Handlebars, seatpost, or steertube. Whatever it is you need to cut down, you can do it with the Titan Steer Tube Cutter. This is a great tool and a "must have" for your bike tool collection.
I prefer a saw and cutting guide. You probably already have at least half of that kit as it is.
It cut my aluminium steer tube well. Left some burrs but a saw will do that as well. There was some very slight mushrooming around the cut, filed it down and the stem slid over it just fine. Have not used on steel so I can't comment, but for my application it did the job.