Issue 30

J. Toribio et alii, Frattura ed Integrità Strutturale, 30 (2014) 424-430; DOI: 10.3221/IGF-ESIS.30.51 429 (a) (b) Figure 7 : Micro-structural damage near to fracture surface: (a) air-cooled steel, (b) steel cooled inside the closed furnace. C ONCLUSIONS he following conclusions have been drawn from this work regarding the conventional mechanical properties of pearlitic steel (obtained by standard tension test) and its fracture surface: (i) The steel’s strength (yield strength and ultimate tensile strength) rises with the increase of the cooling rate during thermal treatment. (ii) Increasing the cooling rate decreases the strain for maximum load (uniform elongation) and increases the reduction in area percentage in the neck (non-uniform elongation). (iii) Macroscopically, the fracture surface under tension presents a more ductile aspect (with more plastic strain) as the cooling rate increases. (iv) The process zone fractography (fracture initiation) is formed by mixing two fracture micromechanisms, microvoids and areas where the pearlite lamellae are observed. (v) As the cooling time increases, in the process zone the surfaces where the ferrite-cementite lamellae are observed increase, while the microvoid zones decrease. A CKNOWLEDGEMENTS he authors wish to acknowledge the financial support provided by the following Spanish Institutions: Ministry for Science and Technology (MICYT; Grant MAT2002-01831), Ministry for Education and Science (MEC; Grant BIA2005-08965), Ministry for Science and Innovation (MICINN; Grants BIA2008-06810 and BIA2011-27870) and Junta de Castilla y León (JCyL; Grants SA067A05, SA111A07 and SA039A08). R EFERENCES [1] Hall, E.O., The deformation and ageing of mild steel: III Discussion of results, Proc. Phys. Soc. Sect., B64 (1951), 747-753. [2] Petch, N.J., The cleavage strength of polycrystals, J. Iron Steel Inst., 174 (1953) 25-28. [3] Karlsson, B., Lindén, G., Plastic deformation of eutectoid steel with different cementite morphologies, Mater. Sci Eng., 17 (1975) 153-164. [4] Marder, A.R., Bramfitt, B.L., The effect of morphology on the strength of pearlite, Metall. Trans., 7A (1976) 365-372. [5] Hyzak, J.M., Bernstein, I.M., The role of microstructure on the strength and toughness of fully pearlitic steels, Metall. Trans., 7A (1976) 1217-1224. [6] Kavishe, F.P.L., Baker, T.J., Effect of prior austenite grain size and pearlite interlamellar spacing on strength and fracture toughness of a eutectoid rail steel, Mater. Sci. Tech., 2 (1986) 816-822. [7] Ray, K.K., Mondal, D. The effect of interlamellar spacing on strength of pearlite in annealed eutectoid and hypoeutectoid plain carbon steels, Acta Metall. Mater., 39 (1991) 2201-2208. T T