Tensile Fracture Behavior of Progressively-Drawn Pearlitic Steels

Abstract

Abstract:In this paper a study is presented of the tensile fracture behavior of progressively-drawn pearlitic steels obtained from five different cold-drawing chains, including each drawing step from the initial hot-rolled bar (not cold-drawn at all) to the final commercial product (pre-stressing steel wire). To this end, samples of the different wires were tested up to fracture by means of standard tension tests, and later, all of the fracture surfaces were analyzed by scanning electron microscopy (SEM). Micro-fracture maps (MFMs) were assembled to characterize the different fractographic modes and to study their evolution with the level of cumulative plastic strain during cold drawing.

Analysis of the Bauschinger Effect in Cold Drawn Pearlitic Steels

“…The diameters of the wires E0 and E3 were, respectively, d E0 = 11.03 mm and d E3 = 8.21 mm [32]. Accordingly, the drawing induced engineering plastic strain in the steel E3 is (d which corresponds to the engineering strain of 3.9 (the details of drawing chain behind the present study can be found in the cited paper [32]). Taking into account elevated levels of test load and rather not large wire diameters, undesirable buckling could appear during testing in the compression loading phase.…”

“…To analyse the BE in high strength steels used in civil engineering, various Bauschinger tests were carried out with the steels corresponding to two stages of the industrial seven-step cold drawing process used for obtaining commercial prestressing steel wires: the initial hot rolled bar not yet subjected to drawing to generate plastic strain (i.e., the drawing induced strain is nil there), which is labelled hereafter as the steel E0, and the steel from the intermediate drawing stage after passing through three drawing dies, which is denoted as the steel E3. The diameters of the wires E0 and E3 were, respectively, dE0 = 11.03 mm and dE3 = 8.21 mm [32]. Accordingly, the drawing induced engineering plastic strain in the steel E3 is (dE0 2 /dE3 2 ) − 1 = 0.80, which is rather moderate in comparison with that generated by the industrial drawing process rendering the diameter of manufactured prestressing wire close to 5 mm, which corresponds to the engineering strain of 3.9 (the details of…”

“…As a consequence, the manufacturing-induced residual stress-strain state is generated that strongly affects the wire failure, in particular, due to hydrogen embrittlement phenomenon [30]. During the drawing process, the material undergoes severe plastic strains and diverse microstructural changes [31][32][33][34][35][36][37].…”

“…To this end, the most relevant BE indicators were evaluated from the experimental data, and the type of appropriate strain hardening model was determined. The tests were performed taking the wires from two stages of a commercial cold drawing process, namely the as-received hot rolled bars (not yet cold drawn) and the wires from an intermediate stage of the cold drawing process, after passing three consecutive diameter reductions when the manufacturing-induced microstructural changes [32] and corresponding material behaviour anisotropy [38] become detectable. Based on the original results obtained in the present work, the most adequate type of material behaviour model is suggested to describe the fatigue performance of cold-drawn pearlitic steels for prestressing wires, which are the key constituents of prestressed concrete.…”

The Role of Overloading on the Reduction of Residual Stress by Cyclic Loading in Cold-Drawn Prestressing Steel Wires

“…This way, loading cycles oscillate between a null stress and a different maximum stress (σ max ) for each case of study. Thus, Load I and Load II applies a maximum load within the material elastic domain (i.e., about 75% and 90% of σ Y = 1300 MPa, 0.002% offset yield strength of a typical prestressing steel used in construction [19]: 1000 and 1200 MPa, respectively). Three additional loading schemes were also considered: a load that reaches the material yield strength at maximum load (Load III), and two loading where the maximum stress overcomes the material yield strength: Load IV, 110% of yield strength (i.e., 1400 MPa) and Load V, 125% of yield strength (i.e., 1600 MPa), respectively.…”