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Up Topic Welding Industry / Processes / Brazing Inconel 625 to 316 S.S.
- - By Justin Russell Date 09-03-2008 19:00
Hello All,

We are working on a project that requires brazing Inconel 625 (female piece) to 316 S.S. (male piece), we plan to use Nicrobraz LM in a vacuum furnace to join the two.  The different rates of thermal expansion are confusing me a little, can someone please verify my work.  With a fit diameter of 2.312", brazing at 2000F, I calculate the thermal expansion of Inconel 625 (CTF 9.0E-6) to be .041", while the expansion of 316 S.S (CTF 11.1E-6) is .051", thus the difference in thermal expansion to be .010".  The brazing compound requires .001" - .004" of clearance for good flow characteristics.  If the preceding is correct, should the 316 S.S. male diameter be 2.301/2.998", if the diameter of the Inconel 625 female piece is 2.312"?

Also, how does one hole these pieces concentric to one another during brazing?

Thank you all in advance.

Justin
Parent - - By DaveBoyer (*****) Date 09-04-2008 05:12
    If You size the parts to have .001" clearance at brazing temperature they will be concentric.

    The question I have is what happens when the parts start to cool down and the theoretical .001" gap starts trying to increase as the brazing alloy starts to solidify? Will it be plastic enough to accomadate the difference in  contraction ?
Parent - - By Justin Russell Date 09-04-2008 19:26
Thanks for the post.  I've figured stresses on the joint using Hooke's law, knowing the strain (~.010"), we back figured to find the stresses, which are very low.  From what I've read, the filler metal will take up some of the volume in question.  Will it be plastic enough?  According to Hooke, the stresses are okay.  Can you verify my pre-braze clearance calculations are correct.  Many thanks!
Parent - By DaveBoyer (*****) Date 09-05-2008 05:04
I dont have any figures for the materials You are using, I just remember 6.4 microinch/inch works for tool steel arround room temperature.
Parent - - By ravi theCobra (**) Date 09-04-2008 15:45
If  you  get  .001  clearance   you  can  stake  them  together  with  a   punch   or   try  3   TIG   weld  tacks
Parent - By DaveBoyer (*****) Date 09-05-2008 05:02
They will have a lot of clearance at room temperature, but if He did the math right at 2000f they should be a close fit.
Parent - By Justin Russell Date 09-05-2008 12:58
Thanks All!  We'll be running several test pieces over the next few weeks.  Please check back and I'll post the results.  Thanks again!

Justin
Up Topic Welding Industry / Processes / Brazing Inconel 625 to 316 S.S.

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