The engineering steel course is part of the steel applications courses. In the first module and introduction to plain carbon steels will be showed. Then, the mechanical properties, test certificate and applications will be introduced. After that, the effects of thermal treatments and applications of plain carbon steel will be explained. The hardness treatment for steel tools, the bright and black bars and surface defects will be introduced. Finally, the last module of effects of other chemical elements on plain carbon steels will introduce how the alloys and other elements affects the mechanical properties of steel.