I am Tig welding heating elements made of Incoloy 840 stainless steel that are about 18 or 20 gauge thick to a mild steel, blank flange that is about 1 inch thick, with 309 stainless rods, using argon shielding. Holes are drilled in the flange and the heating elements are stuck through the holes and welded. The welds are cracking. Longitudinal cracks, some originating at the crater and some not. I have already tried to prevent it by tapering off to the side when terminating my weld. The elements did have a thin coating of something on them. I did not notice any signs of poor shielding when the welds were made. I will remove the coating next time, but for now I need to be able to weld over the previous welds and not have them leak. Any Ideas why they might be cracking? Can I weld over them without them cracking again?
It sounds like you have a classic stainless steel hot cracking problem. It is well known that a little ferrite in an austentic stainless steel weld ( the 300 series stainless steel family) is needed to prevent hot cracking. Incoloy 840 has 20% Nickel, which makes it fully austenitic, no ferrite. 309 typically has about 10 - 15% ferrite in it, which makes it good for dissimilar welding since it can tolerate mixing with the melted base metal (dilution). If you mix about 20% or more of the Incoloy into the 309 weld, it will no longer contain the needed ferrite and it will be prone to hot cracking.
The solutions:
1) Use a nickel based filler metal like Inconel 82 or Inconel 625
much less preferred but possible:
2) Minimize the amount of Incoloy melted into the weld and add a lot of filler metal to reduce the amount of Incoloy in the weld deposit. The results of this will vary since it is a manual process.
Your note on the coating is important as well. Any contamination of the weld will increase the cracking problem. The base metals must be as clean as possible, this is always good welding practice.
Let us know how you make out.
Regards.
By -
Date 10-05-2000 09:18
Thanks for the advice about the Incoloy 840 SS. I did not get a chance to weld the material with the rods you suggested. The company owner had me to re-weld the joints with the same rod I used the first time and I could not keep them from cracking. He paid me and then had someone else weld them again. I didn't ask how it turned out.
By -
Date 09-15-2000 03:01
I have already talked to "Special Metals" a company that I found on the web at www.specialmetals.com. They make and sell Inconel and Incoloy products. You are right on the money pdweldor. I talked to their welding division in North Carolina and they told me the samething. They also said not to allow the weld to become flat or concave, as that would make it prone to cracking also. I haven't done the welding yet. I'll let you know how it goes. Thanks, Louis
I have no experiece with your situation.
I would like to recommend followings if you do not want to use inconel welding consumables;
1) Thin plate with TIG welding means relatively high dilution.
Please decrease the welding current and heat input as possible.
2) Considering Schaffler diagram you should have 100% austenite in your weld metal and centerline hot cracking.
You may try ferritic type, such as 430, rod.
It will give you weld metal with ferrite and martensite(because you weld thin plate I do not worry about high hardness due to martensite)
