How to producehollow steel for drill rods?

The processes of hollow steel for drill rods are as follow:

-smelted by an electric furnace

-refined by an LF furnace

-cast by a bloom caster

-rolling intermediate billet by a blooming mill

-drilling the central hole by a deep hole drilling machine

-adding mandrel

- rolledby a semi-continuous rolling mill

- controlled cooling

- quality inspection

- cut to certain length