Intergranular SCC of Inconel 600

By - Date 09-03-2000 00:04

Kok Ming,
It's been my experience time and again when trouble-shooting SCC in nickle-base materials there are three common denominators that seem to always come to the surface of the sensitization formula.
1. The weld interpass temperature of the WPS was not adhered to.
It should never be allowed higher then 300 degrees F during the weld application with a rapid cooling rate being desired. Beware, many times in reviewing nickle-base WPS's for approval, I've found the noted interpass temperature is well above 300 (usually 500) and the fact is missed by many reviewers. The interpass temperature is as critical to the success fo the weld as the proper filler material when welding nickle-based materials and if the noted interpass temperature is too high in the WPS, you are in trouble before you start.

2. Welders using too slow of a travel speed with a weave bead (carrying a large puddle) which promotes carbide precipitation while holding the interpass temperature too high for too long. A travel speed (regardless of the technique) that is just slow enough to facilitate complete fusion is what I've experienced will go a long way in helping minimize sensitization.

3. If the weldment contains base material that has been in service prior to welding- Insufficent cleaning is the third common denominator. Many think that all that is necessary for adequate cleaning is to grind, flapper wheel, or wire brush the surfaces or maybe use a chlorinated solvent. If the material has been in service none of the methods used alone is correct. The use of a chlorinated solvent should never be used-acetone is much better then grind. Again, if the materials have been in service, most people forget to clean the backside of the joint as well as they cleaned the side they are about to weld on.

To put the first two conditons in perspective and give insight to why they can happen. Welders know that regardless of the process, the hotter (to a point) the nickle-base material is, the better it welds for them! The puddle flattens and wets out nicely, they get better starts & stops, and the finished weld is cosmeticly appealing. But In short, what's good for the welder is not good for nickle-base material!

Hope I've been able to help.

By - Date 09-03-2000 03:37

Seldom :
Thanks for your commets.
1) Even I managed to control my interpass temperature to be below 300F as mentioned by you. How confidence it will be that I will not sensitised the Inconel 600 materials.

2) What type of filler rod is best suitable for this ? How about ErNiCrFe-3 filler wire ?

3) I agreed with you that most of us will be more prone to achieve nice comestic weld and neglect the changes on the properties of the alloy. It is kind of difficult to put the message across to the welder and instruct him to achieve the optimum travel speed that will minimise the sensitisation.

Thanks for your note.

regards
Km Chow

By - Date 09-03-2000 13:04

Km Chow,
To answer your first question of confidence- If interpass is strictly controlled and the overall temperature of the weldment kept cool so that there is not a lingering as it's coming back down through the transformation range and all other varibles controlled as best you can, you have a pretty good chance of not (or severely minimize) sensitizing the HAZ.

Concerning the filler material- It really depends on the service requirements so I have always checked with my metalurgist. In the chemical plant I came from, ErNiCrFe-3 (Inco 182) and ErNiCr-3 (Inco-82) were pretty standard filler materials for the majority of the Inconel 600 service requirements.

By Neal

Date 09-05-2000 01:01

You might want to consider Inco 52. The higher chrome can be helpful. Electric Power Research Institute has done some work on this. Sam Kiser of Inco Alloys (Speciality Metals) may be of some help.