Laser Welding MP35N to 304L 1

[Bisquik]

Greetings.
I work for a medical device company and need advice on methods for laser welding 0.003" wall hypotube MP35N to SS304(L) lap joint.

We require a hermetic seal for high pressure CO2 gas. The MP35N was selected for its high tensile strength and low magnetic permeability but do not require the great corrosion properties. We currently laser weld 17-7PH (290ksi) to the 304L without issue but the higher magnetic permeability of the drawn tubing is causing us issues.

I've read through a few MP35N threads and the only suggestion other than selecting a different material is to use stress relax post weld to increase the strength of the HAZ. Any suggestions would be appreciated for our weld study. We may be open to changing the 304L to a different machine able alloy like MP35N but the additional costs of the part may be prohibitive.

Thanks

 

[metengr]

The MP35N alloy can be welded using a sequence where the material is cold worked, welded and aged between 1000 to 1100 deg F for four hours. However, this sequence can result in unwanted exposure of the 304L to the sensitizatoin temperature range. I would try the above sequence and evaluate the extent of sensitization to 304L material. The other option is to weld the MP35N in the annealed condition, cold work followed by aging and see if this option works.