PSI - Issue 14

Sourabh Shukla et al. / Procedia Structural Integrity 14 (2019) 259–264 Sourabh shukla et al./ Structural Integrity Procedia 00 (2018) 000–000

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Fig. 2 shows the microstructure of SA and CW samples after TA at 700 °C and 900 °C. It is observed that for SA samples, as TA temperature increases grain size decreases due to formation of new grains. For 25 % and 45% CW at 700°C, it is observed that with grain boundary, carbide attack also observed inside the grain area. C.L.Braint et al. (1979), Pednekar et al. (1980), and Srinivas et al. (1980) reported that deformation bands and dislocations provides active sites for carbide precipitates, and hence after thermal ageing carbide precipitation takes place not only at the grain boundary but also inside the grain area. It is also evident that at 45% CW for 700°C, some recovered grains were observed and grain size decreases due to which carbide attack also decreases. It is also observe that at 900°C, in 25% CW it shows less grain area attack due to martensitic reversal and also grain size decreases. However in 45% CW at 900°C, recrystallization of reverted and retained austenite observe and it shows results in grain refinement. It is evident that as we do TA, those dislocation which form during CW started to form subgrain boundary and results in recovery of austenite and as TA temperature increases, recrystallization or grain refinement of austenite phase takes place, F.J.Humphreys et al. (2004). 4.3 Degree of Sensitization Fig.3 shows the DLEPR curve of 45% CW at different thermal ageing temperature. Table 4 shows the %DOS for 25% and 45% CW at 700°C and 900°C.

Fig.3 DOS of CW samples at different TA temperature Fig. 3 shows that reactivation current density increases from as received 45% CW to TA at 700°C and then decreases to 900°C. It is evident that after CW, martensite forms and when it is thermal ageing those carbides not only form at the grain boundaries but also in those grain areas where martensite forms due to which current density and DOS increases. However, after thermal ageing at high recrystallization temperature as 900°C, large fraction of martensite transform to recovered austenite and hence decrease current density and DOS, Jin-Long et al. (2012). Jin long et al. (2012) found that I r increased for 10% CW but decreased for 30% and 40% CW due to rapid healing. In table 4 after CW, we observed that at 700 °C, highest DOS obtained and then it decreases at 900 °C.