An Ruhrstahl Heraeus plant is used in steel making to adjust the chemical composition of the steel right before casting. The process and the setup to generate the images provided in this data set are described more in detail in DOI: 10.1002/srin.202200060. The two major treatment types are degassing and decarbonization. The first focuses on removing desolved gases from the melt. The second includes the removal of carbon from the melt in addition to the degassing. The data set provided here contains images taken from 1 treatment. Each folder contains two subfolders "empty" and "treatment". In the folder "empty" 119 images from the empty chamber right before the treatment starts. The folder "treatment" contains images from the treatment. These have already been filtered using processdata for good viewing conditions. The process data itself is not part of the data set. The INEVITABLE project, carried out in a collaboration with voestalpine Stahl GmbH, has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 869815. This paper reflects only the authors' views, and the European Commission is not responsible for any use that may be made of the information it contains. The authors moreover gratefully acknowledge the funding support of K1-MET GmbH, whose research program is supported by COMET (Competence Center for Excellent Technologies), the Austrian program for competence centers. COMET is funded by the Austrian ministries BMK and BMDW, the provinces of Upper Austria, Tyrol, and Styria, and the Styrian Business Promotion Agency (SFG).