The low cycle fatigue tests of Nb-A286 iron-base superalloy was conducted to investigate the effect of the applied strain range on the cracking at a given temperature of 550 degreesC. The experimental results strongly indicate that the slope change of Coffin-Manson plot is definitely related with the deformation mode that controls the fracture mode. The fatigue cracking mode changes from the transgranular to the predominantly intergranular modes with the applied strain range. The reason for this change of the fatigue cracking with strain range is induced by the combination of mutually competing factors involving the grain boundary precipitate, the density of the slip band, and the concentration of stress at points where the slip bands impinge upon the grain boundaries. (C) 2001 Elsevier Science B.V. All rights reserved.