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Two steels with a base composition of Fe-0.2C-0.8Mn-1.2Cr (wt%) but with different niobium (Nb) contents (0.02 and 0.03 wt%) were employed to study the effect of precipitate evolution on the softening resistance in the austenite region under elevated temperature deformation. The thermomechanical procedure was executed by a deformation-dilatometer and involved double deformation processes with 25% strain at a 0.25 s−1 strain rate at 900, 925, 950, and 1000 °C. The softening ratios, reflecting the competition between recrystallization and precipitation, were evaluated. The results indicated that both steels showed better softening resistance at 900 °C than at other temperatures. However, the softening ratio of 0.03 wt% Nb-containing steel (Steel 3N) rose after 100 s at 900 °C, while 0.02 wt% Nb-containing steel (Steel 2N) maintained a low softening ratio within 300 s at 900 °C, indicating that Steel 3N was relatively non-durable. A microstructural characterization showed that in the Steel 3N sample deformed at 900 °C, recrystallization occurred more strongly than for Steel 2N after a 1000 s holding time. A follow-up analysis then showed that Steel 3N treated at 900 °C revealed a faster coarsening of the carbides than Steel 2N even in the early stage of precipitation, evidencing that Steel 2N exhibited a lower softening resistance at 900 °C. [ABSTRACT FROM AUTHOR]

For study the high temperature application of beta titanium, all experimental creep test temperatures and the pre-aged temperature were lower than the predicted β-transus temperature (1067 K). The creep properties of the pre-aged material were superior to those of the as-received material. The activation energies of the pre-aged creep material under various test conditions were approximately twice those of the as-received material under dynamic-aging creep, even though the stress exponent of the pre-aged material was lower than that of the as-received material. Creep deformation was predominated by the diffusion mechanism. The decline in the hardness of the pre-aged creep material under an applied stress of 200 MPa was ascribed to the coarsening and degeneration of the acicular α (secondary α). • There are very few reports on creep behavior of Ti-15-3 beta titanium alloy. • Creep properties of pre-aged material were better than those of as-received material. • Hardness of pre-aged creep material decreased due to coarsening and degeneration of needle-shaped α. [ABSTRACT FROM AUTHOR]