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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in austenite network. Hence the percolation threshold is reached early at localized spots leading to early necking and failure. Because of very fine blocky austenite in B1Nb, it is more stable and the continuity of austenite is also maintained for a longer time. B1Nb also shows more ductile features compared to B1 as shown in figure 7(b) and (d)

(a)

(c)

(b)

(d)

Fig.8. Impact fractographs of B1 steel (a & b) and B1Nb steel (c & d) at low and high magnifications.

Charpy V notch impact toughness has been measured at room temperature. A slight improvement in toughness has been observed in B1Nb compared to B1. Presence of primary niobium carbide has no detrimental effect on toughness. Fractographs of B1 impact sample shows more of quasi-cleavage features where as B1Nb shows a large fraction of ductile dimples (Figure 8). 4. Summary Influence of Nb microalloying in a high carbon nano bainitic steel has been investigated. Addition of a small amount of Nb leads to accelerated transformation and refinement of bainitic sheaves when austempered at 300 ° C. It