steel rod with a core

Lally column? Gives it extree rigidity/strength, at lower cost than solid steel. Also, NYC parking meters use this strategy so's wise-asses w/ oxy-acetylene cain't just zip off the heads w/ all the money in them. It is *really* tough tryna remove them meters! :)

Sounds like a fuel rod for a nuclear reactor.

Do not machine this. Mater of fact, you should probably submerge it in a swimming pool without delay, and then remove all your clothing and then run into your house and take a very long shower.

Do not induce vomiting, it will only make matters worse. Drink as much milk as you can and call the nuclear regulatory agency in your area. While you are waiting, you may wish to write out any pertinent details like where you found it and whose pool you discarded the material into.

Just kidding.

What is the 'stuff' on the inside?

It kinda looks like cast iron.

Thanks

I was going to slice off a piece with a bandsaw, I guess that won't be possible if it's hardened.

It's experiment time...

It's definitely not filled with concrete, it's some sort of metal.

Shell hardening tool steel? Thats what pavement breakers are made from. When they break you have a sparkly center surrounded by greyish finer grained material.

Thought it might be concrete.

You could weigh a section, calc the sp. gr. Steel is around 7, crete around