Nanoindentation response of interphase precipitation in a Nb microalloyed steel

In this work, dedicated isothermal transformation studies were performed in a Fe-C-Mn-Nb alloy to obtain two types of precipitate morphology embedded in a similar ferritic matrix. Nano-hardness of individual ferrite grain was measured by using an in situ nano-mechanical tester. The peak of nano-hardness distribution from interphase and dispersed precipitate strengthened ferrite corresponds to the nano-hardness range of 2.6-2.8 and 2.5-2.6 GPa, respectively. A wider spread of nano-hardness from interphase precipitate strengthened ferrite was observed and rationalised by considering the variation in inter-particle spacing on slip planes. The 'pop-ins' on the load-depth curve was not able to be correlated with the morphology of a precipitate.