If you are a weldor, here is an opportunity to put yourself ahead of the pack. I don't think you can ever know too much. If you are an engineer, then you NEED to know metallurgy. There are bunches of books, but here are 2 that I started with:
Welding Metallurgy Vol.1,2 by George Linnert. Pub. by AWS.
I have the third edition, but I'm sure there are newer editions available by now. I think I purchased mine in the mid 70s.
-dseman