welding 304 to 17-4

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we have an assembly with 17-4  16ga sheet in the critical components but have some 304 stainless in the less stresses areas.  we will be heat treating this assembly.there was some discussion about 17-4 to 316 stainless.can we safely weld the 304 to 17-4 and what rod should be used?  is 316 a better choice?corrosion is not a high concern.  but we do not want the welds at the transitions to fail.is 309  a good choice?any help here would be greatly appreciated.thanks
Reply:If you're ever in doubt about which electrode to use on SS, use 309L.  It will join almost any pair of alloys as well as stainless to non-stainless.
Reply:Evaro sez:    "We will be heat treating this assembly"....suggest you consider the effect of heat treating (solution??? age?? or what??)on all the alloys involved.Blackbird
Reply:What temperature will you be doing the pwht?
Reply:17-4 is a precipitation hardening, martensitic grade of stainless steel, with very high strength after heat treatment.  304 is an austenitic stainless steel.  Chemistry for typical 17-4PH is:Carbon  0.07 maxChromium  15 - 17.5Copper  3 - 5Iron BalanceManganese  1 maxNickel  3 - 5Niobium  0.15 - 0.45Niobium+Tantalum  0.15 - 0.45Phosphorus  0.04 maxSilicon  1 maxSulphur  0.03 max"Welding - Successfully welded by common fusion and resistance methods, this alloy should not be joined by oxyacetylene welding. AWS E/ER630 filler metal is recommended if required." (ref:http://www.metalsuppliersonline.com/...etals/1752.asp)"Alloy 17-4 PH can be welded with homogeneous filler metals such as E 630 (AWS A5.4) electrodes and ER 630 (AWS A5.9) wires.  Austenitic filler material can be used when the mechanical properties of 17-4 PH steel are not required in the weld and, in this case, no post-weld heat treatment must be applied."(ref:  www.sandmeyersteel.com/17-4PH.html)Chemistry for 304 is:Carbon  0.08 max  Chromium  18 - 20  Iron  Balance  Manganese  2 max  Nickel  8 - 10.5  Phosphorus  0.045 max  Silicon  1 max  Sulphur  0.03 max  "Welding - All fusion and resistance processes have been successfully employed in welding 304. AWS E/ER308 or 312 filler metal is recommended. For cleaner, stronger welds, may users choose 304L which has a controlled low carbon content designed to reduce carbide precipitation at the weld boundaries."(ref:http://www.suppliersonline.com/propertypages/304.asp)Based on this quick internet search, it seems to me that you might be better off using a filler that matches the chemistry of the 17-4PH.  However, the high Copper content and Niobium content of 17-4 might produce some undesireable microstructures and hot cracking issues and/or brittleness problems when diluted with the 304 stainless base metal.  I'm not sure about this, but I think it bears looking into.If you haven't done this ever before, I suggest you make some test welds and subject them to mechanical and corrosion testing before you commit to a particular filler and WPS.  The only other advice I have is that you keep the heat on the 17-4 PH side of the joints as much as possible to limit the dilution that occurs during welding.  (Assuming you're TIG welding here).  Since it sounds like your heat treating these after welding, you're going to heal any changes made in the larger HAZ on the 17-4 side of the joint.The austentic base metal should be unaffected by the heat treatment, but I would also watch for embrittlement on the 304 side HAZ.  The resulting chemistry from dilution may produce some very brittle martensitic structures; particularly when you quench back down to room temperature.This is all guesswork on my part, but hopefully it'll help give you some things to monitor during your initial trials of this process. Originally Posted by evarowe have an assembly with 17-4  16ga sheet in the critical components but have some 304 stainless in the less stresses areas.  we will be heat treating this assembly.there was some discussion about 17-4 to 316 stainless.can we safely weld the 304 to 17-4 and what rod should be used?  is 316 a better choice?corrosion is not a high concern.  but we do not want the welds at the transitions to fail.is 309  a good choice?any help here would be greatly appreciated.thanks
Reply:You may find this link extremely helpful. Not only now, but for future as well. Elia is a man with a LOT of knowledge. He has helped me out a few times. Just click on the "contact us" button & ask your question. He has always gotten back to me with an answer within 24 hrs. http://www.welding-advisers.com/index.html"SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:Originally Posted by evarowe have an assembly with 17-4  16ga sheet in the critical components but have some 304 stainless in the less stresses areas.  we will be heat treating this assembly.there was some discussion about 17-4 to 316 stainless.can we safely weld the 304 to 17-4 and what rod should be used?  is 316 a better choice?corrosion is not a high concern.  but we do not want the welds at the transitions to fail.is 309  a good choice?any help here would be greatly appreciated.thanks
Reply:I believe 312 may be the alloy of choice here, i could not find this online so I will quote off the rod tube... "ER312 is a unique ss alloy which has a mixed Ferritic and Austenitic structure. As a result, it produces the highest tensile and yield strengths on any ss filler metal. It is used to weld many dissimilar , abrasion resistant, and high yield steels, and to join high temp alloys to carbon or low alloy steels, and as abutter layer for hardfacing."
Reply:If in doubt you can always call harris welco or another wire manufacturer and tell them the application and they can recommend a good product for you. Thats what they do after all. They won`t sell more wire if you get bad results from their advice!
Reply:Filler of choice for 17-4PH would be E630 (stick, this filler is a 'match' for 17-4) or ER308 or ER309 for the most part.As the usual filler of choice for 304 is ER308, ER309 is also applicable, I think ER308 or ER309 -should- be compatible between the two alloys (17-4 and 304).304 is not a heat treatable grade of stainless steel, as far as hardening it goes.  If you take the 'big' picture, then -any- steel is heat treatable if you want to include annealing or stress-relieving in your definition of "heat treatment".17-4 heat treatment (for hardening) is mostly relying on the precipitation hardening effect as the amount of carbon in the alloy is too low to get much carbide/martensite from a quench.If corrosion "is not a concern", then why are you using stainless steel and two different stainless alloys at that?And what are you trying to accomplish with the heat treatment?Although 17-4 and 304 are 'close' in physical properties, they still are different alloys.  So you then have thermal expansion differentials, thermal conductivity differentials, magnetic property differentials, etc, etc.What are you trying to do with the two different alloys that is making you use two different alloys in the first place?(sometimes the right question is not the one about how to join two different stainless alloys but why are you using two different stainless alloys in the first place.    )  The best laid schemes ... Gang oft agley ...