316l to 17-4ph welding issues

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Currently TIG welding (no filler rod) 316l ss tube to 17-4 ph bar. The weld is a flush type. Speed and amps are: 30 inches per minute and 40 amps. 2 out of 4 units are helium leak tight to 1 x 10-9 std cc/sec He. We have recut the surfaces for rewelding with no luck. Any suggestions?
Reply:Have you inspected both 'good' and 'bad' welds for tiny, tight cracking?Pics would help, of course.Blackbird
Reply:attached are photos of the good welds as well as a new prep design for the leaking units. We have made heat sinks on either side in hopes of reducing the cracking. I have heard that heating the material to 300-500 degrees F helps prevent the cracking. What are your feelings Attached Images
Reply:Is there a reason for no filler? If you'd bevel the edges a bit, you could add a little filler and maintain the flat top on the bead. From looking at the chemical composition 308 seems like a medium between the two. This is pure conjecture though, I have no experience welding these two types together.Ian TannerKawasaki KX450 and many other fine tools
Reply:I am wondering if the relatively low heat input, combined with the large heat-sinking effect of the joint is causing excess martensite to form in the HAZ.  I would try using a high Ni filler to stabilize the austenite and add some ductility to the weld.Have we all gone mad?