The argon oxygen decarburization (AOD) process is used to make stainless steel and specialty grades of steel, including tool steels, silicon steels, low-alloy steels, and low-carbon steels. In this process the tuyeres are submerged, resulting in high element recovery, rapid and efficient desulfurization, and good control of the slag chemistry.

The two most important steps in this process are decarburization and reduction. Decarburization, which occurs when oxygen is blown through the tuyeres, reduces the amount of carbon in the steel. Decarburization also results in the oxidation of the metals in the steel. To decrease the oxides, aluminum and/or silicon are added during the reduction process. The metallic oxides are transferred from the slag into the metal via the heterogeneous slag-metal reactions. Silicon is the strongest “reducer,” followed by aluminum and titanium.

The AOD process takes place in a vessel that consists of the following components: sub-bottom, bottom, tuyeres, tuyere pad, pour pad, and cone. Refractory selection depends on a number of variables, including chromium pickup, wear mechanisms, desulfurization, spalling, hydration, and processing temperature. Cost and turn-around time are variables that also must be considered.

The leachable chrome values of HarbisonWalker International AOD refractories are less than 1 mg/L (toxicity characteristic leaching procedure, or TCLP), which is significantly lower than the 5 mg/L required by the EPA for landfill disposal. Note that leachable chrome values will change during service, but HWI refractories will not exceed the 5 mg/L limit under normal operating conditions.

HWI offers a proven, comprehensive refractory package for the AOD process. From high-purity, rebonded, fused-grain magnesia-chrome refractories to high-purity, direct-bonded magnesia-chrome refractories, our products provide you with the properties you need to extend campaign performance. We work very closely with our customers to analyze and modify slag chemistry to best interact with magnesia-chrome refractories. Each slag control recommendation is customized to maximize performance.

SFG^® is the brick of choice for the tuyeres and tuyere pads. It contains 100 percent fused magnesia-chrome grain, which makes the brick resistant to mechanical and chemical erosion. S142^® and S145^® are used in the bottom of AODs with S145^® in the impact pad in the bottom. They contain substantial amounts of fused grain, which makes the bricks resistant to slag.