Strengthening mechanisms in a pipeline microalloyed steel with a complex microstructure

The Analysis of the Microstructure and Mechanical Properties of Low Carbon Microalloyed Steels after Ultra Fast Cooling

“…On the other hand, a considerable amount of AFs in the high start cooling temperature (780ºC) condition is formed. It has been well accepted that the AF, in the GB microstructure, comes from a mixed diffusion and shear transformation mode during continuous cooling beginning at a temperature above the upper bainite transformation region temperature 19 . The AF nucleates at intragranular sites and it is characterized by an assemblage of interwoven non-parallel ferrite laths with high density of tangled dislocations, where the most parts of the neighboring lath (subgrain) boundaries have dissimilar orientations 19 .…”

“…It has been well accepted that the AF, in the GB microstructure, comes from a mixed diffusion and shear transformation mode during continuous cooling beginning at a temperature above the upper bainite transformation region temperature 19 . The AF nucleates at intragranular sites and it is characterized by an assemblage of interwoven non-parallel ferrite laths with high density of tangled dislocations, where the most parts of the neighboring lath (subgrain) boundaries have dissimilar orientations 19 . A microstructure of acicular ferrite has the potential of combining high strength and high toughness, because a crack would have to follow a more tortuous path through a microstructure of acicular ferrite 20 .…”

“…When several of the microalloyed elements are present in the alloy, the precipitated carbides or carbonitrides have a complex composition of Ti, Nb and V being more effective as strengthener in the steel 19,22 . The suppression of grain boundary migration due to microalloying is caused by either the solute dragging effect caused by segregation of alloying elements to the boundaries, or the pinning effect caused by carbo-nitride precipitates.…”

“…When the cooling rate increases, the grain size decreases overall, and the volume fraction of bainitic ferrite increases, which leads to the higher strength and the lower ductility and toughness 16 . The fine particle precipitation contributes to the strengthening of the steel 19 . However, the Charpy absorbed energies of steel B do not significantly reduce (Table 2 and Fig.…”

Avaliação Dos Parâmetros Do Processo Termomecânico Da Laminação De Tiras a Quente De Aços Microligados Ao Nióbio

“…Na maior parte dessas pesquisas, os fundamentos da metalurgia física desses aços são abordados. Por exemplo, Morales et al [1] avaliaram as contribuições que os diversos mecanismos de endurecimento trazem ao valor do limite de escoamento de um aço microligado. Nayaka et al [2] estudaram os aspectos da microestrutura de aços microligados para tubos da classe API.…”