Lots of good replies already for this question
My guess would be an alloyed medium carbon steel. But I dont specifically know.
Good question! I have lots of experience driving cranes lifting boats in and out of the water mainly. But I don't really think this ever occurred to me. So I had a look around on the old www - which I do not usually do, much, in 'Answers'. But here's your answer, I reckon (another interesting QA site, too! - I leave you the thread in Source(s).): The steel used for crane hooks are based on the application. For cold temp. use you'll need LCC or low temp carbon steel (requiring Charpy Impact values of 15 foot pounds at - 25 degrees F. The materials used can be either cast ASTM A148, or 9060, or A487 4B or a forged 4140 material. All have the properties in the ASTM specs (see specs on line . com). All of these specs have specific heat treats that are part of the individual specs.
