Repair old garage workbench

Question

I have this old garage workbench that seems very sturdy

The wood is OK, I could replace the door.

But the surface's corner has cracking like this:

This is done from previous owner. I would like to fix it somehow. What is that thin strip of wood outside? It seems like it's harden by some chemical process (not paint or maybe...).

Answer 1

That looks like hardboard, "High density fibreboard" to use its full name.

AKA "Masonite"(tm)