Today I did a little more work on that bobsled. So, yesterday I drove a bolt through the runner and it cracked straight across the 2 inch wide runner. So, today the other runner is bowed and not straight and I need to straighten it out. I put a magnet to both runners and the magnet attaches to the runner. So, not sure why that first runner cracked the runner in two, and not sure how much shaping this second runner will that.

I'm guess they both are steel because magnet likes but why di that one crack like cast. You think just old fatigued and how much pressure and pounding will the second take to get it back in shape.

Any thoughts and advice besides heating it up.

Can you post a picture of the grain structure of the one that broke, then we might be able to tell if it’s cast or not because cast iron is magnetic.

Darn I really feel stupid now Lol. I thought cast wasn't magnetic! I'm not much of an iron fabricator so that doesn't surprise me. I which I could show that broken on but I installed that one already and has a wash and bolt holding that on in place. I'm tryin to et the iron install so I can keep on building wood parts and drilling holes where they need to be. It does have some spring to it not what I known cast to have any and is very ridged.

Yeah cast is very rigid, maybe a hardened steel and just a bad spot in the tempering, don’t beat it a press or at least steady pressure is your best friend, if it’s hardened or cast it’ll be tough without heat, and FYI most stainless steel isn’t magnetic.

Thanks Bob. A Magnet will attach to cast iron then?

I can't see the reasoning of making a sled runner out of cast iron. Bet what you have is some kind of steel.

Cast iron makes great engine blocks. And heavy castings, like for lathes or milling machines. Cast iron is iron with a high carbon content yet un-tempered. Very brittle. It does not weld well. care must be taken to bend or even weld it by heating it up first so it does not crack when it goes through temperature changes.
Wrought iron is not cast iron. They are both iron as is steel. Steel is of course an iron product also. Wrought iron is what the old time blacksmiths used. It has NO carbon content. Carbon must be induced into wrought iron in order to harden it, (case hardening). Yes, cast iron is magnetic.

Yup.

Thank You for the clarification. It just surprised me when that one broke and I totally agree cast would be a terrible iron to use as a runner where it gets all kinds of twisting and uneven ground to go over. Today I will heat things up and apply even pressure with clamps to see if I can straight and form the one runner.
Thank You very much and to all.

Hit it with a grinder cast will show reddish sparks or very few large yellowish sparks carbon steel throws a shower of small yellow sparks unless its old your part is cast steel possibly cracked before you started hammering on it