Primary surface recuperators (PSRs) are compact heat-exchangers made from t
hin-foil type 347 austenitic stainless steel, which boost the efficiency of
land-based gas turbine engines. Compact recuperators are also an essential
technology for some new microturbines. Solar turbines uses foil folded int
o a unique corrugated pattern to maximize the primary surface area for effi
cient heat transfer between hot exhaust gas on one side, and the compressor
discharge air on the other side of the foil. Allegheny-Ludlum produces 0.0
03-0.004 inches thick foil for a range of current turbine engines using PSR
s that operate up to 660 degrees C. One goal of this team-effort project is
to modify the processing to enable improved creep resistance of such 347 s
tainless steel foils at 650-700 degrees C. Laboratory-scale processing modi
fication experiments recently have demonstrated that dramatic improvements
can be achieved in the creep resistance of such typical 347 stainless steel
foils. The modified processing enables fine NbC carbide precipitates to de
velop during creep at 650-700 degrees C, which provides strength even with
a fine grain size. Such improved creep-resistance allows greater flexibilit
y in optimizing the cost-performance relationship as increased demands are
placed on the PSR at higher operating temperatures. The next challenges are
to better understand the nature of the improved creep resistance in these
347 stainless steel foil, and to achieve similar improvements with scale-up
to commercial foil production.