Jesús Toribio, Beatriz González, Juan-Carlos Matos

University of Salamanca, Department of Materials Engineering, E.P.S., Campus Viriato, Avda. Requejo 33, 49022 Zamora, Spain.

toribio@usal.es

ABSTRACT: This paper deals with the influence of the manufacturing process on the fatigue behaviour of pearlitic steels with different degrees of cold drawing. The analysis is focussed on the region II (Paris) of the fatigue behaviour in which da/dN=C (∆K)^m, measuring the constants (C and m) for the different degrees of drawing. From the engineering point of view, the manufacturing process by cold drawing improves the fatigue behaviour of the steels, since the fatigue crack growth rate decreases as the strain hardening level in the material increases. In particular, the coefficient m (slope of the Paris laws) remains almost constant and independent of the drawing degree, whereas the constant C decreases as the drawing degree rises. The paper focuses on the relationship between the pearlitic microstructure of the steels (progressively oriented as a consequence of the manufacturing process by cold drawing) and the macroscopic fatigue behaviour. It is seen that the fatigue crack growth path presents certain roughness at the microscopic level, such a roughness being related to the pearlitic colony boundaries more than to the ferrite/cementite lamellae interfaces.

Keywords: Pearlitic Steel, High Strength Steel, Fatigue Microdamage, Paris’ Law.

RESUMO: Este artigo trata da influencia do processo de fabricaçao no comportamento da fatiga de aços perliticos com graus diferentes de trefilado. A análise é centrada na região II (Paris) do comportamento da fatiga na que da/dN=C(∆K)^m, medindo as constantes (C e m) para os diferentes graus do proceso de fabricaçao. Desde o ponto da vista da engenharia, o processo de fabricaçao polo desenho en frio melhora o comportamento da fatiga dos aços, dende que a taxa de crescimento da fissura da fatiga diminui enquanto aumenta o nível de endurescemento por deformaçao do material. No detalhe, o coeficiente m (inclinação das leis de Paris) permanesce quase constante e independente do grau de trefilado, mentras que a constante C diminui enquanto o grau de trefilado se levanta. O artigo focalizase no relacionamento entre a microstructura perlitica dos aços (orientados progressivamente em consequência do processo de fabricaçao pelo desenho en frio) e o comportamento macroscópico da fatiga. Vê-se que o trajeto do crescimento da fissura da fatiga apresenta determinada aspereza no nível microscópico, tal aspereza está sendo relacionada aos limites da colônia perlítica mais do que puideran influir as intercaras das lamellas de ferrita/cementita.

Palavras chave: Aço Perlitico, Aço de alta ressistença, Microdano por Fatiga, Lei De Paris.

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