I am the captain of a BattleBots team, currently showing on Discovery Channel in the US and streaming worldwide. Among the many engineering challenges we face building combat robots, material selection is critical. I don't only mean choosing steel over aluminum, I mean choosing which kind of steel to use for each application on the bot. In my talk I will cover the basic material science of steel alloys, hardening processes, and how they are used to build combat robots and other industrial applications (and what happens when you make the wrong choice).