Brazing SA-249 Stainless 3

[BrentB96]

Our company brazes SA-249 stainless tubes to SA-36 structural tubing (actually A500 GrB that is qualified to SA-36 via Heat treat). We're having trouble with our latest batch of SA-249 brazing properly. The SA-36 is laser cut and the holes are dead on accurate. Tube geometry is quite good as well, so no tolerance issues.

I received MTR's on the tubes and cannot tell much difference in chemical makeup from last batch. Furnace recipe is exactly the same. Here is the chemical analysis of the last good batch:

C:0.018 Mn:1.67 P:0.032 S:0.00 Si:0.39 Cr:18.2 Ni:9.2 Mo:0.50 Cu:0.40 N:0.04 Fe:Bal. Rockwell B-71

Here's the latest that is not brazing correctly:

C:0.018 Mn:1.62 P:0.033 S:0.00 Si:0.32 Cr:18.3 Ni:9.1 Mo:0.40 Cu:0.39 N:0.04 Fe:Bal. Rockwell B-72

I would appreciate any comments/advice any of you may offer to remedy our current issue.

Thanks!

Brent

 

[metengr]

BrentB96;

We're having trouble with our latest batch of SA-249 brazing properly.

What's the actual problem?

Porosity, lack of bond, cracks???

 

[BrentB96]

No bond of the brazing compound seen. We can see the compound all over both materials, but not at the junction where the capillary flow is supposed to occur. We're bridging a .005-.007" gap.

We have SA-214 tubes that did fine in the same braze. I realize the SA-249 to SA-36 is a P2 to P1, but we've qualified our braze process for both and usually do not encounter this result. That is why we're questioning the material. I'll obtain MTR on the SA-36 as well and post.

Thanks,

Brent

 

[BrentB96]

SA-36 Material:
C:0.200 Mn:0.780 P:0.012 S:0.008 Si:0.014 Al:0.043 Cu:0.040 Cb:0.001 Mo:0.001 Ni:0.010 Cr:0.040 V:0.001

Yield: 37,100 psi
Tensile: 62,800
%Elong: 36.00

Hope this helps.

Thanks,

Brent

 

[metengr]

BrentB96;
There is some confusing information here. First off, SA 214 is a specification for ERW carbon steel tubes. SA 249 is a material specification for austenitic stainless steel tubing.

What is the flux and braze material you selected to join the austenitic stainless steel tube to the carbon steel structural tubing?

 

[BrentB96]

We braze 10,000 lbs of coolers in one braze cycle. Some of them have steel some of them have stainless tubes. The SA-214 to SA-36 is a P1 to P1 braze and the SA-249 to SA-36 is a P2 to P1 braze but they both have the same brazing procedure specification, and both were qualified.

Just letting you know that the SA-214 to SA-36 brazed fine. But the SA-249 to SA-36 did not. And normally they both come out with good brazes in the same cycle. We're using AMS 4777.


Thanks,

Brent

 

[metengr]

BrentB96;
I don't see anything wrong with the ASME SA 249 material, other than you report 0% for sulfur, which is probably typo.

From my background with ASME B&PV Code, the austenitic stainless steel is a P-No 8 material, not a P-No 2 material (unless you have your own methods of typing base materials).

I still believe you have either missed a fluxing operation with the stainless steel or had a cleanliness problem with the joint. Austenitic stainless steels have excellent brazing capability provided the correct flux and braze metal are used.

 

[BrentB96]

Thank you for your reply and comments.

One thing I forgot to add...

We always heat treat (anneal) the coils of stainless when they come in because their rockwell is too great for our processing...

We ramp up to 1910F, hold 45 minutes, then N quench rapidly down to 100F as soon as possible. Then the product is processed & prepped for the braze cycle and placed back in the furnace. We've never encountered a precipitate formation of Chromium carbides problem either, but could this have something to do with it?

Still considering all ideas/comments!

Thanks,

Brent

 

[EdStainless]

Surface condition. What flux are you using? Do you pickle?

My guess is that you have a slight amount of oxidation on the stainless that is preventing wetting and flow.

The A249 should be annealed. You should be able to restrict the upper end of the properties, unless it is your process that is causing the working.
Have you played with your anneal cycle? You don't need the time, just getting it to temp should work.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[deanc]

http://www.brazingandsoldering.org/PDF/semext.pdf

Check this document. It concerns Al,however what is valuable is the process analysis.

P. Roberts is one of the best....his book is well worth the price.

http://www.brazingandsoldering.org/index.html

 

[BrentB96]

The SA-36 comes in with slight mill scale, but after laser machining, it is then run through a (small grit) shot blast. The SA-249 gets an oil treatment (different than SA-214 tubes) in processing, but is supposedly washed off and cleaned (now suspecting something here...)

I've just discovered the oil used for SA-249 processing has parrifins in it and isn't water soluble. We may run some test product through (ultra cleaned) and see if we can get consistency. Will let you know what we discover.

Thanks everyone!

Brent