That's a really interesting question, and I'm not sure what the answer should be. According to the authors, the B2 intermetallic forms in small particles during

That's a really interesting question, and I'm not sure what the answer should be. According to the authors, the B2 intermetallic forms in small particles during recrystallization at 900 C because of the influence of the nickel, so you might expect a similar high rate of particle nucleation in the wake of the melt pool, resulting in small, dispersed particles. Then again, you might get coarse intermetallic phases instead, resulting in a brittle weld. In either case, the advantage of the B2 particles is that they allow a high degree of strengthening during work hardening, which would be done before welding. Any subsequent heat treatment would tend to undo that work hardening.