Are these black spots sunburn?

[WayneByerly]

I have two cacti, one of which I believe to be a Pilosocereus pachycladus (WAS p. azureus) and the other is a Barrel cactus, both of which have these black spots that developed after being exposed to several days of 4 hours per day direct sunllight in middle Tennessee.

I had had it opined that this was sunburn, although I had read that sunburn was red/purple.

IS this sunburn? Or something else. SHOULD I do SOMETHING about this? Is there anything that CAN be done? I feel like such a gonzo!

Will these plants survive? Or should I just save myself as much heartbreak as possible and just pull them up and discard them? The barrel cactus I bought at Lowes and is about 6 inches in diameter and 8 to 10 inches tall. It's really too big for where I live, but I'd hate to have to throw it away.

Pilosocereus pachycladus 1 of 3: Ignore the red spot. I used a magic marker to mark an areole so I could measure growth rate early last summer. You can see the black areas. It doesn't start at the top, although there are a couple of small spots at the top. Not that I think it MATTERS, but this cactus was the top slice of a PIECE of a cactus, about 5 inches tall, and had NO roots when I first got it. And the root system it has now is not terribly well developed.

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Pilosocereus pachycladus 2 of 3: cactus turned about 15 degrees counterclockwise

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Pilosocereus pachycladus 3 of 3: cactus turned about 30 degrees counterclockwise from original orientation. There is no black markings on this side, but a couple of small brown spots.

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Barrel Cactus 1 of 2

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Barrel Cactus 2 of 2: turned about 30 degrees clockwise.

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[greenknight]

Sunburn is not red or purple - that's a plant reacting to stress, which could be from sun or something else. Sunburn starts as a whitish discoloration, if severe it turns to hard brown scars. It's usually worse on the edge of the ribs, where it catches the most sun. See Cacti Care - Pests and Diseases.

That does look like severe sunburn - if it's not soft, and it's on the side the sun hit, you can figure that's what it is.