Susceptibility to Hydrogen Embrittlement of IF Steel with Ultrafine-Grained Structure Produced by Accumulative Roll-Bonding Process

We have investigated the susceptibility to hydrogen embrittlement of interstitial-free (IF) steel with ultrafine-grained microstructure produced by accumulative roll-bonding (ARB) process. The ARB process was conducted to as-received IF steel at 773 K, and repeated to five cycles. The as-received and the ARBed IF steels were cut into tensile specimens, and then hydrogen was electrochemically charged to the specimens in a sulfuric acid solution of pH 2.5 at a cathodic current density of 50 A m(-2) for several charging times. Immediately after the hydrogen-charging process, tensile test was conducted at ambient temperature and an initial strain rate of 3.3 x 10(-4) s(-1). Besides, state and amount of hydrogen absorbed in the specimen were determined with a thermal desorption gas spectroscopy (TDS) at a heating rate of 5.6 x 10(-2) K s(-1). As a result, almost no hydrogen was absorbed in the as-received IF steel charged for a long time of ca. 300 ks, and a fracture strain of the steel was independent of the charging time. On the other hand, amount of hydrogen in the 5-cycle ARBed steel increased with an increase in the charging time, and the fracture strain decreased with an increase in the charging time, indicating that the ARBed steel exhibited susceptibility to hydrogen embrittlement.