PSI- Issue 9

Jesús Toribio / Procedia Structural Integrity 9 (2018) 323–328

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Author name / Structural Integrity Procedia 00 (2018) 000–000

1. Introduction

The importance of high-strength cold drawn pearlitic steels in structural engineering is out of doubts since they are components of prestressed concrete structures. This paper reviews previous research by the author in the matter of microstructure-based anisotropic fracture behavior of progressively cold drawn pearlitic steel and its effect on crack paths, the subsequent deflection being a consequence of the strength anisotropy.

2. Microstructural evolution with cold drawing

The cold drawing process produces important microstructural changes in the steel at the two basic microstructural levels of pearlitic colonies and lamellae. The microstructures of the hot rolled pearlitic steel bar (null degree of cold drawing) and the heavily cold drawn pearlitic steel wire (commercial prestressing steel after six drawing steps) are given in Figs. 1 and 2 (the vertical side of longitudinal sections always corresponds to the wire axis)

Fig. 1. Metallographic longitudinal section in the hot-rolled bar (left) and the cold drawn wire (right), the former randomly oriented and the latter showing orientation and alignment in the drawing direction of both microstructural levels of pearlitic colonies and lamellae.

Fig. 2. Metallographic transverse section in the hot-rolled bar (left) and the cold drawn wire (right), both randomly oriented and the latter showing curling of cementite lamellae in the form of Van Gogh Texture (VGT), as described by Toribio (2017a).

As explained by Toribio and Ovejero (1997, 1998a) the pearlitic colonies ( first microstructural level ) become progressively enlarged and slenderized, and at the same time oriented and aligned in axial direction with cold drawing. Toribio and Ovejero (1998b, 1998c) also analysed the evolution of the ferrite/cementite lamellae ( second microstructural level ) that exhibit a progressive increase of packing closeness associated with a decrease of interlamellar spacing with the level of cumulative plastic strain and at the same time an orientation and alignment in a direction quasi parallel to the wire axis or cold drawing direction, such an orientation and alignment having a relevant impact on crack path deflection and anisotropic fracture of the cold drawn steel, a hierarchically structured material with strength anisotropy in the matter of fracture.