Cheaper Inconel 625 alternative steel with specific properties 2

[ballvalve1337]

Good day,

I wonder if there is a good, cheaper alternative to my reference steel/material "Inconel 625":

Requirements:

- same or better yield strenght
- comparabel or better corrosion resistance (no carbon steel)
- temperature resistant to min. 500°C/930°F. Better 600°C/1110°F
- comparable thermal expansion coefficiant (no austenitic stainless)
- no martensitic material
- Available as forged rod/bar up to Ø700mm
- Most important: At least 20-30% cheaper!


Thanks!

 

[EdStainless]

Nope, it does not exist.
That is why 625 is still in use >70 years after it was developed.
Some of your restrictions don't make sense.
I presume that you mean 'strength at temperature and similar creep resistance'
What environment do you want it to operate in?
No austenitic SS? Why when the CTE is within 10%

Decide what you want to give up, corrosion resistance, strength, or max temp.
The only other choice is to pay the price.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I wanted to suggest A286 as a lower cost high temp high strength corrosion material but you nixed it the no austinitic requirements. It does have a high CoTE.

The next suggestion would be Custom 450 but you nixed it with the no martensitic requirement. Carpenter does say their alloy is weldable. Would that make it acceptable despite being martensitic? It does have very low CoTE.

 

[ballvalve1337]

Thank you both.
I knew there propably is no real alernative to these requirements. I thought maybe i missed something...

No austenitic SS because of the high CTE only, yes. Is not working within the low alloy/carbon steel parts surrounding the internal parts.
I will check Custom 450. Thanks for that!

 

[EdStainless]

Do you just need oxidation resistance or is there more corrosion involved?
If just oxidation then why not consider alloys like these:

https://www.specialmetals.com/documents/technical-bulletins/incoloy/incoloy-alloy-825.pdf

You could use it in the cold finished condition up to 1000F.

https://www.specialmetals.com/documents/technical-bulletins/incoloy/incoloy-alloy-925.pdf

Very good strength.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MagBen]

recommend 901 alloy:

https://www.carpentertechnology.com/blog/selection-of-age-hardenable-superalloys

lower (Ni 42 vs 60%), lower Mo (5 vs 9%) could knock down price by 20-30%
lower Cr leads to lower CTE, however lower Mo boosts CTE. It may have a comparable CTE.

"no austenitic" is kinda misleading. maybe better say least fcc, most bcc. fcc normally owns a higher CTE than bcc due to its higher packing factor.

some basis:
cheaper limits to Fe-Ni based superalloy, or even Fe-based
low CTE asks for low Cr, high Mo/W/Ti. here is a formula:
CTE = 13.8732 + 7.2764x10[sup]-2[/sup] [Cr] + 3.751x10[sup]-2[/sup]([Ta]+1.95[Nb]) + 1.9774x10[sup]-2[/sup][Co] + 1.835x10-2 [Al] – 7.9532x10-2 [W] – 8.2385 x10[sup]-2[/sup] [Mo] – 1.63381 x 10[sup]-1[/sup] [Ti]

For a super low CTE superalloy, look at alloy 909 alloy, less Ni, Cr, but high Co could increase material cost