the affect of doing the Heat treatment twice

[Steven444]

What is the affect of doing the Heat treatment twice on the material?
Does it enhance the mechanical property or the opposite?

 

[metengr]

Steven444;
It really depends on the material and your application (I hate to be general but it is very application specific). For example, most ferrous materials can be subjected to a re-heat treatment to correct past sins. It must be performed under controlled conditions to minimize distortion, and other high temperature effects like decarburization or oxidation of material along exposed surfaces.

On the opposite end of the spectrum, re-heat treatment can adversely effect the original properties that were intended in the material based on the original heat treatment.

If you provide more information, we might be able to help you. There are various types of heat treatment, as well.

 

[mshimko]

The original question is too vague for an answer.

- What type of heat treatment are you're referring to? Solution annealing followed by quench?; tempering? Quench and temper?, etc.

- What type of material is involved?

 

[dbooker630]

Double- and sometimes triple-tempering will reduce retained austenite levels. Usually for high alloy tool materials to enhance stability properties.

 

[Steven444]

I do not have a case but it is general question came to my mind. I was thinking about the SAME vessel, there is heat treatment during the fabrication of plate and after completing the pressure vessel there is another Heat treatment!
My question is mainly about CS.

 

[QAFitz]

Usually, heat treatment after fabrication is limited to the welded area, as in post weld heat treatment. This is generally to minimize stresses built up during the welding operation. I've seen vessels heat treated in their final fabrication condition, again, usually to normalize and minimize any built up stresses.

 

[mshimko]

The most recent posts above show why more information is necessary; there's a BIG difference between (a) solution anneal and (b) stress relieving heat treatments.

 

[jehan17718]

Gents (and ladies),

Please also have a look at the below thread which deals with multiple PWHT cycles.

http://www.eng-tips.com/viewthread.cfm?qid=193335&page=1

Hope it helps.

-jehan