Cutting carbon-steel sheet with a sliding grinder
A right angle disk grinder with an abrasive disk will work for the task you describe. Expect to see the abrasive disk slowly reduce in diameter at first, then more quickly as it gets smaller. This is an aspect of the abrasive material sacrificing itself to move steel.
To prevent destruction of the disk, it is important for it to remain in the plane of the cut. You can purchase a tool into which your right angle grinder will clamp, providing this restraint, or you can build your own from a number of plans and instructions on the internet. I used search terms, &quot;DIY right angle grinder cutting jig&quot; and found too many to list.
There are variations using wood as the construction material as well as metal strap and sheet and plate. Your DIY choice obviously would be based on your skill set, tools and materials available to you. The purchase options vary in cost, yet another parameter to consider.

The image above is from a randomly selected YouTube thumbnail. Videos of different construction options are plentiful.