PSI - Issue 60

B.P. Kashyap et al. / Procedia Structural Integrity 60 (2024) 494–509 B.P. Kashyap et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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Fig. 3. (a) stress-strain curves of SS316L at 973 K, 1123 K, and 1173 K along with the initial microstructure and the final deformed microstructure at 973 K (Kashyap et al., 1988); (b) K L vs. d plot for SS 316L derived from stress-strain curve at 973 K for different grain sizes (Kashyap and Tangri, 1995). In order to examine the dislocation evolution and the role of grain boundaries and grain interior in contributing to flow hardening, the effect of grain size on flow behavior and Hall-Petch type analysis was made as detailed earlier (Kashyap and Tangri, 1995). Presented here isafurther analysis of the same. The Hall-Petch parameters σ 0 and k from Eq. (4) presented earlierare re-plotted in Fig. 4(a) which shows increase in σ 0 and decrease in k with increasing strain. These curves can be expressed by the following (17) By considering σ 0 and k to represent grain interior and grain boundary hardening parameters, respectively, it is obvious that grain boundary is becoming less resistant to dislocation motion than grain interior because the dislocations participating in deformation are arrested in cell wall formation with progressive reduction in cell size and as such making the grain boundary redundant as a source of hardening. The dislocation evolution and roles of grain boundary are all dynamic processes; it will be interesting to examine the interrelationship between the two as proposed earlier by Kashyap and Tangri(1997). Shown in Fig. 4(b) is the plot of k vs. σ 0 .The interrelationship between the two is encouraging as expressed by the following equation. = −0.76 0 +298 R 2 = 1 (18) equations, with good correlation coefficient R 2 . 0 = 62.7 ( ) + 378 R 2 = 0.98 = −35.7 ( ) + 30.4 R 2 = 0.92 (16)

Fig. 4. (a) σ 0 and k obtained from the Hall-Petch analysis of the stress-strain curve at 973 K (Kashyap and Tangri, 1995) for different grain sizes plotted as a function of strain; (b) Interrelating plot of k vs. σ 0 at the same test condition.