Hydrogen Embrittlement of Spring Steel

 
Spring steel is susceptible to hydrogen embrittlement during electroplating. This is caused by atomic hydrogen being diffused along microscopic grain boundaries in the material. This absorbed hydrogen interferes with the "slip" that ordinarily occurs between the crystal planes when deflection takes place.

The higher the carbon content (in the material), the rougher the surface area and the more hydrogen is absorbed. Hydrogen is released from solution whenever an electric current is sent through finishing tanks that plate springs. Therefore all springs, especially those with residual stresses should be stress relieved before plating. Non ferrous metals are immune to hydrogen embrittlement.

Extension springs should not be stretched so that electroplating can occur inside the spring and between the coils. This causes a stress condition which is highly inclined toward embrittlement. Thin spring steel strip is especially susceptible to embrittlement due to the high carbon content.

Springs, unless used with chemical inhibitors in the solution, should not be dipped in strong acid cleaning solutions, as this causes the evolution of atomic hydrogen.

The removing of hydrogen restores springs to their normal condition if done immediately. Baking springs in an oven as soon as possible after plating and washing is the most common way to dehydrogenize springs. A delay of 5 hours may be too long in many cases. The correct time and temperature depends on the type of spring steel. For music wire; 400 degrees F for 45-60minutes is recommended. For all other steels; 420 degrees F for 1 to 2 hours is recommended. Too high of temperature may cause a brownish color that can be removed by bright dip solution.

Nothing can be done to restore springs that have been damaged due to hydrogen embrittlement; they should be scrapped.