Abstract
Creep tests have been carried out at 600°C on type 316 pipe and bar material, some of which was pre-aged to accelerate metallurgical changes. Solute concentrations were assessed by determining the lattice parameters and analyzing extract solutions. A transient strain-induced strengthening of ∼3 × 104 h duration was observed for material containing >0·025 wt-% dissolved carbon before testing; this was ascribed to a Mo–C interaction which progressively pinned dislocations. When the transient had decayed, a steady creep rate was achieved. The transient strain induced strength could be eliminated by pre-aging to reduce the dissolved carbon, and this occurred more rapidly in finer-grained material. In the steady creep regime viscous drag was rate controlling, but the effect of dissolved molybdenum was observed to become saturated in the range 0·8–2·0%. There is some evidence that this was because molybdenum acts in conjunction with nitrogen in the steady creep regime.
MST/489
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