Procurement and screening test data for advanced austenitic alloys for 650 degrees C steam service (Part 1, 14Cr-16Ni steels and 20Cr-30Ni-Fe alloys)

Tests were initiated to evaluate the potential of a group of developmental iron-nickel-chromium alloys for service at 700/sup 0/C with a target design stress of 60 MPa. Tensile, creep, stress rupture, weldability, and microstructural stability tests were conducted on one group of alloys, which are essentially modifications of type 316 stainless steel. The data for the alloys were compared to data for type 316 stainless steel, alloy 800H, and 17-14CuMo stainless steel. Results of the short-time screening tests indicate that the developmental alloys are superior to the commercial alloys in regard to strength. Annealing at 1115/sup 0/C produced a loss in strength, but it was found that the loss could be mitigated by the judicious selection of composition, annealing conditions, and cold work prior to aging. The alloys were found to be unsatisfactory in regard to autogenous weldability; they exhibited a tendency for hot cracking. However, the steels could be joined satisfactorily with Inconel 82 and 17-14CuMo stainless steel filler metals. Compositions were identified that will be produced as small heats of tubing for subsequent fabricability, corrosion, and mechanical testing. Preliminary data relating to the fabricability and short-time mechanical properties were obtained for a second group of alloys. There were modifications of alloy 800H and contained molybdenum, niobium, and boron additions. Results indicated that significant improvement in strength is possible in the alloys containing 20% chromium and 30% nickel. 10 refs., 35 figs., 9 tabs.