<p>Nonmetallic inclusions are detrimental to the quality of steel products and the steelmaking process among which MgO·Al₂O₃ spinel and alumina (Al₂O₃) are some of the most detrimental. Three-dimensional imaging can provide accurate information on the morphology, size, distribution, and chemical composition of nonmetallic inclusions to help with improving the quality and production process of steel products. However, current three-dimensional imaging techniques are time-consuming and/or inaccessible. Here, a technique is presented for applying ionoluminescence (IL) imaging to rapidly acquire three-dimensional images of MgO·Al₂O₃ spinel and Al₂O₃ inclusions in steel products at the laboratory scale. Three-dimensional images were constructed by stacking two-dimensional IL images obtained every 3–6 minutes during argon-ion bombardment at an etching rate of 0.025–0.092 <i>µ</i>m min⁻¹. MgO·Al₂O₃ spinel and Al₂O₃ inclusions around 10 <i>µ</i>m in size were successfully imaged within 5 hours, which matches the maximum allowable size in many steel products. These results demonstrate the potential applicability of IL imaging to enhancing steel quality and production.</p>