Difficulty in stellite-12 welding by bare cast rods

Date 03-21-2007 16:34

I am finding difficulty in repairing porosities in stellite-12 overlayed jobs. Normally, I am using GTAW process. Though there were no cracks (only porosities) during the initial process, they appear only when I start repairing for porosities. For repair, I am preheating the job to 100 degree C and after welding allowing the job to cool slowly (dry powder lime). Please suggest the solution for this.

By PhilThomas (**)

Date 03-21-2007 18:52

100 deg C preheat is probably not enough to do repairs with St. 12. It has a high hardness and is very prone to cracking. You may need at least twice that amount of heat, ensuring a thourough preheat of the part.

Slow cooling is also a must. I'm not sure what you are using to contian the powder, but you might want to consider using a furnace and slow cooling it with the controller.

By jon20013 (*****)

Date 03-21-2007 19:07

We use Stellite 6 and an industrial oven to preheat and control cooling. I normally preheat to around 500F and then hold at 450F for about 1 hour/inch as a hydrogen bake out. Have had moderate to good success with S6 overlays on stainless and moderate success on carbons, also usinig the GTAW process. Make sure you are using clean, dry gas and also a gas lense with the GTAW.

By gyadon

Date 03-22-2007 12:53

It has been a long time since I have worked with Stellite (mid to late 70's). We used it to over lay valve body throats and valve seats. I do not remember any numbers but you must use a high preheat and soak time. Then cool slow and evenly or you will back in the repair stage (cracks). Good Luck I have not wished to think about that process in years.
Gary

By js55

Date 03-22-2007 13:24

The Stellites (6 and 12 specifically, utilize Co, W, and Cr carbides as hardening agents) used predominantly as hardfacing fillers are naturally prone to cracking. The resulting hardnesses achieved (specified mins of 42/48 HRC respectively) would indicate such. In many applications such 'cross checking' is not undesirable. However, porosity may be. Jon is correct, to even come close to eliminate weld related problems high preheats are necessary. It sounds as though your preheats are far too low. I do not know it this will influence the formation of porosity.
Deloro Stellite has a help contact on their website. I would suggest dropping them an email, and would be interested to read what their response is.