Heat treatment of Custom 455 and 17-4PH s/steel 1

[IJEmslie]

Hi. Can anyone help with this heat treatment question?

As part of a heat treatment validation exercise I have measured hardness of materials following the recommended cycle

In the case of Custom 455 S/Steel, the Carpenters Data Sheet states that the maximum material strength is achieved by age-hardening to condition H900 (4 hours at 900oF and air cooled). A hardness of ~ 47-49 HRC is achieved at this condition.

However, I am measuring up to 57 HRC for some components

1)How has this happened? Could it be due to the temperature being too low?

2)If greater hardness than 47-49 HRC is achievable, why do Carpenters not recommend this as a standard cycle?

Additionally, I have experienced similar effects with Stainless Steel 17-4PH. Data sheets suggest that the maximum achievable hardness is 44 HRC, whereas I have measured up to 54 HRC (H900. 1 hour and air cooled).

Any help or explanation would be much appreciated.

Ian

 

[metengr]

Can you describe the hardness testing method you used to validate age hardening heat treatment for the Custom 455 stainless? It might help to provide an answer to your problem.

 

[NickE]

From my recent (very) experience the hardening behavior of the PH Stainless grades can be a very tiresome process to figure out. They dont always produce the hardness in the books. You must be starting the process with heavily cold worked material. (IE: Condition C) this material will produce the highest strength levels when age hardened. For my 17-7 parts I tend to see Right around 51HRc. Although depending on thickness that may be higher or lower.

Search here for other discussions of PH stainless steels. (Also mcguire and israelkk and EdStainless will be around in a bit I'm sure)

Here are some data sheets:

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

http://www.cartech.com/common/frame...5.html&leftn=epg_cspc&lefto=empty&lefti=empty

Nick
I love materials science!

 

[IJEmslie]

Thanks for the replies so far.

The hardness testing is carried out by a sub-contract supplier so this could be a bit sketchy.

I believe that the tests are carried out using Vickers testing apparatus with a 5kg load. The results are then converted from Vickers to Rockwell C scale.

Hope this helps. If not I can get specific details.

Cheers

Ian

 

[israelkk]

If you look on MIL-HDBK-5J you will find that there is no hardness values but only strength values. As I mentioned in other threads the hardness can be off by up to 10Rc for the same heat treatment (such as H1000, H950, H900 etc. Older versions of MIL-HDBK-5 had a table that shows this phenomena for PH alloys however they no longer print it. If the hardness is important then you have to experiment with aging temperature but with every batch you will have to do it again risking lowering the strength.

 

[EdStainless]

Thanks Nick,
You might also try the data at

http://www.alleghenytechnologies.com/ludlum/

Select the alloy of interest and then look at the Blue Sheet for it.

But, to your point. You always need to reanneal PH grades in order to control the properties.
My guess is that if you are seeing such harnesses that the ductility is zero. It could be from prior cold work and you are in effect getting CH material. It could also be because of odd microstructure after the previous anneal.

For recent 17-7 jobs we have been using the RH treatment that requires -100F within 1 hour of the anneal. This has improved both the strength and ductility.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[IJEmslie]

Thanks all for the replies so far.

Unfortunately I do not have the MIL standard. I will have a look online.

I have taken your comments on board and am currently awaiting a response from Carpenters.

Many thanks

Ian

 

[israelkk]

MIL-HDBK-5J and 5H can be found at

http://assist.daps.dla.mil/eAccess/index.cfm?ident_number=53876