Calling this initiative its “highest priority,” the US Department of Defense (DoD) plans to purchase about 10 million pounds of P-900 cast steel armour for use as add-ons to military vehicles. DoD’s US Army Tank and Automotive Command (TACOM) expects to receive the first 2.5 million pounds by the end of 2007 to produce the initial quantity of armour.
The army decided to commercialise the process following a series of successful ballistic tests it performed on the cast steel armour. National Energy Technology Laboratory (NETL) scientists had produced the castings for the armour using a new heat-treating process to optimise ballistic performance.
In late July, DoD had budgeted $200m in fiscal year 2007 funding for the army to procure the first set of castings. Each foundry producing the castings will have to be qualified for its ballistic and production schedule capabilities.
Foundries using NETL’s lost foam process will produce a significant portion of the 100,000-plus initial castings needed by DoD. This process, used industrywide to produce aluminium castings, was modified and patented by NETL scientists in the 1980s and 1990s for iron and steel castings.
The process consists of making a pattern using polystyrene formed in the desired shape, and then adding a polystyrene gating system so that the molten metal flows properly to the pattern. Once this patterned piece is coated with liquid ceramic slurry to protect the fragile polystyrene, it is dried and placed into a double-walled box called a flask, covered in sand, and compacted by vibration. The flask is evacuated and molten steel or iron is poured into the evacuated flask, which vaporises the polystyrene pattern and replaces it with steel.
The gating system is removed and a light touch up is done to produce a casting with a surface finish that is said to compare favourably with much more expensive casting techniques.
The P-900 cast-slotted steel armour was developed and patented by scientists at the Office of Fossil Energy’s National Energy Technology Laboratory