2016 Volume 65 Issue 2 Pages 67-74
An ammonium thiocyanate (NH4SCN) solution is widely used in hydrogen embrittlement evaluations of high-strength steel materials. It is known that an increase in the specific solution volume to the specimen surface area results in a severe evaluation in hydrogen embrittlement testing. The reason for that is explained in this paper based on the change in the solution pH induced by a cathodic reaction, which accompanies thiocyanate ion decomposition and governs hydrogen absorption. In addition, the pH dependence of the cathodic reaction governing hydrogen absorption is made clear by using a sodium thiocyanate solution containing a buffer solution to control the solution pH. It is shown that immersing steel specimens in the pH-controlled sodium thiocyanate solution achieves a higher hydrogen content compared with the level attained with the NH4SCN solution.