Strengthening mechanisms in a pipeline microalloyed steel with a complex microstructure

The microstructure of a commercial pipeline microalloyed steel has been characterized by optical and electron microscopy considering the particularity of the thermomechanical processing without accelerated cooling. The microstructure was a mixture of polygonal ferrite (PF) and granular bainite (GB). The well-known structure-property relationship for PF microalloyed steels is used in structures where high misorientation boundaries in the acicular ferrite are significant. In order to quantify the contributions of the precipitation strengthening as well as the dislocation hardening, representative carbonitride particles and dislocation densities were determined in sample areas by transmission electron microscopy.