What Stainless Alloy to SPF Titanium at 1650 F

[DKirkham]

I am looking for a stainless casting alloy to be used to make the forming die for a super plastic formed part in titanium. The die blank will be cast to rough size and then final machined.

In my research with the titanium SPF guys I have found that 309 is used to prototype parts but they use a proprietary alloy for production runs and wouldn't tell me what is was.

The die will be subjected to repeated cycles of room temp to 1650 F. I want to avoid scaling as much as possible on the die. I have been told 309 scales after every run.

I am inclined to use 347, but I have no idea if this is castable??? 321 and 347 are used in our industry (race cars) for turbo exhaust systems. I don't think 321 with the titanium is very castable, however.

Any thoughts?

Thank you all in advance for your time.

 

[EdStainless]

I don't know what the latest and greatest is, but I recall that they used to use 309 or 310 castings and weld overlay with a Ni alloy. You have to watch thermal fatigue, oxidation and thermal expansion.
Some of the high temp casting grades might work, a 25%Cr Ni based alloy, but it would get expensive fast.

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[unclesyd]

If you want to stay with the SS alloys 310SS is much better than 309SS and 446SS is much better than either as far as scaling resistance goes.
There is another alloy from AK Steel, 18SR, that is a vast improvement on any of the above alloys. I don't know whether it can be cast or used as weld overlay, as mentioned in the previous post, is a matter that will require a call to AK Steel. It carries no Nickel so the cost shouldn't kill you if the material is applicable to your application.

http://www.aksteel.com/pdf/markets_products/stainless/ferritic/18_SR_Data_Sheet.pdf

 

[DKirkham]

Thanks guys for the quick response!

I really appreciate it.

 

[TVP]

ASM HANDBOOK Volume 14B Metalworking: Sheet Forming recommends a heat-resistant stainless grade called 22-4-9 for hot forming/SPF of titanium at high temperatures. Composition is 22Cr-4Ni-9Mn. The article on SPF and the article on Forming of Titanium contain quite a bit of useful information on the subject, including recommendations for lubricants (boron nitride-based).

http://www.asminternational.org/Tem...=Ecommerce/ProductDisplay.cfm&ProductID=12424

 

[metengr]

Also in this same volume, please note below!

Tool materials for the superplastic forming of titanium alloys are a special case (see the section "Superplastic Forming" in this article). They must be able to withstand the high temperatures (870 to 925 °C, or 1600 to 1700 °F) required for superplastic forming, but must not contain more than about 6% Ni, because of the possibility of nickel migration into the work metal at superplastic forming temperatures. Cast ceramics, 22-4-9 stainless steel (Fe-0.5C-22Cr-9Mn-4Ni), and 49M steel are used for this purpose.

 

[DKirkham]

Thanks for all the help. I am now on my way. This site is GREAT! Thank you to everyone who posted.