Strain localization in creep testing of samples with heterogeneous microstructures

A review of non-destructive techniques for the detection of creep damage in power plant steels

“…2, Type I and II cracks both originate in the weld metal, but those of the latter type grow into the heat affected zone (HAZ); cracks of Type III occur in the coarse-grained region of the HAZ, whereas Type IV cracks develop in the often narrow transition region between the fine-grained HAZ and the parent material. The material in this area has lower creep strength [13][14][15] and therefore represents a likely initiation site for creep cracks, which can arise as a result of bending moments, hoop stresses or residual stresses [16]. Experience shows that the concentration of cavities is usually much greater in this area and that Type IV (and to a lesser extent Type III) cracks are indeed among the most common causes of creep failure for low-alloy ferritic steel pipes and headers in power stations [17][18][19][20][21].…”