Should we be baking case hardened parts for Hydrogen Embrittlement?

A. Case-hardened articles are particularly sensitive to hydrogen embrittlement due to internal stress. Most manufacturers of self-drilling, self-tapping screws [sometimes called 'TEKS' (r)] use non-embrittling finishes such as mechanical plating or zinc-rich paints (usually applied over dry phos). There is a risk-reward scenario. If you plate and bake, you can reduce the risk. But you cannot eliminate it. For guidance, see ASTM B850-98 (recommended reading). Alkaline non-cyanide zinc plating is more resistant to hydrogen embrittlement. This seems counter-intuitive because the efficiency is low compared to acid zinc (more hydrogen is generated). But the lamellar structure of alkaline zinc offsets that issue. Any plating of these articles without baking, IMHO, would amount to assuming an excessive amount of risk regardless of the end-use market.

A. Basically, yes.

Then it depends on the geometry of the part, the metal of manufacture, how close it can come to yield strength in actual use and what kind of physical abuse will it possibly get. A 1x2x4 block that has another part rub on it with no great pressure probably would not absolutely have to have it.

The reality is you can sleep better at night if you do post plate bake it. If you do not and it fails, someone is terribly injured, a sharp lawyer gets it you will be sued and he can hire a number of the world recognized authorities that will say--It should have been baked-- It would have prevented this terrible accident. You will lose 99.999% of the time. The bake is the cheapest insurance you can buy. Or, how about you supplied 500,000 auto parts that had to be recalled. Bad news.

A. Yes, you must process the parts through an embrittlement relief heat treatment when they have been carburized. The requirements for time and temperature are specified in ASTM B850-98 or SAE USCAR 5. One point about the hardening of these parts does not seem correct-- 12L14 is not capable of being through hardened to 38-40 HRC, so I do not know how the parts will be certified to meet that requirement.

A. Joel: I don't think he is saying that their 12L14 parts are through hardened; those are different parts from some other raw material which does through harden.

In any case, carburized and hardened parts are susceptible to hydrogen embrittlement of the surface and should be baked.

A. Joel,

You need to bake hardened parts plated with zinc-nickel if their hardness is over 30 HRC. If hardness is lower, there is a minimum risk of hydrogen embrittlement. If hardness is higher, the risk is measurable and you should bake the parts.

Hope you can solve this! Regards!