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jergos (Mechanical) (OP)
20 Nov 09 16:17
I work with stainless steel 17-4 ph cond A and I have to bring it to cond h900. How do I know how long I have to heat up the pieces to get good result? And will I have a different result heating up too long.  
Helpful Member!  unclesyd (Materials)
20 Nov 09 19:24
Condition H900 is one hour @ 900F plus/minus 15F.
This means the metal temperature is at 900F when the clock starts. You can put the part into an oven that is at 900F from room temperature to minimize the metal heat up time. If your oven has circulation I would allow 15 min per in thickness to come up to temperature. If there is no circulation I would allow 25 minutes per inch of thickness if the oven is at 900F. I would not exceed 15 minutes on the clock.

Can you comeback with the size of your part with the thickness section?

If possible the end use as there are some caveats on using 17-4 PH H900.


http://www.aksteel.com/markets_products/stainless_precipitation.aspx
metengr (Materials)
21 Nov 09 13:53
In addition to what was mentioned by unclesyd regarding time at temperature, now is as good of time as any to mention that furnace temperature surveys are important as is monitoring time at temperature.

I can't tell you how many times during audits I have requested the latest temperature survey of a heat treatment furnace and I receive a blank stare.
 
jergos (Mechanical) (OP)
23 Nov 09 9:58
My problem is that I did heat up a little bit longer(2hours)a piece of 1.75" thick, hardness test gave me 38Hrc and hardness is not the same all around the piece.
  Do you think that the fact I heated up to long could be the problem, or could my cooling process be part of the result?...
   I cool up by opening about 2" wide the door of the oven en leaving piece in the oven.

  End use of the the piece is a 20Tons tention Load cell to go on a crane. The crane is located off shore.   
 
unclesyd (Materials)
23 Nov 09 10:47
I would not use this piece any where near a crane.
Your part will need to solution heat treated and re heat treated using the correct temperature, time, and cooling rate.

Before we go any further exactly how is the 17/4 part going to be used, like is it in tension or compression?  

I personally would not use 17/4 @ H900 on any part of a lifting device especially offshore due to it's lower ductility and a higher degree of susceptibility to Chloride Stress Corrosion Cracking.    
jergos (Mechanical) (OP)
23 Nov 09 11:25
The piece will be use in tension. Most Load cells from specialized manifacturer are made of 17-4, final condition can go from H900 to H1100 and H1150+1150... This depend on safety factors that has to be respected.
  Load cells consist in measuring the deflection of the metal. Ductility has to be low to get good result. I know about the higher degree of susceptibility to Chloride Stress Corrosion Cracking, but how exactly can I control it?
  What would be the stainless type you would use for such application.   
jergos (Mechanical) (OP)
23 Nov 09 11:33
Heat treatment depend on safety factors, but also on how big of a deflection they will need to get a good reading.
 
unclesyd (Materials)
23 Nov 09 14:18
I would look at Nitronic 50(High Strength).  You might give HPA a call with your requirements.

The ductility of of Nitronic 50 (HS) is reduced based on the amount of cold work introduced in the metal.   It also has better resistance to SCC than 17/4 SS

http://www.hpalloy.com/NITRONIC/NITRONIC_50/NITRONIC50HS.html
EdStainless (Materials)
24 Nov 09 11:11
I have seen 17-4 used for load cells, with a 20-1 (or greater) safety factor.

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Plymouth Tube

unclesyd (Materials)
24 Nov 09 11:16
EdStainless,

Around saltwater in condition H900 ?
btrueblood (Mechanical)
24 Nov 09 12:39
Syd posted the meta-link earlier, but the discussion of SCC is in this data bulletin:

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

see pages 13 and 14.
EdStainless (Materials)
25 Nov 09 9:08
I am sure that the ones that I worked with were aged at a higher temp.  I didn't check the mechanicals but I seem to recall 1050F.
They were fully painted, either epoxy or powder coated.
And the safety factors were huge.  We had one rated for 25T, it would take 100T without damage to calibration, and at 100T it still had a more than 4:1 factor.  The material was never stressed to over 10% of the minimum yield strength.  

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

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