NO.

The very thin layer of tissue (called phloem) that transports photosynthates from the leaves to the roots and other parts of the tree body is located directly under the bark. As a matter of fact, we call it the 'inner bark'. The removal or death of this phloem tissue, when it occurs all around the trunk, is called 'girdling'. Perhaps you've heard of that term. It's a method of killing a tree or other woody plant. Death of a tree isn't usually immediate, as you have observed. It can take months or years.

Planting too deeply, piling mulch or soil up against the trunk, tree wraps, and other factors contribute to this problem in the home landscape.

You cannot protect the wound or do anything whatsoever to fix the problem at this late date. The phloem has ceased to exist and the essential transport system is gone.

Next time, measure the height of the root ball very carefully and dig the hole so that the root mass will sit HIGHER than the existing grade, not lower.

Thanks Rhizo,
That's the word 'girdling' I couldn't remember. So, if the wound would have happened in just one area instead of all the way around, the tree might have a chance. Is that correct?

Yes, if there is a reasonable amount of phloem tissue all of the way from the branches to the root system, woody plants tend to struggle along. IF all other factors are positive influences, and not negative.

With your situation, it sounds like the wood rotted even before you lifted the bark away. It's very difficult to separate healthy inner bark from the tree body.