Fundamental Evaluations on Microstructure and Mechanical Properties of on-Line Normalizing Processed V-N Microalloyed N80 Class Oil Casings Original Research Article

The thermal-mechanical process of V-N microalloyed N80 casing was simulated using Gleeble-3500 simulator in the laboratory scale, and the complex effects of the nitrogen addition and reheating temperature for on-line normalization on the final microstructure and mechanical properties were examined by optical and transmission electron microscope as well as mechanical testing. It is indicated that the enhanced nitrogen resulted in a high degree of grain refinement in the final microstructures. An increase in reheating temperature brought elevated strength at an expense of toughness. Improved combination of yielding strength in 650 MPa and toughness in 48J at −20°C can be obtained in 33Mn2V steel with nitrogen content of 140ppm at reheating temperature of around 930°C. The results can be used as a reference to determine a reasonable scheme suitable for the on-line normalizing process of nitrogen enhanced V microalloyed seamless oil casings.