EBSD Microstructural studies on quenched-tempered API 5L X65 pipeline steel

Heat treatment is suggested as a means of improving microstructural properties for steels. Three API 5L X65 pipeline steels were subjected to a variety of quenching rates in brine and oil after heating up to 800 degrees C. Thereafter, tempering was performed at a lower temperature of 550 degrees C. Quenching the steels at a slower rate in oil generated refined microstructures consisting of mostly recovered and recrystallised grains with low dislocation cluster. On the other hand, faster quenching in brine created more deformed microstructures comprising of relatively higher local average misorientation. Such variations in structural properties reduced the hardness values obtained after the separate heat treatment procedures. It is notable that the quenching and tempering approach relieved the high stored energy imparted by the thermomechanical treatment, and helped to retained the key properties required for safe pipeline operation. In addition, the risks of HIC was minimised in the oil quenched pipeline steels.

Automated summary

Heat treatment is suggested to improve microstructural properties for steels. Different quenching rates in brine and oil led to variations in microstructures, affecting the hardness values obtained after heat treatment. The quenching and tempering approach relieved high stored energy and retained key properties for safe pipeline operation, with reduced risks of HIC in oil quenched pipeline steels.