AFS/FEF Student Technology Contest
Editors Note: The American Foundry Society and Foundry Education Foundation (FEF) Student Technology Contest was developed to recognize the metalcasting related research activities of students in the FEF school network. The 2009 competition received 13 student submissions from 6 different universities. Angella M Schulte, a graduate stu- dent at Missouri University of Science & Technology was awarded with a scholarship for her presentation on: Quality Improvements of Cast Lightweight Steel P900 Armor. The following projects received special merit honors and were selected for publication in IJMC.
QUALITY IMPROVEMENTS OF CAST LIGHTWEIGHT STEEL P900 ARMOR A. Schulte—Graduate Student
Missouri University of Science & Technology, Rolla, MO, USA
Copyright © 2010 American Foundry Society Background
P900 is a MIL-PRF-32269 class 2 cast steel armor. The plate is designed to induce obliquity to kinetic projec- tiles such as armor piercing bullets. P900 is sometimes referred to as holey armor since the cast plate resembles a honeycomb of elongated holes that are angled at 25°. The weight of a P900 casting is to be 50% of a solid plate of equal dimensions. Filling the intricate honeycomb pat- tern presents interesting challenges to the foundry, but has been successfully cast in 4130 steel. Further weight reduction is possible with a new class of lightweight steel armor; however, the high aluminum of these steels im- pose new challenges in casting. Fe-30wt%Mn-9wt%Al- 1wt%Si-0.9wt%C-0.5wt%Mo steels are austenitic, age hardenable, 12-15% lighter than low alloy steel, castable, oxidation resistant, and have good notch toughness.
Cold Shuts in P900 Armor
Reoxidation is a particular concern with these light- weight steels since filling the honeycomb pattern may promote cold shut defects. Multi-hit capabilities of P900 armor are adversely affected by cold shut defects as shown in Figure 2.
Several factors lead to the formation of cold shut defects. In the case of bonded sand molds a 0° tilt, low superheat
(below 300°C), no or improper mold venting, and reoxida- tion during mold filling promote cold shut formation. MAG- MASOFT and FLUENT software were used to predict the best mold, venting, and superheat combinations for these new lightweight steels.
Modeling
Experimental thermal analysis data was used to create a specific Fe-Mn-Al-C alloy in the MAGMASOFT database. Modeling parameters include:
• sand permeability (MAGMA value for olivine) • • • • •
interface coefficient (c500, no mold wash) superheat (varying from 100-350°C) fill time (14 seconds)
feeding effectivity (30%) venting (none, middle, back)
MAGMASOFT simulations were used to compare the ef- fect of superheat on three different scenarios: horizontal bonded sand mold (Figure 6), a 15° tilt from horizontal bonded sand mold (Figure 7), and a vertically cast ce- ramic shell mold preheated to 800°C (Figure 8). The su- perheats compared are 100°C and 300°C. Each figure has a colored scale bar indicating temperature at 14 seconds, or 100% filled.
International Journal of Metalcasting/Winter 10
59
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