dissimilar metal welding

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I am looking to find if there are any issues with orbital welding 17-4 and 316 stainless or incojim
Reply:They are both SS, they both require heat treating. About the only difference I can think of off hand is in the heat treating process. I know the chemistry of the two are different, but what that is exactly, I don't know. (I could find out.)  As for the heat treating; the 316 usually requires a vacuum solution anneal, where-as the 17-4 requires a vacuum homogenize solution anneal. As for the physical differences, the 17-4 is softer than the 316. What would this welding application be for? "SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:Well I'm not going to bother looking up the details on this, you can look this up yourself, but I have to correct papabear on a couple points.I can tell you for sure that 316 is an austenitic stainless steel, slightly more highly alloyed than 304, for more severe corrosion environments than 304.  316 is not generally heat treated, except maybe in rare applications a solution anneal to re-solutionize carbide precipitation after welding, but it is not a heat treatable alloy for improved strength.And 17-4, commonly known as 17-4 PH, is heat treatable to improve strength through a precipitation hardening aging process.Inco or more properly inconel comes in many varieties 600, 625, 719, etc., and you need to know what alloy you have if your application is critical in any way.So these alloys have different properties, and the weak link will be the 316 or the weld joint.Generally what you look for in nickel alloy dissimilar joints is a Delong, Schaffler, or the latest WRC diagram to see what type of structure the combination of alloys in the weld pool will create upon solidification.  Will it be fully austenitic and prone to centerline cracking, or will it tend to have some ferrite, like 10% to help prevent hot cracking, or will it be martensitic and prone to brittle fracture?If you don't care to be scientific and the application is critical, use 309 SS filler, don't over dilute the puddle with the base materials, and you'll be fine.
Reply:pulser, you are obviously more educated in metallurgy than I am. I am a mere servant in a foundry, where we make precision castings. I do know that some of the thinner 316 castings that we produce require  v_sa. That said, cenmac11, I would follow the advise of  a more educated & experienced individual like pulser.
Reply:Good information. We are making a tubular weldment. The material required was 17-4 tubes welded to a 17-4 manifold. It turns out that 17-4 is not readily available in tubing. We started wire edm the tube sections, and planned on welding them together to make the long section. They are worried about the multiple weld joints. I offered the choice of using an alloy that was compatable with the 17-4 but available in tube form. I hope that i did not shoot myself in the foot. any more info would be greatly appreciated.thanksjim
Reply:i wanted to say that this thread typifies one extreme encountered (by me) on this excellent forum. here is a rational exchange of high tech info between men of good will who seek to learn and  help each other. and also on this same forum, some of us are trying to keep a newb from killing himself  with a torch  as he blunders blindly turning knobs...hooray for weldingweb..