into preheated ceramic shell molds.
International Journal of Metalcasting/Winter 11
77
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