The effects of hydrogen on the creep rupture properties of fe-ni alloys
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formed either on the surface of the steel or internally, causing it to soften and lose creep strength. The effects of hydrogen on the creep properties of relatively pure iron are less clear. Nelson 5 conducted stress-rupture tests on iron specimens at 811 K (1000 ~ and 6.2 MPa (900 psi) hydrogen. Half of the specimens contained 90 ppm carbon and the other half 15 ppm. The rupture strength of the 90 ppm carbon iron was greatly reduced in hydrogen whereas the 15 ppm specimens were unaffected. Harris and Van Wanderham 2 creep tested two iron-base alloys, A286 and AISI 347, at 951 K (1250 ~ and 34.5 MPa (5000 psi) hydrogen and helium pressures. They reported a decrease in the creep life of the A286 but found the AISI 347 to be unaffected. McCoy 3 creep tested Armco and electrolytic iron in hydrogen and argon at a number of temperatures and one atmosphere pressure. He reported the creep properties to be independent of test atmosphere. McCoy reported the same independence to be true for 304 stainless steel tested at 1089 K (1500 ~ but not at 1200 K (1700 ~ where the creep-rupture life was reduced by more than 50 pct. In summary, it appears that if the carbon content of iron is small or if the hydrogen partial pressure is low, then the creep properties of iron are unaffected. This paper reports on results of creep tests on Fe-Ni alloys of nominal composition 100 pct Ni, 75 pct Ni-25 pct Fe, 50 pct Ni-50 pct Fe, 25 pct Ni-75 pct Fe and 100 pct Fe. Tests were conducted in hydrogen and in helium atmospheres at three temperatures (898, 1073 and 1198 K) and stress levels ranging from 6.5 to 80.1 MPa. By studying the effects of hydrogen on the creep properties of this binary system it is hoped that progress can be made in explaining hydrogen-metal interactions and that useful data for the selection of materials for hydrogen environment creep applications will be obtained.
ISSN 0360-2133/80/1013-1657500.75/0 METALLURGICAL TRANSACTIONS A 9 1980 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 11A, OCTOBER 1980--1657
EXPERIMENTAL PROCEDURE Table I is a listing of the heat analyses and grain sizes of the alloys used in this project. All materials were v a c u u m melted in 6 kg heats and hot roiled into strips 3.2 m m (1/8 in.) thick by 38 m m (1 1/2 in.) wide.* The * Fabricated and donated by Armco Steel Company. strips were then cold rolled to reduce the thickness by approximately one-half. The alloys were next machined into tensile specimens having a 35 m m long by 8.1 m m wide reduced section. The machined specimens were surface ground to remove any scale and mechanically polished with 400 and 600 grit SiC and finally with 0/2 emery paper. After mechanical polishing, the specimens were electropolished and annealed at 1523 K (2192 ~ for 24 h in a v a c u u m of 6.67 • 10 -4 Pa (5 x 10 -6 torr). After annealing, fiducial marks were placed along the gauge section at half centimeter intervals using a microhardness tester. In addition, for the purpose of making grain boundary sliding measurements, the gau
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