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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Vα′ � � � � � ∑ �� � � � /� � � � � � ��� �

� � � ∑ �� � � /� � � � � ��� � � � � � ∑ �� � � � /� � � � � � ���

(1)

Where, n represents number of peaks of phase, I is integrated intensity and R is the material scattering factor which is different for each peak. The DOS results obtained by using double loop electrochemical potentiokinetic reactivation test (DL-EPR). The solution used for this test is 0.5 M H 2 SO 4 + 0.01 M NH 4 SCN at room temperature. The ratio of reactivation current density and activation current density was calculated. 4. Results and Discussions 4.1 XRD X-ray diffraction patterns after solution annealing and the as-deformed samples are depicted in Fig. 1. Change in relative intensity of peaks for both phases clearly shows that amount of α-martensite significantly decreases with increasing ageing temperature. This confirms the results of reversal of strain induced martensite into austenite. Table 2 and 3 shows the volume fraction of martensite and hardness. It is observed that as degree of CW increases, hardness and volume fraction increases but as thermal ageing temperature increases, those hardness and fraction values decreases. This is due to martensitic reversal. Depending on degree of cold work (CW), rate of martensite reversal after thermal ageing (TA) changes.

(b)

(a)

(c)

Fig.1 XRD of SA and 45% CW sample at different TA temperature: (a) As Received, (b) 700°C, and (c) 900°C

As it is also observe that at 25% CW, hardness increases at 700°C and then decreases at 45% CW. It is reported that those martensite which formed during cold work provides sites for carbide precipitation inside the grain area after TA and it is observed that those carbides increases the hardness in those grain area, C.L. Braint et al. (1979). As temperature and CW increases, value of hardness decreases due to decrease in the volume fraction of