Solution pH and specific solution volume to specimen surface area on corrosion reactions and hydrogen absorption of steel in solutions containing thiocyanate ion

摘要

An ammonium thiocyanate (NH4SCN) solution is widely used in hydrogen embrittlement evaluations of highstrength 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.