The Oxide Layer of 10Mn5 Medium Manganese Steel for Wear Protection in High-Temperature Friction during Hot Stamping

A custom-designed high-temperature sliding-on-sheet-strip (SOSS) tribo-tester was used to simulate the high-temperature friction process of 10Mn5 medium manganese steel bare plate under actual hot stamping conditions. To reveal its high-temperature friction mechanism in the hot forming process, the high-temperature friction behavior of 10Mn5 steel and 22MnB5 steel was compared. The scanning electron microscope (SEM), energy spectrum analyzer (EDS) and X-ray diffractometer (XRD) were used to investigate the structure of the oxide layer, composition of physical phase, wear surface morphology and elemental composition. The results show that the average coefficient of friction of 10Mn5 steel is 12.7% lower than that of 22MnB5 steel. The cross-section of both steel consists of an oxide layer, an alloying element-rich layer and the matrix. The oxide layer of 10Mn5 steel is mainly composed of Fe3O4, approximately 63.7%, while that of 22MnB5 is mainly composed of Fe2O3, approximately 66.9%. The complete and less flaking scale of 10Mn5 steel provides good wear protection, and the mechanism is abrasive with slight adhesive wear. Meanwhile, oxide particles and fragments are embedded in the 22MnB5 surface thus increasing the wear, and the mechanism evolves into severe abrasive and adhesive wear. The difference in the mechanism between the two steels is mainly caused by different austenitizing temperatures, which for 10Mn5 is lower than 22MnB5, about 100 degrees C. This makes the thermal stress of 10Mn5 from the temperature difference between the furnace and the environment not enough to break the scale and decrease abrasion.