converter

A converter is a large refractory-lined vessel used to refine pig iron into steel by blowing air or oxygen through the molten metal. The most common type is the basic oxygen converter, which injects a water-cooled oxygen lance from above while the charge rotates or tilts. This violent oxidation burns out carbon, silicon, manganese, and phosphorus, raising the temperature to around 1700°C and producing usable steel in 15 to 20 minutes.

The Bessemer converter, now obsolete in most mills, blew air upward through a tuyere in the base; it was faster than hand-puddling but less precise. The modern basic oxygen furnace, or BOF, handles charges of 100 to 250 tonnes per blow and allows tight control of composition by timed oxygen injection and alloy additions. Smaller electric arc furnaces compete for scrap-based steel, but converters remain the workhorse of integrated mills that start from blast furnace output.

Common wear and failure modes

The refractory lining erodes from thermal shock, chemical attack by slag, and mechanical impact. Magnesia-carbon bricks last longer than older magnesite linings but cost more. A worn lining can fail catastrophically, spilling metal; operators monitor interior temperature and acoustic signatures to catch degradation. Tuyere blockage from slag buildup slows oxygen transfer and forces longer blows, wasting energy.

The name reflects the machine's core function: it converts. Early steelmakers distinguished converters from crucibles and reverberatory furnaces by their speed and the violence of the process. Trade terminology varies by region; some mills use furnace, others use vessel or plant, but converter remains standard for any vessel relying on blowing to drive oxidation.