Summary for over-annealed stainless Discussion
Over-annealed stainless is the issue here: Marty King asked whether a 304 stainless lifting ring used for eight years in an annealing furnace could be repaired after weld cracks appeared and a chemical analysis reportedly showed 1.76 carbon content. S.V. Balasubramanian explained that carbon can gradually diffuse into 304 stainless during annealing when carbon dioxide is present in the atmosphere, making the steel brittle. He said that once carbon content rises beyond a certain point, the material cannot be reclaimed, and at 1.76 there is very little chance of recovery. His practical advice was that future annealing should be done in an inert atmosphere to prevent this kind of carbon pickup and embrittlement. The thread does not describe a repair method that would restore the part to safe service, only that the base metal is likely too far degraded.
Q. I have a lifting ring made out of 304 stainless steel. It is a devise used in an annealing furnace. It has been used in the annealing furnace for 8 years. Now some of the welds on this lifting devise are cracking and our customer wants it repaired. I ordered a chemical breakdown on the 304 stainless material. It came back as having 1.76 carbon content after all these years of having been repeatedly annealed. Is this repairable or has the annealing process taken its toll on the base metal.
Marty King
– Trinity, Alabama
2005
 | A. If your analysis is accurate, the stainless steel has been carburized from repeated elevated temperature exposure. The high carbon content is the cause of the cracking. At this carbon level, the ductility of the material will be about nil. Welding on this material would not be successful. It should be replaced, possibly with an alloy that is more resistant to carburization if you want longer service life. Good luck.
2005 A. King, The increase in carbon content of 304 stainless steel during annealing is due to the gradual diffusion of carbon which arises due to the presence of carbon dioxide in the atmosphere. Increase in carbon content makes 304 stainless steel brittle and beyond a point it cannot be reclaimbed. If the carbon content is 1.76, then there is very little chance that it can be reclaimed. To avoid such occurrence in future, it is recommended to use inert atmosphere during annealing. S.V. Balasubramanian |
