PSI - Issue 14

P Ponguru Senthil et al. / Procedia Structural Integrity 14 (2019) 729–737 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig.2. Optical micrographs showing progress of the transformation in (a)-(d) B1 at 2, 4, 8, and 12 hours respectively, (e)-(h) B1Nb at 2, 4, 8, and 12 hours respectively.

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Fig.3. SEM micrographs of (a) B1 and (b) B1Nb.

Mechanical properties of the steels are given in table 2. Nb addition has resulted in a significant increase of total elongation from 16% to 28%. However, yield strength has decreased in Nb added steel and there is no significant change in ultimate tensile strength. The strength of nano bainitic steels is to a large extent determined by bainitic lath size. TEM micrographs are shown in figure 5. It is evident from figure 5 that there is no considerable refinement in the bainitic lath size of B1Nb as a result there is no substantial improvement in the strength. Though Nb addition has resulted in significant reduction of PAGS, the bainitic lath size does not change significantly.