Chaman Lall, Ph.D., MPP Vice President – Technology & Applications Development and Mark Svilar
The change from gasoline to alternate fuels such as those based on methanol, is expected to create material compatibility problems because of the enhanced reactivity of the P/M materials currently in use. These problems are most serious for the steels containing copper or those that have been copper infiltrated. P/M austenitic stainless steels offer the possibility of overcoming the inherent corrosion problems of the current P/M alloys. Test samples of 304L and 316L were processed on production equipment and sintered in pure hydrogen or a simulated dissociated ammonia mixture. Corrosion testing was performed in SAE-approved mixtures of “aggressive methanol” and gasoline (termed CM15A and CM85A). To accelerate the corrosion test and simulate an auto-oxidized fuel mixture, a small amount of t-Butyl Hydroperoxide was added. These preliminary tests confirm that Fe-0.8%C and Fe-2%Cu-0.8%C steels will rust within 24 hours in these test fuels. The austenitic stainless steels were very corrosion resistant if sintered in an atmosphere of pure hydrogen (less than 2% of surface covered in rust after 1500 hours). However, when sintering in a synthetic dissociated ammonia atmosphere (75%H2 + 25%N2), additions of small amounts of Sn and Cu greatly improved corrosion resistance (304LSC and 316LSC grades). The various test fuels for accelerated testing of metal components are identified and suggestions are made for further testing.
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