To guarantee 100% martensite trnasformation. if strip or plate, usually only need 1-2 hours

The reactions times are slow at low temps.
And if you don't get 100% martensite your strengths will come out low.
We have tested and found that for thin material (<0.095") 4 hours was always long enough.
I can see that in thicker sections you would need more time.

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P.E. Metallurgy, Plymouth Tube

Why do Aerospace and industry standards call out 8 to 9 hours?

dek1234-

I'm assuming you are asking about the standard 17-7PH austenite conditioning and transformation treatment for condition R-100. Aerospace HT standards like MIL-H-6875 and AMS2759/3 are based on processes that decades of collective industry experience have shown to provide certain consistent results.



These HT standards provide an excellent procedure to follow in most situations. However, unless you are contractually obligated to comply with one of these standards, you can always develop your own. In your case it might be the AMS2759/3 standard with an exception for the minimum transformation treatment time. As EdStainless noted, it might be possible to get the results you require with a reduced amount of time at -100degF. Section 6.4 of MIL-H-6875 discusses this issue.



Just remember that if you choose to deviate from the HT standard process requirements, you will likely need to validate the modified process.

Good luck to you.

They call out 8hr because they want to make sure that it works for that 16" thick forging that you have....

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P.E. Metallurgy, Plymouth Tube