HWI is a predominant supplier of basic oxygen furnace (BOF) refractories in the United States, where the BOF is the primary device used to produce high-quality integrated steel. Domestic BOF steel production capacity has leveled off due to the significant capital investment required to build new integrated steel mills. The inherent advantage of the BOF is its capability to produce large volumes of high-quality steel, primarily for the automotive industry.

The BOF converts molten iron and scrap to steel by injecting gases at supersonic velocities. The introduction of oxygen through the top lance (BOF) or the bottom tuyeres (in a quick-quiet basic oxygen process, or Q-BOP) creates an exothermic reaction that melts the scrap and removes impurities. Oxygen, nitrogen, argon, or propane is injected through the Q-BOP bottom tuyeres. The multiple tuyeres produce a higher agitation of the steel bath. Increased agitation, along with the chemical reactions produced by the gases, results in lower levels of carbon, phosphorus, and sulfur in the steel.

In the 1980s some mills adopted the technique of slag splashing to extend the life of a campaign. Slag splashing provides a refractory coating over the existing lining. After a heat is tapped, the BOF is rocked to coat the stadium and lower barrel. Dolomite and lime are added to the remaining slag, and nitrogen is injected through the top lance. This process blasts the slag mixture over the existing refractory lining.

BOF vessel capacities can range from 70 to 300 tons. BOF refractory life varies significantly. A campaign can last from 4,000 heats to as many as 50,000 heats, depending on individual shop practices.

HWI provides a full range products for every part of the BOF process, including:

• Safety Lining: NARTAR^® 7, SUPER NARTAR^® R, BOF TANK, and NARMAG^® HRB
• Working Lining: HWI analyzes individual current and historical shop conditions and offers customized lining solutions.
• Bottom/Stadium: customized BOF 700 and 800 series, NARTAR^® TS, NARTAR^® XR, and ISOTAP^®
• Barrel: BOF 700, 800, and 900 series, which have been carefully customized for optimal metal content, carbon levels, and magnesia purity.
• Cone: BOF 700 series, NAREZ AM5, and SUPER NARTAR^® R, with an option for co-molding each product.

BOF Gunning

Gun mixes are used to extend the life of the vessel working lining. On a regular basis, the lining is inspected after the vessel has been tapped. Laser profilers can be used to determine where the lining is becoming thin. A gun mix is applied to the areas needing repair, and after minimal dry-out, the vessel is returned to operation.

Gunning materials are designed to be sticky during application to reduce rebound and have enough green strength to prevent slumping or peeling. Magnesium oxide content, basicity, and binder composition will determine the right material for each application.

HWI has developed several gunning materials for use in the BOF application:

• Cone: BASIC 187 GM-60
• General Vessel Maintenance: BASIC 187 GM-90 and BASIC 187 GM-93
• Taphole Replacement and Maintenance: AMERICLASE 98 S