Limit number of re-heating AISI 4140 1

[epanabdullah]

Dear Experts,
I'm interesting with the comment onthread330-311437, it was mention about the limit number for re quenching at 3, is there any specification or standard that said about it, I would be happy to have one.
My other concern is on the process of the re-heating AISI 4140 and I will practice on it, is there any standard for the dimension of testing sample?

many thanks in advance
ea

 

[redpicker]

The comment in the referenced thread was

Theoretically, you can re-heat treat an infinite number of times. On a practical basis, however, you get some distortion on every quench and after 4 or 5 quenches, the distortion can become a real issue. Most specifications I have seen that limit the number of re-quenching will put the limit at 3 (although very few specifications actually have a limit). Of course, with 4140 you will have to perform an appropriate NDE after heat treatment.

As I was the one who made the comment, I'll explain. I hvae seen some specifications that limit the number of re-heat treatments. Of the few that I have seen that specify a limit, the limit is put at 3. Most specificaitons do not have a limit. All specifications I have seen that have a limit are proprietary and are covered by confidentially agreements.

My point was in response to the question of how many times can the material be re-heat treated. There is no definative answer to this question. In theory, there is no limit, but there are practical issues that need to be addressed in addition to the theory.

You can refer to ASTM A370 for standard test specimen sizes for the various tests that are commonly performed on heat treated steel. I am not sure what you are looking for when you ask

is there any standard for the dimension of testing sample?

There are standard tests and there are standard specimen sizes for those tests, as described in ASTM A370.


rp

 

[swall]

We used to work to 2 re-heats for H-11 due to a concern about grain coarsening. I did some trials and found that the starting grain size had as much influence on final grain size irregardless of the number of re-heat cycles. Normalizing before re-heat didn't change things much either.

 

[arunmrao]

Decarb and grain coarsening are some of the reasons for limiting the number of reheat treats.

Honestly,if even after 2 trials you are unable to get the properties,you need to relook at your material and process. Having a test bar spare,was always a challenge for me in such circumstances.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[epanabdullah]

Really appreciate for all of the comments, I will through on them for my next experiment.
basically, my problem is about the product of AISI 4140 which not reach the expected hardness and I believe that my previous heattreatment is not good, then I should have the proper one for it. My plan is do re-heating on the old product instead produce the new one since it will make the other cost for me. I don't have the experience about the re-heating before,but I will confidence to the "experiment" on re-heating the product from the information above.

best regards,
epan