A comparison of the low cycle fatigue behavior of alloy 800 and alloy 800H

The low cycle fatigue testing was carried out to provide a basis for comparison of the behavior of the two kinds of Alloy 800 (low carbon Alloy 800 and high carbon Alloy 800H). The testing was done at temperatures of 5000C and 6500C either with or without hold. The results obtained were as follows: (1) At 6500C, the low-cycle fatigue life was essentially the same for the two alloys on the basis of strain amplitude, but Alloy 800H had a longer life on the basis of stress amplitude. (2) At 5000C, the two alloys exhibited longer lives than at 6500C, with Alloy 800 exhibiting 2-3 times longer life than Alloy 800H when compared on the basis of plastic strain range. At this temperature the stress range showed the maximum for Alloy 800H. (3) When a creep effect was introduced either by way of a hold time or a reduced frequency, Alloy 800 exhibited a greater reduction in life than in Alloy 800H. (4) At lower temperature the strain aging phenomena became significant with lower frequencies, leading greater strength and reduction of life, while at high temperature creep damage with intergranular cracking was dominant. (author)