Effect of Isothermal Transformation Temperature and Cold-Drawing on Hydrogen Occlusion Behavior in Eutectoid Steel

Hydrogen occlusion behavior of eutectoid steel fabricated by isothermal transformation treatment and cold-drawing treatment has been evaluated by thermal desorption analysis (TDA). Specimens containing different shape cementite were produced under various isothermal transformation temperatures and also under cold-drawing at 85%. The amount of hydrogen occluded in the specimens dipped in 20 mass%NH4SCN solution was measured by using TDA. TDA analysis showed that the hydrogen evolution rate of the isothermally transformed specimens has only one peak, while that of the cold-drawn specimens has two peaks. The cementite shapes can change the hydrogen occlusion behavior in the specimens. The cold-drawn specimens containing longer cementite increase hydrogen released at higher temperature. This hydrogen does not cause delayed fracture. From transmission electron microscopy and TDA, it was suggested the higher temperature peak corresponds to hydrogen released from trapping sites such as interfacial dislocations between ferrite and cementite, and/or the cementite polycrystal interface formed by cold-drawing.