HOME  > Surface Finishing Tutorial  > #004 Hydrogen Embrittlement - The Source
Surface Finishing Tutorial

#004 Hydrogen Embrittlement - The Source

Category : Hydrogen embrittlement
July24, 2009

Plating, in general, has required processes of [Pre-treatment > Surface finish > Post treatment]. Each process is shown in Table 1 as electro-plating as examples.

[Table 1] Plating processes
Immersion degreasingZinc platingChromate coating
Electrolytic degreasingCopper - Nickel - Chrome platingAnti-discoloration, drying
Pickling (acid wash)Nickel - Chrome platingBaking process
Electro-polishNickel - Gold/Silver platingPaint - baking
Plating removalHard-chrome plating, etc. 

Many of these processes may result in hydrogen formation due to dissolution of steel and electrolysis of water. Care must be taken since the hydrogen may penetrate the steel under certain conditions.
The hydrogen penetration levels vary depending on the plating metals and solution bath compositions. However, the possibility of whether hydrogen embrittlement fracture may occur or not will largely depend on the host metal's susceptibility to hydrogen embrittlement.
Carbon steel's hydrogen embrittlement rate per process is shown next.


The pickling process is performed to remove scales and rust from the surface of steel objects to be plated. Normally, this process uses hydrochloric acid, sulfuric acid and the like, and prone to cause hydrogen embrittlement.
If this process is performed unconscientiously, the steel will certainly absorb hydrogen and embrittlement induced fracture will occur. For high tensile strength steel applications where safety is strongly desired, dry processes such as shot blasting and honing are therefore often specified.

(2)Pickling by hydrochloric acid

Pickling bath most typically used for steel alloys is at 10% solution strength, and the steel immersed in this bath in just a few minutes will reach 70% hydrogen embrittlement rate (see [Graph]). This is a significant problem for high tensile strength steel. Higher hydrochloric acid concentration will further raise the embrittlement rate. The immersion rate versus time will saturate beyond a few minutes.
In order to prevent this problem, commercially available inhibitors are usually added to the solution. The inhibitors will be mentioned later.