PSI - Issue 14

Hari Krishan Yadav et al. / Procedia Structural Integrity 14 (2019) 605–611 Hari krishan Yadav/ Structural Integrity Procedia 00 (2018) 000–000

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Fig. 6. Optical micrographs of creep tested (a) CW0; (b) CW1; (c) CW2; (d) CW3; (e) CW4 samples at 973 K and 200 MPa stress level

Grain size varied as new recrystallized grains formed and grain boundary migration of low angle grain boundaries took place, which resulted in large grain size of up to150 µm. Cold working introduced large number of dislocations, which helped for better creep strength. Due to this increased density of dislocations, resistance to plastic deformation increased and finally resulted in better creep life. However, cold working introduced lots of strain energy into the material and higher percentage of cold work led to faster recovery and enhanced recrystallization of material during creep exposure. Latha et al. (2008) reported that precipitation of secondary titanium carbide took place during creep exposure of cold worked 14Cr–15Ni austenitic stainless steel. Fine precipitates mostly pinned near intra granular dislocation tangles and retard the movement of dislocations. M 23 C 6 carbides mostly precipitated near grain boundaries, Latha et al. (2011). Low angle grain boundaries were annihilated as dislocation recovery took place during creep. This