I’ve cut steel but not concrete & I assume you could cut it with a diamond disc cutter. I don't know what you’re using it for but lintels usually have a 150mm minimum bearing each side & so are normally 300mm wider than the opening; it’s also a Building Regs. requirement.
This is for the front of a fireplace where I took the old solid fuel fire out check out my post "supporting a chimney breast"--you'll see what I mean
We will probably fit a small wood burning stove in there so I suppose there's no reason why I can't use steel.
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