17-4 PH Y/T ratio <0.7, low Yield for H1150

[Diegol]

Hello

I have a 17-4 PH forging which was heat treated to:

Solution 1900°F for 4 hours
1st Precipitation hardening 1150°F for 4 hours
2nd Precipitation hardening 1150°F for 4 hours

Sometimes the Y/T ratio is ok 0.85-0.9, but sometimes it is 0.6-0.7 which means that the Yield is very low for a certain hardness.

does anyone might have a clue why this happens even in the same heat? And how can I increase the Y/T ratio?.

one chemical composition is :
C 0.026
Si 0.36
Mn 0.92
P 0.019
S <0.001
Cr 15.78
Mo 0.12
Ni 4.54
Cu 3.2
V 0.02
W 0.02
Co 0.03
Nb 0.24

 

[CoryPad]

Do you have microstructure comparisons? Are there any grain size differences?

 

[MagBen]

What do you expect? I think you double aging hardening was to increase bit of ductility for a sour environment to decrease hydrogen brittlement, is this for a oil gas application?

Double long time aging can give you some reverse austenite, leading to lower yield. if you need higher yield, and higher Y/T, just aging once, or decease aging temperature.

 

[EdStainless]

Even small changes in aging temp will impact strength.
Your second age should be 10F below the first, and neither should ever go above 1150F.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

One note of caution, there is nothing wrong with a 1150 double aging treatment for this material. It is stated as such in the literature. However, if you are using a double aging treatment cycle, you must cool the material to below 100 deg F between aging cycles.