Effect of Austenite Microstructure and Composition on Transformation Behaviour in The Heat Affected Zone of Pipeline Steel

Pipelines represent a challenge in oil and gas distribution in
remote places with extreme weather. It is expected than in the coming years,
the energy consumption will progressively increase to 28% by 2040. In this trend, the
natural gas will increase 1.4% every year. Due to that scenario, pipelines
are crucial to achieve the production improving mechanical properties in the
steel without diminishing the toughness. The aim of this research is to analyse
the effect of precipitates of niobium carbonitrides on the microstructure, in
addition to the tensile strength, elongation and toughness in X80 steel.
This research utilised five different austenitising temperatures between 900°C
to 1300°C, together with three different cooling rates of 0.5°C, 5°C and 50°C
following each of the austenitising treatments. The evolution of
microstructure was analysed using optical microscopy, SEM and EBSD. The precipitation was
evaluated using carbon extraction replicas in the TEM.