Determination of the Precipitation Mechanism for a High-Alloy High-Strength Steel

The thermomechanical process to obtain high alloy high strength steels is based on the control of variables such as temperature, deformation and strain rate to promote hardening mechanisms that directly influence the strength and toughness of the steel. Experimentally, it was determined for an API type steel, that the temperature of potential precipitation during the hot deformation process will be in a range of temperature from 1150°C to 1000°C. Precipitation will occur instantaneously due to temperature, deformation and strain rate (0.1 and 0.2 deformation and 0.5s-1 and 1s-1 strain rate) effect. The incorporation of microalloying elements as Nb in a percentage of < 0.050 significantly influences precipitation hardening preferentially located at austenitic grain boundaries. It was determined that precipitates of between 3 to 5 nanometers in size, distinguished as NbC will be obtained. It was found that the precipitation kinetics for the steel is affected by a single step deformation applied, by the formation of precipitate colonies at 0.1 deformation and strain rate 1s-1, which does not allow the dispersion of precipitates generating a planar interface in the microstructure of the steel. Finally, the preferentially localized precipitation mechanism of the almost continuous type by the grain boundaries was evidenced. This mechanism is crucial for controlling austenitic grain size during deformation, which leads to a final, homogenized microstructure.