The blocking effects of interphase precipitation on dislocations’ movement in Ti-bearing micro-alloyed steels

• Random precipitates and interphase precipitates were observed by applying different coiling temperatures.
• We measured nano-hardness of two precipitations which indicated interphase precipitation provided more hardening effect.
• Plateaus are formed in early stage of load–depth curves for specimens with interphase precipitates.
• The blocking effects of interphase precipitation and random dispersive precipitation on dislocations are discussed.

The effects of interphase precipitation and random dispersive precipitation on dislocations’ movement in ferrite grains and nano-mechanical properties have been investigated by using an in-situ nano-mechanical tester. Through the analyses of load–depth curves, nano-hardness was measured to be 4.19 GPa for interphase precipitation and 3.90 GPa for random dispersive precipitation, respectively. Plateaus are formed in the early stages of load–depth curves for specimens with interphase precipitates, while no plateaus can be observed for specimens with random dispersive precipitates. Mechanism for the interaction between dislocations and precipitates has been established by using Ashby–Orowan theory, which is believed to have been caused by the blockage of parallel precipitates on dislocations, resulting in the drop of applied stress to generate plateaus in load–depth curves.