Ebook: ASM Handbook Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys

Time and time again, I realize that I should have consulted the ASM Handbook earlier and more often during research. While it does not include the most recent research in the field (last update was in the 90's) it is a great primer for background knowledge in various metals phenomena. Each volume is a massive tome, but they offer a prolific "specific usefulness" factor (both by weight and by volume), so do not be intimidated.

And while some may claim that you're not reading them for the plot, the ASM guides offer many plots, tables, and micrographs for your consulting pleasure.