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Alloy 20 is a low carbon, 20 per cent chromium, 30 per cent nickel austenitic stainless steel that contains molybdenum, copper, and columbium as primary alloying elements. The alloy is especially resistant to corrosive attack in sulfuric acid. Although satisfactory for a majority of sulfuric acid applications, there are some areas where its corrosion resistance is somewhat deficient. Another deficiency, of more interest to the producer than the user, is its poor hot workability. This study was designed to develop a modified Alloy 20 with improved corrosion resistance that would have higher product yields through improved workability.
The results of tests on a series of experimental heats indicate that the hot workability of Alloy 20 can be significantly improved by additions of titanium and to a lesser degree by increasing carbon, columbium, and boron and decreasing chromium and molybdenum. The effect of nickel is variable. Copper variations and calcium additions have no effect on workability.
In respect to corrosion resistance in sulfuric acid, all increases in alloying elements produced either no significant effect or a reduction of corrosion resistance, with the exception of nickel. A significant increase in sulfuric acid corrosion resistance was observed with increasing nickel content. A significant detrimental effect on corrosion was observed with increasing amounts of chromium. All other elements studied, including titanium, had no significant effect on corrosion resistance in sulfuric acid.
Black, H. L.
Group metallurgist, Stainless Steel Section, Technology and Development Laboratory, Universal-Cyclops Steel Corp., Bridgeville, Pa.
Lherbier, L. W.
Section metallurgist, Product Development, Technology and Development Laboratory, Universal-Cyclops Steel Corp., Bridgeville, Pa