PAPER REFERENCE: ICF100447OR IMAGE ANALYSIS OF HYDROGEN-ASSISTED MICRO-DAMAGE IN PROGRESSIVELY DRAWN PEARLITIC STEEL J. Toribio, F.J. Ayaso and E. Ovejero Department of Materials Science, University of La Coruña, ETSI Caminos, Campus de Elviña, 15192 La Coruña, Spain ABSTRACT This paper analyzes the evolution of hydrogen-assisted damage topography in progressively drawn pearlitic steels. The fractographic analysis revealed changes in the microscopic topographies depending on the fracture propagation mode, with an evolution from pure tearing topography surface (TTS) in slightly drawn steels to a kind of very deformed TTS (in direction of cold drawing or wire axis) in heavily drawn steels. An image analysis technique was used to analyze the different microscopic fracture modes, thus finding correlations between them. Results showed that the very deformed TTS really observed in heavily drawn steels could be virtually obtained by deforming –in the drawing direction– the micrograph of slightly drawn steels. This fact provides bases to elucidate the real physical micromechanism of hydrogen-assisted fracture in pearlitic steels. KEYWORDS Pearlitic steel, cold drawing degree, hydrogen-assisted micro-damage, fracture micromechanisms INTRODUCTION Cold drawn eutectoid steels are high-strength materials used as constituents of prestressed concrete structures in civil engineering. Previous research [1,2] dealt with the fracture of this kind of steel in aggressive environment, showing that heavily drawn prestressing steels exhibit anisotropic fracture behavior associated with changes in the crack propagation direction and transition from mode I to mixed mode propagation approaching the wire axis direction. In more recent works [3,4] this research line has been developed to analyze steels with intermediate degree of cold drawing, in order to relate –in the materials science manner– the macroscopic behavior of the steels with their microstructure at the two basic microstructural levels of the pearlite colonies [5,6] and the pearlitic lamellar microstructure [7,8], as a function of the cold drawing degree achieved during the manufacturing process to produce the final commercial product. This paper goes further in the research line and studies –by means of image analysis techniques– the evolution of hydrogen-assisted microdamage topographies at the microscopic levels for the different degrees
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