I interpret the white spots are visible in metallographically preparred sections of weld/HAZ.

From article: New Knowledge About 'White Spots' in Superalloys
by; Jackman, Maurer, Widge
in: Advanced Materials and Processes, 5/93

"It is widely accepted that white spot are associated with the inherent characteristics of the vacuum arc remelting process." Their discussion is related to as-cast ingots of the superalloy material.

The authors define three different types of white spots: 'discrete', 'dendritic', 'solidification'.

"In general, discrete and dendritic white spots result from the 'fall-in' of solid material into the molten pool in the VAR furnace. Solidification white spots ... result from thermal perturbations that occur at the interface between the molten pool and the solidifying ingot."

Compositionally, the white spots can be significantly depleted in Nb, and somewhat depleted in Ti, Al, and Mo. There appear to be characteristic locations in the original ingot cross section for each of the respective types. These locational characteristics are probably not directly relevant for forged shapes.

There should be extensive technical discussion of the phenomenon because it was a quality and integrity issue that had to be addressed and understood.

The material integrity consequences of white spots did not appear to be resolved at the time of the article.

Another technical article is:
An Analysis of the Mechanism of White Spot Formation
Felix Shved
Journal of Metals 1/94