Effect of multiple annealing+aging cycles on room temp mechanical properties of 17-4 PH 2

[skailup]

Hello everyone,

I wonder if anyone could point me to articles or studies that determined the effect of multiple annealing+aging cycles on the properties of martensitic PH stainless steel such as 17-4 PH or 13-8 Mo.

Best Regards,

 

[EdStainless]

I'll have to hunt, I don't know if I have them digital or not.
In general the properties of these alloys improve withe repeated anneal+age cycles.
There is some grain refinement that happens each time.
I know that impact toughness will improve.
Yield strength may go down slightly, buy UTS will stay the same and elongations will increase.

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Plymouth Tube

 

[redpicker]

One thing to keep in mind is that with multiple solution annealing cycles, you may get problems with distortion that alter the geometry to the extent that the mechanical capacity of the section is compromised. That is, while the Yield Stress and Tensile Stress (PSI) may remain the same, the Yield Strength and/or Tensile Strength (Pounds) of a section may decrease because of changes in the geometry.

A lot would depend on the cooling from solution treatment temperature, as well as the number of cycles. If you are talking of hundreds of solution treatment cycles using a oil quench, for example, things are going to change quite a bit between the first couple of cycles and the last ones. Your round bar you started with may not be round any more, so it's bending strength may change, even though the yield stress is remaining the same.

rp

 

[skailup]

Thank you all for answers. I am looking into just no more than 5 cycles or so. It wouldn't be economical for us to do too many times.

EdStainless, would you please shed some light on the grain refinement with more cycles? I thought it would cause prior austenite grain growth.

Thank you,

 

[forging82]

As far as grain refinement I've seen a part go from a 2 to a 4.

 

[EdStainless]

I am not sure what the mechanism is, but the grain size will become finer with repeated anneal/aging cycles.
As long as you don't over do the time and temp for the anneals then you will get grain refinement.
I have had projects where welds were required to meet difficult impact toughness requirements.
A cycled heat treat allowed us to get the desired results.

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Plymouth Tube

 

[skailup]

Thanks again.

 

[tbuelna]

Is the component subject to any other processing between the anneal/HT/aging cycles? Also, are all of the anneal/HT/aging process cycles identical?

 

[skailup]

There is not any other processing in between annealing and aging. My inquiry came primarily because I heard about potential improvement with cyclic processing and tried to locate the studies.

A secondary reason is due to quality non-conformance issues. Every once in a while there was a cycle where temperature overshot by a few degrees for a few minutes. In my environment, it is extremely unlikely that such cases can be accepted without further processing. Generally they were scrapped.