<p>Over the past few decades, many methods have been proposed to reveal prior austenite grain boundaries (PAGBs) in steels. However, most are effective only within specific compositional or processing conditions. This work proposes a novel contrast method capable of simultaneously revealing the final microstructure and the original austenitic grain structure in heat-treated steels, without requiring quenching or complex laboratory infrastructure. The method relies on preferential oxidation at PAGBs during conventional heat treatments in oxidizing atmospheres, followed by careful surface preparation and light etching with 2% Nital to generate topographic contrast. To validate the technique, AISI 1010, 1045, and 4340 steels were normalized and analyzed via optical (OM), scanning electron (SEM), and atomic force microscopy (AFM). The method proved effective for the evaluated steels, generating high-contrast images without quenching. Quantitative metallography showed excellent agreement with grain size measurements obtained via traditional picric acid etching. Additionally, the method revealed the final microstructure alongside the PAGBs, offering new opportunities for studying phase transformation mechanisms. This innovative and low-cost approach is applicable to real-size components and various steel types, providing reliable results with minimal equipment requirements.</p>