cddolan74,
quite well fitting in to the discussion from its very beginning, dealing with the use of different terms meaning maybe nonetheless, all the same
*, see:
http://www.specialmetalswelding.com/publica/joining.pdfI found that through doing a search for 'Nickel Alloy Welding +
Scale', instead of "oxides" or "slag".
Please have a look at
page 31 of this remarkable document, and here, specifically have a closer look at the
General Welding Procedure section.
I may be wrong, but as supposed earlier. Some of the major constituents or drivers for any oxide generation "recipe" (to me) are:
- Adequate Chemical Elements (such as Aluminium, Titanium,...)
- Temperature (accelerating reaction processes)
- Time (allowing the reaction/segregation even to occur)
I seem to discern some sort of physical generality. That is. Those elements, known as deoxidisers, will, given partciular boundary conditions, follow their "nature" by forming oxides that either are included within, or segregated from the weld metal.
That is. E.g. aluminium-oxide will "remain" as aluminium-oxide, independent of the parent metal it is formed within.
So, coming back to your question on NiCrMo alloys, we should have a closer look at what the chemical composition of, let's take a quite well-known type of these alloys, say UNS N06625 (ALLOY 625), states in this respect.
To the best of my knowledge the parent metal is allowed to contain ≤ 0.40 wt-% Aluminium and ≤ 0.40 wt-% Titanium.
Provided these are strong deoxidisers one might, given adequate boundary/welding conditions, expect "oxides" to evolve from these conditions. Also, one should not forget, at least in my understanding, that Chromium is capable of forming oxides as well, in this conjunction maybe confirming (in part) my previous statement. That is, the higher the number of elements of the alloy, the greater the complexity of these interactions.
Whereas having a look e.g. at UNS 07718 (ALLOY 718), deliberately alloyed with Aluminium and Titanium, one may anticipate some higher likelihood to end up with "scale", "surface oxides" or "slag". This, btw has yet been stated in the document whose link I did embed in this post.
Finally, as I did mention the physical forces driving the oxides through the liquid pool toward the bead surface. It would be interesting to learn how the viscosity levels, presumably different, i.e. higher, with these complex Nickel-based alloys vs. un- or low alloyed steel grades, affect the inclusion/segregation ratio.
That is. If we would assure constant boundary conditions in terms of welding and amount of deoxidising elements, but only change the parent metal (or matrix); would we obtain similar amounts of "surface oxides", "slag" or "scale" with both deposited weld beads?
Anyway. Maybe I'm completely wrong here with my layman metallurgical hypotheses.
Thank you.
*) As mentioned in a different post/thread but apparently completely misunderstood at that time. Just as "Linda", "Margaret" or "Anny" at the end of the day are different "terms" having the same meaning - a woman. Sorry, I couldn't resist.