Microstructural Features of a Ultra Low Carbon High Strength Acicular Ferrite Steel Thick Plate

A ultra low carbon high strength steel heavy plate (60∼80mm thick) was produced with TMCP at Xiangtan Steel. The steel has a good combination of high strength (σb∼600MPa) and impact toughness (∼300J). The microstructural features were analyzed by optical microscopy and scanning electron microscopy (SEM). Results showed that microstructures consisted of a large amount of acicular ferrite and a small amount of polygonal ferrite. A very few amount of retained austenite was also observed in the microstructures. The formation of fine acicular ferrite resulted in the high strength of the steel plate. The good impact toughness of the steel plate is mainly attributed to the formation of acicular ferrite and a very few amount of retained austenite.