welding altered SS 304

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Hello,We have taken some SS 304 past its melting point (almost double) causing failure and a hole. There is indication of coking. We would like to patch the hole but conventional rods are no longer adhering. Anyone know if there is a rod that may be tried so that we do not have to rebuild the part? Thank you for your help. Stacy
Reply:I hear Hastelloy-W is the wonder rod.  Might help others in providing suggestions if you mention what application this would be pertaining to.  What welding process will you be doing?  Stick?  MIG? TIG? 1st on WeldingWeb to have a scrolling sig! HTP Invertig 400HTP Invertig 221HTP ProPulse 300HTP ProPulse 200 x2HTP ProPulse 220MTSHTP Inverarc 200TLP HTP Microcut 875SC
Reply:Usually cutting and grinding cleans things up enough to get back to welding, but you'll have to remove the cooked SS first though. Sounds like you're running SMAW, try GTAW.SqWave 200Millermatic 190Airco 200 ACHypertherm PM45Boice-Crane Band SawVictor O/A
Reply:We will be using the TIG welding process. Thanks!
Reply:We have cut and cleaned the area to be welded and then placed a large piece of steel over it. We did use GTAW to weld the new piece onto the reactor. This is our typical process in this scenario but this time the new SS did not successfully join onto the existing SS304. We are confused about what the chemical transformation of the SS could have been for us to have this problem. We will try the Hastelloy-W but any other suggestions would be appreciated. Or any ideas as to what happened to the steel...high pressure, high temperature under an oxidizing atmosphere where there is also evidence of coking. Thanks again!!
Reply:I would perform a replica to check the micro structure before doing any repairs.How do you know if the steel is not irreversibly damage in such a critical application?
Reply:We don't. I was wondering if there were any suggestions as to how the microstructure could have changed and what may work to weld to it. We have safety barriers in place so repairing and running again would be easier for us than dismantling everything and rebuilding. Thanks for all input!
Reply:The are a lot of things that can happen. The first that comes to mind is sensitization but normally it would not be so extreme as to not be able to weld it.If you have someone make a replica it will give you information on the microstructure and go from there.A replica is a way to take a "photo" (not actually a photo) of the metal's microstructure which you can then study under the microscope. We use it a lot to assess the remaining life in power plants and wherever there is creep in general.