I think grain growth is the concern. During solution treatment, the grains can potentially grow, depending upon the particular alloy and it's grain-pinning dispersion. If hot-working is going on, solution treatment is not as much of a concern because the recrystallization during forging is...
There is a developmental stainless steel that can achieve >210 ksi yield strength with > 10% elongation and high toughness that was recently discussed at AeroMat2011 - a copy of the presentation is available on QuesTek's website...
Frederick,
My point was that if you have a developed process for a part and material, then it makes sense to use it whether you understand the hows and whys of its mechanism. But not understanding how it works can limit how fast you can apply it to new applications/materials. For example...
It sounds like the problem you have is with the pins, where you need structural steel to the extent that they act as 'axles' but you also need surface wear resistance, like a bearing race or gear flank.
Cryogenic 'tempering' has been studied in a variety of applications, and as far as I can...
I would recommend Ferrium S53. It is a 10Cr steel, so it's in-line with the corrosion resistance you're looking for - much better than non-stainless alloys but not a 316 stainless type. It has 53-55 Rc hardness, through hardened with ~70 ksi-sqrt(in) fracture toughness typical (50 is the design...
Aermet100 requires a double-step temper, with cryo treatment in between. It's properties can be sensitive to the time/temperature, especially of the first step. You might consider Ferrium M54 as an alternative with equivalent strength/toughness but reduced cobalt content to lower raw material...
Considering that you require 400C operating temperature, you probably want an alloy that is tempered above this temperature. If you want the best combination of strength and toughness you might consider an alloy like Ferrium M54:
http://www.questek.com/ferrium-m54.html
Jim
The elongation seems low - you may try reducing the strength through a higher tempering temperature.
The intergranular nature of the crack might imply stress corrosion cracking might be an issue.
Jim
Secondary hardening alloys tempered at ~900F to precipitate M2C strengthening carbides generally have much higher SCC resistance than steels tempered at lower temperature (~500F). These alloys have higher alloy content, so you pay for higher performance. One of the lower alloy content, yet...
Glenn,
You may want to consider Ferrium C64, which is a new, high-performance gear steel alloy. I presented a technical paper about the alloy (and the similar C61 alloy) at AGMA 2009 Fall Technical Meeting...