Creep Crack Growth in an Austenitic Cr-Ni-Mn Steel

Abstract

Effects of grain-boundary sliding and strenthening by serrated grain boundaries on creep-crack growth are investigated using an austenitic 21Cr-4Ni-9Mn steel at 973 K in air. In surface notched specimens, crack growth rate is lower in specimens with serrated grain boundaries than in those with normal straight grain boundaries at the same stress intensity factor (K1), but the difference in crack growth rate between these specimens decreases with crack growth. In smooth bar specimens, growth rate of the largest surface crack is correlated with the average amount of grain-boundary sliding, although a unique relationship is not found between them. Grain-boundary sliding controls the crack growth when the crack size is small, but total creep deformation becomes important and crack linkage occurs with increasing crack length, thus reducing the strengthening effects of serrated grain boundaries.