In this article, experts from http://www.mirachmetallurgy.com share how to take usage of steel bars.  Generally speaking, a steel bar can be used in four fields.

1. A steel bar can be forged on an anvil to create steel weapons and armour, granting 37.5 Smithing experience per bar used. A list of steel items that can be smithed from steel bars and the Smithing levels required can be found on the Smithing tables.
2. Steel bars are commonly used to create cannonballs, ammunition used by the Dwarf multicannon. In order to create cannonballs, players must be a member, complete the Dwarf Cannon quest, possess an ammo mould, have some steel bars, and level 35 Smithing. Cannonballs are made by using a steel bar on a furnace, with an ammo mould in inventory or tool belt, yielding 4 cannonballs per bar. Players gain 25.5 Smithing experience per bar. Smithing cannonballs has a profit of 257 coins per steel bar at current prices.

3. Steel bars are also used in construction and earn 20 construction experience per bar when required. They can be used to make Clockworks on a Crafting table 2 with level 8 Crafting for 15 construction experience.

4. Steel bars are also the tertiary ingredient in infusing Steel minotaur pouches.