Cast 304?? 2

[arunmrao]

Congrats mcguire on starting this new forum.

I had an enquiry from a customer to make end flanges used in autombile exhaust system. This has a DIN number(Equivalent to AISI 304) which I do not remember now. This is for Europe market. Originally this is being made as a forging but now it is intended to convert it into a casting due to cost considerations. This is a small flange about 150 mm OD and ID 130 mm and 10-12 mmthick. The finished weight is 650 grams. Quantities are 15000 peces/month.

My question is will the inspector accept a cast product. As I see the service conditions are not too severe and CF8 casting should well serve the purpose.

Your comments please

 

[mcguire]

I can talk to some technical points, but I do not know the role of the inspector. If the customer specifies CF8,its specification would seem to me what he should be inspecting to.
The technical considerations for a hot-end exhaust flange are the susceptibility to corrosion, oxidation, and mechanical failure. The principal difference is that the cast CF8 will have a more inhomogeneous microstructure. The will be significant delta ferrite which will hasten the formation of sigma at high temperatures, possibly at operating temperature. The result would then be low ductility at ambient temperatures.
It requires a thorough high temperature solution anneal and quench to dissolve and keep carbon in solution, so you won't have sensitization. Even with that you will retain about 10% delta ferrite and non-equilibrium inclusions. The casting behaves like a TIG weld in that it has lower pitting corrosion resistance. The amount equals about 10C on the critical pitting temperature,depending on sulfur level.
These considerations probably don't diminish its functionality as a hot-end flange since high temperature strength and oxidation resistance should approximate those of 304.
Thanks for coming to the forum. I have appreciated your many valuable responses in the other materials forums.

 

[jsummerfield]

I do not know about the European designations, However, the UNS number for SA-182 is S30400 for type 304 SSt and for SA-479 the UNS is S30403 for type 304L SSt.


John

 

[EdStainless]

There are some exhaust flanges in service that are SS PM parts, so castings don't seem out of place at all.

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Corrosion never sleeps, but it can be managed.

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

 

[arunmrao]

Edstainless
I had suggested P/M route for this application. Though this is not my area of work.

 

[mcguire]

PM is a great suggestion:no machining,good high-temperature properties,probably high volume to amortize tooling costs. Gets my vote.