17-4 H900 Concerns 1

[KSor]

We currently use 17-4 PH H900 in many of our products. These are tensile load bearing items in all possible environments (-40°F to +160°F). Looking thru some of the existing threads on Eng-Tips, many of you recommend against using 17-4 in the H900 condition. Can you please explain why? As well, are there any available specs that can document these reasons?

 

[israelkk]

According to MIL-HDBK-5J The impact strength of 17-4PH, especially large size bar in the H900 and H925 conditions, may be very low at subzero temperatures; consequently, the use of 17-4PH for critical applications at low temperatures
should be avoided. For non-impact applications, such as valve seats, parts in the H925 condition have
performed satisfactorily down to -320EF.

 

[unclesyd]

Take a look at this data set for 17/4. As stated before we have used it from it's inception for all sorts of pressure containing components and extrusion dies. From the onset ARMCO did't recommend using 17/4 in the H900 condition, especially in our case where we had a problem with SCC. If we needed the hardness we used the H925 even though it will still crack. Our process dictates that we operate at the upper temperature limit for the alloy. We constanly cycle our parts from RT to 600F to 900F to Rt over a period of a few weeks. As we are operating at the upper temperature limit we do suffer a loss of ductility and and increase in hardness. This manifest itself generally by thread stipping in blind holes. we the use the H1150 + H1150 or the H1150M to partially recover some physicals. The loss of ductility on the an H900 component has a much steeper curve.
We also make a lot of shafts, both large and small, from 17/4 and based on recommendation for ARMCO (AK Steel) we always H1125 or H1150. We buy a lot our shafts in this condition.

We also make a lot parts the we liquid nitride for wear properties. I have some liquid nitrided 17/4 drums/sleeves that have been operating for over 25 years in high pressure water pumps.

http://www.aksteel.com/pdf/markets_products/stainless/precipitation/17-4_PH_Data_Bulletin.pdf

 

[KSor]

What does MIL-HDBK-5J mean by low temperatures? Anything below freezing?