Multiaxial low cycle fatigue and crack propagation of Mod.9Cr-1Mo steel at high temperature

摘要

This paper describes the low cycle fatigue criterion of Mod.9Cr-lMo steel and the fracture mode under multiaxial stress/strain states. Multiaxial tension4orsion low cycle fatigue tests were carried out using plain Mod.9Cr-lMo tubular specimens at823K. Plain, surface notched and through notched specimens were also torsionally fatigued at 823K and room temperature to examine the crack propagation direction. LE strain and the equivalent strain based on crack opening displacement were a suitablestrain parameter for correlating the multiaxial low cycle fatigue lives with a small scatter. Mises' stress was a suitable stress parameter for the correlation. Main crack of the smooth, surface notched and through notched specimens propagated in themaximum shear strain direction in torsion tests, so there was no influence of the notches on the crack propagation direction. Surface oxidation has no effect on the main crack propagation direction, but it has an influence on the subcrack propagationdirection. Oxide films were brittlely broken in the principal direction.