Cutting metal embedded in concrete

[Niscars]

Can someone please give me some advice on a suitable tool for cutting a square end on the sliding garage door channel pictured above. As you can see, the track is encased in concrete and has rotted away on the curve of the door.
I am planning to construct a new section for the curve which will butt up to the original one pictured. In order to butt the two together neatly so the door runs freely in the channel, I need to cut back and square the end on the old one. For scale, the width of the concrete channel is 35mm
I thought, perhaps drilling a line of holes across the metal and then chopping it out with a cold chisel?
Or slicing across the metal and concrete with a disc cutter? Can I get a small blade that will cut both together?
Any better ideas please?
Thanks

 

[Burnerman]

These channels are often hard as hell....if its acceptable to you, I'd use an angle grinder with a stone cutting disc - it will go through steel too. A 115mm disc should be fine.
John

 

[jj4091]

A diamond blade in a grinder will also go through both materials.

 

[Niscars]

Thanks for your replies guys. I think the angle grinder option is a good one as I will have to repair the concrete around the track anyway.
I have some other questions about my plan for the repair, so I may start a new thread on that.
Ta.