Microstructural characteristic of low carbon microalloyed steels produced by thermo-mechanical controlled process

The microstructural characteristic of the low carbon microalloyed steels produced by thermo-mechanical controlled processing was investigated by means of optical and transmission electron microscopies. Polygonal ferrite and acicular ferrite were found in OM; under TEM, acicular ferrite with high dislocation density, ultra-fine grain ferrite, layer of thin martensite film and precipitate phase were identified in 560 MPa grade Ti–Nb and Ti–Nb–V microalloyed steels. An ultra-fine dispersion of precipitate phase was also found in Ti–Nb–V steel. These fine-scale microstructures exhibit excellent strength and fracture toughness, which is the main reason that TMCP is widely used in the production of high-strength low-alloy steels.