Properties of thermal hydrogen desorption and substitution of high-pressure gas charging by electrolysis charging for Inconel 625 and SUS 316L

Abstract

The fundamental properties of thermal hydrogen desorption for Inconel 625 and SUS 316L for face-centered-cubic(FCC) metals have been analyzed. Then, the high-pressure-gas charging of hydrogen has been substituted by electrolysis charging. Hydrogen was charged into Inconel 625 and SUS 316L in H 2SO4 with or without NH4SCN as a catalyst at current densities in the range from 0 to 90(A/m2) and in gaseous hydrogen at the pressure of 0.3,10, 20 and 45 MPa at 9O0C. The states of hydrogen existing trapping sites were compared using thermal desorption analysis (TDA). The diffusion activation energy is 46.5(kJ/mol) and the trap activation energy is 46.3(kJ/mol) for Inconel 625. These close values indicate that the hydrogen released from FCC metals is determined not by desorption from trapping sites but by diffusion in lattice. The hydrogen content of Inconel 625 increased upon the quenching and cold-working. This increase in hydrogen content corresponds to the increase in the densities of vacancies and dislocations. The hydrogen peak consists of solution hydrogen and trapped hydrogen at vacancies and dislocations. The peak temperatures in the hydrogen evolution curves of Inconel 625 and SUS 316L charged by electrolysis and high-pressure gas at 90°C are the same after hydrogen saturation. In addition, hydrogen contents obtained upon charging by electrolysis exceed those obtained by high-pressure gas of 45 MPa. This means that higher-pressure gas environments of at least 45 MPa can be substituted by electrolysis charging. The hydrogen-saturated contents of the metals increase with current density and catalyst content. Sievert's law describes the relationship among hydrogen content, hydrogen gas pressure, and temperature. Therefore, the gas pressures corresponding to electrolysis charging conditions can be obtained. When hydrogen is charged by electrolysis using 0.1 mass% NH4SCN at 50(A/m2), the hydrogen gas pressure of 1200 MPa is actualized by electrolysis charging. © 2008 The Japan Institute of Metals.