Oxidative Wear And Mild-to-Severe Wear Transition Of Ferrous Alloys Under Severe Conditions

Oxidative wear, resulted from friction heat or high-temperature wear, is usually found in material processing, power generation, transportation and many other fields. Oxidative wear is a common wear phenomenon and an important failure mode, deciding the wear behavior and the life of mechanical parts. The transition of mild-severe wear in oxidative wear would lead to rapid failure in the mechanical part; this is a common physical and chemical processes in dry sliding wear conditions, particularly in high-temperature wear. The wear transition in irons and steels is a serious tribology and material science problems under severe conditions; their researches possess important theoretical and engineering application value. In this paper, the friction and wear behavior as well as wear mechanism of typical materials under different conditions were systematically studied; the relationships among the composition, microstructure and performance of the materials, oxidative wear and wear resistance were discussed. Oxidative wear and the transition of mild-severe wear under severe conditions were focused on.With increasing ambient temperature and load, the wear mechanism changed, the transition of mild-severe wear appeared with characteristics of oxidative wear under severe conditions. The transition of mild-severe wear in oxidative wear and the transition region were proposed firstly, thus the physical essence of failure in dry sliding of the steel material under severe conditions was disclosed. The ambiguity in the concept of oxidative wear was pointed out. Oxidative wear and oxidation mild wear were found to presented different wear behaviors. The former was consistent with Quinn's theory of oxidation wear; the latter was beyond the mild wear, its wear behavior depended on the combined action of the oxide and matrix. A clear distinction between the oxidative mild wear and oxidation wear was suggested to use in subsequent research. The problems in wear map of steels proposed by Lim and Ashby were clarified and the original wear map was modified.The wear reduction of the oxides was directly related to the amount (or thickness), and the strength or thermal strength of the matrix, whether or not the oxide reduced wear depended on the hardness or strength of the matrix in wear. The relationship among wear resistance, microstructure of materials and the properties depended on the prevailing wear mechanism. In adhesive wear, high strength or hardness and a certain fracture resistance were required for a good resistance. In high-temperature oxidative wear, a good wear resistance depended on the strength (or hardness), fracture strength (or toughness) and thermal stability. It was found that an increase in chromium content improved the oxidative resistance of steels, and hindered the formation of oxides, delayed the emergence of oxidation wear. High wear resistance of the high-chromium steel was attributed to the strengthening of chromium on the oxides, matrix and its combination. The graphite possessed the lubrication effect, reducing wear at conditions of room temperature and a low load, but increasing wear under a high load. In high-temperature wear, the reduction of tribo-oxide by graphite increased wear.