Characterization of Microstructure in High Strength Microalloyed Steels Using Quantitative X-Ray Diffraction

The mechanical properties of microalloyed steels used in pipelines are strongly affected by microstructure. In this paper, X-ray diffraction (Rietveld method) was used to quantify the microstructure — specifically domain size, microstrain and preferred orientation — for four X80 steels and three experimental X100 steels. Measurements were made at the surface and at several positions below the surface. Nano-sized domains were obtained for all steels tested. A smaller domain size, higher microstrain and stronger preferred orientation were observed in the X100 samples relative to the X80 steels.