Cleaning steel?

Do you mean the varnish on black iron pipe, the firescale on hot rolled shapes, or the grease on cold rolled shapes?

I assume you mean for welding preparation. Cheap paint thinner/mineral spirits takes off greasy coatings well. Acetone for more stubborn cases but since it's much more expensive and toxic, conserve. A wire wheel on your 4 1/2 inch grinder for the rest.

I have found that any strong chlorinated solvent will remove the varnish. Lacquer thinner and some coarse steel wool, works very fast, just use it outside.

For firescale you will need to grind, sand or pickle it, or send it out to a large steel shop with a wheel-abrader.

Grease is best removed with simple green and water. I like to place the pieces outside in my driveway and scrub them with a broom style brush from a bucket of hot water with simple green added. Roll the pieces a few times while scrubbing, then rinse thoroughly and lift one end up on a sawhorse so they drain, and dry.