The surface of stainless steel seamless pipes turns black after being reheated
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Question: For ASTM A312 TP316L, the hardness is too high – it exceeds 90 HRB. After the customer carried out re-heat treatment, the surface of the tubes turned black. What is the reason for this?
I’m sorry, there was a mistake. After solution treatment, among the same batch of tubes, some are white and some are black; this caused you to misunderstand.
When the temperature is high, an oxide scale forms on the surface; it appears black. Isn’t that quite normal? Otherwise, why is pickling still required? Was the requirement for hardness specified by the customer’s procurement technical requirements? It’s not specified in the standards
This post was last edited by Sammy_Wang on 2016-1-13 at 15:34. There’s something wrong with this pipe of yours – its hardness is too high. If you need a pipe, contact me; reach out via the in-site message system
316L stainless steel can only be subjected to solution treatment. Uneven blackening on the surface is due to untimely quenching after exiting the furnace.