HYDROGEN TRAPPING CHARACTERISTICS OF COLD -DRAWN PURE IRON AND EUTECTOID STEEL EVALUATED BY THERMAL-DESORPTION SPECTROMETRY

Hydrogen absorption characteristics of pure iron and eutectoid steel f abricated by cold drawing have been evaluated by thermal desorption sp ectrometry (TDS). The pure iron specimens with ferrite (alpha) structu re and the eutectoid steel specimens with alpha and Fe3C structures, w ere produced under various degrees of reduction and also under various heat treatment conditions. These amount of hydrogen absorbed in speci mens dipped in 20 mass%NH4SCN solution were measured using TDS. TDS an alysis showed that hydrogen evolution rate of pure iron has only one p eak, while that of eutectoid steel has two peaks. From transmission el ectron microscopy and TDS analysis, the lower temperature peak was att ributed to hydrogen released from the trapping sites such as point def ects, clustered defects, and dislocations in alpha. The higher tempera ture peak was found to correspond to hydrogen released from the trappi ng sites such as defects in Fe3C, and/or such as the disordered interf ace between alpha and Fe3C.