Black Oxide Coating and Embrittlement
Black Oxide Coating and Embrittlement
(OP)
Hi all,
Does anyone have experience or know if the black oxide coating process can cause embrittlement, i.e. hydrogen embrittlement? I have parts made of A2 tool steel that are hardened to 54 HRC and subsequently coated with black oxide. We are noticing that lately they have been failing below the proof load. The parts are only 0.040" at the thickest section. I'm not sure what process our vendors uses for the black oxide coating process so I'm not sure if their is a pickling process, or what temperatures the caustic bath is kept at. Also, they could be electroplating for all I know. I'm just wondering, with such a high strength steel, is it necessary to stress relieve these machined parts after coating?
Does anyone have experience or know if the black oxide coating process can cause embrittlement, i.e. hydrogen embrittlement? I have parts made of A2 tool steel that are hardened to 54 HRC and subsequently coated with black oxide. We are noticing that lately they have been failing below the proof load. The parts are only 0.040" at the thickest section. I'm not sure what process our vendors uses for the black oxide coating process so I'm not sure if their is a pickling process, or what temperatures the caustic bath is kept at. Also, they could be electroplating for all I know. I'm just wondering, with such a high strength steel, is it necessary to stress relieve these machined parts after coating?





RE: Black Oxide Coating and Embrittlement
RE: Black Oxide Coating and Embrittlement
To remove hydrogen, the term is called bake out and is not a stress relief. The reason is that the bake out is performed at 450 deg F to 550 deg F to allow nacent hydrogen to diffuse from the substrate. The bake out temperature is well below the temperature required for stress relief.
RE: Black Oxide Coating and Embrittlement