Influence of thermal aging (to 50,000 h) on the tensile properties of modified 9Cr-1Mo steel

FY17 Status Report on the Micromechanical Finite Element Modeling of Creep Fracture of Grade 91 Steel

“…Figure 7-9 graphically summarizes the results described in the previous paragraph by plotting the time to opening as a function of triaxiality at the three loading stresses. The behavior described by Figure 7-9b and by Figure 7-9c has been experimentally observed: both pure notch strengthening for relatively high stress creep experiments [7] and a transition between notch strengthening and notch weakening behavior as triaxiality increases for intermediate stress levels [9]. The behavior shown in Figure 7-9a -pure notch weakening for low loads/creep rates -has not been observed experimentally.…”

“…Note that only the PAGs and packets are approximately equiaxed, the block and lath structures are laminar. Initial dislocation density in Grade 91 is high -around 10 13 m -2 [7]. The lath subgrain boundaries themselves can be viewed as a dense dislocation network.…”

“…• The rate equations for volumetric growth, ! V , reflect fits to finite element results for models containing discrete voids embedded in a creeping solid over a wide range of triaxialities and porosities ( ) 2 / a b , see van der Giessen et al [19,4,5,6,7,8,9,10,13].…”

“…Note that because of the large applied load, the strain rate due to diffusional creep in the grains is 7 1 2 10 hr − − × , which is the lowest mechanism contribution to the total cell strain rate.…”