Heat Treating 17-7 to TH1050; how critical is 60 deg. cool temp ?

[xpantheon]

We manufacture a mostly flat "clip-on" style receptacle, that accepts a 1/4 turn stud. Material is 17-7 stainless, and the appx. dimensions are .032 thick and 1" square. we have it heat treated to TH1050, which reads "heat to 1400 F for 1.5 hours, cool to 60F within 1 hour and hold at 60F for 30 minutes. Reheat to 1050F, and then air cool to TH1050 condition (15N 79.5 - 82)". Some recent parts that were heat treated seem to be taking a "set" after being engaged with the stud for a short time. The parts do not exhibit the "spring-back" that previous lots have. We measured the hardness and it was within the 15N 79.5 - 82 specification. We reviewed the heat treat process and are not confident that the parts are truly being brought to 60F (+0, -10 degrees per the spec), in fact our heat treater advised us that he usually cools the parts to the point that they are "cool to the touch". We are wondering how critical it is to the "spring-back" ability of the part if our heat treater is deviating from the spec and cooling the parts to 90 F (on a summer's day) versus the 60 F called out in the spec. Any help will be greatly appreciated.

 

[Metalguy]

Off the top I don't know about the importance of the 60 deg. (sounds like it is, though), but your problem appears to be lack of yield strength. Hardness correlates with UTS and NOT YS.

 

[McHaney]

It seems most unlikely that there is a significant difference in properties from cooling to 60F vs. 90F. If there really is a problem, it is likely related to one of the higher temperature cycles.