| The effects of sulphur and phosphorus segregated at grain boundaries on the hydrogen trapping in S-steel and Ni-Cr-steel as compared to pure iron have been studied using gas phase hydrogen charging and electrochemical detection techniques. The segregation of sulphur and phosphorus was performed by tempering the Fe-S and the Fe-Ni-Cr-P specimens, respectively. This was ensured form AES spectroscopy and SEM micrography, respectively. The hydrogen trap densities and trap binding energies were determined from plots of time lag against inverse square of input hydrogen pressures. The trap densities for the annealed Fe-S specimen and the tempered Fe-S specimen were found to be about 1.1×10^(-7) and 3.0×10^(-7)㏖/㎤, respectively, and the trap binding energy for the both specimens was determined to be about -57kJ/㏖. In the case of pure iron specimen, the trap density and trap binding energy were 1.2×10^(-7)㏖/㎤ and -56kJ/㏖, respectively. The annealed Fe-Ni-Cr specimen and the tempered Fe-Ni-Cr-P specimen showed the trap binding energies of -53 and -55kJ/㏖, respectively, and the both specimens had approximately the same trap density of 1×10^(-6)㏖/㎤. From the experimental results, it is suggested that sulphur and phosphorus segregated at grain boundaries act as saturable deep trap sites for hydrogen in S-steel and Ni-Cr-steel, respectively. |
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