Structure and properties of a low carbon Cu bearing high strength steel

A low carbon steel alloyed with Ni, Mn, Mo, Cu and microalloyed with Nb and Ti was prepared and the continuous cooling transformation behavior of the steel was evaluated. It is observed that the “C” curve for high temperature decomposition product of austenite i.e. polygonal ferrite or Widmänstatten ferrite has been shifted to an extreme right. A flat top “C” curve with a mixed structure of bainite and martensite has been obtained at lower temperatures and the transformation temperatures do not vary much with a wide range of cooling rates. The steel was thermo-mechanically processed followed by water quenching. The high strength value obtained in the present steel is due to austenite grain refinement, highly dislocated fine lath martensitic structure along with tiny precipitates of microalloying carbide and carbonitride at all finish rolling temperatures. The formation of stable and large TiN/TiCN particles during casting have impaired the impact toughness values at ambient and at −40 °C temperatures.