Designing steel to resist hydrogen embrittlement Part 2–precipitate characterisation
A novel, low-alloy steel has been designed for use in the oil and gas industry. Its high strength and hydrogen trapping potential are derived from a martensitic microstructure containing a dispersion of fine vanadium–molybdenum alloy carbides that evolve during tempering. In this second paper, the effect of quench rate from austenitisation and tempering conditions are investigated with respect to the microstructure. The alloy loses its tempering resistance following slow-cooling from austenitisation as a result of MC precipitation, leading to vanadium depletion and significant M(Formula presented.)C coarsening. This is predicted using computer simulation and confirmed by high energy X-ray diffraction, combined with electron microscopy.