I love this entire little Workshop Practice series of books. If you work with metal or want to, here's one worth getting: Hardening, Tempering and Heat Treatment
From the book description:
A comprehensive exposition of the structure of steels and the effects of different heat treatments, particularly in respect of tools. It includes solid fuel, gas and electric furnaces, case hardening, tempering and other practical information. Features accurate colour temperature charts.
It gets great reviews from quite a few people on Amazon. Here is where you can order Hardening, Tempering and Heat Treatment (Workshop Practice). Be sure to check out the entire line of in the Workshop Practice Series. There are books on every possible aspect of metal and shopw work, tools, and techniques. I wish they sold them as a complete set!