Microstructural modifications induced by hydrogen in a heat resistant steel type HP-45 with Nb and Ti additions

Heat resistant stainless steel type HP45 modified by Nb and Ti additions, which is commonly used in chemical and petrochemical industrial plants, was submitted to hydrogen treatment at low and ultra-high pressures. In the low-pressure experiments, 0.1 Pa, hydrogen was supplied in a quartz tube and the material was heat-treated for 100 It at 1200 K. In the high-pressure experiments, 5 GPa, hydrogen was supplied in a NaCl container and the material heat-treated at 873 and 1073 K for I h. A coarsening of the M23C6, (M=Fe, Cr, Ni) carbides. was observed in both cases, these being of a sharper shape for the low hydrogen pressure condition, compared with previously aged samples. In the high pressure experiments, where the atomic mobility is higher, a more intense coarsening of the carbides and the cracks associated with them was observed, which is deleterious for mechanical properties. The hydrogen-induced phase coarsening can be understood in terms of the vacancy formation that occurs under such conditions. (C) 2003 Elsevier B.V. All fights reserved.