Brazing Stainless at less than 1550F 1

[EdStainless]

I need to braze two stainless alloys together. Since one of them is a 400 series I really don't want to go over 1550F or it will go martensitic on me. But I need to have a material that will be able to take at least 1200F in service.
My first choice was a MetGlas Ni-Cr, but its temps are too high.
This will be a furnace braze with large contact areas. I have fixturing worked out. And, of course it must be flux free.
How about some suggestions of what has worked for you.
tks ed

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Corrosion never sleeps, but it can be managed.

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[metman]

Ed,
1) I don't understand what you mean by avoiding Martensite by keeping under 1500F unless for some reason you reqiuire a relatively rapid cool from the braze temp to room temperature. Suggest you rapid cool to below the solidus temperature of the braze alloy then slow cool from there to room temperature to avoid transformation to Martensite.
2) Why must it be flux free? If you are forced into the 1200-1500F temp range probably you will need to use one of the Ag-Cu based braze alloys which don't wet S.S. nicely so that flux is usually reqiured even in H2 atmospohere. Oh it just dawned on me that you are probably brazing in Vacuum furnace. Can you switch to H2 furnace? I don't think the S.S. will wet nicely in Vac either.

Jesus is THE life,
Leonard

 

[EdStainless]

The temp limit arrises because of hte carbon content of the alloy and its thermal history. It is a ferritic alloy as produced. If it gets re-heated to high it will form martinsite that I can't get rid of.

I was planning on doing this in H, but there will be no air present in the gap. The two items will be formed together with zero clearance. the surfaces will all be pickled bright white prior to braze, so they will be very clean.

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

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

 

[unclesyd]

Here is a site for NicroBraze that worked with us on SS project that required special temperature consideration. I don’t have the specifics but the project was completed. We did weld 430 SS to 304L with 309 Wire. We also use a lot of 430 Ti where we were doing this type welding. All these components were 430 SS annealed.
I appreciate you concerns with the 430 after heating in the 1550°F range as we had 3 drip coolers in 3 HNO3 units that were weld on after the fabrication anneal. Needless to say we lost all three within 72 hours of startup.

This is the experimental alloy site.

http://www.wallcolmonoy.com/Products/EXP_matls/index.htm

Someone else to look at.

http://www.morganadvancedceramics.com/wesgometals/temp.htm

There are some self fluxing alloys out there. I think Eutectic makes one.

 

[mcguire]

Take a look at materialsresources.com. They have some interesting low temperature, fluxless brazing alloys.

 

[metengr]

EdStainless;
In reading your post, the statement regarding the service temperature requirement of 1200 deg F would be unacceptable for most braze filler metals tht would melt atot below 1500 deg F, unless you go to the Ni-Cr or some hybrid, which would have a melting temperature well above 1500 deg F to be able to sustain a 1200 deg F service temperature.

The problem I see is having a braze filler metal that melts at or below 1550 deg F while maintaining bond strength at 1200 deg F. I would expect that any braze filler metal that melts at 1550 deg F will soften considerably upon exposure to 1200 deg F service temperature, resulting in failure of the braze joint from creep.

Is the 1200 deg F service temperature continuous exposure?

 

[EdStainless]

syd, mcg, thanks for the comments and links.

metengr, I am trying to define the temperatures better. You hit the nail on the head.

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

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

 

[metman]

Ed, Maybe AG-Cu eutectic which melts at 1432F and being eutectic the solidus and liquidis are the same so there is no degradation (insipient melting) at 1200F. Of course you will still ahve softening at service temp as metengr comments.

Jesus is THE life,
Leonard

 

[unclesyd]

I have to concur with metman that a eutectic brazing allo is the way to go even if they can be troublesome at times.
Here is the Castolin-Eutectic site. Again you need to get past the front desk.

http://www.eutectic-na.com

I found some old notes on our standards for the use of 430 SS that limited it to 600°F except for short excursions to 900°F. I have no explanation as to why this limitation, as yet.