An additional consequence of the “counterfeit bolt scandal” was that most of the people in the industry learned that the bake had to be within one hour of the parts exiting the plating bath. Industry convinced Congress they would self-regulate. Hydrogen-embrittlement problems seemed to be few and far between for some years after that. Now they seem to be more frequent. At least I hear people claiming to have hydrogen-embrittlement problems more frequently. They may not have studied the following 5-step list.
5 key features that permit proper diagnosis of classical hydrogen embrittlement in hardened steel:
- Delayed cracking under a sustained stress
- Intergranular micro-scale crack features (Fig. 1)
- A known source of hydrogen (often electroplating or pickling)
- A susceptible component (usually where the yield strength approaches the tensile strength)
- Documented freedom from other problems known to promote intergranular fracture (such as improper tempering temperature or slow cooling of very large components from hot processing), especially in the presence of impact loading (Fig. 2)
Even though some companies have allowed the bake cycle to be delayed beyond one hour after plating, it is highly preferable to bake the parts as soon as possible and as close to right after exiting the plating bath as possible. One hour is preferred as the maximum elapsed time before starting the bake cycle.
This is especially important for critical parts that have safety implications or for small parts that are going into expensive assemblies. Consider the cost to get the parts into the bake oven in a timely fashion compared to the cost to fix some indeterminate number of broken parts deep in a complex assembly. Job-shop-type manufacturers of small parts would do well to consider this when quoting small hardened and plated parts.
Minimizing the post-electroplating delay before baking is also critically important for heat-treated parts whose specified hardness is over Rockwell C 40 and for heavily cold-worked parts whatever their hardness value.
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