Occurranceof thermal fatigue cracks and their relation with oxidation


Thermal fatigue is a mode of fatigue by cyclical application of thermal stresses due to thermal contractions and expansions of the material. Components subject to thermal fatigue are mostly parts of combustion engines or tools for the hot forming industry, which are components that are also subjected to oxidizing environments. Although the available literature on metalforming has a large number of works related to thermal fatigue in hot rolling rolls, few authors discuss how this type of damage is influenced by some characteristics of the process – specially the oxidation. This paper draws attention to thermal fatigue laboratory tests and to hot strip rolling rolls. In addition to the thermal cycling and atmospheric conditions, the microstructure of the tool steel was varied. Three distinct formations of cracks could be observed, formed at different stages of the evolution of thermal fatigue damage. Through the monitoring of the phenomenon from the beginning of its formation to the damage of the tool itself, it was possible to verify that the appearance of thermal fatigue cracks starts at points of surface stress risers, such as primary carbides, interfaces or preferential oxidation spots, which generate regions more susceptible to failure during the tool cooling step.Results of mathematical modeling on microscopic scale confirmed the stress rising effects caused by notches on the surface, both in the presence and absence of oxides filling the cavities.

BRAGA, Ana Paola Villalva; LIMA, Luiz Gustavo Del Bianchi da Silva. Ocorrências de trincas de fadiga térmica e suas relações com oxidação. In: CONGRESSO ANUAL DA ABM, 73., 2018, São Paulo. Anais… São Paulo: ABM, 2018. p. 1664-1678.

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