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ROBSON, S.B. Delta ferrite in heat treated bolts characterization and consequences. 2014. 87p. M.Sc. Dissertation – Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 2014. In the process of manufacturing bolts, a coat phosphating is required to serve as anchorage for lubricants and other friction-reducer, facilitating the cold forming process. However, before the beginning heat treatment of quenching and tempering, it is important that the alkaline bath for cleaning be efficient in order to prevent that during austenitizing, the residual phosphorus spread on the steel surface and forms a brittle phase, rich in phosphorus, called delta ferrite (δ). In the presence of this phase, is credited with a decrease in fatigue life of the bolt and embrittlement. The intention in this work was to show the negative influence of this phase on fatigue performance, comparing the S-N curves for specimens with and without ferrite δ. Trials have shown a reduction of up to 40% in life fatigue. The ferrite δ was characterized by SEM, EDS and also performed fractographic analysis.

Ferrita delta em parafusos tratados termicamente: caracterização e consequências