Hydrogen Desorption Behavior Trapped in Various Microstructures of High-Strength Steels Using Thermal Desorption Analysis

Abstract

The relationship between different microstructures and hydrogen trapping states of cold-drawn pearlitic (CD-P) steel, medium-carbon martensitic (MC-M) steel, and high-carbon martensitic (HC-M) steel was studied based on the hydrogen desorption profile, activation energy of hydrogen desorption (Ea), and hydrogen release behavior at room temperature by means of thermal desorption analysis (TDA). The TDA results revealed that hydrogen in CD-P and HC-M was present as both Peak 1H and Peak 2H, but only as Peak 1H in MC-M. Hydrogen release behavior indicated that Peak 1H for all three types of steel was diffusible (Ea ≤ 34 kJ/mol). For CD-P, Peak 2H was non-diffusible (Ea = 62 kJ/mol), but diffusible for HC-M (Ea = 43 kJ/mol). TDA results combined with SEM and/or TEM observation and XRD analysis clarified that the former hydrogen was desorbed from strained incoherent α/θ interfaces in a detrapping-controlled process. The latter hydrogen was desorbed via trapping sites involved in retained austenite in a diffusion-controlled process. It is essential to judge hydrogen trapping states as either diffusible or non-diffusible by analyzing not only hydrogen desorption profiles but also hydrogen release behaviors and Ea values, taking into account microstructure characteristics related to hydrogen trapping and diffusion processes.