The effect of hydrogen on the mechanical properties of high purity iron II. Effect of quenched-in hydrogen below room temperature

Abstract

High purity iron specimens prestrained to 1-2% were hydrogen charged at room temperature and quenched to testing temperatures below room temperature. The yield stress of specimens with a residual resistivity ratio (RRRH) of 4600 or larger was decreased at and above 200 K and increased below 190 K. At 200 K a sharp yield point was observed in specimens with RRRH = 5500. After about 0.5% yield strain a rapid work hardening took place and the flow stress soon exceeded that of uncharged specimens. In low purity specimens (RRRH ≈ 3500) the yield stress was always increased by hydrogen. The effect of hydrogen disappeared on aging for 10-20 min at room temperature after charging. The above observations for the specimens with RRRH = 4600 or larger are satisfactorily explained by two hypotheses: (1) hydrogen atoms trapped at the screw dislocation core increase the mobility of screw dislocations; (2) edge dislocations introduced by prestraining are pinned or heavily dragged by hydrogen atoms in the core below 190 K. © 1979.