PSI - Issue 13

Elena Astafurova et al. / Procedia Structural Integrity 13 (2018) 1129–1134 Elena Astafurova et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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The influence of QT on temperature dependences of true stress – true strain curves, strain-hardening, a yield strength and elongation to fracture are shown in Figure 2. Decrease in test temperature is accompanied by substantial growth of deforming stresses and strain hardening and decrease in plasticity of the steel (Fig. 2). Strong temperature dependence of strength properties and strain-hardening in low-temperature deformation regimes inherits to thermally activated interaction of dislocations with interstitials (nitrogen and carbon atoms), activation of mechanical twinning and deformation- induced γ→ε martensitic transformation , intersection of slip bands, which is characteristic for austenitic steels with high interstitial solid solution (Gavrilyuk and Berns, 1999; Tomota et al., 1998; Chumlyakov et.al., 1999; Wang et al., 2010; Liu et al., 2004).

Fig. 2. The effects of test temperature and QT on (a) true stress-true strain dependencies; (b) strain hardening d σ /d ε versus true strain dependencies; (c) YS; (d) elongation δ in CrMnVCN steel.

Increase in QT weakly changes the stages of plastic flow and total elongation of the steel (Figs. 2 a, d), but increases the yield strength of the CrMnVCN steel in whole temperature range and strain-hardening coefficient in low temperature deformation regime (Figs. 2 b, c). The effect of particle strengthening is lower for specimens treated at higher solution-treated temperature QT=1200°C in comparison with those treated at QT=1100°C, because volume fraction of precipitates gets lower and their mean size increases with increase of QT (Tab.2). Therefore, the growth in the yield strength and strain hardening can be ascribed mainly to increase in solid solution hardening of austenite at the expense of increase in QT of the steel. The total elongation changes in similar way for the steel processed by different solid-solution regimes (Fig. 2d). For the temperature interval (200 — 673)K, the values δ are a bit higher for QT=1200°C compared to those for QT=1100°C. This fact could testify to decrease in particle strengthening effect and to increase in solid-solution