By -
Date 04-14-2005 03:58
peterbil,
Thank you for your kind words. I will never comment on anything in this forum unless I know it to be accurate and true, but also to be able to back up my comments by documented data.
First of all, there is no big deal when welding a pure austenitic material. It requires no formal preheat or post weld heat heat treatment. The austenitic phase of this material allows greater time at temperature without forming the sigma phase, which is the embrittlement of stainless steels. This material is susceptable to hot cracking during welding unless careful monitoring is observed. By this I mean careful control of the interpass temperature (300F or 150C), and allowing the weld to cool down rather slowly. A high nickel alloy will withstand a higher heat input than your 308, 309, etc., but it also takes longer to cool down, so the cooling rate should be somewhat slower. As stated earlier, a pure austenic material will perform at higher heat temperatures due to its austenitic structure, which will counteract the sigma phase for a longer period of time. All 3 of the alloys I mentioned have a carbon content of 0.10% max., so that is an advantage with high temperature service. Even better is the 50Cr-50Ni-Cb, in which the columbium with tie up the carbon and give better resistance to the high heat while resisting any detrimental intermetallic phases. Usually, the filler metal of choice is a 625 filler matrial. Again, this is a pure astenitic material containing approximately 60-63% nickel and around 20-25% chromium and 6% moly. Of course, the most important thing when welding any stainless steel is the ability to start out CLEAN. If you will just use everyday good welding practices you should have no problems. 50%Cr-50%Ni is a very commonly used material, so do not be afraid of welding it. It's strength and weldability is like any other pure austenitic material. I think you will do just fine welding it. Go for it !!
Chuck